Flexible Electrochemical Stripping for Wastewater Ammonia Recovery with On-Demand Product Tunability

Nitrogen in wastewater can be recovered to prevent negative environmental, human health, and economic impacts and to enable distributed chemical manufacturing. We developed novel flexible electrochemical stripping (FECS) for tunable recovery of ammonia/ammonium (total ammonia nitrogen, TAN) from urine as (NH₄)₂SO₄ and aqueous NH₃. Batch and continuous experiments demonstrated that product speciation could be readily controlled by modifying electrochemical cell operation frequency, duration, and applied current without affecting TAN removal. During continuous experiments, FECS recovered NH₃ solutions with concentrations similar to ready-to-use cleaners (1% and 2% NH₃ (w/w) or 8.22 and 16.4 g/L TAN) and cleaner concentrates (5% NH₃ (w/w) or 41.1 g/L TAN), as well as (NH₄)₂SO₄ solutions between 5 and 18.4 g/L TAN, approaching commercial fertilizer concentrations (28.4 g/L TAN). Beyond modifying applied current, future process engineering and operating condition optimization should reduce energy consumption, increase recovery efficiency, and enhance economic viability of FECS. Our findings will enable the development and deployment of electrochemical nitrogen recovery in contexts with varying needs for ammonia-based products, paving the way for circular economies that integrate distributed chemical manufacturing with sanitation systems.