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Anaerobic digestion uses microorganisms to turn organic feedstock, like cow manure or food waste, into biogas, which can be purified into pipeline-grade natural gas. This process allows dairy farms, wastewater facilities, and food processors to turn their waste into energy and other byproducts while both reducing waste and capturing methane -- a powerful greenhouse gas that would otherwise be released into the atmosphere.
The Colorado Energy Office is promoting the development of anaerobic digestion through a number of efforts, including the development of a Market Assessment of Agricultural Anaerobic Digesters and the passage of HB14-1159, which provides a sales tax exemption for anaerobic digestion equipment. As part of these efforts, CEO has compiled the toolkit below to help identify opportunities for anaerobic digesters and guide interested parties through the process of developing a project.
● AgSTAR Checklist: The U.S. EPA has developed a number of useful resources through its AgSTAR program to identify potential digester sites. This checklist identifies some key requirements for initially screening a potential project.
● CSU Anaerobic Digestion Decision Tree: This Decision Tree is similar to the EPA AgSTAR checklist, but focuses on technical aspects of waste collection. The Decision Tree was developed by Jeff Lasker at the Colorado State University as part of his thesis.
● Anaerobic Digestion Feasibility Model with Manure Only / Anaerobic Digestion Feasibility Model with Food Waste Co-Digestion: These two feasibility models were developed by the authors of the Market Assessment. They allow users to manipulate inputs such as dairy cows and food substrate inputs for a given project. They provide a good first step toward identifying feasible anaerobic digestion projects.
● Anaerobic Digestion Contact List
● EPA: Recovering value from waste
● Colorado Market Assessment of Agricultural Anaerobic Digesters
Electricity generated from the combustion of woody biomass is defined as renewable under Colorado’s Renewable Energy Standard, allowing agricultural crops, wood waste, mill residue, and forest slash or brush to be used to generate renewable electricity. Using woody biomass to generate electricity achieves two environmental goals: generation of renewable energy and helping to maintain the health of Colorado’s forests.
Currently, Colorado has one generator using woody biomass exclusively -- Evergreen Clean Energy’s 11.5 MW project in Gypsum, Colorado, which generates electricity primarily using beetle kill trees. Given Colorado’s forest resources, there are other opportunities for electricity from woody biomass and for power plants to co-fire woody biomass with coal.
Pyrolysis of Municipal Solid Waste
Unlike combustion, which burns fuel in the presence of oxygen, pyrolysis is the process of heating material to extremely high temperatures in the absence of oxygen. Heating materials at high temperatures produces synthetic gas (“syngas") -- a combustible gas comprised of hydrogen, methane, carbon monoxide, and other hydrocarbons. Syngas can be combusted to generate electricity much like natural gas.
While not a renewable energy resource, pyrolysis of MSW provides environmental benefits by reducing the amount of waste that ends up in landfills. For this reason, the Colorado General Assembly classified electricity generated from “synthetic gas produced by pyrolysis of municipal solid waste” (MSW) as eligible for Colorado’s Renewable Energy Standard (RES) if the project is greenhouse gas neutral.