Pulsed electric field drives chemical-free membrane stripping for high ammonia recovery from urine

Recovering ammonia from waste streams (e.g., urine) is highly desirable to reduce natural gas-based NH3 production and nitrogen discharge into the water environment. Electrochemical membrane stripping is an attractive alternative because it can drive NH4+ transformation to NH3 via cathodic OH- production; however, the conventional configurations suffer from relatively low ammonia recovery (<80 %) and significant acid/material usage for ammonia adsorption. To this end, we develop a novel stack system that simply uses an oxygen evolution reaction to in-situ produce acid from water, enabling chemical-free ammonia recovery from synthetic urine. In batch mode, the percentage removal and recovery increased respectively from 74.5 % to 97.9 % and 81.8 % to 92.7 % when the electrode pairs increased from 2 to 4 in the stack system. To address the gas-sparging issue that deteriorated ammonia recovery in continuous operation, pulsed electric field (PEF) mode was applied, resulting in similar to 100 % recovery under optimized conditions. At an ammonia removal rate of 35.1 g-N m(-2) h(-1) and electrical energy consumption of 28.9 kWh kg-N-1, our chemical-free system in PEF mode has achieved significantly higher ammonia recovery (>90 %) from synthetic urine. The total cost to recover 1 kg of NH3-N from real human urine was $15.9 in the proposed system. Results of this study demonstrate that this novel approach holds great promise for high ammonia recovery from waste streams, opening a new pathway toward sustainable nitrogen management.