Study on the recovery of a failed nitrifying MBR system
失稳硝化膜生物反应器的性能恢复研究

In this study, we investigated the recovery process of a nitrifying membrane bio-reactor (MBR) system, which failed to achieve complete nitrification under the stress of high hydraulic loading (HRT) (5 h).When the HRT was increased from 5 h to 10 h (the condition permitting complete nitrification previously) at an influent NH4+-N concentration of 500 mg·L-1, an NH4+-N removal of 99% was achieved.However, serious NO2--N accumulation occurred, and the average NO2--N concentration in the effluent was 425 mg·L-1 during the experimental period (60 days).Fluorescence in situ hybridization (FISH) analysis showed that while the percentage of ammonia-oxidizing bacteria (AOBs) in total bacteria did not change (12.9% in this study compared to 9.75% at the HRT of 5 h in previous study), the percentage of fast-growing Nitrosomonas sp.in AOBs decreased from 80% to 40%.The percentage of nitrite-oxidizing bacteria (NOBs) was only half of that at 5 h HRT (from 5.64% to 2.84%), and the slow-growing Nitrospira sp.remained as the dominant nitrite oxidizing population.It is possibly the high NO2- and extracellular (497·1 mg·L-1) concentrations in the reactor that made the nitrate oxidizing function difficult to recover.