Kinetic Modeling of Microbial Inactivation by Ultraviolet Light
Severin, Blaine Frank
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Permalink
https://hdl.handle.net/2142/77326
Description
Title
Kinetic Modeling of Microbial Inactivation by Ultraviolet Light
Author(s)
Severin, Blaine Frank
Issue Date
1982
Department of Study
Civil and Environmental Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
Ultraviolet (UV) light reactors are currently being designed for the disinfection of water and wastewater. However, little information is available relating the effects of mixing, light intensity, reaction time, and water quality to UV disinfection efficiency. This study was designed to develop information on the effects of these variables on disinfection efficiency.
The inactivation of Escherichia coli bacterial virus f2, and Candida parapsilosis was studied in a close-batch reactor and in a completely mixed, flow-through, annular reactor. The UV absorbance of the test waters used in the flow-through reactor was varied over a wide range by the addition of a UV attenuating agent. In batch studies, the order of resistance to UV was f2 virus > C. parapsilosis > E. coli. In the completely mixed reactor, the order was C. parapsilosis > f2 virus > E. coli. This inversion was attributed to the initial resistance of C. parapsilosis and its expression in a completely mixed reactor. Mixed second-order kinetics were unable to fit the batch data or to predict the completely mixed reactor results for yeast and the bacterium. Both multi-target kinetics and series-event kinetics predicted the inactivation of all three organisms in the completely mixed reactor using kinetic parameters developed from batch data.
The degree of mixing affected the efficiency of the flow-through reactor. Two mixing conditions were tested. One of these mixing conditions yielded a more poorly mixed reactor than the other. However, in the poorly mixed condition, dye tracer studies indicated complete mixing, and in waters with low UV absorbance, the inactivation of E. coli and f2 virus was respectively, 200 and 10 times greater than predicted for a completely mixed reactor. With rapid reactions, dye tracer studies are inadequate as a sole indicator of the mixing regime. Series-event kinetics were extended to include theoretical mixing regimes which could qualitatively describe these results.
Many of the mathematical equations describing UV inactivation kinetics can be expressed as functions of the average light intensity. Two intensity models were compared theoretically; a radial approximation of the infinite lamp model and the finite lamp model. The mathematically simpler, infinite lamp model gives a conservative value of the average light intensity for most reactor designs.
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