November 03, 2008

Ethanol's Water Consumption



The Christian Science Monitor published a story today about water consumption and made some remarks about ethanol and biodiesel which aren't true.

Not surprisingly, while gasoline consumes water at 0.15 gallons per mile, biofuels like ethanol slurp an average of 28 gallons per mile. Biodiesel from soybeans comes in at 8 gallons per mile. Electric cars and plug-in hybrids compare favorably with conventional fossil fuels, consuming a bit more than 0.2 gallons of water per mile. The most watertight combo: electric vehicles recharged through renewable sources of electricity. The study appeared in the Nov. 1 issue of Environmental Science and Technology.


As the quote notes, their information is taken from a recent study. The study looked at irrigated and non-irrigated biofuels. The numbers they quote are for irrigated biofuels.

If ethanol is processed from corn grain in irrigated fields, then water consumption is 1.3−62 gal H2O/mile (average of 28 gal H2O/mile) and withdrawal is 6.9−110 gal H2O/mile (average of 36 gal H2O/mile). Ethanol processed from corn grain from nonirrigated fields results in water consumption and withdrawal intensities of 0.15−0.35 gal H2O/mile and 0.33−0.56 gal H2O/mile, respectively.


Their quoted amount of water consumption for biodiesel is also the number for soy from irrigated fields.

Biodiesel derived from irrigated soybean fields has water consumption of 0.6−24 gal H2O/mile (average of 8 gal H2O/mile) and withdrawal of 1.1−26 gal H2O/mile (average of 10 gal H2O/mile). If the soy fields are not irrigated, then just as with ethanol, the consumption and withdrawal are 2 orders of magnitude less at 0.01−0.02 gal H2O/mile and 0.03−0.12 gal H2O/mile, respectively.


The problem with using the irrigated number is that less than 15% of all corn grown in this country is irrigated. So while a small percentage of the ethanol produced in this country may indeed consume the amount of water they say, the vast majority uses a much smaller amount.

I don't have any numbers on how much of the soy crop is irrigated but I think it is safe to say that not all of it is so assigning the higher irrigated number to all biodiesel would also be less than truthful.

I would have expected better from this organization.

Source : Water Intensity of Transportation

2 comments:

Anonymous said...

Hoot, man, were the idiots in power to condescend to read the handwriting on the wall, those power hungry political types in Washington and elsewhere would sensibly permit the drilling for oil any damned place, excepting areas within 5 to ten miles of highly populated locations, within the territory, land and sea, controlled by the United States. For then, vegan folk, the overall price of food stuffs, especially veggies, would go down again, and we would not only be able to eat cheaper in the U.S., but we would be able to export much more food to feed the hungry of the world, such as those in the poorer, more corruptly ruled nations of Africa and Asia.

mus302 said...

First off who is Hoot and where are the vegan folk you are talking to?

I have no problem with opening up areas to domestic drilling, but since oil is a finite resource the measure should be looked at as nothing more than a temporary fix.

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