Research On The Processing Performance And The Membrane Fouling Factors Of Anoxic/Oxic Membrane Bioreactor

Membrane bioreactor (MBR), which is combination of the membrane separation unit and the biological treatment part, has many advantages, high activated sludge concentration, high treatment efficiency, short process and so on. However, the membrane fouling restricts the further development of the MBR. Many studies have been determined that the EPS is the most important biological factors of membrane fouling.The first step of the study was activated sludge acclimation and biofilm. Then the treatment efficiency of COD, ammonia nitrogen, total nitrogen was researched under the conditions of different HRT, different influent concentration and different dissolved oxygen concentration in the A/O MBR. Also the change of EPS and its components content and the effect of EPS on membrane fouling was studied under different influent loading and different dissolved oxygen concentration. On the basis, the changes of the activated sludge microbial population was researched under different dissolved oxygen concentration. The main conclusions are as follows:After26days of activated sludge acclimation, COD removal rate is more than85%, the concentration of the sludge is about3700mg/L, SV is30%and remain stable, when sludge acclimation is successful.When the hydraulic retention time is5h, the average removal rate of COD, ammonia nitrogen and total nitrogen are up to93.1%,92.7%and64.9%; When the influent COD loading is0.3kgCOD/(kgMLSS-d) and the ammonia nitrogen loading is0.025kgNH4+-N/(kgMLSS·d), the average removal rate of COD, ammonia nitrogen and total nitrogen are up to95.7%,94.5% and69.7%; When the dissolved oxygen concentration is about3mg/L, the average removal rate of COD, ammonia nitrogen and total nitrogen are up to95.2%,94.1% and71.6%. The optimal operating conditions of A/O MBR:the hydraulic retention time is5h, he influent COD loading is0.3kgCOD/(kgMLSS·d) and the ammonia nitrogen loading is0.025kgNH4+-N/(kgMLSS·d), the dissolved oxygen concentration is about3mg/L. With the increase of load water, the content of EPS and its components are reduced, membrane fouling rate also will slow down. With the increase of the dissolved oxygen concentration, the content of EPS and its components are first decreased and then increased, the membrane fouling rate trend is consistent with it, but also decreased and then increased. The EPS and its components are the influencing factors of membrane fouling. The content of polysaccharide is more than the protein in the EPS. The membrane fouling is exacerbated as the increase of the polysaccharide and the protein contents, but the protein has a greater influence on membrane fouling.According to the analysis of DGGE profiles, the richness of the microbial community of the dissolved oxygen concentration of3mg/L and6mg/L is higher than the dissolved oxygen concentration of lmg/L. The microbial community structure similar of the dissolved oxygen concentration of3mg/L and6mg/L is higher. When the dissolved oxygen concentration is3mg/L, the microbial communities is in a high degree, the treatment efficiency of the organic matter is the best, the EPS content is lowest and the membrane fouling rate is slowest.