Landfill Gas

Landfill gas (also known as landfill methane) is the gas released from landfills. A landfill is essentially a large hole in the ground that is used to store solid and liquid wastes produced by humanity. There are over 3,000 active landfills in the United States that are accepting waste from our towns, cities, and industries, and an estimated 10,000 inactive landfills.¹ Landfills, as the receptacles of the noxious and odiferous, are producing more than just awful smells. As the waste in landfills is exposed to oxygen, time, and microrganisms, the waste is broken down and a vast number of chemicals are emitted in gaseous and liquid forms. Specficially, landfill gas is produced by bacterial decomposition, volatization, and chemical reactions.² The gas produced by landfills contains anywhere from 45-60% methane (CH4). Methane is a greenhouse gas³ and has 25 times more heat trapping potential than its more famous counterpart in the global climate change debate; carbon dioxide (CO2).⁴ Luckily, methane is only present in the atmosphere at concentrations around 1,800 parts per billion (as opposed to CO2's 385 parts per million).⁵

Background

What is to be done about the emissions of a powerful greenhouse gas from something as prevalent as the town dump? The answer lies in one of the fundamental tenets of the modern environmental movement: reduce waste. Utilizing waste products for other processes helps to reduce the total net waste generated. Methane is widely recognized as one of the six major greenhouse gases that are accumulating in the Earth’s upper atmosphere and are contributing to the steady uptick in global average mean temperatures.⁶ Fortunately, methane is also an excellent fuel source, both in terms of its emissions (burning 1,000 cubic feet of pure methane produces 115 pounds of carbon dioxide)⁷ and in light of the fact that burning methane avoids the emission of a gas with a stronger global warming potential than CO2. In the United States, landfills accounted for twenty three percent of total methane emissions in 2007.⁸ Capturing the gas emitted from landfills is a viable option. The capture and use of methane from landfills not only reduces the total amount of methane generated, it also prevents the release of some carbon dioxide that would beproduced through traditional coal fired power plants.⁹

Landfill Structure

Source: EcoKids. Author: same as source. Permission: No copyright claimed..

Landfill Structure Key

Landfill Gas Production

There are many factors that determine how much landfill gas, including the valuable methane, a given landfill will produce. The most important factors for predicting the quality of the landfill methane that will be produced over the lifetime of a landfilll are found in the following list taken from the Agency for Toxic Substances and Disease Registry, an entity of the Center for Disease Control:

Waste composition. The more organic waste present in a landfill, the more landfill gas (e.g., carbon dioxide, methane, nitrogen, and hydrogen sulfide) is produced by the bacteria during decomposition. The more chemicals disposed of in the landfill, the more likely non-methane organic compounds (NMOCs) will be produced either through volatilization or chemical reactions.
Age of refuse. Generally, more recently buried waste (i.e., waste buried less than 10 years) produces more landfill gas through bacterial decomposition, volatilization, and chemical reactions than does older waste (buried more than 10 years). Peak gas production usually occurs from 5 to 7 years after the waste is buried.
Presence of oxygen in the landfill. Methane will be produced only when oxygen is no longer present in the landfill.
Moisture content. The presence of moisture (unsaturated conditions) in a landfill increases gas production because it encourages bacterial decomposition. Moisture may also promote chemical reactions that produce gases.
Temperature. As the landfill's temperature rises, bacterial activity increases, resulting in increased gas production. Increased temperature may also increase rates of volatilization and chemical reactions. The box on the following page provides more detailed information about how these variables affect the rate and volume of landfill gas production.¹⁰

If a municipality is considering a project to capture landfill methane for use as an electricity source, (burning the methane to power steam generators of other turbine-based generation technology), it is crucial to be able to estimate the landfill's output. The United States Environmental Protection Agency has encouraged municipalities to utilize methane capture technologies.¹¹ Of course, without a proper calculation of how much methane could be extracted from the decomposing wastes in a landfill, a local government could not successfully advocate for methane's capture. New Jersey has been utilizing landfill methane gas as a source of energy and these projects are proving to be successful because of the avoided methane emissions and the use of waste as a feedsource for another necessary process.¹² The United States Environmental Protection Agency, through its Landfill Methane Outreach Program, provides the public with a tool to calculate the economic benefit of a landfill methane capture project.¹³

Landfill methane capture technology

The basic philosophy behind capturing the methane that is emitted by landfills is to place a cap, using a variety of different materials based in part on the waste contents of the landfill, to block the direct emissions of methane into the atmosphere. A common landfill gas capture system is made up of an arrangement of vertical wells and horizontal collectors, usually placed after the landfill has been capped, that is used to direct the flow of the gas.¹⁴ This common type of collection is known as a "passive gas collection system" and the collection wells can be installed during the initial construction of the landfill or after the landfill is permanently closed.¹⁵ There is also a landfill gas collection method called the "active gas collection system." In the active version, a series of pumps move the gas to collection wells and through a series of low-pressure chambers to help direct and control the flow of the gas.¹⁶ The active gas collection method is more expensive than the passive version, but the ability to control the flow rate of gas, coupled with the ability to have multiple collection wells, helps to make the active gas collection system an economically viable option for many landfills. There are nearly 500 landfills in the United States that were capturing methane and either burning it for electricity generation or flaring it, which converts the methane into carbon dioxide, which has a lower global warming potential than methane.¹⁷ The prevalence of these projects is only increasing as greater incentives are presented to landfill companies.

Once the methane is captured at the landfill, it must be altered to more closely resemble the methane used for fuel. As mentioned above, landfill gas consists of roughly 50% methane and 50% carbon dioxide. There are numerous vapor-liquid separators throughout a gas collection system that remove contaminating liquid condensate from the gas. This liquid is mostly made of water and a complex mixture of hydrocarbons.

Avoided emissions

Landfill methane capture and the use of that captured gas for the generation of electricity avoids emissions in two ways. First, by capturing the methane the world avoids the direct emissions of that gas into the atmosphere. Second, by using the captured methane for electricity generation, coal or other fossil fuels that emit much more carbon dioxide, is displaced and not used by the entity using the landfill methane. The total amount of electricity generated via landfill methane capture was approximately 1,180 megawatts in 2008.¹⁸ It takes 2.1 pounds of coal to generate one kilowatt hour of electricity,¹⁹ (1 megawatt=1,000 kilowatts), and so the landfill methane use in 2008 displaced over 2,100,000 pounds of coal. It is estimated that landfill gas energy projects can capture between 60 to 90 percent of the methane emitted from a landfill.²⁰

U.S. Methane Emissions by Source in Millions of Tons CO2 Equivalent
Source	2000	2005	2006	2007
Agriculture--Enteric Fermentation	134.4	136.00	138.2	139.0
Landfills	122.3	127.8	130.4	132.9
Natural Gas Systems	130.8	106.3	104.8	104.7
Coal Mining	60.5	57.1	58.4	57.6
Agriculture--Manure Management	34.5	41.8	41.9	44.0

²¹

Global methane emissions

There would be many benefits if landfills throughout the world are able to implement methane capture and use that captured methane for energy production. As the following graphic shows, there are certain major methane emitting countries that could be targeted for landfill methane capture projects. There are also criticisms levelled at the cost efficacy of these types of projects. As with any technology, the more time that passes the more opportunities there are for innovation and increases in efficiency.

Landfill Methane Emissions by Country Percentage

Source: Global Anthropogenic Emissions of Non-CO 2 Greenhouse Gases 1990-2020 (EPA Report 430-R-06-003) . Author: Methane to Market. Permission: free with attribution.

²²

Footnotes

1. "Landfills: Hazardous to the Environment," Zero Waste America. Access March 1, 2010.

2. "Landfill Gas Primer - An Overview for Environmental Health Professionals," Agency for Toxic Substances and Disease Registry, 2001. Access March 1, 2010.

3. U.N. Framework Convention on Climate Change, GHG Data from UNFCCC, http://unfccc.int/ghg_data/ghg_data_...items/4146.php (last visited Mar. 3, 2010) [hereinafter GHG Data].

4. http://www.sciencedaily.com/releases...0423181652.htm.

5. http://www.sciencedaily.com/releases...0423181652.htm.

6. U.N. Framework Convention on Climate Change, GHG Data from UNFCCC, http://unfccc.int/ghg_data/ghg_data_...items/4146.php (last visited Mar. 3, 2010) [hereinafter GHG Data].

7. Carbon Dioxide Information Analysis Center, http://cdiac.ornl.gov/pns/faq.html.

8. United States Environmental Protection Agency, Landfill Methane Outreach Program, http://www.epa.gov/lmop/basic-info/index.html (last visited Mar. 3, 2010) [hereinafter LMOP] (asserting that there are over 500 landfills that are good candidates for methane capture and energy use).

9. Chicago Climate Exchange, Landfill Methane Emissions Offsets, http://www.chicagoclimatex.com/content.jsf?id=222 (last visited Mar. 3, 2010) (recognizing the offset potential of “[m]ethane collection projects that include electricity generation,” which may qualify “based on displaced emissions”).

10. See http://www.atsdr.cdc.gov/hac/landfil.../ch2.html#t2_1.

11. http://www.cnn.com/2006/TECH/05/25/l...ction=cnn_tech

12. http://www.huffingtonpost.com/2008/1..._n_138076.html

13. http://www.epa.gov/lmop/projects-can...alculator.html

14. http://fpc.state.gov/documents/organ...ion/130799.pdf

15. http://www.atsdr.cdc.gov/hac/landfill/html/ch5.html

16. http://www.atsdr.cdc.gov/hac/landfill/html/ch5.html

17. United States Environmental Protection Agency, Landfill Methane Outreach Program , Energy Projects and Candidate Landfills, http://www.epa.gov/lmop/proj/index.htm.

18. http://www.treehugger.com/files/2008...rgy-biogas.php.

19. http://www.eia.doe.gov/cneaf/electri...co2report.html.

20. http://www.epa.gov/lmop/basic-info/index.html#03.

21. http://epa.gov/methane/sources.html.

22. http://www.methanetomarkets.org/docu...ill_fs_eng.pdf

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