The fate of intracellular and extracellular antibiotic resistance genes during ultrafiltration-ultraviolet-chlorination in a full-scale wastewater treatment plant

Abstract

Effluent from wastewater treatment plants (WWTPs) is recognized as a significant source of antibiotic resistance genes (ARGs) in the environment. Advanced treatment processes such as ultrafiltration (UF), ultraviolet (UV) light disinfection, and chlorination have emerged as promising approaches for ARG removal. However, the efficacy of sequential disinfection processes, such as UF-UV-chlorination on intracellular (iARGs) and extracellular ARGs (eARGs), remains largely unknown. This study investigates the impact of this sequential disinfection process on the fate of iARGs, eARGs, and a crucial mobile genetic element ( intI1 ) within a full-scale WWTP. Our findings revealed that the UF-UV-chlorination process effectively reduced the overall absolute abundance of detected ARGs in the effluent by 1.93 log, and intI1 by 0.86 log, compared to secondary effluent. The majority of these removals was achieved due to the UF and UV disinfection, while chlorination showed negligible impact on the absolute abundance of ARGs in the final effluent. Notably, five genera were identified as potential hosts for intI1 and eight iARGs, including aac(6')-Ib-cr , drfA1 , sul1 , sul2 , ermB , mefA , tetA , and tetX , suggesting a high potential for horizontal gene transfer involving these ARGs. Overall, this study demonstrated that UF-UV-chlorination is a highly effective method for reducing ARGs in effluent from WWTPs. Wastewater treatment plants (WWTPs) are major sources of antibiotic-resistant genes (ARGs) in ecosystems. This study demonstrates that UF-UV-chlorination process effectively removes ARGs in full-scale WWTPs, with ultrafiltration and UV disinfection primarily reducing intracellular and extracellular ARGs, respectively. However, chlorination inadvertently increases eARGs, potentially sustaining ARG levels in the environment. Additionally, some iARGs eliminated by UV reappeared after chlorination, suggesting eARGs were taken up and transformed into iARGs due to chlorination. These findings highlight the importance of advanced treatment techniques for reducing ARGs in WWTP effluent. Implementing appropriate treatment techniques could help mitigate antibiotic resistance, ultimately protecting ecosystems and public health. • Comprehensive evaluation of iARG and eARG fate during advanced treatment in a full-scale plant • Sequential UF-UV-chlorination effectively reduces ARGs in WWTPs • UF plays a major role in reducing intracellular ARGs, achieving a 1.94 log reduction • UV plays a major role in removing extracellular ARGs, achieving a 0.94 log reduction • Chlorination may increase eARGs, potentially sustaining ARG levels

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