| Microbe and extra-cellular polysaccharides (EPS) are two major components of membrane fouling layers in membrane bioreactor (MBR). Developing the studies on these two factors for surface characteristic, EPS structure, fouling mechanism and synergetic effect are of theoretical and practical significance to reveal membrane fouling nature and control membrane fouling.In this study, four dominant strains were screened from membrane fouling layer in a membrane bioreactor for simulated domestic wastewater treatment. Among them, the K. oxytoca was selected and taken as a model for the relevant research of membrane biofouling.The main research results of this dissertation were shown as follows:(1) The MBR showed an excellent treatment effect for the simulated domestic wastewater. Both the removal rates for the COD and NH3-N were above 90%. The phylogenetically identified result of 16SrDNA sequencing showed that four dominant strains isolated from membrane fouling layer were Klebsiella oxytoca, Micrococcus luteus, Rhodococcus erythropolis and Bacillus cereus, respectively.(2) The EPS of K. oxytoca is a homogeneous polysaccharide with the average molecular weight of 116018 Da. The particle size distribution of the EPS ranges from 185 nm to 294 nm and the average hydrodynamic size is 260 nm. The EPS was comprised mainly of rhamnose, fucose, arabinose, xylose, mannose, galactose and glucose with a molar ratio of 0.032968: 0.041085: 0.014653: 0.005126: 0.239307: 0.098622: 0.130377. Some typical polysaccharide absorption peaks corresponded to 3410.31 cm–1, 2924.41 cm–1 and 1384.05 cm–1 were also appeared in the FT-IR spectrum of this EPS. The rheological studies proved that the EPS exhibited non-Newtonian and shearing-thinning behaviors with pseudoplastic properties.(3) The permeate fluxes through the PVDF and PP microfiltration membranes exhibited similar decline trends. The EPS showed higher fouling on the PVDF membrane than on the PP membrane. The fouling mechanisms of the EPS for both the membranes were divided into two phases. During the first phase, more than one fouling mechanism was included and at the later phase, the fouling mechanism tended to cake filtration mode. The PVDF membrane had the larger values of Rt than the PP membrane under the same working conditions. For both the membranes, R f dominated in the fouling resistances with the high percentages and R c acted as the secondary role. The static adsorption of the EPS resulted in a slight membrane fouling. A large fouling from static adsorption was contributed to the PVDF membrane with respect to the PP membrane.(4) The result of surface thermodynamic studies showed that all the membranes and bacteria exhibited typical high electron donors. Although all the bacteria and membranes were hydrophobic based on the negative values of G sws. However, the PP membrane showed a relative stronger hydrophobicity than others. The interfacial surface energies for both K. oxytoca-membrane systems were negative at the special separate distance and the K. oxytoca-PP membrane system had a larger negative value. The adsorption and filtration evaluation also revealed that the PP membrane could adsorb more K. oxytoca than the PVDF membrane, indicating that independently measured surface thermodynamic properties could be used to predict the fouling potential of bacteria-membrane filtration process.(5) With the equal amount of EPS, the membrane flux of K. oxytoca-EPS mixture was decreased with the strain cell amount increasing. The mixture showed the greater fouling propensity for PP membrane than for PVDF membrane under the same working condition. Under the lower cell concentration, the fouling mechanism of mixture was generally transferred from the internal fouling to the external fouling. However, as for the higher cell concentration, the external fouling was the dominant mechanism for all the filtration process. The EPS transmission concentration of mixture was smaller than the EPS solution alone for the rejection of cell cake on the membrane surface. The fouling potential of mixture increased with the EPS concentration increasing, but the EPS transmission had no significant change.
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