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Biological and oxidative treatment of cotton textile dye-bath effluents by fixed and fluidized bed reactors
Bioresource Technology 101 (2010) 1147–1152
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Biological and oxidative treatment of cotton textile dye-bath effluents by fixed and fluidized bed reactors A. Baban a,*, A. Yediler b, G. Avaz a, S.S. Hostede b a b
TUBITAK – MRC Environment Institute, 41470 Gebze, Kocaeli, Turkey Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Institute of Ecological Chemistry, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany
a r t i c l e
i n f o
Article history: Received 28 May 2009 Received in revised form 11 September 2009 Accepted 17 September 2009 Available online 12 October 2009 Keywords: Azo dyes Adsorption COD fractions Ozone oxidation
a b s t r a c t A treatability study for highly polluted and recalcitrant azo reactive dye-baths from cotton textile dyeing processes was conducted by using fixed and up-flow fluidized bed type reactors packed with brown coal. Ozone oxidation was carried out to assess the combination of biological and chemical oxidation. COD removal efficiencies ranged from 70% to 93%, and up to 99% color removal was attained. At a COD loading rate of 25.5 10 6 gCOD/m2-d, COD removal was 85%. Breakthrough of the brown coal used occurred at total organic loading of 0.090 gCOD/g coal. Biodegradable and inert COD fractions of the remazol dyebath were assessed by BOD28 and oxygen uptake rate (OUR) measurements. 50% of total COD was initially inert. The inert fraction was reduced by adsorption and ozone oxidation by 65% and 40%, respectively. Brown coal is an inexpensive material and the system has economical and operational advantages as compared to treatment options such as advanced oxidation processes (AOPs) using UV, O3, H2O2 or electrocoagulation. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Wastewater of textile dyeing and finishing industries consists of unbound colorants, reaction products, dye impurities, auxiliaries and surfactants. These effluents exhibit very slow degradation kinetics and resistance to conventional biological treatment processes (Ciardelli and Ranieri, 2001; Alaton et al., 2002; Zhang et al., 2004; Baban et al., 2004; Turhan and Turgut, 2007, 2009), and conventional physico-chemical treatment has not been proved as an effective method for decolorization and organic matter removal (Krull et al., 1998; Koch et al., 2002). Reactive dyes, among them commonly used azo dyes, are considered to be the problematic components in the wastewater since, in general, only 40–90% of dye is fixed to the fabric during dyeing; the rest appears in the wastewater causing high chemical oxygen demand (COD) and color. (Wu and Wang, 2001; Wang et al., 2002). The relatively low BOD5 (biochemical oxygen demand)/COD ratio (<0.1) of azo reactive dyes implies a very low level of biodegradability (Zhang et al., 2004). Pollution prevention by in-plant measures is the main aim of modern environmental management and is gaining in importance over the ‘‘end of pipe” treatment approach. In this context, segregation of dye-baths, with strong pollutant characteristics, from the waste stream could become highly profitable and treatment * Corresponding author. Tel.: +90 262 6772904; fax: +90 262 6412309. E-mail address: [email protected] (A. Baban). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.09.060
and reuse of relatively clean streams for process purposes may become feasible. Hence, reduction of recalcitrant organic constituents of dye-baths and decolorization have become the focus of research. For example, attempts were made to reduce pollutants by implementation of process modifications or by replacing undesirable chemicals with more environmentally friendly ones (Blackburn and Burkinshaw, 2002). Studies, on azo dye effluents have included physico-chemical techniques, UV or H2O2, oxidations and/or their combinations, electrocoagulation and adsorption (Koch et al., 2002; Georgiou et al., 2002; Neamtu et al., 2002, 2004; Baban et al., 2003; Sostar-Turk et al., 2005; Ozdemir et al., 2004; Yang and McGarrahan, 2005; Alaton et al., 2009). Biological degradation of azo dyes by anaerobic or aerobic processes have also been investigated and combined biological and physico-chemical treatment options for azo dyes have also been studied (Krull et al., 1998; Georgiou et al., 2004). The results revealed that effective decolorization along with about 70% COD removal are achievable by oxidation processes. In this study, treatability of dye-baths by oxidative and biological methods were investigated to represent the condition of segregated dye-bath stream treatment and to facilitate the advantages of water segregation and reuse. Hence, the objectives of the study were assessment of biodegradability of azo dye-baths, determination of the treatability by using a cheap material for adsorption and biofilm attachment media and enhancement of biodegradability by ozone oxidation. For this purpose, samples from defined process lines of remazol dye-bath effluents were collected from two
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152
different textile plants (enterprise I and II) in Istanbul, Turkey. The enterprises are classified under the knit fabric dyeing and finishing subcategory, involving cotton, polyester and polyamide products. Two reactors, having different configurations were set up and operated to treat various concentrations of dye-bath effluents. Brown coal char (lignite), as a low price material, was used in the reactors as packing medium.
a
air supply from the central facility effluent to the drain
influent
2. Methods
peristaltic
2.1. Reactor configuration and operation
pump sintered glass
Vreactor=15.4 l
porous diffusers
packed with 6.0 kg brown coal
Two types of reactor configurations were used. The fixed bed reactor was made of plexiglas, having dimensions of 35 22 25 cm (height). Three baffles were installed in the reactor. The reactor was filled with 6.0 kg of brown coal, which was provided by Rheinbraun Brennstoff GmbH, Köln, Germany. The brown coal had a typical surface area of 300 m2/g, approximate particle size of 1–1.5 mm, specific density of 1.093 g/cm3 and porosity of 41%. The surface area of the brown coal was less than the typical values for activated carbon, which are normally higher than 400 m2/g. The depth of the bed for the fixed bed reactor was 20 cm with a slight expansion of 2 cm during operation. The overall usable volume of the reactor was 15.4 l. Air was introduced from the bottom of each compartment smoothly by circular sintered glass porous diffusers. The up-flow fluidized bed reactor had a diameter of 11 cm, height of 48 cm and a working volume of 3.3 l, was made of plexiglas and contained 0.5 kg of brown coal. The feed solution was supplied from the bottom by a peristaltic pump. Air was supplied through a sintered glass porous plate placed at the bottom. The schematic drawings of both reactors are illustrated in Fig. 1. Since, brown coal included some calcium oxide, and dissolution might increase pH, packing media was first washed with slightly acidified (HCl) tap water having a pH of around 6.0. Both reactors were initially fed by a synthetic solution representing similar pollutant characteristics as domestic wastewater. Activated sludge initially was added to enhance biofilm growth to the feed solution at a rate of 3 l of settled activated sludge to 15 l of feed solution. It is noted that extensive growth of attached bacteria was observed in the first compartment of the fixed bed reactor. This situation is attributable to the low amount of organic matter remaining for the downstream compartments due to the adsorption capacity of the brown coal packing material. Once a biofilm was established, acclimatization of the bacteria to dye-baths was accomplished by gradually increasing the amount of feed solution. The reactors were then operated with 10%, 30% and 100% remazol dye-bath solutions. The feed solution was neutralized with HCl, prior to the feeding.
tive oxygen consumption was determined. The incubated samples were further analyzed to assess the completion of biodegradation. For this purpose incubated samples were mixed with acclimatized and settled activated sludge. The organic matter/ microorganism ratio (Co/Xo) of the mixture was adjusted to 0.6. The OUR’s were measured at 20 min intervals for 3 h to determine the remaining biodegradable organic matter. The same procedure was applied to a blank solution with identical amount of distilled water and activated sludge as control. Hence, once the biodegradable portion was consumed, the remaining part was assumed to consist of the inert fraction.
2.2. Methods of analysis
3. Results and discussion
As the dye-bath solutions contained chloride higher than 1 g/l, COD analysis were carried out according to the DIN 38 409 H412 to avoid interference. Analyses were carried out in triplicate. Absorbance measurements were conducted at the wavelengths, 436, 525 and 625 nm for the assessment of color characteristics. Dissolved oxygen (DO) was measured by a microprocessor, oximeter (WTW MultiLine P4, Weilheim, Germany). Ozone was generated from dried air by an ozone generator (Erwin Sander Elektroapparatebau, Ueltze., Germany). Ozone oxidation was carried out in a 1.2 l glass reactor by bubbling ozone/air mixture at a volume stream of 20 mg/l through a sintered glass (pore size 50–80 lm). Bio-degradation of dye-bath samples was measured during 28 days incubation time in ‘‘Sapromat, Type D” (Voith, Germany). Three cells were used for each sample, and daily cumula-
3.1. Pollutant removal efficiencies of the reactors
feed container
b
effluent to drain overflow to drain
V=3.3 l packed with 0.5 kg brown coal brown coal bed
sintered glass plate peristaltic
influent
feed pump air supply from central feed solution
facilities
container Fig. 1. Schematic illustration of the laboratory models: (a) fixed bed reactor, and (b) fluidized bed reactor.
The remazol dye-bath concentrations and the operational conditions of the reactors are illustrated in Table 1. Various dye-bath concentrations from the two enterprises were investigated for the assessment of treatability of dye-baths. The influent and effluent COD concentrations of the reactors operated under these conditions with different strengths of remazol dye-baths are indicated in Fig. 2. The obtained COD removal efficiencies ranged from 70% to 93%. The fixed and fluidized bed reactor effluents for the enterprise-II had COD concentrations of 124 and 168 mg/l corresponding to 90% and 83% COD removal respectively. The high COD removal efficiency was due to the biofilm and the adsorption capacity of brown coal having high surface
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152 Table 1 Operational data of the reactors fed with remazol dye-baths. Reactor
Fixed bed
Fluidized bed
Source
Enterprise-I
Enterprise-I
Enterprise-I
Enterprise-II
Enterprise-II
Enterprise-II
Enterprise-II
Conc. (%) Flow (l/d) HRT (h)
10 25 14.8
30 15 24.6
100 12 30.8
100 12 30.8
10 2.75 28.8
30 2.5 31.7
100 4.0 19.8
400
color reduction efficiency was around 99% for the fixed bed reactor. The efficiency was slightly lower for the fluidized bed reactor. This condition might be explained by different reactor configurations and the higher amount of packing material in the fixed bed reactor. The obtained efficiencies are considered to be quite high as compared to the processes such as ozonation, H2O2 and UV oxidation. The initial conductivity of 100% dye-bath was about 112 mS/cm, after the treatment a slight decrease of up to 30% was observed. The pH of influent and effluents was in the range of 7.5–8.0. A slight increase in pH for the effluent was detected.
200
3.2. Breakthrough conditions
1400 1200
COD, mg/l
1000
influent efffluent
800 600
0
A B C D E F G enterprise no. remazol dye bath conc. - reactor type
Fig. 2. Influent and effluent COD concentrations for the reactors operated with remazol dye-baths (A, B, C: 10%, 30% and 100% dye-baths of enterprise-I treated by fixed bed reactor, respectively, D: 100% dye-bath of enterprise-II treated by fixed bed reactor, E, F, G: 10%, 30% and 100% dye-baths of enterprise-II treated by fluidized bed reactor, respectively).
area. COD removal efficiencies as a function of COD loading rates are shown in Fig. 3. The removal efficiency increased with the increasing influent COD concentration particularly for the fixed bed reactor. Comparable COD removal efficiency and decolorization potential was attained by Krull et al. (1998), using an anoxic/aerobic sequential batch reactor for remazol dye-bath. The system had a total process cycle time of one week and partial oxidation was achieved with ozone. In the current study, overall hydraulic retention time was up to 1.3 days for the brown coal bed reactors. COD loading rate of 25.5 10 6 g/m2-d resulted in around 85% COD removal efficiency. The color reduction was monitored by absorbance measurements. The influent and effluent average color characteristics for the two reactors operating with the different dye-baths from the two enterprises are illustrated in Fig. 4. The
COD removal efficiency
120 100 80 60 40 20 0 0,00E+00
1,00E-05 2,00E-05 COD loading rate, g/m2.d
3,00E-05
Fig. 3. COD removal efficiency as a function of COD loading rate for fixed and fluidized bed reactors.
The sorption capacity of the coal media was saturated after a period causing a decrease in removal efficiency and leading to occurrence of breakthrough conditions. The characteristics of this phase were determined when the reactor was operated with raw 100% remazol dye-bath of enterprise-II (initial COD 1200 mg/l). The breakthrough phase was monitored by absorbance measurements of the effluent and recording the corresponding amount of dye-bath inlet. Feeding was terminated as the reduction in absorbance was about 60–70%. This state was defined as the occurrence of breakthrough. Volumetric and organic loading rates were calculated based on the unit coal weight. The results are summarized in Table 2. Throughout the operation period of the reactor, measured effluent absorbance values showed 83–88% reduction, whereas, after 17 days of operation the reduction in absorbance started to drop rapidly to 55–70%. The data presented in Table 2 may be used as a reference for calculation of the time period for the replacement or regeneration of the coal bed. Bacterial activity might also occur to help to restore adsorption capacity for prolonged operation times to some extend. 3.3. Biodegradability studies A series of experiments were conducted to assess the biodegradability of dye-baths. For this purpose, BOD28 measurements were carried out on 30% remazol dye-bath from the enterprise-I, its effluent after the treatment by the fixed bed reactor, raw 100% remazol dye-bath from the enterprise-II and 100% remazol dye-bath after 30 min ozone oxidation. The results of BOD28 measurements are outlined in Table 3. Whereas, the results of OUR measurements of the samples incubated for 28 days in the respirometer and the blank (tap water) are illustrated in Fig. 5. The difference for OUR’s with time for blank and treated and untreated dye-bath samples are negligible. For the ozonated and raw remazol dye-bath samples from enterprise-II slightly higher OURs were measured than for the 30% dye-bath samples from enterprise-I. This situation is thought to be caused by the different initial COD concentrations of the samples. Remazol (100%) dyebath effluents had almost four times higher initial COD concentration than the 30% enterprise-I textile dye-bath. Consequently, it was assumed that almost all the biodegradable fraction of COD was used up throughout the incubation period by the bacterial action in the respirometer for all of the samples. Hence, the difference between the initial COD (CODT) and the BOD28 concentration
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152
a
2000 1800 abs. at 625nm inf.
absorbance, m-1
1600
abs. at 525nm inf.
1400
abs. at 436nm inf.
1200 1000 800 600 400 200 0 A
abs. at 436nm inf. abs. at 525nm inf.
B
C
D
abs. at 625nm inf.
E
F
G
enterprise no. - remazol dye bath conc. - reactor type
b
300 275
absorbance, m-1
250 225
abs. at 625nm eff.
200
abs. at 525nm eff.
175
abs. at 436nm eff.
150 125 100 75 50 25 0 A
abs. at 436nm eff. abs. at 525nm eff.
B
C
D
E
abs. at 625nm eff.
F
G
enterprise no. - remazol dye bath conc. - reactor type Fig. 4. Influent (a) and effluent (b) average color characteristics (A, B, C: 10%, 30% and 100% dye-baths of enterprise-I treated by fixed bed reactor, respectively, D: 100% dyebath of enterprise-II treated by fixed bed reactor, E, F, G: 10%, 30% and 100% dye-baths of enterprise-II treated by fluidized bed reactor, respectively).
Table 2 Breakthrough state of brown coal in up-flow fluidized bed reactors. Parameters Effluent absorbance and % reduction based on initial absorbance measured at 625 nm 525 nm 436 nm Operation time (days) Total volume of dye-bath fed (l) Total volumetric feeding to reach breakthrough (l/g-coal) Total organic loading to reach breakthrough (gCOD/g coal)
Enterprise-II remazol dye-bath (100%)
763.9 m 660.1 m 539.1 m 18 37.2 0.0744 0.090
1 1 1
(56.9%) (62.1%) (71.0%)
of each sample was designated as the inert COD fraction (CODI) of the dye-bath. CODI, as a fraction of CODT for raw and 30-min ozonated dyebaths ranged between 40% and 50%, which indicates a considerable amount of non-biodegradable fraction. Although, ozone oxidation was not significantly effective on COD removal, CODI fraction was reduced by 10% or biodegradability was increased by 10% as a result of 30 min of ozonation. Removal of biodegradable COD and a fraction of CODI were achieved by treating the dye-bath with brown coal packed reactors. BOD28/CODT ratio is considered to be an indication of biodegradability. CODI may also be determined by the method given by Orhon et al. (1994, 1999). The method involves biological oxidation of substrate by acclimatized micro-organisms for prolonged
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152 Table 3 The results of biodegradability studies and OUR (oxygen uptake rate) measurements. Parameters
Enterprise-I 30% remazol inf. to fixed bedreactor
Enterprise-I 30% remazol eff. from fixed bed reactor
Enterprise-II 100% remazol dye-bath
Enterprise-II 100% remazol 30 min ozonated
BOD28 (mg/l) CODT (mg/l) BOD28/CODT (%) CODI (mg/l) CODI (% of CODT)
140 270 51.8 130 48.2
15 62 24.2 47 75.8
602 1212 49.7 610 50.3
562 935 60.1 373 39.9
CODI: inert COD; CODT: total COD.
OUR, mg/l.h
a
fraction. The reactors were efficient in removing CODI. 65% of the CODI initially present in the dye-bath was removed by the brown coal bed reactor and about 40% reduction was achieved by 30 min ozonation.
10 9
blank
8
enterprise-II 100% remazol
7
enterprise-II 100% 30min. ozonated
Acknowledgements
6 5 4 3 2 1 0
0
25
50
75
100
125
150
175
200
225
t, min
OUR, mg/l.h
b
10 9 8 7 6 5 4 3 2 1 0
This work has been conducted at the GSF-Institute of Ecological Chemistry (currently Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Institute of Ecological Chemistry) and was partly funded by the German Federal Ministry of Education, Science, Research and Technology (BMBF), within the framework of the agreement between TUBITAK (The Scientific and Technical Research Council of Turkey). Thanks are extended to the International Bureau of Research Center Jülich GmbH, Germany for excellent management and to Prof. Dr. D. Orhon for his valuable comments.
blank
References influent, 30% enterprise-I remazol dye-bath effluent, 30% enterprise-I remazol dye-bath
0
25
50
75
100
125
150
175
200
225
t, min Fig. 5. Oxygen uptake rate (OUR) after incubation for BOD28 measurements: (a) enterprise-II 100% raw remazol dye-bath and 30 min ozonated 100% remazol dyebath, and (b) enterprise-I 30% influent and effluent of the fixed bed reactor.
time periods in batch reactors. Although, the presented approach provided rapid and practical way for the determination of CODI, the inert fractions determined by the present study is probably slightly less than the values that would have been obtained by the method suggested in the literature since the inert COD determination in batch reactors is associated with a much longer biodegradation period as compared to the BOD28 determination in the incubator. 4. Conclusions Treatment of remazol reactive dye-baths by using brown coal packed reactors is advantageous to obtain high removal efficiencies that may not be easy to achieve by conventional systems. The packing material can be replaced, disposed off or regenerated at relatively low costs. The system has operational ease over conventional treatment options. A new approach, based on respirometric measurements, was carried out to determine CODI
Alaton, I.A., Balcioglu, I.A., Bahnemann, D.W., 2002. Advanced oxidation of a reactive dye-bath effluent: comparison of O3, H2O2/UV-C and TiO2/UV-A processes. Water Res. 36, 1143–1154. Alaton, I.A., Kabdasli, I., Vardar, B., Tunay, O., 2009. Electrocoagulation of simulated reactive dye-bath effluent with aluminum and stainless steel electrodes. J. Hazard. Mater. 164, 1586–1594. Baban, A., Yediler, A., Lienert, D., Kemerdere, N., Kettrup, A., 2003. Ozonation of high strength segregated effluents from a woolen textile dyeing and finishing plant. Dyes Pigm. 58, 93–98. Baban, A., Yediler, A., Ciliz, N.K., Kettrup, A., 2004. Biodegradability oriented treatability studies on remaining composite wastewater of a woolen textile dyeing and finishing plant. Chemosphere 57 (7), 731–738. Blackburn, R.S., Burkinshaw, S.M., 2002. A greener approach to cotton dyeings with excellent wash fastness. Green Chem. 4, 47–52. Ciardelli, G., Ranieri, N., 2001. The treatment and reuse of wastewater in the textile industry means of ozonation and electroflocculation. Water Res. 35, 567–572. Georgiou, D., Melidis, P., Aivasidis, A., Gimouhopoulos, K., 2002. Degradation of azoreactive dyes by ultraviolet radiation in the presence of hydrogen peroxide. Dyes Pigm. 52, 69–78. Georgiou, D., Metallinou, C., Aivasidis, A., Voudrias, E., Gimouhopoulos, K., 2004. Decolorization of azo-reactive dyes and cotton-textile wastewater using anaerobic digestion and acetate-consuming bacteria. Biochem. Eng. J. 19, 75– 79. Koch, M., Yediler, A., Lienert, D., Kettrup, A., 2002. Ozonation of hydrolysed azo dye Reactive Yellow 84 (CI). Chemosphere 46, 109–113. Krull, R., Hemmi, M., Otto, P., Hempel, D.C., 1998. Combined biological and chemical treatment of highly concentrated residual dyehouse liquors. Water Sci. Technol. 38, 336–339. Neamtu, M., Siminiceanu, I., Yediler, A., Kettrup, A., 2002. Kinetics of decolorization and mineralization of reactive azo dyes in aqueous solution by the UV/H2O2 oxidation. Dyes Pigm. 53 (2), 93–99. Neamtu, M., Yediler, A., Siminiceanu, I., Macoveanu, M., Kettrup, A., 2004. Decolorization of disperse red 354 azo dye in water by several oxidation processes – a comparative study. Dyes Pigm. 60 (1), 61–68. Orhon, D., Artan, N., Ates, E., 1994. A description of three methods for the determination of the initial inert particulate chemical oxygen demand of wastewater. J. Chem. Tech. Biotechnol. 61, 73–80. Orhon, D., Karahan, Ö., Sözen, S., 1999. The effect of residual microbial products on the experimental assessment of the particulate inert COD in wastewaters. Water Res. 33, 3191–3203. Ozdemir, O., Armagan, B., Turan, M., Celik, M.S., 2004. Comparison of the adsorption characteristics of azo-reactive dyes on mezoporous minerals. Dyes Pigm. 62 (1), 49–60.
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Sostar-Turk, S., Simonic, M., Petrinic, I., 2005. Wastewater treatment after reactive printing. Dyes Pigm. 64, 147–152. Turhan, K., Turgut, Z., 2007. Reducing chemical oxygen demand and decolorization of direct dye from synthetic textile wastewater by ozonization in a batch bubble column reactor. Fresenius Environ. Bull. 16 (7), 821–825. Turhan, K., Turgut, Z., 2009. Decolorization of direct dye in textile wastewater by ozonization in a semi-batch bubble column reactor. Desalination 242, 256–263. Wang, C.H., Yediler, A., Lienert, D., Wang, Z., Kettrup, A., 2002. Ozonation of an azo dye Remazol Black 5 and toxicological assessment of its oxidation products. Chemosphere 52, 1225–1232.
Wu, J., Wang, T., 2001. Ozonation of aqueous azo dye in a semi-batch reactor. Water Res. 35 (4), 1093–1099. Yang, C.L., McGarrahan, J., 2005. Electrochemical coagulation for textile effluent decolorization. J. Hazard. Mater. 127(1–3, 9), 40–47. Zhang, F.F., Yediler, A., Liang, X.M., Kettrup, A., 2004. Effect of dye additives on the ozonation process and oxidation by-products: a comparative study using hydrolyzed C. I. Reactive Red 120. Dyes Pigm. 60 (1), 1–7.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Biological and oxidative treatment of cotton textile dye-bath effluents by fixed and fluidized bed reactors A. Baban a,*, A. Yediler b, G. Avaz a, S.S. Hostede b a b
TUBITAK – MRC Environment Institute, 41470 Gebze, Kocaeli, Turkey Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Institute of Ecological Chemistry, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany
a r t i c l e
i n f o
Article history: Received 28 May 2009 Received in revised form 11 September 2009 Accepted 17 September 2009 Available online 12 October 2009 Keywords: Azo dyes Adsorption COD fractions Ozone oxidation
a b s t r a c t A treatability study for highly polluted and recalcitrant azo reactive dye-baths from cotton textile dyeing processes was conducted by using fixed and up-flow fluidized bed type reactors packed with brown coal. Ozone oxidation was carried out to assess the combination of biological and chemical oxidation. COD removal efficiencies ranged from 70% to 93%, and up to 99% color removal was attained. At a COD loading rate of 25.5 10 6 gCOD/m2-d, COD removal was 85%. Breakthrough of the brown coal used occurred at total organic loading of 0.090 gCOD/g coal. Biodegradable and inert COD fractions of the remazol dyebath were assessed by BOD28 and oxygen uptake rate (OUR) measurements. 50% of total COD was initially inert. The inert fraction was reduced by adsorption and ozone oxidation by 65% and 40%, respectively. Brown coal is an inexpensive material and the system has economical and operational advantages as compared to treatment options such as advanced oxidation processes (AOPs) using UV, O3, H2O2 or electrocoagulation. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Wastewater of textile dyeing and finishing industries consists of unbound colorants, reaction products, dye impurities, auxiliaries and surfactants. These effluents exhibit very slow degradation kinetics and resistance to conventional biological treatment processes (Ciardelli and Ranieri, 2001; Alaton et al., 2002; Zhang et al., 2004; Baban et al., 2004; Turhan and Turgut, 2007, 2009), and conventional physico-chemical treatment has not been proved as an effective method for decolorization and organic matter removal (Krull et al., 1998; Koch et al., 2002). Reactive dyes, among them commonly used azo dyes, are considered to be the problematic components in the wastewater since, in general, only 40–90% of dye is fixed to the fabric during dyeing; the rest appears in the wastewater causing high chemical oxygen demand (COD) and color. (Wu and Wang, 2001; Wang et al., 2002). The relatively low BOD5 (biochemical oxygen demand)/COD ratio (<0.1) of azo reactive dyes implies a very low level of biodegradability (Zhang et al., 2004). Pollution prevention by in-plant measures is the main aim of modern environmental management and is gaining in importance over the ‘‘end of pipe” treatment approach. In this context, segregation of dye-baths, with strong pollutant characteristics, from the waste stream could become highly profitable and treatment * Corresponding author. Tel.: +90 262 6772904; fax: +90 262 6412309. E-mail address: [email protected] (A. Baban). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.09.060
and reuse of relatively clean streams for process purposes may become feasible. Hence, reduction of recalcitrant organic constituents of dye-baths and decolorization have become the focus of research. For example, attempts were made to reduce pollutants by implementation of process modifications or by replacing undesirable chemicals with more environmentally friendly ones (Blackburn and Burkinshaw, 2002). Studies, on azo dye effluents have included physico-chemical techniques, UV or H2O2, oxidations and/or their combinations, electrocoagulation and adsorption (Koch et al., 2002; Georgiou et al., 2002; Neamtu et al., 2002, 2004; Baban et al., 2003; Sostar-Turk et al., 2005; Ozdemir et al., 2004; Yang and McGarrahan, 2005; Alaton et al., 2009). Biological degradation of azo dyes by anaerobic or aerobic processes have also been investigated and combined biological and physico-chemical treatment options for azo dyes have also been studied (Krull et al., 1998; Georgiou et al., 2004). The results revealed that effective decolorization along with about 70% COD removal are achievable by oxidation processes. In this study, treatability of dye-baths by oxidative and biological methods were investigated to represent the condition of segregated dye-bath stream treatment and to facilitate the advantages of water segregation and reuse. Hence, the objectives of the study were assessment of biodegradability of azo dye-baths, determination of the treatability by using a cheap material for adsorption and biofilm attachment media and enhancement of biodegradability by ozone oxidation. For this purpose, samples from defined process lines of remazol dye-bath effluents were collected from two
1148
A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152
different textile plants (enterprise I and II) in Istanbul, Turkey. The enterprises are classified under the knit fabric dyeing and finishing subcategory, involving cotton, polyester and polyamide products. Two reactors, having different configurations were set up and operated to treat various concentrations of dye-bath effluents. Brown coal char (lignite), as a low price material, was used in the reactors as packing medium.
a
air supply from the central facility effluent to the drain
influent
2. Methods
peristaltic
2.1. Reactor configuration and operation
pump sintered glass
Vreactor=15.4 l
porous diffusers
packed with 6.0 kg brown coal
Two types of reactor configurations were used. The fixed bed reactor was made of plexiglas, having dimensions of 35 22 25 cm (height). Three baffles were installed in the reactor. The reactor was filled with 6.0 kg of brown coal, which was provided by Rheinbraun Brennstoff GmbH, Köln, Germany. The brown coal had a typical surface area of 300 m2/g, approximate particle size of 1–1.5 mm, specific density of 1.093 g/cm3 and porosity of 41%. The surface area of the brown coal was less than the typical values for activated carbon, which are normally higher than 400 m2/g. The depth of the bed for the fixed bed reactor was 20 cm with a slight expansion of 2 cm during operation. The overall usable volume of the reactor was 15.4 l. Air was introduced from the bottom of each compartment smoothly by circular sintered glass porous diffusers. The up-flow fluidized bed reactor had a diameter of 11 cm, height of 48 cm and a working volume of 3.3 l, was made of plexiglas and contained 0.5 kg of brown coal. The feed solution was supplied from the bottom by a peristaltic pump. Air was supplied through a sintered glass porous plate placed at the bottom. The schematic drawings of both reactors are illustrated in Fig. 1. Since, brown coal included some calcium oxide, and dissolution might increase pH, packing media was first washed with slightly acidified (HCl) tap water having a pH of around 6.0. Both reactors were initially fed by a synthetic solution representing similar pollutant characteristics as domestic wastewater. Activated sludge initially was added to enhance biofilm growth to the feed solution at a rate of 3 l of settled activated sludge to 15 l of feed solution. It is noted that extensive growth of attached bacteria was observed in the first compartment of the fixed bed reactor. This situation is attributable to the low amount of organic matter remaining for the downstream compartments due to the adsorption capacity of the brown coal packing material. Once a biofilm was established, acclimatization of the bacteria to dye-baths was accomplished by gradually increasing the amount of feed solution. The reactors were then operated with 10%, 30% and 100% remazol dye-bath solutions. The feed solution was neutralized with HCl, prior to the feeding.
tive oxygen consumption was determined. The incubated samples were further analyzed to assess the completion of biodegradation. For this purpose incubated samples were mixed with acclimatized and settled activated sludge. The organic matter/ microorganism ratio (Co/Xo) of the mixture was adjusted to 0.6. The OUR’s were measured at 20 min intervals for 3 h to determine the remaining biodegradable organic matter. The same procedure was applied to a blank solution with identical amount of distilled water and activated sludge as control. Hence, once the biodegradable portion was consumed, the remaining part was assumed to consist of the inert fraction.
2.2. Methods of analysis
3. Results and discussion
As the dye-bath solutions contained chloride higher than 1 g/l, COD analysis were carried out according to the DIN 38 409 H412 to avoid interference. Analyses were carried out in triplicate. Absorbance measurements were conducted at the wavelengths, 436, 525 and 625 nm for the assessment of color characteristics. Dissolved oxygen (DO) was measured by a microprocessor, oximeter (WTW MultiLine P4, Weilheim, Germany). Ozone was generated from dried air by an ozone generator (Erwin Sander Elektroapparatebau, Ueltze., Germany). Ozone oxidation was carried out in a 1.2 l glass reactor by bubbling ozone/air mixture at a volume stream of 20 mg/l through a sintered glass (pore size 50–80 lm). Bio-degradation of dye-bath samples was measured during 28 days incubation time in ‘‘Sapromat, Type D” (Voith, Germany). Three cells were used for each sample, and daily cumula-
3.1. Pollutant removal efficiencies of the reactors
feed container
b
effluent to drain overflow to drain
V=3.3 l packed with 0.5 kg brown coal brown coal bed
sintered glass plate peristaltic
influent
feed pump air supply from central feed solution
facilities
container Fig. 1. Schematic illustration of the laboratory models: (a) fixed bed reactor, and (b) fluidized bed reactor.
The remazol dye-bath concentrations and the operational conditions of the reactors are illustrated in Table 1. Various dye-bath concentrations from the two enterprises were investigated for the assessment of treatability of dye-baths. The influent and effluent COD concentrations of the reactors operated under these conditions with different strengths of remazol dye-baths are indicated in Fig. 2. The obtained COD removal efficiencies ranged from 70% to 93%. The fixed and fluidized bed reactor effluents for the enterprise-II had COD concentrations of 124 and 168 mg/l corresponding to 90% and 83% COD removal respectively. The high COD removal efficiency was due to the biofilm and the adsorption capacity of brown coal having high surface
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152 Table 1 Operational data of the reactors fed with remazol dye-baths. Reactor
Fixed bed
Fluidized bed
Source
Enterprise-I
Enterprise-I
Enterprise-I
Enterprise-II
Enterprise-II
Enterprise-II
Enterprise-II
Conc. (%) Flow (l/d) HRT (h)
10 25 14.8
30 15 24.6
100 12 30.8
100 12 30.8
10 2.75 28.8
30 2.5 31.7
100 4.0 19.8
400
color reduction efficiency was around 99% for the fixed bed reactor. The efficiency was slightly lower for the fluidized bed reactor. This condition might be explained by different reactor configurations and the higher amount of packing material in the fixed bed reactor. The obtained efficiencies are considered to be quite high as compared to the processes such as ozonation, H2O2 and UV oxidation. The initial conductivity of 100% dye-bath was about 112 mS/cm, after the treatment a slight decrease of up to 30% was observed. The pH of influent and effluents was in the range of 7.5–8.0. A slight increase in pH for the effluent was detected.
200
3.2. Breakthrough conditions
1400 1200
COD, mg/l
1000
influent efffluent
800 600
0
A B C D E F G enterprise no. remazol dye bath conc. - reactor type
Fig. 2. Influent and effluent COD concentrations for the reactors operated with remazol dye-baths (A, B, C: 10%, 30% and 100% dye-baths of enterprise-I treated by fixed bed reactor, respectively, D: 100% dye-bath of enterprise-II treated by fixed bed reactor, E, F, G: 10%, 30% and 100% dye-baths of enterprise-II treated by fluidized bed reactor, respectively).
area. COD removal efficiencies as a function of COD loading rates are shown in Fig. 3. The removal efficiency increased with the increasing influent COD concentration particularly for the fixed bed reactor. Comparable COD removal efficiency and decolorization potential was attained by Krull et al. (1998), using an anoxic/aerobic sequential batch reactor for remazol dye-bath. The system had a total process cycle time of one week and partial oxidation was achieved with ozone. In the current study, overall hydraulic retention time was up to 1.3 days for the brown coal bed reactors. COD loading rate of 25.5 10 6 g/m2-d resulted in around 85% COD removal efficiency. The color reduction was monitored by absorbance measurements. The influent and effluent average color characteristics for the two reactors operating with the different dye-baths from the two enterprises are illustrated in Fig. 4. The
COD removal efficiency
120 100 80 60 40 20 0 0,00E+00
1,00E-05 2,00E-05 COD loading rate, g/m2.d
3,00E-05
Fig. 3. COD removal efficiency as a function of COD loading rate for fixed and fluidized bed reactors.
The sorption capacity of the coal media was saturated after a period causing a decrease in removal efficiency and leading to occurrence of breakthrough conditions. The characteristics of this phase were determined when the reactor was operated with raw 100% remazol dye-bath of enterprise-II (initial COD 1200 mg/l). The breakthrough phase was monitored by absorbance measurements of the effluent and recording the corresponding amount of dye-bath inlet. Feeding was terminated as the reduction in absorbance was about 60–70%. This state was defined as the occurrence of breakthrough. Volumetric and organic loading rates were calculated based on the unit coal weight. The results are summarized in Table 2. Throughout the operation period of the reactor, measured effluent absorbance values showed 83–88% reduction, whereas, after 17 days of operation the reduction in absorbance started to drop rapidly to 55–70%. The data presented in Table 2 may be used as a reference for calculation of the time period for the replacement or regeneration of the coal bed. Bacterial activity might also occur to help to restore adsorption capacity for prolonged operation times to some extend. 3.3. Biodegradability studies A series of experiments were conducted to assess the biodegradability of dye-baths. For this purpose, BOD28 measurements were carried out on 30% remazol dye-bath from the enterprise-I, its effluent after the treatment by the fixed bed reactor, raw 100% remazol dye-bath from the enterprise-II and 100% remazol dye-bath after 30 min ozone oxidation. The results of BOD28 measurements are outlined in Table 3. Whereas, the results of OUR measurements of the samples incubated for 28 days in the respirometer and the blank (tap water) are illustrated in Fig. 5. The difference for OUR’s with time for blank and treated and untreated dye-bath samples are negligible. For the ozonated and raw remazol dye-bath samples from enterprise-II slightly higher OURs were measured than for the 30% dye-bath samples from enterprise-I. This situation is thought to be caused by the different initial COD concentrations of the samples. Remazol (100%) dyebath effluents had almost four times higher initial COD concentration than the 30% enterprise-I textile dye-bath. Consequently, it was assumed that almost all the biodegradable fraction of COD was used up throughout the incubation period by the bacterial action in the respirometer for all of the samples. Hence, the difference between the initial COD (CODT) and the BOD28 concentration
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152
a
2000 1800 abs. at 625nm inf.
absorbance, m-1
1600
abs. at 525nm inf.
1400
abs. at 436nm inf.
1200 1000 800 600 400 200 0 A
abs. at 436nm inf. abs. at 525nm inf.
B
C
D
abs. at 625nm inf.
E
F
G
enterprise no. - remazol dye bath conc. - reactor type
b
300 275
absorbance, m-1
250 225
abs. at 625nm eff.
200
abs. at 525nm eff.
175
abs. at 436nm eff.
150 125 100 75 50 25 0 A
abs. at 436nm eff. abs. at 525nm eff.
B
C
D
E
abs. at 625nm eff.
F
G
enterprise no. - remazol dye bath conc. - reactor type Fig. 4. Influent (a) and effluent (b) average color characteristics (A, B, C: 10%, 30% and 100% dye-baths of enterprise-I treated by fixed bed reactor, respectively, D: 100% dyebath of enterprise-II treated by fixed bed reactor, E, F, G: 10%, 30% and 100% dye-baths of enterprise-II treated by fluidized bed reactor, respectively).
Table 2 Breakthrough state of brown coal in up-flow fluidized bed reactors. Parameters Effluent absorbance and % reduction based on initial absorbance measured at 625 nm 525 nm 436 nm Operation time (days) Total volume of dye-bath fed (l) Total volumetric feeding to reach breakthrough (l/g-coal) Total organic loading to reach breakthrough (gCOD/g coal)
Enterprise-II remazol dye-bath (100%)
763.9 m 660.1 m 539.1 m 18 37.2 0.0744 0.090
1 1 1
(56.9%) (62.1%) (71.0%)
of each sample was designated as the inert COD fraction (CODI) of the dye-bath. CODI, as a fraction of CODT for raw and 30-min ozonated dyebaths ranged between 40% and 50%, which indicates a considerable amount of non-biodegradable fraction. Although, ozone oxidation was not significantly effective on COD removal, CODI fraction was reduced by 10% or biodegradability was increased by 10% as a result of 30 min of ozonation. Removal of biodegradable COD and a fraction of CODI were achieved by treating the dye-bath with brown coal packed reactors. BOD28/CODT ratio is considered to be an indication of biodegradability. CODI may also be determined by the method given by Orhon et al. (1994, 1999). The method involves biological oxidation of substrate by acclimatized micro-organisms for prolonged
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A. Baban et al. / Bioresource Technology 101 (2010) 1147–1152 Table 3 The results of biodegradability studies and OUR (oxygen uptake rate) measurements. Parameters
Enterprise-I 30% remazol inf. to fixed bedreactor
Enterprise-I 30% remazol eff. from fixed bed reactor
Enterprise-II 100% remazol dye-bath
Enterprise-II 100% remazol 30 min ozonated
BOD28 (mg/l) CODT (mg/l) BOD28/CODT (%) CODI (mg/l) CODI (% of CODT)
140 270 51.8 130 48.2
15 62 24.2 47 75.8
602 1212 49.7 610 50.3
562 935 60.1 373 39.9
CODI: inert COD; CODT: total COD.
OUR, mg/l.h
a
fraction. The reactors were efficient in removing CODI. 65% of the CODI initially present in the dye-bath was removed by the brown coal bed reactor and about 40% reduction was achieved by 30 min ozonation.
10 9
blank
8
enterprise-II 100% remazol
7
enterprise-II 100% 30min. ozonated
Acknowledgements
6 5 4 3 2 1 0
0
25
50
75
100
125
150
175
200
225
t, min
OUR, mg/l.h
b
10 9 8 7 6 5 4 3 2 1 0
This work has been conducted at the GSF-Institute of Ecological Chemistry (currently Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Institute of Ecological Chemistry) and was partly funded by the German Federal Ministry of Education, Science, Research and Technology (BMBF), within the framework of the agreement between TUBITAK (The Scientific and Technical Research Council of Turkey). Thanks are extended to the International Bureau of Research Center Jülich GmbH, Germany for excellent management and to Prof. Dr. D. Orhon for his valuable comments.
blank
References influent, 30% enterprise-I remazol dye-bath effluent, 30% enterprise-I remazol dye-bath
0
25
50
75
100
125
150
175
200
225
t, min Fig. 5. Oxygen uptake rate (OUR) after incubation for BOD28 measurements: (a) enterprise-II 100% raw remazol dye-bath and 30 min ozonated 100% remazol dyebath, and (b) enterprise-I 30% influent and effluent of the fixed bed reactor.
time periods in batch reactors. Although, the presented approach provided rapid and practical way for the determination of CODI, the inert fractions determined by the present study is probably slightly less than the values that would have been obtained by the method suggested in the literature since the inert COD determination in batch reactors is associated with a much longer biodegradation period as compared to the BOD28 determination in the incubator. 4. Conclusions Treatment of remazol reactive dye-baths by using brown coal packed reactors is advantageous to obtain high removal efficiencies that may not be easy to achieve by conventional systems. The packing material can be replaced, disposed off or regenerated at relatively low costs. The system has operational ease over conventional treatment options. A new approach, based on respirometric measurements, was carried out to determine CODI
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