Effect of single and combined exposures to UV-C and UV-A LEDs on the inactivation of Klebsiella pneumoniae and Escherichia coli in water disinfection

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.

Comparison of Legionella pneumophila and Pseudomonas fluorescens Quantification Methods for Assessing UV LED Disinfection

“…The current standard wavelength for UV treatment is 254 nm. However, new information indicates that wavelengths closer to 280 nm (UVC) hold promise as a reliable and energy-efficient option for water disinfection. , Additionally, debates persist regarding wavelengths >315 nm (UVA), which have the potential to inflict irreparable damage to DNA, proteins, and repair enzymes, thereby impeding photoreactivation mechanisms. , These emerging findings underscore the necessity of exploring alternative wavelengths beyond the conventional 254 nm. ,, …”

“…25,26 These emerging findings underscore the necessity of exploring alternative wavelengths beyond the conventional 254 nm. 20,27,28 There is limited literature examining the use of UV LEDs for inactivating planktonic and biofilm-associated pathogens. 21 Consequently, it is crucial to enhance our understanding of biofilm formation in water distribution systems when using UV LEDs as a treatment method.…”

UV C Light from a Light-Emitting Diode at 275 Nanometers Shortens Wound Healing Time in Bacterium- and Fungus-Infected Skin in Mice

“…UV C (UVC) light within the range of 200 to 280 nm is in widespread use for disinfection of water ( 23 – 25 ), food processing ( 26 ), and air disinfection of hospitals, laboratories, and daily life ( 27 ). It is one of the most common techniques for inactivating pathogenic microorganisms ( 28 ).…”