For　municipal　wastewater　treatment　via　partial-denitrification/anammox　(PD/A)　in　the　anoxic　zone,　the　primary　challenge　is　effective　enrichment　of　anaerobic　ammonium　oxidation　(anammox)　bacteria　with　a　stable　autotrophic　nitrogen　removal　performance.　This　long-term　study　investigated　a　pure-biofilm　anoxic/oxic　reactor　using　real　municipal　wastewater　with　an　ammonia　concentration　of　49.1　±　3.6　mg　N/L,　achieving　a　total　inorganic　nitrogen　concentration　of　11.2　±　3.5　mg　N/L　in　the　effluent,　resulting　in　a　removal　efficiency　of　77.4　±　7.2%.　Driven　by　partial　denitrification,　the　anammox　contribution　to　total　nitrogen　removal　represented　an　ultra-high　level　over　55%,　and　was　considerable　in　the　first　anoxic　zone.　Candidatus　Brocadia,　the　only　anammox　genus　detected　by　16S　rRNA　gene　sequencing,　reached　robust　abundances　of　5.46,　6.49　and　5.79%　in　the　three　sequentially　connected　anoxic　zones.　Metagenomic　sequencing　further　identified　that　the　main　species　was　Ca.　Brocadia　sapporoensis,　which　is　inhibited　by　nitrite　but　not　by　acetate,　supporting　its　high-level　enrichment　under　acetate　conditions　in　the　anoxic　zone.　Batch　tests　indicate　that　heterotrophic　denitrification　activity　decreased　while　anammox　activity　increased　along　the　anoxic　zones,　and　that　excessive　heterotrophic　denitrifying　activity　was　not　conducive　to　increasing　the　anammox　contribution.　This　study　achieved　robust　anammox　bacterial　abundance　using　a　pure-biofilm　system,　shedding　fresh　light　on　the　application　of　mainstream　anammox　in　municipal　wastewater　treatment.　©　2023　Elsevier　B.V.