Synergistic effects of temperature and oxytetracycline stress on continuous anaerobic digestion: Methane production, antibiotic resistance dynamics, and microbial adaptation

Temperature plays a critical role in the biodegradation of antibiotics and the dynamics of antibiotic resistance genes (ARGs) during anaerobic digestion (AD) of livestock manure. This study investigates the impact of temperature disturbance and oxytetracycline (OTC) stress on methanogenesis, ARGs distribution, and microbial responses in AD and proposes an optimal temperature strategy for enhancing methane production and ARGs removal. AD systems were operated at 35°C, 45°C, and 55°C, with OTC concentrations gradually increased (0, 10, 50, and 200 mg/L). In phases I and II, methane yields were highest at 45°C, with values of 204.47 and 188.18 mL/g VS, respectively, 23.67–25.19 % and 22.70–23.78 % higher than at 35°C and 55°C. These results suggest that digesters operating at 45°C produced the highest methane yield under equivalent OTC conditions, likely due to forming a balanced microbial consortium. Methane yield decreased with OTC stress, primarily due to the inhibition of dominant methanogen activity, particularly Methanosarcina. Elevated temperatures also promoted the removal of OTC and ARGs; however, OTC stress induced the proliferation of ARGs by increasing the abundance of potential host organisms. While temperature significantly shapes bacterial and methanogenic communities, OTC stress primarily impacts methanogens.