Submitted to: International Conference on Greenhouse Gasses and Animal Agriculture
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2010
Publication Date: October 3, 2010
Citation: Rotz, C.A., Hafner, S.D. 2010. Whole farm impact of biogas generation and use on a New York dairy farm. Proc. of the 4th Greenhouse Gasses and Animal Agriculture. p. 69-70. Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Abstract: The USDA and the dairy industry have set a goal for reducing greenhouse gas emissions by 25% by 2020. Many mitigation strategies are required to meet this goal, but the use of anaerobic digesters for biogas production is considered to be an important component. Anaerobic digestion removes a major portion of the volatile solids from manure, which reduces the potential for methane and carbon dioxide production during manure storage and following land application. The biogas produced can be used to generate electricity and heat water, both of which reduce secondary emission sources that contribute to the carbon footprint of the farm. As manure moves through a digester, nitrogen and phosphorus availability can change, potentially affecting ammonia emissions, nitrate leaching losses, and phosphorus runoff. An anaerobic digester component was added to the Integrated Farm System Model to obtain a comprehensive evaluation of these various effects on dairy farms. An 1100-cow dairy farm in New York was simulated for 25 years of weather with and without the use of a digester. Farm records were used to verify simulated feed production and use, milk production, biogas production, and electric generation and use. Use of the digester had relatively small effects on feed production and use. Ammonia emission from stored manure increased 5%, which caused a small reduction in the yield and protein content of corn silage produced on the farm. The solubility of phosphorous in the manure was increased, but because manure was incorporated immediately after application, this had little effect on phosphorous runoff. Methane emission from the manure storage was reduced 60%, which reduced the whole farm emission by 15%. Energy saved in water heating and purchased electricity reduced combustion and secondary carbon dioxide emissions by 10% and 50%, respectively. Over all farm sources and sinks, the digester reduced the net greenhouse gas emission and carbon footprint by 22%. If the producer bore the full cost of the $1,300,000 investment in the digester and associated equipment, annual farm profit would be reduced by $50/cow or $0.001/kg of milk produced. The anaerobic digester system could be owned and operated with no reduction in farm profit on this farm if biogas production and use were increased 20%. Data reported for other digesters indicate that greater improvements in efficiency may be obtained. This type of whole-farm evaluation provides a useful tool for evaluating and comparing mitigation options to reduce the carbon footprint of dairy production systems.