Ethanol’s Impacts on Our Water Resources

by Renee Cho | March 21, 2011

This year, global ethanol production will likely reach 23.4 billion gallons with the U.S., the world’s largest ethanol producer, expected to produce over 13.5 billion gallons. Ethanol biofuel can be produced from many feedstocks including corn, sugar cane, sugar beets, sorghum, switchgrass, barley, hemp, potatoes, sweet potatoes, cassava, sunflower, molasses, grain, wheat, straw, and cotton, but 95% of ethanol in the U.S. comes from corn. And corn-based ethanol is controversial because of the amount of land required to grow the crops, and because of its effect on food prices and water resources.

Ethanol production in the U.S. is bolstered by federal mandates, tax credits and a tariff. In 2005, the Energy Policy Act called for 7.5 billion gallons of renewable fuel to be produced annually by 2012. The Energy Independence and Security Act of 2007 upped the ante, requiring 9 billion gallons of renewable fuels to be consumed annually by 2008, and increasing to 36 billion by 2022. 21 billion gallons of the 2022 target must be “advanced biofuel” which are fuels emitting 50% less greenhouse gases than gasoline or diesel, and produced from biomass other than corn—corn ethanol production will be capped at 15 billion gallons per year in 2015.

Ethanol is subsidized by the Volumetric Ethanol Excise Tax Credit, that pays refiners 45 cents a gallon to blend ethanol with gasoline, and a 54-cent per gallon tariff on imported ethanol. Congress extended these incentives at the end of December as part of the bipartisan tax package, but several bills have since been proposed that would eliminate the subsidies, saving taxpayers over $6 billion a year.

Ethanol subsidies have pushed corn prices from $2.37 a bushel in 2002 to $6.66 today, which has resulted in higher food prices worldwide and enticed more farmers into growing corn even on land that is not well suited for it.

The amount of water consumed in ethanol production depends on what crop is used as a biomass, where it is produced, and which technology is used in its processing. 95% of U.S. ethanol production comes from corn grown in the Midwest, which is divided into three regions: Region 5 includes Iowa, Indiana, Illinois, Ohio and Missouri; Region 6 includes Minnesota, Wisconsin and Michigan; and Region 7 includes North and South Dakota, Nebraska and Kansas.

The amount of water it takes to produce ethanol varies according to how much irrigation is needed for the corn, particularly since row crop agriculture for corn is the most water consuming stage of ethanol production. In Ohio, because of sufficient rainfall, only 1% of the corn is irrigated while in Nebraska 72% of the crop is irrigated. It takes 19 gallons of water to produce a bushel of corn in Region 5, 38 gallons in Region 6, and 865 gallons in Region 7. The Baker Institute estimates that producing the corn to meet the ethanol mandate for 2015 will require 2.9 trillion gallons of water.

Most of this irrigation water is drawn from groundwater aquifers in a region that is already water stressed. Conflicts over water allotments have occurred in Kansas and Nebraska, and the Ogallala Aquifer, which lies under the Great Plains and supplies 30% of the nation’s groundwater for irrigation, is in danger of running dry.

Growing corn also requires a great deal of fertilizer, and extensive use of nitrogen fertilizer and pesticides is having severe impacts on water quality now. Fertilizer laden runoff into streams in the Midwest makes its way to the Mississippi River, and eventually contributes to the eutrophication (when algae bloom, then die, depleting the area of oxygen and suffocating plants and animals) in the Gulf of Mexico. In 2010, this dead zone in the Gulf of Mexico was estimated to be almost 8000 square miles and it continues to grow. 2.39 million additional tons of nitrogen fertilizer will be needed to meet the 2015 mandate.

Easily erodible and less productive land set aside by the conservation reserve program, that paid farmers to retire inferior land, is now being pressed back into service due to the lure of high corn prices. This land will likely need additional fertilizer and irrigation to be productive, which will result in more polluted runoff and water consumption.

Although biofuels are promoted because they are said to reduce greenhouse gas emissions, some scientists argue that when the life cycle of ethanol production is compared to that of conventional gasoline, there may be no reduction in greenhouse gas emissions at all. More corn is being planted on more land fertilized with nitrogen, resulting in additional air and water pollution from nitrous oxide, a chemical 300 times more potent than carbon dioxide as a greenhouse gas.

Processing corn to make ethanol requires substantial amounts of water for the grinding, liquefaction, fermentation, separation and drying procedures. Over the last ten years, however, some of the nation’s 200 biorefineries have been able to reduce water use from 6.8 gallons of water per gallon of ethanol to 3 gallons by boosting the efficiency of their equipment. South Dakota based Poet,the world’s largest ethanol producer is aiming to cut its overall water intake by 22% by 2014, and use only 2.33 gallons of water per gallon of ethanol produced. This would reduce its annual water use by 1 billion gallons.

A number of other measures can reduce ethanol’s impacts on water resources. Fertilizer use can be decreased. Runoff can be lessened through contour farming, terraced fields, no-till agriculture, riparian buffers and tile drainage (a system of underground pipes that removes excess water and promotes absorption by plant roots).

What makes most sense, however, is to produce ethanol from crops that are drought tolerant, have high biomass and little need for irrigation. Cellulosic ethanol can be made from perennial grasses, forest wood and crop residue, algae, and municipal waste.

Switchgrass, which is more drought tolerant and protective of soil than corn because it has longer roots, would not necessarily require irrigation, though if grown as a cash crop, farmers might turn to irrigation to increase yields. Without irrigation, switchgrass would use water mainly for processing, and the amount of water would vary with the type of processing technology used.

Argonne, a U.S. Department of Energy laboratory,compared the net amount of water consumed by ethanol production from corn and switchgrass, and by gasoline production. Corn ethanol consumes 10 to 324 gallons of water per gallon of ethanol (the range is due to different irrigation requirements), gasoline consumes 3.4 to 6.6 gallons, and switchgrass consumes 1.9 to 9.8 gallons (the range is due to different production technologies). Detailed data about switchgrass’ water and fertilizer requirements are limited, however, because its technology is not yet ready for commercial production. And as a result, the Environmental Protection Agency has cut its 2011 cellulosic ethanol mandate from 250 million gallons to 6.6 million gallons.

Algae-based ethanol can be grown in the ocean, fresh water, wastewater and even in sewage. ExxonMobil, which is developing algae-based biofuels, claims it would yield 2000 gallons of fuel per acre per year as compared to corn which yields 400 gallons per acre or sugarcane which yields 600-750 gallons. But algae-based ethanol requires more water and energy than corn, canola and switchgrass-based biofuels and would produce more greenhouse gas emissions.

Climate change will likely bring more intense precipitation and droughts, which will mean added stress on our water resources. Since growing energy needs and a 16.5% increase in agricultural water use by 2015 for ethanol production will exacerbate water shortages and conflicts, an understanding of ethanol’s water impacts is key to implementing biofuel policies that are environmentally sustainable.

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