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Jurnal Kejuruteraan 2 (1990) 205-212 EFFECTS OF AERATION ON BIODECOLOURISATlON OF AZO DYE Rakrnl Abdul-Rahman, Mohd. Arlmn Aton and Jallanl Sallhon ABSTRACT A study on the effects of aeration on blodecolourlsation of an azo dye was ca"led out using acclimated culture. Oxidation 'reduction potential was used as a measure of degree of aeration. The results showed blodecolourlsatlon to be dependent on degree of aeration with negative or vel)! low oxidation reduction potentlat being favourable for decolourisatlon. This finding was In line with the postulation that biodecolourisat!on OCCU"ed via azo bond cleavage. ABsmAK Kesan pengudaraan ke atas penyahwamaan secara biologl satu pewama azo telah dikajl dengan menggunakan kultur yang tersesual kepada pewama Itu. Hasil kaJian menunjukkan penyahwamaan bergantung kepada darjah pengudaraan, yang dlukur seOOgai potens; pengoksldaan·penurunan. Penyahwamaan didapati berlaku pada potensl yang sangat rendah atau negatif. Inl dldapatl se/arl dengan pastulat bahawa penyahwamaan berlaku dengan pemutusan Ikatanazo. INTRODUCTION Azo dyes form a major class of dyes used In various Industries producing coloured products such as textile, carpet, paper, Inks, food, cosmetics and so on. These Industries Inevkably discharge dyed (hence coloured) wastewaters. Decolourisation of these wastewaters, for compliance wnh environmental regulations or purpose of water reuse, via the conventional biological processes (mainly activated sludge type of process) has generally been Inefficient due to biological recalcnrance (resistance to biological breakdown) of the dyes. Hence decolourlsation via the more expensive chemical processes (coagulation, oxidation) or physlcal adsorption are generally employed.

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Page 1: A azo as a to - Universiti Kebangsaan Malaysia · 2016-05-04 · Jurnal Kejuruteraan 2 (1990) 205-212 EFFECTS OF AERATION ON BIODECOLOURISATlON OF AZO DYE Rakrnl Abdul-Rahman, Mohd

Jurnal Kejuruteraan 2 (1990) 205-212

EFFECTS OF AERATION ON BIODECOLOURISATlON OF AZO DYE

Rakrnl Abdul-Rahman, Mohd. Arlmn Aton and Jallanl Sallhon

ABSTRACT

A study on the effects of aeration on blodecolourlsation of an azo dye was ca"led out using acclimated culture. Oxidation 'reduction potential was used as a measure of degree of aeration. The results showed blodecolourlsatlon to be dependent on degree of aeration with negative or vel)! low oxidation reduction potentlat being favourable for decolourisatlon. This finding was In line with the postulation that biodecolourisat!on OCCU"ed via azo bond cleavage.

ABsmAK

Kesan pengudaraan ke atas penyahwamaan secara biologl satu pewama azo telah dikajl dengan menggunakan kultur yang tersesual kepada pewama Itu. Hasil kaJian menunjukkan penyahwamaan bergantung kepada darjah pengudaraan, yang dlukur seOOgai potens; pengoksldaan·penurunan. Penyahwamaan didapati berlaku pada potensl yang sangat rendah atau negatif. Inl dldapatl se/arl dengan pastulat bahawa penyahwamaan berlaku dengan pemutusan Ikatanazo.

INTRODUCTION

Azo dyes form a major class of dyes used In various Industries producing coloured products such as textile, carpet, paper, Inks, food, cosmetics and so on. These Industries Inevkably discharge dyed (hence coloured) wastewaters. Decolourisation of these wastewaters, for compliance wnh environmental regulations or purpose of water reuse, via the conventional biological processes (mainly activated sludge type of process) has generally been Inefficient due to biological recalcnrance (resistance to biological breakdown) of the dyes. Hence decolourlsation via the more expensive chemical processes (coagulation, oxidation) or physlcal adsorption are generally employed .

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206 •

Several studies on blodecolourlsatlon have shown textUe dyes to be recalcitrant (Ghosh et ai, 1978, Porter and Snider, 1976, Yang and Pescod, 1977). Saito et aI (1984) found the BOD5 to TOC ratio 01 four azo dyes to be between 0.11 to 0.43, hence resistant to aerobic biodegradation. Possibly due to these early unsuccessful attempts at blodecolourlsatlon, there have been very few reported studies on biodegradation of dyes. However, the recent Interests In biodegradation of recalcitrant organics using acclimated bacteria have led to growing Interests In the use of acclimated bacteria for dye biodegradation. Although the studies reported so far have been mainly on the chemistry of dye degradation, it does show that azo dyes may be biologically decolourlsed. Using shake flask cultures Inoculated with Aeromonas hydrophila (IOOka et ai, 1978) and Pseudomonas cepacia (Idaka et ai, 1987a, and Idaka et ai, 1987b), both obtained from the ditches of azo dye factories, It was shown that azo dye decolourlsatlon occured, to varying degrees, via azo bond reduction. There are as yet no reported studies on the environmental condition Influencing blodecolourlsatlon.

Batch studies using a mixed culture acclimated to several azo dyes Indicated that the unaerated batch containing glucose as cosubstrate decolourlsed fastest (Rakml A. Rahman and Mohd. Arlffln Aton, 1987). Preliminary study of metabolites from blodecolourlsation of several azo dyes Indicated cleavage of azo bond as a step In decolourlsatlon. mechanism (Rakmi A. Rahman and Mohd. Arlffln Aton, 1986). The above findings indicated that aeration may be an Important factor In blodecolourlsatlon of azo dyes. The present study was carried out to determine the degree of aeration that would favour blodecolourlsatlon.

MATERIALS AND METHODS

Inoculum

The biomass acclimated to dye Red B (Reactive Red 22) (Rakml A. Rahman and Mohd. Arlffln Aton, 1987) was maintained In a sequencing batch process. The Inoculum for these experiments was a four day old culture grown by seeding sterilised colourless synthetic wastewater, SWW (Table 1) with 10 mL of mixed liquor from the process.

Blodecolourlsatlon experiments:

The experiments were carried out In 300 mL air tight ground glass stoppered BOD bottles (Wheaton). The volume calibrated bottles (each carrying a magnetic bar) were autoclaved at 121 0C for 20

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minutes. A flask of synthetic wastewater (Table .)'conIaining dye Red B and glucose was simultaneously autoclaved. then cooled to room temperature (about 27°C). Each sterile bottle W88 then asceptically filled with the wastewater and seed liquor to obtain the conditions In Table 2. Duplicates were used for each condition.

The bottles were then placed on a multipoint magnetic stirrer (Varlomag. Germany). The set was Immersed up to the bottle necks In a water bath equiped with a thermoregulator (Therrnornlx 1419. Braun. Germany). The temperatura was maintained at 2~C. The contents were stirred at 150 rpm.

Analysll of aamp'"

After placing the Innocutated bottles In the water bath. samples were taken at scheduled Intervals. Analysis carried out were for dye and biomass concentrations. using a spectrophotometer (Shlmadzu UV-265. Japan) and. after centrifugation at 20.000 rpm for 20 minutes. dissolved organic carbon (using carbon analyser IONICS Model 555. USA).

The oxidation-reduction potential (ORP) readings were also taken at sampling times using ORP probe (Cole Parmer. USA) and an Ion meter (lonanalyser 407A. ORION.USA). The probe was rinsed In alcohol followed by sterOe distilled water before each use to avoid contaminating the experiments.

RESULTS AND DISCUSSION

The results are shown In Figure 1. The result for each condition was confirmed by the duplicate which showed an almost identical result. The average of the two data at each point was used for plotting Figure 1.

Oxidation-reduction potential : The lower aeration level In bottles With higher VF was reflected by the ORP values. Lower aeration level led to lemer ORP values. At the start of the experiment. ORP values wera positive due to tha dissolved oxygen In the SWW and the air space above II. During the rapid (straight line) growth period. ORP rapidly decreased due to the use up of oxygen as electron acceptor In the oxidation of glucose. With growth slowdown. ORP values Increased •. showing lower electron avaDabl1ly In the system. Those for VF=0.4 and VF-0.6 became positive once stationary growths were attained whMe those for VF = 0.8 and VF = 1.0 remained negative due to presence of oxidizable metabolites .

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20B

Growth: Lower VF, hence higher aeration, system showed faster growths and attained higher stationary populations, as expected In systems with greater oxygen avaiabilty. Higher VF, hence Iessef aeration, systems showed slower growth and attained lower popWitlon level, as more organic Intermediates would be produced due to lower avalfabllty of electron ecceptors.

Deco/our/sation: Comparison 01 the trends In dye concentration and OAP curves showed dependence of decolourlsatlon rate on the oxidizing abOIty 01 the system. The InftlaJ lag In decolorlsatlon seemed to correspond to the condftlon of positive OAP. When OAPwas negative decolourlsatlon proceeded at a steady rate for all systems. For VF=0.4 decolourisatlon was steady unta t=30h when OAP became positive; at this point the decolourlsation slowed down then stopped. SlmUarly for VF = 0.6, decolourisatlon slowed down at about t = 4Oh; but it continued on although at a much lower rate, its OAP remained below l00mV for several days. Those for VF=0.8 and VF = 1.0 showed no such slowdown; the OAP for boIh remained negative.

These results show that decolourlsatlon occured fastest when system OAP was negative but stDI could occur, although more slowly when OAP was less than l00mV. Above 100mV, no decolourlsatlon occured. This corresponds wfth an earlier finding that no decolourisatlon occurred In aerated condition (Rakml A. Rahman and Mohd. Ariffln Aton, 1987). As previously mentioned, products which could only have been produced due to cleavage oIazo bond(s) were present In decolourlsed solution with dye Black B and several other dyes (Aakml A. Aahman & Mohd. Ariffin Aton, 1986). Hence, it can be postulated that at high OAP, the system's tendency to accept electron was high hence there was less tendency to use the dye molecule as electron acceptor. At negative or low ~ess than l00mV) OAP, lack of electron acceptor led to the usa of dye molecule as electron acceptor, via the reduction of azo bond(s), thus breaking the colour giving chromophore group.

Alba et al (1973) gave an OAP 01 820 mV for the reaction 2H 2 0.. O2 + 4H + + 4e and 30 mV for the use of fumarate as electron acceptor to form succinate. In the latter reaction, The C=C bond Is reduced. Hence it Is possible that azo bond cleavage could stili occur, although less effIcIentty at OAP less than l00mV, as here It involves N=N bond which Is weaker than a C=C bond. The CaC bond has a bond energy of 146 Kcal/mole while that for N = N bond is only 100 KcaI/moie (Hendrickson et ai, 1970). The significance of the results Is that as decolourlsatlon via azo bond cleavage could only occur et OAP < 100mV, decolourisatlon via this mechanism would not occur In the conventional aerated biological proeess. Decolourisation by the acclimated biomass via the unaerated condition used In the experiments was fairly rapid and should be

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applicable on process scale. From the resulta obtalI1Od here and In a previous study (Rakml A. Rahman and Mohd. AriIftn Aton. 1987). II can be concluded that effective decolourlsatlon would only occur In a process with reducing conditions.

CONClUSION

Biodecolourtsation of azo dye Red B was found to occur only at ORP of less than 100 mV. This IIndlng agrees with an earlier postulation that bIodecolourisatlon proceeded via azo bond(s) cI\NIwge.

ACKNOWLEDGEMENT

This research was supported by Research Grant 66/85 from Unlversltl Kebangsaan Malaysia.

REFERENCES

Alba. S.. Humphrey. A.E.. and Mills, V.F. 1973. Biochemical Engineering. Second ed. Academic Press Inc .• N.Y. & Land.

Ghosh. M.M., Woodard. F.E., Sproul, D.J., Knowlton. P.B., and Guertin, P.E. 1978. Treatability studies and design considerations for textne wastewater. JWater Poliut. Control Fe.d 50(8), 1971).1985.

Hendrickson, J.B., Cram, D.J., and Hammond. G.S. 1970. OrganiC Chemistry. Third ed. McGraw Hili Book ea., N.Y.

Idaka, E .• Ogawa. T .• Horltsu. H .. and Tomoyeda, M. 1978. Degradation of Azo compounds by Aeromonas hydrophlla Var. 24B, J. Soc. Dyers CoIourists 94:91-94.

ldaka E, Ogawa T. and Horitsu H. 1987ab. Reductive metabolism of amlnoazobenzenes by Pseudomonas cepacla. Bull. Environ. Contam. Toxlcal. 39:100-1-7.

Idaka E., Ogawa T. and Horltsu H. (1987b). Oxidative pathway after reduction of p-Amlnoazobenzene by Pseudomonas Capac/a. BUll. Environ. Contam, Toxlcol 39: 108-113.

Porter. J.J. and Snider, E.H. 1976. Long term biodegradability of textRe chemicals. J. Water Pollut. Control Fed. 48(11)2118-2210.

Rakrnl A. Rahman and Mohd. Arlffin Aton. 1986. Biodegradation of textile dyes. Proc. Regional Symposium on Management of Industrial Wastes In Asia and the Pacific, Kuala Lumpur 17-20 Nov., 1986 .

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210 ..

Rakml A. Rahman and Mohd. Arlffin Aton. 1987. Biological Removal 01 Colour from TextHe finishing Wastewater. Jour. Engineering, UKMI .

Salta T., Wldayat, WIwln WInfall, Hagiwara K and Murakami. 1984. Study on Organic pollution parameters for dyes and dyeing auxililartes. Fresemlus Z Anal. Chern. 319:433-434.

Yang, P.T. and Pescod, M.B. 19n. Polymertsation and dyeing wastewater characteristics and their treatability. Proc. 32nd Ind. Waste Conf., Purdue Unlv., 222-241 .

1 Jabatan Kejuruteraan Klmfa & Proses Unlversltl Kebangsaan Malaysia.

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211

Table 1: Composition cI nutrient and buIfer eaIts

Salt Concentration. mg/l

Nt\CI 600

MgCl2 ·6H2 O 100

MnCl2 ·4H 2O 0.5

FeCl3 ·6H2 O 0.5

CaCl2 7.5

KH2 P04 454

Na2 HP04 944

Table 2: Inttlal Condition

Volume Fraction (VF) 0.4 0.6 0.8 1.0

Vol. cI SWW(mL) 100 150 200 250

Vol. of seed(mL) 20 30 40 50

Glucose cone. (mg/L) 833 833 833 833

Dye cone. (mg/L) 19 19 19 19

Biomass cone (mg/l) 80 80 80 80

Page 8: A azo as a to - Universiti Kebangsaan Malaysia · 2016-05-04 · Jurnal Kejuruteraan 2 (1990) 205-212 EFFECTS OF AERATION ON BIODECOLOURISATlON OF AZO DYE Rakrnl Abdul-Rahman, Mohd

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18

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100 ~ 4

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• :::-::==-'"'=- -=. -=--=-r--=- - :--=w:.....::=- - __ • ---..;,;; - ----==e

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300

200

100

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, 10 20 _Ji74O 50 80 70 80 110 l 8! o t(h) -------'{)

-100 i

-200 • VF = 0.4

-300

A VF = 0.8 I o VF = 0.8

I ~ 0 VF - 1.0 . __ J

Figure 1 Variations of Dye and Biomass Concentrations and ORP With limp.

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