| This paper compared the characteristics of two different types of MBR, the composite membrane bio-reactor (CMBR) and the submerged membrane bio-reactor (SMBR), through the treatment of domestic wastewater. Laboratory work had been done on CMBR and SMBR focused on the optimum operation condition, the effect of pollutant removal in long-term operation and the relationships among EPS, the activity of sludge and the membrane contamination.Results of lab tests indicated that the two MBRs had same optimum operation conditions. That is HRT=6 h, DO=2.5 mg/L, pH =7.18.1 and C/N ratio=18.238.9.Long-term operation showed similar removal of COD and NH3-N for both MBR modes. Averagely, more than 95% of COD was removed with the effluent content of less than 20 mg/L, and more than 95% of NH3-N was removed with the effluent content of less than 1.5 mg/L. However, the average removal of TN in CMBR was 67.46%, which was 13.01% higher than that in SMBR. Moreover, the average removal of TP was not effective for both MBR modes, with the removal of 21.97% and 22.99% for CMBR and SMBR respectively. A stable performance could always be maintained during the long-term operation for both MBR modes.The relationships of COD and NH3-N degradation rate with operating time were developed based on Eckenfelder and Monod model respectively. The maximum degradation rates of COD were 3.09 for CMBR with operating time=59d and 2.72 for SMBR with operating time =50d. The maximum NH3-N degradation rates were 7.59 mg/L·h and 9.96 mg/L·h with operating time =50d and 43d respectively.The optimum condition of extracting EPS with cation resin was also a research point on this paper. The outcome showed the extracting effect would be better when the dose of resin was 60g/gVSS, extracting time was 4 h and the frequency of shaker was 200rpm. A mathematical model between extraction quantity of EPS and the influence factors was set up and verified.According to the laboratory results, the content of EPS per unit volume of...
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