Flocculation: A New Way to Treat the Waste Water

Pure water is an essential requirement for the survival of human beings. To meet the requirements of potable, industrial and agricultural water, the immediate need is to treat waste water, particularly the sewage sludges and slimes from the municipal and industrial effluents respectively. These effluents are highly undesirable and unsafe. The removal of contaminants from waste water is a must before they can be reused. The removal of contaminants from these effluents involves the process of flocculation and coagulation. The purpose of the present article is to clarify and explain the processes in details along with the materials involved in the processes. This will be essential for the present day life. 1. Coagulation and Flocculation Colloidal particles in nature normally carry charges on their surface, which lead to the stabilisation of the suspension. By addition of some chemicals, the surface property of such colloidal particles can be changed or dissolved material can be precipitated so as to facilitate the separation of solids by gravity or filtration. Conversion of stable state dispersion to the unstable state is termed destabilisation and the processes of destabilisation are coagulation and flocculation1,2. Often the terms coagulation and flocculation are used synonymously inspite of existing a subtle difference between the two1,3. If destabilisation is induced through charge neutralisation by addition of inorganic chemicals, the process is called coagulation. On the other hand, the process of forming larger agglomerates of particles in suspension or of small agglomerates already formed as a result of coagulation through high molecular weight polymeric materials is called flocculation. No substantial change of surface charge is accomplished in flocculation. The agglomerates formed by coagulation are compact and loosely bound, whereas the flocs are of larger size, strongly bound and porous in case of flocculation. In mineral processing industries, the scope of application of flocculants is much greater than the coagulants. Coagulants find use in the processing of coal, taconite, soda ash