Occurrence of Antibiotic Resistance Genes in a Small Township Wastewater Treatment Plant and the Receiving River

Abstract

Six ARGs (tetX, sul1, qnrS, blaTEM, ermB and intl1) were quantified by qPCR, along with concentrations of inorganic nitrogen (ammonia, nitrite, nitrate), total phosphorous (TP) and chemical oxygen demand (COD). The sewage treatment facilities had elimination effects on the six target genes; absolute abundance decreased from 104–107 copies/mL in the influent to 103–105 copies/mL in effluent, and the removal efficiencies were 74.27–96.51%; the highest removal performance was for tetX. The main treatment units for eliminating ARGs were the aeration tank and the secondary sedimentation tank. Absolute abundances of ARGs in the effluent and downstream water were 3.24–18.83 and 1.86–8.55 times higher than that in the upstream river, respectively. The absolute abundances of different target ARGs were positively correlated (R = 0.6762 ± 0.1777), indicating similar elimination mechanisms, and a positive correlation between ARGs and ammonia nitrogen (R = 0.5025 ± 0.2711). Raw wastewater contained numerous ARGs, which were partially removed by the WWTP. However, there remained a high absolute abundance of ARGs in effluent, causing an increase in water-phase ARGs in the receiving river. Hence, effluent was an important pollution point source for the receiving river.