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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGICAL TREATMENT OF MANURE AND ORGANIC RESIDUALS TO CAPTURE NUTRIENTS AND TRANSFORM CONTAMINANTS

Location: Sustainable Agricultural Systems Laboratory

Title: Economic analysis of small-scale agricultural digesters in the United States

Authors
item Klavon, K -
item Lansing, S -
item Moss, A -
item Mulbry, Walter
item Felton, G -

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2013
Publication Date: April 18, 2013
Repository URL: http://handle.nal.usda.gov/10113/56587
Citation: Klavon, K., Lansing, S., Moss, A., Mulbry III, W.W., Felton, G. 2013. Economic analysis of small-scale agricultural digesters in the United States. Biomass and Bioenergy. 54:36-45.

Interpretive Summary: Anaerobic digestion is a microbial-mediated process in which methanogenic microorganisms utilize organic matter, carbon dioxide, and hydrogen to produce methane, resulting in the creation of renewable energy and decreases in greenhouse gas emissions, organic pollutants, pathogens, and odor. Although anaerobic digesters were widely constructed in the United States during the 1970’s, poor economic viability and technical flaws led to a 60% failure rate of these systems. Through improved designs, the world is currently seeing a revitalization of anaerobic digestion technology with over 30 million manure-based digesters operating globally. The majority of the digesters operating around the world are inexpensive, unmixed systems in the tropics where the ambient temperature is near the optimal digestion temperature of 35°C. As part of an effort to transfer low-cost digestion models from the developing world to medium scale U.S. dairy farmers operating in temperate climates, our research group modified an existing plug-flow design and constructed replicate pilot scale digesters on a USDA research farm in Maryland. The specific research objectives of this study were to: (1) perform an economic assessment of constructed pilot-scale digesters with a 100-cow scale-up of the design, (2) create a small-scale U.S. digester database and perform a cost analysis of these systems, and (3) re-evaluate the minimum size dairy farm needed for economically feasible anaerobic digestion in the U.S. Results showed that only two of the fourteen small-scale anaerobic digesters had a positive cash-flow. Four revenue sources from the digesters were identified. Bedding reuse was the greatest contributor to a positive cash-flow, followed by biogas use, electrical generation and carbon credits. Smaller-scale anaerobic digesters in the U.S. were found to be economically viable for only two of fourteen digesters evaluated when constructed without income from grants or tax credits. Without this additional support, the economic success of small-scale anaerobic digesters in the U.S. is dependent not only on the initial capital investment of the digestion systems but also the willingness of the farmer to invest time and personal energy into the digester operation.

Technical Abstract: Anaerobic digestion is a manure treatment option that is gaining popularity throughout the world due to its multiple environmental and economic benefits. However, further research is needed for anaerobic technology to become more readily available, cost effective and manageable for small-scale to medium-scale dairy facilities in the United States. The objectives of this study were to evaluate eight existing and six theoretical small scale (< 250 cow) dairy manure digester systems with respect to their capital and operational costs and sources of revenue. Costs and revenue sources were also estimated for 100-cow scale versions of pilot-scale digesters that were constructed at a USDA research farm in Maryland. Results showed that only two of the fourteen small-scale anaerobic digesters had a positive cash-flow. Four revenue sources from the digesters were identified. Bedding reuse was the greatest contributor to a positive cash-flow, followed by biogas use, electrical generation and carbon credits. Smaller-scale anaerobic digesters in the U.S. were found to be economically viable for only two of fourteen digesters evaluated when constructed without income from grants or tax credits. Without this additional support, the economic success of small-scale anaerobic digesters in the U.S. is dependent not only on the initial capital investment of the digestion systems but also the willingness of the farmer to invest time and personal energy into the digester operation.

Last Modified: 8/22/2014
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