Edgardo Ortiz Reyes and Robert P. Anex, Department of Biological Systems Engineering, University of Wisconsin-Madison, Madison, WI
Fermentable sugars derived from agricultural production are the raw materials for the production of biofuels and renewable chemicals, and which make a large contribution to the total environmental impacts of biobased products. The prevailing use of fermentable sugars in the production of biofuels and renewable commodity chemicals makes it crucial that different sources of sugars are examined in order to identify alternatives and to improve the environmental performance of bio-based products. Corn is currently the primary source of fermentable sugars in the US, but corn has been criticized for producing significant negative environmental impacts. This study assesses the life cycle greenhouse gas emissions, fossil fuel use and eutrophication potential of non-cellulosic fermentable sugars produced in the US from energycane, sweet sorghum, corn, sugar beet, and compares these with the reference of fermentable sugar produced in Brazil from sugar cane. Energycane is found to result in low environmental impacts relative to other US feedstocks evaluated, and results in environmental impacts similar to Brazilian sugar cane on a per unit product basis. Environmental assessment of the production of fermentable sugars from sugar beet reveals a tradeoff between eutrophication potential and both greenhouse gas emissions and fossil fuel use. Sweet sorghum is found to result in low greenhouse gas emissions and fossil fuel use relative to corn and sugar beet; however, variation in these impacts is greater than that observed for energycane, sugarcane, and corn. We conclude that the US can produce fermentable sugar feedstocks with lower environmental impacts than corn and comparable to those from Brazilian sugar cane. There exist clear trade offs among sugar producing crops in terms of both the size and type of environmental impact.