Hot air

Biogas makes better sense Biogas, an ecofriendly alternative to fossil fuels, has been criticised for releasing methane, a greenhouse gas that is 20-25 times worse than carbon dioxide in causing global warming. It was believed that if methane emissions exceed 5 per cent of biogas produced, then the use of fossil fuels would be preferable. But a new study says biogas would be preferable even if it gave off 10-20 per cent methane emissions -- up to four times as high as the earlier estimate.

"This percentage will vary depending on the fossil fuels replaced and the raw materials used (to produce biogas)," says Maria Berglund of the Lund University in Sweden, the author of the study.

She says about half of all biogas is produced from manure. But methane emissions from manure can vary widely -- by as much as 30 per cent. "One should not draw general conclusions about biogas. The environmental impact depends on what raw material is used and what alternative uses are available for that source material," she adds. All forms of waste treatment have environmental impacts, though in varying degree, but this is seldom mentioned in public debate, Berglund points out.