Trimethoprim (TMP) is often used for the treatment of various bacterial infections. It can be detected in water, and it is difficult to be biodegraded. In this study, the degradation mechanism of TMP through ozonation and the effect of humic acids (HA) were investigated. Excessive ozone (pH 6, 0 °C) could reduce the content of TMP to less than 1% in 30 s. However, when ozone (O3) was not excessive (pH 6, 20 °C), the removal efficiency of TMP increased with the increase of O3 concentration. Four possible degradation pathways of TMP in the process of ozonation were speculated: hydroxylation, demethylation, carbonylation, and cleavage. The presence of HA in water inhibit the generation of ozonation products of TMP. The excitation-emission matrices (EEM) analysis showed that with the extension of ozonation time, the fluorescence value in the solution decreased and the fluorescence peak blue shifted. These results indicated that the structure of HA changed in the reaction and was competitively degraded with TMP. According to the free radical quenching test, the products of pyrolysis, direct hydroxylation and demethylation were mainly produced by indirect oxidation.

中文翻译：

---

天然有机物对水中甲氧苄啶臭氧化机理的影响

甲氧苄啶 (TMP) 常用于治疗各种细菌感染。可在水中检出，难以生物降解。在这项研究中，研究了臭氧化降解 TMP 的机制和腐殖酸 (HA) 的作用。过量的臭氧 (pH 6, 0 °C) 可以在 30 秒内将 TMP 的含量降低到 1% 以下。然而，当臭氧（O3）不过量时（pH 6，20°C），TMP 的去除效率随着 O3 浓度的增加而增加。推测了臭氧化过程中TMP的四种可能降解途径：羟基化、去甲基化、羰基化和裂解。水中HA的存在抑制了TMP臭氧化产物的产生。激发发射矩阵（EEM）分析表明，随着臭氧化时间的延长，溶液中的荧光值降低，荧光峰蓝移。这些结果表明 HA 的结构在反应中发生了变化并被 TMP 竞争性降解。根据自由基猝灭试验，热解、直接羟基化和去甲基化的产物主要通过间接氧化产生。