Textile dyeing wastewater treatment by fluidized-bed fenton process

Abstract

The textile industry involves in the manufacture of fabrics from both natural and man-made fibers. It generates a large amount of wastewater containing various pollutants such as organic matter, solid, oil and grease and dyes. Dyes can be divided into eight types: direct, sulfur, azoic, reactive, vat, acid, basic and disperse dyes. There are several methods for decolorize dye wastewater but they cannot be effectively used individually to deal with the wastewater, containing solube and insoluble dyes. For example, the coagulation process can effectively decolorize the wastewater containing insoluble dyes such as disperse dyes. However, it does not work well for soluble dyes such as reactive dyes widely used in textile industry. Therefore, the fluidized-bed Fenton process was of interested in this investigation. The combination of hydrogen peroxide and a ferrous ion has been referred to as "Fenton's reagent". Fenton reaction exploit the reactivity of the hydroxyl radical (OH.), which has a very high oxidation potential and is able to oxidize almost all organic pollutants quickly with non-selectivity, produced in acidic solution by the catalytic decomposition of H[subscript2]O[subscript2]. This study investigated degradation of reactive dyes by fluidized-bed Fenton process for the removal of color and chemical oxygen demand (COD) from synthetic textile wastewater. In some local case in Taiwan, wastewater color and COD were found to be the only problem in meeting local effluent standards. This investigaion reveals that fluidzed Fenton methods can remove the color and COD of these dyes. The effects of Fe[superscript2+] and H[subscript2]O[subscript2] on dye decolorization and COD removal have been demonstrated in this study. The pH of all experiments was fixed at 3.0. Increasing the dose of ferrous enhanced the dye decolorization and COD removal. The optimal levels of H[subscript2]O[subscritp2] required for the process were also examined. High levels of H[subscript2]O[subscript2] appeared to reduce color and COD removal. However, when the H[subscript2]O[subscript2]concentration was higher than a specific level, the degradation rate of reactive dyes slightly slows down. This can be explained by the so-called scavenging effect. In addition, it is also found that decolorization of reactive dyes underwent a faster reaction rate than COD removal. The second order degradation rate constant values (k) of color and COD were also determined. Then, the COD and color removal by fluidized-bed Fenton process was applied to remove the COD and color of wastewater from textile factory in Taiwan (Nan-Woei Industrial Co., Ltd). Target remaining COD and color for treating the wastewater from textile factory in this study was less than the discharge standard of Taiwan. Due to the discharge standards of 1998, textile industries are required by Environmental Protection Administration of Taiwan to comply with the COD and color less than 100 mg/1 and 400 in American Dye Manufacturer Institute (ADMI) unit, respectively. The Fe[superscritp2+]dosage, initial pH and H[subscript2]O[subscript2] dosage were varied in this part. From the results, the condition for treating the wastewater fo Nan-Woei Industrial Co., Ltd was [COD]: [Fe[superscript2+]:[H[subscript2]O[subscript2] = 1:0.95:7.94, carrier = 74.07 g/1, initial pH = 3.