Landfill gas
Encyclopedia
Landfill gas is a complex mix of different gases created by the action of microorganism
s within a landfill
.
s and microbes acting upon the waste
as the putrescible materials
begins to break down in the landfill. The rate of production is affected by waste composition and landfill geometry, which in turn influence the bacterial populations within it, chemical make-up, thermal characteristics, entry of moisture and escape of gas.
The spatially heterogeneous nature of most landfills means that there will be a wide range of physical conditions and biological ecosystems co-existing simultaneously within most sites. This heterogeneity, together with the frequently unclear nature of the contents, makes landfill gas production more difficult to predict and control than standard industrial bioreactors for sewage treatment
.
Due to the constant production of landfill gas, the increase in pressure within the landfill (together with differential diffusion) causes the gas's release into the atmosphere. Such emissions lead to important environmental
, hygiene
and security
problems in the landfill. Several accidents have occurred, for example at Loscoe
, England in 1986, where migrating landfill gas, which was allowed to build up, partially destroyed the property. An accident causing two deaths occurred from an explosion in a house adjacent to Skellingsted landfill in Denmark in 1991. Due to the risk presented by landfill gas there is a clear need to monitor gas produced by landfills. In addition to the risk of fire and explosion, gas migration in the subsurface can result in contact of landfill gas with groundwater
. This, in turn, can result in contamination of groundwater by organic compounds present in nearly all landfill gas.
Landfill gas is approximately forty to sixty percent methane
, with the remainder being mostly carbon dioxide
. Landfill gas also contains varying amounts of nitrogen, oxygen, water vapour,hydrogen sulphide, and other contaminants. Most of these other contaminants are known as "non-methane organic compounds" or NMOCs. Some inorganic contaminants (for example mercury) are also known to be present in landfill gas. There are sometimes also contaminants (for example tritium
) found in landfill gas. The non-methane organic compounds usually make up less than one percent of landfill gas. In 1991, the US EPA identified ninety-four non-methane organic compounds including toxic chemicals like benzene
, toluene
, chloroform
, vinyl chloride
, and carbon tetrachloride
. At least forty one of the non-methane organic compounds are halogenated compounds (chemicals containing halogens: typically chlorine, fluorine, or bromine). General options for managing landfill gas are: flaring, boiler (makes heat), internal combustion engine (makes electricity), gas turbine (makes electricity), fuel cell (makes electricity), convert the methane to methyl alcohol, clean it enough to pipe it to other industries or into natural gas
lines.
The Environmental Protection Agency estimates that there are approximately six thousand landfills in the United States. Most of these landfills are composed of municipal waste, and, therefore, producing methane. These landfills are the largest source of anthropogenic methane emissions in the United States. These landfills will contribute an estimated four hundred and fifty to six hundred and fifty billion cubic feet of methane per year (in 2000).
Under the Clean Air Act of 1996, it is required that many large landfills install gas collection and control systems, which means that at the very least the facilities must collect and flare the gas. The Environmental Protection Agency estimates that another 600 landfills could support gas to energy projects. The Environmental Protection Agency has also established the Landfill Methane Outreach Program. This program was developed to reduce methane emissions from landfills in a cost-effective manner by encouraging the development of environmentally and economically beneficial landfill gas-to-energy projects.
Federal regulations under Subtitle D of RCRA formed in October 1979 regulate the siting, design, construction, operation, monitoring, and closure of MSW landfills. Subtitle D now requires controls on the migration of methane in landfill gas. Monitoring requirements must be met at landfills during their operation, and for an additional 30 years after. The landfills affected by Subtitle D of RCRA are required to control gas by establishing a way to check for methane emissions periodically and therefore prevent off-site migration. Landfill owners and operators must make sure the concentration of methane gas does not exceed 25% of the EL for methane in the facilities' structures and the LEL for methane at the facility boundary.
due to pressure differentials and diffusion can occur. This can create an explosion hazard if the gas reaches sufficiently high concentrations in adjacent buildings.
installed a landfill gas collection system which collects, cools, dries, and compresses the gas into an 11-mile pipeline. The gas is then used to power an ethanol plant operated by POET Biorefining.
The number of landfill gas projects, which convert the methane gas that is emitted from decomposing garbage into power, went from three hundred and ninety nine in 2005, to five hundred and nineteen in 2009 according to the Environmental Protection Agency. These projects are popular because they control energy costs and reduce greenhouse gas
emissions. These projects collect the methane gas, which is released with twenty times the global warming
potential of carbon dioxide, and treat it, so it can be used for electricity or upgraded to pipeline-grade gas. These projects power homes, buildings, and vehicles.
Waste Management
uses landfill gas as an energy source. Their landfill gas-to-energy projects create enough energy to power four hundred thousand homes every day. This energy production offsets almost two million tons of coal per year. These projects also reduce greenhouse gas emissions into the atmosphere. Waste Management currently has 110 landfill gas-to-energy facilities.This is a good substitute of natural gas and run the vehicles more efficiently.
opposes any government subsidies for them. The Natural Resources Defense Council
(NRDC) believes that government incentives should be directed more towards solar, wind, and energy-efficiency efforts.
. The major components are CO2 and methane
, both of which are greenhouse gas
.
in the gas is oxidized microbially to CO2.
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s within a landfill
Landfill
A landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...
.
Production
Landfill gas production results from chemical reactionChemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s and microbes acting upon the waste
Waste
Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...
as the putrescible materials
Biodegradable waste
Biodegradable waste is a type of waste, typically originating from plant or animal sources, which may be degraded by other living organisms. Waste that cannot be broken down by other living organisms are called non-biodegradable....
begins to break down in the landfill. The rate of production is affected by waste composition and landfill geometry, which in turn influence the bacterial populations within it, chemical make-up, thermal characteristics, entry of moisture and escape of gas.
The spatially heterogeneous nature of most landfills means that there will be a wide range of physical conditions and biological ecosystems co-existing simultaneously within most sites. This heterogeneity, together with the frequently unclear nature of the contents, makes landfill gas production more difficult to predict and control than standard industrial bioreactors for sewage treatment
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
.
Due to the constant production of landfill gas, the increase in pressure within the landfill (together with differential diffusion) causes the gas's release into the atmosphere. Such emissions lead to important environmental
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
, hygiene
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
and security
Security
Security is the degree of protection against danger, damage, loss, and crime. Security as a form of protection are structures and processes that provide or improve security as a condition. The Institute for Security and Open Methodologies in the OSSTMM 3 defines security as "a form of protection...
problems in the landfill. Several accidents have occurred, for example at Loscoe
Loscoe
Loscoe is a small village near Heanor in Derbyshire, England.The research for Highfield House dates back to 1650 or possibly as early as 1630. This may now be the oldest surviving house in Loscoe as many houses in the village were demolished due to subsidence.-1986 landfill gas explosion:Loscoe was...
, England in 1986, where migrating landfill gas, which was allowed to build up, partially destroyed the property. An accident causing two deaths occurred from an explosion in a house adjacent to Skellingsted landfill in Denmark in 1991. Due to the risk presented by landfill gas there is a clear need to monitor gas produced by landfills. In addition to the risk of fire and explosion, gas migration in the subsurface can result in contact of landfill gas with groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
. This, in turn, can result in contamination of groundwater by organic compounds present in nearly all landfill gas.
Landfill gas is approximately forty to sixty percent methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, with the remainder being mostly carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. Landfill gas also contains varying amounts of nitrogen, oxygen, water vapour,hydrogen sulphide, and other contaminants. Most of these other contaminants are known as "non-methane organic compounds" or NMOCs. Some inorganic contaminants (for example mercury) are also known to be present in landfill gas. There are sometimes also contaminants (for example tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
) found in landfill gas. The non-methane organic compounds usually make up less than one percent of landfill gas. In 1991, the US EPA identified ninety-four non-methane organic compounds including toxic chemicals like benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
, toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
, chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
, vinyl chloride
Vinyl chloride
Vinyl chloride is the organochloride with the formula H2C:CHCl. It is also called vinyl chloride monomer, VCM or chloroethene. This colorless compound is an important industrial chemical chiefly used to produce the polymer polyvinyl chloride . At ambient pressure and temperature, vinyl chloride...
, and carbon tetrachloride
Carbon tetrachloride
Carbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
. At least forty one of the non-methane organic compounds are halogenated compounds (chemicals containing halogens: typically chlorine, fluorine, or bromine). General options for managing landfill gas are: flaring, boiler (makes heat), internal combustion engine (makes electricity), gas turbine (makes electricity), fuel cell (makes electricity), convert the methane to methyl alcohol, clean it enough to pipe it to other industries or into natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
lines.
The Environmental Protection Agency estimates that there are approximately six thousand landfills in the United States. Most of these landfills are composed of municipal waste, and, therefore, producing methane. These landfills are the largest source of anthropogenic methane emissions in the United States. These landfills will contribute an estimated four hundred and fifty to six hundred and fifty billion cubic feet of methane per year (in 2000).
Monitoring
Some of the gases produced by landfills are hazardous and monitoring techniques have been developed. Flame ionization detectors can be used to measure methane levels as well as total VOC levels. Surface monitoring and sub-surface monitoring as well as monitoring of the ambient air is carried out.Under the Clean Air Act of 1996, it is required that many large landfills install gas collection and control systems, which means that at the very least the facilities must collect and flare the gas. The Environmental Protection Agency estimates that another 600 landfills could support gas to energy projects. The Environmental Protection Agency has also established the Landfill Methane Outreach Program. This program was developed to reduce methane emissions from landfills in a cost-effective manner by encouraging the development of environmentally and economically beneficial landfill gas-to-energy projects.
Federal regulations under Subtitle D of RCRA formed in October 1979 regulate the siting, design, construction, operation, monitoring, and closure of MSW landfills. Subtitle D now requires controls on the migration of methane in landfill gas. Monitoring requirements must be met at landfills during their operation, and for an additional 30 years after. The landfills affected by Subtitle D of RCRA are required to control gas by establishing a way to check for methane emissions periodically and therefore prevent off-site migration. Landfill owners and operators must make sure the concentration of methane gas does not exceed 25% of the EL for methane in the facilities' structures and the LEL for methane at the facility boundary.
Landfill gas migration
Landfill gas migrationLandfill gas migration
Landfill gas migration is a complex process of the gas moving from the site of original deposition to other places via diffusion. Usually, the gas moves from areas of high concentration to areas of low gas concentration around a landfill. The process is also affected by the permeability of the...
due to pressure differentials and diffusion can occur. This can create an explosion hazard if the gas reaches sufficiently high concentrations in adjacent buildings.
Landfill gas use
The gases produced within the landfill can be collected and flared off or used to produce heat or electricity. The City of Sioux Falls, South DakotaSioux Falls, South Dakota
Sioux Falls is the largest city in the U.S. state of South Dakota. Sioux Falls is the county seat of Minnehaha County, and also extends into Lincoln County to the south...
installed a landfill gas collection system which collects, cools, dries, and compresses the gas into an 11-mile pipeline. The gas is then used to power an ethanol plant operated by POET Biorefining.
The number of landfill gas projects, which convert the methane gas that is emitted from decomposing garbage into power, went from three hundred and ninety nine in 2005, to five hundred and nineteen in 2009 according to the Environmental Protection Agency. These projects are popular because they control energy costs and reduce greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
emissions. These projects collect the methane gas, which is released with twenty times the global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
potential of carbon dioxide, and treat it, so it can be used for electricity or upgraded to pipeline-grade gas. These projects power homes, buildings, and vehicles.
Waste Management
Waste Management, Inc
Waste Management, Inc. is a waste management, comprehensive waste, and environmental services company in North America. Founded in 1894, the company is headquartered in Suite 4000 at the First City Tower in Downtown Houston, Texas, in the United States....
uses landfill gas as an energy source. Their landfill gas-to-energy projects create enough energy to power four hundred thousand homes every day. This energy production offsets almost two million tons of coal per year. These projects also reduce greenhouse gas emissions into the atmosphere. Waste Management currently has 110 landfill gas-to-energy facilities.This is a good substitute of natural gas and run the vehicles more efficiently.
Opposition
Large projects often cost millions of dollars. Some environmental groups claim that the projects do not produce renewable power because trash (their source) is not renewable. The Sierra ClubSierra Club
The Sierra Club is the oldest, largest, and most influential grassroots environmental organization in the United States. It was founded on May 28, 1892, in San Francisco, California, by the conservationist and preservationist John Muir, who became its first president...
opposes any government subsidies for them. The Natural Resources Defense Council
Natural Resources Defense Council
The Natural Resources Defense Council is a New York City-based, non-profit, non-partisan international environmental advocacy group, with offices in Washington DC, San Francisco, Los Angeles, Chicago, and Beijing...
(NRDC) believes that government incentives should be directed more towards solar, wind, and energy-efficiency efforts.
Environmental effects
Landfill gases have an influence on climate changeClimate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
. The major components are CO2 and methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, both of which are greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
.
Microbial oxidation
When landfill gas permeates through a soil cover, a fraction of the methaneMethane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
in the gas is oxidized microbially to CO2.
See also
- Anaerobic digestionAnaerobic digestionAnaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. It is used for industrial or domestic purposes to manage waste and/or to release energy....
- BiogasBiogasBiogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Organic waste such as dead plant and animal material, animal dung, and kitchen waste can be converted into a gaseous fuel called biogas...
- Biodegradability
- Flue gasFlue gasFlue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants...
- Relative cost of electricity generated by different sources
- Underground coal gasificationUnderground Coal GasificationUnderground coal gasification is an industrial process, which converts coal into product gas. UCG is an in-situ gasification process carried out in non-mined coal seams using injection of oxidants, and bringing the product gas to surface through production wells drilled from the surface. The...