Distribution and co-occurrence of antibiotic resistance genes and bacterial pathogens in the effluent of decentralized sewage treatment systems in China

Antibiotic resistance genes (ARGs) and bacterial pathogens (BPs) in wastewater have potential risks to human health, especially for decentralized wastewater treatment facilities (DWTFs) in rural areas where the effluent may directly expose to residents. In this study, ARGs and BPs were investigated in the effluent from five DWTFs having the Anaerobic-Oxic (AO) and AO-Membrane Bio-Reactor (AO-MBR) processes in rural areas of southeastern China. Totally 842 kinds of ARGs and 937 kinds of virulence factors (VFs) were identified. Most of the dominant ARG species (e.g., evgS, macB, and sav1866) were found to be multi-drug ARGs with antibiotic efflux pumping pathways. Most ARGs have higher relative abundances in the effluent of the AO process than the MBRs. Co-occurrence network analysis that explains the dominant pathogens (Pseudomonas, Neisseria, and Streptococcus) were supposed to carry multiple ARGs. Furthermore, typical ARGs and int1 in different ranges of particles were quantified and 51.54%–98.59% ARGs were identified in the samples filtrated in the 0.22–23 μm range, which were hard to be removed. Though AO-MBR processes were more efficient than standalone AO process, the maximum log removal value for the ARGs was only 1.9. Therefore, the results of this study might be referential for evaluating and controlling the risks of co-existed ARGs and pathogens in DWTFs.