Although　biological　nitrogen　removal　via　nitrite　is　recognized　as　one　of　the　cost-effective　and　sustainable　biological　nitrogen　removal　processes,　nitrite　accumulation　has　proven　difficult　to　achieve　in　continuous　processes　treating　low-strength　nitrogenous　wastewater.　Partial　nitrification　to　nitrite　was　achieved　and　maintained　in　a　lab-scale　completely　stirred　tank　reactor　(CSTR)　treating　real　domestic　wastewater.　During　the　start-up　period,　sludge　with　ammonia-oxidizing　bacteria　(AOB)　but　no　nitrite-oxidizing　bacteria　(NOB)　was　obtained　by　batch　operation　with　aeration　time　control.　The　nitrifying　sludge　with　the　dominance　of　AOB　was　then　directly　switched　into　continuous　operation.　It　was　demonstrated　that　partial　nitrification　to　nitrite　in　the　continuous　system　could　be　repeatedly　and　reliably　achieved　using　this　start-up　strategy.　The　ratio　of　dissolved　oxygen　to　ammonium　loading　rate　(DO/ALR)　was　critical　to　maintain　high　ammonium　removal　efficiency　and　nitrite　accumulation　ratio.　Over　85%　of　nitrite　accumulation　ratio　and　more　than　95%　of　ammonium　removal　efficiency　were　achieved　at　DO/ALR　ratios　in　an　optimal　range　of　4.0-6.0　mg　O-2/g　N　d,　even　under　the　disturbances　of　ammonium　loading　rate.　Microbial　population　shift　was　investigated,　and　fluorescence　in　situ　hybridization　analysis　indicated　that　AOB　were　the　dominant　nitrifying　bacteria　over　NOB　when　stable　partial　nitrification　was　established.