| The effect of EPS on membrane fouling while MBR ran regularly and sludge bulking happened was study. Polysaccharide was major fouling substances, and fouling mechanism of polysaccharide on membrane was also investigated.In view of the complex in MBR, Polymeric Substances of polysaccharide formed due to interaction amoung polysaccharide produced by various microorganisms,so polysaccharide produced by some microoganism can not separate and extract. Bacillus subtilis and pseudomonad strain exist in activated sludge and generate levan during metabolic processes. This polysaccharide was chosen to analysises fouling mechanism on Polyvinylidene Fluoride(PVDF)membrane static and dynamic phase. Results were shown as follow:⑴MBR ran regularly, polysaccharide and protein were the major components of EPS both within activated sludge and fouling layer of membrane. The average ratio of polysaccharide to protein was 2.9, which was 5.3 in the fouling layer of membrane. Sludge bulking in MBR belong to non-filamentous sludge bulking, mainly because polysaccharide of high concentrations accumulated in MBR. When the sludge bulking happened, components in EPS was affected The average ratio slightly increased to 4.5 and 5.8, respectively, in activated sludge and the fouling layer of membrane. Accordingly, sludge viscosity was enhanced with an increase in content of polysaccharide, and flux went down faster than without sludge bulking. flux went down from 7.8L/m2·h to 3L/m2·h within five days, after sludge bulking. Polysaccharide was the most important pollutant on membrane.⑵The effect of solution chemistry conditions on levan adsorption onto Polyvinylidene Fluoride(PVDF)membrane was investigated. Levan adsorption on PVDF membrane reached a plateau after 60min of contact. With increasing pH, the amount adsorbed firstly decreased, then increased, and got a minimum value of 20mg/m2 at pH 7.0. As ionic strength increased, adsorption increased, then decreased, and got a maximum value of 39 mg/m2 at ionic strength of 0.004. Adsorption isotherms followed Langmuir laws. The equation parameters and adsorption free energy were obtained at different solution chemistry. According to the adsorption free energy, the interaction between levan and membrane surface may be dominated by electrostatic(EL)and van der Waals(LW)interaction, and adsorption was reversible.⑶Filtration characteristics and mechanism of levan on PVDF membrane fouling were investigated. The relative initial flux and terminal flux were higher while pH=7.0. concentration variation of levan has great influence on membrane fouling. The relative flux decreased more quickly at first 5min,and decrease to a stable value.at higher pressure, and cake resistance increased at high pressure. Cake resistance-limited dominated the most duration of microfiltration process. Membrane fouling can be mainly attributed to the polysaccharide deposition on the surface of membrane.
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