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Wat. Res. Vo l. 28, No . 1, pp. 67-7 5, 1994 0043-1354/94 $6.0 0+0 .00

Printed in Gre at Britain. All rights reserved Copyright © 1993 Pergamon Press Ltd

A S L U D G E B IO T IC I N D E X S B I ) F O R T H E E V A L U A T I O N

O F T H E B IO L O G I C A L P E R F O R M A N C E O F A C T I V A T E D

S L U D G E P L A N T S B A S E D O N T H E M I C R O F A U N A

A N A L Y S I S

PAOLO MADO NI~

Istituto d i Ecologia, Universit~i di Parma, Viale delle Scienze, 43100 Parm a, Italy

First received August 1992; accepted in revised for m April 1993)

Ab stra ct-- An objective index, the Sludge Biotic Index (SBI), based on the microfauna associated w ith

activated-sludge mixed liquor, has been devised to monitor activated-sludge plant performance. The

prop osed m ethod makes it possible to define the biological quality of the sludge using numerical values

(biotic index) of 0-10, and to group SBI values into four quality classes. The method is based on two

principles. First , the dominance of the microfauna keygroups changes in relation to the environmental

and operat ional condi t ions of the plant . In par t icular , some protoz oa such as smal l f lagella tes and the

ciliates

Vorticella microstoma

and

Opercularia

spp have a negative influence on the index value. Secondly,

the number of morphological species is reduced as the performance of the plan t gets worse. The ad vanta ge

of this method over other schemes is that i t provides numerical values which enable the operator to

monitor the prevalent plant operating conditions on a daily basis.

Key words- -pro tozoa ,

activated sludge, Sludge Biotic Index, in dicator species, plant performance

INTRODUCTION

N u m e r o u s b i o t i c i n d i c e s h a v e b e e n d e v e l o p e d t o

a s s e s s t h e d e g r e e o f p o l l u t i o n i n f r e s h w a t e r e c o s y s -

t e m s . F o r r i v e r s , t h e E x t e n d e d B i o t i c I n d e x ( E B I ) b y

W o o d i w i s s ( 1 9 8 0 ) , b a s e d o n m a c r o i n v e r t e b r a t e s , i s

o n e o f t h e m o s t w i d e l y u s e d i n E u r o p e . T h i s m e t h o d

i s b a s e d o n t w o p h e n o m e n a : t h e c h a n g e i n t h e

c o m p o s i t i o n o f t h e t a x o c e n o s i s a s t h e p o l l u t i o n l e v e l

r is e s, a n d t h e r e d u c t i o n i n n u m b e r o f t a x o n o m i c

g r o u p s a s p o l l u t i o n i n c r e a s e s . O b j e c t iv e i n d i c e s su c h

a s t h e E x t e n d e d B i o t ic I n d e x a n d t h e S a p r o b i c I n d e x

( S l a d e c e k , 1 9 7 3 ) , p r e s e n t m e t h o d s f o r c a l c u l a t i n g

f i x e d i n d e x v a l u e s f o r a n y g i v e n c o m m u n i t y , i n d e p e n -

d e n t o f t h e a n a l y s t ' s p e r s o n a l e v a l u a ti o n . B o t h t h e

r a n d o m f l u c tu a t i o n s fo u n d i n s a m p l e s t a k e n u n d e r

t h e s a m e c o n d i t i o n s a n d t h e p e r s o n a l s u b j e c t i v it y i n

s a m p l i n g a n d c o u n t i n g t e c h n i q u e s , r e p r e s e n t tw o

f a c t o r s p o s s i b l y i n t r o d u c i n g a c e r t a i n d e g r e e o f u n -

c o n t r o l l e d v a r i a b i l i t y .

T h e r o u t i n e a n a l y s i s o f t h e m i c r o f a u n a a s a n

i n d i c a t o r o f a c t i v a te d - s l u d g e p la n t p e r f o r m a n c e i s

b e c o m i n g m o r e a n d m o r e c o m m o n . T h i s a n a ly s i s

q u i c k l y g i v e s u s e f u l i n f o r m a t i o n o n t h e b i o l o g i c a l

a c t i v i t y o f t h e s l u d g e b a s e d o n t h e c o m m u n i t y s t r u c -

t u r e o f th e m i c r o o r g a n i s m s p r e s e n t . H o w e v e r , t h e

m i c r o f a u n a i s a l s o u s e d t o i n d i c a t e c h a n g e s i n t h e

p e r f o r m a n c e o f s p e c if i c a c t i v a t e d - s l u d g e p l a n t s ( A I -

S h a h w a n i a n d H o r a n , 1 99 1; E s t e b a n

e t a l . ,

1991) but

t h e s e m e t h o d s c a n n o t n e c e s s a r i l y b e a p p l i e d d i r e c t l y

t o o t h e r s i m i l a r p l a n t s . O n t h e c o n t r a r y , o t h e r

m e t h o d s , b a s e d o n m i c r o s c o p i c an a l y s is c a n b e a p -

p l i e d t o a n y p l a n t t o e s t i m a t e b o t h t h e q u a l i t y o f th e

e f f lu e n t ( C u r d s a n d C o c k b u r n , 1 9 70 b ) a n d t h e p e r -

f o r m a n c e o f t h e p l a n t ( D r a k i d e s , 1 9 7 8; M a d o n i ,

1981, 1988) . S om e o f these m e tho ds , how ever , a r e

s u b j e c t i v e i n d i c e s n o t b e i n g b a s e d o n r i g i d c a l c u -

l a t i o n s , b u t o n t h e a n a l y s t ' s p e r s o n a l i n t e r p r e t a t i o n o f

t h e m i c r o f a u n a t h a t c o l o n i z e t h e a c t i v a t e d s l u d g e

u n d e r i n v e s t i g a t i o n . O b j e c t i v e i n d i c e s h a v e a g r e a t

a d v a n t a g e o v e r s u b j e c t iv e o n e s in t h a t i n d e x v a l u e s

a s s e s s e d b y d i f f e r e n t o p e r a t o r s a r e c o m p a r a b l e .

I n t h i s p a p e r a n o b j e c t i v e i n d e x i s p r o p o s e d t o

e s t i m a t e t h e b i o l o g i c a l q u a l i t y o f t h e s l u d g e i n a n

a e r a t i o n t a n k o f a c t i v a t e d - s l u d g e p l a n t s . T h e m e t h o d ,

t h a t i s i n s p i r e d b y t h e E x t e n d e d B i o t i c I n d e x

( W o o d i w i s s , 1 9 8 0) i s a p p l i c a b l e t o a l l t y p e s o f a c t i -

v a t e d - s l u d g e p l a n t s .

MICROFAUNA IN ACTIVATEDSLUDGE

B i o l o g i c a l s e w a g e - t r e a t m e n t p l a n t s m a y b e r e -

g a r d e d a s m a n - m a d e e c o s y s t e m s s u b je c t e d to e x t r e m e

c o n d i t i o n s . A s i n e v e r y o t h e r b i o l o g i c a l s y st e m , t h e

c o m m u n i t y l i v i n g i n t h e a e r a t i o n b a s i n o f a n a c t i -

v a t e d - s l u d g e p l a n t h a s a p r e c i s e s t r u c t u r e ( c o m -

p o n e n t s a n d f a c t o r s ) a n d f o l l o w s e x a c t d y n a m i c s ( i n

t i m e a n d s p a c e ) . I n a c t i v a t e d s l u d g e s , b i o t i c c o m -

p o n e n t s a r e r e p r e s e n t e d b y d e c o m p o s e r s ( b a c t e r i a ,

f u n g i ) w h i c h u t i l i z e t h e d i s s o l v e d o r g a n i c m a t t e r i n

t h e w a s t e w a t e r , a n d b y c o n s u m e r s ( h e t e r o t r o p h i c

f l a g e ll a t e s, c i l ia t e s , r h i z o p o d s , a n d s m a l l m e t a z o a n s )

w h i c h f e e d o n d i s p e r s e d b a c t e r i a a n d o t h e r o r g a n -

i s m s . I t is w e l l - k n o w n t h a t a c t i v a t e d s l u d g e s d e v e l o p

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PA O L O M A D O N I

Table 1. List of ciliated protozo a com mo nly found in activated sludg es and th eir food h abit

Bacterivorous

Carn ivorous Free-swimming Crawl ing At tached

Holotrichs Colpoda sp Aspidisca cicada Carchesium sp p

A ci ne ri a i n c u r v a t a C o l p i d i u m olpoda Aspidisca lynceus Episo lis spp

Amphileptus sp. Colpidium campylum Chi lodone l la unc inata O pe rc ul ar iaoarctato

Coleps hirtus* Cinetochilum margaritaceum Euplotes affinis Opercularia microdiscus

Litonotus spp Cyclidium glaucoma Euplotes moebiusi Opercularia minima

Spathidium

spp

Dexiotricha

sp.

Euplotes patella Stentor

spp

Sucto r ians Glaucoma scintillans Stylonychia spp Vaginicola crystallina

Acineta spp Loxocephalus sp. Tri thigmostoma cucu Uu lus Vo rt ic e l la om al lar ia

Metacineta sp. Paramecium spp Trochilia minuta Vortwella microstoma

Podophrya spp P s e u d o c o h n i l e m b u susillus Vorticella octava

Tokophrya spp Sathrophilus sp. Zoothamnium spp

Spirostomum teres

Tetrahymena pyriformis

complex

Uronema nigricans

Acineria uncinatat

Drepanomonas revolutat

Trachelophyllum pusillum t

*Omnivorous;

t incertae saedis:

these species are free-swimming forms but their grazing activity seems to be linked to the

floc.

spec if ic com mun i t i e s o f p r o t ozo a w hi ch a r e sus t a i ned

by l a r ge popu l a t i ons o f bac t e r ia . C i l i a ted p r o t ozo a

a r e ve r y nu mer o us i n a l l t ypes o f ae r ob i c b i o l og ica l -

t r e a t m e n t s y s t e m s ; t h e y a r e c o m m o n l y f o u n d i n

densi t i es of abou t 10,000 cell s /ml of ac t ivated s ludge

mi xed l i quor , and cons t i t u t e appr ox . 5 % of t he d r y

w e i gh t o f suspended so l i ds i n mi xed li quor . A l t ho ugh

abo u t 230 spec ie s o f p r o t o zoa hav e been obse r ved

i n t he va r i ous t ypes o f ae r ob i c t r ea t men t sys t ems ,

on l y f ew have been obse r ved f r equen t l y ( C ur ds

and C ockbur n , 1970a ; Madon i and G he t t i , 1981) .

Tab le 1 show s the li st of the mo st im po r tan t c i li a tes

f ound i n ac t i va t ed s l udge . T he ma j o r i t y o f c i l i a t e s

p r e sen t i n b i o l og i ca l w a t e r t r ea t men t p l an t s f eed

upo n d i spe r sed popu l a t i ons o f bac t e r i a . T he bac t e r i vo-

rous c i l i a tes in act ivated s ludge can be subdivided

i n t o t h r ee g r o ups on t he bas i s o f behav i our : f r ee -

sw i mmer s , c r aw l e r s , and a t t ached .

Al l bacter ivorous c i l i a tes re ly upon c i l i ary cur rents

t o f o r ce suspended bac t e r i a i n t o t he o r a l r eg i on . So ,

whi le f ree-swimming and a t tached c i l i a tes are in

com pe t i t i on f o r bac t e r i a d i spe rsed i n t he l i qu i d phase ,

c r aw l i ng f o r ms , t ha t a r e i n c l ose p r ox i mi t y t o su r f ace

gr ow t hs , f eed upon pa r t i c l e s t ha t on l y l i gh t l y adhe r e

t o t he s l udge and t ha t a r e d i s l odged by t he f eed i ng

currents very eas i ly .

~ S l u d g e

F l a g e l l a t e s b a ct e r i a b a c t e r i a

Ca r n i v o r o u s

c i l i a t e s

I Fi l te r - fe ed ing I

v I c i l ia tes

D i sp e r se d

O r g a n i c m a t t e r ( D O M - P O M )

Fig. 1. Trophic web in the activated-sludge process.

C i l ia t ed p r o t ozo a i mp r ove t he q ua l i t y o f t he e f fl u-

ent . In thei r absence the ef f luents f lowing f rom the

sys t em, have an e l eva t ed B O D and a r e h i gh l y t u r b i d

due t o t he p r e sence o f man y d i spe r sed bac t e r i a

( C u r d s e t a l . 1968) . I n t he a e r a t i on t ank o f b i o l og i ca l

processes a t rue t rophic web i s es tabl i shed. A s im-

pl if ied d iagra m of thi s i s i l lus t ra ted in Fig. 1 . The

b i o l og i ca l sys t ems o f t hese p l an t s cons i s t o f popu-

l a t ions i n con t i nu ous com pe t i t i on w i t h each o t he r f o r

f ood . T he r e l a t i onsh ips o f com pe t i t i on and p r eda t i on

c r ea t e osc i ll a t ions and succes si on o f pop u l a t i ons un t il

dynamic s tabi l i ty i s reached (Fig. 2) . This i s s t r i c t ly

d e p e n d e n t o n p l a n t m a n a g e m e n t c h o i c e s b a s e d o n

des i gn cha r ac t e r i s t i c s a i med a t gua r an t ee i ng op t i -

mum ef f ic iency (Madoni , 1986) .

R esu l t s f r om r e sea r ch on t he moda l i t i e s o f co l o -

n i za t i on and o f popu l a t i o n succes s i on in ac t i va t ed

s l udge have been o f g r ea t i mpo r t ance i n unde r s t and-

i ng the r o l e o f p r o t o zoa a s p l an t p e r f o r m ance i nd i -

ca t o r s and demons t r a t ed t he de t e r mi n i ng e f f ec t o f

env i r onment a l cond i t i ons i n t he ae r a t i on t ank on t he

c i li a te com mu ni t y e s t ab li shed ( C ur ds , 196 6 , 1971 ;

M ado n i and Po l i , 1981 ; M adon i , 1982; Ma don i and

Antonie t t i , 1984) .

+ F l a g e l l a t e s

1 0 0 F • S w i m m i n g c i l i a te s

| O A t t a t c h e d c i l i a t e s

,- -- , 8 0 b [] D i sp e r se d b a c t e r i a ~ z r ~

. ~ j n C r a w li ng c i l i a t e s f

~ 6 0 b / + / t : f / . . . .

I+' + \ y m l

\ f

_~ ,

I ~ ' X - . , ~ ? .. L + ~

~ . ~ . - r ~ o ~ _ ~ ¢ ~ Q_

0 10 20 30 40 50 60

T i m e ( d a y s )

Fig. 2. Successions of microorgan isms during the establish-

ment o f an act ivated sludge.

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Sludge Biotic Index

Table 2. Some situations regarding he plant performance ndicated by the dominant group of the m icrofauna (from

M adon i, 1986, 1988 modified)

69

Do min ant group Performance Possible causes

Sm all flagellates Low

Small swim ming iliates Mediocre

Large swim min g ci l iates Mediocre

Craw ling ciliates Goo d

Sessile and crawling Good

ciliates

Sessile ciliates Decreasing

Small naked amoebae Poor

and flagellates

Testate amoebae Good

Poorly aerated sludge; overloading; ermentingsubstances nvolved

Too shor t sewage retention time; poorly aerated sludge

Overloading; poorly aerated sludge

Transient phenomena discontinuous oad, recent sludge extraction)

Very high load, n ot ea sily degradable

T h e s t r u c t u r e o f t h e m i c r o f a u n a is in d e e d a v a l i d

i n d i c a t o r o f p u r i f i c a t i o n p l a n t p e r f o r m a n c e . I n s y n -

t h e s i s , a n e f f ic i e n t a c t i v a t e d s l u d g e p l a n t p r e s e n t s t h e

f o l l o w i n g c h a r a c t e ri s t ic s :

( 1 ) H i g h n u m b e r s o f m i c r o f a u n a c e l ls (> 11 06 o r -

g a n i s m s / l ) ;

( 2) M i c r o f a u n a c o m p o s e d c h i e fl y b y c r a w l i n g a n d

a t t a c h e d c i l i a t e s , w i t h a l m o s t n o f l a g e l l a t e s ;

( 3 ) T h e s p e c ie s a n d c i l ia t e g r o u p s a r e h i g h l y d i v e r -

s if ie d a n d n o n e d o m i n a t e s n u m e r i c a l ly o v e r t h e

o t h e r s b y a f a c t o r g r e a t e r t h a n 1 0 .

W h e n t h i s is n o t t h e c a s e, t h e i d e n t i f i c a t i o n o f th e

d o m i n a n t g r o u p ( k e y g r o u p ) o f t h e m i c r o f a u n a a l lo w s

d i a g n o s i s o f t h e p a r t i c u l a r s t a t e o f f u n c t i o n a l i t y o f t h e

p l a n t ( M a d o n i , 1 98 6) . S o m e e x a m p l e s o f th e s e s it u -

a t i o n s a r e r e p o r t e d i n T a b l e 2 .

T H K Y G R O U PS

Q u a n t i f y i n g th e i n d i c a t o r v a l u e o f t h e m i c r o f a u n a

i s a d i f f i c u l t t a s k b e c a u s e t h e r e a r e g r o u p s wh i c h a r e

m o r e o r l es s to l e r a n t t o a w i d e r a n g e o f e n v i r o n m e n -

t a l f a c to r s , w h i l s t th e p l a n t p e r f o r m a n c e r e s u l t s f r o m

t h e s i m u l t a n e o u s a c t i o n o f m a n y o f t h es e e x t e rn a l a n d

o p e r a t i o n a l c o n d i t i o n s . I n t h i s in v e s t i g a t i o n , t h e r e -

l a t i o n s h i p b e t w e e n t h e v a r i o u s g r o u p s o f t h e m i c r o -

f a u n a a n d t h e m a i n o p e r a t i o n a l c o n d i t io n s o f th e

p l a n t w e r e s t u d i e d b y a w i d e s u r v e y . F o r t y - f o u r

a c t i v a t e d s l u d g e p l a n t s , i n c l u d i n g o x i d a t i o n d i t c h e s ,

c o n v e n t i o n a l a e r a t i o n p l a n t s a n d e x t e n d e d a e r a t i o n

u n i t s , w e r e s a m p l e d a n d t h e i r ch o i c e w a s m a d e i n

o r d e r t o e x p l o r e a d i v e r s e s p e c t r u m o f d i f f er e n t

o p e r a t i o n a l c o n d i t i o n s . T a b l e 3 s h o w s t h e c o r r e l a t i o n

c o e f f i c i e n t s b e t w e e n n i n e g r o u p s o f t h e m i c r o f a u n a

a n d s ix p h y s i c o - c h e m i c a l a n d o p e r a t i o n a l p a r -

a m e t e r s . T h e s e r e s u lt s c o r r o b o r a t e t h e o b s e r v a t i o n s

o f p r e v i o u s a u t h o r s , a n d e n a b l e o n e t o s e l ec t a n d

g r o u p m i c r o f a u n a o r g a n i s m s i n t o p o si t iv e a n d n e g a -

t i v e k e y g r o u p s . T h e p o s i t i v e k e y g r o u p s a r e c r a w l i n g

a n d a t t a c h e d c i l i a t e s , a n d t e s t a t e a m o e b a e ; n e g a t i v e

k e y g r o u p s a r e s m a l l fl a g e ll a te s , s w i m m i n g b a c t e r i v o -

r o u s c i l i a t e s , a n d t h e p e r i t r i c h c i l i a t e s

V o r t i c el l a m i -

c r o s t o m a a n d O p e r c u l a r i a s p p . D e n s i t y a n d d i v e r s i t y

o f t h e m i c r o f a u n a , m o r e o v e r , r e s u l t s to b e h i g h l y

c o r r e l a t e d t o t h e p l a n t p e r f o r m a n c e .

D e n s i t y a n d d i v e r s i t y

M a n y r e c e n t s t ud i e s h av e d e m o n s t r a t e d t h a t t h e

n u m b e r o f c i l ia t ed p r o t o z o a l i v in g in a n o r m a l l y

f u n c t i o n i n g p l a n t i s a b o u t l 06 i n d i v i d u a l s / l . W h e n t h e

n u m b e r f a l l s b e l o w 1 0 4/ 1, i t i n d i c a t e s i n s u f f i c i e n t

p u r i f i c a t i o n ( C u r d s , 1 97 5; D r a k i d e s , 1 98 0; M a d o n i ,

1 9 81 ). I n t h i s c a s e , t h e r e i s a p r o l i f e r a t i o n o f d i s p e r s e d

b a c t e r i a w h i c h m a k e t h e e f f l u e n t t u r b i d a n d c o n s e -

q u e n t l y c a u s e a g re a t l y in c r e a s e d B O D i n th e o u t p u t

w a t e r . A h i g h n u m b e r o f c i l ia t e s ( > 10 7/ 1) o n t h e

c o n t r a r y , a l m o s t a l w a y s i n d i c a t e s g o o d p u r i f i c a t i o n

a n d o p t i m u m p l a n t p er f o rm a n c e . T h e m i c r o f au n a o f

a n o r m a l l y f u n c t i o n i n g s y s t e m i s a l m o s t a l w a y s

h i g h l y d i v e r s i f i e d , n a m e l y c o m p o s e d b y d i f f e r e n t

g r o u p s o f o r g a n i s m s , e a c h g r o u p w i t h s e v e ra l s pe c ie s .

N o g r o u p o r s p e ci es i s e v e r n u m e r i c a l ly d o m i n a n t

o v e r t h e o t h e r c o m p o n e n t s , e v e n i f t h e r a t i o s b e t w e e n

v a r i o u s g r o u p s o r s p e c i es c a n d i f fe r . O n t h e c o n t r a r y ,

a m i c r o f a u n a w h i c h i s d o m i n a t e d b y o n e s p e c i e s o r

g r o u p i s a l m o s t a l w a y s a n i n d e x o f t r o p h i c i m b a l -

a n c e s d u e t o t h e e x i s te n c e o f l i m i t i n g f a c t o rs i m p e d i n g

t h e d e v e l o p m e n t o f m o s t o f t h e o t h e r s p e c i e s a n d

f a v o u r i n g th e g r o w t h o f f o r m s m o r e t o l e r a n t t o t h e s e

f a ct o rs . T h e m o s t c o m m o n l i m i ti n g c o n d i t i o n s a r e

g e n e r a l l y th e p r e s e n c e o f a s h o c k l o a d o f t o x ic

Table 3. C orrelation coefficientsbetween protozoans and plan t operationalconditions,obtained from 44 activated sludge

plants (*P < 0.01, **P < 0.001)

Nitrifying BOD Effluent Sludge

DO ability removed colour age MLSS

Small flagellates -0.652* *

Swimmingciliates - 0.651**

Craw ling ciliates 0.616"*

Sessile ciliates 0.340

V. mk rostoma -0.676**

Opercularia spp -0.745**

Testate amoebae 0.727**

Micro fauna density 0.626**

No. of species 0.778**

-0.596** -0.798** 0.836** -0.583** -0.736**

-0.549** -0.829** 0.725** -0.668* * -0.753* *

0.620** 0.784** -0.6 11* * 0.534** 0.534**

-0.0 29 0.432* -0.5 16" * 0.171 0.266

-0.504** -0.679** 0.648** -0.638** -0.722**

-0.597** -0.763* * 0.676** -0.008 -0.181

0.912"* 0.760** --0.583** 0.464* 0.464*

0.429* 0.762** --0.768** 0.335 0.495**

0.645** 0.923** -0.8 41" * 0.487** 0.591"*

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70 P OLO MJdgONI

d i scha r ge , t he unde r - o r t he ove r l oad i ng , t he s t r ong

s l udge ex t r ac t i on , t he l ack o f ae r a t i on .

R e c e n t d a t a o b t a i n e d f r o m a s u r v e y o f p r o t o z o a i n

seve r a l ac t i va t ed - s l udge p l an t s ( D e Mar co e t a l . ,

1991) , co r r o bor a t e t hese r e su l ts ob t a i ned i n p r ev i ous

w or ks . T hese au t hor s c la ss if ied t he abu ndan ce o f the

microfauna into three c lasses (< 104, 104-106, > 106)

according to the ef f ic iency of the plant (not ef f ic ient ,

poorly efficient , well efficient respectively) and, by

mean s o f t he K r us ka l - W al l i s t e s t o f va r i ance , w ere

a b l e to p o i n t o u t t h a t b o t h o r g a n i c l o a d r e m o v e d a n d

met a l co ncen t r a t i on i n t he mi xed l i quor w er e s i gn if i-

can t l y d i f f e r en t i n t he t r ea t men t p l an t s , a ccor d i ng t o

t he t h r ee c l as se s o f p r o t ozo a abu ndanc e . S t a ti s ti ca l

ana l ys i s app l ied t o t he s t udy o f c i li a te s and o f

phys i co - chem i ca l va ri ab l e s i n ac t i va t ed s l udge s ew age

t r e a t m e n t p l a n t s s h o w e d t h a t t h e n u m b e r a n d d i v er -

s i ty o f c il i at e comm uni t i e s change accor d i ng t o t he

qua l i t y o f en t e r i ng s e t tl ed s ew age and ope r a t i ng

c o n d i t i o n s o f t h e p l a n t ( E s t eb a n

et al . ,

1991; Esteban

and Tellez, 1992).

C r a w l i n g a n d a t t a c h e d c i l i a t e s

T hese t w o c i l i a t e g r oups nor ma l l y co - domi na t e t he

mi c r o f auna i n ac t i va t ed s l udge p l an t s . T h i s i s due t o

t he i r d i f f e r en t f ood hab i t s p r even t i ng t he i r compe-

t i ti on . N eve r t he l e s s , t he r a t io be t w een t he t w o g r oup s

tends to change wi th s ludge loading. Crawl ing c i l i a tes

d i mi n i sh t he i r p r e sence a s s l udge l oad i ng i nc r eases so

t h a t a b o v e 0 . 6 k g B O D / k g M L S S • d , m o s t s p ec ie s o f

t h i s g r oup d i s appea r ( C ur ds and C ockbur n , 1970b ;

Kl im ow icz, 1 970) . Craw l ing c i li a tes are a l so inversely

re la ted to SVI . H igh d ensi t ies of crawl ing c i l ia tes

( > 2000 ml - ~ ) a r e a l w ays a s soc i a t ed t o SV I va l ues

sma l l e r t han 200 ; a t SV I va l ues g r ea t e r t han 400

crawl ing c i l i a tes reduce dras t ica l ly in number

( Pagno t t a and T ommas i , 1979) .

T e s t a te a m o e b a e

T es t a t e amoebae i n ac t i va t ed s l udge a r e r ep -

r e sen t ed by t he t h r ee gene r a :

Arce l la , Di f f tug ia

a n d

E u g l y p h a . T hese p r o t ozoa co l on i ze t he s l udge o f

p l an t s a t ve r y l ow s ludge l oad , i n pa r t i cu l a r t hey a r e

f o u n d n o r m a l l y i n t h e a e r a ti o n b a s i n o f N r e m o v a l

p l an t s ( Poo l e , 1984). T es t a t e amoe bae a r e mo r e abun-

dan t o r domi nan t i n s l udges cha r ac t e r i zed by l ow

l oad i ng , l ong r e t en t ion t i me , and h i gh D O i n ae r a t i on

t ank t ha t enab l e compl e t e n i t r i f i ca t i on ( D r ak i des ,

1978; C h i e r ic i and Ma don i , 1991) . U nd e r t hese con-

di t ions , the q ual i ty o f the ef fluent i s excellent and high

pe r f o r m ance o f t he p l an t is r eached . T es t a te am oebae

a r e mor e abundan t i n p l an t s w i t h a l a r ge s l udge age

s i nce t e s t a t e s have l ow g r ow t h r a t e s . T hey o f t en a r e

s e a s o n a l b e i n g m o r e c o m m o n i n s u m m e r w h e n t e m -

pe r a t u r e and g r ow t h r a t e s i nc r ease . Sasaha r a and

O g aw a ( 1983) f ound t ha t E u g l y p h a a n d Di f f tug ia w er e

a l w ays abundan t i n ac t i va t ed - s l udge p l an t s f o r b r ew -

e r y e ff l uen t w i th l ow s l udge l oad and goo d qua l i t y o f

the ef f luent . When the s ludge load was high

( > 1 k g B O D / k g M L S S . d ) a n d t h e C O D o f th e ef flu -

ent was e levated, these species were replaced by the

per i t r i ch c i l i a te Op e r c u l a r i a and by f r ee - sw i mmi ng

ci l ia tes . Madoni et al . (1993) were able to f ind high

corre la t ion coef f ic ients between the presence

nd

a b u n d a n c e o f te s ta t e a m o e b a e a n d s o m e p r e v a il in g

env i r onm ent a l f ac t o r s and n i t r i f y ing cond i t i ons o f t he

plant . These species , in fact , were associa ted wi th low

a m m o n i a c a l - N c o n c e n t r a t i o n s , h i g h D O v a l u e s a n d

l ow s l udge l oad and SV I va l ues .

A t t a c h e d c il ia t es ( > 8 0 )

Per i t r i ch c i l i a t e s a r e nor ma l l y co - domi nan t i n t he

act ivated s ludge. Never theless , a mass ive increase in

t h e ir n u m b e r ( > 8 0 % o f t h e w h o l e m i c r o f a u n a ) o c -

cur s i n occas i on o f t r ans ien t s i t ua t i ons t h a t r edu ce t he

p l an t pe r f o r mance ( D r ak i des , 1978 ; Madon i , 1981) .

Such t r ans i en t cond i t i ons a r e ( 1 ) a qu i ck i nc r ease o f

t he s l udge l oad due t o l os s o f s ludge and ( 2 ) a

d i s con t i nuous i npu t o f o r gan i c l oad f r om t he i n f luen t .

C ur ds and C ockbur n ( 1970b) f ound t ha t s e s s i l e c i l i -

a r e s w er e ab l e t o g r ow t h r oughou t a l a r ge r ange o f

s l udge i oad ings ; neve r the l e ss , a t va l ues r ang i ng f r om

0.3 t o 0 .6 kg B O D / k g M L S S. d , t he se c il ia te s dom i -

na t ed , and f o r s l udge I oad i ngs o f 0 .6 - 0 .9 s es si le

c i li a tes an d f lagellates c o-d om inate d. Evide nce was

f o u n d b y B e d o g n i

et al .

(1991) which suggested that

t he abundance r a t i o be t w een c r aw l i ng and a t t ached

c il ia te s w as a s soc i a t ed w i t h t he pe r f o r man ce o f t he

p l an t . When r a t i o va l ues w er e h i gh ( >0 .5 ) a be t t e r

qual i ty of the f inal ef f luent was achieved.

A m on g a t t ached c il ia te s some f o r m s such a s V o r t i -

c e l ia m i c r o s t o m a

a n d

Op e r c u l a r i a

spp can su r v i ve and

gr ow i n ac t i va t ed s l udge sub j ec t ed t o s eve r e con-

d i t i ons ( l ack o f oxygen , t ox i can t s , e t c. ). W hen t hese

spec i e s a r e p r e sen t i n h i gh number s , t hey mus t be

cons i de r ed a s s epa r a t e keygr oups ( s ee be l ow ) .

Op e r c u l a r i a s p p

T hr ee speci es a r e com mo nl y f ound i n ac ti va t ed

s ludge: O. coarc ta ta , O. microd i scus , and O . m i n i m a .

L ow num ber s o f these c il ia te s a r e o f t en obse r ved i n

act ivated s ludge. Never theless , Op e r c u l a r i a show s a

c l ose a s soc i a t i on w i t h t he va r i ab l e s conce r ned w i t h

t he qua l i t y o f t he ac t i va t ed s l udge and s t a t i s t i ca l

analys i s conf i rm s that these c i li a tes are qui te useful as

b i o i nd i ca t o r s , because t he i r number i nc r eases w hen

t he ac t i va t ed s l udge is o f bad qu a l i t y ( E s t eban et al . ,

1991) . C ur d s and C ock bur n ( 1970b) f o und t ha t

O p e r -

cularia spp were associa ted wi th high f inal ef f luent

B O D concen t r a t i ons , and K l i mow i cz ( 1970) f ound

t ha t t hese spec i e s w er e among t he mos t abundan t

f o r ms a t h i gh l oad i ngs .

Op e r c u l a r i a

s p p m o r e o v e r c a n

sur v i ve i n s t r e s sed env i r onment s be t t e r t han o t he r

p r o t o z o a n s . S o m e a u t h o r s ( A n t o n i e t t i

e t a l . ,

1982;

Becares , 1991; Card inale t t i and Zi te l li , 1991) , in fact ,

f o u n d t h a t l a r g e n u m b e r s o f

Op e r c u l a r i a

occur i n

s l udge o f p l an t s r ece i v i ng i ndus tr i a l w as t e con t a i n i ng

toxic substances .

Op e r c u l a r i a c o a r c t a t a

m a y b e t h e

o n l y c o m p o n e n t o f t h e m i c r o f a u n a , i n s lu d g es o f

p l an t s t r ea t i ng i ndus t r i a l w as t e con t a i n i ng me t a l

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Sludge Biotic Index

71

sa l t s . O . mi c r o d i s c u s i s a b l e t o s u r v i v e t o s e v e r e la c k

o f o x y g e n f o u n d i n s e d i m e n t a t io n t a n k s w i t h l o w

r e t u r n - s l u d g e r a t i o . M o r e o v e r , t h e s e s p e c i es w e re

a s s o c i a t e d w i t h h i g h fi n a l e f f lu e n t B O D a n d a m m o n i -

a c a l - N c o n c e n t r a t i o n s ( P o o l e , 1 9 84 ; M a d o n i et al . ,

1993).

Op e r c u l a r i a

s p p o f t e n a r e a s s o c i a t e d w i t h V .

m i c r o s t o m a .

V o r t i c e l l a m i c r o s t o ma

T h e c i l i a t e V . m i c r o s t o ma i s q u o t e d i n t h e s a p r o b i c

s y s t e m a s a p o l y s a p r o b i c s p e c ie s ( S l a d e c e k , 1 9 73 ;

F o i s sne r , 1988) . T h i s c i l i a t e is f r equen t ly p re sen t i n

t h e p l a n t d u r i n g t h e f ir s t p h a s e o f c o l o n i z a t i o n b u t i s

s u b s t i t u t e d b y o t h e r s p e c i e s V. conva l lar ia ) w h i c h

b e c o m e d o m i n a n t d u r i n g s t a b l e c o n d i t i o n s . W h e n

t h e r e i s a d r a s t i c r e d u c t i o n i n t h e d i s s o l v e d o x y g e n

c o n c e n t r a t i o n i n t h e m i x e d l i q u o r , a n a l t e r n a t i o n o f

t h e t w o s p e c i es is o b s e r v e d , d u e t o t h e i r d i f f e r e n t

d e g r e e o f t o le r a n c e t o t h e l a c k o f o x y g e n ( M a d o n i

and A nton i e t t i , 1984) . V . m i c r o s t o ma t hus , i nd i ca t e s

a l a c k o f d i s s o l v e d o x y g e n i n t h e a e r a t i o n t a n k ; t h e

g r e a t e s t r e s i s t a n c e t o t h e i n f l u e n c e o f a n o x i c e n v i r o n -

m e n t w a s n o t i c e d f o r t h i s s p e c ie s a l s o b y o t h e r

au thor s (B ick , 1972 ; T om an and R e j i c , 1988) . M as -

s iv e g r o w t h o f t h i s s e s s il e c i l i a te w a s o b s e r v e d i n t h e

a e r a t i o n t a n k s i n o c c a s i o n s o f h i g h w a s t e w a t e r f l o w

a r r i v a l t o t h e s e w a g e p l a n t a n d l o w v a l u e s o f m a s s i c

l o a d i n g a n d w a t e r c o l o u r o f t h e e f f l u e n t ( E s t e b a n

e t a l . , 1 9 9 0 ) . L a r g e n u m b e r s o f V . m i c r o s t o ma in

o c c a s i o n s o f l o w v a l u es o f D O , M L S S , a n d h i g h

v a l u e s o f s lu d g e l o a d a n d S V I , w e r e f o u n d a l s o b y

P o o l e ( 1 9 8 4 ) a n d E s t e b a n et al . (1991).

F r e e - s w i mmi n g c i l i a t e s

S w i m m i n g b a c t i v o r o u s c i l i at e s a r e m o r e a b u n d a n t

i n t h e e a r l y p h a s e s o f a d e v e l o p i n g p l a n t , w h e n s l u d g e

f locs a r e s t i l l s ca rce and , co nseq uen t ly , s e s s i l e c i l i a t e s

a r e a b s e n t . N e v e r t h e l e s s , th e y a r e s o o n s u b s t i t u t e d b y

a t t a c h e d c i l i a te p o p u l a t i o n o w i n g t o c o m p e t i t i o n f o r

d i s p e r s e d b a c t e r i a . A t t a c h e d c i l i a t e s , i n f a c t , a r e

f i lt e r - fe e d e r s m o r e e f fi c ie n t t h a n f r e e - s w i m m i n g f o r m s

t o e n f o r c i n g s u s p e n d e d b a c t e r i a i n t o t h e o r a l r e g i o n

b y m e a n s o f c i l i a r y c u r r e n t s . C u r d s ( 1 97 1 ) w a s a b l e

t o s h o w , b y m e a n s o f c o m p u t e r s i m u l a t io n o f m i c r o -

b i a l p o p u l a t i o n d y n a m i c s , t h a t h i g h - q u a l i t y e f f l u e n t

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

w e r e d o m i n a n t , a s l i g h t l y w o r s e e f f lu e n t q u a l i t y w h e n

f r e e - s w i m m i n g c i li a t e s w e r e d o m i n a n t , a n d a l o w -

qua l i t y e f f l uen t w hen no c i l i a t e s w ere p re s en t a t a l l .

S m a l l f r e e - s w i m m i n g c i l ia t e s ( su c h a s

C o l p i d i u m, C y -

c l i d i u m, T e t r a h y me n a , a n d U r o n e m a ) s o m e t i m e s

d o m i n a t e t h e m i c r o f a u n a o f p l a n t s o p e r a ti n g a t

s l u d g e t o o s h o r t a g e d o r a t b o t h h i g h s l u d g e l o a d i n g

a n d l a c k o f o x y g e n . T h e s e b a c t e r i v o r o u s p r o t o z o a n s

r e q u i r e h i g h c o n c e n t r a t i o n s o f d i s p e r s e d b a c t e r i a

b u t s u r v i v e b e tt e r t h a n o t h e r c o m p o n e n t s o f t h e

m i c r o f a u n a t o t h e t o x i c i t y o f t h e in f l u e n t a n d t o

l a c k o f o x y g e n . S m a l l f r e e - s w i m m i n g c i l i a t e s e v e r

c o u p l e w i t h h e t e r o t r o p h i c f l a g e ll a t e s a n d s o m e t i m e s

t h e s e t w o k e y g r o u p s c o - d o m i n a t e t h e m i c r o f a u n a .

C u r d s a n d C o c k b u r n ( 1 9 7 0 b ) f o u n d t h a t s w i m m i n g

f o r m s w e r e d o m i n a n t a t h i g h s l u d g e l o a d i n g s

( 0 .6 - 0 .9 k g B O D / k g M L S S . d ) .

I t s h o u l d b e e m p h a s i z e d t h a t t o t h i s k e y g r o u p

b e l o n g o n l y b a c t e r i v o r o u s c i l i a t e s ; f r e e - s w i m m i n g

c a r n i v o r o u s f o r m s s u c h a s A mp h i l e p t u s , L i t o n o t u s ,

S p a t h i d i u m, e t c . ( s ee T ab l e 1 ) m us t no t be i n se r t ed

i n t o t h i s k e y g r o u p .

Flage l la te s

S m a l l h e t e r o t r o p h i c f l a g e l l a t e s s u c h a s B o d o , P o l y -

t o ma , a n d T e t r a mi t u s , n o r m a l l y d o m i n a t e t h e m i c r o -

f a u n a d u r i n g t h e s t a r t i n g p h a s e o f th e p l a n t w h e n

f l o c - f o r m i n g b a c t e r i a a r e s t il l s c a rc e l y p r e s e n t . T h e y

f e e d o n d i s p e r s e d b a c t e r i a a n d , i n t i m e , a r e s u b s t i -

t u t e d b y b a c t e r i v o r o u s c i li a t es . B y c o n t r a s t , t h e m a s -

s i v e p r e s e n c e o f t h e s e p r o t o z o a n s i n a m a t u r e

a c t i v a t e d s l u d g e , i s a s s o c i a t e d t o b a d p e r f o r m a n c e o f

t h e b i o l o g i c a l d e p u r a t i o n , d u e t o t h e f o l l o w i n g

c a u s e s : ( a ) p o o r l y a e r a t e d s l u d g e , ( b ) o v e r l o a d i n g ,

( c ) f e r m e n t i n g s u b s t a n c e s i n v o l v e d ( D r a k i d e s , 1 9 7 8 ;

M a d o n i , 1 9 8 6) . F l a g e l l a t e s b e c o m e t h e o n l y p r o t o -

z o a n f o r m p r e s e n t i n s l u d g e s s t r o n g l y l o a d e d

( > 0 . 9 k g B O D / k g M L S S . d ) ( C u rd s a n d C o c k b u r n ,

1 9 70 b ). F l a g e l l a t e s c o n t i n u o u s l y e n t e r t h e p l a n t b y

t h e s e w a g e i n fl u e n t w h e r e t h e y a r e v e r y n u m e r o u s . I n

a n o r m a l l y - f u n c t i o n i n g a c t i v a t e d s l u d g e t h e s e p r o t o -

z o a o u t c o m p e t e t h e b a c t e r i v o r o u s c i l ia t e s a n d , i n

a d d i t i o n , t h e y a r e s t r o n g l y s u b j e c t e d t o p r e d a c e o u s

a c t i v i t y o f o t h e r p r o t o z o a ; s o , t h e i r p r e s e n c e i n

t h e a c t i v a t e d s l u d g e i s l i m i t e d t o f e w i n d i v i d u a l s

( < 1 0 i n d . c o u n t e d a l o n g t h e d i a g o n a l i n t h e

F u c h s - R o s e n t h a l c h a m b e r ) . I n t h e c a s e o f d i sf u n c -

t i o n s o f th e p l a n t , t h e i r n u m b e r c a n i n c r e a s e

( > 1 0 i n d . c o u n t e d ) a n d , c o n s e q u e n t l y , t h i s i n d i c a t e s

a d e c r e a s e i n t h e p l a n t p e r f o r m a n c e . T h e d o m i n a n c e

o f f l a g e ll a t e s b e c o m e a p p a r e n t w h e n t h e y r e a c h t h e

d e n s i t y o f m o r e t h a n 1 00 in d i v i d u a l s a l o n g t h e d i a g -

o n a l i n t h e F u c h s - R o s e n t h a l c h a m b e r . I n t h i s l a s t

c a s e t h e y s h o u l d b e c o n s i d e r e d a s t h e d o m i n a n t

k e y g r o u p .

L a r g e f l a g e l l a t e s s u c h a s E u g l e n a a n d P e r a n e ma ,

a r e i n f r e q u e n t l y o b s e r v e d i n t h e a c t i v a t e d s l u d g e

w h e r e t h e y g r o w h a r d l y i n l a r g e n u m b e r s . T h e i r

p r e s e n c e i s r e la t e d t o i n f lu e n t s c h a r a c t e r i z e d b y v e r y

d i l u t e d o r g a n i c m a t t e r .

THE SLUDGE BIOTIC INDEX

T h e s l u d g e b i o t i c i n d e x ( S B I ) h e r e p r o p o s e d i n

T a b l e s 4 a n d 5 , h a s b e e n s e t u p o n t h e b a s i s o f t h e

r e s u l ts o b t a i n e d b o t h b y t h e n u m e r o u s r e s e a r c h c o n -

d u c t e d o n t h e a c t i v a te d - s l u d g e m i c r o f a u n a d u r i n g

t h e l a s t 2 0 y e a r s a n d i n t h e p r e s e n t r e s e a r c h a s

w e l l ( T a b l e 3 ) , a s s u m m a r i z e d a b o v e . T h e s e n s i t iv i t y

o f t h e p r o p o s e d m e t h o d w a s a s s e ss e d o n t h e b a s i s o f

p h y s i c a l , c h e m i c a l , a n d o p e r a t i n g c o n d i t i o n s o f t h e

p l a n t s . T h i s m e t h o d i s b a s e d b o t h o n t h e d i f f er e n t

s e n s i t iv i t y s h o w e d b y s o m e k e y g r o u p s t o p r i n c i p a l

p h y s i c o -c h e m i c a l a n d o p e r a t i n g p a r a m e t e r s , a n d o n

8/18/2019 Madoni, 1994 (SBI)

6/9

7 2 P A O L O M A D O N I

T a b l e 4 . T w o - w a y t a b l e t o d e t e r m i n e t h e S l u d g e B i o t ic I n d e x ( S B I ) o n t h e b a s i s o f k e y g r o u p s , d e n s i ty a n d n u m b e r o f t a x o n o m i c u n i t s o f

t h e m i c r o f a u n a

D o m i n a n t g r o u p a n d d e n si ty o f t h e m i c r o f a u n a

t h a t d e f i n e th e h o r i z o n t a l r o w o f e n t r a n c e i n

t h e t a b l e

T o t a l n u m b e r o f t a x o n o m i c u n i ts t h a t c o n s t i tu t e t h e m i c r o f a u n a o f

t h e a c t i v a t e d s lu d g e a n d n u m b e r o f s m a l l f la g e l la t e s ( F ) c o u n t e d

a l o n g t h e F u c h s - - R o s e n t h a l c h a m b e r d i a g o n a l

> 10 8- -10 5-7 < 5

D o m i n a n t D e n s i t y

k e yg r ou p (in d. /I ) F < I 0 1 0 < F < 1 0 0 F < 1 0 1 0 < F < I 0 0 F < I 0 1 0 < F < I 0 0 F < I 0 1 0 < F < I 0 0

Cr awl ing + s ess i le* > /106 10 8 9 7 8 6 7 5

c i l i a t e s an d/ or < 106 9 7 8 6 7 5 6 4

t e s ta t e a m o e b a e

Sessile /> 106 9 7 8 6 7 5 6 4

ci l iates* < 106 8 6 7 5 6 4 5 3

> 8 0 %

Opercularia spp /> 106 7 5 6 4 5 3 4 2

< 106 6 4 5 3 4 2 3 I

Vorticella microstoma /> 106 6 4 5 3 4 2 3 1

< 106 5 3 4 2 3 I 2 0

Sw imm ing bac t e r i - > /106 5 3 4 2 3 1 2 0

vo rou s c i l i a t e s < 106 4 2 3 1 2 0 1 0

Sm al l - s w imm ing t> 106 4 3 2 1

flage l lates < 106 3 2 1 0

(> lOO)~

Opercularia s p p a n d Vorticella microstoma n o t a b u n d a n t ; t a l o n g t h e F u c h s - R o s e n t h a l c h a m b e r d i a g o n a l .

t he abun danc e and t he d i ve rs i ty o f the mi c r o f au na : i t

enab l e s us t o de fi ne t he b i o l og i ca l qua l i t y o f t he

s l udge by means o f conven t i ona l numer i ca l va l ues

( b i o t i c i ndex) . T he SB I cons i de r s a l so t he f o l l ow i ng

po i n t s :

- - t he spec ie s r i chnes s t ends t o change w i t h t he s l udge

l oad . T he h i ghe r n um ber o f spec ie s has been

obse r ved w hen l oad i ngs a r e r ang i ng f r om 0 .2 t o

0 .3 k g B O D / k g M L S S - d ( C u rd s a n d C o c k b u r n ,

1970b);

- - t h e d e n s i ty o f th e m i c r o f a u n a d r o p s d o w n a s th e

s l udge l oad l ow er s . I n t he ae r a t i on bas i n o f N

r emov a l p l an t s , a mi c r o f auna l e ss abu nda n t t ha n i n

conven t i ona l p l an t s i s expec t ed .

T he i ndex t o be a sc r i bed t o t he ac t i va t ed s l udge

und e r t e s t is ob t a i ned b y means o f a t w o- w ay t ab l e

( T ab l e 4 ). T he key gr oup s f o l low i ng one ano t he r

f r o m t h e u p p e r p a r t t o w a r d t h e lo w e r p a r t o f t he

t ab le , i nd i ca t e a w or se and w or se b i o l og i ca l qua l i t y o f

t he s l udge . I n t he co l umn head i ngs f our r anges i n

w h i c h t h e t o ta l n u m b e r o f t a x o n o m i c u n i t s o f th e

mi c r o f auna f al ls a r e r epor t ed . T he t w o- w ay tab l e

T a b l e 5 . C o n v e r s i o n o f S B 1 v a l u e s i n t o f o u r q u a l i t y c l a s s e s a n d

r e s p e c t i v e j u d g e m e n t s

S B I

v a l u e C l a s s J u d g e m e n t

8 - 1 0 I

6 - 7 I I

4-5 I I1

0 - 3 I V

V e r y w e l l c o l o n i z e d a n d s t a b l e s l u d g e , e x c el -

l e n t b i o l o g i c a l a c t i v i t y ; v e r y g o o d p e r f o r m -

a n c e

W e l l c o l o n i z e d a n d s t a b l e s l u d g e , b i o l o g i c a l

a c t iv i t y o n d e c r e a s e; g o o d p e r f o r m a n c e

I n s u f f ic i e n t b i o l o g i c a l d e p u r a t i o n i n t h e a e r -

a t i o n t a n k ; m e d i o c r e p e r f o r m a n c e

P o o r b i o l o g ic a l d e p u r a t i o n i n t h e a e r a t i o n

t a n k ; l o w p e r f o r m a n c e

m o r e o v e r c o n si d e rs t h e a b u n d a n c e o f b o t h m i c r o -

fau na (exclu ding flagellates) a nd flagellates. T o deter-

mine the SBI i t i s necessary to se lect the hor izonta l

w a y - i n o n t h e r o w t h a t c o r r e s p o n d s t o t h e d o m i n a n t

keyg r oup oc cupy i ng t he l ow er pos i t i on , t ak i ng i n t o

account i t s dens i ty (more or l ess than 106ind. / l ) .

T he ve r ti ca l w ay- i n i s de t e r mi ned by t he t o t a l num ber

of t axon om i c un i t s and dens i t y o f f lagel la te s a s

well.

O nce bo t h hor i zon t a l and ve r t i ca l w ays a r e i den t -

i f i ed, the SBI value can be determined and thi s i s

s i t ua t ed i n co r r e spondence o f t he i r c r os s . T he t w o-

w ay t ab l e a l l ow s us t o pu t i n a number f r om 0 t o 10

f o r t he b i o l og i ca l qua l i ty o f t he ac t iva t ed s l udge on

the bas i s of two ind icators : the di f ferent sens i t ivity

s h o w e d b y s o m e m i c r o f a u n a l g r o u p s t o e n v i r o n m e n -

ta l condi t io ns o f the s ludge, and the ef fect that these

c o n d i t i o n s p r o d u c e o n b o t h a b u n d a n c e a n d r i c h n e s s

o f t h e p r o t o z o a n c o m m u n i t y .

F i na l l y , the va l ues o f SB I have been g r ouped i n t o

f o u r q u a l i t y c l a s s e s m a r k e d b y a R o m a n n u m b e r

(Table 5) . These c lasses a l low to represent the biologi -

ca l qua l it y o f t he ac t iva t ed s l udge t h r oug h f o ur

r anges o f j udgem ent s r a t he r w i de, a nd t hus o f re l iab l e

diagnost ic value .

V E R I F I C A T I O N

T he s t r i c t app l i cab i l i t y o f t he p r oposed me t hod

was tes ted by inves t igat ing 45 act ivated s ludges . In

each ac t i va t ed s l udge t he mi c r o f auna w as bo t h i den t -

i f i ed and enumer a t ed , and t he p r i nc i pa l phys i ca l ,

chemi ca l , and ope r a t i ona l pa r ame t e r s such a s B O D

a n d a m m o n i u m r e m o v a l , D O , s l u d g e a n d s e w a g e

retent ion t ime, MLSS, ni t r i fying abi l i ty , e tc . were

regis tered. This t es t showed that the method gives

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Sludge Biotic Index 73

c o r r e c t a n a l y s i s o f th e p l a n t p e r f o r m a n c e , i n a l l t h e

c a s e s i n v e s t i g a t e d . T h e t w o - w a y t a b l e d i s p l a y s 8 8

d i f f e r e n t s i t u a t i o n s t h a t c a n b e o b s e r v e d , a n d t h e s e

e v e n t s f a l l i n t o t h e f o u r q u a l i t y c l a s s e s i n t h e p r o -

po r t i o n o f 9 , 18 , 24 , and 37 , r e spec t i ve ly . T he t e s t ,

o b v i o u s l y , w a s u n a b l e t o v e r i f y a l l s i t u a t io n s ; n e v e r -

t he l e s s , s i nce i t w as p oss ib l e t o v e r i fy t he r e l i ab i l i t y o f

t h e m e t h o d a t t h e e x t r e m e S B I v a lu e s f o r e ac h q u a l i t y

c l a s s , i t s e e m s w e l l - f o u n d e d t o e x p e c t a f u l l r e l i a b i l i ty

o f t h e m e t h o d t o t h e i n t e r m e d i a t e S B I v a lu e s t o o .

P R O C E D U R E P R O T O C O L

S i n c e t h e m e t h o d h e r e p r o p o s e d i s b a s e d o n d i v e r -

s i t y a n d d e n s i t y o f t h e m i c r o f a u n a , p a r t i c u l a r a t t e n -

t i o n s h o u l d b e p a i d t o b o t h i d e n t i f i c a t i o n a n d

e n u m e r a t i o n o f t h e s e o r g a n is m s .

Identification of the microfauna

A l t h o u g h a l a r ge n u m b e r o f o r g a n is m s c a n b e

o b s e r v e d i n t h e a c t i v a t e d s l u d g e p r o c e s s , s o m e f o r m s

s u c h a s b o t h n a k e d a m o e b a e a n d d r i f t in g o r g a n i sm s

( a l g a e , c ru s t a c e a n s , i n s e c t s ) , a r e n o t c o n s i d e r e d i n t h i s

m e t h o d . O r g a n i s m s t o i n c l u d e i n t h e m i c r o f a u n a

a re : sm a l l and l a rge f l age l l a t e s , c i l i a t e s , t e s t a t e am oe-

b a e , r o t i f e r s , a n d n e m a t o d e s . A l l t h e s p e c i e s o f c i l i-

a t e d p r o t o z o a a n d t e s ta t e a m o e b a e c o n t r i b u t e t o t h e

d e t e r m i n a t i o n o f t h e m i c r o f a u n a d i v e r s i t y ( v e r t i c a l

w a y i n t he S B I t ab l e ) . S ince fl age l l a t e s , r o t i f e r s and

n e m a t o d e s a r e v e r y d i f f i c u l t t o i d e n t i f y a t s p e c i e s

l e v el , t h e s e g r o u p s c o n t r i b u t e e a c h w i t h 1 s y s t e m a t i c

u n i t o n l y .

C o n c e r n i n g k e y g r o u p s ( h o r i z o n t a l i n t h e S B I

t a b l e ) , i t s h o u l d b e r e m e m b e r e d t h a t o n l y b a c t e r i v o -

r o u s c i l i a t e s b e l o n g i n t h e t h r e e f u n c t i o n a l g r o u p s

( f r e e - sw i m m i n g , c r a w l i n g , a t t a c h e d ) . C a r n i v o r o u s c i l -

i a t e s c o n t r i b u t e o n l y t o t h e t o t a l d e n s i t y a n d d i v e r s i t y

o f th e m i c r o f a u n a . S w i m m i n g p r e d a c e o u s c i l ia t e s

s u c h a s

Litonotus, Amphileptus, Spathidium,

m u s t b e

e x c l u d e d b y t h e " f r e e - s w i m m i n g c i l i a t e s " k e y g r o u p ;

i n t h e s a m e w a y a t t a c h e d p r e d a c e o u s c i l ia t e s s u c h a s

t h e s u c t o r i a n s

Podophrya, Tokophrya,

a n d

Acineta,

m u s t b e e x c l u d e d b y t h e " s e s s i l e c i l i a t e s " k e y g r o u p .

T h e i d e n t i f i c a t i o n o f t h e v a r i o u s s p e c i e s o f p r o t o z o a

i s i m p o r t a n t , i n o r d e r t o o b t a i n a n a c c u r a t e S B I

v a l u e ; h o w e v e r , s o m e k e y s w r i t t e n s p e c i fi c a l ly a b o u t

t h e p r o t o z o a f o u n d i n a c t i v a t e d s l u d g e t r e a t m e n t

p r o c e s s a n d p o l l u t e d w a t e r s a r e a v a i l a b l e ( C u r d s ,

1969; M ad on i , 1981, 1988; S t r eb l e and K r au t e r , 1981;

F o i s s n e r

et al.,

1991, 1992).

I n o r d e r t o l i st t h e s p e c i e s p r e s e n t i n t h e s l u d g e , th e

f o l l o w i n g p r o c e d u r e i s s u g g e s t e d :

- - t o c o m p l e t e a n a l y s e s w i t h i n 5 h f r o m c o l l e c t i o n .

S a m p l e s o f m i x e d l i q u o r f o r m i c r o s c o p i c a l o b s e r -

v a t i o n s m u s t b e k e p t a l i v e d u r i n g b o t h c a r r i a g e a n d

a n a l y s i s p e r i o d , b y a e r a t i n g t h e m s u f fi c i en t l y t o

k e e p a l l s o l i d s i n s u s p e n s i o n ;

- - t o t a k e a l i tt l e d r o p ( 5 0 - 1 0 0 /H ) o f m i x e d - l iq u o r

f o r e x a m i n a t i o n u n d e r m i c r o s c o p e . C o v e r g l a s se s

2 4 x 2 4 m m o r 2 4 x 3 2 m m a r e r e c o m m e n d e d .

Enumeration of the mierofauna

T w o d i f f e r e n t c o u n t s a r e r e q u i r e d : e s t i m a t e o f t h e

m i c r o f a u n a a b u n d a n c e ( e x c l u d i n g s m a l l f l a g e l l a t e s ) ,

a n d e s t i m a t e o f t h e a b u n d a n c e o f s m a l l f l a g e l l a t e s .

T h e f i rs t c o u n t i s n e c e s s a r y t o e s t a b l i s h b o t h t h e c l a s s

o f a b u n d a n c e i n to w h i c h t h e m i c r o f a u n a f a ll s ( < o r

/> 1 06 /1 ), a n d t h e a b u n d a n c e r a t i o ( % ) a m o n g g r o u p s

a n d s p e c ie s . E s t i m a t e o f p o p u l a t i o n d e n s i t y sh o u l d b e

b a s e d o n e n u m e r a t i o n f r o m s u b - s a m p l e s e x t r a c t e d

w i t h a n a u t o m a t i c m i c r o p i p e t te . F o r t h e m o s t a p p r o -

p r i a t e d r o p s i ze a n d n u m b e r o f r e p l i c a t e c o u n t s ,

t o r e f e r t o s u b - s a m p l i n g t e c h n i q u e s d e s c r i b e d b y

M a d o n i ( 1 9 8 4 ) a n d A u g u s t i n

et al.

(1989) speci f ical ly

f o r t h e s lu d g e m i c r o f a u n a . M o s t l y , 2 5 # 1 s u b - s a m p l e s

o f a c t i v a t e d s l u d g e a n d 1 o r 2 r e p l i c a t e s o f t h is

vo lum e a re su f f i c i en t . I n t h i s ca se , cove rg l a s ses o f

1 8 x 1 8 m m a r e r e c o m m e n d e d i n o r d e r t o p r e v e n t a

q u i c k d r y i n g o f t h e s u b - s a m p l e s . C o u n t s s h o u l d b e

m a d e u n d e r m i c r o s c o p e a t l o w m a g n i f i c a t i o n ( × 1 0 0 ).

W h e n c o l o n i a l s p e c i e s a r e o b s e r v e d

Carchesium,

Epistylis, O percularia, Zootham nium ),

a l l in d i v i d u a l s

o f t h e c o l o n y m u s t b e c o u n t e d . I n t h e c a s e o f sp e c i e s

f o u n d i n t h e s c r e e n i n g b u t n o t o b s e r v e d d u r i n g

c o u n t s , t h e s e s h o u l d b e c o n s i d e r e d a s p r e s e n t i n t h e

p r o p o r t i o n o f 1 i n d i v i d u a l/ m l .

E s t i m a t e o f s m a l l f la g e l l a t e p o p u l a t i o n r e q u i r e s

a n a p p r o p r i a t e c o u n t t e c h n i q u e , d u e t o t h e i r v e r y

r e d u c e d s i z e a n d h i g h d e n s i t y , o f t e n r e a c h i n g

1 0 7 - 1 0 8 in d . /l . F o r t h i s p u r p o s e , a 3 . 2 / ~ 1 F u c h s -

R o s e n t h a l c h a m b e r c a n b e u s e f u ll y e m p l o y e d . T h e

c h a m b e r i s 4 x 4 × 0 .2 ( d e p t h ) m m s i z e d a n d i s

sub- d iv id ed i n to 256 squa res , 250 /~ m s i zed : f l age l -

l a t e s i n s i d e th e 1 6 s q u a r e s a l o n g t h e d i a g o n a l o f t h e

c h a m b e r s h o u l d b e c o u n t e d . W h e n f l a g e l l a t e s

c o u n t e d a l o n g t h e d i a g o n a l a r e l es s t h a n 1 0, i t m e a n s

t h a t t h e i r d e n s i t y i n t h e a c t i v a t e d s l u d g e m i x e d l i q u o r

i s l e s s t han 50 , 000 m l ; ov e r 100 f l age l l a t e s a lon g t he

d i a g o n a l c o r r e s p o n d t o t h e d e n s i t y o f 5 . 1 0 8 i n d . / l .

F l a g e l la t e c o u n t s s h o u l d b e m a d e u n d e r m i c r o s c o p e

a t x 200 m ag n i f i ca t i on .

A n e x a m p l e o f e n u m e r a t i o n o f t h e m i c r o f a u n a a n d

u t i l i z a t i o n o f t h e S B I i s r e p o r t e d i n T a b l e 6 .

F I N A L R E M A R K S

I t w a s p o s s i b l e t o c o n s t r u c t a S l u d g e B i o t i c In d e x

b a s e d o n b o t h s t ru c t u r e a n d a b u n d a n c e o f t he m i c r o -

f a u n a i n h a b i t i n g t h e a c t i v a t e d s l u d g e m i x e d l i q u o r .

A s m e t h o d s , t h e S B I w a s a l s o s e t u p o n t h e b a s i s o f

t h e r e l a t i o n s h i p o c c u r r i n g b e t w e e n p l a n t p e r f o r m a n c e

a n d o p e r a t i n g c o n d i ti o n s o n o n e h a n d , a n d s t r u ct u r e

o f t h e m i c r o f a u n a w i t h i n t h e a c t i v a t e d s lu d g e r e a c t o r

o n t h e o t h e r . T h e m e t h o d w a s f o r m u l a t e d w i t h t h e

n e e d s o f a t r e a t m e n t p l a n t o p e r a t o r i n m i n d , s o b o t h

i d e n t if i c at i o n a n d e n u m e r a t i o n o f t h e m i c r o f a u n a

w e r e s u i t a b l e . A f u r t h e r a d v a n t a g e o f t h i s m e t h o d

o v e r o t h e r s c h e m e s i s t h a t i t p r o v i d e s n u m e r i c a l

v a l u es w h ic h e n a b l e t h e o p e r a t o r t o c o m p a r e d a y b y

d a y t h e p r e v a l e n t p l a n t o p e r a t i n g c o n d i t i o n s .

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74

PAOLOMADON

Table 6. Example of the est imation of the microfauna density and

use of the sludge biotic index SB to predict the biological quali ty

of the sludge

Taxa No . 25 pl No./ml %

Swimming cil iates

Paramecium caudatum 1 40 < 1

Crawling ciliates

Aspidisca cicada 312 12,480 45

Aspidisca lynceus 23 920 3

Chilodonella uncinata

16 640 2

Euplotes af f inis - - I - -

Trochilia minuta 24 960 3

Attached ciliates

Vorticella convallaria 203 8120 29

Vorticella m icrostoma 3 120 < 1

Vorticella octava 71 2840 10

Epistylis plicatilis 9 360 1

Opercularia coarctata 18 720 3

Carnivorous ciliates

Litonotus fasciola

8 320 I

Podophrya

sp. 2 80 < I

Testate amoebae

Arcella

3 120 < 1

E ugly pha - - 1 - -

Large flagellates I 40 < 1

Rotifers 3 120 < 1

Total microfau na 697 27,882 100

Sma ll flagellates* < 10

Free-swimming cil iates 1 40 < 1

Craw ling ciliates 375 15,001 54

Attached ciliates 304 12,160 44

Testate amoe bae 3 121 < 1

Do mina nt keygroup : crawling + attached cil iates; microfauna den-

sity: > 106/I; total num ber of taxa = 17; small flagellates: < 10;

SBI = 10; quality class = 1.

*Along the Fuchs-Rosenthal chamber diagonal.

I t s h o u l d b e e m p h a s i z e d h o w e v e r t h a t t h e S B I w a s

s e t u p s p e c i f i ca l ly f o r t h e e v a l u a t i o n o f t h e b i o l o g i c a l

r e a c t o r p e r f o r m a n c e . T h i s i n d e x t h u s , is u n a b l e t o

r e v e a l a n y d i s f u n c t i o n i n th e f in a l s e d i m e n t a t i o n t a n k

( i. e. b u l k i n g , r i s in g ) , e v e n i f s o m e o f t h e s e p r o b l e m s ,

s u c h a s l o s s e s o f s lu d g e , c a n c a u s e , i n t im e , c h a n g e s

i n th e c o m m u n i t y s t r u ct u r e .

T h e i n d e x w a s d e s i g n e d t o b e u s e d i n al l a c t i v a t e d

s l u d g e p l a n t s i n c lu d i n g o x i d a t i o n d i t ch , c o n v e n t i o n a l

a e r a t i o n p l a n t s a n d e x t e n d e d a e r a t i o n u n i t s. T h e

m i c r o f a u n a u s e d i n t h e in d e x g e n e r a ll y h a v e a c o s m o -

p o l i t a n d i s t r i b u ti o n ; w e t h e r e f o r e a s s u m e t h a t t h e

i n d e x i s a p p l i c a b l e t o t h e a c t i v a t e d s l u d g e p l a n t s i n al l

t h e c o n t i n e n t s .

A c k n o w l e d g e m e n t s - - T h e

a u t h o r w o u l d l i k e t o t h a n k D r

D o n a t e l l a D a v o l i a n d a l l m e m b e r s o f t h e A G A C l a b o r a t o r y ,

R e ggi o E mi l i a , fo r t he i r a s s i s t a nc e i n t e s t i ng t he p ropose d

m e t h o d a n d P r o f e s s o r N i c o l a R i c c i, P r o f e s s o r I r e n e o F e r r a r i ,

a n d o n e a n o n y m o u s r e v ie w e r f o r p r o v i d i n g h e l p f u l c r it ic i sm s

on t he ma nusc r i p t . T he i nve s t i ga t i on wa s f i na nc i a l l y sup-

por t e d by I t a l i a n M i n i s t ry fo r Uni ve r s i t y a nd Sc ie n ti fi c &

T e c h n o l o g i c R e s e a r c h ( M U R S T 6 0 % , P . M a d o n i ) .

R E F E R E N E S

A I - S h a h w a n i S . M . a n d H o r a n N . J . (1 9 91 ) T h e u s e o f

p r o t o z o a t o i n d i c a t e c h a n g e s i n t h e p e r f o r m a n c e o f

a c t i v a t e d s l u d g e p l a n t s . W a t . R e s . 25 , 633-638 .

A n t o n i e t t i R . , B r o g l io P . a n d M a d o n i P . ( 19 8 2) V a l u t a z i o n e

d i pa ra me t r i b i o l og i c i c ome i nd i c i d i ef f i c ie nz a d i

d e p u r a z i o n e i n i m p i a n t i a f a n g h i a t t i v i,

l n g e g n . A m b i e n -

t a l e I1 , 472-477 .

A u g u s t i n H . , F o i s s n e r W . a n d B a u e r R . ( 1 9 8 9 ) D i e Z a h l u n g

v o n P r o t o z o e n u n d k l e in e n M e t a z o e n i m B e l e b ts c h l am m .

A c t a h y d r o c h i m , h y d r o b i o l . 17 , 375-386 .

B e c a r e s E. ( 1 9 9 1 ) M i c r o f a u n a o f a n a c t i v a t e d s l u d g e p i l o t

p l a n t t r e a t i n g e f f l u e n t s f r o m a p h a r m a c e u t i c i n d u s t r y .

In B i o l o g i c a l A p p r o a c h t o S e w a g e T r e a t m e n t P r o c e s s :

C u r r e n t S t a t u s a n d P e r s p e c t i v e s

( E d i t e d b y M a d o n i P . ) ,

pp . 105-108 . C e n t ro B a z z uc c h i , Pe rug i a .

B e dogni G . , Fa l a ne l l i A . a nd Pe dra z z i R . (1991) E va l ua t i on

o f t h e a b u n d a n c e r a ti o b e t w e e n c r a w l in g a n d a t t a ch e d

c i li a te s in t h e m a n a g e m e n t o f a n a c t i v a te d s l u d g e s e w a g e -

t r e a t m e n t p l a n t . I n B i o l o g i c a l A p p r o a c h t o S e w a g e T r e a t -

m e n t P r o c e s s : C u r r e n t S t a t u s a n d P e r s p e c t i v e s

( E d i t e d b y

M a d o n i P . ) , p p . 2 2 9 - 2 3 3 . C e n t r o B a z z u c c h i , P e r u g i a.

B i c k H . (1972)

C i l i a t e d P r o t o z o a ,

p . 1 9 8 . W o r l d H e a l t h

O r g a n i z a t i o n , G e n e v a .

C a r d i n a l e t t i M . a n d Z i t e l l i A . ( 1 9 9 1 ) T a x o n o m i c d i s t r i -

b u t i o n o f m i c r o f a u n a i n a j o i n t u r b a n - i n d u s t r i a l a c t i v a t e d

s l u d g e b e n c h - s c a l e u n i t . E f f e c t o f z i n c a d d i t io n . I n B i o -

l o g i c a l A p p r o a c h t o S e w a g e T r e a t m e n t P r o c e s s : C u r r e n t

S t a t u s a n d P e r s p e c t i v e s ( E d i t e d b y M a d o n i P . ) , p p . 5 9 - 7 4 .

C e n t r o B a z z u c c h i , P e r u g i a .

C h i e r i c i E . a n d M a d o n i P . ( 1 9 9 1 ) C o m p a r a t i v e a n a l y s i s o f

t h e a c t i v a t e d s l u d g e m i c r o f a u n a i n s m a l l m u n i c i p a l p l a n t s .

In B i o l o g ic a l A p p r o a c h t o S e w a g e T r e a t m e n t P r o c e s s :

C u r r e n t S t a t u s a n d P e r s p e c t i v e s

( E d i t e d b y M a d o n i P . ) ,

p p . 8 3 -8 7 . C e n t r o B a z z u c c h i, P e r u g i a .

C u rds C . R . (1966) An e c o l og i c a l s t udy o f t he c i li a t e d

p r o t o z o a i n a c t i v a t e d s l u d g e . O i k o s 15, 282 289.

C u r d s C . R . ( 1 9 6 9 ) A n I l l u s t r a t e d K e y t o t h e B r i t i s h F r e s h -

w a t e r C i l i a t e d P r o t o z o a C o m m o n l y F o u n d i n A c t i v a t e d

S l udge . W a t e r P o l l u t i o n R e s e a r c h T e c h n i c a l P a p e r

N o . 1 2 . H M S O , L o n d o n .

C u r d s C . R . ( 1 97 1 ) A c o m p u t e r s i m u l a t i o n s t u d y o f p r e d a -

t o r - p r e y r e l a t i o n s h i p i n a s i n g l e - s t ag e c o n t i n u o u s - c u l t u r e

sys t e m. W a t . R e s . 5, 793 812.

C u r d s C . R . ( 19 7 5) P r o t o z o a . I n

E c o l o g i c a l A s p e c t s o f U s e d

W a t e r T r e a t m e n t ( E d i te d b y C u r d s C . R . a n d H a w k e s

H . A . ) , p p . 2 0 3 - 2 6 8 . A c a d e m i c P r e s s , L o n d o n .

C u r d s C . R . a n d C o c k b u r n A . ( 1 9 7 0 a ) P r o t o z o a i n b i o l o g i -

c a l s e w a g e - t r e a t m e n t p r o c e s s e s . I . A s u r v e y o f t h e p r o t o -

z o a n f a u n a o f B r i t i s h p e r c o l a t i n g f i l t e r s a n d a c t i v a t e d

s l udge p l a n t s . W a t . R e s . 4 , 225-236 .

C u r d s C . R . a n d C o c k b u r n A . ( 1 9 7 0 b ) P r o t o z o a i n b i o l o g i -

c a l s e w a g e - t r e a t m e n t p r o c e s s e s . I I . P r o t o z o a a s i n d i c a t o r s

i n t h e a c t i v a t e d - s lu d g e p r o c e s s .

W a t . R e s .

4 , 237-249 .

C u r d s C . R . , C o c k b u r n A . a n d V a n d y k e J . M . ( 1 9 6 8 ) A n

e x p e r i m e n t a l s t u d y o f t h e r o l e o f t h e ci l ia t e d p r o t o z o a i n

t h e a c t i v a t e d s l u d g e p r o c e s s . W a t . P o l l u t . C o n t r o l 67 ,

312-329 .

D e M a r c o N . , G a b e l li A . , C a t t a r u z z a C . a n d P e t r o n i o L .

( 19 9 1) P e r f o r m a n c e o f b i o l o g i c a l s e w a g e t r e a t m e n t p l a n t s :

s o m e e x p e r i e n c e s o n m u n i c i p a l p l a n t s i n t h e p r o v i n c e o f

P o r d e n o n e ( I t a l y ) . I n B i o l o g i c a l A p p r o a c h t o S e w a g e

T r e a t m e n t P r o c e s s : C u r r e n t S t a t u s a n d P e r s p e c t i v e s ( E d -

i t ed b y M a d o n i P . ) , p p . 2 4 7 2 5 1. C e n t r o B a z z u c c h i , P e ru -

gia .

D r a k i d e s C . ( 19 7 8) L ' o b s e r v a t i o n m i c r o s c o p i q u e d e s b o u e s

a c t i v6e s a pp l i qu6e ~i l a su rve i l l a nc e de s i ns t a l l a t i ons

d ' 6 p u r a t i o n : t e c h n i q u e d ' 6 t u d e e t i n t e r p r e t a t i o n . T . S . M . -

L E a u

73 , 85-98 .

D r a k i d e s C . ( 1 9 8 0 ) L a m i c r o f a u n e d e s b o u e s a c ti v 6 es . E t u d e

d ' u n e m 6 t h o d e d ' o b s e r v a t i o n e t a p p l i c a t i o n a u s u i v i d ' u n

p i l o t e e n p h a s e d e d 6 m a r r a g e . W a t . R e s . 14, 1199-1207.

E s t e b a n G . a n d T e l le z C . ( 19 9 2 ) T h e i n f l u e n c e o f d e t e r g e n t s

o n t h e d e v e l o p m e n t o f c i l ia t e c o m m u n i t i e s i n a c t iv a t e d

s l udge .

W a r . A i r S o i l P o l l u t .

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E s t e b a n G . , T e l le z C . a n d B a u t i s ta L . M . ( 1 9 90 ) E f f e c t s o f

h a b i t a t q u a l i t y o n c i l i a t e d p r o t o z o a c o m m u n i t i e s i n

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E s t e b a n G . , T e l le z C . a n d B a u t i s t a L . M . ( 1 9 91 ) D y n a m i c s

o f c il i a te d p r o t o z o a c o m m u n i t i e s i n a c t iv a t e d - s l u d g e p r o -

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