Experimental Study On Optimization Of Conventional Water Treatment Process For Luan River Treatment

Along with the aggravation of source water pollution, more and more kinds of pollutants appear. Moreover, water quality standards for water supply are continuously upgraded. So the conventional water treatment process can hardly meet the requirements of safe water supply. However, most of the waterworks in Tianjin still use the conventional water treatment process—"coagulation + sedimentation + filtration + disinfection". Therefore, an experimental study is carried out on enhanced conventional water treatment process according to source water quality of Luan River. This study can supply the operational parameters for current waterworks in Tianjin to save water treatment costs and improve treatment efficiency.According to the analysis of water quality indexes of Yuqiao Reservior, the source water quality can be divided into three stages. The pilot study is carried out on enhanced coagulation and enhanced filtration of Luan River water during the periods of high temperature and algae and the periods of low temperature and turbidity. Turbidity and COD_Mn are used as the main indexes for water treatment evaluation. And the conclusions drawn are as follows.1. the period of high temperature and algaeBy comparing the coagulation effects of FeCl₃ and PAC, it is found that under sedimentation process FeCl₃ is better and its optimal dosage is 10～14mg/L; but under flotation process PAC is better and the optimal dosage is 1.0～2.0mg/L. It is proved that preoxidation with PPC, enhanced coagulation & flotation with HCA and enhanced filtration with PAM can significantly improve the effluent water quality. Not only the removal rate of turbidity and pollutant is enhanced, but also the removal rate of algae is raised to over 90%. Compared to sedimentation processes, flotation processes have more powerful algae removal ability and their agent costs are much lower. Moreover, through combinational study of those above advancement measures, it is found that, under the circumstance that the effluent turbity is less than 0.3NTU and that COD_Mn is less than 3.0mg/L , and compared to conventional treatment process, all of those combinational processes can reach removal rate of 90% above for algae in Luan River, meanwhile the agent costs can be saved by 3～10 CNY per kiloton water.2. the period of low temperature and turbidityDuring this period, the effect of PAC for turbidity and COD_mn removal is better than that of FeCl₃. But considering the agent cost, FeCl₃ is properer for water treatment. Using HCA as coagulant aid has no help for the effluent turbidity and COD_Mn, of conventional water treatment process. However, water treatment effect can be improved by increasing the ratio of sodium silicate in the mixture of FeCl₃ and sodium silicate. Adding PAM can reduce the effluent turbidity after filtration. In this case, the growth rate of hydraulic head loss will be accelerated, which cuts down the filtration cycle. By comparing the effects of different filter structures it is found that the optimal value of L/d is 1200 and the proper range of filtration rate is 8～10m/h. Moreover, it is proved that microflocculation direct filtration is feasible for Luan River water treatment in the period of low temperature and turbidity.