The lowly domesticated cow has come in for quite a bit of stick in the global warming debate over time. Being ruminants, they chew cud and partially digest it, before regurgitating and re-chewing it, producing a fair amount of wind in the process. The partially digested material resides in one of the four stomachs – the rumen – where a reservoir of bacteria reacts with the cellulose-rich food matter and produce methane.


A single dairy cow has been estimated to produce up to 500 litres of gas a day, mostly by burping, and the UK’s cows and sheep have been blamed for up to 30% of our methane emissions. Since methane is 23 times more damaging to the environment than carbon dioxide, this as a problem that can’t just be pooh-poohed.

Now a group of researchers at Ohio State University have come up with a method using the cows’ unsociable habits to generate electricity. Hamid Rismani-Yazdi and Ann Christy announced their results at the American Chemical Society meeting in Boston on August 21st.

In one experiment, they extracted the microbe-rich fluid directly from the rumen of live cows, and mixed it with cellulose to make a fuel cell that produced about 600 milliVolts. Each cell used about half a litre of rumen fluid, and two of them would be able to recharge an AA sized battery.

Although the output is small, the ultimate aim is to use not the rumen fluid, but cow manure, to generate electricity, since both undigested cellulose and the rumen bacteria are present in manure. Although the methane from cow manure has been used previously to produce electricity, it has involved burning the gas, and the combustion equipment needed is expensive and inefficient.


At another meeting in Washington DC, just 10 days later, they were able to beef up their claims. Using the manure itself, the team and a group of undergraduates was able to construct fuel cells producing 300 to 400 mV each, and was sustained for over 30 days without a drop in output. In principal, the cells will produce electricity for as long as the reacting components are present – and the cows keep on producing it. “The hope is that one day livestock farmers could use their farm’s livestock waste lagoon as a huge fuel cell and generate enough power for their operation,” Rismani-Yazdi said.

What I find particularly exciting about this idea is that sheep and cattle are farmed all over the world, and so there is potential for cheap electricity generation for developing nations. As Christy pointed out, “Both studies suggest that cow waste is a promising fuel source. It’s cheap and plentiful, and it may someday be a useful source of sustainable energy in developing parts of the world.”




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