Most　municipal　wastewater　treatment　plants　worldwide　rely　on　the　traditional　activated　sludge　process　for　nutrient　removal　and　recovery.　However,　current　research　and　applications　of　mainstream　anammox　primarily　utilize　biofilms　or　granular　sludge　as　media,　which　inevitably　increases　capital　costs　and　operational　complexity.　This　study,　for　the　first　time,　demonstrates　the　long-term　stability　of　partial　denitrification/anammox　(PD/A)　in　a　pure　floc　sludge　system　treating　real　municipal　wastewater　(COD/N:　2.3–3.3)　employing　the　widely-applied　anaerobic-anoxic–oxic　(A2/O)　process.　It　reveals　the　crucial　role　of　extended　sludge　retention　time　(＞　150　days)　and　low　COD/N　(2.7–3.0)　in　achieving　efficient　nitrogen　removal.　Anammox　bacteria　rapidly　accumulated　in　the　floc　sludge　via　natural　shedding　from　the　PD/A　biofilms　and　continued　to　proliferate　after　the　system　shifted　to　a　pure　floc　sludge　configuration,　ultimately　reaching　2.16　×　109　copies/g　SS.　The　pure　floc　system　sustained　stable　PD/A　for　280　days,　with　anammox　contributing　31.7–45.3　%　of　nitrogen　removal.　The　system　achieved　a　nitrogen　removal　efficiency　of　79.2　±　3.8　%,　with　an　effluent　concentration　of　9.8　±　1.7　mg-N/L.　This　study　highlights　the　potential　of　pure　floc　sludge　systems　for　mainstream　anammox　implementation,　presenting　a　simpler,　more　cost-effective　alternative　to　biofilms　and　granular　sludge　systems.　©　2024　Elsevier　B.V.