Oxidation of ammonium in aerobic wastewater by anoxic ferric iron-dependent ammonium oxidation (Feammox) in a biofilm reactor

Anoxic ferric iron-dependent ammonium oxidation (Feammox) is a novel biological nitrogen removal process that oxidizes ammonium to NO2-, NO3- or N-2 using ferric iron as the electron acceptor. In this study, the Feammox process was successfully developed in a biofilm reactor using sponge iron as a Fe source feeding ammonium-containing aerobic water. The results showed that NH4+ was oxidized to NO3- by Feammox. During 300 d of operation, the bioreactor demonstrated an average NH4+ oxidation efficiency and rate of 42.3% and 32.2 mg N L-1 d(-1), respectively. Sponge iron was oxidized to ferric by dissolved oxygen (DO) in the influent and provided ferric and anaerobic conditions for Feammox. Only a small proportion of the generated NO3- was reduced to N-2 by nitrate-dependent Fe(II) oxidation causing nitrogen removal in the Feammox biofilm reactor. A distinct inhibition of Feammox was observed when DO increase to 1.0 mg L-1. Microbiological composition analysis of the Feammox biomass showed that the dominant iron-reducing bacteria were Geobacter spp., Fervidicella, and Geothrix, which may contribute to Feammox. This study provides information on the process development of Feammox.