Fluidized bed cathodes as suitable electron donors for bacteria to remove nitrogen and produce biohydrogen

•A fluidized bed electrode was used in a ME-FBR as fluidized cathode for driving microbial reactions.•Fluidized cathode effectively triggered biological NO3- reduction and H2 production.•The biological NH4+ oxidation was promoted by the electrochemical abiotic O2 production at the anode.•Nitrification and denitrification simultaneously occurred in the ME-FBR.•Nitrogen could be removed in a ME-FBR under continuous mode of operation.