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 (H 2 PO 2 – ). Herein, a single-compartment photoelectrocatalytic (PEC) cell system consisting of a TiO 2 /Ni–Sb–SnO 2 bifunctional photoanode and an activated carbon fiber (ACF) cathode with dosing Fe 2+ ions was developed for recovery of phosphorus in the form of FePO 4 from hypophosphite-laden wastewater. In the PEC process, H 2 PO 2 – 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 H 2 PO 2 – 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 O 3; the ACF cathode can electrogenerate H 2 O 2; H 2 O 2, O 3, and the added Fe 2+ can interact with each other to produce • OH radicals and Fe 3+ ions. • OH radicals mainly from the Fenton process were responsible for oxidation of H 2 PO 2 – to PO 4 3–, which immediately combined with Fe 3+ to form FePO 4 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.