Biogas

Methanogenic archaea are responsible for all biological sources of methane. Some live in
symbiotic relationships with other life forms, including termites, ruminants, and cultivated crops.
Other sources of methane, the principal component of natural gas, include landfill gas, biogas,
and methane hydrate.When methane-rich gases are produced by the anaerobic decay of non-fossil
organic matter (biomass), these are referred to as biogas (or natural biogas). Sources of biogas
include swamps, marshes, and landfills (see landfill gas), as well as agricultural waste materials
such as sewage sludge and manure by way of anaerobic digesters, in addition to enteric
fermentation,particularly in cattle. Landfill gas is created by decomposition of waste in landfill sites.
Excluding water vapor, about half of landfill gas is methane and most of the rest is carbon dioxide,
with small amounts of nitrogen, oxygen, and hydrogen,and variable trace amounts of hydrogen
sulfide and siloxanes. If the gas is not removed, the pressure may get so high that it works its way
to the surface, causing damage to the landfill structure, unpleasant odor, vegetation die-off, and an
explosion hazard. The gas can be vented to the atmosphere, flared or burned to produce electricity
or heat. Biogas can also be produced by separating organic materials from waste that otherwise
goes to landfills. This method is more efficient than just capturing the landfill gas it produces.
Anaerobic lagoons produce biogas from manure, while biogas reactors can be used for manure
or plant parts. Like landfill gas, biogas is mostly methane and carbon dioxide,  with small amounts
of nitrogen, oxygen and hydrogen. However, with the exception of pesticides, there are usually
lower levels of contaminants.

Landfill gas cannot be distributed through utility natural gas pipelines unless it is cleaned up to
less than 3 per cent CO2, and a few parts per million H2S, because CO2 and H2S corrode the
pipelines.The presence of CO2 will lower the energy level of the gas below requirements for the
pipeline.[clarification needed] Siloxanes in the gas will form deposits in gas burners and need
to be removed prior to entry into any gas distribution or transmission system. Consequently it
 may be more economical to burn the gas on site or within a short distance of the landfill using
a dedicated pipeline. Water vapor is often removed, even if the gas is burned on site. If low
temperatures condense water out of the gas, siloxanes can be lowered as well because they
tend to condense out with the water vapor. Other non-methane components may also be removed
to meet emission standards, to prevent fouling of the equipment or for environmental
considerations. Co-firing landfill gas with natural gas improves combustion, which lowers emissions.

Biogas, and especially landfill gas, are already used in some areas, but their use could be
greatly expanded. Experimental systems were being proposed[when?] for use in parts of
Hertfordshire, UK, and Lyon in France.[citation needed] Using materials that would otherwise
generate no income, or even cost money to get rid of,improves the profitability and energy balance
 of biogas production. Gas generated in sewage treatment plants is commonly used to generate
 electricity. For example,the Hyperion sewage plant in Los Angeles burns 8 million cubic feet
(230,000 m3) of gas per day to generate power  New York City utilizes gas to run equipment in
the sewage plants, to generate electricity, and in boilers. Using sewage gas to make electricity is
not limited to large cities. The city of Bakersfield, California, uses cogeneration at its sewer plants.
California has 242 sewage wastewater treatment plants,74 of which have installed anaerobic digesters.
The total biopower generation from the 74 plants is about 66 MW.