USE OF POLYELECTROLYTES IN IMPROVING SETTLING CHARACTERISTICS OF SEWAGE

Abstract

In physico-chemical treatment, Coagulation along with flocculation is well known unit operation for the removal of fine suspended and organic matter from water. Coagulant aids along with Coagulant are well known to increase the settleability and overall removals. The present study is aimed to improve the settling characteristics of sewage using polyelectrolytes as Coagulant aid with alum as Coagulant with regards to SS, COD and BOD removal efficiency. Two polyelectrolytes used here as Coagulant aids are Carborymethyl cellulose derived from a natural source and polyacrylamide, a synthetic polyelectrolyte. Jar test methodology has been adopted for experimentation in Laboratory. Optimum dose with and without the use of polyelectrolyte has been obtained. It was observed that settling in sewage significantly improved and the maximum removal efficiency upto 93%, 961 and 93% of SS, COD and BOD respectively have been achieved when polyacrylamide was used with alum after one minute of fast mixing and for same condition efficiency removal in case of Carborymethyl cellulose. (CMC) was upto 92%, 92% and 74% respectively. The study points out that use Of polyelectrOlyte will go a long way in decreasing the expenditure, on secondary treatment plant.