Modeling drinking water disinfection in ozone bubble-diffuser contactors
Abstract
Ozone is the most powerful biocide among the chemical disinfectants commonly used for drinking water treatment. Its use generally results in better control of disinfection by-products associated with other disinfectants. However, because of a lack of good understanding about the chemistry of ozone, the hydrodynamics and mass transfer characteristics of ozone contactors, and the inactivation kinetics of target microorganisms, a conservative approach based on the CT concept, the product of disinfectant concentration and contact time, is used for regulatory purposes. The objective of this research was to develop an alternative to the CT approach based on the use of a reliable model for assessing disinfection efficiency in ozone bubble-diffuser contactors. More specific objectives were: (1) development of a mathematical model for assessing disinfection efficiency achieved in ozone contactors; (2) theoretical evaluation of contactor CT and the effect of model parameters on dissolved ozone concentration distribution and inactivation efficiency; (3) evaluation of model with experiments performed with a pilot-scale bubble-diffuser contactor; (4) analysis of experimental data available for full-scale contactors and development of contactor design recommendations. A model based on a combination of continuous flow stirred tank reactor (CSTR) and axial dispersion reactor connected in series were found to provide good representation of ozone residuals and disinfection efficiencies in bubble-diffuser ozone contactors. A CT-lag model for the inactivation of Giardia cyst was also developed to simulate kinetic curves with shoulder-effect. A pilot-scale ozone contactor was used to verify the disinfection model. Experimental methods were developed to measure aqueous ozone concentration profiles, and evaluate the mass-transfer characteristics of the pilot-scale contactor, and to measure ozone decay kinetics in a bench-scale batch reactor. Empirical equations developed in this study for major model parameters were compared with literature values. The model developed was extended to represent the performance of full-scale ozone contactors and verified with experimental results reported in the literature. Ozone contactor configurations currently used were theoretically evaluated with the model.
Degree
Ph.D.
Advisors
Marinas, Purdue University.
Subject Area
Civil engineering|Environmental science|Sanitation|Public health
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