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Last Updated: Sunday, 24 December 2006, 00:39 GMT
College harnesses cow pat power
Dairy cows
Methane contributes 7% to the UK's global warming gasses
The humble cow pat could become the latest weapon in the fight against global warming.

An agricultural college is using methane from the muck produced by its dairy herd to power its working farm.

The dairy cows at Walford and North Shropshire College are housed for eight months a year and their dung is collected and pumped into a digester.

There it is converted into methane and used to power a generator. This produces enough energy to run the farm.

Adrian Joynt, farm manager at the college's new 2.7m environmentally friendly Harris Centre, said: "Everything that comes out of the back end of an animal goes in [the digester]."

"We actually get enough energy to supply the farm's electricity for a year."

He added: "If you are going to put food in one end of the cow, we have to accept what comes out of the other. It's about what we do with it.

"We can either spread it on the field or we can put it through this digester and get the methane gas out of it."

Methane emissions

Not only does the anaerobic digester produce electricity, it also reduces the amount of methane - which accounts for around 7% of the UK's greenhouse gas emissions - produced by the dairy herd.

There are 2.2 million dairy cows in the UK which, along with sheep, produce a quarter of the UK's methane emissions.

Roger Higman, of green pressure group Friends of the Earth, said: "Anaerobic digestion is a great idea - not least because manure from animals is also a major cause of water pollution."

The digester works by collecting the cows' dung, in liquid form, and pumping it into an airtight tank.

Here it is heated to a temperature of 35C (95F) - the temperature at which methane producing bacteria are made.

The methane produced is then fed into an engine which runs on the gas and is attached to a generator which produces electricity.

The heat produced by the engine is then recycled into the system to heat the cow dung to the required level.

The technology is used at more than 1,000 farms in Germany but only at a handful in the UK.

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