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

[Display omitted] •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. Microbial Electrochemical Fluidized Bed Reactors (ME-FBR) represent a new concept for promoting proper bacteria-electrode interaction and eventually efficient biocatalysis in Microbial Electrochemical Technologies (METs). In the current work we demonstrate how a fluidized cathode, a dynamic and discontinuous design of electrode, can be an effective electron donor for electroactive hydrogen-generating and nitrate reducing bacteria. Furthermore, the oxygen produced in the anodic reaction promoted ammonium oxidation to nitrate by nitrifying bacteria thus expanding the environmental applications of the system. By coupling both anodic and cathodic reactions, it was possible to simultaneously achieve nitrification–denitrification within one chamber and without external oxygen addition. Our proof-of-concept revealed the removal of 98% ammonium and ca. 29% of total nitrogen (31 g-N m−3reactor d−1) from an effluent with low organic matter under continuous mode. This study reveals for first time how fluidized beds can be integrated in METs not only as anodes but also as cathodes, broadening the opportunities and applications to bioremediation and bioelectrosynthesis processes.