There are generally four factors recognized as delimiting in the study of lignocelluloses for fuel ethanol production, viz., the source of the cellulase-system and its quality characteristics for cellulose hydrolysis, the substrate and pretreatment method, the process for cellulase production and bioreactor design, and the ability of yeast to ferment mixed hexose and pentose sugars. Wheat straw (WS) and T. reesei mutants were used in the study to evaluate the production of cellulase-systems. Hydrolysis of cellulose revealed the superiority of mild NaOH pretreatment over steam explosion for cellulase production with T. reesei MCG 80 and QMY-1. Response surface models were capable of predicting that NaOH could be used for the pretreatment of WS at 4% (w/w) without urea in the fermentation medium to yield optimum filter paper activity (FPA) of 9.9 IU/mL (247 IU/g WS) and beta-glucosidase activity ($ beta$GA) of 6.4 IU/mL (159 IU/g WS) under solid-state fermentation (SSF) conditions. Multiple regression analysis with multiple coefficients of correlation, R, between 0.957 and 0.99 from the experimental data showed close agreement between the cellulase activities (FPA and $ beta$GA) from the experiments and predicted values. / The superiority of SSF over liquid-state fermentation (LSF) in the production of cellulase-systems was also established, and a prototype pan-bioreactor showed good potential for upgrading cellulase production under SSF conditions. The economics of fuel ethanol production was considered in the optimization model that sought to establish threshold cellulase loadings needed to achieve maximum cellulose hydrolysis for fermentation. High substrate concentrations of up to 7.5% were hydrolyzed with cellulase loadings of 24-30 IU/g and fermented by Pichia stipitis to achieve 90-100% conversion into ethanol. / Crude unextracted cellulase yielded over 90% hydrolysis of delignified wheat straw and proved to be better than extracted cellulase and commercial cellulases for the hydrolysis of pure cellulose and pretreated wheat straw. Studies were also conducted to demonstrate the importance of the ratio of $ beta$GA- to FPA in cellulose hydrolysis which showed that ratios closer to one (1), produced more sugars and lowered the cellobiose content in the hydrolysates. It was also shown that the source of the cellulase is important in eliminating the accumulation of cellobiose during hydrolysis as was demonstrated with cellulase from mixed cultures of T. reesei and Aspergillus phoenicis. Higher $ beta$GA from the latter were implicated since A. phoenicis is a good $ beta$-glucosidase producer. / Delignified wheat straw at 5% concentration when subjected to separate hydrolysis and fermentation and simultaneous hydrolysis and fermentation resulted in similar volumetric productivities (g/L/h) of ethanol.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41972 |
| Date | January 1997 |
| Creators | Awafo, Victor Ankang. |
| Contributors | Chahal, D. S. (advisor), Simpson, B. K. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Food Science and Agricultural Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001567332, proquestno: NQ29881, Theses scanned by UMI/ProQuest. |
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