Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation

Twodifferent environments in an electrochemical processallow simultaneous leaching and recovery of phosphorus from wholedigestate. Phosphorus (P) recovery from biosolids can play an importantrolein a circular economy. Herein, an electrochemical phosphorus recoverycell (EPRC) was proposed and examined to recover P from municipalwhole digestate via simultaneous leaching and precipitation.The anode of the EPRC released P as aqueous PO4 (3-)-P through acidification, achieving the highest leaching efficiencyof 93.3% under a current density of 30 A m(-2). Whenthe leached P solution was treated in the cathode, native metals includingCa and Fe facilitated electrochemically mediated PO4 (3-)-P precipitation (EMP) and precipitated & SIM;99%of the leached P in the cathode chamber. Around 54.3-78.7%of total P existed in two harvestable forms: suspended solids in thecathode effluent and immobilized P in the cathode chamber. The solidproducts contained 28.42-33.51% of P2O5, comparable to the high-grade phosphate rock. Higher current densitiesreduced cathode scaling and resulted in a lower content of heavy metalsin the solid products. An acidic solution was reused three times andeffectively maintained cathode performance during a 42-cycle operation,achieving a consistent P recovery efficiency of nearly 80%. Thoseresults have demonstrated the feasibility of the EPRC for recoveringP from P-rich solid wastes.