Partial　nitrification　activated　sludge　immobilized　with　polyvinyl　alcohol-sodium　alginate　(Polyving　Akohol-Sodium　Alginate,　PVA-SA)　was　used　to　treat　domestic　wastewater　and　achieve　stable　partial　nitrification　in　a　continuous　flow　AO　(Anaerobic/Oxic)　reactor.　Using　the　response　surface　method,　the　effects　of　hydraulic　retention　time　(HRT),　internal　recirculation　ratio　and　filling　rate　on　nitrite　accumulation　ratio　(NAR)　and　total　nitrogen　removal　nitrogen　removal　efficiency　(NRE)　were　investigated,　and　a　quadratic　regression　model　was　successfully　established.　The　results　showed　that　the　system　had　the　best　performance　in　nitrogen　removal　with　NAR　and　NRE　reaching　86.22%　and　86.56%　when　HRT,　internal　recirculation　ratio　and　filling　rate　of　aerobic　section　were　controlled　as　6.43h,　2.93,　and　25%,　respectively.　In　addition,　it　was　observed　by　live　and　dead　bacteria　and　Fluorescence　In　Situ　Hybridization　(FISH)　that　the　live　cells　were　mainly　distributed　in　the　range　of　0~500µm　on　the　surface　of　the　particles,　while　the　dead　bacteria　were　distributed　in　the　range　of　0~300µm.　FISH　fluorescence　was　gradually　decreased　in　intensity　with　the　increase　of　depth.　Finally,　16S　rRNA　sequencing　results　showed　that　the　relative　abundance　of　Nitrosomonas　increased　from　0.013%　to　5.02%　and　Nitrospira　increased　from　0.055%　to　1.99%　in　the　immobilized　particles　of　the　long-term　run　compared　with　that　of　the　partial　nitrification　activated　sludge.　The　proportion　of　NOB　in　the　nitrifying　bacteria　was　reduced,　while　the　proportion　of　AOB　was　increased,　which　contributed　to　the　stabilization　of　nitrogen　removal　effect　of　partial　nitrification.　This　study　provides　a　promising　technology　for　the　engineering　application　of　partial　nitrification　in　municipal　wastewater　plants.　©　2024　Chinese　Society　for　Environmental　Sciences.　All　rights　reserved.