UV disinfection and regrowth of antibiotic-resistant bacteria in wastewater: mechanistic insights and engineering implications

The widespread use of antibiotics in healthcare and agriculture has accelerated the emergence of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Municipal wastewater treatment plants (WWTPs) are now recognized reservoirs and conduits for environmental dissemination of resistance elements. Ultraviolet (UV) irradiation is widely used to disinfect wastewater because UV irradiation is chemical-free and highly effective at microbial inactivation; however, post-disinfection repair—via photoreactivation and dark repair—can lead to post-treatment regrowth of ARB. This review examines the molecular mechanisms of UV-induced DNA damage in bacteria (e.g., cyclobutane pyrimidine dimers, oxidative base lesions, single-strand breaks) and summarizes main recovery pathways that follow, including photolyase-mediated repair, base excision repair, and nucleotide excision repair. Omics studies indicate that clinically relevant ARB, such as Escherichia coli ST131, Pseudomonas aeruginosa, and Acinetobacter baumannii can upregulate repair pathways after UV exposure, though responses are strain- and matrix-dependent. We add to this mechanistic base, engineering strategies that suppress repair and regrowth: UV-advanced oxidation processes (e.g., UV/H 2 O 2 , UV/Cl 2 ), dual- or multi-wavelength LED designs, light-isolated post-UV handling, and emerging magnetic-assisted UV systems. These approaches layer orthogonal oxidative injury onto photolesions and can reduce ARG integrity and regrowth potential when appropriately validated. We also highlight monitoring and control frameworks—biosensor- and qPCR-guided surveillance coupled with AI-based predictive models and digital twins—that enable repair-aware, risk-based operation. By integrating molecular microbiology with process engineering and data-driven control, we identify actionable pathways for next-generation UV systems that ensure immediate inactivation and long-term suppression of ARB regrowth and ARG propagation in effluent discharge and reuse.