Enhancing selective NH4+ recovery from wastewater using modified zeolite-based flow electrode capacitive deionization

Despite flow-electrode capacitive deionization (FCDI) is an emerging technology for desalination, contaminant removal, and resource recovery, the application of conventional FCDI in wastewater treatment is hindered by the electrode selectivity and material costs. In this study, we synthesized a low-cost ammonium (NH 4 + ) adsorption electrode material by modifying zeolite using ethylenediaminetetraacetic acid disodium salt (EDTA-2Na). The flow electrode prepared by the mixture of EDTA-zeolite and carbon black exhibits a high selectivity and adsorption capacity for the recovery of NH 4 + from wastewater. The NH 4 + in wastewater passes through the ion exchange membrane and is rapidly adsorbed by the modified zeolite through ion exchange, while Na + is retained in the electrolyte. The decrease in NH 4 + concentration and the increase in Na + concentration in the catholyte lead to a significant change in ion concentration gradient across the membrane. Consequently, the transmembrane selectivity between NH 4 + and Na + reached 3.46. We validated the feasibility of NH 4 + recovery using FCDI with food waste fermentation supernatant. Under optimal operating conditions, 99.15 % of the NH 4 + in the fermentation supernatant was removed, and 95.92 % of the NH 4 + in the electrolyte was stored in the EDTA-zeolite. By gravitational settling, the NH 4 + -rich modified zeolite was separated from carbon black and could be utilized as nitrogen fertilizer. Meanwhile, the mixture of carbon black and brine was used to prepare a fresh electrode suspension. In brief, the FCDI system exhibits a satisfying NH 4 + recovery performance and demonstrates a sustainable wastewater resource recovery strategy.