| This study was accomplished to grasp the influences of coagulant basicity on P removal and alkalinity decrease in sewage water treatment with prepolymerized or monomerized Al-based coagulants. P removal efficiency resulted in the range of 80-96% using the coagulants with different basicities. Al-based coagulants with OH/Al ratios up to 1.8 were dosed to precipitate ortho-P and particles at the same time, while Al polymers with basicities of 2.1 were found to precipitate particles preferably. At higher doses, however, ortho-P was precipitated to an increasing degree. Total removal rate of P seemed to be remarkably influenced by thickness of the water. The coagulant with an OH/Al ratio of 1.1 was the most effective in precitating phosphorus from the thickest water, but in the thinnest water the coagulant with 1.9 was at its best. The alkalinity consumed strongly decreased with increasing basicity of the coagulant used. When the coagulant is dosed in an amount up to the threshold concentration, alkalinity depression was low, but if exceeded, alkalinity showed the significant decrease. Turbidity removal was more effective using the coagulant with OH/Al ratio of 2.1. The presence of Ca ions in sewage water was a positive effect for SS removal due to double layer depression, but they caused to increase the coagulant since Ca ions are favorable to react with P compounds. |
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