Methane (Encyclopedia of Environmental Issues, Revised Edition)
Methane is produced when bacteria digest organic matter under anaerobic (without air) conditions, creating natural gas. Natural gas contains 50-90 percent methane. Most natural gas is found with coal and petroleum deposits buried deep underground and is a product of the decomposition of ancient swamps and bogs.
The sources of methane emissions are both anthropogenic (human-influenced) and natural. Anthropogenic sources include fossil-fuel production, livestock raising (enteric fermentation in the stomachs of animals such as cattle and pigs produces approximately 37 percent of all human-induced methane), rice cultivation, biomass burning, and waste management (sewage treatment and landfills). The Intergovernmental Panel on Climate Change estimates that more than 60 percent of global methane emissions are related to such activities. Natural sources of methane emissions include wetlands, which provide habitat conducive to bacteria that produce methane during their decomposition of organic material; the digestive processes of termites (the second-largest natural source of methane emissions); and oceans, where methane emissions come from anaerobic digestion by marine zooplankton and fish and by methanogenesis in marine sediments.
Methane is also stored as a hydrate (methane hydrate, a crystalline solid consisting of gas molecules surrounded by a cage of water molecules) in immense amounts in marine sediments and in the frozen Arctic...
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Methane Removal from the Atmosphere (Encyclopedia of Environmental Issues, Revised Edition)
According to the U.S. Environmental Protection Agency (EPA), released methane can remain in the earth’s atmosphere for nine to fifteen years. Once emitted, methane can be removed from the atmosphere by a variety of processes, frequently called sinks. The dominant sink is oxidation by photochemically produced hydroxyl radicals (OH). The majority of methane molecules react with OH to form the methyl group CH3 and water in the tropospheric layer of the atmosphere, with smaller amounts of methane destroyed in the stratosphere. These two OH reactions account for almost 90 percent of methane removal. Two smaller sinks are microbial uptake of methane in soils and methane’s reaction with chlorine atoms in the marine boundary layer.
The balance between methane emissions and methane removal processes ultimately determines atmospheric methane concentrations. The methane remaining after methane removal processes can absorb terrestrial infrared radiation that would otherwise escape to space. This property can contribute to the warming of the atmosphere, which is why methane is considered to be a greenhouse gas. It is more than twenty times more effective in trapping heat in the atmosphere than carbon dioxide (CO2) over a period of one hundred years.
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Research Directions (Encyclopedia of Environmental Issues, Revised Edition)
Methane research is proceeding in two major directions: Some focuses on energy generation, seeking ways to make bioconversion of wastes to methane more economically attractive as an alternative fuel, and some focuses on the environment, seeking ways to limit the release of methane into the atmosphere because of its properties as a greenhouse gas. A shared goal of these two areas of research is to find ways in which much of the methane released into the atmosphere could be harnessed for energy production. Methane has advantages over petroleum and coal as a fuel because it burns more cleanly than do those fossil fuels.
In the energy sector, operators of coal mines are looking for ways to isolate the methane produced as a result of mining activities, instead of venting it into the atmosphere. The EPA estimates that up to 40 percent of the methane that migrates to the atmosphere can be used for heat and power generation, injection into pipeline systems for transport, methanol production, or on-site applications such as coal drying. Landfill gas-to-energy projects, which collect the methane that forms in landfills, offer another promising way to reduce atmospheric release and provide inexpensive energy.
The U.S. Global Change Research Program has identified as a priority research activity the development of global monitoring sites to measure atmospheric methane levels. The Carbon Cycle Greenhouse Gases Group of the...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Buell, Phyllis, and James Girard. Chemistry Fundamentals: An Environmental Perspective. 2d ed. Sudbury, Mass.: Jones and Bartlett, 2003.
Demirbas, Ayhan. Methane Gas Hydrate. London: Springer, 2010.
Khalil, M. A. K., ed. Atmospheric Methane: Its Role in the Global Environment. New York: Springer, 2000.
National Academy of Sciences. Climate Change Science: An Analysis of Some Key Questions. Washington, D.C.: National Academies Press, 2001.
_______. Methane Generation from Human, Animal, and Agricultural Wastes. Washington, D.C.: National Academies Press, 2001.
Soliva, Carla Riccarda, Junichi Takahashi, and Michael Kreuzer, eds. Greenhouse Gases and Animal Agriculture. Boston: Elsevier, 2006.
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Where Found (Encyclopedia of Global Resources)
Methane is found throughout the crust of the Earth. The United States, Canada, and Russia have the largest output of natural gas from methane deposits. Methane is also found in mud volcanoes. The decomposition of landfill materials has resulted in the production of significant amounts of methane, and several landfill sites in the United States have been drilled into as a source.
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Primary Uses (Encyclopedia of Global Resources)
Technical Definition (Encyclopedia of Global Resources)
Description, Distribution, and Forms (Encyclopedia of Global Resources)
Methane, a product of the decomposition of plant and animal remains, can be found throughout the Earth’s crust in varying amounts. Where it is found in greater concentrations, methane is the primary constituent in natural gas deposits, which are the target of oil and gas exploration efforts worldwide. Methane is also found in coal deposits as an integral part of the coalification process and can be recovered from wells drilled into the coal in the same manner in which oil and gas are obtained.
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History (Encyclopedia of Global Resources)
Methane was considered a waste by-product of oil production in the past, and trillions of cubic meters escaped into the atmosphere in worldwide operations. Beginning in the 1950’s methane-based natural gas was seen as a viable energy source. Several interstate pipelines have been constructed in the United States, primarily to deliver the gas from its origins in the Gulf Coast and Midwest to the metropolitan areas of the Northeast. As late as the 1960’s, natural gas had little value in some areas, and wells drilled for oil that discovered natural gas instead were frequently abandoned for lack of markets.
Beginning in the 1980’s, methane was touted by some as the fuel of the future. It is clean burning, relatively inexpensive, and fairly easily transported throughout the United States. Its supply is forecast to continue for hundreds of years. Research has attempted to substitute methane-based natural gas as a motor fuel in cars, trucks, and locomotives, and many vehicles have been converted to use it. Its use as a motor fuel will undoubtedly increase as more facilities are constructed to service existing and future vehicles.
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Obtaining Methane (Encyclopedia of Global Resources)
In spite of its advantages, methane has a significant disadvantage: It is explosive if mixed with air in a range of 5 percent to 15 percent by volume, and it has been blamed for several coal-mine disasters. As a result, modern coal-mining practice removes as much methane from coal deposits as possible in advance of mining and maintains the methane-air mixture in the mining environment below 1 percent by volume. Since methane is not life-sustaining, its accumulation in underground coal mines can also cause a condition known as “firedamp,” which may asphyxiate mining personnel if undetected.
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Uses of Methane (Encyclopedia of Global Resources)
Methane is an excellent fuel for fuel cells. Fuel cells produce electricity directly from the interaction of hydrocarbon and a catalyst. This interaction is not dependent on combustion but is a heat-producer, giving rise to the utilization of waste heat in various ways. It is expected that future fuel cell research, together with advances in the transportation sector, will place a greater demand on methane resources.
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Background (Encyclopedia of Global Warming)
Methane is a colorless, odorless gas with the molecular formula CH4. It is the main chemical component of natural gas (accounting for 70-90 percent of such gas). Natural gas makes up up to 20 percent of the U.S. energy supply. Methane was discovered by the Italian scientist Alessandro Volta, who collected it from marsh sediments and demonstrated that it was flammable. He called it “combustible air.”
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Methane as a Greenhouse Gas (Encyclopedia of Global Warming)
As with all greenhouse gases (GHGs), methane in the atmosphere acts similarly to glass in a greenhouse. It allows light energy from the Sun to reach Earth’s surface, but it traps heat energy radiated back from the surface in the form of infrared radiation. Since the beginning of the Industrial Revolution in the mid-eighteenth century, methane concentrations have more than doubled in the atmosphere, causing nearly one-quarter of the planet’s anthropogenic global warming. Continuous release of methane into the atmosphere causes rapid warming, because methane’s contribution to the greenhouse effect is much more powerful than that of carbon dioxide (CO2).
Global warming itself may trigger the release of methane trapped in tundra permafrost or ocean deposits, thereby accelerating climate change in a positive feedback loop. The release of large volumes of methane from such geological formations into the atmosphere has been suggested as a possible cause for global warming events in the past. Methane oxidizes to CO2 and therefore remains in the atmosphere for a shorter time-period of nine to fifteen years, compared to CO2, which may remain in the atmosphere for one hundred years.
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Sources of Methane (Encyclopedia of Global Warming)
According to the U.S. Environmental Protection Agency (EPA), about 60 percent of global methane emissions are a direct result of human-related activities. These activities include creating landfills, treating wastewater, animal husbandry (through enteric fermentation and manure production), cultivating rice fields, mining coal, and producing and processing natural gas. For instance, the livestock sector (including cattle, chickens, and pigs) generates 37 percent of all anthropogenic methane. Landfills are the second largest anthropogenic source of methane in the United States.
Natural sources of methane include wetlands, lake sediments, natural gas fields, termites, oceans, permafrost, and methane hydrates. Wetlands are responsible for up to 76 percent of global natural methane emissions. Surprisingly, according to EPA data, termites contribute about 11 percent of global natural methane emissions. In most of these processes, methane is produced by microorganisms called archaea as the integral part of their metabolism. Such microbes are called methanogens, and the route of methane generation is called methanogenesis.
Archaea live in oxygen-depleted habitats, because the presence of oxygen would kill them instantly. For their food source, methanoges use products of bacterial fermentation such as CO2 and molecular hydrogen (H2); different acids such as acetate, pyruvate, or formate; or even carbon monoxide. That is...
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Methane as a Fuel (Encyclopedia of Global Warming)
In the 1985 science-fiction film Mad Max Beyond Thunderdome starring Mel Gibson, a futuristic city was run on methane generated by pig manure. In reality, methane can be a very good alternative fuel. It has a number of advantages over other fuels produced by microorganisms. It is easy to make and can be generated locally, obviating the need for long-distance distribution. Extensive natural gas infrastructure is already in place to be utilized. Utilization of methane as a fuel is a very attractive way to reduce wastes such as manure, wastewater, or municipal and industrial wastes. In local farms, manure is fed into digesters(bioreactors), where microorganisms metabolize it into methane. Methane can be used to fuel electrical generators to produce electricity.
In China, millions of small farmers maintain simple, small, underground digesters near their houses. There are several landfill gas facilities in the United States that generate electricity using methane. San Francisco has extended its recycling program to include conversion of dog waste into methane to produce electricity and to heat homes. With a city dog population of 120,000, this initiative promises to generate significant amounts of fuel with a huge reduction of waste at the same time.
Methane was used as a fuel for vehicles for a number of years. Several Volvo car models with bi-fuel engines were made to run on methane, with gasoline as a back up....
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Methane Removal Processes (Encyclopedia of Global Warming)
The natural mechanism of methane removal from the atmosphere involves its destruction by the hydroxyl radical (OH). Significant amounts of methane are also consumed by microorganisms called methanotrophs, which use the methane for energy and biosynthesis. These bacteria are prevalent in nature and potentially could be used for methane mitigation.
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Context (Encyclopedia of Global Warming)
Since methane is a powerful contributor to global warming, any efforts to reduce methane emissions will have a rapid impact on Earth’s climate. One way to avoid methane release into the atmosphere is to turn it into a fuel. Supply of fossil fuels, particularly oil, is limited and does not satisfy world energy demands, which consistently increase. The extensive use of fossil fuels causes global warming. Methane utilization in place of fossil fuels as an energy source can provide significant environmental and economic benefits. In the future, landfills and wastewater treatment facilities can possibly be redesigned to optimize methane production. However, further research is needed to better understand archaean-bacterial methanogenic communities in landfills and wastewater treatment facilities in order to improve methane generation.
Some technical obstacles exist to efficiently converting landfill wastes that primarily contain plant lignocellulosic material. Lignocellulose is a combination of lignin, cellulose, and hemicellulose that strengthens plant cell walls. Microbial communities in landfills cannot utilize lignin. Creating efficient methane-producing facilities that are also capable of reducing waste is a feasible option for sustainable development to provide fuel to heat homes, run cars, generate electricity, and eliminate powerful GHG and health hazards.
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Further Reading (Encyclopedia of Global Warming)
Archer, David. Global Warming: Understanding Forecast. Malden, Mass.: Blackwell, 2007. Devotes a chapter to discussion of methane and its greenhouse effects.
Madigan, Michael T., et al. Brock Biology of Microorganisms. 12th ed. San Francisco, Calif.: Pearson/Benjamin Cummings, 2009. Introductory microbiology textbook. Chapter 17 describes methane production by archaea.
National Academy of Sciences. Methane Generation from Human, Animal, and Agricultural Wastes. Washington, D.C.: Author, 2001. Describes the role of disparate sources in methane production.
Nebel, Bernard J., and Richard T. Wright. Environmental Science: Towards a Sustainable Future. Englewood Cliffs, N.J.: Prentice Hall, 2008. Several chapters describe methane as a GHG and an alternative fuel.
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