Optimization of phosphorus removal from secondary effluent using simplex method in Tianjin, China.

Enhanced concentrations of phosphorus entering the aquatic systems have been linked with eutrophication and its associated problems. Jar tests were applied to a secondary effluent in order to determine optimal conditions for coagulation. The coagulants studied were ferric sulfate [Fe2(SO4)3], aluminum sulfate [Al2(SO4)3.18H2O] and polyaluminum chloride (PAC). The experiments were carried out using simplex research technique to determine the optimum conditions of these coagulants for phosphorus removal. For each coagulant examined, 18-25 experiments were carried out until a maximum removal was observed through the experimental procession. Increases of greater than 30% were found for the removal efficiencies of these three coagulants over the course of the experiments. Good removal efficiencies averaging at least 87.25% were obtained through the simplex procession. The orthophosphate removal efficiency was higher than that of total phosphorus for each coagulant. The maximum removal efficiency of total phosphorus obtained from the optimization procedures for ferric sulfate, aluminum sulfate and polyaluminum chloride was 87.3, 95.6 and 94.0%, respectively, and the minimum total phosphorus residual was 0.35, 0.12 and 0.16 mg/L, respectively.