Degradation of levofloxacin in aqueous solutions by Fenton, ferrous ion-activated persulfate and combined Fenton/persulfate systems

• The treatment efficacy was as follows: H2O2/Fe2+ > H2O2/S2O82−/Fe2+ > S2O82−/Fe2+.
• The combined Fenton/persulfate process proved effective in LFX removal.
• Six LFX transformation products were identified in all studied systems.
• HO was proposed as the predominant radical in all studied systems.

The efficacies of Fenton (H2O2/Fe2+), Fe2+-activated persulfate (S2O82−/Fe2+) and combined Fenton/persulfate (H2O2/S2O82−/Fe2+) systems for degrading levofloxacin (LFX) in aqueous solutions were investigated and compared. The LFX degradation by classical Fenton oxidation followed a pseudo-first-order kinetic law during the entire reaction. In the case of the S2O82−/Fe2+ and H2O2/S2O82−/Fe2+ systems, a fast degradation of LFX was observed within the first minute, and then the target compound was gradually degraded within the remaining reaction time. Notably, without consideration of the first minute, the rest of the LFX degradation in the S2O82−/Fe2+ system also followed the pseudo-first-order kinetic model. The application of combined Fenton/persulfate oxidation was promising, and after careful adjustment of oxidants and activator doses, it demonstrated a considerable improvement in LFX degradation compared with the Fe2+-activated persulfate system and a somewhat similar efficacy to the Fenton process. Among the studied processes, the H2O2/Fe2+ system showed the highest performance both in LFX degradation and mineralization, followed by the combined H2O2/S2O82−/Fe2+ process. Six LFX transformation products were identified by LC–MS analysis in all studied systems, indicating that hydroxyl radicals are the predominant oxidative species in H2O2/Fe2+, S2O82−/Fe2+, and H2O2/S2O82−/Fe2+ processes. In summary, all studied radical-based advanced oxidation technologies proved to be promising techniques for the treatment of wastewater and in situ groundwater containing LFX, with a particularly high potential for the combined Fenton/persulfate system.