Effects of solids retention time on the fate of tetracycline resistance in SBRs for the treatment of carcass leachate

Abstract

In the event of a foot and mouth disease outbreak, further spread of the virus is generally prevented by culling of infected animals in burial pits. This practice may eventually lead to groundwater contamination through leaching of wastewater from the animal carcasses. Wastewater from carcass leachate often contains antibiotic resistant bacteria and genes as well as traces of pharmaceuticals, and a high nutrient content. The role of operational parameters used in activated sludge treatment of this wastewater in the spread of antibiotic resistance has not been fully understood. This study investigated the fate of tetracycline-resistant bacteria and genes in sequencing batch reactors with synthetic carcass leachate at different solid retention times. Escherichia coli DH5α was used as the representative tetracycline-resistant bacteria with multiple antibiotic-resistant genes encoded in plasmid pB10. Solids retention time contributed to an increase in antibiotic resistance in SBRC (SRT = 25 days) with TRB values up to 1.25 × 107 CFU/mL which is one log higher than the influent. Microbial community analysis of the DNA samples from effluent of SBRC showed four major phyla: Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria under which are ecologically-important microbial species. It was shown that antibiotic resistance genes cannot be eliminated during treatment of synthetic carcass leachate in a lab-scale sequencing batch reactor.