„Landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a landfill.
The waste is covered and mechanically compressed by the weight of the material that is deposited above. This material prevents oxygen exposure thus allowing anaerobic microbes to thrive. This gas builds up and is slowly released into the atmosphere if the site has not been engineered to capture the gas. Landfill gas released in an uncontrolled way can be hazardous since it can become explosive when it escapes from the landfill and mixes with oxygen. The lower explosive limit is 5% methane and the upper is 15% methane.
The methane in landfillgas is 20 times more potent a greenhouse gas than carbon dioxide. Therefore, uncontained landfill gas, which escapes into the atmosphere may significantly contribute to the effects of global warming. In addition, volatile organic compounds (VOCs) in landfill gas contribute to the formation of photochemical smog.”
cited from: Biogas. (2014, August 22). In Wikipedia, The Free Encyclopedia. Retrieved 07:33, September 12, 2014, from http://en.wikipedia.org/w/index.php?title=Biogas&oldid=622298016
With the implementation of the Landfill Ordinance in 2004 a land filling ban on waste with a high content of organic carbon was introduced in Austria. Therefore the formation of landfill gas from the newly deposited waste is rapidly declining.
Gas collection systems are compulsory
On existing landfills a well-directed gas collection pipe system in combination with surface sealing has to be installed so that the remaining emissions become are marginal. The gas capture system consists of collectors, pipes for gathering gas, compressors, an analysing station, pipes for transporting and finally the gas utilization in form of a cogeneration unit and a flare.
Collected gas can be used
Landfills are emitting gas for a period of approximately 20 years. During this time it is possible to use the landfill gas energetically which, of course, is reasonable from a economic point of view.