VAAFM - Renewable Energy on the Farm - Issues and Opportunities

Vermont Agency of Agriculture

Food and Markets

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Anaerobic Digestion Technology - Issues and Opportunities

Farmers thinking of installing a biodigester system should consider the following points as they go forward: Up front costs: Anaerobic digesters require a digester, piping and controls, a generator, electrical hookups, and, to get the most energy from the digester, heat recycling equipment. The price to get the digester up and running can exceed $1,000 per cow; more on smaller farms. Manure management: Different manure handling systems may need to be installed in dairy cow facilities to add a digester system. Time and know-how: Technical issues can make digesters fairly time consuming to operate. The Vermont Agency of Agriculture is researching ways to make the process as automated as possible, but at present farmers should carefully consider the labor and skill demands of a biodigester and think about who on the farm will be chiefly responsible for the system. Historically, successful digesters are on farms where someone on the farm has taken a keen interest in the system and does the necessary oversight to make the system work. Infrastructure: Large wholesale power systems often requires three-phase power lines to the power company grid, and currently many rural areas lack three-phase power. It is anticipated that the Clean Energy Fund will be a helpful instrument to help offset these costs. Maintenance: Plug flow digesters have a history of filling in with settled solids over time; new technology to prevent this is being tried, but systems should be installed with an easy way to drain the tank and clean it out if needed. Pumps, valves, controls and engines will all need attention and maintenance. Nutrient management: Nutrient management systems and environmental regulations are becoming more complex. Digesters can play a helpful role by reducing the need to spread whole manure and by creating liquid fertilizers that can replace purchased soil amendments, saving money and improving the bottom line. Synergistic opportunities: Since digester biogas burns to produce electricity, a significant amount of heat is created -- a valuable energy product. To get the best value from a biodigester, farmers should consider ways to make use of this valuable heat for dairy operations, greenhouses, farm product manufacture, etc.