Anaerobic　ammonia　oxidation　(Anammox)　exhibits　promise　for　wastewater　treatment,　but　the　enrichment　of　anammox　bacteria　(AnAOB)　in　municipal　wastewater　treatment　plants　is　a　significant　challenge.　This　study　constructed　a　novel　Anoxic-Anaerobic-Oxic　An　aerobic-Oxic　(AAnO)　process　with　a　pure　biofilm　anoxic　zone　fed　with　actual　fluctuating　municipal　wastewater　and　operated　for　six　months　to　enrich　AnAOB　at　ambient　temperature.　High-　throughput　sequencing　(HTS),　qPCR,　and　fluorescence　in　situ　hybridization　showed　that　AnAOB　were　successfully　enriched　in　the　anoxic　biofilms,　reaching　1.56　%　relative　abundance　on　day　75　detected　by　HTS.　During　the　period　from　day　130　to　day　186,　the　anammox　process　contributed　to　55.8　+/-　19.2　%　of　the　nitrogen　removal　in　the　anoxic　zone.　Phylogenetic　analysis　revealed　this　AnAOB　species　was　closely　related　to　Candidatus　Brocadia　fulgida.　.　This　study　provides　technical　support　for　the　application　of　anammox　in　mainstream　wastewater.