Mathematical Modeling and Scanning Electron Microscopic Study of Biofilm on Adsorptive Media (Orthogonal Collocation Method)
Chang, Huai Ted
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https://hdl.handle.net/2142/69952
Description
Title
Mathematical Modeling and Scanning Electron Microscopic Study of Biofilm on Adsorptive Media (Orthogonal Collocation Method)
Author(s)
Chang, Huai Ted
Issue Date
1985
Department of Study
Civil Engineering
Discipline
Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Abstract
A mathematical model, based on fundamental mechanisms, including film transfer, Monod kinetics, biofilm growth, and shear loss, was derived to describe performance of biofilm attached to an adsorbing surface. The model-BFAC model-has three features: substrate diffuses in a growing biofilm (moving boundary problem); the reaction term is nonlinear; and substrate diffuses in a layered-media. An advanced numerical technique, the Global Orthogonal Collocation Method, was employed to solve the model.
Experiments were conducted using fixed-bed columns with high recycle rates to approximate a completely mixed-flow reactor. The feed solution contained phenol or acetate as sole carbon source. The results indicated that biofilm bioregenerated the activated carbon after the biofilm has grown significantly. As the previously adsorbed substrate was bioregenerated, biofilm growth was enhanced because of the extra supply of the substrate from the activated carbon. The results also showed that irregular GAC, which had a rougher surface than spherical activated carbon and glass beads, provided the best protection for biofilm when the biofilm was thin. However, when the biofilm grew very thick, the biofilm grown on protruding area of the irregular GAC apparently suffered higher loss-rate than the biofilm in the protected crevices.
The BFAC model predicted well the experimental substrate concentrations with coefficients obtained from independent suspended-growth experiments and assumed biofilm thickness, suspended biomass concentration, and shear loss coefficient. The model also predicted the sequence and the rate of the bioregeneration.
Biofilm samples were treated with various preparative techniques in an attempt to reveal the true structure of the biofilm using scanning electron microscope. The techniques evaluated included different fixative compositions and drying techniques. Micrographs showed that the biofilm consisted of bacteria and extracellular materials. Garland's fixative, which contained ruthenium red, preserved the microstructures of the biofilm and stained the biological materials so that the biofilm could be seen with a light microscope. Sandwiching the biofilm samples between membrane filters saved biofilm lost in sample handling for evaluation of the extent of the loss. The surface tension of an evaporating liquid crushed the cells and biofilms when they were air dried.
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