High-flux electrochemical phosphorus recovery in an undivided electrolytic cell coupled with microfiltration with low energy consumption

Electrochemical systems are promising for phosphorus (P) removal and recovery from wastewater. However, its industrial application still faces some challenges, including relatively low P recovery efficacy, high energy consumption, and complex configuration of the reactors. This work, developed an undivided electrolytic cell with H+ or OH- extraction from its corresponding electrode surface for P recovery. The experimental results and models validated the superiority of continuously and precisely extracting H+ from the tubular Ti porous anode surface for H+-OH- separation over OH- extraction from the cathode surface. In the electrolytic cell, alkaline effluent with H+ extraction, the P could be precipitated with Ca2+ in the form of insoluble calcium phosphate (Ca-phosphate), which could then be separated from the wastewater by microfiltration. Under the conditions of a current density of 4 mA cm-2, an initial P concentration of 0.6 mM, a influent flow rate of 500 mL min-1, and H+ extraction rate of 50 mL min-1, the P recovery efficiency reached 81 % with the alkaline effluent pH of 10.5. The calculated P recovery rate and treatment capacity were 18.3 g P (m2 h)-1 and 1194 L (m2 h)-1, respectively, at energy consumption of 8.75 kWh (kg P)-1, which were superior over the cutting-edge divided electrolytic systems and the conventional undivided electrolytic systems. The recovered precipitates are composed principally of hydroxyapatite in the minor presence of amorphous calcium phosphate, showing a Ca/P molar ratio of 1.8. Generally, the established undivided electrolytic cell coupled with microfiltration exhibited significant prospects for recovering P from wastewater without acid-base reagents.