Partial　nitrification　(PN)　has　great　significance　in　promoting　both　anaerobic　ammonium　oxidation　(anammox)　and　advanced　nitrogen　removal.　However,　the　kinetics　of　PN　have　not　been　sufficiently　studied.　Deterioration　of　PN　often　occurs　due　to　nitrite-oxidizing　bacteria　(NOB)　outgrowth,　for　which　the　dissolved　oxygen　(DO)　is　a　critical　factor.　This　study　investigated　the　kinetic　parameters　of　ammonia-oxidizing　bacteria　(AOB)　and　NOB　by　varying　the　DO　concentration.　The　partial　nitrification-anammox　(PNA)　process　was　operated　under　sequentially　low　(0.3–0.8　mg/L)　and　high　(4.0–5.0　mg/L)　DO.　The　results　show　that　AOB　could　not　adapt　to　low　DO,　resulting　in　a　significant　decrease　in　the　maximum　AOB　activity　(Vmax,AOB)　and　a　slightly　altered　oxygen　half-saturation　constant　of　AOB　(KO,AOB).　Conversely,　KO,NOB　decreased　and　Vmax,NOB　maintained,　indicating　that　the　main　NOB　genus,　Nitrospira,　was　more　adaptable　to　DO　changes.　Under　high　DO,　AOB　growth　was　weaker　than　NOB,　leading　to　a　low　Vmax,AOB　–　Vmax,NOB　value;　KO,AOB　increased　and　was　larger　than　KO,NOB　and　PNA　was　eventually　destroyed.　The　aerobic　starvation　was　then　adopted　to　restore　PN.　AOB　recovered　faster　and　dominated,　with　Vmax,AOB　greatly　exceeding　Vmax,NOB.　Finally,　NOB　were　inhibited　and　PN　was　recovered.　During　this　process,　KO,NOB　increased　and　was　higher　than　KO,AOB.　Changes　in　the　kinetic　parameters,　especially　the　Vmax,AOB　-Vmax,NOB　value,　have　specific　guiding　significance　for　DO　regulation　during　PNA.　This　work　helps　better　understand　the　effect　of　DO　variations　on　the　nitrifying　microbial　community,　which　influences　oxygen　affinity　and　maximum　activity.　©　2024　Elsevier　B.V.