| Biomass Energy and the Environment |
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Unlike any other energy resource, using biomass to produce energy is often a way to dispose of biomass waste materials that otherwise would create environmental risks. In the following ways, using biomass for energy can deliver unique environmental dividends as well as useful energy.
Reducing Greenhouse Gases: Carbon Dioxide
Carbon dioxide (CO2), methane, nitrous oxide and certain other gases are called greenhouse gases because they trap heat in the Earth´s atmosphere. The global concentration of CO2 and other greenhouse gases is increasing. A natural greenhouse effect of trace gases and water vapor warms the atmosphere and makes the Earth habitable. However, human-caused greenhouse gas emissions are having an effect on regional climate and weather patterns. The rate and magnitude of climate change effects are not yet clear.
Trees and plants remove carbon from the atmosphere through photosynthesis, forming new biomass as they grow. Carbon is stored in biomass. When biomass is burned, carbon returns to the atmosphere in the form of CO2. This cycle makes it possible for biomass energy to avoid increasing the net amount of CO2 in the atmosphere.
There is no net increase in atmospheric CO2 if the new growth of plants and trees fully replaces the supply of biomass consumed for energy. However, if the collection or processing of biomass consumes any fossil fuel, additional biomass would need to be grown to offset the carbon released from the fossil fuel.
In contrast, the combustion of natural gas, coal and petroleum fuels for energy adds CO2 to the atmosphere without a balancing cycle to remove it. Using biomass fuels instead of fossil fuels may reduce the risk of adverse climate change from greenhouse gas emissions.
Reducing Greenhouse Gases: Methane
Compared to CO2, methane has 21 times the global warming potential. Natural decomposition of organic material, especially in wetlands, releases methane. It has been estimated that 60 to 80 percent of methane emissions are the result of human activity. For example, solid waste landfills, cattle feedlots and dairies are sources of human-caused methane emissions. Because human-caused emissions, the global atmospheric concentration of methane increased 6 percent from 1984 to 1994.
Using biomass-derived methane to produce useful energy consumes methane and reduces the risk to the environment that would otherwise result from natural decomposition. In addition, generating electricity with biomass-derived methane fuel can offset power produced from fossil fuels and reduce the net CO2 emissions from electric power generation.
Federal Clean Air Act regulations require collection of methane produced in landfills. The regulations allow operators to use landfill methane for energy production or burn off the gas to avoid the release of methane into the atmosphere. Besides the potential effect of methane emissions on climate, uncontrolled landfill gas emissions cause odor problems and a risk of explosion and fire.
Methane released from decomposition of livestock and poultry manure generates about 9 percent of all human-caused methane emissions in the United States. Processing manure through anaerobic digesters can make the methane available for conversion to useful energy and avoid methane emissions to the atmosphere.
Protecting Clean Water
Livestock manure generated at feedlots and dairies poses a risk of surface and ground water contamination from runoff. Microorganisms such as salmonella, brucella and coliforms in manure can transmit disease to humans and animals. Anaerobic digestion of manure destroys most of these microorganisms. The process produces environmentally stable liquid and fiber residue.
The liquid portion of digester residue (called filtrate) contains approximately 75 percent of the nitrogen present in raw manure but in a more soluble form. In this form, the nitrogen is more available to plants. However, the filtrate should be applied as close to the ground as possible to avoid volatile ammonia emissions. Farmers must carefully manage land application of filtrate to avoid overloading the soil with more nutrients than the plants can use.
Keeping Waste Out of Landfills
Using urban wood waste for fuel reduces the volume of waste that otherwise would be buried in landfills. The ash residue that remains after combustion of waste wood is less than 1 percent of the volume of the wood waste consumed. Uncontaminated ash can be used as a soil amendment to add minerals and to adjust soil acidity.
Reducing Air Pollution
Field burning of agricultural residue emits particulate matter and other air pollutants. Because of air quality concerns, state regulations have reduced the amount of open field burning of grass seed straw in Oregon's Willamette Valley. Grass seed straw and other agricultural residues are potential biomass fuels. These materials are suitable as fuel for appropriately designed combustion boilers to produce heat, steam or electric power. They are also potential feedstock for conver-sion to ethanol.
Smoke emissions from forest fires and slash burning adversely affect air quality. Removing biomass from forested areas where an excess of dead wood has accumulated reduces forest fire risk. Compared to the smoke emitted from forest fires and slash burning, the emissions from using wood fuel for energy are far less harmful. Industrial combustion boilers with pollution control equipment in place burn more efficiently and cleanly than open fires.
Residential woodstoves can be a major source of particulate air pollution. Improvements in stove technology have made woodstoves more efficient and have reduced particulate matter emissions by as much as 90 percent over older woodstoves and fireplaces. In 1983, Oregon became the first state to enact regulations restricting woodstove emissions. New woodstoves currently must meet certification standards of the U.S. Environmental Protection Agency.
Reducing Acid Rain and Smog
Air pollution from burning fossil fuels is the major cause of acid rain. Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) react in the atmosphere with water, oxygen and oxidants to form acidic compounds (sulfuric acid and nitric acid). Some of these compounds fall to earth in the form of acid rain, snow or fog. Acid rain increases acidity of lakes and streams and damages trees at high elevations. Acid rain accelerates the decay of building materials and paints.
Aside from their contribution to acid rain, SO2 and NOx gases and their particulate matter derivatives (sulfates and nitrates) contribute to smog and endanger public health. Tighter control of these emissions is desirable in areas with frequent smog problems and in areas protected for their pristine qualities.
Efficient combustion of biomass results in low emissions of SO2 and production of fewer organic compounds that cause smog compared to emissions from facilities that burn coal or oil. Co-firing biomass with coal can reduce SO2 and NOx emissions at coal-fired power plants. The level of NOx emissions from biomass combustion facilities depends on the design of the facility and the nitrogen content of the feedstock. Pollution control equipment can further reduce NOx and particulate emissions.
Protecting Forests
Dense growth has limited the size and resiliency of trees in some forested areas of the state. In the Blue Mountains of eastern Oregon, for example, the health of large areas of forestland has deteriorated. Similar conditions exist in forests throughout the Western United States. In many areas the natural ecosystem has been significantly altered, creating a high risk of intense wildfire. According to Western Forest Health and Biomass Energy Potential, a study prepared for the Department of Energy, 39 million acres (about 30 percent) of National Forest land in the West is threatened by unnatural fuel accumulations.
The condition of the forest in these overgrown areas is not natural. It is largely the result of fire suppression and past logging practices. Selective thinning would improve the general health of the remaining trees and reduce the risk of fire. With less competition for nutrients and water, the remaining trees would have a better chance of maturing into old growth stands.
The surplus biomass that could be available from thinning unnaturally overgrown forest areas is a large renewable energy resource. Carefully planned forest thinning activities can preserve wildlife habitat and minimize soil erosion so that the use of forest biomass can be done in a sustainable manner.
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