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DABHOLE JOISHY

:

MILD

STEEL

CORROS

ION

REDUCTION

IN

WATER

685

directions. Using Tafel extrapolation method, the

co rres ponding current was plotted

l6

. All experiments

were conducted after 30 min each from the time of

immersion of: (a) Mild steel coupon in

Thane

creek

and cooling tower water sample and (b) Mild steel

coupon

in

Thane creek

and

cooling tower water

sample

containing

Rhod

otorula mucilaginosa 10

5

ce

ll s/mL) .

Corrosion Rate Detection

by

Weight oss

Method

- A laboratory method was devi sed for

detecting corrosion rate reduction. The initial weight

of fourteen mild steel

coupons

were taken and

suspended in 1500 mL Thane creek water (pH 7 .0) in

a round bottom fla sk and

sea

led . 15 mL of

Rhodotorula mucilaginosa

( 10

5

cells/mL)

wa

s

added

to th e

water

f

rom

the side arm. A zero

hour coupon

was taken

out

from the flask.

Th

e

coupons were

incubated for

14

d. Each day

one coupon

was taken

out and

co r

ros ion rate determined. On thirteenth day,

a initially weighed mild steel coupon was inoculated

in

Thane

creek water and corrosion rate was

determined after 24 h.

Results nd Discussion

Five yeast strains were iso lated from Thane

creek and ten from Powai lake water sampl e.

Rhodotorula l11ucilaginosa

was found in

Than

e creek.

Rhodoto rula glutinis was present in Powai lake .

Glucose IS not fermented by Rhodotorula

tnllcilaginosa but assimi lati on of glucose was

observed. In Rhodotorula J11ucilagillosa, maltose and

lactose is not assimilated. Th ese res ults were found to

be s imilar to those reported as a part

of

standard

id

entification of yeasts (Table I ). The mos t common

spec ies reported in water and sediments of lake

Ontario

in

North America are Candida guillermondii

and

Rhodo{o

mla

l17Ltcilaginosa

?

In the present stud y,

it

was obse rved that

Rh odotoru

a

J11ucilagilLosa (24 h o ld) were able to

take up dissolved oxygen within 24 h

of

incuba

ti

on

in

Thane creek water No supplement was prov

id

ed to

Rhodolorula ,

except those present in water sa mple.

I?hodororu

a

u cilaginosa showed hi gh uptake of

disso lved

oxyge

n (2.8

ppm

) as

co

mpar

ed to other

yeas t spec ies (Table 2). As Rhodolom /a spec ies are

w

id

e ly found in mar

in

e water, they are accl imatized

to Thane creek environment. When cadmium chloride

was added to Thane creek water sampl e at different

concentration, the co nsumption

of

uptake

of

dissolved

oxygen was reduced due to

cadmium

tox ic ity at

30

ppm after 72 h. This shows that both Rhodotorula

Table I-Identifica

ti

on

of

RllOdotorula lIlu ciiaginosa

Te st

Fermentation

Assimilation

Glu cose

Galactose

Maltose

Sucrose

Lactose

Glu cose

Galactose

Xylose

Sucrose

Maltose

Laclose

Mannitol

Ethanol

Urea

Nitrate

Diazoni

um

Blue

B

Growth at 25 C,

30

C, 37 C

Note: Allihe tests were performed

in

triplicate sets

Resulls

+

+

+

+

+

+

+

+

Table 2 - Disso

lv

ed oxygen upt

ake

by yeas ts in

Thane

cr

ee

k

water

Yeasts Dissolved

D O uplake

oxygen (ppm) (ppm )

Hallse

ill

ospora

va

rum.

5.6

1 5

Rhodo torula mucilag

ill

osa

4.3 2.8

Debaromyces hallsellii

6.2

0.9

Ca ndida tropicalis

6.7

0.4

Saccharomyces cereviseae

5.4

1

7

Rhodotorula glutinis

5.0 2. 1

Note:

Initi al dissolv

ed

oxygen - 7. 1 mg/L

Dissolved oxygen was determined after 72 h in cubation at roo m

temperature.

species were able to take up di sso lved oxygen

in

Thane creek water below 30 ppm very ef ficiently

Studies ca rried out , us

in

g Rhodot

or

ula u ci/agi

ll

os l

in

coo

ling t

owe

r water indicated di sso lved oxygen

uptake after a pe riod of 24 h.

Th

e dissolved oxygen

uptake

by

Rhod

otorula l11ucilaginosa in

Thane

creek

water(6.9 mg

/L

) was found to be more as

compar

ed to

coo ling tower water (6. 11 mg/L) in the presence of

cadmium chloride (Table 3) .

At pH 5 the

co

rros ion rate

of

mild stee l

in

Thane

creek water reduced to 5.59 mpy from 13.6 mpy upon

addition

of

Rhodotorula mucilaginosa. The initial

dissolved oxygen (6.88 mg/L ) was declined to 5. 17

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686

J SCIIND RES

VOL

62 JULY 2003

Table 3 - Di sso lved oxygen uptake by yeasts

Water sample yeast strains time disso lved oxygen

m

/L

Without

CdC

I

With

CdC

I

2

10 ppm

20 ppm

30

ppm

Thane c reek

RllOdolO mla 24

4.8

5.2

6.1

6.9

Mllcilag ill

osa

48

4 .3

5.0

5.7

6.8

72

4.2

4.9

5.7

0. 8

RhodolOrula

24

5.6

6.0

7.0

7. 1

g

lwilli

s 48

5.4

5.8

6.7

7.0

72 5. 1

5.6

6.7

7.0

Note: pH of Th ane creek - 7. : 2 and initial di sso lved oxygen - 7.2 mg/L

Table 4 - Mild st

ee

l corros ion reduction

in Than

e cree k water by RhodolOrula IIllieilag ill

osa

(p H 5.0)

Sample

Initi al wt

of

Final wt of IW-FW of Metal uptake

Mild stee l ClJ upon+

Th

ane creek water sample

Mild steel coupon+Thane c reek water

sa

mple+C dCl

2

Mild steel coupon+Thane c reek water

sample+RllOdolorula IIllicilaginosa

Mi

ld steel

cO ll

pon+Thane c reek water

sample+CdC I

2

+

RhodolOmla

IIlll

cilagillo.w

mild steel

g)

4.407

6.4847

7. 1683

6.8023

mild steel

mild steel

g) (g)

4.4052

0.0018

6.48 15

0.0032

7. 1662 0.0021

6.8006

0.0017

Corrosion rate

(mpy)

SO

(pp m)

13.6

(0.057)

Ferrous = 8.77

12.3 (0. 152)

5.59

(0.0 1)

Ferrous =

O

157

5.95 (0.025)

CJ dmium=

I .S :

SO - The Standard Deviation is valu e

of

three indepe ndent experiments under id entical condit ions

Initia l di sso lved oxygen - 6.88 mg/L a

ndlin

al di sso lved oxygen - 5. 17 mg/L

mg/L.

The up

ta ke of

cadmium

chlorid

e ( 1.88

ppm

)

and fe rrous (

0.157

ppm) by Rhodotoru a

lIIu

ci/ag inoso sho

wed affinity

towards ca dmium

chl oride. The r

es

ult s a re pr

ese

nted

in Tabl

e 4.

At pH 7 the co rro sion rate was reduced

signifi

ca

nt ly to 1.48 mp y. It can be obse rved that

uptake of cadmium and fe rrous ions is less du e to

hi

gh

up

take

of

disso l\red ox ygen.

These

resu lts

indicate

that

the r

esp

ira ti on by

Rh

odoto

rula

ci/agillos l is a

co

ntinous process during which

cadmium ions are absorbed rapidly, as observed from

Ta b le

5

At pH 9.0, the

co

rr

os

ion rate

did

not chan ge

app rec iab ly indica tin g that alkaline pH cond ition was

not favourabl e for growth and activity

of

Rh

odoto

mLa

IIll1 ci/o ginosa. Further, alkaline

condition itse lf

is

know n to be res ponsible fo r ca using co rros ion.

[n

thi s

case, the uptake

of ca

dmium and ferrous ion s

tS

co nsiderab ly hi gher than at pH 5 and 7 (Table 6). [n

Ta b le 7, when mild

stee

l

co

upon was

inoculated

In

coo

ling

tow

e r

water

at

pH 7.0

in pr

ese

n

ce and

abse nce

of

Rh

odo t

orula

l11ucilaginosa ,

corro s ion rate

was found to be reduced by 50 per

ce

nt F igure I ).

pH 7 was fo und to be idea l for uptake of

ca

dmium and ferrous ion s by Rh

odoto

ru l

a

l11u

cila ginosa.

The

res ults indi ca te that pH pl

ays

a

c ritica l role in re

du

c

in

g co rro sion rate. In a similar

study , a protec tiv e effect of

Ps

eudomonas fragi

and

Esc

herc

hia co

li

DH5 was found to redu e co rros ion

of

stee l

6

.

A lab orat ory method for

co nfirmin

g mild

co rro sion redu ction in water showed that co rr

os

ion

d

ec

r

ease

d

from 4.4 mpy

to 0.85

I

mp

y.

The corrosion

rate dec reased pe

ri

odicall y over 14 d afte r w hi ch the

co

up on inoculated on thirtee nth

day

showed co rr

os

ion

rat e

of

0.850 mp

y. Th

e ex pe riments carried out

showed that mild st

ee

l corrosion in Th an cree k W

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DABHOLE

JOISHY:

MI

LD

STEEL CORROS I

ON

REDUCTI

ON

IN WATER

687

Ta b

le 5 - Mild steel corrosion redu ction in

Thane

creek water by Rh

od ru

la lIIuc

iia

gillosa (pH 7.0)

Sample

Initi al wt of Final wt of IW-FWof

mi ld steel mild steel mild steel

(g) (g)

(g)

Mi

ld steel co

upon+Than

e creek water sa

mple

4.8089

4.8055 0.0034

Mild steel

coupon+Th

ane creek water

4.6578 4.6546 0.0032

sample+CdC

l

2

Mi Id stee l co upon+Thane

creek water

6.4638

6.4633

0.0005

sampl

e+Rhod ru

ia IIIl c

il a

gillosa

Mild steel

coupon+Thane

creek water

7.0571

7.0565 0.0006

sample+CdCl

2

+

Rh

od m la IrIllciiagillo.m

SD - The Standard Deviation is value of three independent

experiments

under identical

conditions

Initial dissolved oxygen - 6.91 mg/L and Final disso lved oxygen - 4.64 mg/L

Corrosion

rate Meta l uptake

(mpy )

SD

(pp m)

9.62 0.0 15)

Ferrous =6.76

9.52 0.04

1)

1.48

0.020)

Ferrous =0.071

1.37

0.026)

Cadmium =0.1

Table 6- Mild stee l corrosion reduction

in

Thane creek water by Rh

od r

llia I/lllcilagi ll osa

p

H 9.0)

Sample

Initi al wt of

Final wt

of

IW-FWof

mi ld stee l

mild steel

mild steel

(g) (g) (g)

Mild stee l

co

up on + Thane creek water

samp

le

4.4628

4.4612

0.0016

Mild stee l coupon + Thane creek wate r

5.6804

5.6781

0.0023

sample+ CdCl

:

Mild steel co upon + Thane creek water

6. 1422 6.1414

0.0008

sample+

Rh

od m la Illl1

ci

lag il losa

Mild steel c

oupon

+

Thane

creek water

5.2446

5.2435

0.0011

sample+ CdCI

2

+

Rh od

rllia l1luciiaginosa

SD - The

standard

deviation is va lu e o f three independent experimen ts under identical conditions

Initial di ssolved oxygen - 7. 14 mg/L and Final dissolved oxygen - 6.83 mglL

Corrosion rate

Met a

luptak

(mpy)

SD

(p pm)

4.49

(

0.035)

Ferrous =4.21

5.36 (

0.02)

3.03

0.047)

Ferrous =

O

13

3.26

0.015)

Cadmium =

0.73

Table

7 - Mild steel

co

rro sion reduc

ti

on in

cooling tower

water by

Rhod ru

ia muciiaginosa (pH 7.0)

Sample

Corrosion

rate Ferrous uptake

(mpy)

SD

(pp m)

Mild steel co upon+Thane creek water samp le

12.3(0. 152)

3.77

Mild steel coupon+Thane creek water sample+CdCl

2

12.2(0.208)

3.4

1

Mild st

ee

l co upon+

Than

e creek water

5.84(0.011 ) 1. 124

sa

mple+Rhod rula 1llllc

il

aginoS{J

Mild st

ee

l cOl.lpon+

Tha

'ne creek water sa mpl

e+CdCl

2

+

6.31 (0.025) I I 13

Rh od m/a

lI1ucilagill oslI

SD - The sta n

da

rd deviation is va lue

of

three

independent experiment

s und er id enti

ca

l

cond

itions

Initial di sso lved oxygen - 7.7 mg/L

CdCI : uptake

Dissolved ox yge n

ppm)

(ppm)

0 7.6

29.91 7.7

0 5.3

2.16 6.11

A619. In batch

cultures

, 16 iso lates s

howed corrosion

reduction than the control

17

Scanning

el

ectron

microscopy

showed

the

presence

of cadmium

and ferrous ions in the

cytoplasmic region

of

the

hodotorula ucilaginosa

as observed from Figure 2 The energy dispers ive

x-ray spectroscopy for

cadmium

and ferrou s ion

detection in hodotorula mucilaginosa showed 41.46

per

cent

as

cadmium

as compared to 13.54 per cent as

ferrous .

The e lectrochemical studies showed that the

c

urrent obtained was direc tl

y proportional to the

8/10/2019 JSIR 62(7) 683-689

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688

J SCI INO RES VOL 62 JULY 2003

Figure

1-

I )

Mild

st

ee

l

co

upon in Thane cr

ee

k water,

2)

Mild

s

te

el coupon in Thane cr

ee

k wat er containing

I< hodolOmla IIIf(r

ilag il l

osa ,(3)

Mild

st

ee

l coupon in

cool ing wa ter, 4) Mild st

ee

l Coupon in Coolin g

wa ter containing RIIOr/u/omla IIl/1 cil agillosa

Figure

:2 -

SEM

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DA

BHOL

E

JOISHY

: MILD

STEEL

C

ORROSION RED

UC

TION

IN

WATER

689

Rhodoto rula l11u cilaginosa a lso known to produce

Siderophore) to reduce oxy gen corrosion of mi ld steel

in water may so lve many problems occulTIng 111

cooling towers.

Acknowledgement

Th e authors are grate ful to Dr H S Srinivasan for

carrying out e lec trochemical studi

es

and hi s views on

experim ents.

They

are also thankful to

Dr

C S

Harendranath and Bh arathi Shetye (IlT, Mumbai) for

SEM and EOX anal ys is.

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