Kinetics of Escherichia coli inactivation with ozone
Abstract
The kinetics of Escherichia coli inactivation with ozone were investigated with semi-batch and continuous-flow tubular reactors in solutions buffered with phosphate at pH 6 and 8, temperatures ranging from 5 to 25$\sp\circ$C, and in the presence and absence of radical scavenger tert-butanol (0.01 M). Ozone concentrations and contact times investigated ranged from 6 to 41 $\mu$g/L, and 1.8 to 33 s, respectively. Inactivation kinetics were found to be first order with respect to both ozone concentration and active microorganism density. The overall second order rate constant was found to be 130 L/mg-s at 20$\sp\circ$C. An activation energy of 37,100 J/mol was estimated from observed temperature dependence of experimental inactivation rate constants. A comparison of experimental results corresponding to tests performed at pH 6 and 8, and in the presence and absence of radical scavenger tert-butanol (0.01 M) confirmed that dissolved molecular ozone was primarily responsible for E. coli inactivation in the range of experimental conditions investigated. To elucidate the mechanisms of ozone inactivation further, E. coli were exposed to different ozone concentrations and examined with a transmission electron microscope. Electron micrographs indicated that low ozone concentrations inactivated the microorganisms within seconds, without any discernible signs. However, exposure to high concentrations of ozone resulted in visible changes in the cell structure of E. coli. Ozone decomposition kinetics in the presence of E. coli were investigated in the continuous-flow tubular reactors, and were found to be first order with respect to ozone concentration, subsequent to an initial ozone demand. Ozone decomposition and disinfection kinetics were also examined for waters having high ozone demand by adding humic acids to ozone demand free solutions.
Degree
Ph.D.
Advisors
Marinas, Purdue University.
Subject Area
Civil engineering|Sanitation|Environmental science
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