Electro-concentration of urine designed for separation of sodium from nitrogen

Abstract Source-separated urine is a natural liquid fertilizer used by humanity for millennia. Urine use in modern nutrient recycling can be hindered by high relative salinity, non-optimal macro-nutrient ratio, presence of pathogens, and organic micropollutants. In this study, an electrochemical system was used to oxidize and concentrate synthetic urine into a product concentrate and a waste concentrate, also releasing a treated low nutrient load effluent. The system comprised two electrochemical reactors with separate concentration chambers and two circulation loops. Each circulation loop was comprised of two electrodes of opposite polarity, one from each of the two reactors. The pH levels in each loop were controlled electrochemically without chemical addition, allowing for selective ammonium (total ammonium nitrogen, TAN) and sodium (Na) separation into the product concentrate and the waste concentrate, respectively. In addition to pH, which was controlled by the relative current of the two reactors, the concentrate characteristics were controlled by the absolute potentials applied, affecting the oxidation reactions present. The double reactor system was able to divert a waste concentrate with a relative volume of 4% vs. the feed. The waste concentrate contained 14% of the influent Na but only 1% of the influent TAN, effectively removing sodium while removing very little TAN. This demonstrates a proof of concept for Na/TAN ion separation using electrochemical pH control. Compared to a single reactor control, between 12 and 17% reduction in Na/TAN ratio was achieved in the product concentrate with a specific energy consumption of 11–22 kWh kgN−1. A total TAN recovery of 56–76% into the product concentrate was demonstrated. A wide range of tailoring parameters could be used for optimizing the redox chemistry and product characteristics. This novel technology shows promise for optimization for fertilizer production from source-separated urine.