(665g) Electrochemical Stripping for Selective Nitrogen Recovery from Wastewaters

Electrochemical stripping was shown to selectively recover nitrogen as ammonium sulfate from wastewaters of varying compositions based on the charge and volatility of ammonia. Electrochemical water treatment replaces chemical inputs with electricity, allowing for fine-tuning of unit processes through control of applied current and potential. These modular systems are flexible to varying degrees of centralization and robust to handle intermittent flows and shock loadings. Recovering nitrogen from wastewater can potentially reduce costs and energy of wastewater nitrogen removal and fertilizer production. Through benchtop experiments with a novel three-chamber, two-membrane system, we demonstrate the recovery of nitrogen as ammonium sulfate using electrochemical stripping, a combination of electrodialysis and membrane stripping. Electrochemical stripping combines electromigration of cations with a cation exchange membrane and separation of volatile species with a polypropylene, gas-permeable membraneNitrogen was selectively recovered with 93% efficiency in batch experiments with real wastewater and required 30.6 MJ kg N^–1 in continuous-flow experiments (slightly less than conventional ammonia stripping). The effects of solution chemistry on nitrogen flux, electrolytic reactions, and reactions with electro-generated oxidants were evaluated using synthetic wastewater solutions. Fates of wastewater-relevant trace organic contaminants, including electrochemical oxidation and reaction with electro-generated chlorine, were investigated with a suite of common pharmaceuticals. Trace organics (<0.1 mg L^–1) and elements (<30 mg L^–1) were not detected at appreciable levels in the ammonium sulfate fertilizer product. We have recently compared bulk kinetic parameters for each nitrogen transformation and transport step. This novel approach holds promise for selective recovery of nitrogen from concentrated liquid waste streams such as source-separated urine, anaerobic digester effluent, hydrothermal liquefaction effluent, and nitrogen-rich food waste.