Abstract
A simple model was developed to predict the survival behavior of E. coli subjected to UV disinfection in a Taylor-Couette reactor. The model includes the CFD evaluation of the counterrotating toroidal vortices developed within the annular space of two coaxial cylinders. The UV lamp was located within the diameter of the internal rotating cylinder. The residence time of the bacteria near the UV lamp is, therefore, a function of both the size of the vortex and its angular velocity. The effect of angular velocity on the formation of counterrotating toroidal vortices and their impact on the kinetics of UV microbial inactivation was experimentally evaluated. The kinetics of microbial inactivation follow an apparent first-order kinetic equation between 300 and 2000 revolutions per minute. Therefore, in this range of angular velocities, a set of k values (indirectly taking into account the hydrodynamic pattern and UV irradiance) was obtained for a given concentration of bacteria. Then, the set of k values was correlated with the range of angular velocities applied using the polynomial equation. A k value can be obtained for an unknown angular velocity through the polynomial equation. Therefore, a simulation curve of microbial inactivation can be obtained from the first-order kinetic equation. The efficiency of bacteria removal improves depending on the angular velocity applied. A good agreement is observed between the simulation of the survival behavior of the microorganisms subjected to UV disinfection with the experimental data.
Highlights
In recent years, UV light exposure has been recognized as one of the best available options for water treatment [1, 2]
It was observed that E. coli is not resistant to UV irradiation in discontinuous experiments performed in the reactor in the absence/presence of a Taylor-Couette vortex
The formation of counterrotating toroidal vortices within the annular space formed well at ~14 rpm, they have no notable impact on the kinetics of microbial inactivation
Summary
UV light exposure has been recognized as one of the best available options for water treatment [1, 2]. The survival behavior of microorganisms subjected to UV disinfection may obey different kinetic models [4,5,6,7,8,9]. For a long time, it was documented that, under certain experimental conditions, the survival behavior of the microorganisms subjected to UV disinfection may obey a simple exponential curve [10]. In the absence of shoulder effects or in the case that they can be ignored, the UV inactivation of microorganisms can be fitted to a first-order decay rate [4, 8, 11]: LogðNt/NÞ = −k UVdose, ð1Þ where N is the initial microbial concentration, Nt is the microbial concentration after contact time t, UVdose is International Journal of Photoenergy the fluence (mW s cm-2), and k is the inactivation rate constant (cm mW-1 s-1). Equation (1) looks simple, the prediction/modeling of a practical microorganism inactivation behavior based in such equation is a challenging task.
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