Controlling　sludge　concentration　is　an　effective　means　to　achieve　PN.　In　this　article,　the　reactor　used　domestic　sewage　as　raw　water　and　promoted　the　high　enrichment　of　anammox　bacteria　by　controlling　the　MLVSS　of　flocs　to　1000–1500　mg/L　and　increasing　the　concentration　of　filler　sludge.　The　measures　to　reduce　the　concentration　of　flocculent　sludge　increased　the　proliferation　rate　of　the　biofilm　and　provided　sufficient　substrate　for　AnAOB.　After　102　days　of　operation,　the　abundance　of　Candidatus　Brocadia　increased　from　0.43%　during　inoculation　to　23.56%　in　phase　VI.　The　ability　of　the　microbial　community　to　utilize　energy　metabolism　and　produce　ATP　was　significantly　improved,　and　the　appropriate　distribution　of　anammox　bacteria　and　nitrifying,　denitrifying　bacteria　in　the　ecological　niche　led　to　its　high　enrichment.　In　summary,　this　study　proposes　a　strategy　to　promote　the　high　enrichment　of　anammox　bacteria　in　mainstream　domestic　sewage　without　adding　any　chemicals.　©　2024　Elsevier　Inc.