Evaluation of a full-scale biogas plant utilizing cow and poultry manure in the presence of veterinary antibiotics

Antibiotics, used in food-producing animals, are excreted at high concentrations into the environment, either in their original or converted forms, via feces or urine. Hence, using animal manure as fertilizer can pose significant risks, including the accumulation of veterinary antibiotics in the environment and the development of antibiotic resistance, which can affect human health. In this regard, anaerobic digestion is a well-known biotechnology for removing antibiotics from animal manure. This study evaluated the performance of the full-scale mesophilic anaerobic digestion system utilizing poultry and cow manure, focusing on biogas yield, solid reduction, and the removal of antibiotics, specifically fluoroquinolones and tetracyclines. Through the anaerobic digestion process, a total solids reduction of 27% and a volatile solids reduction of 38% were achieved, resulting in a biogas yield of 0.94 L/gVS with methane content of 58% and electrical energy generation of 1500 kWh; the overall performance of the full-scale digestion system can be considered satisfactory. Additionally, the removal rates of selected antibiotics were found to be 32%, 38%, 37%, 38% and 67% for tetracycline, chlortetracycline, oxytetracycline, enrofloxacin and ciprofloxacin, respectively, by analyzing original forms without the effects of their conversion forms. Therefore, animal manure containing antibiotics can still pose environmental and public health risks, even after being treated by anaerobic digestion, due to the spreading of antibiotics and their residues into the environment, as well as the development of antibiotic resistance in humans. Considering these factors, digestate should not be used as fertilizer for agricultural purposes unless further treatment is applied.