Life cycle assessment of switchgrass-derived ethanol as transport fuel

Background, aim, and scope The increasing gasoline price, the depletion of fossil resources, and the negative environmental consequences of driving with petroleum fuels have driven the development of alternative transport fuels. Bioethanol, which is converted from cellulosic feedstocks, has attracted increasing attention as one such alternative. This study assesses the environmental impact of using ethanol from switchgrass as transport fuel and compares the results with the ones of gasoline to analyze the potential of developing switchgrass ethanol as an environmentally sustainable transport fuel. Methods The standard framework of life cycle assessment from International Standards Organization was followed. To compare the environmental impact of driving with E10 and E85 with gasoline, power to wheels for 1-km driving of a midsize car was defined as the functional unit. The product system consists of all relevant processes, from agriculture of switchgrass, throughout the production of ethanol, blending ethanol with gasoline to produce E85 and E10, to the final vehicle operations. The transport of all products and chemicals is also included in the system boundaries. An allocation based on energy content was applied as a baseline, and market price-based allocation was applied for a sensitivity analysis. Results and discussion With regard to global warming potential, driving with switchgrass ethanol fuels leads to less greenhouse gas (GHG) emissions than gasoline: 65% reduction may be achieved in the case of E85. Except for global warming and resource depletion, driving with ethanol fuels from switchgrass does not offer environmental benefits in the other impact categories compared to gasoline. Switchgrass agriculture is the main contributor to eutrophication, acidification, and toxicity. Emissions from bioethanol production cause a greater impact in photochemical smog formation for ethanol-fueled driving. Conclusions and recommendations Switchgrass ethanol indeed leads to less GHG emissions than gasoline on a life cycle basis; however, the problem has been shifted to other impacts. Improvement of switchgrass yields and development of ethanol production technologies may be the key to lower environmental impact in the future. For a more comprehensive evaluation of using bioethanol as transport fuel, more impact categories need to be included in the life cycle impact assessment. A comparison with bioethanol from other feedstocks, based on similar methodological choices and background data, would provide more insight in the environmental benefits of switchgrass as a feedstock.