This　study　developed　an　innovative　process　for　the　treatment　of　low-ammonium　wastewater　in　a　single-stage　bioreactor　over　250　days.　Partial　nitritationanammox　and　partial　denitritation-anammox　(PN/A-PDN/A)　processes　were　combined　under　aerobic/anoxic　operation,　and　a　high　nitrogen　removal　efficiency　(94.6%)　was　obtained　at　a　nitrogen　removal　rate　of　0.54　kg　N　m(-3)　d(-1)　and　a　chemical　oxygen　demand　to　total　inorganic　nitrogen　(COD/TIN)　ratio　of　0.28.　Mass　balance　analysis　identified　anammox　as　the　dominant　nitrogen　removal　pathway,　achieving　88.3%　nitrogen　loss.　The　abundance　of　anammox　bacteria　and　their　bioactivity　rapidly　increased　and　were　effectively　maintained,　as　indicated　by　qPCR　and　bioactivity　tests.　The　PN/A-PDN/A　process　provided　two　pathways　of　nitrite　production　for　anammox,　which　favored　the　enrichment　of　anammox　bacteria　and　stable　processing.　In　addition,　the　enrichment　of　anammox　bacteria　was　promoted　by　selective　floc　discharge　since　anammox　bacteria　are　mainly　located　in　granules　(relative　abundance　of　29.64　+/-　7.89%).　Competitive　organisms　(including　heterotrophic　bacteria　and　nitrite　oxidizing　bacteria),　enriched　in　flocs,　were　washed　out.　Overall,　these　findings　confirmed　anammox,　sequentially　combined　with　PN　and　PDN　via　aerobic/anoxic　strategy,　as　a　promising　alternative　for　mainstream　anammox.