S77: Fermentation technologies for ethanol production from wheat straw by a recombinant bacterium

Wheat straw, a globally abundant byproduct of wheat production, contains about 70% carbohydrate that could potentially be used as a low cost feedstock for production of fuel ethanol. Typically four process steps are involved in the production of ethanol from any lignocellulosic feedstock – pretreatment, enzymatic hydrolysis, fermentation, and ethanol recovery.  Integration of two or more steps is important for lowering the ethanol production cost from lignocellulose. Moreover, any lignocellulosic biomass, upon enzymatic hydrolysis, generates a mixture of sugars. The utilization of all sugars is important for improving the economics.  In this presentation, we will present our recent research results of separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), batch, fed-batch and continuous fermentation of wheat straw hydrolyzate using a mixed sugar utilizing ethanologenic recombinant bacterium. We will also present our research on biobatement of dilute acid pretreated wheat straw hydrolyzate and a unique way of fermenting non-detoxified hydrolyzate by the recombinant bacterium. Our data demonstrate that SSF offers distinct advantages over SHF with respect to reduction of total time by about 40%.  Also, fed-batch SSF performed better than batch SSF with respect to shortening the time requirement and increase in ethanol yield. We will show that the bacterium can produce above 4% ethanol from pretreated wheat straw which is considered economical for ethanol recovery by distillation.