Abstract
A coagulation–sedimentation process with polyaluminium chloride (PAC) as a coagulant was used to treat wet-weather sewage flows with high concentrations of contaminants during the initial stages of a rainfall event. Response surface methodology and central composite design were applied to evaluate the optimal operating conditions of pH, turbidity and PAC dose to maximise simultaneous removal of contaminants at wastewater treatment plants. The optimal conditions were found to be a pH of 5, turbidity of 400 NTU and PAC dose of 48 mg/l. This resulted in the removal of 80·5% phosphorus, 79·8% chemical oxygen demand (COD) and 81·8% Escherichia coli. Under the assumption of wastewater with a neutral pH of 7, the optimal turbidity and PAC dose conditions resulted in the removal of 81·0% phosphorus, 76·7% COD and 64·5% E. coli.
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