The Water Behind Ethanol
7 May, 2009 01:42 pm
While last year's "food vs. fuel" controversy has largely died down, thanks to lower corn prices, a new study from the University of Minnesota suggests that some ethanol production uses even more water than previously estimated--as much as 2,000 gallons of it for every gallon of ethanol produced in states where crops must be irrigated.
This finding further undermines the environmental benefits of a fuel that saves significant amounts of oil but requires large inputs of natural gas and other fossil fuels, and thus offers only modest greenhouse gas improvements over gasoline.
As with its other environmental liabilities, most of ethanol's water impact occurs upstream of the ethanol plant. Process water for slurrying corn and boiling, fermenting and distilling fuel ethanol only accounted for 3% of the total water consumption analyzed by Chiu, Walseth and Suh in their paper, "Water Embodied in Bioethanol in the United States". They also reported a remarkably wide range for the ratio of total water consumption (irrigation and process) per unit of produced ethanol by state: under 10:1 in Iowa, Kentucky and Ohio, and over 1000:1 in California, Colorado, New Mexico and Wyoming. Fortunately the latter states contributed just 3% of the 2007 ethanol production tallied in the study, resulting in a national average of 142 gallons of water per gallon of ethanol. However, two significant ethanol-producing states, Kansas and Nebraska, accounted for 14% of ethanol production but more than half of all US water consumed for ethanol, with ratios above 500:1. A useful chart in MIT's Technology Review illustrates these variations from state to state.
These findings add to an already daunting list of concerns about the long-term sustainability of an alternative energy policy that has so far relied mainly on biofuel produced from a food crop requiring extremely high inputs of water and natural-gas-derived fertilizer. The water dependency of corn ethanol looks even more unsustainable under various scenarios of climate change, which ironically this fuel is intended to help mitigate. Simply put, if water in the West and Southwest is likely to be in even tighter supply in the future, the last thing we should be doing with it is to divert it to the production of such a water-intensive oil substitute. The urgency of converting biofuel production to cellulosic feedstocks requiring little or no irrigation is high, at least for those states with water:ethanol ratios above the national average, but unfortunately urgency and bigger research budgets don't guarantee making today's demonstration-scale cellulosic ethanol technologies economical at larger scales. Breakthroughs don't arrive on demand.
The results of Chiu, Walseth and Suh provide further support for a thorough reevaluation of US biofuel policies. Rather than trying to squeeze ever more ethanol into gasoline, with uncertain consequences for motorists, and stretching our agricultural resources by expanding unsustainable crop-based biofuels of questionable value for reducing greenhouse gas emissions, the administration should ask the Congress for authority to freeze the conventional ethanol portion of the Renewable Fuel Standard at its current level of 10.5 billion gallons for 2009. That still represents a 9% increase over 2008's consumption of 9.6 billion gallons, which took well over a trillion gallons of water to produce. Further increases should await either economic cellulose-based biofuel, or the imposition of prudent standards limiting the embodied water and fossil-energy content of this fuel. That won't help today's overbuilt ethanol industry, but it would ensure that its survivors enjoy a more viable, sustainable future.
Originally published on Energy Outlook