Enhanced NH₄ ⁺ Removal and Recovery from Wastewater Using Na-Zeolite-based Flow-Electrode Capacitive Deionization: Insight from Ion Transport Flux

Flow-electrodecapacitive deionization (FCDI) is a promising electromembranetechnology for wastewater treatment and materials recovery. In thisstudy, we used low-cost Na-modified zeolite (Na-zeolite) to preparea composite flow-electrode (FE) suspension with a small amount ofhighly conductive carbon black (CB) to remove and recover NH4 (+) from synthetic and actual wastewater (200 mg-N/L). Comparedwith conventional activated carbon (AC), the Na-zeolite electrodeexhibited a 56.2-88.5% decrease in liquid-phase NH4 (+) concentration in the FE suspension due to its higherNH(4) (+) adsorption capacity (6.0 vs. 0.2 mg-N/g).The resulting enhancement of NH4 (+) diffusionto the electrode chamber contributed to the improved performance ofFCDI under both constant current (CC) and constant voltage (CV) conditions.The addition of CB to the FE suspension increased the conductivityand facilitated Na-zeolite charging for NH4 (+) electrosorption, especially in CV mode. NH4 (+)-rich zeolite can be easily separated by sedimentation from CB inthe FE suspension, producing a soil conditioner with a high N-fertilizercontent suitable for soil improvement and agricultural applications.Overall, our study demonstrates that the novel Na-zeolite-based FCDIcan be developed as an effective wastewater treatment technology forboth NH4 (+) removal and recovery as a valuablefertilizer resource. FCDIis widely applied for desalination but without selectivity.This study used a low-cost Na-zeolite and CB mixture as a flow electrodefor effective ammonium recovery from wastewater.