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Over the last year or so, the promise of biofuels as a clean, renewable source of energy has been overshadowed by growing concerns over the freshwater impacts of large scale biofuel production. Despite these warnings, the National Renewable Fuel Standard program, established in 2007, mandates a four-fold increase in national biofuel production--from 9 billion gallons in 2008 to 36 billion gallons by 2022. While the verdict is still out on the pros and cons biofuels, a mounting body of research suggests that we might want to rethink our lofty biofuel targets.
50 gallons of water per mile. This is the water required to produce the ethanol biofuels needed to drive a car ONE mile, using irrigated corn. This number comes from a recent Environmental Science and Technology (ES&T) journal article by R. Dominguez-Faus, Susan E. Powers, Joel G. Burken, and Pedro J. Alvarez (PDF).
50 gallons per mile. Wow. This is an average value and varies significantly depending on where and how you grow corn or other potential fuel feedstocks. It can be half this value or more than twice as this value, depending on irrigation technology and, especially, climate. But by any measure, it is huge.
Some early assessments of the water implications of biofuels only counted the water needed at the factories themselves and concluded there were no major impacts: according to these early estimates, it takes around 2 to 10 liters (or gallons) of water to make a liter (or gallon) of ethanol. But it turns out that this ignores the biggest water use: the water to grow the corn (or sugar cane or switchgrass or whatever biomass we might use to make ethanol). And that water could otherwise be used to grow food, or to satisfy other water needs.
How does this compare to the water required to produce gasoline? According to Professor Michael Webber at the University of Texas at Austin (in a piece he did for Scientific American in 2008), it takes 0.07 to 0.14 gallons of water to make the gasoline to drive a car one mile. Plug-in hybrids are a bit more water intensive, because you have to count the water to make the electricity too - perhaps 0.25 gallons water per mile. But these pale in comparison to water for biofuels.
The authors of the ES&T study also looked at the implications of the overall national biofuels program. They calculated that if we reach the mandated annual goal of 57 billion liters per year of ethanol (15 billion gallons per year) it would require 44% of the total US corn production (in 2007) and 6 billion cubic meters of water (1.6 trillion gallons, or around 5 million acre-feet) annually - more water than is used for everything in the state of Iowa.
Reinforcing Gleick's summary of the freshwater consequences of large scale biofuel production is a recent study conducted by the Government Accountability Office called Energy and Water: Preliminary Observations on the Links between Water and Biofuels and Electricity Production (PDF):
Corn cultivation for ethanol production can require from 7 to 321 gallons of water per gallon of ethanol produced, depending on where it is grown and how much irrigation is needed. Corn is also a relatively resource-intensive crop, requiring higher rates of fertilizer and pesticides than many other crops. In contrast, little is known about the effects of large-scale cultivation of next generation feedstocks, such as cellulosic crops. Since these feedstocks have not been grown commercially to date, there are little data on the cumulative water, nutrient, and pesticide needs of these crops and on the amount of these crops that could be harvested as a biofuel feedstock without compromising soil and water quality. Uncertainty also exists regarding the water supply impacts of converting cellulosic feedstocks into biofuels.
From an article in the New York Times:
"There are many uncertainties in the energy and water nexus," said Anu Mittal, GAO's director of natural resources and the environment.
In addition to its use for growing crops, water is also needed for biorefining. Current estimates say 1.9 to 5.9 gallons of water are needed to produce a gallon of biofuel from cellulosic feedstocks, the report says.
"Some experts we spoke with said that greater research is needed on how to manage the full water needs of biorefineries and reduce these needs further," the report says. "Similar to current and next generation feedstock cultivation, additional research is also needed to better understand the impact of biorefinery withdrawals on aquifers and to consider potential resource strains when siting these facilities."
In addition to the water quantity issues posed by the massive water demands of increased biofuels production, there are also questions about water quality and contamination. Pollution caused by agricultural runoff is already a major problem in many watersheds. When compared to all other ethanol-producing crops, corn in particular has the greatest application rate of both fertilizers and pesticides per hectare. And there are other concerns as well (from NYT):
Ethanol is highly corrosive and could damage pipelines and storage tanks, which could lead to groundwater contamination, the report says. It recommends an evaluation of the compatibility of higher blend fuels -- such as those containing 15 percent ethanol -- with existing fuel infrastructure.
Algae-derived biofuels' impact on water warrants further research, as well, the report says.
"Algae have the added advantage of being able to use lower-quality water for cultivation, according to experts," the report says. "However, the impact on water supply and water quality will ultimately depend on which cultivation methods are determined to be the most viable."
The information currently available seems to conclude that what little we do know about biofuels is pretty bad from a water perspective (7 to 321 gallons of water per gallon of ethanol!!!), and that there are a large number of unknowns about second-generation biofuels, such as those derived from algae or cellulosic feedstocks such as switchgrass. Due to these uncertainties, policy makers should take a cautionary approach to ramping up biofuel production and freshwater protection groups should pay attention to any policy developments.