| The submerged membrane bioreactor (MBR), a combined process of biological treatment with advanced membrane separation, is a new technology for wastewater treatment and reuse. Process conditions and membrane fouling theory of treating sewage, as well as relevant process planning were investigated in this dissertation. The following results have been obtained:By experiment in a orthogonal design, optimizational process conditions of MBR treating sewage were made certain. The sequence of process conditions was hydraulic retention time (HRT) 5h, dissolved oxygen 3mg/L, suction time 12minand stopping suction time 6min according to influencing size. HRT mainly reflected flux. Influence of wastewater concentration on mixed liquor viscosity was studied through the theory and general relational expression of mixed liquor viscosity & operational conditions was obtained for the first time. In the experiment, 36d of optimal sludge discharge time was obtained, activated sludge concentration of this reactor maximized 12.0151g/L, and it was explained by the theory according to the formula of activated sludge growth rate.By a long-term running test, membrane fouling was investigated in detail. Wastewater cycle and adding oxygen of the reactor were produced by aeration. An increase of influent water cycle flow could result in increased aeration intensity, as well as an increased main chamber depth. Velocity of flow increased with bubble volume andbuoyancy in wastewater rising of main chamber. Aeration buoyancy of main chamber increased through decreasing velocity of subsidiary chamber. Membrane fouling critical velocity of running and back purge was found based on the theory of eliminating membrane outer fouling. The method of decreasing membrane outer non-fouling critical velocity was decreasing suction pressure and main chamber width in the case of stable grain size. Membrane outer fouling was decreasing or membrane fouling was eliminated through decreasing velocity of subsidiary chamber and reasonable control pressure of pipe inner. The chemical cleaning way of resolving membrane fouling was increasing grain size and decreasing appeal of gel & membrane pipe wall. When pipe inner was laminar flow, membrane inner caliber was big, membrane inner pollutant grain size was small, membrane inner non-fouling critical velocity was small. By chemical cleaning, the way of decreasing membrane inner non-fouling critical velocity was decreasing pollutant grain size in the case of laminar low or increasing its size in turbulence. Cohesion of membrane and pollutant need decreasing in spite of laminar flow or turbulence, namely, membrane outer fouling was effectively decreased when the same charge existed between sewage and membrane material. Existing gel of membrane inner had help to antipollution. By aeration, flow velocity of main chamber was water depth function, and it augmented with bubble rising. Membrane fouling was mostly caused by gel development, cake deposition on the membrane outer surface and microbial growth of protonema and staphylococci inside fibers. These protonema by intertwist blocked passage of filtrate moving. Membrane fouling mechanism had four circumstances, which were adsorption on the membrane surface, concentration polarization, gel development and membrane bore blockage. The main control conditions of being achieved long membrane-washing period was to keep good hydraulic cycle, design rational passage of rising and falling flow, control suitable aeration intensity and maintain operational condition steady. Membrane fouling was mostly caused by microbial growth, so the cleaning method adopted the combination of acid and alkalicleaning.By a long-term running test, steady operational performance of MBR treating domestic wastewater was discussed in optimized conditions. It was feasible to adopt fuzzy mathematic in the evaluation of membrane filtration and optimized conditions of selection by compare among conditions. During the whole running, the results of removing organics was steady, COD remained below 50mg/L, and o...
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