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Kinetic analysis of dyestuff and COD removal from synthetic wastewater in an anaerobic packed column reactor
Process Biochemistry 40 (2005) 2545–2550 www.elsevier.com/locate/procbio
Kinetic analysis of dyestuff and COD removal from synthetic wastewater in an anaerobic packed column reactor Ilgi Karapinar Kapdan* Department of Environmental Engineering, Dokuz Eylu¨l University, Buca Tinaztepe Campus, Izmir, Turkey Received 15 April 2004; received in revised form 7 October 2004; accepted 22 November 2004
Abstract An anaerobic packed column reactor was operated continuously at different dyestuff loading rates, (0.05–0.4 g/(l day)) and COD loading rates (1–8 g/(l day)) in order to determine dyestuff and COD removal kinetic constants. The system was operated at room temperature (20 1 8C) and at pH 7 using an immobilized anaerobic bacterial consortium called PDW. Synthetic wastewater containing textile dyestuff Reactive Red 195 was fed from the bottom of the reactor. Around 90% decolourization efficiency was obtained for dyestuff loading rates up to 0.15 g/(l day). COD removal efficiency was obtained between 5 and 35% for the applied loads. Modified Stover–Kincannon model was applied to the experimental data. Saturation value constant and maximum utilization rate constant of Stover–Kincannon model for dyestuff and COD were determined as KB = 17.8 g/(l day), Umax = 19.5 g/(l day) and KB = 37.9 g COD/(l day), Umax = 12.9 g COD/(l day), respectively. The predicted effluent dyestuff and COD concentrations were calculated using the constants and it was found that they are in good agreement with the observed ones. # 2004 Elsevier Ltd. All rights reserved. Keywords: Anaerobic treatment; COD; Decolourization; Kinetic analysis; Stover–Kincannon model
1. Introduction Colour removal under anaerobic condition could be biodegradation of dyestuff by azoreductase activity [1,2] or nonenzymic azo reduction in dyestuff [3–5]. However, the azoreductase cleavage of azo bond may result in formation of aromatic amines which might be toxic [3,6]. But, some reports showed that the effluent of anaerobic decolourization process were completely non-toxic [5,7]. Studies indicated that colour removal under anaerobic conditions is significantly affected by dyestuff structure. Azo type dyestuffs are readily biodegradable while metal complex, antraquanin and indigo group dyestuffs are not [8,9]. In addition, dyestuff can be used as sole carbon sources by the microrganisms in some cases but co-substrate as carbon source addition is required [10–12]. Decolourization of textile dyestuffs have been carried out in UASB, sequencing batch, fed-batch and packed bed operated under * Fax: +90 232 4531143. E-mail address: [email protected]. 0032-9592/$ – see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2004.11.002
anaerobic conditions and high decolourization efficiencies were obtained [13–18]. It was also reported that an aerobic unit after anaerobic decolourization unit act as a polishing step, provides higher pollutant removal, like COD and toxic substances, rather than decolourization [19,20]. Determination of kinetic constants of a bioprocess is a useful tool to be able to describe and to predict the performance of the system. In this study, an anaerobic packed column reactor was operated continuously at different dyestuff and COD loading rates in order to evaluate the decolourization performance and to determine kinetic constants.
2. Mathematical model Monod type kinetic analysis based on substrate, cell mass and dyestuff concentration in batch operation for decolourization purpose have been used [8,10]. Anaerobic decolourization and batch inhibition kinetics of different azo dyes have also been investigated [21,22]. In addition, there are
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kinetic models developed for organic substance removal in continuously operated anaerobic reactors [23–26]. Stover– Kincannon is one of the most widely used mathematical model for determining the kinetic constants in immobilized systems. The model have been applied to continuously operated mesophilic and thermophilic upflow anaerobic filters for treatment of paper-pulp liquors [27] and simulated starch wastewater [28], anaerobic filter for soybean wastewater treatment [29], anaerobic hybrid reactor [30], aerobic treatment of synthetic dairy wastewater in trickling filters [31] and municipal wastewater treatment in submerged biofilters [32]. However, this model has not been applied for determination of decolourization kinetic constants. Therefore, the Stover–Kincannon model was used for the kinetic analysis of COD and dyestuff removal in an upflow anaerobic packed bed reactor in this study. The Stover–Kincannon model considers the organic substance removal rate as a function of organic loading rate at steady state as in Eq. (1). dS Q ¼ ðS0 Se Þ (1) dt V The original Stover–Kincannon model for rotating biofilm reactor is described as in Eq. (2). dS QðS0 Se Þ Umax ðQS0 =AÞ ¼ ¼ (2) dt V KB þ ðQS0 =AÞ where A represents the total disc surface area whereby total biomass concentration immobilized on discs. The suspended biomass concentration is assumed to be negligible compare to that of attached biomass. The simple modification of the original Stover–Kincannon model is the introduction of total organic loading rate, QS0/V into the Eq. (1) instead of QS0/A, resulting in Eq. (3). Since void space has a significant importance in obtaining high removal efficiency in anaerobic filters the modified Stover–Kincannon model has been applied to anaerobic filters and the fixed bed region of hybrid reactors [29,30]. dS QðS0 Se Þ Umax ðQS0 =VÞ ¼ ¼ (3) dt V KB þ ðQS0 =VÞ linearization of Eq. (3) gives the relationship: dS V KB V 1 ¼ ¼ þ (4) dt QðS0 Se Þ Umax QS0 Umax where dS/dt is the substrate removal rate (g/(l day)), S the substrate concentration in the reactor (g/(l day)), Umax the maximum substrate removal rate constant (g/(l day)) and KB is a saturation value constant (g/(l day)). The plot of V/ [Q(S0 Se)], inverse of the loading removal rate, versus V/ (QS0), inverse of the total loading rate will result in a straight line. The intercept and slope of the line results in 1/Umax and KB/Umax, respectively. The substrate balance for the reactor can be written as follows: dS QS0 ¼ QSe þ V (5) dt
substitution of Eq. (3–5) results in QS0 ¼ QSe þ
Umax ðQS0 =VÞ V KB þ ðQS0 =VÞ
(6)
This expression can then be solved for either the effluent substrate concentration (Eq. (7)) or the required volume of the anaerobic filter (Eq. (8)) by substituting kinetic constants Umax and KB. Se ¼ S0 V¼
Umax S0 KB þ ðQS0 =VÞ
QS0 ðUmax S0 =S0 Se Þ KB
(7)
(8)
3. Material and methods 3.1. Microbial culture A facultatively anaerobic bacterial culture, isolated by the Biotechnology Centre at the University of Ulster, N. Ireland [33] was used in decolourization of dyestuff. The facultative anaerobic bacterial consortium called PDW consists of Alcaligenes faecolis and Commomonas acidourans. The culture was grown in flasks at its optimum growth temperature 28 8C and preserved at 4 8C. 3.2. Media composition and dyestuff Nutrient media used for PDW culture had the following composition: 0.5 g/l (NH4)2SO4; 2.66 g/l KH2PO4; 4.32 g/l Na2HPO42H2O and dyestuff. Molasses was used as carbon source. The textile dyestuff used was Reactive Red 195 monoazo based, viniysulphone/monochlorotiazine bifunctional and obtained from EKOTEN Co., Izmir, Turkey in pure form. 3.3. Experimental set-up The anaerobic packed column reactor was made up of chrome–nickel with the reactor liquid volume of 6000 ml. The support particles used for the immobilization of microorganisms were made of mesh of stainless steel metal wire. The total surface area of support material was 192.56 m2. The system was fed from the bottom with dyestuff containing synthetic wastewater by a peristaltic pump and effluent was collected from the top. At the beginning of the experiments, the anaerobic unit was inoculated with dene PDW culture (3 g/l) cultivated in flasks and was operated batch-wise for 2 weeks to immobilize the culture on wire meshes. The system was then operated continuously for 1 month to increase the biomass concentration in the system and to reach stable anaerobic conditions at start-up phase. Each experimental study was carried out at least two weeks until the system
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reached steady state conditions. Nitrogen gas was passed through the reactor to make the conditions anaerobic. 3.4. Analytical methods Daily samples were withdrawn and centrifuged at 5000 rpm until a clear supernatant was obtained. Analyses were carried out on clear supernatants. A scanning spectrophotometer (Novaspec II, Pharmacia Biotech.) was used for colour measurements. Absorbance measurements were done at the maximum absorbance wavelength of the dyestuff Reactive Red 195 (l = 520 nm). Samples were diluted with distilled water prior to measurements if necessary. Absorbance values and dyestuff concentration were evaluated from the developed absorbance–concentration curve. Dyestuff concentration was used in calculation of decolourization efficiency. COD analyses were carried out on clear supernatant according to standard methods [34].
Fig. 2. Variation of dyestuff removal rate with effluent dyestuff concentration.
was obtained as 0.217 g/(l day) with an effluent dyestuff concentration of 0.173 g/l (Fig. 2). 4.2. Effect of organic loading rate on COD removal
4. Results and discussions 4.1. Effect of dyestuff loading rate on dyestuff removal The variation of effluent dyestuff concentration and decolourization efficiency with dyestuff loading rate is given in Fig. 1. The anaerobic unit operated with high decolourization performance between 0.05 and 0.175 g/ (l day) dyestuff loading rates (DLR) with over 90% decolourization efficiency which results in effluent dyestuff concentration lower than De = 0.015 g/l. For higher DLR (>0.3 g/(l day)), the efficiency sharply decreased to 50% with De = 0.150 g/l. These results indicated that anaerobic packed bed column can be operated over 90% decolourization efficiency up to 0.2 g/(l day) dyestuff loading rates. The maximum dyestuff removal rate (r = (Q (D0 De)/V)
Fig. 1. Variation of effluent dyestuff concentration and dyestuff removal efficiency with dyestuff loading rate. (*) Effluent dyestuff concentration; (*) efficiency.
Fig. 3 depicts the variation of effluent COD concentration and COD removal efficiency with COD loading rate (Q S0/V). Effluent COD concentration was around 2 g/l for organic loading rate between OLR = 2.5–4 g/(l day) and then increased to Se = 4 g/l for OLR = 5 g/(l day). For the high OLR (>7 g/(l day)), effluent COD concentration was increased to Se = 7.3 g/l. COD removal efficiency was around 35 % for OLR up to 5 g/(l day) and decreased to 10% for OLR = 8 g/(l day). Almost, no COD removal was obtained at high organic loading rates. The variation of COD removal rate with effluent COD concentration is depicted in Fig. 4. COD removal rate increases from 0.46 to 1.4 g/(l day) by reaching the maximum level for the effluent COD concentration between 0.9 and 3 g/l, respectively and decreases to 0.68 g/(l day) as effluent COD concentration increases to 7.32 g/l. Low COD removal rates are obtained in anaerobic packed column reactor during the decolourization process. This could be
Fig. 3. Variation of effluent COD concentration and COD removal efficiency with organic loading rate. (*) Effluent COD concentration; (*) efficiency.
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Fig. 4. Variation of COD removal rate with effluent COD concentration.
because of operational conditions including temperature (20 8C) and synthetic media composition which was adjusted to obtain colour removal rather than COD removal and do not enhance the growth of methanogenic bacteria which are the main agents in COD removal in the anaerobic process. In addition, the presence of dyestuff or biodegradation end products in the reactor might have had toxic or inhibitory effects on the microbial culture that resulted in low COD removal. In order to improve COD removal, the system can be operated at longer hydraulic retention times or an aerobic unit after anaerobic unit can be used as a polishing step. 4.3. Determination of modified Stover–Kincannon model constants for dyestuff and COD
Fig. 6. Relationship between observed and predicted effluent dyestuff concentrations.
dyestuff removal were determined as Umax = 0.47 g/(l day) and KB = 0.43 g/(l day), respectively. Therefore the rate expression for dyestuff takes the following form: QðD0 De Þ 0:47ðQD0 =VÞ ¼ V 0:43 þ ðQD0 =VÞ
(9)
and effluent dyestuff concentration can be predicted by using the Eq. (9). De ¼ D0
0:47D0 0:43 þ ðQD0 =VÞ
(10)
The modified Stover–Kincannon model was applied to experimental results from the continuously operated up flow anaerobic packed bed reactor for decolourization of textile dyestuff and kinetic constants for dye removal and COD removal were determined. Dyestuff loading rates and removal rates were calculated at different hydraulic retention times and initial dyestuff concentrations. Fig. 5 indicates the plot of dyestuff loading V/(QD0) versus V/ [Q(D0 De)] dyestuff removal rate. From the slope and intercept of a best-fit line (R2 = 0.99), kinetic constants for
Fig. 6 indicates the relationship between observed dyestuff concentrations from the experiments carried out under different operational conditions and predicted dyestuff concentrations calculated by using Eq. (10). There is a good agreement between observed and predicted dyestuff concentrations with R2 = 0.97 regression coefficient. Similarly, when the model is applied to COD removal (Fig. 7), the coefficients are obtained as Umax = 12.99 g COD/(l day), KB = 37.69 g COD/(l day) with high regres-
Fig. 5. Stover–Kincannon model plot for dyestuff removal.
Fig. 7. Stover–Kincannon model plot for COD removal.
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unit can be used as polishing step to enhance the COD removal or system can be operated at higher temperature to increase the activity of methanogenic bacteria. As a result of the kinetic analysis of reactor for dye and COD removal using a modified Stover–Kincannon model, the substrate utilization rate, Umax, and saturation constant value, KB, was determined as Umax = 0.47 g/(l day) and KB = 0.43 g/(l day) for dye and as Umax = 12.99 g COD/ (l day), KB = 37.69 g COD/(l day) for COD removal. There was good agreement between observed and predicted concentrations both for dyestuff and COD means that kinetic constants can be used to design an anaerobic packed column for colour and COD removal from textile effluents. Fig. 8. Relationship between observed and predicted effluent COD concentrations.
Acknowledgement
sion coefficient (R = 0.97). Rate expression for COD takes the following forms,
This study was supported by research funds of Dokuz Eylu¨ l University, Izmir, Turkey and Scientific and Technical Research Council of Turkey.
QðS0 Se Þ 12:99ðQS0 =VÞ ¼ V 37:69 þ ðQS0 =VÞ
References
2
(11)
Fig. 8 indicates the relationship between predicted and observed effluent COD concentration in anaerobic reactor. Predicted effluent COD concentration was calculated by using the following equation: Se ¼ S0
12:99S0 37:69 þ ðQS0 =VÞ
(12)
There is a linear relationship between observed and predicted effluent COD concentrations with R2 = 0.9501 regression coefficient indicting that kinetic constants can be used in predicting effluent COD concentration of anaerobic packed column reactor.
5. Conclusions An upflow anaerobic packed bed reactor was operated continuously at different dyestuff loading and COD loading rates to remove the colour from synthetic wastewater. The colour removal efficiency was around 90% up to 0.15 g/ (l day) dyestuff loading rate with effluent dyestuff concentration of 0.06 g/l. Dyestuff was removed almost at the same rate up to 0.15 g/(l day) dyestuff loading rate means that most of the dye was removed by microbial action. Maximum dyestuff removal rate was 0.217 g/(l day) with effluent dyes concentration of De = 0.17 g/l. COD removal efficiency varied between 10 and 35% for the organic loading rate between 1 and 8 g/(l day). The maximum COD removal rate was obtained as 1.4 g/(l day) with the effluent COD concentration of Se = 4 g/l at OLR = 5 g/(l day). The experimental results indicated that high decolourization can be obtained at anaerobic packed column operated at room temperature (20 1 8C) with low COD removal. An aerobic
[1] Idaka E, Horitsu H, Ogawa T. Some properties of azoreductase produced by Pseudomonas cepacia. Bull Environ Contam Toxicol 1987;39:982–9. [2] Dubin P, Wrigth KL. Reduction of azo food dyes in cultures of Proteus vulgaris. Xenobiotica 1975;5:563–71. [3] Chung KT, Stevens SEJ, Cernigalle CE. The reduction of azo dyes by the intestinal flora. Crit Rev Microbiol 1992;3:175–90. [4] Craliell CM, Barclay SJ, Nidoo H, Buckley CA, Mulholland DA, Senior E. Microbial decolorization of a reactive azo dyes under anaerobic conditions. Water SA 1995;21:61–9. [5] Flores ER, Luijten M, Donlon B, Lettinga G, Field J. Biodegradation of selected azo dyes under methanogenic conditions. Water Sci Technol 1997;36:65–72. [6] Brown MA, DeVito SC. Predicting azo dye toxicity. Crit Rev Environ Sci Technol 1993;23:249–324. [7] Sacks J, Bucley CA. Anaerobic treatment of textile size effluents. In: Proceeding of fourth international symposium on waste management problems in agro-industries. 1981. p. 910–96. [8] Yu J, Wang X, Yue PL. Optimal decolorization and kinetic modeling of synthetic dyes by Pseudomonos strains. Water Res 2001;35:3579–86. [9] Fu L, Wen X, Xu L, Qian Y. Removal of copper–phthalocyanine dye from wastewater by acclimated sludge under anaerobic or aerobic conditions. Process Biochem 2002;10:1151–6. [10] Chang JS, Chou C, Lin Y, Lin P, Ho J, Hu TL. Kinetic characteristics of bacterial azo-dye decolorization by Pseudomonos luteola. Water Res 2001;35:2842–50. [11] Cruz A, Buitron G. Biodegradation of Disperse Blue 79 using sequenced anaerobic/aerobic biofilters. Water Sci Technol 2001;44:159–66. [12] Kapdan KI, Kargi F, McMullan G, Marchant R. Decolorization of textile dyestuff by an anaerobic bacterial consortium. Biotechnol Lett 2000;22:1179–81. [13] Van Der Zee FP, Lettinga G, Field JA. Azo dye decolorization by anaerobic granular sludge. Chemosphere 2001;44:1169–76. [14] Chinwetkitvanish S, Tuntoolvest M, Pansward T. Anaerobic decolorization of reactive dyebath effluents by a two stage UASB system with topica co-substrate. Water Res 2000;34:2223–32. [15] Talarposhti AM, Donnely T, Anderson GK. Color removal from a simulated dye wastewater using two phase anaerobic packed bed reactor. Water Res 2001;35:425–32.
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[16] Lourenc¸o ND, Novais JM, Pinherio HM. Effect of some operational parameters on textile dye biodegradation in a sequential batch reactor. J Biotechnol 2001;89:163–74. [17] Panswad T, Iamsamer K, Anotai J. Decolorization of azo-reactive dye by polyphosphate and glycogen accumulating organisms in an anaerobicaerobic sequencing batch reactor. Bioresour Technol 2001;76:151–9. [18] Chang JS, Lin YC. Fed batch bioreactor strategies for microbial decolorization of azo dye using a pseudomonas luteaola strain. Biotechnol Progress 2000;16:979–85. [19] FitzGerald SW, Bishop PL. Two stage anaerobic/aerobic treatment of sulfonated azo dyes.. J Environ Sci Health Part A 1995;30:1251–76. [20] Kapdan KI, Tekol M, Sengul F. Decolorization of simulated textile wastewater in an anaerobic aerobic sequential treatment system. Process Biochem 2003;38:1031–7. [21] Sponza DT, Isik M. Decolorization and inhibition kinetic of Direct Black 38 azo dye with granular anaerobic sludge. Enzyme Microb Technol 2004;34:147–58. [22] Isik M, Sponza DT. A batch kinetic study on decolorization and inhibition of Reactive Black 5 and Direct Brown 2 in an anaerobic mixed culture. Chemosphere 2004;55:119–28. [23] Lomas JM, Urbano C. Evaluation of pilot scale downflow stationary fixed film anaerobic reactor treating piggery slurry in the mesophilic range. Biomass Bioenergy 1999;17:49–58. [24] Armenante PM, Kafkewitz D, Lewandowski GA, Jou C. Anaerobic– aerobic treatment of halogenated phenolic compounds. Water Res 1999;33:681–92.
[25] Latkar M, Swaminanthan K, Chakrabarti T. Kinetics of anaerobic biodegradation of resorcinol catechol and hydroquinone in upflow fixed bed reactors. Bioresour Technol 2003;88:69–74. [26] Deveci N, C¸ iftc¸i GA. Mathematical model for the anaerobic treatment of Baker’ yeast effluents. Waste Manage 2001;21:99–103. [27] Ahn JH, Forster CF. A comparison of mesophilic and thermophilic anaerobic upflow filters treating paper-pulp-liquors. Process Biochem 2002;38:257–62. [28] Ahn JH, Forster CF. Kinetic analyses of operation of mesophilic and thermophilic anaerobic filters treating simulated starch wastewater. Process Biochem 2000;36:19–23. [29] Yu H, Wilson F, Tay J. Kinetic analysis of an anaerobic filter treating soybean wastewater. Water Res 1998;32:3341–52. [30] Buyukkamaci N, Filibeli A. Determination of kinetic constants of anaerobic hybrid reactor. Process Biochem 2002;38:73–9. [31] Raj SA, Murthy DVS. Comparison of trickling filter models for the treatment of synthetic dairy wastewater. Bioprocess Eng 1999;21:51– 5. [32] Martinez SG, Lippert-Heredia E, Hernandez-Esparza M, Doria-Serrano C. Reactor kinetics for submerged aerobic biofilms. Bioprocess Eng 2000;23:57–61. [33] Nigam P, McMullan G, Banat IM, Marchant R. Decolorization of effluent from the textile industry by a microbial consortium. Biotechnol Lett 1996;18:117–20. [34] Standard methods for the examination of water and wastewater. 17th ed. Washington, DC: APHA; 1989.
Kinetic analysis of dyestuff and COD removal from synthetic wastewater in an anaerobic packed column reactor Ilgi Karapinar Kapdan* Department of Environmental Engineering, Dokuz Eylu¨l University, Buca Tinaztepe Campus, Izmir, Turkey Received 15 April 2004; received in revised form 7 October 2004; accepted 22 November 2004
Abstract An anaerobic packed column reactor was operated continuously at different dyestuff loading rates, (0.05–0.4 g/(l day)) and COD loading rates (1–8 g/(l day)) in order to determine dyestuff and COD removal kinetic constants. The system was operated at room temperature (20 1 8C) and at pH 7 using an immobilized anaerobic bacterial consortium called PDW. Synthetic wastewater containing textile dyestuff Reactive Red 195 was fed from the bottom of the reactor. Around 90% decolourization efficiency was obtained for dyestuff loading rates up to 0.15 g/(l day). COD removal efficiency was obtained between 5 and 35% for the applied loads. Modified Stover–Kincannon model was applied to the experimental data. Saturation value constant and maximum utilization rate constant of Stover–Kincannon model for dyestuff and COD were determined as KB = 17.8 g/(l day), Umax = 19.5 g/(l day) and KB = 37.9 g COD/(l day), Umax = 12.9 g COD/(l day), respectively. The predicted effluent dyestuff and COD concentrations were calculated using the constants and it was found that they are in good agreement with the observed ones. # 2004 Elsevier Ltd. All rights reserved. Keywords: Anaerobic treatment; COD; Decolourization; Kinetic analysis; Stover–Kincannon model
1. Introduction Colour removal under anaerobic condition could be biodegradation of dyestuff by azoreductase activity [1,2] or nonenzymic azo reduction in dyestuff [3–5]. However, the azoreductase cleavage of azo bond may result in formation of aromatic amines which might be toxic [3,6]. But, some reports showed that the effluent of anaerobic decolourization process were completely non-toxic [5,7]. Studies indicated that colour removal under anaerobic conditions is significantly affected by dyestuff structure. Azo type dyestuffs are readily biodegradable while metal complex, antraquanin and indigo group dyestuffs are not [8,9]. In addition, dyestuff can be used as sole carbon sources by the microrganisms in some cases but co-substrate as carbon source addition is required [10–12]. Decolourization of textile dyestuffs have been carried out in UASB, sequencing batch, fed-batch and packed bed operated under * Fax: +90 232 4531143. E-mail address: [email protected]. 0032-9592/$ – see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2004.11.002
anaerobic conditions and high decolourization efficiencies were obtained [13–18]. It was also reported that an aerobic unit after anaerobic decolourization unit act as a polishing step, provides higher pollutant removal, like COD and toxic substances, rather than decolourization [19,20]. Determination of kinetic constants of a bioprocess is a useful tool to be able to describe and to predict the performance of the system. In this study, an anaerobic packed column reactor was operated continuously at different dyestuff and COD loading rates in order to evaluate the decolourization performance and to determine kinetic constants.
2. Mathematical model Monod type kinetic analysis based on substrate, cell mass and dyestuff concentration in batch operation for decolourization purpose have been used [8,10]. Anaerobic decolourization and batch inhibition kinetics of different azo dyes have also been investigated [21,22]. In addition, there are
2546
I.K. Kapdan / Process Biochemistry 40 (2005) 2545–2550
kinetic models developed for organic substance removal in continuously operated anaerobic reactors [23–26]. Stover– Kincannon is one of the most widely used mathematical model for determining the kinetic constants in immobilized systems. The model have been applied to continuously operated mesophilic and thermophilic upflow anaerobic filters for treatment of paper-pulp liquors [27] and simulated starch wastewater [28], anaerobic filter for soybean wastewater treatment [29], anaerobic hybrid reactor [30], aerobic treatment of synthetic dairy wastewater in trickling filters [31] and municipal wastewater treatment in submerged biofilters [32]. However, this model has not been applied for determination of decolourization kinetic constants. Therefore, the Stover–Kincannon model was used for the kinetic analysis of COD and dyestuff removal in an upflow anaerobic packed bed reactor in this study. The Stover–Kincannon model considers the organic substance removal rate as a function of organic loading rate at steady state as in Eq. (1). dS Q ¼ ðS0 Se Þ (1) dt V The original Stover–Kincannon model for rotating biofilm reactor is described as in Eq. (2). dS QðS0 Se Þ Umax ðQS0 =AÞ ¼ ¼ (2) dt V KB þ ðQS0 =AÞ where A represents the total disc surface area whereby total biomass concentration immobilized on discs. The suspended biomass concentration is assumed to be negligible compare to that of attached biomass. The simple modification of the original Stover–Kincannon model is the introduction of total organic loading rate, QS0/V into the Eq. (1) instead of QS0/A, resulting in Eq. (3). Since void space has a significant importance in obtaining high removal efficiency in anaerobic filters the modified Stover–Kincannon model has been applied to anaerobic filters and the fixed bed region of hybrid reactors [29,30]. dS QðS0 Se Þ Umax ðQS0 =VÞ ¼ ¼ (3) dt V KB þ ðQS0 =VÞ linearization of Eq. (3) gives the relationship: dS V KB V 1 ¼ ¼ þ (4) dt QðS0 Se Þ Umax QS0 Umax where dS/dt is the substrate removal rate (g/(l day)), S the substrate concentration in the reactor (g/(l day)), Umax the maximum substrate removal rate constant (g/(l day)) and KB is a saturation value constant (g/(l day)). The plot of V/ [Q(S0 Se)], inverse of the loading removal rate, versus V/ (QS0), inverse of the total loading rate will result in a straight line. The intercept and slope of the line results in 1/Umax and KB/Umax, respectively. The substrate balance for the reactor can be written as follows: dS QS0 ¼ QSe þ V (5) dt
substitution of Eq. (3–5) results in QS0 ¼ QSe þ
Umax ðQS0 =VÞ V KB þ ðQS0 =VÞ
(6)
This expression can then be solved for either the effluent substrate concentration (Eq. (7)) or the required volume of the anaerobic filter (Eq. (8)) by substituting kinetic constants Umax and KB. Se ¼ S0 V¼
Umax S0 KB þ ðQS0 =VÞ
QS0 ðUmax S0 =S0 Se Þ KB
(7)
(8)
3. Material and methods 3.1. Microbial culture A facultatively anaerobic bacterial culture, isolated by the Biotechnology Centre at the University of Ulster, N. Ireland [33] was used in decolourization of dyestuff. The facultative anaerobic bacterial consortium called PDW consists of Alcaligenes faecolis and Commomonas acidourans. The culture was grown in flasks at its optimum growth temperature 28 8C and preserved at 4 8C. 3.2. Media composition and dyestuff Nutrient media used for PDW culture had the following composition: 0.5 g/l (NH4)2SO4; 2.66 g/l KH2PO4; 4.32 g/l Na2HPO42H2O and dyestuff. Molasses was used as carbon source. The textile dyestuff used was Reactive Red 195 monoazo based, viniysulphone/monochlorotiazine bifunctional and obtained from EKOTEN Co., Izmir, Turkey in pure form. 3.3. Experimental set-up The anaerobic packed column reactor was made up of chrome–nickel with the reactor liquid volume of 6000 ml. The support particles used for the immobilization of microorganisms were made of mesh of stainless steel metal wire. The total surface area of support material was 192.56 m2. The system was fed from the bottom with dyestuff containing synthetic wastewater by a peristaltic pump and effluent was collected from the top. At the beginning of the experiments, the anaerobic unit was inoculated with dene PDW culture (3 g/l) cultivated in flasks and was operated batch-wise for 2 weeks to immobilize the culture on wire meshes. The system was then operated continuously for 1 month to increase the biomass concentration in the system and to reach stable anaerobic conditions at start-up phase. Each experimental study was carried out at least two weeks until the system
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reached steady state conditions. Nitrogen gas was passed through the reactor to make the conditions anaerobic. 3.4. Analytical methods Daily samples were withdrawn and centrifuged at 5000 rpm until a clear supernatant was obtained. Analyses were carried out on clear supernatants. A scanning spectrophotometer (Novaspec II, Pharmacia Biotech.) was used for colour measurements. Absorbance measurements were done at the maximum absorbance wavelength of the dyestuff Reactive Red 195 (l = 520 nm). Samples were diluted with distilled water prior to measurements if necessary. Absorbance values and dyestuff concentration were evaluated from the developed absorbance–concentration curve. Dyestuff concentration was used in calculation of decolourization efficiency. COD analyses were carried out on clear supernatant according to standard methods [34].
Fig. 2. Variation of dyestuff removal rate with effluent dyestuff concentration.
was obtained as 0.217 g/(l day) with an effluent dyestuff concentration of 0.173 g/l (Fig. 2). 4.2. Effect of organic loading rate on COD removal
4. Results and discussions 4.1. Effect of dyestuff loading rate on dyestuff removal The variation of effluent dyestuff concentration and decolourization efficiency with dyestuff loading rate is given in Fig. 1. The anaerobic unit operated with high decolourization performance between 0.05 and 0.175 g/ (l day) dyestuff loading rates (DLR) with over 90% decolourization efficiency which results in effluent dyestuff concentration lower than De = 0.015 g/l. For higher DLR (>0.3 g/(l day)), the efficiency sharply decreased to 50% with De = 0.150 g/l. These results indicated that anaerobic packed bed column can be operated over 90% decolourization efficiency up to 0.2 g/(l day) dyestuff loading rates. The maximum dyestuff removal rate (r = (Q (D0 De)/V)
Fig. 1. Variation of effluent dyestuff concentration and dyestuff removal efficiency with dyestuff loading rate. (*) Effluent dyestuff concentration; (*) efficiency.
Fig. 3 depicts the variation of effluent COD concentration and COD removal efficiency with COD loading rate (Q S0/V). Effluent COD concentration was around 2 g/l for organic loading rate between OLR = 2.5–4 g/(l day) and then increased to Se = 4 g/l for OLR = 5 g/(l day). For the high OLR (>7 g/(l day)), effluent COD concentration was increased to Se = 7.3 g/l. COD removal efficiency was around 35 % for OLR up to 5 g/(l day) and decreased to 10% for OLR = 8 g/(l day). Almost, no COD removal was obtained at high organic loading rates. The variation of COD removal rate with effluent COD concentration is depicted in Fig. 4. COD removal rate increases from 0.46 to 1.4 g/(l day) by reaching the maximum level for the effluent COD concentration between 0.9 and 3 g/l, respectively and decreases to 0.68 g/(l day) as effluent COD concentration increases to 7.32 g/l. Low COD removal rates are obtained in anaerobic packed column reactor during the decolourization process. This could be
Fig. 3. Variation of effluent COD concentration and COD removal efficiency with organic loading rate. (*) Effluent COD concentration; (*) efficiency.
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Fig. 4. Variation of COD removal rate with effluent COD concentration.
because of operational conditions including temperature (20 8C) and synthetic media composition which was adjusted to obtain colour removal rather than COD removal and do not enhance the growth of methanogenic bacteria which are the main agents in COD removal in the anaerobic process. In addition, the presence of dyestuff or biodegradation end products in the reactor might have had toxic or inhibitory effects on the microbial culture that resulted in low COD removal. In order to improve COD removal, the system can be operated at longer hydraulic retention times or an aerobic unit after anaerobic unit can be used as a polishing step. 4.3. Determination of modified Stover–Kincannon model constants for dyestuff and COD
Fig. 6. Relationship between observed and predicted effluent dyestuff concentrations.
dyestuff removal were determined as Umax = 0.47 g/(l day) and KB = 0.43 g/(l day), respectively. Therefore the rate expression for dyestuff takes the following form: QðD0 De Þ 0:47ðQD0 =VÞ ¼ V 0:43 þ ðQD0 =VÞ
(9)
and effluent dyestuff concentration can be predicted by using the Eq. (9). De ¼ D0
0:47D0 0:43 þ ðQD0 =VÞ
(10)
The modified Stover–Kincannon model was applied to experimental results from the continuously operated up flow anaerobic packed bed reactor for decolourization of textile dyestuff and kinetic constants for dye removal and COD removal were determined. Dyestuff loading rates and removal rates were calculated at different hydraulic retention times and initial dyestuff concentrations. Fig. 5 indicates the plot of dyestuff loading V/(QD0) versus V/ [Q(D0 De)] dyestuff removal rate. From the slope and intercept of a best-fit line (R2 = 0.99), kinetic constants for
Fig. 6 indicates the relationship between observed dyestuff concentrations from the experiments carried out under different operational conditions and predicted dyestuff concentrations calculated by using Eq. (10). There is a good agreement between observed and predicted dyestuff concentrations with R2 = 0.97 regression coefficient. Similarly, when the model is applied to COD removal (Fig. 7), the coefficients are obtained as Umax = 12.99 g COD/(l day), KB = 37.69 g COD/(l day) with high regres-
Fig. 5. Stover–Kincannon model plot for dyestuff removal.
Fig. 7. Stover–Kincannon model plot for COD removal.
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unit can be used as polishing step to enhance the COD removal or system can be operated at higher temperature to increase the activity of methanogenic bacteria. As a result of the kinetic analysis of reactor for dye and COD removal using a modified Stover–Kincannon model, the substrate utilization rate, Umax, and saturation constant value, KB, was determined as Umax = 0.47 g/(l day) and KB = 0.43 g/(l day) for dye and as Umax = 12.99 g COD/ (l day), KB = 37.69 g COD/(l day) for COD removal. There was good agreement between observed and predicted concentrations both for dyestuff and COD means that kinetic constants can be used to design an anaerobic packed column for colour and COD removal from textile effluents. Fig. 8. Relationship between observed and predicted effluent COD concentrations.
Acknowledgement
sion coefficient (R = 0.97). Rate expression for COD takes the following forms,
This study was supported by research funds of Dokuz Eylu¨ l University, Izmir, Turkey and Scientific and Technical Research Council of Turkey.
QðS0 Se Þ 12:99ðQS0 =VÞ ¼ V 37:69 þ ðQS0 =VÞ
References
2
(11)
Fig. 8 indicates the relationship between predicted and observed effluent COD concentration in anaerobic reactor. Predicted effluent COD concentration was calculated by using the following equation: Se ¼ S0
12:99S0 37:69 þ ðQS0 =VÞ
(12)
There is a linear relationship between observed and predicted effluent COD concentrations with R2 = 0.9501 regression coefficient indicting that kinetic constants can be used in predicting effluent COD concentration of anaerobic packed column reactor.
5. Conclusions An upflow anaerobic packed bed reactor was operated continuously at different dyestuff loading and COD loading rates to remove the colour from synthetic wastewater. The colour removal efficiency was around 90% up to 0.15 g/ (l day) dyestuff loading rate with effluent dyestuff concentration of 0.06 g/l. Dyestuff was removed almost at the same rate up to 0.15 g/(l day) dyestuff loading rate means that most of the dye was removed by microbial action. Maximum dyestuff removal rate was 0.217 g/(l day) with effluent dyes concentration of De = 0.17 g/l. COD removal efficiency varied between 10 and 35% for the organic loading rate between 1 and 8 g/(l day). The maximum COD removal rate was obtained as 1.4 g/(l day) with the effluent COD concentration of Se = 4 g/l at OLR = 5 g/(l day). The experimental results indicated that high decolourization can be obtained at anaerobic packed column operated at room temperature (20 1 8C) with low COD removal. An aerobic
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