UV-254 transformation of antibiotics in water and wastewater treatment processes

Abstract Drinking water and wastewater treatment plants have adopted UV-based disinfection processes to replace traditional chlorine systems and eliminate production of toxic disinfection by-products. As with other disinfection systems, UV irradiation not only inactivates microorganisms but also partially transforms contaminants of emerging concern (CECs). Due to the human health implications associated with antimicrobial resistance, antibiotics are considered priority CECs. This chapter describes the efficacy of UV-based processes to transform fluoroquinolone, macrolide, sulfonamide, and tetracycline antibiotics. After a brief introduction of UV disinfection and general discussion of the antibiotics of concern, the light absorbance properties of antibiotics are discussed by class. The absorbance spectra are deconvoluted as a function of (1) particular moieties in the chemical structure and (2) protonation state. This discussion informs the characteristic absorbance patterns observed for specific classes of antibiotics and highlights the impacts of structural changes and solution pH on absorption of light at different wavelengths. Then, the phototransformation kinetics of representative antibiotics from the four classes of concern are described in terms of fluence-based, pseudo–first-order rate constants and quantum yields. This discussion builds on the description of light absorbance by chemical moieties present in the antibiotic chemical structure to identify transformation sites. The reactions are further contextualized in terms of the antibiotic mechanism of action to highlight whether UV-induced chemical changes result in loss of antimicrobial properties. Overall, this chapter highlights that low transformation efficiencies are expected for antibiotics in typical UV systems; furthermore, the primary transformation products are likely to retain antimicrobial properties, leaving concerns about antimicrobial resistance unresolved.