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Cow Farts and Beefy Burps
March 16, 2011
Safety is always an important consideration when working in a
laboratory. When I was working in
industrial research, my employer had a very comprehensive safety program, part of which was the requirement for us to document any unusual
experiments and have them vetted by the safety department. In one of my experiments, there was a potential for a small quantity of
hydrogen gas to be released. Would this be an
explosion hazard? My calculation showed that the maximum likely hydrogen release would be only six
STP milliliters per hour.
What does this translate to as an explosion hazard? When hydrogen and
oxygen combine, the reaction releases 59
kcal (247
kJ) per
mole of H
2 consumed. My six milliliters, collected over the course of an hour, is just 2.5 x 10
-4 moles of H
2. This would release only 14.75 calories, or 61.7 Joule. Since
nitrogen gas (the major part of air) has a
heat capacity of 29 Joule/mole-K, this
reaction will cause a fifty degree temperature rise in the volume, or just a 17% increase in
pressure. This doesn't even correct for the initial 6 ml of hydrogen and 3 ml of oxygen consumed in the reaction, which will slightly lower the pressure. I characterized the experiment as having "less explosive potential than a fart."[1]
I've recently posted an
article about cows (Geomagnetic Alignment of Cattle, February 11, 2011). People in our modern culture don't think much about cows, but
domestication of cattle was an important milestone in the development of
civilization. Since I was raised in
Upstate New York, where a lot of
dairy farming takes place, I have one
anecdote about cows.
I would often assist my father in his construction business, and every so often we would be called into a rural area to give an estimate. One farm we visited had a big sign at the front gate with a picture of a cow and the words, "
Registered Holsteins," below it. Rural folk know that
Holstein is a breed of cow. My father, however, was a city boy, and he addressed our potential customer as "Mrs. Holstein."
Drawing of a Holstein Cow by Pearson Scott Foresman,
via Wikimedia Commons)
Just a few days away, March 26, will mark
Earth Hour, the one hour of the year in which we're encouraged to turn off the lights to save energy, but mostly to raise our environmental conscience. I've been turning off unnecessary lights and electrical appliances for years, so I don't plan to participate; but the Earth Hour organizers suggest we do other things,
beyond the hour. The popular
Chinese actress,
Li Bingbing, has pledged to adhere to a
vegetarian diet for a hundred days.[2]
The reason cited for Bingbing's pledge is the energy cost and CO
2 emissions associated with
meat production and distribution. It's estimated that it takes about thirteen pounds of
grain to produce one
pound of
beef.[3] Furthermore, land planted with cereals will produce five times more
protein than grazing land for meat production.[3] As if these reasons are not enough, we need to consider
cow fart-induced global warming.
According to a 2006 research report by the
United Nations,[4] cattle farming is responsible for 18% of
greenhouse gases, which is more than that generated
in toto by transportation. Wrote the senior author of this report,[4]
Livestock are one of the most significant contributors to today’s most serious environmental problems. Urgent action is required to remedy the situation."
Cattle emit large quantities of
methane because of the
methanogenic bacteria in their digestive system; but most of the gas is expelled through
burping, not
flatulence. It breaks down into 95% beefy burps, and just 5% cow farts. Although farm machinery generates CO
2, methane is
about twenty times more potent a greenhouse gas than
carbon dioxide. This is because
blackbody radiation for objects near
room temperature (i.e., the Earth) peaks at about a 10 μm
wavelength, That's near where methane does most of its
absorption, as shown in the figure.[5]
Infrared spectra for carbon dioxide and methane. Methane absorbs more strongly in the radiation range for a room temperature blackbody. (Data from NIST).[5]
Estimates are nice, but scientists demand real data. That's why there have been continued efforts to pin down exact numbers for methane emission by cattle. A recent study in the
Journal of Environmental Quality reviews the cattle methane problem, and it describes instrumentation for accurate measurements.[6-7] Such accurate measurement is important to determine whether changes in the bovine diet can lead to reduced methane emission. Instead of measurements from isolated cattle, this new research used open path
lasers to assess methane emission from a herd of eighteen cattle in a paddock. The measurement yielded a methane production that was about 140 g/animal/day.
Using more expensive feed to control the methane released by cattle might even pay for itself. Methane production can reduce the energy content of feed by up to 12%, which is less energy available to produce meat and
milk.
It might not be as exciting as
sharks with laser beams attached to their heads, but the lead author of the paper says that the laser technique is a "significant advancement in assessing greenhouse gas emissions from the cattle industry."[6]
References:
- Disclaimer - Your experiment may not conform to my model and my calculation. No warranty of correctness is either given or implied. In other words, don't take advice from strangers.
- Earth Hour: from switching off to taking action, Agence France-Presse, March 2, 2011.
- Book Review of Eating by Peter Singer and Jim Mason; Peter Singer interview, BBC News, September 4, 2011.
- Christopher Matthews, "Livestock a major threat to environment-Remedies urgently needed," Food and Agriculture Organization of the United Nations (Rome, November 26, 2006).
- NIST Chemistry WebBook, National Institute of Standards and Technology, Standard Reference Data Program.
- Sara Uttech, "Measuring Methane-Researchers Develops Technique to Measure Methane Gas from Cattle," Press Release, American Society of Agronomy.
- S. M. McGinn, D. Turner, N. Tomkins, E. Charmley, G. Bishop-Hurley and D. Chen, "Methane Emissions from Grazing Cattle Using Point-Source Dispersion," Journal of Environmental Quality, vol. 40, no. 1 (January 2011), pp. 22-27.
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Linked Keywords: Safety; laboratory; Research and Development; industrial research; experiment; hydrogen gas; explosion; standard conditions for temperature and pressure; STP; milliliters; oxygen; kcal; kJ; mole; nitrogen gas; heat capacity; chemical reaction; pressure; domestication of cattle; civilization; Upstate New York; dairy farming; anecdote; Registered Holsteins; Holstein; Pearson Scott Foresman; Wikimedia Commons; Earth Hour; beyond the hour; Chinese; Li Bingbing; vegetarianism; vegetarian diet; meat; cereal; grain; pound; beef; protein; cattle - environmental_impact; global warming; United Nations; greenhouse gas; methane; methanogen; methanogenic bacteria; belching; burping; flatulence; carbon dioxide equivalent; carbon dioxide; blackbody radiation; room temperature; wavelength; absorption; NIST; Journal of Environmental Quality; lasers; milk; Dr. Evil; sharks with laser beams attached to their heads.