Optimization of time requirement for rapid mixing during coagulation using a photometric dispersion analyzer

Coagulation involves the rapid mixing of chemicals with raw water to facilitate particle destabilization. This study used a photometric dispersion analyzer (PDA) coupled to a jar stirrer to monitor kinetics during the optimization of alum. The optimal conditions were as follows: sample pH 8; alum dosage, 6 mg/l as Al3+; G-value, 116 s(-1), rapid mixing time, 15 seconds. Kinetic data revealed that the aggregation rate and steady-state variance significantly influenced coagulation-flocculation performance; while average steady-state ratio displayed a minor influence on performance. The results indicated that the PDA instrument can be employed as an additional tool in the optimization of coagulation conditions. (C) 2013 The Authors. Published by Elsevier Ltd.