Abstract
Abstract A system consisting of one UV-A (365 nm) and two UV-C (265 nm) light-emitting diodes (LEDs) was built to evaluate the effect of single and combined exposures to UV-A and UV-C LEDs on Klebsiella pneumoniae and Escherichia coli inactivation and subsequent reactivation. The dose was measured by actinometry using potassium ferrioxalate. Of laboratory prepared samples, 10 mL were irradiated for 20, 30, 45, 60 and 90 s. Logarithmic inactivation and percentages of photoreactivation and dark repair were calculated. E. coli and K. pneumoniae were reduced by more than 7 and 4 logs, respectively, at a dose of 21.5 mJ cm−2 using UV-C. No positive synergistic effect on the inactivation of the two bacteria was observed when using a simultaneous combination of UV-C and UV-A, probably due to a reactivation of the bacteria in the presence of UV-A light, which was not observed in irradiated samples under an individual exposure of 265 nm. For E. coli under 265 nm, the percentage of photoreactivation amounted to 10%, 3 h after irradiation. The results of this study demonstrated the capacity to inactivate E. coli and K. pneumoniae up to a considerable level and provide information for the application of UV LEDs in point-of-use systems.
Highlights
Ultraviolet light emitted by medium- and low-pressure mercury lamps has been used as a water disinfection mechanism for over 50 years
UV-light-emitting diodes (LEDs) batch system configuration A system was built with two 265 nm UV-C LEDs (KL265-50T-SM-WDM2) and one 365 nm UV-A LED (HYR35X43B365KN-D1) with a maximum optical power of 60 mW at 500 mA and 1,500 mW at 700 mA, respectively. 265 nm LEDs were used because at the time of the study, the LEDs with the highest power on the market in the UV-C range corresponded to this wavelength
The results of this study show that 265 nm LEDs have a great germicidal power on E. coli and K. pneumoniae, reaching a logarithmic inactivation rate greater than 7 and 4 logs, respectively
Summary
Ultraviolet light emitted by medium- and low-pressure mercury lamps has been used as a water disinfection mechanism for over 50 years. Mercury-free and longer-lasting light-emitting diodes (LEDs) have been manufactured with wavelengths in the ultraviolet light range (100–400 nm). Their small size and wide wavelength range make them easy to configure into many different arrays. Several studies have been conducted to assess LED inactivation efficacy and found that this varies according to multiple factors including wavelength, type of microorganism, water quality, fluence rate and system hydraulic conditions (Blatchley et al 2008; Würtele et al 2011). A number of different authors have combined wavelengths to improve inactivation efficacy and eliminate or decrease repair processes by simultaneously or sequentially combining different wavelengths. A number of different authors have combined wavelengths to improve inactivation efficacy and eliminate or decrease repair processes by simultaneously or sequentially combining different wavelengths. Chevremont et al (2012) combined UV-A (365 and 405 nm) and UV-C (254 and 280 nm), finding that there is greater efficiency in microbial inactivation of fecal indicators (mesophilic bacteria, fecal enterococci and fecal coliforms) when used simultaneously than when used separately, a result similar to that of Nakahashi et al (2014), who combined wavelengths of 254 and 365 nm to inactivate Vibrio parahaemolyticus
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