Landfill gas

Production

Landfill gases are the result of three processes:

1. evaporation of volatile organic compounds (e.g., solvents)
2. chemical reactions between waste components
3. anaerobic digestion, especially methanogenesis. The first two depend strongly on the nature of the waste. The dominant process in most landfills is the third process, whereby anaerobic bacteria decompose organic waste to produce biogas, which consists of methane and carbon dioxide together with traces of other compounds. Despite the heterogeneity of waste, the evolution of gases follows well defined kinetic pattern. Formation of methane and CO2 commences about six months after depositing the landfill material. The evolution of gas reaches a maximum at about 20 years, then declines over the course of decades.

Conditions and changes within the landfill can be observed with electrical resistivity tomography (ERT) to detect sources of landfill gas, and leachate movements and pathways. Conditions at different locations, such as temperature, moisture levels and fraction of biodegradable material, can be inferred. This information can be used to improve gas production, with optimal well locations over hotspots and interventions such as heap irrigation.

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

Monitoring

Main article: Landfill gas monitoring

Because gases produced by landfills are both valuable and sometimes hazardous, 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. In the U.S., under the Clean Air Act of 1990, 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.

U.S. Federal regulations under Subtitle D of RCRA formed in October 1979 regulate the siting, design, construction, operation, monitoring, and closure of municipal solid waste 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 LEL for methane in the facilities' structures and the LEL for methane at the facility boundary.

Use

Main article: Landfill gas utilization

The gases produced within a landfill can be collected and used in various ways. The landfill gas can be utilized directly on-site by a boiler or any type of combustion system, providing heat. Electricity can also be generated on-site through the use of microturbines, steam turbines, or fuel cells. The landfill gas can also be sold off-site and sent into natural gas pipelines. This approach requires the gas to be processed into pipeline quality, e.g., by removing various contaminants and components. Landfill gas can also be used to evaporate leachate, another byproduct of the landfill process. This application displaces another fuel that was previously used for the same thing.

The efficiency of gas collection at landfills directly impacts the amount of energy that can be recovered; closed landfills (those no longer accepting waste) collect gas about 17% more efficiently than open landfills (those still accepting waste).

Opposition

Capture and use of landfill gas can be expensive. Some environmental groups claim that the projects do not produce "renewable power" because trash (their source) is not renewable. The Sierra Club opposes government subsidies for such projects. The Natural Resources Defense Council (NRDC) argues that government incentives should be directed more towards solar, wind, and energy-efficiency efforts.

Safety

Landfill gas emissions can lead to environmental, hygiene and security problems in the landfill. Several accidents have occurred, for example at Loscoe, England in 1986, where migrating landfill gas accumulated and partially destroyed a property. An accident causing two deaths occurred from an explosion in a house adjacent to Skellingsted landfill in Denmark in 1991.{{cite web |archive-url=https://web.archive.org/web/20110722055429/https://www2.mst.dk/common/Udgivramme/Frame.asp?pg=http://www2.mst.dk/Udgiv/publikationer/2001/87-7944-831-3/html/kap30.htm |archive-date=July 22, 2011

Although usually evolved only in trace amounts, landfills do release some aromatics and chlorocarbons.

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.

By country

Brazil

United States

References

References

1. "What Landfill Operators Should Know about RNG Technologies".
2. Hans-Jürgen Ehrig, Hans-Joachim Schneider and Volkmar Gossow "Waste, 7. Deposition" in Ullmann's Encyclopedia of Industrial Chemistry, 2011, Wiley-VCH, Weinheim. {{doi. 10.1002/14356007.o28_o07
3. (7 August 2024). "IPCC Global Warming Potential Values".
4. (23 December 2015). "Methane Emissions". Environmental Protection Agency.
5. "Landfill Gas and Biogas". U.S. Energy Information Administration.
6. Deep Scan Tech (2022): [https://www.deepscantech.com/news/deep-scan-tech-supports-ukraine-in-improving-its-energy-independence.html Deep Scan Tech supports Ukraine in improving its energy independence].
7. Deep Scan Tech (2022): [https://www.deepscantech.com/news/deep-scan-tech-helps-landfills-protect-the-environment-with-a-demonstration-project-in-ukraine.html Deep Scan Tech helps landfills protect the environment with a demonstration project in Ukraine].
8. 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.
9. "Landfill Gas Control Measures". Agency for Toxic Substances & Disease Registry.
10. Sullivan, Patrick. "The Importance of Landfill Gas Capture and Utilization in the U.S". SUR.
11. "Landfill Gas Power Plants". California Energy Commission.
12. "Landfill Methane Outreach program". EPA.
13. (2015-09-21). "Estimates of solid waste disposal rates and reduction targets for landfill gas emissions". Nature Climate Change.
14. Koch, Wendy. (2010-02-25). "Landfill Projects on the rise". USA Today.
15. Brosseau, J. (1994) Trace gas compound emissions from municipal landfill sanitary sites; Atmospheric-Environment 28 (2), 285-293
16. Christensen, T. H., Cossu, R. & Stegmann, R. (1999) Landfilling of waste: Biogas
17. Williams and Aitkenhead (1991) Lessons from Loscoe: The uncontrolled migration of landfill gas; The Quarterly Journal of Engineering Geology 24 (2), 191-207
18. Kerfoot, H.B., Chapter 3.5 In Christensen, T. H., Cossu, R. & Stegmann, R. (1999)Landfilling of waste: Biogas