Non-radical dominated degradation of bisphenol S by peroxymonosulfate activation under high salinity condition: Overlooked HOCl, formation of intermediates, and toxicity assessment

Abstract

Extensive studies revealed that Cl^- could inhibit the removal of targeted pollutants under low Cl^- conditions in the peroxymonosulfate (PMS) system. However, the enhanced effect of Cl^- has always been overlooked under high Cl^- conditions. Here, we find that high concentration of Cl^- played a critical role in bisphenol S (BPS) degradation by activating PMS using 16%-CoFe₂O₄@PAL (16%-CFO@PAL). The removal of BPS was sharply enhanced after introducing 0.5 and 1.0 M Cl^-, and the corresponding k_obs increased to 0.922 min⁻¹ and 1.103 min⁻¹, which was 6-fold and 7-fold higher than the control (0.144 min⁻¹), respectively. HOCl was demonstrated as the dominant species for removing BPS in 16%-CFO@PAL/PMS system under high Cl^- circumstances. The typical chlorinated BPS intermediates were identified, which showed higher eco-toxicity than BPS. The chlorinated byproducts along with their toxicity could be effectively eliminated after 30 min. The possible formation mechanism of chlorinated products was further revealed by theoretical calculations. Toxicity assessment experiments showed that BPS significantly affected hormone levels of zebrafish and showed toxicity on the testis and liver of zebrafish, which could be reduced using 16%-CFO@PAL/PMS system. This study attracts attention to the overlooked HOCl in PMS-based processes under high salinity conditions.