The operational control conditions for realizing shortcut nitrification in the membrane bioreactor (MBR) process was investigated in a lab-scale anaerobic baffled reactor (ABR)-MBR combined system, which laid the foundation for further research on the performance of denitrification phosphorus removal in the system. The experimental results under different conditions showed that shortcut nitrification in the MBR was achieved by controlling the dissolved oxygen (DO) concentration to low levels (0.5-1.0 mg·L-1 to 0.3-0.7 mg·L-1) and changing the effective volume of the MBR to control hydraulic retention time (HRT), with the HRT in the ABR equal to 6 h, sludge reflux ratio of 100%, NOx--N reflux ratio of 300%, and temperature of 30℃±2℃. Finally, the shortcut nitrification deteriorated as the HRT in the MBR increased from 3 h to 5 h, with nitrite accumulation rate dramatically dropping from 60% to 15%. The analysis of the influencing factors of shortcut nitrification showed that maintaining low DO concentration (0.3-0.7 mg·L-1) and gradually shortening HRT were the key factors. The pH, free ammonia (FA), free nitrous acid (FNA), temperature, and sludge retention time (SRT) had a slightly positive effect on shortcut nitrification. During the period of shortcut nitrification, a stable and high efficiency removal of COD and NH4+-N were achieved, and the average concentration of the effluent of COD and NH4+-N, whose removal rates were above 90%, were below 50 mg·L-1 and 2 mg·L-1, respectively, and the removal efficiency of total nitrogen (TN) reached 72%.
Keywords: ABR-MBR combined process; NOx--N reflux; hydraulic retention time(HRT); nitrite accumulation rate(NAR); shortcut nitrification.