Doctoral Dissertations

Date of Award

3-1986

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Terrence L. Donaldson

Committee Members

Charles D. Scott

Abstract

Experimental and modeling studies were conducted to analyze the dynamic-response behavior of a phenol-oxidizing fixed film. A differential, fluidized-bed bioreactor in a recycle loop with a well-mixed reservoir was used to conduct the unsteady-state experiments. Fresh phenol feed and oxygen were added continuously to the reservoir. With the bioreactor at steady state, a pulse of phenol was added to perturb the system, and the phenol concentration was monitored continuously until steady state was again achieved. The biofilm reaction rate was then calculated using an unsteady-state phenol mass balance.

The experimental dynamics were compared to a dynamic mathematical model based upon diffusion and reaction within the biofilm, liquid mixing, and biofilm growth. Constant-pH experiments could be adequately described using an unstructured, double-Monod kinetic expression with substrate inhibition by phenol. Inclusion of biological structure to account for metabolic regulation phenomena was not necessary.

However, in experiments without pH control, the pH of the liquid phase dropped from 7.0 to 4.5, and damped oscillations were observed in the phenol concentration and reaction rate trajectories. Oscillatory solutions could not be induced in the model, and a linear stability analysis did not reveal any tendencies toward instability or oscillations. The addition of product (pH) inhibition to the reaction kinetics did not produce oscillations. The cause of the experimental oscillations remains unknown.

An active-cell assay technique for biofilms was developed. The method measures electron-transport activity using INT, an organic salt which is reduced to a red dye. The assay procedure involves incubating the biofilm sample with INT, extracting the red product with acetone, and then measuring the optical density of the extract at 490 nm.

The method was found to be quite specific for active biomass. Cells killed with HgCl2 or heat did not react with INT. The assay is not overly sensitive to changes in such process variables as substrate and oxygen concentrations. In addition, it is inexpensive, quick to perform, and requires no highly specialized equipment. It should prove useful in future analyses of biofilm processes.

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