Feammox　(Fe(III)　reduction　coupled　with　anaerobic　ammonium　oxidation)　is　less　studied　for　nitrogen　removal　in　wastewater　treatment,　and　the　limited　studies　show　its　low　removal　efficiency　and　need　for　continuous　resupply　of　Fe(III)　sources.　In　this　study,　sustainable　and　efficient　nitrogen　removal　was　obtained　by　the　Fe　redox　cycle　with　only　1　g/L　Fe2O3　dosage.　The　removal　efficiencies　of　NH4+-N　and　TN　were　100%　and　92.45%,　respectively,　significantly　higher　than　previous　studies　(similar　to　50%).　Fe(III)　was　reduced　to　Fe(II)　by　Feammox　and　subsequently　regenerated　by　NDFO　(NOx--N-dependent　Fe(II)　oxidation)　and　chemical　oxidization.　NOx--N　produced　by　Feammox　was　also　reduced　to　N-2　by　NDFO.　The　iron-reducing　bacteria　(Ferruginibacter　and　Dechloromonas)　and　the　iron-oxidizing　bacteria　(Rhodanobacter　and　Thermomonas)　were　enriched　by　the　addition　of　Fe2O3　and　played　important　roles　in　Feammox　and　NDFO,　respectively.　Results　of　X-ray　diffraction　showed　that　Fe(OH)(2)　was　produced　from　Feammox　and　then　transformed　to　lepidocrocite　by　Fe(II)　oxidation.　Metagenomic　analysis　showed　D/ANRA　(dissimilatory/　assimilatory　nitrate　reduction　to　ammonia)　were　the　potential　nitrogen　conversion　pathways.　N2O　as　an　intermediate　product　of　Feammox　or　NDFO　was　undetected.　The　genes　associated　with　Fe　transport　were　upregulated,　accelerating　the　transfer　of　electrons　between　microorganisms　and　Fe(Hydr)oxide.　The　process　for　nitrogen　removal　by　the　Fe　redox　cycle　requires　no　aeration　and　no　organic　carbon　source,　and　can　reduce　the　need　for　Fe(III)　sources.　It　offers　a　promising　method　for　nitrogen　removal　from　wastewater.