Combined effects of oxytetracycline concentration and organic loading rate on semi-continuous anaerobic digestion of swine wastewater

•The large fluctuation of OLR of swine wastewater was simulated.•0.3 mg/L OTC boosted the biodegradability of the substrate.•8.0 mg/L OTC stimulated four methanogenic pathways (especially CO2 => CH4).•8.0 mg/L OTC reduced the metabolic functions of material swap on the cell membrane.•8.0 mg/L OTC reduced the functions of information recognition on the cell membrane.