| There are many high-turbidity streams and rivers in China, and the studies on its treatment has long begun since last century. Among them, the study of the Yellow River is comparatively systematic and sufficient, and also bears fruit in practice. In terms of the previous reasearch methods, and the situation of the secondary disaster of Mingjiang river basin high-turbidity water induced by earthquakes, this paper focuses on the characteristics of flocculation and settling of high-turbidity water around this area. By means of laboratory experiments, systematic analysis is performed on the dosing order of different sediment concentrations, dosing interval, dosage and the settling characteristics of the flocs. It also explores the possible solutions to proxysmal high-turbidity water, and systematically analyzes the problems that occur at any of the paroxysmal high-turbidity water processing points.The major content and and the results of the experiments:(1) Through analysis of the characteristics and the causes of the high-turbidity water of Minjing River basin, it is found that 5.12 Earthquake in 2008 is the primary cause. Because of the landslides at the upper reaches of Mingjiang River after the earthquake, the rain washed sediment into Mingjiang River under the circumstance of sudden rainstorm. Therefore, Mingjiang River Basin high-turbidity water is of proxysmal nature, and its grain composition and mineral composition are quite different from those of the Yellow River and Yangtze River.(2) The experiments were conducted to determine the dosing order, dosing interval and the dosage of PAC and PAM in high-turbidit water of different sediment concentrations. The settling tests were also employed to ascertain the settling performance in processing flocs under different dosages. The results show that:①There is linear relation between Mingjiang River basin high-turbidity water and the function C = 0.0005T + 0.4705.②The results about the dosing order: when the turbidity of the raw water varies between 10000~30000NTU, adding PAC before PAM is better than the opposite, because the sedimentation velocity is faster, and the remaining turbidity of the supernatant becomes less after 10 minutes settling.③The dosing interval: when the turbidity of the raw water varies between 10000~25000NTU, and adding PAC before PAM, the most desirable time interval is between 60s~120s, and usually the optimum time interval is between 60s~90s.④The dosage: dosing PAC before PAM under the time interval of 60s, and as the turbidity of raw water gradually rises (10000NTU~30000NTU), the optimum coagulation requires corresponding increase in the dosage of coagulant. In the scope of different turbidity level 10000NTU~25000NTU, the optimum dosage is PAC 100-250mg/L, and PAM 0.3~0.8mg/L.⑤The dosage of PAC has miner impact on surface settling, while PAM is of critical dosage: PAM starting dosage, under which the settling performance is the best and the final overall sludge is minor. PAC has less influence on the flocculated settling performance than PAM, but the increase PAC dosage will lead to the increase of ultimate compressing sludge.⑥The water plant, which can handle the volume of 10×104m~3/d during processing Mingjiang River basin high-turbidity water, needs sedimentation basin of 875.5m2, and 2m compressing depth. The maximum density of sludge discharge is 126 kg/m~3, and the discharging cycle is 1h. The Sixth Water Plant of Chengdu demands less water inflow to debug to meet disposal needs.
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