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Landfill gas utilization


Landfill gas utilization is a process of gathering, processing, and treating the methane gas emitted from decomposing garbage to produce electricity, heat, fuels, and various chemical compounds. The number of landfill gas projects, which convert the gas into power, went from 399 in 2005 to 519 in 2009 in the United Kingdom, according to the Environment 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. These projects power homes, buildings, and vehicles.

Landfill gas (LFG) is generated through the degradation of municipal solid waste (MSW) and other biodegradable waste, by microorganisms. Aerobic conditions, presence of oxygen, leads to predominately CO2 emissions. In anaerobic conditions, as is typical of landfills, methane and CO2 are produced in a ratio of 60:40. Methane (CH
4
) is the important component of landfill gas as it has a calorific value of 33.95 MJ/Nm^3 which gives rise to energy generation benefits. The amount of methane that is produced varies significantly based on composition of the waste. Most of the methane produced in MSW landfills is derived from food waste, composite paper, and corrugated cardboard which comprise 19.4 ± 5.5%, 21.9 ± 5.2%, and 20.9 ± 7.1% respectively on average of MSW landfills in the United States. The rate of landfill gas production varies with the age of the landfill. There are 4 common phases that a section of a MSW landfill undergoes after placement. Typically, in a large landfill, different areas of the site will be at different stages simultaneously. The landfill gas production rate will reach a maximum at around 5 years and start to decline. Landfill gas follows first-order kinetic decay after decline begins with a k-value ranging 0.02 yr-1 for arid conditions and 0.065 yr-1 for wet conditions. Landfill Methane Outreach Program (LMOP) provides first order decay model to aid in the determination of landfill gas production named LandGEM (Landfill Gas Emissions Model). Typically, gas extraction rates from a municipal solid waste (MSW) landfill range from 25 to 10000 m³/h where Landfill sites typically range from 100,000 m³ to 10 million m³. MSW landfill gas typically has roughly 45 to 60% methane and 40 to 60% carbon dioxide, depending on the amount of air introduced to the site through active gas extraction. There are many other minor components that comprises roughly 1% which includes H
2
S
, NO
x
, SO
2
, CO, non-methane volatile organic compounds (NMVOCs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), etc. All of the aforementioned agents are harmful to human health at high doses.


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