Water Intensity of Corn-Based Ethanol Needs to Include DDGS Credit

by Gouri Shankar Mishra and Sonia Yeh (Ethanol Producer Magazine) Study recalculates water consumption with expanded system boundaries and coproduct credit

Recent studies have estimated the “consumptive water use,” “water embodied,” and “water footprint” of corn-based ethanol in the U.S, with numbers differing by orders of magnitude. Estimates for liters of water used in corn ethanol per vehicle kilometer traveled (VKT) vary from 1.1 to 335 L/VKT for Iowa and from 59 to 214 L/VKT for Nebraska. The major difference among these studies stems from the debate existing in the water life-cycle analysis (LCA) literature on how to handle the crop evapotranspiration needs met through precipitation, also referred to as green water.

While the use of blue water—water from rivers, canals and aquifers—is consistently included by all studies, we believe that estimation and reporting of green water use is very informative.

...When the proper credits are incorporated for the coproducts of corn ethanol production, the resulting water requirements in the LCA are significantly lower than previous estimates. DDGS displaces other animal feeds such as soybean meal and feed corn, and thus precludes the use of water to grow these feed sources.

...Our estimates are based on “average” water requirements of corn. Policymakers should consider “marginal” water requirements, which are likely to be higher than average. As suggested in literature, higher corn prices, as a result of ambitious production mandates in the renewable fuel standards, could lead to expansion in corn production to marginal lands with lower yield potentials. They could also result in intensification of corn cultivation in existing lands, which increases yield in the short run but could lower future yields. Since water intensity is negatively correlated with yield, such expansion and intensification will increase the water intensity of ethanol. Further, corn expansion is occurring disproportionately on land that requires irrigation, which according to our results has higher average total water (green plus blue water) and blue water consumptive intensities. READ MORE