Assessing the fate of antibiotics and agrochemicals during anaerobic digestion of animal manure

Antibiotics and pesticides are used extensively by the livestock industry. Agricultural chemicals can pose potential human and environmental health risks due to their toxicity and through their contributions to antimicrobial resistance, and strategies to reduce their emission into the environment are urgently needed. Anaerobic digestion (AD) is a sustainable technology for manure management that produces biogas while also providing an opportunity to degrade agricultural chemicals that are present in manure. While the effects of selected chemicals on biogas production have been investigated previously, little is known about chemical transformations during AD. Using lab-scale AD batch reactors containing dairy manure, degradation kinetics and transformation products (TPs) were investigated for twenty compounds that are likely to be present in manure management systems and that we hypothesized would transform during AD. Digestate samples were extracted using a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and analyzed using liquid chromatography – high-resolution mass spectrometry. Eleven of the tested chemicals degraded, leading to the formation of 47 TPs. Three compounds degraded abiotically only, two degraded biotically only, and six degraded both abiotically and biotically. These results suggest that in addition to renewable energy generation, AD contributes to the degradation of chemical contaminants present in agricultural waste streams. However, the potential toxic effects of TPs require further investigation.