Influence of four antimicrobials on methane-producing archaea and sulfate-reducing bacteria in anaerobic granular sludge

• Four antimicrobials were found to have no obvious effect on methanogenesis.
• Distinct sensitivity of microbes to different antimicrobials was discovered.
• The tolerance of granular sludge to antimicrobials was higher than disrupted sludge.
• Cephalexin can be drastically degraded during the anaerobic process.
• Inhibition kinetics parameters of four antimicrobials were calculated.

The influence of Cephalexin (CLX), Tetracycline (TC), Erythromycin (ERY) and Sulfathiazole (ST) on methane-producing archaea (MPA) and sulfate-reducing bacteria (SRB) in anaerobic sludge was investigated using acetate or ethanol as substrate. With antimicrobial concentrations below 400 mg L−1, the relative specific methanogenic activity (SMA) was above 50%, so that the antimicrobials exerted slight effects on archaea. However ERY and ST at 400 mg L−1 caused a 74.5% and 57.6% inhibition to specific sulfidogenic activity (SSA) when the sludge granules were disrupted and ethanol used as substrate. After disruption, microbial tolerance to antimicrobials decreased, but the rate at which MPA utilized acetate and ethanol increased from 0.95 gCOD·(gVSS⋅d)−1 to 1.45 gCOD·(gVSS⋅d)−1 and 0.90 gCOD·(gVSS⋅d)−1 to 1.15 gCOD·(gVSS⋅d)−1 respectively. The ethanol utilization rate for SRB also increased after disruption from 0.35 gCOD·(gVSS⋅d)−1 to 0.46 gCOD·(gVSS⋅d)−1. Removal rates for CLX approaching 20.0% and 25.0% were obtained used acetate and ethanol respectively. The disintegration of granules improved the CLX removal rate to 65% and 78%, but ST was not removed during this process.