Annually, the dairy industry in the United States creates an estimated 249 billion tons of wet manure and 5.8 billion kg of carbon dioxide equivalents.1,2 Manure management accounts for nearly half of the greenhouse gas (GHG) emissions in the dairy industry and for about 6% of the total GHG emission from the agriculture sector in the United States.3 In 2009, the Innovation Center for U.S. Dairy announced a voluntary goal to reduce GHG emissions by 25 percent in 2020.
Manure management is also a major concern for individual dairies because the average lactating cow produces about 150 pounds of manure per day.4 In Idaho, for example, the average dairy has 660 cows, meaning it handles over 18,000 tons of manure annually.5 Manure is conventionally stored in lagoons or open ponds because of the ease of operation and low costs, but these raise concerns about odor control, water quality and GHG emissions.5
This new manure treatment system provides a way to improve the environmental sustainability of dairies and produce marketable by-products including:
In order to address these manure management issues at dairies, the EPA and the Innovation Center for U.S. Dairy are promoting installation of anaerobic digesters, which use bacteria to process manure and produce methane as a byproduct. Methane combustion for electricity provides a source of power and/or revenue to the dairy farm. Despite industry support for installing anaerobic digesters, however, voluntary implementation has been slow. Reasons include higher capital costs, additional operation and maintenance concerns compared to existing methods, and low electricity rates.5,6 In most cases, the sale of electricity alone is not enough to make digesters profitable. Additional sources of revenue are needed in order to make manure anaerobic digesters a financially attractive option for dairies.
Our research focuses on assessing the effectiveness of deploying a two-stage anaerobic digester system coupled to an algal cultivation pond to produce multiple valued-added commodities that enhance and stabilize overall economics while sequestering carbon and reducing nutrient emissions from dairy farms. DAIRIEES is an evaluation platform that facilitates more informed decisions concerning the environmental benefits and economic costs of the integrated manure-algae system. The DAIRIEES model allows the user to change parameters of the system based on the type of manure treatment (proposed or in use) and scales the results based on the size of the dairy herd. While this is just an estimate, the goal is for users to better understand benefits and costs related to implementing this type of manure treatment system. The model is populated with data from experiments at University of Idaho and Boise State University, as well as data from published literature.
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1 BSSC (2008). U.S. Dairy Sustainability Initiative: A roadmap to reduce greenhouse gas emissions and increase business value. Innovation Center for U.S. Dairy.
2 Liebrand C.B. and Ling K.C. (2009). Cooperative approaches for implementation of dairy manure digesters. In: (ed. USDA). USDA-Rural Development.
3 USEPA (2014). Emissions & Generation Resource Integrated Database (eGRID) 9th edition Version 1.0 Year 2010 Summary Tables, updated 02/24/2014, http://www.epa.gov/cleanenergy/energy-resources/egrid/
4 ASABE (2005). Manure Production and Characteristics. ASAE Standard D384.2. March 2005. American Society of Biological and Agricultural Engineers. St. Joseph, Michigan.
5 USEPA (2011). Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009.
6 Zaks, D.P.M., Winchester, N., Kucharik, C.J., Barford, C.C., Paltsev, S. and Reilly, J.M. (2011). Contribution of anaerobic digesters to emissions mitigation and electricity generation under U.S. climate policy.
Environ. Sci. Technol., 45, 6735-6742.
