[Relationship between sewage treatment efficiency and bacterial community diversity in an A/O MBR].

An Anoxic/Oxic Membrane Bioreactor (A/O MBR) was used to treat sewage. Five different working conditions were run to determine the optimal process parameters. Bacterial community structures in both anoxic and oxic tanks were analyzed using denaturing gradient gel electrophoresis (DGGE). The relationship between effluent water quality and bacterial community diversity was established. The experimental results indicated that, under the optimal parameters of hydraulic retention time (HRT) 12 h, sludge retention time (SRT) 10 d, reflux ratio of nitrified effluent 300%, and reflux ratio of sludge 100%, the A/O MBR removed COD, NH4+ -N, and TN effectively and stably with the average removal rates of 96.4%, 99.1% and 75.8%, respectively. The bacterial communities varied markedly in both anoxic and oxic tanks during the sewage treatment experiment. Under a same working condition, the communities in both tanks were often similar with a similarity of more than 50%. The community diversity of the anoxic tank fluctuated depending on different working conditions, while the diversity of the oxic tank increased steadily along with the operation time. A positive correlation between the bacterial community diversity of the anoxic tank and the denitrification efficiency of the A/O MBR was established.