A BIOLOGICAL REACTOR ENGINEERING STUDY OF A METHYLOTROPH ON MULTIPLE SUBSTRATES

CHINSOO LEE, Purdue University

Abstract

In Part I, the biochemical mechanisms for growth on methanol and formaldehyde of a methanol-utilizing bacterium, L(,3), isolated in our laboratory, were investigated and a steady state growth model was formulated. In particular, the role of formaldehyde has been closely examined in determining the growth behavior of this bacterium. The model incorporates the induction and repression of key enzyme syntheses by methanol and formaldehyde as well as inhibition of enzyme activities. Steady state data were obtained using a computer interfaced two-fermentor system for control and data acquisition. Model parameter sensitivities were determined and used effectively in numerical determination of parameters using a sequential fitting of dilution rates, cell concentrations, and cell mass yields in terms of extracellular concentrations of methanol and formaldehyde. In Part II, stability and multiplicity of steady states and oscillations in continuous biological reactors were analyzed. A non-monotonic specific growth rate of this bacterium is responsible for the multiple steady states observed in continuous cultures. Two nontrivial steady states in a fermentor with a sterile feed and three steady states in a fermentor with a nonsterile feed are discussed. The necessary functional forms of (mu) and (sigma) which can lead to limit cycles in a simple continuous stirred tank bioreactor was analyzed using Hopf's bifurcation theorem. Due to a sequence of regulatory enzyme reactions, oscillations of reaction rates appear to be possible. Ineed, dissolved oxygen and carbon dioxide oscillation were observed by varying the dilution rate and the feed formaldehyde concentration to the second reactor in the system of two reactors in series.

Degree

Ph.D.

Subject Area

Chemical engineering

COinS