| This paper investigates the advanced treatment by hollow fiber membrane of the secondary effluent from Beijing Miyun Sewage Treatment Station. Owing to the difference between the techniques utilized in the first and second projects, the water quality of the two effluents was different. In order to fit for the quality standard of reuse, we developed coagulation-ultrafiltration(UF) process and coagulation-sand filter-UF process for the advanced treatment of municipal sewage. At the same time, the mechanism of UF separation is analyzed. The removal of turbidity, COD and NH3-N by the two processes are examined. The effect of coagulation pretreatment on the treatment result is described. The disciplinarian and reason for the decline of flux are also discussed. In the process of this test, the working route of UF system is that the UF operates as the dead-end filter for 30-min followed by backwashing 30s that is divided into two 15s steps, that is, 15mg/L NaClO is added as chemical cleaning in the first step followed by tap water flushing in the second step. The results indicate that the COD removal efficiency is about 20-50% in the case of coagulation-UF process. The coagulation-sand filter-UF process can improve the removal rate of COD up to 60%, owing to dosing aluminum coagulant. In addition, because the sand filter intercepts the coagulation flocs, the pollution of UF membrane is minimized. Whatever coagulation-ultrafiltration(UF) process or coagulation-sand filter-UF process being used, the removal effects of NH3-N and TP is not remarkable. The reason is that the mechanism of UF is screening in which the molecular weight of NH3-N or TP compounds is too small to be easily held back by the aperture of the UF membrane. The SDI of effluents from both processes is less than 3, which satisfies the pretreatment requirement of the reverse osmosis. Accordingly, both processes can be applied to pretreatment procedure of the reverse osmosis for the advanced treatment of municipal sewage.
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