Nitrous Oxide as a Major Product of Anoxic Bioanode Ammonium Oxidation: Pathway Insights and Implications

Anoxic ammonium (NH4+) oxidation at bioanodes offers a feasible alternative to conventional biological nitrogen removal (BNR), eliminating the need for aeration and enabling direct nitrogen gas (N2) production. However, the extent of nitrous oxide (N2O) emissions in this process remain unclear. This study examines N2O emissions during anoxic NH4+ oxidation at a polarized bioanode (+0.55 V vs Ag/AgCl), focusing on the roles of key intermediates, hydroxylamine (NH2OH) and nitrite (NO2-), in N2O formation, and microbial functional groups involved in N2O production, aiming to elucidate the underlying N2O production pathways during bioanodic NH4+ oxidation.