Investigation of degradation and transformation product formation during the UV/H₂O₂-based oxidation process for chemicals of emerging concern

This study aimed to optimize the ultraviolet (UV)/hydrogen peroxide (H₂O₂) process for degrading chemicals of emerging concern (CECs), such as caffeine (CAF), atenolol (ATL), acetaminophen (ACT), and chlortetracycline (CTC). The CECs used in this study were chosen because they are used in various industries, affect water bodies, and are difficult to degrade using conventional oxidation and biological processes. The individual degradation results revealed that the CAF degradation rate increased from 23 ± 2%–80 ± 4% as the UV/H₂O₂ dose increased from 1 to 10 mg·L⁻¹. Similarly, the ATL, ACT, and CTC degradation rates increased from 59.23 ± 2%, 34.21 ± 1.9%, and, 41.36 ± 2.3%–91.24 ± 3%, 68.12 ± 3%, and 91.93 ± 3.1%, respectively. The complex feed water analysis results revealed that CTC had a higher degradation rate than the other targeted contaminants owing to its higher degradation potential. The rate of reaction results revealed that the degradation of these CECs followed the pseudo-first-order reaction, with R² > 0.95 in all cases. liquid chromatography with tandem mass spectrometry (LC–MS/MS) was used to identify the degradation products, and the results revealed the presence of low-molecular-weight organic products due to oxidation. The organic products were formed because of the hydroxylation and demethylation of intermediates and photoproducts, which caused a ring opening and generated several low-molecular-weight carboxylic acids before complete mineralization. These results illustrate that the UV/H₂O₂ process had some significant effects on the complex mixture. However, CTC exhibited a relatively high degradation rate, which is believed to have inhibited the degradation of other chemicals.