Ind. Eng. Chem. Res. 2006, 45, 3969-3973
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Combining Adsorption and Coagulation for the Treatment of Azo and Anthraquinone Dyes from Aqueous Solution Dogan Karadag,*,† Sema Tok,† Eda Akgul,† Kubra Ulucan,† Hulya Evden,† and Mehmet A. Kaya‡ Departments of EnVironmental Engineering and Chemistry, Yildiz Technical UniVersity, 34669 Istanbul, Turkey
The combined process of coagulation and adsorption was studied for the treatment of reactive dye wastewaters. Ferric chloride and organozeolite modified with CTAB were chosen as the coagulant and adsorbent, respectively. Reactive dyes, namely, Reactive Blue 4 (RB4) and Reactive Yellow (RY), were used as representatives of anthraquinone and azo textile dyes. A series of jar-test and batch experiments were conducted to determine the optimum conditions. According to individual dye removal efficiencies, coagulation is the main treatment process of the combined process, and RY has better performance than RB4. Coagulation followed by adsorption was found to be very effective for color removal with more than 99.50% and for COD removal with more than 97.25%. 1. Introduction The rapidly growing textile industries in Turkey produce large amounts of effluents. Dyeing operations are the major sources of textile wastewater. Effluents from the textile industry are a significant pollution source that contains high concentrations of inorganic and organic chemicals and is characterized by residual chemical oxygen demand (COD) and strong color.1 The textile industry utilizes about 10 000 different dyes and pigments, and about 20-30% of the total market comprises reactive dyes.2 Reactive dyes contain functional groups, such as azo, anthraquinone, phthalocyanine, formazin, and oxazine. Azo dyes represent about 60% of all reactive dyes used by the textile industry, and other classes of reactive dyes, namely, anthraquinone and phthalocyanine dyes, are extensively used as either primary or secondary dyes.3 Reactive dyes are extensively used in the textile industry because of their wide variety of color shades, brilliant colors, high wet fastness profiles, ease of application, and minimal energy consumption.4 About 50% of initial reactive dye used in dyeing operations is released in effluents,5 and colored wastewater is mainly caused by dyeing processes with azo dyes.6 Color removal from textile wastewater is of major environmental concern because the discharge of colored wastewater into bodies of water can trigger many significant problems, such as increasing toxicity and decreasing light penetration. Several treatment methods have been proposed for the treatment of reactive dye wastewater.7-13 In recent years, use of combined processes has been growing to overcome the disadvantages of individual treatment processes, such as high operating costs, sludge handling problems, and especially lack of effective color treatment.14-18 The combination of coagulation and adsorption is the most promising process as these steps have high individual treatment efficiencies, low costs, and ease of operation. In this study, coagulation is combined with adsorption for the treatment of azo and anthraquinone dyes. Two combinations of adsorption and coagulation were investigated. Prior to studying the combined treatment, individual processes of * To whom correspondence should be addressed. E-mail: dkaradag@ yildiz.edu.tr. Tel.: 0090-212-2597070. Fax: 0090-212-2619041. † Department of Environmental Engineering. ‡ Department of Chemistry.
Figure 1. Chemical structure of RB4.
coagulation and adsorption were investigated. Ferric chloride was used as the coagulant. Organozeolite was chosen as the adsorbent because it is a low-cost material and Turkey has abundant natural zeolite deposits. Reactive Blue 4 and Reactive Yellow were selected as representative anthraquinone and azo dyes. Performances of combined treatments were evaluated based on COD and dye removal efficiency. 2. Materials and Methods 2.1. Material and Chemicals. The experiments were carried out using two reactive dyes, namely, Reactive Blue 4 (RB4) and Reactive Yellow (RY), which were obtained from Sigma and Daystar Corp., respectively. RB4 is an anthraquinone type and RY is an azo type of reactive dye. The commercial name and Chemical Abstract Service (CAS) registry number of RY are Remazol Yellow RR and 189574-45-6, respectively. The chemical structure of the dyes was made available by the supplier only for RB4, as illustrated in Figure 1. Reactive Yellow is monoazo-type reactive dye and has vinyl sulfone reactive groups. The adsorbent material, zeolite, was obtained from Esen Foreign Trade in West Anatolia, Turkey. The mineralogical content of natural zeolite is 85% clinoptilolite, 10% feldspar, and 5% clay. The chemical composition of natural zeolite is given in Table 1.19 A cationic surfactant, cetyltrimethylammonium bromide (CTAB, C19H42BrN) was used to modify the zeolite surface. CTAB was purchased from Sigma and specified to be 99% purity with a molecular weight of 346.46 g/mol, and its chemical structure is given in Figure 2. FeCl3‚6H2O was purchased from Merck and used as a coagulant. HCl and NaOH solutions were added to adjust the pH using a Jenway pH meter. A Jenway UV/visible spectro-
10.1021/ie060164+ CCC: $33.50 © 2006 American Chemical Society Published on Web 04/26/2006
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Ind. Eng. Chem. Res., Vol. 45, No. 11, 2006
Figure 2. FTIR spectra of natural and organozeolite. Table 1. Chemical Composition of Natural Zeolite constituent
content (%)
SiO2 Al2O3 Fe2O3 K2O MgO Na2O CaO TiO2 MnO2 P2O5 loss of ignition
74.4 11.5 1.1 5.0 0.5 0.6 2.0 0.1
