Abstract
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.
Highlights
In recent years, the emerging persistent organic matter attracted great attention in the environmental protection industry [1,2,3]
Liu et al [57] carried out ozonation experiments on eight kinds of antibiotics, including ampicillin, azithromycin, erythromycin, ozonation experiments on eight kinds trimethoprim, of antibiotics,and including ampicillin, azithromycin, clarithromycin, ofloxacin, sulfamethoxazole, tetracycline, and the results showed erythromycin, clarithromycin, ofloxacin, sulfamethoxazole, trimethoprim, and tetracycline, and the that ozonation rate was highly depended on O3 concentration and contact time, and the removal results showed that ozonation rate was highly depended on 3 concentration and contact time, and efficiency of antibiotics increased with the increase of O3 concentration
Excessive O3 can degrade TMP rapidly, and the addition of humic acids (HA) and methanol had little effect on the reaction, indicating that TMP could be directly oxidized by O3 molecules
Summary
The emerging persistent organic matter attracted great attention in the environmental protection industry [1,2,3] Owing to their high consumption and refractory chemical properties [4], antibiotics are considered as a new persistent organic substances [5,6,7]. Trimethoprim (TMP) is a commonly used antibacterial synergetic agent which can be combined with sulfonamides to greatly enhance their antibacterial activity [11,12]. It is widely used in the treatment of human diseases and animal bacterial infections [13,14]. TMP has been detected in wastewater from sewage treatment plants, surface water environment, drinking water, and other water bodies [19,20,21,22,23]
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