Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 79:1268–1274 (online: 2004)DOI: 10.1002/jctb.1122

Anaerobic/aerobic sequential treatmentof a cotton textile mill wastewaterMustafa Isik and Delia Teresa Sponza∗Dokuz Eylul University, Engineering Faculty, Environmental Engineering Department, Buca Kaynaklar Campus, 35160, Izmir, Turkey

Abstract: The treatment of a wastewater taken from a cotton textile mill was investigated using ananaerobic/aerobic sequential system during an operational period of 87 days. The process units consistedof an upflow anaerobic sludge blanket (UASB) reactor and a continuous stirred tank reactor (CSTR).Wastewater characterization was performed before feeding the reactor system. Glucose-COD, and azodyes were added to the textile wastewater for comparative purposes in the final period of operation. ThepH values in the effluent of the UASB reactor were suitable for optimal anaerobic treatment in all runs.The biodegradable part of the COD in wastewater was removed effectively, with the anaerobic stageimproving the biodegradability of wastewater entering the aerobic stage. The UASB reactor permittedCOD and color removals of 9–51% and 46–55%, respectively, at a hydraulic retention time (HRT) of30 h. COD removal efficiencies were between 40 and 85% and color removal efficiencies were 39–81% innormal and artificially-colored wastewaters at a total HRT of 5.75 days in the UASB/CSTR reactor system.Benzidine produced from the cleavage of azo bond in the anaerobic stage was effectively removed in theaerobic stage, and was identified by comparison of its HPLC spectrum with that of an authentic specimen. 2004 Society of Chemical Industry

Keywords: cotton textile; anaerobic/aerobic; decolorization; sequential; azo

1 INTRODUCTIONTextile wastewaters are characterized by high volumesand extremely variable composition, which can includebiodegradable and non-biodegradable dyes, organicmatter, salts and toxic substances.1 The variabil-ity arises both from the diversity of the typesof industrial processes employed and the immenserange of chemicals and materials involved withineach category. Typically, textile wastewaters containabout 1000 mg dm−3 of chemical oxygen demand(COD) and 300–500 mg dm−3 of biochemical oxy-gen demand of five days (BOD5) corresponding toa BOD5/COD ratio of 0.3–0.5.1 The major pollu-tant types may be summarized as degradable organ-ics (starches, enzymes, fats, greases, waxes, surfac-tants), color (dyes, scoured wool impurities), nutri-ents (ammonium salts, urea and phosphate buffers),NaOH, mineral/organic acids, salts (sodium silicate,sodium sulfate, sodium carbonate), sulfur (as sulfate,sulfide and sulfuric acid), toxicants (heavy metals,reducing agents such as sulfide, oxidizing agentssuch as chloride, peroxide, dichromate and per-sulfate), and refractory organics (surfactants, dyes,resins, synthetic sizes such as polyvinyl alcohol,carboxylmethylcellulose, chlorinated organic com-pounds, organic solvents).2 So far the treatment oftextile wastewaters has been based mainly on aerobic

biological processes, which consist of conventionaland extended activated sludge systems.3 The oxy-gen consumption and sludge yield are generally highand result in high operational costs.4 Moreover, aer-obic processes are in effective in degrading azo dyes,which are the largest group of synthetic colorants(60–70%).5 Highly electrophilic azo bonds can becleaved under anaerobic conditions, and the aromaticamines produced from this cleavage can be removedin aerobic environments.6 Anaerobic pre-treatmentcould be a cheap preliminary to aerobic treatmentreducing the costs for aeration and problems withsludge bulking.2

Recently, research has shown that synthetic andsimulated wastewaters containing azo dyes and otheradditives can be treated effectively in a sequentialanaerobic/aerobic environment.7–12 Although a fewstudies have been carried out on the treatment ofactual textile wastewaters by this process, this treat-ment has not been widely reported in the literature.Therefore, the goals of this study were to investi-gate the anaerobic/aerobic treatability of an actualtextile wastewater by means of the upflow anaerobicsludge blanket (UASB) reactor/continuous stirred tankreactor (CSTR) sequential system and to determinethe removal of color and aromatic amines dur-ing treatment.

∗ Correspondence to: Delia Teresa Sponza, Dokuz Eylul University, Engineering Faculty, Environmental Engineering Department,Buca Kaynaklar Campus, 35160, Izmir, TurkeyE-mail: delya.sponza@deu.edu.trContract/grant sponsor: Turkish Scientific and Technical Research Council (TUBITAK); contract/grant number: 199 Y 110Contract/grant sponsor: Nigde University; contract/grant number: 2002/03, TURKEY(Received 17 March 2004; revised version received 14 May 2004; accepted 17 May 2004)Published online 3 September 2004

2004 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2004/$30.00 1268

Treatment of a cotton textile mill wastewater

2 MATERIAL AND METHODS2.1 Laboratory-scale reactor system, seed andoperating conditionsA continuously fed stainless steel UASB reactor andan aerated CSTR were used in sequence (Fig 1). TheUASB reactor had an effective volume of 2.5 dm3.The CSTR consisted of an aeration tank (effectivevolume = 9 dm3) and a settling compartment (effec-tive volume = 1.32 dm3). Treated effluent passedthrough a U-tube in order to trap biomass beforerunning to the aerobic tank. Wastewater passed fromthe aeration tank to the sedimentation tank throughholes in an inclined plate and sludge was recycledthrough a gap under the plate. Partially granulatedanaerobic sludge was used as seed in the UASB reac-tor and was taken from the methanogenic reactor ofthe Pakmaya Baker’s Yeast Factory, Izmir, Turkey.Activated sludge culture obtained from DYO DyeIndustry. Izmir, was used as seed for the CSTR. Thesuspended solids (SS) and volatile suspended solids(VSS) in the UASB reactor were 31.7 g dm−3 and22.4 g dm−3, respectively while the mixed liquor sus-pended solids (MLSS) concentration in the CSTR

was kept at about 3000 mg dm−3 by adjusting thesludge age to 20 days. The treatability of the wastew-ater with a flow rate of 2 dm3 day−1 was investigatedduring 87 days of operation. The hydraulic retentiontimes (HRTs) of the UASB reactor the CSTR andthe combined UASB/CSTR reactor system were 30 h,4.5 days and 5.75 days, respectively.

2.2 Wastewater characteristicsThe actual wastewater was taken from a cotton textilemill located in Soke, Turkey. It was treated usinga laboratory-scale anaerobic/aerobic reactor systemin which wool dyeing wastewater had been treatedpreviously.13 The pH of the wastewater coming fromthe textile mill was adjusted to 7 in an equilibriumtank at the treatment plant of the factory. Wastewaterwas taken weekly from this tank and transported tothe laboratory for treatment in the laboratory-scalereactor. In the final run of the study, glucose-COD(1000 mg dm−3) was added to the influent of theUASB reactor to provide additional carbon since theraw wastewater had a low COD content (see Table 1).The color of the wastewater coming from the mill

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Figure 1. Laboratory-scale sequential anaerobic UASB/aerobic CSTR system.

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Table 1. Characterization of wastewater from the cotton textile mill

Run

1a 2 3 4 5 6 7 8 9

Parameter Rawwith

additionb Rawwith

additionc

Total COD (mg dm−3) 604 1708 1431 673 615 1215 1038 — — —Soluble COD (mg dm−3) 463 1284 1112 482 493 997 952 305 518 342 1342Inert COD (mg dm−3) 360 200 525 160TOC (mg dm−3) 143 388 292 147 157 289 348 76 — 283Alkalinity (mg dm−3) 500 800 600 520 600 650 320 — 400 530 —pH 7.48 7.25 7.17 7.31 9.2 7.27 7.23 6.89 7.15 7.22 7.46Color (m−1) 20 52 65.5 111 24 79 37 — 935 37 758λmax (nm) — 400 400 400 400 400 420 — 480 530 497SS (mg dm−3) 131 130 167 106 107 103 — — —

a The UASB reactor system was fed with synthetic wastewater with glucose-COD of 2000 mg dm−3 instead of real wastewater in this run.b The dyes were added to the influent at a concentration of 100 mg dm−3 for each dye (Reactive Black 5, Direct Red 28, Direct Black 38, DirectBrown 2, and Direct Yellow 12).c The dyes and glucose were added to the influent at a concentration of 50 mg dm−3 for each dye (Reactive Black 5, Direct Red 28, Direct Black 38,Direct Brown 2, and Direct Yellow 12) and 1000 mg glucose-COD dm−3, respectively.

was much lower than those of synthetic and aciddyeing wastewaters studied previously.13 This can beexplained by the dilution by wastewaters originatingfrom other processes. Therefore, Reactive Black 5,Direct Red 28, Direct Black 38, Direct Brown 2 andDirect Yellow 12 azo dyes were added to the influentof the UASB reactor at levels of 50 and 100 mg dm−3

each in the last two operational runs. (see Table 1).The characteristics of the wastewater taken from themill process are summarized in Table 1. Since thiswastewater contained domestic wastewater from themill mineral elements were not added. It was observedduring batch tests that the fraction of inert COD wasabout the half of the total COD (Table 1).

2.3 AnalysesGas production was measured by the liquid displace-ment method. Total gas was measured by passing itthrough a liquid containing 20 cm dm−3 H2SO4 and100 g dm−3 NaCl.14 The methane concentration inthe biogas was determined by a Drager (Stuttgart,Germany) PacEx methane gas analyzer. The mea-surement of color was carried out following the methoddescribed by Olthof and Eckenfelder15 since variousdyes could be used in the dyeing process. Accordingto this method, the color content is determined as thesum of the absorbances at three wavelengths (445,540 and 660 nm). The absorbances of the effluentsin Runs 1, 2 and 3 were corrected by subtracting theabsorbance values due to metabolic residues measuredin the effluent of Run 1. To convert the absorbancesinto color units the equation given below was used:

α = Ad

× f

where

α = color in(m−1)

A = measured absorbance value

d = sample length (cell width, 10 mm)

f = factor (1000)

The total and soluble COD were measured col-orimetrically using closed reflux methods.16 The bio-logically inert COD of wastewater taken from themill was determined for evaluation of its treatabil-ity, by the glucose comparison method,17 measuringall the soluble forms of COD under aerobic condi-tions. Total organic carbon (TOC) was determinedwith a DOHRMANN type DC-190 Model High-Temperature TOC analyzer. Bicarbonate alkalinity(BA) and total volatile fatty acid (VFA) concentrationswere measured simultaneously using the titrimetricmethod.18 The pH was determined immediately aftersampling to avoid any change due to CO2 evolution,using an NEL type 890 pH meter. Dissolved oxygen(DO) and the temperature of the aeration tank of theCSTR were measured with a WTW (Hamburg, Ger-many) oxygen meter (model Oxi 330/SET). Biomasswas measured as total suspended solids (TSS) andvolatile suspended solids (VSS) in the UASB reactor,and mixed liquor suspended solids and mixed liquorvolatile suspended solids (MLVSS), in the CSTR.Assays were performed according to Ref 16. Totalaromatic amines (TAA) were determined colorimet-rically at 440 nm after reacting with 4-dimethylaminobenzaldehyde-HCl19 using a standard curve calibratedwith benzidine standards.

HPLC analyses were carried out using an LC10 model (Shimadzu, Tokyo, Japan) HPLC-DADequipped with a C18 (Moscow, Russia) chromato-graphic column (id 4 mm, length 250 mm, stationaryphase particle size 7 µm). In the operation a mobilephase of methanol/water (55:45, v/v) was used at aflow rate of cm3 min−1. All samples were diluted in aratio of 1:10 with distilled water.

1270 J Chem Technol Biotechnol 79:1268–1274 (online: 2004)

Treatment of a cotton textile mill wastewater

3 RESULTS AND DISCUSSION3.1 Variations in gas production rate, volatilefatty acids concentrations and bicarbonatealkalinity in the UASB reactorThe variations of volatile fatty acids (VFA) bicar-bonate alkalinity (BA) and pH in the effluent ofthe UASB reactor are shown in Fig 2 for all runs.The VFA concentrations in Runs 1 and 9 wereslightly higher than in the other runs because glu-cose was added to the feed in these runs. Exceptfor Runs 1 and 9, the VFA concentrations were verylow in the UASB reactor effluents due to low CODconcentrations in the influents and excellent reactorperformance. The ratios of VFA/BA and pH values(Fig 3) varied between 0.2 and 0.3, showing that thereactor was operated under steady-state conditions.20

VFA concentrations were 389, 58 and 286 mg dm−3

as CH3COOH while the methane production rateswere 938, 360 and 372 cm3 CH4 day−1 for Runs 1, 6and 9, respectively. In Runs 1 and 9, the VFA con-centrations increased slightly but did not exceed thecritical value of the VFA/BA ratio (0.40), indicatingreactor stability.20 This shows that the organic fractionof the COD in the wastewater was successfully con-verted to methane by methanogenic bacteria, VFA didnot accumulate and the BA was sufficient throughoutmethanogenesis. Even though one of the common dis-advantages of anaerobic treatment is the high alkalinityrequirement18,21 in this study alkali was not added tothe reactor since the pH remained between 7 and 8.

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Figure 2. Variation in methane production rate, VFA concentration,and bicarbonate alkalinity in different operational runs.

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Figure 3. Variation of pH and VFA/bicarbonate alkalinity ratio in theeffluent of UASB reactor.

3.2 COD removal efficiencies duringanaerobic/aerobic sequential treatmentThe COD removal efficiencies of the total reactorsystem exhibited variations during operation sincethe composition of the wastewater taken from themill was variable, as shown in Table 1. The influentCOD and effluent CODs of the whole system areillustrated in Fig 4 for each run. The biodegradablepart of the COD was removed effectively in thesystem, taking into consideration the biologically inertCOD fraction of the influent samples (see Table 1).Germirli et al22 reported that textile wastewater with asoluble COD of 1000 mg dm−3 included a biologicallyinert soluble COD of 190 mg dm−3. The UASBreactor permitted COD removals of 9–51% at anHRT of 30 h. In Run 2 the influent soluble CODof 1248 mg dm−3 decreased to 598 mg dm−3 and226 mg dm−3 in the effluents of the UASB reactor(HRT of 30 h) and the CSTR (HRT of 4.50 days),respectively. In this run, since the wastewater had360 mg dm−3 of inert COD, it is clear that theanaerobic stage improved the biodegradability underaerobic conditions. In particular the readily degradableCOD was removed under anaerobic conditions, asreported by An et al.8 Similar results were obtained inRun 6 in which the COD was reduced to 376 mg dm−3

using the UASB/CSTR system with an initial CODof 1025 mg dm−3 and inert COD of 525 mg dm−3 atthe aforementioned HRTs. This corresponded to 37,40 and 62% removal efficiencies in the UASB, CSTRand UASB/CSTR reactor systems, respectively.

The soluble organics in the effluent of a biologicaltreatment process may include not only the biodegrad-able and non-biodegradable compounds originat-ing from the raw wastewater, but also compoundsformed by microorganisms in the treatment systemitself. Non-biodegradable organics can be classified ascompounds produced from the metabolism of sub-strate, from microbial growth or from the lysis ofmicroorganisms.17 When the system was fed onlywith glucose-COD (2000 mg dm−3) the effluent of thesequential system had a COD of 126 mg dm−3 in Run1. This shows that the fraction of non-biodegradableorganics through substrate metabolism and microbialgrowth in the system was about 5% through anaer-obic/aerobic treatment. Kuo et al23 found that the

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CSTR effluent CODUASB/CSTR

Figure 4. COD removal performance of the UASB/CSTR sequentialreactor system.

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production of soluble microbial products ranged from0.6 to 2.5% in a glucose-fed anaerobic reactor.

3.3 Color removal in the UASB/CSTR reactorsystemThe color of the actual textile industry wastewaterwas reddish-purple. The color measurements basedon the sum of absorbances at wavelengths of 445,540, and 660 nm are shown in Fig 5. Since the colorwas less than the values quoted by O’Neill et al24 fortextile wastewaters, further dye was added to the feedin Runs 8 and 9. Figure 5(a) shows the results takenfrom the actual textile wastewater. The UASB reactorpermitted color removals of 46 and 55% at an HRTof 30 h. For instance, the colors of influent, UASBand CSTR effluents were found to be 111, 57.5,32 m−1, respectively, corresponding to 48, 38, 71%color removals in the UASB, CSTR and UASB/CSTRsystems, respectively, in Run 4. In order to investigatethe effect of the composition of the wastewater ondecolorization a mixture of azo dyes was addedat concentrations of 500 mg dm−3(100 mg dm−3 × 5)

and 250 mg dm−3 (50 mg dm−3 × 5) in Runs 8 and 9,respectively. Figure 5(b) shows the results obtained.The color removal efficiencies in the UASB, CSTRand UASB/CSTR reactor systems were 74, 54 and88% in Run 8 and 59, 5 and 61% in Run 9,respectively. This showed that although the color wasmainly removed in the anaerobic stage, the aerobicstage could also reduce the color. Basibuyuk andForster reported COD and color removals of morethan 83% and 90% at a COD loading rate of

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UASB;Color removal efficiency: CSTTR; UASB/CSTR.

Influent color UASB effluent colorCSTR effluent color

Figure 5. Color removal efficiencies of the system for all runs whenthe reactor was fed with textile mill wastewater (a) and colored textilemill wastewater (b).

5.3 kg COD m−3 day−1 in the anaerobic (UASB) andaerobic (CSTR) stages at HRTs of 6–10 h and 6.5 hin a wastewater from a dye-manufacturing factory witha color of 500 degree.25 Furthermore, in this study itwas reported that >99% color removal was achieved ina sequential anaerobic/aerobic biological filter systemtreating Basic Red at an HRT of 1 day.25

Absorbance spectra of the influent and effluentsamples are shown in Fig 6 for different runs inthe UASB/CSTR reactor system. The absorbanceof the actual wastewater was low. Although thecolor was mainly removed under anaerobic conditions(Runs 4 and 6) it could also be removed underaerobic conditions (Run 3). However, sometimesno additional color was removed under aerobicconditions. It is important to note that althoughthe levels of color were low in this wastewater(<100 m−1), they did not change in the COD testunder aerobic conditions. This shows that anaerobicconditions are important for the removal of thecolor of dyes. An experimental anaerobic/aerobictreatment plant was found to be successful inthe treatment of a polyester and cotton factorywastewater.26 The effluent was principally composedof dyes, polyvinyl alcohol, detergents, acids andalkali salts with COD levels of 600–900 mg dm−3.The mean efficiencies for COD and color removalswere 78% and 72% respectively, and no toxicitywas reported when the HRT and COD loading ofan anaerobic Rotating Biological Contactor (RBC)and aerobic RBC were 7–8 h, 40–50 g m−2 d−1 and30–40 g m−2 d−1, respectively. In a study performedby Yang et al.27 the anaerobic stage consisted of arotating fixed film reactor and loading rates variedbetween 1.66 and 2.71 kg COD m−3 day−1. High color(80%) and COD (92%) removals were reported forthe treatment of a cotton-processing effluent in ananaerobic/aerobic pilot plant followed by activatedcarbon as tertiary treatment. Color removal of 55%was achieved in the anaerobic stage.

3.4 Removal efficiencies of TAA in the reactorsystemAlthough the dye formulations in the mill wastewaterwere not known, aromatic amines are undoubtedlypresent in the structure of dyes. Total aromatic amines(TAA) measurements in the effluent samples areshown in Fig 7. All tests showed that the effluentfrom the UASB reactor had higher TAA values thanthe effluent of the CSTR, showing that the aerobicstage was very important for the removal of aromaticamines. These results agree with findings reported inother studies in relation to removal of azo dyes by ananaerobic/aerobic sequential system.6,12,28

UASB effluent samples had higher TAA concentra-tions in the last two runs when synthetic dyes wereadded to the feed (see Fig 7). It has been reportedthat the maximum dye concentration in textileindustry wastewater is about 100–500 mg dm−3.24

The comparison of the last two runs with the earlier

1272 J Chem Technol Biotechnol 79:1268–1274 (online: 2004)

Treatment of a cotton textile mill wastewater

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Figure 6. Absorbance spectra in influent and effluent of reactor system in different runs.

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Figure 7. TAA removal efficiencies of CSTR reactor.

ones indicated that the actual textile wastewatercontained low TAA concentrations because the dyecontent was lower than that in the dye-added runs.

Figure 8 shows the high performance liquid chro-matograms of the effluents from the UASB and CSTRstages, respectively, and clearly demonstrates that theUV-absorbing aromatic amine, benzidine, producedin the UASB reactor from azo dyes, was degraded byaerobic treatment. The identity of the benzidine peakwas established by comparison with the HPLC of anauthentic specimen (results not shown).

4 CONCLUSIONSIn the treatment of textile wastewater, COD removalefficiencies were found to be between 40 and 85% ata total HRT of 5.75 days in a UASB/CSTR system.Color removal efficiencies were 39–81% in actual andcolor-supplemented textile wastewater. Most of the

color and approximately half of the influent CODwere removed in the UASB reactor. Aromatic aminesformed in the anaerobic stage were removed effectivelyin the aerobic stage with removal efficiencies varyingbetween 37 and 87%. The methane yield, pH andVFA concentration of the UASB effluents showedthat inhibition was not observed.

Azo dyes in textile wastewaters were reductivelydecolorized in the anaerobic stage and mineralized inthe aerobic stage. The inclusion of effluents from thealkaline process of reactive dyeing in the anaerobicstage ensured adequate control of pH. A two-stageUASB/CSTR system eliminates the disadvantages ofeach stage. For instance, high organic loads in textilewastewater may cause sludge bulking and necessitateexpensive aeration in a wholly aerobic system.Anaerobic pre-treatment could reduce aeration costsand produce a much smaller volume of sludge.

Since the 100–500 mg dm−3 dye concentrationsused in this work were higher than the concentrationsin the actual textile wastewater, it can be concludedthat azo dyes will not inhibit the anaerobic treatmentin practice. However aromatic amines formed fromthe azo dyes exhibit resistance and/or are degradedslowly under anaerobic conditions. These aromaticamines are readily degraded under aerobic conditions.As a result of this study, sequential anaerobic/aerobicprocesses are recommended for the treatment of textilewastewater containing azo dyes.

ACKNOWLEDGMENTSThis study was supported by the Turkish Scientificand Technical Research Council (TUBITAK) for

J Chem Technol Biotechnol 79:1268–1274 (online: 2004) 1273

M Isik, DT Sponza

mAbs

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benzidine peak

Figure 8. HPLC chromatograms of effluents of (a) UASB reactor and (b) CSTR.

the project numbered 199 Y 110, and the fund ofNigde University with a project numbered 2002/03,TURKEY. The authors gratefully acknowledge thefinancial support from these organizations.

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