Performance of PAC/PDM composite coagulants for removal of algae from Lake Taihu waters in summer

摘要

The enhanced coagulation of algae-rich raw water from Lake Taihu in summer was studied bynuse of composite coagulants. The composite coagulants were composed of polyaluminumnchloride (PAC) and polydimethyldiallylammonium chloride (PDM) with various intrinsic viscositynvalues (0.55–3.99 dL/g) and different mass percentages (5–20%) in the formulation. For rawnwater with temperature of 28–298C and algae content of 3.60 £ 104n–3.70 £ 104ncells/ml, thenalgae-removal rates of 89.0% and 89.3–93.1% could be realized by using PAC and PAC/PDMn(0.55/5%–3.99/20%) with dosages of 8.37mg/L and 5.93–3.58mg/L, respectively, when 2NTUnresidual turbidity of treated water after sedimentation was required. Compared with using PACnonly, the removal rate of CODMn using PAC/PDM increased at least 4.4% when the dosage wasn8mg/L, and increased at least 5.0% when the dosage was 10mg/L. The composite coagulantsncould still function well when raw water quality deteriorated and algae content reachedn8.00 £ 104ncells/ml. The enhanced coagulation efficiency of PAC/PDM (0.55/5%) could be betternthan that of PAC combined with prechlorination process when the same dosages are used.