Evaluation of industrial dyeing wastewater treatment with coagulants and polyelectrolyte as a coagulant aid.
Wastewater is the major environmental issue of the textile industries besides other minor issues like solid waste, resource wastage and occupational, health and safety. Textile and dyeing mills use many kinds of artificial composite dyes and discharge large amounts of highly colored wastewater. Pretreatment, coloration and after treatment of fibers, usually require large amounts of water and variety of chemicals. Variations in the fabric quality and treatment process results into large fluctuation in daily flow rates and pollutants concentrations. Textile wastewater pollutants are generally caustic soda, detergents, starch, wax, urea, ammonia, pigments and dyes that increase its BOD, COD, solids contents and toxicity. These wastes must be treated prior to discharge in order to comply with the environmental protection laws for the receiving waters. Biological treatment processes are frequently used to treat textile effluents. These processes are generally efficient for biochemical oxygen demand (BOD) and suspended solids (SS) removal, but they are largely ineffective for removing color from the wastewater (McKay, 1979; Taebi Harandi, 1986) because dyes have slow biodegradation rate (Bennett and Reeser, 1988). Now, the treatment technologies recommended meeting color removal requirements are physicochemical treatment operations, including adsorption (Ahmad and Ram,1992; McKay ,1979), ozonation (Lin’s, 1993), oxidation (Boon and Tjoon, 2000), chemical precipitation (Dziubek and Kowal, 1983), etc. Each has its merits and limitations in applied decolorization treatment operations. But Coagulation-flocculation is the most common chemical treatment method for decolorization (Beulker and Jekel, 1993 ; Bennett and Reeser, 1988).