Journ al of Scientific & Industrial Research

Vol. 62 , July 2003, pp 683-689

Mild Steel Corrosion Reduction in Water by Uptake of Dissolved Oxygen by Rhodotorula mucilaginosa

M P Dabhole and K N J oishy*

Department of Microbiology, K J Somaiya College of Science, University of Mumbai , Mumbai 400077

Recei ved: 03 December 2002 ; accepted: 21 February 2003

The study aims at determination of corrosion rate reduct ion in water by uptake o f di ssolved oxygen by RllOdolorula III/Iciiagillosa. Corros ion of mild steel in water due to oxygen is a common phenomena in coo ling towers and process industries. Dissolved oxygen uptake at various pH -acidic, neutral and alkaline conditions indicated that corrosio n reduced at pH 7. The uptake of ferrous ions by Rhodotorula l11ucilagillosa was detected by Atomic Absorption Spectrometry (AAS). The affinity for uptake of cadmium ions by Rhod%mla mucilaginosa in presence of ferrous ions was confirmed by AAS. Both weight loss and electrochemical method gave analogous data in corrosion reduction for Thane creek water.

Keywords: Corrosion, Dissolved oxygen, Mild steel, Rhod% mla mucilaginosa

Introduction

Iron is the mos t versatile transition metal in biological redox reactions. The high affinity of iron fo r oxygen has made iron the act ive site in oxygen based enzy matic react ions l

. Iron is found in mild steel and has been widely used in eng ineering operations and process industri es. Cadmium provides an attracti ve corrosion protecti ve coating over various metals like, steel and cas t iron. Cadmium being anod ic to iron provides protect ion to base metal2.

Corros ion of mild steel in water is known to cause huge losses to process industries. Currently, corros ion is reduced by adding cos tl y corros ion inhibitors. But these che micals pers ist til the environ ment , thereby caus ing environmental po lluti on. The discharge of heavy metals like iron aJid cadmium in to the environment due to industria l operations has a profound effect on the ecosystem and human hea lth . The ex posure to fresh cadnuum fumes during brazing of sta inless steel and low a ll oy steels has resulted in occupati onal di seases' .

In the present in vesti gation, an attempt was made to study the reduction of corros ion of mild steel in water by uptake o f di sso lved oxygen by RhodotorttLa l11ucilaginosa . Not much is known abou t the applicati on of yeast to reduce corros ion of mild

" Authu r fur co rrespundence emai l: drknJoi shy@yahou.co.in; madhav888 @red iffmail .com

steel in water. Recent evidences suggest that aerobically respiring bacteria may protect steel from corrosion4

. Bacterial activity at metal surfaces is known to reduce corrosion). Studies have been carried out on reducing corrosion of mild steel by bacteria like, Pseudomonas fragi and Escherichia coli6

The uptake of di ssolved oxygen by Saccharol11yces cereviseae is well- known? This parameter was taken into consideration during the weight loss and e lectrochemica l study. The di ssolution of iron as Fe2+ and ox idati on to Fe"+ occurs due to high oxygen concentrati on8 The resulting product is the formation of Fe(OHh (ref. 9). Studies have indicated that corros ion rate of iron is a lmost proporti onal to the concentrat ion of disso lved oxygen. Corrosion reduces when all di sso lved oxygen is consumed at neutral pH (ref. 10).

The study aims to dete rmjne the reduct ion of mild steel corros ion in water by uptake of dissolved oxygen, using Rhodotorula l11ucilaginos(f at diffe rent pH at certain time interva l. The study was a lso focused on the affinity of uptake of fe rrous and cadmium ions by Rhodotorula l11ucilaginosa.

Materials and Method

Yeasts from Thane creek water (5 mL) and Powai lake (5 mL) were enri ched in 100 mL steri le Yeast Extrac t Malt Extrac t broth (YM agar) and isolated on steril e YM agar. After e nri chment , yeas ts were isolated on ste ril e YM agar pl ates . A s ingle

684 J SCI IND RES VOL 62 JULY 2003

co lony of yeast was maintained on steri le YM agar slants.

Identification of Yeasts - Fermentation and assim il ati on of carbohydrates form principal physiological criteria for the identification and classification of yeas ts . ]n fermentation test, 3 mL of ste ril e I per cent yeas t extrac t containing 50 mM

sugars with Andrade ' s indi cator and inverted

Durham ' s tube were inoculated with a loopful of overni ght broth culture of yeast. In carbo hydrate

assim ilati on test, the ab ility of yeasts to use organic

compound as sole source of carbon was determined

by standard rep li ca plate method , using 25 mM

carbon source . Similarly the ability . of yeas ts to

utilize different organic compou nds as so le source of nitrogen was tes ted us ing yeas t carbon base

conta ining a single nitrogen sou rce (5 mM). All the

yeast strain s we re ide ntifi ed, based on

morphological, cultura l and physiological c haracte risti cs II .

Dissolved Oxygen (D 0) Uptake - A six sterile 250 mL Erlenmeyer flasks containing Thane creek water ( 100 mL) was inoculated eac h with 24 h culture

of yeast ( 105 ce ll s/mL) and incubated at room

temperature for 72 h. The D 0 uptake was determined

by wi nkler ' s method l2. In another study, a sterile 250

mL Erl enmeyer flask conta ining Thane creek water

( 100 mL) was inocu lated with Rhodotorula I17l1cilaginosa ( 105 cell s I mL) at time intervals of 24 h, 48 hand 72 h. The pH of Thane creek water was determined during collect ion of the water samp le and

confirmed aga in in the laboratory . Similarly 0 0 uptake experiments were carried out us ing

Rhodotorula gll/tinis ( 105 ce ll s/mL) at above dura­ti ons . The D 0 uptake was determined in the absence

and the presence of cadmium chl oride ( 10 ppm, 20 ppm and 30 ppm) using wink ler ' s method .

Weight Loss Method - The initial weight of four clean and dry mild steel coupons was

determined. Each coupon was suspended in 100 mL of Thane c reek water for 24 h. After 24 h the coupons were taken out and weighed 13 . The di ssolved oxygen

of Thane creek water before introduc ing the coupon

and after 24 h incubat ion was determined. The above experiments were carried out at pH 5, pH 7 , and pH 9,

respective ly. Similarly the study was carried out for cooling tower water (co llected from agrochemi cal

industry) at pH 7. The di ssolved oxygen was

determined by Winkler's method. In the following study,

• One mild stee l coupon was suspended in 100 mL of creek water.

• Secondly, one mild stee l coupon was suspended in 100 mL of creek water contai ning cadmium chloride (30 ppm) .

• Thirdly, one mild steel coupon was suspended in 100 mL of creek water containing Rhodotorula mucilaginosa (I ml of 105 cell s/mL).

• Lastly , One mild steel coupon was suspended in 100 mL of creek water containi ng cadmium chloride (30 ppm) and Rhodotorula mucilaginosa( I mL of 105 ce ll s/mL).

3.45 x 106 X L1\\'

Corrosion rate (mpy) = ------

A TD

where 6w = Weight loss of metal, A = Metal area exposed, T = Time of exposure, D = Density of metal.

Scanning Electron Microscopy (SEM) Rhodotorula mucilaginosa (105 ce ll s I mL) was inoculated in 100 mL Thane creek water at pH 7.0 containing mild steel coupon and cadmium ch loride (30 ppm) in steri le cond iti on. After 24 h incubation , the sample was streaked on steri le Sabouraud ' s agar. Following the growth, the ce ll s were sonicated for 2 h. SEM (SU30 cameca) of Rhodotorul{/ mucilaginosa was carried out. The ce lls were spot inocul ated on a clean and dry stub, labe led and dried . The stub was put in a vacuum chamber to remove any moisture present in the ce ll s. Further, the stub was go ld plated for 30 min and loaded into the scann ing chamber for observation on the screen 14 The Energy Dispersive X-ray spectroscopy (Kevex instrument) was carried out to determine the cadmium and ferrolls ions weight per cent in Rhodotorula lI1ucilagillosa . Heavy meta l uptake by AAS was done, according to the earlier method I S.

Electrochemical Study - The corros ion current of mild steel in Thane creek water was measured using EG and G PAR M273A potentiostat with M352 corrosion software. EG2G K0235 flat ce ll was used in a ll the studies . Platinum and Ag/AgCl2 were used as counter and reference e lectrodes. T he mild steel sample of area I cm2 was polarized to 250 mY with respect to open circuit in both cathodic and anodic

DABHOLE & JOISHY : MILD STEEL CORROS ION REDUCTION IN WATER 685

directions. Using Tafel extrapolation method, the corresponding 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 Rhodotorula mucilaginosa (105

ce ll s/mL) .

Corrosion Rate Detection by Weight Loss 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 flask and sealed . 15 mL of Rhodotorula mucilaginosa ( 105 cells/mL) was added to the water from the side arm. A zero hour coupon was taken out from the flask. The coupons were incubated for 14 d . Each day one coupon was taken out and corros ion rate determined. On thirteenth day, a initia lly weighed mild steel coupon was inoculated in Thane creek water and corrosion rate was determined after 24 h.

Results and Discussion

Five yeast strains were iso lated from Thane creek and ten from Powai lake water sample. Rhodotorula l11ucilaginosa was found in Thane creek. Rhodotorula glutinis was present in Powai lake . Glucose IS not fermented by Rhodotorula tnllcilaginosa but assimi lation of glucose was observed. In Rhodotorula J11ucilagillosa, maltose and lactose is not assimilated. These results were found to be s imilar to those reported as a part of standard identification of yeasts (Table I ). The most common spec ies reported in water and sediments of lake Ontario in North America are Candida guillermondii and Rhodo{omla l17Ltcilaginosa l

?

In the present study, it was observed that Rhodotoru /a J11ucilagilLosa (24 h o ld) were able to take up dissolved oxygen within 24 h of incubati on in Thane creek water. No supplement was prov ided to Rhodolorula , except those present in water sample. I?hodororu/a l11ucilaginosa showed hi gh uptake of di sso lved oxygen (2.8 ppm) as compared to other yeas t spec ies (Table 2). As Rhodolom/a spec ies are wide ly found in mar ine water, they are accl imatized to Thane creek environment. When cadmium chloride was added to Thane creek water sample at different concentration, the consumption 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-Identification of RllOdotorula lIluciiaginosa

Test

Fermentation

Assimilation

Glucose Galactose Maltose Sucrose Lactose

Glucose Galactose Xylose Sucrose Maltose Laclose Mannitol Ethanol

Urea Nitrate Di azoni um Blue B Growth at 25° C, 3011 C, 37° C

Note: Allihe tests were performed in triplicate sets

Resulls

+ + + +

+ +

+ +

Table 2 - Di sso lved oxygen uptake by yeas ts in Thane creek water

Yeasts Dissolved D O uplake oxygen (ppm) (ppm)

Hallseillospora II va rum. 5.6 1. 5

Rhodotorula mucilagillosa 4.3 2.8

Debaromyces hallsellii 6.2 0 .9

Candida tropicalis 6.7 0.4

Saccharomyces cereviseae 5.4 1.7

Rhodotorula glutinis 5.0 2.1

Note: Initi al dissolved oxygen - 7. 1 mg/L Dissolved oxygen was determined after 72 h incubation at roo m temperature.

species were able to take up di ssolved oxygen in Thane creek water below 30 ppm very efficiently. Studies carried out , using Rhodotorula l11uci/agill os(l in cooling tower water indicated di ssolved oxygen uptake after a period of 24 h. The dissolved oxygen uptake by Rhodotorula l11ucilaginosa in Thane creek water(6.9 mg/L) was found to be more as compared to coo ling tower water (6. 11 mg/L) in the presence of cadmium chloride (Table 3) .

At pH 5 the corros 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

686 J SCIIND RES VOL 62 JULY 2003

Table 3 - Di ssolved oxygen uptake by yeasts

Water sample yeast strains time di ssolved oxygen (mg/L)

Without CdCI" With CdCI2

10 ppm 20 ppm 30 ppm

Thane creek RllOdolOmla 24 4.8 5.2 6.1 6.9

Mllcilag illosa 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

glwillis 48 5.4 5.8 6.7 7.0

72 5. 1 5.6 6.7 7.0

Note: pH o f Thane creek - 7.!:!2 and initial di sso lved oxygen - 7.2 mg/L

Table 4 - Mild steel corros ion reduction in Thane creek water by RhodolOrula IIllieilagillosa (p H 5.0)

Sample Initi al wt of Final wt of IW-FW of Metal uptake

Mild steel ClJupon+ Thane creek water sample

Mild steel coupon+ Thane creek water sa mple+CdCl 2

Mild steel coupon+ Thane creek water sample+RllOdolorula IIllicilaginosa

Mi ld steel cOll pon+ Thane creek water sa mpl e+CdC I2+ RhodolOmla IIlllcilagillo.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" (ppm)

13.6 (0.057) Ferrous = 8.77

12.3 (0. 152)

5.59 (0.0 1) Ferrous = O. 157

5.95 (0.025) CJdmium= I.S!:!

SO" - The Standard Deviati on is va lue of three independent experiments under identical condit ions

Initia l di ssolved oxygen - 6.88 mg/L andlinal di ssolved oxygen - 5. 17 mg/L

mg/L. The uptake of cadmium chloride ( 1.88 ppm) and fe rrous (0.157 ppm) by Rhodotoru/a lIIuci/ag inoso showed affinity towards cadmium chl oride. The result s a re presented in Table 4.

At pH 7 the corrosion rate was reduced significant ly to 1.48 mpy. It can be observed that uptake of cadmium and fe rrous ions is less due to high uptake of di sso l\red ox ygen. These resu lts indicate that the resp irati on by Rhodotorula 1I111ci/agillos(l is a continous process during which cadmium ions are absorbed rapidl y, as observed from Tab le 5.

At pH 9.0, the corros ion rate did not change app reciab ly indicating that alkaline pH cond iti on was not favourabl e for growth and activity of RhodotomLa IIll1ci/og inosa. Further, a lkaline condition itse lf is known to be responsibl e fo r causing corros ion. [n thi s case, the uptake of cadmium and ferrous ions tS

considerab ly hi gher than at pH 5 and 7 (Table 6). [n Tab le 7, when mild steel coupon was inoculated In

cooling towe r water at pH 7.0 in presence and absence of Rhodotorula l11ucilaginosa , corros ion rate was found to be reduced by 50 per cent (F igure I ).

pH 7 was fo und to be idea l for uptake of cadmium and ferrous ion s by Rhodotorula l11ucilaginosa. The resu lts indi ca te that pH p lays a c riti ca l role in reduc ing corrosion rate. In a similar study, a protective effect of Pseudomonas fragi and Escherchia coli DH5 was found to redu e corros ion of steel6 .

A laboratory method for confirming mild corrosion reduction in water showed that corros ion decreased from 4.4 mpy to 0.85 I mpy. The corrosion rate decreased pe ri odically over 14 d afte r w hi ch the coupon inocul ated on thirteenth day showed corros ion rate of 0.850 mpy. The experiments carried out showed that mild steel corrosion in Th an c reek W<l te r reduced significantly at pH 7 . Compar-a ble resu lts have been obtained by screening of 22 marine iso lates to examjne the ir effect on corros ion of carbon steel

DABHOLE & JOISHY: M ILD STEEL CORROS ION REDUCTION IN WATER 687

Table 5 - Mild steel corrosion reduction in Thane creek water by Rhod%rula lIIuciiagillosa (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 coupon+ Thane creek water sample 4.8089 4.8055 0.0034

Mild steel coupon+ Thane creek water 4.6578 4.6546 0.0032 sample+CdCl2

Mi Id stee l coupon+ Thane creek water 6.4638 6.4633 0.0005

sa mple+Rhod%ruia IIIl1cilagillosa

Mild steel coupon+ Thane creek water 7.0571 7.0565 0.0006 sample+CdCl2 + Rhod%mla IrIllciiagillo.m

SD" - The Standard Deviation is value of three independent experiments under identical conditions Initial disso lved oxygen - 6.91 mg/L and Final di sso lved oxygen - 4.64 mg/L

Corrosion rate Metal uptake (mpy) SD" (ppm)

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 O~

Table 6- Mild steel corrosion reduction in Thane creek water by Rhod%rllia I/lllcilagill osa (pH 9.0)

Sample Initi al wt of Final wt of IW-FWof mi ld stee l mild steel mild steel

(g) (g) (g)

Mild steel coupon + Thane creek water sample 4.4628 4.4612 0.0016

Mild steel coupon + Thane creek wate r 5.6804 5.6781 0.0023 sample+ CdCl :!

Mild steel coupon + Thane creek water 6. 1422 6.1414 0.0008 sample+ Rhod%mla Illl1ci lag ill osa

Mild steel coupon + Thane creek water 5.2446 5.2435 0.0011 sample+ CdCI 2 + Rhod% rllia l1luciiaginosa

SD" - The standard deviation is va lue o f three independent experiments under identical conditions

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

Corrosion rate Metaluptak (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 corrosion reducti on in cooling tower water by Rhod%ruia muciiaginosa (pH 7.0)

Sample Corrosion rate Ferrous uptake (mpy) SD" (ppm)

Mild steel coupon+ Thane creek water sample 12.3(0. 152) 3.77

Mild steel coupon+ Thane creek water sample+CdCl 2 12.2(0.208) 3.4 1

Mild steel coupon+ Thane creek water 5.84(0.011 ) 1. 124 sample+Rhod% rula 1llllcilaginoS{J

Mild steel cOl.lpon+ Tha'ne creek water sample+CdCl 2 + 6.31 (0.025) I. I 13 Rhod% m/a lI1ucilagill oslI

SD" - The standard deviation is va lue of three independent experiments under identical conditions

Initial di sso lved oxygen - 7.7 mg/L

CdCI :! uptake Dissolved ox ygen (ppm) (ppm)

0 7.6

29.91 7.7

0 5.3

2.16 6.11

A619. In batc h cultures, 16 iso lates showed corrosion reduction than the control 17

Scanning electron microscopy showed the presence of cadmium and ferrous ions in the cytoplasm ic region of the Rhodotorula l11ucilaginosa as observed from Figure 2. The energy dispers ive

x-ray spectroscopy for cadmium and ferrou s ion detection in Rhodotorula mucilaginosa showed 41.46 per cent as cadmium as compared to 13.54 per cent as ferrous .

The e lectrochemical studies showed that the current obtained was directl y proportional to the

688 J SCI INO RES VOL 62 JULY 2003

Figure 1- ( I ) Mild steel coupon in Thane creek water, (2) Mild steel coupon in Thane creek water containing

I<hodolOmla IIIf(r ilag ill osa ,(3) Mild steel coupon in cool ing water, (4) Mild stee l Coupon in Coo ling

water con taining RIIOr/u/omla IIl/1cilagillosa

Figure :2 - SEM <Inaly,is or cytop lasmic rrac tion or N/1Ot/% mla

1If(lCilagillosa exposed to cadmiu m chloride (30Pl1m) [2000X I

corros ion rate of Thane creek water sample . The initia l Di sso lved oxygen was found to be 6.8 Illg/L and showed a current of S5 flamp. When Rh odotorul a mll cibginosa was in oc ulated in Thane creek water containin g mild stee l coupon for 24 h, the Disso lved oxyge n redu ced to J.I I11g/L with it current of J.5 f .. lamp (Figure J). When cooling tower water was used, th e initial Di sso lved oxygen was round to be 7.7

-150 r-----------------------------.. ---------.

- 250

- 350

- 450

:;-..s -550 w

- 650

- 750

ad4 ad3

/ /

- 850. L8 ....J.....J...J...L.J..WJ.. 7--'-W.llll:.L-.L...J...J..lJ.wL....J.....L...l.LuuL--<.. .~. w" -"-,; .......:......c...wCllW · 6 · 5 - 4 - 3 - 2

I I area (A I em A 2 ) n 10

Figure 3 - Electrochemical study or mild steel in Thane creek water: ad 4-Mild steel in Thane creek water,ad 3 .. Mild steel in

Thane creek water containing RhodolOmla IIl1 lcilag ill osa

- 250

- 350

- 650

- 750

ad 1 ad2

- 7 - 6 -5 - 4

II area (A I em A 2) n 10

Figu re 4 - Electrochemical sludy or mi ld sleel in coo ling water: ad I-Mild steel in cool ing water, ad 2-M ild steel in L'oo ling W:1ter

con taining Rlwd% mla IIll1 r ilag illol'll

mg/L with a current of II flamp. When Rh odotorul a mucilagin osa was inoculated in coo ling tower water containing mild steel coupon, the di sso lved oxygen reduced to 6. 1 mg/L with a current or 7 flLllnp (Figure 4).

Care was taken to maint ain the so lution vo lume : area rati o and the corrosion rates were d te rmined as per the ASTM standard '6 Thus the measured red uct ion in corros ion current is in {IQree ment with that reported in the literaturel ~ . The ~above stud ies present comparati ve data in both we ight loss and electrochemical meth od for Thane creek \vater.

Conclusion

The work described emphasizes on the uptake of dissolved oxygen by J<hodotorulll Jl lI !(.; ilagillo.m.

Today, Process Industries incur heavy losses due to different types of corros ion. Use of mar ine yeast like,

DABHOLE & JOISHY : MILD STEEL CORROSION RED UCTION IN WATER 689

Rhodotorula l11ucilaginosa (a lso known to produce Siderophore) to reduce oxygen corrosion of mi ld steel in water may solve many problems occulTIng 111

cooling towers.

Acknowledgement

The authors are grate ful to Dr H S Srinivasan for carrying out e lectrochemical studies and hi s views on experiments. They are also thankful to Dr C S Harendranath and Bharathi Shetye (IlT, Mumbai ) for SEM and EOX anal ys is.

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