Seasonal variation and removal efficiency of antibiotic resistance genes during wastewater treatment of swine farms

The seasonal variation and removal efficiency of antibiotic resistance genes (ARGs), including tetracycline resistance genes ( tet G, tet M, and tet X) and macrolide ( erm B, erm F, ere A, and mef A), were investigated in two typical swine wastewater treatment systems in both winter and summer. ARGs, class 1 integron gene, and 16S rRNA gene were quantified using real-time polymerase chain reaction assays. There was a 0.31–3.52 log variation in ARGs in raw swine wastewater, and the abundance of ARGs in winter was higher than in summer. tet M, tet X, erm B, erm F, and mef A were highly abundant. The abundance of ARGs was effectively reduced by most individual treatment process and the removal efficiencies of ARGs were higher in winter than in summer. However, when examining relative abundance, the fate of ARGs was quite variable. Anaerobic digestion reduced the relative abundance of tet X, erm B, erm F, and mef A, while lagoon treatment decreased tet M, erm B, erm F, and mef A. Sequencing batch reactor (SBR) decreased tet M, erm B, and erm F, but biofilters and wetlands did not display consistent removal efficiency on ARGs in two sampling seasons. As far as the entire treatment system is concerned, erm B and mef A were effectively reduced in both winter and summer in both total and relative abundance. The relative abundances of tet G and ere A were significantly correlated with int I1 ( p