TREATMENT OF COMBINED SEWER OVERFLOW USING A NATURAL COAGULANT

摘要

The hazards posed by combined sewer overflows (CSOs) to receiving water bodies cannot be overemphasised. CSOs can be a significant contributor of pollutants to receiving waterbodies. Ontario's F-5-5 procedure stipulates a treatment target of a minimum 50% reduction in suspended solids (SS) and 30% reduction in 5-day biochemical oxygen demand (BOD5) for CSOs in the province. The physicochemical coagulation process is an effective and widely used treatment process to achieve these targets. The City of Windsor, Ontario currently uses a synthetic organic coagulant for coagulation at its retention treatment basin (RTB) for CSO treatment. However, environmental persistence and potential toxic effects on aquatic life are common concerns with synthetic coagulants. These concerns are not expected to be there when coagulants derived from natural (plant or animal) sources are used. In the current study, the effectiveness of a commercially available natural coagulant was evaluated for the treatment of Windsor CSOs. The results show that with natural coagulant dosages ranging between 5 and 30 mg/L, SS and BOD5 removal efficiencies of 37 to 91% and 22 to 56%, respectively, were obtained. Over the duration of the study, natural coagulant dosage of 10 mg/L or higher were able to meet or exceed the treatment targets of Ontario's Procedure F-5-5 for both SS and BOD_5.