Research On The Design,Simulation And Process Operation Of Marine Membrane Bioreactor

Along with marine environmental pollution becoming serious,all countries around the world paid more attention to marine environment with constant increase of sewage discharge standard,which became a challenge to ship environment. Compared with other marine sewage treatment equipment, membrane bioreactor (MBR), with stable treatment effect,strong anti shock and swing and small volume, was paid close attention to. However, it still could be further optimized, such as promoting efficiency and reducing volume. Therefore, this paper carried out an experimental research on improving MBR efficiency, reducing its volume and increasing its ability of anti shock and swing.The small scale MBR device was chose to carry on the experiment. Firstly, the affecting factors of MBR in the treatment of marine domestic sewage were researched, in which the samples of activated sludge and membrane reactor were regularly collected, and enzyme activity and membrane surface pollution of microorganisms were analyzed. Secondly,combining with small scale MBR test, this paper used BP neural network to simulate the key environmental factors of MBR running process and it selected 4-7-1 topology structure of BP neural network. Finally, this paper carried on the design and test of marine MBR.The experimentally research finds out the law between the quantitatively combination of common factors and the removal of pollutant, and it also builds the simulation to optimize the main process parameters. (1) In order to make effluent quality meet the requirements of 2010 IMO emission standard, it should satisfy that hydraulic retention time (HRT)? 4h, with optimum value being of 5?8h, optimum mixed liquor suspended solid (MLSS)?2000mg/L and pH ? 6. When salinity rises to 28g/L, chemical oxygen demand (COD) removal rate decreases to 53%,due to the strong inhibitory effect of salinity on the removal efficiency. (2)BP neural network is used to carry on simulation, diagnosis and identification. The results show that the size order of influence factors on removal efficiency is HRT> salinity ? pH value> influent COD; the size order of influencing ammonia nitrogen removal effect is influent ammonia nitrogen>influent COD>activated sludge settling ratio>MLSS. Therefore,in order to improve the removal efficiency of COD and ammonia nitrogen in sewage, the control of HRT and influent ammonia nitrogen should be strictly controlled.The combination of scanning election with test is used to research on the alkalinity of membrane pollutant, occurring that pore structure in membrane surface constantly decreasing and membrane pollutant becoming serious with the test going on. Physical cleaning is to simply clean the membrane surface, while chemical cleaning can disassemble stubborn sludge.Therefore, chemical cleaning is the nonfundamental solution, whose effect is much better than physical cleaning.By the test of enzyme activity, it obtains that influent COD, MLSS is in positively related to urease and polyphenol oxidase, respectively. While MBR deals with saline sewage,the original activity of nitrate reductase, urease and invertase is respectively of 236.8, 203.3 and 15191, 7226.8?mol/h·gfw. When salinity increases to 35g/L, these four enzyme activities respectively decrease to 158, 66.7, 11895 and 5389?mol/h·gfw. Sewage salinity has a strong inhibitory effect on microbial activity of these four enzymes, being negatively related to microbial enzyme activity. The reason is that salinity affects environmental osmotic pressure and leads to the occurrence of plasmolysis, which controls the microbial activity, directly affecting the removal of pollutant.This paper carried on the design of marine MBR from the point of practical application,using fresh sewage from septic tank to do experiment. It reached the conclusions that: the device had strong capacity of anti shock, stable treatment of domestic sewage about 4000L/d,and the maximum processing capacity could be up to 5000L/d. The effluent COD, BOD5, SS,effluent ammonia nitrogen were stable at 100mg/L, 10mg/L, 10mg/L, 20mg/L, and effluent quality met the new emission standard of 2010IMO.