Employing a novel O3/H2O2 + BiPO4/UV synergy technique to deal with thiourea-containing photovoltaic wastewater

Abstract

Photovoltaic wastewater contains a large amount of thiourea that cannot be directly treated by biological methods because of its biotoxicity. In this study, a novel O₃/H₂O₂ + BiPO₄/UV synergy technique was used as a pre-treatment process to degrade thiourea. The effects of H₂O₂ and catalyst loading were investigated, and the transformation pathway of thiourea was predicted based on the intermediates detected by UPLC-Vion-IMS-QToF. The synergy technique degraded 89.14% thiourea within only 30 min, and complete degradation occurred after 150 min. The TOC removal of O₃/H₂O₂ + BiPO₄/UV was 1.8, 1.5, and 1.9 times that of O₃/H₂O₂ and BiPO₄/UV/H₂O₂ single processes and O₃/H₂O₂ + UV process, respectively, which was due to the synergy between H₂O₂ residues and BiPO₄. In addition, thiourea was mainly degraded by ·OH into thiourea dioxide and melamine (polymerized by other intermediates) and then further degraded into biuret and methyl carbamate by the holes of BiPO₄, followed by complete mineralization into H₂O and CO₂. These results confirm that the O₃/H₂O₂ + BiPO₄/UV synergy technique is a promising option for the degradation of thiourea.