Ph.D. Candidate in BSE
Enzymatic Liquefaction of Sugar Beets as a Feedstock for Biofuel Production
Sugar beets are high yielding plants that produce large quantities of fermentable sugars and offer opportunities for development as a non-food biofuel feedstock. In California, beet ethanol potential of 10,200 L/ha can be supplemented by another 1,400 L/ha with structural components such as cellulose, hemicellulose, and pectin. Beets have a high capacity to entrain liquids which can cause material handling difficulties. Enzymatic liquefaction results in the reduction of viscosity through liberation of water and facilitates improved mixing, pumping, and heating, as well as additional solubilization of components for potential conversion. This research develops and evaluates the technical aspects of a unique liquefied sugar beet based biorefinery concept.
Several methods were used for assessing liquefaction and hydrolysis including a penetrometer method, centrifugation assays, and rotational viscometry. Cellulase and pectinase loadings showed direct correlation with increased liquefaction and ethanol production, as did thermal and freeze-thaw pretreatments. An optimized enzyme developed for beet liquefaction, tested at similar protein loadings, performed significantly better than other enzymes with un-pretreated beets. Thermal pretreatment at 121 °C for 20 minutes, or an order of magnitude increased enzyme loading, was needed to see similar performance with the other enzymes.
Simultaneous Saccharification and Fermentation (SSF) experiments were also conducted at flask, bioreactor, and pilot scale. Bench and pilot scale (5 metric ton, wet) experiments with ground beets at 20-24% total solids achieved maximum ethanol yields of 0.43 g/g TS. Anaerobic digestion of stillage at pilot scale also achieved 87% of theoretical biogas production.
A technical and economic analysis was conducted for a facility designed to produce 3,785 m3/yr (1 million gallons/yr) with a Minimum Ethanol Selling Price (MESP) of $1.08/L needed for a positive net-present-value. Feedstock costs are 40% of production costs and enzymes are a significant operating cost ($0.12/L-ethanol). Enzyme usage reduces processing water input and facilitates production of an additional 6.5% ethanol from lignocellulosic origin. Produced biogas offsets 78% of facility thermal energy demand and allows a calculated net-energy ratio of 9.1. Alternative process configurations were also evaluated.
Cookies and coffee will be served.
2045 Bainer Hall University of California Davis