Comprehensive understanding of fluoroquinolone degradation via MPUV/PAA process: Radical chemistry, matrix effects, degradation pathways, and toxicity.

The wide occurrence of fluoroquinolones (FQs) in aquatic environments has aroused increasing concern about their potential adverse effects on human health. In this study, an emerging advanced oxidation process, i.e., the Medium-Pressure Ultraviolet/Peracetic Acid (MPUV/PAA) process, was used to degrade FQs (e.g., levofloxacin (LEV), norfloxacin, and ciprofloxacin). Compared with the MPUV process alone and the PAA process alone, the MPUV/PAA process significantly promoted degradation of FQs due to the considerable contribution of reactive radicals. Probe experiments revealed that PAA-specific organic radicals (e.g., CHC(O)O• and CHC(O)OO•) were the major radicals responsible for FQ elimination. Rapid degradation of FQs via the MPUV/PAA process was achieved within a wide range of pH values (5-9) by selecting LEV as the target compound, and higher pH values were more favorable for the reaction. The slight impacts of Cl and CO/HCO on LEV removal were observed. The transformation products and pathways of LEV were identified, and nearly all of the transformation pathways occurred on the piperazine ring. Based on Quantitative Structure-Activity Relationship (QSAR) analysis, most of the products had lower toxicities than LEV. Overall, these findings improve our understanding and application of the MPUV/PAA process for degrading emerging contaminants in (waste)water treatment.