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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Environmentally Integrated Dairy Management Research » Research » Publications at this Location » Publication #290871

Title: Inactivation of dairy manure-borne pathogens by anaerobic digestion

item Borchardt, Mark
item Spencer, Susan
item LARSON, REBECCA - University Of Wisconsin
item ALKAN-OZKAYNAK, ASLI - University Of Wisconsin

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2013
Publication Date: 5/17/2013
Citation: Borchardt, M.A., Spencer, S.K., Larson, R.A., Alkan-Ozkaynak, A. 2013. Inactivation of dairy manure-borne pathogens by anaerobic digestion. Meeting Abstract. May 18-21, 2013.

Interpretive Summary:

Technical Abstract: Background: Anaerobic digestion of animal manure has the potential to inactivate enteric pathogens, thereby reducing exposures to livestock and humans when the products of digestion are disposed by land-spreading or irrigation or returned to livestock uses such as bedding. Data on digester effectiveness in inactivating pathogens are limited, particularly for farm-scale anaerobic digesters. Methods: We studied seven privately-operated anaerobic digesters located on dairy farms in Wisconsin, USA, where the primary feedstock was dairy manure. All digesters were mesophilic; five had plug-flow and two were continuously mixed. Samples were collected biweekly, December 2011 to August 2012, from four points along the digestion process: feedstock input, digestate output, and solid and liquid fractions of the digestate following screw-press separation. qPCR was used to measure genomic copy concentrations of two protozoan, seven bacterial, and eight viral pathogens found in dairy manure. Bovine bacteroides concentrations were also measured. Log removal was calculated for each sample date, accounting for retention time. Results: Anaerobic digestion typically reduced pathogen genomic copy concentrations by two logs, although removal was highly variable by date. All digesters experienced periods when removal was only 0.5 log and some digesters reached three-log removal. Removal efficiency did not differ by plug-flow or continuously-mixed digester type. Removal efficiency decreased for all digesters during the summer period. For all farms, screw press separation of the digestate resulted in approximately 99% of the pathogens partitioning to the liquid fraction, with few pathogens remaining in the solids. Conclusion: The anaerobic digesters in this study are operated for maximum methane production. Unlike a process dedicated and controlled for pathogen removal, like drinking water disinfection, pathogen removal by digestion is a side benefit. Removal in this study was too variable to assume mesophilic digestion always results in products with significantly reduced infection risks.