Study finds that environmental impact of corn-ethanol E85 is 23% to 33% higher than that of gasoline; environmental problem-shifting
16 March 2012
When 12 different environmental impacts and the regional differences among 19 corn-growing states are taken into consideration, E85 (85% ethanol, 15% gasoline) blends made with corn ethanol from dry mills show a worse total environmental impact than gasoline, according to a new study by a team from the Universities of Minnesota, Troyes (France), and California, Santa Barbara.
In a paper published in the ACS journal Environmental Science & Technology, the authors reported that if the impacts are aggregated using weights developed by the National Institute of Standards and Technology (NIST), overall, E85 generates approximately 6% to 108% (23% on average) greater impact compared with gasoline, depending on where corn is produced, primarily because corn production induces significant eutrophication impacts and requires intensive irrigation. If greenhouse gas (GHG) emissions from indirect land use (iLUC) changes are included in the analysis, the differences increase to between 16% and 118% (33% on average).
Although ... previous studies have followed the general framework of life cycle assessment (LCA), they have focused almost exclusively on quantifying the energy balance and GHG emissions associated with biofuels production. Such a narrow scope in environmental impact contradicts one of the core principles of LCA: whereby the results of an analysis are meant to prevent problem-shifting between different life-cycle stages and among different environmental impact categories. The singular emphasis on energy balance and the carbon footprint neglects numerous other impacts associated with biofuels production including those related to irrigation, fertilizer application, and pesticide use for feedstock growth.
In a similar way, the full breadth of impacts attributable to conventional gasoline production, such as natural resource consumption and hazardous pollutant emissions, must also be considered in order to make balanced comparisons to biofuels. Few studies have endeavored to make such comparisons between gasoline and corn ethanol on the basis of such a comprehensive set of environmental impact categories, with no study in particular including more than a few environmental impact categories and an assessment of their relative importance.—Yang et al.
The new study uses of a life cycle inventory (LCI) database that the team recently compiled under a project funded by the US Department of Agriculture (USDA). The new LCI database covers a wide array of environmental pressures associated with biofuels production including releases of toxic substances and criteria pollutants to air, water, and land; emissions of nutrients that cause eutrophication; consumption of water; and occupation of land.
|Process flow diagrams for E85 and gasoline. Credit: ACS, Yang et al. Click to enlarge.|
For the study, the team compared the suite of environmental impacts attributable to gasoline with that of corn ethanol produced in 2005, including GHG emissions as a consequence of possible indirect land use change (iLUC), as well as measures of the uncertainty associated with the calculations.
In recognition of the impact of local climate, soil, and topography can all have on corn production, they also conducted an LCA of corn ethanol at the state level and for each of 19 corn-growing states surveyed by the USDA.
This full analysis considered feedstock production, shipment of the feedstock to the refinery, refining/conversion, shipment of the fuel to the refueling station, and vehicle operation. For gasoline, the study reflects the US context in which crude oil is to a large extent imported and refined domestically. They used the amount of fuel required to drive 1 km in an average gasoline-powered car and a flexible-fuel vehicle—both as modeled in the Argonne National Laboratory’s Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model.
They found that E85’s heavy impacts on eutrophication, water use, and land occupation outweigh the modest benefits in other impact categories, such as global warming, ecological toxicity, and fossil energy consumption. To check the robustness of the overall conclusion against different choices of weighting factors, they performed a Monte Carlo simulation. The results of that confirmed the general conclusion that gasoline is more favorable than E85. They also applied an alternative allocation method based on substitution, and found that it did not change the overall conclusions either.
Our study seeks to draw attention to the importance of impacts other than climate change in renewable-energy policies, including Energy Independence and Security Act (EISA), that use narrow environmental criteria. A careful evaluation of environmental impacts other than GHG emissions in those policies would be important to minimize the unintended consequences of biofuel development. Particularly, our analysis shows that addressing eutrophication and water consumption impacts is essential in limiting environmental degradation due to biofuel development. Achieving substantial reductions in the nutrient runoff and water consumption associated with biofuel feedstock production are identified as priorities in the effort to mitigate the overall environmental impact of corn ethanol. For this, our analysis indicates that the significant regional variability in eutrophication and water consumption impacts may play an important role in planning future biofuel feedstock production at minimum environmental costs.
...Given the importance of cultivation stage in the total life-cycle impact of corn ethanol, however, the inclusion of other conversion technologies in the analysis will not affect the central message of our study: that replacing gasoline with corn ethanol may result in problem shifting, especially to eutrophication and local water scarcity.
This study highlighted the environmental impacts of corn ethanol in comparison with gasoline. Biofuel policy, however, needs to consider not only the aggregate environmental impacts but also other socio-economic and political issues which were not analyzed in this study. Biofuel’s potentially positive impacts toward, e.g., energy independence, energy security, job creation, and revitalization of rural economy and stabilization of gasoline price, as well as its other adverse impacts toward, e.g., increasing food price, should be duly considered in biofuel policy.—Yang et al.
Yi Yang, Junghan Bae, Junbeum Kim, and Sangwon Suh (2012) Replacing Gasoline with Corn Ethanol Results in Significant Environmental Problem-Shifting. Environmental Science & Technology doi: 10.1021/es203641p
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