3.4.1. UV254 photolysis
In UV254 photolysis experiments, removal of NOR was comparatively effective after irradiation for 30 min (removal efficiency of 49%). In contrast, UV254 irradiation seemed not efficient in degrading the other three antibiotics.
Degradation of organic pollutants by direct UV photolysis has been reported in previous literatures [17] and [32]. The mechanism is considered to be that organic substrates absorb UV light to form radicals which then react with oxygen, or form electronically excited states, and then an electron from the exited state of the substrates transfers to ground state molecular oxygen [33]. Besides, UV light with shorter wavelengths (λ < 190 nm) could photolyze H2O into radical dotOH and radical dotH [34], which was not the case in our study employing a UV lamp emitting light at 254 nm. This was supported by the result of EPR test of UV254 process. No signal of ROS was observed in the spectrum (see Fig. 6). Under a certain wavelength and intensity of UV irradiation, the degradation of organic substrate by UV photolysis largely depends on the chemical structure of the target compound [32]. Kim et al. found that sulphonamides such as sulfamethoxazole and sulfamonomethoxine, and quinolones such as norfloxacin and nalidixic acid were effectively removed by UV photolysis (removal efficiencies of 86–100%) [35]. In contrast, macrolides such as clarithromycin, erythromycin and azithromycin were removed by 4–7% only. These results were well in accordance with our findings. Among the four antibiotics in our study, only NOR contains a Nsingle bondH bond, which is believed to be easily broken by UV radiation [32]. This could be the reason that it exhibited higher sensitivity to UV254 photolysis than the other three.
3.4.1. UV254 photolysisใน UV254 photolysis ทดลอง การกำจัด ไม่มีประสิทธิภาพที่ดีอย่างหนึ่งหลังจากวิธีการฉายรังสีใน 30 นาที (เอาประสิทธิภาพของ 49%) ในทางตรงกันข้าม วิธีการฉายรังสี UV254 ดูเหมือนไม่มีประสิทธิภาพในการลดยาปฏิชีวนะที่สามอื่น ๆDegradation of organic pollutants by direct UV photolysis has been reported in previous literatures [17] and [32]. The mechanism is considered to be that organic substrates absorb UV light to form radicals which then react with oxygen, or form electronically excited states, and then an electron from the exited state of the substrates transfers to ground state molecular oxygen [33]. Besides, UV light with shorter wavelengths (λ < 190 nm) could photolyze H2O into radical dotOH and radical dotH [34], which was not the case in our study employing a UV lamp emitting light at 254 nm. This was supported by the result of EPR test of UV254 process. No signal of ROS was observed in the spectrum (see Fig. 6). Under a certain wavelength and intensity of UV irradiation, the degradation of organic substrate by UV photolysis largely depends on the chemical structure of the target compound [32]. Kim et al. found that sulphonamides such as sulfamethoxazole and sulfamonomethoxine, and quinolones such as norfloxacin and nalidixic acid were effectively removed by UV photolysis (removal efficiencies of 86–100%) [35]. In contrast, macrolides such as clarithromycin, erythromycin and azithromycin were removed by 4–7% only. These results were well in accordance with our findings. Among the four antibiotics in our study, only NOR contains a Nsingle bondH bond, which is believed to be easily broken by UV radiation [32]. This could be the reason that it exhibited higher sensitivity to UV254 photolysis than the other three.
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