brane modules, with pore sizes of 0.22 and 0.1 μm, were used to investigate their effects on virus rejection at the transmembrane pressure of 8.5 kPa. It was found that 0.1 μm membrane had complete rejection of virus, and 0.22 μm membrane had significant rejection of virus. In the longterm operation of this MBR, no significant difference was observed between both pore sizes because the virus concentrations of the effluent in both cases were in the same order. Effluent virus concentration at steady state of MBR running was less than 2 PFU/mL. The removal ratios of coliphage T4 in MF processes were more than 105.5. The membrane surface deposits played an important role in the rejection of virus. The formation of cake clay on the membrane surface was the main cause of high rejection of coliphage T4 with MF of 0.22 μm.

Virus removal in a membrane bioreactor(MBR) by gravity drain was studied. Coliphage f2(mean size of 25 nm), which is similar in size to human enteric pathogenic viruses, was selected as a model virus. Two microfiltration membrane modules with pore sizes of 0.22 μm and 0.1 μ m were applied to investigate the effects of membrane pore size on the virus rejection. The MBR with these modules could reject virus in a range of 2.6- 5.1 logs. The experimental results showed that the mechanisms of virus removal in the MBR involved rejection and inactivation. The virus rejection depended mainly on the dynamic layer on the membrane surface(not membrane itself) because virus rejection by the membrane modules with pore sizes of 0.1 μm and 0.22 μm were similar. The microbial activity and the aeration oxidation were the two important factors for the virus inactivation. It was found that the inactivation of coliphage f2 was much more rapidly in activated sludge mixed liquor than in clean water, and the effect of aeration was significant.

A new membrane bioreactor with gravity drain for municipal wastewater treatment was tested and its operational factors were investigated in this study. These factors include pressure head, MLSS, aeration intensity(an air flow rate per unit floor area) and temperature. Results of batch experiments showed that a critical pressure head of the MBR was 0.85- 1.5 m- H2O. At a pressure head of 0.85 m- H2O, statistical analysis of batch experiments showed that aeration intensity significantly affected membrane flux, and the MLSS had no impact on membrane flux under a temperature of 22.0± 1.0 ℃. Results of the long- term continuous experiment showed that temperature significantly affected membrane flux. The impact of temperature on membrane flux in this case was about 4- 10 times of that analyzed by using a classical cake layer model. During this experiment, the average removal efficiencies of COD, BOD5 and NH4+- N were over 85%, 97% and 94%, respectively.

the pore sizes of 0.22 and 0.1 μm, respectively. In tap water system, 2.1 ιg rejection of coliphage T4 could be achieved by PVDF membrane compared with complete rejection by PP membrane, while for coliphage f2 with smaller diameter, 0.3- 0.5 lg rejection of the influent virus was removed by the two membranes. In domestic wastewater system, cake layer and gel layer on the membrane surface changed the cut- off size of the membrane so that there was no significant difference between PP and PVDF for each coliphage. The removal ratios of coliphage T4 and f2 in the MBR were more than 5.5 and 3.0 lg, respectively. Compared with 5.5 lg removal for virus T4 in the MBR system, only 2.1 lg(96.8%- 99.9%) removal rate was observed in the conventional activated sludge system with the influent virus concentration fluctuating from 1830 to 57000 PFU/mL. Only 0.8%- 22% virus removal was the effect of adsorption to activated sludge, which showed a decreasing tendency with the retention time, while 75%- 98% was the effect of virus inactivation by microbial activity. It indicated that the major mechanism of virus removal was not the transfer of viruses from the water phase to the sludge phase but inactivation in the biological treatment process.

从公共卫生安全角度出发，分析了污水处理过程中可能存在的卫生学安全问题。综述了膜分离方法对细菌与病毒的去除机理，以及对病原微生物的去除效果，并对膜分离过程中存在的问题进行了初步分析，提出了在污水消毒方面应该注意和需要进一步研究解决的问题。