The　mechanisms　of　Fe2+　on　nitrogen　and　phosphorus　removal　and　functional　bacterial　competition　in　anammox　systems　was　investigated.　Under　0.12　mM　Fe2+,　the　performance　of　nitrogen　and　phosphorus　removal　increased　by　10.08　%　and　151.91　%,　respectively,　compared　with　the　control　stage.　Phosphorus　removal　was　achieved　through　extracellular　polymeric　substance　(EPS)　induced　biomineralization　to　form　Fe-P　minerals,　and　functional　group　C–O–C　in　EPS　played　a　critical　role.　T-EPSs　was　the　major　nucleation　site　due　to　it　maintaining　the　supersaturated　state　(saturation　index　＞　0)　of　Fe-P　minerals　for　a　long　time.　Population　succession　showed　that　Fe2+　weakened　the　competition　between　heterotrophic　denitrifier　(Denitrasoma)　and　anammox　microbe　(Candidatus　Brocadia)　for　space　and　substrates,　which　was　favorable　for　the　enrichment　of　anammox　biomass.　Moreover,　the　variation　in　gene　abundance　(such　as　Hao,　Cyt　c,　and　Nir)　indicated　that　Fe2+　improved　electron　behaviors　(generation,　transport,　and　consumption)　during　the　nitrogen　metabolism　of　anammox　systems.　©　2022　Elsevier　Ltd