Employing a novel O/HO + BiPO/UV synergy technique to deal with thiourea-containing photovoltaic wastewater.

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 O/HO + BiPO/UV synergy technique was used as a pre-treatment process to degrade thiourea. The effects of HO 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 O/HO + BiPO/UV was 1.8, 1.5, and 1.9 times that of O/HO and BiPO/UV/HO single processes and O/HO + UV process, respectively, which was due to the synergy between HO residues and BiPO. 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 BiPO, followed by complete mineralization into HO and CO. These results confirm that the O/HO + BiPO/UV synergy technique is a promising option for the degradation of thiourea.