Unraveling Foulant Deposition Mechanisms on Cation Exchange Membranes during Electrochemical Stripping for Wastewater–Ammonia Recovery

Recovering nutrients as valuable products from wastewater can alleviate environmental issues, including algal bloom formation and greenhouse gas emissions from chemical manufacturing, while creating a circular nutrient economy. However, integrating nutrient recovery into treatment trains requires long-term stability of recovery-focused technologies. Electrochemical stripping (ECS) shows potential for ammonia recovery across diverse wastewaters but is hindered by cation exchange membrane (CEM) fouling due to accumulation of wastewater constituents. This study examined the distribution and speciation of dominant foulants on CEMs during ECS in different wastewaters using advanced X-ray imaging and spectroscopy. Micro-X-ray fluorescence showed substantial deposition of Ca on CEMs, while Ca-K-edge spectroscopy indicated the presence of calcium carbonate polymorphs, calcium phosphates, and calcium organics. Building on these insights, we evaluated the efficacy of complexing agents (citric acid and ethylenediaminetetraacetic 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 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 demonstrate that targeted additives can mitigate scaling, enhancing ECS stability for sustainable nutrient recovery.