| Chinese rural water resources pollution and water environmental destruction threated healthy drinking water life. One reasons for the destruction of Water environment is the rural domestic sewage discharged indiscriminately.Rural sewage can not be collected, and the sewage treatment in a difficult way.Today,decentralized wastewater treatment technology used in developed countries for the treatment of decentralized wastewater,which gaining good influence. In our country, decentralized wastewater treatment technology is still in a fledging period, many technology have disadvantages.Membrane bioreactor acts a wastewater treatment process which combining activity sludge method and membrane filtration technology.The efficiency and flexible, Less space occupation, which recovered many shortcomings of decentralized sewage treatment process. But the membrane fouling and the high energy consumption becomed serious problems, even affecting the marketing promotion of MBR. A large number of studies are working on how to improve the MBR treatment efficiency and reduce the Membrane fouling.This topic aimed at the decentralized sewage treatment technology in Guizhou rural. Making a research for Chetian village sewage plant which used the A2O-MBR process. Exploring the Pretreatment process, the aeration intensity, Sludge reflux ratio, MLSS, membrane fouling cleaning method by building A2O-MBR test. The experimental results showing that:Single factor variable test about mixed liquor reflux ratio concluded that operating the reflux ratio in the scope of 100% to 300%.The removal rate of CODcr and NH3-N at 85%, The removal rate of TN, TP showed a Growth trend at first but a declined trend after. The reason is that excessive reflux ratio destructed the anoxic/anaerobic unit oxygen environment in A2O-MBR, the denitrifying bacteria and phosphorus accumulating bacteria in a high dissolved oxygen environment, which declining the microbial activity. Comprehensive analysis, when mixed liquor reflux ratio at 150%, the A2O-MBR process at a high operation efficiency.Test about the aeration intensity:when the aeration intensity increased from 300 L/m2·h to 1000 L/m2·h, the removal rate of CODcr is stationary,but the removal rate of NH3-N, TN and TP showed a Growth trend at first but a declined trend after. The Low aeration intensity leaded a Inefficient activity of Activated sludge. And high aeration intensity destructed the anoxic/anaerobic unit oxygen environment, which damaged the structure of the floc of sludge, resulting in decreased processing ability. When monitoring the transmembrane pressure, we found that low or high aeration intensity will increase the transmembrane pressure, Aggravate membrane fouling. Analysis shows that the membrane encountered a poor cleaning effect in a aeration intensity working condition, resulting in the accumulation of cake layer; high aeration intensity trend disintegration of sludge floc which causing the membrane fouling. The comprehensive analysis, the best aeration intensity was 500 L/m2·h.Test about the mixed liquid sludge concentration:The test apparatus working for 87 days with no spoil disposal operation, the MLSS increased from 2461mg/L to 10342mg/L. CODcr, NH3-N removal rate changed steadily with the growth of MLSS, but the TN and TP in a low removal rate under the condition of high MLSS. The reasons is that high MLSS influenced the activity of nitrifying bacteria, reduced the phosphorus metabolism ability, hindering the removal of Nitrogen and phosphorus. At the same time, high MLSS working condition causing the membrane fouling and shortening chemical cleaning cycle, The comprehensive analysis, MLSS in the scope of 3500-6500mg/L will promote the system work.Contrast test of casting Polyaluminium chloride(PAC) in A2O-MBR system showed that, PAC contribute little to the Pollutants removal. But PAC improved sludge mixed liquor characteristics, also alleviated the membrane fouling. PAC make the membrane chemical cleaning cycle extension for 4-5d, which alleviate the membrane fouling.Single factor variable test determined the best operation condition of A2O-MBR system, reflux ratio: r=150%, aeration intensity:500 L/m2·h, MLSS:3500mg/L--6500mg/L., The removal rate of CODCr reached 90%, the removal rate of TN was 74%, the removal rate of TP was 75%. The effluent water quality achieved wastewater reclamation and reuse standards. The casting of PAC coagulant, charging the membrane cleaning cycle at 26 days. Prolong the service time of the membrane. Test showed that, the best working conditions improved A2O-MBR system treatment effect, and mitigate membrane fouling.According to Darcy equation, the membrane resistance distribution of membrane itself, filter cake layer and membrane pore blocking found to be 22.3%,19.4%, and,58.3%. The membrane pore blocking was the biggest factor affecting the filtration.According to the membrane resistance distribution, a membrane module cleaning method was proposed. The high-speed water washing?acid chemical cleaning?oxidizing agents cleaning. After cleaning, we found that the high-speed water washing recovered to 21% and acid chemical cleaning recovery to 63%, oxidizing agents cleaning recovery to 96%. The cleaning method is effective and feasible. |
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