[Algae-removal effect of AS/PDM composite coagulants to winter Taihu Lake raw water].

The series of stable AS/PDM composite coagulants prepared by polydimethyldiallylammonium chloride (PDM) and aluminium sulphate (AS) were used to research the algae-removal effect to winter Taihu Lake raw water. The effects of dosage of composite coagulants, composite mass ratios (20:1-5:1) of AS and PDM, intrinsic viscosity values (0.55-3.99 dL/g) of PDM on algae-removal rates were studied through coagulation and algae-removal experiments. The feasibility of using composite coagulants to substitute prechlorination process was analysed. The results show that when residual turbidity of 2 NTU to water after coagulation and sediment is required by water plant, the dosage (based on Al2O3) of AS, AS/PDM (0.55/20:1-3.99/5:1) composite coagulants are 4.24 mg/L, 3.96-1.87 mg/L, and the algae-removal rates are 83.00%, 87.52%-90.93% respectively. When dosage to raw water are 4.24 mg/L, the algae-removal rates of AS, AS/PDM (0.55/20:1-3.99/5:1) composite coagulants are 83.00%, 88.29%-97.66%, and the residual turbidities are 2.00 NTU, 1.76-0.43 NTU respectively. When dosage to chlorine-added water are 4.50 mg/L, the treatment effect of AS/PDM (1.53/10:1) composite coagulant to raw water is better than that of AS to chlorine-added water, and the treatment effect of AS/PDM (3.99/5:1) composite coagulant to raw water is better than that of AS, AS/PDM (0.55/20:1) and AS/PDM (1.53/10:1) composite coagulants to chlorine-added water. So using AS/PDM composite coagulants can enhance evidently the treatment effect of AS to winter Taihu Lake raw water. Compared with using AS solely, the dosage of AS in composite coagulants are saved when the residual turbidities are required in same level, and the treatment effect of AS is enhanced when the dosage of AS in composite coagulants are same as that of using AS solely. Moreover, using composite coagulants can replace the part chlorine-added function on increasing coagulation and algae-removal in prechlorination process and profitably increases safety of drinking water quality.

[Turbidity removal of summer high algae content Taihu Lake raw water using composite coagulants of polyaluminum chloride and polydimethyldiallylammonium chloride].

A series of stable composite coagulants was prepared using polyaluminum chloride (PAC) and polydimethyldiallylammonium chloride (PDM) with different intrinsic viscosity as raw materials. The enhanced coagulation processes of summer high algae content Taihu lake raw water by using the composite coagulants were reported in this paper. Jar tests were used to study the influences of the composite ratios of PAC to PDM and the intrinsic viscosity of PDM on the turbidity removal and precipitating performance. The results showed that for the summer Taihu raw water with temperature of 28-30 degrees C and turbidity of 30-33 NTU, algae content of 2.6 x 10(7) cells/L. When 2NTU turbidity of supernatant from settlement tank was required according to the current process of potable water plant in Wuxi, the dosage of 7.00 mg/L PAC was necessary, the PAC/PDM composite coagulants with the ratios (m/m) of 20:1, 10:1, 5:1 only needed dosage ranges of 3.00-2.83 mg/L, 3.50-3.49 mg/L, 5.37-4.67 mg/L with the increasing of PDM intrinsic viscosity from 0.52 dL/g to 2.46 dL/g. And compared with PAC only used, composite coagulants could decrease the PAC dose by 57.14%-59.57%, 50%-50.14%, 23.29%-33.29% correspondingly. When residual turbidity of 1 NTU was required, the dosage of 10 mg/L were necessary for the treatment with PAC , composite coagulants with the ratios(m/m) of PAC to PDM of 20:1, 10:1, 5:1 and the different intrinsic viscocity of PDM needed dosage of 8.33-3.91 mg/L, and could decrease the PAC dose by 16.7%-60.9%. Therefore, the efficiency turbidity removal and precipitating performance of composite coagulants were remarkably, and the lower the ratios of PAC to PDM and the higher the intrinsic viscosity of PDM, the higher efficiency of turbidity removal.