N2O and N2 production during heterotrophic nitrification by Alcaligenes faecalis strain NR

► Alcaligenes faecalis NR with the capability of heterotrophic nitrification and aerobic nitrogenous gas production was isolated. ► Nitrogenous gas was speculated to be produced via hydroxylamine instead of nitrite. ► A novel aerobic nitrogen metabolism of NH4+→NH2OH→N2O→N2 was discussed. ► Enzyme assay was conducted to further confirm this metabolic pathway. ► This bacterium offers better performances on nitrogen removal without the requirement of redox cycling on complex structures.