Landfill gas (LFG) is a complex mix of many different gases created through the action of microorganisms within a landfill. As the putrescible materials in the landfill begins to breakdown, landfill gas production results. When the chemical reactions and microbes act upon the waste. Production rate is directly affected by landfill geometry and by the waste composition. These factors influence the bacterial populations within the landfill, its chemical makeup, entry of moisture, escape of gas and its thermal characteristics.
Landfills are by nature heterogeneous. Within most sites, there is a wide range of biological ecosystems and physical conditions. The heterogeneity and the unclear nature of the contents makes LFG production difficult to calculate and control compared to the standard industrial bioreactors in sewage treatment. The constant production of landfill gas causes the gas’ discharge into the atmosphere. Environmental, security problems and hygiene issues become great concerns emanating from such emissions. Additionally, the risks of fire, explosion, and the contamination of groundwater by organic compounds exist in nearly all landfills.
Gas produced in the landfills must be monitored due to the risk presented by the LFG as some of these gases produced are hazardous. Monitoring techniques have been developed. To measure methane levels and total VOC levels, flame ionization detectors can be used. Monitoring of the surface, the sub-surface as well as the ambient air has to be carried out regularly.
LFG is about 40% to 60% methane and the rest is mostly carbon dioxide. It also contains varying quantity of water vapor, oxygen, nitrogen, hydrogen sulfide and other contaminants that are non-methane organic compounds (NMOCs). These NMCOs typically make up less than 1% of the LFG. Mercury, an inorganic contaminant may also be found in landfill gas.
LFG are managed through
• Boiler (heat making)
• Internal combustion engine (electricity production)
• Gas turbine (electricity production)
• Fuel cell (electricity production)
• Conversion of methane to methyl alcohol
It has been estimated that there are about six thousand landfills in the US alone. Most of these landfills are composed of municipal waste, thus already producing methane. These are principal sources of anthropogenic methane emission in the US contributing to an estimated 460 billion cubic feet of methane each year.
Gases produced from landfills can be collected and be used to generate heat or electricity. Landfill gasification (converting methane gas into power) projects have increased since 2005. They have been very popular because they control energy costs and lessen greenhouse emissions. Waste management uses LFG as its energy source. It can generate enough energy to power 400 thousand homes every day which in effect can offset nearly 2 million tons of coal each year.