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Poster Presentation 3-28
Cellulosic Fuel Ethanol: Alternative Fermentation Process Designs with Wild-type and Recombinant Zymomonas mobilis
Hugh Lawford and Joyce Rousseau
Bio-engineering LaboratoryDepartment of BiochemistryUniversity of TorontoToronto, ON, Canada M5S 1A8
Telephone: (416) 978-7096; Fax: (416) 978-8548; E-mail: hugh.lawford@utoronto.ca
Iogen Corporation of Ottawa, Canada, is a major manufacturer of industrial cellulase and hemicellulase enzymes for the textile, pulp and paper, and poultry feed industries. Iogen has recently constructed a 50-t/d biomass-to-ethanol demonstration plant adjacent to its enzyme production facility. The location of the ethanol demonstration plant offers the advantages that the enzyme can be used without the expenses of stabilization and preservation, and the process sugars can be used for enzyme production. Iogen has partnered with the University of Toronto to test the fermentation performance characteristics of NREL’s metabolically engineered Zymomonas mobilis. Research has recently focused on strain AX101, a genomic integrant that ferments both xylose and arabinose and that lacks the selection marker gene for Tc resistance. The “Iogen Process” for biomass depolymerization consists of a dilute sulphuric acid catalyzed steam explosion, followed by enzymatic hydrolysis. The idiosyncrasies of various SHF design options impact on the selection of the biocatalyst(s). The purpose of this work was to explore the suitability of both wild-type and recombinant Zymomonas for 3 different process designs options: (a) C5/C6 cofermentation of total hydrolysate, (b) C6 fermentation only of total hydrolysate (with alternative use for C5 sugars), or (c) separate fermentations of hemicellulose and cellulose hydrolysates. Since acetic acid represents a major limiting factor to high performance pentose fermentation, a prehydrolysate conditioning unit would be required to reduce the acetic acid to a tolerable limit of about 2.5 g/L (fermentation pH in the range 5-6). For single-stage continuous fermentations of C6 in total hydrolysate or cellulose hydrolysates (6-10% glucose), wild-type Zymomonas exhibited a 4-fold higher volumetric productivity compared to an industrial yeast.
This work was funded through subcontract ZDH-9-29009-02 to the University of Toronto from the National Renewable Energy Laboratory. This subcontract was a cost-shared project with Iogen Corp.(Canada).
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