Prevention of infection by low-concentrationozone using an excimer lamp
Y. Takano, A. Koike, and I. Serizawa
ORC Manufacturing, Co., Ltd., 4896 Tamagawa, Chino, Nagano, 391-0011, Japan
Abstract -- An excimer lamp is a mercury-free discharge lamp, which emits ultraviolet light to produce ozone. To utilize ozone
gas produced by an excimer lamp for infection prevention, we evaluated the inactivation effect on SARS-CoV-2 and Escherichia coli.
The ozone concentration was held constant at 0.05 while the exposure time was varied. The number of viruses or bacteria decreased
with increasing treatment time, with the decrease rate after 6 h being > 99.9% in SARS-CoV-2 and 98.5% in E. coli. We found thatozone gas can be used to inactivate attached viruses and bacteria.

O2 + hv (λ ≦ 242 nm) → O (3P) + O (3P)O2 + hv (λ ≦ 176 nm) → O (1D) + O (3P)
O (1D) + M → O (3P) + M
O (3P) + O2 + M → O3 + M
O3 + hv (λ ≦ 320 nm) → O2 + O (1D)

(1)
(2)
(3)
(4)
(5)

In recent years, it was revealed that ozone gas
generated by the excimer UV method was shown tocontain no nitrogen oxide (NOx) and cause less corrosionof copper and iron plates, compared with ozone gas fromthe electrical discharge method at the same ozone
concentration [2]. The ozone gas generation method
using the excimer lamp is expected to be used as a spatial
bacteria elimination method to reduce damage to metals
and other materials. This study evaluated the inactivation
effect of ozone gas produced by the excimer lamp on
Escherichia coli and SARS-CoV-2.
II. MATERIALS AND METHODS
A membrane filter dropped with 0.mL of E. coli
(NBRC3301) solution was used as a test specimen.
Specimens were installed in a sealed desiccator andexposed to ozone at concentrations of 0.05 ppm and 0.1
ppm for a fixed period of time. The ozone gas source was
Smart Excimer® UV Lamp. Concentration control wasperformed using an ozone densitometer. After the action
time, the filter was immersed in 10 mL of sterile water tocollect. The collected solution was cultured on a standard
agar medium, and the number of viable bacteria(CFU/mL) was determined.
The evaluation of virus inactivation was entrusted tothe Department of Microbiology and Infectious Diseases
at Nara Medical University. All operations were carriedout under appropriate pathogen containment measures atbiosafety level 3 experimental facilities.
Twenty microliters of the virus (SARS-CoV-2; 2019-III. RESULTS AND DISCUSSION
The number of viable E. coli decreased as ozone
exposure time increased (Fig. 1). Also, the number ofviable bacteria at equal exposure times was lower at 0.1
ppm than at 0.05 ppm ozone concentration.
In the inactivation assays of SARS-CoV-2, theinfectivity decreased as treatment time increased (Fig. 2).
At an ozone concentration of 0.05 ppm, the percentage
reduction in infectivity after 2 h was 99.958 % and99.996 % after 6 h.
The allowable ozone concentration in manned
environments established by the Japan Society for
Occupational Health is less than 0.1 ppm. The results
revealed that E. coli and a novel coronavirus could beinactivated even at the low concentration (0.05 ppm) thatis below manned environmental standards. The effects on
floating viruses and bacteria have not been verified.
(A)

7(B)
Viral load SARS-CoV-2 (PFU/sample)

Ozone gas is widely used for bacteria elimination,cleaning, and deodorization. The ozone gas generation
system is roughly divided into discharge and UV type. In
the UV system, three kinds of reactive oxygen species,
singlet oxygen atom [O (1D)], triplet oxygen [O (3P)], andozone molecule [O3] are generated by the reaction shownin Equations 1 to 5 below [1].

nCoV JPN/TY/WK-521 strain) were coated on the dishand kept static for a certain time, and dried as test
specimens. The ozone treatment method was the same asdescribed above. After the action time, sodium
thiosulfate-containing SCDLP medium was dropped onto
2 ml specimens, and the virus was recovered using a cellscraper. The recovered solution was used to infect Vero
E6 cells. The virus infectivity titer (PFU/sample) wasmeasured by the plaque method.

The number of E. coli (log (CFU/mL))

I. INTRODUCTION

530 ppm
0.05 ppm
0.1 ppm
102

40 ppm60.05 ppm

5432106Time (hours)

026Time (hours)

Fig. 1. Effects of duration for ozone gas treatments inEscherichia coli (A), and SARS-CoV-2 (B)REFERENCES[1] H. Sugimura, J. Surf. Finish. Soc. Jpn. Vol. 69, p58-64, 2018[2] T. Hayakawa and I. Serizawa, Bull. Med. & Hyg.
Ozone Res., vol, 28, p 27-28, 2021