Removal of lead phosphate nanoparticles from drinking water by hydrogen peroxide photolysis combined with point-of-use filtration

Abstract

The U.S. EPA recently announced the revision of the Lead and Copper Rule to establish a new lead action level at 10 μg L⁻¹; however, the formation and release of lead phosphate nanoparticles in drinking water are ubiquitous in lead-containing drinking water distribution systems, and these particles are poorly removed by conventional filters, thus making it challenging for lead control in light of the new regulation. To address this urgent issue, this study developed a treatment train combining hydrogen peroxide photolysis (UV/H₂O₂) pre-oxidation with point-of-use (POU) filtration to efficiently remove lead phosphate nanoparticles (nano-Pb₃(PO₄)_2(s)) from drinking water. The results showed that hydroxyl radicals produced via UV/H₂O₂ oxidized divalent nano-Pb₃(PO₄)_2(s) to tetravalent lead dioxide solid PbO_2(s) and aggregated them into larger cluster particles, facilitating efficient removal by subsequent POU filtration. Without the UV/H₂O₂ pre-oxidation, stand-alone POU filtration was ineffective at reducing the nano-Pb₃(PO₄)_2(s) concentration below 10 μg L⁻¹. Furthermore, UV/H₂O₂ pre-oxidation was effective in diverse drinking water chemical conditions at varying levels of pH (6–8), chloride (0–50 mg L⁻¹), and alkalinity (0–200 mg L⁻¹ as CaCO₃). Overall, this study provides an urgently needed and promising lead removal technology that is robust to guarantee drinking water safety to consumers.