Improving the Environmental and Economic Sustainability of Dairy Farming using Value-Added Products derived from the Anaerobic Digestion of Manure

The aim of this study was to examine how manure-derived value-added products via anaerobic digestion impact the environment and economics of dairy farming. An on-farm anaerobic digester (AD) at Virginia dairy was used in this study. The AD performance evaluated for: (i) biogas production (ii) waste stabilization; and (iii) production of organic fertilizer. Locally available organic waste streams were evaluated for co-digestion with dairy manure to increase biomethane production at the on-farm AD. The effective pasteurization temperature and duration to reduce fecal coliform, E. coli, and Salmonella concentrations in the AD effluent to acceptable levels for use as an organic fertilizer were determined. A partial environmental and economic analysis was conducted on the AD system to determine its effects on the environmental-economic sustainability of dairy farming. The results showed that the manure-derived value-added products from the AD improved environmental health and had the potential to improve the economic sustainability of the dairy farm. The AD stabilized the manure adequately and produced 400 KW of electricity, enough to power 230 US homes. Blending manure with locally available organic materials increased volatile fatty acid production, suggesting the potential to increase biomethane yields. Pasteurization at 70°C is sufficient to reduce pathogen indicating organisms to acceptable levels for the manure to be used as an organic fertilizer. The payback periods range from 4.6 to 11.8 years for the AD investment costs and reductions in direct manure methane emissions of 2,436 tonnes CO2e per year.