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THESE

présentée à

L’I NSTITUT NATIONAL DES SCIENCES APPLIQUEES DE TOULOUSE

pour l’obtention du

DOCTORAT

SCIENCE DES PROCEDES

SPECIALITE : GENIE DES PROCEDES ET DE L’ENVIRONNEMENT

par

Srayut RACHU

Master of Environmental Engineering – Chulalongkorn University, Bangkok, Thaïlande

CONTRIBUTION A LA MISE AU POINT D’UN LOGICIEL DE

CALCUL DE PROCEDES ET FILIERES DE TRAITEMENT D’EAUXRESIDUAIRES HUILEUSES

Soutenance prévue le 16 Décembre 2005 devant la commission d’examen:

M. D. HADJIEV Professeur, IUT, Lorient Rapporteur

M. J. ROLS Professeur, UPS, Toulouse Rapporteur

M. Y. AURELLE Professeur, INSA, Toulouse Directeur de thèse

M. A. LINE Professeur, INSA, Toulouse Directeur de LIPE

M. R. BEN AIM Professeur Emérite, INSA, Toulouse

M. S. SAIPANICH PDG, Progress Technology Consultants Co.,Ltd., Thaïlande

M. H. ROQUE Professeur Emérite, INSA, Toulouse Invité

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Executive summary

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Sommaire

Le traitement des eaux résiduaires huileuses est l’un des sujets de recherche majeurs

dans le laboratoire GPI. L’hydrocarbure ou l’huile est l’un des polluants de l’eau les plus

importants. Une petite quantité de l’huile peut produire le film vastement couvrant la surface

de l’eau, lequel affecte le transfert de l’oxygène et par conséquence ruine l’écosystème. Mêmes’il est biodégradable, il contribue à la demande biologique en oxygène (DBO) importante. En

plus, étant donné ses propriétés, à la haute concentration, il cause l’effet nuisible dans le

procédé de traitement biologique. Toutefois, l’hydrocarbure ou l’huile peut avoir la valeur ou

être récupérée ou recyclée à condition où il peut être séparé de l’eau. En cet effet, les

techniques de la séparation huile/eau sont parmi des recherches principales dans le laboratoire

GPI. Il y a plusieurs études sur les techniques, les procédés et les innovations de la séparation

d’huile initiée par le laboratoire GPI. Chaque étude peut être appropriée à certaine condition

de l’opération ou certain caractéristique des eaux résiduaires.

Ainsi, les buts de cette thèse sont de réexaminer les recherches du laboratoire GPI,

réalisées dans l’Equipe du Professeur AURELLE, sur le procédé de traitement des eauxrésiduaires huileuses ; d’établir le design du procédure générale avec les précautions de tels

procédés ; et, ensuite, valoriser et maximiser l’utilisation de ces connaissances établies sous

forme du logiciel. Ainsi, les objectifs de la thèse ont été définis pour réaliser ces buts ci-

dessus :

1. Réexaminer les technologies de traitement pour les eaux résiduaires huileuses ou les

eaux résiduaires polluées par l’hydrocarbure, dans les recherches de doctorat réalisées

dans l’Equipe du Professeur Yves AURELLE, du commencement jusqu’ au présent.

2.

Généraliser et proposer le modèle de chaque procédé relatif.

3. Composer le textbook sur les eaux résiduaires hydrocarbure-polluées ou les procédés

de traitement des eaux résiduaires huileuses, basés sur le résultat des 1 er et 2ème

objectifs.

4. Développer le prototype du logiciel pour la recommandation de sélection du procédé,

le design des unités procédé et la simulation du plan de procédé de traitement des eaux

résiduaires huileuses.

Sommaire des procédés de traitement des eaux résiduaires huileuses

Les trois premiers objectifs sont accomplis dans la Partie 1 à la Partie 3 de cette thèse.Tous les filières de procédé de récupération d’huile, étudiées dans le laboratoire GPI, avaient

été réexaminées ; et ses modèles mathématiques correspondantes aussi bien que la limitation

du design et les paramètres influents avaient été établis. Ces procédés qui sont réexaminés

sous les buts et objectifs du travail de cette thèse sont ;

1. L’Écrémeur déshuileurs

Ce dispositif est développé pour récupérer sélectivement la couche d’huile de la

surface de l’eau sans entraînant de l’eau avec lui. On a trouvé que le moyen pour réaliser la

bonne sélection d’huile dépend de l’énergie de surface ou de la tension superficielle critique

du matériel écrémeur. Le matériel avec la basse tension superficielle critique convient à êtreutilisé comme matériel écrémeur.

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• Pour le tambour déshuileur, la vitesse périphérique ne devrait pas être supérieure de

0.8 m/s. En fin d’éviter l’entraînement d’eau, la vitesse de 0.44 m/s ou moins est

recommandée.

• Pour le disque déshuileur, la vitesse périphérique ne devrait pas être supérieure de 1.13

m/s. En fin d’éviter l’entraînement d’eau, la vitesse de 0.5 m/s ou moins est

recommandée.• Les modèles se prouvent valides pour les écrémeurs faites de SS, PP, PVC et PTFE.

2. Le Décanteur

Sa théorie importante, à savoir la loi de STOKE, est citée. Selon cette théorie, les

gouttelettes peuvent être récupérées à condition qu’elles entrent dans le décanteur à la

distance ascensionnelle nécessaire pour atteindre la surface de décantation, comme la surface

de l’eau ou la surface de l’intercepteurs d’huile intérieurs, avant d’être entraînées hors du

réservoir par l’eau. D’après ce concept, la relation typique de la taille de gouttelette et son

efficacité de séparation par classe de goutte (ηd) est comme celles montrées dans la fig. 2-1.

V

U

Q

d = dc

d < dc

d > dc

ENTREE SORTIEL

H, D

d

ηd

d c

d < d c

Zone 1 Zone 2

d = or > d c

API

PPI (n plaques)

L

H

H

H1

La cellule “Spiraloil”

(section transversale)

Hauteures sont

differentes.

H2

Figure. 2-1 Schéma et courbe caractéristique de l’efficacitéd’un décanteur

Les modèles mathématiques générales pour les procédé de 3 variétés différentes, c’est-

à-dire le décanteur classique (API), le décanteur lamellaires (PPI), et le décanteur compacte

(Spiraloil) sont proposées et vérifiées :

Pour d ≥ diamètre coupure, dc %100=d η {2.1}

Pour d ≤ dc %100⋅=dc

d

d U

U η {2.2}

La vitesse ascensionnelle d’une

gouttelette (Ud)c

d

d gU

μ

ρ

18

2⋅⋅Δ=

{2.3}

La diamètre de coupure, c’est-à-dire la plus petite taille de gouttelette dont l’efficacité de

séparation est de 100%, est déterminée par les équations suivantes,

Le décanteur simple,

(A = aire ecoulement, Q = debitd’eau)

1/2

ΔρgLA

c18HQμ

cd

⎟⎟

⎠

⎞

⎜⎜⎝

⎛ =

{2.4}

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Les modèles sont valides dans ces hypothèses ;

• 48 < Re < 1100. Re est le terme (ρcVD/μc) dans l’équation. 1 < H/D < 10.

•

La diamètre de coalesceur (D) est environ 5.0 cm. Pour le coalesceur de diamètre

important, il y a un risque de court-circuit par entrainant despassages préférentiels le longdes parois du coalesceur.

• Le modèle est valide pour la diamètre de gouttelette (d) de 1 micron ou plus.

• Vitesse d’écoulement (V) est entre 0.5 et 2.0 cm/s (1.8 - 120 m/h).

• Le diamètre de fibre (dF) = 100 - 200 microns.

• Coefficienct de vide (ε) est 0.845 - 0.96.

• La concentration initiale de hydrocarbure < 1000 mg/l.

•

Les lits sont de type brosse et sont oleophiles.

Pour le coalesceur dynamique (ou brosse tournante),

%100)0.74V0.58

Fd0.03D

0.53 N0.35H0.35ε)(10.580.67d(d

η ⋅−= {3.3}

Les modèles sont valides dans ces hypothèses,

• 52 < Re < 1164. Re est le terme (ρcVD/4c) dans l’équation. 1 < H/D < 2.

• Vitesse de rotation (N) = 0.167 - 3.33 rps (10 to 200 rpm).

• Vitesse d’écoulement (V) = 0.1 - 1.1 cm/s (3.6 to 39.6 m/h).

•

Diamètre de fibre (dF) = 100 - 300 microns.

• Diameter de coalesceur (D) < 11.5 cm.

•

Le modèle est valide pour la diamètre de gouttelette (d) de 10 microns ou plus.• Les lits sont de type brosse et sont oleophiles.

Pout le coalesceur fibreux non-ordonnée (laine d’acier),

%100))()()()(35.3( 36.003..003.023.0 ⋅= −−

D

H

D

d

D

d VD F

c

c

d μ

ρ η

{3.4}

Les modèles sont valides dans ces hypothèses,

•

Re est entre 840 - 2470.

•

La diamètre de fibre (dF) = 40-75 microns.•

Coefficient de vide (ε) est environ 0.95.

• La diamètre de coalesceur (D) = 5 cm.

• La hauteur d’intercepteur tournant (H) = 0.07 - 0.21 m.

• Vitesse (V) = 1 - 2.5 cm/s (36 to 90 m/h).

• Le modèle est valide pour la diamètre de gouttelette (d) de 1 microns ou plus.

• La concentration initiale de hydrocarbure est environ 1000 mg/l.

•

Le lit est oleophile.

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Sommaire

Ur = vitesse relative de decantation

Vr = vitesse relative d’ecoulement

Vr Ur

Vr

Ur

Gouttelette

Lignes de

courant

Bulle

a) Interception directe b) Sédimentation c) Diffusion

Fig. 4-2 Schéma des 3modes de transport

SIEM’s model,

%100)1())(

2

3(

,

exp

⋅−=Φ

−bd

H

AV

ref d eαη

η {4.1}5919.0

exp)(009005.0)( theoη αη =

{4.2}

diff Int sed theo η η η η ++= {4.3}

2)(2

3

b Int

d

d =η

{4.4}

r c

water oilsed

V

gd

μ

ρ η

18

2

/Δ

= {4.5}

3/2)(9.0br

Diff d dV

KT

μ η =

{4.6}

c

bwater air

br

gd U V

μ

ρ

18

2

/Δ== {4.7}

Où μc = Viscosité de phase contenue (eau) (L2/T)

K = Constante de Boltzman (1.38*10-23)T = Température absolue (Kelvin)

d b = Taille de bulle (L)

d = Diamètre de gouttelette (L)Vr = Vitesse relative enter des bulles et des gouttelettes (L/T)

Quant à l’équation de généralisation du modèle de SIEM, fondée sur le concept de

l’équilibre de population, sa forme générale est comme montrée ci-dessous. Le κ2, ref est la

constante, calculée par ηd,ref dans le modèle de SIEM. Mais, le point clé est le moyen

d’adapter la valeur de Φ et τ pour s’approprier à la condition du design et contribue à la

prédiction correcte de l’efficacité, c’est-à-dire, utiliser le Φ de SIEM avec le design τ, ou vice-

versa, dans la calcul. La logique est assez compliquée pour résumer en un paragraphe court, et

donc n’est pas citée ici. Pour de plus ample information, veuillez consulter le rapport principal

de la thèse (Chapitre 6, Partie 3). La logique est d’ailleurs disponible dans le logiciel.

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%100)1()( ,2 ⋅−= Φ− τ κ

η ref ed {4.8}

Les équations pour le design du pressurisateur ou du système de l’eau pressurisésont aussi proposées et vérifiées dans cette thèse ;

La concentration du gaz dissous,

')().( H gas MW P ygasConc ⋅⋅⋅= mg/l {4.9}

Le débit du gas ou d’ air dégazé,

))/(10082.0()(' 33K molmT PPQ R H y atm

⋅×⋅⋅−⋅⋅⋅⋅=Φ − m3/s {4.10}

où H’ = constante de Henry (molair /(m3

water -atm)) et y = fraction molaire du gaz

dans l’air. Pour l’air, y = 1.

La consommation énergétique de la compresseur,

pump

gauge pw

pump

atm pw PQPPQ

Power η η

)()( ⋅

=

−⋅

= Watt {4.11}

La consommation énergétique du pressurisateur au débit Q pw ,

pw

atm

air

comp

Qgas MW

gasConc

P

PT RPower ⋅⋅

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡−⎥

⎦

⎤⎢⎣

⎡⋅⋅=

−

)(

)(1

4.0

1)

4.1

14.1(

η

Watt {4.12}

Où R air = Constante universal du gaz. T = température absolue

5. L’Hydrocyclone

L’hydrocyclone est le procédé de séparation accéléré. Son concept de travail principalest de remplacer l’accélération gravitationnelle qui dirige la vitesse de décantation au moyen

de l’accélération centrifuge supérieure. MA et AURELLE ont proposé une approche nouvelle

de prévoir l’efficacité hydrocyclone, appelée le modèle d’analyse trajectoire pour

l’hydrocyclone biphasique (liquide-liquide), fondée sur la loi de STOKE. En fait, ce modèle

peut prévoir, par l’équation théorique, l’efficacité de séparation par classe des gouttelettes

d’huile de toute taille dans les eaux résiduaires ; à la différence des autres modèles qui sont

basés sur les concepts du modèle empirique et de la similarité. Ainsi, il est très pratique de

comprendre l’effet des paramètres reliés à la performance d’hydrocyclone. Le modèle est

constitué des équations qui dirigent 3 éléments de vitesse des gouttelettes d’huile à l’intérieur

du cyclone, comme montré ci-dessous.

∫=∫L

0 W

dZdR

zvvR U

dR {5.1}

R

V 2

18μ

2Δρd

U = {5.2}

0.65)R

nD)(

2i

πD

Q(V = {5.3}

3

19.1

2

63.81233.3 ⎟⎟

⎠

⎞⎜⎜

⎝

⎛ +⎟⎟

⎠

⎞⎜⎜

⎝

⎛ −+−=

z R

R

z R

R

z R

R

zW

W {5.4}

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2))2/tan(Znπ(0.5D

QzW

β ⋅−= {5.5}

)2

tan(2

β ⋅−= Z

D R n

z {5.6}

)2/5.1tan(

)(25.0o

n D L = {5.7}

Pour le hydrocyclone de type THEW, quand Z = L:

)2/(186.0nVZZ

D R = {5.8}

d = dc

d > dcd < dc

Z

R

L

R d

P a r o i s

LZVV

0.5Dn

0.186Dn

d

ηd

d c

d < d c

Zone 1 Zone 2

d = or > d c

100%

Fig. 5-1 Trajectories of oil droplets and typical efficiency curve

from trajectory analysis model

L’efficacité par classes peut être calculée par les relations:

Pour d ≥ diamètre de coupure,dc %100=d η {5.9}

Pour d < dc

%100

)2

186.0()2

(

)2

186.0(

22

22

⋅−

−=

nn

nd

d D D

D R

η

{5.10}

Les modèles sont valides dans ces conditions,

• Veuillez noter que les équations sont fondées sur la géométrie d’hydrocyclone liquide-

liquide initiée par Professeur THEW, en Angleterre. Pour les utiliser avec d’autres

types d’hydrocyclone, certaines constantes numériques (par exemple 0.63, 3.33, etc.)

dans les éq. 5.3, 5.4 et 5.8 doivent être réexaminées pour s’approprier aux géométries

nouvelles.

• Le modèle est valide pour la taille des gouttelettes (d) de 20 microns et plus.

• Les équations sont valides pour l’hydroclone ayant seulement 2 entrées.

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• Le débit de purge huile à surverse (Qoveflow) est généralement petite, pas plus de 10%.

Son effet sur les profils de vitesse et d’efficacité est petit, et donc, négligeable. La

Qoveflow recommandée est de 1.8 à 2 fois du débit entrant de l’huile.

• Le modèle tend à prévoir l’efficacité plus basse quand d < d80%, et celle plus haute

quand d > d80%. L’erreur dans la prédiction de la diamètre de coupure est environs

10-20%, c’est-à-dire, si la diamètre de coupure prévue est 50 microns, la diamètre decoupure constatée devrait être environs 40-45 microns. Pour de plus ample

information, veuillez consulter la référence.

MA et AURELLE a également inventé une nouvelle type d’hydrocyclone pour la

séparation simultanée de l’huile, des matières en suspension (MES) et de l’eau, appelée

l’hydrocyclone triphasique. Le modèle pour cet hydrocyclone est établi nouvellement dans

cette thèse et également basé sur le concept d’analyse trajectoire.

Solid-liquid Liquid-liquid (de type Thew)

DoDDs

DiDu

Dp

L5 L3L1L3

L4

Note: Di/D=0.25 pour 1- entrée et 0.175 for 2- entrée, Do/D=0.43,Ds/D=0.28, Du/D=0.19, Dp/D=0.034,

L1/D=0.4,L2/D=5, L3/D=15, L4/D=0.3, Solid-liquid :angle =12o, liquid-liquid angle =1.5

o

Fig. 5-2 Hydrocyclone triphasique

Entree

Entree

Sortie eau

Purge MES

Purge huile

Fig. 5.-3 Trajectoires de l’huile (sphere) and MES (cube) dans le hydrocyclone triphasique

Solide-liquide

(RIETEMA)

Liquide-liquide

(THEW)

Fig. 5-4 Profils des vitesses axiales dans le hydrocyclone triphasique

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Généralement, les équations pour l’hydrocyclone triphasique sont similaires à celles

pour l’hydrocyclone biphasique avec un peu de modifications, c’est-à-dire ;

• Remplacer l’éq. 5.3 par l’éq. 5.11.

0.65)R

nD

(2i

D4

π

(Q/2)

0.676V⎟⎟⎟

⎟

⎠

⎞

⎜⎜⎜

⎜

⎝

⎛

= {5.11}

•

Remplacer, dans l’éq. 5.1, « Dn » par « Do » et « L » par « L5 ».

Pour l’efficacité solide-liquide, elle peut être calculée par le model de RIETEMA ou

d’autres modèles compatibles dont la partie solide-liquide de l’hydrocyclone est conforme à la

géométrie de l’hydrocyclone de RIETEMA.

Finalement, les équations de la fuite de pression ou la perte de charge pour

l’hydrocyclone biphasique ou triphasique sont établies dans cette thèse :

Pour l’hydrocyclone biphasique, la perte de charge dans l’entrée/surverse (Po) et

l’entrée/sousverse (Pu) peuvent être calculée par les équations suivantes,1611.0

4

3.2

)1(

6.216 ⎟

⎟ ⎠

⎞⎜⎜⎝

⎛

−⋅=Δ

f n

o R D

QP bar (V : m/s et D : meter) {5.12}

4

2.2

6.4

n

u D

QP =Δ bar {5.13}

Pour l’hydrocyclone triphasique, la perte de charge entre l’entrée et la sortie d’huile

(Poil), entre la sortie d’eau (Pw) et la sortie de MES (PSS) peuvent être calculée par les

équations suivantes,

4D

2.12Q49.8water ΔP = bar {5.14}

4D

2.34Q21ssΔP = bar {5.15}

4D

2.03Q55

oilΔP = bar {5.16}

6. Les procédés membranaires

Le principe de travail

Le procédé membranaire est le procédé de séparation qui est basé, principalement

mais non entièrement, sur le concept de filtration. Physiquement, la membrane est le matériel

perméable ou semi-perméable qui restreindre la motion de certaines espèces. Théoriquement,

on peut toujours séparer certains composants d’émulsion à condition que la membrane choisie

convient à la différence dimensionnelle.

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• Le technique pour prévoir le débit du mélange de 2 émulsions différentes. Ce

technique est également proposé et vérifié dan cette thèse. Il est utile quand

l’émulsion mélangée peut être prévue et sa proportion tend à varier.

Permeat

Retentat

Membrane

pompe

Reservoir

d’alimentation

Alimentation

Po

Pi

Pp

Echangeur de chaleur

Fig. 6-2 Schéma de l’unité ultrafiltration tangentielle en “batch”

Quant au modèle mathématique des procédés membranaires, on met l’accent sur le

modèle de l’UF dans l’opération batch car il joue un rôle majeur dans le traitement d’eaux

résiduaires huileuses. On a adopté deux modèles largement utilisés : le modèle de la couche

de gel et le modèle des résistances en série. Les équations des deux modèles sont comme

montrées ci-dessous,

Le modèle de la couche de gel

)ln(C

C kV J

g β = l/(m2-h) {6.1}

Le modèle de résistance en série,

t m

t

PV RP J

⋅⋅+=

α φ ' l/(m2-h) {6.2}

Les valeurs de k, α ,β, φ, R ’m, et Cg varient selon les caractéristiques des eaux

résiduaires et les types de la membrane.

7. Le procédé thermique

L’intérêt principal du procédé de ce type est à la distillation hétéroazéotropique (DH).

L’application de la DH au traitement des slops de raffinerie ainsi que des retentats issus de

l’UF de l’huile de coupe est réalisée par LUCENA et AURELLE. Le procédé est accompli par

l’addition du produit chimique qui favorise la formation azéotropique (appelée extractant),

généralement les hydrocarbures, dans l’eau résiduaire. Ceci réduira la température d’ébullitiondu système, et donc économisera l’énergie. Ces applications apportent la possibilité de

revaloriser ces matériels résiduaires potentiels. Son application inverse, à savoir le stripping

(pour récupérer la substance volatile de l’eau au moyen de l’addition du vapeur), est

également réalisée.

L’hétéroazéotrope est l’un des phénomènes liés au équilibre vapeur-liquide-liquide

(VLLE). Le diagramme isobare du mélange immiscible hétéroazéotropique est démontré dans

la figure 7-1. Il est constaté que la courbe de bulle de ce diagramme est représentée par une

ligne horizontale à la température constante, appelée « la température azéotropique ». A

cette température, les deux liquides dans le mélange évaporent, quelle que soit la composition

du mélange. La composition de la vapeur est toujours yH jusqu’à ce que il reste seulement une

espèce de liquide dans la phase liquide.

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A

xw = 1

yw = 1

T P = const.

Huile pur Eau pur

xw = 0

yw = 0

Huile +V

xw , yw

Point d’ebullition

de B

Vapeur (V)

Eau + V

Huile+eau

xw = xH

yw = yH

Point d’ebullition

d’eau

THB C

D

xw,1

xw,2

xw,3xw,4=1

xw,5=1

xw,6=1

yw,1’ to yw,4

= yH

yw,5

yw,6

xw,1’

Azeotrope (H)

Fig. 7-1Diagramme d’équilibre isobar: température-concentration de l’eau residuaireshuileuses

Dans le cas des eaux résiduaires huileuses, spécialement celles concentrées comme le

slop ou le retentat de l’UF dérivant de l’UF de l’huile de coupe, si l’extractant est choisi

correctement, elles formeront une condition azéotropique et, pendant son évaporation, extraira

le teneur en eau des eaux résiduaires. L’eau sera extraite jusqu’à ce que le résidu devienne

l’hydrocarbure sans eau. Le vapeur condensera pour former le distillat contenant deux

couches séparées du extractant (la couche supérieure) et l’eau (la couche inférieure) de la

composition xH (= yH). Plus la valeur de yH est haute, mieux la capacité de l’extraction d’eau

est. Les données théoriques de yH, basées sur la loi de Raoult et la loi de Dalton, sont

également proposées comme montrées dans la table 7-1.

Table 7-1 Heteroazeotropic temperature and composition des certaines hydrocarbures

ExtractantMolecular

weight(g/mol)

TH

(deg. C)yH

(by molar)yH

(by volume)y H observed

(by volume)

C6H14 56 61.6 0.209 0.0351

C7H16 100 79.2 0.452 0.0922

C8H18 114 89.5 0.616 0.188

C9H20 128 94.8 0.827 0.3255

C10H22 142 97.6 0.914 0.495 0.468C11H24 156 98.9 0.959 0.6663

C12H26 170 99.5 0.98 0.7953 0.767

C13H28 184 99.8 0.991 0.890

C14H30 198 99.95 0.996 0.9542

C15H32 212 99.999 0.998 0.9702

C16H34 226 ≈ 100 0.999 0.9840

Les équations utilisées dans le calcul de l’entraîneur ou extractant, dans le cas des

eaux résiduaires huileuses et la vapeur, dans le cas du stripping, sont comme montrées ci-

dessous,

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Toutefois, il faut noter que il n’existe pas les produits chimiques et les doses

universels qui sont valides pour toute émulsion. Les types des produits chimiques efficaces,

de la concentration optimal et du niveau des polluants résiduaires doivent être évalués d’abord

d’échelle de laboratoire avant le design du procédé chimique complet.

En tout cas, à l’égard des design du réacteur, ils sont identiques, quel que soit le produit chimique appliqué. Ils sont pratiquement identiques au réacteur utilisé pour la

coagulation/floculation dans le traitement d’eau. Les équations utilisées pour l’évaluation du

réacteur et de l’agitateur, c’est-à-dire 8.1 à 8.3, sont incluses dans le logiciel.

5.0

⎟⎟ ⎠

⎞⎜⎜⎝

⎛ =

V

PG

μ {8.1}

Où G = Gradient de vitisse (t-1, normalement en sec –1)

μ = Viscosité d’eau,

P = Consommation énergétique d’agitateur(ML2s-3,e.g. watt)

V = Volume de réacteur (L3)

Pour les turbines,

ρ 53 Dn N P p= {8.2}

Pour les pales tournantes ,

μ

ρ

V

C nAvG d

2

3

= {8.3}

Où N p = Nombre de puissanceρ = Mass volumique de l’eau usée (= celle de l’eau)

n = Vitesse de rotation (rev/s) (e.q. 8.2)

n = Nombre de pales (e.q. 8.3)

D = Impeller diameter (m)

A = Surface d’une pale (m2)

v = vitesse périphérique (m2)

Cd = Coefficient de traînée des pales (normalement = 0.6)

M

M

Separateur

Bassin de floculationBassin de coagulation

Produit

chemiqueEmulsion

G = 50 s-1 G = 30 s-1 G = 20 s-1

G = 100-300 s-1

Fig. 8-3 L’example de design de coagulation-floculation

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Sommaire

9. Les procédés de finition

Bien que l’huile soit récupérée de l’eau par les procédés précédents, il y a

normalement de l’huile laissée dans l’eau traitée. En plus, les polluants d’autres formes

généralement présents dans les eaux résiduaires huileuses, surtout les agents tensioactifs/co-

tensioactifs, sont encore présents dans l’eau traitée, et contribue au haut niveau de la DOT.Ainsi l’eau traitée est normalement transmise au procédé de finition avant de se décharger au

corps d’eau recevant. Deux procédés de finition largement utilisés, c’est-à-dire le traitement

biologique et l’adsorption sur le charbon actif , sont réalisés.

Comme le procédé biologique est lui-même la science majeure, le calcul détaillé

n’est pas inclus dans les buts et objectifs du travail de cette thèse. Seulement les données

utiles sur le procédé biologique, concernant le traitement des eaux résiduaires huileuses, sont

réexaminées et incluses dans le rapport principal de cette thèse (Partie 3, Chapitre 11).

Les équations du design du filtre CAG, ainsi que la capacité d’adsorption (q) de

certains co-tensioactifs, sont réexaminées et incluses, c’est-à-dire,

Le temps d’opération totale avant le remplacement de lit (t T ):

Quand l’isotherme (q. VS.C relation) et les données du front d’adsorption (Qa et Ha

comme les fonctions de C) sont disponible ;

)( eo

abT

C C Q

Qq HAt

−−⋅⋅

= ρ {9.1}

Où tT = Temps d’opération totale avant le remplacement de lit

H = Hauteur de litA = Section de la colonne

ρ b = Mass volumique de charbon actif

q = Capacité d’adsorption

Qa = Capacité d’adsorption disponible dans la zone de

l’adsorption

Q = Débit

Co,Ce = Concentration initiale et concentration de la solution en

soluté en équilibre avec l’adsorbant

Quand les données mentionnées ci-dessus ne sont pas disponibles ;

)( eo

b

T C C Q

q HA E

t −

⋅⋅⋅

=

ρ

{9.2}

E est la saturation efficace de lit. La valeur recommandée est environs 50-95%.

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Sommaire

Ha

CCo

Ce

H

t = 0

S a t

u r e d

z o n e

Z o n e

d ’ a d s o r p t i o n

CCo

Ce

H

t = tT

Ha

Regeneration

de lit est necessaire.

Lit fixe

de

charbon

actif

HT

ENTREE

SORTIE

Vitesse =V

Fig. 9-1 Evolution du front d’adsorption

Temps de séjour (τ ):

)/( AQ

H =τ {9.3}

Perte de charge (P):

La parte de charge peut être calculée par l’équation Kozeny-Carman.

32

2)1(180

ε ρ

ε μ

⋅⋅⋅

−

= dpg

V H

Pc

m {9.4}

10. La méthodologie générale pour la sélection des procédés

En fin de achever le premier objectif, la méthodologie sur la sélection du procédé

de traitement des eaux résiduaires huileuses est proposé, comme montré dans la table 10-1.

Les filières de procédé recommandés pour le traitement d’émulsion de l’huile de coupe et

l’émulsion secondaire, fondés sur les recherches GPI, sont également proposés, comme

montrés dans les figures 10-1 et 10-2.

[20]

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Sommaire

T a b l e 1 0 - 1 L a m é t h o d o l o g i e

g é n é r a l e p o u r l a s é l e c t i o n d e s p r o c é d é s

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Développement du logiciel

L’objectif final de cette thèse est de développer un logiciel de design et calcul d’une

filière de traitement adoptée à l’épuration des eaux résiduaires huileuses. Ceci vise à valoriser

et appliquer le savoir-faire ainsi que les résultats importants de la recherche, en les présentant

de façon conviviale. Pour réussir à ces objectifs, le logiciel, à savoir le logiciel GPI , est diviséen 4 modes majeurs, c’est-à-dire,

• Le mode de documentation électronique : fournit les connaissances de

fond ainsi que une base de données utile sur la pollution d’huile et les

procédés de traitement. En fait, le textbook dans la Partie 3 est transformé en

directoire « e-book » du logiciel.

• Le mode de recommandation du procédé : fournit les recommandations

pour restreindre la gamme des procédés faisables pour tout influents débits.

Le critère de sélection est comme proposé dans les méthodologies dans la

Partie 3, Chapitre 12.

• Le mode de design (calcul) : est utilisé pour évaluer l’unité procédé. Les

modèles utilisés dans le calcul sont comme résumés dans la Partie 3.

• Le mode d’analyse (simulation) : permet l’utilisateurs d’intégrer tout

procédé de séparation qui est inclus dans la base de données du logiciel, en

but d’établir leur propre filières de procédé de traitement. Et le logiciel va

simuler la filière de procédé pour prévoir l’efficacité de chaque unité.

Le logiciel est développé pour être « upgradable ». Son architecture compose de la

base de données sous forme de fichier texte ordinaire et les « sub-programmes ». Pour« upgrader » le logiciel, il peut se faire facilement en ajoutant les données, comme le nom de

nouveau procédé et son paramètre de lien nécessaire pour le calcul, à la base de données. Le

logiciel liera automatiquement le nouveau procédé à l’interface graphique d’utilisateur. Quant

au calcul du « sub-programme » du nouveau procédé, il peut être développé séparément en

utilisant la langue de programmation Visual Basic. Le moyen le plus facile est de copier le

code de source d’un procédé existant et modifier l’équation pour convenir au nouveau

procédé. Après la compilation dans un fichier exécutable, il peut être copié pour remplacer

l’ancien fichier de logiciel GPI sans réinstaller le logiciel. Ainsi le logiciel pourrait se

développé davantage jusqu’à ce qu’il peut couvrir plus de recherches et procédés dans

l’avenir. Les interfaces du logiciel pour chaque mode sont comme montrées dans les figures

suivantes.

Cette thèse est accomplie par les supports considérables de Professeur AURELLE,

mon directeur de thèse, et M. Surapol SAIPANICH, PD-G de la société Progress Technology

Consultants Co.,Ltd. (Thailand). Je suis très reconnaissant pour leur conseil et

encouragement.

[23]

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étape 1 “Wastewater data input” étape 2 “Process selection”

étape 3 “Process data input” étape 4 “Result”

Fig. 5 L’interface graphique d’utilisateur du mode de design

Graphic editing area

Basic drawing tool bar

Calculation button

Input and result screen(displayed when double clicking at the icon)

Category selection

Process selection

Fig. 6 L’interface graphique d’utilisateur du mode d’analyse

[26]

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Résumé

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Nom : RACHU Prénom : Srayut

COMPUTER PROGRAM DEVELOPMENT FOR OILY WASTEWATER

TREATMENT PROCESS SELECTION, DESIGN AND SIMULATION

562 pagesThèse de Doctorat : Science des procédés

Spécialité :Génie des Procédés et de l’Environnement

I.N.S.A. Toulouse, 2005, n°

Résumé :

The aims of this thesis is to summarize the researches of GPI lab on oily wastewater

treatment processes and establish general design procedure and consideration for such

processes, and then, value and maximize the use of these established knowledge in the form

of computer program.

The first part of the thesis contributes to reviewing the related researches in GPI lab,

directed by Prof. Y. AURELLE. Significant finding of each thesis is realized.

The second part of the thesis is generalization of models. In this part, models proposed

in the researches are cross-verified with other researches and generalised. New models are

also proposed when there is no existing model or the existing models need to be revised.

The third part of thesis contributes to composure of a textbook that includes all

significant finding from every research as well as the generalized models and their limitations

of every process found in the second part. The textbook includes these processes, i.e.

skimmer, decanter, coalescer, dissolved air flotation, hydrocyclone, membrane processes,

thermal process, chemical process, biological treatment and carbon adsorption, as well as

guideline for process selection.

The final part of the thesis is program development. The program developed in this

thesis consists of 4 main features, i.e. process recommendation for the wastewater being

considered, design of unit process, simulation of process train and provision of knowledge on

process design in the form of e-book, based on the text book in the third part.

The textbook, the program and its source code may be available upon request. For

more information, please contact Pr. Y. AURELLE or [email protected]

Mots clés : Skimmer, Decanter, Coalescer, Dissolved air flotation, Hydrocyclone, Membrane,

Distillation, Destabilization, Biological treatment, Adsorption, Program, Oily wastewater

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PRODUCTION SCIENTIFIQUE

Publications dans des actes de congrès avec comité de lecture, sur texte complet

S. Rachu, Y. Aurelle, S. Saipanich .

Simulation program on hydrocarbon polluted wastewater treatment processes

16th International Congress of Chemical and Process Engineering (CHISA 2004),

Prague, Czech Republic, 22-26 August 2004

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Remerciements

J e r emer ci e si ncèr ement Monsi eur l e prof esseur Yves AURELLE pour

m' avoi r accuei l l i dans son équi pe, pour m' avoi r f ai t par t ager ses

connai ssances et ses i dées i nnovant es et pour son assi st ance t out au l ong

de ce t r avai l .

I woul d l i ke t o t hank Dr . Sur apol SAIPANICH f or hi s over whel mi ng

suppor t and encour agement . If not because of him, this work would never happen.

J ' adresse égal ement t ous mes r emer ci ements à :

Monsi eur Di mi t r e HADJIEV , pr of esseur à l ' USB de Lor i ent , , et

Monsi eur J ean Luc ROLS, pr of esseur à l ' UPS de Toul ouse pour avoi r accept é

de j uger ce t r avai l en f ai sant par t i e du j ur y,

Monsi eur BEN AIM , pr of esseur émér i t e à l ' I NSA et Monsi eur Al ai n

LINE, pr of esseur à l ' I NSA, pour avoi r accept é de par t i ci per au j ur y de

cet t e t hèse,

Monsi eur Henr y ROQUES prof esseur émér i t e à l ' I NSA pour sa pr ésence

au j ur y de cet t e t hèse,

I woul d l i ke t o t hank my col l eagues at Progress Technology

Consultants Co. , Lt d ( Thai l and) f or t hei r suppor t and t hei r ki ndness. Many

t hanks t o Kr i sana KHWANPAE f or hi s gr eat support on pr ogr ammi ng. Mygr at i t ude t o Bowornsak WANICHKUL, Chai yaporn PUPRASERT and Pi sut

PAINMANAKUL f or t hei r pr i cel ess advi ce. I owe you guys a boon.

Thank t o t he French Embassy in Thailand f or t hei r f i nanci al suppor t

dur i ng t he f i r st t wo years of my st udi es. Thanks t o the embassy personnel s,

par t i cul ar l y, Khun Hataiporn, Khun Wanpen f or t hei r assi st ance, Khun

Chanida f or her super b t r ansl at i on.

Mes r emerci ement s s' adr essent égal ement à t out es l es per sonnes qui

m' ont beaucoup ai dé t ant à Monsi eur Loui s LOPEZ, Monsi eur Gi l l es HEBRARD,Madame Eugéni e BADORC, Madame Dani èl e CORRADI et Madame AURELLE. J e

r emerci e égal ement mes ami s du l abo, part i cul i èr ement , Ol i ver LORAIN et

Eduar do LUCENA .

Enf i n, j e r emer ci e mes ami s Thaï l andai s de Toul ouse ( P’ Lek, P’ Tou,

P’ Aot e, A, Pond, Por , Pew, Gol f , Mon, Aey- Al exandr e, 1, Fon, Chi n, Chat ,

Pat , Vee, Choke, Si t h, J u, Bomb, et c. ) qui m' ont assur é par l eur humour ,

une ambi ance sympat hi que et per mi s d’ ef f ect uer de gr andes f êtes pendant mon

séj our en Fr ance.

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Table des matières

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Contents

- i -

Contents

Page

Part I Introduction and bibliography

Chapter 1 Introduction 2

Chapter 2 Objectives 4

Chapter 3 Bibliography

3.1 Categories of hydrocarbon-polluted wastewater and treatment 6

processes

3.2 STOKE’s law 7

3.3 Decanting 7

3.4 Coalescer 10

3.4.1 Thesis of AURELLE [3] 10

3.4.2 Thesis of SANCHEZ MARTINEZ [6] 11

3.4.3 Thesis of DARME [7] 12

3.4.4 Thesis of TAPANEEYANGKUL [8] 14

3.4.5 Thesis of DAMAK [9] 15

3.4.6 Thesis of MA [16] 17

3.4.7 Thesis of SRIJAROONRAT [10] 17

3.4.8 Thesis of WANICHKUL [11] 18

3.5 Flotation 18

3.5.1 Thesis of SIEM [12] 18

3.5.1 Thesis of AOUDJEHANE [13] 19

3.5.1 Thesis of DUPRE [14] 203.5.1 Thesis of PONASSE [15] 21

3.6 Hydrocyclone 22

3.6.1 Thesis of MA [16] 22

3.6.2 Thesis of CAZAL [17] 24



3.6.5 Thesis of PUPRASERT [25 ] 26

3.7 Ultrafiltration and other membrane processes 26

3.7.1 Thesis of BELKACEM [18] 27

3.7.2 Thesis of TOULGOAT [19] 29

3.7.3 Thesis of MATAMOROS [20] 303.7.4 Thesis of SRIJAROONRAT [10] 32


3.8 Thermal treatment 33

3.8.1 Thesis of LUCENA[24] 33

3.8.2 Thesis of LORRAIN[23] 34


3.9 Chemical treatment 34

3.9.1 Thesis of ZHU[21] 35

3.9.2 Thesis of YANG[22] 37

3.10 Biological treatment 38


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Contents

- ii -

Contents (Con’t)

Page

3.11 Skimmer 38

3.12 Application researches 39



Chapter 4 Conclusion 44

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Contents

- iv -

Contents (Con’t)

Page

5.1.4 Conclusion and generalized model of two-phase 84

hydrocyclone

5.1.5

Generalized model for pressure drop of two-phase 85hydrocyclone

5.2 Three-phase hydrocyclone 87

5.2.1 Model development and verification for liquid-liquid 87

section

5.2.2 Model development and verification for solid-liquid section89

5.2.3

Generalized Model for pressure drop of three-phase 90

hydrocyclone

Chapter 6 Membrane process

6.1

Ultrafiltration 93

6.1.1

Resistance model 94

6.1.2 Film theory based model 96

6.1.3 Model verification 97

6.1.4 Flux prediction for mixture of cutting oil microemulsion 102

and macroemulsion

6.1.5

Theoretical flux prediction for batch cross-flow UF process 104

6.1.6 UF efficiency 107

6.1.7 Minimum and maximum transmembrane pressure and 108

power required

6.1.8 Conclusion and generalized model of UF 110

6.2

Nanofiltration and Reverse osmosis 110Chapter 7 Heteroazeotropic Distillation

7.1 Theoretical model 113

7.2 Model verification 116

7.3 Conclusion and generalized model of heteroazeotropic distillation 116

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Contents

- v -

Content

Page

Part III Summary of researches: Oily wastewater treatment

Chapter 1 Oily or hydrocarbon-polluted wastewater

1.1 Introduction 119

1.2 Hydrocarbons and oils 119

1.2.1 Hydrocarbons 119

1.2.2 Fats and oils 124

1.2.3 Petroleum and petroleum products 124

1.2.4

Oils in term of oily wastewater 126

1.3 Other compositions of oily wastewater 126

1.3.1 Surfactants 126

1.3.2 Soaps 127

1.3.3

Co-surfactants 1281.3.4 Suspended solids 1281

1.3.5

Other components 128

1.4 Categories of oily wastewater 128

1.4.1

Classification by the nature of the continuous phase 128

1.4.2 Classification by the stability of oily wastewater 128

1.4.3 Classification by the degree of dispersion 129

1.5 Characteristics of certain oily wastewaters 132

1.6 Standards, Laws, and Regulations 133

Chapter 2 Overview for oily wastewater treatment process design

2.1

Decantation velocity and STOKE’s law 1382.2

Application of surface chemistry for oily wastewater treatment 139

2.2.1 Liquid-gas and liquid-liquid interfaces 139

2.2.2 Liquid-solid and liquid-liquid-solid interfaces 142

2.2.3 Capillary pressure and LAPLACE’s law 146

2.3 Important parameters in oily wastewater treatment and 147

their method of analysis

2.3.1

Oil concentration 147

2.3.2 Size distribution , spectrum or granulometry 149

2.3.3

Other parameters 155

2.4 Overview of oily wastewater treatment processes 155

2.4.1

Decanter 156

2.4.2 Coalescer 156

2.4.3 Hydrocyclone 156

2.4.4 Dissolved air flotation (DAF) 157

2.4.5

Skimmer 157

2.4.6 Membrane processes 157

2.4.7 Thermal processes 157

2.4.8 Chemical process 158

2.4.9 Finishing processes 158

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Contents

- vi -

Content (Con’t)

Page

2.5 Determination of degree of treatment 158

2.5.1

Overall degree of treatment 1582.5.2 Degree of treatment of each process 158

Chapter 3 Oil skimmer

3.1 General 162

3.2 Oil drum skimmer 164

3.2.1 Working principles 164

3.2.2 Design calculation and design consideration 169

3.3 Oil disc skimmer 171



3.4 Productivity comparison between drum and disc skimmer 1733.5 Advantage and disadvantage of drum and disc skimmer 174

Chapter 4 Decanting

4.1 General 176

4.2 Simple Decanter or API tank 177


4.2.2 Design calculation 179

4.2.3

Design considerations 182

4.2.4 Construction of simple decanters 183

4.3 Compact decanter 186

4.3.1

Working principles 1864.3.2 Design calculation 190

4.3.3 Design considerations 192

4.3.4 Variations, advantage and disadvantage of compact 193

decanters

Chapter 5 Coalescer

5.1 General 195

5.2 Granular bed coalescer 195



5.2.3 Design consideration 2115.2.4 Variations, advantage and disadvantage of granular 212

bed coalescer

5.3 Guide coalescer 213



5.3.3 Design consideration 215

5.4 Fibrous Bed coalescer 216



5.4.3 Design consideration 227

5.4.4 Variations, advantage and disadvantage of fibrous bed 229coalescer

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Contents

- vii -

Content (Con’t)

Page

Chapter 6 Dissolved air flotation

6.1 General 232

6.2 Working principles 233

6.2.1

Filter based model 233

6.2.2 Population balance model 238

6.2.3 Generalized model of DAF from combination of 240

filtration based model and population balance model

6.2.4 Influent parameters 241

6.3 Design calculation 244

6.4 Design consideration and construction of DAF reactor 254

6.5

Pressurized water system or saturator 262

6.5.1

Working principle and design calculation 2626.5.2 Type of saturator and injection valve 267

6.6 Variations, advantage and disadvantage of DAF 270

Chapter 7 Hydrocyclone

7.1 General 272

7.2 Two-phase hydrocyclone 273


7.2.2

Design calculation 289

7.2.3 Design considerations 292

7.2.4 Variations, advantage and disadvantage of 295

hydrocy clone7.3 Three-phase hydrocyclone 295



7.3.3

Advantage and disadvantage of three-phase 299

hydrocyclone


8.1 General 300

8.1.1 Classification of membrane processes 300

8.1.2 Mode of operation of membrane processes 302

8.1.3

Membrane structure 3028.1.4 Membrane material 303

8.1.5

Membrane module type 306

8.2 Ultrafiltration (UF) 311

8.2.1 Basic knowledge and working principles 311

8.2.2 UF process design for oily wastewater treatment 323

8.2.3 Design consideration and significant findings from 338

GPI’s researches

8.3 Microfiltration (MF) 349

8.3.1

Basic knowledge and working principles 349

8.3.2 Significant findings on MF for oily wastewater 350

treatment from GPI researches

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Contents

- ix -

Chapter 11 Finishing processes

11.1 General 397

11.2 Biological treatment 397

11.2.1 Basic knowledge 397

11.2.2

Design consideration and significant finding on 404 biological treatment for oily wastewater from GPI’s

researches

11.3 Adsorption 405

11.3.1

Activated carbon (AC) 406

11.3.2 Basic knowledge 407


Chapter 12 Guideline for treatment process selection and examples of treatment

processes for certain oily wastewaters

12.1 Guideline for treatment process selection 414

12.1.1

Oil film 41412.1.2

Primary emulsion 416

12.1.3 Secondary emulsion 417

12.1.4 Macroemulsion and microemulsion 418

12.1.5 Concentrated oily wastewater or refinery slops 418

12.2 Examples of treatment processes for certain oily wastewaters 419

12.2.1 Treatment of cutting oil emulsion 419

12.2.2

Treatment of non-stabilized secondary emulsion 420

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Contents

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Contents

Page

Part IV Computer program development

Chapter 1 Program overview

1.1 Introduction 423

1.2 Conceptual design of the program 423

1.2.1 E-book mode 424

1.2.2 Recommendation mode 426

1.2.3 Design mode 427

1.2.4

Analysis mode 428

1.3 Development tools 432

1.3.1 Main development software package 432

1.3.2 Special graphic user interface (GUI) component 433

1.3.3

The third party software 4331.4 Program architecture 434

1.4.1

Forms 434

1.4.2 Modules 437

1.4.3

Modules 437

1.4.4 Class modules 437

1.4.5 Add-in project 437

1.5 Program development 438

Chapter 2 Program reference and user manual

2.1 Overview of the program 439

2.1.1

Main program 4392.1.2

Project window 441

2.1.3 E-books worksheet 441

2.1.4 Recommend worksheet 442

2.1.5 Design worksheet 444

2.1.6 Analysis mode 445

2.1.7 Warning dialog box 447

2.2

Program capability 447

2.3 Program limitation 447

2.4

System requirement 449

2.5 User instruction 449

2.5.1

Program Installation 449

2.5.2 Starting the program 450

2.5.3 Using E-book mode 450

2.5.4 Using Recommend mode 450

2.5.5

Using Design mode 452

2.5.6 Using Analysis mode 454

2.5.7 Printing and file operation 457

2.6 Upgrading procedure and recommendation for further 458

development

2.6.1 Upgrading procedure 458

2.6.2

Recommendation for further development 460

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Contents

- xi -

Contents

Page

Chapter 3 Process references

1)

Drum skimmer 4632)

Disk skimmer 465

3) Simple decanter 467

4)

Compact decanter 470

5) Customized decanter 473

6) Granular bed coalescer 476

7) Brush type bed coalescer 480

8) Dynamic fibrous bed coalescer 484

9) Metal wool bed coalescer 488

10) Dissolved air flotation 492

11) Two-phase hydrocyclone 498

12) Three-phase hydrocyclone 502

13) Ultrafiltration 506

14) Reverse osmosis 510

15) Heteroazeotropic distillation 513

16) Stripping 515

17) Chemical destabilization, coagulation-flocculation 517

18) Biological treatment 520

19) GAC filter 522

20) Customized concentrator 526

21) Customized oil separator 528

22) Customized inline concentrator 53023) Inlet 532

24) Outlet 533

25) Flow merge 534

26) Flow split 536

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Contents

- xii -

Contents

Page

General conclusion 537

Reference 540

Annexe 546

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Nomenclatures

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Nomenclature

xiii

Nomenclature

a Constant for population balance equation

A Flow area (Cross sectional) area of decanter L2

A Cross section area of flotation column L2

A Flow area in membrane module (= HW) L

2

C Considered or required or design oil concentration ML-3

C’g The 1st (or lower or pseudo) gel concentration in film model,

used at the lower range of concentration before inflection

point in flux vs. Log (Concentration) curve (in mass/ volume

or volume/volume)

ML-3

Ca Capillary number = μo V/γo

Cg Gel concentration in film model (in mass/ volume or

volume/volume)

ML-3

Co Initial oil concentration of feed or influent wastewater ML-3

Cod Inlet concentration of the droplet diameter “d” M/L3

Cod Inlet concentration of the droplet diameter “d”, dilution effect

from addition of pressurized water is not included.

M/L3

Conc(Air) Concentration of dissolved air in pressurized water M/L3

Conc(O2) Concentration of dissolved oxygen in pressurized water M/L3

Cy50 Cyclone number of d 50%

d Diameter of dispersed phase, in our case, oil L

D Water depth or L

Diameter of the skimmer or L

Diameter of coalescer bed, such as diameter of brush or L

Nominal diameter of 3-phases hydrocyclone (the largest

diameter of the cyclone) or

L

Hydraulic diameter of flow channel in membrane module

(Channel between membrane surface and membrane module

wall)

L

d b Average diameter of air bubble L

d c Cut size of the decanter or API tank L

d F Diameter of fiber in fibrous-bed coalescer L

Di Diameter of inlet port of hydrocyclone L

Dn Nominal diameter of hydrocyclone. ( = diameter of inlet of

lower conical part for Thew type hydrocyclone)

L

d p Diameter of collector or coalescer bed material, such as resin L

d xx% , d xx Diameter of droplet corresponding to removal efficiency of

“xx”%, such as d 75%, etc. d 100% or d c stands for cut size

M

e Surface roughness of flow channel L

f Friction factor of Darcy-Weisbach’s equationg Gravitational acceleration L/T2

G Turbulent intensity

H Travelling or rising distance of oil drop, depending on

configuration of the decanter. Exp. For PPI, H = distance

between plates or

L

Height of bed, or bed depth of coalescer or L

Height of flow channel in membrane module or L

Height of contact (or effective) zone of flotation column. If

both pressurized water and wastewater are fed at the bottom

of the column, the contact zone is equal to column height.

L

Href H at reference operating condition of DAF reactor L

Hreq H at design or required operating condition of DAF reactor LI Immersion depth of the disk in liquid or L

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Nomenclature

xv

V Empty bed velocity or L/T

Empty bed velocity of DAF (based on sum of pressurized water

and wastewater flow) or

L/T

Tangential velocity of particle or oil drop in hydrocyclone or L/T

Recirculation velocity in cross-flow membrane process L/T

Vol Volume L3

Vr Relative velocity between bubble and oil drop L/T

W Axial velocity of particle or oil drop in hydrocyclone or L/T

Width of flow channel in membrane module L

x Molar fraction in liquid (water) Mol/mol

y Molar fraction in vapor Mol/mol

Z Distance in axial axis of hydrocyclone L

ΔP Pressure drop, (in m of water, for Kozeny-Carman’s equation)

Or pressure drop in bar, for hydrocyclones

ΔPo Pressure drop across inlet and overflow port Bar

ΔPoil Pressure drop across inlet and oil outlet port Bar

ΔPSS Pressure drop across inlet and suspended solids outlet port Bar

ΔPu Pressure drop across inlet and underflow port BarΔPwater Pressure drop across inlet and water outlet port Bar

Greek Letter

Φ Air flowrate in flotation column L3/T

Π Vapor pressure (some references use “Psat”.) LT-2M-1

α Probability of collision or

Exponent of recirculation velocity in gel resistance equation

α.ηexp Corrected experimental removal efficiency factor of the tank

for the droplet diameter “d”

α, α3φ, αThew Correction factor for inlet velocity of hydrocycloneβ Conical angle of lower part of hydrocyclone or

Exponent of recirculation velocity in film model of

membrane

β0, β1, … , βi Adhesion efficiency between bubbles and oil drop/ bubble

agglomerate for population balance equation

ε Porosity or void ratio

φ Constant in gel resistance equation

γo Superficial tension of oil M/T2

γo/w Interfacial tension between oil and water M/T2

γo/w Interfacial tension between oil and water MT-2

ηoverall Overall efficiency of pumpκ Collision rate constant for population balance equation T

-1

κ2 Modified collision rate constant for population balance

equation (κ = κ2Φ)

T-2

κ2,ref Modified collision rate constant at reference condition T-2

κ2,req Modified collision rate constant at design or required

condition

T-2

μ Dynamic viscosity ML-1

T-1

μC Dynamic viscosity of continuous phase, in our case, water L2/T

μd Dynamic viscosity of dispersed phase, in our case, oil L2/T

μo Dynamic viscosity of oil M/(L.T)

νo Kinematic viscosity of oil L2/T

θo/w Contact angle between oil and water surface (180o means the

oil drop in perfectly sphere.)

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Nomenclature

xvi

ρ Density ML-3

ρair Density of air at required operating condition M/L3

ρc Density of continuous phases M/L3

ρm Density of emulsion M/L3

Δρ Difference between density of dispersed and continuous

phases

M/L3

τ Retention time T

ηd Removal efficiency of the tank for the droplet diameter “d” %

ηd,ref Removal efficiency of DAF process for the droplet diameter

“d” at the reference retention time (25 minutes)

%

ηDiff Efficiency factor from diffusion

ηInt Efficiency factor from direct interception

ηSed Efficiency factor from sedimentation

ηSed Efficiency factor from sedimentation

ηt Total Removal efficiency %

ηtheo Theoretical removal efficiency factor of the tank for the

droplet diameter “d”

?A, ?BB Subscript indicating component A and B respectively

?H Subscript indicating heteroazeotropic point

?mac Subscript indicating macroemulsion

?mic Subscript indicating microemulsion

?mix Subscript indicating mixture

?o Subscript indicating initial condition

?ref Subscript indicating reference condition

?θ b Superscript indicating boiling temperature

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I-i

Contents

Page


Chapter 1 Introduction I-2

Chapter 2 Objectives I-4


3.1 Categories of hydrocarbon-polluted wastewater and treatment I-6

processes

3.2 STOKES law I-7

3.3 Decanting I-7

3.4 Coalescer I-10

3.4.1 Thesis of AURELLE [3] I-10

3.4.2 Thesis of SANCHEZ MARTINEZ [6] I-11

3.4.3 Thesis of DARME [7] I-12

3.4.4 Thesis of TAPANEEYANGKUL [8] I-14

3.4.5 Thesis of DAMAK [9] I-15

3.4.6 Thesis of MA [16] I-17

3.4.7 Thesis of SRIJAROONRAT [10] I-17

3.4.8 Thesis of WANICHKUL [11] I-18

3.5 Flotation I-18

3.5.1 Thesis of SIEM [12] I-18

3.5.1 Thesis of AOUDJEHANE [13] I-19

3.5.1 Thesis of DUPRE [14] I-203.5.1 Thesis of PONASSE [15] I-21

3.6 Hydrocyclone I-22

3.6.1 Thesis of MA [16] I-22

3.6.2 Thesis of CAZAL [17] I-24

3.6.3 Thesis of SRIJAROONRAT [10] I-25


3.6.5 Thesis of PUPRASERT [25 ] I-26

3.7 Ultrafiltration and other membrane processes I-26

3.7.1 Thesis of BELKACEM [18] I-27

3.7.2 Thesis of TOULGOAT [19] I-29

3.7.3 Thesis of MATAMOROS [20] I-303.7.4 Thesis of SRIJAROONRAT [10] I-32


3.8 Thermal treatment I-33

3.8.1 Thesis of LUCENA[24] I-33

3.8.2 Thesis of LORRAIN[23] I-34


3.9 Chemical treatment I-34

3.9.1 Thesis of ZHU[21] I-35

3.9.2 Thesis of YANG[22] I-37

3.10 Biological treatment I-38


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I-iii

Table

Page

Table 3.1 Summary of characteristics of wastewaters and sludges for “on site” I-24

experiment

Table 3.2 Summary of characteristics of synthetic wastewaters I-24

Table 3.3 Membranes test by MATAMOROS I-31

Figure

Page

Fig. 1-1 Summary of researches of Prof. AURELLE on hydrocarbon-polluted I-3

wastewater treatment

Fig. 3.1 Schematic of decante I-8

Fig. 3.2 Schematic of Phase inversion coalescer I-15

Fig. 3.3 Three- phase hydrocyclone I-23

Fig. 3.4 Hydrocyclone tested by WANICHKUL I-26

Fig. 3.5 Ultrafiltration models used by BELKACEM I-29

Fig. 3.6 Treatment processes for macro- and microemulsion, recommended I-32

by MATAMORS

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Chapter 1 Introduction

2 I-2

Chapter 1 Introduction

Water pollution is one of the most important environmental problems. Wastewater

from agriculture and industrial processes, as well as domestic wastewater, is the main

pollutant source that causes water pollution problem. There are many substances that can

deteriorate water quality, thus classified as water pollutants, such as, organic matter fromdomestic wastewater, chemicals from industrial wastewater. Some valuable substances, such

as sugar, flour, oil, will become major pollutants when discharged into water bodies.

Among various kinds of pollutants, hydrocarbon, or simply called oil, is one of the

most severe pollutants because of its intrinsic properties. Small amount of hydrocarbon can

spread over wide area of water surface and affect the oxygen transfer, so cause adverse effect

to marine or water ecology. Furthermore, the hydrocarbon contributes to very high

biochemical oxygen demand and is relatively difficult for biodegradation, which is the major

natural self-purification process. So it can last relatively long in the water and causes long -

term effect.

Our laboratory has researched for various treatment processes that cover various types

of wastewater polluted by hydrocarbons. In the few decades of researches, many theses had

been accomplished as shown in Fig. 1.1. Among these, many innovations had been created

and some had been patented and commercialized. Some researches are the key steps to

understand or improve the treatment efficiency and process design. However, because there

are many kinds of oily wastewater, as well as, there are many kinds of treatment processes.

Moreover, treatment efficiency of each treatment process will vary with characteristic of

wastewater. Then, it may cause some difficulties in selecting or designing appropriate process

train that can deal with the wastewater considered as well as predicting effluent quality

accurately.

According to the difficulty stated above, this thesis had been initiated to provide the

solution and tool about how to select and optimize the process or processes train to treat the

specified wastewater to meet required effluent standard, as well as providing details about

hydrocarbon polluted wastewater and each treatment process. It can be, also, applied for

designing the process to recover valuable hydrocarbons from hydrocarbon/water mixtures in

some industries, such as perfume or pharmaceutical industries.

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3 I-3

F i g .

1 - 1 S

u m m a r y o f r e s e a r c h e s o f P r o f .

A U R E L L E o n h y d r o c a r b o n - p o l l u t e d w a s t e w a t e r t r e a t m e n t

H y d r o c a r b o n -

p o l l u t e d o r o i l y

w a s t e w a t e r

t r e a t m e n t

D e c a n t e r

“ S p i r a l o i l ” d e c a n t e r

C H E R I D [ 4 ] , 1 9 8 6

S k i m

m e r

“ D r u m s k i m m e r ” &

“ d i s k s k i m m e r ”

T H A N G T O N G T A W I [ 5 ] , 1

9 8 8

C o a l e s c e r

“ G r a n u l a r b e d c o a l e s c e r ”

A U R E L L E [ 3 ] , 1 9 8 0

“ G r a n u l a r b e d c o a l e s c e r f o r

s t a b i l i z e d e m u l s i o n ”

D A R M E [ 6 ] , 1 9 8 3

“ D y n a m i c f i b r o u s b e d c o

a l e s c e r ”

T A P A N E E Y A N G K U L [ 8 ] , 1 9 8 9

“ P u l s e d g r a n u l a r b e d c o a

l e s c e r ” &

“ P h a s e i n v e r s i o n c o a l e s c

e r ”

D A M A K [ 9 ] , 1 9 9 2

F l o t a t i o n

“ F l o t a t i o n f o r o i l - w a t e r

s e p a r a t i o n ”

S I E M [ 1 2 ] , 1 9 8 3

“ A p p l i c a t i o n o f f l o t a t i o n

o n o i l y

w a s t e w a t e r t r e a t m e n t ”

A O U J E H A N E [ 1 3 ] , 1 9 8

6

“ M a t h e m a t i c s m o d e l o f

D A F ”

D U P R E [ 1 4 ] , 1 9 9 5

“ D e e p s h a f t D A F ”

P O N A S S E [ 1 5 ] , 1 9 9 7

H y d r o c y c l o n e

“ 2 & 3 - p h a s e h y d r o c y c l o n e ”

M A [ 1 6 ] , 1 9 9 3

“ 2 - p h a s e h y d r o c y c l o n e

f o r s t o r m w a t e r t r e a t m e n t ”

C A Z A L [ 1 7 ] , 1 9 9 6

“ H y d r o c y c l o n e w i t h g r i t p o t ” &

“ C o m b i n a t i o n C o a g u l a t i o n

- D A F - H y d r o c y c l o n e ” s e

p a r a t o r

P U P R A S E R T [ 2 5 ] , 2 0 0 4

U l t r a f i l t r a t i o n

& m

e m b r a n e

p r o c

e s s e s

“ U l t r a f i l t r a t i o n f o r c u t t i n g o

i l

e m u l s i o n t r e a t m e n t ”

B E L K A C E M [ 1 8 ] , 1 9 9 5

“ U l t r a f i l t r a t i o n f o r t h e r m

a l

e m u l s i o n t r e a t m e n t ”

T O U L G O A T [ 1 9 ] , 1 9 9 6

“ M e m b r a n e p r o c e s s e s f o r c u t t i n g

o i l e m u l s i o n t r e a t m e n t ”

M A T A M O R O S [ 2 0 ] , 1 9

9 7

T h e r m a l

t r e a t

m e n t

“ C r y s t a l l i z a t i o n f o r o i l - w a t e

r

s e p a r a t i o n ”

L O R R A I N [ 2 3 ] , 2 0 0 2

“ H e t e r o a z e o t r o p i c d i s t i l l a t i o n ”

L U C E N A [ 2 4 ] , 2 0 0 4

C h e m i c a l

t r e a t

m e n t

“ D e s t a b i l i s a t i o n o f e m u l s i o

n ”

Z H U [ 2 1 ] , 1 9 9 0

“ L o w - p o l l u t i o n e m u l s i o

n ”

Y A N G [ 2 2 ] , 1 9 9 3

“ G u i d e d & M i x e d b e d c o a l e s c e r ”

S A N C H E Z M A R T I N E Z [ 5 ] , 1 9 8 2

A p p l i c a t i o n

“ T r e a t m e n t o f

s t a b i l i z e d e m u l s i o n ”

W A N I C H K U L

[ 1 1 ]

, 2 0 0 0

“ T r e a t m e n t o f n o n -

s t a b i l i z e

d e m u l s i o n ”

S R I J A R O

O N R A T [ 1 0 ]

, 1 9 9 8

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5 I-5

treatment processes and key parameters affected their designs and operations, that can lead to

proper design and selection of treatment processes or creating their own variation of process

that suit their own situation.

4. To develop the prototype of program for the design, comparison and simulation

of hydrocarbon-polluted wastewater treatment processes.

At the present, computer comes to play major role in every field and become standard

equipment in almost every household, office and academic institute. Because of its powerful

logical and mathematical calculation, as well as its presentation and interaction capability, it is

very interesting to use computer in the field of hydrocarbon-polluted wastewater treatment.

Up till now, there are many commercial softwares on industrial and wastewater treatment

process calculation. Anyway, those programs are not specifically designed to deal with

hydrocarbon-polluted wastewater treatment. Furthermore, the commercial softwares are

normally developed for expert users, so they do not provide much basic data, thus, render it

difficult for non-expert users to use efficiently. Besides, they normally do not provide any

data for decision supporting, for example they can not compare the efficiency between various processes or recommend the feasible processes for considered wastewater.

So for our 4th objective, we intend to develop the prototype of program for design,

comparison and simulation of hydrocarbon-polluted wastewater treatment processes. The

program will feature;

• E-book: provides background knowledge and useful database about the oil

pollution and the treatment processes,

• Process recommendation part: provides recommendation or narrows the range of

feasible processes for any input influent,• Design (or calculation) part: used for sizing the process unit,

• Simulation part: allows users to integrate any separation processes, included in

the program database, to build their own treatment process train. And the program

will simulate the process train to forecast the efficiency of each unit.

The treatment processes, which can be calculated or simulated by the program built-in

database, will then be based mainly upon the researches reviewed in the 1st to 3rd objective.

However, the source code of the program will be available upon request to allow upgrading to

include more processes in the future.

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6 I-6


3.1 Categories of hydrocarbon-polluted wastewater and treatment

processes

As hydrocarbon or oil requires a great amount of oxygen or oxidizing agent to oxidize,moreover, the hydrocarbon is relatively difficult to biodegrade, thus, it becomes clear that the

use of the biological treatment with high-concentration oily wastewater is not the economical

alternative. Besides there are possibilities to reuse or recover the hydrocarbons in the

wastewater. Then almost all of treatment processes that have been studied in our laboratory

are based on separation, both physical and physico-chemical, techniques in order to separate

oil from water.

Thus, it is more suitable to categorize the oily wastewater by its physical properties.

Among these properties, the degree of dispersion of oil phase in water or the size of oil

droplet is the key parameter that plays an important role in separation process selection. So we

will categorize the oily wastewater into 4 groups, in accordance with its droplet size, i.e.,

• Hydrocarbon in form of film or layer on the surface of wastewater, or hydrocarbon

in form of big oil drops in the wastewater

• Emulsion without surfactants, by the word “emulsion”, it can be easily described

as the water with very fine dispersed oil drops

• Emulsion with surfactants

• Dissolved hydrocarbon

For treatment processes, each process has its own characteristic or limitation so it can

be used to separate some certain ranges of oil droplet. So each group of the oily wastewater

may require certain process or train of processes to separate the oil from the water to theaccepted degree. The treatment processes, studied by Professor AURELLE’s researchers,

covered the entire range of the oily wastewater stated above and can be summarized as

follow;

• Decanting

• Skimmer

• Coaleser

• Flotation

• Hydrocyclone

• Ultrafiltration

• Distillation• Biological treatment

Moreover, there are researches on chemical treatment, which relates to “breaking” the

emulsion to allow the micro droplet to coalesce and make it possible to separate by the

processes stated above. There, also, are some researches contributed to formulation of

environmental-friendly oil product, which can be easily treated and still have the same

essential working properties as the existing product’s.

Furthermore, some researches can be extensively used to solve the problems of some

special types of oily waste, such as slop (viscous mixture between crude oil and water) or

inverse emulsion (fine drops of water dispersed in oil)

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7 I-7

Details of wastewater characteristics and treatment processes are thoroughly described

in Part 3. So, this part emphasizes on reviewing of related researches, categorized by process,

about their scope of work and significant finding, as described in next sections.

3.2 STOKES law

It is important to mention about STOKES law (eq. 3.1), because almost all of

separation processes considered here are based upon modification of parameters in this

equation. The STOKES equation is the relation between rising (or settling) velocity of

spherical object (in our case, droplet of dispersed phase) with very small Reynolds number

(10-4 to 1) and properties of dispersed phase and continuous phase.

c

E d gV

μ

ρ

18

2⋅⋅Δ

= {3.1}

Where V = rising or settling velocity (based on density of the 2 phases)

Δρ = Difference between density of dispersed phase and continuous

phase

dE = Diameter of dispersed phase

μC = Dynamic viscosity of continuous phase

In case of oily wastewater, the dispersed phase is hydrocarbon or oil and the

continuous phase is water. Because the density of hydrocarbons in our wastewater is normally

lower than water’s. It is prone to rise to surface of the water. Even though the STOKES

equation is valid only for certain flow regimes, the equation covers the range of flow

regime normally encountered in wastewater problem. It can be used to explain important

phenomena or applied to many types of processes, even a bit beyond its valid regime, with

satisfactory result. There are few modifications of STOKES law brought about by applyingsome correction factors into basic STOKES law. But the core equation usually remains the

same as shown in eq. 3.1.

Form eq. 3.1, one can increase the rising velocity of the oil drop by modifying 4

variables properly. The separation processes, which are based on the results of STOKES law

or modification of the variables in STOKES law, are decanting, coalescer, flotation process

and hydrocyclone or various types of centrifugal process. The researches on each process can

be summarized as follows.

3.3 Decanting

Decanting (or sedimentation) is the simplest separation process. It makes use of

gravity force and density difference between oil and water to separate them. Rising velocity of

oil or hydrocarbon drop in wastewater depends on its size, density, viscosity of water and

gravity constant, as described by STOKES equation. As shown in fig. 3.1, when the

homogeneous oil/water mixture flows uniformly pass through a control volume, some big oil

drops will rise to the water surface and can be retained, then, separated from the water by

means of proper equipment, such as overflow weir or skimmer. The small oil drop that can

not reach the water surface will be entrained with the water and exit the control volume

without separation.

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8 I-8

V

U

Q

d = cut size

d < cut size

d > cut sizeInfluent Effluent

Fig. 3.1 Schematic of decanter

When the size of the decanter (or settling tank) and the distribution of oil droplets in

the wastewater are known, we can calculate the separation efficiency of the tank by

comparing the time required for each size of oil droplet to reach the surface of the tank within

hydraulic retention time of the tank. The time required for oil droplet to reach the surface can

be calculated from STOKES equation and vertical travelling distance of the droplet. If thedroplet can reach the surface before the wastewater will flow off the tank, we can say that the

droplet can be separated by that decanter. American Petroleum Institute had recommended the

geometry of the decanter, generally known as API tank. This type of decanter has been widely

used.

Because all variables in STOKES equation are practically unchanged during the

separation process by decanter. Then, the efficiency of decanter can be enhanced only by

reducing the vertical travelling distance of oil droplet to the decanting surface. This fact leads

to the modification of simple decanter by inserting submerged plates into the tank. These

plates will act as oil interceptor. Instead of rising up to the water surface, oil droplets that

reach the surfaces of these plates are intercepted, collected, and then separated from the tank.It can be said that these insertions reduce the vertical travelling time of oil drop without the

reduction of hydraulic retention time.

Theoretical efficiency of plate-inserted decanter, known as lamella decanter, parallel

plate interceptor (PPI), etc., can be calculated using the same equation as for API tank with a

little modification on decanting area. However, the selection of the shape and installation of

these plates are the state-of-art processes. The spacing between the plates should be as small

as possible to minimize the size of decanter. However, the flow of water and the collected oil

between the plates shall be taken into account to minimize shear force, thus minimize the

effect of surface distortion or “snap-off”.

Thesis of CHERID [4] is contributed to study on the compact lamella decanter,

known as “SPIRALOIL”, that shows far greater efficiency compared to the simple decanter of

the same size.

The research consisted of,

• Study of interaction between oil drop and surface of lamella plate, and influence of

wettability of lamella material, inclination of lamella plate and characteristic of

wastewater to decanter operation

• Model development for lamella decanter

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10 I-10

8. From the study, the optimum SPIRALOIL configuration is the one with

combination of corrugated hydrophilic and smooth hydrophobic plate insertion,

installed in horizontal position. This configuration will combine the advantage of

enlarging of the oil drop both at the end of the plate (drip point enlargement) and

within the plate (snowball enlargement). Furthermore, the horizontal installation

(inclination = 0) will favor coalescing step.

3.4 Coalescer

From STOKES law (eq. 3.1), rising velocity of the oil droplet is proportional with

square of droplet diameter. So increasing the droplet diameter will make rising velocity

increasing at greater rate than other parameters in the equation. To increase the diameter, we

need a process that can integrate small droplets into the big one. Coalescer is very effective

process that enables coalescing or integrating of a number of small oil droplets in the

wastewater into relatively big drops, which can be easily separated by ordinary decanter.

Because coalescer operation depends upon several parameters or mechanisms and each of

them can be optimized to obtain better efficiency or to fit some specific working conditions,then there are several theses related to coalescer, in order to cover every aspect of the process.

Some researches are dedicated to detailed study of mechanism of the process. Some are

contributed to various type of coalescer bed or modes of operation. While some are devoted to

application on some specific wastewater or working condition. All of these related theses on

coalescer can be outlined as follow.

3.4.1

Thesis of AURELLE [3]

This research contributed to the study on fundamental mechanism of granular bed

coalescer, which was used as a basis and guideline for following researches.


• Influence of essential parameters, i.e., geometry of bed, and operation parameters,

such as feed rate to efficiency of coalescer

• Fundamental mechanisms or phenomena, take place with in coalescer during its

operation

• Model development for granular bed coalescer

Experimental procedure

The experiment was carefully planned to cover every aspect of coalescer operation,i.e.,

• Wastewater characteristic : Hydrocarbons, used in the research, included gasoline,

kerosene at various concentrations, in form of both direct and inverse emulsion.

• Collector material : Alternatives of collector or bed material included;

• Type of material : glass beads, resin, sand, chamotte (porous dried clay)

• Wettability : Oleophilic or Hydrophilic

• Granulometry or size and size distribution of the collectors

• Geometry of colaescer

• Diameter or size of the coalescer tank

• Bed height• Empty bed flow velocity

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11 I-11

Result

The result of this study indicate the important parameters which influent the efficiency

of coalescer. It also shows complex phenomena in coalescer operation by means of

visualization or photographic technique. Model for sizing the coalescer was proposed. The

study also provided significant criteria to select the material of bed and guideline foroptimization and for further development of coalescer

Significant findings

1. The main parameters, which effect the efficiency of the coalescer, consist of :

• Wettability of bed material,

• Bed height,

• Empty bed velocity,

• Granulometry of bed,

• Ratio of hydrocarbon in the wastewater

2. The phenomena or mechanism occur in the coalescer can be divided into 3

fundamental steps as follow.

• Step 1: Interception, which consists of 3 major transport phenomena, i.e.,

sedimentation, direct interception and diffusion. This step is normally the

efficiency-determining step of coalescer. The research makes it possible to

develop the model, based on model of filtration process, which governs all

phenomena in this step.

• Step 2: Adhesion-Coalescence. The efficiency of this step depends mainly on

wettability of bed material. So, this step can be optimized by using oleophilic

material as coalescer bed.

• Step 3: Salting out or enlargement of coalesced liquid. This step depends on4 parameters, i.e. wettability of bed material at the discharge surface, empty

bed flow velocity, interfacial tension and ratio of dispersed phase and

continuous phase in emulsion treated. So, for any given wastewater and bed

material, one can optimize this step only by varying feed flowrate. However,

the research shows that installation of guide, such as woven fibrous metal,

attached to discharge surface of granular bed, can eliminate influences of the

4 parameters described above and allow the coalescer to operate at much

higher velocity. This guide suppresses the limiting step 3 by channeling

coalesced oil directly into decanted oil layer at the decanter surface.

This thesis provides very important concepts and mechanisms of coalescer that leads

to further studies on various types of coalescer.

3.4.2

Thesis of SANCHEZ MARTINEZ [6]

This research contributed to extensive study on granular bed coalescer, first researched

by AURELLE [3]. The research was emphasized on granular bed coalescer with guide, and

mixed bed coalescer.

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12 I-12


• Influence of essential parameters, i.e., geometry of guide, and operation

parameters, such as feed rate and ratio of oil in wastewater to efficiency of

classical coalescer and guided coalescer

• Study on mixed bed coalescer to treat direct and inverse emulsion simultaneously• Application on mixed bed coalescer with guide in phenol extraction


The experiment was conducted with transparent glass coalescer models. Coalescer bed

materials used during the experiment were sand and glass bead. Both materials were specially

coated to acquire oleophilic or hydrophilic property. 2 guides of different sizes of woven fiber

and different porosity were tested. The author intended to study the operation of coalescer for

liquid/liquid extraction. So he chose phenol extraction in this study. Phenol in wastewater can

be extracted by dissolving into appropriate hydrocarbon solvent. Solvent and wastewater will

be intensely agitated to maximize contact, thus, mass transfer. So, they normally becomeemulsion, both direct and inverse. Hydrocarbons used as solvent in the experiment were

L.C.O, medium-cut petroleum, and gasoline.


1. Installation of guide, porous material preferably wetted by dispersed phase, helps

optimizing the 3rd mechanism “salting out or enlarging of dispersed phase”, thus,

allow the granular bed coalescer to work at the flowrate of 1.5 - 6 times higher

than classical coalescer without guide. It helps preventing formation of mousse,

jet at the bed outlet. It also prevents formation of zone of non-coalesced drops

between decanted solvent and clarified water zone. The guided coalescer can beoperated at higher ratio of dispersed phase/ continuous phase than the classical

coalescer. The research confirms the advantage of guided coalescer proposed by

Prof. AURELLE.

2. When both direct and inverse emulsion are simultaneously present in the

wastewater, two-stages process of hydrophilic bed and hydrophobic bed

coalescers, connected in series, may encounter a problem of re-dispersion or re-

fragmentation, thus, lower the total efficiency.

3. Mixed bed coalescer, using combination of both hydrophilic and hydrophobic

bed material, is proven to be the effective way to treat direct and inverse

emulsion simultaneously.4. Application of mixed bed coalescer with guide shows satisfactory result and is

proven to be a good alternative in the field of liquid-liquid extraction process.

3.4.3 Thesis of DARME [7]

This research contributed to the application of coalescer on treatment of stabilized

emulsion. This work was one of successions of the research of AURELLE [3] in order to

understand profoundly about working mechanism, limitation and application of granular bed

coalescer.

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13 I-13


• Influence of surfactant on coalescer operation

• Trials on optimization of each basic mechanisms of coalescer

• Study on mixed bed electrocoalescer


The experiment was conducted with transparent glass coalescer models. Coalescer bed

materials used during the experiment were oleophilic resin and glass bead. To study about

influence of surfactant on wettability, glass, resin and steel were tested. For the study on

mixed bed electrocoalescer, mixed material of aluminium and resin was tested. Emulsion of

kerosene and water was used throughout the experiment, with various dosages of cationic,

anionic and non-ionic surfactants.


1. Surfactants have important effects on emulsion and operation of coalescer as

follow;

• Decreasing average size of droplet in emulsion, then, results in limiting the

efficiency of the 1st mechanism “Interception step” of coalescer.

• Decreasing interfacial tension, increasing electric charge at the surface of the

droplets and increasing viscosity of surface of the droplets, then, result in

poor adhesion between droplets and bed, as well as, ineffective collision

(collision without coalescence) between droplets. These leads to limiting the

efficiency of the 2nd mechanism “Adhesion-coalescence step” of coalescer.

• Decreasing interfacial tension and adsorption of surfactant on enlargement

surface (or grill) results in limiting the efficiency of the 3 rd mechanism“Enlargement step”

2. Trials to optimize the 1st and 3rd mechanism were conducted by;

• Optimization of the 1st mechanism: increasing bed depth

• Optimization of the 3rd mechanism: installation of “guide”

The efficiency of the coalescer after these 2 modifications is not improved.

Hence, it shows that the 2nd mechanism “Adhesion-Coalescence” is the limiting

step in this case.

3. The 2nd mechanism can be optimized by destabilizing the emulsion, chemically

or electrically. To apply only the coalescer to treat stabilized emulsion, withoutadditional chemical process to destabilize or “break” the emulsion, the author

propose to destabilize the emulsion by electrostatic effect. To achieve the

electrostatic effect required, the author proposes to use the combination of

oleophilic resin and metal (such as aluminium) as coalescer bed. With carefully

selected bed materials, the electrostatic effect, caused by electrical potential of

the 2 materials, will be sufficient to subdue the surface charge of droplets,

caused by surfactants. Then, it will improve adhesion and coalescence within the

coalescer.

4. However, this mixed bed is effective only when the emulsion is stabilized by

ionic surfactant. In case of non-ionic surfactant, coalescence is hindered by

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15 I-15

This model is valid when 52<Re<1164. However, scaling-up of the model will

be limited by bed construction itself because the fiber elements of the bed tend to

compact by their own weight. Moreover, if the bed is too large, void ratio at the

tips of fibers will be very different from center’s. This may cause error in

calculation. So, it is recommended to use a number of small coalescers instead of

a single large one.3. This coalescer has several advantages as follow;

• Anti-clogging. No regeneration or backwashing required

• High void ratio, thus, head loss is very low

• Very small size of fiber, compared to granular bed material, ensures good

interception of oil droplets

• Treatment efficiency is adjustable by mean of adjusting rotating speed of bed

3.4.5 Thesis of DAMAK [9]

This research was intended to study another variation of coalescer, i.e., “Pulsedgranular bed coalescer”. This type of coalescer had been initiated to enable the granular bed

coalescer to treat oily wastewater with high suspended solids concentration without

regeneration or backwashing process. This coalescer, in fact, is a classical up-flow coalescer,

except it bottom end is equipped with rubber diaphragm, driven by pneumatic piston. The

diaphragm will be periodically driven up, then released to go back down. This action will

cause brief fluidization of bed and the trapped solids will be released from the bed.

The author also studied a new type of coalescer, called “Phase inversion coalescer”.

For its operation principle, the wasted emulsion will be forced downward through small tubes,

equipped at the top of coalscer column, to produce emulsion drops of required size. These

drops will flow through thick layer of hydrocarbon, which is of the same type as dispersed phase in the emulsion. The drops play the role of micro decanter. Theoretically, hydrocarbon

droplets in the emulsion drops will float to the top of the drops, then, coalesce with

surrounding hydrocarbon layer. With appropriate depth of hydrocarbon layer and size of

emulsion drop, the dispersed phase in emulsion drop will be totally separated and become

only the drop of water phase when it flow out off the hydrocarbon layer into water phase

underneath. The schematic of phase inversion coalescer will be as shown in Fig 3.2.

H y d r o c a r b

o n

l a y e r

Orifice plate

Water layer

Decanting of droplets in

emulsion drop

Influent

emulsion

Top of hydrocarbonlayer

Bottom of hydrocarbon

layer

Emulsion jet

from orifice

Emulsion

drop

Effluent

Hydrocarbon

droplets in emulsion

drop

Fig. 3.2 Schematic of Phase inversion coalescer

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17 I-17

4. This coalescer is suitable for treatment of primary emulsion (dE ≥50 μm). And

the study shows that the efficiency is better than that of the classic decanter.

5. For pulsed coalescer, the study shows that brief pulsation, which causes the bed

to fluidize, can regenerate the bed and clean up the accumulated matters.

6. In classical coalescer, coalescer bed material is usually lightweight resin, whichrequires the top grill to keep the bed in place without carrying over with the

wastewater. However, in this study, it shows the possibility of using of relatively

high density coalescer bed, e.g., stainless steel, without the top grill can replace

the use of lightweight material. When the grill is not required, it allows us to use

pulsating motion to fluidize, thus, regenerate the bed.

7. In this thesis, a mathematical model for sizing and calculating efficiency of

granular bed coalescer was proposed. Unlike the model of AURELLE, which

derived from theoretical mechanisms of coalescence, this model is based on

dimensional analysis. So physical properties of wastewater, which are not shown

in AURELLE’s model, are taken into account. Hence, it covers wider range of

wastewater.

3.4.6 Thesis of MA [16]

This thesis was the main research on hydrocyclone for hydrocarbon/water separation.

So it will be described in detail in section 3.6. However, the author had tested, for the first

time, the efficiency of the combination process of hydrocyclone and coalescer, which worth

describing here.


1. This study shows, for the first time, the possibility to use the combination process of hydrocyclone/coalescer and coalescer/hydrocyclone to improve the

total efficiency of oil/water separation.

3.4.7

Thesis of SRIJAROONRAT [10]

This thesis is an application research on treatment of non-stabilized oil/water

emulsion. This type of thesis provides important data that can be applied in real life situation.

So we will devote one section to review these theses. However, as one part of her thesis,

SRIJAROONRAT had studied on comparison between fibrous bed coalescer of brush type

and random, disorderly type (like a steel wool). She also studied on combination of

coalescer/hydrocyclone to treat non-stabilized emulsion. The idea is to use coalescer toincrease droplet size, permitting a good separation by the following hydroclclone. Her study

on coalescer will be briefly mentioned here to complete the entire coalescer studies.


1. At high empty bed velocity, the coalescer with random bed will coalesce and

enlarge the droplets into relatively large drop, while the coalescer with brush

type bed tends to produce stream of jet, containing small oil drop.

2. However, the disorderly fibrous (steel wool) bed coalescer tends to be clogged

by suspended solids, usually presence in the oily wastewater. So the author

proposed new configuration of fibrous bed in form of combination of 2 brushes.

The internal one is of ordinary brush. The external one will look like coil spring

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19 I-19


Visual study of interaction between oil droplets and bubble had been conducted in

special transparent model, equipped with a microscope and a VDO camera. For the study on

flotation, transparent flotation model was used. Emulsion used during the experiment was gas-

oil/water emulsion.


1. From visual study on interaction between oil droplet and air bubble, it shows that

the bubble will agglomerate within the inside of oil droplet or the oil will form a

thin skin, as a shell, around the air bubble.

2. In this thesis, mathematical model for sizing and calculating efficiency of

dissolved air flotation is proposed. The model is based on filtration model by

assuming that the air bubble is collector (sand or filter media in case of filter).

Prediction results of the model fit well with experimental results. Anyway, the

author did not account for the quantity of pressurized water that used to generatethe bubbles. This amount of water can cause dilution effect, thus, contribute to

reducing in wastewater concentration. So, the model proposed in this research

should be reconsidered again to clarify the efficiency of interception of air

bubble and the efficiency from dilution effect of pressurized water. The revised

model will be described in Part 2 of this thesis.

3.5.2 Thesis of AOUDJEHANE [13]

This research contributed to application of flotation on treatment of hydrocarbon-

polluted wastewater. This work was one of successions of the research of SIEM [12] in order

to understand profoundly about working mechanism, limitation and application of flotation.


• Study on structure of bubble/droplet agglomerate and influence of additional of

flotation reagent in form of the transfer compound( composé transferable)

• Influence of hardness and salinity of pressurized water on production of air bubble

• Study on probability of collision and coalesce of air bubble and oil droplet


Visual study of the interaction between oil droplets and bubble had been conducted inspecial transparent models, equipped with a microscope and a VDO camera. The models are

equipped with 2 syringes, located close to each other. These 2 syringes were used to supply

air (or gas) and oil to form immobilized bubble and oil droplet respectively. Bubble and oil

droplets were brought into contact to study the formation of the agglomerate. For study on

flotation, transparent flotation model was used. Hydrocarbon used in this study was kerosene.

For transfer compounds, ammonia gas, cationic surfactant and methanol were used as

promoter of mass transfer between phases.


1. From visual study on interaction between oil droplet and air bubble, it confirmsthe result of SIEM [12] that the bubble will agglomerate within the inside of oil

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21 I-21

various particles were added. Then, the air was pumped out to create vacuum. This apparatus

was used to observe nucleation of bubble. The 3rd one was a transparent flotation model.


1. The study result, which can be applied to hydrocarbon/water separation, is theone about formation of bubble at pressure reducing valve. The study shows that

efficiency of flotation can be improved if the design of pressure reducing valve is

optimized to generate microbubble in majority.

2. The use of hydrophobic venturi or pipe can cause the increase in size of the

largest bubble generated. These large bubbles, though small in the number,

consume almost all of the gas volume. So the number of generated

microbubbles, which plays an important role in flotation, is left but only in small

proportion.

3. Addition of surfactant in pressurized water can cause augmentation in population

of microbubbles. On the contrary, addition of polyelectrolyte will cause adecrease in electric charge, which is favorable for the coalescence of bubbles.

3.5.4 Thesis of PONASSE [15]

This research contributed to study and trial on improvement of flotation efficiency.

The author had tested several ways to improve formation of microbubble, such as addition of

chemicals, using ultrasound vibrator to create microbubble. She also performed a feasibility

study on “Deep shaft” flotation unit.


• Study on the influence of pressure reducing valve on formation of bubble

• Feasibility study on deep shaft flotation unit

• Feasibility study on combination of pressure reducing valve and ultrasound

vibrator.


To study the influence of pressure reducing valve on formation of bubble, the author

tested several pressure-reducing venturi tubes (convergence-divergence nozzles) of various

divergent angles. Tube materials tested consisted of stainless steel (hydrophilic) and plastic

(hydrophobic). Influence of divergent angle, wettability of tube, length of pipe after the

pressure reducing device and addition of some chemicals were studied.

For study on deep well flotation unit, a 30-m depth deep well unit was tested. The unit

consisted of 2 concentric pipes. The external pipe diameter was 0.15 m. On the top of the

pipes placed settling tank of 1.2*1.2 m, water depth 0.7 m. The wastewater was charged with

various suspended solids, both hydrophobic and hydrophilic. The air was introduced into the

system by several methods, i.e.,

• Direct injection into the wastewater at static mixer

• Via porous plate, located inside the wastewater pipe before enter the deep shaft

reactor

• Via injection chamber, air will forced through small orifice into the chamber

• Via membrane

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23 I-23


• Study on new approach for calculating two-phase hydrocyclone, used for

liquid/liquid separation application

• Study on three-phase hydrocyclone, used for liquid/liquid/solid separation

• Feasibility study on the combination process of three phase hydrocyclone andcoalescer


To study on a new approach for calculation on 2-phase hydrocyclone, the author based

his experiment on “THEW” type hydrocyclone, initiated by Professor Thew, UK. For 3-phase

hydrocyclone, he had initiated this hydrocyclone by integrating the liquid/liquid hydrocyclone

of “THEW” type and the solid/liquid hydrocyclone of “RIETEMA” type to one unit. For

coalescer tested, he used coalescers with various sizes of “brush” type beds. The emulsions

used in the experiment were based on petroleum from the “Sud-Ouest” french oil rig, with

various additions of very fine bentonite (3.7 μm) and calcium carbonate powder (6.2 or 16μm). Average oil droplet in the emulsion tested was 15 to 50 μm.


1. In this thesis, a mathematical model for sizing and calculating efficiency of

THEW type hydrocyclone was proposed. This model, based on calculation of

decanter, can be used to calculate trajectories of oil droplets in the cyclone, as

well as the separation efficiency for each size of oil droplet. Difference between

model prediction and experimental result is around 10%.

2. It is recommended that the optimum angle of conical section of THEW

hydrocyclone should be 8° to 12°. And ratio Dn/D (nominal diameter of cyclone/diameter of cylindrical part of the hydrocyclone) should be around 0.5.

3. The author had designed the 3-phase hydrocyclone by integrating THEW type

hydrocyclone with RIETEMA type hydrocyclone. To do so, the vortex finder of

RIETEMA hydrocyclone is replaced by THEW hydrocyclone, as shown in fig.

3.3. Test results show that the hydrocyclone is capable to separate, efficiently

and simultaneously, lightweight hydrocarbon and heavy suspended solids from

water.

4. The study shows that separation efficiency of hydrocyclone will drop rapidly if

the diameter of oil droplet is smaller than 20 μm.

Solid-liquid part (Rietema’s part) Liquid-liquid part (Thew’s part)

DoD

Ds

DiDu

Dp

L5 L3L1

L3

L4

Fig. 3.3 Three- phase hydrocyclone

Note: Di/D=0.25, Do/D=0.43,Ds/D=0.28, Du/D=0.19, Dp/D=0.034, L1/D=0.4,L2/D=5, L3/D=15, L4/D=0.3

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24 I-24

3.6.2

Thesis of CAZAL [17]

This research contributed to the feasibility study of solid/liquid separation

hydrocyclone on treatment of storm water, domestic wastewater, and thickening of sludge. In

spite of the fact that this research is mainly related to solid/liquid separation process, it

provides useful details about model development and basic concepts of hydrocyclone.Furthermore, oily wastewater always contains some amount of suspended solids. So, some

parts of this thesis can fulfil the study of hydrocyclone for oily wastewater treatment charged

with suspended solids.


• Feasibility study on application of hydrocyclone for treatment of storm water,

domestic wastewater, thickening of primary sludge and biological sludge

• Model development for solid/liquid separation hydrocyclone and study on

influence of shape of suspended solids to separation efficiency

• Study and proposal on multi-hydrocyclone processes for treatment of storm water


For the feasibility study on hydrocyclone for wastewater treatment and sludge

thickening, the author had performed the experiment “on site”, using a pilot plant. The pilot

plant was equipped with storage tank, pumps and piping system that allow to test 2

hydrocyclones instantaneously, both in series and parallel. The hydrocyclones used in the

experiment were product of NEYRTEC, equipped with replaceable outlet. The sizes of

cyclones were tested, i.e., nominal diameter of 75 and 50 mm. Outlet ports of the cyclones can

be changed to study the influence of their sizes on cyclone operation. The wastewater and

sludges were provided by the wastewater treatment plant at Ginestous. Characteristics ofwastewater were as summarized in table 3.1. For study in laboratory, The same pilot plant was

used with synthetic wastewaters, summarized in table 3.2.

Table 3.1 Summary of characteristics of wastewaters and sludges for “on site”

experiment

Domestic

wastewaterStorm water Primary sludge

Biological

sludge

SS (mg/l) 150-490 41-700 22000-16000 4170-6660

Median diameter, d50

(μm)

24-37 10-28.8 160 36-96

Table 3.2 Summary of characteristics of synthetic wastewaters

Calcium

carbonateTalc Talc

Ion

exchange

resin 1

Ion

exchange

resin 2

Name CaCO3 A60 Steamas 29 IRP 69 OG 4B

Density (g/cm3) 2.7 2.7 2.7 1.57 1.57

Median diameter,(μm)

10 25 32 78 56

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25 I-25


1. In this thesis, it shows that the efficiency of hydrocyclone for wastewater

treatment and sludge thickening application are relatively low, compared to

classic decanter or gravity thickener. Main reasons for poor efficiency consist of;

• Shear force from flow pattern in hydrocyclone, which causes deflocculationeffect or decreasing in size of biological floc

• Nature of the wastewater, which normally contains high contents of fiber

agglomerates. These fibers hinder separation phenomena in hydrocyclone

2. The author had tested the operation of hydrocyclones using the range of influent

SS concentrations from 10 mg/l to 20 g/l and maximum purge ratio of 2%. The

result shows that efficiency will increase if influent flowrate is increased.

3. Shape of suspended solid affects the efficiency of hydrocyclone. This influence

is the function of particle’s size. The smaller the size is, the less the influence is.

4. In this study, mathematics model of hydrocyclone is proposed and formcoefficient is introduced.

5. The author proposed the combination of 3 hydrocyclones in series as the

recommended process for storm water treatment. She also proposed installation

of grit pot (the short cylindical chamber), connected to discharge port of the

hydrocyclone, to minimize the influence of particle shape.

3.6.3 Thesis of SRIJAROONRAT [10]

This thesis is an application research on treatment of non-stabilized oil/water

emulsion. SRIJAROONRAT, as one part of her thesis, had studied on the combination of

coalescer/hydrocyclone to treat non-stabilized emulsion. The hydrocyclone used in thisresearch is the product of Dorr Oliver, model DOXIE 5, nominal diameter of 1 cm, 10 cm

long. Her study on hydrocyclone is briefly mentioned here to complete the entire

hydrocyclone studies.


1. Combination between coalescer/ hydrocyclone is proven to provide good

efficiency on the wider range of feed flowrate and size of oil droplet.

3.6.4 Thesis of WANICHKUL [11]

This thesis is an application research on treatment of stabilized oil/water emulsion.

Details of this thesis will be described in the section devoted to application thesis. However,

as one part of his thesis, WANICHKUL had studied on the combination of

coalescer/hydrocyclone and hydrocyclone/coalescer to treat non-stabilized emulsion. It will be

briefly mentioned here. WANICHKUL had been tested the combination of

coalescer/hydrocyclone and hydrocyclone/coalescer. In his experiment, he used Plexiglas

hydrocyclone as shown in fig. 3.4. The influent will be fed through 2 tangential inlet ports,

located at the upper cylindrical section. The oil and treated water will be discharged at each

corresponding outlet port. Because the oil and treated water outlet port locates at the same end

of hydrocyclone, so this configuration of hydrocyclone is called “co-current”.

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27 I-27

or emulsion to pass. The rest will be retained by the membrane. Working principle of

membrane process can be approximately compared to that of filtration.

Membrane processes can be divided into several categories according to the pore size

of membrane, i.e., microfiltration, ultrafiltration, nanofiltration and reverse osmosis. Each

category has different permeability and can retain different size of components. So it is crucialto select the most appropriate membrane process to achieve the required effluent quality. Then

several researches are contributed to membrane selection.

In membrane treatment system, wastewater will be circulated on one side of

membrane. The water and some components that can be passed through membrane pore will

flow to another side of membrane. This portion is called “filtrate” or “permeate”. The portion

that can not pass the membrane will have higher oil concentration because it losses its water

component. It is called “concentrate” or “retentate”. So, the membrane can be considered as a

concentrating process because the pollutant, in our case, oil, is not exactly separated, just

concentrated. Increasing in oil contents of concentrate will cause important phenomena called

polarization concentration. This can be described as oil rich layer that can obstruct flow of permeate. Solid content or some components in wastewater can be trapped in membrane pore

and cause clogging. Concentration polarization and clogging of membrane are the main

problems of this process. So many researches are devoted to solve this problem. All of related

theses on membrane process can be outlined as follows.

3.7.1 Thesis of BELKACEM [18]

This research is contributed to the application of ultrafiltration on treatment of cutting

oil emulsion. This type of emulsion is one of important oily wastewater. In metal industries,

especially metal forming plants and mechanical workshops, machine tools and products needs

good lubrication and cooling to ensure good quality of products and prolonged working life ofthe tools. Water, by its property, is very good cooling liquid and a cost-effective choice. As

well as oil is very good lubricant and anti-corrosion substance. So the combination of oil and

water in form of emulsion provides users with both properties required. To fulfil this purpose,

the emulsion is charged with surfactants and co-surfactants to increase its stabilization. From

user point of view, it yields satisfying result.

However, from environmental point of view, presence of these surfactants or

emulsifiers makes separation process very difficult. This is because the oil phase in the

emulsion is dispersed in form of very fine droplets, which impossible to be decanted naturally.

So it requires special treatment.


• Feasibility study on the application of ultrafiltration on treatment of cutting oil

macroemulsion

• Study on treatment methodology of the cutting oil emulsion by ultrafiltration

process

• Study on membrane washing solution

• Feasibility study on the application of ultrafiltration on treatment of cutting oil

microemulsion

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28 I-28


The experiment was conducted with a batch model and a pilot-scale model. For batch

model, the author used AMICON membrane test module, (fig. 3.5). The batch model was

transparent container with pressure-tight cover. The membrane was placed at the bottom of

the container. Wastewater was added into the container, then the cover was locked in placeand compressed air line was connected to the inlet port at the cover. The wastewater was

forced through the membrane by mean of air pressure, then collected and examined. During

ultrafiltration process, the wastewater was continuously stirred by mean of magnetic stirrer.

For pilot-scale model, the author used commercialized cross flow ultrafiltration test

module, model PLEIADE UFP2 of Tech Sep co,.ltd. (fig. 3.5).Wastewater was circulated

through narrow gap between membrane and transparent wall of the model. In this manner,

wastewater flow was tangential, not perpendicular to, the membrane surface. Some

components would pass through the membrane and become permeate. The rest would be

returned to storage tank, then circulated pass membrane again until it reached some certain

concentration. After being circulated for many times, the concentrate would gain intemperature, so heat exchanger was provided to cool down the flow before re-entered the

UFP2 module.

He also tested the porous fiber membrane in the same way as the plain membrane,

described before. For the membranes, he used plain and porous fiber membrane of various cut

sizes, ranged from 40 to 150 Kdalton.

For the emulsions, he used commercialized cutting oil emulsion of both

microemulsion and macroemulsion types. He also used cutting oil macroemulsion from

mechanical workshops.


1. In this thesis, the author proposed a mathematical model for calculating

ultrafiltration flux of macroemulsion, as function of non-dimensional numbers.

2. The study indicates interesting aspect in integrating ultrafiltration with partial

destabilization, using salt. From this methodology, the membrane will play the

roles of filter and coalescer, which help reducing the influence of polarization

layer and concentration factor. This leads to increasing in ultrafiltration flux for

treatment of macroemulsion.

3. To solve the problem about clogging, the author proposed to use new formulatedmicroemulsion, which is not saturated by oil, to wash the membrane and slow

down clogging process. With a careful selection of surfactants in the

microemulsion, it can be easily treated by the combination process of

polyelectrolyte breaking and ultrafiltration. Because the author used co-

surfactant with poor water solubility, residual pollutant concentration after

ultrafiltration, mainly in dissolved form, was relative low, compared to ordinary

microemulsion.

4. From study on treatment of microemulsion by ultrafiltration, it shows that

ultrafiltration provides good separation between oil and water. However, the

filtrate is heavily polluted by dissolved pollutant, then additional treatment is

inevitably required. The author proposed to use reverse osmosis process to treat

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30 I-30


To study on the entraining of volatile compounds with steam, the author used glass

distillation apparatus, equipped with microscope to observe the condensate. She had tested

several hydrocarbon compounds, such as alcanes with the number of C atoms from 5 to 12

(pentane to dodecane), toluene, benzaldehyde, isobutanol, series of primary alcohols, etc.

To study mechanisms of thermal emulsion formation, hydrodistillation apparatus was

used. It is, in fact, the same device as the first one, with an additional installation of a stirrer.

For the plants used for the experiment, she used several plants, i.e., cinnamon, aniseed, celery,

lavender, etc. Condensate was found in form of decanted essential oil, floating on the top, and

milky thermal emulsion.

For ultrafiltration, she used tubular ceramic membrane of 10 nm. pore size. The

experiment was conducted with membrane test module, model MEMBRALOX T1-70 of SCT

co., ltd. For the emulsion treated, she used synthetic emulsion of kerosene/water as well as

thermal emulsion from extraction of cinnamon, aniseed and celery with various doses ofsurfactants.


1. In this thesis, it shows that the most important parameter in thermal emulsion

formation is the variation of solubility of essential oil with changes in

temperature. She also proposed the minimum variation of solubility that can

cause the formation of thermal emulsion.

2. Condensation time is the important parameter that governs the size distribution

of the emulsion. If the condensation is relatively slow, average diameter of

droplet in the emulsion will increase.

3. The author shows that if the following compounds are present in the essential oil,

thermal emulsion will not be formed;

• Hydrocarbon of high vapor tension

• Hydrophobic hydrocarbon that solubility is not sensitive to temperature

change.

4. To avoid formation of thermal emulsion, she proposed the process called

“hydrodistillation under reduced pressure (sub-atmospheric pressure)”.

5. The study shows that “white water” or milky thermal emulsion, in fact, contains

natural surfactants. So its properties are close to that of stabilized emulsion.

6. Under carefully selected operating condition, ultrafiltration can provide good

separation efficiency between water and essential oil.

3.7.3 Thesis of MATAMOROS [20]

This research is contributed to the study on treatment of stabilized emulsion,

especially cutting oil emulsion, by various membrane processes. This research provides many

useful information and comparison data of several membrane processes.

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31 I-31


• Feasibility study on the application of various membrane processes for treatment

of cutting oil emulsion, of both macroemulsion and microemulsion types

• Feasibility study on the application of combination processes between one of

membranes and chemical destabilizing process for treatment of cutting oilmacroemulsion and microemulsion


The experiment in laboratory scale was conducted with two batch test modules, one

was fabricated in GPI Lab, and another was AMICON test module. For pilot-scale

experiment, the author used cross flow membrane test module, model PLEIADE UFP2 from

Tech Sep co., ltd., for micro- and ultrafiltration process. For nanofiltration and reverse

osmosis, he used test module from OSMONICS.

The membranes used in the research were as tubulated in table 3.3. For emulsions, heused various commercialized cutting oil of macro- and microemulsio typesn.

Table. 3.3 Membranes test by MATAMOROS

Membrane Cut sizeInitial permeate flux

(m.s-1

.pa-1

)Material

Microfiltration 0.10 – 0.45 μm 655 - 125786 Cellulose compounds,

Polyamide and PTFE

Ultrafiltration 40-50 Kda 750*10-12

Polyacrylonitrile,

Acrylonitrile

Nanofiltration 150 – 2000 Da 1.72*10-12

- 20*10-12

Cellulose

Reverse osmosis 150 Da 2.2*10-12

Polyamide


1. The results from this research show that the combination between chemical

destabilization process with micro- or ultrafiltration can increase working

permeate fluxes of the membranes and still obtain good efficiency.

2. For the combination of chemical destabilization and microfiltration, the system

can operate at relatively high flux with moderate transmembrane pressure. Thisleads to development of continuous treatment process of cutting oil because, in

the past, working pressure is always the limiting factor of the process. However,

it requires high amount of salt.

3. For the combination of chemical destabilization and ultrafiltration, the result

conforms to BELKACEM’s [18] that the salt added plays important role, by

double layer compression, and/or adsorption/partial neutralization, in the

reduction of repulsive force and promotion of coagulation and coalescence of

droplets to form a free oil layer. This oil layer can be entrained by recirculation

stream, and then removed at the concentrate storage tank.

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32 I-32

4. The permeates from the combination of two processes stated above contain high

concentration of TOD, which is the result of dissolved pollutants, especially co-

surfactants.

5. Combination between ultrafiltration and reverse osmosis shows good result both

in oil separation and dissolved pollutant elimination in permeate. However,

operating cost is relatively high.

6. The use of nanofiltration shows good efficiency result in good oil separation, as

well as dissolved pollutant elimination, at lower energy consumption than

reverse osmosis.

7. From experimental results, the author recommended 2 treatment process trains

for micro- and macroemulsion as shown in fig. 3.6

Microfiltrtion+

CaCl2

Microfiltrtion+

CaCl2

Reverse osmosisor

Nanofiltration

Reverse osmosisor

Nanofiltration

Granular activatedcarbon or

Biological treatment

Granular activatedcarbon or


EffluentMacroemulsion

Decanter Decanter Decanted oil

Surfactant +

CaCl2

Recycle

Nanofiltration NanofiltrationGranular activated

carbon or


Granular activated

carbon or


EffluentMicroemulsion

Surfactant +

Oil

Fig. 3.6 Treatment processes for macro- and microemulsion,

recommended by MATAMOROS

3.7.4 Thesis of SRIJAROONRAT [10]

This thesis is an application research on the treatment of non-stabilized oil/water

emulsion. As one part of her thesis, SRIJAROONRAT had studied on the application of

ultrafiltration to treat non-stabilized emulsion. In her thesis, SRIJAROONRAT had tested

several types of ultrafiltration membranes, i.e., organic, inorganic and ceramic. Wastewater

used in the experiment consisted of synthetic emulsion of kerosene/water, cutting oil

emulsion, crude oil/water emulsion, and wastewater from textile plant. The result can be

summarized as follows.


1. Ultrafiltration process can be used to treat non-stabilized emulsion with

remarkable efficiency (approx. 100%).

2. Major problem of the ultrafiltration is the rapid decrease in permeate flux, caused

by;

• Presence of suspended solids in wastewater, these solids will deposit on the

membrane surface and/or in the pores and cause clogging.

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33 I-33

• Presence of surfactant, the surfactant will be adsorbed or form micelles

within the membrane pores, as well as membrane surface, thus cause

changing in wettability of membrane.

3. Influence of surfactant on permeate flux also depends on material of membrane.

Inorganic (mineral) based membrane is more sensitive to surfactants than other

membranes.


This thesis is an application research on the treatment of stabilized oil/water emulsion.

WANICHKUL had studied on the application of ultrafiltration on cutting oil emulsion

treatment. He also studied on the treatment of ultrafiltrate by reverse osmosis.


1. The result on the treatment of cutting oil emulsion by ultrafiltration confirms the

result of MATAMOROS that the process is feasible and efficiency of the processis satisfying. The author recommended that operating condition should be in

permanent regime to avoid influence of concentration factor.

2. Using microemulsion with under-saturated oil concentration is an effective

method to regenerate the membrane.

3. The author had studied the efficiency of reverse osmosis on ultrafiltrate

treatment. The result shows that the process provides remarkable efficiency.

4. The result of the comparison on efficiency between ultrafiltration and distillation

on cutting oil emulsion treatment can be concluded that ultrafiltration is suitable

for macroemulsion treatment, while distillation is more efficient for

microemulsion treatment. However, from economic point of view, energyconsumption of ultrafiltration is always lower than distillation’s.

3.8 Thermal treatment

This treatment approach makes use of physical properties of hydrocarbon, water and

their mixture. Because hydrocarbon is only slightly soluble in water, we can say that the

hydrocarbon/water mixture is practically an immiscible binary system. From this fact, we can

apply the basic of phase equilibrium to develop thermal processes for hydrocarbon/water

separation. Such processes are distillation and crystallization. All related theses based on

thermal treatment can be outlined as follows.

3.8.1 Thesis of LUCENA[24]

This research is contributed to the heteroazeotropic distillation for treatment of slop,

the wasted viscous water-in-petroleum emulsion that is usually very difficult and costly to

treat. This process is very interesting innovation that allows hydrocarbon recovery by

separating from water from the slop. Certain type of hydrocarbons, considered as efficient

water extractant or entrainer, is added to the slop, then the slop undergoes distillation to

extract the water. After distillation, the distillate obtained is composed of 2 layers of clear

liquid, the entrainer in the upper layer and the water at the lower. The water can be disposed

or further treated and the entrainer can be reused for next cycle of distillation. The residue

obtained is relatively fluid, contains no water, and can be recycled to refinery unit as crudeoil.

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34 I-34


The experiment in laboratory scale was conducted with a simple glass distillation

apparatus. The author also used the pilot-scale model for on-site treatment tests.


1. The result on the treatment of slop shows that the water is totally separated from

the slop. The residue consists of relatively water-free hydrocarbon. Distillate

consists of 2 separate layers of entrainer and water.

2. Observed quantity of entrainer is slightly different (5-8%) from theoretical value.

So the theoretical method for calculating entrainer quantity is accurate enough

for practical use.

3. Kerosene and gasoline are proven to be good entrainer. Their water-extracting

capacities are almost identical to that of decane and dodecane, respectively.

3.8.2

Thesis of LORRAIN[23]

This research is contributed to crystallization. However, this process has just been

studied by GPI lab for the first time. So we will not include it in this research.


This thesis is an application research on the treatment of stabilized oil/water emulsion.

WANICHKUL had studied on the application of distillation for the treatment of cutting oil

emulsion and permeate from ultrafiltration. He also studied the possibility to treat concentrate

from ultrafiltration of cutting oil emulsion by heteroazeotropic distillation.


1. Comparison on the efficiency between ultrafiltration and distillation on cutting

oil emulsion treatment, the author concluded that ultrafiltration is suitable for

macroemulsion treatment, while distillation is more efficient for microemulsion

treatment. However, from economic point of view, energy consumption of

ultrafiltration is always lower than distillation’s.

2. Heteroazeotropic distillation is proven to be an effective way to treat

“mayonnaise-like” retentate from the ultrafiltration of cutting oil emulsion. The

residue of distillation process is clear liquid, composed of oil without water. Thedistillate consists of 2 separate layers of the entrainer (in this case, decane) on the

top and the water at the bottom. However, TOD of the distillate is still high

(around 2,800 mg/l). So the additional treatment of the distillate (either by

biological treatment or RO) is required.

3.9 Chemical treatment

When we talk about chemical treatment in oil/water separation process, we normally

refer to chemical destabilization, coagulation and flocculation. The process, then, does not

“destroy” oil. Its major role is to transform the oil into the form that facilitates oil/water

separation. So, chemical treatment process usually follows by physical separation processes aswe discussed in previous sections. Normally, chemical treatment will be required when oil or

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36 I-36

• Mono-valence cationic electrolyte, main destabilization mechanisms are

based on Zeta potential reduction and promoting micelle formation of

surfactants.

• Bi-valence cationic electrolyte, main destabilization mechanism is based on

precipitation of surfactant to insoluble form.

• Tri-valence cationic electrolyte, main destabilization mechanisms are basedon the bridging of its cations and hydroxides and precipitation of surfactant

to insoluble form.

2. The result shows that destabilization techniques of fresh macroemulsion can also

be effective for used macroemulsion.

3. For breaking emulsion by acid, the study shows that destabilization mechanisms

for micro- and macroemulsion are different, based on type of surfactant used in

the emulsions.

• For microemulsion- surfactant used is soap. So it is sensitive to pH change.

Then, addition of acid will disturb the equilibrium of ionization of fatty acid

and make it lose its surfactant property. This type of destabilization requires

relatively small amount of acid.

• For macroemulsion- surfactant used is sulfonate type. Main destabilization

mechanisms are based on Zeta potential reduction and promoting micelle

formation of surfactants. So it requires high dosage of the acid.

4. Ferric chloride is an effective destabilization chemical for breaking

macroemulsion. However, it cannot be used to breaking microemulsion because

it will react with surfactants and form complex, which is difficult to separate.

5. High residual pollution which presents after breaking the emulsion is caused by

co-surfactant, which is fatty acid that dissolves very well in water.

6. To destabilize the emulsion stabilized by non ionic surfactant, the author

recommended to use a mixture of anionic surfactant and tri-valence electrolyte

(Alum, FeCL3) as destabilization reagent. Main breaking mechanism is based on

selective reaction between non-ionic surfactant, anionic surfactant and

electrolyte, which form insoluble complexes.

7. Breaking mechanisms of commercial adsorption reagents are based on their

components. So, their efficiencies will be known only by testing.

8. Activated carbon adsorption is proven to be an effective treatment for residual

pollution which is left after breaking the emulsion. However, investment and

operating costs of this system, esp. cost for regeneration or replacement, arerelatively high.

9. The author had proposed, for the first time, to replace fatty acid co-surfactant

with other surfactant with less water solubility to solve the problem about

residual pollutant after breaking the emulsion. In his case, he used decanol,

which is slightly soluble in water, as a co-surfactant. The new emulsion has

satisfying property. But vigorous mixing by ultrasound device is required to

disperse the oil into droplets to create the emulsion.

10. He suggested that new formula of this low pollution emulsion should be further

studied to make it soluble instantly in water, which is the way the users prefer.

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37 I-37

3.9.2

Thesis of YANG[22]

This research is a succession of ZHU’s thesis and contributed to development of low

pollution emulsion. This thesis was a new approach in pollution control because it was one of

the first researches on pollution reduction from the source, as it is presently called “cleaner

product, CP” research, which is the branch of pollution control that is well-known and widelyacceptable now.


• Study on the formulation of low pollution cutting oil emulsion

• Study on the treatment process of that new emulsion


The author had tried to formulate low pollution cutting oil emulsion, using carefully

selected base components, i.e.,

• Base oil: commercial naphthene (cyclic aliphatic compound) based oils and

paraffin based oils,

• Surfactants: various succinic and sulfonate surfactants,

• Co-surfactants: alcohol-based, ester-based, and other co-surfactants with low water

solubility,

• Corrosion inhibitors: fatty acid alcanolamide, oleylsarcosinic acid, and fatty acid

polydiethanolamide,

• Anti-mousse reagents: polysiloxane and a commercial reagent,

• Bactericides: 4-chloro-3methylphenol, isothiazolinone, and parahydroxybenzoic

ester with phenoxyethylic alcohol,

Each emulsion formula was subjected to these 5 tests, i.e.,

• Droplet size distribution measurement: using particle analyzer (granulometer)

• Emulsification test: new products were diluted by water to observe its solubility

and stability.

• Anti-rust test: new emulsions of various concentrations were used to coat on steel

chip and rust forming was observed.

• Anti-mousse test: new emulsions were manually and intensely agitated and

characteristic and stability of mousse were observed.

• Determination of residual pollutant after chemical destabilization process or

ultrafiltration.


1. The author proposed new formulae of low-residual-pollutant microemulsions

and macroemulsions.

2. These new emulsions can be treated efficiently by breaking with calcium

chloride or ultrafiltration. Residual pollution after treatment is 2-57 times lower

than present commercial products.

3. Concentration of emulsion and hardness of dilution water are important

parameters, which affect stability of emulsion.

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38 I-38

3.10 Biological treatment

Biological treatment is the most common wastewater treatment process. Because of its

versatile, efficiency and economic, biological treatment plants are widely used for both

domestic and industrial wastewater treatments. Its working principles depend mainly on

degradation and/or assimilation of pollutants by microorganisms, so called “biomass”, presentin the biological reactor. Key to obtain satisfying treatment efficiency is to optimize the

environment in the reactor to promote function of biomass. Even though oil or hydrocarbons

are biodegradable, presence of some hydrocarbons at some concentrations can cause adverse

effect on the biological treatment mechanisms by;

• Obstructing oxygen transfer: Oxygen content is an important factor in aerobic

biodegradation. Oil layer that covers water surface will obstruct transfer of oxygen

between air and water. Oil may surround biomass floc and impede oxygen transfer

of the floc in biological reactor. This leads to the decrease in treatment efficiency.

• Its high oxygen demand: Oil requires high amount of oxygen for biodegradation. It

will cause problem on insufficient aeration capability in some treatment plants that

did not account for this type of pollutant in the design procedure. It also increases

investment cost and operating cost for aeration system.

• Its toxicity: In petroleum product or industrial oil-based product, they, sometime,

contain toxic substance, such as sulfide, heavy metals, which may be added to the

oil product in form of inhibitor or additive to provide desired product properties.

When these products are discharged to water and become wastewater, these

substance will become toxicity to living water organisms, includes biomass.

There are many studies, includes some from our lab, on the effect of oil contents in

wastewater to biological treatment process and possibility or optimum condition to use biological treatment to treat oily wastewater. However, none of doctoral thesis, directed by

M.Aurelle, is fully devoted to biological treatment of oil wastewater. So we will work on this

process by reviewing the available data from our lab researches as well as outside data.

Anyway, only our lab researches will be summarized here. Synthesized result from reviewing

will be presented as a section of textbook in Part 3 of this thesis.

3.10.1

Thesis of WANICHKUL [11]

This all-purpose thesis is also contributed to biological treatment. The author had

performed biodegradability test of permeate from ultrafiltration of cutting oil emulsion.


1. The study shows that ultrafiltrate of cutting oil emulsion can be treated by

aerobic biological process. The result from biodegradability test shows very high

TOC reduction efficiency (82 to 90% at the retention time of 2 to 5 hours).

3.11 Skimmer

When hydrocarbon is in the form of layer on water surface. It can be simply removed

from the surface by mean of overflow weir, overflow pipe or be scooped out manually. There

is one thesis on skimmer, which is the thesis of THANGTONGTAWI [5]. This research is

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39 I-39

contributed to study on oil drum skimmer and disk skimmer, which are very effective to

recover film or layer of oil or hydrocarbon on the surface of water.


• Influence of skimming materials, geometry of devices and characteristic ofwastewater to skimmer operation

• Model development for oil drum and disc skimmer

• Behavior of skimmers under interesting working conditions, which may affect its

efficiency


The experiment was conducted with various sizes of disc and drum skimmers to verify

effect of skimmer geometry. Various types of skimming material were tested, i.e., stainless

steel, PVC, polypropylene and fluorocarbon coated material. Kerosene and 2 types of

lubricant oil, as well as real wastewater from 4 refineries, were used in the experiment. Effecton interfacial tension was also considered by varying concentration of a commercial

surfactant.

Result

The result of this study provides models for sizing and calculating oil quantity,

recovered by the skimmers. The study, also, provides significant criteria for skimmer material

selection to obtain selective property, which allow the devices to recover only oil, not water.

Design consideration, such as limitation of model, working condition to be avoided, etc. is

included in this study.


1. In this thesis, mathematical models for sizing and calculating oil productivity of

the skimmer are proposed.

2. Influence of skimming material is studied and can be summarized as follow,

• Material of high surface energy, such as stainless steel, which is conditioned

by submerging in oil, will effectively recover or separate the oil from water.

However, when oil film on the surface of the tank is broken and the skimmer

is exposed to water, it will start recover the water immediately. Even after the

oil layer is present again, it will not resume its function of oil recovering.

• Material of low surface energy, such as PVC and PP, can effectively recover

oil. But it will start recovering water after the oil film is broken and the

skimmer is allowed to expose to the water surface for some times. Anyway,

it will resume its function after the presence of oil layer.

• From the study, fluorocarbon coated material, which is patented by ELF, is

the best oil-water selectivity. It always recovers only oil.

3.12 Application researches

To apply treatment processes previously described in real life situation, our lab had

performed some researches that devoted to compare the efficiency of various stand-alone

processes or combination of processes on treatment of certain type of oily wastewater. This

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41 I-41

3. Influence of surfactant on permeate flux, also, depends on material of membrane.

Inorganic (mineral) based membrane is more sensitive to surfactants than other

membranes.

4. Backflushing the membrane with its permeate is proven to be an effective way to

increase the limiting flux. The result shows that duration of ultrafiltrating and

backflushing cycle should be optimized to obtain best efficiency. Normally, the 2cycles is preferred to be short.

5. At high empty bed velocity, the coalescer with random bed will coalesce and

enlarge the droplets into relatively large drop, while the coalescer with brush

type bed tends to produce stream of jet, containing small oil drop.

6. However, the disorderly fibrous (steel wool) bed coalescer tends to be clogged

by suspended solids, usually presence in the oily wastewater. So the author

proposed new configuration of fibrous bed in form of the combination of 2

brushes. The internal one is of ordinary brush. The external one will look like

coil spring with its fiber elements protruding inward and toward the center. This

type of bed is believed to provide good interception, similar to the disorderly

bed, yet remain its anti-clogging properties, like brush-type bed.

7. Combination between coalescer/ hydrocyclone is proven to provide good

efficiency on the wider range of feed flowrate and size of oil droplet.


This thesis is an application research on the treatment of stabilized oil/water emulsion,

one of the most encountered oily wastewaters. The author also extended the research of

SRIJAROONRAT [10] on the combination of coalescer and hydrocyclone by studying the

influence of order of the 2 processes. So, WANICHKUL tested both combinations ofcoalescer/hydrocyclone and hydrocyclone/coalescer as well as the combination on

coalescer/hydrocyclone/coalescer.


• Study on treatment of stabilized emulsion by ultrafiltration and distillation

• Study on treatment of permeate from ultrafiltration by reverse osmosis, biological

treatment and distillation

• Study on treatment of retentate from ultrafiltration by heteroazotropic distillation

• Study on treatment of non-stabilized emulsion combination of coalescer/

hydrocyclone and hydrocyclone/coalescer• Study on multi stage fibrous bed coalescer


The experiment on ultrafiltration was conducted with 3 models, i.e. commercial batch

test module (effective area 37 cm2), lab scale cross flow model (effective area 100 cm2) and

pilot scale cross flow model (effective area 1 m2). For reverse osmosis, he used commercial

test module from OSMONIC co., ltd.

The stabilized emulsions tested consisted of 2 commercial cutting oil emulsions, 1

macroemulsion and 1 microemulsion. For membrane regeneration, he used the microemulsion

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44 I-44

Chapter 4 Conclusion

In this part, we have reviewed all of the researches in our lab, directed by Professor

AURELLE. We can see the attempts to study many aspects of treatment processes to cope

with various type of oily wastewater. The results of each thesis make us understand working

principles and limitation of the processes in many specific cases or frameworks. In the next part, we will analyze these specific data from these theses. And then try to integrate and

generalize them to formulate design criteria or mathematical models that can be used with the

entire (or as wide as possible) range of oily wastewater.

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Part II Generalization of models for

oil-water separation process design

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Part II Generalization of models for oil-water separation process design

II-i

Contents

Page


Chapter 1 Decanting

1.1 Simple decanter or API tank II-2

1.2 Lamella decanter or Parallel Plate Interceptor (PPI) II-3

1.3 Model verification II-4

1.4 Conclusion and generalized model of decanter II-7

Chapter 2 Skimmer

2.1 Drum skimmer II-9

2.2 Disk skimmer II-10

Chapter 3 Coalescer

3.1

Granular bed coalescer II-113.1.1 Filtration-based model II-11

3.1.2 Dimensional analysis-based model II-12

3.1.3 Model verification II-13

3.1.4 Conclusion and generalized model of granular bed II-14

coalescer

3.1.5 Generalized model for guide coalescer II-15

3.1.6 Generalized model for mixed bed coalescer II-16

3.1.7 Generalized model for pressure drop of granular bed II-16

coalescer and guided coalescer

3.2 Fibrous bed coalescer II-18

3.2.1

Dynamic fibrous bed coalescer model II-183.2.2

Simple fibrous bed coalescer model II-18

3.2.3 Model verification II-18

3.2.4 Conclusion and generalized model of fibrous bed coalescer II-21

3.2.5 Generalized model of random or disorderly fibrous bed II-23

coalescer

3.2.6 Generalized model for pressure drop of fibrous bed II-24

coalescer


4.1

Dissolved Air Flotation (DAF) model for oily wastewater II-25

treatment4.2 Model verification II-26

4.2.1 Modification of filtration-based model II-26

4.2.2 Population balance method II-28

4.3 Generalized model for DAF II-30

4.4

Generalized equations for pressurized water system calculation II-35


5.1 Two-phase hydrocyclone II-37

5.1.1

Trajectory analysis-based model II-37

5.1.2 Other models II-38

5.1.3

Model verification II-39

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II-iii

Table

Page

Table 1.1 Summary of tested decanters and operating conditions II-6

Table 6.1 Summary of parameters of resistance model from UF researches on II-51

oilywastewater treatment (reference temperature = 20O C)

Table 6.2 Summary of parameters of film model from UF researches on oily II-54

wastewater treatment (reference temperature = 20O C)

Table 6.3a Summary of RO data on oily wastewater treatment II-67

Table 6.3b Summary of NF data on oily wastewater treatment II-68

Table 7.1 Heterotropic temperature and composition from various extractants II-72

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Contents

II-iv

Figure

Page

Fig. 1.1 Schematic and typical removal efficiency curve of simple decanter II-3

Fig. 1.2 Schematic of PPI decanter II-4Fig. 1.3 “Spiraloil” decanter a) Simple spiral b) Mixed spiral II-5

Fig. 1.4a Comparison between observed efficiency (1',2',3') and predicted II-6

efficiency (1,2,3) for Simple Spiral "Spiraloil" decanter

Fig. 1.4b Comparison between observed efficiency (1',2') and predicted II-6

efficiency (1,2) for Mixed Spiral "Spiraloil" decanter

Fig. 2.1 Drum and disk skimmer II-10

Fig. 3.1(a) Schematic diagram of granular bed coalescer, (b) photo of bed material II-11

with coalesced oil on their surface and (c) coalesced oil drops at the

discharge surface of bedFig. 3.2a Relation between droplet diameter VS. model's error II-14

Fig. 3.2b Comparison between observed efficiency and predicted efficiency from II-14

DAMAK's model

Fig. 3.3 Relation between observed pressure drop of granular bed coalescer and II-17

predicted upper & lower limits from Kozeny-Carman's porosity = 0.13 and 0.23

Fig. 3.4 Comparison between observed efficiency and predicted efficiency from II-19

SRIJAROONRAT's model, Verified by MA's and WANICHKUL's data

Fig. 3.5 Comparison between observed efficiency and predicted efficiency by II-

20TAPANEEYANGKUL's model for simple fibrous bed (Assume rotating speed = 450

rpm)


modified SRIJAROONRAT's model (eq. 3.8b)

Fig. 3.7 Relation between observed efficiency and predicted efficiency from random II-23(or

disorderly) fibrous bed coalescer model and simple fibrous bed model

Fig. 4.1 Schematic diagram of DAF II-25

Fig. 4.2 Relation between theoretical efficiency factor and observed efficiency II-27

factorFig. 4.3 Relation between obseved efficiency and predicted efficiency of DAF II-27

from modified SIEM's model

Fig. 4.4 Relation between absolute pressure in pressure tank and dissolved quantity II-36

and released air volume

Fig. 5.1 Schematic diagram and trajectories of droplets in two-phase hydrocyclone II-37


Ma's and Thew-Colman's models

Fig. 5.3a Relation between observed pressure drop (inlet/overflow) of Thew cyclone II-42

and predicted pressure drop

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Part II Generalization of model for oil-water separation process design

II-1

Part 2 Generalization of model for oil-water separation process design

In this part, the models or researches collected and summarized in the part I are

analyzed and then generalized to obtain the model or models that governs the entire range (or

as wide as possible) of oily wastewater that we are interested in. Basic concept of each model

is briefly described here providing that it will be fully described in the next part. Then themodels and their limitations will be presented. After that, models will be tested using various

sets of data to cover the considered range of wastewater. Finally the generalized model will

then be proposed.

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Chapter 1 Decanting

II-2

Chapter 1 Decanting

Decanting or sedimentation is a non-accelerated process, which every input

parameters in STOKES law are not modified. According to the researches reviewed in Part I,

there are several types of decanters studied in GPI laboratory, i.e.,

1.1 Simple Decanter or API tank

Simple decanter, which is made well known and standardized by American Petroleum

Institute (API), is the simplest oil-water separation process based on classical STOKES law.

Concept of operation of the process is to provide sufficient time for droplets to float to the

surface, where it will accumulate into oil layer, before it flows out with the water at the water

outlet.

The model that governs the operation of the process is derived from comparing the

time required for the droplet to reach the surface with retention time of the tank. Fig. 1.1

shows again the diagram of decanting process. From the figure, the longest path to reach thesurface is the path starts at the bottom of the tank. The smallest droplet size that can reach the

surface is called the cut size. The droplet of cut size or bigger is always separated from

wastewater stream with 100% removal efficiency.

The smaller droplet can be also separated providing that it enters the tank near the

water surface. When uniformly distributed influent flow is valid, which is true for almost all

of properly designed tank, the removal efficiency of the droplets smaller than cut size is

proportional to its corresponding rising velocity. From these concepts, the models of

decanting process are as shown in eq. 1.1 to 1.4.

⎟ ⎠

⎞⎜⎝

⎛ = S

Q

dcU {1.1}

From STOKES law

c18μ

2dgΔρ

dU

⋅⋅= {1.2}

Then1/2

SgΔρ

c18Qμcd ⎟⎟

⎠

⎞⎜⎜⎝

⎛

⋅⋅= {1.3}

For oil droplet size, d ≥ cut size,dc

100%d

η = {1.4a}

For oil droplet size, d ≤ cut size,dc

100%

dcU

dU

dη ⋅= {1.4b}

( ) 100%maxd

mind od

Cd

η1

tη ⋅∑ ⋅=

oC

out Q

Q {1.4c}

∑−=max

min

d

d

od d

d

out C QQQ η ρ

{1.4d}

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II-3

U

V

Q

d = cut size

d < cut size

d > cut sizeInfluent Effluent

d

ηd

d c

d < d c

Zone 1 Zone 2

d = or > d c

Fig. 1.1 Schematic and typical removal efficiency curve of simple decanter

Typical characteristic of the removal efficiency of decanter is as shown in fig. 1.1. The

equations are valid while these conditions are satisfied i.e.,

1.

Reynolds number, Re, of droplet is between 10-4 to 1, which is the range that

STOKES law is valid.

2. The oil droplets are uniformly distributed across the cross section area of the

tank.

3. The oil droplet is spherical, which is normally true.

1.2 Lamella Decanter or Parallel Plate Interceptor (PPI)

This type of decanter is the basic modification of the simple decanter. The concept is

to decrease the rising distance of droplet to intercepting surface without decreasing the

retention time. This can be achieved by inserting plates into the simple decanter to act as the

interceptors for the rising oil droplets. Rising or travelling distance (H) is the distance

between the plates, not the depth of water (D) as shown in fig. 1.2. Some times, the plates are

inclined with angle (α) as related to horizontal axis. In this case, rising distance will becomeH / cos α.

The model that governs the operation of the process is modified from the model of

simple decanter, as shown in eq. 1.5. From the equation and figure, it can be implied that the

simple tank is divided into (N+1) small decanters.

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II-5

Where Q = Wastewater flowrate

H = Rising distance of oil drop, depends on configuration of the decanter

L = Length of interceptor surface

A = Flow area (Cross sectional) area of decanter

Removal efficiency can be calculated using eq. 1.4. From the equations, we can seethat the models of simple decanters and PPI are modified forms of eq. 1.9 by simple relations

of flow velocity and tank geometry. However the models described before are derived from

basic rectangular tank and flat insertion plates.

But, in real life situation, decanters are designed or produced in various forms, such as

corrugated plate inserted tank, concentric annular insertion decanter, etc. So, sometimes, it is

very difficult to define H. Then, we propose to simplify the general model by neglecting

complicate analyzing to define H, and using concept of decanting area (Sd) instead. Sd is

calculated from the sum of every surface area within the decanter that can intercept oil

without considering whether the values H of these areas are identical or not. The other form

of general model is shown in eq. 1.9b.

1/2

dSgΔρ

c18Qμcd

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⋅⋅= {1.9b}

To verify the theoretical model, we select the research of CHERID [4] on 2 sets of the

“SPIRALOIL” decanter, i.e.,

• “Simple Spiraloil”; fabricated from concentric annular plates as shown in fig. 1.3a

• “Mixed-spiral Spiraloil”; ”; fabricated from concentric annular plates with

corrugated plates spacer as shown in fig. 1.3b

We will use these decanters to compare the removal efficiency calculated from model

to experimental result from the research. Geometry of the decanter and operating parameters

used in the experiment are summarized in Table 1.1 and Annex A1.

Solid core,

radius = r

R

H

e

Annular plates

a) b)

Fig. 1.3 “Spiraloil” decanter a) Simple spiral b) Mixed spiral

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Chapter 1 Decanting

II-6

Table 1.1 Summary of tested decanters and operating conditions

Description Simple spiral “Spiraloil” Mixed spiral “Spiraloil”

Geometry

Nominal radius R (mm) 50 50

Core radius r (mm) 10 10

Length of decanter L (mm) 300 300

Total length of inserted plates (m) 3.88 N/A

Spacing between concentric annular plate (mm) 2 3

Plate thickness (mm) 0.3 0.2 for annular plates0.4 for corrugated plates

Interceptor (decanting) area (m2) 1.66 2.1

Inclination of decanter Horizontal Horizontal

Operating conditions

Flow velocity (cm/s) 0.4-1.6 0.5-1.5

(m/h) 14.4-57.6 18-54

Wastewater used Kerosene-water mixture Kerosene-water mixture

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 10 20 30 40 50 6

Droplet diameter (micron)

R e m o

v a l e f f i c i e n c y ( % )

0

1'1 3'

2 2'

3

V = 1.6 cm/s (3, 3')

V = 0.8 cm/s (2, 2')

V = 0.4 cm/s (1, 1')

Fig. 1.4a Comparison between observed efficiency (1',2',3') and predicted efficiency (1,2,3) for Simple Spiral "Spiraloil" decanter

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 10 20 30 40 50 6


R e m o v a l e f f i c i e n c y ( % )

0

1 (V = 0.5 cm/s)1'

2' 2 (V = 1.5 cm/s)

Fig. 1.4b Comparison between observed efficiency (1',2') and predicted efficiency (1,2) for Mixed Spiral "Spiraloil" decanter

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II-7

Comparison graphs between observed efficiency and predicted efficiency from model

for both Spiraloil decanters are shown in fig. 1.4. These graphs show that;

1.

Predicted values for cut size are relatively accurate.

2.

Predicted efficiencies of the droplets smaller than cut size are always lower than

observed value because, in our simplified model, coalescing between rising oildrops is not accounted. Furthermore, in case that the plates are placed very close

to each other like in “Spiraloil”, oil film will accumulated at the surface of plate,

then helps reducing rising height oil droplet, thus increasing the efficiency.

3.

Correction factor for efficiency prediction of these small droplets may not be

established accurately. However, the predicted cut size can be used to design the

tank with relative high accuracy. So it is reasonable to select the cut size to cover

the majority of droplet size distribution. The predicted efficiency of smaller

droplets, which is the minority part, will cause no harm but slightly

underestimation on the total efficiency.

1.4 Conclusion and Generalized Model of decanter

From model verification result, we can conclude and propose the generalized model,

as well as, its limitation as follows,

1.

To solve oil or hydrocarbons removal efficiency of decanter, the cut size of the

decanter will be determined first. Then, graded efficiency (efficiency of each size

of droplet) and then total removal efficiency can be determined.

2. The cut size of the decanter can be determined from eq. 1.9. When configuration

of decanter is not complicate and rising distance of oil drop to interceptor can be

clearly determined, Using eq. 1.9a will give very accurate prediction. However,when configuration of the decanter is so complicate to determine the rising

distance accurately, eq.1.9b provides relatively accurate result for the cut size.

For PPI tank, the cut size can be calculated from eq. 1.5, which is the modified

form of eq. 1.9a.

1/2

ΔρgLA

c18HQμcd ⎟⎟

⎠

⎞⎜⎜⎝

⎛ = {1.9a}

1/2

dSgΔρ

c18Qμ

c

d

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⋅⋅= {1.9b}

1/2

1)(NP

ΔρgS

c18Qμcd

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

+= {1.5}

3.

To determine graded and total removal efficiency, use eq. 1.4.

For oil droplet size, d ≥ cut size, dc

100%d

η = {1.4a}

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Chapter 1 Decanting

II-8


100%

dcU

dU

dη ⋅= {1.4b}

For total removal efficiency

( ) 100%maxd

mind od

Cd

η1

tη ⋅∑ ⋅⋅⋅=

oC

out Q

Q {1.4c}

∑−=max

min

d

d

od d

d

out C Q

QQ η ρ

{1.4d}

4. To use the models described above, the following conditions need to be satisfied

and the assumptions and limitations would be noted.

1) Reynolds number, Re, of oil droplet is between 10-4 to 1, which is the range

that STOKES law is valid.

2) The oil droplets are uniformly distributed across the cross section area of

the tank, which can be achieved by proper design of inlet chamber. And the

oil droplet is spherical, which is normally true.

3) For PPI or others forms of plate inserted decanter, the plates are identical in

size and are inserted evenly and horizontally. For PPI tank with incline

plates, S p in eq. 1.5 will be replaced by S p cos α. α is the inclination angle,

related to horizontal axis.

4) If the decanter or the inserted plates are inclined, the rising distance will be

the spacing between plates, but will be measured in vertical direction. Sothe shortest distance is obtained from the same spacing between plates,

when the plates are located horizontally.

5)

Prediction of cut size from eq.1.9b, even with its simplification, is

relatively accurate for the cut size larger than 20 microns.

6) For droplets smaller than 20 microns, they are subject to Brownian motion

and cause error in the prediction of the efficiency. So it is recommended to

avoid using the decanter for the wastewater with majority part of oil

droplets smaller than 20 microns. However, if these small droplets are the

minority part of pollutants, the models can be used to predict the efficiency

without any harm because its prediction is usually lower than observedvalue, thus make the prediction result on the safe side.

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Chapter 3 Coalescer

II-14

-30%-20%-10%

0%10%20%30%40%

50%60%70%80%90%

100%

0.0E+00 5.0E-06 1.0E-05 1.5E-05 2.0E-05 2.5E-05 3.0E-05 3.5E-05 4.0E-05 4.5E-05

Droplet diameter (m)

E r r o r ( %

)

DAMAK's model AURELLE's model

Fig. 3.2a Relation between droplet diameter VS. model's error

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Observed efficiency %

P r e d

i c t e d e f f i c i e n c y %

ηd = 58 (dE/dp)0.2

(H/dp)0.12

(ρc dp V2/γo/w )

-0.08(μd/μc)

0.09(Δρ/ρc)

0.09

-10%

+10%

Fig. 3.2b Comparison between observed efficiency and predicted efficiency from DAMAK's model

3.1.4 Conclusion and generalized model of granular bed coalescer

From model verification result, we can conclude and propose the generalized model as

well as its limitation as follow,

1. To predict removal efficiency of coalescer, graded efficiency (ηd) can be

calculated by eq. 3.5. If the result from eq. 3.5 is greater than 100%, then it will

be rounded up to 100%. Total removal efficiency can be calculated by eq. 3.4.

%1000.09)

cρ

Δρ(0.09)

μc

μd(0.08)

o/wγ

dpVc

ρ(0.12)

dp

H(0.2)

dp

d58(

dη ⋅

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ −= {3.5}

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II-17

• Lower zone or critical zone: This zone represents effective zone of coalescer bed.

The maximum height of this zone is called “critical height (Hc)”. When bed height

is greater than critical height, the efficiency will increase only slowly (From eq.

3.5: η ∝ H 0.12). In this zone, the bed will be soaked with oil so the porosity will be

low.

•

Upper zone: If the bed is higher than Hc, practically, all of oil will be trapped in

critical zone. Then in higher zone, there will be enough oil in lower zone to flow

continuously through the bed in form of “flow channeling”. So the porosity in this

zone will be lower than critical zone.

We use data from various researches [3], [26], [27] to verify the value of bed porosity.

The verification result is shown in Annex A2.2 and fig. 3.3. We can conclude that pressure

drop of granular bed can be calculated by Kozeny-Carman’s equation (eq. 3.6), using the

following recommendations, i.e.,

• When Hc is known (from literatures, etc.), pressure drop in the lower and upper

part of bed can be calculated separately, using eq. 3.6. Recommended porosity (ε)for the lower (critical) part of bed (H<Hc) is between 0.14 to 0.19. Recommended

porosity for the upper part of bed (H>Hc) is between 0.23 to 0.30.

• If it is certain that H design < Hc, use single step calculation with ε = 0.14 - 0.19.

• However, Hc is usually unknown, then it is recommended to use single step

calculation with ε = 0.13 and 0.23 to estimate minimum and maximum pressure

drop respectively (as shown in fig. 3.3).

• Because of the fact that “guide” of guided coalescer has relative high porosity (0.9

approx.), then, The pressure drop is very low, compared to granular bed, and can

be negligible. So eq. 3.6 can also be used for guided coalescer.

0

20

40

60

80

100

120

140

160

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Run number

P r e s s u r e d r o p ( m )

Observed data

Upper limit (porosity = 0.13)

Lower limit (porosity = 0.23)

Fig. 3.3 Relation between observed pressure drop of granular bed coalescer and predicted upper & lower limits from Kozeny-

Carman's porosity = 0.13 and 0.23

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Chapter 3 Coalescer

II-18

3.2 Fibrous bed coalescer

This type of coalescer uses relatively porous fibrous material as a bed to promote

coalescing between oil droplets, as shown in fig. 3.4. Due to its high porosity, this type of bed

is hardly clogged and can handle wastewater containing suspended solids efficiently. It also

causes much less pressure drop than granular bed coalescer. However, fibrous element, whichis normally very small, can be deflected, especially in large-scale unit, and causes unpredicted

channeling, then decreasing in efficiency. Three basic steps for granular bed coalescer,

proposed by AURELLE [3], can also be used to describe phenomena taking place within the

coalescer. However, mathematical models, derived from dimensional analysis, are proven to

be more accurate.

There are 2 main categories of fibrous bed coalescers, i.e., simple fibrous bed

coalescer and dynamic (or rotating) fibrous bed coalescer. The latter is the modified form of

the former, by the installation of driving unit to drive the bed.

3.2.1

Dynamic fibrous bed coalescer model

The method is proposed by TAPANEEYANGKUL [8]. The model is based on the

classic dimensional analysis, which is an efficient tool when exact theory of the processes can

not be established. The author had conducted his research thoroughly and covered every

necessary aspect of the equipment. So his model and its limitation will be quoted here again,

as shown in eq.3.7, without the need for further verification.

%1000.74V0.58

Fd0.03D

0.53 N0.35H0.35ε)(10.580.67d

dη ⋅

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ −

= {3.7}

The model is verified under these conditions i.e.;

• 52 < Re < 1164.

• Rotating speed of the bed is between 10 to 200 rpm.

• Empty bed velocity is between 0.1 to 1.1 cm/s (3.6 to 39.6 m/h).

• Diameter of coalescer bed is around 11.5 cm.

• Diameter of fiber is around 100 to 300 microns.

• The beds, used in the experiment, are “bottle brush” types, made of polyamide or

polypropylene with stainless steel shaft.

3.2.2 Simple fibrous bed coalescer model

This coalescer is a predecessor of dynamic bed coalescer, described in the previous

section. However, the researches on this type of coalescer are based mainly on its application

and design consideration, rather than model development. So there is no model proposed by

GPI researchers for this equipment.

3.2.3 Model verification

After reviewing existing experimental data, it shows that each research presents onlysome parameters related to its own objectives. However we have tried to develop a model,

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Chapter 3 Coalescer

II-20

For this, data from several researches [10], [11], [16] have been used to verify

TAPANNEYANGKUL’s model. The data, used to verify the model, has been limited to the

droplet size of 10 microns and greater. For smaller droplet, it is difficult to measure the

concentration of these droplets accurately. So observed data is not complete and seems

erroneous. Comparison between observed and predicted efficiency is shown in fig. 3.5.

From the graph, it shows that TAPANEEYANGKUL’s model can be adapted to

predict the efficiency of simple fibrous bed coalescer with acceptable degree of accuracy (±

20% error) when using the rotating speed = 450 rpm. This speed is too high to be reasonable.

This may be due to the fact that TAPANEEYANGKUL’s model is verified from relatively

short bed (H/D < 2) while other researches operate at H/D up to 10. So the exponent of (H/D)

from both models is quite different. In this case, we can conclude that TAPANEEYANGKUL

may not be applied to simple fiber bed coalescer.

However, it is still interesting to assume that the effect of porosity in

SRIJAROONRAT’s model should be the same as TAPANEEYANGKUL’s. So we add the

term “(1-ε)0.35

” into eq. 3.8a and solve for a new constant to replace 45.005. The modifiedmodel is shown in eq. 3.8b. Comparison between observed and predicted efficiency is shown

in fig. 3.6. The graph shows that MA’s data are better predicted, using eq. 3.8b. The model

still cannot cover WANICHKUL’s data for it is tested at very high oil inlet concentration

(7950 mg/l). However, the predicted efficiency is still on the safe side to use as a guideline.

( ) %1000.694)D

H(0.35ε10.18)

D

Fd

(0.18)D

d(0.77)

cμ

VDc

ρ104.5(

dη ⋅⎟

⎟

⎠

⎞

⎜⎜

⎝

⎛ −−−= {3.8b}

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

0.0% 20.0% 40.0% 60.0% 80.0% 100.0% 120.0%Observed efficiency (%)

P r e d i c t e d e f f i c i e n c y ( % )

-20%

+20%

Fig 3.5 Comparison between observed efficiency and predicted efficiency by TAPANEEYANGKUL's model for simple

fibrous bed (Assume rotating speed = 450 rpm)

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II-21

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% 100.0%

Observed efficiency (%)

P r e d i c t e d e f f i c i e n

c y ( % )

SRIJAROONRAT's data

MA's data

WANICHKUL's data

-20 %

+20 %

Fig. 3.6 Comparison between observed efficiency and predicted efficiency from modified SRIJAROONRAT's model (eq.

3.8b)

3.2.4 Conclusion and generalized model of fibrous bed coalescer

From model verification result, we can conclude and propose the generalized model as

well as its limitation as follows,

Dynamic fibrous bed coalescer

1. To predict removal efficiency of coalescer, graded efficiency can be calculated

by eq. 3.7. If the result from eq. 3.7 is greater than 100%, then it will be roundedup to 100%. Total removal efficiency can be calculated by eq. 3.4.

%1000.74V0.58

Fd0.03D

0.53 N0.35H0.35ε)(10.580.67d

dη ⋅

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ −

= {3.7}

( %maxd

mi

)n

d odC

dη

1t

η ∑ ⋅⋅⋅=o

C out

Q

Q {3.4a}

∑−=max

min

d

d

od d

d

out C Q

QQ η ρ

{3.4b}

2. The model is verified under these conditions i.e.;

• 54 < Re < 1164.

• 1 < H/D < 2. However, the maximum H/D shows in

TAPANEEYANGKUL’s research is 6. Using H/D > 2 in the model can be

also applied for comparison purpose only.

• Rotating speed of the bed is between 10 to 200 rpm. However, recommended

minimum rotating speed is 75 rpm. Using lower speed may not provide any

additional benefit over simple fibrous bed coalescer.• Empty bed velocity is between 0.1 to 1.1 cm/s (3.6 to 39.6 m/h).

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Chapter 3 Coalescer

II-24

From the graph, it shows that SRIJAROONRAT’s random fibrous bed model (eq. 3.9)

can accurately predict the efficiency of the coalescer. SRIJAROONRAT’s simple fibrous bed,

(eq. 3.8b) is used to calculate the efficiency of the coalescer for comparison. However, from

the graph, it shows that the result from eq. 3.8b tends to underestimate the efficiency from 2 to

6 times. From this, we recommend the following procedure to calculate the efficiency of

metal wool bed coalescer.

1.

Apply SRIJAROONRAT’s random fibrous bed model (eq. 3.9) if these

conditions are satisfied, i.e.,

• Velocity is between 1 to 2.5 cm/s or 36 to 90 m/h.

• Inlet concentration is around 1000 mg/l.

• The model is developed from metal wool bed coalescer, diameter = 5 cm.,

fiber diameter = 40 microns, and porosity = 0.95.

• The wool is coated with silicone, so it becomes oleophilic.

2. Even though eq. 3.9 is developed from small set of data and tortuosity can not be

established in the form of numerical factor. But, from graph 3.6, it can beestimated that the disorderly bed coalescer is 2 to 6 times more efficient that

simple bed. However, it will be clogged easily if suspended solids are present in

the wastewater.

3. Internal diameter of coalescer casing, which contains the bed, should be as close

to the diameter of the bed as possible to avoid channeling problem.

3.2.6 Generalized model for pressure drop of fibrous bed coalescer

Many researcher [8], [10], [11], [16] observed pressure drop of fibrous bed coalescers

and reported that these coalescer causes very low pressure drop due to very high porosity oftheir beds. There is no proposed model on pressure drop.

In order to calculate the pressure drop, we recommend to use any general piping loss

equations, such as Darcy’s, Colebrook-White’s or Hazen-William’s equation with the safety

factor of 2 to 5, multiplied to the actual length of the bed. However, the pressure drop of

fibrous bed coalescer is normally low (< 104 N/m2), compared to piping system pressure drop.

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Flotation is an accelerated separation process by increasing density difference between

continuous phase and dispersed phase. This is accomplished by mean of adding gas or air into

the wastewater to promote formation of air-solids or air-oil agglomerates. There are several

researches on flotation, its modification and applications, studied in GPI laboratory, such as

mechanical flotation, diffused air flotation, dissolved air flotation, etc. Here, we will consider

only the application of dissolved air flotation (DAF) on oily wastewater treatment.

4.1 Dissolved Air Flotation (DAF) model for oily wastewater treatment

For Dissolved Air Flotation, air bubbles are generated from pressurized (or air –

saturated) water. At GPI laboratory, the model of DAF for oily wastewater treatment is

proposed by SIEM [12]. In his study, SIEM applies filtration-based model for granular bed

coalescer, proposed by AURELLE [3], by assuming the air bubble as collector (or filter

media), as shown in eq. 4.1. However, in this case, the media is also moving. Schematic

diagram of DAF is shown in fig. 4.1.

Separated

Droplet

/bubble

agglomerate

Oil droplet

Pressurized

water system

Oily

wastewater

Air

bubble

Clarified

water

Fig. 4.1 Schematic diagram of DAF

Removal efficiency (or probability) factor of DAF is calculated from summation of

theoretical efficiency factors of 3 transport phenomena, i.e. sedimentation, direct interception,

and diffusion, as shown in eq. 4.2, and adjusted to fit with observed data, as shown in eq. 4.3.

%100

)

bd

H)

exp(α

AV

Φ

2

3(

e1d

η ⋅

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛ −

−=

η

{4.1}

diff η

Intη

sedη

theoη ++= {4.2a}

r 18μ8

2Δρgd

sed

η = {4.2b}

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II-26

2)

bd

d(

2

3Int

η = {4.2c}

2/3)

bdr μdV

KT0.9(

Diff η = {4.2d}

Vr = |V-U b| {4.2e}

0.507)theo

0.0074()exp(α η η = {4.3a}

4.2 Model verification

4.2.1 Modification of filtration-based model

From the model in section 4.1, air or gas flowrate (Φ) and the term “AV” can be

written in form of Qt as shown in eq. 4.4.

air ρ

Conc(air)

tQ

pwQ

AV

Φ⋅= {4.4a}

)x

tQ

pwQ(= {4.4b}

Normally, under certain design condition, Q pw/Qt is constant. Solubility of air in water

(Conc(air)) and air density are intrinsic (internal) property, depends on pressure, and

temperature of pressurized water, which are constant for any given pressurized water system.

Then, from eq. 4.4, it shows that the term “Φ/(AV)” is flow-independent.

From, eq. 4.2, it shows that the effciency factors vary with flowrate via relative

velocity between air bubble and oil droplet. Rising velocity of bubble (U b) is calculated by

STOKE’s law, so it does not depend on wastewater flowrate. However, if we consider eq.

4.2d, it can be implied that if we lower the flowrate until V = U b, Vr is, therefore, equal to 0.

Or when V >> U, it will seem to some one that happen to be on an oil droplet, which will be

carried along with the flow, that he run pass very slow bubble, or bubble will stay in the

reactor longer than oil drop. This cannot be true because the bubble will be carried along with

the flow as well. Furthermore, from its lower density and its bigger size, the bubble will

usually rise up faster than oil drop at the same diameter.

In fact, relative velocity (Vr ) is equal to difference between absolute velocity of bubble

(V+U b) and flow velocity of water (V) (eq. 4.2f). If we replace Vr with U b, it will cause some

changes in eq. 4.3a. We have already recalculated the eq. 4.3a (see fig. 4.1) and found that it

can be rewritten as shown in eq. 4.3b (modified SIEM’s model). Fig. 4.2 shows comparison

between observed efficiency and predicted efficiency calculated from eq. 4.1, 4.2a to 4.2d,

4.2f and 4.3b. From the graph, prediction error is about 20%.

Vr = V+U b-V = U b {4.2f}

0.5919)theo

0.009005(η)(αexp

=η {4.3b}

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Population balance method is one of popular concepts, used by many researchers, to

develop DAF model. In our lab, DUPRE [14] uses this method in her research on application

of DAF for liquid-solid separation. Concept of this method is that rate of change in the

number of oil droplets which are free or attached by 1, 2 or more air bubbles is the function of

the number of air bubble and oil droplet, as shown in eq. 4.5. Oil droplet that is attached by at

least 1 bubble, so-called oil-bubble agglomerate, will be separated. So the rate of change innumber of oil droplets represents removal efficiency.

Main assumption of population balance method is that the number of bubble is

assumed to be constant. From many researches [14], [34], It is proven that, for liquid-solid

separation, the number of bubble (N) can be safely assumed as constant without serious error,

because there are a lot more bubbles than pollutant if normal range of (Q pw/Qt) is applied.

However, in case of oily wastewater, many researches [12], [13] show that bubble-oil

agglomerates are in form of oil shell with air inside and these agglomerates are still able to

intercept more oil droplets. Those researches also show that coalescence of oil and bubble is

more effective than that of the same species. So it should be safely assumed that the number

of bubble in this case is more or less constant and the population balance method is, then,applicable.

N0

n0

k βdt

0dn

−= {4.5a}

Ni

ni

k β N1i

n1i

k βdt

idn

−−−−= {4.5b}

i = 0 to imax

3 bd6

π

Φ N = {4.5c}

no and ni represent the number of oil droplet which is free and attached by i bubbles

respectively. κ represents collision rate constant, from Saffman and Turner’s (1956)

coagulation theory, and β represents adhesion efficiency or probability that the collision

between oil drop and bubble will be successful. Removal efficiency can be written as (ni/n0),

which can be achieved by integrating eq. 4.5.

To integrate eq. 4.5, complex numerical method is required. MATSUI and LEPPINEN

[34], [37] solve the equation by Laplace transforms and suggest the solution as shown in eq.

4.6.

i

1

2 b

/d2d

κτ

eκτ)(

ei:x N

in

⎟⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜⎜

⎝

⎛

−−⋅= ⎟

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

{4.6a}

i = 0 to imax –1

)1)...(2)(1i(i

1))(i1)...(xx(xi:x

−−−−

= {4.6b}

2 b

/d2dx = {4.6c}

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II-31

r 18μ8

2gdoil/water

Δρ

sedη = {4.2b}

2)

bd

d(

2

3

Int

η = {4.2c}

2/3)

bdr μdV

KT0.9(

Diff η = {4.2d}

0.5919)theo

0.009005(η)exp(α =η {4.3b}

c18μ

2 b

gdair/water

Δρ

bUr V == {4.2f}

2.

To use the models described above, the following conditions need to be satisfied;

1) Inlet oil concentration should not be greater than 1,200 mg/l (before

dilution) or 435 mg/l (after dilution). Using the model with higher oil

concentration will result in underestimating the efficiency.

2) The model is tested at the following operating conditions;

• Φ/AV = 0.0516. Only this value must be used in the equations. As

long as this value is fixed, SIEM’s operating condition still holds and

the model is still valid.

• Retention time (τ), based on Qt, is around 25 minutes.

•

Droplet diameter (d) tested is between 2 to 40 microns. • Diameter of air bubbles (d b) varies from 15 to 130 microns. Tested

average diameter is 70 microns, which is used to verify the model, and

standard deviation of bubble diameters is 34.5 microns. The range of

bubble sizes is common for commercial pressurized water system or

saturator. The pressure of the test system is 4 atm (absolute).

• Tested air flowrate (Φ) is 0.42 cm3/s (4.2e-7 m3/s).

• Tested wastewater flowrate (Q) is 3.9 cm3/s (3.9e-6 m3/s)

• Tested effective water depth (H) is 0.70 m. The value of H can be

freely changed as long as (Φ/AV) is fixed. However, H between 1.8 to

2.7 is recommended by API [45].

•

Diameter of flotation column is 0.15 m Cross section area of column(A) is 0.01767 m2.

•

Ratio of pressurized water to wastewater (Q pw/Q) is 1.76.

• Air to pollutants ratio used is around 0.12 kg. air/ kg. oil.

• Ratio of number of bubble/ oil droplet tested is around 1.4 oil droplet/ 1

air bubble.

• Hydraulic loading rate or flow velocity (V), based on Qt, is 1.6 m/h

3. Because of the limitation of the pilot model, tested ratio of pressurized water to

wastewater is quite high (around 92%), compared to that of general DAF for

solid/liquid separation (less than 50%) [13]. However, API [45] recommended

air/wastewater ratio of 0.35 std. ft3

/ 100 gal of total flow for full-flow DAF process. This value is equivalent to 84% of 4-atm (abs) pressurized water/

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II-33

)ref τreqΦ

ref 2,κ (

e1d

η−

−= {4.15a}

Because we use τref , instead of τreq, the calculated efficiency will be

lower than the real value.

•

To decrease ( req < ref ), as well as, τ (τreq < τref ):

This will cause increasing of V, so G will increase. Then κ2 (see eq.

4.9) will be higher. Again, we do not know how much exactly. So, to

be on the safe side, we will assume that κ2 = κ2,ref . The efficiency can

be calculated by eq. 4.15b. And again, the calculated efficiency will be

lower than the real value.

)reqτreqΦref 2,

κ (e1

dη

−−= {4.15b}

• To increase ( req > ref ) and decrease τ(τreq < τref ):

This can be done by increasing pressurized water flowrate. However,

the ratio of pressurized water/ wastewater is already high (176%). Thus,

this case is unlikely to heppen. In this case, κ2(see eq. 4.9) will be

higher. Like the former case, the efficiency can be calculated by eq.

4.15b.

• To increase ( req > ref ), as well as, τ(τreq > τref ):

This case does not exist because it means that we have to decrease

wastewater flowrate. As stated above, the ratio of pressurized water/

wastewater is already high (92%). If we decrease wastewater flow,

quantity of pressurized water flow will exceed that of wastewater,which is not feasible because we have to recycle effluent at 100% plus

additional makeup water to feed the pressurized water system.

There is no obvious limit for the 4 adaptations, shown above. However

we recommend using the values within general range, shown in item 2. to

4.

7) Outlet concentration can be calculated from eq. 4.16a. If DAF effluent is

recycled to pressurized system, Cod,dil will be calculated as shown in item

8. If pressurized water comes from additional clean water, Outlet

concentration can be calculated by eq. 4.16b. In this case, effluent

quantity is equal to Qt, not Q. The subscript “dil” represents the conditionafter dilution with pressurized water.

dilod,)C

dη(1

dC −⋅=

out Q

Q {4.16a}

)

tQ

Q(

od)C

dη(1

dC −⋅=

out Q

Q {4.16b}

∑⋅−=max

min

d

d

od d

d

out C Q

QQ η ρ

{4.16c}

DAF efficiency ( DAF), which is the efficiency based on flotation effect

alone, can be calculated by the following equation.

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II-35

Batch experiment, such as Flota-test , will provide valuable result, if not

exact, for design propose and can be used to compare with model result.

4.4 Generalized equations for pressurized water system calculation

An important system that plays very significant role in DAF process is pressurizedwater system, since, as shown in previous section, it is the source of air bubble and ratio of

air/oil droplet is one of the key parameters in DAF process. It is still the component that

consumes almost all of the energy required in DAF process. The other required energy is

pressure drop of the process caused by hydraulic elements of the reactor, such as pipeline,

outlet weir, etc., which can be calculated by familiar pressure drop equations. This pressure

drop is substantially lower than required energy of the pressurized water system.

The power for pressurized water pump can be calculated by normal pump equation

(Power =ρgQ pwH/η pump). Head of pump (H) can be assumed to equal the absolute pressure of

the pressurized water system. For the power required for an air compressor as well as the

quantity of air released by the pressurized water will be as show below.

To calculate quantity of pressurized water that can supplied the required amount of air

bubbles, our researches show that theoretical equations based on Henry’s and Dalton’s law

give relatively accurate result. The equations can be summarized as follows,

1. To predict molar fraction of dissolved gas in the water (x), Henry’s law (eq.

4.18) will be applied. Normally, we use the molar fraction of air (y air ), which

equals to 1 , to calculate. Anyway, if we need to know the quantity of some

certain gases, i.e., oxygen or nitrogen, etc. It can also be calculated by Henry’s

law, using molar fraction of oxygen gas and nitrogen gas in air (yO2 and y N) of

0.11 and 0.89 respectively (in permanent regime). For the absolute pressure ofthe saturator or pressurized water system (P), it is recommended to use pressure

within the standard of commercial equipment range (around 4 atm(abs)). The

higher the pressure, the more the amount of bubble generated and the greater the

energy required. Henry’s constant (H) of air, oxygen, and nitrogen are 4.04 x104,

8.04 x104, 6.64 x104 atm/mole respectively

H

yPx = {4.18}

2. When we know the molar fraction of dissolved air or gas (x) in water, we can

convert it to mg/l of dissolved air or gas or volume of air or gas per unit volumeof water by general conversion factor. The equation for calculating mg/l of

dissolved oxygen or air in pressurized water is shown in eq. 4.19a and 4.19b

respectively (using P in atm). Ratio of air flow to pressurized water flow at 20 o

C, assuming %saturation of air or gas in water is equal to 95%, are as shown in

eq. 4.20 (using P in atm).

4.5893P)2

Conc.(O = {4.19a}

22.965PConc.(air) = {4.19b}

.01910.0191P)

pwQ

Φ( −= {4.19c}

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Hydrocyclone is an accelerated separation process by replacing gravitational

acceleration with higher centrifugal acceleration. Hydrocyclones are widely used in many

processes, i.e., classification and separation between solid-liquid and liquid-liquid. In our

scope of work, we will consider mainly on the mathematical model of liquid-liquidhydrocyclone. There are 2 main types of hydrocyclones studied in GPI laboratory, i.e., two-

phase hydrocyclone and three-phase hydrocyclone.

5.1 Two-phase hydrocyclone

5.1.1 Trajectory analysis-based model

Every commercial hydrocyclone has its own shape and ratio between each component.

So it is difficult to develop the model to cover every type of them. In our lab, main research

on hydrocyclone is based upon MA’s study [16] on two-phase hydrocyclone for oil/water

separation. In his research, he bases his experiment on “THEW” type hydrocyclone, which isinitiated by Prof. THEW, UK. So, in our research, we will emphasize only on this type of

hydrocyclone.

MA develops hydrocyclone model, based upon trajectory analysis, which is normally

used in decanter calculation. The concept of the model is that oil droplet in the hydrocyclone

is subjected to 3 velocity components, i.e., radial velocity (U), tangential velocity (V) and

axial or vertical velocity (W), as shown in fig. 5.1. For the tangential velocity, he assumed

that the oil droplet has the same tangential velocity as the liquid, which follows the free vortex

pattern (VR n = const.). In the case of THEW’s hydrocyclone, n is equal to 0.65. The equation

of V for THEW’s hydrocyclone is a sshown in eq. 5.1c. He also assumed that vertical velocity

(W) of the droplet is similar to that of the liquid. Vertical velocity profile can be devided into2 regions. The external region, near to the wall of the hydrocyclone, has downward flow,

while the internal region has upward flow. The equation of W is in 3rd order polynomial form

as shown in eq. 5.1d and 5.1e. For the radial velocity of the droplet, he assumed that it is

governed by STOKE’s law. His assumption is that if the droplet can reach certain radial

distance where the vertical velocity starts changing from downward to upward direction (R =

R ZVV, “ZVV” means zero vertical velocity), it will be carried upward to the overflow port,

then separated from the main stream, which will flow out at the bottom (underflow) outlet.

Dn

W

V

U

Di

Do

R

Z

β

D

Ds

Z

d = dc d > dcd < dc

R

Z

R

Z

R R d

L

%100=η %100=η

a ) Schematic diagram b) Trajectory of each size of oil droplets

Note: Dn/D=0.5, Ds/D=0.25, Do/D<0.05, Di/D=0.25, β =1.5 deg

Fig. 5.1 Schematic diagram and trajectories of droplets in two-phase hydrocyclone

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II-39

commercial liquid-liquid hydrocyclone, such as Vertoil. So it should be applied only with that

specific hydrocyclone. Extrapolation of model is normally not guaranteed.

For THEW hydrocyclone, used by MA in his research, Prof. THEW, himself, and his

colleague, COLMAN, have proposed the model for the hydrocyclone (eq. 5.3a). However, it

is an empirical model, which seems to be obtained from curve fitting. CHEBELIN [29]quoted THEW-COLMAN’s correlation for solving d75% in his research, as shown in eq.

5.3b.

%100)e1(d

η0.19))

d

d1.8((

75% ⋅−=−−

{5.3a}

0.5

QΔρ

3)n(0.001D0.00001μ61075%

d⎥⎥⎦

⎤

⎢⎢⎣

⎡

⋅

⋅= {5.3b}

5.1.3

Model verification

To verify the models, we will compare predicted efficiency, calculated from MA’s

model, with observed data. Moreover, since MA’s model is developed from THEW

hydrocyclone. So it will be interesting to compare the MA’s model with THEW’s model. We

use the data from MA’s study, based on THEW hydrocyclone, nominal diameter 2 cm.

Operating condition used is tabulated in table 5.1. For COLMAN’s model, we used observed

value of d75% in eq. 5.3.Comparison between result from the 2 models and observed data is

shown in fig. 5.2.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%110%

0.00 10.00 20.00 30.00 40.00 50.00 60.00


E f f i c i e n c

%

Colman's model

Observed data

Ma's trajectory analysis

Fig. 5.2 Comparison between observed efficiency and predicted efficiency from Ma's and Thew-Colman's models

From the graph, it shows that, at droplet size > 20 microns, MA’s and COLMAN’s

models give relatively accurate result (± 10% error). However, at d > d 80%, COLMAN’s

model seems to cause higher degree of error and predict too high value of cut size. This may

because the researchers used different assumptions or operating condition to develop their

models. In effect, it is very difficult to point out that which model is more accurate.

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II-42

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

Observed pressure drop (bar)

P r e d i c t e d p r e s s u r e d r o p ( b a r )

+10%

-10%

Δ po (bar) = 16 Q2.3

/Dn4

Fig. 5.3a Relation between observed pressure drop (inlet/overflow) of Thew cyclone and predicted pressure drop

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0


P r e d i c t e d p r e s s u r e d r o p ( b a r )

+10%

-10%

Δ pu (bar) = 4.6 Q2.2

/Dn4

Fig 5.3b Relation between observed pressure drop (inlet/underflow) of Thew cyclone and predicted pressure drop

From THEW’s research [28], Split ratio (R f ) or ratio between overflow and inlet flow

has some effect on pressure drop. However the effect of this parameter on under flow pressuredrop is very small, thus, negligible. There is more effect on overflow pressure drop. From

THEW’s and MA’s data, we can find the empirical correlation between split ratio and then

can transform eq. 5.5a to account for the split ratio. The modified equation is as follow;

0.1611

)f

R (1

2.6

4nD

2.3Q16oΔ p

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−⋅= {5.5c}

However, the correlation is developed from relatively small set of data. Furthermore,

range of split ratio, generally used, is around 1 to 10%. Within this range, eq. 5.5a alone can

predict the efficiency with an error of only 10-20%. So we recommend using eq. 5.5a and

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5.5b to predict the pressure drop of the hydrocyclone. Anyway, to allow for prediction error,

safety factor of 1.2 should be applied.

5.2 Three-phase hydrocyclone

Prof. AURELLE and MA develop the three-phase hydrocyclone in order to create anew type of hydrocyclone that can separate both oil and suspended solids simultaneously in

the same unit. From this concept, MA proposed the new hydrocyclone, which is the

combination between THEW liquid-liquid hydrocyclone and RIETEMA solid-liquid

hydrocyclone, as shown in fig. 5.4. Geometry of this hydrocyclone is nearly identical to the 2

originals with slight adaptation.

Solid-liquid part Liquid-liquid part (Thew’s part)

DoDDs

DiDu

Dp

L5 L3L1L2

L4

Note: Di/D=0.25 for 1- inlet and 0.175 for 2- inlet, Do/D=0.43,Ds/D=0.28, Du/D=0.19, Dp/D=0.034,

L1/D=0.4,L2/D=5, L3/D=15, L4/D=0.3, Solid-liquid part cone angle=12o , for liquid-liquid part=1.5

o

Fig. 5.4 Three-phase hydrocyclone

MA testd the performance of the prototype of this hydrocyclone. It showed very good

efficiency, which relatively conforms to the efficiency obtaining from separate solid-liquid

and liquid-liquid hydrocyclone. He also studied the influence of important parameters to

efficiency of this new hydrocyclone. However he did not propose the model. So we have to

develop new model for three-phase hydrocyclone. Model development detail will be

described in section 5.2.1.

5.2.1 Model development and verification for liquid-liquid section

From the fact that three-phase cyclone is the combination between THEW and

RIETEMA hydrocyclone. New model for liquid-liquid and solid-liquid part should conformto that of each separate hydrocyclone.

For liquid-liquid hydrocyclone, we will apply the model of MA’s, as stated in section

5.1, to three-phase hydrocyclone. The problem is how to adapt MA’s model to this new

hydrocyclone. From MA’s research, he observed that the phenomena in three-phase

hydrocyclone, such as oil central core formation, etc., are relatively identical to THEW

hydrocyclone. From this, we assume that the driving force of oil part in the hydrocyclone

should be identical to normal THEW hydrocyclone at the same flowrate and nominal diameter

(Dn in fig.5.1 = Do in fig. 5.4 = ND.). The driving force in hydrocyclone is generated by

energy of feed flowrate. From geometry in fig. 5.1 and 5.4, we get the following equations.

( ) i(Thew)V

Thewα

3iV

3α ⋅=⋅

φ φ

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( ) ⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ ⋅=

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

⋅2)

i(Thew)π(D

4Q0.5

2)3i

π(D

4Q3

α

φ φ

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅=

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅2))

0.5

NDπ(0.25(

4Q0.52))

0.43

NDπ(0.25(

4Q3

αφ

676.0

2

0.43

0.50.5

3α =⎟

⎠

⎞⎜⎝

⎛ ⋅=⋅φ

{5.6}

We use α3φ in eq. 5.6 with the model in eq. 5.1 and 5.2 to predict the efficiency of the

oil part of three-phase hydrocyclone and compare the result with observed value from MA’s

data [16]. Comparison result in fig. 5.5 shows that the error from prediction is ± 20%, which

is acceptable. We have tried to select the value of α3φ arbitrarily and found that;

•

If the value of α3φ is lower, the model will predict too low efficiency.

• For higher value of α3φ, it may provide better curve fitting but we do not have any

data to support the use of it. The value of 0.676 seems more appropriate.

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% 100.0%


P r e d i c t e d e f f i c i e n c y ( % )

+20%

-20%

Fig. 5.5 Relation between observed efficiency and predicted efficiency of liquid-liquid (Thew) part of three-phase

hydrocyclone

From model verification result, we can conclude and propose the model of liquid-

liquid part of three-phase hydrocyclone as well as its limitation as follows,

1. To predict removal efficiency of three-phase hydrocyclone, graded efficiency

can be calculated by eq. 5.7 and 5.8.Dn in this case is equal to Dc. And L in this

case is equal to L5.

∫=∫L

0 WdZ

dR

vzzR U

dR {5.7a}

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R

V 2

18μ

2Δρd

U ⋅= {5.7b}

0.65)

R

nD(

2i

D4π

(Q/2)0.676V

⎟⎟

⎟⎟

⎠

⎞

⎜⎜

⎜⎜

⎝

⎛

= {5.7c}

3

zR

R 1.19

2

zR

R 8.63

zR

R 123.33

zW

W⎟⎟ ⎠

⎞⎜⎜⎝

⎛ +⎟⎟

⎠

⎞⎜⎜⎝

⎛ −+−= {5.7d}

2))2/tan(Znπ(0.5D

QzW

β ⋅−= {5.7e}

For d ≥ dc,

100%d

η = {5.8a}

For d < dc,

%100

)2)2

nD(0.1862)

2

nD((

)2)2

nD(0.186

2d

(R

dη ⋅

−

−= {5.8b}

2. To design the hydrocyclone by the model, it is recommended to select the cut

size that covers majority of oil droplet in the wastewater and provide a safety

factor around 10% to 25%, because the model is apt to predict too small cut size.

For example, if the desired cut size is 50 microns, it is recommended to select50(1-0.25) = 37.5 microns for eq. 5.7 and 5.8.

3. To use the models described above, the following conditions need to be satisfied

and the assumptions and limitations would be noted;

1) The model is valid for three phase hydrocyclone with geometry of the oil

part conforms to that of THEW.

2)

It is recommended to use the model only for droplet diameter of 20

microns or greater. For smaller droplet, the model can also be applied, but

for comparison purpose only.

3) Eq. 5.7c is valid for the hydrocyclone with 2 inlet ports only. If the

hydrocyclone has only 1 inlet port, replace Q/2 with Q. However, using 2inlet ports is recommended for its hydraulics stability. Please note that the

size of 2 inlet ports will be smaller than single inlet port to keep the inlet

area constant.

5.2.2 Model development and verification for solid-liquid section

From the same reason as oil-part model development, we will base our model for

solid-liquid separation on RIETEMA hydrocyclone’s model. In MA’s research, he used only

2 sizes of suspended solids. So the data is not sufficient to develop the model. However,

geometry of this part of three-phase hydrocyclone is identical to RIETEMA’s. So RITEMA’s

model should be applied without any modification.

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Membrane process is a separation process based, mainly but not entirely, on filtration

concept. It can be said that the membrane is a very fine screen or filter. Theoretically, we can

always separate one or more components from fluid stream providing that the filter chosen is

suitable for size difference. Membranes can be categorized by their separation characteristics,i.e., microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).

MF and UF have relatively large pore sizes, so they work rather like screens or sieve filters.

While separation by NF and RO, which have very tiny pore sizes, is not simply by size alone

but involves more complex factors, such as osmotic pressure. So we can group the membranes

processes into 2 categories, i.e., 1) MF and UF, 2) NF and RO.

Membrane process design depends mainly on wastewater characteristics. So, the best

way to design the membrane process is to perform feasible study in lab scale or pilot scale.

However, our lab has several researches on UF. From these researches, we have gained some

understanding of phenomena taking place in the process. Then we can use our result to set a

guideline for conceptual design or preliminary evaluation of membrane process.

6.1 Ultrafiltration

Because of their pore sizes, MF and UF are suitable for finely dispersed emulsion,

such as, secondary emulsion, macroemulsion and microemulsion. However, there is only one

research on MF of oily wastewater treatment in Prof. AURELLE’s team. Then, despite of its

feasibility on cutting oil emulsion treatment, which is one of the important applications of

membrane processes on oily wastewater treatment, we will not include MF in our thesis for

there is insufficient data. So we will emphasize on UF.

There are 2 main types of UF, as well as other, membrane processes, based on flow pattern, i.e., dead-end and cross-flow. In dead end reactor, wastewater will be fed in

perpendicular direction to membrane surface. So this mode of operation is rather like cake

filtration. Dead-end process is normally used in bench scale experiment. For cross-flow,

wastewater will be fed in tangential direction, parallel to membrane surface. It is this mode of

operation that is widely used in real life situation. So our researches are related to this process.

For wastewater treatment, our aim is to reduce the quantity of the wastewater as much

as possible while the effluent quality still meets effluent standard. So wastewater will be

recycled repeatedly until its volume reaches required limit. In this case, UF system is

normally designed as batch processes, as shown in fig. 6.1.

Permeate

Retentate

Membrane

Feed pump

Storage

tank

Fig. 6.1 Typical schematic diagram of Cross-flow membrane process

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From fig. 6.1, we have to apply enough pressure to force components that can pass

through the membrane pores to the other side. The components of influent that can pass

through the membrane is called permeate. The rest that can not pass is called retentate. The

pressure difference between retentate side and permeate is called transmembrane pressure (Pt).

The retained components will accumulate at the surface of membrane and its concentration

will be increased. This accumalation and high concentratio, called concentration polarizationor gel polarization, will hinder the permeate flow. Some components may lodge in the pores.

These phenomena will make the membrane clog and rate of permeate passing through the

membrane or permeate flux will decrease. In cross-flow process, we can alter the superficial

(or recirculation) velocity at the membrane surface (V) by changing recirculation flowrate to

reduce the effect of polarization. From this brief operating principle, we can see that there are

several parameters, relates to membrane process design. So models of membrane will be

developed to describe the relation between these parameters.

There are several researches in our lab [10], [11], [18]-[22] on membrane processes.

However, they were based mainly on application. Only some of them provided models.

Furthermore those models are limited by their scopes of the experiment, then they are not ingeneral forms to apply to general case. In this thesis, we will try to develop the generalized

models, based on well-accepted theoretical models, i.e. resistance model and film model.

6.1.1 Resistance model

General form of resistance model [38], [54], [18], [11] is similar to the equation for

electrical calculation as shown in eq. 6.1.

gR f

R mR

tPJ

++= {6.1a}

Membrane resistance (R m) and fouling resistance (R f ) are property of membrane and

relatively unaffected by operating condition [38]. So it is normally be summed together and

called intrinsic membrane resistance (R’m). Eq. 6.1a , then, will become,

gR m'R

tPJ

+= {6.1b}

Gel resistance (R g) is the function of Pt and V as shown in eq. 6.2. α and φ are

numerical constants.

t Pα

VgR ⋅= φ {6.2}

This model can give the accurate evolution of flux with Pt, starting from pressure

controlled region, which the flux varies with Pt, to mass transfer controlled region, which the

flux is relatively constant, as shown in fig. 6.2.

From researches in our lab, we can summarize the value of R’m, φ and α for many

operating conditions, as tabulated in table 6.1. φ and α are dependent of wastewater inlet

concentration so it can be applied only to their corresponding concentration only.

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T

a b l e 6 . 1

S u m m a r y o f p a r a m e t e r s o f r e s i s t a n c e m o d e l f r o m U F

r e s e a r c h e s o n o i l y w a s t e w a t e r

t r e a t m e n t ( r e f e r e n c e t e m p e r a t u r e = 2 0 O

C )

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Pressure controlled

region

Mass transfer

controlled region

W a

t e r f l u x Higher recirculation flow

Higer temperature

Lower concentration

Transmembrane pressure (P )

Flux

Fig. 6.2 Typical relation between flux and various parameters

6.1.2 Film theory based model

This model is developed under the assumption that the process is in the mass transfer

controlled region. So flux is assumed to be controlled by mass transfer phenomena and

independent of Pt. Operating UF in this region will maximize the flux, thus minimize the size

of membrane. The general form of film theory based model [38], [54] is shown in eq. 6.3.

)oC

gCln(

βkVJ = {6.3}

From the equation, k is mass transfer coefficient. Cg is gel concentration, which

depends on type of wastewater. V is recirculation velocity. Two typical characteristic curves

of flux VS. retentate concentration are shown in fig. 6.3b. (Other curves also exist, but they

are very rare cases)

For the first type, the curve is flat without inflection point. This type of curve willcross the horizontal axis at C . This Cg g remains constant for the whole range of retentate

concentration.

For the second type, The curve presents an inflection point. In this case, we can say

that there are two Cg. The first one is obtained from extending the steeper part of the graph to

cross the X-axis. But it is not the real Cg and used only for flux calculation at lower range of

retentate concentration. The real Cg is obtained from the graph after inflection point. UF of

cutting oil emulsion will be in this category. In this case, the real C g normally crosses the X-

axis at approximately 100% concentration. This can imply that, theoretically, we can use UF

to filter the oily wastewater until the retentate become water-free oil. However, the flux will

become very low and the operation may become unacceptable from economic point of view.

Log (Concentration)

V1

Cg

Flux V2>V1

Fig. 6.3a Relation between flux and concentration at any recirculation velocity [38]

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Log (Concentration)

1 2

Cg

case 1

Cg

case 2

C’g

case 2

Flux

Fig. 6.3b Typical characteristic curve of concentration VS. Flux (Log-Normal scale) [38]

From researches in our lab, we can summarize the value of k, Cg and β for various

kinds of membranes for many types and inlet concentration of wastewater, as tabulated in

table 6.2.

6.1.3

Model verification

From section 6.1.1, it shows that the resistance model can predict flux at any pressure.

However, the constants in eq. 6.2 are valid for only their own specific operating conditions,

esp. the influent oil concentration. On the other hand, eq. 6.3, even though it is supposed to be

valid only in mass transfer region, can be used to predict flux at any influent oil concentration,

providing that the Cg is known. So, it is interesting to combine eq. 6.2 and 6.3 to see if they

can be used to predict flux at any influent concentration and pressure or not. The procedures

used to combine film theory and resistance theory, which are divided into 2 cases, are as

shown below.

Case 1: Know k, and Cg

1.

Find JC,Vref

If we know the value of k and β at one known velocity (called reference velocity,

Vref ), we can calculate limiting flux at any required concentration (called C) by the film

theory.

)C

gCln(

βref

kVVref C,

J = {6.4a}

However, even the film theory is supposed to be pressure-independent, it should be noted that k and β are obtained from experimental data, which are conducted at certain

value of pressure. At that reference pressure (Pref ), the flux may not yet fully reach the mass

transfer controlled region. In fact, we frequently find that flux/concentration curve never the

reach really flat part within the recommended operating range of pressure (generally 0 to 4

bar), especially when velocity is high.

In this case, we have tried to verify if the film theory is still valid. We studied the

flux/concentration relation of cutting oil macroemulsion (Elf SeraftA) at P = 2 and 3.5 bar, V

from 0.7 to 2.8 m/s from Belkacem’s data [18]. We found that eq. 6.3 is valid at P = 3.5 bar,

where is in the mass transfer controlled region. And we also found that the form of eq.6.3 still

holds at P = 2, where flux does not yet reach fully mass transfer controlled region at low Cand/or high V. But there are some little differences in the values of k, β and Cg.

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O C

)

T a b l e 6 . 2

S u m m a r y o f p a r a m e t e r s o f f i l m m o d e l f r o m U F r e s e a r c h e s o n o i l y w a s t e w a t e r t r e

a t m e n t ( r e f e r e n c e t e m p e r a t u r e

= 2 0

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II-56

Besides using the reference velocity and required velocity, other dummy velocities

can also be used to cross-check the value of αc and φc. Calculated values of the two

parameters may not be exactly the same as those calculated from Vref and V, since there is

normally some calculation error. Using average values of these αc and φc is recommended.

From αc and φc, we can calculate flux at any transmembrane pressure and at the required

concentration by the resistance theory (eq. 6.7).

tPαcVCmR

tP

PtV,C,J

φ += {6.7}

To verify the procedure from eq. 6.4 to eq. 6.6, we use data from many researches

[10], [11], [18], [20], which φ, Cg, and α of corresponding cases are available. Example of

verification data is provided in Annex A5. In this case, we use φ, Cg, and α obtained from UF

test of cutting oil macroemulsion (Elf SeraftA) at influent concentration (C ) of 4% V/V, Pref ref

= 2 bar, Vref = 1.4 m/s as a reference condition to predict flux/ pressure relation at C = 2 and 8

% V/V. Predicted relations and comparison between observed flux and predicted flux are as

in fig. 6.4 and 6.5. From the graphs, it shows that eq. 6.4 to 6.6 can be effectively used to

extend the range of eq. 6.1, 6.2 and 6.3 to cover any influent concentration.

0

20

40

60

80

100

120

140

160

180

0 0.5 1 1.5 2 2.5 3

Transmembrane Pressure (Bar)

P r e d i c t e d

F l u x ( l / ( h . m

2 ) )

Observed, C = 2% Predicted, C = 2% Observed, C = 8% Predicted, C = 8% Reference, C = 4%

Fig. 6.4 Relation between UF permeate flux and Transmembrane pressure at reference concentration (C) of = 4%, V = 1.4 m/s

and Predicted relations at C = 2 and 8%

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0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

0 20 40 60 80 100 120 140 160 180

Observed flux (l/ (h.m2))

P r e d i c t e d F l u x ( l / ( h . m

2 ) )

-10%

+10%

Fig. 6.5 Relation between observed and predicted flux by resistance model for ultrafiltration of macroemulsion 4% conc. and

extend to cover other conc. by film model

Case 2: Know , φ and Cg

1. Find JCref,V

From resistance theory, we can find J , when φ and αCref,V Cref Cref are known, by the

following equation.

ref PαCref V

Cref m'R

ref P

VCref,J

⋅+=

φ

{6.8}

Again, we recommend selecting the reference pressure as high as possible to

make sure that the calculated flux is in the mass transfer controlled region.

2. Find JC,V

From film theory, we can write that;

)

ref C

gCln(

)C

gCln(

VCref,J

VC,J = {6.9}

3. Find JC,Vref

In the same way as 1 and 2, we can find J , when φ and αC,Vref Cref Cref are known,

by the following equation.

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{6.10b}micoil,

Cmacoil,

Cmixoil,

C +=

Flux of macroemulsion and microemulsion at the total oil concentration (Jmac:Coil,mix

and Jmic:Coil, mix) can be calculated by the procedure described in the previous section.

Therefore, the flux of the mixture can be calculated by the following equation.

mixoil,C

mixCoil,mic,J

micoil,C

mixCoil,:macJ

macoil,C

mixJ

+= {6.11}

To verify this idea, we used reference data of flux of pure macroemulsion and

microemulsion, as used in section 6.1.3, to predict flux of various ratios of

micro/macroemulsion mixture. Relations between predicted values and observed data are

presented in fig. 6.6 and 6.7. Even though, the error from prediction is around 20%, this

procedure will be a useful tool for the preliminary estimation of mixture flux, especially when

UF test data on the wastewater is not available

(Module: UFP2, Membrane: IRIS 3042, T = 20o C., data from [11]. The lines show predicted value.)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Pressure (bar)

F l u

x ( l / ( s q . m . h

) )

4% Macro

1% Micro

V = 2.8 m/s

4% Macro

4% Micro

V = 2.0 m/s

4% Macro

2% Micro

V = 1.0 m/s

Fig 6.6 Comparison between predicted flux and observed flux for UF of micro/ macroemulsion mixture (Conc. shown as

% by volume of concentrate)

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Vol)o(Vol

oVoloCC

−= {6.14}

Eq. 6.9 can be rewritten as,

AdtoVoloC

gVol)Co(Vol

lnβ

kVdVol ⎟⎟ ⎠

⎞

⎜⎜⎝

⎛ −

⋅= {6.15a}

∫=∫

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −

t

0Adt

βkV

lfinal

Vo

oVol

oVoloC

gVol)Co(Vol

ln

dVol {6.15b}

However, the system may not be operated in the mass transfer controlled region for the

whole time. In this case, the function J(c) in eq. 6.12 can be calculated by eq 6.7. Eq. 6.12 and

6.15b are in the form of integration of [1/ln (x)], so they can not be written in general form

since the equation will be infinity at x =1. However, a definite integration is possible, using

numerical method that can be calculated by computer.

In this thesis, we have compared the theoretical result, using reference data stated in

section 6.1.3, with observed results from UF test on used cutting oil macroemulsion (3% V of

concentrate or 2.4%V of oil, from Willamette SAS factory) from WANICHKUL’s research

[11], as shown in fig. 6.8a. The x-marked circles indicate the observed flux of fresh emulsion.

From the graph, it shows that the model can accurately predict flux of fresh (unused) emulsion

as the circles are closed to the theoretical flux curve.

Comparing with observed flux of the used emulsion, the graph shows that, at low

concentration, theoretical flux is greater than observed value. This simply because additionalfouling from foreign material in the emulsion. However, at high concentration, theoretical

flux is, somehow, lower than observed value. This can be explained by partial degradation of

the used emulsion. During its working lifetime, cutting oil emulsion will subject to many

foreign material, such as coated oil on specimen surface, small scraps of specimen, leaked

lubricant, and heat. So its quality, as well as its stability, will gradually deteriorate. This is

proven by milky appearance of used emulsion, compared with the translucent or transparent

characteristic of fresh emulsion. When partial oil is destabilized to be free oil, this means the

concentration of oil in emulsion form may be lower than its initial value. At lower

concentration, the effect of fouling overwhelms the effect of reduced concentration, so the

theoretical flux is higher than the observed value. However, at higher concentration where theconcentration effect is stronger, the theoretical flux shows lower value.

Fig. 6.8b shows evolution of permeate volume with time, the result from integration of

eq. 6.12. From the observed data, it confirms that the macroemulsion can be ultrafitrated until

the retentate is relatively pure oil. In this case, initial volume of 1643 l of 2.4%V of oil is

ultrafiltrated to the final volume of 40 l. The theoretical time required to do so is 45 hours,

compared to observed value of 34 hours. However, the theoretical volume of permeate is

higher until almost at the end of the operation. Fig.6.8c shows evolution of theoretical flux

with concentration. It must be noted that eq 6.12 to 6.15 are based on the assumption that no

additional emulsion is added to the storage tank. If the emulsion is added, eq. 6.12 must be

modified to account for it.

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(Used cutting oil macroemulsion :initial volume 1643 l, final volume 40 l,

initial concentration 2.4% by volume of oil (not concentrate): Module UFP10: membrane IRIS 3042)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0 200 400 600 800 1000 1200 1400 1600 1800

Permeate volume (l)

f l u x ( l / ( s q . m . h

) )

Theoretical data at P = 1.0 Bar, v = 1.17 m/s) Observed data Theoretical data at P = 1.5 Bar, v = 1.40 m/s)

= Observed data from UF test of new

cutting oil at the same condition

P = 1.0 bar, v = 1.17 m/s P = 1.5 bar, v = 1.40 m/s

Fig. 6.8a Relation between Flux VS. theoretical and observed permeate volume

(Used cutting oil macroemulsion :initial volume 1643 l, final volume 40 l,

initial concentration 2.4% by volume as oil (not as concentrate): Module UFP10: membrane IRIS 3042)

0

200

400

600

800

1000

1200

1400

1600

1800

0.000 5.000 10.000 15.000 20.000 25.000 30.000 35.000 40.000 45.000 50.000Time (h)

P e r m e a t e v o l u m e ( l )

Theoretical data at P = 1.0 Bar, v = 1.17 m/s) Theoretical data at P = 1.5 Bar, v = 1.4 m/s) Observed data

P = 1.0 bar, v = 1.17 m/s P = 1.5 bar, v = 1.40 m/s

Fig 6.8b Relation between time VS. theoretical and observed permeate volume

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(Elf SeralfABS cutiing oil macroemulsion: Membrane IRIS 3042, 20oC)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

1 10 100

Retentate concentration (% V of oil)

P e r m e a t e f l u x ( l / m

2 . h )

P = 1 bar, V = 1.17 m/s P = 1.5 bar, V = 1.4 m/s

Fig. 6.8c Relation between theoretical flux VS. concentration of oil in retentate

6.1.6

UF efficiency

From many researches, with appropriate UF membrane pore size, it clearly shows that

oil, even in form of very tiny droplets in macroemulsion and microemulsion, cannot pass the

membrane. We can say that the removal efficiency of UF is 100%. Selection of membraneinvolves many parameters. However, AURELLE [quoted by [18]] have grouped these

parameters and proposed 3 brief criteria, i.e.,

• Pore size of membrane: To prevent oil droplets to pass through the membrane

pore, the size of the pore, firstly, must be smaller than the droplets. From

researches in our lab, we recommend that minimum pore size should be 1/4 to 1/3

of average droplet size.

• Characteristic of membrane: for oil/water separation, membrane should be

hydrophilic. Membrane material should not react with the wastewater, which can

cause pour clogging. Hydrophilic material, such as polyacrylic, cellulose acetate,

zirconium oxide, etc., is recommended. Naturally without special treatment orcoating, polysulfonate tends to be fouled by oil, resulting in low flux and frequent

washing.

• Operating condition: Operating pressure should be less than capillary pressure

required to force the oil droplets through the membrane pores. Capillary pressure

increases with the hydrophilicity of membrane and decreasing of pore size.

However, if pore size and hydrophilicity are carefully selected, the capillary

pressure is normally higher than recommended maximum pressure of the

membrane.

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⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−

⎟⎟

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜

⎜⎜⎜⎜⎜

⎝

⎛

+−+⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−−= 1

1/3

)o/w

θ3sino/w

sinθ(2o/w

cosθ

3

r

dr

4

2o/w

θ3coso/w

3cosθ

r

o/wcosθ

o/w2γcapP {6.17}

Normally, the value of the capillary pressure is higher than the maximum operating

pressure. For example, for UF of macroemulsion, θo/w= 135o, γo/w = 0.033 N/m, r d = 150 nm

and r = 100 nm, the capillary pressure is 11.45 bar while the maximum pressure

recommended by the manufacturer is only 4 bar.

(Elf SeralfABS cutiing oil macroemulsion, 20oC, 100% = pure cutting oil concentrate = 80% V(approx) oil )

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

0 10 20 30 40 50 60 70 80 90 10

Oil concentration (% V of cutting oil concentrate in water)

V i s c o s i t y ( c p )

0

Fig. 6.9 Relation between oil concentration VS. viscosity of emulsion

For the power requirement of UF system, main power consumption is the power

required to maintain transmembrane pressure at require flowrate (or recirculation velocity).

This power can be calculated straightforwardly by the basic equation

overallη

AVP

overallη

QPPower

⋅⋅=

⋅= {6.19}

Q in this case means recirculation flowrate, not the permeate flowrate. V is the

recirculation velocity and A is the flow area of liquid in UF module (the channel between the

membrane surface and the UF module wall). P in the equation is pump discharge pressure,

which is the summation of transmembrane pressure and other headloss from pipe and values

system. It should be noted that transmembrane pressure is average value of the pressure at

the inlet and outlet of UF module. Overall efficiency of pump depends on pump type. For

progressive cavity pump or progressive screw pump, the efficiency should be around 50-70%.

109

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II-67

T a b l e 6 . 3 a S u m m a r y o f R O d a t a o n o i l y w a s t e w a t e r t r e

a t m e n t

111

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II-68

T a b l e 6 . 3

b S u m m a r y o f N F d a t a o n o i l y w a s t e w a t e r t r e a t m e n t

112

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Chapter 7 Heteroazeotropic Distillation

II-70

2 ph.vapor

Bubble curve

Pure H2O

Temperature

Azeotrope (H)

2 ph. liquid

1 ph.vapor +1 ph. liquid

Pure

hydrocarbon x,y yH

Dew curvesBoiling point

of hydrocarbonBoiling point

of water

TH

Fig. 7.1 Isobar equilibrium diagram : Temperature-Concentration characteristic of

immiscible binary mixture

From the figure, we can set the steps of calculation to create isobar diagram asfollows,

1)

Find bubble curve

For binary mixture

sat B

Psat A

P +=+=+

= θ b

BΠ

θ bA

Πθ b

BAΠP {7.1}

Relations between vapor pressures (Πθ b or Psat) and boiling temperature of A and

B, in our case, water and hydrocarbons, can be found in any standard property tables, such as

PERRY’s [2]. Then, we obtain the relation between vapor pressure and boiling temperature ofthe mixture from the summation of the vapor pressure of A and B, as shown in eq. 7.1. This

can be done easily by a graphical method, as shown in fig. 7.2. When we select our design

pressure (normally 1 atm), we can obtain heteroazeotropic temperature (TH) from the graph.

TH Temperature

Pressure

Pure A

Pure B

A+B

Pdesign

Fig. 7.2 Graphical method to find heteroazeotropic temperature

114

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II-71

2)

Find dew curves

From DALTON’s law

PA

yA

p ⋅= {7.2a}

AndP

By

B p ⋅= {7.2b}

On the dew curves, partial pressure is equal to vapor pressure, then For

condensation of A

P

θdA

Π

Ayθd

AΠP

Ay

A p =→=⋅= {7.3a}

For condensation of B

P

θdBΠ

Byθd

BΠP

By

B p =→=⋅= {7.3b}

At any temperature between boiling points of pure substances and

heteroazotropic temperature (TH), we can find their corresponding vapor pressures (Π) from

fig. 7.3a. Then, from eq. 7.3, we can obtain yA and yB. This can be done easily, again, by the

graphical method as shown in fig. 7.3

T1 Temperature

Pressure

Pure A

Pure B

A+B

ΠA 1

ΠB 1

T2

ΠA 2

ΠB 2

Pure H2O

Temperature

Pure

hydrocarbon x,yyH

TH

T1

T2

yB 1

yB 2 yA 2 yA 1

Calculate yA and yB from ΠA,ΠB

by eq. 7.3, then, plot T,yA and T,yB

to obtain dew curves

Fig. 7.3 Graphical method to find dew curves

3)

Find heteroazeotropic composition

Heteroazeotropic composition (yH) can be calculated, based on eq. 7.1 and 7.3,

as shown in eq. 7.4,

P

θ bA

Π

Ay

Hy == {7.3a}

From eq. 7.1,

θ bB

Πθ bA

Π

θ bA

Π

Hy

+

= {7.4}

115

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Chapter 7 Heteroazeotropic Distillation

II-72

Vapor pressures of A and B (water and hydrocarbons) can be obtained from any

standard property tables [2]. yH indicates capability of extractant to extract water from

wastewater. For example, if yH = 0.5 mole/mole, it means 1 mole of extractant can extract 1

mole of water. The higher the yH , the better the extractant.

7.2

Model verification

From section 7.1, we can find yH of pure hydrocarbon that can be used as an

extractant, i.e., alkane with the number of carbon from 6 atoms (n-Hexane) to 16 (n-

Hexadecane). Theoretical values of yH of each alkane are tabulated in table 7.1. To compare

the theoretical value to experimental result, we use data from LUCENA’s thesis on slop

treatment, using decane and dodecane. Comparison result in table 7.1 shows that the

theoretical values are slightly higher (3.5-5.5%) than observed values.

Table 7.1 Heterotropic temperature and composition from various extractants

ExtractantMolecular

weight

(g/mol)

TH

(deg. C)

yH

(by molar)

yH

(by volume)

y H observed

(by volume)

[24]

C6H14 56 61.6 0.209 0.0351

C7H16 100 79.2 0.452 0.0922

C8H18 114 89.5 0.616 0.188

C9H20 128 94.8 0.827 0.3255

C10H22 142 97.6 0.914 0.495 0.468

C11H24 156 98.9 0.959 0.6663C12H26 170 99.5 0.98 0.7953 0.767

C13H28 184 99.8 0.991 0.890

C14H30 198 99.95 0.996 0.9542

C15H32 212 99.999 0.998 0.9702

C16H34 226 ≈ 100 0.999 0.9840

7.3 Conclusion and generalized model of heteroazeotropic distillation

From data verification result, we can conclude that the theoretical model, stated insection 7.1, provides very good prediction of heteroazotropic composition (yH). However, the

safety factor (S.F) of 1.05 or 1.1 is recommended. When we know the water volume in our

treated wastewater and determine the type of extractant, we can find quantity of extractant

required for extracting the water from the following equation. yH in eq. 7.5 will be by volume

basis, determined by the model in section 7.1. Heteroazeotropic distillation is suitable to treat

or recover valuable residue, such as slop or retentate from UF of cutting oil emulsion, which

is contaminated by relatively small amount of water.

Hy

)H

y(1

water VolumeS.FextractantVolume−

⋅= {7.5}

116

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II-73

On the other hand, for stripping, we can find the theoretical quantity of steam or water

required for extracting the design volume of volatile hydrocarbons from the following

equations. Please note that the calculated volume of steam is the quantity required for

heteroazeotropic distillation only. Additional heat may be required to raise the temperature up

to the design point. Stripping is suitable to treat the waste polluted by small amount of volatile

substance. The concept is also applied to essential-oil extraction from herbs or flowers in perfume or chemical industries.

)H

y(1

Hy

nhydrocarboVolumeS.FsteamVolume

−⋅= {7.6a}

Or

)H

y(1

Hy

wastewater Volumenhydrocarbo

ionConcentratS.FsteamVolume−

⋅= {7.6b}

117

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Part III Summary of researches :

Oily wastewater treatment

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III-ii

Content (Con’t)

Page

2.5 Determination of degree of treatment III-41

2.5.1

Overall degree of treatment III-412.5.2 Degree of treatment of each process III-41


3.1 General III-45

3.1 Oil drum skimmer III-47

3.1.1 Working principles III-47

3.1.2

Design calculation and design consideration III-52

3.2 Oil disc skimmer III-54


3.2.2 Design calculation and design consideration III-56

3.3

Productivity comparison between drum and disc skimmer III-563.4 Advantage and disadvantage of drum and disc skimmer III-57

Chapter 4 Decanting

4.1

General III-59

4.2 Simple Decanter or API tank III-60


4.2.2 Design calculation III-62

4.2.3 Design considerations III-65

4.2.4 Construction of simple decanters III-66

4.3 Compact decanter III-69

4.3.1

Working principles III-694.3.2

Design calculation III-73


4.3.4 Variations, advantage and disadvantage of compact III-76

decanters

Chapter 5 Coalescer

5.1 General III-78

5.2 Granular bed coalescer III-78


5.2.2 Design calculation III-925.2.3 Design consideration III-94

5.2.4 Variations, advantage and disadvantage of granular III-95

bed coalescer

5.3 Guide coalescer III-96



5.3.3 Design consideration III-98

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III-iii

Content (Con’t)

Page

5.4 Fibrous Bed coalescer III-99

5.4.1

Working principles III-995.4.2 Design calculation III-109

5.4.3 Design consideration III-110

5.4.4 Variations, advantage and disadvantage of fibrous bed III-112

coalescer


6.1

General III-115

6.2 Working principles III-116

6.2.1 Filter based model III-116

6.2.2 Population balance model III-121

6.2.3

Generalized model of DAF from combination of III-123filtration based model and population balance model

6.2.4

Influent parameters III-124

6.3

Design calculation III-127

6.4 Design consideration and construction of DAF reactor III-137

6.5 Pressurized water system or saturator III-145

6.5.1 Working principle and design calculation III-145

6.5.2 Type of saturator and injection valve III-150

6.6 Variations, advantage and disadvantage of DAF III-153


7.1

General III-1557.2

Two-phase hydrocyclone III-156




7.2.4 Variations, advantage and disadvantage of III-178

hydrocy clone

7.3

Three-phase hydrocyclone III-178

7.3.1

Working principles III-178

7.3.2 Design calculation and design consideration III-182

7.3.3 Advantage and disadvantage of three-phase III-182

hydrocyclone


8.1 General III-183

8.1.1 Classification of membrane processes III-183

8.1.2 Mode of operation of membrane processes III-185

8.1.3

Membrane structure III-185

8.1.4 Membrane material III-186

8.1.5 Membrane module type III-189

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III-iv

Content (Con’t)

Page

8.2 Ultrafiltration (UF) III-194

8.2.1

Basic knowledge and working principles III-1948.2.2 UF process design for oily wastewater treatment III-206

8.2.3 Design consideration and significant findings from III-221

GPI’s researches

8.3

Microfiltration (MF) III-232

8.3.1 Basic knowledge and working principles III-232

8.3.2 Significant findings on MF for oily wastewater III-233

treatment from GPI researches

8.4 Reverse osmosis (RO) III-235


8.4.2 Significant findings on RO for oily wastewater III-236

treatment from GPI’s researches8.5

Nanofiltration (NF) III-239


8.5.2 Significant findings on NF for oily wastewater III-239

treatment from GPI’s researches

8.6 Comparison of membrane processes on emulsion treatment III-242

Chapter 9 Thermal processes

9.1 General III-245

9.2

Basic knowledge on distillation III-245

9.2.1 Basic knowledge on vapor/liquid equilibrium of III-245

mixtures9.2.2 Equilibrium of various mixtures III-248

9.3 Heteroazeotropic distillation of oily wastewater III-250


9.3.2 Raoult’s law and Dalton’s law III-251

9.3.3 Calculation of azeotropic temperature and composition, III-252

dew curve and bubble curve.

9.3.4 Application of heteroazeotropic distillation on III-254

treatment of inverse emulsion or concentrated oily

wastewater

9.3.5 Application of heteroazeotropic distillation on III-257

treatment of the wastes polluted by trace hydrocarbons:

Steam stripping

9.3.6

Design calculation and design considerations III-257

9.4 Classical or conventional distillation of oily wastewater III-259


9.4.2 Significant findings on classical distillation for oily III-259

wastewater treatment from GPI’s researches

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III-vi

Table

Page

Table 1.2.1-1 Properties of some normal alkanes [1],[2] III-3

Table 1.2.1-2 Properties of some unsaturated aliphatic hydrocarbons [1],[2] III-5

Table 1.2.1-3 Properties of some benzene-series hydrocarbons [1],[2] III-6

Table 1.4.3-2 Summary of oily wastewater classification III-14

Table 1.5-1a Data of pollution from certain oils, oil products and serfactants. III-15

Table 1.6-1a Industrial effluent standard of Thailand III-17

Table 1.6-1b Industrial effluent standard of France (1998) III-18

Table 1.6-1c Industrial effluent standards of USA, categorized by pollutant sources III-19

Table 2.1-1 Summary of equations for rising velocity calculation [41] III-22

Table 2.2.1-1a Data of surface and interfacial tension (N/m) for some liquids at 20°C III-24

Table 2.2.2-1 Relation between contact angle, work adhesion, interfacial tension III-28

and spread coefficient of oil/water/solid system [42]

Table 2.3.2-1a Example of the decanting test of oil/water emulsio III-35

Table 2.3.2-1b Example of the decanting test of oil/water emulsion: sorting of the III-36

result from table 2.3.2-1a

Table 2.3.2-2 Criteria for visual observation of size distribution [22] III-37

Table 2.3.2-3 Criteria for visual observation of surface oil film [45] III-38

Table 3.2.1-1 Work adhesion and contact angles of oil, water and various materials III-48

Table 3.2.2-1 Critical surface tensions of certain materials [42] III-53

Table 5.4.1-1 Coalesced kerosene droplet size at various velocities and bed heights III-108from oleophilic “bottle brush” coalescer (d F = 100 microns,

D = 0.05 m,Co = 1 g/l, 120oC) [10]

Table 5.4.1-2 Comparison between the individual efficiency of oleophilic bottle III-108

brush coalescer, hydrocyclone, theoretical and observed efficiency of the

coupling of coalescer/hydrocyclone [10]

Table 6.3-1 General design criteria of DAF from various literatures and III-130

manufactures (hydraulic loading rate us based on total flowrate)

Table 6.4-1 Data on efficiency and coagulant concentration of various oily III-141

wastewater treatments by DAF [51]

Table 6.5-1 Constant for calculation of concentration and quantity of gas for III-148

saturator design (Operating pressure of DAF = Patm, T = 20oC)

Table 6.5-2 Air characteristic and solubility at Patm [51] III-148

Table 8.1.4-1 Advantages and disadvantages of inorganic membrane [38] III-188

Table 8.1.4-2 Summary on membrane polymeric materials [38], [54], [57] III-189

Table 8.1.5-1 General characteristic of various membrane module [38], [54], [57] III-193

Table 8.2.2-1 General design criteria of UF process from various literatures III-208

Table 8.2.2-2 Summary of parameters of film model from UF researches on oily III-209

wastewater treatment (reference temperature = 20oC)

Table 8.2.2-3 Summary of parameters of resistance model from UF researches on oily III-210wastewater treatment (ref. temperature = 20oC)

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III-vii

Table (Con’t)

Page

Table 8.2.2-4 Procedure to predict flux/pressure relation for case 1: Know k, III-211

β, Cg and R’m

Table 8.2.2-5 Procedure to predict flux/pressure relation for case 2: Know φ, α, III-213

Cg and R’m

Table 8.2.3-1 Composition of the special cleaning microemulsion concentrate [18] III-230

Table 8.4.2-1 Summary of RO data on oily wastewater treatment III-240

Table 8.5.2-1 Summary of NF data on oily wastewater treatment III-243

Table 8.6-1 Comparison of membrane processes on cutting macroemulsion III-244

treatments (based on Elf Seraft ABS at 4% by V of oil)

Table 9.3.3-1 Heterotropic temperature and composition from various III-254

hydrocarbons [24]Table 9.3.4-1 Water extracting performance of various commercial hydrocarbons [24] III-257

Table 10.2.4-1 Results from ZHU’s research on destabilization of various emulsions III-272

Table 10.3.2-1 Recommended value of gradient and detention time III-277

Table 11-2.1-1 Rate coefficient for selected wastewaters [51] III-282

Table 11.2.1-2 Biodegradability and biotoxicity data [51] III-284

Table 11.2.1-3 Concentration of certain metals affecting biological systems [45] III-287

Table 11.2.2-1 Case studies on biological treatment of oily wastewater [66] III-287

Table 11.3.1-1 Examples of PAC and GAC properties III-289

Table 11.3.1-2 Adsorptive capacity of AC for some hydrocarbons [65] III-291Table 11.3.3-1 Adsorption isotherm and MTZ data of some co-surfactants [21] III-295

Table 12.1-1 Guideline for oily wastewater process selection (based on III-298

GPI’s researches)

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III-viii

Figure

Page

Fig. 1.2.1-1 Examples of normal alkanes and derivatives with equal number of III-4

carbon atomsFig. 1.2.1-2 Examples of benzene series III-6

Fig. 1.4.3-1 Relation between droplet sizes and rising velocity of primary and III-13

secondary emulsion [11]

Fig. 1.4.3-2 Classification of oily wastewater by degree of dispersion III-14

Fig. 2.1-1 Free body diagram of oil drop in water and relation between III-21

Cd and Re [55]

Fig. 2.2.1-1 Force diagram of oil drop in water III-23

Fig. 2.2.1-2 Model for visualization of γ [40][42] III-24

Fig. 2.2.1-3 Model for visualization of adhesion work III-25Fig. 2.2.2-1 Diagram of Oil drop on solid surface in water III-25

Fig. 2.2.2-2 Model for visualization of cohesion work III-26

Fig. 2.2.2-3 Effect of surface roughness on contact angle III-27

Fig. 2.2.3-1 Section of air bubble in water III-29

Fig. 2.2.3-2 Diagram for visualizing the capillary pressure III-30

Fig. 2.3.2-1 Example of the size distribution of oil droplet in cutting oil III-32

macroemulsion (Elf Seraft 4% V of concentrate), measured by Coultronics nanosizer NDM4 [11]

Fig. 2.3.2-2 Granulometer (Source: above - Ankermid Techcross / below - CILAS) III-33

Fig. 2.3.2-3 Decanting test column III-33

Fig. 2.3.2-4 Relation between accumulated C/Co (% of C/Co when the droplet size III-36 is

equal or smaller than the given dE) and oil droplet size

Fig. 2.3.2-5 Example of estimated size distribution of oil droplets from III-37

decanting test

Fig. 2.5.2-1 Cut size determination III-43

Fig. 2.2.5-2 Economics of processes (least cost criteria) III-44

Fig. 3.1-1 Examples of oil skimming devices III-46

Fig. 3.2.1-1 Lab-scale drum skimmer: Major components are shown. III-47(Source: GPI lab)

Fig. 3.2.1-2 Surface energy or superficial tension of materials, oil and water III-48

Fig. 3.2.1-3 Influent parameters on drum skimmer performance III-52

Fig. 3.2.2-1 Occurrence of eddy currents from drum operation and no oil zone III-54

or non-productive zone that affects the productivity of the skimmer

(Source: Oil Spill Cleanup)

Fig. 3.5-1 Application of the skimmers III-58

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III-x

Fig. 5.4.3-1 Examples of fibrous bed coalescer casing III-111

Fig. 5.4.3-2 Various types of bed tested by WANICHKUL [11]: From left, a) III-112

Simple spiral, b) Double spiral, c) Solid plastic spiral, d) A module of

multi-stage bed [No. of stage can be added by increase the number of

module into the same center shaft]

Figure (Con’t)

Page

Fig. 5.4.3-3 Characteristics of oil and water drops on silicon coated (oleophilic) III-112

steel fibers and non-coated (hydrophilic) steel fibers

Fig. 6.2-1 Example of schematic diagram of DAF (Source: Aquatec Maxcon) III-115

Fig. 6.2.1-1 Diagram for considering relative velocity of bubble and oil in flotation III-117

column

Fig. 6.2.1-2 Schematic diagram of the 3 transport phenomena III-117

Fig. 6.2.1-3 Schematic of single bubble and entire height of flotation column III-118

Fig. 6.2.1-4 Relation between theoritical efficiency factor and observed efficiency III-120

factor

Fig. 6.2.4-1 Typical relation between efficiency of DAF and various parameters III-124

Fig. 6.2.4-2 Solid-bubble agglomerate and formation of oil-bubble agglomerate [14] III-126

Fig. 6.3-1 Pilot-scale DAF test and Flota-test III-135

Fig. 6.4-1 Example of necessary equipment and component details of DAF system III-

140(Source: Environ Treatment System)

Fig. 6.4-2 Necessary equipment and reactor components of DAF system III-141

Fig. 6.4-3 Examples of characteristics of scum from DAF processes III-145

Fig. 6.5-1 Example of good bubble formation from pressurized water III-146

(Source: Cornell DAF pump)

Fig. 6.5-2 Relation between power required for pump, compressor and absolute III-149

pressure of saturator for pressurized water flowrate of 10 m3/h (assume %air saturation = 95%)

Fig. 6.5-3 Schematic diagrams of saturator systems (Source: Edur pump) III-151

Fig. 6.5-4 Examples of saturator system III-152

Fig. 6.5-5 Examples of injection valve III-153

Fig. 7.1-1 Basic flow pattern and examples of hydrocyclones III-155

Fig. 7.2.1-1 General flow pattern and features of hydrocyclones III-158

Fig. 7.2.1-1 General flow pattern and features of hydrocyclones III-159

Fig. 7.2.1-2 Velocity components in hydrocyclone III-159

Fig. 7.2.1-3 Tangential velocity profile in hydrocyclone and various typed of vortex III-160

Fig. 7.2.1-4 Examples of tangential velocity profile III-161

Fig. 7.2.1-5 Example of axial or vertical velocity profile III-162

Fig. 7.2.1-6 Example of radial velocity profile [30] III-163

Fig. 7.2.1-7 Forces on oil droplets or particles in hydrocyclone III-163

Fig. 7.2.1-8 Components of velocity of oil droplets or particles in hydrocyclone III-163

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III-xii

Fig. 8.2.1-9 Diagram of polarization layer and effect of velocity on flux in film III-201

theory

Fig. 8.2.1-10 Various resistances in UF processes III-203

Fig. 8.2.2-1 Examples of flux VS. oil concentration in UF of macroemulsion III-211

Fig. 8.2.2-2 Case 1: find flux/pressure relation when k, β, Cg and R’m are known III-211Fig. 8.2.2-3 Relation between UF permeate flux and Transmembrane pressure III-212 at

Cref

= 4% by volume of oil , V = 1.4 m/s and Predicted relations at C = 2 and 8% (Oil: Elf SeraftA

cutting oil macroemulsion, Membrane: IRIS 3042 PAN )

Figure (Con’t)

Page

Fig. 8.2.2-4 Relation between Flux VS. theoretical and observed permeate volume III-216

Fig 8.2.2-5 Relation between time VS. theoretical and observed permeate volume III-217

Fig. 8.2.2-6 Calculation of required storage volume of equalization tank by III-218

graphical method

Fig. 8.2.2-7 Relation between oil concentration VS. viscosity of emulsion III-220

Fig. 8.2.3-1a Flux of non-stabilized emulsion III-222

Fig. 8.2.3-1b Photographs of non-stabilized emulsion influent, retentate and permeate III-

222(from left) [10]

Fig. 8.2.3-2 Typical relation between CaCl2 concentration and flux at low Pt III-223

Fig. 8.2.3-3a Partially destabilization by salt and coalesce of oil droplets III-224

Fig. 8.2.3-3b Magnified images (x100) of oil droplets from original (left) and III-224

partially destabilized macroemulsion (right) [11]

Fig. 8.2.3-3c Magnified images of new membrane surface (left) and the surface after III-224

UF of macroemulsion at 3 bars without salt (middle) and with salt

addition (600 mg/l CaCl2) [11]

Fig. 8.2.3-4 Relation between fluxes VS. pressure and calculated VS. observed oil III-225

concentration in retentate for partially destabilized emulsion

Fig. 8.2.3-5 Examples of feed emulsions and their corresponding UF permeates III-226

Fig. 8.2.3-6 Examples of flux enhance techniques [38] III-228

Fig. 8.2.3-7 Example of evolution of flux of macroemulsion UF with periodical III-229

cleaning with macroemulsion (membrane IRIS 3042, P = 1 bar,

V=1.5 m/s. 25oC) and schematic of interaction between membrane/

surfactants [18]

Fig. 8.2.3-8 Examples of UF test modules III-231

Fig. 8.3.1-1 Examples of MF membranes III-232

Fig. 8.3.2-1 Evolution of flux from MF (with salt addition) of macroemulsion [20] III-234

Fig. 8.4-1 Examples of RO membranes III-235

Fig. 8.4.1-1 Working principles of reverse osmosis III-235

Fig. 8.4.2-1a Typical relation between flux and pressure of RO III-237

Fig. 8.4.2-1b Typical relation between flux and log of concentration III-237

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III-1

Part 3 Summary of researches: Oily or hydrocarbon-polluted wastewater

treatment

In this part, we will use the data reviewed and verified in Part 1 and Part 2 to

summarize and compose the textbook that covers every research of Prof. AURELLE. The text

will consists of;

• Types and characteristics of oily wastewater

• Related theories on oily wastewater treatment

• Oily wastewater treatment processes, based mainly on researches of Prof.

AURELLE with additional data from well-proven literatures

• Special treatment process trains for some specific oily wastewater, based on

Professor AURELLE’ s researches

118

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III-2


1.1 Introduction

Water pollution is one of the most important environmental problems. Wastewater

from agriculture and industrial processes, as well as domestic wastewater, is main pollutantsource that causes water pollution problem. There are many substances that can deteriorate

water quality and, then, can be counted as water pollutants, such as, organic matter from

domestic wastewater, chemicals from industrial wastewater. Some valuable substances, such

as sugar, flour, oil, will become major pollutants when discharged into water bodies.

Among various kinds of pollutants, hydrocarbon or oil is one of the most severe

pollutants because of its intrinsic properties. Examples of adverse effects of hydrocarbons or

oil when it is discharged into water bodies or environment can be summarized as follow;

• Even the small amount of oil can cause unpleasant odor and taste, so the water can

not be used in potable water production system. Some hydrocarbons, such as benzene series, are noted for their carcinogen property.

• Presence of oil or hydrocarbons in visible form on the water surface is

objectionable from aesthetic and recreation point of view.

• For ecosystem, floating oil layer is dangerous for it can directly harm aquatic

animals such as fishes and waterfowls. It may coat and destroy algae thereby

destroying food sources of aquatic animals.

• Small amount of hydrocarbon can spread over wide area of water surface. API

reports that only 40 liters of oil can cover 1 km2 of water surface in form of visible

film. It can affect photosynthesis and oxygen transfer, so causes adverse effect tomarine or water ecology.

• The hydrocarbon contributes to very high biochemical oxygen demand (BOD) and

is relatively difficult for biodegradation, which is main natural self-purification

process. So it can last relatively long in the water and cause long term effect.

Therefor, it is obligatory to separate or remove oil from wastewater before disposal. In

European countries, standard for hydrocarbons in effluent is normally 5 mg/l (see section 1.6).

The first step to proper oily wastewater treatment design is to have basic knowledge

on types and characteristics of oily wastewater, which are described in the following sections

1.2 Hydrocarbons and oils

This section will provide background knowledge on definitions and basic chemistry of

various from of hydrocarbons and oils, normally present in oily wastewater.

1.2.1 Hydrocarbons

Chemically, the hydrocarbons are compounds of carbon and hydrogen. They are also

in the family of organic compounds, thus can be divided into 3 types, according to formation

of characteristic groups i.e., aliphatic hydrocarbons, aromatic hydrocarbons and heterocyclic

hydrocarbons.

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1.2.1.1 Aliphatic Hydrocarbons

The aliphatic hydrocarbons are the hydrocarbon compounds those in which the carbon

atoms are linked to a straight line. There can be subdivided into 2 groups i.e., saturated and

unsaturated aliphatic hydrocarbons.

1. Saturated aliphatic hydrocarbons

The saturated aliphatic hydrocarbons are the compounds in form of CnH2n+2.The

compounds are also called Methane series, Alkanes or Paraffins. Principle source of these

compounds is petroleum.

Properties: These saturated hydrocarbons are normally colorless, relatively

odorless, and relatively insoluble, particularly those with five or more carbon atoms. They are

present in form of gas, liquid and solid. Alkanes with 1 to 5 carbon atoms are gases at

ambient, those from C 6 to C 17 are liquids, and those above C 17 are solids. Saturated aliphatic

hydrocarbons are quite inert toward most chemical reagents. They are readily soluble in manysolvents. However, their water solubility is relatively low. Solubility decreases with

increasing size or molecular weight, while boiling and melting point increase with increasing

molecular weight. Like common chemicals, properties of these hydrocarbons are subject to

change with pressure and temperature.

Nomenclature: The hydrocarbons that form to a straight line are the basic form,

called normal alkanes or n-alkanes, such as n-butane. The names and properties of some

normal alkanes are shown in table 1.2.1-1. There are also another formations of hydrocarbons

with the same number of carbon atoms as shown in fig. 1.2.1-1. These hydrocarbons are

named differently from n-alkanes. To name such hydrocarbons, the IUPAC system is

commonly used, somehow, will not be presented here.

Table. 1.2.1-1 Properties of some normal alkanes [1],[2]

Name Formula

Melting

point(

C/ 1

atm)

Boiling point

(

C/1 atm)

Specific

gravity

(20/4

)

Solubility

(at 25

C)(mg/l)

Methane CH4 -182.4 -161.5 0.423 -162C

Ethane C2H6 -182.8 -88.6 0.545 -89C

Propane C3H8 -187.6 -42.1 0.493

25C

Butane C4H10 -138.2 -0.5 0.573 25C

n-Pentane C5H12 -129.7 36 0.626 40

n-Hexane C6H14 -95.3 68.7 0.655 10

Cyclohexane C6H14 55

n-Heptane C7H16 -90.6 98.5 0.684 3

n-Octane C8H18 -56.8 125.6 0.699 25C 0.66

Isooctane C8H18 2

Nonane C9H20 -53.5 150.8 0.718

Decane C10H22 -29.7 174.1 0.730

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III-8

sulfur, 0.65 of nitrogen and also trace amount of iron, calcium, sodium, potassium, and other

elements [39]. The density of crude oils is around 650 to 1,200 kg/m3.

Crude oils normally consist of paraffins, olefins, naphthenes and aromatic

hydrocarbons. Oxygen, sulfur and nitrogen are present in the forms of compounds. Normally,

paraffins of 5 to 16 atoms of carbon are present in the form of liquid. They are importantcomponents in gasoline and kerosene, as well as, desire components of diesel and lubricant

oil. Paraffins of 17 carbon atoms or more are solids.

Olefins are found relatively rarely and in significant amount. Because of their highly

reactive and easily polymerizing, they are relatively undesirable components in fuels and

lubricant oils.

Naphthenes are normally found in forms of cyclo-pentane and cyclo-hexane. They are

also important components of fuels and lubricant oils for their temperature resistance

property.

Aromatic hydrocarbons of 1 to 4 rings are also found in crude oils. These compounds

have the greatest density, compared to other hydrocarbons. They provide good viscosity-

temperature property to petroleum product. They are also good solvents

Solubility of crude oils is low. The solubility of petroleum fractions decreases in the

following order: aromatic compounds – naphthenes – paraffins. It also decreases with

increasing in molecular weight.

1.2.3.2 Petroleum products

Petroleum products are the product derived from crude oils through processes such as

catalytic cracking and fractional distillation. These products have physical and chemical

characteristics that differ according to the type of crude oils and subsequent refining

processes. Several examples of refined petroleum products and their physical properties are as

follow:

Gasoline: a lightweight product that flows easily, spreads quickly, and may evaporate

completely in a few hours under temperate conditions. It poses a risk of fire and explosion

because of its high volatility and flammability, and is more toxic than crude oil. Gasoline is

amenable to biodegradation, but the use of dispersants is not appropriate unless the vapors

pose a significant human health or safety hazard.

Kerosene: a lightweight product that flows easily, spreads rapidly, and evaporates

quickly. Kerosene is easily dispersed, but is also relatively persistent in the environment.

No. 2 Fuel Oil: a lightweight product that flows easily, spreads quickly, and is easily

dispersed. This fuel oil is neither volatile nor likely to form emulsions, and is relatively non-

persistent in the environment.

No. 4 Fuel Oil: a medium weight product that flows easily, and is easily dispersed if

treated promptly. This fuel oil has a low volatility and moderate flash point, and is fairly

persistent in the environment.

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interfaces), it means the work required to form new surfaces. The substances that can decrease

the level of surface energy are called “ surface-active substances” or “ surfactants”. They are

also called by other names, such as, detergents (for solid/liquid interface, e.g. in washing or

cleaning process ), emulsifier, or dispersant, etc. With proper amount of surfactants, surface

energy can be substantially decreased until almost to zero. This makes it possible to create a

lot of new surface.

In our interest, surfactants can help making a lot of new surfaces of oil in the water.

This means the oils can be divided into very small droplets, which contributes to many new

surfaces, in the water, called emulsion. Theory of surface energy will be described in chapter

2. Effect and some further details of surfactants and co-surfactants will be described again

in chapter 10 “Chemical treatment processes”.

All surfactants have rather large functional groups. One end of the molecule, which

normally is organic group, is particularly soluble in oil. The other (polar group) is soluble in

waters. There are 4 main types of surfactants i.e., cationic, anionic, non-ionic and ampholytic

surfactants

1.3.1.1 Cationic surfactants

These surfactants are generally salts of quaternary ammonium hydroxide. The surface-

active properties are contained in the cations. Besides their surface-active properties, the

compounds are known for their disinfecting properties.

1.3.1.2 Anionic surfactants

These surfactants are generally sodium or potassium salts. The common ones are

sulfates and sulfonates. The surface-active properties are contained in the anions.

1.3.1.3 Non-ionic surfactants

These surfactants do not ionize and have to depend upon groups in the molecule to

render them soluble. All depend on polymers of ethylene oxide (C2H4O) to give them this

property.

1.3.1.4 Ampholytic (or amphoteric) surfactants

For these surfactants, they contain both cationic and anionic functional groups.

1.3.2

Soaps

Ordinary soaps are derived from fats and oils by saponification with sodium

hydroxide. Saponification is the special case of hydrolysis in which an alkaline agent is

present to neutralize the fatty acids as they are formed. The fats and oils are split into glycerol

and sodium soaps. The nature of the soap depends on the type of fat and oil used. Sodium and

potassium soaps are normally soluble. If the water contains hardness, calcium, magnesium

and other hardness-causing ions will precipitate soap to form metallic soap. Soap will

precipitate all hardness ions first, after that it becomes a surfactant.

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1.3.3 Co-surfactants

In emulsions, especially microemulsion, they contain co-surfactants. These

compounds are normally alcohol, such as butyldiglycol, or benzylic alcohol. These

compounds are readily soluble in water thus provide good solubility to certain products, such

as cutting oil emulsion. They also increase the stability to the emulsion by promoting bothelectrical stability and mechanical stability.

1.3.4

Suspended solids

Suspended solids are commonly found in oily wastewater, especially when combined

collection systems are used. Types and concentration of suspended solids, present in oily

wastewater, depends on the sources of the wastewater. Some oil separation processes, esp. the

ones that are based on filtration concept such as granular bed coalescer and membrames, are

sensitive to the suspended solids. Suspended solids can cause adverse effect on oil separation

processes, unless it has already accounted for and mitigation measure is provided.

1.3.5 Other components

Others components found in oily wastewater depend on their source. Normally they

are the additives of the oil product, such as anti-foaming agents, anti-mousse agents,

bactericides, dyes, or anti-corrosion agents, etc. Some can present adverse effect on treatment

processes. Some may be present as residual pollutants in the effluent after oil separation

processes. So it will be very helpful if we know in advance the components of the oily

wastewater considering.

1.4 Categories of oily wastewater

Oil/water mixture systems can be categorized by many criteria. However, as stated

before that the treatment processes summarized in this book are based mainly on separation

processes, the criteria, used to categorize these oil/water mixtures, are based upon physical

properties. There are 3 main criteria, i.e., the nature of continuous phase, the stability of oily

wastewater, and the degree of dispersion.

1.4.1 Classification by the nature of the continuous phase

In binary mixture systems of oil and water, their components can be divided into 2

main phases, i.e., continuous phase, which is the majority of the two, and dispersed phase.

Direct emulsion: If continuous phase is the water, the mixture will be called “direct

emulsion”, and can be written as “o/w emulsion”, which stands for emulsion of oil in water.

Inverse emulsion: On the other hand, if the continuous phase is oil, the mixture will

be called “inverse emulsion” or “w/o emulsion”.

The treatment processes described herein this book will emphasize on oily wastewater,

which is direct emulsion. However, some processes can also be applied to inverse emulsion.

1.4.2 Classification by the stability of oily wastewater

By these criteria, oily wastewater can be divided into 2 groups:

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10-3

1 10 100 1000

Droplet diameters (microns)

R i s i n g v e l o c i t y ( m / s )

10-4

10-5

10-6

10-7

10-8

10-9

10-10

0.60 0.70 0.75

0.80 0.98 0.90

Oil

density

Secondaryemulsion

Primary

emulsion

Secondary

emulsion

Primary

emulsion

Fig. 1.4.3-1 Relation between droplet sizes and rising velocity of primaryand secondary emulsion [11]

4.

Macroemulsion

This type of emulsion contains droplet size between 0.06 to 1.0 microns. It

usually contains surfactant (and co-surfactant). This type of emulsion has a milky appearance.

A common example of this emulsion is cutting oil macroemulsion.

5. Microemulsion

This type of emulsion contains droplet size between 10 to 60 nm. It containsextensive amount of surfactants and cosurfactants. Since the droplets is very small, this type

of emulsion is usually transparent (sometimes, translucent if dyes are present or amount of o-

surfactants is low). A common example of this emulsion is cutting oil microemulsion.

Details of microemulsion amd macroemulsion will be described in details in the

chapter 10, related to “emulsion destabilization”.

From the three criteria stated above, some classes of oily wastewater from

different criteria might be overlapped. So, to summarize all of three criteria, oily wastewater

can be categorized as shown in fig. 1.4.3-1 and table 1.4.3-2.

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T a b

l e 1 . 5 - 1 a D a t a o f p o l l u t i o n f r o

m c

e r t a i n o i l s , o i l p r o d u c t s a n d s e r f a c t a n t s .

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III-19

Table 1.6-1c Industrial effluent standards of USA, categorized by pollutant sources

(1) CFR 40 part 419—Petroleum refining point source category

Kg / 1000 m3 of feed stock

Effluent characteristicsMaximum for any 1 day

Average of daily values for 30consecutive days shall not exceed

BOD5 34.6 18.4

COD 210.0 109.0

TSS 23.4 14.8

Oil and grease 11.1 5.9

Phenolic compound 0.25 0.120

Ammonia as N 23.4 10.6

Sulfide 0.22 0.099

Total chromium 0.52 0.30

Chromium (hexavalent) 0.046 0.020

pH 6.0-9.0 6.0-9.0

Note: 1 The limits shown in the table are to be multiplied by the process factors and size factor

to calculate the maximum for any one day and maximum average of daily values for

thirty consecutive days

(2) CFR 40 part 437—The centralized waste treatment point source category

Effluent characteristics Maximum daily (mg/l) Maximum monthly average (mg/l)


pH 6.0-9.0 6.0-9.0

TSS 74.1 30.6 Metals

Arsenic 2.95 1.33

Cadmium 0.0172 0.0102

Chromium 0.746 0.323

Cobalt 56.4 18.8

Copper 0.500 0.242

Lead 0.350 0.160

Mercury 0.0172 0.00647

Tin 0.335 0.165

Zinc 8.26 4.50

Organic parameters

Bis(2-ethylhexyl) phthalate 0.215 0.101

Butylbenzyl phthalate 0.188 0.0887

Carbazole 0.598 0.276

n-Decane 0.948 0.437

Fluoranthene 0.0537 0.0268

n-Octadecane 0.589 0.302

Note: 1 The limits shown in the table arebased on best practicable control technology currently

available (BPT)

General note: The standards may be amended and some special remarks for each type of receiving

water and type of industry, which refers to other notification or decree, are notcompletely included in this chapter.

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Table 1.6-1c Industrial effluent standards of USA, categorized by pollutant sources (Cont.)

(3) CFR 40 part 417—Soap and detergent manufacturing point source category

Kg / 1000 kg of anhydrous product

Effluent characteristics

Maximum for any 1 dayAverage of daily values for 30

consecutive days shall not exceed

BOD5 0.90 0.30

COD 4.05 1.35

TSS 0.09 0.03

Surfactants 0.90 0.30


pH 6.0-9.0 6.0-9.0

(4) CFR 40 part 438—Metal products and machinery point source category

Effluent characteristics Maximum daily (mg/l)

TSS 62.0

Oil and grease (as HEM) 46.0

General note: 1 The standards may be amended and some special remarks for each type of

receiving water and type of industry, which refers to other notification or decree,

are not completely included in this chapter.

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Chapter 2 Overview for oily wastewater treatment process design

This chapter provides basic theories, which are important to understand the

phenomena, taking place in oily wastewater, and to understand operating principle of oily

wastewater treatment processes. The analysis methods of some important parameters and

overview of oily wastewater treatment processes are also described.

2.1 Decantation velocity and STOKES law

Oily wastewater can be considered as an immiscible binary mixture system of oil and

water, with the oil as a dispersed phase, because the solubility of oil in water is very low (<

1g/ 100 g of water). So the oil will be present in the water in form of oil droplets, which is the

result of surface tension, which will be described in the next section. Because of its low

specific gravity, these droplets will try to separate themselves from the water by “floating” or

“rising” to the water surface. Consider a single oil drop, when the oil drop is rising, it will be

subject to 2 forces as shown in fig. 2.1-1. The first one (F1) is the gravitational force,

calculated from oil drop size and density difference of oil and water (eq. 2.1.1). The secondforce is called “drag force”, which is the resultant of the resistance inertia force and viscous

force (eq. 2.1.2).

F2

F1

Water

Oil drop,

dia. = d A

V

gd

F c )(6

13

ρ ρ π

−= {2.1.1}

2

2

12 AV C F cd ρ = {2.1.2}

Fig. 2.1-1 Free body diagram of oil drop in water and relation between C d and Re [55]

Cd is a numerical constant, called drag coefficient , which depends on the flow region,represented by Reynolds number (Re) as shown in fig. 2.1-1. A is the projection area of oil

drop. In this case, the oil drop is spherical, then A is the cross sectional area of the sphere.

The oil drop will start to rise from a stationary position (V = 0 m/s, F2 = 0). After

some time, it will reach the terminal velocity or rising velocity, which will remain constant

along its course. At this velocity, F1 = F2. So, from this condition, the rising velocity (V) can

be written as follows.

2/1

)1(3

4⎟⎟ ⎠

⎞⎜⎜⎝

⎛ −= g

c

d V

cd ρ

ρ {2.1.3}

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Chapter 2 Basic theory for oily wastewater treatment process design

III-24

Tip To visualize the surface tension [42], we will consider a tank that one side

wall can be moved as shown in fig. 2.2.1-2. If we try to move the wall to extend the

surface of liquid, we have to apply the force F. Then, the wall move by the distance dl.

From this, the work done or effective work can be written as:

dlF W ⋅= {2.2.2a}

When the wall is moved, we increase the surface area of the liquid, which can

be written as shown in eq. 2.2.2b.The increasing in energy of the system is as shown in

eq. 2.2.2c.

L

dl

F

F

Section

Plan

dl L A ⋅= {2.2.2b}

AG ⋅=Δ γ {2.2.2c}

We assume the process is isothermal and

reversible, so there is no heat loss. Then,

work done will be equal to energy (eq.

2.2.2d). From this, we will see that the

surface tension can be derived as shown in

eq. 2.2.2e and eq. 2.2.1

dl LdlF ⋅⋅=⋅ γ {2.2.2d}

L

F or

A

W

dl L

dlF ==

⋅⋅

=γ {2.2.2e}

Fig. 2.2.1-2 Model for Visualization of γ

Table. 2.2.1-1a Data of surface and interfacial tension (N/m) for some liquids at 20° C

[40][42]

NameSurface

tension

Interfacial

tension

(/water)

NameSurface

tension

Interfacial

tension

(/water)

Water 72.8 Ethanol 22.3

Benzene 28.9 35 n-Octanol 27.5 8.5

Acetic acid 27.6 n-Hexane 18.4 51.1

Acetone 23.7 n-Octane 21.8 5038

CCl4 26.8 45.1 Mercury 485 375

Polar organic

compounds

22-50 Aqueous

detergent

solutions

24-40

Hydrocarbon 18-30 Fluorocarbon 8-15

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Adhesion work: Interfacial tension between oil and water (or any two liquids) can

relate to surface tension of each liquid by DUPRE’s equation (eq. 2.2.3a). This equation can

be also applied to solid-liquid interface, as shown in eq. 2.2.3b. γs represents surface energy of

solid.

)(owadhwoowW −+= γ γ γ {2.2.3a}

)(soadhosso W −+= γ γ γ {2.2.3b}

Tip To visualize the concept of adhesion work [42], we will consider a tank that

one side wall can be moved, filled with 2 liquids (oil and water). When we move the

wall, from eq. 2.2.2, it can be described that:

γo

γw

γo/w F

OilWater

• We increase the surface of oil and water

by γo and γw, respectively.

•

Then we attach the oil and water surfacetogether. For this, we recover an amount

of energy, called “ adhesion work”

Fig. 2.2.1-3 Model for visualization of

adhesion work

2.2.2

Liquid-solid and liquid-liquid-solid interfaces

2.2.2.1 Wetting, Contact angles, Adhesion work, and YOUNG’s equation

Wetting is the displacement from a surface of one fluid by another [40]. Therefore, it

involves three phases and, at least two phases must be fluid. To understand this, we will

consider the oil drop on a solid surface in water, as shown in fig. 2.2.2-1.

θso

γow

γsoγsw

Water

Solid

Oil droplet

Fig. 2.2.2-1 Diagram of Oil drop on solid surface in water

Contact angle: The angle between tangential line of oil drop’s surface and the surface

of solid is called “contact angle”. In case that the oil remains as a drop, it means the system is

in equilibrium. We will have definite contact angle θso. Equilibrium of force on the dropletcan be written as shown in eq. 2.2.4, known as YOUNG’s equation.

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III-28

Table 2.2.2-1 Relation between contact angle, work adhesion, interfacial tension and spread

coefficient of oil/water/solid system [42]

Contact angle

soWadh(so)w

Relation beween

interfacial tensionCharacteristic of oil drop

= 0° > 2γow > 0 γsw > γso + γow

γso

γow

γsw

= 0° = 2γow = 0 γsw = γso + γow

γso

γow

γsw

0°<θso<90o γow <W< 2γow < 0 γsw > γso θ

γso

γow

γsw

= 90o

W = γow < 0 γsw = γso θ

γso

γow

γsw

90°<θso<180

o

0<W < γow < 0 γsw < γso θγso

γow

γsw

=180o W = 0 < 0 γso = γsw+γow

γso γsw

γow

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2.2.3 Capillary pressure and LAPLACE’s law

2.2.3.1 LAPLACE’s law

LAPLACE’s law is the relation of pressure difference across the surface of liquid of

surface tension γ. If we consider the air bubble in water, at one fraction of the bubble with theradius of curvature R1, and R2 on 2 perpendicular plains (fig. 2.2.3-1), the pressure

difference, by LAPLACE’s law, will be as shown in eq. 2.2.11:

R 1 R 2Section of

surface of air

bubble in water

P (Outside pressure)

P’(Inside pressure)

Fig. 2.2.3-1 Section of air bubble in water

)11

('21 R R

PPP +=−=Δ γ {2.2.11}

From the equation, we can calculate the

pressure difference of the following

systems, i.e.,

• A soap bubble of radius R in air

RP γ 4=Δ

Because there are 2 interfaces of air/soap.

• An air bubble of radius R in water

RP

γ 2=Δ

• A cylindrical jet of water in airγ

P =Δ R

Because R 2 is infinity.

2.2.3.2

Capillary pressure

Capillary effect is an important phenomenon for oil/water separation process when we

consider flowing through porous media, such as ultrafiltration membrane. This phenomenon

will be described by fig. 2.2.3-2. When the tube with very small diameter (capillary tube) is

plunged into liquid surface. Because of surface tension of liquid, the liquid will rise into the

tube to the height h. From equilibrium, we can calculate the capillary pressure (Pc) as follow:

catmb PghPP ==− ρ {2.2.12}

From LAPLACE’s law,

r RPP atmb

θ γ γ cos22 ==− {2.2.13}

From eq. 2.2.12 and 2.2.13,

r Pc

θ γ cos2= {2.2.14a}

And

gr h

ρ

θ γ cos2= {2.2.14b}

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Method of analysis

1. Solvent extraction [1]

This method is the standard method of examination of oil and grease. They are at

least 4 variations. However, they all involve an initial extraction of oil and grease by hexaneor CFC-113. The 4 variations include,

• Partition-gravimetric method: Hexane will be used to extract the oil. Then

it will be separated from water and then evaporated. The residue will be used

as an inditator of oil and grease content.

• Partition-infrared method: CFC-113 will be used as extractant. Then it will

be measured with infrared scanning. This method is faster than gravimetric

method. The accuracy depends on selection of oil standards for calibration.

The oil used for calibration should be the same type as oil in the wastewater.

•

Soxhlet extraction: It involves the initial step of acidification and thenhexane extraction. This method tends to retain more volatile hydrocarbons.

However, it is time consuming.

• Hydrocarbon analysis: Silica gel is added to hexane to remove fatty

materials. And then the hexane will be analyzed by the first method.

2.

Turbidity measurement

Oil concentration can be measured by light loss (turbidity) or light scatter from

oil droplets in the wastewater [43]. The main advantage of this method is its simplicity and

fast response. However, it will be difficult to distinguish between oil droplets and other

particles. Some manufacturer claim that this effect can be minimized by the selection of theangle of scatter and detector. In GPI lab, some researchers use this method to measure the oil

concentration. It is suitable to use for relatively clear wastewater, such as condensate.

However, in most situations, oily wastewaters are usually contaminated by color materials and

suspended solids. This method, thus, may not provide accurate result on oil concentration.

3.

TOD measurement

If total oxygen demand (TOD) measuring instrument is available, oil

concentration can also be measured as TOD. Again, the main advantage of this method is its

fast response. However, it will be difficult to distinguish between TOD of oil and other

substances, especially surfactants and co-surfactants. So this fact should be taken intoaccount. In GPI lab, some researchers use this method to measure the oil concentration. The

data from the researches are presented in chapter 1. It must be noted that TOD includes

oxygen demand from non-organic factors, such as ammonia, sulfide. Thus its value is usually

higher than BOD.

4.

Other methods

Total organic carbon (TOC) is also widely used to measure pollutant

concentration. Its working principle bases on oxidizing of the sample, usually at high

temperature, to convert carbons to carbondioxide, which will be measured by IR, UV probe.

TOC machine can cover from ppm to ppt range. It is very useful for online control. But it doesnot account for nitrogen compounds, which have much higher oxygen demand than carbons.

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There are also others techniques to measure the oil concentration. However, some techniques

are developed for specific application. Some are not widely used or not suitable for

wastewater analysis. So they will not be described in detail here. Such techniques include

direct infrared absorption, ultraviolet absorption, optical fiber sensor, gas chromatography,

etc.

2.3.2 Size distribution , spectrum or granulometry

The size distribution, spectrum or granulometry is the data on the number of each size

of oil drop, air bubbles, particles or other dispersed material in continuos phase. Normally, it

is reported in the form of percent of total number of dispersed material or percent by volume

or percent by weight . Example of the size distribution of oil droplet in cutting oil

macroemulsion is shown in fig. 2.3.2-1.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

10.0 17.8 31.6 56.2 100.0 178.0 316.0 562.0 1,000.0 1,780.0

Droplet diameter (nm)

P e r c e n t b y w e i g h t ( % )

Fig. 2.3.2-1 Example of the size distribution of oil droplet in cutting oil macroemulsion (Elf Seraft 4% V of

concentrate), measured by Coultronics nanosizer NDM4 [11]

Oil drop or particle’s diameter is one of the parameters in the STOKES equation.

Since treatment efficiency of several separation processes, which will be described in the

following chapters, are based on the rising velocity that is governed by STOKES law. So the

diameter is one of the key parameters to calculate the efficiency of the process. Furthermore,each process can provide acceptable or competitive efficiency in only a certain range of

droplet size. So the size distribution is an important data to select feasible treatment process.

Method of analysis

1. Particle size analyzer or Granulometer

“Particle size analyzer” or “granulometer” or “nanosizer” is the specific

equipment designed for measuring size and quantity of particle in liquid. There are many

generations of granulometer with different operating principles. However, present

granulometers are based on laser detection technology. This equipment can be used to

measure size distribution of oil droplet or particle down to the range of submicron size

(depend on manufacturers). It can report the result in the form of table or graph of size

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distribution, both by number and by volume or weight. An example in fig. 2.3.2-1 was also

measured by the granulometer. Fig. 2.3.2-2 shows the picture of granulometer.

Fig. 2.3.2-2 Granulometer (Source: above - Ankermid Techcross / below - CILAS)

2. Decanting test

When the use of granulometer is not available, there is a simple method to

measure the size distribution, which is called “decanting test”. This method requires a simple

equipment as shown in fig. 2.3.2-3.

0 min 5 min 10 min …. t min

h1h2

h3

h4

Fig. 2.3.2-3 Decanting test column

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Analytical procedure

1) Pour the wastewater into the decanting test column and stir. Make sure it is

homogeneous.

2) Leave the wastewater to decant, taking the water samples from various

heights of the column at preset interval.

3) Analyze the samples to find the oil concentration or other parameters that

are directly proportional to the oil concentration, such as TOD, turbidity,

etc.

4) From the collected data, we can calculate the granulometry, using this

procedure:

• At t = 0, the wastewater is homogeneous, then the oil concentration is

Co throughout the column.

• At t = t1 and height (from the bottom of the column) = h1, the

corresponding rising velocity Vh1t1 = h1/t1.

• So at this point, the oil drop that have rising velocity greater than Vh1t1

will rise past the height h1 then will not be found in the sample taken

from h1. From Vh1t1, we can calculate the corresponding droplet

diameter d h1t1 by STOKES law.

• If the oil concentration at this point is Ch1t1, and the calculated droplet

diameter is d h1t1, we can conclude that:

The fraction of d < d h1t1 = Ch1t1/Co

5) Repeat step 4), at other t and h. then, use the fraction of d < d hx tx to plot the

size distribution curve.6)

Concentration of each droplet size can be roughly represented by the

differences between value of adjacent % of accumulated C/Co. Please note

that the size and %C/Co are estimated values only. But it can provide an

idea of how the sizes of droplet are distributed.

An example of the analysis of decanting test data is shown in tab. 2.3.2-1 and fig.

2.3.2-4 and 2.3.2-5.

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Table 2.3.2-1a Example of the decanting test of oil/water emulsion

Time

At sampling height

(from the bottom

of column)

Corresponding rising

velocity

Oil concentration of

the sample

% accumulated C/Co

when d <

dEht

Corresponding droplet

size (from STOKES

law)

h Vh,t

Ch,t

% Ch,t/C

odE

h,t

sec m m/s mg/l % micron

0 0.5 86 100

900 0.5 5.56E-04 57 66.28 72.8

1800 0.5 2.78E-04 25 29.07 51.4

2700 0.5 1.85E-04 8 9.30 42.0

3600 0.5 1.39E-04 3 3.49 36.4

5400 0.5 9.26E-05 1 1.16 29.7

7200 0.5 6.94E-05 0 0.00 25.7

0 1.25 86 100

900 1.25 1.39E-03 83 96.51 115.0

1800 1.25 6.94E-04 63 73.26 81.3

2700 1.25 4.63E-04 49 56.98 66.4

3600 1.25 3.47E-04 37 43.02 57.5

5400 1.25 2.31E-04 16 18.60 47.0

7200 1.25 1.74E-04 6 6.98 40.7

7200 1.25 2.06E-03 80 93.02 140.0

Note: Assume the oil is kerosene so the density (20o C) = 790 kg/m3. Water dynamic

viscosity = 1.08E-3 (N.S)/m2.

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Table. 2.3.2-1b Example of the decanting test of oil/water emulsion: sorting of the result

from table 2.3.2-1a

Corresponding droplet size Corresponding rising velocity

% accumulated C/Co

when d

< dEht

Estimated C/Co for

each droplet size

dE Vh,t

% Ch,t/C

o%C/Co

micron m/s % %

25.72 6.94E-05 0

29.70 9.26E-05 1.16 1.16

36.38 1.39E-04 3.49 2.33

40.67 1.74E-04 6.98 3.49

42.00 1.85E-04 9.30 2.33

46.96 2.31E-04 18.60 9.30

51.44 2.78E-04 29.07 10.47

57.52 3.47E-04 43.02 13.95

66.41 4.63E-04 56.98 13.95

72.75 5.56E-04 66.28 9.30

81.34 6.94E-04 73.26 6.98

115.03 1.39E-03 96.51 23.26

0

10

20

30

40

50

60

70

80

90

100

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00

Oil droplet size (dE) (micron)

% A

c c u m u l e t e d C / C o

Accumulated conc. curve h = 0.5 m h = 1.25 m

Fig. 2.3.2-4 Relation between accumulated C/Co (% of C/Co when the droplet size is equal or smaller than the

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given dE) and oil droplet size

0

5

10

15

20

25

26 30 36 41 42 47 51 58 66 73 81 115

Droplet size (micron)

% b

y w e i g h t

Fig. 2.3.2-5 Example of estimated size distribution of oil droplets from decanting test

3.

Visual observation

To roughly estimate the granulometry of oily wastewater, there are simple

criteria for visual observation as shown in table 2.3.2-2. However, these criteria may be used

only when the wastewater is not polluted by suspended solids or other substances that makes

it opaque. In case of surface oil layer, API [45] recommended useful guide to evaluate oil

thickness as shown in table 2.3.2-3.

Table 2.3.2-2 Criteria for visual observation of size distribution [22]

Visual aspect Average particle size Example

Particles visible by eye 500 micron Very fine sand

Not clearly visible by eye 100 micron Starch

Opaque milky 10 micron Milk

Whitish milky 1 micron Homogenized milk

Bluish milky 0.1 micron Macroemulsion

Semitransparent 50 nm Microemulsion

Transparent 10 nm Microemulsion

Transparent 2-6 nm Micelles

Transparent 1 nm Molecules

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Table 2.3.2-3 Criteria for visual observation of surface oil film [45]

Film thickness

(micron)Appearance

Approximate volume of oil

for film 1 km2 in area (l)

38.1 Barely visible under mostfavorable light conditions

37

76.2 Visible as silvery sheen on

surface of water

74

152.4 First trace of color may be

observed

148

304.8 Bright bands of color are visible 296

1016 (1 mm) Colors begin to turn dull 985

2032 (2 mm) Colors are much darker 1970

2.3.3 Other parameters

Each treatment process may require some special data for its calculation. However,

common data required by several processes include:

• Interfacial tension

• Viscosity of oil

These data can be analyzed by specialized laboratories. However, if we know the

source of the oily wastewater, we can estimate these parameters. Even when we can notspecify the exact source of oil, we still can estimate them, using the general data of oil or from

references, without too much error. These data can also be found in chapter 1 and this chapter.

2.4 Overview of oily wastewater treatment processes

As hydrocarbon or oil requires a great amount of oxygen or oxidizing agent to oxidize,

moreover, the hydrocarbon is relatively difficult to biodegrade, thus, it becomes clear that the

use of biological treatment with high-concentration oily wastewater may not be the

economical alternative. Besides there are possibilities to reuse or recover the hydrocarbons

in the wastewater. Then, if possible, it is reasonable to separate oil from the wastewater,

rather than destroy or change them into other forms.

Thus almost all of treatment processes that have been studied in GPI laboratory are

based on separation process, both physical and physico-chemical, techniques in order to

separate oil from water. From chapter 1, it shows that oily wastewaters can be divided into

several categories, mainly depending on their stability and degree of dispersion. And in the

previous sections on this chapter, it shows that physical separation of oil from water depends

on STOKES law.

Thus, to enhance separation between water and oil, it can be archived by modification

of parameters in STOKES law in the manner that make the rising velocity of oil droplets

increase. Actually, almost all of oil/water separation processes covered by Prof. AURELLE’sresearch team are STOKES law-based processes, i.e. decanter, coalescer, hydrocyclone, and

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dissolved air flotation (DAF). Thus each process will has its own limitation, bound by

assumptions of STOKES law as well as its unique working characteristic.

Apart from STOKES law-based processes, there are other oil/water separation

processes that based on other physical properties between oil and water. In GPI lab, Prof.

AURELLE’s teams also studied these processes, i.e. skimmer (which is based on interfacialtension concept), membrane process (which depend on mass transfer phenomena), thermal

process (which depends on thermodynamic properties), and chemical process (which depends

on chemical reaction).

Thus, to design an efficient oily wastewater treatment process, designer should

understand working principle and limitation of each process. The following chapters will

devote to each oily wastewater treatment processes studied and perfected by Prof.

AURELLE’s team within 3 decades. However, in this section, description of each process will

be described briefly as follows,

STOKES law-based processes

2.4.1

Decanter

Decanter is an oil separation process that depends purely on STOKES law without

modification of their parameters. The oil droplets in wastewater will allow to decant (or rise)

naturally to the surface of water .It is very simple and proven to be very good process for

separation of free oil and primary emulsion. Rising velocity depends mainly on the droplet

size. In case of very small droplets, it may take too long time for the droplets to reach the

surface or it may need so large tank to become economical. However, performance of

decanter can be enhanced by reducing of rising distance of droplets, such as by lamella-plate

insertion. Actually, GPI lab had initiated a very compact decanter by this concept, called“Spiraloil”, which is commercialized by Elf Total Fina. Decanter is described in details in

chapter 4.

2.4.2 Coalescer

Coalescer is a modified or accelerated STOKES law-based separation process by

increasing the size of oil droplet. Since rising velocity is proportional to square of droplet

size, theoretically, coalescer can enhance oil separation efficiency more rapidly than other

process that work on other parameters. AURELLE is one of the pioneers on granular bed

coalescer, which was patented and, later, commercialized by Elf Total Fina. He also initiated

other type of coalescer, i.e, granular bed coalscer with guide to handle wastewater with highoil concentration, fibrouse bed coalescer that can handle wastewater with SS. Coalescer can

handle secondary emulsion effectively. However, its performance with stabilized emulsion is

not so good since the droplets are very table and unlikely to coalesce with each other.

Coalescer is described in details in chapter 5.

2.4.3 Hydrocyclone

Hydrocyclone is a modified or accelerated STOKES law-based separation process by

increasing the acceleration of the system. Hydrocyclone replaces gravity acceleration (g)

with centrifugal acceleration, which can reach several hundreds times of g. Thus it is very

compact separation process. AURELLE and MA had initiated three-phase hydrocyclone thatcan separate oil, solids and water simulteneously. Hydrocyclone use its inlet flow energy to

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operate. So it is noted for its increase in efficiency with the increase of inlet flow, which is

unique advantage of the system. It can handle secondary emulsion effectively. However, its

operation has high shear characteristic. Furthermore, it driving force come only from its inlet

flow so the centrifugal force is limited. So it can not separate very small droplets (<10

microns). It must also be noted that hydrocyclone is actually a concentrator. It can not

separate water-free oil. Separated oil usually contains some water. Thus it need to be furthertreated by other process. Hydrocyclone is described in details in chapter 6.

2.4.4 Dissolved air flotation (DAF)

DAF is a modified or accelerated STOKES law-based separation process by

decreasing density difference between oil and water. It can be obtained by addition of gas

bubble or air bubble to wastewater to form agglomerates with oil droplets. Since air or gas has

low density the agglomerates, then, has lower density than oil drops, resulting in higher rising

velocity. DAF is noted for its versatility. It can separate both solids and oil. Its efficiency

depends on formation of oil-bubble agglomeration. Thus its performance is low if droplets are

very small, since collision between air bubble and oil drops is difficult. In practice, DAF will be used after coagulation-flocculation process, which can increase the droplet sizes

chemically. DAF is described in details in chapter 7.

Other processes

2.4.5 Skimmer

Skimmer is the device designed to remove oil film from the water surface. GPI lab had

studied and perfected skimmer’s oil performance so it can selectively remove only oil without

drawing the water with it. Operating principle of the oleophilic oil skimmer is based on

surface tension concepts. The skimmer studied in GPI lab was also commercialized. Detailsabout skimmer are described in chapter 3.

2.4.6 Membrane processes

Membrane processes are the promising separation processes that gain popularity in

these recent years. The key part of the processes is the membrane, which is porous material

with various ranges of pore size to suit the sizes of material to be retained or separated. Its

working principle can be compared, but not exactly identical, to that of filtration process.

With properly selected pore size, membrane processes can separate target materials with

relatively high efficiency. GPI lab had studied application of various membrane processes,

i.e., microfiltration, ultrafiltration, nanofiltration and reverse osmosis on oily wastewatertreatment. The lab also initiated studies on capacity (or flux) enhancement of membrane

process for cutting oil emulsion treatment. Membrane processes are described in details in

chapter 8.

2.4.7 Thermal processes

Thermal process is the separation process based on thermodynamic properties of

oil/water mixture. GPI lab emphasizes on heteroazeotropic distillation, which can be carried

out at the temperature that is lower than those of pure water and pure hydrocarbons. It is

achieved by addition of proper hydrocarbons, called entrainer or extractant, into the

wastewater to azeotrope point, where oil, water and vapor co-exist , during distillation. The process can be used to separate water from refinery slops and permeate from membrane

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process of oily wastewater treatment. Thus it provides opportunity to recover these supposed-

to-be-wasted oil and treat the most problematic waste. Thermal processes are described in

details in chapter 9.

2.4.8 Chemical process

Chemical process for oily wastewater treatment is mainly destabilization process for

destabilizing of stable emulsion. It consists of 2 main mechanisms, i.e. destabilization of oil

droplets and coalescence or flocculation of destabilized oils. This process is necessary when

the wastewater to be treated contains stable or stabilized emulsion, otherwise it can not be

treated by STOKES law-based processes. Destabilization chemicals includes salts, acids, and

polyelectrolytes. GPI lag had studied destabilization mechanisms of each chemical which

provide understanding and knowledge on chemical selection. The detail is discussed in

chapter 10.

2.4.9 Finishing processes

To meet the effluent standards, effluent from aforementioned processes may need

further treatment before discharge to receiving water body. The most widely used processes

for finishing propose are biological treatment and adsorption (by activated carbons). These

processes are not the main interest in Prof. AURELLE’s team, which emphasize of physical

processes. However, to fulfil the whole oily wastewater treatment processes, biological

treatment and adsorption are briefly described in chapter 11.

The theories and details of each processes described in section 3 to 11 will, then, be

used to develop the software for design and simulation of oily wastewater process train,

which is the scope of work of this thesis.

2.5 Determination of degree of treatment

2.5.1 Overall degree of treatment

Before designing oily wastewater process, required overall degree of treatment or

effluent quality of the treatment system must be set. In case that the effluent is discharged to

public receiving water body, such as sewage system or natural stream, the final effluent

quality must conform to every applicable law. Examples of effluent standards are shown in

chapter 1. In case that the water is recycled or reused, required water quality for those

purposes, such as standard of recycled water quality, standard of recycled cooling water, etc.,

will determine the overall degree of treatment.

2.5.2 Degree of treatment of each process

Since the performance of every treatment process depends mainly on wastewater

characteristic, for existing facilities, wastewater must be thoroughly analyzed to obtain its

detailed characteristic. For new facilities, its characteristic must be carefully estimated. In

case of oily wastewater, performances of oil separation processes are based on degree of

dispersion and stability of the wastewater. When these data are available and limitation as

well as expected performance of each treatment process is thoroughly understand, it is

possible to select feasible process train that can treat the wastewater to meet the required

degree of treatment .

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Example A: consider wastewater from in-land refinery contains 230 mg/l of non-

stabilized secondary emulsion and 10 mg/l of emulsified oil. If applicable effluent standard in

this case is 12.0 mg/l, in this case, the degree of treatment of the system is (10+230-

12)/(10+230)*100 = 95%. We can separate the secondary emulsion by compact decanter,

coalescer or DAF, which secondary emulsion removal efficiency is expected at 90%. So it

requires further treatment and the degree of treatment required in the next stage is at least 100-((100-950)/(100-80)) = 50%. In this case, It can be archieved by sending to the water to mix

with domestic wastewater and treat by biological treatment. The concentration of 12.0 mg/l

may be met by dilution effect of domestic wastewater alone. Moreover the biological process

can be reduced the oil concentration at least 50%. Thus it can be certain that the effluent

concentration of 12 mg/l is guaranteed at all times.

2.5.2.1 Graded efficiency and total removal efficiency

As stated before that efficiency of most separation process depends on the size of oil

droplets, most of researches in GPI lab had common aim to establish the relation between

the efficiency and droplet size, which will be shown in the following chapters. Ifgranulometry data (see fig. 2.3.2-5) is available, it will provide clear data on percentage of

each size of oil droplets. So it is very useful for removal efficiency calculation of each droplet

size ( graded removal efficiency) of each process. Summation of graded efficiency of each

process results in total removal efficiency of that process corresponding to that particular

wastewater , which is more accurate than the estimated value from literatures alone. In case

that the treatment system consists of several processes, overall efficiency can be determined

from summation of greaded effeciecny of ecah process, as shown in eq. 2.5.1.

100))1)....(1)(1(1( ,2.1,, ⋅−−−−= id d d overalld η η η η % {2.5.1a}

( )%100

,

,,

,

max

min ⋅⋅

=∑

io

d

d

iod id

it C

C η

η {2.5.1b}

( )%100

max

min

,

⋅

⋅

=∑

o

d

d

od overalld

overallC

C η

η {2.5.1b}

Where ηoverall = Overall efficiency of the treatment process train

ηd,overall = Graded removal efficiency of the treatment process train

ηd,i = Graded removal efficiency of the process “i”, calculated by

equation of each process shown in the following chaptersηt,i = Total removal efficiency of the process “i”

Co = Oil inlet concentration of the treatment process train

Co,i = Oil inlet concentration of the process “i”

Cod,i = Graded oil inlet concentration of the process “i”

i = the number of processes in the process train, i ≥ 1

To achieve the required effluent standard, overall efficiency of the system must be

equal of higher than the required degree of treatment, established in section 2.5.1.

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2.5.2.2 Cut size determination

Since the bigger oil drops are realtively easier to remove than the smaller ones, it is

recommended to select the treatment process to handle the range of oil drops from the biggest

to the smallest size that contributes to the required degree of treatment (in case that the

granulometry data is known). This smallest size in the range described above is called cut size.

For example, if the granulometry of the wastewater is as shown in fig. 2.3.2-4, if the

required degree of treatment is 90%, from the curve, the cut size will be 90 microns.

The cut size is very useful in process design for it can be used as a representation of

the whole wastewater to calculation the required size of separation process. It can save

calculation time when many processes are to be compared. However, sizing of the process

calculated from this theoretical cut size may not be exactly equal to the degree of treatment

since the cut size is selected based on the assumption that the graded removal efficiency of

droplet equal to larger than cut size is 100% (see fig. 2.5.2-1). Thus some adjustments should be made after detailed calculation of the efficiency by eq. 2.5.1.

Droplet size

R e q u i r e d d e g r e e

o f t r e a t m e n t

Theo.

cut size

100%

Acc. %

(by weight)

Droplet diameter

ηoverall

Real eff.Theo. eff

η R = Required degree

of treatment

Theo.

cut size

Real

cut size

100%

ηR

Fig. 2.5.2-1 Cut size determination

2.5.2.3 Economics of the processes

Performance of each separation process also depends on other parameters apart from

the droplet size. Change in these parameters will also make the performance of the process

change. Thus the process train can be optimized by changing influent parameters, usually the

geometry, of each process in the process train to make the overall efficiency as close to the

required degree of treatment as possible.

Treatment capability of processes may overlap in some range of droplet sizes, which

will be summarized again in chapter 12. For example, droplet size around 20 microns can be

treated by coalescer or compact decanter. This leads to several combinations of process trains.

For example, the process train in example A may be divided into 2 alternatives, i.e. (1)

Compact decanter+activated sludge (AS), (2) Coalescer+Activated sludge. In each alternative,

the sizes of equipment and reactors can be varied within its own valid range. Thus, to select

the best alternative and process sizes, economics of each alternative should be compared.

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3.1 General

The most basic form of oily wastewater is the presence of oil film or layer on the

water surface. The most severe case of this form of oily wastewater is the large-scale oil spill,caused by tanker or offshore platform accident. The oil will spread over wide area and cause

adverse effect on ecosystem. When the accident occurs, the oil confinement, such as booms, is

arranged to limit the spreading area. Then, the spilled oil is, sometimes, dispersed by chemical

dispersant to form tiny droplets, then left to biodegrade. Biological accelerating agents may

be added to promote biological degradation. Sometimes, specific adsorbents are added to the

oil to make it settleable or in more manageable form, such as floating agglomerate scum.

These methods may still cause adverse effect on the environment. Thus, if possible, the oil

layer is preferably removed in form of water-free oil for it can be reused.

In oily wastewater treatment process, the goal of almost all of the separation processes

is to separate the oil droplets and form an oil layer on the water surface. After that, it is alsocrucial to remove this oil layer as water-free oil, otherwise it will become new oily

wastewater. In a small container, the oil layer can be removed manually or by simple devices,

such as weir, bell mouth pipe. Anyway, in case of oil spill at sea, or upscale tank, it is difficult

to remove only oil without getting water with it even though the oil film is visibly stratified

from the water. In these cases, specific devices that have good oil selectivity are required.

There are many variations of these devices as shown in fig. 3.1-1. However, they can be

generally divided into 2 concepts i.e.,

•

Pumping or hydraulic devices: The oil will be directly pumped out or intercepted

by controlled hydraulic devices, such as adjustable-weir. Important factor that

governs the performance is the oil layer thickness. So, some mechanisms are provided to locally thicken the oil layer before removing it. Examples of the

devices include pump skimmer and weir skimmer.

• The devices based on adsorption property: This group of devices makes use of

difference between oil and water adsorption property of material to remove the oil.

The oil selectivity of material is based on the concept of interfacial tension, as

described in chapter 2. When design properly, the device can remove virtually

water-free oil from the wastewater. Examples of the devices include drum

skimmer, disc skimmer, belt skimmer, etc.

This chapter emphasizes on the drum and disk skimmer, which are thoroughlyresearched in GPI lab.

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a) Disc skimmer (source: Highland tank) b) Belt skimmer (Source: Ultraspin)

c) Drum skimmer (source: ELF/GPI lab) d) Mop skimmer (source: Ultraspin)

e) Weir skimmer (Source: Skimoil) f) Pump skimmer (Source: Ro cleandesmi)

g) Dispersant spray (Source: Ro-cleandesmi) h) Absorbent (Source: Ro-cleandesmi)

Fig. 3.1-1 Examples of oil skimming devices

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3.2 Oil drum skimmer

3.2.1

Working principles

Oil drum skimmer is the equipment that has a rotating drum which its surface acts as

an oil-skimming surface (fig. 3.2.1-1). The oil will adhere to the skimming surface, lift upfrom the surface by the skimmer’s rotating movement, and then be scraped off by a scrapper

blade into a receiving channel or container.

Drum skimmer

Scrapper

Oil receiving

trough

Oil layer

Water

Fig. 3.2.1-1 Lab-scale drum skimmer: Major components are shown. (Source: GPI lab)

The working principle of oil drum skimmer, as well as other absorption based devices,

is based on surface energies of hydrocarbon, water and skimmer material. To obtain water-

free oil, the material must have good oil selectivity. THANGTONGTAWI [5] had studied theeffect of surface energies on oil selectivity and concluded that oil selectivity of the material

depends on the difference between its critical surface tension (see chapter 2) and the

superficial (surface) tensions of hydrocarbon and water.

Water normally has higher superficial tension (around 72 dyne/cm, depending on the

temperature) than oil (25 – 40 dyne/cm). The diagram in fig. 3.2.1-2 shows surface energy of

water, oil and various materials. Adhesion of oil or water at the material surface can be

explained in term of the adhesion work (see chapter 2, eq. 5.2.5) as shown in table 3.2.1-1. If

the adhesion work of oil on solid surface in presence of water (Wadh(so)w ) is greater than that

of water on the surface in presence of oil (Wadh(sw)o), the oil film will adhere to the skimmer

surface and not be replaced by water film when the skimmer is rotated until the oil film

submerges in water. Thus, it still adheres to the surface when it is lifted from the liquid and

then removed by the scraper.

From this concept, the oil selectivity of materials can be summarized as follows,

• Material of high surface energy (or critical surface tension), such as stainless steel

(γ > 72 dyne/cm), tends to be adhered by water, rather than oil.

• Material that have the surface tension in the vicinity of oil’s, such as

polyvinylchroride (PVC), polypropylene (PP), tends to adhered by oil, rather than

water. It can be adhered by water if the oil film is not present. However, it willstart recovering oil once the oil is present again.

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• Material that has very low critical surface tension (lower than surface tension of

oil), such as PTFE and fluorocarbon variations, is proven to have very good oil

selectivity since its surface energy is so low that it is hardly adhered by water.

When used as a skimmer material, it recovers only oil and hardly or does not

recover water.

2010 30 40 50 60 70

PTFE

(19)PP

(30)

PVC

(39)

Water

(72)Stainless steel

(> 72)

25 35

Material of low

surface energy

Material of high

surface energy

oil

Surface energy

(dyne/cm)

Fig. 3.2.1-2 Surface energy or superficial tension of materials, oil and water

Table 3.2.1-1 Work adhesion and contact angles of oil, water and various materials

MaterialContact angle of oil

drop in water (θ)

Wadh(so)w =

(γow(1+cos θ))

Wadh(sw)o =

(γow(1+cos 180−θ))

Stainless steel (SS) 124o 0.01543 N/m 0.05457 N/m

PVC 26

o

0.06650 N/m 0.0035 N/mPP 17o 0.0685 N/m 0.0015 N/m

PTFE 47o 0.0589 N/m 0.0111 N/m

Note: The oil used is kerosene. γ ow (at 20o C) = 35 dyne/cm.

It is interesting to note that the stainless steel, which is the most oleophilic material

(oil can spread over its surface), makes the worst oil selectivity. This, sometimes, causes

confusion since the device is, sometimes, called oleophilic oil drum skimmer . So, It should be

reminded that the device got its name from its oil selectivity, but the skimming material itself,

even though can considered as oleophilic (contact angle < 90o), is selected from its low

surface energy, rather than its oleophilicity.

3.2.1.1 Exposure history

Another important characteristic of material related to oil selectivity is the “exposure

history” or the order and duration of contact between solid and liquids. THANGTONGTAWI

study shows that,

Material of high critical surface tension

• Even the high critical surface tension material can remove oil if it is exposed to

pure oil first. Performance from SS, PVC, PP and PTFE skimmers in this case areabout identical. In case of SS, this does not seem to conform to the adhesion work

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The model will be valid when these conditions are satisfied, i.e.;

• Superficial tension of oil is in the range of 27 – 34 dynes/cm, which practically

covers all common oil.

• Capillary number (Ca = μo V/γo) is in the range of 0.2 – 1.0.

•

Oil density is around 0.79 – 0.83 kg/m3. Oil dynamic viscosity (μ) tested is

between 1.35x10-3 to 291x10-3 (N.s)/m2 (1.35-291 cp).

• Peripheral or tip velocity should not be greater than 0.8 m/s. To avoid water

entraining, velocity of 0.44 m/s or less is recommended.

• Recommended minimum immersion depth is 1.0-2.0 cm.

• Drum skimmer surface used for model development is polypropylene. But it is

proven to be valid for SS, PVC, and PTFE [5]. As shown in fig. 3.2.1-2.

Oil removal efficiency of the skimmer is usually 100%, if the conditions stated above

are satisfied.

100%tη = {3.2.2}

3.2.1.3 Influent parameters

Parameters that affects the performance of drum skimmer are as summarized below.

Graphical presentation of effect of various parameters on the performance of the skimmer is

shown in fig. 3.2.1-3.

1.

Diameter of drum

The oil productivity is proportional to drum diameter because it directly relates

to the skimming surface area. The larger the diameter, the bigger the area, thus the

productivity. However, the study on the oil film thickness on the surface of the drum [5]

shows that the diameter has only little effect, thus negligible, on the film thickness, which

direct relates to the skimmer performance. So the diameter of the drum could be selected to

suit the tank freeboard.

2. Length of drum

The oil productivity is proportional to drum length because, again, it directly

relates to the skimming surface area. The longer the drum, the bigger the area, thus the productivity. It does not affect the oil film thickness on the surface of the drum. So there is no

effect on the performance. However, the rotation of the drum will cause eddy current at the 2

ends of the drum. This turbulence will propel the oil film and prevent it to contact with the

parts of drum surface. If the drum is long, the area of eddy zone, compared to the entire length

of drum, will be small. So the length of drum will help improving the skimmer performance in

this sense.

3. Oil layer thickness

Oil layer thickness on the water surface will affect the oil productivity of the

skimmer when it is thinned out until it cannot supply the oil fast enough to the skimmer. Thenthere will be some part of skimmer that does not contact with the oil layer and has no

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productivity. So the overall productivity will drop. The layer thickness of 0.4 – 0.5 cm is

considered thick enough to ensure continuous supply of oil to the skimmer.

4. Immersion depth of drum

Immersion depth means the height of the part of the drum that is lower thanwater surface, measured from the bottom of oil layer. At immersion depth of 1-2 cm.

THANGTONGTAWI reported that this parameters does not practically affect the

performance of the skimmer. The author has tested at the immersion depth around 5 - 7 cm.

The result still confirmed THANGTONGTAWI’s conclusion.

5. Immersion depth of drum

Immersion depth means the height of the part of the drum that is lower than

water surface, measured from the bottom of oil layer. At immersion depth of 1-2 cm.

THANGTONGTAWI reported that this parameters does not practically affect the

performance of the skimmer. The author has tested at the immersion depth around 5 - 7 cm.The result still confirmed THANGTONGTAWI’s conclusion.

6. Roughness of drum surface

Surface roughness affects the contact angle, thus wettability, as described in

chapter 2. However, in case oil skimmer, this change is overshadow its affect on difficulty to

remove film from the drum surface. Concavity on the surface may cause some difficulty to

scrape the oil film off the drum surface even though the oil thickness may be increased by the

roughness. So it is recommended to use relatively smooth drum surface.

7. Velocity of drum

Rotating velocity directly affects the oil productivity as shown in eq. 3.2.2. The

higher the velocity, the higher the productivity. However, the velocity also governs the

entraining of water by the dynamic force. If the velocity is too high, the rotation of the drum

will draw the water up too fast until it can reach the scrapper blade and entrain with the

skimmed oil. It is recommended to use peripheral velocity (or tip speed) of 0.44 m/s or less to

prevent water entraining.

8. Viscosity of oil

Oil productivity, as well as the oil film thickness on the surface of the drum, will

increase if the viscosity of the oil increase, as clearly shown in eq. 3.2.1.

9. Superficial tension of water and interfacial tension of oil/water

Surfactant is usually present in oily wastewater. The presence of the surfactants

lowers the superficial tension of water and interfacial tension of oil/water. Effect of surfactant

on the skimmer operation can be divided into 2 cases, i.e.,

• When oil layer is present: The efficiency of the drum skimmer is proven to

be practically independent of the presence of the surfactant [5]. So change in

superficial tension of water and the interfacial tension of oil/water does not

affect the performance of the skimmer.

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• When oil layer is absent: After the oil is removed and the skimming surface

is exposed to water. The surfactant will lower superficial tension of water

until it is close to naturally interfacial tension of oil/water. So there is no

difference between oil and the water. Thus the skimmer will lose its

selectivity, even in the case of PTFE, and start recovering the water.

O i l P r o d u c t i v i t y ( P )

Tip speed

of drum

Increase D, L

Increase oil viscosity

0.8 m/s

(max of

model)

0.44 m/s

(recommended)

a) Oil productivity of various drum materials

when the oil layer is not a limiting factor [5]

b) Effect of parameters on drum skimmer

performance

Fig. 3.2.1-3 Influent parameters on drum skimmer performance

3.2.2

Design calculation and design consideration

1 Drum skimmer sizing

The size of the skimmer can be calculated by eq. 3.2.1. If oil concentration or

quantity of inlet oil is known, it could be used as required oil productivity of the skimmer.Then, the oil productivity, geometry of tank (width, length), tank freeboard and available

installation space of the skimmer and oil outlet pipe should be taken into account in order to

select a suitable size of the skimmer.

Energy requirement of the skimmer is the energy for driving the skimmer. It can

be calculated by simple product of torque and speed. The torque required depends on the

structure, weight and size of the drum.

2 Design consideration

2.1

Limitations of the equation

The mathematical model of drum skimmer (eq 3.2.1) is valid only under its

limitations shown in section 3.2.1. Application of the model beyond its limitation may cause

unpredictable error.

2.2 Practical design consideration

Besides the limitations of models shown in section 3.2.1, there are some

assumptions or operating condition that affect the performance of the skimmer but cannot be

expressed in the form of equation. To design a skimmer, these assumption and precaution, as

described below, should be taken into account to ensure good performance of the skimmer.

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1) The model is developed under the assumption that the scrapper can

totally remove or scrape the oil film from the drum surface. So in the

real situation, scrapper should be designed properly to make sure that

it will not be a limiting factor in the operation. Scrapper should be

made of flexible material to ensure its close contact to the entire

length of the drum. However it should have good abrasive resistance.

2) The oil productivity in eq. 3.2.1 is valid under the condition that the

oil layer is not the limiting factor and the entire length of drum can

contact to the oil film. To ensure these condition, the following

precaution should be considered;

•

The drum should be properly sized to accommodate the inlet oil

quantity. So it can operate continuously without the problem

about lack of oil layer.

• Automatic control should be provided to stop the skimmer when

the oil layer in the tank is too thin to avoid the recovery of water,

esp. when high or moderate critical surface tension is used asskimming material, or when there is a risk of the presence of

surfactant in wastewater.

•

If possible, the skimming surface should be of low critical

surface tension material, such as variants of flouorocarbon, to

guarantee good oil selectivity and avoid exposure history

problem. Critical surface tensions of certain materials are listed in

table 3.2.2-1.

Table 3.2.2-1 Critical surface tensions of certain materials [42]

Materialγc (dyne/cm, 20 oC)

Poly(1,1-dihydroperfluoroctyl methacrylate) 10.6

Polyhexafluoropropylene 16.2

Polytetrafluoropropylene 18.5

Polytrifluoretylene (PTFE) 22

Poly (vinylidene fluoride) (PVDF) 25

Poly(vinyl fluoride) 28

Polyethylene ({PE) 31

Polytrifluorchloroethylene 31

Polystyrene 33

Poly (vinyl alcohol) 37Starch 39

Poly (methylmethacrylate) 39

Poly (vinyl chloride) (PVC) 39

Poly (vinylidene chloride) 40

Poly (ethylene terephthalate) 43

Cellulose 45

Poly (hexamethylene adipiamide) 46

•

Operation of the skimmer can cause eddy current around the ends

of the drum that causes the oil layer in this area vanished quicker

than other area. It results in non-productive zone of the skimmer(see fig. 3.2.2-1). To avoid this, the oil layer should be kept at

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3.3.1.1 Mathematical model of disc skimmer

Mathematical model of oil disc skimmer, proposed by THANGTONGTAWI, was

derived from dimensional analysis approach, using Buckingham Pi theory under a wide range

of material and wastewater properties as well as operating parameters. The model is as shown

in eq. 3.3.1

0.332g

1.17I0.452

o ν1.212 N1.2581.328D

P = {3.3.1}

Where P = Oil productivity of two sides of the skimmer (m3/s)

D = Diameter of skimmer (m)

N = Rotational speed of the skimmer (rev/s)

νo = Kinematics viscosity of oil (m2/s)

I = Immersion depth of the skimmer (m), I ≤ D/2.g = Gravitational acceleration (m/s2)

γo = Superficial tension of oil (kg/s2 or N/m = 1000 dyne/cm)

The model will be valid when these conditions are satisfied, i.e.;

•

Superficial tension of oil is in the range of 27 – 34 dynes/cm, which practically

covers all common oil.

• Capillary number (Ca = μo V/γo) is in the range of 0.04 – 3.6.

• Oil density is around 0.79 – 0.83 kg/m3. Oil dynamic viscosity (μ) tested is

between 1.35x10

-3

to 291x10

-3

(N.s)/m

2

(1.35-291 cp).• Peripheral or tip velocity should not be greater than 1.13 m/s. To avoid water

entraining, velocity of 0.5 m/s or less is recommended.

• Disc skimmer surface used for model development is PVC. But it is proven to be

valid for SS, PP, and PTFE [5].

The major difference between drum and disc model is that the disc model is the

function of immersion depth while this parameter hardly affects the drum skimmer

performance.

Oil removal efficiency of the skimmer is usually 100%, if the conditions stated above

are satisfied.

100%tη = {3.3.2}


Parameters that affect the performance of disc skimmer are identical to that of the

drum skimmer, as described in section 3.2.1.2, except the immersion depth. Graphical

presentation of effect of various parameters on the performance of the skimmer is shown in

fig. 3.2.1-2.

Immersion depth of disc skimmer, in this case, represents the depth of a part of the

disc that is under the liquid free surface. From eq. 3.3.1, it shows that oil productivity incerase

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with increase in the immersion depth. However the immersion depth is limited by the

diameter of the disc (I ≤ D/2)

3.3.2 Design calculation and design consideration

1

Disc skimmer sizing

The size of the skimmer can be calculated by eq. 3.3.1. If oil concentration or

quantity of inlet oil is known, it could be used as required oil productivity of the skimmer.

Then, the oil productivity, geometry of tank (width, length), tank freeboard and available

installation space of the skimmer and oil outlet pipe should be taken into account in order to

select a suitable size of the skimmer.

Like the drum skimmer, energy requirement of the skimmer is the energy for

driving the skimmer. It can be calculated by simple product of torque and speed. The torque

required depends on the structure, weight and size of the drum.

2 Design consideration

2.1 Limitations of the equation

The mathematical model of disc skimmer (eq 3.3.1) is valid only under its

limitations shown in section 3.3.1. Application of the model beyond its limitation may cause

unpredictable error.

It must be noted that the oil productivity from eq. 3.3.1 is for two sides of the disc. If scrapper is installed at only one side of the disc, the productivity can be safely

assumed to be 50 % of the value from eq. 3.3.1. Productivity of several discs are the product

of the result from eq. 3.3.1 and the number of the disc “n”.

2.2 Practical design consideration

Like the case of drum skimmer, besides the limitations of models shown in

section 3.3.1, there are some assumptions or operating condition that affect the performance

of the skimmer but cannot be expressed in the form of equation. The precaution proposed for

the drum skimmer can also be applied for the disc skimmer. Like the drum skimmer,

operation of disc skimmer also results in non-productive zone of the skimmer, starting at the

axis of the skimmer (see fig. 3.3.1-1), when the oil layer is almost totally recovered. To avoid

this, the oil layer should be kept at certain thickness to cope with this effect. The thickness of

1.0 cm is considered safe [5].

3.4 Productivity comparison between drum and disc skimmer

To compare the productivity of drum disc skimmer, THANGTONGTAWI had

proposed the alternative model of the disc skimmer (eq. 3.4.1) that has the same exponents as

the drum skimmer except for that of geometric parameters (D, L, I).

( ) ⎥⎦⎤

⎢⎣⎡ −−= 54.2)5.0(54.25.0

0.514

g

0.486o ν

1.5413.464NP I D D {3.4.1}

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III-59

Chapter 4 Decanting

4.1 General

Decanting or sedimentation is the most basic separation process. Its working principle

bases only upon properties of oil and water, which tend to separate from each other naturally.This process is widely used, even becomes legal standard for some industries, such as

refineries in USA. Because of its working principle, which bases on natural unadapted

properties, decanting is suitable for separating oil in form of big oil drop or primary emulsion.

There are many variations of decanting process, however they can be categorized into 2

groups, i.e.,

• Simple decanter: This group of decanter is the most basic process. They may vary

in geometry and details of some components. But they all use the same working

principle of natural unadapted decanting. The well known example of this type of

decanter is API tank, as shown in fig. 4.1-1.

• Compact decanter: This group of decanter is the modified version of the first

group, intended to upgrade the capacity of the existing simple decanter. Or it can

be newly designed equipment. The objective of compact decanter design is to

enhance the efficiency of decanter, making it handle more capacity, using smaller

footprint. This can be achieved by the modification of decanter geometry, such as

the insertion of lamella plates. However, the working principle is still identical to

that of the simple decanter as, theoretically, there is no modification of any natural

properties. Examples of this type of decanter are shown in fig. 4.1-1. Among these,

GPI lab has developed one of the most compact decanter, called “Spiraloil”. Its

special features and technical design consideration will be presented hereinafter.

a) API tank (Source: Pan American

Environmental)

b) “Spiraloil” compact decanter c) Oil layer at the surface of API tank

Fig. 4.1-1 Examples of decanters

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d) Example of up-scale API tank with tank enclosure (Source: USFilter)

e) Graphical image of lamella plate decanter

(Source: USFilter)

f) Corrugated plate module of corrugated plate

decanter (Source: Dewaterworks)

Fig. 4.1-1 Examples of decanters (Con’d)

4.2 Simple Decanter or API tank

4.2.1 Working principles

Simple decanter, which is made well known and standardized by the American

Petroleum Institute (API), is the simplest oil-water separation process. Its working principle

bases on classical STOKES law (cf. Chapter 2). Concept of the operation of the process is to

provide sufficient time for oil droplets to float to the water surface and accumulate into oil

layer before they have a chance to flow out with the water at the water outlet. The equation

that governs the operation of the process is derived from comparing the time required for the

droplet to reach the surface with retention time of the tank (τ), as shown in eq. 4.2.1.

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Chapter 4 Decanting

III-63

• Theoretical limitation: Since the decanter’s working principle is based on

STOKES law, it can be applied only when the droplet behavior conforms to

the law. Thus, it can not be used with very small droplet sizes for they are

subjected to Brownian’s motion and their rising velocity are not governed by

STOKES law. Commonly, the simple decanter is used for primary emulsion

treatment (d ≥ 100 microns).

• Economic limitation: As stated before that the process is a non-accelerated

process, its required footprint or installation area may be unacceptable if too

small cut size is selected.

Thus, the suitable cut size will be considered by accounting for the 2 limitations

above. API recommends the cut size of 150 microns for API tank.

2. Decanter sizing

The size of the decanter can be determined, based on the equation in section

4.2.1, as follow:

Bottom surface area (S): The decanter size is based mainly on its bottom

surface area. In general case, it is identical to the tank surface area. Presence of some

structures or components, such as effluent trough or gutter or tank cover (at the water

surface), may affect the efficiency of the decanter. However, if these structures are present in

the ways that make the rising distance of oil droplets decrease, they will help enhancing the

efficiency. However, their effects are normally small, thus, negligible, unless they

substantially reduce the rising distance of oil drops. In latter case, the tank will become a

compact decanter, which will be described in the next section. Bottom surface area of the

simple decanter can be calculated from the rising velocity of the cut size, as shown in eq.

4.2.6. The example of relation between kerosene droplet size and its corresponding rising

velocity as shown in fig. 4.2.2-1.

⎟⎟ ⎠

⎞⎜⎜⎝

⎛ =

dcU

QS {4.2.6a}

c

c

dc

d gU

μ

ρ

18

2⋅⋅Δ= {4.2.6b}

Flow velocity (V): Flow velocity means the velocity of total wastewater along

the tank, determined from wastewater flowrate and cross sectional area of the tank. Using

high flow velocity may cause turbulent or eddy current, especially when the wastewatercollides to the far end of the tank. Turbulence in the tank may interfere the decanting of

droplets, as well as suspended solids, which are usually present in the wastewater. This may

cause carry-over of oil drop and suspended solids with the effluent of the tank.

API recommends that V should not be greater than 0.15 m/s or greater than

15V dc , whichever is smaller.

Water depth (D) and width (W): Theoretically, the efficiency of the tank does

not depend directly on these parameters. However, they have some effects on the tank

operation since they are ones of the parameters that govern the flow regime of the tank.

Furthermore, if they are not selected properly, they can cause adverse effect, such as eddy, orshort circuit.

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0

20

40

60

80

100

120

140

160

180

200

0 100 200 300 400 500 600 700 800

Cut size (micron)

H y d r a u l i c l o a d i n g r a t e

( ( m 3 / h ) / m 2 )

0

0.01

0.02

0.03

0.04

0.05

R i s i n g v e l o c i t y o f d r o p l e t ( m / s )

Fig. 4.2.2-1 Relation between rising velocity, hydraulic loading rate of simple decanter and kerosene droplet size

API recommends that the ratio D/W should not be smaller than 0.3. The value of

0.5 is recommended. The depth (D) should be in the range of 0.9 to 2.5 m.

3. Removal efficiency

To determine the removal efficiency, the graded efficiency (ηd ) will be

calculated first by eq. 4.2.7a and b. Then, the total removal efficiency (ηt) can be determined

from eq. 4.2.7e.

For oil droplet size, d ≥ cut size,d c

%100=d η {4.2.7a}

For oil droplet size, d ≤ cut size,d c

%100⋅=dc

d

d U

U η {4.2.7b}

It must be noted that the graded efficiency described above is not yet accounted

for effect of flow splitting between water outlet flow and separated oil outlet flow. To

calculate graded outlet oil concentration, the effect must be taken into account, as shown ineq. 4.2.7c.

od d

out

d C Q

QC )1( η −= {4.2.7c}

Qout is outlet flow at treated water outlet port of the process. Qout is calculated

from difference between inlet flow and separated oil (in relatively pure condition) as shown

below.

d

d

d

od d

out

C Q

QQ ρ

η ∑ ⋅

−=

max

min

)(

{4.2.7d}

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Chapter 4 Decanting

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( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η {4.2.7e}

ηt = Total Removal efficiency of the tank

ρd = Density of dispersed phase, which is oil, for oily wastewater

Cod = Inlet concentration of the droplet diameter “d”

4. Energy required

The simple decanter does not require extra energy to make it function. The

energy is required only to feed the water into the tank, then the water will flow, naturally,

through the tank by gravity. Pressure drop across the tank and piping system depend on tank

and piping design. This pressure drop can be calculated by general hydraulic equations, such

as Darcy-Weisbach’s, Manning’s, or Hazen-William’s equation, thus will not de described

here.

4.2.3 Design considerations

1.

Limitations of the equations

The equations described above are developed from the following assumptions.

Thus, it is necessary to ensure that these assumptions are valid when design your decanter.

1) Reynolds number, Re, of droplet is between 10-4 to 1, which is the range


c

d c d U

μ

ρ ⋅⋅=Re {4.2.8}

2) The oil droplets are uniformly distributed across the cross section area of

the tank, which can be achieved by proper design of inlet chamber.

3) The oil droplet is spherical, which is normally true.

4) For droplets smaller than 20 microns, they are subjected to Brownian

motion and cause error in the prediction of the efficiency. So it is

recommended to avoid using the decanter for the wastewater with the

majority part of oil droplets smaller than 20 microns. However, if these

small droplets are the minority part of pollutants, the models can be used to

predict the efficiency without any harm because its prediction is usually

lower than observed value, thus make the prediction result on the safe side.

2. Safety factors

Since the design equations are simplified by many assumptions, it is

recommended to provide some safety factors to the sizing, calculated from the equations, to

cover some unexpected effects such as short circuit flow or local turbulent flow.

API recommends the safety factor for turbulent flow (Ft) as the function of

(V/U), as shown in eq. 4.2.9. U represents hydraulic loading rate or overflow rate, based ontotal flow and bottom area. For effect of short circuit, API recommends the safety factor (Fs)

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of 1.2. Then the total safety factor (F), by API recommendation, is the product of Ft and Fs

(eq. 4.2.9c). Factor F will be used to multiplied the value of S, calculated from eq. 4.2.6.

9617.0)(0355.0)(0005.0 2 ++−=U

V

U

V Ft {4.2.9a}

t st F F F F ⋅=⋅= 2.1 {4.2.9b}

4.2.4

Construction of simple decanters

There are many variations of simple decanters, as shown in fig. 4.2.4-1. The most

famous one is API tank, which is the rectangular tank. However, they use the same working

principles, can be calculated by the same equations and consists of relatively the same

components.

To design the decanter, besides the sizing stated above, proper details of construction

of decanter components are also important to guarantee good efficiency. Design

considerations for important components of decanter are described hereby.

1. Inlet chamber

Inlet section, as shown in fig. 4.2.4-2, is an important of decanter for it helps

assuring that uniformly distribution of oil droplet is achieved. For this purpose, the inlet

chamber should be equipped with baffles or energy dissipation devices or structure. Widely

used structures include vertical columns, perforated wall or vertical partition. Design of inlet

section is a state of art process. So it is recommended to study the successful design from

many references and adapt to fit with the condition considering.

2. Separation section

Sizing of this section is obtained from the equations. In this section, not only the

oil will be separated, suspended solids will also settle. So sludge hopper or sludge draw-off

pipe, or other provisions for sludge removal should be provided. Geometry of this section

should be as recommended in the previous section to ensure good hydraulic condition. This

section may be covered, if necessary, to prevent accidental ignition and to prevent the loss of

volatile hydrocarbons by evaporation. Sludge hopper, sludge scrapper and surface skimmer,

should be provided, as shown in fig. 4.2.4-2.

3. Effluent and oil removal devices

Effluent and oil will be removed at the downstream end of the tank. Normally oil

retention underflow baffle is installed to prevent the oil to flow out with the effluent. API

recommends that this baffle should be installed with a maximum submergence of 55% of the

water depth and should be located as close as possible to the oil removal device. The baffle

should be extended to the top of the tank or, at least, higher than water surface.

For oil removal devices, in small unit, the weir or slotted pipe is sufficient. For

upscale tank, those simple devices may draw the water off along with the oil. So the separated

oil still contains some water, and may not be suitable for downstream reuse or recycle

process. In this case, the device with more selective property, such as rotating slotted pipe or

oil skimmer, is required. There is a chapter in this book, devoted to oil skimming process.

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For effluent, it is normally removed from the tank by a weir. In some small units,

bell mouth pipe is acceptable. Design consideration for effluent removal device is that it

should be of sufficient size to prevent undesired turbulence and provide good flow

distribution in the tank. Normally, the weir across the width of the tank is sufficient.

a) Example of up-scale simple decanter with inlet diffuser wall, equipped with

mechanical skimmer (Source: Monroe)

b) Example of small to medium size simple decanter with simple elbow type inlet

diffuser and weir for collecting oil (Source: Pan American)

Fig. 4.2.4-1 Variations of simple decanters

a) Graphic image shows important components of API tank (Source: US filter)

Fig. 4.2.4-2 Important components of simple decanter

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Figure. 4.3.1-2 “Spiraloil” decanter a) Simple spiral b) Mixed spiral

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 10 20 30 40 50 6


R e m o v a l e f f i c i e n c y ( % )

0

1'1 3'

2 2'

3

V = 1.6 cm/s (3, 3')

V = 0.8 cm/s (2, 2')

V = 0.4 cm/s (1, 1')

Fig. 4.3.1-3a Comparison between observed efficiency (1',2',3') and predicted efficiency (1,2,3) for Simple Spiral

"Spiraloil" decanter

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 10 20 30 40 50 6


R e m o v a l e f f i c i e n

c y ( % )

0

1 (V = 0.5 cm/s)1'

2' 2 (V = 1.5 cm/s)

Fig. 4.3.1-3 Comparison between observed efficiency (1',2') and predicted efficiency (1,2) for Mixed Spiral "Spiraloil"

decanter

From the graphs, it shows that;

1.

Predicted values for cut size are relatively accurate.

2.

Predicted efficiencies of the droplets, smaller than cut size, are always lower

than observed value. This can be explained by the phenomena taking place

within the decanter, which will be described hereby.

3.

Correction factor for efficiency prediction of these small droplets may not beestablished accurately. However, the predicted cut size can be used to design the

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such as hydraulic force, head loss, etc., in the decanter. CHERID [4] recommends the value of

0.4-1.6 cm/s or 14.4-54 m/h., 2.6 to 10.6 times higher than simple decanter.


To determine the removal efficiency, the graded efficiency (ηd ) will becalculated first by eq. 4.3.6a and b. For graded outlet concentration (Cd ), flow splitting effect

between treated water outlet port and separated oil outlet flow must be taken into account, as

shown in eq. 4.2.7c and 4.2.7d. Then, the total removal efficiency (ηt) can be determined fromeq. 4.3.6c.

For oil droplet size, d ≥ cut size,d c

%100=d η {4.3.6a}

For oil droplet size, d ≤ cut size,d c

%100⋅=dc

d

d U U η

{4.3.6b}


( ) %1001 max

min

⋅⋅⋅= ∑d

d

od d

o

t C C

η η {4.3.6c}

ηt = Total Removal efficiency of the tankCod = Inlet concentration of the droplet diameter “d”

Qout = Treated water outlet flow (eq. 4.2.7d)

5.

Energy required

The compact decanter does not require extra energy to make it function. The

energy is required only to feed the water through the decanter. Pressure drop across thedecanter and piping system depends on decanter and piping design. This pressure drop can be

calculated by general hydraulic equations, such as Darcy-Weisbach’s, Manning’s, or Hazen-William’s equation, thus will not de described here. However, velocity through decanter is

relatively low, compared to velocity in pipe (0.6-2.5 m/s). So the estimated value of pressuredrop across the decanter around 0.5-1.0 m. is normally acceptable, regardless of its size and

configuration.

4.3.3

Design considerations

1.


The equations described above are developed from the following assumptionsand limitations. Thus, it is necessary to ensure that these assumptions are valid when design

your decanter.

1) The tank is operated under laminar flow regime. Reynolds number, Re, is between 10-4 to 1, which is the range that STOKES law is valid.

2)

The oil droplets are uniformly distributed across the cross section area ofthe tank, which can be achieved by the proper design of inlet chamber.

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III-81

2)(2

3

dp

d Int =η {5.2.1}

2. Sedimentation

Consider oil drops of diameter “d” flow along with the streamline. Because of itsdensity, the droplets will be subjected to rising velocity (U), calculated by STOKES law. When

they are far from the media, the rising velocity and flow velocity (V) will have the samedirection. When they come close to the media, the flow velocity will deviate, as shown by the

streamline, while the oil drops will be subjected to both flow velocity and their own rising

velocity. So the resultant velocity will not totally conform to streamline. And in some cases, itwill make the oil drops collide to, thus, sediment on the media. The efficiency factor for this

phenomenon can be calculated by eq. 5.2.2.

V

gd

V

U

csed

μ

ρ η

18

2Δ== {5.2.2}

3. Diffusion

For very small droplets (d < 5 microns), They will be subjected to Brownian’s

motion. These random motions can cause the droplets to collide to the media. The efficiencyfactor for this phenomenon can be calculated by eq. 5.2.3. K , in this equation, represents the

Bolzmann constant and T represents the absolute temperature.

3/2

9.0 ⎟⎟ ⎠

⎞⎜⎜⎝

⎛

⋅=

dpV d

KT

c Diff

μ η {5.2.3}

4.

Combined efficiency of step1 : Interception

From steps 1 to 3, we can calculate the efficiency factors of each transport phenomena for single collector. Theoretical efficiency factor of interception step for single

collector is the summation of the efficiency factors of those three transport phenomena, as shown

in eq. 5.2.4. From the equation, it shows that, at the same operation condition, the theoreticalefficiency factor of the single collector will vary with the droplet diameter, as shown in fig. 5.2.1-

2.

Diff Sed Int theo η η η η ++=

Thus

3/22

2

9.0)(2

3

18 ⎟⎟ ⎠

⎞⎜⎜⎝

⎛

⋅++

Δ=

dpV d

KT

dp

d

V

gd

cctheo

μ μ

ρ η {5.2.4}

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1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

0.01 0.1 1 10 100


E f f c i e c n c

y f a c t o r

Diffusion efficiency factor Interception efficiency factor

Sedimentation efficiency factor Theoretical efficiency factor

Fig. 5.2.1-3 Relation between oil droplet diameter and efficiency factors of each

transportation phenomena

From the graph, the range where the theoretical efficiency factors are minimal is between 0.25 to 5 microns. So the droplets in this range is theoretically the most difficult to

separate.

To adapt the efficiency of a single collector to the entire coalescer bed, we will

consider the simplified diagram of single spherical collector, placed in laminar flow regime, as

shown in fig. 5.2.1-3a. V represents the flow velocity. The fraction of wastewater flowing pass

the single collector will be the flow that passes through the projected area of the collector (q), asshown in eq. 5.2.5a. Then, some oil drops in this fraction of the wastewater will be intercepted bythe collector. The quantity of intercepted oil drops of the single collector (c’) will be calculated

from the theoretical efficiency factor, as shown in eq. 5.2.5b.

V d q p ⋅= 2

4

π {5.2.5a}

C V d c ptheo ⋅⋅⋅= 2

4'

π η {5.2.5b}

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III-83

q = Vπd 2/4

V

d p

Collectorsize =d p,

Void ratio = ε

V

H

IN:

Micro drop

Dia. = d

OUT:

Large drop Dischargescreen

Inletscreen/support

V

a) b)

Fig. 5.2.1-4 Schematic of a single collector and the entire bed of coalescer

C is the inlet concentration of oily wastewater. For the entire coalescer bed, we will

consider a very small slice of bed of the height dH (see fig. 5.2.1-3b). The number of collector

particles in this slice can be calculated from the cross sectional area of bed (Ao), the size of

collector (d p) and the void ratio of the bed (ε), as shown in eq. 5.2.5c.

Then, the total concentration of intercepted oil for this slice of bed will be equal tothe product of c’ and the number of collector particles. However, not all of the intercepted oil

drops will adhere to the collector. So the probability coefficient (α) will be applied to adapt the

quantity of intercepted oil drops to the quantity of adhered oil drops (c”), as shown in eq. 5.2.5d.

The number of collector particles in the slice dH3

6

)1(

p

o

d

AdH

π

ε −= {5.2.5c}

3

2

6

)1(

4" p

o ptheo

d

AdH

C V d c π

ε π

η α

−

⋅⋅⋅⋅⋅= , α < 1 {5.2.5d}

If dC represents the concentration of oil reduced after passing through the bed dH,

then we have got eq. 5.2.5e and f;

"cdC AV o =⋅⋅− {5.2.5e}

3

2

6

)1(

4 p

o ptheoo

d

AdH C V d dC AV

π

ε π η α

−⋅⋅⋅⋅⋅=⋅⋅− {5.2.5f}

Therefore,

dH d C

dC theo

p

αη ε )1(2

3−−= {5.2.5g}

Integration of eq. 5.2.5g will give the value of the oil concentration reduced by theentire bed, as shown in eq. 5.2.6.

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III-84

ptheo

o d

H

C

C αη ε )1(

2

3)log( −−= {5.2.6}

Thus, the theoretical removal efficiency of the coalescer, based on step 1:“Interception”, can be written as shown in eq. 5.2.7.

%1001%1001)()1(

2

3

, ⋅⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −=⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛ −=

⋅−− theodp

H

o

theod eC

C η α ε

η {5.2.7}

5.2.1.2 Step 2: Adhesion and coalescence

After being intercepted from step 1, the oil droplets will be separated from the wastewater

stream if they can adhere to the surface of the collectors. After that, in good coalescers, theadhering oil drops will coalesce to each other and flow separately from the water stream, as oil

stream within the bed. Phenomena taking place in this step is shown in fig. 5.2.1-4. So themechanism in this step depends mainly on the wettability of the bed. AURELLE had tested the

effect of wettability, using hydrophilic and olephilic material as coalescer bed for secondary o/w

emulsion treatment. The result shows that:

• For Oleophilic material: The oil droplets will adhere to the collector surfaces then

form the oil film around the collectors. The oil films will accumulate in the bed until itreaches saturate level at certain height of the bed, called “ critical height” (Hc). Afterthat the oil will start to flow as a separated oil stream, called “ channeling”.

• For Hydrophilic material: The oil droplets will be trapped in the void between

collectors. These trapped oil droplets will, then, be play the role of collectors by their

own to intercept the following oil droplets. Then they will coalesce into bigger dropsand flow through the void with the wastewater stream.

Even though both materials can cause coalescence, from test result, the oleophilic material

yields good efficiency up to higher range of flow velocity. It means that oleophilic bed coalescer

can be used at higher loading rates, thus makes it more compact in size. So it is recommended touse oleophilic material as the bed for direct emulsion treatment.

5. 2.1. 3 Step 3: “Salting out” or enlargement of coalesced oil

The coalesced oil that flows through the bed in the manner of channeling will finally

reach the topmost of the bed. Then it will leave the bed for the water surface. In good coalescer,the coalesced oil will leave the bed in the form of big oil drops (diameter 2-3 mm or more).Characteristic or size of the oil drops that leave the bed depends on the phenomenon, taking place

at the top surface of the bed. AURELLE has studied this phenomenon, comparing between

oleophilic material and hydrophilic material. The result shows that:

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Chapter 5 Coalescer

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a) “Oil mousse” forming. Note that contact

angle < 90o.

b) Re-fragmentation of oil when the

mousse raptures

Oleophilic “salting out” surface

c) Formation of big oil drops. Note that contact

angle > 90o.

d) Oil jet and re-fragmentation of oil at high

velocity or high oil concentration

Hydrophilic “salting out” surface

Fig. 5.2.1-6 Phenomenon in step 3: “Salting out” or enlargemant of coalesced oil

• For Hydrophilic material: The drip points will appear as well. But the oil will not

form the film over the collector surface. But the film will locate between the collectors

and will grow to big oil drops and, then, be snapped off as big oil drops, withoutforming oil mousse. However , at high flow velocity or high concentration of oil,hydraulic force from water flowing out of the bed will be high. The oil will be

snapped off as a jet of oil and then, from the high hydraulic force, will be “ re-

fragmented ” to small droplets.

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III-87

From the result described above, it shows that efficiency of this step depends on 4

parameters, i.e., wettability of discharge surface, flow velocity or empty bed velocity, interfacial

tension, and concentration or ratio of oil to water . To optimize the efficiency of this step,AURELLE suggestd the following methods:

• Design the coalescer at the proper velocity to avoid the re-fragmentation effect.

• Use hydrophilic material as the top layer of the bed or use top grill of hydrophilic

material, to avoid mousse formation. At the same removal efficiency, it is proven thatthe bed with hydrophilic material on the top layer can be operated at higher velocity

than that with the oleophilic top layer.

5.2.1.4 Comparison between observed efficiency and theoretical efficiency

The 3 steps mechanisms, proposed by AURELLE, can effectively describe the phenomena taking place within the coalescer bed. However, to apply it for efficiency prediction,

we have to use many assumptions to simplify them. The most important assumption is that the

efficiency mechanisms in steps 2 and 3 are optimized, so their efficiency is 100%. It means all ofoil that has been intercepted and adhered to collectors in step 1 can be separated. So the removalefficiency of coalescer can be calculated by eq. 5.2.4 and 5.2.7.

AURELLE had studies the relation between observed efficiency (α.ηexp) and thetheoretical efficiency and found that the observed values are quite different from the calculated

value in complex fashion, as shown in fig. 5.2.1-6. Relation between observed efficiency and

theoretical efficiency, suggested by AURELLE, is shown in eq. 5.2.8a. So the theoretical

efficiency in eq.5.2.7 can be modified by replacing αηtheo with α.ηexp. The efficiency of granular

bed coalescer, then, can be calculated by eq.5.2.8b.

5143.0

exp )(5484.0 theoη η α =⋅ {5.2.8a}

%1001%1001)()1(

2

3exp

⋅⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −=⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛ −=

⋅−− η α ε

η dp

H

o

d eC

C {5.2.8b}

AURELLE’s model is developed under these following assumptions and conditions:

• The key assumption of this model is that mechanisms in step 2 and step 3 of thecoalescer are optimized.

•

The shape of the collector is relatively spherical. The size of the collector tested (dp)

is between 0.2 – 1 mm.

• The collector shall be wetted by dispersed phase. In case of direct (oil in water)

emulsion, the collector, then, shall be oleophilic. For inverse emulsion, oleophilic

resin is recommended.

• Range of empty bed velocity (V) shall be not greater than 0.35 cm/s (12.6 m/h)

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DAMAK [9] used HAPPEL’s theory to adapt AURELLE’s theoretical efficiency

equation, however, the accuracy is not improved. So it seems that the mechanism taking place in

the coalescer bed is so complex that it cannot be simplified to develop an accurate theoretical

model. Thus, when the exact theoretical based model can not be found. DAMAK proposed an

empirical equation for coalescer efficiency prediction, based on the dimensional analysis, as

shown in eq. 5.2.10. Typical characteristic curve between efficiency and droplet size is shown infig.5.2.1-7.

%100)()()()()(58.0 09.009.008.0

/

12.02.0 ⋅⎟⎟ ⎠

⎞⎜⎜⎝

⎛ Δ= −

cc

d

wo

c

d

dpV

dp

H

dp

d

ρ

ρ

μ

μ

γ

ρ η {5.2.10}

The model is developed under these conditions i.e.;

• The model is tested at the range of dp from 0.36 to 0.94 mm. and interfacial tension

(γow) of 11 to 42 dyne/cm. (T.I.O.A, Heptane, Anisole, Toluene and Kerosene)

•

The velocity (V) tested is in the range of 0.09 to 0.54 cm/s.

• The density difference between dispersed phase (oil) and continuous phase (water)

(Δρ) is between 83 to 314 kg/m3.

• The bed used is spherical glass bead with silicon coated to achieve oleophilicity.

• The inlet concentration of hydrocarbon tested is around 1,000 mg/l.

• If the result from eq. 5.2.10 is greater than 100%, it will be rounded up to 100%.

Verification result, using AURELLE’s experimental data, confirms that DAMAK’s model

can predict the removal efficiency with only ±10% error. It implies that the model is also valid at

the operating condition tested by AURELLE. From these test conditions, it seems that thisempirical model covers the range of the oily wastewater commonly found in real situation. Thus,

it is recommended to use this model (eq.5.2.10) for granular bed coalescer calculation.


Main parameters that affect the efficiency of the granular bed coalescer include:

1. Bed height (H)

Typical relation between the bed height and the removal efficiency is as shown in

fig. 5.2.1-7. From the graph, the efficiency of coalescer will increase with increasing height, thenit will stay relatively constant. This height is called “ critical height (H c )”. The occurrence of

critical height can be described by phenomena in step 2 : adhesion- coalescence, as described

before in section 5.2.1.2. If the bed height is shorter than the critical height, it can be said thatthere is not enough accumulated oil film to trap the oil droplets and provide continuous coalesced

oil stream to form perfect “channeling”. Hc depends on wettability, roughness and size of media.

From eq. 5.2.10, it shows that the efficiency is proportional to H0.12

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Droplet size (d)

Efficiency (η)

100%

Lower limit of

the model:

10 microns

Bed height (H)

Efficiency (η)

Increase V, d pMore hydrophilic

Less roughness

Hc

Fig. 5.2.1-8 Typical relation between efficiency of granular bed coalescer and various

parameters

2. Size of collector or media particle (dp)

The effect of the size of media is shown in fig. 5.2.1-7. Under the same operatingcondition, the smaller the collector size, the better the efficiency. From eq. 5.2.10, it shows that

the efficiency is proportional to d p-0.4

3. Flow velocity or empty bed velocity (V)

The effect of velocity is relatively small, compared to other parameter. From eq.

5.2.10, it shows that the efficiency is proportional to V-0.08

. However, this is true only within the

valid range of the model. At higher velocity, mousse or jet formation will occur, thus theefficiency will drop rapidly and no longer conform to eq. 5.2.10. The velocity that the mousse or

jet starts appearing is called “critical velocity”. It is recommended to use velocity not more than0.54 cm/s to avoid mousse and jet formation.

4. Wettability of bed material

The effect of wettabiblity of media is shown in fig. 5.2.1-7. It is recommended to

use oleophilic material as the coalescer bed with the thin top layer of hydrophilic material as drip

point surface.

5. Ratio of oil to water

Even though this parameter is not included in eq. 5.2.10, but it is an important

parameter that limit the working range of coalescer. In fact, the model in eq. 5.2.10 is valid for oil

concentration not greater than 1,000 mg/l. Higher oil concentration will result in mousse or jet

forming, which will greatly lower the efficiency of the coalescer. To expand the working range ofgranular bed coalescer, it is necessary to modify basic granular bed coalescer by additional

installation of oil guide, which will be described in the following section.

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III-91

6. Interfacial tension and presence of surfactants

Surfactant will lower the interfacial tension, then make the oil droplets more

stabilized. This leads to poor adhesion between droplets and surface, ineffective collision

(collision without coalescence), and re-fragmentation of oil drops. So the presence of surfactantdirectly limits the efficiency of step 2 “adhesion-coalescence”. To optimize the efficiency of step

2, it is recommended to destabilize (or breaking or cracking) the emulsion before sending to thecoalescer.

7. Temperature

Properties of oil and water, such as viscosity, change with temperature. Sotemperature is inevitable an important parameter that affects coalescer efficiency. Then it is

important to design the process by taking the possible range of temperature into account. Normally, the efficiency will, more or less, increase with the temperature. The equations in this

section are developed under the temperature range between 15 to 25oC, which is the general

practical operating range.

8. Surface roughness of bed material

Surface roughness affects adhesion of oil on the surface of the solid, as shown in

chapter 2. The roughness makes the wettablity of the surface more eminent. So oleophilic

material will show more oleophilicity if its surface is rough. Contact angle of oil on the material

surface will be lower. In this case, it helps promoting direct emulsion separation.

5.2.1.7 Pressure drop

Pressure drop across coalescer bed (p), in metre, can be calculated by Kozeny-Carman’s

equation (eq. 5.2.11) (use SI unit, e.g. m, kg, second).

32

2)1(180

ε ρ

ε μ

⋅⋅⋅

−=

dpg

V H p c m {5.2.11}

All variables except porosity (ε) will be determined by designer. For the porosity of

coalescer bed, from many researches [3], [26], [27], it shows that bed porosity varies with beddepth and can be divided into 2 zones, i.e.,

• Lower zone or critical zone: This zone represents an effective zone of coalescer bed.

The maximum height of this zone is called “critical height (Hc)”. When bed height is

greater than the critical height, the efficiency will increase only slowly (from eq.5.2.10: η ∝ H

0.12). In this zone, the bed will be soaked with oil so the effective

porosity will be low.

• Upper zone: If the bed is higher than Hc, practically, all of oil will be trapped in

critical zone. Then in the higher zone, there will be enough oil in lower zone to flow

continuously through the bed in form of “channeling”. So the effective porosity in thiszone will be lower than critical zone.

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From data of various researches [3], [26], [27], it can be concluded that the pressure drop

of granular bed can be calculated by Kozeny-Carman’s equation, using the following

recommendations, i.e.,

• When Hc is known (from literatures, etc.), pressure drop lower and upper part of bedcan be calculated separately, using eq. 5.2.11 and corresponding H of each zone. For

example, if Hc is 0.1 m. and total bed height is 0.15 m, H for lower zone will be equalto Hc because Hc is lower the total height. And H for the upper zone will be 0.15 - 0.1

= 0.05 m.

• Recommended porosity for the lower (critical) part of bed (H<Hc) is between 0.14 to0.19.

• Recommended porosity for the upper part of bed (H>Hc) is between 0.23 to 0.30.

• If it is certain that H design < Hc, use single step calculation with ε = 0.14 - 0.19.

• However, Hc is usually unknown, then it is recommended to use the single step

calculation with ε = 0.13 and 0.23 to estimate minimum and maximum pressure drop,

respectively.

•

The value of ε described above can be used for the range of dp from 0.20 to 1.0 mm.

5.2.2 Design calculation

Design procedure for granular bed coalescer is based upon the equations, shown in the

previous section. To design the coalescer, the required cut size will be determined first. After that,the size of the coalescer can be calculated. Then, graded efficiency (efficiency of each size of

droplet) and, hence, the total removal efficiency can be determined. Calculation procedure for

each step is described below.

1. Cut size determination

The cut size can be determined from the degree of treatment required as well asfrom the limitation of the coalescing processes. The cut size determination from degree of

treatment is described in chapter 3. For the limitations of the process, it is mainly model

limitation. Since the model used for calculation is based on empirical data, it can be applied onlywithin its valid range. Extrapolation of model may cause unpredictable errors. The limitation of

model will be described in section 5.2.3. It should be noted that the cut size must be greater than10 microns since it is the lower limit of the model. For smaller droplets, the efficiency will be

very low and unpredictable.

2. Coalescer sizing

The size of the granular bed coalescer can be determined, based on the equation insection 5.2.1. The main equation for coalescer designed will be based on the empirical model, as

shown is eq. 5.2.10. Design cut size will be used to calculate the dimension of the coalescer by

assuming that the graded efficiency at the cut size is 100%.

%100)()()()()(58.0 09.009.008.012.02.0 ⋅⎟⎟ ⎠

⎞⎜⎜⎝

⎛ Δ= −

cc

d

ow

c

d

dpV

dp

H

dp

d

ρ

ρ

μ

μ

γ

ρ η {5.2.10}

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Dimension of the coalescer can be arbitrarily selected under the limitations of the

model, as shown in section. 5.2.3, to make eq. 5.2.10 consistent. However, it is recommended to

select the lowest possible media diameter and highest velocity for the first trial because it willgive the most compact diameter of the coalescer. If the result is acceptable, it can be fine-adjusted

to get the most suitable dimension. If the result is unacceptable, normally too big, it may be

necessary to increase the number of units.

Fig. 5.2.2-1 shows the result of calculation from eq. 5.2.10 at various cut sizes. The

calculation is based on kerosene-water emulsion, which may be used as a guideline for coalescer

size estimation. The collector diameter, used in the graph, is 0.35 mm.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

0 10 20 30 40 50 60

Cut size (micron)

B e d h e i g

h t ( m )

V = 1.94 m/h

V = 3.2 4m/h

V = 11.3 m/h

Fig 5.2.2-1 Relation between cut size and coalescer dimension

3.

Removal efficiency

To determine the removal efficiency, the graded efficiency (ηd ) will be calculated

first by eq. 5.2.10. If the result from eq. 5.2.10 is greater than 100%, then it will be rounded up to

100%.

It must be noted that the graded efficiency from the equation is not yet accounted for

effect of flow splitting between water outlet flow and separated oil outlet flow. To calculate

graded outlet oil concentration, the effect must be taken into account, as shown in eq. 5.2.12a.

od d

out

d C Q

QC )1( η −= {5.2.12a}

Qout is outlet flow at treated water outlet port of the process. Qout is calculated from

difference between inlet flow and separated oil (in relatively pure condition) as shown below.

d

d

d

od d

out

C Q

QQ ρ

η ∑ ⋅

−=

max

min

)(

{5.2.12b}

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( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η {5.2.12c}

ηt = Total Removal efficiency of the tankρd = Density of dispersed phase, which is oil, for oily wastewaterCod = Inlet concentration of the droplet diameter “d”

4. Pressure drop

Pressure drop (in metre) can be calculated from Kozeny-Carman’s equation (eq.

5.2.11). Recommended value of bed porosity (ε) and other criteria are as shown in section

5.2.1.7. For diluted wastewater, the values of μ and ρ can be replaced by those of water (μc, ρc).

32

2)1(180

ε ρ

ε μ

⋅⋅⋅

−=

dpg

V H p m {5.2.11}

5.2.3 Design consideration

1. Limitations of the equations

The equations described above are developed from the following assumptions andlimitations. Thus, it is necessary to make sure that these assumptions are valid when design your

coalescer.

1) Coalescer bed shall be oleophilic and relatively spherical in shape.

2) Tested size of bed media (dp) is between 0.20 – 1.0 mm. The larger the mediasize, the lower the efficiency.

3) Tested range of bed height (H) of the model is between 1 to 10 cm. However,

bed height as low as 1 cm is not recommended. The greater the bed height, thesafer the coalescer operation. However, it also results in higher pressure drop.

4) The velocity (V) should be in the range of 0.09 to 0.54 cm/s or 3.2 to 19.4 m/h.

5) Tested interfacial tension (γow) is between 11 to 42 dyne/cm or 0.011 to 0.042 N/m. (such as, T.I.O.A, Heptane, Anisole, Toluene and Kerosene)

6) Different density between dispersed phase (oil) and continuous phase (water)

(Δρ) is between 80 to 315 kg/m3(approx.).

7)

The equation is valid for droplet size (d) of 10 microns or bigger. For smaller

droplets, result from eq. 5.2.10 may not be accurate because it is beyond thedata that has been used to verify the model.

8) The model is valid for inlet concentration between 100 to 1,000 mg/l. At

higher concentration, mousse or jet formation may occur, resulting in

unpredictable decreasing of the efficiency.

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2. Construction and material selection

Granular bed coalescer consists of 2 major components, i.e., casing and bed.

1) The casing

The casing is the component that contains the bed and other importantappurtenances, such as wastewater inlet, wastewater outlet, oil outlet, clean out, etc. Researches

in GPI lab normally emphasize on working mechanisms and developing of a model so there is nodirect study on characteristic of the casing. However, because of the fact that the coalescer is

usually designed as a pressure vessel in the same manner as a pressure filter, then, casing or tank

construction criteria of the pressure filter can be readily applied to the coalescer. However, somedetails, such as oil outlet pipe, water outlet pipe and internal baffle should be adapted to ensure

good separation between oil and water. As outlined in chapter 4 “Decanting”, the internal baffleshould be installed in the manner that it can promote oil drop decanting, prevent short circuit of

oil drops to the water outlet pipe. The pipe and baffle arrangement shown in fig. 5.1-1 can be

used as a guideline for casing design.

2) The bed

From many GPI researches, it is recommended that resin is the most suitable

material for coalescer bed, because:

• It is widely used in many industries, and available in every country.

• It is produced in wide range of size and normally spherical.

• It can be coated to achieve required wettability.• Its cost is competitive.

• Its physical properties, such as hardness, etc., are also good.

Other materials that have been used as coalescer bed include glass beads, smallstainless steel balls. Material that is heavier than water, such as stainless steel, has an advantage

for it can be used without installation of top grille to prevent it from carry-over. So it can becleaned by backwash process or scouring process because the material is not retained by top

grille, then can be expanded or floated freely.

For wettability, oleophilic bed with thin layer of hydrophilic material on the

top or with hydrophilic top grille is recommended (see section 5.2.1.2). Guideline on

oleophilicity of materials is described in chapter 2. Some hydrophilic material that has goodmechanical properties can acquire oleophilic property by coating with proper substance, such as

silicone. Oleophilicity of bed may change with time from deterioration of the coating or reactionwith wastewater. It may need re-coating or replacement if decreasing in efficiency is

unacceptable.

5.2.4 Variations, advantage and disadvantage of granular bed coalescer

Variations of granular bed coalescer: There are several modifications of granular bedcolaescers, normally, on bed materials, such ad resin bed coalescer, glass bead bed coalescer.

There are 3 major modified granular bed coalescer studied at GPI lab, i.e., mixed bed coalescer ,

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down-flow coalescer and guide coalescer . The latter will be fully described in the next section.

Mixed bed coalescer is another modified form of granular bed coalescer, used for mixed

direct/inverse emulsion separation, which is usually found in liquid-liquid extraction process. In

mixed bed coalescer, the bed will consist of separate layers of oleophilic and hydrophilicmaterials, placed in series in the same column. From research [6], ratio of oleophilic and

hydrophilic material and order or configuration of column (upper hydrophilic layer/loweroleophilic layer or vice versa) depends on wastewater characteristic. So it is difficult to

determine the efficiency of the coalescer by fixed equation. In this case, it is recommenced to

perform pilot test to find optimum design criteria.

Furthermore, there are also variations of coalescers, based on flow patterns i.e., up-flowcoalescer and down-flow coalescer. The researchs conducted in GPI lab are generally based on

up-flow coalescer. For down-flow coalescer, the flow pattern in this case will be identical to that

of deep-bed filter. This type of coalescer is intentionally designed to use with the oily wastewaterthat contains suspended solids. The wastewater will be fed from the top of the bed. The oil will be

coalesced in the same manner as the up-flow coalescer. However, the coalesced oil will flow up

against the wastewater stream to the inlet water surface, then be skimmed out of the reactor. Thisflow patterns can eliminate the top grille that is used for preventing carry-over of bed media in

up-flow coalescer. This allows us to clean the bed by air scouring, back washing or any propermechanism, such as pneumatic pulsation that can make the bed move up or partially fluidize to

unclog the trapped solids. Working principles of this coalescer is generally identical to that of up-flow coalescer. However, there is not enough research data to develop the math model. So it is

recommended to use the equation of up-flow coalescer for roughly estimation of efficiency.

Anyway, the exact efficiency would be obtained from pilot scale testing.

Advantage: Granular bed coalescer has a major advantage in its compactness. Testedloading rate of coalescer is 3.2 – 19.4 m/h and it can be used with the droplet size from 10

microns while, for simple decanter, the loading rate is about 0.04 m/h for 10-micron dropletseparation.

Disadvantage: The bed of this type of coalescer has relatively low porosity (0.14-0.19).

So, at high loading rate, the pressure drop may be very high. Moreover, it can make the bed clog

relatively easily. So the granular bed coalescer is sensitive to the presence of suspended solids.

5.3 Guide coalescer


Guide coalescer is the modified form of simple granular bed coalescer. In guide coalescer,high-porosity oleophilic material, such as woven metal fiber or woven mesh, will be placed next

to downstream end of the granular and extended up to water surface. Coalesced oil drop will be

guided along this material until it combines with oil layer at the water surface. So, this material iscalled “ guide”. Structure of the guide shall be self-sustained or installed in perforated structure,

so the treated water can flow freely out of the guide structure, then be discharged from thecoalescer. The pictures of guide coalescer are shown in fig. 5.3.1-1.

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efficiently. To apply to higher concentration or beyond the limit stated above, bench

scale or pilot scale testing is highly recommended

This type of coalescer have been developed for 2 purposes, 1) to increase the hydraulic

loading rate of the granular bed coalescer, 2) to make it possible to use the granular bed with thewater containing very high concentration of oil, such as in liquid-liquid extraction process.


Steps of calculation, as well as cut size determination, for the guide coalescer is identical

to those of basic granular bed coalescer. However, there are some difference in details of sizing

and pressure drop calculation as described below.

1. Coalescer sizing

The size of guide coalescer can be calculated by eq. 5.2.10. For velocity less than

0.54 m/s, actual velocity will be used in the equations. However, if design velocity is greater than

0.54, the velocity of 0.54 m/s will be used, regardless of the actual velocity. The size from thecalculation can be, theoretically, used at velocity from 0.54 to 0.8 cm/s.


The removal efficiency can be calculated from the selected dimension, using eq.

5.2.10 and 5.2.12.

3. Pressure drop

Because of the fact that the “guide” in guided coalescer has relative high porosity

(0.9 approx.), then, The pressure drop is very low, compared to the granular part, and can be

negligible. So Kozeny-Carman’s equation (eq. 5.2.11) and recommended value of porosity fromsection 5.2.2 can also be used to predict pressure drop of guided coalescer.



The limitations in this case are identical to those of granular bed coalescer (see

section 5.2.3) except for the velocity and oil concentration, which will conform to section 5.3.1.

2. Material selection

For direct emulsion treatment, granular bed in guide coalescer shall be oleophilic

material. However, instead of top layer or grill of hydrophilic media, guide will be placed on thetop of the granular bed. The guide should be made of metal or rigid material and properly coated

to obtain oleophilic property. It should have high porosity and self-sustained structure because it

is not supported by the wall of the coalescer. If the selected guide is not self-sustained, perforated

oleophilic material shall be provided to support the guide. Commercial woven wire-meshes or

metal wool, such as MuitiKnit™, Knit meshTM

, 3MTM

, etc., can be efficiently used as a guide.

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5.4

Fibrous Bed coalescer


This type of coalescer uses high porous fibrous material, such as fibrous bottle brush, as a

bed to promote coalescing between oil droplets. Due to its high porosity, this type of bed ishardly clogged and can handle wastewater containing suspended solids efficiently. It also causesmuch less pressure drop than granular bed coalescer. However, fibrous element, which is

normally very small, may deflect at its tip, especially in large-scale unit, and causes unpredictablechanneling of untreated wastwater, then decreasing in efficiency.

From other point of view, this coalescer can be considered as a modified form of guide

coalescer that granular bed is removed and the guide is additionally used to intercept oil, besides

its role to provide coalesced oil flow channel.

Three basic steps for granular bed coalescer, proposed by AURELLE [3], can also be

used to describe phenomena taking place within the coalescer. However, mathematics models,

derived from dimensional analysis, are proven to be more accurate.

There are 2 main categories of fibrous bed coalescers, i.e., Simple fibrous bed coalescer

and dynamic (or rotating) fibrous bed coalescer, as shown in fig. 5.4.1-1. The latter is themodified form of the former, by installation of driving unit to drive the bed.

5.4.1.1 Simple fibrous bed coalescer model

This type of coalesceruses uses fibrous material, normally, in the form of “bottle brush”

as a coalescer bed. The brush has relatively high porosity, compared to granular material. So this

coalescer causes much lower pressure drop and is hardly clogged. Furthermore, from the three-

step phenomena of coalescer, described in section 5.2.1, it shows that the efficiency of coalescerwill increase if the size of the bed media is small. For fibrous bed coalescer, the size of fiber isaround 100- 200 microns, much smaller than granular media’s. By this way, the efficiency can be

improved.

GPI lab has been studied the possibility to use this type of material as a bed for sometimes. However, the researches on this type of coalescer are based mainly on its application and

design consideration, rather than model development. So there is no model proposed for this

coalescer. Anyway, these researches, especially the study of SRIJAROONRAT [10], providesufficient raw data to formulate an empirical model. This newly formulated model, which will be

called “SRIJAROONRAT’s model”, is as shown in eq. 5.4.1. The model has been verified, usingdata from MA’s and WANICHKUL’s researches, as shown in fig. 5.4.1-2.

( ) %100)(1)()()(5.104 694.035.018.018.077.0 ⋅⎟⎟ ⎠

⎞⎜⎜⎝

⎛ −= −−

D

H

D

d

D

d VD F

c

c

d ε μ

ρ η {5.4.1}

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a) Simple fibrous bed coalescer [11] b) Graphical image of dynamic fibrous bed

coalescer

c) Examples of “brush” d) Coalesced oil drops from dynamic fibrous bed

coalescer

Fig. 5.4.1-1 Fibrous bed coalescer (Source: GPI lab)

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Where d F = Diameter of fiber

d = Diameter of dispersed phase, in our case, oil

D = Diameter of coalescer bed, such as diameter of brushH = Height of bed, or bed depth

V = Empty bed velocity

ε = Porosity or void ratio of the bedμC = Dynamic viscosity of continuous phase, in our case, water

ρc = Density of continuous phases

The model is developed and verified under these conditions i.e.;

• 48 < Re < 1100. Re is the term (ρcVD/μc) in the equation.

• 1 < H/D < 10.

• Diameter of coalescer bed (D) tested is around 5.0 cm. Using bigger coalescer

diameter may cause deflection at the tips of fibers because of longer overhung length,

which may cause channeling of untreated wastewater and error in efficiencycalculation.

• The model is valid for droplet size (d) of 1 microns and greater.

• Empty bed velocity (V) used in the researches [10], [11], [16] is between 0.5 to 5.0cm/s (1.8 to 180 m/h). However available raw data used to verify the model is

between 0.5 to 2.0 cm/s. Using velocity > 2.0 cm/s may cause unpredictable error oncalculated efficiency.

• Fiber size (d F) used in the researches [10], [11], [16] is between 40 to 200 microns.

However available raw data used to verify the model is between 100 to 200 microns.

Using fiber size < 100 microns may cause unpredictable error on calculated

efficiency.• Void ratio of the bed (ε) is around 0.845 to 0.96.

• The model is valid for droplet size (d) of 1 microns and greater.

• The model is verified at inlet oil concentration up to 1000 mg/l. Applying the model to

the concentration > 1000 mg/l will cause underestimation of predicted efficiency, as

shown in fig. 5.4.1-2 for WANICHKUL’s data (C = 7950 mg/l) [11].

• The beds used in these researches vary from “bottle brush” type, simple spiral typeand combination of internal bed of “simple spiral” and concentric “coil spring–like”

external bed with the tip of the fibers pointed to the centerline. However, they are alloleophilic. There is some difference in efficiency between each type, but there is too

few data to make a conclusion. However, because of its rigidity, the “simple spiral in

coil spring- like” bed tends to operate more stable without decreasing in efficiencywith time, while others tend to be deflected by weight of accumulated oil drops. In

fact, this type of bed is invented to take advantage of spiral bed for its non-cloggingand disorderly bed (section 5.4.1.3) for its rigidity and good interception efficiency.

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The equation is developed and verified under these conditions i.e.;

• 52 < Re < 1164. Re is the term (ρcVD/μc) in the equation.

• 1 < H/D < 2. However, the maximum H/D shown in TAPANEEYANGKUL’s

research [8] is 6. Using H/D > 2 in the model can be also applied for comparison

purpose only.

• Rotating speed of the bed (N) is between 0.167 to 3.33 rps (10 to 200 rpm). Pleasenote that N is in form of revolution per unit time, not radian per unit time).

Recommended minimum rotating speed is 75 rpm. Using lower speed may not

provide any additional benefit over simple fibrous bed coalescer because the effect of

rotating on interception probability may be cancelled out by the shear effect, whichcauses fragmentation of oil drops.

• Empty bed velocity (V) is between 0.1 to 1.1 cm/s (3.6 to 39.6 m/h) .

• Diameter of fiber (d F) is around 100 to 300 microns

•

Diameter of coalescer bed (D) is not greater than 11.5 cm. Using bigger diameter maycause deflection at the end of fibers from longer overhung lengths, which may cause

channeling of untreated wastewater and error in calculation.

• It is recommended to use the model only for the droplet size (d) of 10 microns or

greater. For smaller droplet, the model can also be applied, but for comparison

purpose only.

• The beds, used in the experiment, are “bottle brush” types, made of oleophilic polyamide or polypropylene with stainless steel shaft, as shown in fig. 5.4.1-1c.

5.4.1.3 Random or disorderly fibrous bed coalescer

There is another special case of simple fibrous bed coalescer that uses random ordisorderly fibrous material (such as metal wool, etc.) as coalescer bed. SRIJAROONRAT’s

research shows that removal efficiency of this coalescer is higher than that of coalescer that uses brush type bed. For this, it can be concluded that tortuosity of bed also affects the removal

efficiency. From SRIJAROONRAT’s raw data, an empirical model, based on dimensionalanalysis, can be derived as shown in eq. 5.4.3. However, this model is developed from rather

small set of data. There is an effort to verify if the simple bed model (eq. 5.4.1b) is still valid for

random fibrous bed coalescer. Comparison between efficiency from eq. 5.4.1b, eq. 5.4.3 andobserved value is shown in fig. 5.4.1-3.

%100)()()()(35.3 36.003..003.023.0 ⋅⎟⎟ ⎠ ⎞⎜⎜

⎝ ⎛ = −−

D H

Dd

Dd VD F

c

cd

μ

ρ η {5.4.3}

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0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

110.00%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%


P r e d i c t e d E f f i c i e n c y ( % )

+10%

-10%

Fig. 5.4.1-3 Relation between observed efficiency and predicted efficiency fromrandom fibrous bed coalescer model and simple fibrous bed model

From the graph, it shows that SRIJAROONRAT’s random fibrous bed model (eq. 5.4.3)

can accurately predict the efficiency of the coalescer while the result from the simple bed model

(eq. 5.4.1b) tends to underestimate the efficiency from 2 to 6 times. This confirms that tortuosityof the bed plays very important role in efficiency of fibrous bed coalescer. However, tortousity

can not be effectively established in form of numerical value so it can not be included as a parameter in mathematics model. Eq. 5.4.3, then, can be applied only when design condition is

close to the test condition from SRIJAROONRAT’s research.

Eq. 5.4.3 is developed and verified under these conditions i.e.;

• The beds used in the experiment are highly disorderly bulk of stainless steel fiber, d F =

75 microns, and steel wool, d F = 40 microns (see fig. 5.4.1-4). However, only thelatter case, which raw experimental data is available, is used to develop the model.

The minimum size of oil droplet tested is 1 micron.

• Tested Reynolds number is between 840 to 2470.

• Porosity of the bed (ε) is around 0.95.

• Diameter of the coalescer (D)= 5 cm.

• Height of the coalescer bed (H) is between 0.07 to 0.21 m.

• Velocity (V) is between 1 to 2.5 cm/s or 36 to 90 m/h.

• Inlet concentration is around 1000 mg/l.

In case that the conditions stated above are not fully compliant, it is recommended to useeq. 5.4.1b to calculate the efficiency of the coalescer because it is proven to be valid within wider

range. In this case, predicted result from eq. 5.4.1b tends to underestimate the efficiency of thecoalescer.

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a) Highly disorderly stainless steel fibers b) Steel Wool

c) Magnified picture of (a) d) Magnified picture of (b)

Fig. 5.4.1-4 Random or disorderly fibrous bed, used in the research of SRIJAROONRAT

5.4.1.4

Influent parameters

Even though each type of fibrous bed coalescer is governed by different equation, all ofthe equations is in about the same mathematics form, as shown in eq. 5.4.4. Thus, main

parameters that affect the efficiency of the fibrous bed coalescer can be commonly summarizedas shown in fig. 5.4.1-5.

))1(,,,,1

,1

,1

( ε η −= N H d d DV

f F

d {5.4.4}

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Chapter 5 Coalescer

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Droplet size (d)

Efficiency (η)

100%

Lower limit of

the model:

1 micron

Droplet size (d)

Efficiency (η)

Increase V, D, d FDecrease H, (1-ε), NLess tortousity

100%

Fig 5.4.1-5 Typical relation between efficiency of fibrous bed coalescer and various

parameters

However, besides the parameters shown in eq. 5.4.4, there are some important parametersthat affect the efficiency of the coalescer, i.e.,

1. Tortousity

If the bed is more tortuous, the probability to intercept oil droplets will be increased.

The efficiency, then, is increased, as clearly shown in the case of wool coalescer. However, it will

tend to be clogged if suspended solids are present in wastewater.

2. Wettability of bed

From the 3 mechanisms of AURELLE [3] (section 5.4.1.1), wettability of the bed isthe key parameter that governs the step 2 “adhesion-coalescence”. In case of direct (oil in water)

emulsion treatment, he bed material shall be oleophilic to optimize the adhesion-coalescence phenomena.

3. Interfacial tension and presence of surfactants

Surfactant will lower the interfacial tension, then make the oil droplets more

stabilized. This leads to poor adhesion between droplets and surface, ineffective collision

(collision without coalescence), and re-fragmentation of oil drops. So presence of surfactantdirectly limits the efficiency of step 2 “adhesion-coalescence”. To optimize the efficiency of step

2, it is recommended to destabilize, (breaking or cracking) the emulsion before sending to thecoalescer

4. Temperature

Properties of oil and water, such as viscosity, change with temperature. Sotemperature is inevitable an important parameter that affect coalescer efficiency. Then it isimportant to design the process by taking the possible range of temperature into account.

Normally, the efficiency will, more or less, increase with the temperature. The equations in this

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Steps of calculation, as well as cut size determination, for fibrous bed coalescer is

identical to those of basic granular bed coalescer. However, there are some difference in details of

sizing and pressure drop calculation as described below.

1.

Cut size determination

The ut size can be determined from the degree of treatment required as well as fromthe limitation of the coalescing processes. Cut size determination from degree of treatment is

described in chapter 3. For the limitations of the process, it is mainly model limitation. Since the

model used for calculation is based on empirical data, it can be applied only within its validrange. Extrapolation of model may cause unpredictable error. The limitation of each model is

described in section 5.4.1.

2. Coalescer sizing

The size of various types of fibrous bed coalescer can be calculated by eq. 5.4.1 to5.4.3. Design cut size will be used to calculate the dimension of the coalescer by assuming thatthe graded efficiency at the cut size is 100%. Dimension of the coalescer can be arbitrarily

selected under the limitations of each equation, as described in section 5.4.1.1 to 5.4.1.3.However, it is recommended to select the possible lowest fiber diameter and highest velocity for

the first trial because it will give the most compact diameter of the coalescer. If the result is

acceptable, we may try to fine-adjust the parameters to get the most suitable dimension. If theresult is unacceptable, normally too big, we may have to increase the number of units.


After the dimension of the coalescer is determined, graded efficiency (ηd ) can becalculated by eq. 5.4.1, 5.4.2 or 5.4.3. If the result from eq. 5.2.10 is greater than 100%, then it

will be rounded up to 100%.

It must be noted that the graded efficiency from the equation is not yet accounted for

effect of flow splitting between water outlet flow and separated oil outlet flow. To calculategraded outlet oil concentration, the effect must be taken into account, as shown in eq. 5.2.12a.

od d

out

d C Q

QC )1( η −= {5.2.12a}

Qout is outlet flow at treated water outlet port of the process. Qout is calculated from

difference between inlet flow and separated oil (in relatively pure condition) as shown below.

d

d

d

od d

out

C Q

QQ ρ

η ∑ ⋅

−=

max

min

)(

{5.2.12b}

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( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η {5.2.12c}

ηt = Total Removal efficiency of the tankρd = Density of dispersed phase, which is oil, for oily wastewaterCod = Inlet concentration of the droplet diameter “d”

4. Pressure drop

As stated in section 5.4.1.5, in order to calculate the pressure drop, it is

recommended to use any general piping loss equations, such as Darcy’s, Colebrook-White’s orHazen-William’s equation (eq. 5.4.5) with the safety factor of 2 to 5, multiplied to the actual

height (H) of the bed. CHW is Hazen william’s constant, depending on surface roughness of

coalescer. Recommended value is 110-130 for steel column.

167.185.1

582.6 ⎟

⎠ ⎞⎜

⎝ ⎛

⎟⎟ ⎠ ⎞

⎜⎜⎝ ⎛ =

D

H

C

V P

HW

m {5.4.5}



The equations described above are developed from the following assumptions and

limitations. Thus, it is necessary to make sure that these assumptions are valid when design thecoalescer. Limitation of each design equation (eq. 5.4.4 to 5.4.3) is described in section 5.4.1.

2.

Construction and material selection

Fibrous bed coalescer consists of 2 major components, i.e., casing and bed.

1) The casing

The casing is the component that contains the bed and other importantappurtenances, such as wastewater inlet, wastewater outlet, decanting section, oil outlet, clean

out, etc. Researches in GPI lab normally emphasize on working mechanisms and developing of amodel so there is no direct study on characteristic of the casing. However, the size of the fibrous

bed coalescer is usually small to avoid deflection at the tip of fibers, it is, then, designed as inline

unit or in the form of pipe (see fig. 5.4.1-1 and 5.4.3-1). Batteries or multi-coalescer unit is alsoavailable. Downstream decanter may be integrated or placed separately from the coalescer as

shown in fig. 5.4.3-1. As described in section 5.4.1, diameter of the decanter is normally equal tothat of coalescer or a bit bigger to facilitate placement and construction of internal baffle, water

and oil outlet pipe.Casing of coalescer can be made of any material (plastic, steel, glass, etc.) that

can withstand the operating condition. If possible, it should be oleophilic.

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a) Lab scale coalescer with integrated

decanter (The bed is placed in the steel

column just below the decanter)

b) Inline-style fibrous bed coalescer [11] c) Assembly of the coalsecer and separated

decanter (Source: Elf, GPI lab)

Fig. 5.4.3-1 Examples of fibrous bed coalescer casing

2)

The bed

The bed is the most important part in the coalescer. From section 5.4.1, thereare 2 major types of fibrous beds, i.e., simple or brush type and random or disorderly type.

Difference in operating efficiency between the two is already discussed. However, one property,

which both beds have in common, is that, for direct emulsion treatment, the bed shall be

oleophilic.

Material of the bed varies from steel, stainless steel and variety of plastic, scuhas polyamide, polypropylene as shown in fig. 5.4.1-1, 5.4.1-4 and 5.4.3-2. For simple brush type,

the efficiency of the coalescer varies only slightly for various types of bed shown in the figure.

The factor that governs the efficiency for this type of bed is its oleophilicity. Guideline onwettability of material is described in chapter 2. To preliminary test olephilic property of the bed,

it can be done easily by dip or have the bed contact with oil or water. If the drop of oil or water isalmost sphere, it can be approximately concluded that the material is hydrophilic or oleophilic

respectively (see fig. 5.4.3-3)

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6.1 General

Flotation is an accelerated separation process, operated by increasing density

difference between continuous phase and dispersed phase. This is accomplished by mean ofadding gas or air into the wastewater to promote formation of air-solids or air-oil

agglomerates. There are several researches on flotation, its modification and applications of

various types of flotation such as mechanical flotation, diffused air flotation, dissolved air

flotation (DAF), etc. Among these, DAF, with its finest air bubble size, is the most efficient

process. So it became the main flotation process studied in GPI lab.

6.2 Working principles

From STOKES law (eq. 6.2.1), difference density between dispersed phase and

continuos phase (Δρ) is one of the parameters that governs rising or decanting velocity of the

dispersed phase. Flotation is the separation processes of which aims to increase the densitydifference to increase the decanting velocity.

c

gd U

μ

ρ

18

2Δ= {6.2.1}

For dissolved air flotation, pressurized water which is (or almost) saturated with air or

gas will be fed to wastewater at lower, usually, atmospheric pressure. The air or gas will be

released from the pressurized water in form of tiny bubbles. These bubbles, while rise up to

the surface, will collide with dispersed phase, in case of oily wastewater oil droplets, in the

wastewater. Some will attach to the droplets and form oil-bubble agglomerates. Since the

bubble has much less density than oil and water. Density of these agglomerates will be lower

than that of oil droplets alone, thus, make the rising velocity increase. General schematic

diagram of DAF process is as shown in fig. 6.2-1.

Fig. 6.2-1 Example of schematic diagram of DAF (Source: Aquatec Maxcon)

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C is inlet concentration of oily wastewater. For the entire flotation column, we will

consider a very small slice of rising bubbles of the height dH (see fig. 6.2.1-3b). The number

of bubble particles in this slice can be calculated from the cross section area of bed (A), the

size of the bubble (d b) and the ratio of volume of water to total volume (ε), as shown in eq.

6.2.7c.

Then, the total concentration of intercepted oil for this slice of rising bubbles will be

equal to the product of c’ and the number of bubbles. However, not all of the intercepted oil

drops will adhere to the bubbles. So the probability coefficient (α) will be applied to adapt the

quantity of intercepted oil drops to the quantity of adhered oil drops (c”), as shown in eq.

6.2.7d.

The number of bubbles in the slice dH3

6

)1(

bd

AdH

π

ε −= {6.2.7c}

3

2

6

)1(

4"b

btheo

d

AdH

C V d c π

ε π

η α

−

⋅⋅⋅⋅⋅= , α < 1 {6.2.7d}

If dC represents the concentration of oil reduced after past through the slice of bubbles

dH, then we have got eq. 6.2.7e and f;

"cdC AV =⋅⋅− {6.2.7}

3

2

6

)1(

4b

btheo

d

AdH C V d dC AV

π

ε π η α

−⋅⋅⋅⋅⋅=⋅⋅− {6.2.7f}

Therefore,

dH d C

dC theo

b

αη ε )1(2

3−−= {6.2.7g}

Integration of eq. 6.2.7g will give the value of the oil concentration reduced by the

entire column height, as shown in eq. 6.2.8a.

b

theo

o d

H

C

C αη ε )1(

2

3)log( −−= {6.2.8a}

However, void ratio (e) of DAF system can be calculated directly from air flowratedischarged from pressurized water and total water flow as shown in eq. 6.2.8b.

AV Qt

Φ=

Φ=− ε 1 {6.2.8b}

Thus, the theoretical removal efficiency DAF, based on filtration model, can be

written as shown in eq. 6.2.8c.

%1001%1001)(

2

3

, ⋅

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ −=⋅⎟⎟

⎠

⎞⎜⎜

⎝

⎛ −=

⋅⋅Φ

⋅− theodp

H

AV

o

theod e

C

C η α

η {6.2.8c}

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air t

pw air Conc

Q

Q

AV ρ

)(⋅=

Φ {6.2.10a}

Or

X RQ

RQ X Q

Q

t

pw ⋅+=⋅= 1 {6.2.10b}

Normally, under certain design condition, Q pw/Qt or Q pw/Q (= R)is constant. Solubility

of air in water (X) and air density are intrinsic (internal) properties, which are constant at any

given pressure and temperature. So, from eq. 6.2.10, it shows that Φ/AV is flow-independent.

From these, it seems that predicted DAF efficiency from the filtration-based model ismathematically flow-independent. However, In fact, effect of wastewater flowrate,

sometimes, described in form of velocity or retention time, is studied by many researchers. Itis widely accepted that DAF efficiency varies with retention time. So, considering SIEM’s

research, it can be interpreted that the effect of retention time is already included in eq. 6.2.9a.Since eq. 6.2.9a is evaluated from one set of operating condition (Φ/AV = 0.0516) and

retention time (25 minutes (approx.)), it may be valid only for that condition. To expand validrange of SIEM’s model, some criteria or model that contains flowrate-dependent parameter(such as retention time, etc.) is required.

6.2.2 Population balance model

Population balance model is one of popular concepts, used by many researchers, to

develop DAF model. In GPI lab, DUPRE [14] uses this method in her research on applicationof DAF for liquid-solid separation. Concept of this method is that rate of change in the

number of pollutants which is free or attached by 1, 2 or more air bubbles is the function ofthe number of air bubble and oil droplet, as shown in eq. 6.2.11. Oil droplet that is attached by

at least 1 bubble, so-called oil-bubble agglomerate, will be separated. So rate of change innumber of oil droplets represents removal efficiency.

Main assumption of population balance method is that the number of bubble isassumed to be constant. From many researches [14], [34], It is proven that, for liquid-solidseparation, the number of bubble (N) can be safely assumed as constant without serious error,

because there are a lot more bubbles than pollutant if normal range of (Q pw/Qt) is applied.However, in case of oily wastewater, many researches [12], [13] show that bubble-oil

agglomerates are in form of oil shell with air inside and these agglomerates are still able to

intercept more oil droplets. Those researches also show that coalescence of oil and bubble ismore effective than that of the same species. So it should be safely assumed that the numberof bubble in this case is more or less constant and the population balance method is, then,

applicable.

N nk dt

dn00

0 β −= {6.2.11a}

N nk N nk dt

dniiii

i β β −−= −− 11 {6.2.11b}

i = 0 to imax

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It should be noted that eq. 6.2.13 is about the same form as eq. 6.2.9b, but the value of

κ, represented by eq. 6.2.11d, clearly represents effect of every interesting parameter,including retention time. So population balance model is flow-dependent and, then, can be

used to extend the valid range of SIEM’s model, as described in section 6.2.3.

6.2.3

Generalized model of DAF from combination of filtration based model andpopulation balance model

From section 6.2.1, it shows that SIEM’s filtration based model can be used to predict

the efficiency of DAF at any diameters of oil droplets and bubbles, as long as design retentiontime and F/AV still conforms to SIEM’s condition. And from section 6.2.2, it shows that

population balance model gives the equation that is flow-dependent. So it is possible to usethese two models to extend the valid range of SIEM’s model to another operating condition.

To do so, firstly, SIEM’s model will be used to calculate the efficiency at his operating

condition. Then, at any d and d b, eq. 6.2.11d and 6.2.13 can be rewritten in form of a function

of a parameter that we want to vary from SIEM’s condition, i.e., retention time and gasflowrate. while other parameters still conform to SIEM’s (eq. 6.2.14). When the efficiency at

SIEM’s condition is known, the efficiency at other condition can be predicted from eq. 6.2.14and relation between design value and SIEM’s value of that parameters (eq. 6.2.15 and6.2.16).

τ κ τ κτ Φ=Φ= 2.Gconst {6.2.14a})( 211

τ κ κτ η Φ−− −=−= ee {6.2.14b}

If “x” represents the variable Φ or τ that we want to vary from SIEM’s while anothervariable still conforms to SIEM’s condition, eq. 6.2.14b can be rewritten as show below.

x Ae ⋅−−=1η {6.2.14c}

Where A = constant

Ifx = B.x ref {6.2.15}

Where B = Constant

Xref = x at SIEM’s condition

Then

)(

)(

1

1

ref Ax

Ax

ref e

e−

−

−

−=η

η

{6.2.16a}

)(

)(

1

1

ref

ref

Ax

ABx

ref e

e−

−

−

−=

η

η {6.2.16b}

B

ref )1(1 η η −−= {6.2.16c}

However, changing of τ of Φ will also cause some parameter in eq. 6.2.11d change.

For example, increasing of retention time from SIEM’s condition will make V decrease. Then

G will decrease. So the constant “A” at design condition is not equal to “A” at SIEM’scondition. In this case, eq. 6.2.16 is not valid. And it is not possible to know the value of “A”

at design condition. So, the best estimation in this case is to use the value of A at some

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condition that we are sure that will underestimate efficiency at design condition. Design

reactor in this case will be larger than it should be. Then it can be considered as safety factor.

Guideline to predict the efficiency from combination of SIEM’s model and population

balance model will be described again in details in section 6.3.

6.2.4 Influent parameters

From models described in section 6.2.1 and 6.2.2, main parameters that affect theefficiency of DAF can be summarized as shown in fig. 6.2.4-1.

Droplet size (d)

Efficiency (η)

100%

Lower limit of

the model:

2 micron

Droplet size (d)

Efficiency (η)

Increase d b

Decrease τ, Φ, H

100%

Fig. 6.2.4-1 Typical relation between efficiency of DAF and various parameters

From the models, it can be summarized that, efficiency of DAF can be improved by:

•

Increase the size of oil droplets. This can be done by coagulation-flocculation process.

• Decrease the size and quantities of bubbles. This can be achieved by using high

performance injection valve.

• Increase quantity of air/pollutant ratio by increasing pressurized water flowrate or

using higher saturator pressure. However, operating cost should be considered.

• Increase column height to increase retention time.

However, there are some more phenomena and parameters that also effect theefficiency of DAF, which will be described below,

1. Characteristic of bubble-pollutant agglomerate and transfer compound

Characteristic of bubble-pollutant agglomerate

Since DAF performance depends on formation of bubble-pollutant agglomerate,some researches in GPI lab [13], [14] had been conducted to study characteristics of theagglomerate. Fig. 6.2.4-2 shows characteristic of bubble-solid and bubble-oil agglomerate.

For bubble-solid agglomerate, certainly, bubbles will attach to the surface ofsolid in side-by-side manner. On the contrary, for bubble-oil agglomerate, side-by-side

characteristic is only temporary or intermediate condition. Finally, oil and bubble willintegrate in form of spherical thin film or shell of oil with air core inside. This can be

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explained by the concept of spreading, described in chapter 2, section 2.2.2.2. Consider

interfacial tension between kerosene, water and air as shown below,

Oil-water: γow = 35 dynes/cm

Air-water: γw = 72 dynes/cm

Air-oil: γo = 28 dynes/cm

From chapter 2, oil will spread over the air bubble when γw > γo+ γow. From the

values of interfacial tension, it clearly shows that this condition is confirmed (72 > 28 + 35).

So the oil will spread over air bubble and form a thin film around the air.

The four ways to improve the efficiency of DAF described earlier in fig. 6.2.4-1is actually the way to improve collision probability. However, one of the most encountered

problems in DAF operation is collision between bubble and pollutant without attachment.According to the study in static transparent model [13], to form agglomerate, bubble and

pollutant must be collide or come close to each other at some certain distance for sufficient

period of time to drain water film between them and made bond to each other. To solve this problem, some chemically active agents are used to adapt properties of bubble andwastewater. The chemicals are called “transfer compound”.

Effect of transfer compound on bubble-pollutant agglomerate

Transfer compound is chemical added either as gas to bubble-forming air or as

chemical to water. Major role of the compound is to help promoting bubble-pollutantagglomerate and strengthen the bond between them. It will cause mass transfer, where it gotits name, from bubble to water or vice versa that change local interfacial or surface tension of

pollutant or bubble. This change will facilitate agglomerate formation. This effect of local

change in surface tension is known as the Marongoni effect. There are 2 major types of thecompounds, i.e., transfer gas and transfer compound for water.

• Transfer compound for water is practically a surfactant added to

pressurized water. The surfactant will reduce surface tension of water . In

case of solid separation, the effect is relatively the same as that when using

surfactant in a washing machine. Bubbles and solids will attach to each othereasier and stronger. Efficiency will be improved. This idea is actuallycommercialized by many companies, such as SAFTM (suspended air

flotation) from Enprotec.

• Transfer gas is typically a gas of highly soluble chemicals, such asammonia, which is added to bubble-forming air. The concept is that the gas

would transfer from bubble into water and make the water film raptureeasier. This will help interaction time between bubble and pollutant and

make them attach immediately after collision. In GPI lab, AOUDJEHANE[13] shows that small amount of ammonium gas added into the air actually

helps reducing coalescence time between bubble and oil droplet. However, it

also promotes coalescence between bubble and bubble. So, these effects tendto cancel out each other. The efficiency is relatively the same.

In case of oily wastewater , however, presence of surfactant in water causes the

droplet smaller and more stable. So it make the efficiency decrease. Anyway,AOUDJEHANE shows that if the surfactant is firstly added to oil and mass transfer of

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surfactant is in the direction from oil toward water. It will help rupturing the water film then

improving efficiency of coalescence between bubble and oil. However, doing so in real

situation may not be possible because we cannot add surfactant into oil before it becomeswastewater.

a) Solid-bubble agglomerate. Please notice side-by-side formation. [14]

b) Bubble and oil droplet come close to

each other.

c) The bubble and droplet collide. Water

film between them is draining.

d) Water film rapture after been draing for

some times. Oil starts to enclose air bubble

in very brief time.

e) Then, oil-bubble agglomerate is form of

thin oil film around air core is generated.

Fig. 6.2.4-2 Solid-bubble agglomerate and formation of oil-bubble agglomerate [14]

2.

Turbulence in flotation column

As shown in eq. 6.2.11 and 6.2.13, the efficiency of DAF depends on gradient or

turbulence within the reactor. If turbulence increases, probability of collision between bubbleand pollutants will also increases. However, turbulence also causes adverse effect on

fragmentation of oil droplets or flocs. AOUDJEHANE had studied the effect of turbulence inspecial DAF model equipped with mechanical mixer, reported that efficiency of DAF

increases with increasing turbulence or mixing intensity until some certain limit. Then theefficiency will be stable or slightly decrease with increasing turbulence. It seems that

turbulence has both advantage and disadvantage. Normally, DAF is designed in smoothlaminar flow region. Increasing the efficiency of DAF by increasing turbulence is to be done

very carefully. Pilot-scale observation or CFD analysis should be conducted.

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3. Presence of surfactant

Effect of surfactant in wastewater is as discussed in “effect of transfercompound”. In presence of surfactant, oil droplets will become more stable and their sizes

will be smaller. Efficiency of DAF, then, will decrease. So it is recommended to destabilize

(or break or crack), coagulate/flocculate the wastewater before using DAF.

4. Formation of air bubbles

From, filtration-based model efficiency of DAF will increase if the size of

bubbles decreases. So pressurized water system shall be designed to make majority of verytiny droplets and avoid generating big bubbles. DUPRE [14] had studied bubble generation in

venturi-style injection vale and reported that using hydrophobic material for valveconstruction may result in bigger bubbles. She also reported that addition of surfactants in

pressurized water causes augmentation of population of microbubbles, while addition of polyelectrolyte gives the opposite result. Details of pressurized water system or saturator will

be described in section 6.5.

6.3 Design calculation

From previous sections, it shows that there are many parameters, such as wastewatercharacteristic, reactor configuration and operating condition, that effect efficiency of DAF

reactor. So, design of DAF reactor is generally based on hydraulic loading rate and some proven reactor configuration. However, to valorize the researches conducted in GPI lab,

design procedure for DAF, recommended in this section, will be based upon the models,shown in the previous sections as well as general design practices. Calculation in each step isdescribed below.

1. Cut size determination and required efficiency

The cut size can be determined from the degree of treatment required as well as

from the limitation of the DAF processes. Cut size determination from degree of treatment isdescribed in chapter 3. However, in general practice, DAF is hardly used alone but will be

combined with coagulation-floculation process (see chapter 10). After coagulation-flocculation process, granulometry of size distribution of dispersed phase in the wastewater

will be changed from that of initial wastewater. The size distribution after coagulation-flocculation may be roughly estimated, as shown in chapter 10. However, it is clear that it is

no longer possible to determine the cut size from the initial size distribution. Then the degree

of treatment (such as effluent oil concentration, etc.) will be used to calculate the requiredefficiency. This required efficiency or the required degree of treatment would be used tocompare to general recommended criteria of DAF to determine if it is feasible to use DAF for

such wastewater.

In case that there is no general design criteria or recommended efficiency for thewastewater to be treated, it is strongly recommended to perform DAF test, such as Flota-test,

to evaluate the feasibility and efficiency of DAF before designing the real unit.

2.

DAF reactor sizing

The size of the DAF can be determined based on (1) mathematics models fromsection 6.2, (2) general design criteria and (3) pilot-scale test result. Designing an efficient

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DAF reactor, as well as other processes, is the state-of-art and requires experience. However,

result from the models and some useful criteria acquired from many researches, esp. GPI

researches, will be provided here to be a guideline for DAF reactor sizing.

2.1. General design criteria

Recommended design criteria from various literatures and manufacturers aresummarized in table 6.3-1. It should be noted that the values in the table are summarized fromexperiences and researches with various operating conditions and types of wastewater, then,

should be used as a guideline. It is recommended to review related researches for the type ofwastewater to be treated. If possible, DAF test, using lab-scale batch test, such as flota-test, or

pilot-scale test with the real wastewater should be performed.

2.2. DAF design by combination of filtration based model and population

balance model

From the 2 models in section 6.2, they can be used to size DAF reactor andestimate graded efficiency of DAF process at any operating condition. If direct scale-up of

SIEM’s model ( the same V and Φ/AV) is used, the cut size at H =0.70 m. is around 35microns.

If DAF is used alone without coagulation-flocculation process and cut size can

be determined, the cut size can be used to calculate surface area of DAF reactor (A) by

assuming that the efficiency at the cut size is 100%.

If cut size can not be determined, approximate size of DAF reactor can be

calculated from general criteria, described in table 6.3-1. It is recommended to use the reactor

size calculated from the general criteria as a guideline to calculate the efficiency. Then, it can be fine adjusted again to fit specific constraint of each project.

Calculation procedure and model limitation will be as described below.

2.2.1. Design DAF at SIEM’s condition ( /AV is at SIEM’s condition. H can

be varies)

1. To predict removal efficiency of DAF, reference graded efficiency

(based on Qt) can be calculated by SIEM’s model. If the result

from the equations is greater than 100%, then it will be rounded up

to 100%. The values of (Φ/AV) have to be the same as SIEM’scondition (see item 3).

%1001))(

2

3(

,

exp

⋅⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −=

Φ−

bd

H

AV

ref d eαη

η {6.2.9b}

5919.0

exp)(009005.0)( theoη αη = {6.2.9a}

diff Int sed theo η η η η ++=

2)(2

3

b Int

d

d =η {6.2.3}

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r c

water oil

sed V

gd

μ

ρ η

18

2

/Δ= {6.2.4}

3/2)(9.0br

Diff d dV

KT

μ η = {6.2.5}

c

bwater air

br

gd U V

μ

ρ

18

2

/Δ== {6.2.2a}

Where μc = viscosity of continuous phase (water) (L2/T)

K = Boltzman constant (1.38*10-23

)T = Absolute temperature (Kelvin)

2. To use the equations described above, the following conditions will

be satisfied;

1) Inlet oil concentration should not be greater than 1,200 mg/l

(before dilution) or 435 mg/l (after dilution).

Using the modelwith higher oil concentration will result in underestimating ofefficiency.

• Φ/AV = 0.0516. Only this value must be used in the

equations. As long as this value is fixed, SIEM’s operating

condition still holds and the model is still valid.

• Retention time, based on total flowrate (Qt), is around 25minutes.

• Droplet diameter (d) tested is between 2 to 40 microns.

• Diameter of air bubbles (d b) varies from 15 to 130 microns.

Tested average bubble diameter is 70 microns, which is used

to verify the model, and standard deviation of bubblediameters is 34.5 microns. The range of bubble sizes iscommon for commercial pressurized water system or

saturator. The pressure of the test system is 4 atm (absolute).


• Tested wastewater flowrate (Q) is 3.9 cm3/s (3.9e-6 m

3/s)

• Tested effective water depth (H) is 0.70 m. The value of H

can be freely changed as long as (Φ/AV) is fixed. However,

H between 1.8 to 2.7 is recommended by API [45].

• Diameter of flotation column is 0.15 m Cross section area of

column (A) is 0.01767 m2.

•

Ratio of pressurized water to wastewater (Q pw/Q) is 1.76.

• Air to pollutants ratio used is around 0.12 kg. air/ kg. oil.

• Ratio of number of bubble/ oil droplet tested is around 1.4

oil droplet/ 1 air bubble.

• Hydraulic loading rate or flow velocity (V), based on Q t, is

1.6 m/h

2) he model is tested at the following operating condition;

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T a

b l e 6 . 3 - 1 G e n e r a l d e s i g n c r i t e r i a o f D A F f r o m v a r i o u s l i t e r a t u r e s a n d m a n u f a c t u r e r s ( h y d r a u l i c l o a d i n g r a t e i s b a s e d o n t o

t a l f l o w r a t e )

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3. To apply SIEM’s condition to other wastewater flowrate, area (Aref )

and gas flowrate (Φref ) corresponding to that flowrate can be

calculated from the following equations. The subscript of A and Φ

in this case is “ref” to indicate that SIEM’s condition (or referencecondition) still holds.

01767.0109.3 6mod

mod

⋅×

=⋅= −req

el

el

req

ref

Q A

Q

Q A m2 (Q as m3/s) {6.3.1}

01767.0

102.4 7

mod

mod

req

el

el

req

ref

A

A

A −×=Φ⋅=Φ m3/s {6.3.2}

4. If H is changed from 0.70 m. to Hreq, τ will be changed from 25

min. to τref by the following equation. The subscript of τ in this caseis “ref” to indicate that SIEM’s condition (or reference condition)

still holds.

3600

1

00046.0mod

mod

⋅=⋅= req

el

el

req

ref

H

H

H τ τ hour {6.3.3}

5. Because of limitation of the pilot model, tested ratio of pressurizedwater to wastewater is quite high (around 92%), compared to that ofgeneral DAF for solid/liquid separation (less than 50%) [13].

However, API [45] recommended air/wastewater ratio of 0.35 std.

ft3/ 100 gal of total flow for full-flow DAF process. This value is

equivalent to 84% of 4-atm (abs) pressurized water/ wastewater.

Anyway, it is interesting to adapt the model to calculate theefficiency at lower ratio of pressurized water by the procedure in

item 2.2.2.

6. Tested hydraulic loading rate or overflow rate (based on Qt) is 1.6

m/h, which is relatively low, compared to normal rate of 3-15 m/hfor domestic wastewater treatment. The value recommended by the

American Petroleum Institute (API) [45] is between 4.8-6.1 m/h. Soit is also interesting to adapt the model to calculate the efficiency at

higher overflow rate by the procedure in item 2.2.2.

2.2.2. Design DAF at other condition from SIEM’s condition

To calculate graded removal efficiency at other operating conditionthan SIEM’s model, esp. at higher overflow rate or lower ratio of pressurizedwater/wastewater, calculation procedure will start from direct scale-up of

SIEM’s condition (the same as 2.2.1). After that, adaptation by population

balance model will be applied.

Direct scale-up of SIEM’s condition (Φ/AV is at SIEM’s condition. Hcan be varied.)

1. Calculate the reference efficiency (ηd,ref ) of the model at requiredheight (Hreq), average bubble diameter (d b) and droplet sizes (d)

using eq. 6.2.2 to eq.6.2.5 and eq. 6.2.9. Use Φ/AV = 0.0516 inorder that the operating condition of SIEM still holds.

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2. Scale up the area from 0.01767 m2 to required area (Areq). Other

operating condition from section 2.2.1 still holds. So efficiency

from section 2.2.1 remains the same. This required area could beapproximated from recommended hydraulic loading rate (Vreq) and

ratio of pressurized water to wastewater ((Q pw/Q)req) as shown in

table 6.3-1.

req

req pw

req

reqV

Q

QQ

A

⎟ ⎠

⎞⎜⎝

⎛ +=

)(1

{6.3.4}

3. Find Φref , corresponding to the area Areq, by following equation,

01767.0

102.4 7

mod

mod

req

el

el

req

ref

A

A

A −×=Φ⋅=Φ m3/s {6.3.2}

4. Find τref , corresponding to the height Hreq, by following equation,

60

25

70.0mod

mod

⋅=⋅= req

el

el

req

ref

H

H

H τ τ Hour {6.3.3}

Change Φ and τ from SIEM’s condition by population balance

model

5. From population balance method, calculate κ2,ref corresponding to

Areq, Hreq, τref and Φref from the reference efficiency (from item 1)

by the following equations. Please note that, at this point, SIEM’s

condition still holds. κ2,req has to be calculated separately for each

droplet diameter.

ref ref

ref d

ref τ

η κ

⋅Φ

−−=

)1ln( ,

,2 {6.3.5a}

Or

)(

,,21 ref ref ref eref d

τ κ η

Φ−−= {6.3.5b}

6. Find Φreq from required ratio of pressurized water to wastewater(see table 6.3-1 for the recommended value) by following

equations.

Q RVolume

VolumeQVolume

Volume

pw

air

pw

pw

air

req ⋅⋅=⋅=Φ {6.3.6a}

Then, from Henry’s law (section 6.5)

)10082.0()('3

3

K mol

mT PPQ R H y atmreq ⋅

⋅−⋅⋅⋅=Φ − {6.3.6b}

For air, y =1. H’ in this case in in the form of mol air /(m3 water. atm).

Henry’s constant of air at any temperature can be calculated from

an empirical equation, shown in section 6.5.

7. Choose τreq from recommended criteria (see table 6.3-1).

8.

To change Φ and τ from SIEM’s, the following procedure is

recommended and precautions should be noted.

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• To decrease ( req < ref ) and increase

τ

(τreq >

τref ):

This will cause decreasing of V, so G will decrease. Then κ2

(see eq. 6.2.11, 6.2.14) will be lower. However we do not knowhow much exactly. So, to be on the safe side, we will assume

that only Φ decrease but τ = τref . In this case, κ2 will remain thesame and be equal to κ2,ref . The efficiency can be estimated by

eq. 6.3.7a.

)( ,21 ref reqref ed

τ κ η

Φ−−= {6.3.7a}

Because we use τref , instead of τreq, the calculated efficiency will

be lower than the real value.

•

To decrease ( req < ref ), as well as,

τ

(τreq <

τref ):

This will cause increasing of V, so G will increase. Then κ2 (see

eq. 6.2.11, 6.2.14) will be higher. Again, we do not know how

much exactly. So, to be on the safe side, we will assume that κ2 = κ2,ref . The efficiency can be calculated by eq. 6.3.7b. And

again, the calculated efficiency will be lower than the real value.

)( ,21 reqreqref ed

τ κ η

Φ−−= {6.3.7b}

•

To increase ( req > ref ) and decrease

τ

(τreq <

τref ):

This can be done by increasing pressurized water flowrate.However, the ratio of pressurized water/ wastewater is already

high (92%). So there is only a small gap to increase Φ (from

Q pw/Q = 92% to 100%). In this case, κ2(see eq. 6.2.11, 6.2.14)

will be higher. Like the former case, the efficiency can becalculated by eq. 6.3.7b.

• To increase ( req > ref ), as well as,

τ

(τreq >

τref ):

This case is not feasible because it means that we have to

decrease wastewater flowrate and increase pressurized water

flowrate. As stated above, the ratio of pressurized water/wastewater is already high (92%). If we decrease wastewater

flow, quantity of pressurized water flow will exceed that ofwastewater, which is not feasible because we have to recycle

effluent at 100% plus additional makeup water to feed the pressurized water system.

There is no obvious limit for the 4 adaptations, shown above.

However it is recommended to use the values of each parameter(d, d b, C, etc.) within general range, shown in item 2.2.1 andtable 6.3-1.

The procedure described in paragraph 2.2 will result in efficiency ofDAF reactor corresponding to firstly approximate size. If the calculated

efficiency dose not meet the required efficiency, the reactor size will beadjusted until it gives a satisfying efficiency.

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2.3. DAF test

It must be noted that there are many other parameters that can affect efficiencyof DAF, such as presence of coagulation-flocculation process, reactor hydraulic design,

contact zone configuration, design of pressurized water system (or saturator) and injection

valve, etc. These parameters can cause some discrepancies in efficiency prediction especiallywhen coagulation-flocculation is used since the granulometry of influent will be totallychanged. In this case, pilot-scale or small batch experiment, such as Flota-test , will provide

valuable data for design propose and can be used to compare with model result to determine

the final design criteria. In fact, it is strongly recommended to perform DAF test, if possible,every time before designing DAF system. Pictures of DAF test are as shown in fig. 6.3-1

a) Pilot-scale for DAF test b) Flota-test set (Source: GPI lab)

c) Flota-test of cutting oil emulsion with

coagulant addition. Notice the float at the

surface of the reactors. (Source: GPI lab)

d) Magnified photos of non-coagulant float

(left) and flocculated float from Flota-

test(Source: GPI lab)

Fig. 6.3-1 Pilot-scale DAF test and Flota-test

3. Removal efficiency and outlet concentration

3.1. Outlet concentration

Outlet concentration and graded concentration of oil after DAF (C and Cd) can

be calculated by the following equation

dilod d out

d C Q

Q

C ,)1( η −= {6.3.8a}

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∑ −=max

min

,)1(d

d

dilod d

out

C Q

QC η {6.3.8b}

∑−=max

min

,

d

d

dilod d

d

out C Q

QQ η ρ

{6.3.8c}

Co,dil and Cod,dil are the inlet concentration after dilution with pressurized water.Q/Qout represents the effect of flow splitting between treated water and oil outlet port. In labscale, where pressurized water comes from oil-free water, outlet concentration can be writtenin form of Co and Cod, which are the initial concentration of oil in wastewater before dilution

by pressurized water, as shown in eq 6.3.8d. However, in this case, effluent quantity willincrease from the initial wastewater flow (Q) to total flow (Qt), which is summation of

wastewater flow and pressurized water flow.

∑ −⋅=max

min

)()1(d

d t

od d

out Q

QC

Q

QC η {6.3.8d}

If pressurized water comes from treated effluent, remaining oil in the effluentwill effect the inlet concentration after dilution. The value of Cod,dil and Co,dil in this case can be calculated with accounting for mass balance, as shown in item 3.4.

3.2. DAF efficiency

DAF efficiency (ηDAF), which is the efficiency based on flotation effect alone,can be calculated by the following equation.

( ) %100)1(1 max

min

, ⋅⋅−⋅= ∑d

d

dilod d

o

DAF C C

η η {6.3.9a}

In lab scale, where pressurized water comes from oil-free water. DAF efficiencycan be written in form of Co and Cod, which are the initial concentration of oil in wastewater before dilution with pressurized water, as shown in eq 6.3.9b.

( )( ) %100)1(

1

)(

)()1()1(max

min

max

min

max

min

,

,

⋅⋅−=⎟⎟ ⎠

⎞⎜⎜⎝

⎛ ⋅−

=

⋅−

= ∑∑∑ d

d

od d

o

t

o

d

d t

odld

dilo

d

d

dilod d

DAF C C

Q

QC

Q

QC

C

C

η

η η

η {6.3.9b}

However, if treated water is recycled to the pressurized water system, the values

of Co,dil and Cod,dil will be affected by remaining concentration in recycled stream and will be

required more complex calculation as shown in item 3.4.

3.3. Total removal efficiency

When pressurized water comes from DAF effluent: Total removal efficiency

(ηt), which is defined as ratio between oil mass removed from water and initial oil mass, can

be calculated by the following equation.

%100⋅−

=o

o

t C

C C η {6.3.10a}

When pressurized water comes from additional clean water: Total removal

efficiency (ηt) can be calculated by the following equation. Please note that effluent quantityin this case is equal to Qt, not Q.

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%100

)(

⋅−

=⋅−

=o

t

o

o

t o

t C

Q

QC C

QC

QC QC η {6.3.10b}

3.4. The value of C od,dil and C o,dil when DAF effluent is used in the pressurized

water system

If the effluent from DAF is recycled to pressurized water system, some oil left inthe effluent will be returned to the system. In this case, mass balance of oil has to be taken

into account. Thus, Cod,dil will be modified by adding this return oil repeatedly, as shown ineq. 6.3.11. Theoretically, r max in eq.6.3.11 should be infinity. The value of Cod,dil will

eventually convert to an asymptote. Anyway, using r max around 30 will practically give the

result sufficient accuracy, esp. when ηd > 20%. However, if coagulation-flocculation is used

before DAF process, the value of ηd will be so high that Cod,dil in this case is only slightly

higher than Cod.Q/Qt.

t

od

r

r

r d

t

pwdilod

Q

QC

Q

QC

x

⋅⎥⎥⎦

⎤

⎢⎢⎣

⎡−= ∑=

−

max

1

1, )1( η

{6.3.11a}

Where Q pw = R.Q. Above summation can be simplified as shown in eq. 6.3.11b.

t

od

d

r

d

dilod Q

QC

R

R

R

R

C ⋅−−

+

−−+=

−

1)1(1

)1))1(1

((1

,

max

η

η {6.3.11b}

( )∑=max

min

,,

d

d

dilod dilo C C {6.3.11c}

4.

Energy required

DAF reactor does not require extra energy to make it function. The energy is

required only to feed the water and pressurized water into the tank, then the water will flow,naturally, through the tank by gravity. Pressure drop across the tank and piping system depend

on tank and piping design. This pressure drop can be calculated by general hydraulicequations, such as Darcy-Weisbach’s, Manning’s, or Hazen-William’s equation, weir

equation, orifice head loss equation, thus will not de described here.

However, it is the pressurized water system that requires most energy in DAFsystem. Design of pressurized water system or saturator will be described separately in section

6.5

6.4 Design consideration and Construction of DAF reactor

1. Reactor material

DAF reactor can be made of concrete, steel or any material that can withstandwastewater characteristic and operating condition. Special protective coating may benecessary in case of corrosive wastewater. Otherwise normal coating is sufficient.

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2. Reactor geometry and internal baffle configuration

As shown in section 6.2.4 that turbulence in reactor effects efficiency of DAF forit effects probability of collision between oil droplets and air bubbles. Theoretically,

efficiency increases with increasing turbulence or velocity gradient (G). This concept could be

applied in DAF without coagulation. However, for DAF with coagulation-flocculation, highgradient may result in re-fragmentation of flocs, which makes efficiency decrease. Besides,more turbulence may cause some undesirable eddy, which can cause carry-over of droplet

along with effluent. So geometry or configuration of internal baffle in the tank are usually

designed to minimize undesirable turbulence. However, to maximize contact or collision between bubbles and oil droplets, as well as, to ensure uniform flow distribution in the tank,DAF reactor is normally equipped with inlet baffle as shown in fig. 6.4-1. The configuration

of internal baffle is based mainly of experience. Nowadays, as computerized fluid dynamics

(CFD) tool is easier affordable, it is wildly used as a tool to design or perfect the configurationof DAF reactor

There are some attempts to design of DAF reactor to imitate the conditionwithin the flota-test, which is closest to quiescent condition. Examples of this design are

KROFTA reactor and DAF Corp. reactor, as shown in fig. 6.4-2. In KROFTA tank,

wastewater and pressurized water are fed by the rotating arm into the reactor in order thatthere is least lateral velocity.

For tank geometry, DAF reactor can be designed as rectangular or circular tank.Both shape of tank, when properly designed, can operate at about the same efficiency, eventhough some literatures [49] might claim that circular shape is superior for its better bubble

and water distribution. So other factors, such as shape of land, convenience of construction,availability and O&M cost of necessary equipment, such as scraper, skimmer, etc. should be

taken into account to determine the most suitable shape of tank.

3. DAF necessary equipment and component details

Like other treatment processes, DAF performance depends both on proper

calculation and proper equipment and component design. Nowadays, there are a lot of

packaged DAF systems and commercial products related to DAF process. Designer or ownercan contact various suppliers for more details. However, in this chapter, some details ofnecessary equipment and component details will be provided as a guideline of what is

necessary to consider in DAF process.

Fig. 6.4-1 is a good example to show necessary equipment and components ofDAF system. Brief of each equipment and component will be as described as follow.

• Inlet port or inlet channel: Inlet port or inlet channel should be designed toguarantee well bubbles and water distribution. Details of inlet port might

vary from simple branch pipes with throttling valves to big manifolds with

flow control devices (fig. 6.4-2). For circular tank, water is normally fed atthe center feed well of the tank. In this case, annular perforated pipe will be

used. Combination of good inlet port and inlet baffle, described in previousitem, will contribute to good performance of DAF system. Pressure reducing

valve or injection value or injector of pressurized water is one of the most

important component of DAF system for it plays important role in bubble

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formation. The finer the bubbles, the better the efficiency. The pressure

reducing valve will be described in section 6.5.

•

Effluent outlet: Effluent outlet is normally designed as weir or bell mouth

pipe. It plays important role to control water level in the reactor so it should be designed to be adjustable. Effluent from DAF will overflow off the weirof bell month into gutter or trough, which is normally equipped with a pipe to

recycle some portion of effluent to saturator system. For rectangular channel,

outlet port normally locates at the opposite end of inlet port. However, insome designs, outlet port will locate at the same side as inlet port to

maximize agglomerate paths. Internal baffle or lateral draw-off pipe should be properly located to ensure that only clarified water will be withdrawn tothe weir or bell mouth.

• Scum or float skimmer: air-pollutant agglomerate will float and form a

layer at the surface of the tank. The float layer is normally removed by meansof skimmer. Typical skimmer for rectangular tank is chain and flight type.

For circular tank, skimmer is normally rotating skimmer blade, attached tothe same central driving unit or rotating bridge as the bottom scraper. In

some designs, skimmer for circular tank is designed as a rotating scoop (seefig. 6.4-2) to scoop off the scum and transport via its center trough that also

serves as a shaft to scum hopper. Scum hopper or scum receiving structurewill be placed a little higher than water outlet port in order to prevent water

from overflow into the structure.

• Sludge draw-off : Settleable solids are normally present in the wastewater

and will be settled within any tanks, include DAF reactor. So sludge draw-off

system should be provided. Components of the system might vary from

simple draw-off pipes to sludge hopper with sludge scrapper. For circulartank, scraper will be either peripheral driven or central driven type. For

rectangular tank, there are several types of scraper, i.e., chain and flight,auger or screw conveyor.

4. Add-on process of DAF

Coagulation-flocculation: Efficiency of DAF depends on many factors includedinfluent oil droplet sizes. Even though DAF can be used as stand alone process, its

performance is normally erratic esp. when oil droplet size is very small. To make the

performance rather steady, coagulation-flocculation process is usually included to increase the

size of pollutant to be floated. Coagulation-flocculation process consists of 2 maincomponents, i.e., rapid (or flash) mixing part for coagulant-water mixing, and flocculation (or

slow mixing) part for floc formation. There are a lot of coagulants using for wastewater

treatment, such as metal salts, polyelectrolyte. Type and dosage of coagulant vary withwastewater characteristic and can be archived by pilot testing, such as jar test or flota-test.

Details of this add-on process will be described in chapter 10. Pictures of coagulation-flocculation from flota-test of cutting oil emulsion are shown in fig. 6.3-1. Examples of casestudies on oily wastewater treatment are shown in table. 6.4-1.

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F i g . 6 . 4 - 1 E x a m p l e o f n e c e s s a r y e q u i p m e n t a n d c o m p o n e n t d e t a i l s o f D A F s y s t e m (

S o u r c e : E n v i r o n T r e a t m e n t S y s t e m

)

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Table. 6.4-1 Data on efficiency and coagulant concentration of various oily wastewater

treatments by DAF [51]

Oil concentration

WastewaterCoagulant

(mg/l)Influent Effluent %Removal

Refinery 0 125-170 35-52 70-72

100 alum 100 10 90

130 alum 580 68 88

Oil tanker ballast water 100 alum + 1 polymer 133 15 89

Paint manufacture 150 alum + 1polymer 1900 0 100

Aircraft maintenance 30 alum + 10 activated silica 250-700 20-50 >90

Meat packing 3830 270 93

4360 170 96

Addition of transfer compound: Sometimes, efficiency of DAF is limited by

probability of air-pollutant agglomerate. In case of oily wastewater, the most frequentencountered problem is ineffective collision between bubble and oil droplets (collision

without agglomerate forming). There are some attempts to solve this problem by addingchemically active agent, called transfer compound, to change some properties of bubble or oildroplet to facilitate oil-bubble agglomerate forming. These chemicals can be added to either

wastewater or as a gas to bubbles. Examples of these chemicals are ammonium gas,

surfactants, etc. In GPI lab, DUPRE [14] had studied the effect of various transfer compoundand concluded that addition of surfactant in pressurized water can cause augmentation in population of microbubbles. On the contrary, addition of polyelectrolyte will cause decreasing

in electrical charge, then favor coalescence of bubbles.

Even though this method is used with some success for water-solid separation,

which the chemical helps forming stronger bond between bubble and solid surface, there is noclearly evidence, at least in GPI lab, that it is feasible on oily wastewater treatment (see

section 6.2.4). So it is recommended to perform DAF test with the real wastewater beforedesign this add-on system. Otherwise, coagulation-flocculation may be more suitable.

a) KROFTA’s inlet manifold with flow

control devices (Source: KROFTA)

b) Example of inlet branch pipes

(Source: Leopold)

Fig. 6.4-2 Necessary equipment and reactor components of DAF system

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c) Inclined inlet baffle at the center of the

tank (Source: WR DAF)

d) Perforated pipe inlet

(Source: HUBER)

e) Bell mouth pipe outlet (Source: ETS) f) Example of weir outlet (Source: HUBER)

g) Lateral perforated pipes for effluent

draw-off (Source: Leopold)

h) Chain and flight scum skimmer

Fig. 6.4-2 Necessary equipment and reactor components of DAF system (Con’t)

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i) Rotating scoop skimmer

(Source: DAF corp.)

j) Detail of rotating scoop skimmer

(Source: DAF corp.)

k) Example of CFD analysis on bubble

density in DAF reactor

(Source: InfilcoDegrémont)

l) Example of CFD analysis on velocity

distribution in DAF reactor


m) Typical flow pattern in DAF system

(Source : InfilcoDegrémont)

n) Folded flow pattern in DAF reactor

(Source: WR DAF)

o) Rectangular DAF reactor

(Source: WR DAF)

p) Circular DAF reactor

(Source: KROFTA)


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q) Example of shallow DAF reactor

(Source: WR DAF)

r) Graphical image of shallow DAF reactor

(Source: KROFTA)

s) Feed manifold and rotating internal baffle

in shallow DAF reactor (Source: WR DAF)

t) 4 effluent draw-off pipes in shallow DAF

reactor (Source: WR DAF)

u) Flocculation tank (Source: Aqua-

pak systems)

v) Flocculation pipe (the array of pipe

beside DAF reactor) (Source: WR DAF)


5.

Characteristic of float or scum

Characteristic of float or scum of DAF depends on characteristic of wastewater.Fig. 6.4-3 shows some examples of scum from DAF. However, for refinery wastewater, petroleum or oil-related industries, which oils are components of the wastewater, scum will be

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rich in oil. Some literatures [50] report that oil concentration in DAF scum is as high as 50%

by weight for DAF process with coagulation-flocculation. For oil-rich scum, it could be

possible to use oleophilic oil skimmer, which is widely used for API tank.

However, solids and other pollutants are usually present in oily wastewater, the

scum, then, contains these solids and pollutants and is in form of thick froth layer. DAFsystem can produce scum, which is normally more dense than settled sludge from settlingtank. Average concentration of 1% (solid content) could be expected. Higher concentration,

such as 3%, is reported by many sources [51].

a) Scum for petroleum industry (Source:

www.environmentalleverage.com)

b) Scum from high rate DAF reactor


c) Scum from circular DAF reactor

(Source: KROFTA)

d) Example of side window of DAF tank. Notice

float layer and bubble (Source: KROFTA)

Fig. 6.4-3 Examples of characteristics of scum from DAF processes

6.5 Pressurized water system or saturator

6.5.1 Working Principle and design calculation

Because air bubble is the heart of DAF operation, pressurized water system, then, is a

very important component of DAF for it is the source of air bubbles. Basic principle of pressurized water system or saturator is to dissolve the air into the water at high pressure.After that the pressurized water will be injected into the wastewater at operating pressure,

normally ambience. When the pressure decreases, solubility of air in water will decrease so

the excess air will become gas and cause air bubble within the water.

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There are 3 major modes of pressurization in DAF process, i.e.,

• Full-flow pressurization: In this mode, whole wastewater is pressurized. It mightoperate at lower pressure since the quantity of pressurized water is high, low

dissolved concentration of air is sufficient. Reactor in this case is designed only to

handle wastewater quantity. However, pollutants, esp. suspended solids, may causesome problems to the saturator system, esp. injection valve and packed saturationtank. It can not be used if coagulation-flocculation is employed for it may cause re-

fragmentation of floc by the saturator packing.

• Partial flow pressurization: In this mode, only some portion of wastewater is pressurized and then sent to mix with the rest of wastewater to reactor. However,

pollutants in wastewater might still cause some problem to the saturator system.

• Recycled flow pressurization: This mode of operation is the most popular. Some portion of treated water is recycled to use as pressurized water. Quantity of thewater is relatively good for it has been treated. So it does not cause any problem to

the packed saturation tank. However, the reactor has to handle wastewater plusrecycled flowrate.

However, the pressurized water system for every mode of pressurization is identical.

Good saturator system has to provide a number of very tiny bubbles. Characteristic of good

pressurized water is that, when it is discharged into the reactor, it will have cloudy and milkappearance for relatively long period of time, as shown in fig. 6.5-1.

a) Example of propagation of bubbles generated by pressurized water when injected

into the top of test tank.

b) Cloudy, milky appearance of bubbles generated by pressurized water

Fig 6.5-1 Example of good bubble formation from pressurized water (Source:

Cornell DAF pump)

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From GPI research [12], theoretical equations, such as Henry’s law and Dalton’s law,

can be used to calculate pressurized water system with relatively high accuracy. To size the

pressurized water system, the following procedure is proposed.

1. Quantity of air or gas in pressurized water

Solubility or concentration of air in water in saturator is practically governed byHenry’s law (eq. 6.5.1).

H

yP x = {6.5.1}

Where x = molar fraction of dissolved gas in water (mol/mol)

Y = molar fraction of gas in air (mol/mol) For air: y = 1 For oxygen:y(O2) = 0.21 (=0.11 in permanent regime) For nitrogen: y(N) =

0.79 (= 0.89 in permanent regime)P = absolute pressure of saturator (atm, or conforms to unit of H

used)H = Henry’s constant, depending on type of gas (20oC), i.e., For air:

H = 4.04x104 atm/mol For oxygen: H = 8.04x10

4 atm/mol For

nitrogen: H = 6.64x104 atm/mol

Eq. 6.5.1 can be used to calculate the value of “x” or molar solubility of gas in

saturator at any given pressure (P). Normally, saturator is operated at around 4 atm (abs).

Concentration of air or gas discharged within DAF reactor at ambience condition can becalculated by eq. 6.5.2.

1000)(

)().( ⋅

⋅⋅=

water MW

gas MW xgasConc water ρ mg/l {6.5.2a}

Where MW(gas) and MW(water) are molecular weight of gas and water

respectively.

Substitute x from eq. 6.5.1.

P A H water MW

gas MW P ygasConc water ⋅=⋅

⋅

⋅⋅⋅= 1000

)(

)().(

ρ {6.5.2b}

1000)(

)(⋅

⋅

⋅⋅=

H water MW

gas MW y A water

ρ {6.5.2c}

To facilitate calculation of dissolved air or gas, Henry’s constant can beexpressed in the form of molair (or gas)/(m3 water.atm), called H’. Eq. 6.5.2d can be used tocalculate the value of H’ at any temperature. Temperature is in Kelvin. From this concept, eq.

6.5.2b can be rewritten as shown in eq. 6.5.2e.

2472.1)273(02745.0)273(00039.0)273(000002.0' 23 +−−−+−−= T T T H {6.5.2d}

1000

')().(

H gas MW P ygasConc

⋅⋅= mg/l {6.5.2e}

For quantity of gas discharged in DAF reactor, it can be calculated from

difference between concentration of dissolved gas in at saturator’s pressure and that atambience pressure, 20 as shown in eq. 6.5.3.

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Energy for compressor can be practically calculated by adiabatic process

equation (PV1.4

= Constant) with satisfactory accuracy (see eq. 6.5.4). ηcomp is overallefficiency of compressor, which can be safely assumed to be around 60-70%.

pw

atmcomp

Q

gas MW

gasConc

P

P RT Power ⋅⋅

⎥⎥

⎥

⎦

⎤

⎢⎢

⎢

⎣

⎡−⎥

⎦

⎤⎢⎣

⎡⋅=

−

)(

)(1

4.0

1)

4.1

14.1(

η

{6.5.4}

Using R = 8.314 Pa.m3/(mol. K), Conc(air) in g/l and Q pw in m3/s will result in

power as Watt. Molecular weight (MW) of air is 28.95 g/mol. Fig. 6.5-2 shows relation between calculated power required for compressor and absolute pressure of saturator (P) for

10 m3/h of pressurized water.

Energy for pressurized water pump can be practically calculated by general

equation by assuming overall efficiency of the pump (η pump) around 60-70%.

pump

gauge pw

pump

atm pw PQPPQPower

η η

)()( ⋅=

−⋅= {6.5.5}

Using Q pw in m3/s and pressure (P) in Pa. will result in power as Watt. Fig. 6.5-2shows relation between calculated power required for pump and absolute pressure of saturator

(P) for 10 m3/h of pressurized water.

Energy for DAF pump The DAF pump is a special type of saturator thatintegrate the function of compressor and pressurized water pump into a single machine.Details of the pump will be described in the next section. Its energy required is theoretically

equal to summation of energy for compressor and energy for pressurized water pump.

However, single step estimation, using eq. 6.5.5 alone with η pump around 50-60% is

acceptable. The exact energy required can be obtained from manufacturer’s information.

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4 5 6 7 8

Saturator pressure (atm. (absolute))

P o w e r

r e q u

i r e d f o r c o m p r e s s o r

( W a t t

/ 1 0 m

3 / h o

f w a t e r )

0

500

1000

1500

2000

2500

P o w

e r r e q u

i r e d f o r p u m p

( W a

t t / 1 0 m

3 / h o

f w a t e r )

Compressor

(η = 100%)

Compressor

η = 70%

Pump

(η = 100%)

Pump

η = 70%

Fig. 6.5-2 Relation between power required for pump, compressor and absolute pressure of saturator for

pressurized water flowrate of 10 m3/h (assume %air saturation = 95%)

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6.5.2 Type of saturator and injection valve

1. Saturator

Saturator can be divided into 2 main categories, i.e.,

• Combination of pump and saturation tank: Schematic diagram of thissystem is generally as shown in fig. 6.5-3. Working principle of the system is

relatively the same as packaged booster pump or pump/pressure tank systemin water distribution work. However, the saturation tank has to be specially

designed to maximize air dissolution into water. For conventional system, thetank is designed as packed column, using ring packing or likewise, as shown

in fig. 6.5-4. Saturation tank in this case is classified as pressure vessel, so, insome countries, its design must conform to applicable law or regulation of

pressure vessel.

• In some designs, the pressure tank is replaced by other air-water mixing

device, which is equivalent in performance but less complex and lessexpensive. An example of this device is mixing pipe as shown in fig. 6.5-4.

• Generally, air compressor for DAF is installed. However, in case that there is

common compressed air supply, it can be readily used in DAF. In fewdesign, the pressure tank with automatic air intake system, which is widely

used in packaged pump-pressure tank system, is used.

• DAF pump: This device is combination of pump and air saturation systeminto one machine. Air will be either sucked from ambience by the pump itself

or supplied by compressor into pump suction or pump casing. The air willmix with the water within the pump. It eliminates the use of saturation tank.

Schematic diagram and examples of DAF pump are as shown in fig. 6.5-3and 6.5-4.

2. Injection valve

Injection valve or pressure reducing valve or pressure release valve is a devicethat practically generates air bubbles at the working point. The valve will reduce the pressure

of pressurized water to ambience, which cause excess dissolved gas to convert to gas bubbles.

In GPI lab, there are few researches on the value [14], [15]. From the researches, it shows thatthe gas will be firstly generated in form of large gas pocket and then will be fragmented byhydrodynamic force to form microbubbles (see fig. 6.5-5). So geometry of the valve, which

determines hydraulic condition, is the key parameter to obtain microbubbles. Many types ofvalves are shown in fig. 6.5-5. Selection of the valve is based mainly on experience. However,

it is recommended to install the value as close to mixing zone between wastewater and pressurized water as possible.

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a) Conventional pressurized water system or saturator system

b) Saturator system using DAF pump

Fig. 6.5-3 Schematic diagrams of saturator systems (Source: Edur pump)

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a) Packed tower to air saturation

(Source: Leopold)

b) Packed column for air saturation

(Source: Enprotec)

c) Air mixing tube for air saturation

(Source: DAF corp.)

d) Installetion of DAF pump

(Source: WR DAF)

e) Example of DAF pump

(Source: Edur pump)

f) Graphical image shows working principle

of DAF pump (Source: Hellbender pump)

Fig. 6.5-4 Examples of saturator system

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a) Examples of injection valves [14]

b) Magnified photos of air pocket formation and fragmentation in convergence-

divergence nozzle type injection valve [14]

Fig. 6.5-5 Examples of injection valve

6.6 Variations, advantage and disadvantage of DAF

There are many variations of DAF system in many ways such as tank shape, flow

pattern, equipment, loading rate, as described before in this chapter. So selection and designof DAF is state-of-art, like many other processes, and based mainly on experience. However,data from DAF test, such as Flota-test, and studies on successful projects for the same or

related type of wastewater are useful to design DAF system.

Advantages:

1. It requires less footprint area than conventional decanter.

2. Since it is accelerated process, we have some control over many operating

parameters, such as coagulant dosage, quantity of pressurized water, etc. Then it

has more flexibility to handle variation of wastewater characteristic.3. DAF is less effected by temperature, compared to other processes.

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Disadvantages:

1. Capital cost and operating is higher than conventional decanter.

2. DAF system consists of a lot of equipment, so the maintenance is higher than

conventional decanter. Moreover, it may require more skill of the operator.

3. Its efficiency depends on many parameters as described before, so it maydecrease if some parameters in not optimized.

4. Coagulation-flocculation process is normally required. This causes more expenseon chemicals.

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7.1

General

Hydroyclone is an accelerated separation process. Its main working concept is to

replace the gravitational acceleration that governs decanting velocity by higher centrifugalacceleration. Hydrocyclones are widely used in many processes, i.e., classification and

separation between solid-liquid and liquid-liquid. Unlike other centrifugal machines, driving

force of hydrocyclone is generated solely from its inlet velocity. The higher the velocity (or

flowrate), the higher the efficiency. Or it can be implied that, at the same flowrate, smaller

will have higher performance that the smaller one. This is the most interesting advantage of

hydrocyclone.

Commercial hydrocyclones come in various shapes (single conical, long double

conical, etc.) and configurations (co-current or counter current, based on direction of water

and oil outlet flow). However, because it is used to make the separation between 2 phases

(such as, liquid-liquid, solid-liquid.), it will be called here as “two-phase hydrocyclone”. InGPI lab, almost all of the researches are based on this type of hydrocyclone. In this chapter,

we will consider particularly on application of hydrocyclone on oil/water separation. For

oil/water separation, the hydrocyclones usually come in the form of elongated conical

hydrocyclone, as shown in fig 7.1-1a. Vortex or spiral movement in hydrocyclone will make

oil move inward to the center where it is purged to an overflow port, as shown in fig. 7.1-1.

Treated water will flow out at an underflow port. Studies on two-phase hydrocyclone for

oil/water separation will be described in section 7.2.

However, there is another type of hydrocyclone that is initiated by AURELLE and

MA [16] in GPI lab. This special hydrocyclone is an innovation designed for simultaneous

separation of oil and suspended solids from water. Studies on this “three-phase hydrocyclone”will be summarized in section 7.3.

a) Graphical image shows vortex and oil

core in 2-phase counter current hydrocyclone

(Source: Ultraspin)

b) Graphical image of three-phase

hydrocyclone [16]

Fig. 7.1-1 Basic flow pattern and examples of hydrocyclones

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1 2 0

2 5 5

5 3

4 2 8

10

50

Entrée

Sortie eau

Sortie huile

Entrée

Sortie eau

Sortie huile

Tube d'aspiration

Surface intérieure

Surface extérieure

c) Industrial scale counter current 2-

phase hydrocyclone (Source: Krebs)

d) Co-current lab scale 2-phase

hydrocyclone (Source: GPI lab)

Fig. 7.1-1 Basic flow pattern and examples of hydrocyclones (Con’d)

7.2 Two-phase hydrocyclone

7.2.1

Working principles

As mentioned earlier, working principle of hydrocyclone is based on modifying an

acceleration in STOKES law (eq. 7.2.1). From the law, rising or decanting velocity (U d) of oil

droplet is proportional to acceleration (a). Generally, this acceleration means gravitational

acceleration (g). However, in centrifugal machine, liquid is forced to spin or centrifuged

around the axis of the machine. So the liquid is subjected to another acceleration, which is

centrifugal acceleration. If the liquid spins fast enough, the centrifugal acceleration (ac) will

overcome the gravity acceleration. The decanting velocity of oil droplets, as well as, removal

efficiency, will increase. The higher the centrifugal acceleration is, the better the efficiency is.

c

d

d aU

μ

ρ

18

2⋅⋅Δ= {7.2.1}

Where d = Diameter of dispersed phase, in this case, oil droplets

a = Corresponding acceleration of oil droplets

Δρ = Difference between density of dispersed phase and continuous phase

μC = Dynamic (or absolute) viscosity of continuous phase, which is water, for

oily wastewater

Ud = Rising or decanting velocity of the droplet diameter “d”

So, efficiency of hydrocyclone can be described in term of ratio between centrifugal

and gravity acceleration, called the factor of acceleration (ζ), as shown in eq. 7.2.2 .For

hydrocyclone, the driving force that makes the liquid rotate or spin comes from energy of its

own inlet flowrate. Theoretically, pressure head of feed flowrate can be converted to velocity

by energy conservation law, as shown in eq. 7.2.3.

D

V a

c

22= {7.2.2a}

gD

V

g

ac22

==ς {7.2.2a}

gH V 2= {7.2.3}

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From eq. 7.2.2a and 7.2.3, ζ can be rewritten as follow,

gD

gH 2)2(2

=ς {7.2.4a}

D H 4=ς {7.2.4b}

Where ζ = Factor of acceleration

V = Tangential velocity in hydrocyclone

D = Diameter of rotation, in this case, hydrocyclone diameter

H = Head or pressure drop across hydrocyclone

Eq. 7.2.4b signifies that,

• Efficiency of hydrocyclone is direct proportional to its pressure drop.

• As stated earlier in section 7.1, efficiency of hydrocyclone will increase if the size

of hydrocyclone decreases. It can be implied that, at the same flowrate, smaller

hydrocyclone is always more efficient than the bigger one.

7.2.1.1 General flow pattern and feature of hydrocyclone

General feature

Generally, hydrocyclone consists of cylindrical section, where inlet port(s) is

tangentially placed, and conical section, which may be a smooth cone (fig. 7.1-1d and 7.2.1-

1a) or has an inflection point (fig. 7.1.1a,c and 7.2.1-b).

There may be one or two inlet ports. And it may have circular or rectangular opening.

For typical hydrocyclone, there will be an outlet port at the center of the cover of cylindrical

section. This port is always called overflow port. The port locate at the pointed end of conical

section is called underflow port. The wall of overflow port is, usually but not always,

protruded into the hydrocyclone. If it exists, this part is called vortex finder.

However, many manufacturers had separately engineered the shapes of their

hydrocyclones to fit their applications. For examples, there might be another cylindrical

section at the end of the conical section. Or there might be 2 concentric underflow without

overflow ports. Anyway, their working principal is always based on centrifugal acceleration.

Liquid-liquid hydrocyclone for oil/water seperation

Because of relatively low density difference between oil and water, compared to that

of solid and water, shape of liquid-liquid hydrocyclone for oil/water seperation has to be

adapted from typical solid-liquid hydrocyclone as shown in fig. 7.1-1 and 7.2.1-1f. The shape

of the oil/water hydrocyclone shown in the figure was researched and proposed by Prof.

THEW of University of Souththamton, UK. From the figure, another conical section with

small cone angle is added, and then followed by another cylindrical section. Overflow oil

outlet port is smaller than that of solid-liquid one. And there is no vortex finder since it is not

essential to prevent short circuit of oil to oil outlet. Moreover, THEW also shows that

presence of vortex finder resulted in lower efficiency. This hydrocyclone is widely accepted

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as a typical design of oil/water separation. In GPI lab, MA [16] also used THEW’s type

hydrocyclone for his model development.

General flow pattern

As mentioned earlier, general spiral flow pattern of typical hydrocyclone, which has 1overflow and 1 underflow port, is as shown in fig. 7.2.1-1a. From the figure, there are both

upward and downward flow. Upward and downward flow pattern might be difference in case

of co-current hydrocyclone, which has 2 concentric underflow ports. Nevertheless, flow

pattern will always be spiral, which causes centrifugal acceleration.

From centrifugal acceleration and density difference between oil and water, oil

droplets will tend to move toward the axis of hydrocyclone and form an oil rich zone or oil

core at the axis (fig. 7.2.1-1d) that can be purged to an oil outlet port. Water, on the other

hand, will be centrifuged outward and flow out at water outlet port, as shown in fig. 7.1-1a

and 7.2.1-1b. Oil core normally contains both oil and water (fig. 7.2.1-1e). So oil removed

from hydrocyclone still contains some amount of water. Then hydrocyclone is rather oilconcentrator than oil separator. To separate oil from this concentrated mixture, other

separation process, such as coalescer, may be required.

Sometimes, there is an air core forming at the center of oil core (fig. 7.2.1-1c). It does

not provide any separation efficiency and, sometimes, makes the operation unstable. Presence

of air core can be avoided by providing back pressure, such as valve throttling, at the outlet

port.

Oily wastewater

Concentrated oil

Treated water

Underflow port

Overflow portInlet port

a) General spiral flow

pattern in typical

hydrocyclone [30]

b) Typical trajectory of oil droplets

in liquid-liquid hydrocyclone

c) Example of

presence of air core

[30]

Fig. 7.2.1-1 General flow pattern and features of hydrocyclones

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d) Oil core formation (thin red strip at

the center of the hydrocyclone) [11]

e) Magnified photo of oil core, shows tiny

oil droplets suspending in water [16]

Di

D

Dn

Ds

L1

L3

Do

θ

β

Dn/D=0.5, Ds/D=0.25, Do/D<0.05, L1/D=1, L3/D=15-20 , β =1.50

o , θ =20

o

Di/D=0.25 for 1 inlet and 0.175 for 2 inlet ports, total length/D =45 (approx.)

f) THEW’s type liquid-liquid hydrocyclone for oil/water separation

Fig. 7.2.1-1 General flow pattern and features of hydrocyclones

7.2.1.2 Velocity distribution in hydrocyclone

Flow pattern in hydorcyclone, as shown in the previous section, can be described in

the form of velocity within the hydrocyclone. Velocity at any point in the hydrocyclone can

be divided into 3 components, i.e., tangential, radial and axial velocity (fig. 7.2.1-2).

Characteristic of each velocity components will be described as follow.

VzVt

Vr

Z

R

Axial axis

H y

d r o c

y c l o n e w

a l l

Vr = Radial velocity

Vt = Tangential velocity

Vz = Axial (or vertical) velocity

Fig. 7.2.1-2 Velocity components in hydrocyclone

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1. Tangential velocity

Outer zone: When water is fed tangentially into the hydrocyclone, it will cause

vortex flow pattern around axial axis on the hydrocyclone. Generally, in accordance with

conservation of angular momentum, tangential velocity (Vt) will increase as radial distance

from the axis of the hydrocyclone (R) decreases. Relation between tangential velocity andradial distance in this zone is as shown in eq. 7.2.5.

.const RV n

t = {7.2.5}

If “n” is equal to 1, this means conservation of the momentum is complete. The

vortex formed under this condition is called “free vortex”. However, for general

hydrocyclone, there is some loss within the hydrocyclone so there is no complete conservation

of the momentum. Normally, the value of “n” is between 0.5 –1.0, depending on

configuration of hydrocyclone. This type of vortex, when “n” in not equal to 1.0, is called

“semi-free” vortex.

Inner zone: When small values of R are reached, flow pattern will change in the

manner that tangential velocity decreases with decrease in radial distance. The relation

between tangential velocity and radius becomes that of solid body rotation, corresponding to

constant angular velocity, as shown in eq. 7.2.6. This flow pattern is called “forced” vortex.

.1 const RV t =− {7.2.6}

Then, tangential velocity profile within general hydrocyclone will be as shown in

fig. 7.2.1-3c, where tangential velocity profiles of various types of vortex are also shown.

R

VtR n = Const. n=1

n<1

R

Vt/R = Const.

R

Ra

Vt/R = Const. VtR n = Const

a) Free vortex (n=1) and

semi-free vortex (n<1)

b) Forced vortex c) Combined vortex (general

case of hydrocyclone)

Fig. 7.2.1-3 Tangential velocity profile in hydrocyclone and various typed of vortex

Driving force of hydrocyclone come from inlet velocity. Theoretically, tangential

velocity at the wall of hydrocyclone at the inlet port level (Vc) should be equal to inlet

velocity (Vi). However, since there is some loss within the hydrocyclone, there is some

reduction of the tangential velocity from the inlet velocity. The ratio of the tangential velocity

to inlet velocity is called “α”.

i

c

V

V =α , α < 1 {7.2.7}

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The value of α varies with the shape of hydrocyclone. From eq. 7.2.5 and 7.2.7,

tangential velocity at any radial distance can be written as shown below.

n

i

n

c

n

t

DV

DV RV )

2()

2( α == {7.2.8a}

n

it R

DV V )

2(α = {7.2.8b}

Where VI = Velocity in the inlet port of hydrocyclone

D = Diameter of hydrocyclone (measured at the same level as the

inlet port)

R = Radial distance

It should be noted that tangential velocity depends on “radial distance (R), and is

independent of axial distance (Z). The velocity at the same “R” will be practically identical at

any axial distance from inlet level of hydrocyclone (Z), as shown in fig. 7.2.1-4.

Vr1

Vr1

Vr1

Vr1

R= r1

a) Source: Krebs b) Data from KELSALL[30]

Fig. 7.2.1-4 Examples of tangential velocity profile

2. Axial velocity

As shown in fig. 7.1-1 and 7.2.1-1 that the outer and inner layers of liquid in

hydrocyclone move in opposite direction, axial velocity (Vz) profile will consist of both

upward and downward velocity, as shown in fig. 7.2.1-5. Axial velocity profile depends on

shape of hydrocyclone, such as angle of cone, and operating condition, such as presence of air

core. Even in the same hydrocyclone, characteristic of axial velocity profile at various zones,

such as conical zone, inlet cylindrical zone or near apex zone. etc., are not similar. However,

typical axial velocity profiles at the effective conical section of hydrocyclone can be

simplified as shown in fig. 7.2.1-5b and 7.2.1-5c. Fig. 7.2.1-5b is typical axial velocity profile

for solid-liquid separation, proposed by RIETEMA [quoted by [16]]. For fig 7.2.1-3c, it is the

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axial velocity profile, proposed by THEW and COLMAN [quoted by [16]] for of liquid-liquid

hydrocyclone, as well as, proposed by KASSELL [quoted by [30]] for solid-liquid separation.

There is no general relation or equation of axial velocity for hydrocyclone.

However, equations of axial velocity profile for specific shapes of hydrocyclone are available,

such as COLMAN’s equation for THEW’s type liquid-liquid hydrocyclone. The equation(shown in the next section) will be used for 2-phase hydrocyclone model development.

(Source: Krebs) (Source: [52]) (Source: Bradley [30])

a) Examples of axial velocity profiles from various sources

Locus of zero

vertical velocity

Locus of zero

vertical velocity

R

Z

L o c u

s o

f z

e r o

v e r

t i c a

l v

e l o

c i t y

H y d

r o c y

c l o n e w a l l

Axial axis

b) Axial velocity profile

with 2 downward and 1

upward flows

c) Axial velocity profile

with 1 downward and 1

upward flows

d) Axial velocity profile

predicted by COLMAN’s

equation

Fig. 7.2.1-5 Example of axial or vertical velocity profile

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3. Radial velocity

Radial velocity (Vr ) normally has a maximum value near to the wall of

hydrocyclone in inward direction. Then it will decrease with decreasing of radial distance. It

might or might not reach zero value and become outward radial velocity, depending on the

shape and axial position considering. Example of radial velocity profile is shown in fig. 7.2.1-6. KELSALL [30] proposed the estimated value of radial velocity in the conical section as

shown in eq. 7.2.9.

)2

tan(θ ⋅=W U {7.2.9}

Fig. 7.2.1-6 Example of radial velocity profile [30]

7.2.1.3 Forces on particle in hydrocyclone

From the velocity fields of liquid or continuous phase decsribed above, dispersed

particles, in this case, oil droplets, suspended in hydrocyclone will subject to many

components of forces. Consider an oil droplet (or particle) in hydrocyclone as shown in fig.

7.2.1-7. The oil droplet will subject to several clearly-defined forces, such as,

F4Fr

F1

Z

R

F2

F3

F5

WV

U

Z

R

Axial axis

H y

d r o c

y c l o n e w

a l l

Resulting V

Fig. 7.2.1-7 Forces on oil droplets or particles in hydrocyclone

Fig. 7.2.1-8 Components of velocity of oildroplets or particles in hydrocyclone

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• Centrifugal force in radial axis (F1)

6

32

1

d

R

V F

π ρ ⋅⋅Δ= {7.2.5a}

• Drag force or hydraulic force in radial axis (F2)

421

2

22 d U Cd F c π ρ ⋅⋅= {7.2.5b}

• Gravity force (F3)

6

3

3

d gF

π ρ ⋅Δ= {7.2.5c}

• Drag force or hydraulic force in axial axis (F4)

42

1 22

4

d W Cd F c

π ρ ⋅⋅= {7.2.5d}

• Drag force or hydraulic force in tangential direction (F5)

42

1 22

5

d V Cd F c

π ρ ⋅⋅= {7.2.5e}

Where U = Radial velocity (or decanting velocity) of oil droplets

V = Tangential velocity of oil droplets

W = Axial velocity of oil droplets

Please note that three components of velocity are of oil droplets (fig 7.2.1-8), which

are not exactly the same as the three velocities (Vx, Vy, Vz) of liquid , described in the previous

sections. There are also other forces, such as lift force, etc. These forces will make the oil

droplets move in hydrocyclone and determine if those droplets can be totally, partially

separated or can not be separated by the hydrocyclone. Normally, it is not possible to exactlycalculate some components of forces or account for all forces to find the exact resultant force

that governs movement of oil droplets.

Thus, to predict if oil droplets can be separated by hydrocyclone or, on the other hand,

efficiency of hydrocyclone, there are 2 major approaches, i.e.,

• Theoretical based model, such as trajectory analysis, equilibrium orbit or

retention time based model. Well proven laws, such as STOKES law, are applied

to these models under some assumption or simplification. This type of model

might or might not be very accurate, compared to empirical model derived from

experimental data. The accuracy of the type of model depends on degree ofsimplification used by the researchers. But it is useful tool to understand the effect

of parameters to the effciency of hydrocyclone.

• Empirical based model, such as the model and reducing efficiency curve,

proposed by Yoshioka and Hotta [30], Dalstorm’s, and Plitt’s , as well as THEW-

COLMAN’s model.

7.2.1.4 Trajectory analysis model

GPI’s trajectory analysis model for oil/water separation is the work of MA [16].

Concept of MA’s model is adapted from the concept of decanter. Major assumptions thatunderlines this model are that;

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• The concept of decanter that oil droplets will be separated by hydrocyclone, if the

oil droplets can reach the decanting surface before flowing out with water is

applied (see fig. 7.2.1-9). Decanting surface in this case is assumed to be the locus

of zero vertical velocity (LZVV). If the droplets can reach this line, next moment,

they will start to travel upward to oil outlet port, then, are separated from the

wastewater.

• There is equilibrium of forces in radial direction and oil droplet travels in the radial

direction at terminal velocity of immersed object in fluid stream.

• Radial velocity is governed by STOKES law.

• For tangential and axial velocity of oil droplet, it is assumed that oil droplets are

entrained by the water and have the same tangential and axial velocity as the water

at that point. So V = Vt and W = Vz.

• THEW’s type hydrocyclone is used. So tangential and axial velocity profiles are

calculated from the equations proposed by THEW, COLMAN [quoted by [16]] for

this type of hydrocyclone.

Three velocity components, used for model development, are governed by eq. 7.2.6 to

7.2.8.

Radial velocity: derived from STOKES law;

R

V d U

c

22

18⋅

Δ=

μ

ρ

{7.2.6}

Tangential velocity: derived from energy conservation law (see eq. 7.2.8) and verified by experimental data to find α and n. For THEW hydrocyclone, α = 0.50 and n = 0.65. Please

note that eq. 7.2.7b is valid only for 2-inlet ports hydrocyclone only.

65.0)2

(50.0 R

DV V i= {7.2.7a}

Or 65.0

2

4

)2

(50.0 ⎟

⎠

⎞⎜⎝

⎛

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

= R

D

D

Q

V n

i

π

{7.2.7b}

Axial velocity: COLMAN [quoted by 16]] observed axial velocity profile in lower

conical section of THEW hydrocyclone, which is the effective section, and developed axial

velocity equation in form of the 3rd order polynomial equation, as shown in eq. 7.2.8. Z-axis

starts from the bigger end of lower conical section, where R is equal to Dn/2, toward the lower

cylindrical section.

32

19.163.81233.3 ⎟⎟ ⎠

⎞⎜⎜⎝

⎛ +⎟⎟

⎠

⎞⎜⎜⎝

⎛ −+−=

z z z z R

R

R

R

R

R

W

W {7.2.8a}

2))2/tan(5.0( β π ⋅−=

Z D

QW

n

z {7.2.8b}

)2tan(2

β

⋅−= Z

D

R

n

z

{7.2.8b}

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Q represents wastewater inlet flowrate. Dimensions of the hydrocyclone (Di, Dn, etc.)

conform to fig. 7.2.1-1f. To find trajectory, relation between R and Z has to be found. Firstly,

consider equation of U and W as follow;

t

RU

δ

δ −= {7.2.9a}

t

Z W

δ

δ = {7.2.9b}

From above equations, we have;

W

U

Z

R=−

δ

δ {7.2.10a}

W

Z

U

R δ δ =− {7.2.10b}

Integration of eq. 7.2.10b will result in the relation between R and Z, as shown in eq.

7.2.10c.

∫∫ =− L R

RW

Z

U

R ZVV

0

δ δ {7.2.10c}

R ZVV represents any points on the locus of zero vertical velocity (LZVV), which is

normally in conical shape. However, since conical angle of the lower cone is very small

(1.5o), it can be safely assume that LZVV is cylindrical with the radius of R ZVV at the small

end on the cone (Z=L). At Z = L, from eq. 7.2.8, R ZVV is equal to 0.186(Dn/2). So relation

between R and Z or trajectory of oil droplets can be rewritten as shown in eq. 7.2.11.

Integration of the equation is transcendental and requires complex numerical method, such as

Runge-Kutta. However, it can be done by advanced calculator or computer program,including the program being developed in this research.

∫∫ =− L

RW

Z

U

R Dn

0

)2/(186.0

δ δ {7.2.11}

d = dc

d > dcd < dc

Z

R

L

R d

H y d r o c y c l o n e w a l l

LZVV

0.5Dn

0.186Dn

d

ηd

d c

d < d c

Zone 1 Zone 2

d = or > d c

100%

Fig. 7.2.1-9 Trajectories of oil droplets and typical efficiency curve

from trajectory analysis model

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Efficiency determination

Fig. 7.2.1-9 shows the trajectories of oil droplets in lower conical section of

hydrocyclone. As stated before, decanting surface in this case is the locus of zero vertical

velocity (LZVV), which can be calculated from eq. 7.2.8, where W = 0. To simplify the

calculation, it is assumed that LZVV is cylindrical with R = 0.186(Dn/2).

From the figure, the longest path to reach the LZVV is the path starting at the wall of

the hydrocyclone at larger end of the cone to the zero-vertical-velocity point at the lower end

of the cone (fig. 7.2.1-9a). The smallest droplet size that can reach this point is called the cut

size (dc). The droplets of cut size or bigger are always separated from wastewater stream with

100% removal efficiency (eq. 7.2.12a).

For d ≥ dc %100=d η {7.2.12a}

The smaller droplets can be also separated providing that they enter the cone near tothe axis of the hydrocyclone. When uniformly distributed influent flow is valid, which is

practically true, the removal efficiency of the droplets smaller than cut size are proportional to

corresponding radial distance (R d) that makes the droplets reach the ZVV point at the lower

end of the cone, as shown in eq. 7.2.9b. Typical efficieny curve of the trajectory analysis

model is shown in fig. 7.2.1-12b.

For d < dc %100

)2

186.0()2

(

)2

186.0(

22

22

⋅−

−=

nn

n

d

d D D

D R

η {7.2.12b}

7.2.1.5 Other models

There are several researches that suggests the model to predict the efficiency of

hydrocyclone, both theoretical and empirical based, such as Bradley’s, Rietema’s,

Dahlstrom’s, Chebelin’s, Plitt’s, Lynch’s, etc. [16],[28]- [34]. However, most of models are

developed from solid-liquid hydrocyclone. Some models are developed for specific

commercial oil/water hydrocyclone, such as Vertoil’s. So it should be applied only with that

specific hydrocyclone. Extrapolation of model is normally not guaranteed.

For THEW’s type hydrocyclone, used by MA in his research, Prof. THEW, himself,

and his colleague, COLMAN, have proposed the model for the hydrocyclone (eq. 7.2.13a).

However, it is empirical model, which seems to be obtained from curve fitting. The equation

for estimation of d75% for THEW’s hydrocyclone, quoted by CHEBELIN [29], is as shown in

eq. 7.2.13b (use unit in kg, m, second.)

))19.0%75

(8.1(

1

−−−= d

d

d eη {7.2.13a}

5.03

%75

)(01.0⎥⎦

⎤⎢⎣

⎡

⋅Δ

⋅=

Q

Dd n

ρ

μ {7.2.13b}

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7.2.1.6 Comparison between observed efficiency and theoretical efficiency

MA’s model was verified by observed data obtained from crude oil/water treatment.

Fig. 7.2.1-10 shows the efficiency curve from MA’s trajectory analysis model (eq. 7.2.6 to

7.2.8, 7.2.11), THEW-COLMAN’s model (eq. 7.2.10 and 7.2.11) and observed efficiency

[16]. From the figure, it shows that, at droplet size > 20 microns, MA’s and THEW-COLMAN’s models give relatively accurate result (± 10% error). However, at d > d 80%,

THEW-COLMAN’s model seems to cause higher degree of error and predict too high value

of cut size. This may because the researchers used different assumptions or operating

condition to develop their models.

Difference between MA’s model and observed value can be explained by effect of the

assumptions used to develop the model as follow;

• Radial velocities of oil droplets are not exactly governed by STOKES law.

STOKES law is valid only in laminar flow regime (Re of droplets < 1). However,

in some cases, esp. when droplet size is large, Re might be greater than 1. And

from very short retention time, the droplets may not reach the terminal velocity,

governed by STOKES law. Furthermore, radial velocity of water, which can carry

the oil droplets along and add-up to the decanting velocity from, is not accounted.

So the value of U used in the model is, generally, lower than actual value. This is

the reason why the predicted efficiency is lower than the observed value.

• Effect of eddy current, lift forces, drag forces in vertical and tangential direction is

assumed to be negligible and cancelled. Anyway, they, in fact, can cause some

discrepancies in the prediction result.

• Effect of hinder settling, esp. near to the center of hydrocyclone

However, Ma’s model is developed from theoretical assumption and does includemany parameters, such as viscosity, feed flowrate, and size of the hydrocyclone, etc., which

can be used to explain or verify the effect of these parameters to the efficiency. So, it provides

valuable tool to designer and will be used in the computer program being developed under the

scope of work of this research. Furthermore, the trajectory analysis model is developed under

the assumptions that give underestimated result. So the predicted efficiency is on the safe side.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

0.00 10.00 20.00 30.00 40.00 50.00 60.00


E f f i c i e n c y

( % )

Thew-Colman's model

Observed data

Ma's trajectory analysis

Note: Dn = 0.02 m, Q = 1.943 m3/h, Vi = 7.12 m/s: Wastewater used is crude oil/water emulsion: Δρ =

98 kg/m3, μ = 0.0011 Ns/m2, β = 15o, d = 15 to 50 microns

Fig. 7.2.1-10 Comparison between observed efficiency and predicted efficiency form MA’s model and THEW-COLMAN’s model

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There is no tested evidence about the valid range of MA’s model. However, from the

assumptions used, the model should be valid for every THEW’s type hydrocyclone as long as

operating condition is in valid range of STOKES law (laminar flow region: Re < 1). Anyway,

working condition and performance of hydrocyclone are also governed or limited by other

parameters or factors. So it is more suitable to state that the model is valid in laminar flow

region when other factors also confirm to working limit of hydrocyclone, as described insection 7.2.1.7.


Parameters that affect the performance of hydrocyclone are those presenting in model,

as shown in section 7.2.1.4. However there are some factors that have influent on the

efficiency of hydrocyclone that can not be expressed in form of numerical function. Influent

parameters of hydrocyclone, collected from GPI researches and many literatures, can be

summarized as follow;

1.

Droplet size (d)

Efficiency of hydrocyclone increases with increasing of droplet size, as clearly

shown in fig. 7.2.1-10. So it is recommended to avoid any action that can cause oil drops to

break-up into smeller droplets, such as using high-shear feed pump (Ex. high speed

centrifugal pump, or regenerative turbine pump). On the contrary, putting some process that

can increase the size of droplets at upstream of hydrocyclone, such as high-rate coalescer, will

help increasing hydrocyclone performance.

2. Feed flowrate (Q)

From eq. 7.2.4, efficiency of hydrocyclone will increase, if feed flowrateincreases for it will make inlet velocity, which is a driving force of hydrocyclone, increase.

However, this is true before velocity in the cyclone reaches the value that droplet re-

fragmentation occurs. There are evidences [16], [28] that the inlet velocity (V i) as high as 7

m/s is used without causing any adverse effect on efficiency. This value of Vi can be

compared to velocity of 1.7 m/s, using nominal diameter (Dn) of the cyclone. Please note that

increasing of flowrate also cause pressure drop to be increased, which effects operating cost.

Pressure drop will be described separately in section 7.2.1.8.

3. Shape of hydrocyclone

Shape of hydrocyclone substantially effects its velocity profiles and vortexformation. So it certainly effect its performance. But it can not be expressed in form of

numerical equation. Many researchers have studied effect of dimension of each component of

solid-liquid hydrocyclone (such as inlet port, overflow, underflow port, vortex finder, etc.).

For oil/water hydrocyclone, THEW has thoroughly studied the effect of geometry and

proposed the optimized shape of the cyclone, which is used in GPI researches. In fact, we

usually design hydrocyclone system from standard commercial product, which, more or less,

conform to THEW’s geometry. Anyway, MA [16] had carried out some profound studies of 2

components. The result is as shown below.

• Conical angle θ : Using lower θ (from 20o to 8o) result in decreasing of

pressure drop about 11% (from 4.5 to 4.0 bar at 1.6 m3/h, Dn = 16 mm, crudeoil/water emulsion) while the efficiency is relatively unchanged.

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• Ratio Dn/D: Lower Dn/D from 0.5 to 0.43 can increase efficiency (+5% for

Q = 1 to 1.6 m3/h) but pressure drop is also considerably increased (+0.5 bar

for Q = 1 to 1.6 m3/h, D = 32 mm, Dn = 16 and 14 mm).

It must be noted that the models in section 7.2.1.4 and 7.2.1.5 are valid only for

THEW’s type hydrocyclone only.

4. Inlet oil concentration (Co)

For low concentration oily wastewater (Co < 1%), the concentration has

practically no effect on efficiency. For higher concentration, theoretically, it should effect the

performance from hinder settling effect and changing of viscosity. However, THEW [28]

shows that the efficiency is little affected even at the concentration as high as 10 – 15%.

5. Purge ratio or split ratio(Rf )

For oily/water separation, oil will be purged to outlet overflow port. Purge ratio

(R f ) (or split ratio) is the ratio between oil outlet flowrate (overflow) to water feed flowrate

(Q). Theoretically, flowrate of overflow should be as close as possible to the flowrate of oil

components in the water to get relatively pure separated oil. However, in practice, it is

impossible to do so because pressure drop will be too high and some oil will entrain to

underflow port. It is recommended to use R f around 1.8 to 2.0 times of flowrate of inlet oil

[28]. For general oily wastewater, which inlet oil concentration less than 5% (by volume),

purged oil flow is relatively small compared to the whole flow. So it does not effect velocity

profile and efficiency of hydrocyclone. But it effects pressure drop, which will be described in

the next section.

6.

Wastewater characteristic and presence of surfactant

Wastewater characteristic inevitably affects efficiency of hydrocyclone. The

model in section 7.2.1.4 has included general parameters that represent characteristic of

wastewater, such as Δρ, μc, etc. So it is useful tool to understand effect of parameters on

cyclone performance. Some indirect parameters can be determined if it effects the

performance or not by considering its effect on those parameters included in the equation.

For example, presence of salinity will increase density difference, so it favors

efficiency. Presence of surfactant will lower interfacial tension, resulting in fragmentation of

droplets, so it causes adverse effect on hydrocyclone.

7.

Temperature (T)

Proporties of oil and water always change with parameter. So it is inevitable that

temperature will effect hydrocyclone efficiency. Rising in temperature make water viscosity

decrease, then favors the efficiency. However, it will decrease interfacial tension and density

difference, then has adverse effect on the efficiency. So effect of temperature on individual

waster will be accounted on these facts. Anyway, for petroleum/water emulsion at normal

working condition (<40o C), increasing of temperature, more or less, favors hydrocyclone

efficiency.

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8. Presence of air core

Air core could form at the axis of hydrocyclone from presence of low-pressure

region generated by vortex, especially when it is purged directly to atmosphere. It is also

formed by changing in solubility of gas in water from decreasing of pressure. Presence of air

core might partially block the overflow port and result in instability of performance. Air coreformation can be suppressed by avoiding direct purge to atmosphere and the use of

backpressure. However, many system operating with several percent of air core (by volume)

still give satisfactory result. So throttling should be made until the efficiency is optimized

without over-emphasizing on air core formation. In fact, its formation could not be visible in

commercial opaque hydrocyclone.


Pressure drop is very important parameter since it directly relates to driving force of

the hydrocyclone, as shown in eq. 7.2.4. Furthermore, purge ratio and back pressure control to

suppress the air core is normally be done by valve throttling at the two outlet ports, whichdirectly effects the pressure drop.

Pressure drop can be divided into 2 types, i.e., pressure drop across inlet and overflow

port (ΔPo) and pressure drop across inlet and underflow port (ΔPu).

Like the case of efficiency, equations of the pressure drop of hydrocyclone were

proposed, based on both theoretical and empirical approach. However, there is no pressure

drop model for THEW’s type hydrocyclone, which we knew of. Anyway, many literatures

[16], [28] – [34] show that general model of pressure drop relation is as shown in eq. 7.2.14.

)/(4.2

n

xx DQ f P =Δ {7.2.14}

From GPI researches, there are sufficient data to formulate semi-empirical models of

pressure drop from the general model, as shown below.

For pressure drop (bar) across inlet and overflow port (oil outlet);

1611.0

4

3.2

)1(

6.216 ⎟

⎟ ⎠

⎞⎜⎜⎝

⎛

−⋅=Δ

f n

o R D

QP {7.2.15a}

Flowrate and hydrocyclone diameter are in m3

/s and m, respectively. R f is lower than1.0. However, effect of purge ratio is verified from relatively small set of data, so it might

cause some error. Firthermore, for low concentration wastewater (Co<5%, Rf <10%), effect

or Rf is very small. Eq. 7.2.15a can be rewritten as eq. 7.2.15b, which can be safely used

without causing serious error.

17.1164

3.2

×=Δn

o D

QP {7.2.15b}

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For pressure drop (bar) across inlet and underflow port (water oultet);

4

2.2

6.4

n

u D

QP =Δ {7.2.15c}

From above equations, it should be noted that:

• Pressure drop of overflow is always higher than that of underflow. So it is used for

pump sizing. If multi-stage hydrocyclone system is used, available pressure for the

next stage is equal to (ΔPo-ΔPu). The unit of Q is in m3/s, D in meter.

• Underflow pressure drop is practically independent of split ratio. While overflow

pressure drop is slightly affected by the split ratio.

• For oily wastewater treatment, which involves low concentration of oil,

characteristic of wastewater does not affect the pressured drops.

General working pressure range of hydrocyclone is up to 6.5 bar. THEW [28]

recommended the value of 1-5 bar. Hydrocyclone selection is to be compromised between

efficiency, size (capital cost) and pressure drop (operating cost).


Design procedure for hydrocyclone is based upon the equations, shown in the previous

sections. To design two-phase hydrocyclone for oily wastewater treatment, the required cut

size will be determined first. After that, the size of the hydrocyclone can be preliminary

selected. Then, graded efficiency (efficiency of each size of droplet) and then total removal

efficiency can be determined. The procedure will be repeated until the optimum size isselected. Calculation in each step is described below.

1

Cut size determination

The cut size can be determined from the degree of treatment required as well as

from the limitation of the decanting processes. Cut size determination from degree of

treatment is described in chapter 3. For theoretical limitation, since the model is based on

STOKES law, it can be applied only when the droplet behavior conforms to the law. Thus, it

can not be used with very small droplet sizes for they are subjected to Brownian’s motion and

their rising velocity are not governs by STOKES law. There are also some limitations from

characteristic of hydrocyclon itself that governs the cut size selection. Generally,recommended smallest diameter that can be separated (but only partially) by hydrocyclone is

about 20 microns. For smaller droplets, the efficiency will be very low and erratic.

To design the hydrocyclone by MA’s model, it is recommended to select the cut

size that covers majority of oil droplet in the wastewater and provide a safety factor around

10% to 20%, because the model is apt to predict too small cut size. For example, if the desired

cut size is 50 microns, it is recommended to select 50(1-0.20) = 40 microns.

2 Hydrocyclone sizing

The size of the hydrocyclone could be roughly estimated by general designcriteria, such as maximum working pressure, hydraulic loading, etc. Fig. 7.2.1-1 shows the

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relations between flowrate, inlet velocity, velocity at lower conical section (at dia. = Dn) VS.

diameter of the cylindrical part of hydrocyclone (D) at Po = 3 and 5 bars, which are generally

used as design pressure. For the exact size, the mathematical model can be used. Then the

model will be used again to find the graded efficiency of the hydrocyclone. After that, the size

may be fine adjusted again to obtain the required efficiency.

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0 10 20 30 40 50 60 70 80 90 10

Diameter of cylindrical section of hydrocyclone (D) (mm)

F l o w r a

t e ( m

3 / h ) a n

d V e

l o c

i t y ( m / s )

Q at P = 5 bar

Q at P = 3 bar

Inlet V at P = 5 bar

Inlet V at P = 3 bar

V at Dn

at P = 5 bar

at P = 3 bar

0

Fig. 7.2.1-1 Corresponding flowrate and velocities of various sizes of hydrocyclones at

overflow pressure drop (Po) = 3 and 5 bars

To size the hydrocyclone and calculate greaded efficiency of the hydrocyclone,

the following procedure, based on MA’s model, is recommended.

2.1 Calculate the size of hydrocyclone (D n )

The size of the hydrocyclone can be calculated by integrating eq. 7.2.11, using

the design cut size from item 1. The corresponding R will be equal to (D n/2). The integration

can be done by the use of a scientific calculator, general mathematical software or the

computer program developed in the scope of work of this research.

∫∫ =− L

RW Z

U R

Dn

0

)2/(186.0

δ δ {7.2.11}

R

V d U

c

22

18μ

ρ Δ= {7.2.6}

65.0

2

4

)2

(50.0 ⎟

⎠

⎞⎜⎝

⎛

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

= R

D

D

Q

V n

i

π {7.2.7b}

32

19.163.81233.3 ⎟⎟

⎠

⎞⎜⎜

⎝

⎛ +⎟⎟

⎠

⎞⎜⎜

⎝

⎛ −+−=

z z z z

R

R

R

R

R

R

W

W {7.2.8a}

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III-174

2))2/tan(5.0( β π ⋅−=

Z D

QW

n

z

{7.2.8b}

)2

tan(2

β ⋅−= Z

D R n

z

{7.2.8b}

)2/5.1tan(

)(25.0o

n D

L =

{7.2.16}

2.2 Calculate corresponding radial entering distance (Rd)

For the droplet smaller than the cut size, it is necessary to calculate the

corresponding R d that makes the droplet reach the radial distance R = 0.186(Dn/2) at Z = L.

To calculate R d, eq. 7.2.11 need to be integrated again, using every value of “d” that is smaller

than the cut size.

3 Outlet concentration and removal efficiency

Graded efficiency

Graded efficiency (or centrifugal efficiency), in this case, represents the

efficiency calculated from the trajectory analysis method. For d ≥ dc, graded efficiency will be

equal to 100%.

For d ≥ dc %100=d η {7.2.12a}

For the droplet smaller than the cut size, the theoretical graded efficiency can be

calculated, using the R d from item 2.2, by the following equation.

For d < dc %100

)2

186.0()2

(

)2

186.0(

22

22

⋅−

−=

nn

n

d

d D D

D R

η {7.2.12b}

Outlet concentration

Outlet oil concentration at the underflow (water) and overflow (oil) outlet can be

calculated from theoretical efficiency and purged ration as shown in eq. 7.2.17a and b,

respectively. The equation is valid only when the purged flow is greater than the oil

quantity in the wastewater. Otherwise the oil that can reach the oil core will not be purged

entirely and then entrain with the underflow.

)1(

)1(

f

od d

d R

C C

−

−=

η {7.2.17a}

f

od d

overflowd R

C C

η =,

{7.2.17b}

Global efficiency and removal efficiency

Graded efficiency is not the actual efficiency of hydrocyclone because it does

not account for purged or split flow. Even though this split flow is small and hardly affects the

flow regime in the hydrocyclone, it, somehow, affects the oil concentration calculation. As

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described in section 7.2.1.7, the purged flow must be greater than the oil quantity in the

wastewater. Otherwise the oil that can reach the oil core will not be purged entirely.

Total removal efficiency (ηt) of the hydrocyclone represents ratio of oil

concentration between underflow and inlet flow, which can be calculated from the following

equation.%100

1

)1(

1 max

min

⋅⋅⋅−

= ∑d

d

od d

o f

t C C R

η η {7.2.18}

Co = Inlet oil concentration of the wastewater

Cod = Inlet concentration of the droplet diameter “d”

R f = Split ratio (= Qoverflow/Q)

4 Pressure drop and energy required

The pressure drop (in bar) can be calculated from the following equations.

Generally, the overflow pressure drop is greater than that of underflow and will be used as

design pressure for feed pump selection. The unit of Q is in m3/s, D in meter.

1611.0

4

3.2

)1(

6.216 ⎟

⎟ ⎠

⎞⎜⎜⎝

⎛

−⋅=Δ

f n

o R D

QP {7.2.15a}

4

2.2

6.4

n

u D

QP =Δ {7.2.15c}

7.2.3 Design considerations

1.


The equations described above are developed from the following assumptions

and limitations. Thus, it is necessary to ensure that these assumptions are valid when design

your hydrocyclone.

1) The model is valid only for THEW’s type hydrocyclone or other cyclones

with relative identical geometry.

2) It is recommended to use the model only for droplet diameter of 20

microns or greater. For smaller droplet, it can also be applied, but for

comparison only.

3)

Eq. 7.2.7a is valid for the hydrocyclone with 2 inlet ports only. If thehydrocyclone has only 1 inlet port, Q in the equation will be modified as

shown in eq. 7.2.7a’. However, using 2 inlet ports is recommended for its

hydraulics stability. Please note that the size of 2 inlet ports will be smaller

than a single inlet port to keep the inlet area constant.

0.65)R

nD)(

2i

πD

Q2(V = {7.2.7a’}

4) For general oily wastewater with the oil concentration of 5% or less,

overflow quantity is small, not greater than 10%. So its effect on velocity

profiles and efficiency is small, thus, negligible.

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5) From the assumptions used for model development, the model prediction

has some discrepancies from the actual value. However, as stated in section

7.2.1.6, it is a useful tool for understanding the effect of each parameter.

6) The hydrocyclone should be designed within the limitations shown in

section 7.2.1.7. The size of hydrocyclone should conform to commercial

standard sizes.7) From eq. 7.2.4b, it is recommended to select the smallest possible

hydrocyclone. However, the pressure drop, clogging problem from the

presence of suspended solids and cost should be taken into account.

8) From the high shear characteristic, it is reasonable to assume that there is

no coalescense taking place within the hydrocyclone. Re-fragmentation can

be avoided by following the recommended range for pressure and flowrate.

So it can imply that the overall size distribution of oil droplets is not

affected by the hydrocyclone. This assumption is useful for considering the

size distribution of each stage of multi-stage hydrocyclone system.

2.

Construction and system integration

Normally, we select the hydrocyclone from commercial products. So we cannot

do anything about its design and fabrication. However, it is necessary to study the product to

make sure if it conforms to our model limitation.

Hydrocyclone efficiency depends on the sizes of the oil droplets, so the

processes that can make the droplets smaller, such as pumping, should be avoid or kept to

minimum, at the upstream of the hydrocyclone. Or the hydrocyclone should be installed as

close to the wastewater source as possible.

Generally, oily wastewater contains some suspended solids. So the hydrocyclonesystem is designed as a coupling of soild-liquid and liquid-liquid hydrocyclone, as shown in

fig.7.2.3-1. In this case, the feed pressure of the first stage hydrocyclone should be sufficient

for the next stage hydrocyclone(s). Installation of booster pump between each stage is

possible but not recommended since it will make the oil droplets smaller.

a) schematic diagram b) An example of commercial set

Fig. 7.2.3-1 An example of the coupling between solid-liquid and liquid hydrocyclone for thetreatment of oily wastewater containing suspended solids (Source: Ultraspin)

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7.2.4 Variations, advantage and disadvantage of hydrocyclone

Variation of two-phase hydrocyclone

There are some variations of liquid-liquid hydrocyclone, for example in flow pattern

(counter current, co-current), etc. (see fig. 7.1-1). In any case, the majority of the liquid-liquidhydrocyclone still conforms or relativelty close to THEW’s type. Nowadays, there are several

suppliers that commercialize these products, such as Neyrtec, Dorr Oliver, Krebs, Ultraspin,

etc. So designers can find further information from these suppliers.

However, there is another type of liquid-liquid hydrocyclone preliminary tested in GPI

lab [11] that should be mentioned here, i.e. “the co-current hydrocyclone” (fig. 7.1-1d). Main

advantage of this hydrocyclone comes from its shape which is considerable shorter (around

8.5 times of D) than THEW’s type (about 45 times of D). So it requires less installation space.

There is no study on comparison between THEW’s and the co-current cyclone efficiencies in

GPI lab. However, WANICHKUL [11] proposed useful relation between oil and water outlet

velocity of the co-current hydrocyclone. He used an oil extract pump, instead of typical outletvalves, to control oil outlet flowrate. From fig. 7.2.4-1, the effects of relation between water

outlet velocity (V1) and oil outlet velocity on oil removal efficiency are summarized below.

Oil outlet

Water outlet

V1

V2

Oil outlet

tube, dt

Case I: V 1≥ V 2 and

d t > Oil core

Case II: V 1<V 2 and

d t > Oil coreCase III: V 1≤ V 2 and

d t < Oil core

Case IV: V 1>>V 2 and

d t < Oil core

Fig. 7.2.4-1 Relation between oil and water outlet velocity in co-current hydrocyclone

• V1 ≥ V2 and the concentric oil outlet tube is greater than diameter of oil core

The oil will be largely removed. The efficiency is high.

• V1 < V2 and the oil outlet tube is greater than diameter of oil core The oil willalso be largely removed. But some oil will be entrained with the water. The

efficiency is slightly lowered.

• V1 ≤ V2 and the oil outlet tube is smaller than diameter of oil core The oil will

flow out at both oil outlet and water outlet ports. The efficiency is low.

• V1 >>V2 and the oil outlet tube is smaller than diameter of oil core The

efficiency is, somehow, relatively high from the effect of high oil outlet velocity.

These facts are useful for the co-current cyclone operation. However, the efficiency of

the co-current hydrocyclone cannot be calculated by MA’s trajectory analysis model. To

design this cyclone, designers should consult the manufacturers or find more researches on

this type of hydrocyclone.

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Advantages: Main advantages of the hydrocyclone include.

• Its compactness and it has no moving part.

• Its efficiency increases with flowrate (eq. 7.2.4b). This is the most distinguished

advantage of the hydrocyclone.

• No additional chemicals (such as coagulant, floccuclants) required.• The operation is not complicate.

• Its modular construction facilitates upgrading or optimization.

Disadvantages: Main disadvantages of the hydrocyclone include,

• It is a pollutant concentrator, rather than a separator. However, GPI lab has

developed the oily wastewater treatment system which is the combination of

hydrocyclone and coalescer to make it possible to obtain relatively pure separated

oil. The details will be discribed in chapter 12.

• The hydrocyclone cannot remove the oil and the suspended solids simultaneously.

So it needs at least 2 hydrocyclones of different shape. To overcome thisdisadvantage, GPI lab has initiated a special hydrocyclone that can separate both

the oil and suspended solids at the same time. The details will be described in the

following section.

7.3 Three-phase hydrocyclone


As mentioned in the previous section, a limitation of general hydrocyclone is that it

cannot be used to separate solid and liquid pollutant from the wastewater simultaneously.

Coupling of standard solid-liquid and liquid-liquid hydrocyclones are normally used for this purpose (fig. 7.2.3-1). To obtain these two separations simultaneously, AURELLE and MA

[16] had initiated a new type of hydrocyclone, known as “three-phase hydrocyclone”, as

shown in fig. 7.3.1-1. The idea behind its geometry is the fusion between liquid-liquid cyclone

of THEW and solid-liquid cyclone of RIETEMA. The vortex created by inlet flow will be

used as a driving force for the 2 parts of the hydrocyclone. Three-phase hydrocyclone does

not require an inter-connecting pipe between 2 cyclones like typical 2-cyclone system (fig.

7.2.3-1). Theoretically, it means the energy loss of the system is reduced. Thus the efficiency

should be better. Installation space is also reduced.


DoDDs

DiDu

Dp

L5 L3L1L2

L4

Note: Di/D=0.25 for 1- inlet and 0.175 for 2- inlet, Do/D=0.43,Ds/D=0.28, Du/D=0.19, Dp/D=0.034,

L1/D=0.4,L2/D=5, L3/D=15, L4/D=0.3, Solid-liquid part cone angle=12o , for liquid-liquid part=1.5

o

Fig. 7.3.1-1 Three-phase hydrocyclone

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Fig. 7.3.1-2a shows the trajectories of oil droplets and suspended solids. The solids

will be centrifuged outward to the wall of cyclone and be purged at the annular solid outlet

port at the apex of RIETEMA’s conical section. The oil droplets will move toward the axis in

the RIETEMA part and flow up into THEW part, where they will join the oil core. The oil

core will spirally flow at the axis down to the RIETEMA part again, and then be purged to oil

concentric outlet tube.

Generally, working principle of this hydrocyclone is still similar to that of two-phase

hydrocyclone. However, The result from MA’s Plexiglas model showed that the vertical

velocity in RIETMA part is slightly changed to account for the central oil core, as shown in

fig. 7.3.1-2b.

Wastewater inlet

Wastewater inlet

Water inlet

Solid annular outlet port

Concentric oil outlet tube

Fig. 7.3.1-2a Oil drop (sphere) and particle (cube) trajectories in three-phase hydrocyclone

Solid-liquid

(RIETEMA) part

Liquid-liquid

(THEW) part

Fig. 7.3.1-2b Typical vertical velocity profiles in three-phase hydrocyclone

7.3.1.1 Model for liquid-liquid part

MA reported that the flow pattern and formation of the oil core inside the THEW (oil)

part of three-phase hydrocyclone is identical to THEW’s hydrocyclone. But no mathematical

model had been proposed. However, from the identical flow pattern compared to THEW’s

cyclone, it can be safely assumed that the driving force of this hydrocyclone is identical to

THEW’s type hydrocyclone and MA’s trajectory analysis for THEW’s type hydrocyclone

should be applicable for this cyclone as well.

From the assumption that two and three-phase hydrocyclone have identical drivingforce, which is the fraction of their own inlet velocity, we have the following equation;

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( ) i(Thew)V

Thewα

3iV

3α ⋅=⋅

φ φ

( )

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ ⋅=

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

⋅2)

i(Thew)π(D

4Q0.5

2)3i

π(D

4Q3

α

φ φ

From the geographies of the cyclones (fig. 7.2.1-1f and 7.3.1-1),

Dn in fig.7.2.1.1f = Do in fig. 7.3.1-1 = ND.

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅=

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅2))

0.5

NDπ(0.25(

4Q0.5

2))0.43

NDπ(0.25(

4Q3

αφ

676.0

2

0.43

0.50.5

3α =⎟

⎠

⎞⎜⎝

⎛ ⋅=⋅φ

{7.3.1}

The subscript “3φ” and “THEW” represent that the variables belong to three-phase

hydrocyclone and THEW’s type hydrocyclone, respectively.

From above equations, MA’s model as shown in section 7.2.2 can be adapted for

three-phase hydrocyclone design by changing the value of φ in eq. 7.2.7b from 0.50 to 0.676 .

D n in the equations of 2-phase hydrocyclone is replaced by D o in case of 3-phase hydrocyclone. L in those equations is also replaced by L 5. The model was verified by the

observed data from MA’s research. The result showed that the model could predict the

theoretical oil removal efficiency of the three-phase hydrocyclone with ± 20% accuracy.

7.3.1.2

Model for solid-liquid part

MA did not propose model for solid-liquid part either. Anyway, since the geometry of

this part of three-phase hydrocyclone is similar to RIETEMA’s cyclone, the assumption that

the driving force of this cyclone is identical to standard RIETEMA hydrocyclone should be

valid. So the model derived for RIETEMA hydrocyclone, which is general form of solid-

liquid hydrocyclone, should be applicable to three-phase hydrocyclone.

RIETEMA [30] defined the performance of the hydrocyclone in the form of d50% and

the dimensionless number Cy50, as shown in eq. 5.9. To find graded efficiency besides d50%,

correlation of YOSHIOKA and HOTTA [30], for 2% < ηd <98%, may be applied (eq. 5.10).

50Cy

Qcρcη

Δ p)4

L2

)(Lcρss(ρ2

50d

=⋅−−

{7.3.2}

30.115)

50%d

d(

e1SSd,

η

−−

−= {7.3.3}

RIETEMA recommended the value of Cy50 around 3.5 for RIETEMA type

hydrocyclone, which MA used as one part of his hydrocyclone. So it is recommended to use

Cy50 =3.5 to calculate the efficiency of solid part of three-phase hydrocyclone.

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MA proposed the model for pressure drop calculation for his prototype hydrocyclone.

For the prototype, he used Do = 14 mm and D = 32 mm. Pressure drops across various ports of

the prototype (in bar) can be calculated from the following equations,

2.111.364Qwater ΔP = {7.3.4a}

2.340.951QssΔP = {7.3.4b}

03.2140.3 QPoil =Δ {7.3.4c}

The equations are valid only for 14/32-mm. three-phase hydrocyclone. Thus, to extend

the valid range of the equations or to develop generalized model. We consider 2 approaches.

• Similarity approach

From TRAWINSKY [33], he suggested that hydrocyclone, like other centrifugalmachines, is subject to concept of similarity or affinity law.

Δρ2

50%d

1DΔP

−−∝ {7.3.5}

So combination of eq. 7.3.4 and 7.3.5 can be used to predict the pressure drops of

any size of three-phase hydrocyclone by calculating the pressure drops of 14/32-mm.

hydrocyclone at given flowrate by eq. 7.3.4 first, then use eq. 7.3.5 to find the flowrate at

given hydrocyclone diameter and given characteristic of wastewater.

• Empirical approach

Similarity approach is theoretical based. In practice, many factors may cause some

discrepancies from theoretical value. To account for these factors, empirical approach is

introduced. We base our model on eq. 7.2.14 that we successfully applied for two-phase

hydrocyclone.

To develop and verify empirical model, we use the data from MA’s and THEW’s

research [16], [18]. The empirical models for predicting of the pressure drop across inlet and

various outlet ports are as shown in eq. 7.3.6 (ΔP in Bar, Q in m3/s, D in m.).

4D

2.12Q49.8

water ΔP = {7.3.6a}

4D

2.34Q21ssΔP = {7.3.6b}

4D

2.03Q55

oilΔP = {7.3.6c}

The equations are in the similar forms to MA’s models. However, substituting the

value of D = 32 mm in eq. 7.3.6 will not result in the exact eq. 7.3.4 because eq. 7.3.6 are

verified from wider range of data.

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Comparisons between the predicted pressure drops of the 2 approaches, using data

from [16], [28], are as shown in fig. 7.3.1-3. The graphs show that the two approaches give

very accurate results. However, using eq. 7.3.4 and 7.3.5 may cause some difficulty because it

requires calculation for d50% first. So using eq. 7.3.6 may be more convenient.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00


P r e

d i c t e d p r e s s u r e

d r o p

( b a r )

= Pressure drop across oil outlet port

= Pressure drop across water outlet port

= Pressure drop across SS outlet port

S e m

i - e m p

i r i c a

l

S i m i l a r i t y

Fig. 7.3.1-3 Comparison between observed pressure drop and predicted valued from the 2

approaches (similarity and semi-empirical model)

7.3.2 Design calculation and design consideration

Because the mathematical models of three-phase hydrocyclone is adapted from two-

phase hydrocyclone, design procedure as well as design consideration for the three-phase

hydrocyclone will be identical to that of the two-phase, as shown in section 7.2.1 and 7.2.2.

But the efficiency and pressure drop across solid outlet port of the solid-liquid part will be

calculated additionally by eq. 7.3.2, 7.3.3 and 7.3.6b.

7.3.3 Advantage and disadvantage of three-phase hydrocyclone

Advantage: Main advantage of this hydrocyclone is that it can remove solid and oil

simultaneously. It can replace typical two-stage system. The installation space is reduced. It

also helps saving the piping work

Disadvantage: Various types of three-phase hydrocyclone are developed and patented, such as AURELLE and MA’s and few American designs. However, it is available

as custom-made equipment, rather than mass product. So it may not be cheap and may cause

some inconvenient in maintenance or part replacement. The oil and solids removal

efficiencies are also inter-related for they share the same driving force. So, in some case, to

obtain one good removal efficiency (either oil or solid), the other removal performance may

not work at the optimized condition. So the flexibility of the system is, somehow, less than

that of the coupling between 2 cyclones.

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8.1 General

Membrane process is a separation process based, mainly but not entirely, on filtration

concept. Physically, membrane is permeable or semi-permeable material, which restricts themotion of certain species [54]. Theoretically, we can always separate one or more components

from fluid stream providing that the membrane chosen is suitable for size difference.

Membrane process becomes one of the most promising separation process due to its

characteristics that fulfill modern needs, proposed by AURELLE [56], i.e.,

• Its efficient

•

Its compactness

• Its closed-system characteristic, no odor, no noise pollution

•

Its automatic control capability

Nowadays there are a lot of books, literatures and researches on membrane processes.

Membrane manufacturers can also provide useful data from their own experiences. Thus, in

this chapter, the main context will emphasize on the researches of GPI lab on the treatment

of oily wastewater by membrane processes. Only some basic principles and mathematical

model, related to the researches, will be present to provide basic understanding. UF is the

main membrane process of the GPI researches on oily wastewater treatment since its

separation characteristic practically covers the range of oil droplets found in general oily

wastewater, esp. macro- and microemulsion. Thus, majority of this chapter devotes to UF

study. For other processes, only some basic knowledge and the significant findings from the

GPI researches will be presented.

8.1.1 Classification of membrane processes

There are several types of membrane separation processes. Here will be considered

only the pressure-driven membrane processes. Other processes that use other forms of driving

forces, such as electrodialysis (electrical potential), dialysis (concentration gradient),

pervaporation (concentration and vapor pressure), will not be considered here. Pressure-driven

membrane processes can be categorized by their separation characteristics, i.e.,

microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). An

example of relation between material sizes and their corresponding membrane processes is as

shown in fig. 8.1.1-1. From the relations shown in the figure, separation characteristic of eachmembrane process can be summarized as shown in fig. 8.1.1-2. Membrane are classified

either by pore size or “molecular weight cut-off” (MWCO). The latter is determined by

relation between the sizes of materials to be separated by the membranes and their molecular

weights. It should be noted that manufactures, sometimes, use different kinds of material to

determine the MWCO, i.e., proteins (globulin, albumin, etc.), saccharides (dextrans), etc.

Thus there is some difference in the relation between the pore size and molecular weight. It is

recommended to confirm with the manufacturers. The size of material, defined by MWCO,

may not be exactly equal to the pore size of the membrane. But it is the size that the

membrane can be separated with acceptable efficiency (about 90%), not absolute (100%). So

it is usually called “normal MWCO” or “NMWCO”, to distinguish from “absolute MWCO”

that which is normally not specified.

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MF and UF have relatively large pore sizes, so they work rather like screens or sieve

filters. While separation by NF and RO, which have very tiny pore sizes, is not simply by size

alone but involves more complex factors, such as osmotic pressure. So we can group the

membranes processes into 2 categories, i.e., (1) MF and UF, (2) NF and RO.

Fig. 8.1.1-1 Material sizes and corresponding membrane processes (Source: Osmonics)

Fig. 8.1.1-2 Separation characteristic of membrane processes

(Source: Koch membrane system)

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8.1.2 Mode of operation of membrane processes

In membrane process, wastewater or mixture that contains the objects or materials to

be separated (called “ feed ”) will be fed to membrane module. Only certain component of feed

will be able to pass through the membrane. The component that can pass through the

membrane is generally called “permeate” or “filtrate”. The rest, which is retained by themembrane, will remain in the feed side and be called “retentate” or “concentrate”.

Mode of operation, categorized by flow direction of feed, can be generally divided

into 2 modes, as shown in fig. 8.1.2-1, i.e.,

• Dead-end mode- Flow direction of feed is perpendicular to the membrane surface.

Retained component will accumulate on the membrane surface so its operation is

rather like a cake filtration. This cake could obstruct the permeate flow, resulting

in lower permeate flowrate. However, because of its simplicity, no complex piping

required, it is normally used in slab-scale for preliminary testing of membrane.

Anyway some upscale dead-end membrane, such as pleated MF, is also available.• Cross-flow or tangential flow mode- Unlike dead-end mode, the feed is pumped

over the surface of the membrane, resulting in two product streams i.e., permeate

and retentate. The later is sometimes recycled to the feed side and fed to the

membrane again until it reaches the design concentration, esp. in case that the

concentrate is the required product. General commercial membranes are

configured to be operated in this mode of operation. It is practically used in real

life situation. So, in this chapter, we emphasize only on the cross flow mode.

a) Dead end b) Cross-flow

Fig. 8.1.2-1 Mode of operation of membrane process [11]

8.1.3 Membrane structure

Application of a membrane depends on its mechanism, which, in turn, based upon its

structure. Many authors may suggest difference number of membrane structures. By some

criteria, some structures may be only sub-types of other structure. However, it can be

generally summarized into two major structures, i.e. symmetric and asymmetric membrane.

• Symmetric membranes are the membranes of uniform structure. Their separation

mechanism can be compared to in-depth filtration. Microporous membrane is

categorized in to this type of the structure. Normally, inorganic membranes, such

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as ceramics, microporous glasses, metals, come under this structure. This type of

membrane may be produced by these manufacturing processes, i.e.,

•

Sintering or stretching

• Casting

•

Phase inversion and etching

•

Extrusion

• More details can be provided by membrane manufacturers or from literatures and

books. Sometimes, symmetric membranes are undergone coating process to

achieve some specific properties. In this case, it will become asymmetric

membrane with composite structure.

• Asymmetric membranes are the membranes of non-uniform structure, which

separation process takes place a thin denser “skin” layer of the membrane. Their

separation mechanism can be compared to screening or sieving. They can be

produced of a single polymer. In this case, they will be called “integrally skinned”.

Sometimes, a thin dense polymer skin is formed on the microporous support.

Then, it will be called “composite” or “non-integrally skinned” membrane.

Asymmetric membrane may be produced by these manufacturing processes, i.e.,

• Casting of skin and laminating to support film

•

Dip-coating of skin-forming polymer onto microporous support

• Phase inversion

• Gas-phase deposition of the barrier layer from a glow-discharge plasma

• Interfacial-polymerization of reactive monomers on the surface of support film

a) Symmetric structure b) Asymmetric

Fig. 8.1.3-1 Membrane structures (Source: SCT, Millipore)

8.1.4 Membrane material

Membrane material plays very important role on separation. To obtain efficient

separation, the membrane material should posses the following properties;

• Chemical resistance to feed and cleaning agents

• Mechanical and thermal stability

• High selectivity and permeability

•

Stable operation

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The properties mentioned above depend on types of membrane material as well as

feed or, in our case, wastewater. Membrane materials can be divided into 2 groups, i.e.,

• Polymeric material

•

Inorganic material

Some polymeric membrane materials and their properties are briefly summarized, as

shown in table 8.1.4-2. For inorganic materials, they generally include ceramics, glasses and

metals. Almost all of inorganic membranes are in tubular form, either single-channel or multi-

channel module. For ceramic membranes, they are generally of asymmetric (composite)

structure with fine-grain skin, such as titania (TiO2) or zirconia (ZrO2), over porous support,

such as alumina (Al2O3) or zirconia. There are many variants of these composite materials,

such as zirconia/alumina, titania/alumina, carbon/zirconia, carbon/carbon, etc. For metal

membranes, stainless steel is used as support layers with sintered or coated skin, such as

zirconia. Inorganic membranes are, sometimes, coated with polymeric skin to produce the

membranes of required pore with very durable support layer, which can be re-coated when the

skin is damaged. General advantages and disadvantages of inorganic membranes are astabulated in table 8.1.4-1.

Properties and characteristic of the two types of membranes described in this section

can be used as a preliminary guideline for material selection. However, its properties may be

modified by modern coating or other process to obtain required characteristic of each

application. Furthermore, there are other materials that can be used for membrane production.

So it is recommended to consult the manufacturers and perform feasibility test before design

the system.

a) Regenerated CA, regenerated PS (above),

effect of surface thickness on void formation

b) PP(above) and Polycarbonate from

irradiation and chemical process

Fig. 8.1.4-1 Membrane materials (Structures depend on manufacturing processes.)

(Source: Millipore, Orelis, WWW.Scienceinafica.co.za)

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e) Polysulfone UF d) Ceramic

Fig. 8.1.4-1 Membrane materials (Structures depend on manufacturing processes.)

(Source: Millipore, Orelis, WWW.Scienceinafica.co.za) (Con’t)

Table 8.1.4-1 Advantages and disadvantages of inorganic membrane [38]

Advantage Disadvantage

Very good chemical resistance to chlorine,

acids, alkalis, common solvents. However,

even though the membrane is very durable,

chemical resistance of other accessories, such

as seals, must be considered.

Initial cost is much more expensive than

polymeric membranes. However, lifetime and

saving in replacement cost must be taken into

account.

Wide range of pH (0.5-13, even 0-14 for

some types) and temperature (up to 125o C,

even 350o C for some types).

Ceramic membranes are naturally brittle. It

could be damaged if dropped or subjected to

severe vibration.

High pressure limit (up to 10 bar), which is

usually the limit of seals.

Require high tangential velocity (2-6 m/s). So

large pumping capacity is required.

Extended operating lifetime, more than 10

years-lifetime is reported.

Narrow range of pore size, normally available

only in MF and UF forms.

Backflushing capability allows effective

cleaning of membrane.

In general, high permeate flux.

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Table 8.1.4-2 Summary on membrane polymeric materials [38], [54], [57]

MaterialType of

membraneAdvantage Disadvantage

Cellulose acetate

(CA)

MF, UF, RO Inexpensive

Wide range of pore size,

Hydrophilicity

Good fouling resistance to oil

and fat.

Narrow pH (3-6) and

temperature range (<40oC),

Moderate chlorine resistance

(<1 mg/l free Cl)

Biodegradable

Polyamide ,

aromatic (PA)

MF, UF, NF,

RO

Wide range of pH (2-12) and

temperature (to 70 o

C)

More permselectivity than

CA

Low resistance to free

chlorine, esp. in alkali solution

Biodegradable.

Polysulfone (PS) MF, UF, RO

substrate

Wide range of temperature

(up to 75oC –125

oC) and pH

(1-13)

Good chlorine resistance (to

200 ppm)

Good chemical resistance to

alcohols, acids, halogenated

hydrocarbons

Hydrophobicity,

Low range of pressure (< 7 barfor plate, <1.7 bar for hollow

fiber)

Moderate chemical resistance

to aromatic hydrocarbons,

ketones, ethers, esters

Polyacrylonitrile

(PAN)

MF, UF, RO

substrate

Hydrophilicity (modified

form)

Good chemical resistance

Narrow range of pore size

Require co-polymer to make

less brittle

Polypropylene (PP) MF, UF Inexpensive

Wide range of temperature

Good chemical resistance

Hydrophobicity

Polytetrafluoro-

ethylene (PTFE)

MF, UF Very good chemical and

thermal stability

Hydrophobicity

Expensive

Polyvinylidene

fluoride (PVDF)

MF, UF Very good chemical

resistance to chlorine, acid,

alkali, common solvents

Hydrophobicity (can be

modified to obtain

hydrophilicity), Expensive

Note: Bold letters are most usual application. [57]

8.1.5

Membrane module type

There are several types of membrane module available. However, they can be divided

into 5 types (fig. 8.1.5-1), categorized by their geometry, i.e.,

•

Tubular module

• Hollow fiber module

• Plate module

• Spiral wound module

• Other types, such as dead-end pleated module, rotating disc module, etc.

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Here will be described only the first 4 types for they are normally applied on oily

wastewater treatment. General characteristic of each type of membrane module can be

summarized as shown in table 8.1.5-1. Please be noted that technologies are improved

everyday. So some data (cost, efficiency, some features, etc) need to be updated regularly.

a) Tubular (Source: Orelis, Koch) b) Hollow fiber (Source: Koch, Romicon)

c) Plate (Source: Millipore, Orelis) d) Spiral wound (Source: Orelis, ALTO japan)

Fig. 8.1.5-1 Membrane modules

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e) Pleated module

(Source: Vivendi water, Sentry)

f) Rotating disk system (above) and vibrating

membrane system (Source: IGB, VSEP)

Fig. 8.1.5-1 Membrane modules (Con’t)

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8.2 Ultrafiltration (UF)

8.2.1

Basic knowledge and working principles

8.2.1.1 Pore size and molecular weight cut-off (MWCO) of UF

Ultrafiltration (UF) membrane can retain material of the size larger than 0.001-0.02

microns (1-20 nm) [38], which is the size of finely dispersed oil droplet in emulsions. So the

researches in GPI lab emphasized on the application of UF, rather than other membrane

processes. UF membranes are normally specified by the molecular weight cut-off “MWCO”.

To relate the membrane to MWCO, PORTER [59] proposed the relation based on globular

proteins as shown in fig. 8.2.1-1. Please note that if the specified MWCO is not based on the

proteins, the graph will not be valid. Hence, the exact pore size information should be

confirmed by the manufactures.

1

10

100

1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04

Molecular weight cut-off (MWCO) as Kilo Daltan (kd)

P o e r s i z e ( m i c r o n s )

Fig. 8.2.1-1 Relation between pore sizes and MWCO [59]

Removal or retaining efficiency of membranes are usually described in the term of

“rejection (R)”, which is defined by eq.8.2.1.

R

P

C

C

R −=1 {8.2.1}

Where CP = Solute or pollutant concentration in permeate

CR = Solute or pollutant concentration in retentate

If the pollutants are completely rejected by the membrane, CP will become zero and R

will be equal to 1 or 100%.

Typical characteristic of rejection or removal efficiency of a membrane and molecular

weight is a shown in fig. 8.2.1-2. Existing UF membranes often posses “diffuse cut-off”,

rather than “sharp cut-off”, characteristic because of its wide distribution of pore sizes. .

NMWCO is the molecular weight at the rejection of 90%. This percentage may not be

practically exact but it is the generally accepted value. So the pore size shown in fig. 8.2.1-1 is

the effective value, corresponding to its NMWCO.

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Log (molecular weight)1,000

R e j e c t i o n o r

R e m o v a l e f f i c i e n c y

Sharp

cut-off

Diffuse

cut-off

10,000 100,000

0 %

100 %

90 %

NMWCO

Ideal cut-off

Fig. 8.2.1-2 Typical characteristic curves of UF membrane

To select the appropriate membrane to separate the oil droplet or particles from the

wastewater, AURELLE summarized and proposed 3 basic considerations as follows,

• Pore size of membrane: To prevent oil droplets to pass through the membrane

pore, the size of the pore, firstly, must be smaller than the droplets. From

researches in GPI lab, it is recommended that minimum pore size should be 1/4 to

1/3 of average droplet size. Some researches [38] even proposed the ratio of 1/10.

• Characteristic of membrane: for oil/water separation, membrane should be

hydrophilic. Membrane material should not react with the wastewater, which can

cause pour clogging. Hydrophilic material, such as polyacrylic, cellulose acetate,

zirconium oxide, etc., is recommended. Naturally without special treatment orcoating, polysulfonate tends to be fouled by oil, resulting in low flux and frequent

washing.

• Operating condition: Operating pressure should be less than capillary pressure

required to force the oil droplets through the membrane pores. Capillary pressure

increases with the hydrophilicity of membrane and decreasing of pore size.

However, if pore size and hydrophilicity are carefully selected, the capillary

pressure is normally higher than recommended maximum pressure of the

membrane. The capillary pressure of oil drop can be calculated by the modified

form of the capillary equation (see chapter 2), proposed by NAZZAL (quoted by

[10], [11]) as shown in eq. 8.2.2.

⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−

⎟⎟⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜⎜⎜

⎝

⎛

+−+⎟⎟ ⎠

⎞⎜⎜⎝

⎛

−−= 1

1/3

)o/w

θ3sino/w

sinθ(2o/w

cosθ

3

r

dr

4

2o/w

θ3coso/w

3cosθ

r

o/wcosθ

o/w2γcapP {8.2.2}

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θ

r d

2r

Membrane

Oil droplet

θ

Pore

Where r d = Radius of oil droplet (L)

r = Pore radius (L)

θ = Contact angle

γo/w = interfacial tension ofoil and water (MT

-2)

Fig. 8.2.1-3 Oil drop at membrane pore

8.2.1.2 Characteristic of cross-flow ultrafiltraton

Because almost all of the ultrafiltration processes in real life situation are in cross-flow

mode, characteristics and theories presented in this chapter, then, will be based on cross-flow

ultrafiltration. For wastewater treatment process, the aims of the process are (1) to separate

the pollutants from the water and (2) to reduce the volume of the retentate as much as

possible. So the UF processes are normally designed as a batch system, shown in fig.8.2.1-4,

which will be used to describe the characteristics of cross-flow UF in this section. In this

section, only characteristic curves are presented but the explanation and the models that

govern the characteristics will be described in the next section.

Permeate

Retentate

Membrane

Feed

pump

Storagetank

Feed

Po

Pi

Pp

Heat

exchanger

Fig. 8.2.1-4 Typical schematic of cross-flow UF for wastwater treatment

1.

Permeate flux and transmembrane pressure

From fig. 8.2.1-4, the feed will be pumped by feed pump into the cross-flow UF

module. The pressure on the feed side (P F ) will be higher than the pressure on the permeate

side (P p ), which is normally equal to atmosphere. So the solvent and the solutes that cannot be

retain will be forced through the membrane as permeate. Difference between the pressure on

feed and permeate sides (eq. 8.2.3) is called the “ transmembrane pressure” (Pt). Since the

feed inlet pressure (Pi) and outlet pressure (Po) is not identical due to losses in the membrane

module, PF is an average value of Pi and Po (eq. 8.2.4). Flowrate of permeate is usually

defined as “ permeate flux”, which is the flowrate per unit area of the membrane, such as litre

per square meter per hour (LMH).

pF t PPP −= {8.2.3}

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2. Permeate flux and feed concentration

Relations between feed concentrations and permeate fluxes in log/normal scale

are as shown in fig.8.2.1-6. The typical relation is linear, as shown in curve 1. However, in

case of oily wastewater, the curve is proven to be as shown in curve 2 [11], [18]. Other shapes

of graphs also exist but are scarcely found.

Log (Concentration)

1 2

Cg

case 1

Cg

case 2

C’g

case 2

Flux

Fig. 8.2.1-6 Characteristic curves of permeate flux and feed concentration

3.

Permeate flux and time

Constant feed concentration

Evolutions of flux with time when the feed concentration is kept constant are

shown in fig. 8.2.1-7. The flux will decrease rapidly at first, then the rate of decrease will be

slower. After that the flux will be relatively constant or steady. The fluxes shown in fig. 8.2.1-

4 are the value of flux in this steady zone. The period of time before the flux reaches steadyvalue may take few minutes or several minutes, depending on the type of wastewater, type of

membrane and operating conditions, as shown in fig 8.2.1-7. In fig. 8.2.1-7a, the relation that

the flux increases with time is scarcely observed. It occurs when the feed concentration is very

low and the cross-flow velocity is high.

Flux

Time

Higher cross-flow velocity

Lower concentration

Time

FluxHigher Pt

a) Effect of velocity and feed concentration b) Effect of transmembtane pressure

Fig. 8.2.1-7 Typical characteristics of permeate flux VS. time for constant feed conc. system

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Non-constant feed concentration

Evolution of flux with in this case will be varied with wastewater characteristic,

membrane properties and operating condition. For oily wastewater treatment, the retentate is

returned to the storage tank where fresh wastewater may and may not be added, as shown in

fig. 8.2.1-4. Then it is fed repeatedly to the membrane until it reaches a requiredconcentration, or the flux is unacceptable low. In this case, the concentration of feed, as well

as flux, varies with time.

General characteristic of UF of oily wastewater in batch process described above

is as shown in fig. 8.2.1-8. At first, the flux drops relatively rapid, then rate of decrease is

lower. The flux decreases slower until it reaches a certain concentration. Then rate of decrease

in flux is higher until it become about zero.

Time

Flux

Fig. 8.2.1-8 An example of characteristic of flux VS. time for non-constant feed conc. system

8.2.1.3

Flux model in pressure controlled region

From characteristics of UF processes described above, Many researchers had tried to

explain them in term of related theories and established mathematical models to predict the

characteristics of UF. To predict flux of UF in pressure controlled region (fig.8.2.1-5b), the

widely accepted model is the one based on flow through porous channel, which is governed

by Hagen-Poiseuille law, as shown in eq. 8.2.5.

μ μ

ε t t p P

AP

x

d J ⋅=⋅⎟

⎟ ⎠

⎞⎜⎜⎝

⎛

Δ⋅

⋅=

32

2

{8.2.5}

Where J = Flux (L3L-2T-1, i.e. LMH or gallon per ft2 per day (GFD))

ε = Surface porosity of the membrane

d p = Pore diameter (L)

Pt = Transmembrane pressure (LT-2

M-1)

Δx = Length of the channel, in this case, the thickness of “skin” layer of

the membrane (L)

μ = Dynamic viscosity of feed (ML-1

T-1

)

A = Membrane permeability coefficient (L)

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The model is valid the following assumptions are satisfied [38];

1. The flow is in laminar regime. Re < 2100. It is usually true under certain

conditions, such as (1) low pressure (2) low feed concentration, (3) high cross-

flow velocity.

2.

Density is constant. The liquid is incompressible.3. The flow is independent of time (steady state condition).

4. The liquid is Newtonian.

5. End effects are negligible.

This equation can also be used to calculate the water flux of the membrane. Normally,

it is difficult to determine geometry parameters in the equation, such as ε, Δx, d p. However,

these parameters are constant. So the group of parameters in the parenthesis can be

determined experimentally by UF test with a known liquid, such as water. After that, it can be

applied to other liquids by changing the viscosity.

From the equation, the flux varies linearly with the transmembrane pressure.However, when the pressure is higher, the properties of liquid, such as viscosity, etc., and the

effect of mass transfer phenomena is prevailing. Characteristic of UF will change to mass

transfer controlled region. Eq. 8.2.4 will be no longer valid.

For the water flux, it is usually governed by eq. 8.2.4. However, deviation may occur

in some cases, as shown in fig. 8.2.1-5a. This can be described by the deformation of the

membrane pores under high pressure or pore blocking due to trace material in the water. The

latter case usually occurs when tap water is used to determine the water flux.

8.2.1.4 Concentration polarization

In mass transfer controlled region, the flux is relatively constant and independent of

pressure, as shown in fig. 8.2.1-5b. To explain this, mass transfer phenomena in the UF

module should be considered. One of the important transport phenomena is the formation of

concentration polarization.

When the mixtures, solution, or wastewater is fed to the UF, particles, solutes,

macromolecules or pollutants are rejected by the membrane. These materials, then, tend to

accumulate and form a layer of high concentration of the materials at the membrane surface

(fig. 8.2.1-9). This layer is called “polarization layer”, “CP layer”, or “gel layer” [38].

However, gel layer is usaually refered to a layer of gel, which concentration is quite constant,

while polaization layer is the transition zone which concentration increase from bulkconcentration to that of gel. Characteristic of the layer depends on the type of the materials.

This layer is believed to hinder and restrict permeate flow by one of the two mechanisms, i.e.,

1.

High solute concentration increases the osmotic pressure within the polarization

layer. The osmotic pressure will oppose or counter the transmembrane pressure

and make the effective driving force of the process decrease. So the flux is

decreased.

2. High solute concentration in the polarization layer causes the solute to transport

back into the bulk liquid by concentration gradient. At certain concentration, the

transport of solute to the layer by convection and the back-transport will

counterbalance, resulting in steady flux.

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Important notes on polarization layers are,

1. It is assumed to be dynamic. Changes in operating condition, such as cross-flow

velocity, pressure, will change the polarization layer. The layer will disappear if

the system does not operate. This fact makes it different from the fouling of

membrane, which will not disappear unless the membrane is cleaned.2.

It is believed to make the flux pressure-independent in mass transfer controlled

region. Change in pressure will change the polarization layer, thus, the osmotic

pressure or back-transport will be changed accordingly, resulting in

counterbalance of the system. For example, if the pressure is higher, the flux will

be briefly higher and then drop back to the previous value.

8.2.1.5 Mathematical model for mass transfer controlled region: film theory

One of the widely used model for flux prediction in mass transfer controlled region is

film theory model . It is derived by balancing the convection mass transfer and the

concentration-gradient back-transfer. The model is as shown in eq. 8.2.6a

)ln()ln(P

Pg

P

Pg

C C

C C K

C C

C C D J

−

−=

−

−=δ

{8.2.6a}

Where J = Flux (L3L-2T-1, i.e. LMH or gallon per ft2 per day (GFD))

D = Diffusion coefficient or diffusivity (L2T-1)

δ = Thickness of polarization layer (L)

K = Mass transfer coefficient (L3L-2T-1)

Cg = Gel concentration

CP = Permeate concentration, (= 0 since oil rejection is normally100%)C = Bulk concentration

Gel concentration is theoretically the concentration of gel layer at the surface of

membrane. C g is assumed to be constant for a given solution or wastewater. From fig. 8.2.1-

5b, it shows that the flux in mass transfer controlled region still varies with cross-flow

velocity. Many researchers including GPI’s [11], [18] proposed that the model could be

modified to account for the effect of cross-flow velocity (V) as shown in eq. 8.2.6b. The effect

of V on the flux is as shown in fig. 8.2.1-9. The values of k, K, and C g depend on the type

of wastewater and membrane and are usually obtained by experiment.

Membrane

Polarization layer

Permeate

Bulk concentration

CB

Cg

C p

Gel layer

Cg Log (Concentration)

V1

lux V2>V1

Fig. 8.2.1-9 Diagram of polarization layer and effect of velocity on flux in film theory

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)ln(C

C kV J

g β = {8.2.6b}

The equations for determining the value of K, based on Buckingham π theory are also

widely used (eq. 8.2.6c - e) [38]. However, to use the equations, it is necessary to know the

value of Cg and D. The value of D also depends on the type of solution or wastewater.

For turbulent flow, Re>4000 33.08.0Re023.0 ScSh = {8.2.6c}

For laminar flow,

Re< 1800, Lv<L, Lc>L

33.033.033.0 )/(Re86.1 Ld ScSh h= {8.2.6d}

For laminar flow,

Lv>L, Lc>L

50.033.05.0 )/(Re664.0 Ld ScShh

=

{8.2.6e}

Where Sh = Sherwood number = kdh/D

Re = Reynolds number = ρdhV/μ

Sc = Schmidt number = μρ/D

dh = Hydraulic diameter = 4. flow area / wet perimeter (L)

Lv = Entrance length, based on velocity profile or the distance from the

entrance of membrane module flow channel that the velocity profile

becomes steady (L)

Lc = Entrance length, based on concentration profile (L)

L = Length of membrane module flow channel (L)

Eq. 8.2.6c to 8.2.6e are universal models, derived from many assumptions. So they can

provide only the approximate value of K. Eq.8.2.6a and b are also developed from

concentration-gradient assumption, described in the previous section. So it may not exactly fitreal flux/pressure curve. Some researches [54] reported that the concentration at the

membrane surface is not constant, but varies with operating condition. However the model is

accepted as an effective mathematical tool to estimate the flux in mass transfer controlled

region.

8.2.1.6 Resistance model

The porous flow model and film model cannot be used to predict the flux in both

pressure and mass transfer controlled region. So other models ware developed to govern the

whole range of flux/pressure behavior, such as resistance model and osmotic pressure model.

Here will be described resistance model for its mathematical simple that facilitates its use.

For resistance model, the concept of resistance-in-series, like in heat transfer, is

adapted. General form of the model is as shown in eq. 8.2.7.

∑=

R

P J t {8.2.7}

ΣR represents the summation of various resistances (see fig. 8.2.1-10) i.e.,

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Gel /Polarization

layer

Gel resistance (R g)

Fouling resistance (R F)

(Adsorption)

Fouling resistance (R F)

(Pore Blocking)Membrane

resistance (R )

M e m b r a n e

Feed

Permeate

PF

P p

Fig. 8.2.1-10 Various resistances in UF processes

1. Membrane resistance or intrinsic membrane resistance (R m ): It is the

resistance of membrane determined using pure water as the feed. It is the inverse

of A in eq. 8.2.5. R m is theoretically constant and depends only on the type of the

membrane.

W

t

m J

P R = {8.2.8}

2. Fouling resistance (R F ): Membrane fouling, unlike concentration polarization,

is characterized by irreversible decline in flux, caused by interaction between

feed and membrane as well as deposition and accumulation of some feed

components on the membrane surface (external fouling) and/or with in the

membrane pores (internal fouling). The nature and extent of membrane fouling

as well as evolution of fouling with time are strongly influenced by nature of

membrane and characteristic of the feed. Many forms of equation to predict the

fouling are proposed, such as Hermia’s [54], Cheryan’s [38], etc. Generally, it

can be characterized by powered or exponential equation as examples shown in

eq. 8.2.9.

0: >= nt R R n

oF {8.2.9a}

Or

0: >= ne R R nt

oF {8.2.9b}

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R o is initial fouling resistance. However, since fouling from feed/membrane

interaction is assumed to be because of physicochemical, it will be unaffected by

operating condition. So R F in this case can be included in R m as R m’, as shown in

eq. 8.2.9c. Many researchers [10], [11], [18] studied applications of UF on oily

wastewater treatment, using newly prepared cutting oil emulsions. They

concluded that fouling resistance of membrane, in this case, scarcely occurs, and if any, can be assumed to be constant without varying with time. So the

concept of R’m in eq. 8.2.9c is valid. However, in case of real wastewater,

fouling from foreign material deposition may be present Thus R F, in this case,

will vary with time and should be observed by pilot-scale test.

F mm R R R +=' {8.2.9c}

3. Polarization or gel resistance (R g ): This resistance is caused polarization layer.

In some literatures, it is divided into 2 separate resistances, i.e., gel resistance

and polarization resistance. However, many researches and literatures also prove

that using the resistance in a single term of R g provides sufficiently accurateresult. As described in section 8.2.1.4, the resistance is reversible and changes

with operating condition. General equation of R g is as shown in eq. 8.2.10, which

α and φ are empirical constants.

t g PV R ⋅⋅= α φ {8.2.10}

Thus, from the equations of various resistance and assumptions stated above, the

resistance model of UF on oily wastewater treatment can be rewritten as shown in eq. 8.2.11

t m

t

PV R

P J ⋅⋅+

=α φ '

{8.2.11}

Eq. 8.2.11 provides a flux/pressure curve that more or less fits the observed data both

in pressure and mass transfer controlled region. Like film model, the values of φ and

depend on type of wastewater as well as membrane and have to be obtained by experiment.


Apart from feed concentration, velocity and pressure, of which effects on described in

the previous section, important parameters that affect the performance of UF process aresummarized below.

1. Viscosity

Viscosity is an important parameter that affects flow regime and shear rate. Thus

it affects the polarization layer and make the mass transfer coefficient (k) in eq. 8.2.6 change.

Generally , viscosity increases with increasing feed concentration. This can explain the

inflection point in flux/concentration curve in fig. 8.2.1-6, which is the case of general oily

wastewater. For oil/water mixture, when the concentration reaches certain value, viscosity,

thus mass transfer coefficient, changes dramatically (see fig.8.2.2-7). So the graph is shifted

from a straight line.

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2. Temperature

Since many physical properties, such as viscosity, density, change with

temperature, it is inevitably one of the influent parameters on UF performance . Permeate flux

generally increases with increasing temperature. So it is beneficial to operate the UF process

at the highest possible temperature, providing that there is no unusual effect such as extrafouling due to high temperature precipitation. CHERYAN [38] proposed water flux-

temperature correlation as shown in eq. 8.2.12a. In the research on cutting oil emulsion

treatment, both fresh and used conditions, WANICHKUL [11] used permeate flux-

temperature relation as shown in eq. 8.2.12b. It was proven to be quite accurate. However, it

should be noted that higher temperature may also result in lower interfacial tension of feed

components, thus lower size of liquid dispersed phase, such as oil droplets in water.

C C C ooo J J J

155025276.1615.0 == {8.2.12a}

))(0239.0( A B

C BC Ae J J oo

−−= {8.2.12b}

3. Membrane properties

Major membrane properties that affect the performance of UF are as shown

below,

• Hydrophilicity: For UF of aqueous feed, generally, the membrane should be

hydrophilic to avoid absorption of hydrophobic or amphoteric components in

the membrane, which can cause fouling. Hydrophilicity can be roughly

determined by measurement of contact angle of oil drop on the surface of

membrane, as described in chapter 2. Membrane material can be used to

estimate membrane hydrophilicity. However, surface-coating process, whichcan modify its original properties, should be taken into account.

• Surface roughness: The membrane with smooth surface is likely to foul

less. Surface roughness of membrane also affects the contact angle

measurement and may cause error in hydrophilicity determination.

• Charge of the membrane: To separate charged particles, the membrane

should be of the same charge to take advantage of mutual repulsive force.

•

Pore sizes: As described in section 8.2.1.1, the pore sizes of membrane

should be suitable for the pollutants to be separated. GPI recommended pores

size is around 1/3 to 1/4 of the size of the pollutants (see some exception insection 8.2.3.1). Too large pore size may affect in higher initial flux but it is

clogged easily, resulting in lower flux in long term and frequent washing

process. Too small pore size also results in low flux and high energy

consumption.

•

Turbulence: As described before, flux increases with increase in turbulence.

Normally, turbulence or flow regime is controlled by cross-flow velocity.

However, there are some attempts to enhance the flux by the use of turbulent

promoters, such as inserting wire mesh or grid in membrane flow channel.

Caution is that it also promotes clogging. Some techniques choose to move

membrane, rather than liquid, to increase turbulence, such as rotating disc

membrane module.

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4. Interaction between feed and membrane

Some components in feed may react or coat membrane of certain material,

resulting in adverse affects, such as fouling or decrease in rejection. For example, oils can

cause fouling to PVDF membrane for the oil structure is similar to the functional group of the

material. So it is recommended to perform UF test with real feedstream before designing the process.

8.2.2

UF process design for oily wastewater treatment

In this section, Design procedure and design consideration as well as some significant

findings about application of UF on oily wastewater treatment, based mainly on GPI

researches, are described.

8.2.2.1 Membrane selection

Pore size or MWCO: Under proper operating condition, UF membranes with MWCO

of 40 to 150 kilo-Dalton were proven to be effectively used to separate oil from secondary and

macroemulsion with rejection of 100% [10], [11], [18], [19], [20]. The oily wastewater tested

were both in fresh and used condition with the droplet sizes around 0.11-0.21 micron for

macroemulsion and 11 microns for the secondary emulsion. For microemulsion (droplet size

of 20 –100 nm or 0.02 – 0.1 μ), the membranes of MWCO of 40 – 50 kD can be used with oil

rejection of 100%. From GPI researches, it is recommended that pore size should be around

1/3 –1/4 of droplet size to be separated for stabilized emulsion. For non-stabilized emulsion,

it is recommended to use maximum pore size of 100 nm. to prevent the oil from passing

through the membrane (see section 8.2.3).

Membrane material: Apart from the pore size, membrane material and module areimportant parameters that affect membrane selection. Every research in GPI lab confirms that

hydrophilic material is the most suitable choice for oily wastewater treatment. For

polymeric materials, cellulose acetate, acrylics and polyacrylonitrile (PAN) are hydrophilic,

while PVDF and polysulfone are generally hydrophobic. In GPI lab, most experiments were

carried out by PAN membrane. For inorganic membrane, composite membranes with zirconia

(zirconium oxide) and alumina skin also provide good hydrophilicity. However, other factors,

such as limiting pressure, chemical resistance, fouling, and cost, should be taken into account

for membrane material selection. These data can be obtained from pilot scale test. It must be

noted that the membranes of the same pore sizes may give different performance it they are

made of different materials.

Membrane module: In GPI lab, all of the UFresearches were based on plate and

tubular modules. The tubular modules used in the experiments were inorganic membrane

while the plate modules were polymeric types. Thus the result can not be directly compared.

However, from many literatures, every type of module, described in section 8.1.5, is reported

to be effective for oily wastewater treatment [38]. Hence the flux obtained, fouling and cost

should be considered to select the most suitable membrane.

8.2.2.2 Prediction of permeate flux

The size of membrane is determined from the quantity of wastewater, permeate flux

and required operating cycle of the system (such as continuous 48 hours, etc.). Permeate fluxof UF membrane can be determined based on (1) mathematics models from section 8.2.1, (2)

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general design criteria and (3) pilot-scale test result. The latter, if available, is the most

significant data for final decision on membrane process design since modular structure of

membrane makes it possible to scale-up the process from the test data in relatively linear

manner. However, flux result from the models and general criteria acquired from many

researches, esp. GPI researches, will be provided here to be a guideline to narrow the choices

of membranes to be test or for preliminary technical and economic analysis.

1. General design criteria

Recommended design criteria from various literatures and manufacturers are

summarized in table 8.2.2-1. It should be noted that the values in the table are summarized

from experiences and researches with various operating conditions and types of wastewater,

then, should be used as a guideline. It is recommended to review related researches for the

type of wastewater to be treated.

2. UF flux prediction by mathematical models

In case that the data required for mathematical models are available, the models

can be used for permeate flux estimation. Many literatures provide the values of important

parameters for the models, obtained from various types of wastewater and operating

conditions, which can be adapted to design the membrane process for similar wastewater.

Since almost all of GPI’s researches were interpreted using film model and

resistance models. In this section is emphasized on these 2 models. Summaries of important

parameters for film model and resistance model from GPI’s researches are tabulated in table

8.2.2-2 and 8.2.2-3. Applications of the models are summarized as follows,

(1)

Film model: The model (eq. 8.2.6a and b) can be used to predict the flux inmass transfer controlled region, where the flux is theoretically pressure-independent. It can

be used to calculate the flux at any wastewater concentration, which is very useful because

volume reduction of the wastewater, that makes the concentration change, is one of major

objectives of oily wastewater treatment process.

Flux/pressure relation graph for UF of macroemulsion contains an infection

point as shown in fig. 8.2.1-6 [11], [18]. In this case, it can be said that there are two Cg. The

first one is obtained from extending the steeper part of the graph to cross the X-axis. But it is

not the real Cg and used only for flux calculation at lower range of retentate concentration.

The real Cg is obtained from the graph after inflection point. For macroemulsion, the real C g

crosses the X-axis at approximately 100% concentration (fig. 8.2.2-1). This can imply that, theoretically, we can use UF to filter it until the retentate becomes water-free oil [18] .

However, the flux will decrease and become so low that it may become uneconomic.

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III-207

R e f .

[ 3 8 ] , [ 5 9 ]

[ 5 4 ]

[ 3 8 ]

[ 3 8 ]

[ 3 8 ]

[ 3 8 ]

[ 3 8 ]

[ 3 8 ]

R e m a r k

F r e e o i l m u

s t

b e r e m o v e d

f i r s t .

K o c h ’ s d a t a

K o c h ’ s d a t a

T h e a u t h o r

r e c o m m e n d e d

G M p l a n t ,

M a x i c o

R e t e n t a t e

c o n c .

4 0 - 8 0 %

U p t o 4 0 % V

o i l 6 0 %

U p t o 1 0 0 %

3 0 - 5 0 %

5 0 % o i l , 1 0 %

S S , 9 9 .

5 %

v o l u m e

r e d u c t i o n

R e j e c t i o n

o r o u t l e t

o i l c o n c .

< 1 0 - 5 0

p p m

< 1 0

- 1 0 0

p p m

o i l

7 5 p p m

F O G

1 0

0 %

r e j e c t i o n

F l u x /

O p e r a t i n g

c o n d i t i o n

5 0 L M H ,

2 5 o C , 3 .

5 b a r

1 0 0 L M H ,

2 5 o C , 3 .

5 b a r

4 0 G F D f o r

s p i r a l , 1 6 0 -

1 2 0 G F D f o r

d i s c , n o o t h e r

d a t a

s p e c i f i e d

P o r e

s i z e o r

M W C O

5 0 - 2 0 0

k D

M e m b r a n e u s e d

C o n v e n t i o n a l U F

K o c h 2 5 2 , 1 ” t u b u l a

r ,

6 0 m

2

K o c h 2 5 2 , 1 ” t u b u l a

r ,

6 0 m

2

M e m b r e x E S P , s p i r a l

2 - s t a g e s s y s t e m o f

M e m b r e x ( s p i r a l

w o u n d + r o t a t i n g d i s c )

C a r b o s e p M 9

I n l e t o i l / d r o p l e t s

s i z e

0 . 1

- 1 0 % o i l

3

- 5 % o i l

1

- 2 % o i l

< 0 . 5 % o i l

5 - 6 % V o i l

1 , 0 0 0

p p m F O G ,

5 0 0 p p m S S

2 0 p p

m t o t a l H C ,

3 0

p p m S S

T a

b l e 8 . 2 . 2 - 1 G e n e r a l d e s i g n c r i t e r i a o f U F p r o c e s s f r o m v a r i o u

s l i t e r a t u r e s

W a s t e w a t e r

C u t t i n g o i l w a s t e w a t e r o r

s t a b i l i z e d o i l y w a s t e w a t e r

W

a s t e w a t e r c o n t a i n i n g s p e n t

c o o l a n t a n d l u b r i c a n t s

O

i l y w a s t e w a t e r c o n t a i n i n g

e m u l s i f i e d o i l

F o o d w a s t e w a t e r , w a s t e w a t e

c o n t a i n i n g s u r f a c t a n t ,

c h e m i c a l

G

e n e r a l o i l y w a s t e w a t e r

S p e n t c o o l a n t

A

u t o m o b i l e m a n u f a c t u r i n g

p l a n t w a s t e w a t e r

E f f l u e n t o f b i o l o g i c a l

t r e a t m e n t o f p e t r o l e u m o i l

r e

f i n e r y

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T a b l e 8 . 2 . 2 - 2 S u m m a r y o f p a r a m e t e r s o f f i l m m o d e l f r o m U

F r e s e a r c h e s o n o i l y w a s t e w a t e r t r e a t m e n t ( r e f e r e n c e t e m p e r a t u r e = 2 0 o C )

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III-209

T

a b l e 8 . 2 . 2 - 3 S u m m a r y o f p a r a m

e t e r s o f r e s i s t a n c e m o d e l f r o m

U F r e s e a r c h e s o n o i l y w a s t e w

a t e r t r e a t m e n t ( r e f . t e m p e r a t u

r e = 2 0 o C )

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III-210

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

1 10

Retentate concentration (% V of oil)

P e r m e a t e f l u x ( l / m

2 . h )

10 0

P = 1 ba r, V = 1 .1 7 m / s P = 1 .5 ba r, V = 1.4 m /s

Fig. 8.2.2-1 Examples of flux VS. oil concentration in UF of macroemulsion

Cg Log (C)

Vref Flux V

JC,V

JC,Vref

At Pref

CPt

FluxJC,V

JC,Vref

Pref

Vref

V

a) Graph from film model a) Graph from resistance model

Fig. 8.2.2-2 Case 1: find flux/pressure relation when k, β , C g and R’m are known

Table 8.2.2-4 Procedure to predict flux/pressure relation for case 1: Know k, β , C g and R’m

Item Procedure Variables Equation

1 Find JC,V,Pref C, V)ln(Pr ,,

C

C kV J

g B

ef V C =

{8.2.13a}

2 Find JC,Vref,Pref C,Vref )ln(

Pr ,, C

C kV J

g B

ref ef Vref C

= {8.2.13b}

3 Find αC ,derived from

resistance model at one

value of C and two values

of V

R’m (or R m)

)V

ref V

ln(

ref PmR

VC,J

β)

ref V

V(ref

PmR VC,

J

ln

Cα

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

−

−

=

{8.2.13c}

4 Find φC

Pref V,C,J

ref PαcV

mR Pref V,C,

Jref

P

C

−=φ

{8.2.13d}

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5 Flux/pressure relation at

conc. = CtPαcV

CmR

tP

tPV,C,

Jφ +

= {8.2.13e}

The subscript “ref” represents the parameter at reference condition that the graph

8.2.2-2a is derived from. Normally the reference condition is in mass transfer control region.Otherwise the graph will not be a straight line as shown in the figure. However the equations

are proven to provide acceptable result even when the reference pressure is in the transition

zone between pressure- and mass transfer control region. In any case, it is recommended to

select the reference pressure as high as possible and should be greater than 50% of

recommended operating range.

Eq. 8.2.13e can be used to predict flux at concentration “C” and cross-flow velocity

“V” over the entire range of working transmembrane pressure “P t”, usually recommended by

membrane manufacturers. Examples of prediction result from this concept are shown in fig.

8.2.2-3. The graphs show that the results are relatively accurate (±10%).

0

20

40

60

80

100

120

140

160

180

0 0.5 1 1.5 2 2.5 3

Transmembrane Pressure (Bar)

P r e d i c t e d F l u x ( l / ( h . m

2 ) )

Observed, C = 2% Predicted, C = 2% Observed, C = 8% Predicted, C = 8% Reference, C = 4%

Fig. 8.2.2-3 Relation between UF permeate flux and Transmembrane pressure at C ref = 4% by volume of oil , V = 1.4

m/s and Predicted relations at C = 2 and 8% (Oil: Elf SeraftA cutting oil macroemulsion, Membrane: IRIS

3042 PAN )

(3.1) Case 2: Know φ, , Cg and R’m

The procedure to find flux/pressure relation (“JC,V,Pt”) at any concentration and

pressure is as described in table 8.2.2-5.

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III-213

• Calculate total oil concentration of the mixture (Coil,mix)

micoilmacoilmixoil C C C ,.. += {8.2.15a} or

micmicmacmacmixoil RC RC C +=, {8.2.15b}

Where Coil,mix, Coil,mac, Coil,mic are oil concentration of the mixture,

macroemulsion portion and microemulsion portion, respectively. While Cmac and Cmic

represents the concentration of cutting oil concentrate of macro- and microemulsion

portions. R mac and R mic are the ratio of oil in the emulsion concentrate. For macroemulsion, the

majority part of concentrate is oil, R mac is around 80%. While R mic is around 20-30%.

For example, when macroemulsion at concentration of 4% by volume of

concentrate mixes with microemulsion of 2% by volume of concentrate, if Rmac and Rmic =

80% and 20%, total oil concentration in the mixture (Coil,mix) will be (4x0.8)+(2x0.2) =

3.6% by volume of oil.

•

Calculate permeate flexes of whole macroemulsion and wholemicroemulsion at the oil concentration of Coil,mix (Jmac:Coil,mix and

Jmic,Coil,mix) by the procedure decribed in table 8.2.2-4 and 8.2.2-5.

• Estimate the flux of the mixture by the following equation. Error of

prediction is around 20%.

mixoil,C

mixCoil,mic,J

micoil,C

mixCoil,:macJ

macoil,C

mixJ

+= {8.2.15c}

8.2.2.3

Prediction of evolution of flux, wastewater and permeate volume with time and membrane size for batch cross-flow UF system

In real situation, UF process may be designed as batch process, continuous process,

single stage process or multi stage process, depending on objectives. However, for wastewater

treatment process, UF is normally designed as batch system, as shown in fig. 8.2.1-4. In batch

process, the concentration of retentate will be increased up to required limit or as much as

possible. Then the process will be stopped and the retentate will be hauled away for final

disposal or recycling. After that the batch will start over again.

Process flux will decrease continuously with increase of the concentration. The models

and procedure described in the previous paragraph can be used to predict the permeate flux atany concentration. Thus it is possible to estimate evolution of retentate volume, permeate

volume, and flux with time. These data is important to design UF process to meet the required

operating time. However, it must be noted that predictions are based on the assumption that,

• Flux at any moment is equal to the value calculated by the model described in the

previous section.

• There is no fouling from any other foreign materials.

To find permeate volume, we consider that a small volume of permeate (dVol),

passing through a UF membrane of area “A” at a small time (dt), will be defined by the

following equation.

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III-214

AdtJ(c)dVol ⋅= {8.2.16}

If the system is operated in the mass transfer controlled region, the film theory (eq.

8.2.6b) can be applied. Eq. 8.2.16, then, can be rewritten as follows,

AdtCg

ClnβkVdVol ⎟⎟

⎠

⎞⎜⎜⎝

⎛ ⋅= {8.2.17}

If we start with initial wastewater volume Volo and concentration Co and the rejection

of oil is totally completed, which is true from our every test, the concentration C will be the

function of the permeate volume at that moment V.

Vol)o(Vol

oVoloCC

−= {8.2.18}

Eq. 8.2.17 can be rewritten as,

AdtoVoloC

gVol)Co(Volln

βkVdVol

⎟⎟

⎠

⎞⎜⎜

⎝

⎛ −⋅= {8.2.19a}

∫=∫

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −

t

0Adt

βkV

finalVol

oVol

oVoloC

gVol)Co(Vol

ln

dVol

{8.2.19b}

However, the system may not be operated in the mass transfer controlled region for

the whole time. In this case, the function J(c) in eq. 8.2.16 can be calculated by eq 8.2.11. Eq.8.2.19b is in the form of integration of [1/ln (x)], so it can not be written in general form since

the equation will be infinity at x =1. However, a definite integration is possible, using

numerical method that can be calculated by computer .

An example of flux/time prediction is shown in fig. 8.2.2-4. The flux is predicted

based on the data (Cg, k, φ, α, β, R’m ) of fresh Seraft ABS cutting oil macroemulsion and

IRIS 3042 membrane, shown in table 8.2.2-2 and 8.2.2-3. The membrane area used is 1 m2.

However, in this example, it is assumed that the system is in mass-transfer controlled region.

So eq. 8.2-19b is used.

The predicted flux/time relation is compared with the results from UF test on used cutting oil macroemulsion (Co = 3% V of concentrate or 2.4%V of oil, from Willamette SAS

factory) from WANICHKUL’s research [11], as shown in fig. 8.2.2-4. The x-marked circles

indicate the observed flux of fresh emulsion. From the graph, it shows that the model can

accurately predict flux of fresh (unused) emulsion as the circles are closed to the theoretical

flux curve.

Comparing with observed flux of the used emulsion, the graph shows that, at low

concentration, theoretical flux is greater than observed value. This is simply because of

additional fouling from foreign materials in the emulsion. From the data, the system was

undergone rinsing for 5 times, every 300-400 l of permeate volume on the average.

Furthermore, at low concentration, the system does not fully reach mass transfer controlled

region so the predicted flux from film model is higher than the actual.

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III-216

0

200

400

600

800

1000

1200

1400

1600

1800

0.000 5.000 10.000 15.000 20.000 25.000 30.000 35.000 40.000 45.000 50.000

Time (h)

P e r m e a t e v o l u m e ( l )

Theoretical data at P = 1.0 Bar, v = 1.17 m/s) Theoretical data at P = 1.5 Bar, v = 1.4 m/s) Observed data

P = 1.0 bar, v = 1.17 m/s P = 1.5 bar, v = 1.40 m/s

Fig 8.2.2-5 Relation between time VS. theoretical and observed permeate volume

Average process flux estimation: Since the equations stated in this section is very

complex and could not be solved without calculation or computer program, a rough approach

to estimate average flux has been devised and, actually, used even for real design. Average

process flux (Javg) can be calculated from the flux at the beginning (J begin) and the end of batch

(J end). In this case, the fluxes at these only 2 points are required. If the final concentration is

relatively Cg, J end can be assumed to be zero. This Javg will be preliminary used to calculate

evolution of permeate volume (eq. 8.2.20b) in stead of the integration result from eq. 8.2.19.Observed and calculated average flux from beginning to zero-flux from UF of macroemulsion

at 4% of concentrate volume, as shown in the example, are around 47 and 44 LMH,

respectively [11].

2

end begin

avg

J J J

+= {8.2.20a}

Acc. t J Vol avg permeate = {8.2.20b}

These estimated evolution data also provides the idea about the approximate size of

membrane required. If the estimated operation time is not suitable, the area of membrane can

be adjusted until it results in the required operating time. If should be noted that the predicted

result does not include the time for rinsing or cleaning the membrane, which may take as 1-2

hours per cycle, depending on method and cleaning agent.

8.2.2.4 Sizing of related facilities

General components of UF system for wastewater treatment are shown in fig. 8.2.1-4,

i.e.,

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1. Equalization or storage tank

Here, only single-stage batch process is considered. Details of other types of the

processes, such as continuous process, multi-stage process, etc. can be found in many

literatures, listed in the bibliography.

For batch process without addition wastewater during UF operation, the

volume of the equalization or storage tank is simply equal to the volume of wastewater

generated during the operating cycle of the UF process. In this case, the system must have at

least 2 tanks. While one tank is being feed to the membrane, another is used to received the

incoming wastewater. Then they will be switched over when the wastewater on the first tank

is completely treated. Flux/time and wastewater volume/time relations in this case can be

directly calculated by the equations described in section 8.2.2.3. Final volume of retentate in

this case is not used for volume calculation. It is the simplest method for UF process

calculation. However, the volume of the tanks in this case will be relatively large.

For batch process with continuous or intermittent incoming wastewater into the same tank, the volume of the storage tank can be calculated by mass balance. Minimum

required storage volume is equal to the maximum difference between accumulated permeate

volume and accumulate influent wastewater volume. Graphical presentation for minimum

storage volume calculation is shown in fig. 8.2.2-6. Evolution of accumulated influent

wastewater depends on influent wastewater flow characteristic, such as constant discharge

continuously for 8 hours/ day, etc.

Time

Accumulated

volume

Permeate

Influent

wastewater Volume

required

for storage

tank

Final retentate

volume required

End of batch

End of filtration

Start cleaning

Influent stops

Fig. 8.2.2-6 Calculation of required storage volume of equalization tank by graphical method

Final retentate volume required can be estimated from recommended Cg for

similar wastewater, For evolution of accumulated permeate volume, it is more difficult to

achieve. It can be preliminary estimated by the concept described in section 8.2.2.3. However,

since the permeate flux depends on retentate concentration, which, in turn, depends on mass

balance of recycled retentate, remaining wastewater in the tank and addition influent, eq.

8.2.19b is not valid and needs to be modified. This will complicate the calculation process

even more. However, the concept of average process flux, also described in section 8.2.2.3,can be used to simplify the calculation.

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2. Feed pump

Here will consider only the system with single feed pump, which is generally

used in UF process of wastewater treatment. The feed pump is an equipment that supply

wastewater to the membrane as well as maintain recirculation flowrate, thus cross-flow

velocity, in UF module.

For the flowrate, the pumping system is sized to cover the maximum

recirculation flowarate, which is normally higher than permeate flowrate and capable of

turning down to handle the minimum flowrate.

For the pressure, the pump is sized to handle the design working pressure of the

system, which may need to be varied to optimize the system performance. There are key

values of pressure that should be aware of in pumping system design, i.e.,

• Capillary pressure of the membrane: Transmembrane pressure must be

lower than the capillary pressure between oil droplets and membrane, asshown in eq. 8.2.2. So this pressure should be taken into account for pump

selection. However, for properly selected membrane, this value is normally

higher than recommend maximum operating pressure of the membrane.

• Pressure drop from membrane module friction and piping system: The

pressure drop has to be taken into account in pump design. Otherwise it may

not be able to provide the design working transmembrane pressure. For feed

and return piping system, the pressure drop can be calculated by general head

loss equations.

For membrane module, the major loss from wall friction of flow channel in

membrane module can be calculated from well-known formula, such as Darcy-Weisbach’s(eq. 8.2.21a).

2

2V

D

Lf =

major lh {8.2.21a}

For laminar flow, Re

64f = {8.2.21b}

For turbulent flow (Colebrook’s equation),

)0.5f Re

2.513.7e/Dlog(2

0.5f

1

⋅+⋅−= {8.2.21c}

“e/D” is ratio of roughness to diameter. For plate membrane, the flow channel is

usually rectangular. D of this channel can be calculated as hydraulic diameter, as shown in eq.

8.2.21d. H and W are height and width of the rectangular channel respectively.

W)2(H

4HWD

+= {8.2.21d}

The minor loss can be estimated using standard minor loss equation (h l minor (in

metre) = K minor V2

/(2g)). The latter becomes the majority of head loss when the recirculationvelocity is high.

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Even though this pressure drop is not high (normally < 0.5 bar), it may become

of significant effect when the UF is operated at low transmembrane pressure, such as 0.5 to1

bar or when the concentration of retentate is high. For oily wastewater, viscosity will vary

rapidly in some range of concentration, as shown in fig. 8.2.2-7. This will cause extra pressure

drop. So, maximum viscosity expected during the operation should be accounted in pump

selection.

(Elf SeralfABS cutiing oil macroemulsion, 20oC, 100% = pure cutting oil concentrate = 80% V(approx) oil )

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

0 10 20 30 40 50 60 70 80 90 10

Oil concentration (% V of cutting oil concentrate in water)

V i s c o s i t y ( c p )

0

Fig. 8.2.2-7 Relation between oil concentration VS. viscosity of emulsion

For the power requirement of UF system, main power consumption is the

power required to maintain transmembrane pressure at require flowrate (or recirculation

velocity). This power can be calculated straightforwardly by the basic equation

overallη

AVP

overallη

QPPower

⋅⋅=

⋅= {8.2.21e}

Q in this case means recirculation flowrate, not the permeate flowrate. V is the

recirculation velocity and A is the flow area of liquid in UF module (the channel between the

membrane surface and the UF module wall). P in the equation is pump discharge pressure,

which is the summation of transmembrane pressure and other headloss from pipe and values

system. It should be noted that transmembrane pressure is average value of the pressure at

the inlet and outlet of UF module. Overall efficiency of pump depends on pump type. For progressive cavity pump or progressive screw pump, the efficiency should be around 50-70%.

In case that the data required for mathematical models are available, the models

can be used for permeate flux estimation. Many literatures provide the values of important

parameters for the models, obtained from various types of wastewater and operating

conditions, which can be adapted to design the membrane process for related wastewater.

3. Heat exchanger

For oily wastewater treatment, when the retentate is repeatedly pumped into

membrane process, it will accumulate heat loss from feed pumps and friction so it will gain intemperature. If the temperature is too high, it may cause adverse affect to the membrane and

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seals. Thus, heat exchanger is required to maintain the temperature of feed stream within the

recommended temperature range of membrane or at the design temperature. Heat load of the

system depands on piping and components design.

To estimate the maximum heat load, it can be assumed that energy loss from

input power supply is converted solely into heat. Thus the heat load can be roughly calculatedfrom modification of eq. 8.2.21e as follows,

PQeat ⋅⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ −= 1

overallη

1H {8.2.22}

Rising in temperature ( T) can be roughly calculated by basic heat capacity

equation (Heat = M.C.ΔT). C is specific heat. M is mass flowrate of feed pump. When the

heat, ΔT, and the required temperature are known. It is possible to design or select the heat

exchanger. But the design of the heat exchanger is a science into itself, which will not be

described here. It can be selected from commercial product of specially designed by heat

exchangers designers.

8.2.2.5 UF efficiency on oily wastewater treatment

From many researches in GPI lab, it clearly shows that, with appropriate UF

membrane pore size hydrocarbon or oil, even in the form of very tiny droplets in

macroemulsion and microemulsion, cannot pass the membrane. It can be said that the removal

efficiency of UF is 100%. By the way, the efficiency will be lowered after prolonged

operation, mainly from normal wear and tear problem. Characteristics of wastewater, such as

presence of free-oil or non-stablized oil may lower the oil rejection of the membrane (see

section 8.2.3-1). So oil concentration in permeate can be expected in the range of 0-100 ppm,

depending on wastewater characteristic and membrane (see table 8.2.2-1).

Even though the oil rejection is generally complete, it does not mean that there is no residual pollutant in the permeate since there may be other components of pollutants in the

wastewater that can pass through the membrane, such as surfactants and co-surfactants. Extent

of residual pollutants depends on components of the wastewater. Examples of residual

pollutants of cutting oil emulsions permeate are shown section 8.2.3 . These residual

pollutants need to be further treated, such as by RO, distillation, biological treatment,

which will be described later in the related chapters.

8.2.3

Design consideration and significant findings from GPI’s researches

In this section, design consideration and significant findings from related researches of

GPI’s lab on oily wastewater treatment by UF will be described.

8.2.3.1 Design consideration and significant finding on secondary emulsion treatment

Almost all of the researches on oily wastewater treatment by UF are based on

stabilized emulsion since it cannot be separated effectively by other single process. However,

SRIJAROONRAT [10] has researched on UF of non-stabilized secondary emulsion. Her

study provides useful information to understand the performance of UF when free-oil is

present, which is frequently found in general oily wastewater. Significant findings of the

research can be summarized as follows,

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1. Flux/pressure curve of non-stabilized emulsion shows some decline at high

pressure (fig. 8.2.3-1a). For this, SRIJAROONRAT described that it causes by

pore clogging of the oil film. Since the oil is not stabilized, it can be coalesced

and coated the membrane surface. At high pressure, the oil film is pinned against

the membrane and causes the blocking more predominant. Flux was reported to

range from several hundreds to few thousands LHM [10] . However, itsfeasibility should be considered comparing to other possible processes, such as

coalescer.

2. If the pore size of membrane is selected by the same criteria as for stabilized

emulsion, i.e. 1/3 to1/4 [GPI] or 1/10 [38] of droplet size, the pore will be

relatively large, which causes lowering in capillary pressure. Thus the working

pressure may high enough to overcome the capillary pressure, resulting in

presence of oil in permeate. Permeate flux in this case will be very low.

Evidence on coalescing of oil drop in the permeate is also observed. Thus it is

recommended to select the pore size of 50-100 nm for non-stabilized emulsion

treatment. If the pore size is properly selected, oil rejection will be or almost100% (fig. 8.2.3-1b)

3. Presence of surfactant causes adverse affect on flux and oil rejection.

SRIJAROONRAT showed that, at ratio of surfactant to oil of 2% and Pt = 3 bars,

the oil can pass through the membrane and present in the permeate even when

the membrane of 100 nm is used. Operating at low-pressure (i.e. 1 bar) help

alleviating this problem. Her research can be used to explains why the rejections

of UF of real wastewaters are not equal to 100%, unlike in the lab result. This is

because free oils or tramp oils are usually present in real wastewater while they

are usually not present in synthetic wastewater used in the experiment.

4.

Residual pollutant, measured in term of TOD, varies with membrane’s efficiency

or oil rejection as well as presence of surfactants/co-surfactants or other soluble

components in the wastewater. In case that the surfactants are present, it will

tribute to main TOD in the permeate. And if their concentration are high enough,

they will make the oil pass through the membrane. The TOD in this case will be

very high from presence of oil in the permeate.

Flux of

stabilized emulsion

Pt

Flux

Flux of non-

stabilized emulsion

Fig. 8.2.3-1a Flux of non-stabilized

emulsion

Fig. 8.2.3-1b Photographs of non-stabilized emulsion

influent, retentate and permeate (from left) [10]

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8.2.3.2 Design consideration and significant findings on macroemulsion treatment

Cutting oil emulsion is the major source of this type of wastewater. All of related

GPI’s researches prove that UF process is very efficient for treatment of this wastewater.

Design consideration and significant findings from GPI’s lab on macroemulsion treatment are

summarized as follows,

1. The value of Cg

Flux/pressure curve of macroemulsion follows the typical pattern as shown in

fig. 8.2.1-5b. But for the flux/concentration relation, BELKACEM [18] proven that the

relation can be approximated as being linear with an inflection point, as shown in fig.8.2.2-1.

The real Cg is about 100% of oil. It means that we can recycle the retentate to the UF module

until it is about pure oil. This result was also confirmed by WANICHKUL [11] (see example

in section 8.2.2.3). BELKACEM explained the lower values of Cg from other researches by

the assumption that they are tested within relatively short periods of time. Thus extension of

the results in log/normal scale will intersect the concentration axis at the first virtual Cg (Cg’ infig. 8.2.1-6 and 8.2.2-1) or somewhere between C’g and Cg.

2.

Flux enhancement by salt addition

Flux enhancement by salt addition was confirmed by many researches [11], [18],

[20]. The salt used in the experiments was CaCl2. Working principle of the process is that the

salt will be added to the wastewater in a certain amount to cause partial , not complete,

destabilization of the emulsion. Typical effect of salt concentration on the flux from dead-end

batch test at low Pt is as shown in fig. 8.2.3-2a. In cross-flow module, the graph is almost

identical but the difference between complete and partial destabilization is relatively smaller

and the salt requirement for partial destabilization is slightly higher from the effect of cross-flow to polarization layer formation.

Partial

destabilization

CaCl2 concentration

FluxComplete

destabilization

Lower initail

oil concentration

Partial

destabilization

CaCl2 concentration

FluxComplete

destabilization

a) From dead-end mocule b) From cross-flow module

Fig. 8.2.3-2 Typical relation between CaCl2 concentration and flux at low Pt

The effect of salt that cause changing in stability of the emulsion is reducing the

repulsive forces between droplets as well as potential barrier by modification of Zeta potential

and conductivity of the solution. This favors coalescence of oil droplets (see fig. 8.2.3-3).

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Flux of

stabilized emulsion

Pt

Flux

Flux of partially

destabilized emulsion

Theoretical

Observed

concentration

Calculated

concentration

Free-oil is not separated

from storage tank.

Free-oil is separated.

Co

Fig. 8.2.3-4 Relation between fluxes VS. pressure and calculated VS. observed oil

concentration in retentate for partially destabilized emulsion

Other significant findings and precautions on flux enhancement by salt addition

are summarized below.

•

Other types of salt can be used, such as NaCl, ferric salt or aluminium salt,

etc. The higher the valence electron of the salt, the better the destabilization

as well as the lower the salt concentration required. Thus NaCl is considered

not suitable for it required concentration is high and cause high chloride in

permeate. For Fe and Al salts, they are more expensive than CaCl2.

Furthermore, laws and regulation in many countries limit presence of high-

valence ions in effluent.

•

Presence of free-oil may cause some problem at high Pt and V, as described

in section 8.2.3.1. It can cause pore blocking, resulting in decrease in flux at

high Pt (see fig. 8.2.3-4), esp. at high value of V because it can cause high

mixing effect and turbulence, so the free-oil in the surface of tank is drawn

back with the feed stream to the UF module. This effect is also more eminent

when the membrane is hydrophobic (such as PVDF or Polysulfone). Thus, it

is recommended to separate this free-oil off the recycled stream, by

coalescer.

• Some membrane material, such as ZrO2, may interact with calcium

complexes and cause serious decrease in flux. Furthermore, membrane withlarge pore size (i.e., 150 kD) will be blocked relatively easily by free-oil, as

described in section 8.2.3.1.

3. Residual pollutant in permeate

Oil rejection or removal efficiency is about 100%. Theoretical oil concentration

in permeate is 0 ppm (see fig. 8.2.3-5). However, actual oil concentration in permeate may

greater than 0 ppm, depending on condition of equipment, wastewater characteristic and

operating condition, such as presence of free-oil or fouling materials (foulants).

Even though the oil is about completely rejected by UF. Permeate still containssurfactants/co-surfactants and some additives that, naturally, can pass through the membrane.

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Some surfactants may react with other substances and form complex or integrates with its

species to form micelles that can not pass the membrane. However, it can be safely assumed

that the concentration of surfactants/co-surfactants in permeate is equal to free

surfactants/co-surfactants in inlet wastewater . For example, Elf Seraft A concentrate

contains 10% by weight of surfactant (sodiumsulfone, sodium carboxylate, triethanolamine

carboxylate), 5% of co-surfactant (benzylic alcohol), and 4% additives. Its permeate contains pollutant, measured as TOD, around 650 mg/l per 1% by volume of oil in the inlet

wastewater. Many researches [10], {11], [18] pointed that TOD removal efficiency of UF for

macroemulsion is greater than 95%.

In case that the salt is added to the wastewater, surfactants/co-surfactants will

react with the salt to form complex. However, there is not enough data to conclude its effect

on residual pollutants in permeate. So, to be on the safe side, it can be assumed that the TOD

in this case is identical to the no-salt case. And the salt will also be present in the permeate as

described in the previous paragraph.

a) Fresh macroemulsion b) Used macroemulsion c) Microemulsion

Fig. 8.2.3-5 Examples of feed emulsions and their corresponding UF permeates

8.2.3.3 Design consideration and significant findings on microemulsion treatment

Design consideration and significant findings from GPI’s lab on microemulsion

treatment are summarized as follows,

1. Flux/pressure relation and Cg

Flux/pressure relation of microemulsion is of typical pattern, like

macroemulsion. Even though the droplet size of microemulsion is always smaller that that

of macroemulsion, Its flux may be higher or lower than macroemulsion’s, depending on its

components. For example, Elf Seraft A macroemulsion (dE 150- 200 nm) has higher fluxthan Elf Emulself G3 microemulsion (dE = 50 nm.) but lower than Emulself XT (dE = 20 nm)

at the same oil concentration and operating condition. For the Cg of microemulsion, there is

no experiment that was conducted until the flux was about zero. The maximum value,

proposed by BELKACEM and based on Elf Emulself G3, (see table 8.2.2-2), is 45% by

volume of oil.

2. Oil rejection and residual pollutants in permeate

Recommended MWCO of UF membrane for microemulsion treatment is around

40-50 kD. Oil rejection, based on fresh emulsion, is 100%. For used emulsion, presence of

free-oil or foulant may cause decrease in oil rejection.

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Permeate of microemulsion contains much more residual pollutants than that of

macroemulsion since it contains very high concentration of surfactants/co-surfactants and

additives (around 80% by weight). For example, Elf Emulself G3 microemulsion contains

surfactants/co-surfactants and additives around 80-85%. Its permeate contains TOD of 2,660

mg/l per 1% by volume of oil in the inlet wastewater. Many researches [10], {11], [18]

pointed that TOD removal efficiency of UF for microemulsion is around 80-90 %. Because ofhigh residual TOD, the permeate need to be further treated by RO or other feasible processes.

Flux enhancement by salt addition had never been studied in GPI’s lab.

Theoretically, the effect of salt in this case should be identical to that of macroemulsion.

However, since concentrations and types of emulsifier of the two emulsions are greatly

different. Salt requirements should be different. Thus it is recommended to perform UF test to

find salt requirement, rate of increase in flux and residual salt in the permeate before design.

8.2.3.4 Fouling and cleaning of membrane

Fouling is a major problem of membrane process. Unlike polarization, Decrease influx from fouling is irreversible. The flux will decrease with time, even when operating

condition is constant, and not recover unless proper regeneration or cleaning process is

applied. Fouling is represented in the resistance model in the form of “fouling resistance” R F(see section 8.2.1.6). Its mathematical equations are of power or exponential types. The exact

equation for each wastewater is achieved only from the experiment.

There are several references, literatures and books about fouling and cleaning of

membranes, as listed in bibliography. Here, only fouling and cleaning related to oily

wastewater will be mentioned.

1.

Typical foulants

Fouling materials, which are usually found in oily wastewater, include.

• Hydrocarbons, fats, oils and grease: These substances are usually listed as

a major foulant for UF process. Their presence should be avoided or

minimized. However, for oily wastewater treatment, its rejection becomes

the objective of the process. Free-oil cause more problems than emulsified

oil, as described in section 8.2.3-1. To reduce the fouling from oil, one

should start with the right membrane material. Hydrophilic membrane, such

as PAN, is recommended. Free oil should be removed from UF feed stream.

•

Suspended solids: For cutting oil wastewater or wastewater from mechanicalworkshops, scraps or small bits of materials from manufacturing processes

are major source of SS. Extent of clogging depends mainly on the size of the

SS. It is recommended to separate these materials from UF feed steam.

Heavy and relatively larger scraps can be settled. For smaller SS, it may be

separated by physical processes, i.e. hydrocyclone or prefilter. Generally, the

materials, which are larger than 1/10 of membrane flow channel, should be

prefiltered .

2. Flux enhancement

Many techniques are invented to slow down fouling process, resulting in longer period of high flux. Examples of these techniques, shown in fig. 8.2.3-6, include,

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• Back flushing (sometimes called “backpulsing”, “backwashing”) This

method has been tested by SRIJAROONRAT [10], using “Membralox T1-

70” inorganic tubular module, active surface of 0.005 m2, equipped with

automatic backflushing equipment. After normal UF operating of 1-3

minutes, the permeate of 3 ml is automatically injected in the direction of

permeate side to feed side every 0.7 to 5 seconds. For UF of kerosene/watersecondary emulsion with backflushing, increases in flux up to 2 times were

reported. In present, this technique is commercially available, esp. for

ceramic membrane.

• Turbulence promoter: Moving of membrane, such as in rotating disc

module, or insertion of wire, mesh into the membrane flow channel can

increase turbulence, thus increase permeate flux.

• Other techniques, such as (1) co-current permeate flow, which required a

permeate pump, (2) permeate backpressure by throttling of permeate outlet

valve to optimize Pt or (3) use of pulsating feed, etc.

Fig. 8.2.3-6 Examples of flux enhance techniques [38]

3. Cleaning of membrane

When flux decreases to an unacceptable level, the membrane needs to be cleaned

to restore the flux up to or almost to the original value. Cleaning procedures always involve

combination of these means, i.e.

• Chemical, in the form of detergents, acids, alkalis, water or cleaning reagents

• Thermal, in the form of heat

•

Mechanical, in the form of hydrodynamic force.

To remove oil from the membrane, many reagents are recommended such as

alkali, alcohol, detergents or even pure water. Selection of cleaning reagent depends on type

of product (for manufacturing process), type of foulants, chemical and thermal resistance of

membrane material.

For oily wastewater treatment, rinsing with water and/or cleaning with detergents

or surfactants are generally used. Rinsing with water is proven to be efficient enough forcleaning UF membrane of used macroemulsion treatment from mechanical workshop [12],

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(see fig. 8.2.2-4). Use of surfactants provides better cleaning efficiency pluses that the

surfactants will somehow bond to the membrane surface in the form of oleophobic layer

consisting of micelles, resulting in more hydrophilicity of membrane. This oleophobic layer,

formed by surfactants, will prevent the oil from attaching to the membrane. Thus, it helps

reducing fouling, resulting in prolonging period of high flux [18], (see fig. 8.2.3-7).

-

-

- --

-

-

Fig. 8.2.3-7 Example of evolution of flux of macroemulsion UF with periodical cleaning with

macroemulsion (membrane IRIS 3042, P = 1 bar, V=1.5 m/s. 25oC) and schematic of

interaction between membrane/surfactants [18]

Cleaning of UF membrane by microemulsion

GPI lab had researched on the use of microemulsion as a cleaning reagent [18],

[11], since it contains high concentration of surfactants. Recommended cleaning procedure

starts with rinsing of the membrane with water for 20-30 minutes, then circulation of themicroemulsion for 15 minutes. WANICHKUL [11] recommended another water einsing after

the emulsion circulation. Throttle valves in the system should be fully open during the

cleaning process. Recommended concentration for the cleaning solution is Around 2% by

volume of concentrate. The used cleaning emulsion can be stored and used for several times

until it is saturated by oil. The result shows that the procedure can restore the flux up to 98%

of original value. Advantages of this concept include;

• Microemulsion is normally available in factories or mechanical workshops.

No need to purchase surfactants. Its efficiency is very good. It also helps

forming micelles as described in the previous paragraphs.

•

The result is relatively identical to the use of surfactants since it can prolong period of high flux as shown in fig. 8.2.3-7.

• For its very high surfactant concentration, it can be reused for several

cleaning cycles until it is saturated by oil. Thus this concept is quite

economical.

• Used cleaning microemulsion can be treated by chemical breaking, following

by UF.

• Apart from the use of commercial microemulsion, BELKACEM also

recommended a formula of the special cleaning microemulsion, which

generates low-pollutant permeate from its treatment by UF. Its concept is based on the use of low-solubility surfactants/co-surfactants. The

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a) Dead- end test module

(Source: Millipore)

b) Plate membrane test module (Source: Orelis, Osmonics)

c) Spiral wound test set (Source: Millipore) d) Pilot-scale test set (Source: Millipore)

Fig. 8.2.3-8 Examples of UF test modules

Almost all of the researches on oily wastewater treatment by UF are based on

stabilized emulsion since it cannot be separated effectively by other single process. However,

SRIJAROONRAT [10] has researched on UF of non-stabilized secondary emulsion. Her

study provides useful information to understand the performance of UF when free-oil is

present, which is frequently found in general oily wastewater. Significant findings of the

research can be summarized as follows,

8.2.3.6 Miscellaneous design consideration

Most of the design considerations for each category of oily wastewater are described

in the previous sections. In this section, some general remarks and common design

considerations, summarized from synthesis of literatures and GPI researches, will be

presented as follows,

• From GPI’s researches as well as other literatures, it is recommended to operate

UF system for oily wastewater around a certain flux to prolong the operating time per cycle (before cleaning) and maintain relatively steady flux. This concept

is called “critical flux”. At this flux, deposition of foulants can be counterbalanced

by shear force from cross-flow velocity. Thus the fouling resistance is relative

steady (not changing with time). This can be normally achieved by the use of

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moderate pressure (1-1.5 bar). The use of higher pressure may give higher flux

but the rate of decrease in flux is higher to, resulting lower overall flux.

•

UF performance is sensitive to type of membrane, characteristic of wastewater and

operating condition. So it should be very careful to use the data from literatures or

researches to design the system. Experimental procedures of the researches should

be considered. The common mistakes on the use of researches on UF of oily

wastewater treatment are about, (1) pore size, sometimes MWCO and pore sizes

are confusing, and (2) concentration of oil, they are reported in various forms (%

by volume of oil, % by volume of concentrate in case of cutting oil emulsion, % by

weight, etc.), (3) Effect of concentration factor, some experiments carried out by

recycling the permeate to the feed stream, so the concentration of feed were

constant. The concentration effect is not included.

•

The cost of membrane system is high and the performance on secondary emulsion

treatment is not better than general separation processes. The UF, then, should be

used for some specific wastewater, separating from main stream wastewater.

8.3 Microfiltration (MF)

8.3.1

Basic knowledge and working principles

Microfiltration (MF) membrane can retain material in the range of 0.1 to about 5

microns (100-5,000 nm). It is mainly used as a clarification technique, separating suspended

solids from dissolve substance [38]. Size of MF is defined in the form of pore size, rather than

MWCO. MF membranes are available in various geometry and materials as UF. Its main

applications are separation of suspended particles in biotechnology, food and pharmaceutical

industries such as bacteria, red blood cells, latex emulsion, dairy product, etc. Examples of

MF membrane are as shown in fig. 8.3.1-1

Tubular module

(Source: Koch)

b) Plate module

(Source: Millipore)

c) MF membrane structure

(Source: Millipore)

Fig. 8.3.1-1 Examples of MF membranes

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Theoretically, working principle of MF is relatively identical to that of UF. Theories,

models and characteristic curves of UF can be applied to MF. Main difference between MF

and UF is the pore size. Since the pore size of MF is relatively large. Its corresponding

capillary pressure is relatively low (around 0.1 bar). Thus, its maximum or limiting pressure is

much lower than UF. Its pore is about the same size as droplets in macroemulsion, so some oil

droplets can pass the MF membrane and be present in permeate. This is the main reason whyMF had not been studied seriously on oily wastewater treatment.

However, GPI lab had researched on the feasibility of combination between chemical

destabilization and MF for macroemulsion treatments as will be described in the following

section.

8.3.2 Significant findings on MF for oily wastewater treatment from GPI researches

As stated above that MF pore size is close to that of oil droplets in macroemulsion, to

use MF for this wastewater, the droplet size must be increased. MATAMOROS applied the

concept of flux enhancement by salt addition, like the case of UF, to MF. Significant findingsfrom the research are as described below,

1.

Recommended pore size is around 0.2 μ for MF (with salt addition) of

macroemulsion treatment. The use of too large pore results in very low or zero

oil rejection. Both oil and water can pss through the membrane. The use of

smaller pore is not possible, since its maximum pressure, calculated from pore

size, is not enough to drive the separation process. Both water and oil cannot

pass the membrane. If we increase the pressure, it can force the oil through the

membrane, resulting in very low or zero oil rejection anyway.

2. Quantity of salt required is much higher (about 3 times) than that of UF and

relatively close to the quantity required for total destabilization. Optimum dose

of CaCl 2 for macroemulsion, based on Elf Seraft ABS cutting oil macroemulsion

[20], is about 95 mg/l of Ca++

or 350 mg/l of CaCl 2 per 1% by volume of oil in

wastewater.

3. Result from dead-end test module of MF with salt addition shows very high flux,

relatively close to that of water flux. However, in case of cross-flow module, the

initial flux is about identical to the water flux at the beginning of the operation.

Then, the flux decreases rapidly within very short time (few hours), more rapid

than that of UF. The steady flux is relatively low and may not be higher than that

of UF’s flux (see fig. 8.3.2-1). Steady flux, based on Seralf ABS 4% at 0.1 bar, is

around 25 LMH.

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Fig. 8.3.2-1 Evolution of flux from MF (with salt addition) of macroemulsion [20]

4.

The difference between dead-end and cross-flow model may be caused

difference in test volume since the dead-end module is much smaller than the

pilot scale cross-flow module.

5.

Rapid decrease in flux can be explained by deposition and coalesce of free-oil at

the surface as well as within the pore size of membrane since the pore size of MF

is relatively large.

6. When the membrane is properly selected, oil rejection is about 100% at low

operating pressure (about 0.05-0.1 bar). Increase in pressure beyond the capillary

pressure results in presence of oil in permeates. Since the pressure is much lower

than (about > 10 times lower) that of UF, energy consumption of MF is very

low, compared to UF.

7. Residual TOD comes from the surfactants/co-surfactants. Concentration of

residual salt and TOD are relatively identical to that of UF with salt addition,described in section 8.2.3.2.

8. To reduce fouling, MATOMAROS recommends the use of other separation

process, such as coalescer or hydrocyclone, to separate the free-oil from MF feed

stream.

9. Since quantity of salt added into the wastewater is high, the emulsion is largely

destabilized already since it is in the storage tank, indicated by presence of oil

layer on the surface. Thus, the use of MF should be compared to the combination

of destabilization and other basic process, such as decanter, coalescer.

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8.4 Reverse osmosis (RO)

Reverse osmosis is the ultimate pressure driving membrane process that capable of

retaining ionic-range materials, the range of 0.1 nm. Structure of RO membrane is dense,

compared to porous structure of UF and MF’s (see fig 8.4-1). Its main application is

production of ultra pure water for many industries, such as, pharmaceutical, electronic, food,and nuclear (water for reactor). RO membranes are available in various materials and

modules, i.e. plate, etc., as described on section 8.1.

Cutaway-view of RO module

(Source: Desal)

RO pure water system

(Source: Koch)

Fig. 8.4-1 Examples of RO membranes

8.4.1 Basic knowledge and working principles

Working principles of RO is based on the concept of osmosis. Osmosis phenomenon

can be explained by considering the system of 2 compartments, separating by dense

membrane, as shown in fig. 8.4.1-1. Each compartment contains the solution at different

concentration.

Osmosis phenomenon is defined by mass transfer of the solvent through the

membrane, from the diluted solution to the concentrated one. Increase in pressure on the

concentrated side can lower or stop the mass transfer. To stop the mass transfer, the pressure

required shall be equal to “ osmotic pressure” , as shown in fig. 8.4.1-1b. If the applied

pressure is higher than the osmotic pressure, the solvent will inversely travel from concentrate

side to the diluted side (fig. 8.4.1-1c). This is the phenomenon taking place in RO and give the process its name.

DC

Posmotic

DC

P = Posmotic

DC

P = Posmotic

a) Osmosis phenomenon b) Osmotic pressure c) Reverse osmosis

Fig. 8.4.1-1 Working principles of reverse osmosis

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Osmotic pressure is the function of concentration and usually defined by Van’t hoff as

shown in eq. 8.4.1.

...3

3

2

21 +++= C AC AC Aπ {8.4.1}

Where π = Osmotic pressure

C = Concentration of solutionAn = Virial coefficients of the solution

The value of A1, A2, A3, etc. depends on type of solution. The virial coeeficients of

large molecules or materials are relatively small. Thus the osmotic pressure is low and usually

negligible, as in case of MF and UF. For low molecular-weight molecules, supposed to be

separated by RO, the values of high-ordered A are high so the osmotic pressure becomes

significant.

Mathematical model for RO

Mathematical model of RO can be written in the form of resistance model, as shown ineq. 8.4.2. For RO, transmembrane pressure is countered by osmotic pressure, so the effective

driving force for the process is the difference between the two pressures. RO resistance

mainly consists of the membrane resistance. Mass transfer resistance in the boundary layer

may be accounted in some cases.

M

M t

R

P J

π −= {8.4.2}

Where J = Permeate flux

πΜ = Osmotic pressure, calculated from the concentration at themembrane surface

R M = Membrane resistance

RO may find its application in industrial water reuse process. However, due to its

minuscule pore size and very high osmotic pressure, pressure requirement, thus energy

consumption, of RO is very high. So it is scarcely used on general wastewater treatment. In

GPI lab, RO had been studied for its performance on treatment of highly polluted permeate

from UF of wasted emulsion. The studies will be summarized in the following section.

8.4.2 Significant findings on RO for oily wastewater treatment from GPI’s researches

BELKACEM [18], MATAMOROS [20] and WANICHKUL [11] had studied on

application of RO on treatment of highly polluted permeates from treatment of wasted cutting

oil emulsion. Significant findings of the researches are as summarized below,

1. RO is proven to be an efficient process for treatment of UF permeate of macro-or

microemulsion, which contains very high concentrations of surfactants/co-

surfactants that are not retained by the UF membrane. When retentate and

permeate are recycled, relation between flux and pressure from RO of

microemulsion’s permeate from UF is linear up to the maximum test pressure of

60 bars as shown in fig. 8.4.2-1a.

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Pt

Flux

Lag due to

osmotic pressure

Min recommended

pressure Log (conc.)

Flux

Fig. 8.4.2-1a Typical relation between flux

and pressure of RO

Fig. 8.4.2-1b Typical relation between flux

and log of concentration

2.

Evolution of RO flux from treatment of microemulsion’s and macroemulsion’s

UF permeate, both in used and fresh condition, are relatively identical as shown

in fig. 8.4.2-2. The graph is for RO operation in batch process (see fig.8.2.1-4)without return of permeate so effect of factor of concentration is already

included.

0

20

40

60

80

100

120

140

160

180

0 2000 4000 6000 8000 10000 12000 14000

Time (sec)

F l u x ( L / ( m 2 . h ) )

Microemulsion Macroemulsion Used macroemulsion

Fig. 8.4.2-2 Examples of flux evolution from RO of the UF permeates of various emulsions (the RO permeate are not recycled) [11]

3. Flux decreases with increase in concentration factor (fig. 8.4.2-1b). There is no

clear evident if the relation between flux and factor of concentration will have

inflection point like that of UF of macroemulsion (fig. 8.2.1-6) since the

experiments were usually stopped before the zero-flux was reached. The

maximum factor of concentration (or volume reduction factor) ever tested in GPI

lab is 2.5 (at 25 bars, 30oC, V = 1.8 m/s)[18].

4. BELKACEM [18] reported that permeate’s TOD generally increases with time

or concentration factor (shown in fig. 8.4.2-3a). However, WANICHKUL

showed [11] that TOD may decrease with time or concentration factor, as shownin fig. 8.4.2-4. Decrease in permeate TOD, in this case, may be explained by

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formation of micelles on the membrane surface when the concentration of feed is

continuous increased along the process time until it reaches the critical micelle

concentration (CMC) [11]. These micelles cannot pass through the membrane so

the quantity of pollutant in permeate is decreased. Formation of micelles depend

on type and concentration of surfactants/co-surfactants in the permeate, as well

as interaction between those pollutants and other material such as calcium thatmay cause formation of complexes as well as electrical charge of membranes.

Thus, exact result should be obtained from RO test.

5. Typical relation of rejection or removal efficiency with pressure, based on salt, is

as shown in fig. 8.4.2-3b [59]. But MATAMOROS [20] indicates that, for UF

permeate of microemulsion, the rejection decreases at high pressure (the dashed

line in fig. 8.4.2-5b). There is not sufficient data to evaluate the cause of this

decrease. However, it is recemmeded to use moderate transmembrane pressure

(about 20-25 bars) to obtain good rejection.

Concentration factor

Rejection and

TOD permeate

1

Rejection

TOD

Rejection

Min recommended

pressureP

t

Fig. 8.4.2-3a Relation between rejection,

TOD of permeate and concentration factor

Fig. 8.4.2-3b Relation between rejection and

transmembrane pressure

0

1

2

3

4

5

6

0 2000 4000 6000 8000 10000 12000 14000 16000

Time (sec)

T O D o f p

e r m e a t e ( m g / l )

Microemulsion Macroemulsion Used macroemulsion

Fig. 8.4.2-2 Examples of permeate TOD evolution from RO of the UF permeates of various

emulsions (the RO permeate are not recycled) [11]

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6. Guidelines for RO design or evaluation, summarized from various GPI’s lab, are

as shown in table 8.4.2-1. Membrane material used is polyamide. MWCO is

around 100-150 Daltons.

8.5 Nanofiltration (NF)

Nanofiltration is an intermediate membrane process between ultrafiltration and reverse

osmosis. It is a relatively new technology, compared to others membrane processes. NF

membrane pore sizes are between those of UF and RO. It can retain the meterials of the size

around 100 – 600 nm. Thus it can be used to separate dissociated form of a compound from

the undissociated form [38]. For example, lactic, citric, and acetic acids can pass through to

NF at low pH but are rejected at high pH when in their salt forms. NF is generally used in

many industries, such as biotechnology, food, and drinking water as well as in environmental

applications. Apparently, structure and module of NF are relatively identical to those of RO.

8.5.1 Basic knowledge and working principles

Separation in NF membrane is based on both size difference, like UF, and diffusion

mechanism, like RO. Generally, NF membranes are charged so they can be used for selective

separation of charged materials. Uncharged membranes are available but very rare and not

popular. Separation mechanisms in NF membrane are not well understood. But they are

generally described in 2 approaches, i.e. ionic exclusion and, like RO, solution-diffusion.

For ionic exclusion approach, separation of charged materials by NF depends on the

charges of ions in solution to be separated and of membranes. Ions of the same charge as the

membrane will be pushed while the counter-charged ion will be attracted by the membrane

charges. For uncharged membrane, the modified form of solution-diffusion model, as shown

in eq. 8.4.2-2, was used to explain the separation mechanisms in the NF membranes by someresearchers. Applications of NF on oily wastewater treatment are known of but they are

privately designed and there are not many publications on the issue.

In GPI lab, MATAMOROS [20] performed the feasibility study on application of NF

for cutting oil emulsion treatment. The result will be summarized in the next section.

8.5.2

Significant findings on NF for oily wastewater treatment from GPI’s researches

MATAMOROS [20] had studied the performance of NF on the treatment of cutting oil

emulsions as well as permeates from UF of cutting oil emulsions, using cellulose membranes,

i.e. Desal 5 (600 Da), SV10 (100-300 Da) and SG15 (2000 Da). Significant findings of theresearch are as summarized below,

1. From the research, NF is proven to be an efficient process for treatment of UF

permeate of macro-or microemulsion, which contains very high concentrations

of surfactants/co-surfactants that are not retained by the UF membrane.

Rejection is slightly lower than that of RO. But the energy consumption is about

half of RO’s, since its pressure range is around 4 –20 bars, compared to the

range of 20 – 60 bars for RO. Evolution of flux with time and with pressure for

NF of permeate are relatively identical to that of RO (fig. 8.4.2-1 and 8.4.2-2).

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T a b l e 8 . 4 . 2 - 1 S u m m a r y

o f R O d a t a o n o i l y w a s t e w a t e r

t r e a t m e n t

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2. NF performances on macro- and microemulsion treatment were also studied.

The result showed that, at constant feed concentration, relation between pressure

and flux of NF for macro- and microemulsion treatment are divided into 2

regions i.e. pressure controlled and mass transfer controlled region (fig 8.5.2-1),

like that of UF.

3. Relation of flux and theoretical concentration of feed, when permeate is not

recycled, is as shown in fig. 8.5.2-2. The relation is not linear so it is not

governed by film model (section 8.2.1.5). This can be explained by

destabilization in-situ of emulsified oil during NF operation, justified from

presence of oil layer in the storage tank. Destabilization of oil, like the case of

UF with salt addition, makes the real feed concentration lower than theoretical

value.

4.

Results of MATAMOROS are as shown in table 8.5.2-1. From the table, TOD

removal efficiencies of UF are always higher than UF. This means the oil is

completely separated and the surfactants/co-surfactants are retained with higherefficiency. However, it should be noted that the results are based on fresh

emulsion. For used emulsion, result may differ and should be obtained by pilot

test.

Fig. 8.5.2-1 Relation of flux and transmembrane pressure of NF for macroemulsion

(Elf Seraft ABS) and microemulsion treatment (Elf Emulself G3 EAB), using desal5

membrane at 20oC [20]

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Fig. 8.5.2-2 Relation of flux and theoretical feed concentration of NF for macro-

and microemulsion treatment [20]

8.6 Comparison of membrane processes on emulsion treatment

Major objective of GPI’s researches on oily wastewater treatment by membrane

process is the treatment of stabilized emulsion. From the previous sections, they show that

performance of each process or combinations of processes on emulsion treatment are

different. To compare the performance of processes or combinations of membrane processes,

MATAMOROS had performed pilot test of various processes using the same macroemulsion.His results are tabulated in table 8.6-1. However, It should be noted that,

1. The results are based on specific operating conditions, types of wastewater and

membrane. Since performances of membrane processes are sensitive these

parameters, the results can be used as a guideline for preliminary evaluation

only.

2.

Fresh emulsions were use so fouling due to foreign materials was not included.

3.

Evolutions of flux with time are not present. In real design, this data is important

for membrane sizing and determination of operating and cleaning cycle. For

example, NF and MF+CaCl2 may be very interesting from their relative lowenergy consumption. But they may foul easily, resulting in low flux for long-tern

operation and more frequent cleaning.

4. Even though the efficiency of each process is very high. It does not mean that the

permeate always conforms to the related standard. For example, permeate’s

TOD from RO of UF+RO of macroemulsion at 4% by volume of oil is around

1,250 mg/l, which is still high and may need further treatment or to be mixed

with relatively diluted wastewater and treat by conventional treatment system.

5. From the previous sections, it is obvious that membrane process is very versatile

and efficient process. But its performance is sensitive to many parameters. So it

is, again, strongly recommenced to perform pilot test before design the realmembrane process.

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T a b l e 8 . 5 . 2 - 1 S u m m a r y o f N F d a t a o n o i l y w a s t e w a t e r t r e a t m e n t

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Table 8.6-1 Comparison of membrane processes on cutting macroemulsion treatments

(based on Elf Seraft ABS at 4% by V of oil)

MF+CaCl2 UF UF+RO UF+NF NF

Membrane MS11107 Iris3042 Iris3042 +MS10 Iris3042+Desal5

Desal5

Global TOD

removal efficiency

(%)

97.2 95.8 99.1 97.9 97.4

TOD of final

permeate (g/l)

2.76 4.5 0.92 2.2 2.7

Pt (bar) 0.1 1 1+30 1+10 10

Flux (LMH) 24.9 52.92 52.92/42.12 52.92/30.96 27

Specific energy

consumption

(KWh/m3)

Not available 3.2 3.2+40.2 3.2+22.8 22.2

Remark See note 1 See note 2

Note 1 Initial flux of MF is very high, compared to that of water, but the membrane is

rapidly clogged by free-oil. The flux, thus, drops sharply. The final flux is

relatively low.

2 Evolution of time was not present in the original research. But the membrane tends

to be clogged by free-oil from destabilization in-situ.

3 No comparison data of microemulsion treatment was proposed.

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9.1 General

Thermal processes are separation processes that involve changing of phases of the

materials to be separated. For distillation, it involves liquid and gas. For crystallization andzone refining, they involve liquid and solid. Since the processes involve phase changing, they

inevitably consume high energy. This is the reason why they are scarcely used for general

wastewater treatment. However, it may become economical alternative if the product from the

treatment can be recycled or relative easier for ultimate disposal.

Oily wastewater is actually binary system, containing, mainly, 2 immiscible liquids i.e.

oil and water. So it could be separated by thermal processes. In GPI lab, there are some

researches on applications of thermal processes on oily wastewater treatment. Most of all

were based on distillation. Only few were based on crystallization. So, in this chapter will be

emphasized on distillation, which can be divided into 2 major types, i.e. conventional

distillation and enhanced distillation, called “heteroazeotropic” distillation.

It must be noted that the researches are based on lab-scale experiments to study the

theoretical concepts that underline process operation. In real processes, the distillations are

usually carried out in distillation columns, which their designs are a major science into itself.

So it will not be mentioned here. However, the researches can be used as a guideline to

understand and evaluate the feasibility of the processes.

9.2 Basic knowledge on distillation

Since distillation always involves liquid and vapor phase of mixtures, it can be

described by the concept of vapor/liquid equilibrium. The mixtures may have two or morecomponents. However, to provide basic knowledge of the process, it is sufficient to simply

consider the mixture of 2 components, called “binary” mixture.

9.2.1 Basic knowledge on vapor/liquid equilibrium of mixtures

Since distillation always involve the mixture of two or more components, it is

necessary to know a certain number of variables to describe or characterize the equilibrium

stage of the system. The number of required variables, called “ degree of freedom” is

calculated by the phase rules, as shown in eq. 8.2.1.

N F +−= π 2

{9.2.1}

Where F = Degree of freedom

π = The number of phases, for vapor/ liquid system, π = 2

N = The number of species in the mixtures

For example, to describe a binary mixture system, required degrees of freedom are 2-

2+2 = 2, which are normally pressure and temperature. Generally, distillation processes

operate at constant pressure, so operating parameter that is used to control the process is

temperature.

To understand vapor/liquid equilibrium of a binary system, consider a binary mixture

of specie A and B in the container, as shown in fig. 9.2.1-1. Assume that overall pressure of

the system is constant at 1 atm. When the mixture is heated, temperature of the mixture will

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increase, as shown in fig. 9.2.1-2. When it reaches a certain temperature, called “bubble

point”, the first bubble of vapor will appear. From this point, the mixture will exist in both

vapor and liquid phases. Unlike a pure substance, temperature of the system during

evaporation period continuously changes, rather than being constant. When the temperature

reach a certain value, called “dew point”, the last drop of liquid will disappear.

Liquid phase

Vapor phase

P = constant

Heat

Specie B

Specie A

Time

T

Dew point

Liquid Liq Gas Gas

Bubble point

P = const.

Fig. 9.2.1-1 Diagram of a binary mixture

system

Fig. 9.2.1-2 Evolution of temperature of a

binary mixture at a constant P

Dew temperature and bubble temperature of a binary mixture varies with pressure. An

example of relation between pressure and temperature is shown in fig. 9.2.1-3. Characteristic

of P-T curve depends on types of components in the mixture.

Critical locus

T

P

C

C

Bubble curveDew curve

Methanol/Benzene

mixture

T

P

0% Methanol

100% Methanol

Fig. 9.2.1-3 Examples of P-T diagram

At a binary system at constant pressure, the dew- and bubble points of the system vary

with composition of the mixture. Compositions of the mixture are usually reported in the from

of molar fraction “x” and “y”. The value “x i” represents the ratio of moles of species i in

liquid phase (ni,l) to summation of moles of every species in liquid phase (nl) (eq. 9.2.2). On

the other hand, the value of “yi” is the ratio of moles of species i in vapor phase (ni,v) to

summation of moles of every species in vapor phase (nv) (eq. 9.2.3).

l

li

in

n x

,= , ∑ =

i

i x 1

{9.2.2}

v

vii

nn y ,= , ∑ =

i

i y 1 {9.2.3}

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When the bubble points at various values of x1 are plotted, the curve is called the

“bubble curve” or “saturated liquid line”. On the other hand, when the dew points at various

values of yi are plotted, the curve is called the “dew curve” or “saturated vapor line”.

Generally, dew curve and bubble curves are plotted on the same coordinate. They can be

plotted both on T-x-y scale and P-x-y scale as shown in fig. 9.2.1-4a and b. Since distillation

process usually operates at a constant P, T-x-y curve is normally used. Relations between pressure, temperature, x and y can be combined into a three-dimension coordinate, resulting in

P-T-x-y diagram as shown in fig. 9.2.1-5.

xA = 1

yA = 1

T P = const.

Pure B Pure A

xA = 0

yA = 0

xA , yA

C

CC


xA = 1

yA = 1

P T = const.

Pure B Pure A

xA = 0

yA = 0

xA , yA

C

C

C


a) T-x-y diagram b) P-x-y diagram

Fig .9.2.1-4 Examples of T-x-y and P-x-y diagrams

To understand phase changing taking place in distillation process, we will consider a

P-x-y diagram as shown in fig. 9.2.1-6. From the figure, the points on the dew curve representsaturated vapor. the area above the dew curve (T-y i) is of superheated vapor. The points on the

bubble curve represent saturated liquid. The area below the bubble curve (T-xi) is of

subcooled liquid. The area between the 2 curves is the two-phase region. The two curves meet

at the edges of the diagram where saturated liquid and saturated vapor of the pure species

coexist.

P

T

1

0

yA

xA

Critical

P u r e

A

P u r e

B

xA = 1

yA = 1

T

P = const.

Pure B Pure A

xA = 0

yA = 0

yA = 0.4

= 0.6

Superheated vapor

= 0.8xA xA

a

b b’

c’ c

yA = 0.6

Subcooled liquid B u

b b l e

c u r v

e

D e w

c u r v

e

Fig. 9.2.1-5 An example of P-T-x-y diagram Fig. 9.2.1-6 An example of T-x-y diagram

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From fig. 9.2.1-6, if we heat the subcooled liquid of 60 mol-% of specie A and 40 mol-

% of specie B (so xA = 0.6, xB = 1-0.6 = 0.4) under a constant P from point a, the first bubble

will appear when the temperature reaches the bubble curve at point b. The molar fraction of

specie A in this very first bubble will be determined by drawing the horizontal line from point

b to meet the dew curve at point b’. If we continue heating, more vapors will appear while the

quantity of liquid will decrease. The compositions of liquid will follow the bubble curve from point b (xA = 0.6) to c (xA ≈ 0.8) and the composition of vapor will follow the dew curve from

b’ (yA ≈ 0.8) to c’ (yA = 0.6), respectively. When the temperature reaches point c, the last drop

of liquid disappears. The mixture will become entirely vapor with yA = 0.6. Continuing

heating, the vapor will have higher temperature and become superheated vapor. Cooling of

vapor can be explained by the same manner described above.

9.2.2 Equilibrium of various mixtures

Characteristics of vapor/liquid equilibrium curves depend on types of components of

the mixture, pressure and temperature. Examples of various types of vapor/liquid equilibrium

are as shown in fig. 9.2.2-1. The first 3 curves are of miscible mixtures. For some mixtures,the T-x-y diagrams present a maximum or minimum point where the boiling liquid at this

point produces a vapor of exactly the same composition. This point is called the “ azeotrope”.

At some conditions, liquid/liquid equilibrium (LLE) coexists with vapor/liquid

equilibrium (VLE), this give rise to vapor/liquid/liquid equilibrium (VLLE) [61], as shown in

fig. 9.2.1-1 d to f. The state that VLLE is present is called “ heterogeneous azeotropic” or

“ heteroazeotropic”. As stated before, VLLE varies with intensive properties (P,T) and may

become only VLE at certain conditions as shown in fig. 9.2.2-2.

xA = 1

yA = 1

T

Pure B Pure A

xA = 0

yA = 0

xA , yA

Locus ofazeotropeHigh P

Low P

Fig. 9.2.2-2 Examples of evolution of VLE and VLLE with pressure

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Example

Methanol-Water

Ethanol-Water

Acetone-Chloroform

N-butanol-Water

Decane-Water

Polypropylene oxide-

Water

Azeo

Azeo

Azeo

Azeo

Azeo

Azeo

Azeo

Azeo

V

V

L+V

L

L+V

L

V

L+V

L

V

L+V

L

2 L

L

V

L+V

2 L

L+V

2 L L

L

L+V

V

T Y

XX , Y

T Y

XX , Y

T Y

XX , Y

T Y

XX , Y

T Y

XX , Y

T Y

XX , Y

Type

Without azeotrope

Minimum-temperature

azeotrope

Maximum-temperature

azeotrope

Heteroazeotrope

(Partially miscible)

Demixtion

Heteroazeotrope

(Immiscible)

Fig. 9.2.2-1 Examples of various types of vapor/liquid equilibrium

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9.3 Heteroazeotropic distillation of oily wastewater

Heteroazeotopic distillation, in this chapter, is technically referred to the distillation

process that a proper substance, called entrainer, is added to the feed to ensure the formation of heteroazeotrope. It does not include the process that the azeotrope occurs

naturally. However, their working principles are identical. Details of the heterotropicdistillation process are described below.


Since hydrocarbons or oils have very low water-solubility, it is generally acceptable to

assume that oily wastewater, which is actually the oil/water mixture, is immiscible binary

mixture. Typical characteristic of T-x-y diagram at a constant pressure (called “isobar

diagram”) of oily wastewater is as shown in fig. 9.3.1-1. Generally, hydrocarbons have

higher boiling point than that of water.

A

xw = 1

yw = 1

T P = const.

Pure Oil Pure water

(W)

xw = 0

yw = 0

Oil +V

xw , yw

Boiling T

of BVapor (V)

W + V

Oil+water

xw = xH yw = yH

Boiling T

of Water

THB C

D

xw,1

xw,2

xw,3xw,4=1

xw,5=1

xw,6=1

yw,1’ to yw,4

= yH

yw,5

yw,6

xw,1’

Azeotrope (H)

Fig. 9.3.1-1 Typical isobar diagram oily wastewater

From the diagram, it shows that the wastewater can be boiled at the temperature lower

than that of pure water and pure oils. Heteroazeotropic distillation, which is the distillation

when the VLLE is present, makes use of this fact so it requires lower energy than classical

distillation.

From the figure, the bubble curve in this case will look like a figure “U” with square

legs (Line ABHCD). If the original wastewater contain 70 mol-% of water (xw,1 = 0.70), itwill boil at the temperature TH. The composition of this very first bubble can be determined

by drawing the horizontal line to meet the dew curve (Curve AHD). In this case, they will

intersect at point H. Thus the molar fraction of water (yw) in the bubble is that of azeotrope

(yH, xH). Continuing heating, the liquid volume gradually decreases and its composition

gradually change from xw,1 to x.w,2, xw,3, etc. However, by drawing the horizontal lines from

these values of xw, the compositions of yw are always equal to yH. During this period the

temperature is automatically constant at TH. When xw finally reaches 1, this means the

residue becomes pure water. All of oils are separated from water and in vapor phase.

After this, the temperature rises until it reaches the boiling point of pure water. The

value of xw is constant at 1. The value of yw increases from yH to yw,4, yw,5, etc. since the purewater continues boiling at add more steam to the overall vapor phase.

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The vapor phase is usually condensed to recover oil vapor. If the vapor is condensed

while xw < 1, the composition of vapor will be constant at yH. From fig. 9.3.1-1, these vapors

will condense at the temperature T H , resulting in the distillate of oil and water at xw = y H .

From GPI’s research by TOULGOAT [19], the distillate will not be formed as an

emulsion if the hydrocarbons have high vapor tension and/or their water solubility is very lowand not sensitive to temperature change. This condition is usually satisfied for oily wastewater

treatment polluted by petroleum-base oil or for the carefully selected entrainer (described in

section 9.3.4). Thus the distillate from heteroazeotropic distillation of oily wastewater is

usually in the form of 2 separate layers of water and oil.

9.3.2 Raoult’s law and Dalton’s law

To define dew curve and bubble curve of a binary mixture, the following equations are

generally used, i.e. eq. 9.3.1 and eq. 9.3.2 ( Dalton’s law)

sat iii P x p = {9.3.1}

P y pii = {9.3.2}

Where pi = Partial pressure of specie i

PP

sat = Vapor pressure of specie i

P = Pressure of overall system, which is normally kept constant, e.g. 1 bar

From eq. 9.3.1 and 9.3.2, it gives rise to Raoult’s law (eq. 9.3.3). The equation is

valid under the assumption that the vapor phase is an ideal gas and the liquid phase is an

ideal liquid .

sat

iii P xP y = {9.3.3}

If the system is not ideal system, eq. 9.3.3 will be modified as shown in eq. 9.3.4

( modified Raoult’s law).

sat

iii

sat

ii f xP y γ φ = {9.3.4}

γi is called “ activity coefficient”, which is normally obtained from experiments. If γ =

1, this means the system is ideal. The equation will become Raoult’s law. The vapor pressureis replaced by the term “ fugacity” (f) and “ fugacity coeficienct“ (φ). Relation between Psat, f

and φ are as shown in eq. 9.3.5.

sat

i

sat

isat

iP

f =φ {9.3.5}

For application of oily wastewater treatment, the use of eq. 9.3.3 is proven to be

accurate enough [24], [11]. These equations will be used to determine the dew curve and

bubble curve, as well as azeotropic point of oily/water mixture, as described in the next

section.

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9.3.3 Calculation of azeotropic temperature and composition, dew curve and bubble

curve.

To calculate the isobar diagram of VLLE of oily wastewater or oil/water mixture, the

following procedure, based on the theories described in the previous section, is recommended.

1. Find the azeotropic temperature (TH) and bubble curve (T-x)

For immisible bunary mixture of A and B, it can be imagined that the two

liquids are separately located in the container. Each liquid exerts the corresponding vapor

pressure. Thus the vapor pressure of the system is the summation of the vapor pressures of

every species, as shown in eq. 9.3.6. On the bubble curve, the mixture will boil when the

vapor pressure of the mixture is equal to the overall pressure of the system (P) (eq. 9.3.6).

PPPP sat

B

sat

A

sat

B A =+=+ {9.3.6}

To find the temperature TH that corresponds to eq. 9.3.6. Relation between vapor pressure and temperature of both liquids must be known. For general liquids, their properties

can be found in many references, e.q. Perry’s [2]. If the relations are provided in the form of

data table, it may be more convenient to use graphical method to find T H, as shown in fig.

9.3.3-1. Curves of liquid A and B are drawn, using the data from the reference. Curve of the

mixture A+B is obtained by the sum of vapor pressure of A and B at the same temperature.

This curve is the relation between azeotropic temperature (TH) and pressure. Thus TH at any

given operating pressure of distillation process can always be found.

TH Temperature

Pressure

Pure A

Pure B

A+B

Pdesign

Fig. 9.3.3-1 Graphical method to find heteroazeotropic temperature

Sometimes, Relation between Psat and T of pure liquid is given in the form of

equation, called “ Antoine equation” (eq. 9.3.7).

C T

B AP T sat

−−=)ln( ,

{9.3.7}

T is temperature. A, B and C are numerical constants, depending on the types of

liquids. These constants can be also found in many references. From Antoine equations of the

two liquids, eq. 9.3.6 can be rewritten in the form of T. After solving the equation at a given

P, the resulting T is the azeotropic temperature TH. The bubble curve of an immiscible binary

mixture can de drawn as a straight horizontal line at the temperature T H on the T-x,y diagram.

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2. Find the Dew curve (T-y)

At every point on the dew curve, the liquid A and B will condense so,

T sat

A A P p,

= {9.3.9}T sat

B B P p

,

=

{9.3.11}

From eq. 9.3.2, the values of y A at any T (yA,T) in the region A-V (fig. 9.3.1-1),

which A will condense, can be calculated from the following equation.

P

P yPP y p

T sat

AT

A

T sat

A

T

A

T

A

,, =→== {9.3.12}

In the same manner, the values of y A at any T (yA,T) in the region B-V

(fig. 9.3.1-1), which B will condense, can be calculated from the following equation

P

P y

P

P yPP y p

T sat

BT

A

T sat

BT

B

T sat

B

T

B

T

B

,,, 1−=→=→== {9.3.13}

By varying the values of T, yA at various value of T can be calculated . Plotting

the values of y A and T on T-x-y diagram result in a dew curve. The curve will be calculated

easily by graphical method as shown in fig. 9.3.3-2. Generally, specie A represents water. So

the value of x and y represent the molar fraction of water in liquid and vapor phase,

respectively.

T1 T2

Psat,T1

B

Temperature

Pressure

A (Pure water)

B (Pure oil)

Water+oil

Psat,T1

A

Psat,T2

A

Psat,T2

B

Pure

water (A)

Temperature

Pure

oil (B) x,yyH

TH

T1

T2

yB 1

yB 2 yA 2 yA 1

Calculate y A and y B by eq.

9.3.12 and 9.3.13, then, plot

T,y A and T,y B to obtain dew

curves

Fig. 9.3.3-2 Graphical method to find dew curve

3. Find heteroazeotropic composition (xH, yH)

From eq. 9.3.2, azeotropic composition (yH) in the form of molar fraction of “A”

can be calculated from the following equation,

P

p y A

H = {9.3.8}

At TH, liquid A (and B) will condense so,

H T sat

A AP p ,= {9.3.9}

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Thus,

H H

H H

T sat

B

T sat

A

T sat

A

T sat

A

H PP

P

P

P y

,,

,,

+== {9.3.10}

This means that, at azeotropic point, liquid phase will contain (100yH) mol-% of

specie A and 100(1-yH) mol-% of specie B. For the vapor phase, it will also contain (100yH)

mol-% of specie A and 100(1-yH) mol-% of specie B. Heteroazeotropic temperature (TH) and

composition (yH) of common hydrocarbons, calculated from theoretical equation described

above, are tabulated in table 9.3.3-1. Observed values of yH from LUCENA [24] are also

presented in the table. It shows that the theoretical equations can be used to predict the

characteristic of real process with high accuracy.

Table 9.3.3-1 Heterotropic temperature and composition from various hydrocarbons [24]

ExtractantMolecular

weight (g/mol)

TH

(deg. C)

yH

(by molar)

yH

(by volume)

y H observed

(by volume) [24]

C6H14 56 61.6 0.209 0.0351

C7H16 100 79.2 0.452 0.0922

C8H18 114 89.5 0.616 0.188

C9H20 128 94.8 0.827 0.3255

C10H22 142 97.6 0.914 0.495 0.468

C11H24 156 98.9 0.959 0.6663

C12H26 170 99.5 0.98 0.7953 0.767

C13H28 184 99.8 0.991 0.890C14H30 198 99.95 0.996 0.9542

C15H32 212 99.999 0.998 0.9702

C16H34 226 ≈ 100 0.999 0.9840

9.3.4 Application of heteroazeotropic distillation on treatment of inverse emulsion or

concentrated oily wastewater

In spite of its lower energy consumption than the classical distillation,

heteroazeotropic distillation still consumes relatively high energy. So it may not be

economical to treat general wastewater by this process. However, for the wastewater

containing high concentration of oil or inverse (water in oil) emulsion (e.g. slops from

refineries), the portion of water to be separated is relatively small and the residue from

distillation process, which is water-free oil, become valuable for it can be re-processed or

recycled. In these cases, heteroazeotropic distillation may become economically feasible.

GPI had studied applications of heteroazeotropic distillation on treatment of slop [24]

and retentate from UF of cutting oil emulsion [11]. Significant findings from the researches

are summarized as follows,

1. Addition of entrainer (or extractant)

Even though slop or retentate is naturally oil-water mixture, it may or may notcontain a component that forms an azeotrope. Sometimes, in self-entraining mode, obtained

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From the figure, the temerature will rise from ambience to azeotropic

temperature (TH), and then remain constant until the water is totally separate. After that, the

temperature will rise up to the boiling point of the entrainer. From the example, the entrainer

is decane, theoretical TH (table 9.3.3-1) is 97.6oC, relatively identical to the observed value.

Then the temperature rises to 174oC, which is corresponding to the boiling point of decane.

The evolution of temperature is natural, without controlling of any kind. It indicates that the process is relative easy to operate.

3. Performance of the process

Condensation of the vapor phase results in the distillate consisting of 2

separate layers of entrainer (upper layer) and water (lower layer). The residue is dehydrated hydrocarbons, which is very fluid, compared to mayonnaise-like, viscous slop or UF

retentate. The pictures of feed, residue and distillate of the slop and UF retentate are as shown

in fig. 9.3.4-3.

a) b) c) d) e)

Slop (a), distillate and residue (b), magnified pictures of slop (c)and residue (d)

UF retentate (30% vol of oil),residue and distillate (e)

Fig. 9.3.4-3 Pictures of feed, residue and retentate of slop and UF retentate of used

macroemulsion (30% by volume of oil) [24], [11]

The entrainer can be simply decanted and then reused for the next distillation

cycle. For the water, even though its appearance is transparent and seems clean, it may

contain some soluble pollutants, such as some volatile chemicals or surfactants, depending

on characteristic of the feed. WANICHKUL [11] reported that TOD of the water from UF

retentate of cutting oil emulsion is around 1,000 – 2,800 mg/l. In this case, it needs to be

further treated.

In case of slops, the residue can be sent back to refinery process for

reproduction. For UF retentate, the residue, which is mainly base oil from cutting oil

emulsion, has high calorific value so it can be reused. Generally, mechanical workshops or

cutting oil users will send their UF retentates to central treatment facilities, where they can be

treated more economically. Heteroazeotropic distillation can be used in such treatment

facilities to treat these kinds of wastes.

4. Performance of entrainers

As stated before, the performances of entrainers depend on their capability toextract water from wastewaters, represented by their corresponding yH. The higher the yH, the

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better the extracting performance. LUCENA had proven that the value of theoretical yH is

close to the observed value, as shown in table 9.3.3-1. Apart from pure hydrocarbons, he also

tested some general commercial hydrocarbons. The results are tabulated in table 9.3.4-1. From

the result, kerosene and gasoline are suitable to use as entrainers.

Table 9.3.4-1 Water extracting performance of various commercial hydrocarbons [24]

NameRatio of water in the distillate

or yH ( by volume)Remark

Kerosene 0.635

Gasoline 0.75

BTX cut (or fraction) 0.134

“Charge réformat “oil 0.15, 0.23, 0.455 See note 1

“Cœur FCC ” oil 0.08, 0.144, 0.343 See note 1

Note 1. These oils contain several fractions of hydrocarbons so they start extracting water with thelowest-yH hydrocarbon. When it is used up, the next higher-yH hydrocarbons are used.

9.3.5 Application of heteroazeotropic distillation on treatment of the wastes polluted by

trace hydrocarbons: Steam stripping

Steam stripping is another, in effect the reverse, form of heteroazeotropic distillation

that the small amount of relatively volatile materials, such as volatile hydrocarbons, hydrogen

sulfide or ammonia, are removed from large amount of less volatile material or wastewater.

In this case, water will be used as an entrainer to extract the pollutants. For wastewater, even

though it contains water and has self-entraining property, steam is normally used to heat the

wastewater and reduce the effective pressure in the distillation apparatus to save the energyrequired. Stripping with inert gas is also available.

Stripping reactor is generally a packed column to provide efficient vapor-liquid

contact. The waste is fed at the top of the column while the steam enters at the bottom. The

quantity of steam required to remove pollutants depends on the types of the pollutants. The

vapor of steam and pollutants flows out at the top of the column to further process, depending

on the type of pollutants. Condensate of oil and water is sent to oil separation process for

recovery of oil. Hydrogen sulfide or ammonia may be sent to flare of furnace or disposed off,

if possible. It should be noted that steam stripping is based on different concept from air

stripping, which is based on solubilty of gas governed by Henry’s law.

9.3.6 Design calculation and design considerations

9.3.6.1 Quantity of entrainer required

As stated before that the column design will not be discussed here, the major

calculation of the process is quantity of entrainer required to separate the pollutants. It can be

divided into 2 cases as follows,

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1. Heteroazeotropic distillation of concentrated oily wastewaters or slops

In this case, the entrainer is selected hydrocarbons and the pollutant is water.

Theoretical quantity of entrainer can be calculated from yH of the entrainer and quantity of

water to be removed by the following equation.

H

H

water entrainer y

yVolumeF S Volume

)1(.

−⋅= {9.3.11}

The yH of various entrainers are listed in table 9.3.3-1 and 9.3.4-1. If other

entrainer will be used, its yH can be determined from experiment or calculated by the

procedure shown in section 9.3.3. If the theoretical value of yH is used, S.F of 1.05 to 1.2 is

recommended [24].

2. Steam stripping

In this case, the entrainer is steam and the pollutant is volatile material in the

wastes. Theoretical quantity of steam can be calculated from quantity of pollutants to be

removed and their corresponding yH by the following equation.

)1(. tan

H

H ts pollusteam

y

yVolumeF S Volume

−⋅= {9.3.12}

Please note that the calculated quantity of steam is the quantity required for

heteroazeotropic distillation process only. Additional heat (sometimes, also in the form of

steam) may require to raise the temperature of the system up to the design point.

9.3.6.2 Design considerations

From GPI’s researches, design considerations can be summarized as follows,

1. In case of treatment of slop or concentrated wastewater, quantity of water should

be determined before addition of entrainer. Excess dosage of entrainer results in

more energy consumption. Since the temperature required to recover this excess

entrainer will be equal to the boiling point of the entrainer, not the azeotropic

temperature (see fig.9.3.4-2). Otherwise, this excess part will be wasted with the

residue and not be recycled.

2.

If possible, it is recommended to perform lab-scale tests or pilot-test to evaluate

the type of entrainer, its required quantity and the efficiency of the process, such

as TOD of distilled condensate, before design the real process. Since some

unknown factors, e.g. presence of surfactants, volatile substances, etc., may

affect the performance of the process.

3. For steam stripping, the components of pollutants, sometimes, may be unknown.

Thus it is strongly recommended to perform lab-scale tests or pilot tests. To

evaluate the feasibility of the system and the quantity of steam required.

4.

The process operates at high pressure. Thus presence of some chemicals, such as

hydrogen sulfide, may give rise to high-corrosive environment. So these precautions need to be taken into account in the distillation reactor design.

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5. The distillation system is generally costly and consumes high energy. Economic

analysis of the system should be performed, compared to other competitive

processes, e.g. stripping VS. chemical treatment or solvent extraction or

adsorption.

9.4 Classical or conventional distillation of oily wastewater


Classical or conventional distillation in this chapter is referred to the distillation

process that no entrainer is added to the feed to force the formation of azeotrope. Working

principle of classical conventional distillation is similar to that of the heteroazeotropic except

that there is no addition of entrainer to the feed. However it may contain azeotrope in case

that there are some components in the feed that can act as entrainer.

If the azeotrope is not naturally formed, the boiling point in this case will not be

lowered by azeotropism. So, more energy is required to rise the temperature up to operatingvalue. In case of oily wastewater, the temperature is around than 100oC, which is the boiling

point of the water at 1 atm. Since it consumes high energy, its application on wastewater

treatment is limited. Distillation under reduced pressure is reported to be used for emulsion

treatment in Germany. In GPI lab, WANICHKUL [11] had studied the application of

distillation on oily wastewater, as will be described in the next section.

9.4.2 Significant findings on classical distillation for oily wastewater treatment from

GPI’s researches

WANICHKUL [11] had divided his research into 2 parts, i.e. (1) distillation of

stabilized emulsion and (2) distillation of permeate from UF of stabilized emulsion.Significant findings from the research are as summarized below,

9.4.2.1 Distillation of stabilized emulsion

WANICHKUL [11] had studied the performance of distillation on stabilized

emulsions, using both macro- and microemulsion. The result shows that,

Distillation of cutting oil macroemulsion

1. The evolution of temperature of macroemulsion (based on Elf Seraft ABS 4% by

volume of concentrate) is as shown in fig. 9.4.2-1. From the figure, the

temperature rises from the initial value to 92oC and remains constant throughoutthe experiment. This can be explained that the process contains a self-induced

azeoptrope since the boiling point of the mixture is lower than the boiling point

of water (100oC).

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0

50

100

150

200

250

300

0 20 40 60 80 100 120 140 160

Time (minute)

T e m p e r a t u r e ( o C ) ,

D i s t i l l a t e v o l u m e ( m l ) .

0

3

6

9

12

15

18

T O D

o f d i s t i l l a t e ( g / l )

Temperature Accumulated distillate volume TOD of water part TOD of oil+water part

Fig. 9.4.2-1 Evolution of temperature, volume of distillate, TOD of mixed distillate and TOD

of water part of the distillate (Based on Elf Seraft ABS, 4% by volume of concentrate) [11]

2. Other evidence for self-induced azeotropism is that the distillate consists of two

separate layers of oil and water, as shown in fig. 9.4.2-2. These two parts are

readily separated. The oil part is mainly dehydrated hydrocarbons portion in the

cutting oil and can be reused or recycled.

Fig. 9.4.2-2 The feed, residue and distillate from distillation of the macroemulsion [11]

3.

Some pollutants are found in the water part of the distillate. Evolution of TOD in

the distillate is very complex, resulting from complicate ingredient of the

emulsion, as shown in fig. 9.4.2-1. From the experiment, TOD of the water part

is around 2,000-7,000 mg/l. TOD removal efficiency is around 96%, based on

cutting oil TOD of 120,000 mg/l.

4. The efficiency of the process is close to that of UF (98%) but the energy

consumption distillation process is much higher. UF, generally, requires energy

around 10-20 kWh.m-3 while energy requirement of distillation is around 625

kWh.m-3

[11]. Thus if the treatment of permeate is not concerned, UF seems to be more feasible than distillation for macroemulsion treatment.

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5. From complexity of cutting oil formulation, x-y diagram of the mixture can not

be established. But the result can be used as a guideline to evaluate the feasibility

of distillation on this kind of application

Distillation of cutting oil microemulsion

1. The evolution of temperature of microemulsion (based on Elf G3 EAB 4% by

volume of concentrate) is as shown in fig. 9.4.2-3. From the figure, the

temperature rises from the initial value to 99oC and remains constant throughout

the experiment. So the process also contains an azeotrope.

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90

Time (minute)

T e m p e r a t u r e ( o C ) ,

D i s t i l l a t

e v o l u m e ( m l ) .

0

3

6

9

12

15

18

T O D o f d i s t i l l a t e

( g / l )

Temperature Accumulated distillate volume TOD of water part TOD of oil+water part

Fig. 9.4.2-3 Evolution of temperature, volume of distillate , TOD of mixed distillate and TOD

of water part of the distillate (Based on Elf G3 EAB, 4% by volume of concentrate) [11]

2. The distillate also consists of the layers of oil and water, which are readily

separated (fig. 9.4.2-4). Evolution of TOD is complex, like the case of the

macroemulsion. TOD of the water part of the distillate varies from 1,200 to

2,200 mg/l. TOD removal efficiency is around 98%, based on cutting oil TOD of

75,000 mg/l. The efficiency is higher that that of UF (approx. 85%)

Fig. 9.4.2-4 The feed, residue and distillate from distillation of the microemulsion [11]

3. Energy consumption for microemulsion is relatively similar to that of

macroemulsion (approx. 625 kWh/m

-3

) . So it consumes much more energy thanUF ( < 20 kWh/m-3) [11].

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Chapter 10 Chemical treatment processes

10.1 General

Naturally, oils or hydrocarbons tend to separate from water. In their natural form,

separation of oil droplets is governed by their size. Large oil droplets separate from waterwithin a short time while small droplets take longer time to be decanted or separated .

Efficiency of most of physical separation processes aforementioned decreases with the

decrease of oil droplet sizes.

Furthermore, if the droplet sizes are small enough (< 5 microns), the oil droplets will

subject to Brownian motion. Thus theirs rising velocity are no longer governed by STOKE’s

law and can be negligible. These droplets will remain dispersing in the water without

decanting. (In fact, they may probably decant but take very long time, such as years.) In this

case, it can be said that the oil is stabilized. The oil/water mixture is called stabilized

emulsion or stable emulsion.

In some applications, it is necessary to disperse oil into water phase and keep it in the

stabilized form. Examples for these applications include some dairy product processing,

washing process using detergents or the use of cutting oil emulsion. In case of machanical

workshops, the stabilized mixture of oil and water, called “ cutting oil emulsion” is needed to

perform very important roles in lubrication of machine tools and specimens, cooling, washing

away the scraps and impurities away and protecting the tools from corrosion. The oil has to be

dispersed homogeneously in the water to provide consistent properties. For washing, greasy

dirt on the clothes needs to be removed and suspended in wash water without coming back to

the clothes again. To make the oil stable, apart from oil and water, the third components

called “ surface active agents” is always required.

When this stabilized emulsion is no longer suitable to use and then wasted, it will

become one of oily wastewater that is most difficult to treat. Thermal and membrane

processes are proven to be applicable for this kind of wastewater .

STOKE’s law-based physical separation processes (e.g. decanter, coalescer, DAF),

can not be directly used in this case since the wastewater contains very small and stable

droplets. To use these physical processes, the wastewater needs to be undergone necessary

chemical treatment processes.

Main objectives of chemical treatment processes for stabilized emulsion treatment are,

• To destabilize the emulsion and

• To make the oil drops ready to separate from the water, e.g. to increase the size

of the droplets.

GPI lab had studied chemical processes for oily wastewater treatment, which can be

summarized as shown in the following sections.

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10.2 Basic knowledge

10.2.1

Stability of the emulsion

Stability of emulsion refers to the ability of the emulsion to maintain its properties,

esp. its dispersion. Stable or stabilized emulsion can, practically, maintain its oil dispersionwithout changing with time. So its required qualities, such as cooling or lubricating capacity,

are relatively consistent. Stability of emulsion are generally based on 2 factors,

• Droplet size: The oil droplet size must be very small. So they are not decanted

naturally or by STOKE’s law-based separation processes.

• Resistance to coalesce: The oil droplets must have good resistance to coalesce. So

their size distribution remain relatively constant.

From section 2.2.1, the droplet size is proportional to effective work and inverse of

interfacial tension (1/γo/w). Thus, to obtain stabilized emulsion, it is reasonable to decrease the

interfacial tension between oil and water and prevent the interaction between oil droplets.However, low interfacial tension is not the only factor that guarantees the stability of the

emulsion. AURELLE and ZHU [21] proposed the properties that give rise to stable emulsion,

which will be described in section 10.2.3. To achieve these properties, the third component,

called “ surface-active agents” or “ surfactants”, is required. Details on surfactants are

described in the following section.

10.2.2 Surface-active agents

Surface-active agents, or surfactants, are practically the materials that are soluble both

in oil and water. They usually localize themselves and form a layer (generally,

monomolecular layer) at the surfaces or interfaces. This phenomenon is called surfaceactivity, which give the materials their names. Chemically, they always comprise of large

polar functional groups. One end of the molecules that is soluble in oils is usually a long chain

of aliphatic or aromatic or both forms of organic groups with 8 to 18 carbon atoms. Being a

long chain, this hydrophobic part is usually called “ tail ” of the surfactants. Another end,

which is water soluble or hydrophilic, is usually called “ head ” of the surfactant. Thus the

symbol of surface-active agents is usually drawn as a circle with long tail as shown in fig.

10.1.2-1.

or

Hydrophilic

“head”

Hydrophobic

“tail”

-

+ + -

Anionic

Cationic Amphoteric

Nonionic

-

-

-

Oil

- Micelle

-

-

Fig. 10.2.2-1 Symbols of surface active agent and its localization at oil/water interfaces

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Types of surface-active agents or surfactant are categorized by charge of their head as

follows,

1. Anionic surfactant is the surfactant that ionizes to yield a positive charge, free

ion and a negative charge (surface active ion) which localizes at the interface. Its

symbol contains a “minus” sign in the head. This type of surfactant is relativelycheap and widely used in industries. Common anionic surfactants are, i.e.,

• Soaps are usually sodium or potassium salt, derived from fats and oils by

saponification (hydrolysis with presence of alkaline agent) with sodium

hydroxide.

• Sulfate surfactants are salts of sulfated alcohol, such as dodecyl or lauryl

alcohol. General formula of these surfactants is in the form of R-OSO3-M+,

where M+ represent positive-charge ion, such as sodium or potassium.

• Sulfonate surfactants are sulfonated compound, mainly derived from esters,

amides and alkylbenzenes. An example of these surfactants is sodium

alkylbenzene sulfonate. General formula is R-SO3-M+.

2. Cationic surfactant is the surfactant that the surface-active part is cation. It is

usually salt of quaternary ammonium hydroxide, which its hydrogen of the

ammonium ion have been replaced with alkyl groups. Cationic surfactants are

quite expensive. But they are noted for their disinfecting (bactericidal) property

[1]. The symbol of the surfactant contains “plus” sign.

3.

Non-ionic surfactant is the surfactant that does not ionize and have to depend

on groups in the molecule to make it soluble [1]. The groups are usually

polymers of ethylene oxide (C2H4O). The symbol of the surfactant, in this case,

contains no sign. Examples of the surfactants are polyethyleneglycol mono-oleate, nonylphynol ethoxylene of ethylene oxides. The surfactants are noted for

adjustable hydrophil-lipophil properties.

4. Amphoteric surfactant is the surfactant that contains both positive and negative

surface-active part. Its symbol contains 2 circles, one with minus sign, another

with plus sign.

In production of industrial emulsions, esp. manufacturing of cutting oil , surface-

active agents are divided into 2 types, i.e.,

1.

Surfactants are the main surface-active agents used to lower the oil/waterinterfacial tension, thus, stabilize the oil droplets. They are usually of anionic

type. Thus they forms anionic stabilized emulsion. However, nonionic emulsions

are also available.

2. Co-surfactants are normally nonionic surfactants such as fatty alcohol. Their

localization at the surface of oil droplets among the main surfactants helps

reducing the repulsive force between the ionic heads of surfactants. Thus they

give rise to smaller droplet sizes and more stable emulsion.

Effect of surfactant: Surfactants lowers the oil/water interfacial tension (as well as

surface tension of water, in case of air/water interface) by the mechanism described in thenext section. Relation between interfacial tension and concentration of surfactant is as shown

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in fig. 10.2.2-3. From the graph, interfacial tension decreases rapidly at the beginning. Then

the rate of decrease lowers until the concentration of surfactant reached a certain value, called

“ critical micelle concentration” (CMC). After that, the tension remains relatively constant.

This can be explained by the formation of groups of surfactant molecules called “ micelle” (fig

10.2.2-1). These surfactants will no longer localize at the surface of droplets, so they have no

effect on the tension.

Time

γow or

CMC

γw

Fig. 10.2.2-2 Diagram of the electrical double layer

10.2.3

Important properties to obtain stable emulsion

As mentioned in section 10.2.1, emulsion must have one or more of the following

properties, proposed by AURELLE and ZHU [21], to become stable emulsion.

1. Thermodynamic stability

Normally, interfacial tension of oil is positive. To increase the stability of oildroplets, the interfacial tension should be lower to increase the area, thus decrease the

diameter of the droplets. Addition of surfactant can lower the interfacial tension by its

localization at the droplet surface. The surfactant will try to stretch or increase the surface of

oil droplets as much as possible in order to locate itself at the surfaces. It results in virtual

force (p) that tries to stretch the surface, countering to the interfacial tension (γo/w) that tries to

contract the surface (see fig. 10.2.3-1). Effective interfacial tension is the difference between

these two forces, as shown in eq. 10.2.1.

p p

γowγow

Surfactants,

co-surfactants

Droplet surface

Water

Oil

γow = 0 γow = 0γow < 0

Coalesce Redistribute

Fig. 10.2.3-1 Interfacial of oil and water with

the presence of surfactants

Fig. 10.2.3-2 Coalescence and redistribution

of droplets in thermodynamiclly stabilizedemulsion

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their bridging properties or adsorb the oil droplets and from scum or sludge. They may

contain the salts that can destabilize the emulsion by the mechanism mention above.

Examples of these chemicals are the products of DEGUSSA and Primafloc.

10.2.4.2 Coagulants and destabilization chemicals

Chemicals or materials generally used to archive the destabilization mechanisms

described above include,

1.

Monovalent electrolytes

Examples of this type of salt are NaCl and H2SO4. Main destabilization

mechanism is reduction of diffuse layer. Thus required dosage is quite high in order to

provide sufficient concentration of positive ions in the entire emulsion to destabilize the

droplets. For certain types of surfactants, e.g. soaps, acid can cause destabilization be

neutralization of saponification process that gives rise to the soaps. In this case, required

concentration is much lower. Main disadvantage is the formation of saline or acid pollutants after destabilization. So it seems like the pollution changes from oily waste to saline or acid

wastes.

2.

Bivalent electrolytes

Examples of this type of chemicals are CaCl2, Ca(COOH)2 (Calcium formiate),

MgSO4 and MgCl2. Main destabilization mechanism is precipitation of surfactants. Free

surfactants in water will react with Ca or Mg ions and form complexes. Equilibrium between

adsorbed, ionized surfactants on the droplet surfaces and free surfactants is shifted . So ionized

surfactants will reverse into free surfactants thus, reduce the stability of droplets. This effect is

practically governed by solubility product of the surfactants. Required dosage in this case islower than that of monovalent ones. If inorganic electrolytes are used, they may also cause

high saline waste, depending on required dosage. Organic salts, such as calcium formiate

(Ca(COOH)2) may be more interesting since the residual pollutants is (COOH)2 which is

organic and biodegradable.

3. Multivalent electrolytes

Examples of this type of chemical are ferric chloride (FeCl3) and alum. They

are generally more effective in destabilization than the previous two chemicals. But it may not

be used with some surfactants, such as certain types of soaps. Main destabilization

mechanisms are combination between precipitation of surfactants as well as sweepcoagulation. So the actual dosage is lower than that calculated from solubility product alone

and usually lowest among the first three electrolytes

4. Surfactants of opposite charge

Examples of cationic surfactants that may be used for emulsion destabilization

are N-cetylpyridinium chloride and salts of quaternary ammonium hydroxide. Main

destabilization mechanism is adsorption and charge neutralization. Overdose must be avoided

to prevent charge reversal and re-stabilization.

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5. Commercial adsorbents

Oil destabilization and absorbents are commercializes. Destabilization

mechanisms and efficiency vary with its components and emulsion ingredient.

10.2.4.3

Destabilization of emulsion stabilized by nonionic surfactants

The mechanisms stated above are generally based on emulsions stabilized by ionic

surfactants. In case of those stabilized by nonionic surfactants, the mechanisms that involve

reduction or elimination of electrical barrier are invalid since the droplets carry, practically,

no charge. Main destabilization mechanism in this case must base on precipitation of the

surfactants to form insoluble complexes. ZHU proposed original chemical destabilization

method of the emulsion stabilized by nonionic surfactants of fatty acid based by addition of

anionic surfactants (such as alkylsulfate of fatty alcohals) and cationic trivalent electrolytes

(such as alum, ferric chloride).

10.2.4.4

Dosage, efficiency and residual pollution

ZHU had tested various type of chemicals to destabilize many kinds of emulsion,

both macro- and microemulsion, both fresh and used conditions. Efficiency, residual pollution

and examples of optimum dosage are summarized as follows,

1. The emulsions and destabilization chemicals were tested in lab scale by simple

mixing and decanting.From ZHU’s criteria, chemicals are considered to be

effective destabilization reagents for that emulsion when the oil is separated

in the form of free oil at the surface within 1 hours. However, in effective

cases, the decanting is carried out within relatively short time, less than 20-30

min. Oil removal efficiency varies from 0 (cannot destabilized) up to 40-70% or 99%, depending on types of destabilization chemical and emulsion.

2. Residual pollutant after decanting of free oil is mainly co-surfactants, esp. in

the form of fatty alcohol , which is highly soluble. Concentration of this soluble

pollutant depends on ingredient of emulsion treated and initial concentration of

concentrate (in case of cutting oil emulsion) in the emulsion. This pollutant

contains high TOD and must be further treated, as previously discussed in

chapter 8 “Membrane processes”.

If salts, e.g. NaCl, etc. or acids are used to destabilization, they also cause

residual pollutants in form of saline and acid. If the residual TDS

concentration is high, it may not conform to effluent standard. This is the maindisadvantage of destabilization by salt. Effluents from destabilization with

acids, ferric chloride or alum have low pH and must be neutralized before

discharge.

3. There are no universal chemicals and dosages valid for every emulsion .

Types of effective chemicals, optimum dosages, and residual pollutants level

must be evaluated first in lab scale before design the full-scale chemical

process. However, test result from fresh emulsion can generally be applied for

used emulsion. [21]. Results from ZHU’s study on destabilization of certain

emulsions are shown in table 10.2.4-1.

4.

Increase of temperature, generally, helps improving destabilization efficiency by [21],

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• Increase of Brownian motion that favors collisions of droplets

• Decrease of water viscosity that favors draining of water film around

droplets

• Partial dehydration that helps weaken mechanical barriers of droplets

Table. 10.2.4-1 Results from ZHU’s research on destabilization of various emulsions

A) Emulsions tested

Surfactant Co-surfactantsType/ appearance

%

OilName % Name %

%

Addi

-tive

%

Water

A Milky anioninc

macroemulsion

80 Sodium

alkylbenzene

sulfonate, sodium

carboxylate,

triethanolaminecarboxylate

11 Benzylic

alcohol, PEG

ester.

4 5

B Milky anioninc

macroemulsion

7 Soduim sulfonate,

alkylphosphate

33 Butyldiglycol 4

C Transparent

anioninc

microemulsion

25 Mixed soaps of

mono- and

diethanolamine of

fatty acids

38 Butyldiglycol 8 2 27.5

D Transparent

anioninc

microemulsion

6 Amine caboxylate

and K alcanolamine

30 Butyldiglycol 12

E Milky nonioninc

macroemulsion

80 PEG mono-oleate,

nonylphenolethoyla

te (8 moles of

C2H4O)

20

Note: PEG = Pltyethylene glycol

B) Results on destabilization of emulsion A at conc. of 2% by volume of concentrate, 20oC

Dosage

Chemicals

g/l meq/l

Oil

removal

eff. (%)

TOD

removal

eff. (%)

Effluent

TOD

(g/l)

HC in

effluent

(mg/l)

pH o/w

dyn/cm

H2SO4 18.3 355 97.1-97.5 99.5-99.9 1.21-1.38 470-543 0.5-0.9

NaCl 20 339 96.3-96.6 99.6-99.7 1.62-1.81 630-705 8.3-8.5

CaCl2 1.5 20 96.3-96.5 99.6-99.9 1.67-1.81 658-705 7.6-8.0 1.4

MgCl2 1.8 17 96.3-96.6 99.6-99.8 1.62-1.79 630-696 8.3-8.4

MgSO4 3 24 96.3-96.6 99.4-99.6 1.65-1.79 639-696 8.3-8.5 1.0

FeCl3 0.6 11 96.4-96.9 99.1-99.5 1.52-1.75 620-714 2.1-2.5 1.8

Alum 1 9 96.2-96.7 99.4-99.7 1.60-1.84 724-855 3.8-3.9 2.1

Ca(COOH)2 1.5 23 90.8-95.9 1.99-4.45 602-639 7.4-7.5

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C) Results on destabilization of emulsion B at conc. of 2% by volume of concentrate, 20oC

Dosage

Chemicals

g/l meq/l

Oil

removal

eff. (%)

TOD

removal

eff. (%)

Effluent

TOD

(g/l)

HC in

effluent

(g/l)

pH o/w

dyn/cm

H2SO4 13.7 265 80.5-82.5 6.10-6.69 3.92-4.37 1.8-2.4

NaCl 20 339 75.0-76.5 8.50-9.00 5.27-5.60 8.4-5.8

CaCl2 2 27 80.5-81.0 6.70-6.90 4.26-4.67 8.0-8.2

MgCl2 2 19 77.5-80.0 7.10-8.10 4.48-5.04 8.3-8.6

MgSO4 3.5 28 78.5-79.5 7.30-7.70 4.59-4.82 7.6-8.2

FeCl3 1.25 23 80.0-81.0 6.70-7.10 4.26-4.48 2.7-3.8

Alum 3 27 80.0-81.0 6.70-7.10 4.26-4.48 4.3-4.6

Ca(COOH)2 2 30 73.5-78.0 7.90-9.60 4.59-5.72 8.3-8.4

D) Results on destabilization of emulsion C at conc. of 2% by volume of concentrate, 20oC

Dosage

Chemicals

g/l meq/l

Oil

removal

eff. (%)

TOD

removal

eff. (%)

Effluent

TOD

(g/l)

HC in

effluent

(g/l)

pH o/w

dyn/cm

H2SO4 3.7 71 76.3-87.3 3.90-7.70 2.60-4.90 0.6-2

NaCl 60 1016 10.5-71.5 9.30-9.60 5.80-6.00

CaCl2 2 27 70.0-71.0 9.40-9.80 5.92-6.12

MgCl2 2.5 24 69.5-70.3 9.70-9.90 6.07-6.22

Alum 6.2 55 71.0-71.5 9.30-9.40 5.81-5.92

Ca(COOH)2 3 46 64.0-70.0 9.80-11.8 6.12-7.34 3.9-4.2

E) Results on destabilization of emulsion D at conc. of 2% by volume of concentrate, 20oC

Dosage

Chemicals

g/l meq/l

Oil

removal

eff. (%)

TOD

removal

eff. (%)

Effluent

TOD

(g/l)

HC in

effluent

(mg/l)

pH o/w

dyn/cm

H2SO4 1.83 35 54.0-58.0 11.3-12.6 8.71-9.54 1.9-3.5

NaCl 50 947 46.5-53.0 13.0-15.1 9.75-11.1 9.2

CaCl2 2 27 50.5-52.0 13.3-13.8 9.95-10.3 8.7-8.8

MgCl2 2 19 53.5-55.5 12.2-12.8 9.23-9.64 8.7

MgSO4 2.5 20 53.5-54.5 12.5-12.8 9.44-9.64 8.7-8.8

Alum 4 36 52.5-57.0 11.6-13.2 8.92-9.85 4.2-6.2

Ca(COOH)2 1.5 23 43.0-52.0 13.3-16.3 9.95-11.8 7.7-8.8

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F) Results on destabilization of emulsion E at conc. of 2% by volume of concentrate, 20oC

Anionic

surfactants

(%)Chemicals

(g/l)

Cmin Cmax

Oil

removal

eff. (%)

TOD

removal

eff. (%)

Effluent

TOD

(g/l)

HC in

effluent

(mg/l)

pH o/w

dyn/cm

Ferric chloride

0.6 0.6 0.8 87.5-89.5 4.85-5.80 1.92-2.29 3.0-3.1

1.0 0.6 1.5 87.1-97.3 1.14-1.32 0.46-0.53 2.7-3.2

1.2 0.6 2.0 96.8-97.7 1.05-1.46 0.42-0.59 1.7-3.0

1.5 0.6 3.0 92.3-97.0 1.37-3.60 0.55-1.42 2.6-3.1

2.0 0.6 3.5 95.2-97.4 1.19-2.22 0.48-0.89 2.7-2.8

Alum2 4 5 79.5-84.5 7.15-9.40 2.84-3.76 3.9

3 4 8 93.0-98.0 0.92-3.30 0.37-1.28

4 4 11 93.3-97.7 1.08-3.10 0.43-1.23 4.0-4.1

6 4 16 92.5-98.0 0.92-3.35 0.37-1.37 4.0-4.7

Note: The anionic surfactant used in the experiments was Melanol CL30 (for FeCl3) and Melanol V90

(for alum). They are products of SEPPIC, contains 30 and 90% of fatty acid alkylsulfate, respectively.

10.3 Process design

Even though there are many types of destabilization chemicals, from the point of

view of process design, the reactions require the same kind of reactors. The reactors in this

case are actually the same as those required for coagulation-flocculation process in potable

water treatment. In fact, destabilization process can be counted as coagulation–flocculation

process. Generally, the process is divided into 2 steps, i.e.,

• Mixing or rapid mixing

• Flocculation

Design of each step is described below,

M

M

To separation

process

Flocculator Rapid mixing

Destabilization

chemicals

Emulsion

Fig. 10.3-1 Schematic diagram of chemical process for emulsion destabilization

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Fig. 10.3.1-2 Relation between N p and Re [63]

Calculation procedure is as shown below,

1. Select required gradient (G) and detention time (τ).

2. Calculate required volume (V) from τ and wastewater flowrate (Q). Geometry

of the tank should be cubic.

τ /QV = {10.3.3}

3. Calculate require power (P) by eq. 10.3.1.

4. Calculate n and D for required power by eq. 10.3.2. Impeller diameter should

be around ½ of tank width. Mechanical mixers are commercially available,

thus it can be selected from manufacturer catalog to suit the required tank

volume.

10.3.2

Flocculator

Floculator is designed to provide mildly mixing to make the destabilized droplets or

flocs collide and coalesce into bigger drops of flocs. There are many variants of flocculator,

also categorized mainly by their mixing methods, e.g.. Baffle type, mechanical mixer type.

However, for industries, mechanical mixers are widely used for its flexibility (variable speed

drive can be used) and reliability. The industries always have personals that can due with

O&M of these machines. So there is no problem form maintenance point of view. So we will

emphasize on the mechanical mixing flocculation tank. Design criteria of flocculation tank

are based on velocity gradient (G) and detention time ( ). Recommended values are tabulated

in table 10.3.2-1

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Table 10.3.2-1 Recommended value of gradient and detention time

Parameter Range Ref.

Velocity gradient (G) 20-80 s-1 [46]

20-75 s-1 [41]

20-150 s-1 Kawamura S.

Detention time (τ) 10-30 min [46]

20-30 min Kawamura S.

Product of G.τ 23,000-210,000 [41]

For mechanical mixing flocculation tanks, they are usually divided into 3

compartments of the same volume to avoid short circuit. The gradient will vary from the

highest value at the first compartment to the lowest at the final compartments (e.g. 75 s-1

to30-40 s-1 t0 20-30 s-1). There are 2 major types of mechanical mixers used in the flocculation

tanks, i.e. impeller type, like the rapid mixing tank, and paddle type, as shown in fig. 10.3.2-1.

Fig. 10.3.2.1 Paddle type mixers (Source: Norfolk WTP, Aqua Pak)

Design procedure of floccuclation tank is relatively identical to that of the rapid

mixing tank. For paddle type mixer, its sizing can be calculated by eq. 10.3.4 [64].

μ

ρ

V

C nAvG

d

2

3

=

{10.3.4}

Where G = Velocity gradient (t-1, normally in second –1)

n = The number of paddle blades

A = Surface area of one paddle (m2)

v = Tip speed of paddle (m/s)

Cd = Drag coefficient (normally = 0.6)

V = Tank volume (m3)

ρ = Density of wastewater, normally about that of water, (kg/m3)

μ = Dynamic viscosity of wastewater, normally about that of water

(kg/(m.s))

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10.4 Design consideration

Process design of the chemical treatment is relatively simple. However, it must be

noted that,

1.

There are no universal chemicals and dosages valid for every emulsion .Types of effective chemicals, optimum dosages, removal efficiency and

residual pollutants level must be evaluated first in lab scale (e.g. jar test) before

design the full-scale chemical process.

Fig. 10.4-1 Jar test equipment (Source: ECE engineering)

2. Normally, there are residual pollutants in the form of soluble co-surfactants, as

well as residual salt or acid pollutants from destabilization chemical, whichneed to be further treated. The extents of residual pollutants depend of type of

destabilization chemical as well as ingredient and initial concentration of

emulsion.

3. In case of effective destabilization, destabilized oil drops can be decanted

within relatively shorts time (20 min to less than 1 hour). For mathematical

point of view, it is reasonable to use this decanting time to find the diameter of

destabilized droplets. The recommended value is 200 microns (see fig. 10.4-

2), which can be used for further calculation of the downstream separation

process, such as DAF. For the non-stabilized oil droplets (since oil removal

efficiency is < 100%), we can not be sure of its size distribution. To be on thesave size, it may be estimated that the size distribution or granulometry of non-

stabilized oil droplets remain the same as that before chemical treatment.

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Fig. 10.4-2 Example of stabilized emulsion before (right) and after chemical treatment (left)

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11.1 General

From the previous section, various oily wastewater treatment processes are

described. At their best conditions, most processes can treat the wastewater at the oil removalefficiency more than 90%. However, in cases of high concentration wastewater, residual

pollutants from those processes may yet conform to related effluent standards. Furthermore,

there are some residual pollutants that are not exactly oils or hydrocarbons but come from

other components usually present in emulsion or oily wastewater. These pollutants are mainly

surfactants, co-surfactants, esp. in the form of fatty alcohol. Some treatment processes also

add residual pollutants to the effluent, such as salt, TDS, or acid from chemical destabilization

processes. Thus these effluents need to undergo finishing treatment processes to ensure that

their qualities meet the effluent standard.

There are 2 common finishing processes, generally used to treat the effluents of oily

wastewater from physico-chemical or physical treatments, i.e. biological treatment and adsorption.

These processes are extensively studied for long times. Details of the processes are

available in many sources, including books, journals, literatures, as well as references from

users or system manufacturers. For biological treatment, it is actually a science by its own

right. Moreover, the researches of GPI lab, directed by Prof. AURELLE do not emphasize on

these processes. Thus, in this chapter, they are only briefly described to fulfil the whole

content of oily wastewater treatment processes.

11.2 Biological treatment

11.2.1 Basic knowledge

Biological treatment processes are referred to the treatment processes that use

microorganisms to eliminate pollutants in wastewater. The pollutants may be utilized by the

microorganisms as substrates ( biodegradation), which is, then, transformed to new cells and

non-pollutant substances, e.g. CO2, H2O, etc. Sometimes, the pollutants are trapped ( sorption)

in flocs of microorganisms. Biological reactors are designed to provide controlled

environment to suit the microorganisms for their growth and utilization of the pollutants. The

reactors are also designed to prevent most of the microorganisms from carrying over with

effluent, since their presence in the effluent can be considered a kind of pollutants as well.

Biological treatment processes can be categorized by many criteria. According to the

types of microorganisms, they are generally divided into 2 types, i.e.,

• Aerobic processes, which microorganisms depend on aerobic respiration. In

these processes, oxygen is an important factor for it is used as the electron

acceptor in the respiratory metabolism of microorganisms

• Anaerobic processes, which microorganisms do not depend on oxygen. The

microorganisms in these cases generate energy by fermentation metabolism that

does not require oxygen as an electron acceptor. Some anaerobic

microorganisms use other substances as electron acceptors such as nitrate,sulfate, or carbondioxide.

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From the point of view of reactor design, biological processes are generally divided

into 2 major types, i.e.,

• Suspended growth, which microorganisms are suspended within the water. The

major suspended growth aerobic system is the activated sludge process (AS).

General schematic diagram of AS is as shown in fig. 11.2.1-1. Themicroorganisms are controlled to form flocs that can be easily separated from the

water in sedimentation tanks.

• Attached growth, which microorganisms are mainly attached to solid surfaces in

the biological reactors. Examples of these processes are trickling filter,

biocontact reactor and anaerobic filter.

M Inlet wastewater

Q, So

X

QR , XR

Se

Effluent

QW, XR

Wasted sludgeSedimentation tank

or clarifier

Biological reactor

or aeration tank

Fig. 11.2.1-1 General schematic diagram of activated sludge

11.2.1.1

Mechanisms of pollutant removal by biological processes

Removal of pollutants in biological treatment are complex and consists of many

phenomena, such as removal of suspended solids by enmeshment in the floc, physico-chemical

adsorption of colloidal material and biosorption or biodegradation by microorganisms [51].

Many researches had studied these mechanisms and proposed many mathematical models to

predict the performance of the processes.

Generally, pollutants are measured in the form of the oxygen demand required to

oxidize them. If the oxygen demand is based on biological reaction, it is called biochemical

oxygen demand (BOD). If it is based on chemical reaction, such as oxidation with

dichromate, it is called chemical oxygen demand (COD). However, pollutant removal can bewritten in the form of general mathematical model as shown below [51],

n

o

nS

S X k

dt

dS ⎟⎟ ⎠

⎞⎜⎜⎝

⎛ −= {11.2.1}

Where S = COD (or BOD) concentration at time “t” (ML-3, normally in mg/l)

So = Initial COD (or BOD) concentration (t = 0) (ML-3, normally in

mg/l)

t = Time (T, normally, in day)

k n = Rate coefficient (T-1

, normally, in day-1

)

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X = Effective biomass concentration. In case of As, X represents

MLVSS

(Mixed Liquor (the mixture in aeration tank) Volatile Suspended

Solids)

(ML-3, normally in mg/l)

n = Function power order (e.g. n = 0 zero order, n = 1 first-order,etc.)

For completely mix reactor where BOD reduction ratedecreases with time since

readily biodegradable is gradually used up. Eckenfelder [51] proposed the simplified model as

follows,

S

S k

t X

S S eeo =⋅

−

{11.2.1}

Where Se = COD (or BOD) concentration of effluent (ML

-3

, normally in mg/l)

Biodegradability of substance is presented by its rate coefficient (k). The higher the

value of k, the better the biodegradability. Examples of rate coefficient for some types of

wastewater are listed in table 11.2.1-1

Table 11.2.1-1 Rate coefficient for selected wastewaters [51]

Wastewater k (d-1

) Temperature (oC)

Domestic wastewater (soluble) 8.0 20

Potato processing 36.0 20

High nitrogen organics 22.2 22

Organic phosphates 5.0 21

Cellulose acetate 2.6 20

Vegetable tannery 1.2 2.0

11.2.1.2 Biodegradability of oily wastewater

Hydrocarbons or oils are considered biodegradable but the degree of

biodegradability of each type of hydrocarbons are different, depending on theircharacteristics, such as molecular structure. Generally, small molecular hydrocarbons, such as

hexane, octane, are readily biodegradable while complex or large molecular hydrocarbons,

such as dodecane, are considered low- or non-biodegradable.

Examples of biodegradable organic compounds include common aliphatic alcohols,

aliphatic aldehydes, phenols, and aliphatic esters. Surfactants, such as alkyl benzene

sulfonates and glycols, are biodegradable. These surfactants/co-surfactants are main residual

pollutants in effluent from physical and physico-chemical treatment of oil wastewater. So it is

feasible to treat these effluent by biological processes.

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Examples of substances generally resistant to biological degradation includes some

hydrocarbons, esp. long chain aliphatic and aromatics, ethers, tertiary aliphatic alcohols, and

tertiary aliphatic sulfonates.

However, biodegradability also depends on reactor design and cultures (or species)

of microorganisms. Moderate biodegradable substances may be treated if the reactor is properly design, e.g. the solid residence time (or sludge age) is long enough. Some special

cultivated bacteria can decompose oil effectively. For example, commercial mixture

containing certain emulsifier and microorganisms are used to treat sea oil spill.

On the other hand, hydrocarbons, mainly in the form of free oil, are considered to be

biotoxic substances for microorganisms. Free oils can cover the surfaces of floc and water,

thus disturb the oxygen transfer. Emulsified oil cause much less problem and usually

biodegradable. Presence of some hydrocarbons at some concentration can cause adverse effect

on the performance of the biological treatment process. Biodegradability and biotoxicity of

certain substance are presented in table 11.2.1-2. EC50% means effective concentration of the

corresponding substances that, if present in the wastewater, reduces the performance of the process to 50% of the maximum or nominal value. Nitorsomonas and heterotrophs represent

the species of bacteria for nitrification (nitrogen removal) and generally organic oxidation

( BOD removal), respectively.

It should be noted that biodegradability, shown in the table, is expressed in the form

of ratio of BOD/TOD. TOD means total oxygen demand. This parameter can be conveniently

measured by automatic sensor. So it is widely used in process control because it can be

measured in real-time mode. TOD value includes non-organic oxygen demand such as

ammonium. Thus it is usually higher than BOD. In laboratory, some researches, including

GPI’s, presented the oxygen demand in the form of TOD. When relation between BOD and

TOD is known (table 11.2.1-2) , it can be used to convert TOD, shown in the researches, to BOD for biological process design.

Some toxic substances, esp. heavy metals, may present in oil products. API recommended

the toxic threshold of some metals for biological system as shown in table 11.2.1-3.

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Table 11.2.1-2 Biodegradability and biotoxicity data [51]

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Table 11.2.1-2 Biodegradability and biotoxicity data [51] (Cont.)

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Table 11.2.1-2 Biodegradability and biotoxicity data [51] (Cont.)

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Table 11.2.1-3 Concentration of certain metals affecting biological systems [45]

Conc. (mg/l) Chromium (6) Copper Nickel Zinc

Threshold 10 1 1.0-2.5 5.0-10.0

Harmful 500 75 50-200 160

11.2.2 Design consideration and significant finding on biological treatment for oily

wastewater from GPI’s researches

GPI’s lab had also studied on feasibility of biological process for treatment of

residual pollutants from oil/water separation processes, discussed in the previous chapters

[11]. Design consideration and some significant findings on biological treatment of oily

wastewater are summarized below,

1.

Maximum inlet concentration of oil and expected effluent concentration

It may not be possible to designate the exact values of maximum inlet oil

concentration and expected effluent concentration since there are many parameters involved,

such as type of oil, reactor design, etc. Furthermore, biological process is noted for its

versatility. If the reactor is properly acclimated, the microorganisms can adapt to use the

existing pollutants as their main substrate. So even hydrocarbons may be treated. Apart from

the data in section 11.2.1.2, some case studies are summarized from many sources to provide

some ideas about the performance of biological treatment of oily waster, as shown in table.

11.2.2-1.

Table 11.2.2-1 Case studies on biological treatment of oily wastewater [66]

Process Inlet oil concentration (mg/l) Effluent oil (mg/l)

Activated sludge (AS) 5-100 5-40

Aerated lagoon 5-100 5-40

Stabilization pond 5-100 5-50

Chemical treatment + DAF +AS 5-100 2-20

Using data from several AS plants for petroleum refineries, API [45] reported

that BOD and COD removal efficiency is around 50-87% and 60-70%, respectively. MLSS

ranged from 1200 to 5000 mg/l. Retention time varied from 2.8 - 29 h. Eckenfelder [51]

showed that the biological processes were used effectively in petroleum refinery wastewater

treatments. He reported that, with BODin = 138-575 mg/l and CODin = 275-981 mg/l, effluent

COD is around 42-106 mg/l and rate coefficient are 1.11-1.7 d -1 and 2.74-7.97 d -1, based on

BOD and COD respectively. It shows that, with properly designed reactor, biological process

can be used to treat the oily wastewater to meet effluent standard.

2. Treatment of surfactants/co-surfactants

For the treatment of surfactant/co-surfactants, which is the main residual

pollutant in permeate of membrane process and other separation processes, WANICHKUL

[11] had performed the biodegradability test of the permeate from UF of cutting oil emulsion

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(TOD > 3600 mg/l). The result showed that, after 4 days acclamation period, total organic

carbon (TOC) removal from 5-hour biodegradation test is 82-90% at the fifth and the sixth

day. Thus it can be concluded that biological process is feasible to treat the surfactants-rich

effluent from oil/water separation.

3.

General design consideration

General design consideration on biological treatment design for oily

wastewater, summarized from many literatures, include.

• For industrial wastewater, since oily wastewater is usually only one portion

of the whole wastewater, it is recommended, if possible, to treat the oily

wastewater separately by physical or physico-chemical process. After that

the effluent from those process may be sent to mix with relatively

biodegradable wastewater, e.g. canteen wastewater, before sending to

biological treatment. This will prevent adverse effect on the biological

process by the presence of oil. It also helps saving the energy required foraeration system to cover high oxygen demand of oil. Furthermore, these

domestic wastes can provide nutrient (e.g. nitrogen and phosphorus)

required for biological treatment, which are usually not present in oily

wastewater from industrial processes . General ratio of BOD to nutrients

is BOD: N: P = 100: 5: 1. If nutrient quantities in the wastewater are not

sufficient, they must be added in the form of chemicals, e.g. urea,

anhydrous ammonia and phosphate.

• Since hydrocarbons or oils have very high oxygen demand. Their presence

must be taken into account for aeration or oxygenation system in aerobic

process, otherwise it may cause some shortage in oxygen level in the

reactor, resulting in low performance or, even, plant failure.

11.3 Adsorption

Adsorption process is referred to the process that uses special material that is capable

to adsorb molecules or colloids into its surface. This special material is called “ adsorbent”.

The molecules or colloids adsorbed are called “ adsorbate”. For its ability to remove dissolved

matters and molecules that somehow remain in the effluent of main treatment processes, the

adsorption process is usually used as a tertiary treatment or polishing process, which is the

last process before the effluent being discharged. It also used in recycled water treatment

system.

Adsorption phenomenon is caused by non-equilibrium of surface force field of the

adsorbent. Thus it tends to adsorb the molecules or colloids into itself in order to gain self-

equilibrium. Attractive forces between adsorbent and adsorbate are Van Der Waal force and

chemical bonds.

Major characteristic of adsorbent is its high surface area, which is the result from its

highly porous structure. This characteristic is indicated by a parameter called “ specific

surface area”, normally on m2/g. Adsorbates are actually adsorbed to the surface of the

material, both external surface and pore surfaces. When the adsorbent is saturated by

adsorbates, it loses its adsorptive capacity. Some adsorbents can be regenerated , normally by

heat, to recover its adsorptive capacity by removing of the adsorbates from its pores and

surfaces.

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W a t e

r f i l m

P o r e d i f f u

s i o n

Adsorption to

surface

F i l m

d i f f u

s i o n

Fig. 11.3-1 Schematic diagram of adsorption

Adsorbents can be divided into 3 major types, i.e.,

• Natural adsorbents, such as natural clays, bone char, activated silica. Important

limitation of these adsorbents is that they can adsorb only some kinds of

molecules.

• Synthetic adsorbents, such as ion exchange resins. Thy have moderate specific

surface area (300-500 m2/g). Its main advantage is that it can be regenerated

relatively easily and less expensive, such as regeneration by NaCl.

• Activated carbon (AC). AC can be classified as synthetic adsorbents. But, from

its very high specific surface area (600-1100 m2/g), it is widely used. So it is

classified as its own class. Adsorption process, described in this chapter andmany literatures, is usually referred to activated carbon adsorption process.

11.3.1 Activated carbon (AC)

Activated carbon can be made of various materials, such as coconut shells, coals,

bones, etc. These materials will be subjected to dehydration process (at low heat) then

carbonization (heat at 400-600 oC), following by activation (heat at 750-950 oC) to eliminate

tar in its pore. AC can be divided into 2 type, i.e., powder activated carbon (PAC) and

granular activated carbon (GAC). AC is the most popular adsorbent for its adsorption

efficiency and very specific surface area. Examples of PAC and GAC properties are as shown

in table 11.3.1-1. From the table, Iodine number is the parameter that indicates performance of

AC on adsorption of small molecules. The higher the number, the better the performance.

Table 11.3.1-1 Examples of PAC and GAC properties

Property GAC PAC

Specific surface area (m2/g) 600-1100 600-1100

Particle size 0.55-1.0 mm 100 – 325 mesh (< 0.15 mm)

Apparent density 430-600 kg/m3 520-650 kg/m3

Specific gravity 1.30-1.55 1.4-1.5Iodine number 850-1050 700-900

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AC is capable to adsorb many kinds of substances, including heavy metals, phenol,

surfactants and hydrocarbons. Thus it is widely used as adsorbent material for polishing

process of industrial effluents. Absorption capacities of some hydrocarbons are listed in table

11.3.1-2. However, AC cannot absorb very small molecules (atoms of C < 3), such as small

molecular of organic acid and some alcohol. Anyway, they are readily biodegradable

substances, which can be easily eliminated by biological process.

For oily wastewater treatment polishing process, AC is usually used in the form of

GAC filter. Its hydraulic working principle is similar to that of sand filter or granular bed

coalescer, described in chapter 5. Thus, in this chapter, only this application will be described.

11.3.2 Basic knowledge

11.3.2.1 Isotherm diagram

The adsorptive capacity (q) at a specific temperature is normally presented in the

form of graph, called isotherm diagram (fig. 11.3.2-1). The graph is normally obtained byexperiment. In the experiment, the water to be treated (initial concentration = Co) and the

adsorbents are put in contact in a constant stirred reactor for a sufficient time to approach

equilibrium. Concentration will decrease from Co to equilibrium concentration (Ce).

1. Freundlich model, as shown in eq. 11.3.1

)/1( n

eC k q ⋅= {11.3.1}

Where q = Adsorptive capacity (amount of adsorbates adsorbed per

unit weight of adsorbent) (M/M)

k,n = Empirical constants

Ce = Equilibrium concentration (ML-3)

2. Langmuir model, as shown in eq. 11.3.2

e

e

bC

C abq

+

⋅=

1 {11.3.2}

Where a, b = Empirical constants

It is recommended to fit the empirical isotherm with the both models and usethe one that give more accurate correlation.

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Table 11.3.1-2 Adsorptive capacity of AC for some hydrocarbons [65]

0

50

100

150

200

250

300

0 1000 2000 3000 4000 5000 6000

Equillibrium concentration (Ce), mg/l

A d s o r p t i v e c a p a c

i t y ( q ) , m g / g

Fig. 11.3.2-1 Examples of adsorption isotherm diagrams

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11.3.2.2 Process analysis for GAC filter

In GAC filter (or contactor), as wastewater passes through the bed at a design rate,

the pollutant will be adsorbed and its concentration will be reduced as shown in fig. 11.3.2-2.

The height of the bed in which adsorption occurs is called the mass transfer zone (MTZ).

After of MTZ, the pollutant is practically eliminated, so there is no adsorption in the lower bed under MTZ. Upper portion of bed is exposed to the pollutant first so this portion is the

first to be saturated. After it is saturated, it no longer has adsorptive capacity. The adsorption

will occur at the lower portion of bed instead. Thus it seems that the MTZ moves along the

depth of the bed as shown in fig. 11.3.2-1. When it move to the bottommost of the bed, it

signifies that the bed is expired. Pollutant concentration no longer meets the required value.

Thus the bed should be replaced.

Ha

CCo

Ce

H

t1

CCo

Ce

H

< t2

S a t u r e d

z o n e

Ha M

T Z

CCo

Ce

H

< t3

Ha

CCo

C = Ce

H

< t4

Bed needs to

be replaced.

Outlet C does not

meet requirement.

GAC bed.HT

Feed

Outlet

Fig. 11.3.2-2 Evolution of pollutant concentration along the bed depth

MTZ is obtained from experiment. The wastewater will be fed to a GAC bed at a

constant rate. Effluent concentration and feed quantity of wastewater is collected and plotted

as shown in fig. 11.3.2-3. Then, the bed height of MTZ (or adsorption height (H a )) can be

calculated by eq. 11.3.3, which is derived based upon the symmetry between C/V curve and

C/H curve.

Vc

C

Co

Ce

H

C

Co

Ce

Ha VaV b Ve

Qa Qa

Fig. 11.3.2-3 C/V curve and C/H curve

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)( ce

ac

aV V

V H H

−= {11.3.3}

Where Hc = Bed height corresponding to the concentration “C” (L)

Vc = Accumulated feed volume corresponding to the concentration “C”(L3)

Ve = Accumulated feed volume at equilibrium (L3)

Va = Accumulated feed volume required to saturate the MTZ (L3)

From fig.11.3.2-2, when the MTZ moves to the bottommost of the bed, it does not

mean that the whole bed is saturated . Only the portion above the MTZ is saturated. The bed

is the MTZ is partially saturated otherwise the effluent concentration will not meet the design

value. This means the bed in the MTZ cannot be fully utilized up to it capacity. If the MTZ is

large, this means partially utilized zone is large too. The available capacity left form

utilization in the MTZ, represented by a toned area in fig. 11.3.2-3, can be calculated eq.

11.3.4.

∫ −=Ve

Vb

ca dV C C Q )( 0 {11.3.4a}

∫ −=Ve

Vb

c

a

a dV C C m

q )(1

0 {11.3.4b}

Where Qa = Total available (or left) capacity of absorbent in MTZ (M)

Co = Initial concentration (ML-3)

q a = Available adsorption of MTZ (M/M)ma = Mass of absorbent in MTZ (M)

C/V curve and C/H curve vary with empty bed velocity (or flowrate per unit area of

bed), as shown in fig. 11.3.2-4. It means that the value of Ha and Qa also vary with empty bed

velocity (v). If wastewater flowrate and empty bed velocity (v) are specified and the C/H or

C/V at that “v” and isotherm diagram are known from experiments, total bed height (HT)at

any given total operating period (tT) before the adsorbent needs to be replaced can be

calculated from basic mass balance equation, as shown in eq. 11.3.5.

abT eoo Qq AH C C V −=− ρ )(

{11.3.5a}

T T ot Avt QV ⋅⋅=⋅= {11.3.5b}

Where V0 = Total accumulated feed volume before the bed needs to be replaced

(L3)

tT = Total operating time before bed replacement ( or regeneration)

(ML-3)

A = Cross section area of GAC bed (L2)

HT = Total Bed depth (L)

ρ b = Bulk (or apparent) density of bed (ML-3)

v = Empty bed velocity (LT-1)

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The value of q is obtained from isotherm diagram while the value of Qa is calculated

by eq. 11.3.4 from C/V relation obtained from experiments. Empty bed velocity can be

chosen arbitrarily but it will affect the value of Qa as described on the previous paragraph.

Recommended value of v is around 2.5 m/h per every 0.30 m of bed height (e.g. v = 7.5 m/h

for bed height of 0.90 m.). Total operating time (tT) can be chosen to match main

manufacturing process plant shutdown, in case of industrial wastewater, such as 1 year, etc.Recommended retention time is not less than 5 min.

Since the bed is not totally saturated, effective saturation of bed (E) can be

calculated by eq. 11.3.6a and b. The value of E is normally between 0.5 – 0.95 (average 0.75).

))1(1(100(%) H

H e E a−−⋅=

{11.3.6a}

ao

a

V C

Qe −=1 {11.3.6b}

From the concept of E, eq. 11.3.5a can be rewritten in the form of E, as shown in eq.

11.3.6c

q EAH C C bT eoo ρ =− )( {11.3.6c}


Important parameters that affect the performance in adsorption process include,

1. Types of adsorbate: Adsorptive capacities of AC for each molecule are

different. If possible, isotherm test on the pollutants to be removed should be performed.

2.

Specification of carbon: Adsorptive capacity depends mainly on surface area of

AC. The higher the surface, the better the capacity.

3.

Temperature: Since the process is exothermal, adsorptive capacity will

decrease with increase of temperature.

4. pH: pH affects ionization of molecules. Thus it may affect the ionization of the

molecule to be adsorbed.

5.

Turbulence: Adsorption also depends on mass transfer of adsorbates to the

surface. So turbulence of reactor affects the performance. In GAC filter, film

diffusion is usually rate determining step. Design parameters such as empty

bed velocity can be optimized in lab-scale test to obtain good performance.

Generally, recommended design criteria is proven to provide good result.

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11.3.3.1 GAC filter sizing

To calculate the size of GAC filter, the following procedure is recommended,

1.

Find the reference about isotherm and relation between Qa and V at various

values of v. ZHU recommended these relation for some common co-

surfactants, usually found in effluent of cutting oil emulsion after physical or

physico-chemical processes, as shown in table 11.3.3-1.

2.

Select design empty bed velocity (v) and total operating time (tT)

3. From required wastewater flowrate (Q), calculate cross section area of GAC

filter (A) from

vQ A /= {11.3.7}

4.

Calculate q and Qa at the selected value of v, if the relation q VS. v and Q a VS.v are known from item 1.

Table 11.3.3-1 Adsorption isotherm and MTZ data of some co-surfactants [21]

Co-surfactants Relation

Benzylic alcohol

Adsorption isotherm [Lungmuir model], in mg/g (Ce in mg/l)

e

e

C

C q

31077.81

19.2−×+

=

Height of mass transfer zone, in cm (v in m/h) va H 112.01026.6 ×=

Available capacity of the bed in MTZ (by volume) AQ v

a ××= 078.01083.3

Butyldiglycol

Adsorption isotherm [Lungmuir model], in mg/g (Ce in mg/l)

e

e

C

C q

31016.41

39.1−×+

=

Note: q in mg/g, Ha in cm, Qa in cm3, A in cm

2, C in mg/l

5. Calculate Vo and HT from eq. 11.3.5.

6.

When relation between Qa and v or Ha and v are not available. It can be

assumed that Qa = 0, replace q in eq. 11.3.5 with q/ S.F , then use procedure in

step 2 to step 5 to calculate HT. The value of safety factor is between 1.3 to 2.

However, it is recommended to perform lab-scale to obtain the data about Qa

and Ha.

7. In case that the isotherm data is not available, it is strongly recommended to

perform lab-scale test. The data of other substances of the same kind can be

used to estimate the size of the filter, but for preliminary evaluation only.

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11.3.3.2 Headloss

Headloss of the filter can be calculated in the same manner as that of sand filter or

granular coalescer. The size of GAC is around 0.5-1.0 mm, about identical to that of coalescer

bed. Thus headloss of GAC bed should be calculated using the equation (Koseny-Carman)

and other data of the coalescer bed, e.g. porosity data, described in chapter 5.

11.3.3.3 Filter construction and accessories

GAC filter construction and accessories are relatively identical to those of sand

filter. So feed pumps, piping, underdrain and backwash system can be designed in the same

way as for sand filter. However specific gravity of GAC is around that of anthracite (1.3 –

1.5), which is lower than sand’s. Thus recommended backwash rate is around 20 – 50 m/h.

Bed expansion is about 50%. It should be noted that wet GAC is corrosive. Rubber liner or

equivalent anti-corrosion material must be used.

a) Granular activated carbon b) Powder activated carbon

c) AC plant (Source: Carbonel) d) Example of GAC filter (Source: NFS)

Fig.11.3.3-1 Examples of AC and GAC filter

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Chapter 12 Guideline for treatment process selection and examples

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Chapter 12 Guideline for treatment process selection and examples of

treatment processes for certain oily wastewaters

12.1 Guideline for treatment process selection

From detail of each process, described before in the previous chapters, it is clearlyshown that each process has its own limitation and can be effectively used on some range of

oily wastewater. In this case, the treatment system will consist of several processes connecting

together as a process train. On the other hand, for some ranges of oily wastewater, there is

more than one process that can be applied to treat them. To design practical wastewater

treatment system, designers should understand the nature and limitation of each process, both

from technical and economic points of view.

It must be noted that treatment process selection and design is a state-of-art. It is

very difficult to decide that which one is the most suitable one. Normally, engineers base their

design on their experience. In some situation, it is still difficult to choose the best process train

because there are more than one applicable process. In this case, to select the most suitable process, advantages, disadvantages and economic constraints and theoretical comparison of

removal efficiency between each feasible process shall be taken into account. Concept of least

cost method can be used, as described previously in chapter 2.

In previous chapters, many researches, covering almost all of the possible range of

oily wastewater and their treatment processes, have been reviewed. These researches can be

summarized to formulate a guideline for process selection and to develop a computer program

for design and simulation of oily wastewater treatment process.

The guideline, categorized by the types of oily wastewater, can be summarized as

shown in table 12.1-1 and section 12.1.1 to 12.1.4.

12.1.1 Oil film

The oil film is the simplest form of oily wastewater. Technically, the oil in this case

is already separated from the water and presents in the form of 2 separate layers of oil and

water, rather than homogeneous mixture of oil and water. This type of oily wastewater might

be raw wastewater from the source or the result from other treatment processes, such as

decanted oil from decanter or destabilized oil retentate from UF process.

Oil layer can be removed or skimmed from water surface in several ways. The

simplest form of skimmer is overflow device, such as weir, bell mouth pipe. GPI lab hasdeveloped oil disk skimmer and oil drum skimmer based on surface chemistry concept, as

described in chapter 3. These types of skimmers have good selectivity for they recover

relatively water-free oil.

To select the skimmer, one should consider:

• Usage of skimmed oil: If the water-free skimmed oil is required, the skimmers

with good oil-water selectivity, such as drum skimmer or disk skimmer, may be

required to assure efficient separation.

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T a b l e 1 2 . 1 - 1 G u i d e l i n e f o r o i l y w a s t e w a

t e r p r o c e s s s e l e c t i o n ( b a s e d o n

G P I ’ s r e s e a r c h e s )

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• Geometry or size of the decanter or oil retaining vessel : If the size of the tank

is not so large. Simple hydraulic device, such as bell mouth, can work

effectively. To enhance its oil-water selectivity, the thickness of oil layer can be

increased to avoid carry-over of water with the skimmed oil. In case of small

tank, this can be done because the open surface of tank is small. So loss of

volatile oil in this case is quite acceptable. However, it may not be practical forlarge tanks.

• Economic point of view: investment and operating cost of skimmer and

recovered benefit from usage of skimmed oil and other related cost and benefit

(if any) should be taken into account.

12.1.2 Primary emulsion

For primary emulsion, the oil droplets in the wastewater are relatively big and can be

separated by natural or non-accelerated process, i.e. decanter However, besides the oil droplet

size, presence of suspended solids in the wastewater is an important factor that has to be taken

into account. Guideline for treatment process selection in this case, categorized by presence of

suspended solids, will be as described below.

• Primary emulsion without presence of suspended solids: Examples of this

case are condensate and process waters from industries. In this case, both simple

decanter and lamella decanter are applicable. Without presence of suspended

solids, there is no risk of clogging. So, compact decanter or closely inserted

lamella decanter, such as Spiraloil, can be used.

• Primary emulsion containing coarse suspended solids: Example of this case is

wastewater from general washing, etc. In order to consider if the suspended

solids are classified as coarse suspended solids, the rising velocity of droplet andthe settling velocity of the solids will be compared. If the settling velocity of

solids is greater than the rising velocity, the suspended solids, then, tend to settle

within the oil separator. In this case, the suspended solids are considered as

“coarse” suspended solids. For API tank, design cut size of oil droplet is around

150 microns, then the suspended solids that can be classified as “coarse” will be

around 50 microns in diameter. For this type of wastewater, API tank, inclining

tube settler or lamella decanter with large spacing between plate are

recommended for they can serve 2 purposes, i.e., solids and oil separation.

Closely inserted decanter is not recommended for risk of clogging. Dissolved Air

Flotation is also a good choice in this case.

• Primary emulsion containing fine suspended solids: Example of this case is

stormwater. If these solids are fine, it will not settle in the oil separator. In this

case, theoretically, it can be treated in the same way as condensate’s. However,

the solid separation process should be provided . DAF is recommended in this

case because it can separate both oil and solids alike.

Among these 3 categories, the second or combination between the second and the

third categories are more common. Other accelerated processes, such as hydrocyclone, are

also applicable. But it requires further treatment process, such as coalescer, to treat the

separated oil. Thus it may not be economical choice when simple process can do the job as

well. In effect, when the land is not the restricting condition, the process with relatively lowloading rate, such as decanter or DAF, may be useful. Because they can serve as both solid

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and oil separation, as stated above. Their voluminous size can be used to dampen any

transient conditions occurring. And they can always be upgraded or changed to other

processes that require smaller footprint in the future. Membrane process and thermal process

are applicable but not recommended for economic reason. After oil separation, the wastewater

may need finishing processes (e.g. biological treatment and carbon adsorption), depending on

amount of residual pollutants.

12.1.3 Secondary emulsion

For secondary emulsion, the oil droplet sizes in the wastewater are between 5 to 100

microns. However, since lower limitations of some treatment processes are around 20

microns, it is reasonable to divide the emulsion into 2 groups, i.e. (1) droplet size between 20-

100 microns and (2) droplet size from 5-20 microns. In both groups, the treatment processes

are still affected by presence of suspended solids. Guideline for treatment process selection,

categorized by presence of suspended solids, will be as described below.

12.1.3.1

Droplet size between 20-100 microns

• Emulsion without presence of suspended solids: Examples of this case are

condensate and oil-contaminated process waters from industries. In this case,

decanter alone is unable or uneconomical to completely treat this emulsion.

However, lamella decanter and spiraloil may be used as preliminary treatment

(but not necessary) since it can handle the upper range of oil droplets in the

emulsion. Lamella decanter is the better choice between the two because it is

more voluminous so it can handle some strayed solids, if any, or equalize some

shock load better than spiraloil. Every type of coalescers and hydrocyclones can

treat this group of emulsion effectively. However, for hydrocyclone, it always

requires further process to treat the separated oil. Combination of hydrocyclone/ coaleser is recommended. Hydrocyclone can reduce the amount of wastewater

to be treated. Then the concentrated wastewater is sent to a small coalescer since

it handles only small portion of wastewater.

• Emulsion containing coarse suspended solids: Example of this case is

wastewater from general washing, etc. In this case, Upflow granular bed

coalescer is not recommended since it can be clogged and its cleaning is very

difficult. Downflow granular bed coalescer, fibrous bed coalescer (only brush

type) and hydrocyclones are applicable. Solids can be separated by API tank or

lamella separator, which can be used as preliminary treatment process otherwise

specific solid separation process must be provided. DAF is recommended for its

solid and oil separation capability.

• Emulsion containing fine suspended solids: Example of this case is

stormwater. In this case, theoretically, it can be treated in the same way as

condensate’s. However, the solid separation process should be provided . DAF

is recommended in this case because it can separate both oil and solids alike.

12.1.3.2 Droplet size between 5 - 20 microns

In this range of droplet size, these two processes are not applicable. Fibrous bed

coalescer or hydrocyclone alone still cannot treat this emulsion. Recommended process is

DAF or combination of coalscer/ hydrocyclone/ coalescer. For the latter case, the firstcoalscer will partially coalesce the oil droplets to bigger sizes (around 10-20 microns), which

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are sufficient to separate by the hydrocyclone. Concentrated wastewater from the

hydrocyclone will be treated by the downstream coalescer. In case that SS is present, solids

separation process must be provided

Membrane process and thermal process are applicable but not recommended for

economic reason. After oil separation, the wastewater may need finishing processes (e.g. biological treatment and carbon adsorption), depending on amount of residual pollutants. It is

possible that surfactants may be present in this type of wastewater.

Effect of surfactants on the performance of each process is provided in the previous

chapters. When the efficiency equation includes the interfacial tension, efficiency of process

with presence of surfactants can be readily calculated. If not, its effect can be compensate by

applying some safety factors.

12.1.4 Macroemulsion and microemulsion

For macro- and microemulsion, the oil droplet sizes in the wastewater are between0.1 to 5 microns and 10 – 60 nm, respectively. At these ranges of dropets, Brownian motion is

predominant. Furthermore the droplets are stabilized by surfactants so they cannot coalesce.

STOKE’s law-based process without destabilization of emulsion are completely not

applicable. Recommended treatment processes are divided into 3 groups, i.e.,

• Chemical destabilization process and decanter or DAF: Major step of this

process train is destabilization of the emulsion. Detail of this process is described

in chapter 10. After destabilization, the droplets can coalesce or flocculate, then

be separated by decanter of DAF. The use of coalescer and hydrocyclone may

not provide further advantage since the interfacial after destabilization is still low

which is unfavorable for these two processes. Precaution for this process train isthe residual pollutants, depending on characteristic of wastewater and

destabilization chemicals. Finishing process is normally required.

• Membrane process: Membrane processes, esp. UF, are capable of treating these

emulsions. However, residual pollutant, esp. co-surfactants, concentration are

always high. Permeate from UF of emulsion treatment can be sent to RO to

remove these soluble pollutants. Anyway, RO effluent still contains relatively

high residual pollutants and needs further polishing treatment, such as biological

treatment or carbon adsorption.

• Thermal process: the emulsion can also be treated by classic distillation.

However energy cost will be high. Again, dissolved residual pollutant can befound in the distillate. So it needs polishing process.

12.1.5 Concentrated oily wastewater or refinery slops

Concentrated oily wastewater in this case refers mainly to retentate from membrane

process of stabilized emulsion treatment, such as cutting oil treatment. Refinery slops refers to

residue from refinery process in the form of viscous, concentrated oily wastewater, Slops

usually compose of 40-80% of water, 20-50% of hydrocarbon and 1-10% of suspended solids.

Because of their high concentration and viscous characteristic, they cannot be treated

effectively by normal physical processes. To treat these wastes, GPI lab recommends the use

of heteroazeotropic distillation (chapter 9). The process provide the opportunity to recycle theoil, esp. in case of slops, since the separated oil is relatively water-free and ready to be sent

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III-302

back to refinery process. In case of retentate, the separated oil, also water-free, can be

disposed of as used oil or reused in fuel for incinerator.

12.2 Examples of treatment processes for certain oily wastewaters

Apart from detailed studies on each process, GPI lab also conducted feasibilitystudies on treatment process trains of certain oily wastewaters, i.e. non-stabilized emulsion

and cutting oil emulsion. Recommended processes trains for the two wastewaters, based on

GPI’s researches, are summarized as follows,

12.2.1 Treatment of cutting oil emulsion

Cutting oil emulsion is one of the most difficult-to-treat wastewater. From it

components, it contains relatively high concentration of oil and surfactants. Concentrate of

macroemulsion contains around 80 % of oil and 15 % of surfactants/co-surfactants. For

microemulsion, it contains 20-30 % of oil, 40-50 % of surfactants/co-surfactants and 5-10%

of water. Generally, the concentrates are mixed with water at 2-6 % by volume of to preparecutting oil emulsion. Oil and surfactants/co-surfactants contribute to very high concentration

of oxygen demand. Oil droplets are very small and very stable. Thus they cannot be treated by

STOKE’s law-based processes alone.

WANICHKUL [11] had compared the performance of many possible process trains,

e.g. combination of various membrane processes, thermal processes and biological processes.

The result showed that the feasible treatment process train, as shown in fig. 12.2.1-1, should

consist of the following processes, i.e.,

1. Ultrafiltration: UF is used to treat wasted cutting oil emulsions from sources.

It is recommended to perform lab-scale or pilot-scale test to find the optimumtype of membrane and operating condition before design the real system.

Operation at mid- or lower side of recommended pressure range might result in

less clogging and high average long-term flux. In case of macroemulsion,

partially destabilization by addition of salt, as shown in section 8.2.3.2, may

enhance permeate flux. But a skimmer should be provided to remove

destabilized oil otherwise it will clog the membrane, resulting in lower flux.

Outlet oil concentration of 0-10 mg/l can be expected.

2. Reverse osmosis: RO is used to remove major part of residual pollutants,

mainly dissolved co-surfactants, from UF permeate. At optimum operating

condition, which depends on types of emulsion and membrane, TOD removal

efficiency around 80-90% can be expected. However, since the inlet TOD is

very high, esp. in the case of microemulsion, RO permeate may still contain

high residual pollutants and need polishing treatment. Retentate from RO can

sent to treat together with the UF retentate.

3. Heteroazeotropic distillation: It is used to treat the retentate from UF and

RO. With proper entrainer, residue from the distilltion will contain relatively

water-free oil, which is the base oil in cutting oil concentrate. The residue can

be disposed as oil, not waste, or can be recycled or used in an incinerator. The

distillate is 2 separate layers of entrainer, which can be recyled for the next

distillation cycle, and oil which somehow still contain some dissolved

pollutants. It is recommended to send this distillate to mix with the UF permeate for treatment by RO.

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III-303

Heteroazeotropic distillation

M

X

Return sludge

Effluent

Wasted

sludge

Clarifier Aeration tank Distillate

TI

Heater

Permeate

Retentate

Membrane

Feed

pump

Storage

tank Feed

Po

Pi

Pp

Heat

exchanger R O P e r m e a t e

Retentate

Membrane

Feed

pump

Feed

Po

Pi

Pp

Heat

exchanger

Effluent

dischared

(If possible)

Inlet

wastewater

Entrainer

Heat

exchanger


Ultrafiltration Reverse osmosis W a s t e d r e t e n t a t e

W a s t e d r e t e n t a t e

Fig. 12.2.1-1 Schematic diagram of cutting oil emulsion treatment system

4. Biological treatment: Distillate and RO permeate are treated by biological

treatment before discharge to receiving water. WANICHKUL showed that the biological treatment can use dissolved pollutants in RO as main substrate with

TOC removal efficiency more than 90%. So higher efficiency can be expected

if the permeate is mixed with the wastewater of more biodegradability, such as

domestic wastewater from office or canteen.

12.2.2 Treatment of non-stabilized secondary emulsion

This emulsion can be treated with very high efficiency by various methods. So the

efforts to enhance the performance are based mainly on minimization of process footprint.

Conventional oily wastewater treatment system is usually based on DAF, as shown in fig.

12.2.2-1, which is also effective when surfactant is present.

However, in case of non-stabilized wastewater, GPI lab proposes the compact

treatment process train for this emulsion (fig. 12.2.2-2), consisting of the following processes.

1. Upstream in-line fibrous bed coalescer: The coalescer can partially coalesce

oil droplets of diameter into bigger oil droplets. The fibrous bed is used since it

is hardly clogged by suspended solids. Empty bed velocity of the coalsecer is

reported to be as high as 130 m/h or more [11].

2. Hydrocyclone: The hydrocyclone will concentrate the partially coalesced oily

wastewater from the upstream coalescer. Since the oil droplets are partially

coalesced, thus bigger. The efficiency of cyclone is improved. The water can

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III-304

be discharged or sent to further treatment if some SS or other pollutants are

still present. Concentrated oil will be sent to downstream coalescer.

3. Downstream fibrous bed coalescer: The coalescer receives the concentrated

or purged oily wastewater from the cyclone. Since the quantity of wastewater

is much reduced, the coalescer can be designed and operated at low loading

rate to ensure high efficiency without consuming unacceptable footprint. The

oil will be separated from the water and then reused or disposed of as oil. The

water can be discharged or sent to further treatment if SS or other pollutants

are still present.

Inlet

wastewater

M

X

Return sludge

Effluent

Clarifier Aeration tank

API tank

Biological treatmentDAF

To sludge

treatment

To sludge

treatment

To

sludge

treatment

Saturator

Primary sedimentation tank

OilOil

Oil

Skimmer

Skimmer

Wasted

sludge

GAC filter

(if required)

M M

Chemicals

Chemical

treament

Fig. 12.2.2-1 Schematic diagram of conventional oily wastewater treatment system

Inlet

wastewater

M

X

Return sludge

Effluent

Clarifier Aeration tank

Biological treatmentPrimary

sedimentation

tank or API tank

Oil

Wasted

sludge

GAC filter

(if required)Oil

Fibrous coalescer/

Hydrocyclone/

Fibrous coalescer

Fig. 12.2.2-2 Schematic diagram of compact oily wastewater treatment system for Non-stabilized secondary emulsion

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IV-i

Contents

Page



1.1 Introduction IV-2

1.2

Conceptual design of the program IV-2

1.2.1 E-book mode IV-3

1.2.2 Recommendation mode IV-5

1.2.3 Design mode IV-6

1.2.4 Analysis mode IV-7

1.3 Development tools IV-11

1.3.1 Main development software package IV-11

1.3.2

Special graphic user interface (GUI) component IV-12

1.3.3

The third party software IV-121.4 Program architecture IV-13

1.4.1 Forms IV-13

1.4.2 Modules IV-16

1.4.3 Modules IV-16

1.4.4

Class modules IV-16

1.4.5 Add-in project IV-16

1.5

Program development IV-17


2.1 Overview of the program IV-15

2.1.1

Main program IV-182.1.2 Project window IV-20

2.1.3 E-books worksheet IV-20

2.1.4 Recommend worksheet IV-21

2.1.5

Design worksheet IV-23

2.1.6 Analysis mode IV-24

2.1.7 Warning dialog box IV-26

2.2 Program capability IV-26

2.3 Program limitation IV-26

2.4 System requirement IV-28

2.5

User instruction IV-28

2.5.1

Program Installation IV-28

2.5.2

Starting the program IV-29

2.5.3 Using E-book mode IV-29

2.5.4 Using Recommend mode IV-29

2.5.5 Using Design mode IV-31

2.5.6 Using Analysis mode IV-33

2.5.7 Printing and file operation IV-36

2.6

Upgrading procedure and recommendation for further IV-37

development

2.6.1 Upgrading procedure IV-37

2.6.2

Recommendation for further development IV-39

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IV-ii

Contents

Page


1)

Drum skimmer IV-422) Disk skimmer IV44

3) Simple decanter IV-46

4) Compact decanter IV-49

5) Customized decanter IV-52

6) Granular bed coalescer IV-55

7) Brush type bed coalescer IV-59

8) Dynamic fibrous bed coalescer IV-63

9) Metal wool bed coalescer IV-67

10) Dissolved air flotation IV-71

11) Two-phase hydrocyclone IV-77

12) Three-phase hydrocyclone IV-81

13) Ultrafiltration IV-85

14) Reverse osmosis IV-89

15) Heteroazeotropic distillation IV-92

16) Stripping IV-94

17) Chemical destabilization, coagulation-flocculation IV-96

18) Biological treatment IV-99

19) GAC filter IV-101

20) Customized concentrator IV-105

21) Customized oil separator IV-107

22) Customized inline concentrator IV-10923) Inlet IV-111

24) Outlet IV-112

25) Flow merge IV-113

26) Flow split IV-115

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IV-iii

Table

Page

Table 2.2-1 The processes included in the GPI program IV-27

Table 1-1 Related parameters of drum skimmer IV-42Table 1-2 Influent parameters for drum skimmer IV-43

Table 2-1 Related parameters of disk skimmer IV-44

Table 2-2 Influent parameters for disk skimmer IV-44

Table 3-1 Related parameters of simple decanter IV-47

Table 3-2 Influent parameters for simple decanter IV-48

Table 4-1 Related parameters of compact decanter IV-50

Table 4-2 Influent parameters for compact decanter IV-51

Table 5-1 Related parameters of customized decanter IV-53

Table 5-2 Influent parameters for customized decanter IV-54Table 6-1 Related parameters of granular bed coalescer IV-56

Table 6-2 Influent parameters of granular bed coalescer IV-58

Table 7-1 Related parameters of brush type bed coalescer IV-60

Table 7-2 Influent parameters of brush type bed coalescer IV-62

Table 8-1 Related parameters of dynamic fibrous bed coalescer IV-64

Table 8-2 Influent parameters of dynamic fibrous bed coalescer IV-66

Table 9-1 Related parameters of metal wool bed coalescer IV-68

Table 9-2 Influent parameters of metal wool bed coalescer IV-70

Table 10-1 Related parameters of metal wool bed coalescer IV-74Table 10-2 Influent parameters of DAF IV-76

Table 11-1 Related parameters of two-phase hydrocyclone IV-79

Table 11-2 Influent parameters of two-phase hydrocyclone IV-80

Table 12-1 Related parameters of three-phase hydrocyclone IV-83

Table 12-2 Influent parameters of three-phase hydrocyclone IV-84

Table 13-1 Related parameters of ultrafiltration IV-87

Table 13-2 Influent parameters of three-phase hydrocyclone IV-88

Table 14-1 Related parameters of RO IV-90

Table 15-1 Related parameters of heteroazeotropic distillation IV-93Table 16-1 Related parameters of stripping IV-95

Table 17-1 Related parameters of chemical destabilization IV-97

Table 18-1 Related parameters of biological treatment IV-100

Table 19-1 Related parameters of GAC filter IV-103

Table 20-1 Related parameters of customized concentrator IV-106

Table 21-1 Related parameters of simple decanter IV-108

Table 22-1 Related parameters of chemical destabilization IV-110

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IV-iv

Figure

Page

Fig. 1.2-1 Flow chart of the program under the scope of work of this thesis IV-4

Fig. 1.2.1-1 Detailed flowchart of e-book mode IV-5Fig. 1.2.2-1 Detailed flowchart of recommendation mode IV-6

Fig. 1.2.3-1 Detailed flowchart of design mode IV-8

Fig. 1.2.4-1 Detailed flowchart of design mode: Data input operation IV-9

Fig. 1.2.4-2 Detailed flowchart of design mode: Analysis and result display operation IV-10

Fig. 1.2.4-3 Detailed flowchart of design mode: file management operation IV-11

Fig. 1.4-1 Structure of the program IV-13

Fig. 1.4.1-1 Main form (under construction) IV-14

Fig. 1.4.1-2 Project form IV-15

Fig. 1.4.1-3 Input data form IV-15Fig. 2.1.1-1 Graphic user interface of the main program IV-20

Fig. 2.1.3-1 Graphic user interface of the E-book worksheet IV-21

Fig. 2.1.4-1 Input screen ( a tabbed worksheet in project window) IV-22

Fig. 2.1.4-2 Result screen. The program will put tick marks in the first column. IV-22

Fig. 2.1.4-3 Flowchart of recommendation logic IV-23

Fig. 2.1.5-1 User interfaces of design worksheet IV-24

Fig. 2.1.6-1 User interface of analysis worksheet IV-25

Fig. 2.1.7-1 Example of warning dialog box IV-26

Fig. 2.5.3-1 Using E-book mode IV-29Fig. 2.5.4-1 Using recommend mode: Input data screen IV-30

Fig. 2.5.4-2 Using recommend mode: Result window IV-30

Fig. 2.5.5-1 Using Design mode: Step 1 “Wastewater data input” IV-31

Fig. 2.5.5-2 Using Design mode: Step 2 “Process selection” IV-32

Fig. 2.5.5-3 Using Design mode: Step 3 “Process data input” IV-32

Fig. 2.5.5-4 Using Design mode: Step 4 “Result” IV-33

Fig. 2.5.6-1 Using Analysis mode: Draw the schematic diagram IV-34

Fig. 2.5.6-2 Using Analysis mode: Process data input IV-35

Fig. 2.5.6-3 Using Analysis mode: Viewing result in the diagram IV-36

Fig. 2.5.6-4 Using Analysis mode: Exporting the result to excel IV-36

Fig. 2.6.1-1a Configuration of the database IV-37

Fig. 2.1.6-1b Examples of existing database IV-38

Fig. 2.1.6-2 Example on database upgrading. When new category is added in the IV-38

database (left), Related field in the program will be automatically

updated (right)

Fig. 1-2a Icon of drum skimmer IV-43

Fig. 1-2b Graphical diagram of drum skimmer IV-43

Fig. 2-1a Icon of disk skimmer IV-45Fig. 2-1b Graphical diagram of disk skimmer IV-45

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IV-v

Figure (Con’t)

Page

Fig. 3-1a Icon of simple decanter IV-47

Fig. 3-1b Graphical diagram of simple decanter IV-47Fig. 4-1a Icon of compact decanter IV-51

Fig. 4-1b Graphical diagram of compact decanter IV-51

Fig. 5-1a Icon of customized decanter IV-53

Fig. 5-1b Graphical diagram of customized decanter IV-53

Fig. 6-1a Icon of granular bed coalescer IV-57

Fig. 6-1b Graphical diagram of granular bed coalescer IV-57

Fig. 7-1a Icon of brush type bed coalescer IV-60

Fig. 7-1b Graphical diagram of brush type bed coalescer IV-60

Fig. 8-1a Icon of dynamic fibrous bed coalescer IV-64Fig. 8-1b Graphical diagram of dynamic fibrous bed coalescer IV-64

Fig. 9-1a Icon of metal wool bed coalescer IV-69

Fig. 9-1b Graphical diagram of metal wool bed coalescer IV-69

Fig. 10-1a Icon of DAF IV-75

Fig. 10-1b Graphical diagram of DAF IV-75

Fig. 11-1a Icon of 2-phase hydrocyclone IV-79

Fig. 11-1b Graphical diagram of 2-phase hydrocyclone IV-79

Fig. 12-1a Icon of 3-phase hydrocyclone IV-83

Fig. 12-1b Graphical diagram of 3-phase hydrocyclone IV-83Fig. 13-1a Icon of ultrafiltration IV-88

Fig. 13-1b Graphical diagram of ultrafiltration IV-88

Fig. 14-1a Icon of RO IV-91

Fig. 14-1b Graphical diagram of RO IV-91

Fig. 15-1a Icon of heteroazeotropic distillation IV-93

Fig. 15-1b Graphical diagram of heteroazeotropic distillation IV-93

Fig. 16-1a Icon of stripping IV-95

Fig. 16-1b Graphical diagram of stripping IV-95

Fig. 17-1a Icon of chemical destabilization IV-98

Fig. 17-1b Graphical diagram of chemical destabilization IV-98

Fig. 18-1a Icon of biological treatment IV-100

Fig. 18-1b Graphical diagram of biological treatment IV-100

Fig. 19-1a Icon of GAC filter IV-103

Fig. 19-1b Graphical diagram of GAC filter IV-103

Fig. 20-1a Icon of customized concentrator IV-106

Fig. 20-1b Graphical diagram of customized concentrator IV-106

Fig. 21-1a Icon of customized separator IV-108

Fig. 21-1b Graphical diagram of customized separator IV-108

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IV-vi

Figure (Con’t)

Page

Fig. 22-1a Icon of inline concentrator IV-110

Fig. 22-1b Graphical diagram of inline concentrator IV-110Fig. 23-1a Icon of inlet IV-111

Fig. 24-1a Icon of outlet IV-112

Fig. 25-1a Icon of flow merge IV-114

Fig. 26-1a Icon of flow split IV-115

Fig. 26-1b Graphical diagram of flow split IV-115

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IV-1


In this part, we will use the data reviewed and verified in Part 1 and Part 2 as well as

the text book composed in Part 3 as main theories to develop a computer program for design,

calculation and simulation of oily wastewater treatment processes.

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IV-2


1.1 Introduction

The final objective of this thesis is to develop a computer program for design,

calculation and simulation of oily wastewater treatment process or process train, whichincludes every process reviewed in the previous three parts. The program is developed based

on 4 major aims, i.e.,

• To provide background knowledge on oily wastewater treatment and working

principle, design formula and design consideration on each oily wastewater

treatment process.

• To provide preliminary guideline on oily wastewater treatment process selection to

suit the wastewater to be treated.

•

To calculate or size the oily wastewater treatment process under the designcondition given by user, based on GPI researches under direction of Prof.

AURELLE reviewed in Part 1 to 3.

• To simulate the oily wastewater treatment process train designed by user at any

operating condition.

In this chapter, development procedure and details of the program in development

stage are described. Details and user manual of the finished program will be described in

chapter 2.

To develop the software under the scope of work of this thesis, the following procedure is used, i.e.,

1. Conceptual design of the program

The outline of software is preliminary designed to fulfil the 4 aims described

above. Conceptual design of the program will be described section 1.2.

2. Review of related data

Related data can be divided into 2 parts, i.e. data on oily wastewater treatment

and data relating to program development. The former is thoroughly reviewed in the first 3

part of this report. The latter will be described in section 1.3.

3. Program development and debugging

Detail of each step is summarized as follows.

1.2 Conceptual design of the program

To fulfil the aims described above, the program is divided into 4 major modes, i.e.,

• E-book mode: provides background knowledge and useful database about the oil


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IV-3

• Process recommendation mode: provides recommendation to narrow the range

of feasible processes for any input influent,

• Design (or calculation) mode: used for sizing the process unit,

• Analysis mode: allows users to integrate any separation processes, included in the

program database, to build their own treatment process train. And the program willsimulate the process train to forecast the efficiency of each unit.

Framework of the program is as shown in the flowchart in fig. 1.2-1. The program is

developed as a Windows-based program to make use of many standard and useful features of

Windows and to facilitate link to other common Windows-based program, such as MS Office

software package. It also operates in multi-tasking mode so users can toggle freely from one

mode to another and can work on more than one project (meaningly, can open more than 1

window) at a time.

Conceptual design and features of each mode are described in the following sections.

1.2.1 E-book mode

E-book mode is one part of the program that is designed to provide knowledge and

useful database about the oil pollution and the treatment processes. The program in this mode

is designed to provide the following features,

1. Facilitate access or selection of the information. List of e-book files and their

brief description about the context of the file is provided. After access to the file,

detailed contents of each file are also provided to assure quick access to the

required information.

2.

E-book and help files are developed in general file formats, i.e. Acrobat and MS

office software package, to take advantage of useful features of these software,

such as browsing, word searching, printing, copy/paste capability, etc. Moreover,

users are usually familiar with these file formats so they can readily handle the

files.

3. Facilitate upgrading of the program to cover more processes in the future. The

program is versatilely designed so it can be upgraded. List of e-book files is not

fixedly coded but linked to a database that can be easily added or editing. Once

that user adds new e-book file names, their short description text, and their

location (path and directory), the program will automatically include them in theinterface (screen) of e-book mode, ready to use.

The detailed flowchart of e-book mode is as shown in fig. 1.2.1-1.

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IV-4

P r o c e s s u n i t

l i b r a r y

O p e n f i

l e

m a n a g e m

e n t

w i n d o w

I n p u t

w a s t e w a t e r

c h a r a c t e r i s t i c

S e l e c t

s a v e d

f i l e

F i g . 1 . 2 - 1 F l o w c h a r t o f t h e p r o g r a m u n d e r t h e s c o p e o f w o

r k o f t h i s t h e s i s

S t a r t

S e l e c t m o d e

O p e n E - b o o k

w

i n d o w

S e l e c t

E - b

o o k

D i s p l a y

E - b o o k

( A c r

o b a t )

E - b o o k

/ H e l p

l i b r a r y

O p e n

R e c o m m e n d a t i o n

w i n d o w

I n p u t

w a s t e w a t e r

d a t a

R e c o m m e n d

a p p l i c a b l e

p r o c e s s e s

O p e n

D e s i g n

w i n d o w

S e l e c t

t r e a t m e n t

p r o c e s s

D i s p l a y

c a l c u l a t i o n

r e s u l t

I n p u t

r e q u i r e d d a t a

O

p e n A n a l y s i s

w i n d o w

C r e a t e o r e d i t

p r o c e s s t r a i n

O p e n f i l e

O p e n n e w

o r s e l e c t e d

f i l e

I n p

u t s i z e

o f e

a c h u n i t

p r o c e s s

D i s p l a y

c a l c u l a t i o n

r e s u l t

P r o g r a m c a l c u l a t e

t h e p e r f o r m a n c e

o f p r o c e s s e s

P r i n

t o u t

A c r o b a t

O p e n M S E x c e l &

a u t o m a t i c a l l y

c r e a t e w o r k b o o k

C o n t i n u e

F i n i s h

P r i n t / E x p o r t

E x i s t i n g

N e w ( d e f a u l t )

A l l m o d e

O n l y f o r s i m u l a t i o n

N

o

N

o

Y e s

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IV-5

Start

Select mode

SelectE-book

tab

Select

E-book by

double-click

Display E-book

(Acrobat)

E-book

data in

srachu.mdb

Print out by

the software

Acrobat,Close the software

and return to

E-book worksheet

Other E-book

Finish

Print/ExitPrint

Exit

No

Yes

E-book

worksheet

activated

Open the E-book file

by suitable software,

e.g. Acrobat

User can use all fuction

of the software, e.g

search, copy, print, etc.E-book

files in

C:/../EBooks

Select other tab or

quit the program

E-book

To other

modes

Fig. 1.2.1-1 Detailed flowchart of e-book mode

1.2.2

Recommendation mode

Recommendation mode is one part of the program that is designed to provide

recommendation to narrow the range of feasible processes for any input influent. The program

in this mode is designed to provide the following features,

1. Facilitate data input. Interface of this part is designed to be interactive to

prompt user to input all necessary data required for decision.

2. Provide help to guide the user through each input step. It is usually that the

users do not know some required wastewater information, such as which

categories of oily wastewater they have. Thus the interface of recommendation

mode is provided with links to these data in e-book mode.

3. Provide recommendation about the feasible processes in user friendly form as

a table with important precautions provided.

The detailed flowchart of recommendation mode is as shown in fig. 1.2.2-1.

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Start

Select mode

Select

Recommend

tab

Input required data,follow on-screen

instruction

Display resultas new window

Required

parameters

data in

srachu.mdb

Print out by

the program

Finish

Print/ExitPrint

Exit

No

Yes

Recommend

worksheet

activated

Program performs

logic calculation

E-book

files inC:/../EBooks

Select other tab or

quit the program

Recommendation

To other

modes

Click calculate

botton to start

calculation

Continue Need help on

some parameters

Click

recommend

parameter / reference

Display E-book

(acrobat, excel)Acrobat,

MS office

Open the E-book file

by suitable software,

e.g. Acrobat, excel

Print/Exit

Recommend parameter subroutine

New/Load/save file

subroutine

(fig. 1.2.4-3)

New/Load/save file

subroutine

(fig. 1.2.4-3)

Fig. 1.2.2-1 Detailed flowchart of recommendation mode

1.2.3 Design mode

Design mode is one part of the program that is designed for sizing the process unit.

The program in this mode is designed to provide the following features,

1. Calculate any required parameters of considering unit process when the rest

data are provided . For example, users can provide the program with geometry ofthe process to find the efficiency or vice versa.

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2. Provide help to guide the user through each input step in case that some data is

not known. So the interface of this mode also provides links to related data files.

3. This mode is provided with printing capability so users can print out the data

and result as a hard copy. Moreover, the data can be saved for further use.

The detailed flowchart of design mode is as shown in fig. 1.2.3-1.

1.2.4 Analysis mode

Analysis of simulation mode is one part of the program that is designed to allow users

to integrate any separation processes, included in the program database, to build their own

treatment process train. And the program will simulate the process train to forecast the

efficiency of each unit process. The program in this mode is designed to provide the following

features,

1. Allow users to freely integrate any unit processes into a process train in the

form of graphical schematic diagram.

2. The program will provide with user-friendly graphic editing interface with all

common useful features, such as drag/drop, automatic snap-to-object connectors,

basic drawing and text tools. This kind of interface is a kind of common feature

in well-known software, such as MS PowerPoint, and other simulation software

(e.g. Superpro, etc.). So it can be readily handle by users.

3. Provide help to guide the user through each input step in case that some data is

not known. So the interface of this mode also provides links to related data files.

4.

The program can calculate graded efficiency, total efficiency and other

necessary components of every process, reviewed in Part 3, e.g. pressure drops

for hydrocyclone, or saturator power requirement for DAF.

5. This mode is provided with printing capability so users can print out the data

and result as a hard copy for further use.

6. The data and result can also be exported to MS Excel to use its efficient and

useful features, such as formatting, chart building, etc., for advance display and

printing of the data and the result. It also helps saving the time for developing

these existing features.

7. The data and result can be saved for further reviewing in the future.

The detailed flowcharts of analysis mode, categorized by groups of operations, are as

shown in fig. 1.2.4-1 to 1.2.4-3. They consist of,

• Data input operation

• Analysis and result display operation

• File management operation

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Start

Select mode

SelectDesign

tab

Input wastewater

data, follow on-

screen instruction

Required

parameters

data in

srachu.mdb

Print out by

the program

Finish

Print/Exit

Print Exit

No

Yes

Design

worksheet

activated

Program perform

calculation /send result

to Step 4 /

Select other tab or

quit the program

Design

To other

modes

Click calculate

botton/ step 4 tab

Edit/

Continue

Need help on

some parameters

Select step

Recommend

paremeter

subroutine

(see fig. 1.2.2-1)

select required

process by click

at category

and process

Step 1: WW

data input screen

activated

Step 2:select

process screen

activated

Input required

data, follow on-

screen instruction

Step 3:Input

process data

screen activated

Step 4 : Result

screen

activated

Display result

parameters

for result

in

srachu.mdb

Edit

Edit

Edit

New/Load/save file

subroutine

(fig. 1.2.4-3)

Yes

Built-in

process

data in

srachu.mdb

A

A

No

Yes

NoYes

Help can be

accessed at all

time

New/Load/save file

subroutine

(fig. 1.2.4-3)

Required

parameters

data in

srachu.mdb

Fig. 1.2.3-1 Detailed flowchart of design mode

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Start

Select mode

SelectAnalysis tab

Analysis

worksheet

activated

Analysis

To other

modes

Need help on

some parameters

Recommend

paremeter

subroutine

(see fig. 1.2.2-1)

New/Load/save file

subroutine

(fig. 1.2.4-3)

A

A

Help can be

accessed at all

time

select required

process by clickat process name

Program loads the

icon of the process

to the screen

move the mouse over

the icon until the

“hand” cursor appears at

the required position

More process

No

Yes

To connectthe icons

Click mouse, hold down,

move the mouse to another

required position

To edit connectoror icon position

Edit

Click mouse to

select the item

Click at the position

on the connector to

be edited, hold down &

move to new location

Double click

at the icon

Display input

data form

of the process

Input required

data, follow on-

screen instruction

Required

parameters

data in

srachu.mdb

Select operationTo enter/ edit data

of the process

No

Click OK to

close the form

Yes

Click at

required

drawing tool

button

Click and hold down mouseat require position to place

drawing object (line, text, circle, etc.)

To adddrawing object

To other operations

Icons in

C:/../Unitp

rocess

Fig. 1.2.4-1 Detailed flowchart of analysis mode: Data input operation

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Click calculate

button

Program sends results

to result screen

No

Yes

To view result

in the program

Edit

No

Yes

To other operations

Formula in

UnitProcessLib

Program validates

the process train

Pass

Display warning

message

Program calculates

the result

Select operation

Double click at icon

on the process train

Display input

data form

of the process

Click at result tab

Display result form

of the process

Click OK to close

To print by the program

Click print button

or “Impremer”

in “Fichier” menu

Display print form

Click “Print”

Print out

Click OK to close

To export

to Excel

Click “Exporter”

in “Donnee”

Program open Excel and

export data and result

User can perform all

Excel operation, even

save the file in *.xls.

Operation does not

affect the program

Close excel or

click programwindow to return

To edit data

Double click at

the icon

To data

input

fig. 1.2.4-1

Result

parameters

from

srachu.mbd

From Input data

Fig. 1.2.4-1

Fig. 1.2.4-2 Detailed flowchart of analysis mode: Analysis and result display operation

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Start

Select operation

Select “Ouvrir”

Display file

management

form

Program perform

requested operation

To other operations

Select “Nouveau”Select “Supprimer

de ficher”

Select

“Enregistrer”Select “Fermer”

New file Select filename

Yes

Display file

management

form

Display file

management

form

Display file

management

form

Select filenamePrompt to save

Program open

new project

Program open

the file

Click “Fichier”

menu

No

Save

Select filename

No Yes

No

Fig. 1.2.4-3 Detailed flowchart of file management operation

1.3 Development tools

Related data for program development are reviewed. Tools and programming

techniques are evaluated and carefully selected to suit the objective of program development.

Evaluation criteria include,

• Capability of development tools to fulfil program features described in section 1.2,

• Developing time of each tool. Suitable tool should provide ready-to-use features

required without extra code writing,

• Availability of the tools. The possible tools are firstly considered from the

development packages that are readily available without additional procurement.

Or they should be free-ware so it can be used without license problem.

From the criteria mentioned above, the program in this thesis is developed using the

following development tools, i.e.,

1.3.1 Main development software package

The program is developed using Microsoft Visual Basic programming language,

Version 6.0 (VB 6.0). The software is used under the permission of the software licensee,

Progress Technology Consultants Co., Ltd . (Thailand) (PTC). The software features ready-to-use tools to create Windows-based application, such as builders of windows, forms and

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other user interfaces, e.g. input boxes, buttons, database link engines, etc, which fulfil every

development requirement. It has event-driven feature, such as start working by mouse click or

after enter the data, that is suitable for development of interactive graphic user interface.

1.3.2 Special graphic user interface (GUI) component

Graphic user component in analysis mode is developed on a special GUI component,

FlowChartX version 3.2, the product of MindFusion limited . The component is actually an

ActiveX component that can be used as an add-on of MS VB 6.0. It features presenting and

producing of drag/drop graphic image, connectors, basic drawing tools and useful VB 6.0

compatible methods and properties. The software used in our program is free demo edition,

which, somehow, provides sufficient features for our scope of work.

1.3.3 The third party software

Apart from its own VB program file, the program in this scope of work makes use of

the third party software for their useful features, i.e.,

1. Microsoft Excel

Microsoft Excel is one of the most famous spreadsheet software with a lot of

versatile and efficient features, e.g. calculation capability, chart builders, macro programming,

searching, editing, formatting and printing tools. Thus in our program, recommend

parameters, such as interfacial tension data, etc, are in excel file formats (*.xls) to facilitate

searching or copying the data to the program. In analysis mode, the result can be exported to

Excel to use its graph builder and formatting/printing facilities. Thus, to use the program of

this thesis, MS Excel is required otherwise some help file will not be available and some

results will not be exported . The program is compatible to MS excel 2000 or newer.

2. Adobe Acrobat reader

As described in section 1.2, e-book files are in acrobat format (*.pdf) to make

use of its efficient searching and categorizing features. Other useful features are that it can

operate in any platforms, e.g. Windows, Macintosh, etc., and it eliminates the problem about

the font so the file is always readable on every computer. Acrobat reader is free ware so

everybody can have a copy without purchasing. The e-book files are created by Adobe

Acrobat professional version 7.0, under the permission of the software licensee, Progress

Technology Consultants Co., Ltd . (Thailand) (PTC). To use the program of this thesis,

Acrobat reader is required otherwise some e-book files will not be available. It isrecommended to use Acrobat reader 6.0 or newer. The older version may be used but there

may be a problem about using index and fonts, which makes some letters unreadable.

3. Microsoft Access

MS Access is used as open data source connectivity (ODBC ). It allows the main

program to connect to MS Access database file format (*.mdb), which is used as principle

database of the program . To use the program, it requires only MS Access driver, which is

usually provided with Windows OS. The program will automatically acquire the driver from

the Windows in setup procedure of the program. However, if users want to change the

database, such as addition of more process, or e-book files, they will

need full MS Access

program. The database is compatible to MS Access 2000 or newer.

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1.4 Program architecture

In this section, program architecture will be described to provide the idea about how

the program is developed and relation between components of the program. This information

is also helpful for further program development in the future.

Major program file is a Visual Basic program group named “prjThesis”(prjThesis.vbp). To fulfil the conceptual design described in section 1.2, program architecture

of “ prjThesis”, based on VB 6.0, is divided into following components, i.e. (see fig 1.4-1).

Fig. 1.4-1 Structure of the program

1.4.1 Forms

Forms are practically the graphic interface of the program. They will consists of many

controls (such as buttons, menu, etc.), which, in turns, consists of many source codes to

handle activity or event happening to the interface, such as button clicking. The program is

divided into 3 major forms, i.e.,

1.4.1.1 Main form

Main form ( frmain.frm) is the major form of the program that includes a workspace of

the program as well as command button and the menu that control basis operation and file

management operation. It is the first form that is open when the program is run. The interface

of the form is as shown in fig. 1.4.1-1.

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Fig. 1.4.1-1 Main form (as seen in source code)

1.4.1.2 Project form

Project form ( frDesigngrid.frm) is the form that is used as a workspace for operation

of the program in every mode (recommendation, design, anlysis and e-book.) for one project.

It is divided into 4 tabbed worksheets that represent 4 modes of operation. Users can freely

toggle between sheets to work in each mode. The data keyed in one worksheet still remains

while working in other worksheets. Data in each field in this form will be saved as encrypted

data in the preset database file of the program. Each tabbed worksheet will contain controls

and corresponding source code required for operation in each mode, as shown in fig. 1.4.1-2.

The texts display in each fields are linked to a database file (srachu.mdb)

1.4.1.3 Input data form

Input data form ( frInputdata.frm) is the form that is used for data input in analysis

mode. Unlike the first two forms, it is normally not shown on the screen. The form will appear

when a new unit process is inserted to the schematic diagram in the analysis mode or by

double click at the process icon in the diagram. It is also used to display the result of each

process in the analysis mode after the calculation is finished.

However, Other miscellaneous forms are also developed to fulfil purposes other than

process calculation, such as frPrintMain.frm for “printing” task, frOpenDialog.fr m for “Open

file” task, etc.

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Fig. 1.4.1-2 Project form

Fig. 1.4.1-3 Input data form

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1.4.2 Modules

Modules are the source codes that govern the overall operation of the program, which

is not linked to events. The major module is Main module (modMain.bas). It governs basic

tasks of the program, such as starting the program, file path setting, etc.

There are also other supplementary modules, i.e. modDatefunctions.bas,

modDBManager.bas and modUtil.bas. These modules are the customized source codes that

govern basic file operations (such as open and save file, link to database) which are written by

AWS Co., Ltd. (Thailand), system service provider of PTC . These modules are used under

the permission of the company. The use of the modules allows us to save the time to develop

the codes for these fundamental tasks.

1.4.3 User controls

User controls are special or add-in components besides standard components that

come with standard VB development packages. In our case, one user control component’called “ctlGrid”, is added to use in various input and output form in our program.

1.4.4 Class modules

Class module is special module which can be developed to have its own customized

properties, e.g., in our case, “.isdroplet” (used to check if the process has its droplet data or

not), etc. It greatly facilitates program development. In our program, class modules are used to

control link of each type of data, i.e. process category name, unit process name and variables,

etc., between the database file and the corresponding fields in the forms. For examples, it will

link the file names and short descriptions of e-books file to display in grid table in the e-book

form. Lists of class modules are shown in fig.1.4-1.

1.4.5 Add-in project

To facilitate upgrading of the program and versatile operation of the program, the sub-

programs used for calculation of each unit process are separated as another Visual Basic

project, namely “UnitProcessLib” (UnitProcessLib.vbp). It consists of module and class

modules, i.e.,

1.4.5.1 Module

There is two modules in this add-in project. The first module is called

“ModUNPFunction” (modUNPFunction.bas). It is used to manage operation in the analysisworkspace, such as load the picture of selected unit process and run the tag number for each

unit process. It can handle more addition unit process without any modification, in case that

more processes are added in the future.

The second module is “ModExcelFunction”(ModExcelFunction.bas). It is used to

control excel operation, such as calculation of some processes, import & export data between

excel and our program.

1.4.5.2 Class modules

There are a lot of class modules in the add-in project. Each class module devotes toeach unit process (see fig. 1.4-1). Thus, if more processes are to be added, all that have to do

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about coding is add the corresponding modules for those processes and add their variables

and corresponding help or e-book file data in the database file “srachu.mdb”. The rest of

the program needs no modification.

To develop new class modules for new processes, one of the old class modules can be

used as a prototype. Developers just change the equation and solving procedure (such asiteration, etc.) to suit the new process and then add them into the add-in project. Details and

equations used in calculation of each process are described in chapter 2.

1.5 Program development

After the conceptual design is set, all components and source codes of the program are

developed in accordance with the flowcharts aforementioned.

When all components described above are completely developed, the program then

undergoes debugging process to iron out any syntax errors and error from wrong coding.

After that, the Visual Basic source codes are complied to make a ready-to-use or

executable file and setup file, using VB compiler and the third party VB setup file builder,

called “Wise Installation system”. User will not see the components or source codes described

above. They will see only a group of executable files and supplementary files. Details and

user manual of the compiled program will be described in chapter 2.

The “setup” file, as well as the source code, of the program is submitted to Prof.

AURELLE, thesis director. So it may be available upon request. For more information,

please contact Prof. AURELLE or [email protected].

The copyright of the program, as well as the textbook shown in Part 3 of this thesisand as e-book files in the program, is registered with the Copyright office, Department of

Intellectual Properties, Thailand and under international agreement on copyright (TRIPs).

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2.1 Overview of the program

The program developed under the scope of work of this thesis is the computer program

that can calculate the size of processes and simulate or analyze the performance of processtrain, defined by users, without limitation on the number and configurations of the process.

The program is intended to be upgradable to cover more process in the future . However, in

this scope of work, the program covers only wastewater treatment processes, based on GPI ’s

researches under the supervision of Prof. AURELLE. Thus, it is named “GPI” program.

GPI program is developed in accordance with the conceptual design described in the

previous chapter. Thus, GPI program can be divided into 4 main modes, i.e.,

• E-book mode: provides background knowledge and useful database about the oil


•

Process recommendation mode: provides recommendation to narrow the range

of feasible processes for any input influent,

• Design (or calculation) mode: used for sizing the process unit,

• Analysis mode: allows users to integrate any separation processes, included in the

program database, to build their own treatment process train. And the program will

simulate the process train to forecast the efficiency of each unit.

However, from the user point of view, it is more convenient to describe each mode of

program by the screens or graphic user interfaces (GUI). From this, the program can be

divided into 2 major parts, i.e. main program and project window. Their relations can

compare to those of the main Excel program and its workbook (which contains many

worksheets). Details of each part of completely developed program are shown in section 2.1.1

to 2.1.4. They will describe the features of each part and show that how the conceptual design

is transformed into real working program.

2.1.1 Main program

Main program is the main graphic user interface (see fig. 2.1.1-1) including main

menu and a blank area that are used as workspaces for project window(s). The main program

is developed from the common tasks of each mode, i.e.

•

File management operation (open, save, close, etc.) of every mode,

• Basic edit tool (such as cut, copy, paste) for certain components,

• Print and export operation of every mode,

• Access to E-books and help that can be commonly accessed by any modes of

program at any time.

Main components of this GUI is menu and tool bars. The menu, written in French

language, provides common basic functions for all modes, i.e.,

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1. Fichier (File) menu: consists of the following functions or operations, i.e.,

• Nouveau (New): open new (blank) project window. User can use more than 1

project window independently at the same time. Change active project

window from one to another can be done by click at any area on the new

active window, like standard Windows-based softwares.• Ouvrir (Open): open existing project, which can be save as encrypted data in

database of the program.

• Fermer (Close): close active project.

• Enregistrer (Save): save active project as encrypted data in database of the

program.

• Supprimmer de fichier (Delete file): delete unwanted project from the

database.

• Imprimer (Print): print selected screen to printer in built-in preset format.

User cannot alter the format. However, data in analysis mode can beexported (see menu “donneé’”) to Excel for advance presentation or report

formatting.

• Quitter: exit the program.

2. Edition (Edit) menu: consists of the standard edit functions, i.e., resto (undo),

redo (redo), couper (cut), coupier (copy) and coller (paste) for some applicable

fields.

3. Donneé (Data) menu: consists of data transfer functions, i.e.,

• Exporter d’image (Export picture): export active process train diagram (only

in Analysis mode) as a bitmap file, compatible with presentation or graphic

editing software, such as PowerPoint, or PhotoShop.

• Exporter (Export): export active input data and result to MS Excel.

4. Aide (Help) menu: consists of help and information functions, i.e.,

• Utilisation du programme (help contents and index): open program help file,

which is exactly brought from the context of section 2.2 in this chapter.

• Documentation électronique (E-book): open E-book mode. Clicking at E-

book tab in a project window also gives the same operation.

• A propos de (About): open program information (names, version, etc.) dialog

box.

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open the selected e-book (see fig. 2.1.3-1). E-book worksheet is developed under the

conceptual design, shown in fig. 1.2.1-1.

The help or e-book file names and short descriptions are stored in a database, namely

“ srachu.mdb”. If there are more help files or e-books to be added into the program. Users can

simply input the filenames and their short description (as normal text data) into the databasefile, using MS Access, and copy the new help file or e-books into the existing “ Ebooks”

directory.

Overviewofoilywastewatertreatment

DecanterSTOKE’slaw,Interfacialtension,Capillary

API,PPI,Spiraloil,

Fig. 2.1.3-1 Graphic user interface of the E-book worksheet

2.1.4 Recommend worksheet

Recommend worksheet is one of the tabbed worksheets in project window (fig. 2.1.4-

1). It can provide recommendation about possible or potential processes (based on guideline

summarized from GPI’s researches in Part 3, chapter12), corresponding to input wastewater

data. Recommend worksheet is developed under the conceptual design shown in fig. 1.2.2-1.

Users just answer the preset questions to provide the closest description to the

wastewater to be treated. The questions start at the topmost frame, while the rest frames are

still disabled to avoid confusion. The frame corresponding to the previous answer will be

shown next. Fig. 2.1.4-2 is the retouched screen to show all frames at the same time. After

clicking calculation button, the program will display the result screen (fig. 2.1.4-2) and put

tick mark () in the first column to indicate the categories of the wastewater to be treated.

This mode of operation is designed for oily wastewater treatment process only since

decision logic is relatively complex so it needs fixed source code. The logic used to

recommend feasible processes is as shown in flowchart (fig. 2.1.4-3).

Thus, to upgrade the program to cover other process categories (such as air pollution

treatments) in the future, it can be done by addition of checklists in the form of help files or e-

books in e-book worksheet instead. It may not be interactive but it would be equally

effective.

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Fig. 2.1.4-1 Input screen ( one of tabbed worksheets in project window)

Fig. 2.1.4-2 Result screen. The program will put tick marks in the first column.

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Finish

By source/

granulometry

Categories

Start

Select

categories

Source /

granulometry

Display result

as new window

Program puts tick

mark in

corresponding cells

d>100μ

D=1-100μ

D<1μ Oil layer

WW contains

oil layer.

WW contains

primary emulsion.

WW contains

secondary emulsion.

WW contains

macro/micro emulsion.

Oil/HC, sheared by pump

Storm water/

condensate

Wash water w/

surfactants

Oily WW

w/o surfactants

Slop/ retentate/

conc. oily WW

Cutting oil/ stabilized

emulsion

Oil lyer + Primary +

secondary emulsion.


secondary emulsion.


secondary emulsion.

Primary +

secondary emulsion.

Slop/ retentate/

conc. oily WW

Macro/microemulsion

Known

categories J u s t s h o w

t h e g u i d e l i n e

By source

By granulometry

Fig. 2.1.4-3 Flowchart of recommendation logic

2.1.5 Design worksheet

Design worksheet is one of the tabbed worksheets in project window. It is used to

calculate any parameter providing that the remaining parameters are given, e.g. find efficiencyfrom the given size of process at the given wastewater data. Thus its operation can compare to

programmable calculator. Design mode, in this thesis, is developed for oily wastewater

treatment processes and can be expandable to cover other types of processes in the future (by

others). Design mode worksheet is also divided into 4 tabbed worksheets, devoting to each

design step, i.e.,

1. Step 1: input wastewater properties. (fig. 2.1.5-1a) Required data includes

influent parameters on oily wastewater treatment process, i.e, oil concentration,

physical properties, such as densities and viscosities of oil and water, as well as

size distribution data (granulometry). In case that some parameters are not

known, user can consult built-in parameter database, by clicking “recommend parameters” button. The database is in MS Excel format, to facilitate additional,

editting and cut/paste operation. The files are stored in directory “ RefFiles”.

2. Step 2: select the process to be calculated (fig. 2.1.5-1b). Oily wastewater

treatment processes included in the program are based on every process

reviewed and described in Part 3, i.e.,

• Skimmers

• Decanters

• Coalescers

•

Dissolved air flotation• Hydrocyclones

• Membrane processes

• Heteroazeotropic distillation

• Chemical process

(Destabilization)

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fig. 2.1.6-1. User can select the process category in the top left list box. Then, the program

will display list of available process in that category in the lower list box. In this thesis, there

is only one category available, namely “oily wastewater treatment”.

User can insert required process by double clicking at the name of the process. Then,

the program will insert the icon (picture) of the process into the graphic-editing screen. Theicons can be move freely by normal drag/drop method. Each icon will be automatically

labeled by a code, indicating its type of process and number, such as SD-01 for simple

decanter no. 1. These tag numbers are useful for calculation of the program.

The program is equipped with automatic connector capability that can connect the

processes just by mouse clicking and dragging. Basic graphic tools, such as text box, line,

rectangular, circle, are provided. Users can add/edit these items into the diagram without

affect on calculation of the program.

Sizing of each process is specified by double clicking at the icon. Data input screen

will be displayed. After the schematic diagram and data input are ready, user can startcalculation by clicking at “calculation button” or “calcul” menu. The program will validate

the data and prompt for correction in case of error until it is cleared. Then it will analyze the

process to find efficiency of the process as well as other important parameters of each process,

such as pressure drop for hydrocyclone, etc. The details will be described in chapter 3. The

result will be displayed within the program or exported to Excel. User instructions on drawing

the diagram, calculation, etc. are described in section 2.5.

Graphic editing area

Basic drawing tool bar

Calculation button

Input and result screen(displayed when double clicking at the icon)

Category selection

Process selection

Fig. 2.1.6-1 User interface of analysis worksheet

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2.1.7 Warning dialog box

Warning dialog box is the text box that is displayed when the program finds some

error, e.g. in data typing, or wants to prompt users on some events or information, e.g. SD-01:

specified droplets are beyond limit of the process. Example of warning dialog box is as shown

in fig. 2.1.7-1. It can be closed by clicking OK or close (X) button at its corner.

Fig. 2.1.7-1 Example of warning dialog box

2.2 Program capability

Capability of program, from the point of view of process calculation, can be divided

into 2 parts, in accordance with 2 main modes of the program, i.e. design and analysis mode.

The processes included in the program are mainly the treatment processes that are

reviewed in Part 3. However, there are some additional processes that are included as logical

module in the analysis mode, e.g. inlet module and outlet module, or to represent a

customized process that is not included in those of Part 3. All processes included in designand analysis mode are summarized in table 2.2-1. Equations and related parameters, as well as

guideline for data input, for each process are described in chapter 3 “Program references”.

2.3 Program limitation

Since the program is newly developed, it has some limitations, based on programming

techniques, limitation from scope of work of the thesis, as well as attempts to generalize the

program to support upgrading in the future. General limitation of the program are as

summarized below.

1)

In this scope of work, GPI program includes only oily wastewater treatment process.

2)

The unit of every parameter (e.g. kg, m. second, etc.) is fixed to lessen the

complication of the program.

3) The program includes only calculation of oil separation. Other pollutants, such as

suspended solids, are not taken into account. However, from its open

architecture, it can be upgraded to cover other treatment or other type of process

in the future.

4) The process train in the program can contain only 1 outlet since it is an important

logical module, used in program loop. In case that there is more than 1 outlet in

the real process train, user can combine those outlets, using flow merge module,

into 1 outlet. However, to do so, it does not affect calculation result.

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Table 2.2-1 The processes included in the GPI program

Name Design mode Analysis mode

Skimmer

1 Drum skimmer Yes Yes2 Disk skimmer Yes Yes

Decanter

3 Simple decanter Yes Yes

4 Compact decanter Yes Yes

5 Customized decanter Yes Yes

Coalescer

6 Granular bed coalescer Yes Yes

7 Brush type bed coalescer Yes Yes

8 Dynamic fibrous bed coalescer Yes Yes9 Metal wool bed coalescer Yes Yes

Dissolved air flotation

10 Dissolved air flotation Yes Yes

Hydrocyclone

11 2-phase hydrocyclone Yes Yes

12 3-phase hydrocyclone Yes Yes

Membrane processes

13 Ultrafiltration Yes Yes

14 Reverse osmosis Yes YesThermal processes

15 Heteroazeotropic distillation Yes Yes

16 Stripping Yes Yes

Chemical process

17 Chemical destabilization Yes Yes

Finishing processes

18 Biological process Yes Yes

19 GAC filter Yes Yes

Customized process20 Customized oil concentrator Yes

21 Customized oil separator Yes

22 Inline oil concentrator Yes

Logical module

23 Inlet Yes

24 Outlet Yes

25 Flow merge Yes

26 Flow split Yes

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5) Some influent parameters can not be interpreted in the form of equation, such as

tortousity of bed in coalescer process, thus can not be accounted in calculation.

However, effect of these parameters can be compensated by the use of correction

factor (CF).

6)

The program requires third party program to operate, such as MS excel, Acrobat.

Some of these programs are not free-ware and may cause some expense if they

are not readily available.

7) From the limitation of VB 6.0, its control components, such as text box, menu,

table, etc., support only one font, which is Windows (English version) default

font (as seen in the windows explorer and menu of every program in the

Windows). So we cannot use symbols, Greek letters or the letters with accent ,

such as γ, τ, é, etc. in the program.

2.4 System requirement

To use the program, these hardware and software, based mainly on the requirement ofWindows, VB and Excel, are needed.

Hardware

1. Computer and processor: PC with 300 megahertz or higher processor clock

speed recommended; 233 MHz minimum required (single or dual processor

system);* Intel Pentium/Celeron family, or AMD K6/Athlon/Duron family, or

compatible processor recommended.

2.

Memory: 128 MB of RAM or greater (minimum of 256 MB is recommended.)

3. Hard disk: 50 MB of available hard-disk space

4.

Display: Super VGA (800x600) or higher resolution5. CD-ROM or DVD drive

Software

1. Windows 2000 with service pack 3 (SP3), Windows XP or higher

2. Adobe Acrobat reader 6.0 or higher

3. Microsoft Excel 2000 or higher

4. Microsoft Access 2000 or higher (Optional for database editing)

2.5 User instruction

GPI program is Windows-based program so it features familiar graphic user interface

and basic Windows function, e.g. drag/drop, etc. Thus it is quite ready to use for Windows

users. In this section, instructions for using customized features of the program are described

2.5.1 Program Installation

Setup files of the GPI program are contained in a CD. To install program;

1. Insert CD into a drive

2. The program will run setup program automatically. If auto run is not operated,

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2.1 Use any browsing programs, such as window explorer, to browse the

contents on the CD and then <double click> at “Setup.exe”.

2.2 <Click> Windows’s “Start” button, <Click> “Run” Then type “<your CD-

ROM drive>:setup”, such as “d:setup”

3.

Follow on-screen instruction.

4. Set program will install GPI program to the computer and automatically create

an icon on the desktop and add the program into the Programs menu of the

Windows.

2.5.2 Starting the program

1. <click> Windows’s “Start” button, then <click> “Programs” and <Click> the

program name.

2. Or <double click> at the shortcut on the desktop (created by user).

3. Or <click> Windows’s “Start” button, then <click> “Programs” and <Click> the

program name.

4. The Main form and a new project window will appear on the screen. The

program is ready to use.

2.5.3 Using E-book mode

Fig 2.5.3-1 Using E-book mode

1

3

2, 4

1. <Click> “E-book” tab or “documentation électronique” in “Aide” menu.

2.

<Click> at the name of an e-book to be open3. <Click> “Open” button

4. Or <Double click> at the name

5. The program will open Acrobat and display the selected file.

2.5.4 Using Recommend mode

1. <Click> “Recommend” tab

2. <Click> a radio button to select the suitable answer for your wastewater in the

topmost frame

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Fig. 2.5.4-1 Using recommend mode: Input data screen

12

5

Fig. 2.5.4-2 Using recommend mode: Result window

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3. The frame corresponding to your first answer will be displayed. <Click> another

radio button. Other frames will be disabled to avoid confusion.

4.

<Click> suitable list box. You can select more than one box.

5.

When data input is sufficient, “Calculate” button will be enabled. <Click> the

button to start calculation and display the result.6. Result window (fig.2.5.4-2) is shown. Your wastewater is indicated by tick

marks. <Click> “X” button to close the result. To start over, go back to step 1.

2.5.5 Using Design mode

1. <Click> “Design” tab

2. <Click> “Step 1” tab. Wastewater data input screen is shown.

3. Input the data in input fields (text boxes and table) by <Click> at the selected

field, then type your data

4.

To move to next field, user arrow keys (<↓>,<↑>) or <enter> or <click> at the

next field

5. When data in step 1 is complete, <Click> “Step 2” tab or <click> “next” button.

Process selection data is shown.

Fig. 2.5.5-1 Using Design mode: Step 1 “Wastewater data input”

2

1

54

6. <Click> at required category name and process name. The text boxes on the left

hand will display short description of the selected category and process. In this

thesis, these are only 1 category, i.e. oily wastewater treatment.

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Fig. 2.5.5-2 Using Design mode: Step 2 “Process selection”

1

6 6

6

Fig. 2.5.5-3 Using Design mode: Step 3 “Process data input”

7

8

9

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7. When selection is done, <click> “Next” button or “Step 3” tab. Process data

input screen is shown.

8.

Input the data in input fields (text boxes and table) by <Click> at the selected

field, then type your data. To move to next field, user arrow keys (<↓>,<↑>) or

<enter> or <click> at the next field. The field that we want to find the answer

must be left blank. <Click> “Recommend parameters” or “Reference” for more

information on the value of each parameter and related equations and limitation

of each process.

9. When data in step 3 is complete, <Click> “Calculate” button. The program will

calculate the result and put it in the result screen “Step 4”. If the data is not

sufficient or redundant, the program will not calculate and will display a

warning.

10. After calculation, the result screen (step 4) will be automatically shown.

11. To edit some data in each step, <click> the required tab or <click> “Back” and

“Next” button. When the data is edited, the result is cleared to avoid confusion.

Fig. 2.5.5-4 Using Design mode: Step 4 “Result”

11

2.5.6 Using Analysis mode

1. <Click> “Analysis” tab

2. <Click> at require category name in the upper left box. List of processes in that

category will be shown in the lower left box. In this thesis, there is only 1

category, i.e. oily wastewater treatment.

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1 5

Drag and drop to move

<Double click> to insert

3

Fig. 2.5.6-1 Using Analysis mode: Draw the schematic diagram

3.

Input your process train by drawing the schematic diagram, using the unit processes provided in the lower left box on the screen. To insert an icon or

graphic representative of the process, <Double click> at the process name. The

corresponding icon is shown in the graphic editing area.

4. To move the icon to proper location, move the cursor over the icon until it turns

into a “4-direction arrow” ( ) sign. Then <click> and hold the mouse button to

drag and release the button to drop the icon at new location.

5. Insert other processes using step 3 and 4 until all required processes are inserted.

To connect the processes together, move the cursor over the icon until it turns

into a “hand” (

) sign. Connecting points of the process will be shown as smallred squares. Move the “hand” to the required connecting point, <click> the

mouse, hold the button to a required connecting point of another process to be

connected and release the mouse. The program will draw the connecting line

automatically. Users will actually see the line while they hold and move the

mouse. User can add non-active graphic, e.g. text box, line, etc. into the diagram,

using drawing tools.

6. After connecting the processes, User must input the size of each process. To

input or edit the data of a process, <double click> at its icon. Process data input/

result screen is shown. However, the result tab will be disabled unless the

calculation is completed. The process train must contain only 1 outlet module.

But there can be several inlet modules. See chapter 3 for details and restriction ofeach module.

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Fig. 2.5.6-2 Using Analysis mode: Process data input

7

7. After data input procedure is completed. <Click> “Calculate” button or “Calcul

Now” in “Calcul” menu to start caluculation. The program will validate the data

and display warning to prompt users to correct the errors. After the errors are

cleared, the program will calculate the result of each process. In analysis mode,

the program can calculate process performance (e.g. graded efficiency, outletconcentration of oil, etc.) only. It can not be used for sizing the process, as in the

design mode.

8. To view the result, <Double click> at required process icon. The data input/

result will be displayed. After calculation in step 8, the “Result” tab is enabled.

<Click> the tab to view the result of the process. The result tab is just the same

as that of design mode, shown in fig. 2.5.5.4.

9.

Total outlet concentration of each process will also be shown as a text box under

each icon for evaluation of the performance at-a-gaze (fig. 2.5.6-3)

10. To display result in more complex format, it must be exported to Excel. To do

so, <Click> “Exporter” in “Donneé” menu. The program will open Excel and

automatically create a workbook. Each worksheet in the workbook devotes to

result of each process (fig 2.5.6-4). User can also save this excel file. User can

formulate their own formats of result such as building graph showing graded

efficiency of every process, etc., in Excel. The diagram can also be exported to

any Windows-compatible software, such as PowerPoint, PhotoShop, etc., by

<click> at “Exporter d’image” in “Donneé” menu.

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Fig. 2.5.6-3 Using Analysis mode: Viewing result in the diagram

Fig. 2.5.6-4 Using Analysis mode: Exporting the result to excel

2.5.7 Printing and file operation

1. Every screen in the program can be printed in pre-set format. To print, <click>

“Imprimer” in “Fichier” menu. Print dialog box will be shown. User can select

the mode(s) that they want to prink, then click “OK”.

2. Data and result of design and analysis can be saved in the database. To conduct

file operation (new, open, save, delete, close), <click> required operation in“Fichier” menu. File operation dialog box will be shown.

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2.6 Upgrading procedure and recommendation for further development

As described in previous section that the program is designed to facilitate upgrading in

the future, in this section, upgrading procedure and recommendation for further development

are described.

2.6.1 Upgrading procedure

Upgrading procedure can be divided into 2 major parts, i.e. upgrading of database and

source code upgrading.

2.6.1.1 Upgrading of the database

Every data related to process calculation, as listed below, is linked to the database,

namely “ srach.mdb”, which is automatically installed in setup procedure.

1.

Process categories (see fig. 2.5.5-2, and 2.5.6-1)2.

Unit processes of each process category, as shown in table 2.2-1 and sub-routine

names (called “class” as described the previous chapter)

3. Wastewater input data for each process category (see fig. 2.5.5-1 and 2.5.6-2)

4. Input data for each unit process, as well as its icon file and help file (see fig.

2.5.5-3 and 2.5.6-2)

5. Output data for each process (see fig. 2.5.4-4 and chapter 3)

6. E-book (see fig. 2.5.3-1)

These data are in the form of tables in the database file, as shown in fig. 2.6.1-1. Ifusers want to add new process or process categories, it can be easily done by add related data

into the tables. The additional data will be automatically displayed in the related screens of the

program without any additional coding, as shown in fig. 2.6.1-2. This procedure does not

require Visual Basic development package.

Process category:

Table name:

tbProcessCategory

Unit process:

Table name:

tbUnitProcess

Input/output data

for oily wastewater

category :

Table name:

tbVariableDef

Standard result

(such as Cout

, etc. :

Table name:

tbStdResult

Unit process:

Input data for other

wastewater

category :

Standard result for

that category

For future upgrading Existing

Ebook file:

Table name:

tbEBook

Fig. 2.6.1-1a Configuration of the database

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Fig. 2.1.6-1b Examples of existing database

CAT000001

CAT000002 Airpollutiontreatment

Airpollutiontreatment

Fig. 2.1.6-2 Example on database upgrading. When new category is added in the database

(left), Related field in the program will be automatically updated (right)

2.6.1.2 Source code updating

Even though the program’s interfaces can be easily upgraded by updating the database

file. To add sub-routines (or classes) of new processes into the program, the new classes have

to be written in Visual Basic. The simplest way to write a new class is to copy one of the old

class and change the formula or equation to suit the new process. To do so, Visual basic

development package and the original source code of any process is required. Developers can

define their own variable easily in the database file. So, in their new classes, they can use

these variables in the new equations.

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After writing the new classes in VB, the classes need to be recompiled into executable

file. Then, the file will be copied to replace the old compiled class file without reinstallation

of the whole program.

The reason that we developed the program in the manner that it requires source code

for updating is that we can control the development of the program to proper developers. The

source code of the program is submitted to thesis director, Prof. AURELLE.

2.6.2 Recommendation for further development

Since this program in newly developed so it have some limitations as discussed in

section 2.3. However it may have prospect for further development, at least, in the following

approach.

1. To upgrade to include more process categories,

2. To add a subroutine for unit conversion (metric, US customary, etc.), which

would be very useful in case that some users may be familiar with different kindof unit.

3. To develop or include some advanced components, which may be present in the

newer version of VB, to enhance the performance of the program or make it

operate in stand-alone mode without requiring third-party software (such as

Excel). It is also useful to enhance its text display capability so it will be able to

display Greek letter, subscript, or superscript.

4. Recommend mode should be enhanced by replacing the fixed-coded source

codes with sub-program written with logical programming language, such as

Prolog.

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Process references, which include the parameter to be calculated, equations used and

specific constraints of each process, are described in the following sections. This information

is included in the help file of the program, (<Click> “Utilisation du program” in “Aide”

menu), or (<Click> “Reference” button in any input forms or user interfaces).

Common parameters

Common parameters or variables that are used for every process module are

summarized as follows,

Parameter DescriptionVariable name in

the program

Unit used in the

program

Cod Granulometry or oil droplet size

distribution : graded concentration(concentration of oil at each droplet size)

Cind mg/l

Concentration of inlet oil in the form of

oil layer or film

Cinlayer mg/l

Co Total oil inlet concentration Co mg/l

d Granulometry or oil droplet size

distribution : droplet size

din micron

Q Wastewater flowrate Qin m3/h

T Temperature temp Celcius

ρc Dynamic (or absolute) viscosity of

continuous phase, which is water, for oily

wastewater

Denc Kg/m3

ρd Density of dispersed phase, in this case, oil Dend Kg/m3

μC Dynamic (or absolute) viscosity of


wastewater

Muc N.s/m2

(= 1000 cp)

μd Dynamic (Absolute) viscosity of

dispersed phase, in this case, oil

Mud N.s/m2

(= 1000 cp)

γow Interfacial tension between oil and water gow kg/s2

or N/m

(= 1000 dyne/cm)

Values of these parameters will be given by user via inlet module (See section 23).

They will be used to calculate the results, which are usually divided into 2 streams, i.e., water

outlet and oil (or concentrated oily wastewater outlet. Generally, the result will contain the

parameters mentioned above. But the values will be changed in accordance with

corresponding model or equations of each process. Then they will be sent as input data for

downstream process until the end of process train (outlet module).

General remarks and precautions of the program

General remarks and precautions of the program are as shown below,

•

The program is valid only when the oil is lighter than water.

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• The processes available in the program generally consists of 1 inlet port and 2

outlet ports, i.e., outlet port of treated water, called “water outlet port ”, and outlet

port of separated pure oil or concentrated oily water, called “Oil outlet port ”.

• Graded concentration is specified as quantity of oil (mg) per volume of wastewater

(= volume of oil+water).

• Graded efficiency (ηd) in the program is based solely oil mass removal, regardless

of flow splitting effect. To calculate outlet concentration, flow splitting between

oil outlet port and water outlet port of each process will be taken in to account.

Thus, in some processes, outlet oil concentration is not exactly equal to (1-ηd)Cod.

• Total efficiency (ηt) in the program can be generally used to calculate total inlet

concentration. Total outlet oil concentration is equal to (1-ηt)Co in some processes.

However, there may be some exceptions in certain processes. See reference of

each process for more information.

• The pictures or icons of processes in analysis mode generally contain 3

connections or hot spots (there may be only 1 or 2 spots in some processes.) The black connection represents inlet point of the process. The red one represents oil

outlet port and the blue one represents treated water outlet port.

• In E-book mode, the e-book files are designed for a fixed directory, named

c:/SR/E-book. The directory contains an Acrobat index file

“E_book_oily_wastewater”. This index facilitates users to search for any words or

topics in all e-book files in the directory. However, it is developed by Acrobat 7.0,

it may not be run on some old versions of Acrobat reader. In this case, it is

recommend to set option of the option “ All PDF documents in” in Acrobat’s

search window to the e-book directory. It can substitute the use of the index file.

•

The program is linked to MS Excel for parameter recommendation, calculation ofsome processes and for result display. In case that, Excel security is set to “high

level”, it will happen that the program is not allowed to link to Excel. To solve or

avoid this problem, you can choose one of these options,

• Set security of Excel to medium or low. (in Menu “Tools”>Options>Security).

• If high or highest security level is needed, try setting the macro in the file

“Process_calculation.xls” as a trusted source (in Menu

“Tools”>Options>Security). Consult your corresponding Excel’s help file for

more information.

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1) Drum skimmer

1. Process abbreviation: DRM

2. Process description : Oleophilic oil drum skimmer

3.

Reference : Part 3, chapter 34.

List of outputs and related equations

4.1 Graded efficiency: 100% for oil film or layer and 0% for droplet.

4.2 Total efficiency: 100% for oil film or layer and 0% for droplet.

4.3 Graded outlet oil concentration in water outlet flow: This parameter is not

valid for this process.

4.4 Total outlet oil concentration in water outlet flow: This parameter is not

valid for this process.

4.5 Graded outlet oil concentration in oil outlet flow: the outlet oil in the oil

outlet flow is in pure condition (100% oil).

4.6 Total outlet oil concentration in oil outlet flow: the outlet oil in the oil


4.7 Inlet flow: the process is valid only for separated oil flow from upstream

process.

4.8 Water outlet flow: This process does not have this property.

4.9 Oil outlet flow: flowrate or oil productivity (m3/h) is governed by the

following equation.

0.514g

L0.486

o ν1.541 N1.5413.035D

P ⋅= CF {1.1}

5. Related parameters: Related parameters are as summarized in the following

table.

Table .1-1 Related parameters of drum skimmer

Parameter Description Variable name inthe program

Unit used in theprogram

CF Efficiency correction factor, CF ≤ 1 CF

D Diameter of skimmer D M

g Gravitational acceleration Constant = 9.81 m/s2

L Length of the skimmer L M

N Rotational speed of the skimmer N Rev/s

P Oil productivity of the skimmer Prod m3/h

γo Superficial tension of oil go kg/s2

or N/m

(= 1000 dyne/cm)

νo Kinematics viscosity of oil (used μ/ρ) m2

/s

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6. Related graphics: Icon in analysis mode and graphic diagram for input screen for

this process are as shown below.

Drum Skimmer (DRM-??)

Scrapper

Oil layer

D

L

Fig. 1-1a Icon of drum skimmer Fig .1-1b Graphical diagram of drum skimmer

7.

Constraints and limitations

7.1

Superficial tension of oil is in the range of 27 – 34 dynes/cm, which

practically covers all common oil.

7.2

Capillary number (Ca = μo V/γo) is in the range of 0.2 – 1.0.

7.3

Oil density is around 790 – 830 kg/m3. Oil dynamic viscosity (μ) tested is


7.4 Peripheral or tip velocity should not be greater than 0.8 m/s. To avoid

water entraining, velocity of 0.44 m/s or less is recommended.

7.5

Recommended minimum immersion depth is 1.0-2.0 cm.7.6

Drum skimmer surface used for model development is polypropylene. But

it is proven to be valid for SS, PVC, and PTFE.

7.7 Skimmer can only be connected to pure oil outlet flow of upstream process.

8. Influent parameters: Effects of certain parameters, when they are increased, on

the oil removal performance of the process are summarized as follows. For more

details, see chapter 3, Part 3.

Table 1-2 Influent parameters for drum skimmer

ParameterEffect on process performance if

the parameter is increased

Length of drum + is

Diameter of skimmer + is

Oil viscosity +

Velocity ±

Present of surfactants -

Note: “+” means “increases performance”, “-“ means “decreases performance”, “± ” means

“have both positive and adverse affects”, “is” means “effect is insignificant”.

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D i s k

Disk Skimmer (DSK-??)

I

Scrapper

D

Fig. 2-1a Icon of disk skimmer Fig. 2-1b Graphical diagram of disk skimmer

7. Constraints and limitations.

7.1 Superficial tension of oil is in the range of 27 – 34 dynes/cm, which

practically covers all common oil.7.2 Capillary number (Ca = μo V/γo) is in the range of 0.04 – 3.6.

7.3 Oil density is around 790 – 830 kg/m3. Oil dynamic viscosity (μ) tested is


7.4 Peripheral or tip velocity should not be greater than 1.13 m/s. To avoid

water entraining, velocity of 0.5 m/s or less is recommended.

7.5

Disc skimmer surface used for model development is PVC. But it is proven

to be valid for SS, PP, and PTFE.

7.6

Skimmer can only be connected to pure oil outlet flow of the upstream

process.

8.

Influent parameters: Effects of certain parameters, when they are increased, onthe oil removal performance of the process are summarized as follows. For more


Table 2-2 Influent parameters for disk skimmer



Immersion depth +

Diameter of skimmer + is

Oil viscosity +

Velocity ±

Present of surfactants -



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3) Simple decanter

1. Process abbreviation: SD

2. Process description: API tank or any decanter that does not have any oil

interceptors installed in the tank so the rising distance of oil drops is equal to the

water depth.

3. Reference : Part 3, chapter 4

4. List of outputs and related equations

4.1 Graded efficiency (η d ): Graded efficiency of the process is governed by the

following equation.


%100⋅= CF d η {3.1}


%100⋅⋅=dc

d

d U

U CF η {3.2a}

For oil droplet size, d ≤ 20 microns

%0=d η {3.2b}

Rising velocity (U), m/s, of the droplet “d” or of the cut size “d c” is

calculated from the following equations.

c

d

d gU

μ

ρ

18

)10( 26−⋅⋅⋅Δ= {3.3}

⎟ ⎠

⎞⎜⎝

⎛ ⋅

=S

QU dc

3600 {3.4}

Cut size is calculated by the following equation.

6

2/1

103600.

18⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛

⋅⋅Δ=

S g

Qd c

c ρ

μ micron {3.5}

4.2 Total efficiency (η t ):

( )

%100

max

min ⋅

⋅

= ∑o

d

d

od d

t C

C η

η

{3.6}

4.3 Graded outlet oil concentration in water outlet flow (C d ):

)1(d od

out

d C Q

QC η −⋅⋅=

mg/l {3.7}

4.4 Total outlet oil concentration in water outlet flow (C ):

∑=max

min

d

d

d C C mg/l {3.8}

4.5

Graded outlet oil concentration in oil outlet flow (C oild ): The outlet oil inthe oil outlet flow is in pure condition (100% oil).

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4.6 Total outlet oil concentration in oil outlet flow (C oil): The outlet oil in the

oil outlet flow is in pure condition (100% oil).

4.7 Inlet flow (Q): Inlet flow of the process is equal to the outlet flow of the

upstream process.

4.8

Water outlet flow (Qout ):

)1000//)(1( oiloout C C QQ ρ −−=

m3/h

{3.9}

4.9 Oil outlet flow(Qoil):

out oil QQQ −=

m3/h

{3.10}

4.10 Customized output :

4.10.1 Theoretical cut size (d c): cut size is calculated by eq. 3.5.

5.

Related parameters: Related parameters are as summarized in the following table

Table 3-1 Related parameters of simple decanter


the program

Unit used in the

program

dc Cut size of the decanter dc micron

S Bottom projection area of the tank S m2

Ud Rising velocity of the droplet diameter “d” Ud m/s

Udc Rising velocity of the droplet at cut size “dc” Udc m/s

Δρ Difference between density of dispersed

phase and continuous phase

Denc-Dend Kg/m3

ρc Density of continuous phase, in this case,

water

Denc Kg/m3



wastewater

Muc N.s/m2

(= 1000 cp)




Simple decanter (SD-??)

Ud

V

Q

d = cut size

d < cut size

d > cut size

Influent

L

Oil droplets

Separated

oil layer

S

Fig. 3-1a Icon of simple decanter Fig. 3-1b Graphical diagram of simple decanter

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7.1 Reynolds number of droplet, Re, is between 10-4 to 1, which is the range


c

d c d U

μ

ρ ⋅⋅=Re {3.11}

7.2 The oil droplets are uniformly distributed across the cross section area of


7.3

ηd of oil layer is 100%.

7.4

The oil droplet is spherical, which is normally true.

7.5

For droplets smaller than 20 microns, they are subjected to Brownian




small droplets are the minority part of pollutants, the models can be used to predict the efficiency without any harm because its prediction is usually


7.6 Oil outlet point of the process can only be connected to the skimmers only.




Table 3-2 Influent parameters for simple decanter



Hydraulic loading rate -

Droplet diameter +



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4) Compact decanter

1. Process abbreviation: CD

2. Process description: Parallel plate interceptor, lamella separator, or other types of

plate insertion decanter that the rising distance of the droplets is equally divided

and can be clearly specified .




following equation.


%100⋅= CF d η {4.1}


%100⋅⋅=dc

d

d U

U CF η {4.2a}


%0=d η {4.2b}

Rising velocity (U) of the droplet “d” or of the cut size “dc” is calculated

from the following equations.

c

d

d gU

μ

ρ

18

)10( 26−⋅⋅⋅Δ= m/s {4.3}

⎟⎟

⎠

⎞⎜⎜⎝

⎛

⋅+⋅=⎟⎟

⎠

⎞⎜⎜⎝

⎛

⋅=

α cos)1(36003600 N S

Q

S

QU

pd

dcm/s {4.4}

Cut size (micron) is calculated by the following equation.

6

2/1

10cos)1(3600

18⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛

⋅+Δ⋅=

α ρ

μ

N gS

Qd

P

cc

micron

{4.5}


( )%100

max

min ⋅⋅

= ∑o

d

d od d

t C

C η η

{4.6}


)1(d od

out

d C Q

QC η −⋅⋅=

mg/l

{4.7}


∑=max

min

d

d

d C C mg/l

{4.8}

4.5 Graded outlet oil concentration in oil outlet flow (C oild ): The outlet oil in the


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4.6 Total outlet oil concentration in oil outlet flow (C oil): The outlet oil in the oil



upstream process.

4.8

Water outlet flow (Qout ):

)1000//)(1( oiloout C C QQ ρ −−= m3/h

{4.9}


out oil QQQ −= m3/h

{4.10}



4.10.2 Foot print area of the decanter (S): It is assumed to be identical to

Sp.

5.


Table 4-1 Related parameters of compact decanter


the program

Unit used in the

program

dc Cut size of the decanter dc micron

N The number of plates N

S p Area of one inserted plate (only 1 side and

measured perpendicularly to the platesurface.)

Sp m2


Udc Rising velocity of the droplet at cut size “dc” Udc m/s

α Inclination of plate from horizontal axis (0-

90 degree)

incl degree

Δρ Difference between density of dispersed

phase and continuous phase

Denc-Dend Kg/m3


water

Denc Kg/m3



wastewater

Muc N.s/m2

(= 1000 cp)




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C o m p a c t

Compact decanter (CD-??)

QInfluent

H

Inserted plates

(No. of plates = N)

Sp

Fig. 4-1a Icon of compact decanter Fig. 4-1b Graphical diagram of compact decanter




c

d c d U

μ

ρ ⋅⋅=Re {4.11}



7.3

The oil droplet is spherical, which is normally true. ηd of oil layer is 100%.

7.4



recommended to avoid using the decanter for the wastewater with themajority part of oil droplets smaller than 20 microns. However, if these

small droplets are the minority part of pollutants, the models can be used to

predict the efficiency without any harm because its prediction is usually






Table 4-2 Influent parameters for compact decanter




Droplet diameter +

Inclination of plates (0o = horizontal axis) - but helps draining the sludge from

the plate surfaces



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5) Customized decanter

1. Process abbreviation: CTD

2. Process description: Decanter that decanting area or oil interception area is

specified. Decanting area is the area of every surface that can intercept oil

droplets, regardless of rising distance of oil droplets. However, majority of rising paths should be identical. An example of the decanters is closely inserted plate

interceptor, e.g. “Spiraloil”.




following equation.


%100⋅= CF d η

{5.1}


%100⋅⋅=dc

d d

U

U CF η {5.2a}


%0=d η {5.2b}

Rising velocity (U) of the droplet “d” or of the cut size “dc” is calculated

from the following equations.

c

d

d gU

μ

ρ

18

)10( 26−⋅⋅⋅Δ= m/s {5.3}

⎟⎟ ⎠

⎞⎜⎜⎝

⎛

⋅=

d

dcS

QU

3600

m/s {5.4}

Cut size is calculated by the following equation.

6

2/1

103600

18⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛

Δ⋅=

d

cc

gS

Qd

ρ

μ micron {5.5}

4.2

Total efficiency (η t ):

( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η

{5.6}


)1( d od

out

d C Q

QC η −⋅⋅= mg/l {5.7}


∑=

max

min

d

d d C C

mg/l {5.8}

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4.5 Graded outlet oil concentration in oil outlet flow (C oild ): The outlet oil in

the oil outlet flow is in pure condition (100% oil).



4.7

Inlet flow (Q): Inlet flow of the process is equal to the outlet flow of theupstream process.

4.8 Water outlet flow (Qout ):

)1000//)(1( oiloout C C QQ ρ −−= m3/h {5.9}


out oil QQQ −=

m3/h

{5.10}



5.


Table 5-1 Related parameters of customized decanter


the program

Unit used in the

program

dc Cut size dc micron

Sd Decanting area ( the area of all surfaces in the

decanter that can intercept oil droplets)

Sd m2


Udc Rising velocity of the droplet at cut size Udc m/s

Δρ Difference between density of dispersed phase

and continuous phase

Denc-Dend Kg/m3


water

Denc Kg/m3

μC Dynamic (or absolute) viscosity of continuous

phase, which is water

Muc N.s/m2

(= 1000 cp)


6.

Related graphics: Icon in analysis mode and graphic diagram for input screen for


C u s t o m

Customized decanter (CTD-??)

QInfluent

Sd

Fig. 5-1a Icon of customized decanter Fig. 5-1b Graphical diagram of customized decanter

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c

d c d U

μ

ρ ⋅⋅=Re {5.11}



7.3


7.4

The oil droplet is spherical, which is normally true.

7.5





small droplets are the minority part of pollutants, the models can be used to predict the efficiency without any harm because its prediction is usually



7.7 Loading rate of the decanter can be as high as 14.1-54 m/h.

7.8 Calculated efficiencies of closely inserted plate interceptor are usually

lower than observed values. Prediction of cut size is relatively accurate so

the difference of ± 20% can be expected.


the oil removal performance of the process are summarized as follows. For moredetails, see chapter 4, Part 3.

Table 5-2 Influent parameters for customized decanter

ParameterEffect on process performance if the parameter

is increased


Droplet diameter +

Inclination of plates (0o

= horizontal axis) - but helps draining the sludge from the platesurfaces

Decanting area +

Rising distance of oil - but too small distance may cause clogging.

Presence of surfactants - for closely inserted plate interceptor



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6) Granular bed coalescer

1. Process abbreviation: GCC

2. Process description: Granular bed coalescer in this program is based on upflow

pattern. However, it can be applied to downflow coalescer since the rising

velocity of droplet are usually small, compared to flow velocity. So relativevelocity between oil droplets and bed can be safely assumed to equal flow

velocity.




following equation.

%100)()()()()10

(58.009.009.008.012.02.0

6

⋅Δ⋅

⋅= −

−

cc

d

ow

c

d

dpV

dp

H

dp

d CF ρ

ρ

μ

μ

γ

ρ η

{6.1}

And %100≤d η {6.2}


( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η {6.3}


)1(d od

out

d C Q

QC η −⋅⋅=

mg/l

{6.4}


∑=max

min

d

d

d C C mg/l {6.5}






upstream process.


)1000//)(1( oiloout C C QQ ρ −−= m3/h {6.6}


out oil QQQ −= m3/h {6.7}


4.10.1

Theoretical cut size (d c): Cut size is calculated from eq. 6.1 byassuming that the graded efficiency is 100%.

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4.10.2 Range of pressure drop (P): Pressure drop is calculated from

Kozeny-Carman equation, as shown in eq. 6.8. Recommended

minimum and maximum value of porosity are 0.13 and 0.23,

respectively.

32

2

)1(180ε ρ ε μ ⋅⋅⋅ −= dpg

V H Pc

c

m

{6.8}

5. Related parameters: Related parameters are as summarized in the following table

Table 6-1 Related parameters of granular bed coalescer


the program

Unit used in the

program


d p Diameter of collector or bed material dpc mH Bed height (height of granular bed) H m

P Pressure drop across the bed Pdropmin,

Pdropmax

m

V Flow velocity or empty bed velocity V m/s

ε Porosity or void ratio of the bed (= void

volume / total volume)

Constant 0.13 and

0.23


or N/m

(= 1000 dyne/cm)

Δρ Difference between density of dispersed phase and continuous phase

Denc-Dend Kg/m3


water

Denc Kg/m3



wastewater

Muc N.s/m2

(= 1000 cp)

μd Dynamic (or absolute) viscosity of

dispersed phase, which is oil, for oily

wastewater

Mud N.s/m2

(= 1000 cp)

ρd Density of dispersed phase, in this case,oil

Dend Kg/m3



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Granular bed

coalescer

(GCC-??)

Collector

size = d p

Void ratio = ε

Bed height

= H

Influent

Flow = Q

Effluent

Oil outlet

Velocity = V

=Q/A

Cross section area

= A

Fig. 6-1a Icon of granular bed coalescer Fig. 6-1b Graphical diagram of granular bedcoalescer


7.1 Coalescer bed shall be oleophilic and relatively spherical in shape.

7.2 Tested size of bed media (d p) is between 0.20 – 1.0 mm. The larger the

media size, the lower the efficiency.

7.3

Tested range of bed height (H) of the model is between 1 to 10 cm.

However, bed height as low as 1 cm is not recommended. The greater the

bed height, the safer the coalescer operation. However, it also results in

higher pressure drop.

7.4 The velocity (V) should be in the range of 0.09 to 0.54 cm/s or 3.2 to

19.4 m/h.

7.5 Tested interfacial tension (γow) is between 11 to 42 dyne/cm or 0.011 to

0.042 N/m. (i.e. T.I.O.A, Heptane, Anisole, Toluene and Kerosene)

7.6 Different density between dispersed phase (oil) and continuous phase

(water) (Δρ) is between 80 to 315 kg/m3 (approx.).

7.7 The equation is valid for droplet size (d) of 10 microns or bigger. For

smaller droplets, result from the equation may not be accurate because it

is beyond the data range that has been used to verify the model.

7.8 The model is valid for inlet concentration between 100 to 1,000 mg/l. At

higher concentration, mousse or jet formation may occur, resulting in

unpredictable decreasing of the efficiency.

7.9 ηd of oil layer is 100%.

7.10 Within the valid range of model, error in efficiency prediction is less than

±10%.

7.11 Oil outlet point of the process can only be connected to the skimmers

only.

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7.12 Recommended minimum and maximum value of porosity are 0.13 and

0.23, respectively. For pressure drop calculation, since wastewater is

rather diluted, it is assumed that density and viscosity of water is used in

the equation.

8.

Influent parameters: Effects of certain parameters, when they are increased, on



Table 6-2 Influent parameters of granular bed coalescer



Empty bed velocity -

Droplet diameter +

Collector or bed material diameter -

Hydrophilicity of bed -

Surface roughness of bed +

Bed height +

Ratio of oil to water -

Presence of surfactants -

Temperature +



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7) Brush type bed coalescer

1. Process abbreviation: BCC

2. Process description: Brush type bed coalescer refers to the coalescer whose

fibrous elements are in aligned neatly in radial direction, like bottlebrush.


4.



following equation.

( ) %100)(1)()10

()(5.104 694.035.018.018.06

77.0 ⋅−⋅

⋅= −−

−

D

H

D

d

D

d VDCF F

c

cd ε

μ

ρ η {7.1}

And %100≤d η

{7.2}


( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η {7.3}


)1(d od

out

d C Q

QC η −⋅⋅=

mg/l

{7.4}


∑=max

min

d

d

d C C mg/l {7.5}






upstream process.

4.8 Water outlet flow (Qout

):

)1000//)(1( oiloout C C QQ ρ −−= m3/h {7.6}




4.10.1 Theoretical cut size (d c): Cut size is calculated from eq. 7.1 by

assuming that the graded efficiency is 100%.

4.10.2

Pressure drop (P): Pressure drop is calculated from Hazen –

William equation, using equivalent length of the coaleser. The

equivalent length is assumed to be 5 times of the actual length of

coalescer column.

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167.185.1

582.6 ⎟

⎠

⎞⎜⎝

⎛ ⎟⎟

⎠

⎞⎜⎜⎝

⎛ =

D

H

C

V P

HW

m

{7.8}

5.


Table 7-1 Related parameters of brush type bed coalescer


the program

Unit used in the

program

CHW Hazen William’s C, depanding on material. C

of 130 is recommended for steel column.

Constant = 130


D Diameter of coalescer column or of brush,

which should be relatively closed.

Dcc m

dF Diameter of fiber element dF mH Bed height (height of granular bed) H m

P Pressure drop across the bed Pdrop m

V Flow velocity or empty bed velocity By calculation m/s


volume / total volume) (must be < 1)

Void

ρc Density of continuous phase, in this case, water Denc Kg/m3


phase, which is water, for oily wastewater

Muc N.s/m2

(= 1000 cp)

ρd Density of dispersed phase, in this case, oil Dend Kg/m

3

6.



Brush type bed

coalescer

(BCC-??)

Effluent

Oil outlet

Fiber elementsize = dF

Void ratio = ε

Bed height

= H

Influent

Flow = Q

Velocity = V

=Q/A

Cross section area

= A

Fig. 7-1a Icon of brush type bed coalescer Fig. 7-1b Graphical diagram of brush type bed

coalescer

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7.1 48 < Re < 1100. Re is the term (ρcVD/μc) in the equation. 1 < H/D < 10.

7.2 Diameter of coalescer bed (D) tested is around 5.0 cm. Using bigger

coalescer diameter may cause deflection at the tips of fibers because of

longer overhung length, which may cause channeling of untreatedwastewater and error in efficiency calculation.

7.3 The model is valid for droplet size (d) of 1 micron and greater.

7.4 Empty bed velocity (V) is between 0.5 to 5.0 cm/s (1.8 to 180 m/h).

However available raw data used to verify the model is between 0.5 to

2.0 cm/s. Using velocity > 2.0 cm/s may cause unpredictable error on

calculated efficiency.

7.5 Fiber size (dF) is between 40 to 200 microns. However available raw data

used to verify the model is between 100 to 200 microns. Using fiber size

< 100 microns may cause unpredictable error on calculated efficiency.

7.6 Void ratio of the bed (ε) is around 0.845 to 0.96.

7.7 The model is valid for droplet size (d) of 1 microns and greater.

7.8 The model is verified at inlet oil concentration up to 1000 mg/l. Applying

the model to the concentration > 1000 mg/l will cause underestimation of

predicted efficiency.

7.9 The beds used in these researches vary from “bottle brush” type, simple

spiral type and combination of internal bed of “simple spiral” and

concentric “coil spring–like” external bed with the tip of the fibers

pointed to the centerline. However, they are all oleophilic. There is some

difference in efficiency between each type, but there is too few data to

make a conclusion. However, because of its rigidity, the “simple spiral in

coil spring- like” bed tends to operate more stable without decreasing in

efficiency with time, while others tend to be deflected by weight of

accumulated oil drops.

7.10


7.11

Within the valid range of model, error in efficiency prediction is less than

±20%.


only.

8.




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Table 7-2 Influent parameters of brush type bed coalescer



Empty bed velocity -Droplet diameter +

Diameter of fiber element -

Coalescer diameter -


Porosity -

Bed height +

Tortousity of bed +

Presence of surfactants -Temperature +



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8) Dynamic fibrous bed coalescer

1. Process abbreviation: DCC

2. Process description: Dynamic fibrous bed coalescer is actually the brush type

bed coalescer whose bed is rotated by outside prime mover.


4.



following equation.

( ) %100)()(1)()()(76.1 53.035.035.058.058.021.0 ⋅⋅

−⋅= −−

V

N D

D

H

D

d

D

d VDCF F

c

c

d ε μ

ρ η {8.1}

And %100≤d

η {8.2}


( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η

{8.3}


)1(d od

out

d C Q

QC η −⋅⋅= mg/l {8.4}


∑=max

min

d

d

d C C mg/l {8.5}






upstream process.

4.8

Water outlet flow (Qout ):)1000//)(1( oiloout C C QQ ρ −−= m3/h

{8.6}






4.10.2 Pressure drop (P): Pressure drop is calculated from Hazen –


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coalescer column.

167.185.1

582.6 ⎟

⎠

⎞⎜⎝

⎛ ⎟⎟

⎠

⎞⎜⎜⎝

⎛ =

D

H

C

V P

HW

m {8.8}


Table 8-1 Related parameters of dynamic fibrous bed coalescer


the program

Unit used in the

program

CHW Hazen William’s C, depanding on material. C

of 130 is recommended for steel column.

Constant = 130


D Diameter of coalescer column or of brush,which should be relatively closed.

Dcc m

dF Diameter of fiber element dF m

H Bed height (height of granular bed) H m

N Rotating speed of bed N Rev/s




volume / total volume)

void

ρc Density of continuous phase, in this case, water Denc Kg/m3

μC Dynamic (or absolute) viscosity of continuous phase, which is water, for oily wastewater Muc N.s/m

2

(= 1000 cp)




Dynamic bed

coalescer

(DCC-??)

InfluentEffluent

Oil outlet

Fiber element

size = dF

Void ratio = ε

Bed height= H

N rev/s

Influent

Flow = Q

Velocity = V

=Q/A

Cross section area

= A

Fig. 8-1a Icon of dynamic fibrous bedcoalescer

Fig. 8-1b Graphical diagram of dynamic fibrousbed coalescer

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7.1 52 < Re < 1164. Re is the term (ρcVD/μc) in the equation.

7.2 1 < H/D < 2. Using H/D > 2 in the model can be also applied for

comparison purpose only. However, the maximum H/D is 6.

7.3

Rotating speed of the bed (N) is between 0.167 to 3.33 rps (10 to 200 rpm).

Please note that N is in the form of revolution per unit time, not radian per

unit time). Recommended minimum rotating speed is 75 rpm. Using lower

speed may not provide any additional benefit over simple fibrous bed

coalescer because the effect of rotating on interception probability may be

cancelled out by the shear effect, which causes fragmentation of oil drops.

7.4 Empty bed velocity (V) is between 0.1 to 1.1 cm/s (3.6 to 39.6 m/h).

7.5 Diameter of fiber (dF) is around 100 to 300 microns

7.6 Diameter of coalescer bed (D) is not greater than 11.5 cm. Using bigger

diameter may cause deflection at the end of fibers from longer overhunglengths, which may cause channeling of untreated wastewater and error in

calculation.

7.7

It is recommended to use the model only for the droplet size (d) of 10

microns or greater. For smaller droplet, the model can also be applied, but

for comparison purpose only.

7.8 The beds, used in the experiment, are “bottle brush” types, made of

oleophilic polyamide or polypropylene with stainless steel shaft. The area

of shaft should not be greater than 30% of cross section area of the bed

otherwise it will affect the efficiency.

7.9

Void ratio of the bed (ε) is around 0.845 to 0.96

7.10


7.11

Within the valid range of model, error in efficiency prediction is less than ±

10%.





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Table 8-2 Influent parameters of dynamic fibrous bed coalescer







Rotating speed + within the upper limit

Porosity -

Bed height +

Tortousity of bed +Presence of surfactants -

Temperature +



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9) Metal wool bed coalescer

1. Process abbreviation: WCC

2. Process description: Metal wool bed coalescer is one of fibrous bed coalescer

that uses disorderly (random) or woven fiber material, like steel wool for kitchen

use, as a bed. The bed is actually not necessary to be of metal. It is just named torefer to general appearance of bed.

3.

Reference : Part 3, chapter 5

4.



following equation.

%100)()()()(35.3 36.003..003.023.0 ⋅⋅= −−

D

H

D

d

D

d VDCF F

c

cd

μ

ρ η

{9.1}

And %100≤d η

{9.2}


( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t C

C η

η

{9.3}


)1( d od

out

d C

Q

QC η −⋅⋅= mg/l {9.4}


∑=max

min

d

d

d C C

mg/l

{9.5}






upstream process.


)1000//)(1( oiloout C C QQ ρ −−= m3/h {9.6}






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4.10.2 Pressure drop (P): Pressure drop is calculated from Hazen –



coalescer column.

167.185.1

582.6 ⎟ ⎠ ⎞⎜

⎝ ⎛ ⎟⎟

⎠ ⎞⎜⎜

⎝ ⎛ =

D H

C V P HW

m

{9.8}


Table 9-1 Related parameters of metal wool bed coalescer


the program

Unit used in the

program

CHW Hazen William’s C, depanding on

material. C of 130 is recommended forsteel column.

Constant = 130


D Diameter of coalescer column or of bed,

which should be relatively closed.

Dcc m

dF Diameter of fiber element dF m

H Bed height (height of granular bed) H m



ρc Density of continuous phase, in this case,water

Denc Kg/m3



wastewater

Muc N.s/m2

(= 1000 cp)




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Metal wool bed

coalescer

(WCC-??)

Collector

size = d p

Void ratio = ε

Bed height

= HEffluent

Oil outlet

Influent

Flow = Q

Velocity = V

=Q/A

Cross section area

= A

Fig. 9-1a Icon of metal wool bed coalescer Fig. 9-1b Graphical diagram of metal wool bed

coalescer


7.1 The beds used in the experiment are highly disorderly bulk of stainless

steel fiber, dF = 75 microns, and steel wool, dF = 40 microns (see fig.

5.4.1-4). However, only the latter case, which raw experimental data is

available, is used to develop the model. The minimum size of oil droplet

tested is 1 micron.

7.2 Tested Reynolds number is between 840 to 2470.

7.3

Porosity of the bed (ε) is around 0.95. But there is not sufficient data toinclude it into the model.

7.4 Diameter of the coalescer (D) = 5 cm. However, according to rigidity

and, controversially, density uniformity of this type of bed, the diameter

in the model should be scaled up or down without causing serious error.

7.5 Height of the coalescer bed (H) is between 0.07 to 0.21 m.

7.6 Velocity (V) is between 1 to 2.5 cm/s or 36 to 90 m/h.

7.7

Inlet concentration is around 1000 mg/l.


7.9

Within the valid range of model, error in efficiency prediction is less than

± 10%.


only.

8.




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Table 9-2 Influent parameters of metal wool bed coalescer


is increased





Porosity not sufficient data to verify but should be -

Bed height +

Tortousity of bed + but can cause clogging

Presence of surfactants -Temperature +



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10) Dissolved air flotation

1. Process abbreviation: DAF

2. Process description: Dissolved air flotation (DAF) in this case does not include

the coagulation/flocculation process, which is separated into another module.


4.


4.1 Graded efficiency (η d ): Graded efficiency of the process is governed by

SIEM’s model (INSA thesis 1983) and its scale-up procedure, derived in

the scope of work of this program.

SIEM’s model

%100)1())(

2

3(

,

exp

⋅−⋅=Φ

−bd

H

AV

ref d eCF αη

η {10.1}

5919.0exp )(009005.0)( theoη αη = {10.2}

diff Int sed theo η η η η ++=

26

)10

(2

3

b

Int d

d −⋅

=η {10.3}

r c

sed V

d g

μ

ρ η

18

)10( 26−⋅Δ= {10.4}

3/2))273(

(9.0br c

Diff d dV

T K

μ η

+= {10.5}

c

bwater air br

gd U V

μ

ρ

18

2

/Δ

== {10.6}

And %100≤d η {10.7}

The model is valid only when Φ/AV = 0.0516. However H can vary.

Scale-up from SIEM’s condition by population balance method

1) Calculate the reference efficiency (ηd,ref ) of the model at required

height (Hreq

), average bubble diameter (d b) and droplet sizes (d) using

eq. 10.1 to eq.10.7. Use Φ /AV = 0.0516 in order that the operating

condition of SIEM still holds.

2) Scale up the area from 0.01767 m2 (Amodel) to required area (Areq). At

this step, SIEM’s operating condition still holds. So efficiency from

above equations remains the same. This required area could be

approximated from recommended hydraulic loading rate (Vreq) and

ratio of pressurized water to wastewater ((Q pw/Q)req). Refer to

reference for more detail.

req

req pw

req

reqV

Q

QQ

A

⎟ ⎠

⎞⎜⎝

⎛ +

=

)(1

{10.8}

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3)

Find Φref , corresponding to the area Areq, by following equation,

01767.0

102.4 7

mod

mod

req

el

el

req

ref

A

A

A −×

=Φ⋅=Φ m3/s {10.9}

4)

Find τref , corresponding to the height Hreq, by following equation,

3600

1

00046.0mod

mod

⋅=⋅= req

el

el

req

ref H

H

H τ τ Hour {2.610.10}

Change Φ and τ from SIEM’s condition by population balance model

5)

From population balance method, calculate κ2,ref corresponding to

Areq, Hreq, τref and Φref from the reference efficiency (from item 1)) by

the following equations. Please note that, at this point, SIEM’s

condition still holds. κ2,req has to be calculated separately for each

droplet diameter.

ref ref

ref d

ref

τ

η κ

⋅Φ

−−=

)1ln( ,

,2 {10.11}

Or)(

,,21 ref ref ref eref d

τ κ η

Φ−−= {10.12}

6) Find Φreq from required ratio of pressurized water to wastewater (see

reference for the recommended value) by following equations.

3600

Q R

V

V Q

V

V

pw

air pw

pw

air ⋅⋅=⋅=Φ m3/s {10.13a}

Then, from Henry’s law

Q R H K molmT PP y atm ⋅⋅⋅⋅×⋅+⋅−⋅=Φ −))/(10082.0()273()( 33 {10.13b}

For air, y = 1. H is Henry’s constant as molair /(m

3

water .atm). Henry’sconstant of air can be calculated from the following equation.123 10)472.122745.00039.000002.0( −⋅+⋅−⋅+⋅−= T T T H {10.14}

7) Choose τreq from recommended criteria (see reference).

8) To change Φ and τ from SIEM’s, the following procedure is

recommended and precautions should be noted.

• To decrease ( req < ref ) and increase τ (τreq > τref ):

In this case, κ2 is assumed to remain the same and be equal to

κ2,ref . Φreq and τref are used. The efficiency can be estimated by eq.

10.15a.)( ,21 ref reqref ed

τ κ η

Φ−−= {10.15a}

The calculated efficiency will be lower than the real value.

• To decrease ( req < ref ), as well as, τ (τreq < τref ):

In this case, κ2 = κ2,ref . Φreq and τreq are used. The efficiency can

be calculated by eq. 10.15b. The calculated efficiency will be

lower than the real value.)( ,21 reqreqref ed

τ κ η

Φ−−= {10.15b}

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• To increase ( req > ref ) and decrease

τ

(τreq <

τref ):

Like the former case, the efficiency can be calculated by eq.

10.15b.

•

To increase ( req > ref ), as well as,

τ

(τreq >

τref ):

This case is not feasible because it means that we have to

decrease wastewater flowrate and increase pressurized water

flowrate.

There is no obvious limit for the 4 adaptations, shown above.

However it is recommended to use the values of each parameter

(d, d b, C, etc.) within general range (see reference).

It must be noted that the graded efficiency in this case is independent of

source of water that is used as pressurized water.

4.2 Total efficiency (η t ): The value depends on the source of water that is used

as pressurized water. In the program, it is assumed that DAF effluent isused to prepare pressurized water.

%100)(

⋅−

=o

ot

C

C C η

{10.16a}

4.3 Graded outlet oil concentration in water outlet flow (C d ): In the program, it

is assumed that DAF effluent is used to prepare pressurized water. Thus

residual oil in the effluent is recycled. So oil of certain droplet sizes may

accumulate in the system, depending on their ηd.

dilod d

out

d C Q

QC ,)1( η −⋅= mg/l {10.17}

t

od

d

r d

dilod Q

QC

R

R R

R

C ⋅−−

+

−−+=

−

1)1(1

)1))1(1

((1max

,

η

η mg/l {10.18}

The r max is an assumed number of loop, which effluent is recycled until the

concentration reaches steady stage. Ideally, r max must approach infinity.

However, the value of r max in the program is set at 30, which is generally

sufficient to make the equation reach steady stage (esp. when ηd > 20%). If

the value of Cod,dil from r = 30 differs from Cod, dil at r = 29 more than 10%,

the program will display the warning box, showing that the oil may

accumulate in the system.


∑=max

min

d

d

d C C

mg/l

{10.19}





4.7

Inlet flow (Q): Inlet flow of the process is equal to the outlet flow of theupstream process.

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IV-74


)1000//)(1( oiloout C C QQ ρ −−=

m3/h

{10.20}


oiloil QQQ −= m3/h {10.21}


4.10.1 Ratio of air/oil (W/W)

1000

3600

0

⋅⋅

⋅Φ=

C QW

W air req

oil

air ρ

kg air / kg oil {10.22}

4.10.2 Theoretical energy (watt) required for air compressor:

pw

atmcomp

air Qair MW

air Conc

P

PT RPower ⋅⋅

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡−⎥

⎦

⎤⎢⎣

⎡

⋅+

=

−

)1000/)((

)(1

4.0

)273()

4.1

14.1(

η

{10.23}

R air = universal gas constant (8.314)

1000

)().(

H air MW P yair Conc

⋅⋅⋅= mg/l

{10.24}

4.10.3 Theoretical energy required for pressurized water pump:

pump

atmc

pump

atm pw PPgQ RPPQPower

η

ρ

η ⋅⋅−⋅⋅⋅⋅

=⋅

−⋅=

3600

10)(

3600

)( watt {10.25}

P is measured in atm.

4.10.4 Hydraulic loading rate

A

RQ

V

)1( +

=

m/h

{10.25}

4.10.5 Retention time (based on total flow (Q+Q pressurized water ):

60⋅=V

H τ min {10.25}

5.


Table 10-1 Related parameters of DAF


the program

Unit used in the

program

A Cross section area of DAF column A m2

d b Diameter of bubble db m

H Column height DAFH m

P Absolute pressure of saturator DAFP atm

R Recycled ratio (R = Q pressurized water /Q) R

ηcomp, η pump Efficiency of air compressor and pressurized

water pump (always < 100%, 60-70% is

recommended)

Constant = 70%

Note: Other parameters are internally used. Users do not need to input. For list of others parameters, see reference.

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IV-75




(DAF-??)

Pressurized water

flow = Q pw

Oil outlet

Effluent

Influent

H

Area = A

Fig. 10-1a Icon of DAF Fig. 10-1b Graphical diagram of DAF


7.1 Inlet oil concentration should not be greater than 1,200 mg/l (before

dilution) or 435 mg/l (after dilution). Using the model with higher oil

concentration will result in underestimating of efficiency.

7.2 SIEM’s model is tested at the following operating condition;

• Φ/AV = 0.0516. Only this value must be used in the equations. As

long as this value is fixed, SIEM’s operating condition still holds and

the model is still valid. • Retention time, based on total flowrate (Qt), is around 25 minutes.

•

Droplet diameter (d) tested is between 2 to 40 microns.

• Diameter of air bubbles (d b) varies from 15 to 130 microns. Tested

average bubble diameter is 70 microns, which is used to verify the

model, and standard deviation of bubble diameters is 34.5 microns. The

range of bubble sizes is common for commercial pressurized water

system or saturator. The pressure of the test system is 4 atm (absolute).


• Tested wastewater flowrate (Q) is 3.9 cm3/s (3.9e-6 m3/s)

•

Tested water depth (H) is 0.70 m. H can be freely changed as long as

(Φ/AV) is fixed. Anyway, H around 1.8 to 2.7 is recommended by API. • Diameter of flotation column is 0.15 m Cross section area of column

(A) is 0.01767 m2.

• Ratio of pressurized water to wastewater (Q pw/Q) is 1.76.

•

Air to pollutants ratio used is around 0.12 kg. air/ kg. oil.

• Ratio of number of bubble/ oil droplet tested is around 1.4 oil droplet/ 1

air bubble.

• Hydraulic loading rate or flow velocity (V), based on Qt, is 1.6 m/h

7.3

Within the valid range of model, error in efficiency prediction is less than ±

20%. If SIEM’s condition does not holds and procedure described in item

8) is used, error in efficiency prediction depends on difference between

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IV-76

SIEM’s and actual condition. However, the predicted efficiency is usually

lower than actual value.



7.6

It is assumed that DAF is operated at Patm. Thus Equations and some

constants, e.g. air density, are fixed and valid for Patm only.

8.




Table 10-2 Influent parameters of DAF


is increased

Retention time +

Droplet diameter +

Diameter of bubble -

Air flowrate +

Column height +

Presence of transfer compound ± see reference


Turbulence in column ± see reference



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11) Two-phase hydrocyclone

1. Process abbreviation: 2CY

2. Process description: The process is based on THEW type, liquid-liquid

hydrocyclone.


4.



following equation.

For d ≥ dc, %100=η {11.1}

For d < dc,

%1002)2nD

(0.1862)2nD

((

2)2

nD(0.186

2d

(R

dη ⋅−

−

= {11.2}

R d (Radial distance from axial axis to entry position of droplet “d”

(Z=0))can be calculated from the following equations. If R d in eq. 11.3a is

equal to Dn/2, the corresponding “d” will be equal to dc.

∫=∫L

0 W

dZdR

zvvR U

dR {11.3a}

R

V 2

18μ

2)6-10Δρ(dU ⋅

⋅= m/s {11.3b}

0.65)R

nD)(

2i

πD

Q(V = m/s {11.3c}

3

19.1

2

63.81233.3 ⎟⎟ ⎠

⎞⎜⎜⎝

⎛ +⎟⎟

⎠

⎞⎜⎜⎝

⎛ −+−=

z R

R

z R

R

z R

R

zW

W {11.3d}

2))

2

tan(Znπ(0.5D

QzW

β ⋅−

= m/s {11.3e}

)2

tan(2

β ⋅−= Z

D R n

z m {11.3f}

)2/5.1tan(

)(25.0o

n D L = m {11.3g}

For THEW’s type hydrocyclone, when Z = L:

)2/(186.0 nVZZ D R = {11.3f}


∑ ⋅−

=max

min

%100)1(

1 d

d f

od d

o

t R

C

C

η η

{11.4}

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IV-78


)1(

)1(

f

od d

d R

C C

−

−=

η

mg/l

{11.5}


∑=max

min

d

d

d C C mg/l

{11.6}

4.5 Graded outlet oil concentration in oil outlet flow (C oild ): Unlike other true

separation process, hydrocyclone only concentrates oil. Thus concentrated

oily wastewater, not pure oil, is obtained at oil outlet (overflow) port.

f

od d overflowd oild

R

C C C

η == ,

mg/l {11.7}

4.6 Total outlet oil concentration in oil outlet flow (C oil):

∑=

max

min

d

d

oild oil C C

mg/l

{11.8}


upstream process.


)1( f out RQQ −= m3/h {11.9}


f oil RQQ ⋅= m3/h {11.10}

4.10

Customized output :

4.10.1 Theoretical cut size (d c): Cut size is calculated from item 4.1.

4.10.2 Pressure drop (P): Pressure drops across inlet/overflow (Po) and

inlet/underflow (Pu) ports of 2-phase hydrocyclone are governed

by the following equations.

1611.0

4

3.2

)1(

6.2)3600/(16 ⎟

⎟ ⎠

⎞⎜⎜⎝

⎛

−⋅=Δ

f n

o R D

QP bar {11.11a}

4

2.2)3600/(6.4

n

u D

QP =Δ bar {11.11b}


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Table 11-1 Related parameters of two-phase hydrocyclone

Parameter DescriptionVariable name

in the program

Unit used in the

program

dc Cut size dc micronDn Nominal diameter of hydrocyclone Dn m

R f Split ratio (Qoverflow/Q), R f < 1.

Recommended value of Qoil is 1.8 to 2

times of inlet oil flowrate.

Rf

Note: Other parameters are internally used. Users do not need to input. For list of others

parameters, see reference.

6.



Di

L1

D

Dn

Ds

L3

Do

θ

β

L

Oil out

Water out

Water in

2-phase

hydrocyclone

(2CY-??)

Dn/D=0.5, Ds/D=0.25, Do/D<0.05, L1/D=1, L3/D=15-20 ,

β =1.50o , θ =20o ,Di/D=0.25 for 1 inlet and 0.175 for 2 inlet ports,

total length/D =45 (approx.)

Fig. 11-1a Icon of 2-phase

hydrocyclone

Fig. 11-1b Graphical diagram of 2-phase hydrocyclone

7.

Constraints and limitations.

7.1 The model is valid for THEW hydrocyclone or other cyclones with

relative identical geometry.

7.2 It is recommended to use the model only for droplet diameter of 20

microns or greater. For smaller droplet, it can also be applied, but forcomparison only. In analysis mode and design mode when “Find

efficiency” is selected, efficiencies of droplets smaller than 20 microns

are assumed to be 0%. ηd of oil is 100%.

7.3

The equations are valid for the hydrocyclone with 2 inlet ports only.

7.4

Overflow quantity (Qoveflow) is usually small, not greater than 10%. Its

effect on velocity profiles and efficiency is small, thus, negligible.

Recommended Qoveflow is 1.8 to 2 times of inlet oil flowrate.

7.5 The model tends to predict lower efficiency when d < d80% and higher

efficiency when d > d80%. Error of cut size prediction is around 10-20%,

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e.g. if predicted cut size is 50 microns, observed cut size should be

around 40 – 45 microns. For more details, see reference.

7.6 Graded efficiency (ηd) in this case is based on ratio between outlet oil

quantity at water outlet port to that of inlet wastewater. Effect of split

flow is not yet taken into account.

8.




Table 11-2 Influent parameters of two-phase hydrocyclone



Flowrate +

Droplet diameter +

Split ratio is

Inlet oil concentration is

Pressure drop +


Temperature +



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12) Three-phase hydrocyclone

1. Process abbreviation: 3CY

2. Process description: The process is based on 3-phase hydrocyclone, initiated by

MA and AURELLE. Geometry of liquid-liquid separation of the hydrocyclone is

based on Thew type. For solid-liquid, it is based on Rietema type. It can be usedfor simultaneous separation of oil and suspended solids from wastewater.

Calculation procedure and equation are relatively identical to that of 2-phase

cyclone with only little modification. Solid removal efficiency is not included in

this program.




following equations. Dn in this case is equal to Do and L is equal to L5 (See

graphical diagram).

For d ≥ dc, %100=η {12.1}

For d < dc,

%1002)

2

nD(0.1862)

2

nD((

2)2

nD(0.186

2d

(R

dη ⋅

−

−= {12.2}

R d (Radial distance from axial axis to entry position of droplet “d”

(Z=0))can be calculated from the following equations. If R d in eq. 12.3a is

equal to Dn/2, the corresponding “d” will be equal to dc.

∫=∫L

0 W

dZdR

zvvR U

dR {12.3a}

R

V 2

18μ

2)6-10Δρ(dU ⋅

⋅= {12.3b}

0.65)R

nD(

2

iD4

π

(Q/2)0.676V

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

= {12.3c}

3

19.1

2

63.81233.3 ⎟⎟ ⎠

⎞⎜⎜⎝

⎛ +⎟⎟

⎠

⎞⎜⎜⎝

⎛ −+−=

z R

R

z R

R

z R

R

zW

W {12.3d}

2/2))tan(Znπ(0.5D

QzW

β ⋅−= {12.3e}

)2

tan(2

β ⋅−= Z

D R n

z {12.3f}

)2/5.1tan()(25.0 o

n D L = {12.3g}

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For THEW’s part hydrocyclone, when Z = L:

)2/(186.0 nVZZ D R = {12.3f}


∑ ⋅−=

max

min

%100)1(

1 d

d f

od d

o

t R

C

C

η η

{12.4}


)1(

)1(

f

od d d

R

C C

−−

= η mg/l

{12.5}


∑=max

min

d

d

d C C mg/l 12.6}


separation process, hydrocyclone only concentrate oil. Thus concentratedoily wastewater, not pure oil, is obtained at oil outlet (overflow) port.

f

od d oild

R

C C

η = mg/l {12.7}


∑=max

min

d

d

oild oil C C mg/l {12.8}


upstream process.


)1(SS f out R RQQ −−= m3/h {12.9}


f oil RQQ ⋅= m3/h {12.10}


4.10.1 Theoretical cut size (d c): Cut size is calculated from item 4.1.

4.10.2 Purged flow for SS removal:

SS ss RQQ ⋅=

{12.11}4.10.3

Pressure drop (P): Pressure drops across inlet/overflow (Po) and

inlet/underflow (Pu) ports of 2-phase hydrocyclone are governed

by the following equations.

4D

2.12(Q/3600)49.8water ΔP = bar {12.12a}

4D

2.34(Q/3600)21ssΔP = bar {12.12b}

4D

2.03(Q/3600)55

oilΔP = bar {12.12c}

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Please not that R SS is not included in the model so the pressure drop for SS

port and water port are estimated value only. But for oil port, R f is usually

small so ΔPoil is relatively accurate and hardly affected by R f .


Table 12-1 Related parameters of three-phase hydrocyclone


in the program

Unit used in the

program


D Diameter of the biggest cylinder of

hydrocyclone (refer to related graphic)

D3cy m

R f Split ratio (Qoil /Q), Rf < 1.

Recommended value of Qoil is 1.8 to 2times of inlet oil flowrate.

R SS Split ratio (QSS/Q). Recommended value

is 0.2.

Note: 1. Other parameters are internally used. Users do not need to input. For list of others


2. Rss is calculated by Yoshioka and Hotta relation [30]: 1-R f =0.95/((Du/Ds)4+1).




DoDDs

DiDu

Dp

L5 L3L1L3

L4

3-phase

hydrocyclone

(3CY-??)

Note: Di/D=0.25 for 1- inlet and 0.175 for 2- inlet,

Do/D=0.43,Ds/D=0.28, Du/D=0.19, Dp/D=0.034,

L1/D=0.4,L2/D=5, L3/D=15, L4/D=0.3, Solid-liquid part cone

angle=12o , for liquid-liquid part=1.5

o

Fig. 12-1a Icon of 3-phase

hydrocyclone

Fig. 12-1b Graphical diagram of 3-phase hydrocyclone


7.1

The model is valid for THEW hydrocyclone or other cyclones with relative

identical geometry.

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7.2 It is recommended to use the model only for droplet diameter of 20

microns or greater. For smaller droplet, it can also be applied, but for

comparison only. In analysis mode and design mode when “Find

efficiency” is selected, efficiencies of droplets smaller than 20 microns are

assumed to be 0%. ηd of oil is 100%.

7.3

The equations are valid for the hydrocyclone with 2 inlet ports only.

7.4

Purged quantity at oil outlet port (Qoil) is usually small, not greater than

10%. Its effect on velocity profiles and efficiency is small, thus, negligible.

7.5 The model tends to predict lower efficiency when d < d80% and higher

efficiency when d > d80%. Error of cut size prediction is around 10-20%,

e.g. if predicted cut size is 50 microns, observed cut size should be around

40 – 45 microns. For more details, see reference.

7.6 SS removal coefficient is not calculated since it is not major scope of work

of this thesis so it cannot connect to other model. Only purged flow of SS

port is calculated

7.7

R SS is not included in the model so the pressure drop for SS port and water

port are estimated value only. But for oil port, R f is usually small so ΔPoil is

relatively accurate and hardly affected by R f .

7.8 Graded efficiency (ηd) in this case is based on ratio between outlet oil

quantity at water outlet port to that of inlet wastewater. Effect of split flow

is not yet taken into account.




Table 12-2 Influent parameters of three-phase hydrocyclone



Flowrate +

Droplet diameter +

Split ratio (R f ) is

Inlet oil concentration isPressure drop +


Temperature +



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13) Ultrafiltration

1. Process abbreviation: UF

2. Process description: Flux calculation of UF in the program is based on film

model and resistance model. Flux prediction is available in DESIGN mode only.


4.


4.1 Graded efficiency (η d ): For stabilized emulsion wastewater, oil removal

efficiency of UF can be safely assume to be 100%. The program will use

the value of CF.100%.

%100⋅= CF d η

{13.1a}

For wastewater containing free oil or non -stabilized emulsion, the

efficiency is lower but, somehow, unpredictable. Anyway, for such

wastewater, the use of UF is not necessary. However the program will,nonetheless, assume that the efficiency is CF.100%.

4.2 Total efficiency (η t ): Total efficiency falls into the same case as that of

hydrocyclone. For UF, users normally set their final volume of filtrated

wastewater or retentate (Volretentate), which will be used for total efficiency

calculation. UF calculation in the program is based on batch system

without additional feed during operation period. So the concentration

depends on initial wastewater volume (Volo) and feed duration (tf )

∑∑ ⋅−

−=⋅

−

−=

max

min

max

min

%100

)1

1(

)1(1%100

)1(

)1(1 d

d

od d

o

d

d

o

retentate

od d

o

t

F

C

C

Vol

Vol

C

C

η η η

{13.1b}

F is factor of concentration, which is specified by user.


)1(

)1(

o

retentate

od d

d

Vol

Vol

C C

−

−=

η mg/l {13.2}


∑=max

min

d

d

d C C

mg/l

{13.3}


separation process, UF only concentrate oil. Thus concentrated oily

wastewater, not pure oil, is obtained as retentate. Granulometries of the

retentate were not studied. Coalescence and partial destabilization, which

leads to formation of oil film, were reported. However, to be on the safe

side, the program will assume that there is no coalesce occurring.

F C VolVol

C C od d

oretentate

od d oild η

η ==

)/( mg/l {13.4}

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∑=max

min

d

d



upstream process.4.8 Water outlet flow (Qout ): Actual water outlet flow from the membrane is the

product of permeate flux, which varies with time, and membrane area.

However, since the process is usually designed as batch system, outlet flow

can be chosen freely, providing that permeate storage tank is big enough.

User can freely specify permeate discharge time (td). To imitate a

continuous process, it can be assumes that default permeate discharge

duration (td) is equal to wastewater inlet duration.

)1

1()(

F t Q

t

Volt QQ f

d

retentate f

out −⋅⋅=

−⋅= m3/h

{13.6}

4.9

Oil outlet flow (Qoil): Like water outlet flow, oil outlet flow or retantateflow depends on its discharge duration (tdoil). This duration should be equal

to that of tf and td to fully imitate continuous process.

doil

f

doilretentateoilt F

t Qt VolQ

⋅

⋅== / m3/h

{13.7}


4.10.1 Permeate flux and volume evolution: Flux varies with time since

concentration of the feed (actually, retentate) increases from

continuous loss of its permeate. The program can calculate the

flux under the assumption that there is no fouling, which is

practically proven in case that suitable pretreament is provided.Flux will be calculated using 2 models, i.e. Film model and

Resistance model, and the related equations,

)ln(C

C kV J

g β = l/(m2-h) {13.8}

t m

t

PV R

P J

⋅⋅+=

α φ ' l/(m2-h) {13.9}

))(0239.0( A B

C BC Ae J J oo

−−= {13.10}

The values of K, Cg, etc. for certain wastewaters are provided in

help file.

If two types of wastewater with different values of k, Cg,

etc.(such as microemulsion mixes with macroemulsion.) are

encountered, the flux will be calculated using weight average

method (eq. 13.11). This calculation exists only in design mode.

mixoil,C

mixCoil,mic, J

micoil,C

mixCoil,:mac J

macoil,C

mix J +

= {13.11}

Evolution of permeate flux and volume is governed by the

following equation.

AdtJ(c)dVol ⋅= {13.12}

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Integration of eq. 13.11 is carried out using step method by

dividing total permeate volume (eq. 3.12) into 100 parts.

4.10.2 Time required to complete one batch for a specified amount of

wastewater : It is also governed by eq. 13.12. It must be noted that

the program can calculate the flux/time evolution under the

condition that there is no additional inlet wastewater during UF

operation.


Table 13-1 Related parameters of ultrafiltration


the program

Unit used in the

program

A Membrane area AreaUF m2

C’g, C’

g2 Gel concentration for low range of

concentration (if any) of 1st and 2nd emulsion

Cg1low, Cg2low % oil volume/total

volume

Cg, Cg2 Real gel concentration of 1st and 2

nd emulsion

(see reference)

Cg1High,

Cg2High

% by volume of oil

Cref1, Cref2 Reference concentration of 1st and 2

ndemulsion

(conc. that is used to acquire the value of

model constants)

Cref1, Cref2 % by volume of oil

Co1/(Co1+Co2

)

Oil concentration ratio of wastewater no.1 to

total oil concentration[2], always < 1

Rofoil1 in the unit of bar,

(m/s) and l/h-m2

k’1, k’2 Constant for film model for low range of oil

concentration of 1st and 2nd emulsion

Kreflow1,

kreflow2

in the unit of bar,

(m/s) and l/h-m2

k 1, k 2 Constant for film model for high range of oil

concentration of 1st

and 2nd

emulsion

Krefhigh1,

krefhigh2

in the unit of bar,

(m/s) and l/h-m2

Pt Transmembrane pressure UFP bar

Q Flowrate of inlet wastewater Q m3/s

Rm (or R’m) Modified membrane resistance (= membrane

resistance + fouling resistance (if any))

Rm in the unit of bar,

(m/s) and l/h-m2

td Duration for discharge the permeate (after UF

operation is finished), recommended to be

equal to tf .

td h

tdoil Duration for discharge the retentate (after UF


equal to tf .

tdoil h

tf Duration to fill the storage tank by inlet

wastewater before the wastewater is stopped

and UF operation starts.

tf h

V Recirculation velocity UFV m/s

F Concentration factor (Volo /Volretentate) ConcF

α1, α2 Constant for resistance model of 1st and 2

nd

emulsion

alpharef1,

alpharef2

in the unit of bar,

(m/s) and l/h-m2

β1, β2 Constant for film model of 1st and 2

nd emulsion bref1, bref2 in the unit of bar,

(m/s) and l/h-m2

φ1,φ2 Constant for film model of 1st and 2

nd emulsion Phiref1,Phiref2 in the unit of bar,

(m/s) and l/h-m2



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Ultrafiltration

(UF-??)

UF

Permeate

Retentate

Membrane

Feed

pump

Storage

tank

Feed

Po

Pi

Pp

Heat

exchanger

Pt = ((Pi+Po)/2)-P p

V

No influent added during filtration process

Fig. 13-1a Icon of ultrafiltration Fig. 13-1b Graphical diagram of ultrafiltration


7.1 Flux calculation of mixed wastewater exists only in design mode.

7.2 The process can be used for microfiltration and nanofiltration if they can be

represented by film model and resistance model.

7.3 The program can calculate only batch operation.

7.4

Accuracy of the models are governed by that of constants used, and

deviation of real operation from their assumption, thus unpredictable. If

possible, it is recommended to perform UF test, using real wastewater.




Table 13-2 Influent parameters of ultrafiltration



Viscosity of feed -

Temperature +

Membrane properties ±

Reaction between feed and membrane ±



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14) Reverse osmosis

1. Process abbreviation: RO

2. Process description: RO in this case is used as a finishing treatment process to

treat the effluent of UF or distillation only. Its main purpose is to remove soluble

pollutants, normally surfactants/co-surfactants, left after oil separation.Furthermore, process calculation is based mainly on specific data from

manufacturer. Thus, the module exists only in ANALYSIS mode.



4.1 Graded efficiency (η d ): It is assumed to be 100%. CF is not allowed in this

process.

4.2 Total efficiency (η t ): It is assumed to be 100%.

4.3

Graded outlet oil concentration in water outlet flow (C d ):Cd = 0 mg/l


C = 0 mg/l


separation process, RO only concentrate oil. Thus concentrated oily

wastewater, not pure oil, is obtained as retentate. The program will assume

that droplet sized and numbers are not changed.

F C VolVol

C C

od d oretentate

od d

oild

η η

==)/(

mg/l {14.1}


∑=max

min

d

d



upstream process.

4.8 Water outlet flow (Qout ): Actual water oultet flow from the membrane is the

product of permeate flux, which varies with time, and membrane area.

However, since the process is usually designed as batch system, outlet flow

can be chosen freely, providing that permeate storage tank is big enough.User can freely specify permeate discharge time (td). To imitate a

continuous process, it can be assumes that default permeate discharge

duration (td) is equal to wastewater inlet duration.

)1

1()(

F t

t Q

t

Volt QQ

d

f

d

retentate f

out −⋅⋅

=−⋅

= m3/h {14.3}

4.9 Oil outlet flow (Qoil): Like water outlet flow, oil outlet flow or retantate

flow depends on its discharge duration (tdoil). This duration should be equal

to that of tf and td to fully imitate continuous process.

doil

f doilretentateoil

t F t Qt VolQ

⋅⋅== / m3/h

{14.4}

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4.10.1 TOD of water outlet flow (TODwater ): Since characteristic of inlet

wastewater for RO varies only slightly. TOD removal efficiency

(ηTOD) is within the certain range around 70-90% (see reference).

So the program will calculate the TOD from TODo and the

efficiency, using the following equation.

)/11(

1)1())((

F mg

mgC TODTOD TOD

oil

TODoowater −

⋅−⋅⋅−= η {14.5}

4.10.2 TOD of oil outlet flow (TODoil):

F F

TODTODTOD water ooil ⋅−⋅−= ))1

1(( {14.6}


Table 14-1 Related parameters of RO


in the program

Unit used in the

program

mgTOD/

mgoil

Unit TOD of oil. For more information, see

reference

unitTOD

td Duration for discharge the permeate (after UF


equal to tf .

td h

tdoil Duration for discharge the retentate (after UF

operation is finished), recommended to beequal to tf .

tdoil h

tf Duration to fill the storage tank by inlet

wastewater before the wastewater is stopped

and UF operation starts.

tf h

TODo TOD of the inlet wastewater TODin mg/l

F Concentration factor (Volo /Volretentate) ConcF

ηTOD TOD removal efficiency. It includes only

soluble TOD. TOD from oil is not included.

effTOD %

Note: 1. Other parameters are internally used. Users do not need to input. For list of others parameters, see reference.



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RO

Reverse osmosis

(RO-??)

Permeate

Retentate

Membrane

Feed

pump

Storage

tank

Feed

Po

Pi

Pp

Heat

exchanger

Pt = ((Pi+Po)/2)-P p

V

No influent added during filtration process

Fig. 14-1a Icon of RO Fig. 14-1b Graphical diagram of RO


7.1 The process is included in the program to fulfil the entire process train of

oily wastewater treatment only. Thus, its calculation is based on data from

researches, rather than mathematical model.

7.2 The process should be connected only to the water outlet port of UF or

distillation since it can used only with oil-free water or water with only

trace of oil. If connected to other unit, the program will display warning.

7.3 The program can calculate only batch operation.

7.4

Calculated TOD is an internal result of the model. It cannot be exported to

other process because of programming limitation.

7.5 This module is available only in ANALYSIS mode.

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15) Heteroazeotropic distillation

1. Process abbreviation: HD

2. Process description: Heteroazeotropic distillation is an enhanced distillation

process by addition of certain chemical, usually hydrocarbons, as an entrainer to

lower the boiling point of the system and extract the water from the waste to betreated. The process can be used to treat slop or UF retentate from cutting oil

treatment or concentrated oily wastewater.




process.



Cd = 0 mg/l4.4 Total outlet oil concentration in water outlet flow (C ):

C = 0 mg/l

4.5 Graded outlet oil concentration in oil outlet flow (C oild ): Outlet oil is in the

form of water-free oil (100% oil).

4.6 Total outlet oil concentration in oil outlet flow (C oil): Outlet oil is in the

form of water-free oil (100% oil).


upstream process.

4.8 Water outlet flow (Qout ): Water outlet flow is equal to water content of inlet

wastewater under the assumption that size of the process is sufficient tohandle inlet flowrate on real time basis.

)1000//)(1( oiloout C C QQ ρ −−= m3/h {15.1}

4.9 Oil outlet flow (Qoil): Oil outlet flow is equal to oil content of inlet

wastewater.



4.10.1 Required quantity of entrainer: Quantity of entrainer depends on

the type of entrainer and the quantity of water to be removed,

which can be calculated by the following equation.

H

H out entrainer

y

yQQ

)1( −= m3/h {15.3}

The values of yH (azeotropic composition) of certain entrainers

are provided in the help file.


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Table 15-1 Related parameters of heteroazeotropic distillation


in the program

Unit used in the

program

yH Azeotropic composition (Ratio of volume ofwater in ditillate to total distillate volume)

yH Vol/vol

Note: 1 Other parameters are internally used. Users do not need to input. For list of others




A z e o t r o p i c

Heterozeotropic

distillation (HD-??)

2 ph.vapor

Bubble curve

Pure H2O

Temperature

Azeotrope (H)

2 ph. liquid

1 ph.vapor +

1 ph. liquid

Pure

hydrocarbon x,y yH



of water

TH

Fig. 15-1a Icon of heteroazeotropic

distillation

Fig. 15-1b Graphical diagram of heteroazeotropic

distillation


7.1 Calculation is based on theoretical equation, regardless of distillation

column design.

7.2

There is some TOD present in the distillate, caused by volatile pollutants,

which depends on wastewater characteristic. Thus it can not be accurately predicted. Distillate TOD of 2000 –3000 mg/l is recommended for

distillation of UF retentate from cutting oil treatment.

7.3 Entrainer can be continuously reused.

7.4 If possible, pilot-test should be conducted to verify the value of yH and

observe other problems that may be present, such as release of hydrogen

sulfide.

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16) Stripping

1. Process abbreviation: ST

2. Process description: Stripping is reversed version of heteroazeotropic distillation.

It is an enhanced distillation process by addition of water, as an entrainer to

lower the boiling point of the system and extract the hydrocarbon from the wasteto be treated. The process can be used to treat water with trace volatile

hydrocarbons.




process.



Cd = 0 mg/l4.4 Total outlet oil concentration in water outlet flow (C ):

C = 0 mg/l

4.5 Graded outlet oil concentration in oil outlet flow (C oild ): Outlet oil is in the

form of water-free oil.

4.6 Total outlet oil concentration in oil outlet flow (C oil): Outlet oil is in the

form of water-free oil.


upstream process.

4.8 Water outlet flow (Qout ): Water outlet flow is equal to water content of inlet

wastewater under the assumption that size of the process is sufficient tohandle inlet flowrate on real time basis.

)1000//)(1( oiloout C C QQ ρ −−= m3/h {16.1}

4.9 Oil outlet flow (Qoil): Oil outlet flow is equal to oil content of inlet

wastewater.



4.10.1 Required quantity of entrainer: Quantity of entrainer, in this case,

water, depends on the type and the qauntity of hydrocarbon to be

removed, which can be calculated by the following equation.

)1( H

H oilsteam

y

yQQ−

=

m3/h

{16.3}

The values of yH (azeotropic composition) of certain

hydrocarbons are provided in the help file.


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Table 16-1 Related parameters of stripping


in the program

Unit used in the

program

yH Azeotropic composition (Ratio of volume ofwater in ditillate to total distillate volume).

The value for various hydrocarbons are

recommended in the help file.

yH Vol/vol





S t r i p p i n g

Stripping (ST-??)

2 ph.vapor

Bubble curve

Pure H2O

Temperature

Azeotrope (H)

2 ph. liquid

1 ph.vapor +

1 ph. liquid

Pure

hydrocarbon x,y yH



of water

TH

Fig. 16-1a Icon of stripping Fig. 16-1b Graphical diagram of stripping

7.


7.1 Calculation is based on theoretical equation, regardless of distillation

column design.

7.2 The quantity of steam calculated by the program is not included the steam

for heating requirement.7.3 Entrainer ( water) can be continuously reused.

7.4 If possible, pilot-test should be conducted to verify the value of yH and

other problems that may be present.

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17) Chemical destabilization, coagulation-flocculation

1. Process abbreviation: CH

2. Process description: Calculation is based on reactor design, which can be applied

to any type of chemical or coagulant. Mixing is provided by mean of mechanical

mixers. The process is classified as inline concentrator and consists of 1 mixingtank and 3 flocculation tanks. Droplets smaller than 200 microns are assumed to

successfully coalesce to form droplets of 200 micros. For bigger oil droplets,

they are assumed to remain the same.



4.1 Graded efficiency (η d ): This parameter is actually not valid since no oil is

removed from the wastewater. However, the term ηd in this case represents

removal efficiency due to coalesce. From this definition, the value of ηd are

as follows,

For d < 200 microns, ηd = CF.100%

For d = or > 200 microns, ηd = 0%

However, for d=200 microns, its concentration (if already existed) will

increase since coalesced droplets are assumed to be of this size.

4.2 Total efficiency (η t ): This parameter is not valid since no oil is removed.

4.3 Graded outlet oil concentration in water outlet flow (C d ): It is assumed that

all oil droplets are coalesced or flocculated to form big oil drop of 200

microns in diameter. ThusCd = Co for d > 200 microns and Cd = 0 for other values of “d”.

For d= 200 microns, its Cd is summation of its initial concentration and the

sum of concentration of droplets smaller than 200 microns.


C = Co mg/l

4.5 Graded outlet oil concentration in oil outlet flow (C oild ): This parameter is

not valid since no oil is removed.

4.6 Total outlet oil concentration in oil outlet flow (C oil): This parameter is not

valid since no oil is removed.


upstream process.

4.8 Water outlet flow (Qout ): Outlet flow of the process is equal to the inlet

flow.

4.9 Oil outlet flow (Qoil): This parameter is not valid since no oil is removed.


4.10.1 Retention time:

60⋅=QV τ

min

{17.1}

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4.10.2 Product between G and τ

4.10.3 Power required (P) or Velocity gradient (G) of each tank: G and

P of each tank can be calculated by the following equations,

depending which value is specified by users.5.0

⎟⎟ ⎠ ⎞⎜⎜

⎝ ⎛ =

V PGμ

{17.2}

For turbine mixer,

ρ 53 Dn N P p= {17.3a}

The program features built-in Np for pitched blade turbine mixer

and propeller mixer.

For paddle mixer,3)(v A N Cd P c ⋅⋅⋅⋅= ρ {17.3b}

If turbine mixer option is selected, the program will calculate both

pitch blade and propeller type.

5.


Table 17-1 Related parameters of chemical destabilization


in the program

Unit used in the

program

A Area of one paddle blade (single side) AreaPaddle m2

Cd Drag coefficient of paddle blade Constant = 0.6

D Diameter of impeller of mixer DMixer m

G Velocity gradient Grapid,

Gfloc1,2,3

Sec-1

n Rotating speed of mixer RPS1-4 Rev/s

N Number of blades NumBlade

N p Power coefficient for turbine mixer Built-in

P Power required for mixer1 of mixing tank and

mixer 2,3,4 of flocculation tanks

Prepid,

Pfloc1,2,3

Watt

v Tip speed of paddle (= 2πn (D/2)) VolRapid,

VolFloc1,2,3

m3

V Volume of mixing tank and flocculation tanks VolRapid,

VolFloc1,2,3

m3

ρc Density of continuos phase, in this case,

water

Denc Kg/m3



6.



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Chemical

destabilizaion

(CH-??)

M

MEffluent

Flocculator Rapid mixing

Destabilization

chemicalsInfluent

G = 100-300 s-1

G = 50 s-1 G = 30 s-1 G = 20 s-1

The values of G in the figure are general values.

Fig. 17-1a Icon of chemical

destabilization

Fig. 17-1b Graphical diagram of chemical destabilization

7.


7.1

The program assumes that destabilization is successful and the oil droplets

coalesce to form bigger drops that can be decanted within 20 min. to 1

hour. So the final droplet size of 200 microns is proposed, Users can

change this value in the input screen.

7.2 Dosage of chemical varies with wastewater characteristic, type of

chemicals used. Thus it cannot be calculated and must be confirmed by jar

test.

7.3 For ANALYSIS mode, The configuration of the process is fixed, i.e. 1

mixing tank and 3 flocculation tanks, all with mechanical mixers.

7.4 For DESIGN mode, the program can be used for sizing 2 types of mixers,

i.e. turbine and paddle mixers. Turbine mixers are also divided into 2 cases,

i.e. pitched blade turbine and propeller. However, they will be calculated

simultaneously by the program.

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18) Biological treatment

1. Process abbreviation: Bio

2. Process description: Biological process in this case is used as a finishing

treatment process to treat the effluent of other process. It is included in the

program to fulfil the entire process train of oily wastewater treatment. The process is not intended to refer to any specific type of biological system. Its

calculation is based on user-specified total TOD and oil removal.



4.1 Graded efficiency (η d ): This parameter is equal to total efficiency.

4.2 Total efficiency (η t ): This parameter is specified by user.


od d d C C )1( η −=

mg/l

{18.1}


∑=max

min

d

d

d C C mg/l {18.2}


not valid since oil is not removed but destroyed or transform into other

forms.


valid since oil is not removed but destroyed or transform into other forms.4.7 Inlet flow (Q): Inlet flow of the process is equal to the outlet flow of the

upstream process.


flow.



4.10.1 TOD of water outlet flow (TOD): It can be calculated by the

following equation. TODo, unit TOD and ηTOD are given by users.

)1())()1(( TOD

oil

TODot omg

mgC TODTOD η η −⋅⋅−−= mg/l {18.1}


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Table 18-1 Related parameters of biological treatment


in the program

Unit used in the

program

mgTOD

/mgoil Unit TOD of oil. For more information, seereference file

unitTOD

TODo TOD of the inlet wastewater TODin mg/l

ηt Total oil removal efficiency. efft %

ηTOD TOD removal efficiency. It includes only

soluble TOD. TOD from oil is not included.

effTOD %



6.

Related graphics: Icon in analysis mode and graphic diagram for input screen forthis process are as shown below.

Biologicaltreatment

(Bio_??)

Influent

Effluent

Biological reactor

Clarifier

(if any)

Wasted biomass

(if any)

Fig. 18-1a Icon of biological treatment Fig. 18-1b Graphical diagram of biological treatment

7.


7.1

The process is included in the program to fulfil the entire process train of

oily wastewater treatment only. Thus, its calculation is based on data fromresearches, rather than mathematical model.

7.2 The module is available only in ANALYSIS mode.

7.3 Flowrate of wasted sludge is assumed to be negligible. Thus outlet flow is

equal to inlet flow.

7.4 It is assumed that there is no coalescence taking place within the process.

7.5 Calculated TOD is an internal result of the model. It cannot be exported to

other process because of programming limitation.

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IV-101

19) GAC filter

1. Process abbreviation: GAC

2. Process description: GAC filter in this case is used as a finishing treatment

process to treat the effluent of other process. It is included in the program to

fulfil the entire process train of oily wastewater treatment. Its calculation is basedon user-specified TOD removal. For oil removal, the efficiency is assumed to be

100%. Since its main objective is removal of residual pollutant, its inlet oil

concentration should be not greater than 50 mg/l. If the inlet wastewater contains

higher oil concentration, the program will display warning.



4.1 Graded efficiency (η d ): It is assumed to be 100%.



Cd = 0 mg/l


C = 0 mg/l


not valid since oil adsorbed into the bed.


valid since oil is adsorbed into the bed.


upstream process.


flow.

4.9 Oil outlet flow (Qoil): This parameter is not valid.


4.10.1 Adsorptive capacity (q): The program can predict adsorptive

capacity, using 2 well-known Isotherm models, i.e.,

• Lungmuir’s model: po

po

bC

aC q+

=1

mg/g {19.1a}

• Frendlich’s model: )/1( n

poC k q ⋅= mg/g {19.1b}

A, b, k and n are numerical constant, acquired from experiment.

User can select the model from on-screen option button.

4.10.2 Bed life span or total operation time before bed replacement (t T ):

When isotherm (q VS. C p relation) and mass transfer zone data

(Qa, Ha or E as the functions of C p) are available;

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IV-102

)( p po

ab

T C C Q

Qq HAt

−

−⋅⋅=

ρ {19.2a}

Or,

)( p po

bT

C C Qq HA E t

− ⋅⋅⋅= ρ {19.2b}

)/(10100

11 AQd

c H

E ⋅⋅⋅

⋅−= {19.3}

E is effective saturation of bed. The recommended valued is

around 50-95% (average 75%). In the program, eq. 19.2b is used.

H and V are in m and m/h, respectively.

4.10.3

Hydraulic loading rate:

A

QV = m/h {19.4}

4.10.4 Retention time (τ ):

60)/(

⋅= AQ

H τ min {19.5}

4.10.5 Headloss (P): Head loss of the bed can be calculated from

Kozeny-Carman’s equation. Built-in minimum and maximum

void ration is 0.18 to 0.25, respectively.

32

2)1)(60/(180

ε ρ

ε μ

⋅⋅⋅

−=

dpg

V H P c

{19.3}


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IV-103

Table 19-1 Related parameters of GAC filter


the program

Unit used in the

program

A Cross section area of bed A m2

C p Required outlet pollutant concentration Polout mg/l

C po Inlet concentration of pollutant Polin mg/l

dp GAC particle size Dpc m

Ε Effective saturation of bed, E < 100% GACE %

H Bed height GACH m

P Pressure drop Pdropmin,

Pdropmax

m

q Isotherm data (mass of adsorbate/ mass of

adsorbent)

GACq mg/g

V Empty bed velocity or hydraulic loading rate GACV m/h

a, b Empirical constant for Lungmire’s model C po in mg/l m/h

k, n Empirical constant for Freundlich’s model C po in mg/l m/h

c, d Empirical constant for mass transfer zone data C po in mg/l m/h

ε Bed porosity or void ratio, recommended value is

0.18 – 0.25.

Void

ρc Density of continuous phase Denc kg/m3

ρ b Bulk density of bed (430 – 600 kg/m3) DenGAC kg/m

3

Note: 1. Other parameters are internally used. Users do not need to input. For list of others parameters, see reference.



GAC filter

(GAC-??)

Ha

CCo

Ce

H

t = 0

S a

t u r e d

z o n e

M T Z

CCo

Ce

H

t = tT

Ha

Bed needs to

be replaced.

GAC bed.HT

Influent

Effluent

Velocity=V

Fig. 19-1a Icon of GAC filter Fig. 19-1b Graphical diagram of GAC filter

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IV-104


7.1 Calculation is based on research data, given by users.

7.2 If possible, it is recommended to conduct is lab test, using real wastewater,

to find the exact data about isotherm adsorptive capacity (a, b, k, n), and

mass transfer zone (c and d) data of GAC bed.

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IV-105

20) Customized concentrator

1. Process abbreviation: CC

2. Process description: The process works as an oil concentrator, e.g. hydrocyclone.

But users are allowed to specify graded efficiency of the process.

3. Reference : None

4.


4.1 Graded efficiency (η d ): User-defined in the form of a table. Graded

efficiency of the droplet size that falls between 2 specified values will be

obtained by interpolation or extrapolation.


∑ ⋅−

−=

max

min

%100)1(

)1(1 d

d f

od d

o

t R

C

C

η η {20.1}

4.3

Graded outlet oil concentration in water outlet flow (C d ):

)1(

)1(

f

od d

d R

C C

−

−=

η mg/l

{20.2}


∑=max

min

d

d

d C C mg/l {20.3}

4.5 Graded outlet oil concentration in oil outlet flow (C oild ):

f

od d oild

R

C C

η = mg/l {20.4}


∑=max

min

d

d

oild oil C C {20.5}


upstream process.


)1( f out RQQ −= m3/h {20.6}

4.9

Oil outlet flow(Qoil):

f oil RQQ ⋅= m3/h {20.7}

4.10 Customized output : None

5.


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IV-106

Table 20-1 Related parameters of customized concentrator


the program

Unit used in the

program

R f Split ratio (Qoil/Q) Rf

d, ηd Specified droplet size and graded efficiency

of the process

Customdin,

Customeffd

Micron, %



Custom

concentrator

(CC-??)

Oil outlet

Influent

Effluent

Fig. 20-1a Icon of customized

concentrator

Fig. 20-1b Graphical diagram of customized

concentrator

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IV-107

21) Customized oil separator

1. Process abbreviation: CS

2. Process description: the process works as an oil separator, e.g. decanter. But

users are allowed to specify graded efficiency of the process.

3. Reference : None

4.


4.1 Graded efficiency (η d ): User-defined in the form of a table. Graded

efficiency of the droplet size that falls between 2 specified value will be

obtained by interpolation.


( )

%100

max

min ⋅

⋅

=∑

o

d

d

od d

t

C

C η

η {21.1}

4.3 Graded outlet oil concentration in water outlet flow(C d ):

)1( d od

out

d C Q

QC η −⋅⋅= mg/l {21.2}


∑=max

min

d

d

d C C mg/l {21.3}






upstream process.


)1000//)(1( oiloout C C QQ ρ −−= m3/h {21.4}


out oil

QQQ −= m3/h {21.5}



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IV-108

Table 21-1 Related parameters of customized separator


the program

Unit used in the

program

d, ηd Specified droplet size and graded efficiencyof the process

Customdin,Customeffd

Micron, %



Custom separator

(CS-??)

Influent

Effluent

Oil outlet

Fig. 21-1a Icon of customized separator Fig. 21-1b Graphical diagram of customized

separator


7.1

Oil outlet point of the process can only be connected to the skimmers only.

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IV-109

22) Customized inline concentrator

1. Process abbreviation: IC

2. Process description: the process work as an inline oil concentrator, e.g.

coagulation-flocculation, or inline coalescer. But users are allowed to specify

graded efficiency of the process.



4.1 Graded efficiency (η d ): This parameter is actually not valid since no oil is

removed from the wastewater. However, the term ηd in this case represents

removal efficiency due to coalesce, defined by user in the form of a table.

Graded efficiency of the droplet size that falls between 2 specified value

will be obtained by interpolation or extrapolation. However the

concentrated oil is not separated from the wastewater but assumed to

coalesce to form bigger oil drops of a specified size (d coalesce). From thisdefinition, the value of ηd are as follows,

For d < dcoalesce, ηd is as specified by user. The rest of the droplets that are

not separated will partially coalesce to form bigger droplets at the size of

dcoalesce.

For d = or > dcoalesce, ηd is as specified by user.

However, for d = dcoalesce, its concentration (if already existed) will increase

since coalesced droplets are assumed to be of this size.

4.2 Total efficiency (η t ): This parameter is not valid since no oil is removed.

4.3

Graded outlet oil concentration in water outlet flow (C d ): It is assumed that

separated oil droplets coalesce to form big oil drop which is classified as

oil layer.

And as described above, it is assumed that there are partially coalesces of

the small oil droplets. These droplets will coalesce and form bigger oil

droplets “dcoalesce”. Or all droplets smaller than dcoalesce will coalesce to form

the droplet size “dcoalesce”.

Thus, for d < dcoalesce,

0=d C mg/l {22.1a}

For d = dcoalesce,

∑ −=coalsced

d

d d d C C min

)1( η

mg/l

{22.1b}

For d > dcoalesce,

)1( d od d C C η −⋅= mg/l {22.1c}

For oil layer,

∑+=max

min

,

d

d

d layer olayer C C C mg/l {22.1d}

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IV-110


C = Co mg/l


not valid since no oil is removed.

4.6

Total outlet oil concentration in oil outlet flow (C oil): This parameter is notvalid since no oil is removed.


upstream process.


flow.



5.

Related parameters: Related parameters are as summarized in the followingtable

Table 22-1 Related parameters of customized inline concentrator


the program

Unit used in the

program

dcoalesce Diameter of partially coalesced oil drop

from the process

customDcoalesce micron

d, ηd Specified droplet size and graded efficiency

of the process

Customdin,

Customeffd

Micron, %

6.



Inline concentrator

(IC-??)

Influent

Effluent

Fig. 22-1a Icon of inline concentrator Fig. 22-1b Graphical diagram of inline concentrator

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IV-111

23) Inlet

1. Process abbreviation: IN

2. Process description: This module is used to input the wastewater into a process

train. There can be more than one input module in a process train.

3. Reference : None

4.

Input parameters


the program

Unit used in the

program

Cod Granulometry or oil droplet size distribution :

graded concentration (concentration of oil at

each droplet size)

Cind mg/l

Concentration of inlet oil in the form of oil

layer or film

Cinlayer mg/l

Co Total oil inlet concentration Co mg/l

d Granulometry or oil droplet size distribution :

droplet size

din micron

Q Wastewater flowrate Qin m3/h

T Temperature temp Celcius

ρc Dynamic (or absolute) viscosity of continuous


Denc Kg/m3




Muc N.s/m2

(= 1000 cp)

μd Dynamic (Absolute) viscosity of dispersed phase, in this case, oil

Mud N.s/m2

(= 1000 cp)


or N/m

(= 1000 dyne/cm)

5. Related graphics: Icon in analysis mode for this process are as shown below.

InletInlet

Inlet

(IN-??)

Fig. 23-1a Icon of inlet

6. Constraints and limitations

6.1 There can be more than one inlet module in a process train.

6.2 Graded concentration is specified as quantity of oil (mg) per volume of

wastewater (= volume of oil+water).

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IV-112

24) Outlet

1. Process abbreviation: -

2. Process description: This module is used to specify the outlet point of the process

train. It is also used as a logical checkpoint of the program to perform

calculation. Thus there can be only one outlet in a process train.

3. Reference : None



OutletOutlet

Outlet

Fig. 24-1a Icon of outlet

5. Constraints and limitations

5.1 There can be only one outlet in a process train.

5.2 Location of the outlet in the process train does not need to be an actual

location. However, it is recommended to place it at the end of main process

stream for faster calculation.

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IV-113

25) Flow merge

1. Process abbreviation: FM

2. Process description: This module is used to combine or merge any 2 streams of

wastewater together.

3. Reference : None

4.

Output parameters:

4.1 Wastewater flowrate (Q): It is calculated from the summation of the

flowrate of the two streams.

4.2 Granulometry or size distribution of oil droplets in the wastewater : It is

calculated from weight average value, as shown in the following equation.

21

22,11,

QQ

QC QC C

d d

d +

+=

{25.1}

4.3

Total oil concentration (C):

∑=max

min

d

d

d C C

{25.2}

4.4 Oil density (ρd): as kg/m3. It is assumed to be equal to the weight average

value, as shown in the following equation.

2211

222,111,

QC QC

QC QC d d

d +

+=

ρ ρ ρ {25.3}

4.5 Water density (ρc):

21

2211

QQQQ cc

c ++= ρ ρ

{25.4}

4.6 Oil viscosity (μd): as N.s/m2. It is assumed to be equal to the weight

average value, as shown in the following equation.

2211

222,111,

QC QC

QC QC d d

d +

+=

μ μ μ {25.5}

4.7 Water viscosity (μc):

21

2211

QQ

QQ ccc +

+=

μ μ μ

{25.6}

4.8

Temperature (T):

21

2211

QQ

QT QT T

++

= Celcius {25.7}

4.9 Interfacial tension (γow): It is assumed to be equal to the weight average

value, as shown in the following equation.

2211

222,111,

QC QC

QC QC owow

ow +

+=

γ γ γ

{25.8}

5. Related graphics: Icon in analysis mode for this process are as shown below.

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IV-114

2

1

Flow merge(FM-??)

Fig. 25-1a Icon of flow merge

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IV-115

26) Flow split

1. Process abbreviation: FS

2. Process description: This module is used to divide or split a stream of wastewater

into 2 streams.

3. Reference : None

4.

Output parameters:

4.1 Wastewater flowrate (Q1 and Q2):

Q RQ f =1

{26.1a}

Q RQ f −= 12 {26.1b}

4.2 Granulometry or size distribution of oil droplets in the wastewater :

od d d C C C == 2,1, {26.2}

4.3 Total oil concentration (C):

oC C C == 21 {26.3}

4.4 Oil density (ρoil):

oiloiloil ρ ρ == 2,1, {26.4}

4.5 Temperature (T):

T T T == 21 {26.5}

4.6

Interfacial tension (γow): It is assumed to be equal to the weight averagevalue, as shown in the following equation.

owowow γ γ γ == 2,1, {26.6}



2

1

Flow split

(FS-??)

2

1

Influent

Q1 = R f Q

Q2 = 1- R f Q

Fig. 26-1a Icon of flow split Fig. 26-1b Graphical diagram of flow

split

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Part V General conclusion

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General conclusion

V-1

General conclusion

One of the main objectives of this thesis is to review all of the researches on various

oily wastewater treatment processes, directed by Prof. AURELLE and summarize and

establish general theory or mathematical models that govern the performance and design of

such processes.

This objective is accomplished in Part 1 to Part 3 of this thesis. Every unit processes

for oil separation, studied in GPI lab, had been revised and their corresponding mathematical

models as well as design limitation and influent parameters had been found. These processes

revised under the scope of work of this thesis include,

1. Oil skimmer

This equipment is developed to selectively remove oil layer from the water

surface without carrying over the water with it. It is found that the key to achieve good oil

selectivity depends on the surface energy or critical surface tension of skimmer material. Thematerial with low critical surface tension is suitable to use as skimmer material. Mathematical

models of 2 types of skimmer, i.e. drum skimmer and disk skimmer are verified.

2.

Decanter

Its underlining theory, namely STOKE’s law, is quoted. General mathematical

models for 3 different varieties of the processes, i.e. simple decanter (e.g. API tank), parallel

plate interceptor (e.g. PPI and lamella separator), and compact decantor (e.g. Spiraloil) are

proposed and verified.

3.

Coalescer

Theoretical model, proposed by AURELLE, based on filtration model, is

reviewed. The model provides clear ideas about influent parameters on coalescer

performance. Several initiative ideas for coalescer performance enhancemen, e.g. the use of

guide to increase oil loading of the coalescer and the use of mix bed material to treat mixture

of direct/inverse emulsion simultaneously are realised. Finally, the empirical models, which

are verified by relatively wide range of data, are proposed for 4 varieties of coalescer, i.e.

granular bed coalescer , brush type bed coalescer, dynamic fibrous bed (rotating brush)

coalescer, and disorderly fibrous bed (metal wool) coalescer. Headloss equations are also

proposed in this thesis.

4.


Mathematical model based on filtration concept, proposed by SIEM [12] is

reviewed. The model is useful for understanding effects of influent parameters on DAF

performance. Extension equations of SIEM’s model , based on population balance theory, is

established within this thesis to extend the valid range of SIEM’s model to cover the range of

oily wastewater frequently found. Equations for saturator or pressurized water system

design are also proposed and verified within this thesis.

5. Hydrocyclone

Trajectory analysis model for 2-phase (liquid-liquid) hydrocyclone, the new

concept based on STOKE’s law, is proposed and verified. The model can actually predict

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General conclusion

V-2

graded oil removal efficiency of any sizes of oil droplet in the wastewater by theoretical based

equation, unlike other models which are based on curve fitting and similarity concepts. Thus

it is very useful to understand the effect of related parameters on hydrocyclone performance.

Models of three-phase hydrocyclone, GPI innovation for simultaneous removal of oil,

suspended solids amd water, are also established within the scope of work of this thesis. The

model is also based on trajectory analysis concept. Finally, headloss equations for 2- and 3- phase hydrocyclone are established in this thesis.

6.

Membrane processes

Applications of membrane processes, i.e. microfiltration (MF), ultrafiltration

(UF), nanofiltration (NF) and reverse osmosis (RO) on oily wastewater treatment in GPI lab

had been reviewed. Several useful facts from those researches are realized and calculation

techniques are established in this thesis, i.e.,

• Flux enhancement for UF on cutting oil emulsion treatment by partial

destabilization. Additional of salt, in lower amount than that for totaldestabilization, into the feed helps increasing permeate flux, thus saving on

energy consumption and membrane size. The downside of this technique,

concluded in this thesis, is that the destabilized oil can clog the membrane if

it is not properly partition or removed from recirculated feed stream.

• Cleaning of UF membrane after treatment of cutting oil by cleaning

microemulsion. It can effectively wash accumulated oil or foulants from the

membrane. It can be reused for many times until it is saturated by oil.

• Technique to extend the UF performance data at 1 condition to cover other

condition, based on combination of film model and resistance model . This

technique is proposed and verified in this thesis. It is useful when onlylimited data on the wastewater is available. It allows us to estimate evolution

of flux and permeate volume with time, which is useful for process design.

• Technique to predict flux of mixture of two different emulsion. This

technique is also proposed and verified in this thesis. It is useful when mixed

emulsion can be expected and its ratio is likely to vary.

7. Thermal process

The main interest of this type of process is heteroazeotropic distillation (HD).

Application of HD to remove water content from refinery slops and UF retentates from UF of

cutting oil emulsion is reviewed. The process is achieved by addition of certain chemical that promotes azeotropic formation (called entrainer), usually hydrocarbons, into the wastewater.

It will lower the boiling temperatur of the system, thus save the energy. These applications

provide prospects on re-value these supposed-to-be-wastes. Its reverse application, namely

stream stripping (for removing volatile substance from water by addition of stream), is also

realized. Theoretical data to calculate required amount of entrainer are also proposed.

8. Chemical process

Destabilization (or breaking or cracking) mechanism of emulsion by addition

of various chemicals, i.e. mono valence salt, bivalence salts, polyelectrolytes, acid and special

absorbates are reviewed. Equations for mixing tank and mixer designs are also reviewed andincluded in the program.

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General conclusion

V-3

9.

Finishing processes

Two widely used finishing processes, i.e., biological treatment and carbon

adsorption, is realized. Useful data on biological process, related to oily wastewater

treatment, and design equations of GAC filter, as well as absorptive capacity of certain

chemicals, are reviewed and included in the program.

To complete the first objective , guideline on oily wastewater treatment process

selection and recommended treatment processes for certain oily wastewater are proposed.

The final objective of the thesis is to develop the program for calculation, design and

simulation of wastewater treatment process train in order to value and make use of the know-

how and significant finding from the researches by presenting them in the form of user-

friendly program. To fulfil this objective, the program, namely GPI program, is developed. It

is divided into 4 major modes, i.e.,

•

E-book mode: provides background knowledge and useful database about theoil pollution and the treatment processes. Actually, the textbook in part 3 is

transformed into e-book files used in this mode,

• Process recommendation mode: provides recommendation to narrow the range

of feasible processes for any input influent. Selection criteria are as proposed in

the guideline in Part 3, chapter 12.

• Design (calculation) mode: used for sizing the unit process. The models used

for calculation are as summarized in Part 3.

• Analysis (simulation) mode: allows users to integrate any separation processes,

included in the program database, to build their own treatment process train. And

the program will simulate the process train to forecast the efficiency of each unit.

The program is developed to be upgradable. Its architecture consists of the database in

the form of common text database file and sub-programs. To upgrade the program, it can be

done conveniently by adding the data, such as name of new process, its related parameter

needed for calculation, into the database. The program will link the new process into the

graphic user interface automatically. For sub-program for calculation of the new process, it

can be separately developed using Visual Basic programming language. The easiest way is to

copy the source code of an existing process and change the equation to suit the new process.

After compilation in to an executable file, it can be copied to replace the old GPI program file

without re-installation of the program. So the program could be further developed to cover

more researches and processes in the future.

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Reference

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Reference

1 Sawyer C., Mccarty P., Parkin G.

Chemistry for environmental engineering and science

Book, 5th edition, Mcgraw-Hill, 2003

2

Perry R., Green D.Perry's chemical engineering's handbook


3 Aurelle Y.

Contribution a l'etude des mechanismes fondamentaux de la coalescence des

emulsions sur lit granulaire

Thèse de doctuer d'etat, Université Pual Sabatier,1980

4 Cherid S.

Conception et etude de nouveaux separateurs lamellaires hydrocarbon-eau de

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Separation par coalescence des emulsions hydrocarbure/eau stabilees par desagents tensio-actifs


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Etude et modilisation d'une nouvelle generation de coalesceurs liquide-

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9 Damak L.

Nouveaux separateurs d'emulsions huile/eua chargee en matiers en

suspension - Separateur a inversion de phase - coalesceur granulaire a lit

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10 Srijaroonrat P.

Nouvelles techniques de traitement des emulsion hydrocarbure-eau non

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11 Wanichkul B. Etude des potentialities de nouveaux procedes de traitement d'emulsions

hydrocarbure-eau: ultrafiltration, distillation et couplage coalesceur-

hydrocyclone


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12 Siem N.Contribution a l'etude des separations hydrocarbure-eau par flottation


13 Aoudjehane M.

Traitement par flottation des effluents aqueux charges en hydrocarbures


14 Dupre V. Etude des mecanismes et de la modilisation procedes de flottation a air

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15 Ponasse M. Elements theoriques et experimentaux en vue de l'amelioration des

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flottateurs


16 Ma B. Epuration des eaux residuraires de l'industrie petreliere Par hydrocyclonage


17 Cazal E.

Etude des potentialities des hydrocyclones dans domaine du traitement des

eaux residuaire urbains et des eaux de ruissellement


18 Belkacem M. Nouvelle methodologie dans le traitement des huiles de coupe par

ultrafiltrationThèse de doctorat, INSA-Toulouse, 1995

19 Toulgoat K.

Etude des macanismes de formation des emulsions thermiques; potentialites

de separation par ultrafiltration


20 Matamoros H.Procedes membranaires pour le traitment des emulsions stabilisees de type

fluid de coupe


21

Zhu S. Etude des traitement physico-chimiques d'epuration des emulsion d'huile de

coup; Influence de leur formulation


22 Yang C. Developpement de nouvelles formulations de fluides de coupe peu polluants,

mise au point de techniques de traitement adaptees


23 Lorain O.

Contribution a l'etude du traitement des eaux par congelation : potentialites et

applicationsThèse de doctorat, INSA-Toulouse, 2002

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24 Lucena E. Nouveau procede de traitement des slops de l'industrie petroliere par

distillation heteroazeotropique: comparaison avec d'autres procedes


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Contribution a la mise au point d'application specifique des hydrocyclones en

traitement des eaux


26 Aurelle Y.

Contribution a l'etude du traitement des eaux polluees par des hydrocarbures

emulsionnes par coalescence sur resines oleophiles

Thèse de doctorat, Universite Pual Sabatier de Toulouse, 1974

27 Tan PraponTheoritical study of Coalescer and its application to treatment of wastewater

for vegetable oil industry

Master degree thesis, Chulalongkorn University, Thailand, 1984

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Hydrocyclones for liquid-liquid separation

Lecture on the intensive short course, University of Bath, September 1984

29 Chebelin T.

Separation compacte: modilisation des hydrocyclones

Document de stade de fin d'etude, INSA-Toulouse, 1984

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Book, 196531 M.a B., Aurelle Y., Seureau J.

Three phase hydrocyclone for simultaneous separation of solids from liquid-

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Publication, source unknown

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Efficiency estimation of liquid-liquid hydrocyclones using trajectory analysis

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Hydrocyclones


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Environmeantal sciences and Technology, No. 11, 1971

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Ultrafiltration and microfiltration handbook

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Book, Allerton press inc., 1983

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Introduction to colloid and surface chemistry

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Physical and chemical treatment techniques Paper on short course seminar:

Faculty of engineering, Chulalonkorn university, ThailandBook, Chulalongkorn University, September 1985

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Chulalongkorn University

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Pollution control instrument for oil and effluents

Book, Graham & Trotman, 1987

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spherical particles

AIChE journal, Vol. 4 No. 2, 1985

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Book, 1st edition, 1969

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Book, 3rd edition, Mcgraw-Hill, 1991

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Pollution control in petroleum industryBook, Noyes data corperation , 1973

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the newest (third) one (DAF in turbulent flow conditions)

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Wastewater treatment handbook

Book, 5th edition, John Wiley & son, 1979

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545

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Annexe

8/15/2019 Rachu.pdf


Annex A.1.1 Comparison between calculated efficiency and experimental result

for simple spiral "Spiraloil" decanter

Ref. [4] pp.79

Case Droplet

diameter

Empty

bed

velcity

Calculated

removal

efficiency

Observed efficiency

from experiment(by

droplet size)

Difference in

calculated and

observed efficiency

d V d d observed

micron m/s % %1 1.8 0.4 1.04% 0.00% -1.04%

2.3 0.4 1.71% 0.00% -1.71%

2.95 0.4 2.81% 0.50% -2.31%

3.7 0.4 4.42% 21.42% 17.00%

4.65 0.4 6.99% 51.80% 44.81%

5.9 0.4 11.25% 59.92% 48.67%

7.45 0.4 17.95% 68.96% 51.01%

9.45 0.4 28.57% 82.62% 54.05%

11.85 0.4 45.41% 93.20% 47.79%

14.95 0.4 72.29% 97.98% 25.69%

18.85 0.4 100.00% 99.35% -0.65%

23.7 0.4 100.00% 100.00% 0.00%

29.85 0.4 100.00% 100.00% 0.00%

37.65 0.4 100.00% 100.00% 0.00%

47.5 0.4 100.00% 100.00% 0.00%

55.5 0.4 100.00% 100.00% 0.00%

2 1.8 0.8 0.52% 0.00% -0.52%

2.3 0.8 0.85% 0.00% -0.85%

2.95 0.8 1.40% 0.00% -1.40%

3.7 0.8 2.21% 0.00% -2.21%

4.65 0.8 3.49% 1.70% -1.79%

5.9 0.8 5.62% 14.25% 8.63%

7.45 0.8 8.96% 48.01% 39.05%

9.45 0.8 14.26% 49.72% 35.46%

11.85 0.8 22.67% 72.10% 49.43%

14.95 0.8 36.09% 85.20% 49.11%

18.85 0.8 57.37% 94.00% 36.63%

23.7 0.8 90.70% 98.90% 8.20%

29.85 0.8 100.00% 100.00% 0.00%

37.65 0.8 100.00% 100.00% 0.00%

47.5 0.8 100.00% 100.00% 0.00%

55.5 0.8 100.00% 100.00% 0.00%

3 1.8 1.6 0.26% 0.00% -0.26%

2.3 1.6 0.42% 0.00% -0.42%

2.95 1.6 0.70% 0.00% -0.70%

3.7 1.6 1.10% 0.00% -1.10%

4.65 1.6 1.74% 0.00% -1.74%

5.9 1.6 2.81% 0.00% -2.81%

7.45 1.6 4.48% 0.00% -4.48%

9.45 1.6 7.23% 0.00% -7.23%

11.85 1.6 11.33% 5.40% -5.93%

14.95 1.6 18.04% 26.20% 8.16%

18.85 1.6 28.35% 54.80% 26.45%

23.7 1.6 45.35% 80.20% 34.85%

29.85 1.6 71.94% 95.30% 23.36%

37.65 1.6 100.00% 98.80% -1.20%

47.5 1.6 100.00% 99.90% -0.10%

55.5 1.6 100.00% 100.00% 0.00%

546

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Annex A1.2 Comparison between calculated efficiency and experimental result

for mixed spiral "Spiraloil" decanter

Ref. [4] pp.88

Case Droplet

diameter

Empty

bed

velcity

Calculated

removal

efficiency

Observed efficiency

from experiment(by

droplet size)

Difference in

calculated and

observed efficiency

d V d d observed

micron m/s % %

1 1.80 0.5 1.88% 52.22% 50.34%

2.30 0.5 3.08% 58.83% 55.75%

2.95 0.5 5.07% 67.54% 62.47%

3.70 0.5 7.97% 72.08% 64.11%

4.65 0.5 12.60% 79.89% 67.29%

5.90 0.5 20.29% 84.97% 64.68%

7.45 0.5 32.35% 89.00% 56.65%

9.45 0.5 51.50% 94.01% 42.51%

11.85 0.5 81.85% 97.02% 15.17%

14.95 0.5 100.00% 98.22% -1.78%

18.85 0.5 100.00% 99.40% -0.60%

23.70 0.5 100.00% 100.00% 0.00%

29.85 0.5 100.00% 100.00% 0.00%

37.65 0.5 100.00% 100.00% 0.00%

47.50 0.5 100.00% 100.00% 0.00%

53.00 0.5 0.00%

2 1.80 1.5

2.30 1.5

2.95 1.5

3.70 1.5

4.65 1.5 4.20% 43.18% 38.98%

5.90 1.5 6.76% 61.82% 55.06%

7.45 1.5 10.78% 67.27% 56.49%

9.45 1.5 17.17% 71.82% 54.65%

11.85 1.5 27.28% 75.45% 48.17%

14.95 1.5 43.18% 77.27% 34.09%

18.85 1.5 70.00% 84.54% 14.54%23.70 1.5 100.00% 92.73% -7.27%

29.85 1.5 100.00% 100.00% 0.00%

37.65 1.5 100.00% 100.00% 0.00%

47.50 1.5 100.00% 100.00% 0.00%

55.50 1.5

547

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Annex A2.1 Comparison between calculated efficiency and experimental result for granular bed coalescer

Ref. [3] pp.285 & 321, [9], pp.174

Case Total

hydrocarbon

concentration

Droplet

diameter

Bed

media

diameter

Bed

height

Dispersed

phase

density

Continuous

phase

density

Density

difference

Dynamic

viscosity

of

dispersed

phase

Dynamic

viscosity of

continuous

phase

Empty

bed

velcity

Interfacial

tension

Calculated

removal

efficiency

from

DAMAK's

model

Observed

efficiency

from

experiment(by

droplet size)

Co d dp H ρd ρc ρ

μd μc V γo w ηd ηd observed

mg/l m m m kg/cu.m kg/cu.m kg/cu.m (N.s)/m2

(=1000cP

(N.s)/m2

(=0.1000cP)

m/s N/m

(=1000dyn/cm

% %

1 1000 41.00 0.37 0.01 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 99.79% 95.00%

1000 41.00 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 98.70%

1000 41.00 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 41.00 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 32.65 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.99%

1000 32.65 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 32.65 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 25.90 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.00%

1000 25.90 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 25.90 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 20.57 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 99.18% 98.00%

1000 20.57 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 20.57 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 16.36 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 94.74% 96.00%

1000 16.36 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 16.36 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 12.99 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 90.47% 94.30%

1000 12.99 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 96.19% 99.70%

1000 12.99 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 10.30 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 86.37% 92.00%

1000 10.30 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 91.83% 98.70%

1000 10.30 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 99.79% 100.00%

2 1000 41.00 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 98.60%

1000 41.00 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 41.00 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.40%

1000 32.65 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.00%

1000 32.65 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 32.65 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.40%

1000 25.90 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 98.60%

1000 25.90 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 25.90 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.00%

1000 20.57 0.37 0.03 793.4 998 204.6

1.07E-03 1.08E-03 0.00351 4.20E-02 99.18%

97.00%1000 20.57 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 20.57 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 98.60%

1000 16.36 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 94.74% 94.60%

1000 16.36 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 99.60%

1000 16.36 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 98.60%

1000 12.99 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 90.47% 92.60%

1000 12.99 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 96.19% 99.20%

1000 12.99 0.37 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 98.60%

1000 10.30 0.37 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 86.37% 88.80%

1000 10.30 0.37 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 91.83% 97.40%

1000 10.30 0.37 0.1 793.4 998 204.6

1.07E-03 1.08E-03 0.00351 4.20E-02 99.79%

98.20%3 1000 41.00 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 93.83% 97.00%

1000 41.00 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 99.76% 99.00%

1000 41.00 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 32.65 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 89.66% 93.00%

1000 32.65 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 95.32% 97.00%

548

8/15/2019 Rachu.pdf



Ref. [3] pp.285 & 321, [9], pp.174

Case Total

hydrocarbon

concentration

Droplet

diameter

Bed

media

diameter

Bed

height

Dispersed

phase

density

Continuous

phase

density

Density

difference

Dynamic

viscosity

of

dispersed

phase

Dynamic

viscosity of

continuous

phase

Empty

bed

velcity

Interfacial

tension

Calculated

removal

efficiency

from

DAMAK's

model

Observed

efficiency

from

experiment(by

droplet size)




(=1000cP

(N.s)/m2

(=0.1000cP)

m/s N/m

(=1000dyn/cm

% %

1000 32.65 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 100.00% 100.00%

1000 25.90 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 85.60% 90.20%

1000 25.90 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 91.01% 96.40%

1000 25.90 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 98.90% 100.00%

1000 20.57 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 81.74% 83.20%

1000 20.57 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 86.91% 94.40%

1000 20.57 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 94.45% 99.40%

1000 16.36 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 78.08% 74.80%

1000 16.36 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 83.02% 91.20%

1000 16.36 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 90.22% 98.00%

1000 12.99 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 74.56% 61.00%

1000 12.99 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 79.28% 87.20%

1000 12.99 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 86.15% 96.60%

1000 10.30 0.60 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 71.18% 58.20%

1000 10.30 0.60 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 75.68% 84.00%

1000 10.30 0.60 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 82.25% 93.40%

4 1000 41.00 0.75 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 85.82% 89.60%

1000 41.00 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 91.25% 98.00%

1000 41.00 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 99.16% 100.00%

1000 32.65 0.75 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 82.00% 85.20%

1000 32.65 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 87.18% 93.20%

1000 32.65 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 94.75% 100.00%

1000 25.90 0.75 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 78.29% 75.80%

1000 25.90 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 83.24% 96.20%

1000 25.90 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 90.46% 99.60%

1000 20.57 0.75 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 74.76% 61.00%

1000 20.57 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 79.49% 95.40%

1000 20.57 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 86.38% 99.00%

1000 16.36 0.75 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 71.42% 56.00%

1000 16.36 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 75.93% 90.80%

1000 16.36 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 82.52% 96.60%

1000 12.99 0.75 0.03 793.4 998 204.6

1.07E-03 1.08E-03 0.00351 4.20E-02 68.20%

42.60%1000 12.99 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 72.51% 83.20%

1000 12.99 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 78.80% 90.80%

1000 10.30 0.75 0.03 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 65.10% 24.60%

1000 10.30 0.75 0.05 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 69.22% 78.80%

1000 10.30 0.75 0.1 793.4 998 204.6 1.07E-03 1.08E-03 0.00351 4.20E-02 75.22% 84.20%

5 1000 10.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0009 1.10E-02 90.55% 95.00%

1000 14.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0009 1.10E-02 96.85% 96.50%

1000 20.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0009 1.10E-02 100.00% 98.00%

1000 28.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0009 1.10E-02 100.00% 99.00%

1000 40.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0009 1.10E-02 100.00% 100.00%

1000 10.00 0.36 0.02 914.5 998 83.5

2.10E-03 1.07E-03 0.00136 1.10E-02 84.81%

91.00%1000 14.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00136 1.10E-02 90.71% 94.00%

1000 20.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00136 1.10E-02 97.42% 97.00%

1000 28.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00136 1.10E-02 100.00% 99.00%

1000 40.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00136 1.10E-02 100.00% 100.00%

1000 10.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 75.99% 75.00%

549

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Ref. [3] pp.285 & 321, [9], pp.174

Case Total

hydrocarbon

concentration

Droplet

diameter

Bed

media

diameter

Bed

height

Dispersed

phase

density

Continuous

phase

density

Density

difference

Dynamic

viscosity

of

dispersed

phase

Dynamic

viscosity of

continuous

phase

Empty

bed

velcity

Interfacial

tension

Calculated

removal

efficiency

from

DAMAK's

model

Observed

efficiency

from

experiment(by

droplet size)




(=1000cP

(N.s)/m2

(=0.1000cP)

m/s N/m

(=1000dyn/cm

% %

1000 14.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 81.28% 86.00%

1000 20.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 87.29% 92.00%

1000 28.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 93.37% 97.00%

1000 40.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 99.00%

1000 10.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00406 1.10E-02 71.19% 67.00%

1000 14.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00406 1.10E-02 76.15% 79.00%

1000 20.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00406 1.10E-02 81.78% 84.00%

1000 28.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00406 1.10E-02 87.47% 92.00%

1000 40.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00406 1.10E-02 93.94% 94.00%

1000 10.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00541 1.10E-02 68.00% 61.00%

1000 14.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00541 1.10E-02 72.73% 65.00%

1000 20.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00541 1.10E-02 78.11% 71.50%

1000 28.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00541 1.10E-02 83.54% 85.50%

1000 40.00 0.36 0.02 914.5 998 83.5 2.10E-03 1.07E-03 0.00541 1.10E-02 89.72% 92.00%

1000 10.00 0.36 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 79.78% 85.00%

1000 14.00 0.36 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 85.34% 90.00%

1000 20.00 0.36 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 91.65% 94.50%

1000 28.00 0.36 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 98.03% 98.00%

1000 40.00 0.36 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 100.00%

1000 10.00 0.36 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 84.83% 89.00%

1000 14.00 0.36 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 90.73% 92.00%

1000 20.00 0.36 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 97.44% 96.00%

1000 28.00 0.36 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 99.00%

1000 40.00 0.36 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 100.00%

1000 10.00 0.36 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 92.18% 93.50%

1000 14.00 0.36 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 98.60% 95.00%

1000 20.00 0.36 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 99.00%

1000 28.00 0.36 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 100.00%

1000 40.00 0.36 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 100.00%

1000 10.00 0.56 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 66.86% 71.00%

1000 14.00 0.56 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 71.51% 76.00%

1000 20.00 0.56 0.03 914.5 998 83.5

2.10E-03 1.07E-03 0.0027 1.10E-02 76.80%

80.00%1000 28.00 0.56 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 82.15% 85.00%

1000 40.00 0.56 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 88.22% 94.00%

1000 10.00 0.56 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 71.08% 78.00%

1000 14.00 0.56 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 76.03% 81.00%

1000 20.00 0.56 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 81.66% 85.00%

1000 28.00 0.56 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 87.34% 92.00%

1000 40.00 0.56 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 93.80% 98.00%

1000 10.00 0.56 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 77.25% 86.00%

1000 14.00 0.56 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 82.63% 90.00%

1000 20.00 0.56 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 88.74% 98.00%

1000 28.00 0.56 0.1 914.5 998 83.5

2.10E-03 1.07E-03 0.0027 1.10E-02 94.91%

98.00%1000 40.00 0.56 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 100.00% 99.00%

1000 10.00 0.73 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 60.13% 60.00%

1000 14.00 0.73 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 64.32% 65.00%

1000 20.00 0.73 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 69.07% 70.00%

1000 28.00 0.73 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 73.88% 76.00%

550

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Ref. [3] pp.285 & 321, [9], pp.174

Case Total

hydrocarbon

concentration

Droplet

diameter

Bed

media

diameter

Bed

height

Dispersed

phase

density

Continuous

phase

density

Density

difference

Dynamic

viscosity

of

dispersed

phase

Dynamic

viscosity of

continuous

phase

Empty

bed

velcity

Interfacial

tension

Calculated

removal

efficiency

from

DAMAK's

model

Observed

efficiency

from

experiment(by

droplet size)




(=1000cP

(N.s)/m2

(=0.1000cP)

m/s N/m

(=1000dyn/cm

% %

1000 40.00 0.73 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 79.34% 91.00%

1000 10.00 0.73 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 63.93% 63.00%

1000 14.00 0.73 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 68.38% 69.00%

1000 20.00 0.73 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 73.44% 75.00%

1000 28.00 0.73 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 78.55% 81.00%

1000 40.00 0.73 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 84.36% 95.00%

1000 10.00 0.73 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 69.48% 71.00%

1000 14.00 0.73 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 74.31% 76.00%

1000 20.00 0.73 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 79.81% 84.00%

1000 28.00 0.73 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 85.36% 90.00%

1000 40.00 0.73 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 91.68% 98.00%

1000 10.00 0.94 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 54.35% 53.00%

1000 14.00 0.94 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 58.13% 58.00%

1000 20.00 0.94 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 62.43% 61.00%

1000 28.00 0.94 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 66.77% 66.00%

1000 40.00 0.94 0.03 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 71.71% 75.00%

1000 10.00 0.94 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 57.78% 57.00%

1000 14.00 0.94 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 61.81% 61.00%

1000 20.00 0.94 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 66.38% 65.00%

1000 28.00 0.94 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 71.00% 71.00%

1000 40.00 0.94 0.05 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 76.25% 82.00%

1000 10.00 0.94 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 62.79% 63.00%

1000 14.00 0.94 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 67.17% 67.00%

1000 20.00 0.94 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 72.13% 72.00%

1000 28.00 0.94 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 77.15% 78.00%

1000 40.00 0.94 0.1 914.5 998 83.5 2.10E-03 1.07E-03 0.0027 1.10E-02 82.86% 92.00%

1000 10.00 0.73 0.03 795 998 203 1.35E-03 1.07E-03 0.0027 4.20E-02 69.68% 68.00%

1000 14.00 0.73 0.03 795 998 203 1.35E-03 1.07E-03 0.0027 4.20E-02 74.53% 77.00%

1000 20.00 0.73 0.03 795 998 203 1.35E-03 1.07E-03 0.0027 4.20E-02 80.04% 84.50%

1000 28.00 0.73 0.03 795 998 203 1.35E-03 1.07E-03 0.0027 4.20E-02 85.61% 90.00%

1000 40.00 0.73 0.03 795 998 203 1.35E-03 1.07E-03 0.0027 4.20E-02 91.94% 92.00%

1000 10.00 0.73 0.03 994.1 998 3.9

1.09E-03 1.07E-03 0.0027 1.60E-02 44.33%

40.50%1000 14.00 0.73 0.03 994.1 998 3.9 1.09E-03 1.07E-03 0.0027 1.60E-02 47.42% 45.50%

1000 20.00 0.73 0.03 994.1 998 3.9 1.09E-03 1.07E-03 0.0027 1.60E-02 50.93% 51.00%

1000 28.00 0.73 0.03 994.1 998 3.9 1.09E-03 1.07E-03 0.0027 1.60E-02 54.47% 56.00%

1000 40.00 0.73 0.03 994.1 998 3.9 1.09E-03 1.07E-03 0.0027 1.60E-02 58.50% 73.00%

1000 10.00 0.73 0.03 684 998 314 4.20E-04 1.07E-03 0.0027 3.62E-02 64.47% 62.00%

1000 14.00 0.73 0.03 684 998 314 4.20E-04 1.07E-03 0.0027 3.62E-02 68.96% 66.00%

1000 20.00 0.73 0.03 684 998 314 4.20E-04 1.07E-03 0.0027 3.62E-02 74.06% 72.10%

1000 28.00 0.73 0.03 684 998 314 4.20E-04 1.07E-03 0.0027 3.62E-02 79.21% 89.00%

1000 40.00 0.73 0.03 684 998 314 4.20E-04 1.07E-03 0.0027 3.62E-02 85.07% 90.00%

1000 10.00 0.73 0.03 860 998 138 7.16E-04 1.07E-03 0.0027 3.03E-02 61.93% 57.50%

1000 14.00 0.73 0.03 860 998 138

7.16E-04 1.07E-03 0.0027 3.03E-02 66.24%

64.50%1000 20.00 0.73 0.03 860 998 138 7.16E-04 1.07E-03 0.0027 3.03E-02 71.14% 75.00%

1000 28.00 0.73 0.03 860 998 138 7.16E-04 1.07E-03 0.0027 3.03E-02 76.09% 83.00%

1000 40.00 0.73 0.03 860 998 138 7.16E-04 1.07E-03 0.0027 3.03E-02 81.71% 89.00%

551

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Annex A.3 DAF tested by SIEM

[12] pp.130

Value

Wastewater

flowrate

Qin cu.m/s 3.9E-06

Pressurized

water flowrate

Qwater cu.m/s 4.2E-06

Qin/Qwater 0.92

Total flow Qtotal cu.m/s 8.14E-06

l/hr 29.31

Column cross

section area

Ao m2 0.0177

Velocity based

on total flow

Vo m/s 4.60E-04

Air flowrate

degassed in

DAF column

Φ cu.m/s 4.20E-07

Dissolved air

quantity in

pressurized

water

kg/cu.m 0.119

Effective

column height

H m 0.7

Bubble diameter dB m 7.00E-05

Dispersed phase density

ρd kg/cu.m 850

Continuous

phase density

ρc kg/cu.m 998

Air density kg/cu.m 1.201

Dispersed

phase viscosity

μd kg/m.s 0.0011

Continuous

phase viscosity

μc kg/m.s 0.00108

Bolzman

constant K 1.38E-23Temperature T Kelvin 293

Description

554

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Annex A.3 Comparison between observed efficiency and predicted efficiency for DAF

[12] pp.130

Item Bubble

diameter

Droplet

diameter

Rising

velocity

of dro let

Rising

velocity of

bubble

Relative

velocity

Sedimentati

on

efficienc

Interception

efficiency

Diffusio

n

efficienc

Theoritica

l totla

efficienc

Predicted

efficiencdB dE u U U-u S I D t theo exp

m m m/s m/s m/s predicted1 7.00E-05 2.10E-06 3.29E-07 2.46E-03 2.46E-03 1.34E-04 1.35E-03 4.3E-04 1.91E-03 2.21E-04

2 7.00E-05 2.60E-06 5.05E-07 2.46E-03 2.46E-03 2.05E-04 2.07E-03 3.7E-04 2.64E-03 2.68E-04

3 7.00E-05 3.30E-06 8.13E-07 2.46E-03 2.46E-03 3.30E-04 3.33E-03 3.2E-04 3.98E-03 3.42E-04

4 7.00E-05 4.10E-06 1.26E-06 2.46E-03 2.46E-03 5.10E-04 5.15E-03 2.7E-04 5.93E-03 4.33E-04

5 7.00E-05 5.10E-06 1.94E-06 2.46E-03 2.46E-03 7.89E-04 7.96E-03 2.4E-04 8.99E-03 5.54E-04

6 7.00E-05 6.50E-06 3.16E-06 2.46E-03 2.46E-03 1.28E-03 1.29E-02 2.0E-04 1.44E-02 7.32E-04

7 7.00E-05 8.20E-06 5.02E-06 2.46E-03 2.46E-03 2.04E-03 2.06E-02 1.7E-04 2.28E-02 9.61E-04

8 7.00E-05 1.03E-05 7.92E-06 2.46E-03 2.46E-03 3.23E-03 3.25E-02 1.5E-04 3.58E-02 1.26E-03

9 7.00E-05 1.30E-05 1.26E-05 2.46E-03 2.45E-03 5.15E-03 5.17E-02 1.3E-04 5.70E-02 1.65E-03

10 7.00E-05 1.64E-05 2.01E-05 2.46E-03 2.44E-03 8.22E-03 8.23E-02 1.1E-04 9.07E-02 2.17E-03

11 7.00E-05 2.06E-05 3.17E-05 2.46E-03 2.43E-03 1.30E-02 1.30E-01 9.4E-05 1.43E-01 2.85E-03 12 7.00E-05 2.59E-05 5.01E-05 2.46E-03 2.41E-03 2.07E-02 2.05E-01 8.1E-05 2.26E-01 3.74E-03

13 7.00E-05 3.27E-05 7.99E-05 2.46E-03 2.38E-03 3.35E-02 3.27E-01 7.0E-05 3.61E-01 4.93E-03

555

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Annex A3.1 Two-Phases hydrocyclone tested by MA

Ref. [26] pp.105

Description Value

Flowrate Q cu.m/s 5.40E-04Diameter of upper

c lindical ar

D m 4.00E-02

Nominal diameter of

h droc clone

Dn m 2.00E-02

Inlet diameter (2 ports) Di m 7.00E-03

Overflow diamete Dover m 2.00E-03

Underflow diamete Dunder m 1.00E-02

Angle of conical par Rad 2.62E-02

Dispersed phase densit ρd kg/cu.m 9.00E+02

Continuous phase c kg/cu.m 9.98E+02

Viscosit c Ns/m2 1.00E-03

Comparison between Observed efficiency and predicted efficiency from Ma's

and COLMAN's model for Two-Phases hydrocyclone

Ref. [26] pp.105, [16] pp.49

d75% for COLMAN model is based on [29] pp.15.

Efficienc

y

Observed

data

from

16 105

Droplet

diameter

predicted from

COLMAN 16

Droplet from

Ma's

Trajectory

methodeff% dE dE dE

% m m m

5% 8.49

10% 9.66

15% 10.89

20% 12.19 13.08

25% 13.58

30% 22 15.10 17.91

35% 16.70

40% 24 18.43 22.52

50% 25.6 22.36 26.63

60% 28.12 27.18 30.58

70% 30.75 33.39 34.12

75% 37.32

80% 34.7 42.12 37.26

90% 40 57.13 40.09

95% 72.05

99% 55.78 105.49 42.33

100% 156.93 42.54

556

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Annex A3.2 Three-Phases hydrocyclone tested by MA

Ref. [16] pp.151

Description Value

Flowrate Q cu.m/h 1.40E+00Diameter of

upper

c lindical

D m 4.00E-02

Nominal

diameter of

inlet of oil

Do m 1.40E-02

Inlet

diameter (2

Di m 5.60E-03

Underflow

diameter for

SS

Du m 6.00E-03

Underflow

diameter for

oil

Dp m 1.00E-03

Angle of

conical oil1.5

o

Angle of

conical SS

art

12o

Split ratio 2%

Comparison between Observed efficiency and predicted efficiency for

Three-Phases hydrocyclon

Ref. [16] pp.51

Efficiency

%

Droplet from

predicted

efficiency

curve micron

Droplet from

observed

efficiency

curve micron

10 5.07 8.520 9.00 9

30 12.46

40 15.81 10.5

50 18.82 12

60 21.73 14.25

80 26.83 20.5

100 31.02 42

100 50

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Annex A5.1 Comparison between calculated flux and experimental result from resistance model of UF (reference temparature 20oC)

Item Transmembrane

pressure

Velocity Concentratio

n (by volume

of oil, not

the

Observed flux Membrane

resistance

Gel resistance

coefficient (Rg

= Φ Vα Pt)

Alpha

(exponent of

V)

Gel

concentration

Predicted

flux (J = Pt/

(Rm + Rg))

Ref.

P or Pt V Co Jobserved Rm α Cg Jpredicted

bar m/s % l/(h.m2) % l/(h.m

2)

1 0 2.8 4 0 0.430 0.022 -1.500 16.200 0.00 see note1

2 0.1 2.8 4 14 0.430 0.022 -1.500 16.200 20.97 see note13 0.5 2.8 4 70.8 0.430 0.022 -1.500 16.200 75.21 see note1

4 1 2.8 4 114 0.430 0.022 -1.500 16.200 111.17 see note1

5 1.5 2.8 4 137.29 0.430 0.022 -1.500 16.200 132.24 see note1

6 2 2.8 4 150.8 0.430 0.022 -1.500 16.200 146.08 see note1

7 2.5 2.8 4 162.16 0.430 0.022 -1.500 16.200 155.87 see note1

8 3 2.8 4 165.4 0.430 0.022 -1.500 16.200 163.16 see note1

9 3.5 2.8 4 168.6 0.430 0.022 -1.500 16.200 168.80 see note1

10 0 2.1 4 0 0.430 0.022 -1.500 16.200 0.00 see note1

11 0.24 2.1 4 33.5 0.430 0.022 -1.500 16.200 39.77 see note1

12 0.5 2.1 4 60 0.430 0.022 -1.500 16.200 63.17 see note1

13 1 2.1 4 84.32 0.430 0.022 -1.500 16.200 86.74 see note1

14 1.5 2.1 4 97.3 0.430 0.022 -1.500 16.200 99.05 see note1

15 2 2.1 4 107.6 0.430 0.022 -1.500 16.200 106.62 see note1

16 2.5 2.1 4 110.8 0.430 0.022 -1.500 16.200 111.74 see note1

17 3 2.1 4 114 0.430 0.022 -1.500 16.200 115.44 see note1

18 0 1.4 4 0 0.430 0.022 -1.500 16.200 0.00 see note1

19 0.24 1.4 4 33.5 0.430 0.022 -1.500 16.200 32.05 see note1

20 0.5 1.4 4 45.4 0.430 0.022 -1.500 16.200 45.70 see note1

21 1 1.4 4 54 0.430 0.022 -1.500 16.200 56.88 see note1

22 1.5 1.4 4 59 0.430 0.022 -1.500 16.200 61.93 see note1

23 2 1.4 4 60 0.430 0.022 -1.500 16.200 64.80 see note1

24 2.5 1.4 4 62 0.430 0.022 -1.500 16.200 66.66 see note1

25 3 1.4 4 62.7 0.430 0.022 -1.500 16.200 67.96 see note1

26 3.5 1.4 4 63.24 0.430 0.022 -1.500 16.200 68.92 see note1

27 0 0.7 4 0 0.430 0.022 -1.500 16.200 0.00 see note1

28 0.1 0.7 4 14 0.430 0.022 -1.500 16.200 12.41 see note1

29 0.5 0.7 4 31.9 0.430 0.022 -1.500 16.200 21.66 see note1

30 1 0.7 4 33.5 0.430 0.022 -1.500 16.200 23.89 see note1

31 1.5 0.7 4 33.5 0.430 0.022 -1.500 16.200 24.73 see note132 2 0.7 4 33.5 0.430 0.022 -1.500 16.200 25.18 see note1

33 2.5 0.7 4 33.5 0.430 0.022 -1.500 16.200 25.46 see note1

34 3 0.7 4 33.5 0.430 0.022 -1.500 16.200 25.64 see note1

35 1.0 1.0 3.2 36.51 0.640 0.019 -1.401 16.200 40.07 see note2

36 1.5 1.0 3.2 48.68 0.640 0.019 -1.401 16.200 43.82 see note2

37 2.0 1.0 3.2 48.68 0.640 0.019 -1.401 16.200 45.96 see note2

38 2.5 1.0 3.2 48.68 0.640 0.019 -1.401 16.200 47.36 see note2

39 3.0 1.0 3.2 48.68 0.640 0.019 -1.401 16.200 48.33 see note2

40 1.0 2.0 3.2 60.85 0.640 0.019 -1.401 16.200 74.47 see note2

41 1.5 2.0 3.2 93.31 0.640 0.019 -1.401 16.200 88.53 see note2

42 2.0 2.0 3.2 101.42 0.640 0.019 -1.401 16.200 97.76 see note2

43 2.5 2.0 3.2 109.54 0.640 0.019 -1.401 16.200 104.29 see note2

44 3.0 2.0 3.2 117.65 0.640 0.019 -1.401 16.200 109.14 see note2

45 1.0 2.8 3.2 97.37 0.640 0.019 -1.401 16.200 92.70 see note246 1.5 2.8 3.2 109.54 0.640 0.019 -1.401 16.200 115.55 see note2

47 2.0 2.8 3.2 133.88 0.640 0.019 -1.401 16.200 131.79 see note2

48 2.5 2.8 3.2 154.16 0.640 0.019 -1.401 16.200 143.94 see note2

49 3.0 2.8 3.2 170.39 0.640 0.019 -1.401 16.200 153.35 see note2

Note 1 Ref. [18] pp.86&88, Macroemulsion: Elf Seraft A, UF membrane: IRIS3042 (polyacrylic membrane), MWCO: 50 Kdalton (15 nm.)

2 Ref. [11] , Microemulsion: Elf G3EAB, UF membrane: IRIS3042 (polyacrylic membrane), MWCO: 50 Kdalton (15 nm.)

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Annex A5.2 Comparison between calculated flux and experimental result from film model of UF (reference temperatur

Item Velocity Transme

mbrane

pressure

Concentration

(by volume of

oil, not the

concentrate

Observed flux Constant Constant Constant Predicted flux J =

k Vα

ln (Cg/Co)

Ref

V P or Pt Co Jobserved k Cg Jpredictedm/s bar % l/(h.m

2) % l/(h.m

2)

1 2.8 3.5 4 168.6 34.953 1.165 15.60 157.86 see no

2 2.1 3.5 4 114 34.953 1.165 15.60 112.91 see no

3 1.4 3.5 4 64 34.953 1.165 15.60 70.40 see no

4 0.7 3.5 4 33.5 34.953 1.165 15.60 31.40 see no

5 1.4 3.5 2 105.6 34.953 1.165 15.60 106.25 see no

6 1.4 3.5 8 36 34.953 1.165 15.60 34.55 see no

7 2.8 2 4 150.8 33.554 1.092 16.20 144.39 see no

8 2.1 2 4 107.6 33.554 1.092 16.20 105.48 see no

9 1.4 2 4 61.6 33.554 1.092 16.20 67.76 see no10 0.7 2 4 33.5 33.554 1.092 16.20 31.80 see no

11 1.4 2 2 101.6 33.554 1.092 16.20 101.34 see no

12 1.4 2 8 36 33.554 1.092 16.20 34.18 see no

13 1.4 2 20 28.57 12.293 1.092 100.00 28.57 see no

14 1.4 2 30 21.78 12.293 1.092 100.00 21.37 see no

15 1.4 2 40 17.14 12.293 1.092 100.00 16.27 see no

16 1.4 2 50 11.78 12.293 1.092 100.00 12.30 see no

17 1 3 0.64 42.56 15.448 1.146 14.505 48.21 see no

18 1.5 3 0.64 99.72 15.448 1.146 14.505 76.72 see no

19 2 3 0.64 113.59 15.448 1.146 14.505 106.67 see no20 2.3 3 0.64 130.72 15.448 1.146 14.505 125.19 see no

21 2.8 3 0.64 142.60 15.448 1.146 14.505 156.84 see no

22 2.8 3 1.28 110.91 15.448 1.146 14.505 122.00 see no

Note 1 Ref. [18] pp.86&88, Macroemulsion: Elf Seraft A, UF membrane: IRIS3042 (polyacrylic membrane), MWC

2 Ref. [11] , Microemulsion: Elf G3EAB, UF membrane: IRIS3042 (polyacrylic membrane), MWCO: 50 Kda

3 For item 13 to 16, Cg changes from 16.2% (of item 7-12) to 100%. So there is an inflection point in

flux vs. ln(Co) curve. In this case, the concentration at the inflection point is around 8.0%.

4 Data in tiem 1-6 and item 7 to 12 are observed from the same emulsion but at different pressure.

559

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