The current Energy Secretary, Steven Chu, is no fan of corn-based ethanol, presumably because a variety of studies have suggested that it takes a significant amount of energy to produce, diluting its impact on carbon emissions. Nevertheless, the Energy Independence and Security Act sets hard targets for ethanol produced from biofuels, and the US has largely met those through corn-based ethanol to date. A study that appeared in the journal Environmental Science & Technology suggests that we should carefully consider how we meet future goals, as different regions in the US require radically different amounts of water to get the ethanol to market.
Past studies have suggested that the cost in water use for ethanol derived from corn might be high—as high as several hundred liters of irrigation water for each liter of ethanol to make it to the pump, with an added 40 liters of water used in the process of converting the corn to ethanol. Still, those estimates were based on models of irrigation use that didn't account for regional variations in use, and relied on evapotranspiration models to estimate the amount of water needed.
The new study avoids these issues by diving down into data that's available from a variety of governmental organizations. These include the Census of Agriculture and the Farm and Ranch Irrigation Survey, made available by the US Department of Agriculture and the US Geological Survey. These provide a state-by-state breakdown of the use of irrigation water, while the USDA has data on the amount of corn produced at the county level.
Crunching the numbers revealed radical differences among the states. Some of the major corn-producing states, like Iowa and Illinois, required very little irrigation to get a liter of ethanol to market (5 and 11 liters, respectively). At the other end of the spectrum, drier states like Colorado and California required staggering amounts: nearly 1,200 liters for Colorado, and a staggering 2,138 for California.
Wednesday, April 15, 2009
Another reason to get rid of taxpayer subsidies for ethanol: wasted water resources.