Hybrid Thermochemical/Biological Processing: The economic hurdles and opportunities for biofuel production from bio-oil

Hybrid thermochemical/biological processing, the integration of thermochemical conversion of biomass and subsequent biological conversion into fuels and chemicals, represents a new frontier in biofuel production. Thermochemical conversion can deconstruct a wide range biomass, producing significant amounts levoglucosan, a potential biofuel feedstock.  However, utilization of levoglucosan faces significant challenges, as levoglucosan is not naturally fermentable to biofuels by any known microorganisms and bio-oil harbors a variety of microbial inhibitors.  As research pursues development of engineered microbes and communities that can utilize levoglucosan in the presence of these inhibitors, the economic opportunities for processing levoglucosan to biofuels must be assessed. An economic study was conducted to evaluate the production of several target biofuels, including ethanol, hydrogen, and methane, from fermentation of levoglucosan. Ethanol production by Saccharomyces cerevisiae was considered, while hydrogen and methane were assumed to be produced by cultures of hydrogenogenic and methanogenic bacterial communities, respectively. Ethanol production represented a lower minimum selling price (MSP) per gigajoule (GJ) of energy produced, but represented a higher capital cost. Methane production represented the minimum capital cost per GJ produced. A challenging aspect of using communities for conversion to fuels was the yield of fuel produced. Analysis indicates that there are opportunities to enhance the economic viability of gaseous biofuel production from levoglucosan by improving yield, potentially through engineering of microbial communities optimized for direct levoglucosan fermentation and tolerance of bio-oil inhibitors. This would combine a lower cost of entry while maintaining a similar MSP GJ^-1 for gaseous biofuel production compared to ethanol production.