14-04: Comparison of ethanol production in high solids SSF of SPORL and dilute acid pretreated aspen

            Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses (SPORL) has demonstrated robust performance for bioconversion of woody biomass to sugars and ethanol, especially for softwoods.  Dilute acid (DA) pretreatment is the most studied process for biomass conversion.  The advantages of SPORL over DA are obvious when applied to softwoods.  To demonstrate the minimum advantages of SPORL over DA, a low recalcitrant feedstock, a native aspen, Populus tremuloides, was used.  It was found that SPORL produced only about 10% more ethanol than DA when simultaneous enzymatic saccharification and fermentation (SSF) was conducted at solids loading of 10%.  High solids SSF using SPORL and DA pretreated native aspen were compared in this presentation.  Two substrates were produced at 170 °C with a liquid to oven dry wood ratio of 3 at acid charge on wood of 1.11%. Sodium bisulfite charge on wood was 0 for DA and 3.0% for SPORL.  The study first evaluated the effect of wet pressing-induced fiber hornification on enzymatic digestibilities of the SPORL and DA substrates. Wet-pressing is needed to produce substrates for high solids experiments.  Preliminary results indicate that the SPORL substrate produced significantly more ethanol of about 25% than that from the DA substrate.  SPORL also reduced mixing energy consumption for high solids saccharification.  The effect of solids loading on ethanol yield and entire mass and energy balance comparison will be presented.  The effects of wet-pressing and pretreatment on cellulose accessibility (measured by cellulase adsorption) along with physical and chemical properties of the two substrates will be presented to explain the difference in ethanol productivity.