Degradation of ciprofloxacin using UV-based advanced removal processes: Comparison of persulfate-based advanced oxidation and sulfite-based advanced reduction processes

Highlights: • Comparison of SR-AOPs and ARPs for the degradation of ciprofloxacin • In-depth assessment of influential parameters and produced reactive species • Insight in the reaction mechanisms by studying the ciprofloxacin defluorination In this study, the degradation of ciprofloxacin (CIP) in wastewater was investigated using UV-based sulfate radical advanced oxidation processes (SR-AOP) and UV-based advanced reduction processes (ARP). More specifically, a comparison of the UV-based persulfate advanced oxidation process (the UV/PS process) and the UV-based sulfite advanced reduction process (the UV/sulfite process) was made. Considering the UV-based SR-AOPs, the UV/PS process was much more efficient than the UV-based peroxymonosulfate advanced oxidation process (the UV/PMS process), with pseudo first order reaction rate constants (k_obs) of 0.752 and 0.145 min⁻¹, respectively. For the UV-based ARPs, the UV/sulfite process was the most efficient, compared to the UV/sulfide and the UV/dithionite process (k_obs of 0.269, 0.0157 and 0.0329 min⁻¹, respectively). The optimal process parameters for both the UV/PS and the UV/sulfite process were determined and the contribution of the produced reactive species were identified. For the UV/PS process, maximal CIP degradation was found at pH 8, and both OH and SO₄⁻ were responsible for CIP degradation. For the UV/sulfite process, H and e_aq⁻ were responsible for CIP degradation, with e_aq⁻ being the predominant radical at pH 8.5. Although CIP degradation was much faster for the UV/PS process, the UV/sulfite process was determined to be much more efficient in the defluorination of CIP.