Adding　Fe3+　to　anaerobic　ammonia-oxidizing　(Anammox)　systems　presents　several　challenges,　altering　the　rate　and　efficiency　of　nitrogen　removal　and　leading　to　a　degree　of　sludge　mineralization　at　concentrations　that　still　need　to　be　explored.　This　study　investigates　the　role　of　Fe3+　in　the　iron-nitrogen　cycle　and　its　effect　on　the　metabolism　of　Anammox　microorganisms.　Fe3+　influences　Anammox　metabolism　and　initiates　novel　nitrogen　cycling　processes.　Results　show　that　Fe3+　concentration　significantly　affects　nitrogen　removal　efficiency　(NRE).　In　the　short-term　dosing　phase　(0-10　days),　the　highest　NRE　(80.15　%)　was　observed　at　40　mg/L　Fe3　+.　However,　in　the　long-term　dosing　phase　(0-70　days),　increasing　Fe3+　concentration　led　to　a　decline　in　NRE,　with　the　lowest　value　(3.72　%)　at　110　mg/L.　Microbial　community　changes　up　to　day　70　were　strongly　correlated　with　Fe3+　concentration.　The　abundance　of　Candidatus_Brocadia　decreased　from　24.24　%　to　5.75　%,　while　denitrifying　genera　(OLB13,　Bosea)　and　nitrate-dependent　Fe2+-oxidizing　(NDFO)　genera　(e.g.,　Comamonas,　Thermomonas,　Bdellovibrio)　increased　from　0.31　%　to　13.36　%.　These　findings　highlight　the　beneficial　role　of　soluble　Fe3　+　salts　in　the　Anammox-Feammox-NDFO-denitrification　system,　with　regulation　of　Fe3+　concentration　critical　for　optimizing　NRE　and　preventing　system　degradation.　Future　research　should　focus　on　the　impact　of　Fe3+　on　microbial　metabolic　pathways　and　explore　its　potential　to　enhance　integrated　nitrogen　removal　processes,　with　a　focus　on　practical　application　and　long-term　viability.