Cow Power - where there's muck there's megawatts

Two Texas-based researchers have calculated that the billion tonnes of manure made annually in the US could be used to cut carbon emissions by 150 million tonnes and supply 3% of the US's electricity needs. And the same sums could also apply in other western countries.

Amanda Cuellar and Michael Webber present their theory in this month's edition of the journal Environmental Research Letters. They point out that most of the manure produced by US livestock farmers currently ends up in lagoons where it is left to rot away. As it does so, apart from producing a health hazard and an unattractive stench, it also belches out powerful greenhouse gases like methane (21 times more powerful than CO2 as a greenhouse agent) and nitrous oxide (310 times more powerful than CO2). Together these are the greenhouse equivalent of pumping out 536 million tonnes of CO2 per year.

The solution, say the researchers, is to feed the manure into "digesters", which break down the organic matter to produce an odour-free sludge that makes good fertiliser, and 'biogas' (methane) that can be collected. This methane can then be burned in gas turbines to produce up to 100 billion kilowatt hours of energy, enough to supply millions of homes and offices. The result is a saving for the planet because although burning the methane produces CO2, the strategy prevents the release of the more potent greenhouse agents.

Furthermore, the electricity produced means that less coal or oil is burned, saving the net equivalent of up to 150 million tonnes of CO2 per year. 'In the light of criticism that has been levelled against biofuels, biogas production from manure has the less controversial benefit of re-using an existing waste source and has the potential to improve the environment,' say the researchers. 'Nonetheless, the logistics of widespread biogas production, including feedstock and digestates transportation, must be determined at the local level to produce the most environmentally advantageous, economical and energy-efficient system.'