Expanded Life Cycle Assessment of Biofuels: Mass Flows and Greenhouse Gas Emissions During Bioethanol Production From Switchgrass and Sweet Sorghum

EPA Grant Number: FP917326
Title: Expanded Life Cycle Assessment of Biofuels: Mass Flows and Greenhouse Gas Emissions During Bioethanol Production From Switchgrass and Sweet Sorghum
Investigators: Emery, Isaac R
Institution: Purdue University
EPA Project Officer: Zambrana, Jose
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Science & Technology for Sustainability: Green Engineering/Building/Chemical Products & Processes/Materials Development


Ethanol and other biofuels are currently the most promising candidates to replace a large fraction of U.S. gasoline consumption, but producing feedstocks on a large scale raises issues of land use, greenhouse gas emissions and water quality. This project addresses these concerns by developing a methodology for mapping carbon and nitrogen flows during biofuel feedstock production, and assessing the effects of crop storage on the life cycle impacts of biofuels.


Switchgrass and biomass sorghum grown at Purdue University will be stored as bales and silage to generate the data necessary for a life cycle assessment. Controlled laboratory storage experiments will be used to determine direct emission rates of the greenhouse gasses CO2, CH4 and N2O, as well as the effects of temperature and moisture on biomass loss during dry and wet storage. Larger scale, 12-month field storage trials of bales and silage will be conducted to validate laboratory data under realistic storage conditions. Results of these studies will inform a life cycle assessment of ethanol production from switchgrass and biomass sorghum, conducted by modifying the GREET model to accommodate biomass storage.

Expected Results:

Dry matter loss during storage is expected to range from 3 percent to 10 percent at low moisture to 10 percent to 35 percent at high moisture, and 5 percent to 15 percent in silage. Modeling storage at a bioethanol facility will increase substantially the greenhouse gas and water quality impacts of the fuel through a combination of increased production requirements, direct greenhouse gas emissions and changes in feedstock composition during storage. Ensiling of sorghum bagasse is expected to have a greater impact than dry bale storage of switchgrass, but the net impact may be reduced by the high yield and sugar fraction of sweet sorghum. The methodology developed will provide a framework for future research, enabling the assessment of many more scenarios and feedstocks by guiding data collection of storage studies to fit into the life cycle assessment framework.

Potential to Further Environmental / Human Health Protection

Identifying nutrient flows between the field and the fuel production plant is necessary to reduce sources of greenhouse gasses and other pollutants in the biofuel logistics chain, ensure that essential nutrients are recycled to the soil, and to better understand the relationships between crop fertilization, biomass storage and greenhouse gas emissions. Biofuel production cannot be considered sustainable if it contributes substantially to eutrophication or generates greenhouse gas emissions similar to fossil fuels. By identifying areas where losses of nutrients and dry matter are most significant, this research may reveal where “best practices” could greatly reduce the environmental impact of biofuels from agricultural feedstocks.

Supplemental Keywords:

biofuels, biomass storage, greenhouse gases, nitrogen, life cycle assessment, biomass logistics

Progress and Final Reports:

  • 2012
  • 2013
  • Final