EVALUATION OF A MICRO CARRIER WEIGHTED COAGULATION FLOCCULATION PROCESS FOR THE TREATMENT OF COMBINED SEWER OVERFLOW

ISSN： 0959-3330

Source： Environmental Technology, Vol.28, Iss.7, 2007-07, pp. : 761-770

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Abstract

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="" m="" and="" at="" 3="" g="">^-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.