The recovery of phosphorus (P) from high-strength acidic waste streams with high salinity and organic loads is challenging. Here, we addressed this challenge with a recently developed electrochemical approach and compared it with the chemical precipitation method via NaOH dosing. The electrochemical process recovers nearly 90% of P (∼820 mg/L) from cheese wastewater in 48 h at 300 mA with an energy consumption of 64.7 kWh/kg of P. With chemical precipitation, >86% of P was removed by NaOH dosing with a normalized cost of 1.34–1.80 euros/kg of P. The increase in wastewater pH caused by NaOH dosing triggered the formation of calcium phosphate sludge instead of condensed solids. However, by electrochemical precipitation, the formed calcium phosphate is attached to the electrode, allowing the subsequent collection of solids from the electrode after treatment. The collected solids are characterized as amorphous calcium phosphate (ACP) at 200 mA or a precipitation pH of ≥9. Otherwise, they are a mixture of ACP and hydroxyapatite. The products have sufficient P content (≤14%), of which up to 85% was released within 30 min in 2% citric acid and a tiny amount of heavy metals compared to phosphate rocks. This study paves the way for applying electrochemical removal and recovery of phosphorus from acidic P-rich wastewater and offers a sustainable substitute for mined phosphorus.

Hypophosphite (P(I)) is ubiquitous in some waste streams. It may contribute to the eutrophication of water bodies, yet conventional methods are ineffective in treating P(I)-laden wastewater. Here, we propose a novel CaO2/ultraviolet (UV) system that can simultaneously remove P(I) and recover Ca-phosphate. This system lies in the simultaneous release of OH–, Ca2+, and H2O2, with the last being activated and producing reactive oxygen species (ROS) under UV irradiation. Subsequently, the generated ROS converts P(I) to phosphite and phosphate, forming Ca-phosphate with the released Ca2+ at pH 11.0. Beyond activating H2O2, UV light also promotes the dissolution of CaO2 powders. The system removes 97.0% of 1.0 mM P(I) in 6 h with dosing 2.0 mM CaO2. The presence of 5.0 mM HCO3 – drops P(I) removal from 97.0 to 14.1% by competing with P(V) toward Ca2+. Nitrate and humic acid show similar effects by adsorbing UV light or quenching ROS. However, we may overcome the adverse effects with an enhanced CaO2 dose. For example, with 10 mM CaO2, the CaO2/UV system removed more than 78% of non-ortho P from actual electroless rinse water. These results confirmed that CaO2/UV is an exciting all-in-one system for treating P(I)-laden wastewater and recovering valuable P products.

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