| How to improve permeation flux and control the permeability decline is one of the key problem in application of membrane in drinking water treatment. In this paper,we analyed the effect of natural organic matter characteristics on UF membrane flux and intensively studied the effects and mechanism of the coagulation and PAC pretreatment avoided UF membrane flux decline. The main results were as follows:1. In this paper, four different micro-polluted raw water were selected to do the filitration test for studying UF membrane fouling by NOM. It can be concluded that DOM in raw water was often the major contributor to membrane flux decline and the more DOC concentration and higher content of hydrophobic fraction, the more flux decline. The research also indicated that when raw water was directly filtrated by UF membrane, flux was declined obviously due to the more hydrophobic fraction rejected.2. The four NOM fractions were separately filtered by UF membrane in the same condition. It can be concluded that the membrane flux was different. The lowest was the strong hydrophobic fraction and then was the weak hydrophobic fraction, the charged hydrophilic fraction, the raw water and neutral hydrophilic fraction, respectively. The results also indicated that the order of organic fraction rejected in membrane was as follows: raw water>the strong hydrophobic fraction>the charged hydrophilic fraction>the weak hydrophobic fraction>the neutral hydrophilic fraction.3. Based on the coagulation test of four different micro-polluted raw water, the test results showed that coagulation pretreatment made contribution not only to improving membrane flux,but also to retarding flux decline, and the membrane flux was increased with the increase of coagulant dosages. Coagulation was more effective in removing hydrophobic fraction, especially the strong hydrophobic fraction, while it was less effective for hydropholic fraction. From the molecule...
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