Sodium tetraborate simultaneously enhances the degradation of acetaminophen and reduces the formation potential of chlorinated by-products with heat-activated peroxymonosulfate oxidation.

In this study, sodium tetraborate (NaBO) was introduced to enhance the degradation of acetaminophen (ACT) in heat-activated peroxymonosulfate (PMS) process. The elimination of ACT in NaBO/heat/PMS process followed the pseudo-first order kinetics. The corresponding k value with 10 mM NaBO was 33.1 times higher than that in heat/PMS process. O and HO· were identified as primary reactive species via quenching experiments and electron paramagnetic resonance technology. B(OH), the hydrolysis product of NaBO, reacted with PMS to generate HOOB(OH). O was generated by the self-decomposition of PMS using B(OH) as catalyst, while HO· was produced via the breakage of peroxide bond of PMS and HOOB(OH)under high temperature. ACT was degraded by reactive species via the pathways of -NH- bond breakage, -OH replacement, -NH oxidation and benzene ring cleavage. Nine transformation intermediates were detected by LC/Q-TOF/MS, and the toxicity of reaction solution decreased significantly with the elimination of ACT. Increasing NaBO dosage, PMS concentration, initial pH and reaction temperature were conducive to ACT elimination. Humic acid, Cl and CO inhibited the degradation of ACT heavily, while SO and NO had the negligible effects. Moreover, B(OH) could react with free chlorine to the inert B(OH)OCl and further significantly suppress the formation of chlorinated by-products for the treatment of Cl-containing water in NaBO/heat/PMS process. This study provided an effective way to enhance the oxidation capacity of heat/PMS process and suppress the formation of chlorinated by-products in chloride-containing water, and the findings had important implications for using borate buffer in the studies of PMS-based advanced oxidation processes.