Impact of roxithromycin on waste activated sludge anaerobic digestion: Methane production, carbon transformation and antibiotic resistance genes.

The macrolide antibiotic roxithromycin is widely detected in varying aquatic environments, especially in the wastewater systems, as an emerging contaminant and leads to significant impacts on the microorganisms involved. In this study, the impact of a shock load of roxithromycin on waste activated sludge (WAS) anaerobic digestion was comprehensively investigated. The biochemical methane potential tests showed that the methane production from WAS anaerobic digestion was significantly inhibited by roxithromycin. With the dosage of roxithromycin increasing from 0 to 1000 μg/L, the maximum cumulative methane production decreased from 163.5 ± 2.6 mL/g VS to 150.9 ± 4.5 mL/g VS. In particular, roxithromycin inhibited the acidogenesis and methanogenesis in WAS anaerobic digestion, leading to the decreased methane production. The methanogenic archaea in the studied system mainly belonged to the genera of Methanoseata, Candidatus Methanofastidiosum and Methanolinea and their relative abundances also decreased with roxithromycin addition. The analysis of antibiotic resistance genes (ARGs) in the digested sludge indicated that the abundances of most ARGs detected in this study were increased with roxithromycin exposure, suggesting the potential of growing antibiotic resistance, which was probably caused by enhancing the effect of esterases, methylases and phosphorylases. This work reveals how roxithromycin affects the WAS anaerobic digestion and the change of ARGs in the anaerobic digestion with roxithromycin exposure, and provides useful information for practical operation.