Evaluating the Impact of Cl₂^•- Generation on Antibiotic-Resistance Contamination Removal via UV/Peroxydisulfate

The removal of antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) using sulfate anion radical (SO₄^•-)-based advanced oxidation processes has gained considerable attention recently. However, immense uncertainties persist in technology transfer. Particularly, the impact of dichlorine radical (Cl₂^•-) generation during SO₄^•--mediated disinfection on ARB/ARGs removal remains unclear, despite the Cl₂^•- concentration reaching levels notably higher than those of SO₄^•- in certain SO₄^•--based procedures applied to secondary effluents, hospital wastewaters, and marine waters. The experimental results of this study reveal a detrimental effect on the disinfection efficiency of tetracycline-resistant Escherichia coli (Tc-ARB) during SO₄^•--mediated treatment owing to Cl₂^•- generation. Through a comparative investigation of the distinct inactivation mechanisms of Tc-ARB in the Cl₂^•-- and SO₄^•--mediated disinfection processes, encompassing various perspectives, we confirm that Cl₂^•- is less effective in inducing cellular structural damage, perturbing cellular metabolic activity, disrupting antioxidant enzyme system, damaging genetic material, and inducing the viable but nonculturable state. Consequently, this diminishes the disinfection efficiency of SO₄^•--mediated treatment owing to Cl₂^•- generation. Importantly, the results indicate that Cl₂^•- generation increases the potential risk associated with the dark reactivation of Tc-ARB and the vertical gene transfer process of tetracycline-resistant genes following SO₄^•--mediated disinfection. This study underscores the undesired role of Cl₂^•- for ARB/ARGs removal during the SO₄^•--mediated disinfection process.