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

Jingru Du, Yong Hu, Weikang Qi, Yanlong Zhang, Zhaoqian Jing, Michael Norton, Yu-You Li

Tohoku University, Graduate School of Environmental Studies, Aoba 6-6-06, Aramaki, Aoba-ku, Sendai, Miyagi, Japan.

Abstract

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·(gVSSd)^-1 to 1.45 gCOD·(gVSSd)^-1 and 0.90 gCOD·(gVSSd)^-1 to 1.15 gCOD·(gVSSd)^-1 respectively. The ethanol utilization rate for SRB also increased after disruption from 0.35 gCOD·(gVSSd)^-1 to 0.46 gCOD·(gVSSd)^-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.

Keywords: Anaerobic granular sludge; Antimicrobial; Methane-producing archaea; Sulfate-reducing bacteria.