Sustainable ammonia recovery in electrochemical membranes: The critical role of electromigration

Abstract

Ammonia (NH₃) is a vital chemical widely used in fertilizers, industry, and as a potential energy carrier. However, conventional ammonia production via the Haber-Bosch process is highly energy-intensive, consuming approximately 13.9 kWh per kg of nitrogen. Additionally, nitrogen-rich wastewater contributes to eutrophication and aquatic toxicity, necessitating sustainable recovery solutions. This study introduces an electrochemical membrane stripping (EMS) system incorporating hydrophobic, electrically conducting membranes (ECMs) to enhance ammonia recovery. By applying a controlled electric field and optimizing cathodic potential and crossflow velocity, the system efficiently transports ammonium (NH₄⁺) toward the cathodic membrane, where a localized pH shift converts it into free ammonia (NH₃), eliminating the need for chemical pH adjustment.

Under optimal conditions, the EMS system achieved 88 % ammonia recovery with a high flux of 37 ± 1.45 g m⁻² d⁻¹, representing a 33.5 % improvement over conventional methods. Mass balance analysis confirmed electromigration as a key transport mechanism, leading to a threefold increase in ammonia concentration at the membrane surface. Additionally, the system demonstrated high energy efficiency, with a specific energy consumption of 2 ± 0.15 kWh per kg of nitrogen, making it a cost-effective alternative for liquid fertilizer production.

As a proof-of-concept, the EMS system was successfully tested on real municipal wastewater, highlighting its practical viability. However, further research is needed to assess long-term stability, scalability, and integration with wastewater treatment infrastructure. This study demonstrates EMS as a promising technology for sustainable nitrogen recovery, supporting circular economy initiatives.