Simultaneous　partial　nitrification,　anammox　and　denitrification　(SNAD)　process　was　successfully　realized　for　treating　low　C/N　ratio　sewage,　nitrogen　and　COD　removal　achieved　to　3.26　kg　m　(3)　d　(1),　81%,　respectively.　The　nitrogen　removal　performance,　microbial　community　and　distribution　of　the　functional　microorganisms　were　investigated.　Results　suggested　that　the　presence　of　COD　performed　activity　inhibition　on　both　aerobic　ammonia-oxidizing　bacteria　(AerAOB)　and　anaerobic　ammonia-oxidizing　bacteria　(AnAOB),　and　led　to　the　number　decreasing　of　both　AerAOB　and　AnAOB.　Even　though　COD　presence　resulted　in　the　biodiversity　increasing　of　AerAOB　and　decreasing　of　AnAOB,　the　dominant　species　were　always　Nitrosomonas　and　Candidatus　brocadia　during　the　whole　experiment.　Clone-sequencing　of　16S　rRNA　results　suggested　the　emergence　of　five　different　denitrifying　species,　which　then　led　to　a　higher　nitrogen　removal.　Results　in　this　study　demonstrated　that　the　applied　start-up　strategy　was　feasible　for　SNAD　process　treating　low　C/N　ratio　sewage.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.