Abstract
Life of living or non-living being depends on water; in short, water is life. But these days, with the growing industrialization, it is spoiling a lot. Wastewater contains contaminants like acids, bases, toxic organic and inorganic dissolved solids, and colors. Out of them, the most undesirable are colors caused mainly by dyes. Color and other compounds present in water are always not desirable for domestic or industrial needs. The wastes of dyes are predominant amongst all the complex industrial wastewater. This water is dark in color and highly toxic, blocking the sunlight and affecting the ecosystem. Among all the dyes, azo dyes contribute to commercial dyes used widely in textile, plastic, leather, and paper industries as additives. The removal and degradation of azo dyes in aquatic environment is important because they are highly toxic to aquatic organisms. For every industry, clean technology has become an important concern. In this chapter, the authors discuss about existing processes as well as promising new technologies for textile wastewater decolorisation.
TopIntroduction
The consumption of water and chemicals in textile industries is tremendous for the wet processing of textiles. The reagents used varies from inorganic or organic compounds to polymers (Mishra & Tripathy, 1993; Juang et al. 1996). The low concentration of dye effluent presence in water is visible and not desirable (Nigam et al. 2000). Almost there are more than 100,000 dyes are available commercially and over tons of dye-stuff are produced annually (Meyer, 1981). Dye has complex structure and due to that they are resistant for degradation to light and also to many chemicals (Poots & Mckay, 1976a). The dyes according to structural varieties are classified as acidic, basic, disperse, azo, diazo, anthroquinone based and metal complex dyes. Municipal sewerage systems are not effective in decolouration of textile dye effluent (Willmott et al. 1998). There are other varieties of dyes like cationic, nonionic or anionic type. Anionic dyes are the acid, direct as well as reactive dyes. The most problematic are those dyes which are bright in colour, water-soluble, reactive and acid dyes because they are unaffected by the conventional treatment systems. The general aerobic municipal treatment systems are not effective in removal of these dyes (Moran et al. 1997). The nonionic dyes are disperse dyes as they do not ionise in an aqueous medium. There is great concern because most of the dyes used in textile industry are highly carcinogenic such as benzidine and other aromatic compounds (Baughman & Perenich, 1988). Azo and nitro-compounds are reduced in sediments (Weber & Wolfe, 1987) and similarly (Chung et al. 1978) illustrated their reduction in the intestinal environment, resulting in the formation of toxic amines. Because of fused aromatic ring structure the anthroquinone-based dyes are most resistant to degradation. The ability of some disperse dyes for bioaccumulation has also been demonstrated (Baughman & Perenich, 1988).
Key Terms in this Chapter
Photo-Catalysis Process: Photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalysed photolysis, light is absorbed by an adsorbed substrate.
Advanced Oxidation Process (AOPs): Advanced oxidation processes (AOPs) in a broad sense, are a set of chemical treatment procedures designed to remove organic or sometimes inorganic materials in water and wastewater by oxidation through reactions with hydroxyl radicals (OH).
Fenton Process: Fenton process is attractive alternative to conventional oxidation processes in effluent treatment of recalcitrant compounds. The oxidation of organic substrates by iron (II) and hydrogen peroxide is called the “Fenton chemistry” and it was first described by H.J.H. Fenton.