Anammox　is　widely　considered　as　the　most　cost-effective　and　sustainable　process　for　nitrogen　removal.　However,　how　to　achieve　the　enrichment　of　anammox　biomass　remains　a　challenge　for　its　large-scale　application,　especially　in　mainstream　wastewater　treatment.　In　this　study,　the　feasibility　of　enrichment　of　anammox　biomass　was　explored　through　the　realization　of　partial　denitrification　and　the　addition　of　bio-carriers.　By　using　ordinary　activated　sludge,　a　sequencing　batch　reactor　(SBR)　followed　by　an　up-flow　anaerobic　sludge　bed　(UASB)　was　operated　at　25　+/-　2　degrees　C　for　214　days.　The　long-term　operation　was　divided　into　five　phases,　in　which　SBR　and　UASB　were　started-up　in　Phases　I　and　II,　respectively.　By　eliminating　oxygen　and　adjusting　the　inflow　ratios　in　Phases　III-V,　advanced　nitrogen　removal　was　achieved　with　the　effluent　total　nitrogen　being　4.7　mg/L　and　the　nitrogen　removal　efficiency　being　90.5%　in　Phase　V.　Both　in-situ　and　ex-situ　activity　tests　demonstrated　the　occurrence　of　partial　denitrification　and　anammox.　Moreover,　16S　rRNA　high-throughput　sequencing　analysis　revealed　that　Candidatus　Brocadia　was　enriched　from　below　the　detection　limit　to　in　biofilms　(0.4%　in　SBR,　2.2%　in　UASB)　and　the　floc　sludge　(0.2%　in　SBR,　1.3%　in　UASB),　while　Thauera　was　mainly　detected　in　the　floc　sludge　(8.1%　in　SBR,　8.8%　in　UASB),　which　might　play　a　key　role　in　partial　denitrification.　Overall,　this　study　provides　a　novel　strategy　to　enrich　anammox　biomass　driven　by　rapid　achievement　of　partial　denitrification　through　the　addition　of　bio-carriers,　which　will　improve　large-scale　application　of　anammox　processes　in　mainstream　wastewater　treatment.　(c)　2023　The　Research　Center　for　Eco-Environmental　Sciences,　Chinese　Academy　of　Sciences.　Published　by　Elsevier　B.V.