Landfill Gas

Landfill gas is composed of approximately 50% methane and 50% carbon dioxide and is produced by the decomposition of organic waste under anaerobic conditions. The United States Environmental Protection Agency estimates that there are about 6000 landfills in the U.S., mostly made up of municipal solid waste, that are producing methane. This is the largest source of anthropogenic (man-made) methane emissions in the U.S., and will contribute an estimated 8.8 to 12.7 terragrams (450-650 billion cubic feet) per year in the year 2000.

Aside from environmental concerns of methane emissions and unpleasant odors associated with landfill gas, uncontrolled landfill gas can present a serious explosion hazard. It has been known to migrate underground to adjoining property and be set off by such things as furnace pilot lights. For this reason, Federal regulations require that the gas from large landfills be controlled, usually by the drilling of wells into the landfill and establishing a system of collection pipes to draw the gas out of the landfill. As a result of the slight vacuum used in these collection systems, air may be drawn in adding another contaminant to the methane, particularly in wells near the perimeter of the landfill. Most of this gas is flared, but over the last twenty years an increasing number of landfill operators have found ways to convert a liability into an asset by using landfill gas to produce energy for sale.

Currently there are about 360 landfill gas-to-energy projects in the United States, most of these producing electricity by using the low BTU gas directly as fuel for internal combustion engines or turbines. The development of this technology has been encouraged over the last several years by a tax credit, amounting to about $1 per million BTU, for energy produced from landfill gas. This tax credit expired on June 30, 1998, but a new version was enacted into law in late 2004..

In addition, regulations implemented under the Clean Air Act in March, 1996  require that an estimated many large landfills install gas collection and control systems, which means that at the very least they will have to collect and flare the gas. The EPA estimates that another 600 landfills have the potential to support gas to energy projects. This represents a good opportunity for the use of technology such as GST's Carbo-X process that will enable the economical enrichment of landfill gas to pipeline quality gas without reliance on an off-and-on a tax credit. When air is also present, the Air-X process might also be used to increase the BTU content.

To encourage further utilization of landfill gas for energy, the U.S. Environmental Protection Agency has established the Landfill Methane Outreach Program. ( The stated mission of the program is "To reduce methane emissions from landfills cost-effectively by lowering the barriers to and encouraging development of environmentally and economically beneficial landfill gas-to-energy projects." To this end the EPA is recruiting Allies from industry, utilities and state organizations that have interests in the production, purchase or regulation of landfill gas and landfill-gas-to-energy projects. Gas Separation Technology has enrolled in the LMOP as an Industry Ally.