Anaerobic digestion of livestock and poultry manures spiked with tetracycline antibiotics

Authors: KASUMBA, JOHN - Western Kentucky University; APPALA, KEERTHI - Western Kentucky University; Agga, Getahun; Loughrin, John; CONTE, ERIC - Western Kentucky University

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2019
Publication Date: 9/25/2019
Citation: Kasumba, J., Appala, K., Agga, G.E., Loughrin, J.H., Conte, E.D. 2019. Anaerobic digestion of livestock and poultry manures spiked with tetracycline antibiotics. Journal of Environmental Science and Health. 55(2):135-147. https://doi.org/10.1080/03601234.2019.1667190.
DOI: https://doi.org/10.1080/03601234.2019.1667190

Interpretive Summary: Tetracycline antibiotics are the most widely used antibiotics to prevent, control or treat diseases in animals. However, most of the administered antibiotics are excreted through feces and urine with potential environmental contamination and public health impact by selecting for resistant bacteria. Anaerobic digestion of animal waste produces useable energy while reducing the amount of waste. The impact of anaerobic digestion of animal waste on the persistence of tetracycline antibiotics is not well understood. Three tetracycline antibiotics (tetracycline, oxytetracycline and chlortetracycline) were added to swine, cattle, and poultry manure diluted in distilled water. The diluted manure was anaerobically digested inside air-tight laboratory-made batch reactors for 64 days at room temperature. Samples were taken every 8 days and analyzed for the tetracyclines and their main transformation products. The concentrations of the tetracyclines reduced in the ranges of 4 - 73%, 26 - 72%, and 69 - 88% for tetracycline, oxytetracycline and chlortetracycline in the three manure types. The highest degradation rate of chlortetracycline was observed in swine manure while its lowest degradation rate was observed in poultry litter. It takes 43 to 161 days for chlortetracycline, 89 to 141 days for oxytetracycline, and 93 to 340 days for tetracycline to reduce by half from their initial concentrations. In general, tetracyclines degrade faster in cattle manure compared to swine and poultry manure. This study demonstrates that tetracycline antibiotics, although significantly reduced in concentration, are persistent in the animal manure after anaerobic digestion, which can potentially lead to development and persistence of antibiotic resistant bacteria in the environment.

Technical Abstract: We investigated the anaerobic degradation of tetracycline antibiotics (tetracycline [TC], oxytetracycline [OTC] and chlortetracycline [CTC]) in swine, cattle, and poultry manures. The manures were anaerobically digested inside polyvinyl chloride batch reactors for 64 days at room temperature. The degradation rate constants and half-lives of the parent tetracyclines were determined following first-order kinetics. For CTC the fastest degradation rate was observed in swine manure (k = 0.016 ± 0.001 d-1; half-life = 42.8 days), while the slowest degradation rate was observed in poultry litter (k = 0.0043 ± 0.001 d-1; half-life = 161 days). The half-lives of OTC ranged between 88.9 (cattle manure) and 99.0 days (poultry litter), while TC persisted the longest of the tetracycline antibiotics studied with half-lives ranging from 92.4 days (cattle manure) to 330 days (swine manure). In general, the tetracyclines were found to degrade faster in cattle manure, which had the lowest concentrations of organic matter and metals as compared to swine and poultry manures. Our results demonstrate that tetracycline antibiotics are persistent in the animal manure after anaerobic digestion, which can potentially lead to emergence and persistence of antibiotic resistant bacteria in the environment when anaerobic digestion byproducts are land applied for crop production.