| The coagulation-ultrafiltration process was increasingly concerned in the field ofdrinking water treatment as the water quality standards are improving and the cost ofmembrane is decreasing. Membrane fouling could be effectively lessen when flocformed in the coagulation and gathered on the membrane surface, so, combinedcoagulation-ultrafiltration had a better performance on the raw water treatment. Apilot-scale experiment of coagulation-ultrafiltration was studied, aiming to optimize theperformance, was carried out in a water treatment plant in Tianjin. The operationalparameters were also been determined. The main results are as follows.(1) The performance of the coagulants is that PAC> FeCl3> AS. Since the mixtureof the three coagulants has the similar performance as alone, it is claimed that PAC isthe best coagulant. The optimum doses of PAC in the low temperature period, thenormal temperature period and the high temperature period are6mg/L,4mg/L and4mg/L, respectively.(2) Increasing coagulant dosage, reducing the membrane flux, shorting the filterbackwash time, and taking several pretreatment measures can alleviate the membranefouling in the low temperature period and the high temperature period. Based on theresult of the test, the impaction that organic substance had on the membrane fouling isstrong hydrophobic organic substance>hydrophilic organic substance> weakhydrophobic organic substance.(3) The operational parameters were that the membrane flux, filter backwashtime and emptying times is18.2L/(m~2·h),90min and5times, respectively in the lowtemperature period while the parameters were25L/(㎡·h),90min and5times, and22L/(㎡·h),75min and5times in the normal temperature period and the high temperature period, respectively.(4) Results of this pilot study indicated that the quality of effluent from thiscoagulation–ultrafiltration was satisfactory and stable, while the turbidity of theeffluent was below0.1NTU, and the removal efficiency for algae could reach to100%. |
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