Abstract
Fluoroquinolones (FQs) are ubiquitously present in aquatic environments, garnering considerable research attention. Ciprofloxacin (CIP), the most extensively utilized FQ antibiotic, features high aqueous residual levels and ranks among the most frequently detected antibiotics in environmental matrices. It also acts as a precursor of disinfection byproducts (DBPs). In recent years, ultraviolet-based combined disinfection has been widely used. This study investigated the removal efficiency of CIP and the identification of DBPs under four disinfection systems: UV irradiation, UV/PS, UV/CaO(2), and UV/H(2)O(2). Microcystis aeruginosa (M. aeruginosa), a dominant algal species in eutrophic freshwater ecosystems, was selected as the test organism to investigate the toxicity of DBPs generated via distinct disinfection approaches. The results demonstrated significant variations in CIP removal efficiency among the four disinfection methods. The removal rates reached 93-99% under UV/H(2)O(2), UV/CaO(2), and UV/PS, while single UV irradiation achieved only 87%. Sixteen DBPs were identified during the process. The DBPs produced under different disinfection methods exhibited varying inhibitory effects on M. aeruginosa growth. DBPs formed under the UV/H(2)O(2) and UV/CaO(2) systems displayed the strongest inhibition, with maximum inhibition rates of 42.1% and 36.2% within 12 days, respectively. In contrast, DBPs formed under the UV/PS and UV systems showed weaker inhibition (25.3% and 22.1%, respectively), and their inhibitory effects decreased at higher disinfection byproduct (DBP) concentrations. The results indicate that while combined UV disinfection enhances CIP removal, it may also increase the toxicity of the resulting DBPs to aquatic organisms. Overall, the UV/PS process demonstrated the highest degradation efficiency for CIP and produced disinfection byproducts (DBPs) with lower toxicity, making it the most effective and environmentally friendly method for treating water contaminated with ciprofloxacin.