Transient　anoxia　due　to　the　periodic　anoxic/aerobic　operation　is　beneficial　for　the　nitrite-oxidizing　bacteria　(NOB)　suppression.　A　continuous　reactor　of　modified　University　of　Cape　Town　process　treating　municipal　wastewater　was　equipped　with　alternating　anoxic/aerobic　zones　to　maintain　nitritation.　Higher　nitrite　accumulation　ratio　in　the　oxic　zones　was　achieved　through　transient　anoxia　and　shorter　aerobic　actual　hydraulic　retention　time　(15　min),　but　it　steeply　deteriorated　from　above　95.0%　to　21.0%　after　elevated　temperature　(25　degrees　C).　Batch　experiments　indicated　that　the　existence　of　initial　nitrite　at　the　starting　of　aerobic　phase　promoted　the　recovery　of　NOB　activity　from　transient　anoxia　and　inhibited　the　activity　of　ammonium-oxidizing　bacteria.　Furthermore,　a　supplemental　modeling　further　confirmed　that　the　specific　growth　rates　of　NOB　(mu(NOB))　decreased　at　the　anoxic　phase　and　the　recovery　extent　of　mu(NOB)　after　anoxic　exposure　have　a　positive　correlation　with　the　initial　concentrations　of　nitrite,　leading　to　the　failure　of　maintaining　nitritation.