Long-term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

Nitrogen in wastewater has negative environmental, human health, and economic impacts but can be recovered to reduce costs and environmental impacts of wastewater treatment and chemical production. To recover ammonia/ammonium (TAN) from urine, we operated electrochemical stripping (ECS) for over a month, achieving 83.4% TAN removal and 73.0% TAN recovery. With two reactors, we recovered sixteen 500 mL batches (8 L total) of ammonium sulfate approaching commercial fertilizer concentrations and often having greater than 95% purity. While evaluating operation and maintenance needs, we identified pH, full-cell voltage, product volume, and water flux into the product as informative process monitoring parameters that can be inexpensively and rapidly measured. Characterization of fouled cation exchange and omniphobic membranes informs cleaning and reactor modifications to reduce fouling with organics and calcium/magnesium salts. To evaluate the impact of urine collection and storage on ECS, we conducted experiments with urine at different levels of dilution with flush water, extents of divalent cation precipitation, and degrees of hydrolysis. ECS effectively treated urine under all conditions, but minimizing flush water and ensuring storage until complete hydrolysis would enable energy-efficient TAN recovery. A preliminary cost assessment indicated that ECS-derived ammonium sulfate from urine was competitive with other nitrogen treatment technologies and commercially available fertilizer. Our experimental results and cost analysis motivate a multi-faceted approach to improving ECS’s technical and economic viability by extending component lifetimes, decreasing component costs, and reducing energy consumption through material, reactor, and process engineering. In sum, we demonstrated urine treatment as a foothold for electrochemical nutrient recovery from wastewater while supporting applicability of ECS to seven other wastewaters with widely varying characteristics. Our findings will facilitate scale-up and deployment of electrochemical nutrient recovery technologies, enabling a circular nitrogen economy that fosters sanitation provision, efficient chemical production, and water resource protection.