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