Effects of the Antibiotics Chlortetracycline and Enrofloxacin on the Anaerobic Digestion in Continuous Experiments

Significant quantities of antibiotics are used in modern livestock husbandry and are found in livestock waste. Such waste has been reported to exert inhibitory effects if used as a substrate in biogas facilities. The goal of this study is to analyze the inhibitory effect of the antibiotics chlortetracycline (CTC) and enrofloxacin (EFX) on biogas production with pig slurry. Antibiotic concentrations up to 8,000 mg kg(-1) dry matter (DM) pig slurry were added in continuous fermentation tests. Impacts on methane production and on the microbial community structure were analyzed. The results clearly show that chlortetracycline and enrofloxacin negatively affect biogas production. Higher concentrations of antibiotics led to lower methane production. The addition of 200 mg kg(-1) DM of CTC or EFX reduced the specific methane yields up to 49 and 44 %, respectively. The microbial community did not show any changes at this concentration. When chlortetracycline was added at a concentration of 8,000 mg kg(-1) DM, the biodiversity changed slightly compared to the control without antibiotics.