Novel oxidant-free VUV/Fe2+/oxalate process for high-efficiency removal of norfloxacin: Oxidation performance and synergistic mechanism

Abstract

Based on Vacuum UV (VUV) in situ cracking water to generate reactive oxygen species (ROS) and promote Fe²⁺/Fe³⁺ redox cycle, a novel oxidant-free VUV/Fe²⁺/oxalate (Ox) homogeneous oxidation process was built to efficiently degrade norfloxacin (NOR). The performance and synergistic mechanism of VUV/Fe²⁺/Ox for NOR degradation under near-neutral conditions were investigated. Compared with sub-processes, VUV/Fe²⁺/Ox obviously accelerated NOR oxidation and reduced energy consumption, and its synergistic factor of NOR removal was 2.32. Effects of operating parameters Fe²⁺, Ox dose and solution pH on VUV/Fe²⁺/Ox and their mechanisms were analyzed. Synergistic mechanisms of NOR degradation via VUV/Fe²⁺/Ox, such as in situ generation of H₂O₂, Fe²⁺/Fe³⁺ redox cycle, ROS characterization and contribution analysis, NOR degradation pathways and its toxicity changes were also investigated. Through the use of ROS fluorescence characterizations and quenching experiments, hydroxyl radical and superoxide radical were identified as primary ROS in VUV/Fe²⁺/Ox, and their contributions to NOR degradation were 73.17 % and 20.91 %, respectively. Besides, synergistic mechanisms of VUV/Fe²⁺/Ox process, which mainly included the respective roles of VUV irradiation, Fe²⁺ and Ox, were also recommended. Furthermore, effects of chelators and water matrices on NOR degradation via VUV/Fe²⁺/Ox were also researched. VUV/Fe²⁺/Ox process showed satisfactory NOR degradation effects in actual waters, indicating its practical application potential. The degradation of NOR by novel VUV/Fe²⁺/Ox process significantly reduced its environmental and health hazards.