cow power

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Waste Not, Watt Not

"The cow is of the bovine ilk;

One end is moo; the other, milk."

If Ogden Nash were writing this poem today, he might want to add a line or

two. In the new millennium, both ends of our bovine friends are under

scrutiny - but for very different reasons. While governments are trying to

figure out how to control cow burping, a significant factor in global

warming, cow manure is gaining popularity as one of Earth's greenest

sources of electricity.

Many United States farmers already know the meaning of "cow power." They

collect the methane given off by fermenting cow manure and use it to

generate electricity. The procedure is relatively simple: manure is stored

in huge tanks - anaerobic digesters - which are deprived of oxygen and kept

at temperatures of 100°F. The conditions are designed to let anaerobic

bacteria thrive and do the work of breaking the manure down. The large

volume of "biogas" released - which contains about 90% methane - is piped

to an engine which burns the gas and uses the heat energy to generate

electricity. The leftover manure is compressed; fluid is drained away and

used as fertilizer; and the solids are dried out and used as bedding for

the herd and compost.

The method offers a neat solution to the manure waste problem. America's

100 million cattle produce their fair share of manure - on Tinedale Farm,

in Milwaukee, the 1800 Holsteins produce about 48,000 pounds per day, much

of which is processed to generate electricity. By using manure in this way,

farmers are transforming problematic waste into new, useable commodities:

electricity, compost, and fertilizer.

According to Environomics, a company that manufactures manure-digesters, 32

farms in the United States are using the digesters for

electricity-generation. The technology has not been more widely adopted

because the systems are expensive to install, costing from $200,000 to

$1,000,000 each, depending on the size of the herd. To encourage farmers to

generate their own electricity, the state of California's Energy Commission

is making $10 million in funding available to support farmers' initiatives.

It is currently reviewing about 30 applications for grants and plans to

install several digesters by this summer.

A Bad Case of Gas

While manure-derived methane is proving very useful, the methane cows burp

is causing problems. Methane is a greenhouse gas and, in the atmosphere,

contributes to global warming. Cows burp an abundant supply of it every day

- about 280 liters per animal (in other words, the average cow could fill

140 two-liter soda bottles with gas daily). Unfortunately, burped methane

is more difficult to collect, with the result that about six million metric

tons of it float blissfully up into the atmosphere every year. And that's

just from herds in the United States. (Worldwide, ruminant livestock -

including cattle, sheep, goats, and buffalo - produces about 80 million

metric tons of methane per year, accounting for 22% of anthropogenic

methane emissions.)

Methane is second only to carbon dioxide in the list of greenhouse gases.

According to the Intergovernmental Panel on Climate Change, it's 21 times

better at trapping heat in the atmosphere than CO2 (a fact that can be

attributed to the larger size of CH4 molecules). The six million tons of

methane that North American cows burp annually are equivalent to 36 million

tons of carbon dioxide.

Why do cows burp so much methane? As with the anaerobic digester, the

answer lies with bacteria. Billions of bacteria are busy at work in the

cow's rumen (the first of the four chambers in its stomach), breaking down

grass and hay in a process known as enteric fermentation. The bacteria -

which live symbiotically in the cow's gut - are essential to its digestive

process. One of the anaerobic bacteria produces large quantities of methane

as a byproduct, which the cow gets rid of by burping.