The feasibility of thermophilic anaerobic digestion (AD) for the attenuation of antibiotic resistance genes (ARGs) in biomass wastes under high antibiotic concentrations remains unclear. In this study, a thermophilic completely stirred digester (55 °C) was fed with municipal excess sludge spiked with increasing concentrations of oxytetracycline (OTC) (0-1000 mg/L) over a period of 280 days. Results showed that thermophilic AD could maintain stable methane production (338.40 ± 26.26 mL/d/gVS) even at an OTC dose of 1000 mg/L with the sludge phase OTC concentration reaching around 24,000 mg/kg. More important, the abundance of resistome detected by high-throughput quantitative PCR in the substrate was reduced (p < 0.01) by 55.54%-86.27% by thermophilic AD over the whole period. Partial canonical correspondence and network analyses showed that the reduction of ARGs was achieved mainly through two ways: eliminating the original hosts of ARGs in the substrate (from 41.74% ± 2.60% in the substrate to 12.08% ± 1.02% in digested sludge), and blocking the horizontal proliferation of ARGs in the digested sludge by reducing the abundance of mobile genetic elements and restricting their horizontal exchange within a small number of thermophilic genera. This study showed that thermophilic AD is feasible for the attenuation of ARGs in biomass even containing high level of OTC.
Keywords: Antibiotic resistance gene; Excess sludge; Metagenomics; Reduction; Thermophilic anaerobic digestion.
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