| In recent years surface water has been widely contaminated in China, conventional drinking water treatment processes can no longer meet the requirements of increasingly stringent drinking water quality standards, and the development of new water treatment technology would be urgently needed. With the advances in membrane technology, low-pressure microfiltration and ultrafiltration (UF) were found to meet the requirements, in which ultrafiltration effluent quality is better and get more attention. Immersed UF membrane has a wider range of potential applications because of it has a larger filtration area and relatively easy to operate, but there are still some key issues to be resolved in the practical applications.This research focused on the effect of membrane characteristics, pretreatment and operating conditions on the filtration performance of immersed UF membrane, membrane fouling control technology was developed from the two aspects of pretreatment and operating conditions. The optimized operation programs were proposed, and the feasibility of conventional treatment process to be replaced by submerged UF membranes was analyzed, which could provide important technical support for the practical application of the water plant.In this paper the effect of different materials and molecular weight cutoff on on the organic pollutants removal by membrane in surface water was first to be studied, and the results showed that the removal efficiency of turbidity and organic matters was increased gradually with the decrease of molecular weight cutoff membrane, but the removal of dissolved organic matters was lower. The removal of organic matters by UF membranes of different materials was different, indicating that different membrane materials and organic could interact with each other. Furthermore, tests on the effect of membrane material and organic matter on membrane fouling were studied, the results showed that the hydrophilic and hydrophobic organic acids with the molecular weight cutoff more than 30KDa were the main substance caused reversible membrane fouling, and the hydrophilic organic matter with the molecular weight cutoff less than 1KDa is the main substance caused irreversible fouling. But membrane fouling caused by different materials was varying and the types of organic matter which could cause membrane fouling are also different. In the long-term membrane filtration, the adsorption of organic matter with the molecular weight of less than 1K and 1K~3KDa by PVDF membrane was faster than PVC and PS membrane, membrane fouling is also faster, PS membrane had better resistance to organic pollution. Since the removal of organic matter by submerged membrane was limited and the membrane fouling was faster, pretreatment and pre-filtration were studied to improve water quality and to control fouling. Pretreatment methods included coagulation, powdered active carbon (PAC) adsorption-coagulation, sludge recycling, PAC-sludge recycling. The results showed that the efffcts of pretreatment on raw water turbidity and organic matter were better, which can significantly improve the membrane effluent quality, and PAC-sludge recycling was most effective with the DOC,UV254,CODMn,BDOC and THMFP removal 93.8%,37.3%,41.1%,48.7%,83.0%和57.9%. Four kinds of membrane pretreatment could reduce the TMP since the organic matters and particles could be removed in different degree, and thus the membrane fouling was delayed. The analysis on the membrane resistance during the operation showed that pretreatment could reduce the surface cake layer resistance and concentration polarization resistance, while the PAC-sludge recycling pretreatment could also reduce adsorption resistance, and its total resistance value the lowest, which was mainly due to the turbidity, organic matters with the molecular weight cutoff more than 30KDa and less than 1KDa had been better removed efficiently. In the pre-filtration experiment, the cake layer resistance decreases with the pre-filter membrane pore size or molecular weight cutoff decreases, the pore blocking resistance also decreased significantly, but adsorption resistance mainly caused by the of organic with small molecules could not be effectively reduced.Operating conditions is also an important factor to affect the membrane filtration performance. The effects of operating conditions on membrane effluent quality and membrane fouling were investigated and the influencing factors of critical flux were also studied. The results showed that the removal of particulate matter and organic matter had little difference in the constant pressure and constant flux conditions. In the long run, the constant pressure filtration could caused more serious irreversible fouing than the constant flux condition, and constant flux could make membrane filtration remain stable in a long run by selecting a reasonable flux and cleaning method. Aeration, intermittent filtration and intermittent aeration and coagulation could enhance the critical flux of ultrafiltration membrane, and the combination of these operating modes could effectively alleviated membrane fouling in long-term operation. In addition, critical flux value from the short-term flux-steps tests could have a good guidance to the practical application of immersed UF membrane.Two pilot experiments of immersed membrane in two typical kinds of surface water were researched based on the previous study. In the pilot study in Suzhou, coagulation, PAC-coagulation, sludge recycling, PAC-sludge recycling pretreatment could improve UF effluent quality. The removal of particulates and organic matters by PAC-sludge recycling was better than the other three kinds of pretreatment, and thus PAC-sludge recycling could hae more effective mitigation of membrane fouling. Study on the operating conditions showed that the combination of aeration and intermittent filtration could have better control of fouling, but reasonable aeration intensity should be selected in application. Coagulation pretreatment can reduce the TMP, and the the combination of coagulation, aeration and backwashing could have better mitigation of membrane fouling. In the study of Dongjiang, treating the membrane effluent turbidity had an advantage over the sand filter during the same period, the tubidity of which were maintained less than 0.1NTU, but the removal of organics was the same as sand filter. The test on optimization of operating conditions found that a relatively high flux could be selected in Dongjiang of better water quality, membrane filtration cycle should be shortened appropriately, and effective physical cleaning and auxiliary to short-term Enhanced Flux Maintenance (EFM) cleaning would ensure the long-term stable operation of membrane filtration. The combination with NaClO and HCl cleaning could have a greater degree of recovery on membrane performance.
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