Effect of the ultraviolet/chlorine process on microbial community structure, typical pathogens, and antibiotic resistance genes in reclaimed water

Urban wastewater contains a wide range of pathogens and antibiotic resistance genes (ARGs), which are a serious concern if reusing treated wastewater. However, few studies have explored the microbial communities in reclaimed water using ultraviolet (UV)/chlorine treatment and assessed the changes of the resistome. This study investigated the occurrence of typical pathogens, ARGs, and bacterial communities in UV/chlorine-treated reclaimed water samples. The numbers of culturable and viable but non-culturable pathogens were effectively reduced to 0 CFU/mL within 1–10 and 10–30 min after UV/chlorine treatment, respectively. Meanwhile, the physicochemical indices of water quality were not affected. UV/chlorine treatment could significantly change the bacterial community structure of reclaimed water, showing a decrease in bacterial abundance and diversity. Chlorine-resistant Acinetobacter and Mycobacterium were the dominant bacterial genera (> 50%) after UV/chlorine treatment. Moreover, the number of ARGs and mobile genetic elements (MGEs) decreased with an increase in UV/chlorine exposure. However, eight ARGs and three MGEs were consistently detected in more than three seasons, making these major concerns because of their potential role in the persistence and dissemination of antibiotic resistance. Overall, the results of this study suggest that UV/chlorine treatment can potentially improve the microbiological safety of reclaimed water. And more attention should be paid to the pathogens that are both chlorine-resistant and carry MGEs because of their potential for resistance transmission.