The fate of oxytetracycline in two‐phase and single‐phase anaerobic cattle manure digesters and its effects on microbial communities

BACKGROUND The fate of veterinary antibiotics in manure digesters is of great concern because of poor biomethane recovery and potential development of antibiotic resistant bacteria in the environment. RESULTS Manure samples collected from therapeutically treated cattle (a standard veterinary practice of 50 mL OTC solution as 20 mg kg−1 cattle weight) were used in digestion studies. The methane yields of OTC‐medicated two‐phase and single‐phase digesters were 99 ± 8 and 72 ± 9 mL CH4 g−1 VS in the presence of 3.11 ± 0.12 and 3.07 ± 0.14 mg OTC L−1, respectively; whereas, non‐medicated two‐phase and single‐phase digesters had 43% and 52% higher methane yields, respectively. Fluorescence in situ hybridization results indicated that the relative abundance of Firmicutes and Gammaproteobacteria was negatively correlated with the presence of OTC. Methanobacteriales seemed to be a resistant order of methanogenic Archaea to OTC and comparatively higher methane yield in two‐phase non‐medicated cattle manure digester might be the result of the poor cell activity of Methanosarcinales in two‐phase OTC‐medicated cattle manure digester. CONCLUSION Higher OTC removal and biomethane production were achieved by two‐phase configuration, thus, it can be an alternative to treat antibiotic‐medicated manures in full‐scale applications in order to reduce its adverse effects.