Ammonia-Rich Solution Production from Wastewaters Using Chemical-Free Flow-Electrode Capacitive Deionization

Conventional technologies for ammonia recovery from wastewaters are based on ammonia enrichment/separation methods (i.e., electrochemical stripping, air stripping and ion exchange) followed by acid adsorption to produce ammonium salts with these processes requiring large amount of chemicals and high energy consumption. Instead of producing low-value ammonium salts, we present in this study a proof of concept approach using activated carbon particle-based flow-electrode capacitive deionization (FCDI) that enables recovery of much higher value ammonia solution. During electrosorption, ammonium and other cations undergoing treatment migrate across the ion exchange membrane and accumulate in the flowable activated carbon cathode with an increase in local pH due to the Faradaic reactions resulting in the deprotonation of ammonium to uncharged NH3(aq). Following the reversal of the polarity, the constantly charged ions (typically Na+, K+ and Ca2+) that are present are largely released back into the waste stream while NH3(aq) can be selectively trapped in the cathode with an ammonia-rich solution, a valuable resource, subsequently produced. Results show that the selectivity of the FCDI process for ammonium ions toward other cations reached 3.7 to 11.4 with the formation of ammonia solution dominating the fate of the nitrogen containing species present under optimal operating conditions.