Generation mechanisms of active free radicals during ciprofloxacin degradation in the ultrasonic/KSO system.

Ciprofloxacin (CIP) removal efficiency in aqueous solutions in the ultrasonic (US), KSO, and US/KSO systems was investigated. The free radical generation and action ratio were studied based on variations of KSO concentration, ultrasonic power, pH, and the addition of isopropanol (ISP) or tert-butyl alcohol (TBA) in the US/KSO system. The results showed that under conditions of 20 mg·L CIP concentration, 20 mmol·L KSO concentration, an ultrasonic power of 360 W and pH = 7, CIP removal efficiency in the US/KSO system was 92.20% after 180 min. The reaction in the US/KSO system was explicitly divided into two stages: free radical generation and pollutants degradation. The ultrasonic and chain reaction facilitated enhanced generation of SO and HO. The presence of KSO can promote HO generation and KSO concentration also exerted a significant effect on SO generation, however, high concentrations were not beneficial to the reaction. Quenching reactions occurred under high concentrations of HO and SO. During the initial stage of the reaction, HO played a more prominent role than SO, however, the role of SO gradually increased as the reaction proceeded and eventually surpassed HO.