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Greenhouse gasses from landfill sites could be treated with biofilters to reduce their impact on global warming according to new American research.

As organic matter rots it releases methane. In older landfill sites this gas is released as a small trickle that it is not currently viable to trap and use for biofuel so goes up into the atmosphere, where methane is a major contributor to the greenhouse effect.

Methane has a much greater impact on global warming per amount of gas than carbon dioxide and landfills account for 12% of global anthropogenic methane emissions.

The researchers - Tarek Abichou and Jeffery Chanton of the Florida State University, Jose Morales of Environmental and Geotechnical Specialists, Inc., Tallahassee, Florida and Lei Yuan of Geosyntec Consultants in Columbia, Maryland - tried to find an alternative to just releasing or burning off this gas.

They tested two biofilters which turn methane into carbon dioxide and water by passing methane through bacteria which cause it to oxidise. Radial filters with a high surface area produced the best results. These radial filters oxidised more than 20% of the methane passed through them at an optimum air temperature of 20 to 36 Celsius.

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