Treatment of textile wastewater with an anaerobic fluidized bed reactor

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Desalination 237 (2009) 357–366

Treatment of textile wastewater with an anaerobic fluidizedbed reactor

Mahdi Haroun*, Azni IdrisDepartment of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia,

43400 UPM, Serdang, Selangor, MalaysiaTel. +60 (3) 8946-6185; Fax: +60 (3) 8656-7120; email: [email protected]

Received 19 March 2006; Accepted 7 January 2008

Abstract

The discharge of textile wastewater containing dyes in the environment is worrying for both toxicological andesthetical reasons as dyes impede light penetration, damage the quality of the receiving streams and are toxic to foodchain organisms. A fluidized bed reactor (FBR) with activated carbon as support material has been used to investigatethe removal efficiency of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and color of textilewastewater. The FBR was fed continuously without supplemented (Phase 1 and 2) and supplemented with glucose(Phase 3–5) at hydraulic retention times (HRT) of 4 h, and increased to 8 and 12 h with flow rates of 36, 18,12 L/d,respectively. The HRT was operated for a duration of 14 days. The effect of operational conditions such as organicloading rate (OLR), (HRT), and influence of glucose concentration as substrate additives was investigated to achievethe maximum removal efficiency in the reactor. Results indicated that anaerobic treatment of textile wastewater waspossible with the supplementation of substrate additives as external carbon sources such as glucose (about 0.6 g/l).A further increase in the external carbon source added to textile wastewater did not improve the color removalefficiency of the anaerobic FBR reactor. The study implied that 98% soluble COD, 95% BOD5, and 65% colorreduction were possible by an anaerobic FBR.

Keywords: Textile wastewater; Anaerobic; Fluidized bed reactor; COD; BOD

1. Introduction

Wastewater generated by different productionsteps of a textile mill have high pH, temperature,detergents, oil, suspended and dissolved solids,

*Corresponding author.

toxic and non-biodegradable matter, color andalkalinity. Wastewater from fabric and yarn print-ing and dyeing pose serious environmentalproblems both because of their color and highCOD [1]. Important pollutants in textile effluentare mainly recalcitrant organics, color, toxicants,

doi:10.1016/j.desal.2008.01.0278

M. Haroun, A. Idris / Desalination 237 (2009) 357–366358

and surfactants, chlorinated compounds (AOX),pH and salts effect.

The majority (60–70%) of industrially synthe-sized dyes are azo compounds which can bereduced and decolorized not only by bacteriaunder anaerobic conditions, but also by reduc-tants such as sodium dithionite and sodiumsulfide [2]. Fixation rates for reactive dyes tend tobe in the range of 60–70% although the valuestend to be higher in dyes containing two reactivegroups [3]. Therefore, up to 40% of the color isdischarged in the effluent from reactive dyeingoperation resulting in a highly colored effluent[3].

Physicochemical methods are applied for thetreatment of this kind of wastewater, achievinghigh dye removal efficiency [4]. On the otherhand, in recent years there is a tendency to usebiological treatment systems to treat dye-bearingwastewater [5]. The recalcitrant nature of azodyes, together with their toxicity to microorgan-isms, makes aerobic treatment difficult [2]. Colorremoval under anaerobic condition could be bybiodegradation of dyestuff by azoreductase acti-vity or by non-enzymatic azo reduction of dye-stuff. However, azoreductase cleavage of the azobond may result in formation of aromatic amines,which induce cancer in man and tumors in someexperimental animals [6]. But some reportsshowed that the effluent of anaerobic decolori-zation process was completely non-toxic [5].Another problem with anaerobic color removal isthe reverse colorization of anaerobic degradationproducts upon exposure to oxygen, which couldbe because of unstable characteristics of bio-degradation products, aromatic amines, whichdeteriorate to give color [6].

An electron-donating carbon source such asstarch, volatile fatty acids (VFA) or glucoseprovides the required electrons. In addition, it isknown that methanogenic and acetogenic bacteriain anaerobic microbial consortium contain uniquereduced enzyme co-factors, such as F430 andvitamin B12, that could also potentially reduce

azo bonds [7,8]. Unfortunately, as suspect muta-gens and carcinogens, the aromatic amines cannotbe regarded as environmentally safe end products.

Several high rate anaerobic reactor configu-rations have been developed for treating waste-water at relatively short hydraulic retention times(HRT). Of these the anaerobic fluidized bedreactor (FBR) has been one of the technologicaladvances. It has been successfully employed in abroad spectrum of wastewater including bothreadily and hardly biodegradable wastes [9,10].Table 1 provides a summary of the performanceof different anaerobic systems treating real andsynthetic textile wastewater reported in theliterature, respectively.

Fiber manufacturing and dyeing are predomi-nant in the Malaysian textile sector, which is oneof the most important industrial sectors in thecountry both in terms of its contribution to theeconomy and environmental emissions. There-fore, the aim of this study was to investigate theanaerobic treatment of a textile wastewater in aFBR. To this purpose, a FBR with carbon as thesupport material was operated. The effect ofoperational conditions such as OLR, HRT, andinfluence of glucose concentration as co-substrateadditives was also investigated.

2. Materials and methods

2.1. Fluidized bed reactor

The reactor was made of a clear acryliccolumn 80 mm in diameter, 750 mm in height,with a volume of 3.75 L (Fig. 1). The expandedsection acted as a solid settling chamber. It had adiameter of 150 mm with a volume of 2.25 L baseon the liquid phase volume. The conical flowdistributor supplies a uniform fluidization alongthe height of the column and has a volume of0.12 L. The enlarged top section was used as agas–solid separator. The bottom of the reactorwas flat with symmetrically placed four poresthrough which flow was equally distributed into

M. Haroun, A. Idris / Desalination 237 (2009) 357–366 359

Table 1Performance of different anaerobic systems treating real textile wastewater

% Efficiency in removal, % HRT Refs.

Method COD ColorTwo-phase anaerobic packed bed reactor 78 90 5 days [11]Anaerobic/aerobic using sequencing batch reactors 76 94 2.6 days [12]Anaerobic/aerobic sequential treatment system 90 85 48 h [6]

Fig. 1. Schematic diagram of fluidized bed reactor.

the reactor. The recycle flow was drawn from thetop section using a peristaltic pump and then fedupward into the reactor. Gas produced in thereactor was transferred through water trap to pre-vent the intake of oxygen from the atmosphere.The reactor was placed in a temperature-controlled room at 35EC. Activated carbon witha diameter of 0.02–0.25 mm and volume of 1 L

equivalent to 25cm height was used as supportmaterial in the FBR.

Activated carbon used in this study has thefollowing characteristics: (1) bulk density: 0.6262gm/cc, (2) ash content: 3.55, pore space: 189.82cc/100 gm, (3) surface area: 5000 m2/g, (4): truedensity: 2.51 gm/cc. It has an extraordinarilylarge surface area and pore volume that gives it aunique adsorption capacity. The specific mode ofaction is extremely complex, and has been thesubject of much study and debate. Activatedcarbon has both chemical and physical effects onsubstances where it is used as a treatment agent.Activity can be separated into (1) adsorption,(2) mechanical filtration, (3) ion exchange and(4) surface oxidation.

2.2. Start-up period

The purpose of the start-up period was toattain biofilm formation on the support material.Palm oil sludge (1 L) contained a mixed anaero-bic culture with mixed liquor suspended solids(88.7 g/l) and mixed liquor volatile suspendedsolids (22.65 g/l) obtained from the anaerobicpalm oil mill treatment plant. The feed containedmethanol, glucose, and yeast extracts as well asmacro- and micronutrients such as CaCl2.2H2O(50 mg/l), (NH4)2.HPO4 (80 mg/l), FeCl2.4H2O(40 mg/l), NH4Cl (800 mg/l), Na2S.9H2O(300 mg/l), CuCl2.2H2O (0.5 mg/l), MgSO4.7H2O(400 mg/l), H3BO3 (0.5 mg/l), MnCl2.4H2O(0.5 mg/l), NaWO4.2H2O (0.5 mg/l), AlCl3.6H2O(0.5 mg/l), Na2SeO3 (0.5 mg/l), cysteine (10


Table 2Organic loading and % feeding during start up period

Time, days 0–5 6–10 11–15 16–20COD loading, kg COD/m3/day 0–4 4–10 10–16 16–21Methanol, % of the total COD 75 50 25 0Glucose +yeast, % of the total COD 25 50 75 100NH4Cl 25 50 75 75

Table 3Operating conditions of the fluidized bed reactor

Parameters Phase 1 Phase 2 Phase 3 Phase 4 Phase 5

Operation, days 1–14 15–28 29–42 43–56 57–70HRT, h 4 12 8 12 12OLR, kg/m3/d 4.9 1.5 3.3 4.4 8.4Flow rate, L/d 36 12 18 12 12Influent COD, mg/l 810 797 1097 2200 4200Feeding composition TW TW TW+G TW+G TW+G

TW = textile wastewater; G = glucose.

mg/l), KCl (400 mg/l), ZnCl2 (0.5 mg/l), NaHCO3

(3000 mg/l), NaMoO4.2H2O (0.5 mg/l), CoCl2.6H2O (10 mg/l), KI (10 mg/l), and NiCl2.6H2O(0.5 mg/l), which are necessary for optimumanaerobic microbial growth. During the start-upperiod, the COD loading was gradually raised byincreasing the feed rate (Table 2) while keepingthe influent COD constant at around 800 mg/l.

The contribution of methanol in the total influ-ent COD was decreased to 50%, 25%, and 0% ondays 10, 15, and 20, respectively, by replacing itwith glucose. Moreover, NH4Cl concentrationwas gradually increased to its value in nutrient(900 mg/l) to obtain high initial C/N ratios duringthe start-up period (part of this N used by bacteriawith carbon for bilding up of the new cell so theoverall C/N ratio will increased) to encourageextra cellular polymer production, which aidsbacterial attachment on solid surface (Table 2).The yeast extract concentration in the feed was 10mg/l and the remaining COD was supplied by

methanol and glucose at different ratios (Table 2).Methanol, which provided 75% of the total influ-ent COD, initially encouraged the growth of anoptimum environment [13].

2.3. Operation period

In the operational period the reactor was fedwith real textile wastewater obtained from thefactory located in the Balakong, Selangor State,in Malaysia. The FBR was operated under threedifferent hydraulic retention times, 12, 8, and 4 h,respectively, with the operating conditions show-ing in Table 3, which were divided into fivephases. Each of the phases lasted for 14 days inorder to allow biomass flocs to develop inside thereactors for biodegradation of the influent organicsubstrate. Wastewater characterization was donefor the textile wastewater used for experimentalpractice (Table 4).


Table 4Characteristics of textile wastewater used in the presentstudy

Parameter Value

pH 7.8COD, mg/l 810 ±50.4BOD5, mg/l 188 ± 15.2TSS, mg/l 64 ± 8.5VSS, mg/l 56 ± 4.2Color (at 669 nm) 0.15

2.4. Analytical methods

Liquid effluents were analyzed according toStandard Methods for Examination of Water andWastewater [14]. The following parameters weredetermined: COD, BOD, VSS, TSS, and tempera-ture. The pH measurements were performed witha pH meter (Model 2906, Jenway, UK) and a pHprobe (G- 05992-55, Cole Parmer Instrument,USA). TSS and VSS were measured as describedin Standard Methods 2540 D, E. [14]. Color wasmeasured by a UV-Vis spectrophotometer (Var-ian Cary 100 Conc, Australia) at a peak absorp-tion wavelength of real textile wastewater(669 nm). Before analysis, samples were filteredthrough 0.45 mm filters to remove suspendedmatter.

3. Results and discussion

The start-up period was completed in 20 days.The attached volatile solid (AVS) concentration(0.0752 g VSS/g support) attained at the end ofthe start-up period was within the typical rangereported in the literature such as 0.074–0.11 [15]and 0.0375–0.429 g VSS/g support [16]. Table 5shows operational parameters obtained at the endof start-up period. The bed expansion was 15%during the start-up period. It was increased to andkept between 30% and 35% in the operationperiod, which is in the typical range reported in

Table 5Operational parameters at the end of start-up period forFBR

Operational parameters FBR

OLR, kg COD/m3/d 13HRT, h 4Expansion, % 15Volume of expanded bed, cm3 600VSS/g support, g 0.0752Total VSS, g 40.6VSS/l expanded bed, g 60.5

the literature [17,18]. After the start-up period,the textile wastewater was fed to the reactor. Asseen in Table 3, the FBR was operated under fivedifferent operating conditions (phases) with theaim of increasing the removal efficiency of COD,BOD, and color in the reactor for a 70-dayperiod.

3.1. Phase 1 (days 1–14)

In this phase, a real textile wastewater was fedto the reactor. Average COD concentration of realtextile wastewater was 810 mg/l. During Phase 1,the OLR was kept at around 4.9 kg COD/ m3/d.HRT applied to the reactor was around 4 h(Table 3). The pH of the effluent was around 7.8(Fig. 2), which did not vary much during theoperation period. The optimum reactor operatingconditions were achieved in anaerobic systemswhen volatile fatty acid (VFA) value is less than150 mg/l, and when pH, and alkalinity, aregreater than 6.5, and 500 mg (as CaCO3) respec-tively (Fig. 3). Both alkalinity and VFA data sup-port that the reactor was operating successfully.COD concentration in the reactor during Phase 1varied over time (Fig. 4). COD removal effi-ciency decreased from 50% to 33%, correspond-ing to 40 mg/l and 65 mg/l respectively betweenday 5 and 9, possibly due to the toxic effect ofreal textile wastewater. After acclimation of


Fig. 2. pH during the operating period.

Fig. 3. Volatile fatty acid and alkalinity concentration during the operating period.

anaerobic microorganisms to real textile waste-water, a gradual increase in the COD removal ratewas recorded. On day 14, the effluent CODconcentration reached the value of 35 mg/l,corresponding to removal % of 75 and from thatpoint on it did not change many. Fig. 5 showsthat BOD5 removal rate in Phase 1 reflects thesame pattern with COD removal. On day 5, theBOD5

value was 70 mg/l, corresponding to a 60%

removal; however it decreased to 100 mg/l BOD,corresponding to a 44% removal in 4 days. Afterthe cultures were acclimated to the feed, theBOD5 removal increased to 73%, correspondingto the effluent concentration value of 50 mg/l onday 14 and did not vary considerably for the restof this stage. During the first 8 days, no colorremoval was observed in the effluent (Fig. 6).This period was considered as the acclimation


Fig. 4. COD concentration during the operating period.

period after which the onset of color removal wasobserved with the increase in COD removal rate(Fig. 6). The color removal was 35% on day 14.

3.2. Phase 2 (days 15–28)

In Phase 2, HRT applied to the reactor wasincreased from 4 to about 12 h (Table 3) toobserve the effect of this increase on the colorremoval efficiency of the system. Since the influ-ent COD concentration was the same (around797 mg/l), the OLR decreased to 1.5 kg COD/m3/d. With the increase in HRT from 4 to 12 h,the COD and BOD5 removal rates decreased toabout half of their values at the end of Phase 1. Inother words, COD and BOD5e effluent valueswere dropped to 55 and 95 mg/l, corresponding toremoval rates of 38% and 37%, respectively. As

seen from Fig. 6, the color removal rate alsodecreased to 20% during phase 2 (day 28).

A decrease in COD, BOD5 and color removalperformances with the decrease in OLR may beattributed to low synthesis of unique reducedenzyme co-factors (F430 and vitamin B12) respon-sible for color reduction under anaerobic con-ditions. Therefore, it can be stated that anincrease in HRT alone did not result in theincreased of COD, BOD5, and color removal andthis statement is in line with [19].

3.3. Phase 3 (days 29–42)

In Phase 3, an external carbon source wasadded to the textile wastewater in the form ofglucose at a concentration of about 300 mg/l,yielding an influent COD concentration of about


Fig. 5. BOD concentration during the operating period.

Fig. 6. Percent color removal during the operating period.


1097 mg/l (Table 3). At the same time the HRTof the reactor was decreased from 12 to about 8 h,which resulted in an OLR of 3.3 kg COD/ m3/d.With the addition of 300 mg/l of glucose as theexternal carbon source and corresponding in-crease in the influent COD concentration, BOD5

and COD removals increased to 83% and 80%,corresponding to the effluent concentration of 28and 48 mg/l, respectively, while the colorremoval increased to 45% (Fig. 6). A significantincrease in the color removal performance of theFBR is remarkable in this phase. This improve-ment was due to the addition of external carbonsource, which helps to establish a reducing envi-ronment and possibly increase the concentrationof enzyme co-factors, such as F430 and vitamin B12

in the reactor that could also potentially reduceazo bonds and hence result in better colorremoval [5].

3.4. Phase 4 (days 43–56)

After observing the simulative effect of theaddition of 300 mg/l of glucose as the externalcarbon source in Phase 3, glucose concentrationwas increased to double, i.e., about 600 mg/l toobserve the effect of increasing the concentrationof the external carbon source. With this increasein the glucose concentration, the influent CODconcentration and OLR applied to the reactorincreased to about 2200 mg/l and 4.4 kg COD/m3/d, respectively (Table 3). COD and colorremoval rates increased to 98% and 65% fromearlier values of 80% and 45%, respectively(Figs. 3 and 5), while the BOD5 value was40 mg/l, corresponding to a removal rate of 95%(Fig. 5). From these figures it is clear thatincreasing the glucose concentration from 300 to600 mg/l resulted in drastically better perfor-mance of the FBR both in terms of organic andcolor removal.

3.5. Phase 5 (days 57–70)

In Phase 5, the concentration of glucose as the

external carbon source was increased further toabout 900 mg/l to observe any additional im-provement in the performance of the FBR. Asseen in Table 3, this change in the glucose con-centration increased the influent COD concen-tration to around 4200 mg/l and the OLR to8.4 kg COD/m3/d. In this phase the COD andBOD5 and color removal rates did not increasesignificantly and remained around the previousvalues in phase 4 (Figs. 4–6). As a result, it wasobserved that further increase in the glucose andinfluent COD concentration did not improve theCOD, BOD5, and color removal efficiency of thesystem significantly. Therefore we concluded thatPhase 4 (textile wastewater with 600 mg/l glucoseaddition) represented the optimum condition formaximum COD, BOD5, and color removal in thereal textile wastewater investigated in this study.Therefore, the optimum value of external carbonsource mentioned in this study (600 mg/l) isdifferent from other available studies [19], whichmight be due to the weakness in protecting micro-bial cells from possible toxic effects due to pol-lutant metabolites or changes in the environmentconditions, attack of organisms to dyestuff toprovide extra carbon source to survive in thepresence of insufficient readily available carbonsource like glucose, and washout of cells.

In comparison to other studies (Table 1), themaximum decoloration achieved in this study wasrather low, this due to HRT, environmentalconditions such as temperature (30–35EC), andthe media composition specific to the anaerobicFBR, which should be adjusted to enhance thegrowth of microorganisms for decoloration pur-poses (optimum 37EC).

4. Conclusions

Anaerobic treatment of a real textile waste-water was investigated in a FBR with activatedcarbon as the supporting material. The resultsindicated that the anaerobic treatment of thetextile wastewater studied was found to be opti-


mal with the addition of an external carbonsource in the form of 600 mg/l glucose (with theinfluent COD concentration of 2200 mg/l).

COD, BOD5, and color removals achievedwere around 98%, 95%, and 65%, respectively.

The observed improvement in the colorremoval with the addition of 600 mg/l of glucoseis in agreement with the literature, which under-lines the significance of external carbon sourcesupplementation to anaerobic reactors treatingdye/textile wastewater. Further increase in anexternal carbon source did not improve theorganic and color removal efficiency of thesystem. The addition of glucose as the peripheralcarbon source to the textile wastewater with aconcentration of 600 mg/l might be of concern interms of the realistic applicability of anaerobicbehavior. However, biological treatment (anae-robic) compared to physicochemical methods stilloffers a viable option in terms of cost.

For the toxicity of the final effluent we pro-pose the simultaneous processes utilize anaerobiczones within basically aerobic bulk phases, suchas observed in biofilms [20], which generatemicro-environmental conditions in which anae-robic and aerobic microniches develop and co-exist within a single biocatalytic particle, so thatoxidative and reductive activities can be accom-plished simultaneously, resulting in clean finaleffluent [21]. Therefore, a multi-step comple-mentary biodegradation process can be conductedas a single stage. In this case a time of adaptationis necessary for bacteria to attach the inner sur-face (‘‘anaerobic phase’’) where reduced metabo-lites are generated and then degraded by asso-ciated microorganisms at outer surface (‘‘aerobicphase’’), which complete the mineralizationprocess.

Acknowledgements

The authors gratefully acknowledge the finan-cial support given by MOSTE/NBD under theTop down Bioremediation Processes (No.08-01-01-001/ BTK/ ER/020).

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Treatment of textile wastewater with an anaerobic fluidized bed reactor