Direct oxidation of antibiotic trimethoprim by unactivated peroxymonosulfate via a nonradical transformation mechanism

Application of activated peroxymonosulfate (PMS) to generate sulfate radical or hydroxyl radical is a promising strategy for wastewater treatment, while our knowledge on the background reaction, namely, the direct interaction between PMS and target contaminants is quite limited. In this contribution, the degradation kinetics, stoichiometry, products and mechanism of the reaction between unactivated PMS and trimethoprim (TMP), one of the most commonly detected micro-pollutants in the aquatic system were investigated systematically. The results indicated that TMP was susceptible to degradation by direct PMS oxidation via a non-radical process. By recording the decay of two reactants simultaneously, the stoichiometric ratio between PMS and TMP was estimated to be approximately 1. Higher PMS levels exhibited a promotion effect on PMS decay. And the degradation was pH-dependent, basic conditions were favorable for TMP degradation, which could be well modeled based on the species-specific reactions. The two amine groups on the pyrimidine ring were identified as the reactive sites. After direct attacks by PMS, they would be oxidized to form hydroxylamine-products, namely, N-8-OH-TMP and N-9-OH-TMP. These two hydroxylamine-products were quite stable and resistant to further oxidation by PMS, preventing the formation of more toxic nitroso- and nitro-products. The new findings in the present work would provide beneficial information on the strategy choice for the elimination of specific pollutants, like TMP, as PMS also exhibits relatively high reactivity towards them. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study found that unactivated PMS can directly oxidize TMP through a non-radical process, promoting PMS decay, with alkaline conditions favoring TMP degradation. The two amine groups on the pyrimidine ring were identified as reactive sites, and the oxidation products were stable.