Strong enhancement on acetaminophen elimination and effective control of chlorinated/brominated by-products generation in heat/peroxymonosulfate system with sodium perborate

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The application of heat/peroxymonosulfate (PMS) system was severely constrained due to the high O–O bond dissociation energy of PMS and the high risk of forming halogenated by-products. Interestingly, this work found that sodium perborate (NaBO3) could significantly improve the removal of acetaminophen in heat/PMS system. The proposed NaBO3/heat/PMS system could achieve 100 % elimination efficiency of ACT within 15 min and exhibited an excellent pseudo-first-order rate constant (kobs), which was 35.6-folds higher than heat/PMS system. 1O2 and OH were identified as the primary reactive species in NaBO3/heat/PMS system. NaBO3 can hydrolyze to produce BO2− and H2O2, where BO2− can subsequently hydrolyze to generate B(OH)4− having strong buffer capacity. The HOOB(OH)3/HOOBO, characterized by their asymmetric O–O bonds, can be formed through the reaction of PMS with BO2− and B(OH)4−. 1O2 mainly originated from the reactions of PMS with the formed HOOB(OH)3/HOOBO, and OH primarily originated from the cleavage of O–O bond in HOOB(OH)3/HOOBO and PMS. Three removal pathways of acetaminophen were proposed. The toxicity of acetaminophen solution was reduced following the treatment using NaBO3/heat/PMS system. Humic acid, CO32−, Br− and Cl− suppressed the acetaminophen removal in NaBO3/heat/PMS system, while initial pH, NO3− and SO42− had minimal impact. Notably, the kobs of acetaminophen removal in actual waters (e.g., groundwater and lake water) were greater than that in ultrapure water. More importantly, NaBO3/heat/PMS system can effectively control the formation of chlorinated/bromine by-products, which was achieved by converting HClO to inert B(OH)3OCl− with B(OH)4−, and reducing the HBrO and HClO to Br– and Cl– with deprotonated H2O2 (HO2−). This study proposed a promising approach for improving heat/PMS system and underscored its application potential in treating water containing Cl−and Br−.