Stable　supply　of　nitrite　is　often　a　major　obstacle　for　achieving　mainstream　anammox　due　to　washout　failure　of　nitrite　oxidizers　(NOB)　at　low　influent　ammonia　of　municipal　wastewater.　In　this　study,　an　integrated　nitrification,　partial　denitrification　and　anammox　(INPDA)　as　a　one-stage　mainstream　nitrogen　removal　alternative　was　established　in　a　low-oxygen　sequencing　batch　biofilm　reactor　treating　synthetic　sewage.　The　overall　nitrogen　removal　and　nitrous　oxide　(N2O)　emission　were　mainly　investigated　at　50　mg/L　NIH4+-N　influent　with　a　low　carbon/nitrogen　(C/N)　of　2.5.　Continuous　operation　demonstrated　that　as　high　as　98.8%　NH4+-N　and　94.1%　TN　were　removed　in　SBBR　system.　Cyclic　experiment　verified　sequential　completion　of　nitrification,　partial　denitrification　and　anammox　were　responsible　for　high-rate　TN　removal.　During　one　typical　cycle,　the　trend　of　N2O　emission　was　characterized　by　firstly　rapid　rise,　then　fluctuant　decrease　followed　by　rapid　decrease　and　finally　slow　disappearance.　The　maximum　N2O　emission　rate　reached　up　to　6.7　mu　g/(L.min)　occurred　at　75　min.　High-throughput　sequencing　revealed　the　co-existence　of　nitrifying,　denitrifying　and　anammox　species　and　large　detection　of　key　functional　genes　(Hzs,　Hdh,　Hao,　Nor)　in　an　oxygen-limited　SBBR,　thereby　highly　correlating　nitrogen　removal　and　N2O　emission　characteristics.　Nitrogen　metabolic　pathways　analysis　further　suggest　denitratation(NO3--N　to　NO2--N)-based　anammox　is　a　main　route　for　mainstream　nitrogen　removal.　Moreover,　N2O　might　be　generated　by　both　hydroxylamine　oxidation　step　in　nitrification　and　also　heterotrophic　denitrification　pathway.　The　research　findings　provide　more　deep　understandings　of　enhanced　nitrogen　removal　and　mitigated　N2O　footprint　from　a　single　mainstream　anammox-based　system.