Unraveling foulant deposition mechanisms on cation exchange membranes during electrochemical stripping for wastewater ammonia recovery

Recovering nutrients (nitrogen and phosphorus) as valuable products from wastewater can alleviate environmental issues, such as algal bloom formation and greenhouse gas emissions from chemical manufacturing, while creating a circular nutrient economy. However, integrating nutrient recovery into wastewater treatment trains requires long-term stability of recovery-focused technologies. Electrochemical stripping (ECS) has shown promise for ammonia recovery across diverse wastewaters, but its long-term operation is hindered by cation exchange membrane (CEM) fouling where constituents present in wastewater accumulate on the membrane surface. In this study, we identified the distribution and speciation of dominant foulants on CEMs during ECS-based ammonia recovery from hydrolyzed urine, reverse osmosis concentrate, and anaerobic digester effluent using advanced X-ray imaging and spectroscopy techniques. Micro-X ray fluorescence showed substantial deposition of Ca, P, and S on the CEM, and Ca K-edge spectroscopy indicated the presence of calcium carbonate polymorphs, calcium phosphates, and calcium associated with organic matter. Building on these insights from spectroscopic investigations, we evaluated the efficacy of complexing agents (citric acid,ethylene diamine tetraacetic acid [EDTA]) and antiscalants (acrylate- and phosphonate-based) in preventing fouling. Aqueous measurements showed that EDTA and an acrylate-based antiscalant inhibited Ca precipitation without compromising ammonia recovery. Ex-situ µ-XRF and µ-XANES characterization further quantified the spatial distribution and chemical forms of residual foulants, demonstrating effective mitigation by selected additives. These results provide mechanistic insight into inorganic fouling on CEMs and highlight how tailored chemical additives can target specific scaling pathways, supporting the long-term viability of ECS and advancing sustainable, membrane-based nutrient recovery technologies.