Degradation and transformation of norfloxacin in medium-pressure ultraviolet/peracetic acid process: An investigation of the role of pH

Given that fluoroquinolone antibiotics (FQs) are frequently detected in aquatic environments, there is an urgent need for the development of efficient water treatment technologies for their removal. Peracetic acid (PAA)-based advanced oxidation processes (AOPs) have increasingly attracted attention as promising technologies for water decontamination in this regard. In this study, a novel PAA-based AOP (the medium-pressure ultraviolet (MPUV)/PAA process) was employed to degrade norfloxacin (NOR), which is an extensively applied FQ that is widely present in water. Mechanistic and kinetic aspects of the role of pH on this NOR degradation process were investigated. The results obtained showed that the MPUV/PAA process could effectively degrade NOR (pH = 5–9), and the degradation efficiency was significantly enhanced at pH 7 and 9 compared with that at pH 5. This observation could be attributed to the effect of pH on the ionic forms of NOR and the generation of reactive oxygen species (ROS). Further, the rate of PAA photolysis, which resulted in the formation of reactive radicals, increased with pH, as evidenced by the observed increase in the molar absorption coefficient of PAA (εPAA). Electron paramagnetic resonance (EPR) tests also indicated that the generation of ROS was significantly enhanced when the pH increased from 5 to 7, and at pH 9, a large amount of •OH were possibly consumed by PAA to form organic radicals, leading to a decrease in the •OH signal. Furthermore, it was observed that •OH is primarily responsible for NOR degradation in the MPUV/PAA process at pH 5, whereas organic radicals were primarily responsible for the degradation at pH 7 and 9. The identification of the transformation products (TPs) led to the observation of different NOR transformation pathways owing to the MPUV/PAA process under different pH conditions. Overall, this study provides a comprehensive understanding of the role of pH on the MPUV/PAA degradation behavior of FQs.