Textile and dyeing mills use many kinds of artificial composite dye and discharge large amounts of highly colored wastewater. 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 removal (TSS) but they are largely ineffective for removing color from the waste (Aziz et al., 2007; Basava Rao and Maohan Rao, 2006). Consequently treated waste effluents may contain appreciable amounts of color when discharged. Now, the treatments are physico-chemical treatment operations, including adsorption, oxidation, chemical precipitation etc. Each has its merits and limitations in application.
In recent years, considerable research has been done on the removal of color from textile effluents. In general these studies involved use of inorganic coagulants such as alum, lime, ferric or ferrous sulfate and polyaluminum chloride (PAC) etc. In most cases coagulation has been effective in removing color especially for wastewaters, containing dissolvable solids. However high chemical dosages are usually required and large amounts of sludge volume must be disposed off. The cost of sludge disposal results in relatively high process costs.
Organic coagulants such as polydiallyldimethylammonium chloride (poly-DADMAC) and polyamine have been shown to be an effective alternative to inorganic coagulants and can enhance removal of impurities or pollutants in the treatment of wastewater. The zero production of sludge almost eliminate sludge disposal problems and significantly reduce treatment costs.