摘要：

The enhanced coagulation processes to autumn Yangtze River raw water using steady composite coagulants,prepared by polyaluminum chloride(PAC) and Polydiallyldimethylammonium chloride(PDM) with different intrinsic viscosity,were reported in this paper.Jar tests were used to investigate the influences of the composite ratios of PAC to PDM and the intrinsic viscosity of PDM on the turbidity removal and settlement performance.The results showed that for the Yangtze River raw water with temperature of 16～18 ℃ and the turbidity of 70 NTU,the efficiency of turbidity removal of composite coagulants was remarkable.For the current process of potable water treatment,the residual turbidity of the supernatant from the settlement tank must be below 6 NTU.The dose of PAC and composite coagulants with the mass ratios of 20∶ 1,10∶ 1,5∶ 1 and the PDM intrinsic viscosity of 0.524,1.53,2.47 dL/g were 1.66,1.38～1.26,1.19～1.14,1.16～1.13 mg/L respectively,and the composite coagulants could decrease the PAC dose by 16.87%～24.10%,28.31%～31.32%,30.12%～31.93%.In case that the residual turbidity of 2 NTU will be required in the future,the dosage of 3.35 mg/L is necessary for treatment by PAC,but composite coagulants will decrease the PAC dose by 19.10%～30.45%.In general,PDM can assist PAC to increase the density,improved the turbidity removal efficiency and settlement performance.The lower the mass ratios of PAC to PDM and the higher the intrinsic viscosity of PDM,higher the efficiency will be.

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