Comparative study of UV radiation action of XeBr-excilamp and conventional low-pressure mercury lamp on bacteria

ABSTRACT The study of features of XeBr-excilamp (282 nm) and low-pressure Hg-lamp (253.7 nm) radiation impact on Escherichia coli bacterial culture are presented. It is shown for the first time that both sources of radiation have comparable germicidal action. The prospects of a new bactericidal radiation source – XeBr-excilamp – are discussed. Key words : exciplex lamp (excilamp), UV-inactivation, Es kherichia coli , low-pressure mercury lamp. 1. INTRODUCTION When radiation suppresses the vital activity of a biological system, one deals with an inactivating effect or, in other words, the inactivation of a biological system (e.g. biomolecule or cell). The term “inactivation” can be applied either to a cell or its single subsystem. UV irradiation has proved to be a powerful tool for the purposes of inactivation both microorganisms and cells, such as bacteria, viruses, protozoan parasites, some spores, living ce lls and subsystems such as en zymes, aminoacids, lipids (see refs in [1]). Thus, UV inactivation has become a productive option for cleaning wastewater an d air, food and medical treatments, as well as for scientific studies. Among UV inactivation advantages is the fact that irradiation is a physical process, so no chemicals have to be added. The germicide effect of UV light on bacteria and viruses is primarily due to the formation of thymine, thymine-cytosine (pyrimidine) and cytosine dimers in DNA (listed in prevalence of order). It is represented by the so-called action spectrum. The most effective action of radiation was revealed at the wavelengths in the range of 200-295 nm (so-called bactericide or germicide range) [ 2,3]. The low-pressure mercury lamps (LP Hg lamps) were devel oped in 1936-1940 as economic germicide light sources (see refs in [ 2]). Nowadays, LP Hg lamps are well-known disinfecting devices. Such sources emit about 70% of radiant power within the UV region of 250-370 nm, and 60% of such radiant power belongs to mercury resonance line at 253.7 nm related to the maximum bactericide effect. The mercury lamps are in wide use owing to their simple power-supply systems and easy maintenance. However, the radiant power of LP Hg lamps is very sensitive to ambient thermal changes, which should be considered in LP Hg disinfection reactors engineering. Besides, in a view of microorganisms inactivation the powerful medium-pressure Hg lamps (MP Hg lamp) have demonstrated wide acceptance among sterilization methods. Unfortunately, these lamps spectra consist of broadband continua with no more than 19% of radiant power concentrated in the germicidal range (e.g. a MP Hg lamp tested in [ 4] emits 11.4% of radiant power only at 200 < O < 300 nm). The VUV or UV excilamps appear as an interesting option to conventional light sources for UV disinfection. Thus, one should distinguish between two different disinfection methods: the inactivation of microorganisms by UV irradiation (e.g. by KrCl-, XeBr-, KrBr-excilamps) or their total VUV-induced photomineralization (by Xe