Lew P. Christopher
Director and Professor
Center for Bioprocessing Research & Development
Department of Civil and Environmental Engineering
South Dakota School of Mines & Technology
Rapid City 57701, SD
Sustainable biofuels production is presented through utilization of renewable lignocellulosic biomass such as bioenergy crops (switchgrass, SWG and prairie cordgrass, PCG) and biomass waste including agri-waste (corn stover) and municipal solid waste (MSW). SWG is viewed as one of the most promising energy crops for the U.S. conditions and its production is predicted to increase ten-fold within the next ten years. On the other hand, the handling and disposal of MSW is of a growing concern in the U.S. with nearly 5 lb/capita/day. MSW contains approximately 60% of biodegradable material which can be processed biologically. Production of biofuels from biomass would reduce dependence on fossil fuels, enhance energy security and contribute to the effort of preventing global warming and pollution. To date, lignocellulose biodegradation presents one of the major technological challenges to the economics of biofuels production due to the relatively slow hydrolysis of biomass, high enzyme costs, end-product inhibition, time- and temperature-dependant loss of activity, etc. From this perspective, the search for and the discovery of novel thermophilic microorganisms and thermostable enzymes with enhanced capabilities for biomass bioprocessing could greatly assist in the establishment of a cost-efficient and environmentally-benign biomass to biofuels process. To this end, consolidated bioprocessing (CBP), combining several process steps into one, is considered as the ultimate approach to a commercially viable biological conversion of biomass to biofuels and value-added bioproducts. The advantages of employing thermophilic microorganisms and enzymes in lignocellulose bioprocessing include increased reaction/conversion rates due to improved mass transfer rates; improved substrate accessibility resulting in increased yields of fermentable sugars; increased substrate solubility and reduced viscosity of feedstock allowing the use of higher solids loadings; decreased risk of contamination, etc. The use of higher solids loadings, processing temperatures and integration of processing steps has proven beneficial for the significant reduction of capital and operating costs of biofuels production. Novel thermophilic isolates discovered in the unique environments of the Yellowstone National Park (WY, USA) and the deep subsurface of the former Homestake Mine (SD, USA) have been employed in the production of bioethanol, biohydrogen and biodiesel. Results from thermophilic bioprocessing of different biomass sources will be presented and discussed.