Comment▼ Ethanol and water use For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled. —Richard Feynman (1918–1988)
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thanol, as a transportation fuel, is the “stone soup” of energy independence. Everyone wants it to be made from next to nothing. But, unfortunately, some pretty big environmental ingredients are associated with it, and change looms on the horizon. The ethanol produced from corn kernels has some very high inputs of water, energy, pesticides, fertilizers, sediments, and subsidies in its current manifestation— simply much more than stones in your soup. That’s what I learned while chairing the recent National Research Council (NRC) Colloquium on Water Implications of Biofuels Production in the U.S. (www.nas.edu). The colloquium focused mostly on water. But how can you limit yourself to only one aspect when everything is connected? The real world requires integration of all the environmental costs and benefits into a decision, whether it’s acceptable or not. Reality bites. The “public relations” of what’s driving the growth of ethanol is energy independence or, at least, greater energy security. But as American physicist Richard Feynman said, “Nature cannot be fooled.” So how should we measure ethanol’s success? Is our goal simply to produce the cheapest domestic liquid fuel, or should we factor in environmental costs? If so, we should consider sustainability metrics such as the energy obtained per energy invested, per volume of water required, per ton of fertilizer/pesticide/sediment exported, and per ton of greenhouse gases emitted during the entire life cycle of ethanol production. Currently, ethanol doesn’t perform so well on these metrics. Recent literature indicates that the energy return on energy invested is only ~1.3 (Environ. Sci. Technol. 2006, 40 [6], 1744–1750). That is, ethanol’s energy is only 30% greater than the energy required for its production. True, ethanol is a high-quality transportation fuel, but we primarily use a pretty good fuel—natural gas—to produce it. Can’t we do better than that? It takes 3–5 gal of water for every gallon of ethanol produced. So an ethanol facility that makes 100 million gal/yr will use ~400 million gal of water. That’s equivalent to the usage of a small town of 10,000 people. Such water demand is not unusual for manufacturing industries, but it may present a problem for those companies that seek to open a new ethanol production plant if drawdown of aquifers in arid locations or from confined
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strata is an issue. More importantly, irrigated corn consumes >2000 gal of water per gallon of ethanol produced. That’s a huge demand on water resources if the corn is irrigated (at locations where irrigation was not practiced previously). Unsustainable mining of petroleum reserves shouldn’t be replaced with unsustainable mining of water resources unless absolutely no other alternative exists. To grow corn for ethanol, each year, farmers release >1000 kg/km 2 of nitrogen fertilizer into the Mississippi River, contributing to hypoxia in the Gulf of Mexico. This amounts to 8 g of nitrogen (the mass of three pennies) per gallon of ethanol produced. Soil erosion of 5–10 tons per acre per year represents a loss of 20–40 lb of soil for every gallon of ethanol produced. Fill ’er up—with good old midwestern soil! This year, the nation will produce 6 billion gal of biofuels, fulfilling ~4% of U.S. transportation needs. Imagine—the government estimates that if every motorist properly inflated their tires, it would improve gas mileage by 3.3% (www.fueleconomy.gov). That’s almost enough fuel savings each year to match our current ethanol production without any environmental impacts whatsoever. It’s completely renewable—we simply continue to inflate our tires several times each year. Alternatively, suppose the U.S. adopted a modest improvement of 6 mpg in its Corporate Average Fuel Efficiency (CAFE) standards? That would save >35 billion gal/yr of fuel and meet the goal of the U.S. Department of Energy for biofuels by 2017. Isn’t it crazy that we aren’t conserving energy rather than flailing about trying to produce it from grain? Shouldn’t we be emphasizing energy efficiency as the first policy instrument toward energy independence? Somebody has to say this stuff—Richard Feynman is dead. All is not lost. The reality (not the public relations) of why we’re producing so much ethanol from corn is as much due to politics and farm policy and lobbyists and subsidies as it is to energy independence. There will be more efficient, sustainable, and environmentally benign ways to produce transportation fuels in the future. The NRC report shows us where we might be heading.
Jerald L. Schnoor Editor
[email protected] OCTOBER 1, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 6633
