Enhancing Resource\nRecovery through Electro-Assisted\nRegeneration of an Ammonia-Selective Cation Exchange Resin

Ammonia-selective\nadsorbents can manage reactive nitrogen\nin the\nenvironment and promote a circular nutrient economy. Weak acid cation\nexchangers loaded with zinc exhibit high ammonia selectivity but face\ntwo implementation barriers: the stability of the zinc–carboxylate\nbond in complex wastewaters and energy- and logistics-intensive adsorbent\nregeneration with acidic solutions. In this study, we examined the\nstability of zinc–carboxylate bonds in varying solutions (pure\nammonium solution, synthetic urine, and real urine) and during electro-assisted\nregeneration. For electrochemical regeneration, both electrolyte concentration\nand current density influenced the trade-off between ammonia regeneration\nand zinc elution. Using 10 mM K<sub>2</sub>SO<sub>4</sub> anolyte\nat a 0.08 mA/cm<sup>2</sup> current density, we achieved 4% zinc elution\nand 61% ammonia regeneration. In contrast, using 100 mM K<sub>2</sub>SO<sub>4</sub> at 4.96 mA/cm<sup>2</sup> improved the regeneration\nefficiency to 97% but eluted 60% of zinc. We found that electrolyte\nconcentration was the key factor influencing the regeneration efficiency\nof the NH<sub>3</sub>-selective adsorbents. Due to prevalent zinc\nelution, we designed an <i>in situ</i> procedure for reforming\nthe zinc–carboxylate bond and achieved similar adsorption densities\nbetween pre- and post-regenerated resins, thus enabling multiple cycle\nresin use. Ultimately, this study advances understanding of ammonia-selective\nresins that can facilitate high-purity, selective, and durable recovery\nof nutrients from waste streams.