Antibiotic fate in the environment and during anaerobic digestion and composting

Human and veterinary antibiotics are contaminants of emerging concern due to the human and ecological health risks associated with the continued biologically activity of antibiotics present in waste streams. In this study, four common classes of antibiotics, beta-lactams, amphenicols, macrolides, and sulfonamides, were investigated for their degradation efficiency in water under different pH and temperature conditions, anaerobic digestion, and pilot-scale static pile composting.;Antibiotic hydrolysis rates were highest for the beta-lactam antibiotics. Half-lives ranged from 5.3 to 27 d in water at pH 7 and 25°C. The amphenicol and macrolide antibiotics only hydrolyzed at 50°C and 60°C. Degradation products were characterized, confirming that hydrolysis reactions occurred.;Antibiotics added to anaerobic digestion reactors inhibited biogas production at concentrations greater than 200 mg/L for a beta-lactam, macrolide, and sulfonamide antibiotic, but an amphenicol antibiotic was more toxic to the anaerobic digestion process where 13 mg/L caused 20% biogas inhibition. All the antibiotics degraded completely within 10 d of anaerobic digestion except for a sulfonamide antibiotic. The antibiotic degradation products found were relatively more persistent compared to the parent compounds, and many products were not completely removed after the 40 d anaerobic digestion process. The results suggest that biogas production may be un-affected with antibiotic-contaminated mixed feedlot manure; however, antibiotics and degradation products may be present in anaerobic digestion effluent, causing an environmental health concern when the effluent is land applied.;Greater than 90% of the antibiotic concentrations added to manure and biosolids compost bins were removed after 28 d. The temperatures in the compost bins reached >55°C for more than 3 d, which aided the rapid antibiotic removal. Another factor aiding in the rapid antibiotic removal was the presence of the compost particulate matter. The results showed that static pile composting manure and biosolids, operating under optimized temperature and moisture conditions, effectively removed antibiotics in the amphenicol, macrolide, and sulfonamide classes. The antibiotics were removed during composting as opposed to anaerobic digestion, so static pile composting manure can be used to degrade antibiotics prior to solids land application.