Evaluation of Single-Pass Disinfection Performance of Far-UVC Light on Airborne Microorganisms in Duct Flows

Abstract

Far-UVC irradiation (222 nm) is considered an emerging and sustainable solution for future infection and pandemic challenges. We examined the disinfection performance of a kryptonchloride lamp, with a quasi-monochromatic UVC peak at 222 nm, for inactivating airborne microorganisms in a full-scale ventilation duct system. Single-pass disinfection efficacy of far-UVC was determined and compared with that of a conventional mercury-type UVC (254 nm) lamp. Four bacteria, Escherichia coli (E. coli), Pseudomonas alcaligenes (P. alcaligenes), Serratia marcescens (S. marcescens), and Staphylococcus epidermidis (S. epidermidis), as well as bacteriophage P22, were tested under UV exposure with different velocities of duct flows. The data revealed that as the air velocity increased from 0.7 to 4 m/s, the far-UVC disinfection efficacies would decrease by 42, 47, 35, 39, and 33% for these five microorganisms, respectively. The inactivation rate constants to far-UVC light were 4.9, 7.5, 3.3, 6.3, and 3.0 cm 2 /mJ for aerosolized E. coli, P. alcaligenes, S. marcescens, S. epidermidis, and bacteriophage P22, respectively. Far-UVC irradiation showed a comparable disinfection ability on airborne microorganisms compared with the 254 nm UV irradiation. This first study of far-UVC in real duct applications provides a better understanding of the disinfection performance of this solution in bioaerosol inactivation. It offers a valuable database in the sizing and design of excimer lamps for novel portable air purifiers or induct disinfection units.

Nitrate Protects Microorganisms and Promotes Formation of Toxic Nitrogenous Byproducts during Water Disinfection by Far-UVC Radiation

“…18,29−31 This suggests that Far-UVC may pose higher inactivation efficiency than UVC at 254 nm. This hypothesis is supported by recent publications about inactivation of various pathogens by Far-UVC in aerosol, 15,16,19,20,32 water, 3,13,29,33−42 and on surfaces. 43,44 inactivating bacteriophage Phi6 and human coronavirus 229E in buffered deionized water.…”

“…The UV absorption of DNA/RNA of microorganisms has been reported to be comparable (∼1 fold) at 222–254 nm, but that of proteins is much higher (∼20 fold) at 222 nm. ,− This suggests that Far-UVC may pose higher inactivation efficiency than UVC at 254 nm. This hypothesis is supported by recent publications about inactivation of various pathogens by Far-UVC in aerosol, ,,,, water, ,,,− and on surfaces. , For example, Ma et al reported that 222 nm is 12-fold and 1.4-fold, respectively, more effective than 254 nm in inactivating bacteriophage Phi6 and human coronavirus 229E in buffered deionized water . Another study also reported that the inactivation rate constant of SARS-CoV-2 in buffered deionized water is 1.8-fold higher at 222 nm than 254 nm on the same UV fluence basis .…”

“…13−16 The KrCl* excimer lamp has no mercury and a reasonably high wall plug efficiency (0.5− 7.0%) compared to Far-UVC-LEDs (<0.5%). 17,18 It generates a negligible amount of ozone during use, 19,20 and the radiation at 222 nm is safer than 254 nm to human tissues (e.g., skin and eyes) in air/surface disinfection applications since 222 nm photons barely penetrate through the dead cell layer of skin (stratum corneum). 18,21−27 The penetration of Far-UVC in deionized water is not a problem since water molecules (H 2 O) barely absorb UV radiation at 222 nm.…”

“…Far-UVC radiation in the range of 200–230 nm has emerged as a promising UV disinfection tool during the COVID-19 pandemic. It can be provided via several UV radiation sources (e.g., excimer lamps and UV light-emitting diodes), among which the krypton-chloride excimer (KrCl*) lamp with an emission peak at 222 nm is the most mature and commercially available one. − The KrCl* excimer lamp has no mercury and a reasonably high wall plug efficiency (0.5–7.0%) compared to Far-UVC-LEDs (<0.5%). , It generates a negligible amount of ozone during use, , and the radiation at 222 nm is safer than 254 nm to human tissues (e.g., skin and eyes) in air/surface disinfection applications since 222 nm photons barely penetrate through the dead cell layer of skin (stratum corneum). ,− The penetration of Far-UVC in deionized water is not a problem since water molecules (H 2 O) barely absorb UV radiation at 222 nm . The UV absorption of DNA/RNA of microorganisms has been reported to be comparable (∼1 fold) at 222–254 nm, but that of proteins is much higher (∼20 fold) at 222 nm. ,− This suggests that Far-UVC may pose higher inactivation efficiency than UVC at 254 nm.…”

Long-persistent far-UVC light emission in Pr3+-doped Sr2P2O7 phosphor for microbial sterilization

“…This is because far-UV radiation has been demonstrated to be seriously detrimental to bacteria but without skin-damaging effects. 36,37 For example, Brenner's group utilized 222 nm UV light to kill bacteria efficiently but without damaging human cells in skin tissue (a bandpass filter was used to remove the lower-and higher-wavelength components of a krypton-chlorine (Kr-Cl) excimer lamp). 38,39 They demonstrated that 222 nm light is safe for mammalian skin because it cannot penetrate typical human cells, while it has enough penetration to efficiently kill bacteria and viruses that are physically very small (less than 1 μm in diameter).…”