Experimental Investigation On Enhanced Coagulation For Micro-Polluted Water

Recently, the quality of the effluent from the Furi water treatment plant in Gaomi failed to match the class III of surface water quality standards all year around, called as micro-polluted raw water, owing to the increasingly water pollution and eutrophication. In summer, current treatment facility cannot fulfilled requirement of effluent quality due to some serious problems, such as algae explosion, increasing organic content and odor.Based on the characteristics of the raw micro-polluted water, enhanced coagulation experiments were investigated and conducted by dosing different combination of coagulants and coagulant aids, such as ferric chloride, polyaluminum chloride, and aluminum sulfate, as well as polyacrylamide, powdered activated carbon, PPC, diatomite, and zeolite powder.The results of coagulant comparison test showed that:the effect on coagulation of PAC was better than that of Al2(SO4)3and FeCl3. When adding15mg/L of PAC, the coagulation effect was maximum with the removal rates of turbidity, chroma, CODMn, and UV254higher than73.60%,51.61%,41.44%, and51.61%, respectively. In the coagulant aid test of PAM, when dosing15mg/L PAC and0.04mg/L PAM, the average removal rates of turbidity, chroma, CODMn and UV254could reach70.63%,45.00%,32.08%, and29.25%, respectively. It was also found that the optimized pH value was7.8.The results of the experiments of combining powder activated carbon with PAC and PAM, showed that the removal rates of turbidity, chroma, CODMn and UV254could reach65.98%,64.00%,26.82%,31.71%, respectively, when adding12mg/L powder activated carbon,15mg/L PAC and0.04mg/L PAM. For the test of combining PPC with PAC and PAM, when adding0.5mg/L PPC,15mg/L PAC and0.04mg/L PAM, the removal rates of turbidity, chroma, CODMn and UV254could reach61.35%,52.38%,30.06%,28.38%, respectively, which increased by3.44%,19.05%,8.11%and3.47%, respectively, compared with the combination of PAC and PAM only. According to the comparison experiments, the combination of PPC with powder activated carbon, PAC, and PAM qualified better enhanced coagulation effect than dosing separately PPC or powdered activated carbon with PAC and PAM.The results of combined diatomite with PAC and PAM showed that, when dosing15mg/L diatomite,15mg/L PAC and0.04mg/L PAM, the removal rates of turbidity, chroma, CODMn, and UV254could reach78.99%,76.19%,22.77%, and29.63%. The optimal pH was6-7. For combined zeolite powder with PAC and PAM, when adding25mg/L zeolite powder,15mg/L PAC and0.04mg/L PAM, the removal rates of turbidity, chroma, CODMn and UV254could reach55.95%,52.00%,23.46%, and30.99%. The optimal pH value was7-8. When conducting the enhanced coagulation under the same conditions of raw water, the effect of zeolite powder was better than that of diatomite.The results of combined powdered activated carbon and zeolite powder showed that, when the dosage of15mg/L PAC,0.04mg/L PAM, and40mg/L powdered activated carbon and zeolite powder mixture (mass ratio of2:1), the odor removal was performed well. Meanwhile, the removal rates of turbidity, chroma, CODMn and UV254could reach59.18%,70.00%,37.50%, and49.09%, respectively. When dosing15mg/L PAC and0.04mg/L PAM,1.2mg/L PPC, and20mg/L powdered activated carbon, the odor of water was reduced to0class after settlement and the removal rates of turbidity, chroma, CODMn and UV254could reach49.61%,65.00%,27.89%,40.19%., respectively. Generally speaking, the combination of PPC and powdered activated carbon was more suitable for practical application, owing to the lower dosage.The enhanced coagulation epxeriments on raw water of Furi water tresatment plant in Gaomi presented that:the combination of PPC and powdered activated carbon, selected for enhanced coagulation treatment, could improve the coagulation efficiency, and the odor removal of raw water which also benefited the consequent treatment process.