Life Cycle Greenhouse Gas Emissions Fossil Energy Use and Eutrophication

Donal F. Day, Attaway, Denise  |  11/26/2014 2:28:49 AM

Figure 1. Energycane is the fermentable carbohydrate feedstock with the lowest emission of greenhouse gas followed by Brazilian sugarcane, sweet sorghum, corn and sugar beets when allocated by energy and market value.

Figure 2. Energycane has the lowest use of fossil energy for production of fermentable carbohydrates followed by sweet sorghum, corn and sugar beets when allocated by energy. Brazilian sugarcane is slightly lower than energycane followed by sweet sorghum, corn and sugar beets when allocated by market value.

Figure 3. Sugar beets have the lowest freshwater eutrophication potential when allocated by market value and energy. Energycane has the lowest saltwater eutrophication potential with both allocation methods.

The production of biofuels and commodity biochemicals relies mostly on fermentable carbohydrate from agricultural feedstocks. According to several studies, agricultural feedstock used to produce these products usually is a dominant source of environmental impacts (Tokunaga et al., 2014, Cai et la. 2013).

Choosing a low-environmental-impact feedstock for fermentable carbohydrate is an important part of establishing a sustainable biofuels and commodity-renewable chemical industry.

Research, funded by the United States Department of Agriculture’s National Institute of Food and Agriculture, compared the environmental impacts of the sources of easily extractable carbohydrates from energycane, sweet sorghum, sugar beet and corn in the United States, as well as sugarcane from Brazil. Environmental Life Cycle Assessment (LCA) was used to quantify the emissions and resource consumption of production, starting from the production of fertilizer right through to the production of fermentable carbohydrate.

The study found energycane and sweet sorghum have the lowest greenhouse gas emissions of the U.S. feedstocks evaluated. The study also found that energycane and sweet sorghum grown in the Gulf Coast region have similar impacts as Brazilian sugarcane.

Researchers found that coproducts from these feedstocks can significantly reduce the environmental burden of the carbohydrates produced because making more products means less burden per product. Sweet sorghum and energycane have comparable impacts and can be grown under similar conditions. Because of this, these two feedstocks can be processed using existing sugar mills, which can extend usage of the mills, resulting in an increased revenue for mill owners.

In addition, the study found sugar beet has high greenhouse gas emissions and use of fossil fuel. The study also shows sugar beet grown in the Red River Valley has low eutrophication potential per unit of carbohydrate produced. Eutrophication potential is used to assess the possibility that nutrients lost from a production system could eventually result in the depletion of oxygen in lakes, rivers and estuaries, harming aquatic species.

The scenario locations used in this study were the Gulf Coast for the production of energycane and sweet sorghum, the Red River Valley for sugar beet, U.S. Midwest for corn and Brazil for sugarcane (Figure 1). The boundary of the study includes the manufactur of agricultural inputs, agricultural production of the feedstock crop, transportation of feedstock and the production of fermentable carbohydrate (Figure 2). Energycane has the lowest saltwater eutrophication potential with both allocation methods. (Figure 3).

Edgardo Ortiz-Reyes
Robert P. Anex
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