Electrochemical Recovery of Ammonium and Potassium from Livestock Wastewater Using Nickel Prussian Blue Analogue

Recovering nitrogen and potassium from agricultural wastewater is crucial for sustainable resource circulation. However, potassium has rarely been treated as a recoverable nutrient. In this study, we developed an electrochemical adsorption method using nickel Prussian blue analog electrodes to simultaneously recover potassium (K+) and ammonium (NH4+) from synthetic agricultural wastewater containing sodium (Na+) as a competing ion. Under high-concentration conditions (ca. 1000–2000 mg L–1), both NH4+ and K+ were efficiently recovered with recovery efficiencies of ∼70%, whereas Na+ uptake remained negligible. By optimizing the constant current operation at low concentrations (ca. 100 mg L–1), stable adsorption was achieved, enabling selective recovery of NH4+ and K+ with efficiencies of ∼40%. Desorption experiments confirmed that the captured ions were effectively released and concentrated by more than one order of magnitude. Apparent selectivity coefficients of NH4+ and K+ relative to Na+ were similar across conditions, indicating that electrochemical separation performance was governed primarily by ion transport limitations. The electrodes demonstrated stable performance over 10 cycles. These findings demonstrate a practical electrochemical approach for the co-recovery and concentration of nitrogen and potassium, highlighting the potential of potassium recovery as a valuable resource-recovery strategy for agricultural wastewater treatment.