“There’s too much attention on water usage by ethanol plants,” says Sangwon Suh, assistant professor, Bioproducts/Biosystems Engineering, University of Minnesota. “The bigger elephant is irrigation.” As production technology has advanced and ethanol plants have improved water recycling efforts, it takes an average of less than four gallons of water to produce a gallon of ethanol. This is down from about 10 gallons of water per gallon of ethanol produced a decade ago. Depending on where conventional oil is sourced and the type of recovery method used, it can take from three to five gallons of water to produce a gallon of gasoline. Each gallon of gasoline recovered from oil sands can consume up to eight gallons of water.
The water issue takes on greater significance in areas where crops are irrigated. Suh calculates that when both ethanol process water and irrigation are taken into account, its takes 142 gallons of water to produce a gallon of ethanol. A study conducted by Suh and colleagues at the University of Minnesota highlights the need to promote ethanol development in states with lower irrigation rates. The study, “Water Embodied in Bioethanol in the United States,” was published in the March 10 issue of Environmental Science & Technology (http://pubs.acs.org/doi/full/10.1021/es8031067).
Since irrigation may be used on crops destined for feed grain or other products, it is impossible to assign the precise amount of water consumed only to ethanol. Improved irrigation water management is critical in areas where water is scarce, add the authors of a related study, “Consumptive Water Use in the Production of Ethanol and Petroleum Gasoline.” (M.Wu, M. Mintz, M. Wang and S. Arora, Argonne National Laboratory). The study is available at www.transportation.anl.gov/pdfs/AF/557.pdf.
- By Lynn Grooms