In the mid-February 2010 edition of Farm Industry News (page 24), I reported that ethanol is not a water hog. The short article noted that as production technology has advanced, ethanol plants now use an average of less than four gallons of water to produce a gallon of ethanol, down from about 10 gallons of water need to produce the same amount of ethanol a decade ago.
The article also pointed out that it can take from three to five gallons of water to produce a gallon of gasoline, depending on where conventional oil is sourced.
Just this week, POET, the Sioux Falls, SD-based ethanol producer, announced its plants to decrease water consumption in the production of ethanol by 22 percent in the next five years. POET figures that if successful, it will reduce its water consumption from an average of three gallons to 2.33 gallons to produce each gallon of ethanol. “We have seen tremendous efficiency gains in the 22 years I’ve been in this business, but we can and will continue to do better,” said Jeff Broin, POET CEO this week.
POET reports that the reductions will come from the Total Water Recovery Process that it has installed already in three of its ethanol facilities. These facilities (in Bingham Lake, Minn.; Caro, Mich.; and Hudson, S.D.) now average two to 2.5 gallons of water to produce a gallon of ethanol. At both the Caro and Hudson plants, the company has eliminated wastewater discharge by installing the Total Water Recovery system. The system, which filters and recycles water, saves the Caro plant and the city of Caro more than 118,000 gallons of discharged water per day. It saves the Hudson plant and surrounding community more than 108,000 gallons of discharged water per day.
What’s more, water leaving these plants is limited to process steam and water in the ethanol producer’s Dakota Gold dried distillers grains.
Looking at Irrigation
POET also reports that it will be surveying its feedstock producers to determine how much of their crops are irrigated.
Sangwon Suh, assistant professor, Bioproducts/Biosystems Engineering, University of Minnesota, says the water issue takes on greater significance in areas where crops are irrigated. He 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 .