Effect of high-stress mixing on polyelectrolyte conditioning of sludges

Abstract

Experiments were performed on samples of alum and activated sludges to determine if these sludges, conditioned with polymers under high-stress, would achieve favorable dewatering rates. Tests were conducted using a variable high speed mixer with root mean square velocity gradient (G) values ranging from 560 - 2000 sec⁻¹ with both anionic and cationic high molecular weight polymers. Capillary suction time (CST) was used to measure relative changes in dewatering rates. Results indicated that readily dewatered sludges can be obtained when subjected to high-stress mixing conditions. The most significant parameters governing high-stress conditioning were determined to be polymer dose and total mixing energy input (Gt). It was discovered that as Gt increases, polymer dose requirements increase as well, so as to maintain an optimum dewatering rate. Also, the activated sludges tested in the study appear to be resistant to the effects of polymer overdosing.