Abstract

The waste water and industrial effluent treatment may be treated either with inorganic or organic coagulants and flocculants. Efficient flocculants can reduce the total amount of disposed effluent into the atmosphere. Broadly, for coagulation and flocculation, although the basic function remains the same, subtle distinction is made between these two terms. The coagulation means the destabilization of a stabilized system (eg., colloidal system) but flocculation means the floc formation of the destabilized colloidal system, where the addition of flocculent to the destabilized colloidal system results in flocculation. The flocculants may be either inorganic or organic type. Among the inorganic flocculants, the multivalent metallic compounds like aluminum and iron salts are generally used. The organic polymeric flocculants are preferred due their ease in handling, low dosage requirements, less sensitivity to system pH, existence of large cohesive forces between the flocs and the ease in synthesizing the flocculants. Polysaccharides such as starch, amylase, amyl pectin, guar gum, xanthan gum and carboxymethyl cellulose have been used for long as natural flocculants. However, they are less effective flocculating agents when compared with synthetic flocculants. The polyacrylamides have also been used for long as synthetic flocculants. Although their flocculation efficiencies are higher than the natural flocculants, these synthetic polyacrylamide flocculants are easily amenable to shear degradation although they are very efficient drag reducing and flocculating agents even at low ppm concentrations. Whereas, polysaccharides are fairly shear stable but are not very efficient drag reducers and flocculants. Their aqueous solutions are also subjected to rapid biodegradation.