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

Abstract

Flow-electrode capacitive deionization (FCDI) is a promising electromembrane technology for wastewater treatment and materials recovery. In this study, we used low-cost Na-modified zeolite (Na-zeolite) to prepare a composite flow-electrode (FE) suspension with a small amount of highly conductive carbon black (CB) to remove and recover NH 4 + from synthetic and actual wastewater (200 mg-N/L). Compared with conventional activated carbon (AC), the Na-zeolite electrode exhibited a 56.2−88.5% decrease in liquid-phase NH 4 + concentration in the FE suspension due to its higher NH 4 + adsorption capacity (6.0 vs. 0.2 mg-N/g). The resulting enhancement of NH 4 + diffusion to the electrode chamber contributed to the improved performance of FCDI under both constant current (CC) and constant voltage (CV) conditions. The addition of CB to the FE suspension increased the conductivity and facilitated Na-zeolite charging for NH 4 + electrosorption, especially in CV mode. NH 4 + -rich zeolite can be easily separated by sedimentation from CB in the FE suspension, producing a soil conditioner with a high N-fertilizer content suitable for soil improvement and agricultural applications. Overall, our study demonstrates that the novel Na-zeolite-based FCDI can be developed as an effective wastewater treatment technology for both NH 4 + removal and recovery as a valuable fertilizer resource.

Molten Alkali-Assisted Formation of Silicate Gels and Its Application for Preparing Zeolites

“…Furthermore, the recyclability of adsorption performance was also investigated. As shown in Figure 8 d, after 5 cycles of reuse (recovery at 1 M KCl solution) [ 28 , 29 , 30 ], the ammonium adsorption performance of the obtained zeolite reaches a stable state and the ammonium removal rate reaches 34%. Compared with the first ammonium removal rate of 52%, it can be concluded that the ammonium exchange might occur just at the surface of the zeolite.…”

Ion-Selective Metathesis Design of Flow-Electrode Capacitive Deionization for Energy-Saving and Anti-Scaling Softening of Brackish Water

“…Furthermore, it is speculated that the FCDI combined with ion-exchange resin or zeolite developed in recent years cannot be used to treat brackish water with high SO 4 2− and Ca 2+ contents. 37,38 Brackish Water Softening in ISM-FCDI. The performance of ISM-FCDI for brackish water softening was evaluated (Figure 4a,b).…”

Ammonium Disrupts Vivianite Crystal Hydration to Enhance Crystallization Rate for Phosphorus Recovery

“…The reaction medium comprised three distinct solutions: solution A containing 8.33 mM Na 2 H 2 PO 4 , solution B containing 12.3 mM FeCl 2 , and solution C containing either ultrapure water or NH 4 + at varying concentrations, depending on the specific experiment. In wastewater such as livestock one, digestion liquid, and landfill leachate, NH 4 + concentrations generally range from 150 to 1000 mg-N/L . Therefore, the initial concentration of NH 4 + was selected as 300, 600, and 800 mg-N/L.…”

“…Phosphate-rich wastewaters, such as those from livestock wastewater, digestion liquid, and landfill leachate, serve as excellent phosphate sources for the vivianite crystallization method. However, besides phosphate, these wastewater typically contain ammonium (NH 4 + ), often reaching concentrations of several hundred milligrams per liter. , Considering the significance of NH 4 + in the phosphate recovery process through the vivianite crystallization method, this aspect is particularly crucial. Previous research has demonstrated that NH 4 + can exert an impact on mineral crystallization processes as well as on crystal morphology and structure.…”