Degradation difference of ofloxacin and levofloxacin by UV/H2O2 and UV/PS (persulfate): Efficiency, factors and mechanism

Chiral quinolone antibiotics, as racemate and in enantiomerically form, have been attracted extensive attention due to their same molecular structure and different pharmacological properties and toxicity in environment. The present study focused on the difference of degradation efficiency and pathway of chiral antibiotics by different AOPs technology. The degradation behaviors and differences of chiral pollutants were firstly identified. Among them, UV/PS process exhibited the best performance for the elimination of chiral pollutants removal and reduction of total organic carbon (TOC). The degradation of ofloxacin and levofloxacin revealed pronounced pH dependence in UV/H2O2 and UV/PS processes, where the impact on Levofloxacin (LEV) was greater than that on Ofloxacin (OFLO). Only a slight variation of TOC was observed to be less than 50%, where the removal efficiencies were all above 96%. SO4•− generated in UV/PS process yields a greater mineralization of antibiotics than •OH in UV/H2O2 process. Cl−, NO3− and NOM had inhibitory effects on OFLO and LEV degradation in both processes, while SO42− showed positive effect on UV/PS degradation. Meanwhile, chairal antibiotics removal was dominated by •OH with the second-order rate constants of 3.97 × 109 and 2.48 × 109 M−1s−1 in UV/H2O2 process, while SO4•− played the key role in UV/PS system with second-order rate constants of 2.19 × 1010 and 2.66 × 1010 M−1s−1, respectively. The results of acute toxicity assay shown that OFLO exhibited higher acute toxicity than LEV, while TTC dehydrogenase activity of intermediate products of OFLO was lower than LEV. This study demonstrated that AOPs (especially UV/PS) were efficient for removing fluoroquinolone antibiotics, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.