Conversion of ammonium to nitrous oxide in a microbial electrochemical cell

Ammonium (NH₄⁺) is a major pollutant in wastewater, and its removal using conventional methods is often energy-intensive and costly. This proof-of-concept study investigates microbial electrochemical cells (MECs) as a sustainable alternative for NH₄⁺ removal and nitrous oxide (N₂O) recovery. The study focuses on partial nitrification and partial denitrification processes occurring in MECs, emphasizing the electrochemical and microbial mechanisms responsible for NH₄⁺ conversion. Using ¹⁵NH₄⁺ tracer analysis, the study demonstrates a 76 % conversion of NH₄⁺ to N₂O, driven by biofilms containing denitrifying microorganisms, such as Simpliscispira and Thiobacillus, and as well as planktonic species like Phycisphaerae, Anaerobacterium, Rikenellaceae, and Synergistaceae. MECs exhibited high energy efficiency, requiring only 1.64 kWh/kg of N-NH₄⁺ removed, a value significantly lower than conventional methods. These findings underscore the potential of MECs as a promising technology for sustainable nitrogen management, demonstrating both nitrogen removal and N₂O valorization for industrial application. Further optimization of microbial communities and operational parameters is needed to maximize process efficiency and scalability.