The water samples were fractionated by PES ultrafiltration (UF) membranes with molecular weight cutoffs (MWCOs) of 10kDa□30kDa and PVDF UF membrane with MWCOs of 100kDa, and these permeates were filtrated by PVDF UF membrane with MWCOs of 150kDa and CA microfiltration (MF) membrane with a 0.1μm pore size, as to investigate influence of nature organic matter (NOM) with different MWCOs on flux. The results demonstrated that NOM larger than 30kDa accounting for 15% of total organic matter resulted in 86% of flux decline for MF and 54% for UF, respectively. It was shown that coagulation removed the NOM larger than 100kDa that resulted in over 40% of flux decline. As a result, in spite of removing only 10% of NOM, coagulation enhanced flux substantially. Powdered active carbon (PAC) removed NOM smaller than 30kDa that showed little contribution to flux decline. Therefore, PAC removed 76% of NOM but showed little contribution to enhance flux. It can be concluded that the effect of pretreatment on enhancing flux can not be depended on amounts of NOM removed but on its contribution to flux decline.

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