Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation
Zixuan Wang, Daran Anand, Zhen He
Abstract
Phosphorus (P) recovery from biosolids can play an important role in a circular economy. Herein, an electrochemical phosphorus recovery cell (EPRC) was proposed and examined to recover P from municipal whole digestate via simultaneous leaching and precipitation. The anode of the EPRC released P as aqueous PO 4 3– –P through acidification, achieving the highest leaching efficiency of 93.3% under a current density of 30 A m –2 . When the leached P solution was treated in the cathode, native metals including Ca and Fe facilitated electrochemically mediated PO 4 3– –P precipitation (EMP) and precipitated ∼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 the cathode effluent and immobilized P in the cathode chamber. The solid products contained 28.42–33.51% of P 2 O 5, comparable to the high-grade phosphate rock. Higher current densities reduced cathode scaling and resulted in a lower content of heavy metals in the solid products. An acidic solution was reused three times and effectively maintained cathode performance during a 42-cycle operation, achieving a consistent P recovery efficiency of nearly 80%. Those results have demonstrated the feasibility of the EPRC for recovering P from P-rich solid wastes.