Biological treatment of acid dyeing wastewater
Enzyme and Microbial Technology 38 (2006) 887–892
Biological treatment of acid dyeing wastewater using a sequential
anaerobic/aerobic reactor system
Mustafa Is ??k a , Delia Teresa Sponza b ,?
a Nig ? d e University, Aksaray Engineering Faculty, Environmental Engineering Department, 68100 Aksaray, Turkey
b Dokuz Eylul University, Engineering Faculty, Environmental Engineering Department, Buca Kaynaklar Campus, 35160 Izmir , Turkey
Received 16 March 2004; received in revised form 25 April 2005; accepted 22 May 2005
Abstract
The treatment of the wastewater taken from a wool dyeing processing in a wool manufacturing plant was investigated using an anaerobic/aerobic sequential system. The process units consisted of an anaerobic UASB reactor and an aerobic CSTR reactor. Glucose, alkalinity and azo dyes were added to the raw acid dyeing wastewater in order to simulate the dye industry wastewater since the raw wastewater contained low levels of carbon, NaHCO 3 and color through anaerobic/aerobic sequential treatment. The UASB reactor gave COD and color removals of 51–84% and 81–96%, respectively, at a HRT of 17 h. The COD and color removal efficiencies of the UASB/CSTR sequential reactor system were 97–83% and 87–80%, respectively, at a hydraulic retention time (HRTs) of 3.3 days. The aromatic amines (TAA) formed in the anaerobic stage were effectively removed in the aerobic stage.
? 2006 Elsevier Inc. All rights reserved.
Keywords: Acid wool dyeing; Azo dyes; Sequential; Biological treatment
1. Introduction
Textile processing industries produce COD at varying high quantities and composition in the effluent depending on the wet processes employed. The aqueous content of such efflu- ents was summarized by Correria et al. [1] at between 3 and 9 dm ?3 kg ?1 for cotton desizing and up to 334–835 dm ?3 kg ?1 for wool washing in the textile industry. In the acid dyeing of wool the major pollutant types may consist of the salts (sodium chloride and sodium sulphate used for neutralizing the zeta potential of the fibre), acids (acetic and sulphuric acid for pH control), bases (sodium hydroxide for pH control) and dyes (for dyeing the fibre). Residual dyes coupled with the auxil- iary chemicals are responsible for the color, dissolved solids and the COD in the dyeing wastewaters. The characteristics of
acid dyeing
wastewater depend on the type of dye, the fiber and the dyeing method. Horning [2] reported that wool-acid dyeing wastewaters contained an average color load of 3200 ADMI (American Dye Manufacturers Institute Unit), a total organic carbon (TOC) of 210 mg dm ?3 , a suspended solid (SS)
? Corresponding author. Tel.: +90 232 4531008/1119; fax: +90 232 4531153.
E-mail address: delya.sponza@https://www.sodocs.net/doc/8b13403147.html,.tr (D.T. Sponza).
of 9 mg dm ?3 and a pH of 4 through different dyeing pro- cesses. Generally the dyeing effluents have a high color content and high dissolved solids (DS) coupled with moderate BOD values [1]. Dyes are required to be removed by appropriate technologies, as they are problematic in the receiving water. To date the treatment of textile wastewaters has been based mainly on aerobic biological processes, consisting mainly of conventional and extended activated sludge methods [3]. The oxygen consumptions and the sludge yields are generally high and incur high operational costs [4]. Moreover, aerobic pro- cesses are unable to degrade azo dyes and the largest group of synthetic colorants (60–70%) [5]. The highly electrophilic azo bond can be cleaved through azo dye decolorization under anaerobic conditions. The aromatic amines that are produced
from such azo cleavage can be removed in aerobic environments
[6]. Recent researches have shown that synthetic and simulat- ing wastewater, containing azo dyes and other additives, can be effectively treated in a sequential anaerobic/aerobic environment [7–14]. However, the treatment of wool dyeing wastewaters using anaerobic/aerobic sequential reactor systems has not been reported.
In this study, the treatment of a wastewater taken from a wool dyeing processing from the wool manufacturing plant located in Izmir, was investigated using a sequential upflow anaerobic
0141-0229/$ – see front matter ? 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2005.05.018
888 M. Is??k, D.T. Sponza / Enzyme and Microbial Technology 38 (2006) 887–892
Table 1
Characterization of acid dyeing wastewater during the operation period
Operation periods (days)Run 1 (1–7)Run 2 (8–17)Run 3 (18–33)Run 4 (34–49)
Addition a Raw Addition a Raw Addition a Raw Addition a Total COD (mg dm?3)6061593––499
Soluble COD (mg dm?3)1908375141421210544761445 Inert COD (mg dm?3)––200
TOC (mg dm?3)88463––170487 Alkalinity (mg dm?3)1930380146011013501201220
pH8.677.268.43 5.867.68 6.418.33λmax (nm)480480540520500500 Absorbance 1.0150.9290.080 1.728 1.874 1.945 Glucose, alkalinity and dyes were added to feed in order to simulate the acid dyeing wastewater since the raw wastewater contained low level of carbon (COD), NaHCO3 and color. COD is required for the reductive conditions through the cleavage of azo bonds under anaerobic conditions. The values given in second colon represent the data measured through the experiments.
sludge blanket reactor (UASB)/aerobic continuous stirred tank reactor (CSTR) system.
2. Material and methods
2.1. Laboratory-scale reactor system, seed and operating conditions
Continuously fed stainless steel anaerobic UASB and aerobic CSTR reac- tors were used in sequence for the experimentation. The UASB reactor had a 2.5 dm?3 of effective volume with an internal diameter of 6 cm and a height of 100 cm. The CSTR reactor consisted of an aeration tank (effective vol- ume=9 dm?3) and a settling compartment (effective volume = 1.32 dm?3). Treated effluent was passed through a U-tube to trap the biomass before it was allowed to run to the aerobic tank under steady-state conditions. The wastew- ater passage from the aeration tank to the sedimentation tank was through the holes in the inclined plate. The sludge recycle was through the gap under the plate. The effluent of the anaerobic UASB reactor was used as the influent of aerobic CSTR reactor. Partially granulated anaerobic sludge was used as a seed in UASB reactor and was taken from the methanogenic reactor of Pakmaya Yeast Baker Factory in Izmir. An activated sludge culture, obtained from the DYO Dye Industry in Izmir, was used as seed for the aerobic CSTR reactor. The suspended solid and volatile suspended solid (VSS) concentrations in the UASB reactor were 31.7 g dm?3 and 22.4 g VSS dm?3, respectively, while the mixed liquor suspended solid (MLSS) concentration in CSTR reactor was about 3000 mg dm?3 by adjusting the sludge age to 20 days. The flowrate was kept constant at 3.5 l day?1 throughout 49 days of operation period. The hydraulic retention time (HRTs) of UASB, CSTR and total UASB/CSTR reactor system were 17 h, 2.6 days and 3.3 days, respectively. UASB/CSTR reactor system was fed with synthetic wastewater and dye in order to simulate the acid dye- ing wastewater since the raw wastewater contained low COD and color. The characterization of wastewater is given in Table 1.
2.2. Acid dyeing wastewater
Wastewater was taken from the wool dyeing processing unit and transported to the laboratory for feeding the sequential UASB/CSTR reactor system. This system was previously used for the treatment of a synthetic wastewater contained azo dyes at a concentration as high as 4000 mg dm?3 [6,13,14]. Characterization of the wastewater taken from the wool dyeing unit was performed before feeding the sequential anaerobic/aerobic reactor system. In the fabric treatment, acid dyeing was carried out with the treatment of 15 kg of dye, 15 kg of sulphuric acid, about 2 dm?3 of anti-foam to prevent foaming and 30–35 kg of salt (sodium sulphate) after 550–600 kg of the wool was boiled to yield the desired color (personal reviewing). The characterization of the real wastewater taken from the dyed wool fabric is summarized in Table 1. The characteristics of wastewater used in this study were similar that of acid dyeing wastewaters produced from the wool dyeing [1]. As can be seen in this table, the dissolved COD, inert COD and TOC were 476, 200 and 170 mg dm?3, respectively, in Run 4.
The laboratory-scale UASB/CSTR reactor system was fed with 2000 mg dm?3 of glucose-COD, 3000 mg dm?3 of NaHCO3 and 25 ml dm?3 of V anderbilt mineral medium during 7 days of start-up period in the Run 1. In this run no dye was added to the wastewater since it was fed synthetically. In the treatment studies of acid dye wastewaters, 1000 mg dm?3 of glucose-COD and 2000 mg NaHCO3 dm?3 alkalinity were added in Runs 2, 3 and 4 in order to simulated dye the wastewater since the acid dye wastewaters contained low level of color, carbon and alkalinity (see Table 1). Suitable alkalinity provides stable neutral pH conditions for anaerobic microorganisms through anaerobic treat- ment. Furthermore it neutralizes the acidity and the volatile fatty acids produced through anaerobic treatment. Carbon source provides reducing environments for reductive cleavage of azo bonds. On the other hand in order to stimulate the anaerobic treatment a COD concentration as high as 1500–2000 mg dm?3 should be provided to wastewater. 200 mg dm?3 of azo dye was added to raw wastewater in Run 3 since the raw wastewater contained low color through the operation of UASB/CSTR reactor system. The reason for using 200 mg dm?3 of azo dye is owing its maximum availability in real dye industry wastewater. In this study it was aimed to determine the maximum COD and color removal efficiencies and methane gas productions through anaerobic treatment by addi- tion of carbon, alkalinity and dye. Table 2 summarizes the characterization of the dyes that were used in the dyeing processing of the fabric and the dyes added to the laboratory-scale UASB/CSTR reactor system.
2.3. Analytical procedures
Gas production was measured using a liquid displacement method. Total gas was measured by passing the gas through a liquid containing 2% (v/v) H2SO4 and 10% (v/v) NaCl [15]. The percentage of methane in biogas was determined by use of a Dra¨ger Pac?Ex methane gas analyzer. The measurement of color was carried out following the approaches described by Olthof and Eckenfelder [16] for the various dyes used in the dyeing process. According to these methods, the color content was determined by measuring the absorbance at three wavelengths (445, 540 and 660 nm), taking the sum of the absorbances at these wavelengths. The absorbance of effluents in Runs 1, 2 and 3 was corrected by subtracting the absorbance values measured in the effluent of Run 1 due to metabolic residues. To convert the absorbance value into m?1, the equation given below was used: A
α=
d
× f
where αis the color in m?1 unit (m?1 = A/10 mm ×1000), A the measured absorbance value from spectrophotometer, d the sample length (cell width, 10 mm) and f is a factor (1000).
The soluble COD was measured colorimetrically using closed reflux meth- ods [17]. The inert COD content of the acid dyeing wastewater was determined using the glucose comparison method developed by Germirli [18] measuring all the soluble forms of COD under aerobic conditions. Bicarbonate alkalinity
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Table 2
The dyes used through acid dyeing in operation period
Name Formula of dyes Information
Acid Blue 113 C.I. 26360
This dye was used in acid dye process- ing of the fabric (Run 2). This dye was added to the raw wastewater in Run 3 at 100 mg dm ?3
C 32 H 23 N 5 O 6 S 2 , 682 g mol ?1
Direct Black 22 C.I. 35435
This dye was used in acid dye process- ing of the fabric (Run 2). This dye was added to raw wastewater in Run 3 at 100 mg dm ?3
C 44 H 32 N 13 N a 3 O 11 S 3 , 1084 g mol ?1
Sarasit Blue SR
Chemical formula was not found
This dye was used in acid dye pro- cessing of the fabric (Run 3). The dyes mentioned above were added to wastewater since the synthetic wastewater had low absorbance
(B.Alk.) and total volatile fatty acid (VFA) concentrations were measured simul- taneously using the titrimetric method of Anderson and Yang [19]. The pH was determined immediately after sampling to avoid any change due to CO 2 evolu- tion, using a pH meter, type NEL pH 890. The dissolved oxygen (DO) and the temperature of the aeration tank of the CSTR were measured using an oxygen meter (model Oxi 330/SET) manufactured by WTW (Germany). The biomass was measured as the total suspended solids (TSS) and the volatile suspended solids in the UASB reactor, and as the mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (ML VSS), in the aeration tank of CSTR. Assays were performed according to standard methods for examination of water and wastewater [17]. Total aromatic amines were determined colorimetrically at 440 nm after reacting the samples with 4-dimethylamino benzaldehyde –HCl according to the method described by Oren et al. [20] and calibrated with ben- zidine standards [20].
The data given in figures are the mean of three repetitive samplings with standard deviation (S.D.) values.
2.4. Statistical analysis
Regression analysis between variables was performed using the EXCELL in Microsoft Windows TM (HP , USA). The linear correlation was assessed with r 2 . The r 2 value is the correlation coefficient and reflects statistical significance between dependent and independent variables. Analysis of variance (ANOV A) (SAS ANOV A procedure) test was used to assess the data obtained in reactors using the EXCELL in Microsoft Windows TM (HP , USA).
3. Results and discussion
3.1. Variations in the methane production rate, the VFA and the B.Alk. in the UASB reactor
The variations of VFA, B.Alk. and methane production rate in effluent of UASB reactor are shown in Fig. 1 for all runs. The VFA, B.Alk. levels and methane gas production rates were 40 mg CH 3 COOH dm ?3 , 1593 mg CaCO 3 dm ?3 and 1437 ml CH 4 day ?1 , respectively, through Run 3 when Acid Blue 113 and C.I. Direct Black 22 of 100 mg dm ?3 were added
to the raw wastewater. In this run the reactor system was oper- ated under favorable conditions (low VFA and high methane gas production rates). No significant linear correlation between VFA and methane gas production was observed (r 2 = 0.49, P = 0.39, F = 1.43). The ratios of VFA/B.Alk. and pH values are illustrated in Fig. 2. In Run 4, the VFA concentrations increased slightly but did not exceed the critical value for VFA/B.Alk. (0.4). The VFA/B.Alk. ratios were about 0.15 in Run 4, indicating the sta- bility of the UASB reactor [21] while the VFA/B.Alk. ratio was determined to be 0.025 in Run 3. The measured pH values were suitable (6.5–7.5) [22] for optimum anaerobic treatment through all runs. As the B.Alk. values decreased the methane production rates decreased. The regression analysis indicated that the lin- ear relationship between B.Alk. and methane gas production was statistically significant (r 2 = 0.79, P = 0.09, F = 7.55). As the B.Alk. values decreased the VFA concentration increased.
Fig. 1. V ariation in methane production rate, VFA and B.Alk. concentrations in four operation runs.
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Fig. 2. V ariation of pH and VFA/B.Alk. ratios in the effluent of UASB reactor.
A significant linear correlation between B.Alk. and VFA con-
centration was observed (r 2 = 0.81, P = 0.07, F = 8.76).
3.2. COD removal ef ?ciencies of UASB/CSTR reactor system
The COD removal efficiencies in the total system are shown in Fig. 3. It may be said that the COD was removed with removal efficiencies varying between 85 and 95 in Runs 1, 2 and 3 while 75% COD removal efficiencies was observed in Run 4. In Runs 2, 3 and 4, 1000 mg dm ?3 of the glucose-COD was added to raw wastewater while the wastewater contained only glucose- COD of 2000 mg dm ?3 in Run 1. The effluent glucose-COD was reduced to as low as 60 mg dm ?3 at a total HRT of 2.3 days in the UASB/CSTR sequential system in Run 1 since it contained only glucose-COD. This COD value could be attributed to COD associated with inert soluble microbial products since glucose is a readily degraded organic matter and consumed completely by the anaerobic microorganisms [23]. COD from the soluble microbial products (SMP) through substrate metabolism and biomass decay should be considered because the effluent soluble COD might be mostly SMP (50–90%) as reported by Kuo et al. [23]. With the following runs, the final COD values were higher than the COD values obtained in Run 1 since the raw wastewater contained considerable inert COD values. In Run 4, the effluent
Fig. 3. The COD removal performance of the UASB/CSTR sequential system.
Fig. 4. Determination of inert COD in raw wastewater through Run 4.
COD of the system was decreased to about 257 ± 27 mg dm ?3 since the inert COD level of raw wastewater was 200 mg dm ?3 (see Fig. 4). The anaerobic system could be removed all the degradable COD and some of the inert COD from the total sol- uble COD fraction. COD removal efficiencies of UASB and UASB/CSTR system decreased to 51% and 83% from 84% and 94% in Run 4. It can be suggested that the differences in inert COD ratio, the ratio of slowly and readily degradable organic substances, VFA and aromatic amine ratios of acid dye- ing wastewater caused changes in the removal efficiencies of the anaerobic/aerobic sequential reactor system. ANOVA test indi- cated that there were no significant differences between UASB reactor and whole (UASB/CSTR) reactor system based on COD removal efficiencies (p = 0.05, F = 0.19, d.f. = 3).
3.3. Performance of color removal in UASB/CSTR reactor system
In the total system the efficiency of color removal was not decreased lower than 80% (Fig. 5). Color was reduced mainly in the anaerobic stage. In Runs 3 and 4, the aerobic stage helped in the removal of color since the intermediate products released from the degradation of azo dye were ultimately decolorized. For instance, in Run 3 the color of UASB influent, and effluent and CSTR effluent were 285, 93 and 44 m ?1 corresponding to color
removal efficiencies of 83%, 23% and 91%, in the UASB, CSTR
and UASB/CSTR reactor systems, respectively. It is important to note that, in Run 1, the influent color originated from Van- derbilt mineral medium and not from the dye since the synthetic wastewater contained no dye. However, in this run, the color measured in anaerobic and aerobic effluents produced from the metabolic activity of the biomass through the metabolization of substrate. In other words, since the effluents of the control reac- tor (Run 1) contained only some colloidal organic matters such as metabolic excretes and dead cells these substances interfered the color measurements. Therefore, in order to measure the real color removal the absorbance values of the Runs 2, 3 and 4 reac- tors were calibrated with the control samples containing no dye.
M. Is??k, D.T. Sponza / Enzyme and Microbial Technology 38 (2006) 887–892891
Fig. 5. Color removal efficiencies of the system through the operation of 49 days.
Therefore, color removal efficiency was not calculated in Run 1 as shown in Fig. 5.
As above, similar results were obtained in a study per- formed by Kuai et al. [4] concerning the treatment of a tex- tile wastewater taken from carpet dyeing and printing facto- ries using a laboratory-scale anaerobic (UASB)/aerobic semi- continuous activated sludge (SCAS) reactor system. The COD and color in effluent was decreased to 79–219 mg dm?3 and 0.02–0.07 absorbance units (at a wavelength of 500 nm) from 6000 mg dm?3 and 0.8 absorbance units in the aforementioned system at a total HRT of 1–2 days. During the treatment of a wastewater from a dye manufacturing factory with a COD con- centration of 1200 mg dm?3 and a color of 500 degree (dilution factor) in a UASB reactor (4.5 l) and an activated sludge tank (5 l), COD and color were removed by more than 83% and 90% at HRTs of 6–10 and 6.5 h for the anaerobic and aerobic stages, respectively [9].
Fig. 6 shows the absorbance measurements at varying wave- lengths in a UASB/CSTR system, treating acid dyeing wastew- aters in Run 4. The influent spectrum had two peaks in the visible region at wavelengths of 500 and 620 nm. In the anaer- obic treated sample, the peaks occurred in the UV region at a wavelength of 360 nm, indicating the cleavage of the azo bond, thus providing evidence of the decoloration of dye. The effluent
Fig. 6. Absorbance spectra in influents and effluents of the reactor system at different wavelengths in Run 4.
Fig. 7. TAA removal efficiencies in CSTR reactor.
sample from the CSTR reactor exhibited maximum absorbance spectra at low wavelengths (325 nm) due to aromatic amines produced under anaerobic conditions was removed under aer- obic conditions. This shows that the parent dye was converted to other intermediate organic forms in UASB reactor, and then these intermediates were degraded in the CSTR reactor.
ANOVA test indicated that there were no significant differ- ences between color removal efficiencies between UASB reac- tor and whole (UASB/CSTR) system through operation days (p = 0.05, F = 0.23, d.f. = 3).
3.4. Variation of TAA in UASB/CSTR sequential system
The acid dyeing wastewater contains TAAs released through the cleavage of azo dyes under anaerobic conditions. Fig. 7 shows the TAA concentrations in the effluent of reactors and TAA removal efficiencies obtained in CSTR reactor. The aero- bic stage had the ability to decrease the TAA concentrations to lower than 5 mg dm?3 of TAA, as shown in Fig. 7. This result shows that the aerobic stage is very important for the removal of aromatic amines and agrees with the previous studies [24,25].
ANOVA test indicated that there were significant differences between TAA concentrations in UASB and CSTR reactor efflu- ents (p = 0.05, F = 12.3, d.f. = 3).
4. Conclusions
The treatment of real textile wastewater has been carried out using aerobic biological processes, physico/chemical processes and their modifications. The addition of an anaerobic stage prior to the aerobic stage could be favorable in the treatment of the acid dyeing wastewaters since anaerobic stage can degrade the azo dyes resulting in decolorization of textile wastewater and reduce the organic loading rate on aerobic stage. The reducing environment prevailing in the UASB reactor by the electrons releasing from the azo dyes and its intermetabolite products (TAA) provide the color removal. The UASB/CSTR combined rector system showed a stable performance for the treatment of acid dyeing wastewater. Therefore, this system would have a potential to meet the effluent discharge limitations of the receiv- ing medium for the acid dyeing wastewaters on the basis of COD,
892 M. Is??k, D.T. Sponza / Enzyme and Microbial Technology 38 (2006) 887–892
BOD and color removal, although color removal has no limita- tions yet in the Turkish receiving water discharge standards. Acknowledgements
This study was supported by the Turkish Scientific and Tech- nical Research Council (TUBITAK), and fund of Nig? de Univer- sity, Turkey. The authors gratefully acknowledge the financial support from these organizations.
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