Turbidity Removal of Winter Taihu Lake Raw Water with Low Temperature Using Composite Coagulants of Polyaluminum Chloride and Polydimethyldiallylammonium Chloride in Process of Pre-chlorination

Abstract

A series of stable composite coagulants is prepared by using polyaluminum chloride(PAC) and polydimethyldiallylammonium chloride(PDM) with different intrinsic viscocity as raw materials.Jar tests are used to study the turbidity removal effect and precipitating performance of the composite coagulants on treating winter Taihu lake raw water pretreated by chlorine with low temperature.The results show that for the winter Taihu lake raw water with temperature of 5～9 ℃,turbidity of 25～26 NTU and under the process of pre-chlorination,the dosage of 3.29 mg/L,2.66～2.53 mg/L,2.81～2.68 mg/L,2.98～2.79 mg/L are necessary for the treatment with PAC and composite coagulants with the ratios(w/w) of PAC to PDM of 5∶1,10∶1,20∶1 and increasing of intrinsic viscocity 0.55 dL/g,1.53 dL/g,2.47 dL/g of PDM,respectively,when presently residual turbidity of 2 NTU is required.It means the composite coagulants can decrease the PAC dose by 19.15%～23.10%,14.59%～18.54%,9.42%～15.20%.When residual turbidity of 1 NTU is required for the future,the dosages of more than 4 mg/L are necessary for the treatment with PAC,composite coagulants with the ratios(w/w) of PAC to PDM of 20∶1,10∶1,5∶1 need dosage of 3.90～3.16 mg/L.Therefore,under the existing pre-chlorination production process,the efficiency turbidity removal and precipitating performance of the composite coagulants is remarkable.The lower the ratios of PAC to PDM is,the higher the intrinsic viscosity of PDM is,and the more the efficiency of turbidity removal is.