Elimination of sulfonamides and tetracyclines during anaerobic fermentation - A “Cheshire Cat” phenomenon

Abstract

Tetracyclines and sulfonamides are among the most commonly applied antibiotics in veterinary medicine and can be frequently detected in manure samples worldwide. The treatment of contaminated manure within the anaerobic digestion process of biogas plants is often discussed as possible route for the degradation of antibiotics. To test this assumption, various parameters of the anaerobic fermentation process (temperature, addition of cellulolytic enzymes, separate hydrolysis unit) were investigated concerning their impact on the elimination of four commonly used veterinary antibiotics (sulfadiazine, sulfamethazine, tetracycline and chlortetracycline). Elimination rates of the antibiotics varied between 17% and 88% with chlortetracycline showing the highest rates due to the pH-mediated formation of iso-chlortetracycline. Based on the various experimental approaches, abiotic processes such as sorption rather than biotic transformation were considered as relevant elimination pathways. Therefore, sorption studies were carried out in liquid digestate matrix with varying amounts of solid matter. A (significantly) increased compound elimination with increasing solid matter amount was found. Furthermore, it was proven that the antibiotics can desorb again from the solids. Consequently, anaerobic fermentation should not generally be regarded as effective tool of reducing the release of antibiotics into the environment.