Date of Award

1982

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Abstract

Using immobilized microorganisms for ethanol fermentation from biomass has attracted much interest in recent years. Such a system offers unique advantages over traditional fermentation processes, e.g. higher productivities, higher ethanol tolerance, and continuous operation. The goals of this research were as follows: (1) to study the growth behavior of immobilized yeast cells and diffusion characteristics of the support, (2) to develop immobilization technology and improve the physical properties of the support, (3) to develop a generally applicable parameter estimation method for the complex reaction kinetics of immobilized biocatalysts, and (4) to determine ethanol fermentation kinetics using immobilized yeast cells. In intial studies on the immobilization of yeast cells on agar, the formation of an active layer on and near the surface of the support was observed. The thickness of this layer was found to be constant regardless of the size or shape of the support. It was also independent of substrate concentration. Both the growth of cells and the production of carbon dioxide reduced the diffusional resistance of the gel, an indication that the gel network underwent significant structural changes. A new method was developed for treating agar or carrageenan gel with polyacrylamide to form a more rigid support. The size and shape of the gel beads were unaffected by this treatment, but the physical strength was much improved. The productivities achieved for ethanol production were as high as or higher than those reported in the literature. A method was also developed for estimating intrinsic kinetic parameters for reaction systems of immobilized cells and enzymes under the influence of internal and external diffusion resistances. The technique was found generally applicable to any reaction system which follows either Michaelis-Menten kinetics with product and/or substrate inhibition, or any exponential reaction rate expression. The method employs orthogonal collocation into which Powell's nonliner least square minimization algorithm is incorporated. Finally, the above method for kinetic parameter estimation was successfully applied to ethanol fermentation. Statistical analysis showed that Monod's model, both with substrate and product inhibition, and with product inhibition alone, fitted the experimental data.

Pages

275

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