CaO<sub>2</sub>/UV Process for One-Step Phosphorus Removal and Recovery from Hypophosphite: Simultaneous Oxidation and Precipitation
Shaopeng Zhang, Bingnan Song, Runhua Wang, Zhengshuo Zhan, Michel Saakes, Renata D. van der Weijden, Cees J.N. Buisman, Yang Lei
Abstract
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 CaO 2 /ultraviolet (UV) system that can simultaneously remove P(I) and recover Ca-phosphate. This system lies in the simultaneous release of OH –, Ca 2+, and H 2 O 2, 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 Ca 2+ at pH 11.0. Beyond activating H 2 O 2, UV light also promotes the dissolution of CaO 2 powders. The system removes 97.0% of 1.0 mM P(I) in 6 h with dosing 2.0 mM CaO 2 . The presence of 5.0 mM HCO 3 – drops P(I) removal from 97.0 to 14.1% by competing with P(V) toward Ca 2+ . Nitrate and humic acid show similar effects by adsorbing UV light or quenching ROS. However, we may overcome the adverse effects with an enhanced CaO 2 dose. For example, with 10 mM CaO 2, the CaO 2 /UV system removed more than 78% of non-ortho P from actual electroless rinse water. These results confirmed that CaO 2 /UV is an exciting all-in-one system for treating P(I)-laden wastewater and recovering valuable P products.