Rubrivivax　gelatinosus　has　the　potential　of　biomass　resource　recycling　combined　with　sewage　purification.　However,　low　biomass　production　and　yield　restricts　the　potential　for　sewage　purification.　Thus,　this　research　investigated　the　improvement　of　biomass　production　and　yield　and　organics　reduction　by　Fe3+　in　R.　gelatinosus　wastewater　treatment.　Results　showed　that　10-30　mg/L　Fe3+　improved　biomass　yield　in　wastewater　to　a　level　found　in　culture　medium.　With　optimal　dosage　(20　mg/L),　biomass　production　reached　4,300　mg/L,　which　was　1.67　times　that　of　the　control　group.　Biomass　yield　was　improved　by　43.3%.　Chemical　oxygen　demand　(COD)　removal　reached　above　91%.　Hydraulic　retention　time　was　shortened　by　25%.　Mechanism　analysis　indicated　that　Fe3+　enhanced　the　succinate　and　NADH　dehydrogenase　activities　and,　bacteriochlorophyll　content　in　three　energy　metabolism　pathways.　These　effects　then　enhanced　adenosine　triphosphate　(ATP)　production,　which　led　to　more　biomass　accumulation　and　COD　removal.　With　20　mg/L　Fe2+　dosage,　succinate　and　NADH　dehydrogenase,　coproporphyrinogen　III　oxidase　activities,　bacteriochlorophyll　content　and　ATP　production　were　improved,　respectively,　by　48.4,　50.8,　50,　67　and　56%　compared　to　those　of　the　control　group.　©　IWA　Publishing　2014