Evaluation of a micro carrier weighted coagulation flocculation process for the treatment of combined sewer overflow

Modified bench scale jar tests were conducted to evaluate a treatment strategy for combined sewer overflow (CSO) generated during wet-weather conditions in Windsor, Ontario, Canada. Alum and an anionic polymer (Polymer A-3330) were used as a primary coagulant and coagulant aid, respectively. Commercially available silica sand was employed as the micro carrier. Under the operating conditions optimized in the study, alum dose of 9.7 - 17.8 mg l(-1) as Al3+ and polymer dosage of 1.0 - 1.8 mg l(-1) were observed to be the most effective in solids removal. Addition of the micro carrier (MC) up to 3 g l(-1) significantly increased the settleability of suspended solids, and about a five-fold increase in settleability was observed with 3 g l(-1) MC. In the size range of < 300 microm and at 3 g l(-1) concentration, the effect of MC size on the performance of the process was observed to be insignificant. Using the developed process, suspended solids and BOD removal efficiencies of > 98% and > 60%, respectively, were obtained with wet-weather flow after 8 minutes of settling, under both low and high suspended solids conditions.