Chemical-free electrochemical system with membrane cathode assembly Enables efficient ammonia recovery from urine

Abstract

The extraction of ammonia from waste sources, such as urine, presents significant potential for its utilization as fertilizers and chemical precursors. Conventional recovery techniques, such as air stripping and chemical precipitation, face limitations due to their high energy demands and substantial chemical usage. Although electrochemical alternatives offer improved selectivity for ammonia recovery, they remain constrained by slow ammonia mass transfer. In this work, we have designed an electrochemical system incorporating a parallel plate stack design with a membrane electrode assembly. This innovation leverages the benefits of electrochemical base production coupled with rapid ammonia separation and recovery from urine. The system achieved an ammonia removal rate of 19.4 g-N m−2h−1, with removal and recovery efficiencies recorded at 72.7 % and 93.5 %, respectively, while consuming 19.5 kWh per kg-N. The system’s performance and robustness were then evaluated using real urine. Over 96 h of continuous operation, at an ammonia removal rate of 14.5 g-N m−2h−1 and an energy consumption of 33.1 kWh per kg-N, the removal and recovery efficiencies stabilized at 84.2 % and 78.4 %, respectively. The chemical scale that formed on the assembly was easily removed using a 0.1 M citric acid solution. Overall, the findings underscore the critical role of the nickel-based membrane cathode assembly in achieving chemical-free and efficient ammonia separation and recovery from urine, which may facilitate broader applications of membrane electrode assemblies in waste management and related fields.