Life Cycle Assessment of Biofuel Greenhouse Gas Emissions and Net Energy Yields Using the BESS Model.

Standardized life cycle assessment methods to evaluate performance of a given biofuel system are necessary to meet targets for GHG emissions reduction and to ensure environmentally sound industry expansion. The USA Energy Independence and Security Act of 2007 requires that domestically produced biofuels meet GHG reduction targets; other countries are developing similar measures. The Biofuel Energy System Simulator (BESS model, www.bess.unl.edu) was developed to provide a platform for certification of environmental impact of corn-ethanol systems. The BESS model was used to analyze dry-mill ethanol biorefineries under a range of biorefinery designs and crop production conditions. The GHG-intensity of corn production contributed up to 65% of life-cycle GHG emissions depending on biorefinery design, and there is substantial variability in the GHG emissions from crop production depending on state average yields and crop production inputs. Co-products off-set 21-42% of life-cycle GHG emissions by displacing corn and urea in cattle diets, which is the current “best use” for distillers grains. Based on data on energy use in ethanol plants from recent industry surveys and updated values for corn yields and management, corn-ethanol production reduces GHG emissions compared to gasoline by 50% to 62% for natural gas powered dry mill plants, the largest sector of the industry. The BESS model is currently being expanded to analyze the life-cycle of cellulosic ethanol production systems using corn residue or switchgrass, and results will be presented. The energy yields and GHG reduction of these biofuel systems will be compared with other major crop-based biofuel systems from developing countries, including results from a meta-analysis of life-cycle studies. Conclusion from this analysis documents that biofuels have the potential to substantially mitigate GHG emissions and provide energy for developing countries when all direct effects are considered in the LCA.