To　achieve　stable　partial　nitrification,　activated　sludge　from　a　wastewater　treatment　plant　using　free　ammonia　(FA)　inhibition　was　immobilized　in　a　polyvinyl　alcohol　carrier.　After　FA　treatment　at　16.44　mg　L−1　for　1　day,　due　to　the　increased　growth　rate　gap　between　ammonium-oxidizing　bacteria　(AOB)　and　nitrite-oxidizing　bacteria　(NOB),　AOB　enrichment　and　NOB　inhibition　were　achieved　within　12　days,　with　AOB　and　NOB　accounting　for　65.61　and　0.05%,　respectively.　Subsequently,　with　dissolved　oxygen　concentrations　of　4−5　mg　L−1,　pH　of　7.6–7.8　and　temperature　of　25　±　1　°C,　the　immobilized　carrier　made　of　activated　sludge　achieved　more　than　90%　and　more　than　86%　of　nitrite　accumulation　rate　at　the　influent　ammonia　concentration　of　90−110　mg　L−1　and　35−50　mg　L−1,　respectively.　After　50　days　operation,　the　NOB　content　was　0.10%,　indicating　the　immobilized　carrier　provided　favorable　conditions　for　maintaining　the　low　NOB　content.　Furthermore,　due　to　the　low　NOB　content　in　the　inoculum　and　the　oxygen-limited　environment　formed　by　the　increase　in　the　AOB　numbers　in　the　carrier,　immobilized　carrier　with　different　initial　biomass　(1,　2.5　and　5%)　can　achieve　stable　partial　nitrification.　©　2020　Elsevier　Ltd