Municipal Solid Waste (MSW) Landfill: virtual
tour
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What is landfill gas composed of?
 Landfill gas is composed of a mixture of hundreds of different
gases. By volume, landfill gas typically contains 45% to 60% methane
and 40% to 60% carbon dioxide. Landfill gas also includes small
amounts of nitrogen, oxygen, ammonia, sulfides, hydrogen, carbon
monoxide, and nonmethane organic compounds (NMOCs) such as trichloroethylene,
benzene, and vinyl chloride.
How is landfill gas produced?
Three processes—bacterial decomposition, volatilization,
and chemical reactions—form landfill gas.
Bacterial decomposition
Most landfill gas is produced by bacterial
decomposition, which occurs when organic waste is broken down by
bacteria naturally present in the waste and in the soil used to
cover the landfill. Organic wastes include food, garden waste,
street sweepings, textiles, and wood and paper products. Bacteria
decompose organic waste in four phases, and the composition of
the gas changes during each phase.
 Volatilization
Landfill gases can be created when certain wastes, particularly organic compounds,
change from a liquid or a solid into a vapor. NMOCs in landfill gas may be the
result of volatilization of certain chemicals disposed of in the landfill.
 Chemical
reactions
Landfill gas, including NMOCs, can be created by the reactions
of certain chemicals present in waste. For example, if chlorine
bleach and ammonia come in contact with each other within the landfill,
a harmful gas can be produced.
 The
MSW landfill MACT rule intent is to insure better control of NMOCs
many of which are listed HAPs. NMOCs are organic compounds (i.e.,
compounds that contain carbon). (Methane is an organiccompound
but is not considered an NMOC.) NMOCs may occur naturally or be
formed by synthetic chemical processes. NMOCs most commonly found
in landfills include acrylonitrile, benzene, 1,1-dichloroethane,
1,2-cis dichloroethylene, dichloromethane, carbonyl sulfide, ethyl-benzene,
hexane, methyl ethyl ketone, tetrachloroethylene, toluene, trichloroethylene,
vinyl chloride, and xylenes.
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