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Waste-to-energy technologies employ a variety of approaches to the goal of developing clean, sustainable energy from biomass (carbonaceous plant material or animal material). One well-known example is the use of municipal landfill gas (methane) as a source of energy for generating electricity. The Environmental Protection Agency's (EPA) Environmental Technology Verification (ETV) program is providing performance information for a number of commercial-ready technologies that produce or use fuels generated from biomass.

Background

Fuels from waste, called "opportunity fuels," are usually byproducts or waste streams from other processes such as wastewater treatment, animal feeding operations, wood waste, and municipal solid waste. Although these fuels do not have the same heating value characteristics as conventional fossil fuels, they are still beneficial as a potential source of alternative energy, especially when used with distributed (existing, onsite) generation systems. For example, the EPA estimates that thousands of U.S. dairy and swine operations are potential candidates for anaerobic digestion and manure biogas production. Similarly, while approximately 410 U.S. landfills already collect landfill gas for energy recovery, another 500-plus are good candidates for further gas energy recovery. Lastly, the more than 500 municipal wastewater treatment facilities in the U.S. with influent flow rates greater than 5 million gallons per day are also potential sites for anaerobic/combined heat and power systems for generating electricity.

The ETV program recently reported on a series of technologies that use or clean up raw biofuel generated from biomass wastes. Two of these are biogas processing systems that remove hydrogen sulfide and other sulfur species from biogas so it is amenable for distributed generation (DG) use. During verification testing, one of these systems increased the low heating value of the gas by 8.5 percent. There are four other verified DG systems: one fuel cell, two internal combustion engines, and one micro-turbine in a heat and power application. All four DG systems were operated onsite, using either landfill gas or anaerobic digester gas generated from animal waste or municipal sludge.

Two additional systems were tested under ETV's Environmental Sustainability Technology Evaluation (ESTE) project and involved biomass co-fired boilers using wood waste. This verification, completed in 2008, was a collaborative project between the EPA Office of Air and Radiation's Office of Air Quality Planning and Standards and the Office of Resource Conservation and Recovery. The results could be used to support the development of a new area source control technology standard.

Selected Outcomes

A total capacity of 28 megawatts (MW) of program-verified fuel cells and micro-turbines has been installed in the United States. Based on ETV case studies, it is estimated that these new systems:

• Reduce carbon dioxide (CO₂) emissions by 53,000 tons per year and nitrogen oxides (NO_x) by 240 tons per year, with associated climate change, environment, and health benefits.
• Increase the use of renewable fuels, resulting in the reduction of natural resource consumption. Fuel cells that use anaerobic digester gas are responsible for two megawatts of the capacity of the four ETV-verified DG systems and 14,000 tons per year of the CO₂ reductions.

Assuming that annual sales continue at the same rate as in 2005, ETV estimates that total installed capacity of verified fuel cells should reach 89 MW by 2010, reducing CO₂ by 191,000 tons per year and NO_x by 600 tons per year.

Complete verification reports for the technologies discussed in this story can be accessed at the ETV program's Greenhouse Gas Technology Center Verified Technologies. The ETV program operates largely as a public-private partnership through competitive cooperative agreements with nonprofit research institutes. ETV does not endorse the purchase or sale of any products or services mentioned in its documents.