Reduction of Pathogens in Bovine Manure in Three Full-scale Commercial Anaerobic Digesters

Abstract

Two field studies were conducted to determine the effect of anaerobic digestion (AD) on the presence and levels of pathogens in post-AD materials. In the first study, samples of pre-AD liquid, post-AD liquid, and post-AD solid were assayed bi-weekly, for six sampling events from a continuous mix and plug-flow AD. In the second study, samples were taken from multiple locations pre-AD and post-AD before and after liquid-solid separation. Samples were assayed for generic E. coli (GEC), Enterococci, Mycobacterium avium subsp. paratuberculosis (MAP), bovine Enterovirus, Campylobacter spp., and Salmonella spp., Escherichia coli O157:H7. Anaerobic digestion resulted in declines of 99% for GEC and 85 to 95% for Enterococci. Twenty-five samples of composted solid manure from the plug-flow digesters indicated a reduction of > 99% for GEC and > 99% for Enterococci. Bovine Enterovirus and MAP were isolated on numerous occasions from both pre- and post-digestion samples and composted material. Salmonella spp. and Campylobacter were found in 50 to 92% both post-digestion, and remained at a detection level of 21 to 96%, respectively, in liquid manure immediately post-AD. Composting of AD solids did reduce the detection of Salmonella to 10% and Campylobacter to 0%. While substantial quantitative reductions occurred for GEC and Enterococci, the minimal survival of these indicator organisms along with the frequent survival of Enterovirus and MAP indicates that AD, even followed by composting, would not remove all biosecurity hazards.