Transfer, Elimination and Accumulation of Antibiotic Resistance Genes in Decentralized Household Wastewater Treatment Facility Treating Total Wastewater from Residential Complex

Abstract

The excessive consumption of antibiotics has led to a global surge in antibiotic resistance genes (ARGs), threatening human and environmental well-being. Decentralized household wastewater treatment facilities (DHWWTFs) are hotspots for ARGs where the fate of ARGs remains unclear. In this study, targeting on a representative DHWWTF that receive all wastewater from 150 residential households, the transfer, elimination and accumulation of ARGs were quantitively investigated through real-time PCR-based quantification, mass balance evaluation and existing state analysis based on size fractionation. Significant abundance changes of ARGs were observed in the biological reaction and sedimentation processes due to microbial growth and ARG accumulation into sludge, and abundance increases in the process of post-aeration were also observed. tetG and sul1 revealed increases in their flux against respective input in the influent. Although substantial portions of the increased genes were found accumulated in excess sludge, ARGs remaining in the discharge were still high, with the average being about 3.4 × 1014 copies/d. The abundance of ARGs in wastewater and sludge showed a general trend of reduction as sludge accumulated gradually in its storage tank within two months after desludging. Classification of ARGs based on particle sizes indicated that while the major part of ARGs were distributed in particles with larger sizes, ARGs in smaller particles and free ARGs still existed, which may pose a greater threat to water environment due to their poor settleability. This study clarified the complex dynamics of ARGs in DHWWTF, emphasized the importance in enhancing the settleability of slow-settling and transferable small particles. The results achieved can be use as references for optimizing on-site maintenance and operation of the DHWWTF to eliminate the transfer of ARGs.

Keywords: Antibiotic resistance genes, Decentralized wastewater treatment, Biological treatment, activated sludge