Simultaneous　anammox-denitrification　process　is　capable　of　complete　nitrogen　removal.　To　acquire　a　suitable　influent　(NO2--N/NH4+-N　＞　1.32)　for　it,　the　wastewater　could　be　treated　by　partially　oxidizing　ammonium　to　nitrite.　Although　many　studies　regarding　partial　nitritation　in　treating　high　ammonium　wastewater　have　been　reported,　very　little　research　has　been　undertaken　on　real　domestic　wastewater　for　long　term.　This　study　presents　a　partial　nitritation-sequencing　batch　reactor　(PN-SBR)　to　treat　domestic　wastewater　with　low　SCOD/TN　ratios　(2.3　+/-　0.6).　During　the　600　days＇　operation,　the　NO2--N/NH4+-N　ratios　in　the　effluent　mostly　varied　between　1.32　and　10.07　and　thus,　stable　partial　nitritation　was　maintained.　Moreover,　during　each　PN-SBR　cycle,　similar　to　47.6%　of　organics　in　raw　wastewater　were　efficiently　utilized　for　denitrifying　nitrite,　by　which　the　aeration　for　the　oxidation　of　organic　matters　was　decreased,　and　stable　nitritation　was　further　assured　due　to　the　lack　of　substrate　for　nitrite　oxidizing　bacteria.　High-throughput　sequencing　analysis　revealed　that　the　dominant　nitrifying　bacteria　were　Nitrosomonas　belonging　to　ammonia　oxidizing　bacteria,　while　no　nitrite　oxidizing　bacteria　were　detected.　During　the　idle　period　of　a　PN-SBR　cycle,　the　obvious　nitrite　decrease　without　observed　COD　consumption　might　be　due　to　the　predominance　of　Ottowia,　which　functioned　in　fermentation　and　denitrification,　for　which　nitrite　was　denitrified　by　using　readily　biodegradable　organic　matters　biodegraded　by　Ottowia　bacteria.