The GAO says it requires bewteen 7 and 321 gallons of water per gallon of corn ethanol, but when it comes to second generation biofuels, we have very little good data. Photo: Don O'Brian via flickr
By this point, the water intensity of using first generation feedstocks such as corn to make biofuels is pretty well known. Though it does vary from region to region, it requires a lot of water to make a little ethanol. What's less known and what needs much more study, a new report from the Government Accountability Office says, is the water intensity of second-generation biofuels such as cellulosic ethanol and biodiesel made from algae. Cellulosic Biofuel Water Impact Not Known at Commercial Scale
"Energy & Water: Preliminary Observations on the Links between Water and Biofuels and Electricity Production" says that, due to their newness, second-gen biofuels' water requirements when these are produced at a commercial scale. We simply don't know the cumulative effect of water, fertilizer and pesticide usage of these fuels, nor how much could be produced without negatively impacting water and soil quality.
Furthermore, while water intensity at the refining stage has been declining—the report says the current average is about 3 gallons of water per gallon of ethanol is used during refining—we simply don't know the situation with large scale refining of cellulosic biofuels.
Even Less Known About Algae Water Impact
On algae biofuels, the GAO says even less is known about their impact on water quality than cellulosic feedstocks. The report points out that though lower quality water can be used for cultivation, the overall impact on water quality and quantity is simply not fully known.
At Least We Know We Don't Know
I never thought I'd ever write this, but I wish Donald Rumsfeld was still kicking around to give us one of his pithy, quasi-poetic utterances on this matter. The gist of this report seems to be that when it comes to second-generation biofuels and water intensity, we're dealing with a lot of unknowns, but now at least they're known unknowns.
More: "Energy & Water: Preliminary Observations on the Links between Water and Biofuels and Electricity Production"
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