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

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.