[Effects of polymer aluminum hydrolysis on phosphorus distribution in coagulation]

Coagulation treatment was conducted by using coagulants of different basicity (ratio of OH(-)/Al); contents,distributions and algal availability of phosphorus in water were studied before and after coagulation. Results show that: phosphorus removals and its distribution in water were markedly different according to the coagulant with different basicity used; Al(a) plays an important role in the coagulation experiment for P removal. The lower the coagulant basicity was, the higher phosphorus removal was achieved; and PACl0 showed the best performance. Dissolved and particulate phosphorus reduced gradually with the increase of the coagulant (PACl0). They were entirely turned into deposit phosphorus when the coagulant dosage was above 10 mg x L(-1). The demand of coagulant for turbidity control was proved to be unequal to that for phosphorus removal. The coagulant dosages of about 3-5 mg x L(-1) achieved the best turbidity removal in the experiment; while much higher dosage was needed to get desired phosphorus removal. The amount of AAP (algal available phosphorus) in the sediments changed according to coagulant (PAC10) dosages. AAP increased with the increase of coagulant dosage when the dosage was less than 5 mg x L(-1), then it decreased with further addition of coagulant above 5 mg x L(-1). It was proved that release of phosphorus in sediments would be controlled effectively by addition of coagulant overdosed compared to the need for turbidity removal, which is important to long-term control of phosphorus. It was indicated that the dosage of coagulant used for phosphorus removal can not use the sole criterion for turbidity removal; the need for total phosphorus removal, sediment release of available phosphorus (such as AAP) and other phosphorus control requirements should be considered; and a larger dosage would be needed.