Anaerobic Oxic

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Che mo sphere, V ol . 33, No. 12, pp . 2533-2542. 1996Copyr ight 0 1996 E lsev ier Sc ience Ltd

Pr in ted in Great Br i ta in . A l l f i ghts resewedPII: ?4045-6535(%)00349-0 W45-6535/96 $15.00+0.00

Biological Treatment of Dye Wastewaters Using an Anaerobic-Oxic SystemHuren An*, Yi Qian, Xiasheng Gu , Walter 2. Tang**Dept of Civil & Environm ental Engineering, Florida International University, Miami, FL 3 3 199 , USADepartment of Environmental Engineering, Tsinghua University, Beijing 100084, P.R.China(Received in USA 8 Apri l 1996; accepted 16 Septemb er 1996)

Abstract: Three dye solutions, namely, C.I. Acid Yellow 17, C.I. Basic Blue 3, and C.I. Basic Red 2, weretreated in an upflow anaerobic sludge blanket (U ASB) reactor followed by a semi-continuous aerobic activatedsludge tank. When hydraulic retention time was about 1 2 hours, no significant color removal was observed in theaerobic stage. In the anaerobic stage, Acid Yellow 17, Basic Blue 3, and Basic Red 2 were removed by 20 %,72% , and 78% , mqectively. To treat wastewater horn a dye manufacturing factory with CO D concentration of120 0 rngfl and Color of 500 degree (dilution factor), an UASB reactor (4.5 liters) and an activated sludge tank(5 liters, adjustable), CO D and color were removed by more than 83% and 90 % at a COD loading rate of 5.3 kgCOD /mday in the anaerobic stage, and at the hydraulic retention time of 6- 10 hours for the anaerobic stage and6.5 for the aerobic stage. The anaerobic stage of the A/O system removes both color and COD . In addition, italso improves biodegradability of dyes for further aerobic treatment.Copyright 0 199 6 Elsevier Science LtdKeywords : Anaerobic-Oxic System; Dye Wastewater ; Decolorization

IntroductionDye wastewaters usually contain refractory dyes and other organic chemicals. Many studies

demo nsuamd that traditional activated sludge systems were not effective in removing these ch emical co mpou nds(1). Therefore, anaerobic processes become more and more popu lar because of their effectiveness intreating many wastewaters containing synthetic organics such as organochlorine and phenol compounds whichare refractory under aerobic conditions (2,3). Biodegradability studies on various dyes showed that anaerobicprcxxsses can also be used to decolorize dye wastewaters and improve the wastewater biodegrad ability for aerob ictreatment (4,5). To date, most an aerobic treatment stud ies investigate the treatment of azo dyes. For example.Seshadri et al. reported that an anaerobic fluidized-bed reactor to accomplish the cleavage of azo bond, leadingto decolorizing azo dyes of Acid Orange 7, Acid Orang e 8, Acid Orange 10, and Acid Red 14. Completecleavage of azo bond can be accomplished under hyd raulic retention time of either 12 or 24 hours (6). Th epotential decolorization of azo dyes by anaerobic microorganisms was also explored by Carliell et al. (7). Th edegradatio n kinetics of azo dyes a nd limiting steps in the reaction were inv estigated. Harmer and Bishop reportedthat 18% o 97% removal of Acid Orange 7 in a synthetic mun icipal wastewater could be achieved using lab-scale, rotating drum biotilm reactors (8).

In order to investigate the biodegra dability of different classes of dyes by anaerobic-oxic (A/O ) system,three dye solutions, namely, Acid Yellow 17, Basic Blue 3, and Basic Red 2, were studied. The efficiency inremoving color and C OD and the improvement of biodegradability of the dyes for further aerobic treatment by

*To whom all the correspondences should be addressed.

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2534anaerobic stage were evaluated. In addition, the feasibility to use the A/O system to treat an dye-manufacturingdye wastewater was also investigated.Material and Method s

A laboratory scale anaerobic-oxic system as shown in Figure 1 was used in this study. An upflowanaerobic sludge blanket (U ASB) reactor was used at the anaerobic stage and an adjustable aeration tank w itha maximum volume of 5 liters and settling volume of 2.0 liter w as used at the aerobic stage. The UASB reactorhas 3.5 liters of reaction volum e, 7 cm in diameter and 9 0 cm in height, 1 O liter settling volume, 10 cm indiameter, and 35 cm in height.

1 r aeration-settling tankinfluent pumr effluent

Figure 1. The A-O SystemEach dye solution contained about 40 mgil of dye and 1 000 mgIl of COD , which w as contributed mainly

by glucose. The CO D:N:P ratio of the solution was about 200:5: 1 and 600-90 0 mg/l (as CaCO ,) of alkalinitywas added. In terms of chemical structure of the dyes studied, Acid Yellow 17 has a pyrazole ring attached toa mono-azo bond. Basic Blue 3 is a phenoxazine dye and Basic R ed 2 is an acridine dye. The dye concentrationwas measured by a W-visible spectrophotom eter (Shim adz) using the calibration curve established beforeexperiments, Colo r was measured using colormetric analysis after dilution , in which the dilution factor wasdetermined by comparing with the blank. The molecular structures of the three dyes are shown in Figure 2.

=-+=QcHIr+ c sm .

Acid Yellow 17 Basic Blue 3 Basic Red 2Figure 2. The Molecular Structure of the Dyes


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2.535The industrial wastewater containing dyes contained about 120 0 mg/l of average CO D and 500

degree (d&ion factor) of average color. It was a mixture of neutralized discharge from a dye manu facturing milland glucose solution simulatmg municipal wastewater at a vo lume ratio of 3: 1. The average water qu ality of theoriginal wastewater from the dye manufacturing mili was: 55 mg!l SS, pH 7.0 - 7.2, 250 0 mg/l CO D, 50 00degree color dilution factor, 0 mg/l NH,-N, and 320 mg/l BOD ,. The compositions of synthetic glucose solutionwere: 500 mg/l glucose, 27 rngfl urea, 22 ms/l KH,PO,, and 1 000 mg/l Na$O,.

The anaerobic seed sludge was obtained from an municipal anaerobic digester and used afterscreening. T he sludge had a VSS concentration of 27.6 g/l, with a VSWSS ratio of 0.38, a sludge loading rateof 0.269 gCOD /gVSSday, and a SV of 95% with poor settleability. The aerobic seed sludge was obtained froma wastewater treatment plant and was used after settling and incubation. The sludge had a VSS/SS ratio of 0.5 1and a SVI of 34. Operational parameters used in anaerobic treatment of the three dye solutions were: averageHR T of 1 2 hours with maxim um 20 hours and minimum 8 hours, 12 g/l MLSS, organic loading rate of 2-2.4gCOD /m3-day, and an operation time abo ut one month for each dye solution. Part of the anaerobic effluent ofeach dye solution was treated by the semicontinuous activated sludge process in a shake flask w ith 2 g/l of MLS Sat a HRT of 23 hours and temperature of 25-30C.

Results and DiscussionAnaerobic-oxic (A/O) treatment of dye solutions: Figure 3 presents the results after anaerobic

treatment of Basic Red 2 dye solution. The trend in terms of percentage removal of Basic Blue 3 is similar tothat of Basic Red 2. During the first ten days, both C OD and dye removal rate declined from rather high valueat the beginning to very low removal rate. It appears that both the adsorption of dye onto anaerobic sludge anddegrada tion of dye by bacteria contribu te to remov al of dyes from the solution. In a continuous flow system,adsorption may reach equilibrium in about ten days. If no degradation occurs, dye will be adsorbed to sludgegradually until the equilibrium concentration was reached, the color removal rate will decrease along w ith thedecrease of the adsorption capacity. Therefore, it can be concluded that the high initial remov al rates are mainlydue to the adsorption of dye to the sludge, while little dye degradation occurred in the first ten days. However,after the adsorption equilibrium was reached, the steady-state color removal should be contributed throughbiological degradation. As shown in Figure 3, CO D &rd dye removal rates increased gradually afterten days until the steady state was reached, indicating significant degradation occurred, which suggests theacchmatio n of the bacteria to the dye. It implies that alth ough the dyes can inhibit the anaerob ic process at thebeginning , the bacteria were quick ly acclimated within ten days. Since aerobic bacteria co uld not digest dyes aftervery long time acclim ation, it can be concluded that the acclim ation of the anaerobic bacteria to various d yes isfaster than th at of aerobic bacteria. The acclimation of aerobic bacteria to dyes is a difficult process. Fo r


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2536example, Shaul et al. reported that 15 out of 1 8 azo dyes passed through the activated sludge system substantiallyuntre&d even after more than 80 days of acclimation (9). Ganesh et al. concluded that dye removal in aerobicprocess was mainly due to dye adsorbed or trapped by activated sludge iu stead of acclimatio n of bacteria to dyes(10). The anaerobic process was very effective in removing color and C OD . At steady state, color removal rateswere 20% , 7 2%, and 78% for Acid Yellow 17, Basic Blue 3, and Basic Red 2, respectively. The differentdegradatio n efficiencies seem obe greatly influeaced by the mole cular structu re of th e dye. For example, anionicdyes are more degradable than other dyes under anaerobic conditions, the color removal rate of Basic Blue 3 andBasic Red 2 are higher than tbat of Acid Y ellow 17. No adaptation time of the anaerobic sludge to Acid Yellow17 were observed. The removal rate was maintained at about 20% during the experimental period.

Figure 3. Anaerobic Degradation of Basic Red 2

App arently, adsorption plays an important role in removing dyes in the aerobic process followed. Thee&ent fromhe naerobic reactor was fed to the aerobic reactor. Table 1 lists the C OD and dye removal ratesafter aerobic treatment of the effluents containing the three dyes, separately. It shows that dyes were removedby sludge adsorption in the fn-st week. How ever, no significant remo val of dyes was observed aRerw ards. AcidYellow 17 concentration was remained at high level, which indicates that the dye was not effectively removedby the anaerobic process. The aerobic process did not further remove the dye except at the beginning due toadsorption. Basic Blue 3 was removed at the first 8 days with declining removal rate, no color removal wasobserved r&r 8 days, Therefore, the color removal during the 8 days should be contributed by adsorption.


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2537Table 1. Aerobic Treatment of Anaerobic Effluent

16.6

35.8 36.9 33.632.2 33.512.7 0

759 1065156 556 11779.4 47.818.8 13.9 2.913.2 10.1 2.929.8 27.3 0869 68470 32 52

91.9 95.3

100 100 100

15 16118 11575 62

36.4 46.132.7 33.532.5 33.0

0 0203 25590 6755.7 73.73.2 3.22.8 3.212.5 0117 12631 35

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Anaerobic-oxic treatment of a dye manufacture waste w ater: The biodegradability of wastewaterfrom a dye manufacturing factory was also studied. Since the major organic compounds in the dye manufactorywastew ater were commercial dyes, they were refractory u nder aerobic conditions. In addition, o ther dyes an d dyeprecursors are also present. T herefore, feasibility of using anaerobic-o xic system to treat the wastew aterhas to be experimentally studied.

Experim ents were carried out in three stages, namely , start-up, acclimation , and operation. The start-u pstage was the first 27 days, the influent was the glucose solution only, with no dye wastewater added. Thepurpose of this stage was to increase the sludge activity. The stage was completed after COD removal exceeded80% and both the settleability of sludge and the sludge loading rate were improved. The acclimation stage w astkrm the 27th to the 47th day. To acclimate he bacteria to the dye wastewater, the dye wastewater was gradually


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2538added to the infhtent until the dye concentration was the sam e as the dye wastewater at volume ratio of 3:1, Dyeconcentrations were changed after the color remov al rate become constan t, The acclimation time of 20 daysappears to be the same as reported in previous study when anaerobic bacteria was acclimated to various dyes,After the acclimation stage, the CO D removal rate by the A/O system was abou t 85% . Treatability andoperational parameters were analyzed during the operation period from the 47th to 77th day. The aerobic reactorwas operated only on the second and the third stages at HRT of 6.5 h, 4 g/l MLSS, and 3 g/l DO.

The COD concentration and COD removal rates during the three stages are shown in Figures 4 and 5.The figures indicate that C OD removal rate reached 80% at the end of the start-up stage, and slightly decreasedwhen the dye wastewater was added during the acclimation period, after which the COD removal rate becameconstant, CO D removal rate by the anaerobic stage in o perational period w as above 60 % at HR T of 8- 10 hours,and the removal rate of the whole system was about 85%.

Figure 4. CO D Changes During the Process


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Figure 6. Effect of the HRT of Anaerobic Reactoron Treatment Efficiency

2 3 4 5 6 7Ckga~cLnadingRate k&IUD/m d)

80 the A-OSy&n the Anaaobic Ructor

Figure 7. EMu ent CO D vs OrganicLoading Rate

The role of the anaerobic p r o c e s s : T h e anaerobic process plays an essential role in removing colorand C OD , and in improving the biodegradability of the wastewater under aerobic conditions. More than 60%of CO D was removed in the anaerobic reactor. Figure 8 demonstrates the color removal at different HR Ts, whichindicates that anaerobic process is very important in decolorization. It contributes to more than 80% of colorremoval when HR T was 8-10 hours. However, the color removal rate decreased at the HRT of 6 hours. Thecolor removal of the whole system is above 90%. On the other hand, the aerobic process removed only smallportion of the color, possibly by adsorption. Another im portant role which anaerobic process plays is toimprove biodegradability in erms f BOD JCOD ratios. Generally, the wastewater is considered biodegradablewhen BO DJC OD ratio is above 0.25. Figure 9 shows the BOD ,/COD before and after the anaerobic treatment.When HR T was longer than 6 hours, BO DJO D ratio increased from abou t 0.2 for the influent to more than 0.3for the effluent, which indicates the improved treatability of wastewater under aerobic conditions. One of themost reasonable explanation for this improvement is that anaerobic process apparently changed the molecularstructure of the dyes into different !Yagments,which was readily degradable u nder aerobic conditions.


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Conditions, Chemosuhere., & 397, (198 3)Hum , A., Yi, Q.,aud Xashmg, G., A Way for Water Polhuion Control in Dye Manufacturing Industryoceedines of Purdue IndustliaJ waste conference, 49th, 771-77 5, (1994 )rSeshadri, S., Bishop, P. L., and Agha, A. M., Anaerobic/aerobic Treatment of Selected Azo Dyes inWastewater , Waste Manaoement, j& 127-1 37, (1994) .Carliell, C. M., Barclay, S. J., Naidoo, N., Buckley, C. A., M ulhollaud, D.A., and Senior, E., MicrobialDecolourisation of a Reactive Azo Dye under Anaerobic Condition Water S .A. 2 1~,.-..._. 61-69, (1995).Hatmer, C ., and Bishop, P., Transformationof Azo Dye AO-7 by Wastewater Biotilms, Water Scienceand Technolow, & 627-636, (1992).Shaul, G. M ., Dempsey, C. R., and Do& al, K. A., Fate of Water Soluble Azo Dyes in the ActivatedShtdge Process EPA/600/S2-88/30, Water Engineering Research Laboratory, Cincinnati, OH, (1988)Ganesh, R, Boardman, G. D., and Michelsen, D., Fate of Azo Dyes in Sludge Wat. Res. 28 1367 -->_)1376, (1994).Lettinga, G., Anaerobic Tmatment of Sewage and Low Strength Wastewater , Proceedines of the 2ndlntemational Svmnosium on Anaerobic D ieestion, (1 98 1).Gratt, P., Textile Industq Wastewaters Treatment , Water Science & Technology, 24 _ 97-10 3, (199 1).

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