Landfill Gas

Production of landfill gas

Landfill gas is a mixture of gases. It contains 45-60% of methane by volume, with the rest being mainly carbon dioxide and a trace amount of nitrogen, hydrogen, ammonia, sulfur dioxide and carbon monoxide. When municipal solid wastes are deposited in a landfill, the wastes undergo a number of simultaneous biological, physical and chemical processes to give out landfill gas and other compounds. These processes include decomposition in which wastes are decomposed by bacteria under aerobic and anaerobic conditions, and volatilization in which wastes in liquid or solid form are vaporized into gaseous form. The decomposition of wastes in a landfill can be divided into 4 phases with different types of bacterial activities and various landfill gas compositions in each phase. Methane is produced in the third phase by methanogenic bacteria under anaerobic conditions (see figure below).

The rate and volume of landfill gas production are site specific and are determined by the waste characteristics (such as the types and ages of wastes buried in the landfill) and the environmental factors like temperature, moisture, and oxygen availability in the landfill. Field experience has suggested that landfill gas appears within 3 months to 1 year after waste disposition, reaching a peak at 5 to 10 years after the waste is buried, and then tapering off for a period of up to 25 years or more. It is possible for a landfill to give off landfill gas for a total of 30 years or more.