In　addressing　the　issue　of　the　unstable　supply　of　electron　acceptors　(nitrite)　during　Anammox,　researchers　have　often　overlooked　that　the　electron　transfer　process　in　anammox　bacteria　(AnAOB)　is　not　restricted　to　the　intracellular,　extracellular　electron　transfer　can　also　serve　as　an　alternative　pathway.　This　study　utilized　Fe3+　as　an　adjunctive　electron　acceptor,　coupling　Anammox　with　ferric　iron　reduction　(Feammox)　by　introducing　polymeric　ferric　sulfate　(PFS)　in　the　Anammox　system.　This　approach　achieved　effective　nitrogen　removal　even　when　nitrite　was　deficient.　At　a　NO2--N　to　NH4+-N　ratio　of　0.5,　the　Feammox-Anammox　combined　system　maintained　stable　nitrogen　removal　under　the　dual　electron　acceptor,　with　total　nitrogen　and　NH4+-N　removal　efficiency　of　85　%　and　91　%,　respectively.　The　contribution　of　Feammox　and　Anammox　to　NH4+-N　removal　was　45　%　and　55　%,　respectively.　TEM-EDS　confirmed　the　presence　of　iron　elements　across　the　periphery,　periplasm,　and　cytoplasm　of　AnAOB,　suggesting　the　involvement　of　PFS　in　the　metabolic　and　electron　transfer　processes.　Notably,　the　introduction　of　Fe3+　and　the　limitation　of　nitrite　availability　resulted　in　increased　relative　abundances　of　FeOB　(Thermomonas)　and　FeRB　(Ignavibacterium)　to　30　%　and　3.6　%,　respectively,　indicating　that　the　electron　transfer　process　with　Fe3+　as　the　electron　acceptor　was　continuously　intensified,　as　well　as　a　cycle　of　Fe3+　/　Fe2+　was　established.　Due　to　unique　nitrogen　metabolism　mode　and　high　Fe3+　tolerance,　the　abundance　of　Candidatus_Brocadia　was　enriched　up　to　7.2　%,　which　alternately　dominated　the　Anammox　process　with　Candidatus_Kuenenia,　providing　favorable　conditions　for　AnAOB　to　carry　out　the　extracellular　electron　transfer　process.　These　findings　provide　a　novel　strategy　for　improving　the　stability　and　efficiency　of　the　Anammox　process　under　deficient　nitrite　supply.