(150a) Ethanologens Vs. Acetogens: Environmental Impacts of Two Bioethanol Fermentation Pathways

Ethanologens vs. Acetogens:  Environmental impacts of two bioethanol
fermentation pathways.


Bioconversion production of bioethanol from cellulosic
feedstock is generally proposed to use direct fermentation of sugars to
ethanol.  Another potential route for
ethanol production is fermentation of sugars to acetic acid followed by hydrogenation
to convert the acetic acid into ethanol. 
The advantage of the acetogen pathway is an increased ethanol yield;
however, using an acetogen requires the additional hydrogenation, which could
substantially affect the life cycle global warming potential of the
process.  Assuming a poplar feedstock, a
cradle to grave Life cycle assessment (LCA) is used to evaluate the
environmental impacts of an acetogen based fermentation pathway.  An LCA of a fermentation pathway that uses
ethanologen fermentation is developed for comparison.  It is found that the ethanologen and acetogen
pathways have Global Warming Potentials (GWP) that are
97 % and 50 % lower than the GWP of gasoline, respectively.  When the absolute GWP reduction compared to
gasoline is calculated using a unit of land basis, the benefit of the higher
ethanol yield using the acetogen is observed as the two pathways achieve
similar GWP savings.  The higher ethanol
yield in the acetogen process plays a crucial role in choosing a
lignocellulosic ethanol production method if land is a limited resource.