Life cycle environmental impacts of non-cellulosic fermentable carbohydrates for the production of biofuels and chemicals

Fermentable carbohydrates (FC) are raw materials from agriculture common in the production of bio-based products like biofuels and renewable chemicals. The production of these raw materials contribute significantly to the total environmental life cycle impacts of these bio-based products. No study has yet assessed and compared the non-cellulosic FC sources in the USA.

To this aim, the environmental life cycle assessment method was used to compare FC derived from conventional agricultural feedstocks. The study compared four agricultural feedstocks from the USA and one additional feedstock that was used as a reference. The feedstocks from the USA were energycane (a.k.a energy cane), sweet sorghum, maize (a.k.a., corn), and sugar beet. This study used Brazilian sugarcane (BSC) as a reference of low environmental impacts. The environmental impacts assessed were greenhouse gas (GHG) emissions, fossil fuel use, and eutrophication potential. The environmental assessment included a Monte Carlo simulation to assess the uncertainty of the results. A sensitivity analysis was also executed by using the method of changing one variable at a time to identify the most influential input variables.

The assessment showed that FC from energycane has low overall environmental impacts relative to the other US feedstocks evaluated and it resulted in environmental effects similar to those of the BSC. This life cycle assessment shows that US sugar beet has a different impact profile compared to the other feedstocks evaluated; having low eutrophication impact and high in both GHG emissions and fossil fuel use impacts. FC from sweet sorghum has low GHG emissions and fossil fuel use relative to maize (also known as corn) and sugar beet; however, the uncertainty associated with these impacts is greater than that of energycane, sugarcane, and maize.

The assessment shows there are fermentable carbohydrates sources in the USA with lower environmental impacts than the maize feedstock, currently dominant in the USA, and the impacts of the best performing of these are comparable to BSC.