Integrated processing of sugar beets at the lab and pilot scale for bioethanol and biogas production

As an extremely efficient, high-yielding industrial crop, sugar beets have the potential to supplement growing demands for renewable and advanced biofuels in the very near term.  A non-traditional approach employing enzymatic liquefaction and fermentation of whole sugar beets for bioethanol combined with anaerobic digestion of stillage was developed and tested in the lab at 1-5 L bioreactor scales.  A pilot demonstration of this process was conducted at the UC Davis Biogas Energy Project facility using approximately 40 tons of beets grown and harvested on campus.  To achieve rapid scale-up objectives, low severity pretreatment, readily available process equipment, commercial enzymes, industrial unmodified S. cerevisiea and minimal fermentation controls were employed. Triplicate 5-ton batch SSF fermentations averaged 0.36 gram-ethanol per gram-initial total solids, which was approximately 90% of that achieved in the lab under similar conditions.  Biogas production from stillage at both lab and pilot operations indicate specific biogas production rates over 350ml CH₄/gVS are achievable and could be sufficient to offset a majority of facility fuel requirements at industrial scale. These results indicate the new beet to ethanol and biogas conversion system is simple and robust and encourage continuing research into process refinements and evaluation of economic and environmental parameters at the demonstration and commercial scale.