Combined ozonation-biological activated carbon process for antibiotic resistance control in treated effluent from...

Biological activated carbon (BAC) treatment plays a crucial role in wastewater treatment plants due to its economic and effective promotion of organic matter degradation or mineralization. However, whether the changes in antibiotic resistance (AR) resulting from BAC or O₃-BAC treatment are related to environmental factors remains unclear, as previous studies have primarily focused on isolated aspects, or have combined these aspects without systematically comparing the BAC and O₃-BAC treatment processes or analyzing their interrelationships. In this study, to gain a clearer understanding of the factors related to AR during the BAC treatment, the treatment process of BAC and O₃-BAC were comprehensively compared, including antibiotics removal, wastewater matrix changes, antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and bacterial community characteristics. The roles of O₃ pretreatment and the bed depth of BAC were also clarified. ARGs were found to be not as sensitive to ozone as ARB. In addition, further strengthening of control measures should be needed for trimethoprim and tetracycline, due to their low removal efficiencies by ozone pretreatment, and their close relationship with the increased AR. Besides, 2 mg/L ozonation pretreatment could significantly influence the microbial community composition of wastewater and biofilm samples, while 1 mg/L ozonation could not. Finally, the correlation of environmental factors, bacterial communities, and ARGs revealed that to reduce the AR risks of O₃-BAC treatment, antibiotics in wastewater should be strictly controlled, since they were positively correlated with the accumulation of ARGs and Pseudomonadota, Actinomycetota, and Bacteroidota, which were responsible for carrying and disseminating ARGs. The results showed that higher dose ozonation pre-treatment and longer bed depth of BAC process could help control the AR of BAC.