Concurrent Nitrogen and Phosphorus Recovery Using Flow-Electrode Capacitive Deionization

This study presents that flow-electrode capacitive deionization (FCDI) can concurrently remove salts and nutrient ions from wastewater effluent and recover them as concentrate efficiently. Compared with complex biological nutrient removal, this electrochemical method utilizes the ionic nature of salts and nutrient species (NH ₄ ⁺ -N, NO ₃ ^- -N, PO ₄ ^3- -P) to enable simple nutrient removal and desalination. The FCDI with separated anode and cathode (FCDI-S) removed 70-98.5% salinity, 49-91% PO ₄ ^3- -P, 89-99% NH ₄ ⁺ -N, and 83-99% NO ₃ ^- -N under the 5-15 wt % electrode loadings. When a reverse potential was applied, more than 80% of the removed nutrient ions were recovered in the concentrate during discharging operation. Furthermore, when connected flow operation (FCDI-C) was implemented that allowed external electrode mixing, more adsorption sites were freed up, which resulted in 43.5 ± 2.2% increase in PO ₄ ^3- -P removal, 12.3 ± 1.1% increase in NH ₄ ⁺ -N removal, and 9.9 ± 0.3% increase in NO ₃ ^- -N removal. This electrochemical method provides a new alternative nutrient removal and recovery solution especially for distributed applications.