The performance of several enhanced treatment processes for treatment of algae-containing raw water in typical seasons

摘要

The turbidity and algae removal effects of enhanced treatment processes, including the pre-chlorination process and the enhanced coagulation process using composite coagulants composed of poly-aluminum chloride and poly-dimethyldiallyl ammonium chloride (PDMDAAC) for algae-containing raw water in Taihu Lake, were investigated through jar tests in situ in this paper. And the dependence of the treatment effects on both the water quality in the typical seasons and the working mechanism of enhanced processes was analyzed and summarized. The results indicated that the pre-chlorination improved the treatment effect of conventional coagulation process in both the turbidity and algae removal effect for the raw water with the characteristics of high temperature, high algae and organic pollutants content in summer, and it improved also the algae removal effects, but weakened the turbidity removal effects for the raw water with the characteristics of low temperature, low algae content and tiny organic pollutants in winter. However, the enhanced coagulation process using composite coagulants improved even more remarkably the treatment effect of the conventional process using poly-aluminum chloride (PAC) only, for the algae-containing raw water both in summer and in winter. Especially, the improvement extent of the effects of using composite coagulants for algae-containing raw water in summer was more obviously than that in winter due to the characteristics of PDMDAAC and raw water. Besides, the turbidity and algae removal effects of enhanced coagulation process using composite coagulants could not only exceed that of the combined process of pre-chlorination and conventional coagulation using inorganic coagulants, but also indubitably replace the function of pre-chlorination for reducing the risks caused by excessively used chlorine.