The efficacy of anaerobic digestion in inactivating pathogen indicator Escherichia coli levels in flushed dairy manure

Abstract. In the U.S., more than 210¹² kg of dairy waste is generated annually, which can be a potential feedstock for producing renewable energy source such as biogas. The use of granules as an inoculum is reported to accelerate these processes, and biogas production. The goal of this study is to understand the impact of anaerobic digestion process on flushed dairy manure-borne Escherichia coli reductions and biogas production. A series of anaerobic experiments were performed using the flushed manure inoculated with granule inoculum. The anaerobic digestion batch experiments were performed at multiple temperatures including room temperature (~ 22 °C), 37 °C, and 55 °C. Results showed that under room temperature, no significant reduction of E.coli concentration was found at the end of 33 days compared with the initial condition. In 37 °C, E.coli concentration was reduced substantially on day 7 and subsequently low levels of E. coli was observed. At 55 °C, E. coli reduction was considerable higher than that of at room temperature and 37 °C within 24 hours of digestion. In addition to E. coli levels, biogas composition was measured using a gas chromatography (GC) with Flame Ionization Detector (FID) and Electron Capture Detector (ECD). CO₂ concentration was relatively consistent over the time of digestion. Granule inoculum significantly enhanced methane concentration. Methane concentration was higher when the temperature is increased. We anticipate that this preliminary study provides information with regards to pathogen indicator survival during anaerobic digestion of flushed manure, and changes in biogas content.