Taihu Lake Water To Strengthen The Coagulation Off A Cloud In The Pilot Study

The turbidity removal effects of treating summer eutrophicated Taihu Lake raw water by using PAC/PDM stable composite coagulants or AS/PDM stable composite coagulants which were composed by polyaluminum chloride(PAC) with polydimethyldiallylammonium chloride(PDM) and aluminium sulfate(AS) with PDM,respectively,were studied in this paper.According to the practical process of water plants around the Taihu Lake,two parallel pilot water plants were installed.One run under the condition of using inorganic coagulants,and the other one run under the condition of using composite coagulants.By monitoring the residual turbidity of processed water of each unit,the turbidity removal effects of each unit in conventional process when using PAC or AS and the improvement of turbidity removal effects when using PAC/PDM or AS/PDM composite coagulants were studied.Based on the results,jar tests and pilot scale tests were compared and analysised.Besides,the relationship between turbidity,COD_Mn and algae content removal efficiencies were also studied.The results showed that under condition of pilot scale tests,33.3%～54.0%turbidity of effluent could be descreased by using PAC/PDM composite coagulants compared with that by using PAC in the same dosages.20.0%～37.5%dosage could be reduced by using PAC/PDM composite coagulants compared with that by using PAC under the condition of controlling similar effluent turbidity.41.6%～50.6%turbidity of effluent could be descreased by using AS/PDM composite coagulants compared with that by using AS in the same dosages.20.0 %～42.3%dosage could be reduced by using AS/PDM composite coagulants compared with that by using AS under the condition of controlling similar effluent turbidity.Compared with results of jar tests,the turbidity removal effects of pilot scale tests were weaker.It maybe due to the coagulation intensity of pilot plant was lower than that of jar tests.In conventional water treatment process,prechlorination and disinfection processes hardly had turbidity removal effects,coagulation-sedimentation processes and filtration process could remove 80 %～90%and about 4%turbidity from raw water under the condition of using PAC respectively.The turbidity removal efficiency of filtration could be raised 15%while composite coagulants were used.Composite coagulants could remove 66%COD_Mn and 98% algae content while 99%turbidity was removed.PAC/PDM composite coagulants and AS/PDM composite coagulants could still function well for enhancing coagulation under the weak coagulation intensity of the pilot plant. Coagulation-sedimentation were the main turbidity removal processes in conventional treatment.The turbidity removal effect of filtration process was also enhanced when using composite coagulants.Enhanced coagulation process of summer Taihu Lake raw water by using composite coagulants could not only get better turbidity removal effect,but also improve the finished water quality totally.