UV-LED fluence determination by numerical method for microbial inactivation studies

The Ultraviolet Light-Emitting Diode (UV-LED) is a new UV source suitable for small to mid-size water disinfection units. The design of a UV-LED reactor entails the integration of hydrodynamics, radiation, and kinetics data. The kinetics of microbial inactivation are necessary for UV-LED reactor design and the determination of kinetic rate constants depends on the accuracy of fluence rate measurement. However, there is not an easy way to measure the fluence rate inside a solution. In this study, a computational method is proposed to calculate irradiance and fluence rate based on the LED's relative radiation profile and its radiant power, which are two standard pieces of information available in an LED's datasheet. UV-LED was modeled as a polychromatic point source with a specific radiation profile and the fluence rate was calculated by solving the Radiative Transfer Equation by considering the refraction, reflection, and absorption of the medium. The irradiance and fluence rate predictions on the surface of the water were evaluated successfully by radiometry and actinometry measurements, respectively. The fluence rate imposed by 265-nm UV-LED and 275-nm UV-LED in Petri dishes with internal diameters of 5 cm and 9 cm were measured using biodosimetry with E. coli and MS2, when the UV-LED germicidal factor was obtained by considering the LED emission spectrum and the microorganism action spectra. Biodosimetry experiments using E. coli and MS2 at exposure times over 200 s indicated a close agreement between the simulation and experimental data. Such results are indicating the kinetic rate constants of a microorganism can be estimated without performing kinetic study using the action spectrum of microorganisms. Further, the results showed the proposed method can be applied for fluence rate determination for any LED's radiation profile, LED position, and the experimental apparatus's regardless of the availability of the action spectrum of microorganisms.