Recovery of Phosphorus from Hypophosphite-Laden Wastewater: A Single-Compartment Photoelectrocatalytic Cell System Integrating Oxidation and Precipitation.

Recovery of phosphorus through precipitation from hypophosphite-laden wastewater is more difficult than from orthophosphate-laden wastewater because of the higher solubility of hypophosphite (H2PO2-). Herein, a single-compartment photoelectrocatalytic (PEC) cell system consisting of a TiO2/Ni-Sb-SnO2 bifunctional photoanode and an activated carbon fiber (ACF) cathode with dosing Fe2+ ions was developed for recovery of phosphorus in the form of FePO4 from hypophosphite-laden wastewater. In the PEC process, H2PO2- with an initial concentration of 1.0 mM was completely oxidized and recovered within 30 min at 3.0 V, and the pseudo-first-order rate constant of H2PO2- oxidation was ∼4 times than that in the electrocatalytic process and even ∼89 times than that in the photocatalytic process. The bifunctional photoanode can simultaneously generate •OH radicals and O3; the ACF cathode can electrogenerate H2O2; H2O2, O3, and the added Fe2+ can interact with each other to produce •OH radicals and Fe3+ ions. •OH radicals mainly from the Fenton process were responsible for oxidation of H2PO2- to PO43-, which immediately combined with Fe3+ to form FePO4 at the optimized conditions to realize recovery of phosphorus. The long-term stability of this system was demonstrated. The efficiency for actual electroless nickel plating effluents was exhibited.