Methane generation in landfills

Methane gas is a by-product of landfilling municipal solid wastes (MSW). Most of the global MSW is dumped in non-regulated landfills and the generated methane is emitted to the atmosphere. Some of the modern regulated landfills attempt to capture and utilize landfill biogas, a renewable energy source, to generate electricity or heat. As of 2001, there were about one thousand landfills collecting landfill biogas worldwide. The landfills that capture biogas in the US collect about 2.6 million tonnes of methane annually, 70% of which is used to generate heat and/or electricity. The landfill gas situation in the US was used to estimate the potential for additional collection and utilization of landfill gas in the US and worldwide. Theoretical and experimental studies indicate that complete anaerobic biodegradation of MSW generates about 200 Nm3 of methane per dry tonne of contained biomass. However, the reported rate of generation of methane in industrial anaerobic digestion reactors ranges from 40 to 80Nm3 per tonne of organic wastes. Several US landfills report capturing as much as 100 Nm3 of methane per ton of MSW landfilled in a given year. These findings led to a conservative estimate of methane generation of about 50Nm3 of methane per ton of MSW landfilled. Therefore, for the estimated global landfilling of 1.5 billion tones annually, the corresponding rate of methane generation at landfills is 75 billion Nm3. Less than 10% of this potential is captured and utilized at this time.