Doctoral Dissertations

Date of Award

12-1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Paul R. Bienkowski

Abstract

Microorganisms are capable of degrading organic compounds into carbon dioxide, water, organic acids and salts. Biocatalytic processes can effectively remove volatile organic compounds in hazardous waste gasses. In these processes, waste gasses are fed to a packed bed reactor and are degraded by bacteria. The purpose of this research was to use a previously developed, membrane-based, radial flow, vapor-phase bioreactor (RFR) for the biodegradation of toluene and trichloroethylene (TCE) from a toluene/TCE/air/water system. Pseudomonas putida TVA8 were immobilized on sand within concentric cylindrical porous metal membranes, which were separated by 0.91 cm in the radial direction. A toluene feed stream was added to induce enzyme production necessary for TCE degradation, and the toluene served as the primary carbon source for the bacteria. The proposed research investigated the possibility of simultaneously degrading both toluene and TCE from a vapor-phase waste stream. The reactor system addressed the mass transfer, charmeling, and scale-up problems associated with conventional packed bed systems. The RFR had a relatively short bed length and a low pressure drop. The radial flow design resulted in a large surface area for contact between the pollutants and the bacteria. The high surface area of the packing increased mass transfer between the bulk vapor and biofilm. Uniform distribution of the feed helped to prevent dry spots and channeling in the bed. Mass transfer rate was determined to be fast relative to the reaction rate for toluene. Between 0 and 30 mg toluene/L in a batch culture, initial toluene degradation rate was a linear function of specific bioluminescence. Specific bioluminescence is also a function of toluene concentration in a batch culture. Because the initial toluene degradation rate is a measure of toluene dioxygenase enzyme activity, a correlation was developed for the functional dependence of enzyme activity on toluene concentration. For both toluene and TCE reaction rates, the competitive-inhibition form of the Michaelis-Menten kinetic expression was modified by adding the correlated enzyme activity parameter. A mathematical model was developed consisting of elemental mass balances on the bulk vapor-phase toluene and TCE. The reaction kinetic equations for both toluene and TCE degradation were based on the modified form of the Michaelis-Menten enzyme kinetics. The transport equations were solved by the finite element method with a Galerkin weak statement formulation. With the added dependence of the enzyme activity on toluene concentration in the reaction kinetic equations, the mathematical model prediction agreed with the experimental data. The proposed model provides a mathematical tool to optimize and to predict the dynamics in a highly nonlinear biological process.

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