Enhanced nitrogen removal and in situ microbial community in a two-step feed oxic/anoxic/oxic-membrane bioreactor (O/A/O-MBR) process

BACKGROUND The carbon in raw sewage can be reclaimed to reduce nitrate for the advanced denitrification in municipal wastewater treatment plants. A novel two-step feed oxic/anoxic/oxic-membrane bioreactor (O/A/O-MBR) process was proposed to improve carbon-use efficiency. RESULTS The flow distribution ratio (FDR), aeration mode and hydraulic loading were optimized to minimize the effluent total nitrogen (TN) concentration. When the FDR was 1:1, the intermittent aeration mode was 4 min air-on/6 min air-off and the influent flow was 5 L h(-1), the nitrate removal efficiency in the post-denitrification tank rose to 87.0% and the effluent TN concentration decreased below 15.0 mg L-1. The intermittent aeration strategy in the post oxic-membrane tank effectively promoted TN loss. The N-15-DNA based stable isotope probing experiment illustrated that Proteobacteria (35.09%), Actinobacteria (20.56%) and Chloroflexi (16.67%) dominated the intermittently aerated biofilm, and Nitrospira (9.06%) was the major nitrite oxidizing bacteria rather than Nitrobacter, representing a dominant simultaneous nitrification and denitrification pathway for nitrogen removal. CONCLUSION The integration of autotrophic nitrifying bacteria and heterotrophic denitrifying bacteria enhances the terminal TN removal under intermittent aeration mode. The two-step feed O/A/O-MBR process has the potential to solve carbon limitation in sewage wastewater treatment. (c) 2018 Society of Chemical Industry