ADVANCED OXIDATION OF TEXTILE DYEING EFFLUENTS: COMPARISON OF Fe +2 /H 2 O 2, Fe +3 /H 2 O 2, O 3 AND CHEMICAL COAGULATION PROCESSES

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1 ADVANCED OXIDATION OF TEXTILE DYEING EFFLUENTS: COMPARISON OF Fe +2 /H 2 O 2, Fe +3 /H 2 O 2, O 3 AND CHEMICAL COAGULATION PROCESSES Seval K. Akal Solmaz, Gökhan E. Üstün, Aşkın Birgül and Taner Yonar * Uludag University, Engineering and Architecture Faculty, Environmental Engineering Department, Görükle, Bursa 159, Turkey ABSTRACT In this study, the treatment efficiency of different advanced oxidation (Fe +2 /H 2 O 2, Fe +3 /H 2 O 2, O 3 ) and chemical coagulation processes were investigated. Wastewater samples were taken from two different textile industries. Optimum efficiencies in color and COD removal were determined based on the applications of different chemical species and ph. 1 mg/l FeSO 4 at ph 12 has provided the maximum color and COD removal efficiency in chemical coagulation experiments for textile industry 1. For textile industry 2, maximum color and COD removal efficiencies were obtained with Fe +2 /H 2 O 2 (Fenton) process at ph 3 (FeSO 4 2 mg/l and H 2 O 2 2 mg/l dosages). The operating costs of all proposed treatment systems were also evaluated in this study. KEYWORDS: Textile industry; Fe +2 /H 2 O 2, Fe +3 /H 2 O 2, ozonation, chemical coagulation, treatment costs. INTRODUCTION In the scope of volume and the chemical composition of the discharged effluent, the textile dyeing and finishing industry is one of the major polluters among industrial sectors. Textile industry dyes are intentionally designed to remain photolytically, chemically and biochemically stable, and thus are usually not amenable to biodegradation [1]. Like many other industrial effluents, textile industry wastewater varies significantly in quantity, but additionally in composition [2]. Textile wastewater is strongly colored which creates an environmental as well as aesthetic problem. As regulations are becoming ever more stringent, the need for technically and economically more efficient means of decolorization and mineralization is obvious. Effluents from the dyeing and finishing processes in the textile industry are known to contain strong color, high amounts of surfactants, dissolved solids, fluctuating temperature, high ph and possibly heavy metals (e.g. Cu, Cr, Ni) [3]. Existing physicochemical technologies, such as membrane filtration or activated carbon adsorption, are expensive and commercially unattractive. Furthermore, these processes just transfer pollutants from one phase to another rather than eliminating them from the water matrix. Recovery and reuse of certain chemical compounds present in dye bath effluents is currently under investigation [4]. At present, so called ''integrated processes'' involving various combinations of biological, physical and chemical treatment methods are used for decolorization of textile effluents but with limited success [5-7]. The chemical limitations of conventional chemical oxidation techniques can be overcome by development of so-called advanced oxidation processes (AOPs) which use strong oxidizing agents (O 3, H 2 O 2 ) and/or catalysts (Fe +2, Fe +3, Mn, TiO 2 ) in the presence or absence of an irradiation source [8]. Homogenous (Fenton's reagent, light-assisted Fenton's oxidation, H 2 O 2 /UV treatment, ozonation at high ph etc.) and heterogeneous (semiconductor-mediated photocatalysis) advanced oxidation systems have been thoroughly and comparatively evaluated for a variety of organic compounds and wastewaters in the past. Also several investigations have demonstrated that AOPs are effectively removing color and partially organic content of dyestuffs [9,]. The oxidation system based on the Fenton s reagent (hydrogen peroxide in the presence of a ferrous salt) has been used for the treatment of both organic and inorganic substances under laboratory conditions as well as real effluents from different resources like chemical manufacturers, refinery and fuel terminals, engine and metal cleaning etc. [11]. Also, the oxidation system can be effectively used for the destruction of toxic wastes and nonbiodegradable effluents to render them more suitable for a secondary biological treatment [12]. Fenton process can be useful with regard to both higher color and COD removal efficiencies, even at lower concentrations and simple treatment plant modifications [13, 14]. It should again be noted that the importance of Fenton s reagent as an oxidation system cannot be underestimated and the oxidation degree can be substantially increased when used in combination with other advanced oxidation techniques, such as photocatalysis and/or ultrasonic irradiation. Most importantly, it is also applicable to the solar-driven photocata- 1

2 lytic methods and, hence, this combination (photo Fenton oxidation) can be relatively cheaper than the other advanced oxidation processes [15]. Ozone is a very powerful oxidizing agent (E = 2.7 V) that can react with most species containing multiple bonds (such as C=C, C=N, N=N, etc.), but not with singly bonded functionality, such as C C, C O, O H, at high rates. This is mainly due to the fact that there is no easy chemical path-way for the oxidation to take place. Ozone can be used for treatment of effluents from various industries relating to pulp and paper production (bleaching and secondary effluents), shale oil processing, production and usage of pesticides, dye manufacture, textile dyeing, production of anti-oxidants for rubber, pharmaceutical production etc [16]. Among the variety of the chemical oxidation process in-vestigated for the treatment of the dyes and dye-house effluent, ozonation at alkaline ph offers several advantages [17-2], ozone decomposes quickly to free radicals and reacts with dye molecules at diffusion-controlled rates [21, 22]. In this manner, ozone can be effectively applied at the natural alkaline ph of most dye-house effluents eliminating cost associated with ph adjustment [23]. However, inorganic salts present in dye-house effluents (Na 2 SO 4, Na 2 CO 3 or NaCl) at high concentrations (25- g/l Na 2 SO 4 or NaCl, and 2- g/l Na 2 CO 3 ) [24] could principally inhibit the effective decolorization and mineralization of actual dyehouse wastewater by acting as free radical scavengers. A major limitation of ozonation process is the relatively high cost of ozone generation coupled with the very short halflife period of ozone. Thus, ozone needs to be generated always at site. However, maximum concentration of ozone produced in air or oxygen is approximately 4-8%, respectively [25] which coupled with very low (5-%) energy efficiency of the production [26, 27] and requirement of absolutely dry input (oxygen or air with low dew point of approximately -52 to -58 C) may result in an uneconomical operation for the use of ozone alone in large-scale wastewater treatment applications. The aim of this study is to compare the performance of chemical coagulation, Fenton s oxidation (Fe +2 /H 2 O 2, Fe +3 /H 2 O 2 ) and ozonation for the removal of COD and color from two different textile effluents. MATERIALS AND METHODS Composite wastewater samples were taken at different time periods from the discharge point of a wastewater treatment plant of two different textile factories in Bursa, Turkey. Existing wastewater treatment plants have physical, chemical and biological treatment units on site. Wastewater treatment plant 1 (WWTP 1) is one of the biggest towel producers in Turkey and making yarn dyeing using only reactive dyes. Consequently, single-type wastewater originated from this plant. Wastewater treatment plant 2 (WWTP 2) is also using reactive dyes and disperses them for dyeing wastewater originating from this plant. 12 tons of yarn/day (75% cotton and 25% polyester) is the production rate in this dyeing plant. The effluent characteristics of WWTP 1 and 2 are given in Table 1. TABLE 1 - Characterization of wastewater samples. Parameter Unit WWTP1 WWTP2 Effluent Effluent ph COD mg/l 78 1 SS mg/l 37 TDS mg/l Alkalinity mg/l CaCO 3 7 Hardness mg/l CaCO 3 1 Chloride mg/l Conductivity µs/cm Absorbance ( nm) 1/cm SS = suspended solids, TDS = total dissolved solids. The WWTP 1 and 2 meet the discharge criteria enforced by the Turkish Water Pollution Control Legislation (WPCL), and these treatment plants have shown appropriate treatment performances. Treatment performances of plants are appropriate for existing discharge regulations. Chemicals used in the experiments were H 2 O 2 (hydrogen peroxide, 35% w/w; Merck, Darmstadt, Germany), FeSO 4.7H 2 O (Merck), FeCl 3.6H 2 O (Merck), NaOH (Merck), and H 2 SO 4 (Merck). The experiments were undertaken at room temperature (2 2 C) on the wastewater samples, in order to remove color and COD. Experiments were carried out on the effluent samples by applying chemical precipitation, Fenton, Fenton-like processes and ozonation. Coagulation Experiments In chemical coagulation experiments, Jar test apparatus (Velp Scientifica FC6S), FeSO 4.7H 2 O (Merck) and FeCl 3.6H 2 O (Merck) were used at different dosages between -3 mg/l. Optimum ph and reagent dosages that provide best color and COD removal were determined. Each chemical (different dosages) was examined separately in 1 L wastewater samples. The wastewater samples were left to precipitation for 1 h, after 5 min of rapid mixing at rpm and 3 min of slow mixing at 3 rpm were applied, respectively. At the end of the 1 h precipitation, supernatants were analyzed for COD and color removal. Fenton (Fe +2 /H 2 O 2 ) and Fenton-like (Fe +3 /H 2 O 2 ) Experiments Fenton and Fenton-like experiments were conducted using different FeSO 4 and H 2 O 2 dosages and phs. The ph values were manually adjusted to desired range (2-7) using 1N H 2 SO 4 and/or NaOH before starting the experiments. During determination of optimum ph value, FeSO 4 and H 2 O 2 dosages were fixed for WWTP effluent 1 (E1) 1 mg/l and for WWTP effluent 2 (E2) 2 mg/l. After the optimum ph was determined, FeSO 4 and H 2 O 2 dosages were changed between -3 mg/l for E1 and - mg/l for E2, respectively. Two hour sedimentation was applied following the ph adjustment (7.5-8) after 2 min of rapid mixing at rpm and 2 min of slow mix- 2

3 ing at 3 rpm in Jar-test setup. After 2 h precipitation, ml supernatant was taken for COD and color analyses. Ozonation Experiments The ozonation experiments were performed in a 2 L capacity cylindrical column made of Pyrex glass. An Opal OG3 model ozone generator with a production rate of 3 g/h produces the ozone needed in the reaction. The ozone produced by using oxygen with a purity of 99.5% was bubbled into the reactor by means of a sintered glass plate diffuser. Teflon tubing line was used for the connection between ozone generator and reactor. All experiments were performed using 1.5 L wastewater samples. Inlet and outlet of ozone were directed to gas washing bottles filled with 2% KI solutions for the determination of ozone concentration. Ozone concentration was measured by iodometric method purposed by IOA (International Ozone Association) [28]. The experiments with ozone alone were carried out at varying ph values 3-12 at 2 C. COD and color analyses were undertaken on samples collected at specific times. Analytical Procedure Due to interferences of ferrous ions and H 2 O 2 with the analytical measurements, ph of supernatant increased with the addition of NaOH around >11 for the precipitation of ferrous ions as Fe (OH) 3 and MnO 2 powder was added to destroy residual H 2 O 2 in the treated solution [29, 3]. The concentration of residual H 2 O 2 in the test solution was controlled by use of test strips (Merck Merckoquant Peroxide Test). Before each analysis, wastewater samples were filtered on.45 µm Millipore membranes (Millipore, Billerica, MA, USA) to remove Fe(OH) 3 and MnO 2. Color values of samples were determined with UV-VIS spectrophotometer (Jenway, Model 65, Barloword Scientific, Jenway, UK) according to the Method 212 C in Standard Methods (SM). COD (SM 522C), SS (SM 25B), TDS (SM 25C), alkalinity (SM 232B), hardness (SM 23C), and chloride (SM -Cl - -B) were measured in accordance with Standard Methods [31]. RESULTS AND DISCUSSIONS Coagulation Processes Coagulation processes have been used intensively for the treatment of textile effluents, in general with limited COD and color removal efficiencies [32, 33]. In chemical precipitation, FeSO 4.7H 2 O (Merck) and FeCl 3.6H 2 O (Merck) coagulants were used with varying dosages under varying ph conditions. During the experiments to determine optimum ph value, FeSO 4 and FeCl 3 dosages were fixed at 2 mg/l for E1 and mg/l for E2, respectively. The results are shown in Figs. 1 (a) and (b). The optimum COD and color removal efficiencies were obtained at ph 12. At this ph value, COD and color removals were obtained for E1 as 57 and 83%, respectively, when FeSO 4 was used as coagulant, and 53 and % for FeCl 3, respectively. In the same way, results for E2 were 58 and 79%, respectively, with FeSO 4 as coagulant, but 52 and 76% for FeCl 3, respectively. After optimum ph was determined as 12 for FeSO 4 and FeCl 3, varying coagulant dosages between -3 mg/l for E1 and E2 were applied. COD and color removal efficiencies obtained at different dosages of FeSO 4 and FeCl 3 are given in Figs. 2 (a) and (b). Optimum color and COD removal efficiencies were determined when FeSO 4 and FeCl 3 were used for E1 (1 mg/l) and for E2 (2 mg/l), respectively. At these dosages for FeSO 4, COD removal efficiency was found to be 48% for E1 and 71% for E2, and those of color removal were found to be 94% for E1 and 97% for E2, respectively. At these dosages for FeCl 3, COD removal efficiency was found to be 71% for E1 and 56% for E2, color removal efficiencies were found to be 89% for E1 and 88% for E2, respectively. COD removal, % FeSO4 E1 FeSO4 E2 FeCl3 E1 FeCl3 E ph FIGURE 1a - COD removal efficiencies fixed FeSO 4 and FeCl 3 dosages at different ph values (for E1 FeSO 4 =2 mg/l and FeCl 3 =2 mg/l, for E2 FeSO 4 = mg/l and FeCl 3 = mg/l). 3

4 Color removal, % FeSO4 E1 FeSO4 E2 FeCl3 E1 FeCl3 E ph FIGURE 1b - Color removal efficiencies fixed FeSO 4 and FeCl 3 dosages at different ph values (for E1 FeSO 4 =2 mg/l and FeCl 3 =2 mg/l, for E2 FeSO 4 = mg/l and FeCl 3 = mg/l). FeSO4 E1 FeSO4 E2 FeCl3 E1 FeCl3 E2 COD removal, % Chemical dosages, mg/l FIGURE 2a - COD removal efficiencies obtained at varied dosages of FeSO 4 and FeCl 3. FeSO4 E1 FeSO4 E2 FeCl3 E1 FeCl3 E2 Color removal, % Chemical dosages, mg/l FIGURE 2b - Color removal efficiencies obtained at varied dosages of FeSO 4 and FeCl 3. 4

5 Akal Solmaz et al. [34] reported optimum dosages of 1 mg/l FeCl 3, 7 mg/l for FeSO 4 and mg/l for Al 2 (SO 4 ) 3.18H 2 O in wastewater containing mostly textile Organized Industrial District (OID) effluent. At these dosages, COD removal efficiencies were determined to be 56%, 42% and 54%, respectively. Ciner et al. [35] studied treatability of textile dyeing wastewater and found optimum dosages of mg/l FeCl 3, mg/l for FeSO 4 and Al 2 (SO 4 ) 3.18H 2 O. COD removal efficiencies were 87%, 75% and 62%, respectively. In another study, conducted with textile effluent, at ph 12, optimum dosages were determined to be 4 mg/l for FeSO 4 and 3 mg/l for FeCl 3 in chemical coagulation processes. At these dosages, COD and color removal efficiencies of 62 and 99% were observed for FeSO 4, but 64 and 91% for FeCl 3, respectively [36]. In this study, COD and color removal results of chemical coagulation studies are shown parallel to literature. Fenton and Fenton-like Processes Affecting parameters the Fenton process are operating ph and dosages of FeSO 4 and H 2 O 2. Operating ph of the system has been observed to significantly affect the degradation of pollutants [12,37]. The optimum ph has been observed to be 3 in the majority of the cases [38, 39], and hence is recommended as the operating ph. At operating ph of >4, the decomposition rate decreases because of the decrease of the free iron species in the solution, probably due to the precipitation of ferric oxyhydroxides which inhibit the regeneration of ferrous ions. Also, the oxidation potential of hydroxyl radicals ( OH) is known to decrease with an increase in ph []. Usually, the rate of degradation increases with an increase in concentration of ferrous ions [41,42] though the extent of the increase is sometimes observed to be marginal above a certain concentration as reported [43,44]. Also an enormous increase in the ferrous ions will lead to an increase in unutilized quantity of iron salts, which will contribute to an increase in TDS content of the effluent stream, and this is not permitted. Concentration of hydrogen peroxide plays a more crucial role in deciding the overall efficacy of the degradation process. Usually, it has been observed that the percentage degradation of the pollutant increases with an increase in hydrogen peroxide dosage [38,39,41,43-45]. For many chemicals, ideal ph for the Fenton reaction is between 3-4, and the optimum catalyst to peroxide ratio is usually 1:5 wt/wt [16]. During the determination of optimum FeSO 4 and FeCl 3 dosages, studies were conducted at constant H 2 O 2 dosages of mg/l for E1 and 2 mg/l for E2, respectively, at ph 3. Different dosages of FeSO 4 and FeCl 3 from - 3 mg/l were applied. Removal efficiencies of color and COD at different dosages of FeSO 4 and FeCl 3 and constant concentration of H 2 O 2 are illustrated in Figs. 3a and 3b. As seen from Fig. 3a for E1, maximum COD and color removal efficiencies were obtained at 1 mg/l FeSO 4 for Fenton process and 2 mg/l FeCl 3 for Fenton-like process, respectively. For E2, maximum COD and color removal efficiencies were obtained at 2 mg/l FeSO 4 and FeCl 3 for Fenton and Fenton-like process (Fig. 3b). During the determination of optimum H 2 O 2 dose, studies were carried out at constant FeSO 4 and FeCl 3 dosages (1 mg/l and 2 mg/l for E1, and 2 mg/l FeSO 4 and FeCl 3 for E2). Different dosages of H 2 O 2 from -3 mg/l were applied. Efficiencies of color and COD removal at various dosages of H 2 O 2 and constant concentrations of FeSO 4 and FeCl 3 are illustrated in Fig. 4a for E1, and 4b for E2. As seen from Figs. 4a and 4b, maximum COD and color removal efficiencies for constant FeSO 4 and FeCl 3 were obtained at 1 mg/l H 2 O 2 for E1 and 2 mg/l H 2 O 2 for E2. COD and color removal efficiencies were determined to be 49 and 94% for Fenton process, as well as 45 and 94% for Fenton-like process, respectively. Removal,% COD removal Fenton Color removal Fenton Fe salts dosages,mg/l COD removal Fenton-like Color removal Fenton-like FIGURE 3a - Efficiencies of COD and color removal due to the varied concentrations of FeSO 4 and FeCl 3 at Fenton process for E1 (ph=3, H 2 O 2 = mg/l, t=2 C, 2 min of rpm rapid mixing, 2 min of 3 rpm slow mixing). 5

6 Removal, % COD removal Fenton COD removal Fenton-like Color removal Fenton Color removal Fenton-like H2O2 dosages,mg/l. FIGURE 3b - Efficiencies of COD and color removal due to the varied concentrations of FeSO 4 and FeCl 3 at Fenton process for E2 (ph=3, H 2 O 2 =2 mg/l, t=2 C, 2 min of rpm rapid mixing, 2 min of 3 rpm slow mixing). 9 COD removal Fenton Color removal Fenton COD removal Fenton-like Color removal Fenton-like Removal,% Fe salts dosages,mg/l FIGURE 4a - Efficiencies of COD and color removal due to the varied concentrations of H 2 O 2 at Fenton process for E1 (ph=3, FeSO 4 =1 mg/l, FeCl 3 =2 mg/l, t=2 C, 2 min of rpm rapid mixing, 2 min of 3 rpm slow mixing). 6

7 Removal, % COD removal Fenton COD removal Fenton-like Color removal Fenton Color Removal Fenton-like H2O2 dosages, mg/l FIGURE 4b - Efficiencies of COD and color removal due to the varied concentrations of H 2 O 2 at Fenton process for E2 (ph=3, FeSO 4 =2 mg/l, FeCl 3 =2 mg/l, t=2 C, 2 min of rpm rapid mixing, 2 min of 3 rpm slow mixing). The optimal ratios of chemicals in the Fenton process recommended in the literature are ratios of H 2 O 2 /catalyst from :1 to :1 [46-49]. In this study, ferrous sulphate dosage was based on initial molar ratio H 2 O 2 /Fe +2 of 8/1 for both effluents, respectively. However, initial COD and color pollutant parameter values of E2 are being higher than that of E1 because in Fenton process Fe and H 2 O 2 concentrations are getting higher. Many authors have worked with Fenton s reagent and found different COD and color removal. For example, Lin et al. [43] found optimum concentrations of FeSO 4 and H 2 O 2 as 9 and mg/l, at ph 3. Meric et al. [] found optimum ratio of H 2 O 2 /Fe +2 =.55, and at this dosage, COD and color removal efficiencies were determined to be.6 and 99%, respectively. Akal Solmaz et al. [36] found optimum dosages of mg/l for FeSO 4 and 2 mg/l for H 2 O 2, respectively, as well as corresponding COD and color removal rates of 78 and 95%, respectively. Macro and/or micro pollutants present in the reaction medium may trap. OH. Therefore, inorganic compounds in medium, such as Cl -, HCO - 3, CO -2 3, and S -2, act as effective radical scavengers during the application of AOPs [51]. According to Figs. 3a and 4a, there is almost no difference between Fe 2+ and Fe 3+ by COD removal, although the OH-radicals could be produced much more effectively by using Fe 2+ ions rather than Fe 3+ by Fenton-like process, characterized by much less effective production of OH radicals. Since the OH radical production by Fenton process is much more effective that of Fenton-like processes, and since decolorization depends on the reaction between chemical double-bonds in dye substance and OH radicals, the color removal by Fenton process must be more effective than Fenton-like process, as it can be seen in both Figs. 3 and 4. Ozonation Some of the specific examples of ozone use for treatment of wastewaters can be cited as textile effluent treatment in terms of color removal [] or degradation of effluent from dyes industry etc [7,52,53]. In ozonation process, main operating parameters are ph and contact time. In order to determine the optimum ph, which gives better efficiencies of COD and color removal in ozone oxidation studies, phs of wastewater samples were adjusted to 3, 5, 7, 9, and 11 applying 23 mg/min ozone to the samples for min. COD and color removal efficiencies for E1 and E2, obtained after this period, due to the varied ph values are shown in Fig. 5. As seen from Fig. 5, maximum COD and color removal efficiencies were obtained at ph 9 for E1 and E2. COD and color removal efficiencies for E1 and E2, obtained at ph 9, due to the varied contact times, are illustrated in Fig. 6. The highest removal efficiencies were obtained at ph 9 for COD and color (Fig. 6). COD and color removal efficiencies were also examined for varied contact times and ozone dosages at this ph. During this examination, 9% of color removal was provided in the first 5 min for both effluents of ozonation, whereas just 13 and 3% of COD for E1 and E2 were removed within the same period. At the end of 1 h ozonation, and 54% efficiencies of COD for E1 and E2 were reached, respectively. At the same time, 96 and 99% color removal efficiencies were observed for E1 and E2, respectively. Azbar et al. [3] studied textile effluents and obtained 92% COD and 9% color removal efficiencies at ph 9 and C O3 2 g/h. Akal Solmaz et al. [36] applied ozonation to textile wastewaters and found 43% COD and 97% color removal efficiencies at ph 9 and C O3 1.4 g/h. 7

8 9 COD removal effluent-1 Color removal effluent-1 COD removal effluent-2 Color removal effluent-2 Removal, % ph FIGURE 5 - COD and color removal due to the constant dosage of ozone and varied values of ph (C O3 = 2 mg, t=2 C). 9 COD removal effluent-1 Color removal effluent-1 COD removal effluent-2 Color removal effluent-2 Removal, % Time, min FIGURE 6 - COD and color removal due to the varied contact times (ph=9, C O3 = 21 mg, t=2 C).. TABLE 2 - Operating costs for the studied processes* Reagents Basis Cost ($) Process Treatment Cost ($/m 3 ) E1 E2 FeSO 4.7H 2 O kg.35 Coagulation with FeSO FeCl 3.6H 2 O kg.43 Coagulation with FeCl O 3 $ /kg 2.42 Ozonation H 2 O 2 kg.51 Fenton Electricity kw/h.629 Fenton-like H 2 SO 4 kg.2 NaOH kg.2 *Costs of laboratory and sludge disposal not included 8

9 Cost Evaluation Different AOP and chemical coagulation processes were applied to 2 different WWTP effluents. To estimate the costs of the different treatment methods, separate consideration of treatment units is necessary. A cost profile was performed considering the operational costs (chemical and electricity) and is summarized in Table 2. The calculated costs could be considerably high but when wastewater quantity and quality of treated water were considered, it should not be neglected that these systems would be necessary in the future for Turkey to advance in European Union progress. Therefore, this study can be approved as feasibility work, in this respect. CONCLUSIONS In this study, removal efficiencies of COD and color were examined by applying different AOPs and coagulation processes to compare 2 different textile effluents, and their performances are summarized in Table 3. TABLE 3 - Optimum dosages and removal efficiencies of studied processes. Optimum dosages, mg/l Removal (%) Process E1 E2 COD Color ph FeSO 4 FeCl 3 H 2 O 2 O 3 ph FeSO 4 FeCl 3 H 2 O 2 O 3 E1 E2 E1 E2 Chemical Coagulation Fenton Process Fenton-like Process Ozonation The following results were obtained and summarized below: (a) In chemical coagulation process, for E1 at 1 mg/l FeSO 4 dosages, COD and color removal efficiencies of 71 and 94% were obtained, respectively. For E2 at 1 mg/l FeSO 4 dosages, COD and color removal efficiencies were 56 and 88%, respectively. Removal efficiencies for both coagulants used in chemical coagulation, were rather close the each other. COD and color removal rates were 62 and 92%, respectively, when using FeSO 4, but 64 and 91% when using FeCl 3. (b) Removal efficiency obtained from Fenton process is better than that from Fenton-like processes. Removal efficiencies of COD and color were 49 and 94% (E1) and 58 and 97% (E2) for doses of 1 mg/l FeSO 4 and 1 mg/l H 2 O 2 in Fenton process for E1, 2 mg/l FeSO 4 and 2 mg/l H 2 O 2 for E2. (c) In Fenton-like processes, color removal efficiencies were at same levels (92%). COD removal efficiencies were 43% for E1 and 54% for E2. (d) COD and color removal rates of and 96% were obtained for E1, as well as 54 and 99% for E2, at 23 mg O 3 /L. min ozone dosage during 1 h ozonation, respectively. (e) When the costs of processes were compared for E1, the coagulation gives better results (costs.18 $/m 3 ). For E2, the best removal efficiencies were obtained in Fenton process (costs.59 $/ m 3 ). ACKNOWLEDGEMENTS Marine Sciences Research Grant Group Project Number: ICTAG-A55 (4I137). The authors would like to thank the Chemical Engineer Mr. Ercan ASIL for the technical support of this research. REFERENCES [1] Pagga, U and Brown, D. (1986) The degradation of dyestuffs: Part II Behaviour of dyestuffs in aerobic biodegradation tests. Chemosphere. 15, (4), [2] Correia, V.M., Stephenson, T., and Judd, S.J. (1994) Characterisation of textile wastewaters-a review. Environ Technol. 15, [3] Grau, P. (1991) Textile industry wastewaters treatment. Water Sci. Technol. 24, [4] Erswell, A., Brouckaert, C.J. and Buckley, C.A. (1988) The reuse of reactive dye liquors using charged ultrafiltration membrane technology. Desalination., [5] Bahorsky, M.S. (1997) Textiles. Wat. Environ. Res. 69, [6] Akal Solmaz, S.K., Ustun, G.E., Birgul A. and Taşdemir, Y. (27) Treatability studies with chemical precipitation and ion exchange for an organized industrial district (OID) effluent in Bursa, Turkey. Desalination. 217, [7] Wu, J., Eiteman, M.A. and Law, S.E. (1998) Evaluation of Membrane Filtration and Ozonation Processes for Treatment of Reactive-Dye Wastewater. J. Environ. Eng. 124 (3), [8] Legrini, O., Oliveros, E. and Braun, A.M. (1993) Photochemical processes for water treatment. Chem. Rev. 93, This work was supported by the Research Fund of The University of Uludag Project Number: M-24/29, and TUBITAK (The Scientific and Technical Research Council of TURKEY) Environmental, Atmospherical, Earth and [9] Kuo, W.G. (1992) Decolorizing dye wastewater with Fenton's reagent. Water Res. 26, [] Marechal, M.L., Slokar, Y.M. and Taufer, T. (1997) Decoloration of chlorotriazine reactive azo dyes with H 2 O 2 /UV. Dyes Pigm. 33,

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