Factors influencing the removal of extracellular resistance genes in activated sludge process

Abstract

Extracellular antibiotic resistance genes (eARGs) contribute to antimicrobial resistance spread in the environment, yet their removal mechanisms in activated sludge remain poorly understood. Here, an artificial resistant plasmid (PUC57-sul1) and its corresponding sul1 amplicon were treated in aerobic reactors under varying conditions. The removal of eARGs was significantly affected by sludge disinfection, biomass concentrations, aeration rate, and temperature. The results indicated that the influencing factors for eARGs are similar to those for small-molecular-organic compounds. At optimal conditions (5 g/L biomass concentration, 400 mL/min aeration rate, and 30°C), the removal efficiency at 12-h was 88.7 % for the amplicon and 67.4 % for the plasmid, respectively, indicating that eARG removal was largely affected by size and conformation. A transient increase of eARGs was observed when actual hospital wastewater was treated, likely due to the lysis of ARG-carrying bacteria. In undiluted hospital wastewater, the concentration of sul1 was reduced by 15.3 % relative to its peak concentration, even under the optimized conditions. In contrast, when the wastewater was 10-fold diluted, the concentration of sul1 was reduced by 81.3 %, confirming the effectiveness of the activated sludge process when toxicity was reduced. Microbial inhibition may be the key factor limiting eARG removal. These findings contribute to a better understanding of factors facilitating the degradation of eARGs, potentially guiding future strategies for improving wastewater treatment practices.