Landfill gas

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill.[1]

Production[edit]

Landfill gas production results from chemical reactions and microbes acting upon the waste as the putrescible materials begins to break down[2] in the landfill. The rate of production is affected by waste composition and landfill geometry, which in turn influence the microbial populations within it, chemical make-up of waste, thermal range of physical conditions, and the 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 continual production of landfill gas, the increase in pressure within the landfill (together with differential diffusion) causes the gases release into the atmosphere. Such emissions lead to important environmental, hygiene and security problems in the landfill.[3][4] Several accidents have occurred, for example at Loscoe, England in 1986,[5] 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.[6] 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.[7]

Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Landfill gas also contains varying amounts of nitrogen and oxygen gas, water vapour, hydrogen sulphide, and other contaminants. Most of these other contaminants are known as "non-methane organic compounds" or NMOCs. Some inorganic contaminants, such as mercury, are also present in the gas of some landfills. There are sometimes also radioactive contaminants, such as 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, such as chlorine, fluorine, or bromine). General options for managing landfill gas are: flaring, boiler (makes heat), internal combustion engine (makes electricity), gas turbine (makes electricity), convert the methane to methyl alcohol, clean it enough to pipe it to other industries or into natural gas lines.[8]

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, produce 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).[9]

Monitoring[edit]

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.[10]

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.[11]

Landfill gas migration[edit]

Landfill gas migration 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[edit]

Figure 1[12]

The gases produced within a landfill can be collected or flared off. Once collected, the gas has several different pathways it can take. The landfill gas can be utilized directly on site by a boiler or any type or combustion system. This provides raw heat for processes. Electricity can also be generated on site through the use of micro turbines, steam turbines, or fuel cells. [13] The landfill gas can also be sold off site and sent into natural gas pipelines. This requires the gas to be processed into pipeline quality by removing the water, carbon dioxide, nitrogen, hydrogren, oxygen and any other trace contaminants. Once in the general supply of natural gas, it can be used at power plants producing electricity or in home boilers. [14]

Landfill gas can also be used to evaporate leachate, another byproduct of the landfill process. This displaces another fuel that was previously used for the same thing.[15]

Figure 2[16]

The number of landfill gas projects went from 399 in 2005, to 594 in 2012[17] 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 and treat it, so it can be used for electricity or upgraded to pipeline-grade gas. (Methane gas has twenty times the global warming potential of carbon dioxide.) These projects power homes, buildings, and vehicles.[18]

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.[19]

Opposition[edit]

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 Club opposes any government subsidies for them.[20] The Natural Resources Defense Council (NRDC) believes that government incentives should be directed more towards solar, wind, and energy-efficiency efforts.

Environmental effects[edit]

Landfill gases have an influence on climate change. The major components are CO2 and methane, both of which are greenhouse gas. Methane is considered over 20 times more detrimental to the atmosphere than Carbon Dioxide[21]

Microbial oxidation[edit]

When landfill gas permeates through a soil cover, a fraction of the methane in the gas is oxidized microbially to CO2.[22]

See also[edit]

References[edit]

  1. ^ Landfill gas, www.clarke-energy.com, retrieved 9th December 2013
  2. ^ Burdekin, O. (2003) An investigation into the continuous monitoring of landfill gas and the commercial viability of the Intelysis landfill gas monitor, Manchester University, Unpublished thesis
  3. ^ Brosseau, J. (1994) Trace gas compound emissions from municipal landfill sanitary sites; Atmospheric-Environment 28 (2), 285-293
  4. ^ Christensen, T. H., Cossu, R. & Stegmann, R. (1999) Landfilling of waste: Biogas
  5. ^ Williams and Aitkenhead (1991) Lessons from Loscoe: The uncontrolled migration of landfill gas; The Quarterly Journal of Engineering Geology 24 (2), 191-207
  6. ^ Danish EPA
  7. ^ Kerfoot, H.B., Chapter 3.5 In Christensen, T. H., Cossu, R. & Stegmann, R. (1999)Landfilling of waste: Biogas
  8. ^ "Primer on Landfill Gas as "Green Energy"". Energy Justice Network. Retrieved 2010-04-25. 
  9. ^ "Landfill Gas". Gas Separation Technology LLC. Retrieved 2010-04-26. 
  10. ^ "Landfill Gas". Gas Separation Technology LLC. Retrieved 2010-04-26. 
  11. ^ "Landfill Gas Control Measures". Agency for Toxic Substances & Disease Registry. Retrieved 2010-04-26. 
  12. ^ https://en.m.wikipedia.org/wiki/File:Leachate_evaporation_system.JPG. Retrieved 27 September 2013.  Missing or empty |title= (help)
  13. ^ Sullivan, Patrick. "The Importance of Landfill Gas Capture and Utilization in the U.S". SUR. Retrieved 27 September 2013. 
  14. ^ "Landfill Gas Power Plants". California Energy Commission. Retrieved 27 September 2013. 
  15. ^ "Landfill Methane Outreach program". EPA. Retrieved 27 September 2013. 
  16. ^ https://commons.wikimedia.org/wiki/File:Landfill_gas_collection_system.JPG. Retrieved 27 September 2013.  Missing or empty |title= (help)
  17. ^ "Landfill Gas to Energy". EPA. Retrieved 2012-07-29. 
  18. ^ Koch, Wendy (2010-02-25). "Landfill Projects on the rise". USA Today. Retrieved 2010-04-25. 
  19. ^ "Landfill Gas to Energy". Waste Management. Retrieved 2010-04-26-2010. 
  20. ^ Koch, Wendy (2010-02-25). "Landfill Projects on the rise". USA Today. Retrieved 2010-04-25. 
  21. ^ "Methane". Environmental Protection Agency. Retrieved 20 September 2012. 
  22. ^ Scheutz, C., Kjeldsen, P., Bogner, J.E., De Visscher, A., Gebert, J., Hilger, H.A. & Spokas, K. (2009) Microbial methane oxidation processes and technologies for mitigation of landfill gas emissions. Waste Manage. Res. 27:409-455.

External links[edit]