MODERN DIRECTIONS FOR THE DEVELOPMENT OF THE BACTERICIDAL RANGE OF UV SOURCES

ABSTRACT

Over the last decade, the use of ultraviolet radiation sources has developed rapidly. They are widely used in many domestic, medical and industrial applications, especially in the disinfection of air, water, and some surfaces.

This article discusses the development of the use of ultraviolet radiation sources to disinfect, i.e. disinfection. For these purposes, ultraviolet irradiation intervals corresponding to the bactericidal range are most effective. Low and medium-pressure mercury lamps have made the most progress. However, today the process of removing mercury not only from the domestic but also from industrial circulation has intensified. This, in turn, required the development of mercury-free sources of UV radiation. These include excimer lamps, ultraviolet LEDs, as well as representatives of the new direction - cathodoluminescent sources of ultraviolet, especially lamps with an auto-emission cathode.

The article presents a review and technical characterization of worldwide experience in the use of the bactericidal spectrum of ultraviolet radiation at the level of DNA, one of the main modern technologies for disinfecting surfaces, air, and water from bacteria.

АННОТАЦИЯ

С последнего десятилетия стремительно развивается использование источников ультрафиолетового излучения. Они широко используются во многих бытовых, медицинских и промышленных целях, особенно в области дезинфекции воздуха, воды и некоторых поверхностей.

В данной статье рассматриваются разработки использования источников ультрафиолетового излучения с целью обеззараживания, т.е. дезинфекция. Для этих целей наиболее эффективны интервалы ультрафиолетового облучения, соответствующие бактерицидному диапазону. Наибольшего прогресса добились ртутные лампы низкого и среднего давления. Однако сегодня активизировался процесс изъятия ртути не только из бытового, но и промышленного оборота. Это, в свою очередь, потребовало разработки безртутных источников УФ-излучения. К ним относятся эксимерные лампы, ультрафиолетовые светодиоды, а также представители нового направления - катодолюминесцентные источники ультрафиолета, особенно лампы с автоэмиссионным катодом.

В статье представлен обзор и техническая характеристика мирового опыта использования бактерицидного спектра ультрафиолетового излучения на уровне ДНК, одной из основных современных технологий обеззараживания поверхностей, воздуха и воды от бактерий.

Keywords: ultraviolet, disinfection, bactericidal spectrum, cathodoluminescence, cell, DNA, microorganisms, auto-emission, mercury, pulsed radiation, etc.

Ключевые слова: ультрафиолет, обеззараживание, бактерицидный спектр, катодолюминесценция, клетка, ДНК, микроорганизмы, автоэмиссия, ртуть, импульсное излучение и др.

Introduction

Ultraviolet rays (UV rays) are electromagnetic rays that take on a spectral range between visible and X-rays. The wavelength of ultraviolet radiation is 10 to 400 nm (7.5⋅1014-3⋅1016 Hz) [1].

There are many uses for ultraviolet light in the world today (both beneficial and harmful), but there are no natural sources on our planet that can emit the full spectrum of ultraviolet light. For us, the natural source of ultraviolet radiation is the sun, but not all ultraviolet radiation reaches the Earth's surface because we have an ozone layer and water vapor in the atmosphere, which blocks most of the ultraviolet rays, so there is life on our planet. It is known that a wide spectrum of ultraviolet radiation is capable of destroying living cells of organisms [1].

Quartz ultraviolet lamps have long been used in medical and other facilities to disinfect rooms. They are so named because their bulbs are capable of transmitting almost the entire spectrum of ultraviolet radiation, including wavelengths less than 200 nm, and are made of special quartz glass that promotes the formation of ozone in the air. It is known that ozone is an allotropic modification of oxygen, consisting of atomic O3 molecules. Simply put, ozone is a blue gas with a high oxidizing capacity, which allows it to kill various microorganisms, bacteria, and viruses. In nature, ozone is formed when lightning strikes as a result of the electrical discharge of lightning, so after a thunderstorm, the air is clean because all the dust is washed away by the rain and the bacteria are partially destroyed by ozone.

In general, the use of ultraviolet radiation is widespread. Ultraviolet rays accelerate chemical reactions, so they are used in cosmetology, dentistry, and other fields. Under the influence of ultraviolet light on human skin, Vitamin D is formed in the body. Therefore, it is useful for children to be in the sun more often. But we are more interested in the disinfecting effect of ultraviolet light.

1. Research Methods

UV sterilization occurs due to photochemical reactions within microorganisms [3; 4]. In addition, ultraviolet mainly affects all molecules of the cell, but only biopolymers - membrane proteins and nucleic acids (especially the DNA of the cell nucleus) absorb it effectively. The sensitivity of proteins included in the membranes is large in the wavelength range <230 nm, and long-wave radiation acts very poorly. DNA-forming nucleotides have the maximum absorption of ultraviolet radiation in the range of 250-270 nm (Fig. 1). Because of the convenience of long-wavelength radiation sources, many sources used to sterilize ultraviolet rays, especially when sterilizing liquids (water quickly absorbs wavelengths <230 nm), affect cell or virus nuclei, destroying their DNA. For this reason, such treatment is not called sterilization, but disinfection - after the destruction of cellular DNA, the bacterium can survive (i.e., metabolic processes do not stop there), but it cannot reproduce.

Figure 1. UV absorption curves of proteins and nucleotides [2]

Note that due to the small transverse dimensions of cells, only no more than 5% of UV radiation passing through a single typical bacterial cell is absorbed in it - thus, cell membranes and other organelles cannot serve as an effective shielding for nuclei. But as cell size increases, microorganism sensitivity decreases, so the resistance of mold cells to UV radiation is higher than that of bacterial cells. The graph in Fig. 2(a) shows that the most effective UV sources have a wavelength of about 265-270 nm (generally speaking, different microorganisms have different sensitivity to UV irradiation, including spectral sensitivity - but, in most cases, the sensitivity curves are qualitatively close to the nucleotide sensitivity curve, which makes it possible to rely on it when choosing UV sources for practical applications). However, radiation sources, as a rule, have complex spectra - either wide or with many lines that do not always fall into the region of maximum cell photosensitivity. Therefore, sources with different spectra, other things being equal, have different bactericidal efficiency. To describe it, the concept of relative spectral bactericidal efficiency is introduced - a dimensionless quantity, convolution of the source spectrum with the sensitivity curve. The bactericidal flux (measured in watts) is the product of power and the dimensionless bactericidal efficiency, bactericidal output is the ratio of the bactericidal flux to the electrical power consumed by the UV source.

Figure 2. a) Ultraviolet absorption spectra of protein and DNA; b) Ultraviolet spectra required for cell destruction [6]

Because some molecules absorb ultraviolet light, certain biological reactions strongly influence the wavelength of the cell.

The spectrum of action makes it impossible to distinguish between DNA and RNA as target molecules because they both have similar absorption spectra. Two other UV-C action spectra for cell death (Figure 1-2), one for mammalian tissue and one for individual mammalian cells, are shown using mammalian tissue samples as hanging particles.[6] The advent of single-celled mammalian breeding techniques and the unique smooth geometry that mammalian cells adopt in monolayer cultures allowed this research to begin. Consequently, the action spectrum for the destruction of cultured mammalian cells showed data similar to those for bacteria.

2. Research results

Disinfection of microorganisms in water with ultraviolet light of a certain intensity (a sufficient wavelength of 260.5 nm for the destruction of microorganisms) for a certain period (the amount of UV dose required to reduce the number of microorganisms by a factor of ten depends on their type and 2–20 mJ/cm² for many bacteria and viruses of a number) is carried out by irradiation with ultraviolet light. As a result of such irradiation, microorganisms "microbiologically" die, since they lose their ability to reproduce. UV radiation in the wavelength range of about 260 nm penetrates well through water and the cell wall of the water-borne microorganism and is absorbed by the microorganism's DNA, causing dimerization of thymine. The accumulation of such changes in the DNA of microorganisms leads to a slowdown in their reproduction and extinction.

Recently, germicidal air recirculators have become popular, they are nothing but a closed-type emitter. The essence of their work is very simple. Bactericidal lamps are installed inside, and with the help of a fan, the air from the room is driven through the recirculator and there disinfected. Bactericidal lamps also emit ultraviolet light and can only be used in enclosed emitters in the presence of people.

In this test, we will test the bactericidal lamp of the company - "Armed", which is installed in the recirculator of this manufacturer. The power of the lamp is 30 watts. 

In this test, we will check the germicidal lamp of the company - "Armed".

The effectiveness of the lamp will be tested on the simplest microorganisms living in the water. We will take four samples of liquid with microorganisms and place the first sample at a distance of five centimeters from the lamp, the second sample at a distance of one meter from the lamp, and the third at a distance of two meters. We will control the process with a microscope.

Figure 3. The method of placement of samples under the ultraviolet lamp

This is how all three samples look before turning on the lamp. We turn on the lamp and note the time.

Figure 4. View the sample before turning on the lamp

We checked the near sample after one minute, and no special changes were found, but after 3 minutes in the sample, which was five centimeters from the lamp, all the microorganisms died. At the same time in the middle sample, nothing has changed. After 5,10 and 15 minutes, it was the same. For example, let's show a sample at a distance of one meter from the lamp after 20 minutes. And only after 40 minutes in the average sample died small single claws, larger continue to run. It should be noted that the samples slightly dried up, that is, the thickness of the liquid decreased slightly. In the lower sample for 40 minutes, no special changes were observed.

After an hour of irradiation, it was decided to end the experiment. As you can see (Figure 5), during this time in the sample at a distance of 1 meter - mostly small microorganisms died, and in the sample with a distance of 2 meters all actively running.

Figure 5. Test results after 1 hour

3. Discussion

Based on the research experiment, we will discuss the principle of operation and the economic profitability of the bactericidal lamp. First of all, it should be noted that in the experiment, compared to bacteria, the irradiated microorganisms have more survivability than bacteria. Plus they were in a humid environment. Ultraviolet light travels well through the air. So, the effectiveness of the lamp against bacteria and viruses on dry surfaces or in the air will be higher.

According to the test results, it can be seen that at a close distance, the lamps are quite effective.

From an environmental point of view, an important advantage of UV curing is that only 100% reactive substances are used in this case and therefore there are no problems associated with solvent regeneration. The energy consumption is low. The curing takes place at room temperature, so it is possible to cure coatings on substrates sensitive to high temperatures. But the most important advantage of this method is the economic factor. The curing speed is high, the plant is relatively easy to operate, and the work requires minimal floor space and a minimum of manpower. An undoubted advantage is that the final products are of high quality.

Cathodoluminescent UV sources can provide an arbitrary spectrum of radiation in the bactericidal range, and achieve spectral efficiency superior to low-pressure mercury lamps. Such auto-emission UV sources will have a high lifetime (10,000 - 50,000 hours), low cost, high reliability, and stability of operation in a wide temperature range, and with full environmental safety will be able to fully replace mercury lamps for all applications.

Conclusion

As a biological weapon, ultraviolet attacks bacteria in three directions at once. Firstly, it changes the structure of DNA functions, secondly, it destroys proteins, and thirdly, it damages bio-membranes. What is interesting, is that in this process there are several phases, some cells die, and the surviving cells continue to divide, but the rate of division slows down some die. And only after 2-4 weeks comes either the final death or the recovery of surviving cells. Thus, it turns out that we have a weapon against viruses and bacteria. But the problem is that man is a living organism and exposure to quartz lamps is just as destructive. If you can hide from direct UV rays, using goggles, clothing, or special design lamps, then there is no way to get away from the ozone. That's why there should be no people in the room when using quartz lamps, and after using quartz you need to ventilate the room. But progress does not stand still and there are bactericidal ultraviolet lamps. The bulbs of such lamps are made of glass, which does not pass the ozone-forming part of the spectrum of UV radiation.

Auto-emission UV lamps are the most suitable for UV curing because, unlike UV diodes, mercury lamps, and excimer lamps, the technology used in auto-emission emitters allows the construction of flat lamps half a centimeter thick with a large radiating surface area (tens and hundreds of square centimeters), which in turn allows the construction of compact and inexpensive curing systems.

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