NO more! Reducing Nitrous Oxide Emissions in Wastewater via Ammonia Electrolysis

Ammonia is a major nitrogenous constituent of municipal wastewater and poses environmental challenges when discharged to receiving waters. Conventional biological treatment processes can be limited by operational instability, sensitivity to loading conditions, and greenhouse gas emissions, motivating the investigation of alternative treatment approaches. This thesis investigates electrochemical ammonia depletion from real municipal wastewater using a laboratory-scale alkaline electrolyzer operated under galvanostatic conditions.
Experiments were conducted using both model electrolytes and real wastewater to assess the influence of wastewater complexity on system behavior. The effects of supporting electrolyte addition, current density, membrane selection, and initial ammonia concentration were systematically evaluated.
Ammonia depletion was monitored over time, alongside measurements of cell voltage and electrolyte pH, to characterize operational performance and stability.
The results show that, when supported by sufficient alkalinity, electrochemical ammonia depletion in real wastewater proceeds in a manner comparable to that observed in model electrolytes. The presence of a supporting electrolyte was found to be essential for practical operation, as experiments conducted
without added KOH required substantially higher cell voltages. Increasing current density accelerated ammonia depletion but led to diminishing gains at higher values due to increased electrical demand.
Across the investigated concentration range, ammonia depletion exhibited linear behavior consistent with apparent zero-order kinetics with respect to ammonia concentration over the observed operating window. Membrane selection influenced pH stability and species distribution between compartments, with
anion exchange membranes providing more stable alkaline operation than cation exchange membranes.
Overall, the findings demonstrate that electrochemical ammonia depletion from real municipal wastewater is technically feasible under alkaline conditions and is primarily governed by operational parameters rather than wastewater complexity alone. The results provide a baseline understanding of system behavior and highlight key considerations for future optimization and scale-up of electrochemical ammonia treatment technologies.