RU2386451C2 - Method of indoor air disinfection - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to indoor air disinfection. The method of indoor air disinfection involves in air passing through a titanium dioxide photocatalyst layer exposed to UV radiation of power more than or equal to the width of the forbidden band of the photocatalyst, and continuously sprayed with water.

EFFECT: invention ensures fast stable disinfecting effect of the whole indoor space, and maintaining low level of air contamination even in the presence of steady infection sources.

2 dwg, 6 tbl

Description

The invention relates to the field of air disinfection in rooms, including medical, where maintenance of air contamination is required at an epidemiologically safe level before work and during the stay of people.

Known methods for disinfecting indoor air with ultraviolet (UV) radiation of the bactericidal range. Disinfection is carried out using recirculators, passing through which air is exposed to UV radiation from bactericidal lamps, which suppresses the vital activity of microorganisms in the air. The bactericidal disinfection efficiency of air passing through the recirculator reaches 99.99%.

There is also a method of disinfecting air by irradiation with powerful pulsed UV radiation of a continuous spectrum with a pulse duration of 10 ^-6 -10 ^-3 and an intensity of more than 100 kW / m ² using a plasma radiation source (WO 98/42624, 01.10.1998, C02F 1 / 32). At the same time, the effectiveness of disinfecting indoor air can reach 99.99%. However, air disinfection should only be carried out in the absence of people.

A known method of disinfecting indoor air, which consists in using a synergistic effect formed by a combination of electrostatic precipitation and photocatalytic oxidation. The air flow passes in the space between the grounded plates connected to the voltage source and coated with a layer of photocatalyst based on titanium dioxide. Due to electrostatic deposition, microorganisms are removed from the air and fall on the photocatalytic layer, which is irradiated with light with radiation energy comparable to the band gap of the photocatalyst. Microorganisms are electrostatically retained on the layer for the time necessary for the photocatalytic reaction to occur, destruction and decomposition into carbon dioxide and water. Sterilization of the chamber with a volume of about 2000 cm ^{3 was} achieved in 60 minutes (US Patent No. 5993738, A61L 9/18).

A known method of disinfection and purification of air from chemical contaminants in ventilation and air conditioning systems of enclosed spaces, which consists in the fact that air is passed through a system containing many surfaces with photocatalytic layers deposited on them. Each photocatalytic layer consists of many photocatalytic particles and has upper and lower surfaces. The lower surface is deposited on a solid substrate and includes an electrically conductive layer made in the form of metal combs, consisting of strips with gaps between them, through which UV radiation penetrates the photocatalytic layer. The energy of UV radiation is greater than or equal to the band gap of the photocatalyst. The electrically conductive layer deposited on the surface of the photocatalyst should be made of a material that ensures the passage of radiation into the photocatalyst. A structure with an electrically conductive layer is used to remove part of the electrons generated in the layer from contact with holes. As a result of using this structure, the recombination of photogenerated particles is reduced, the efficiency of photooxidation and, consequently, the removal of microorganisms and contaminants from the air increases (US Patent No. 7063820, B01J 19/08, 2006). This method is selected for the prototype of the invention.

A significant drawback of the known technical solutions, including the prototype, is that the bactericidal efficacy indicators for these methods are valid for air directly at the outlet of the reactor, and the effect on the airborne contamination of the room strongly depends on the volume of the room and the performance of the air cleaner. The smaller the room and the greater the productivity, the higher the air disinfection efficiency. However, this situation is valid only if there is no additional source of microbial contamination in the room (people, animals). Otherwise, it is possible that the number of additional microorganisms arriving will decrease slowly, or even increase.

In addition, in the prototype method, the main process that ensures air disinfection is electrostatic deposition, as a result of which dust particles and the microorganisms contained in them are in contact with the surface of the photocatalyst on which the photocatalytic oxidation process occurs, which complicates the method and requires the creation of complex multilayer structures.

The problem to which the invention is directed, is to create a method for disinfecting indoor air, in which airborne contamination is maintained at an epidemiologically safe level even with additional sources of infection.

The technical result achieved by the implementation of the invention is to increase the effectiveness and efficiency of disinfection while maintaining a high level of disinfection in the entire volume of the room, the possibility of additional disinfection of surfaces in the room, as well as simplifying the method.

The essence of the invention lies in the fact that the processed air is passed through a layer of a photocatalyst based on titanium dioxide, which is exposed to ultraviolet radiation, the energy of which is greater than or equal to the band gap of the photocatalyst. The specified result is achieved by the fact that the photocatalyst layer is continuously irrigated with water.

Upon irrigation with water, a thin water film (10-50 μm) is created on the surface of the photocatalyst. In the process of blowing air through the photocatalyst layer, moisture evaporates and captures active oxygen-containing particles, which are strong oxidizing agents and disinfectants, in quantities sufficient to effectively disinfect the entire volume of the room and maintain the required level of air disinfection, even if there are sources of infection in the room. In this case, the remaining unevaporated and passed through the photocatalyst water is also disinfected and acquires bactericidal properties.

In addition, the proposed method allows the disinfection of surfaces in the premises due to exposure to bacteria located on these surfaces, oxygen-containing particles resulting from the passage of air through a layer of titanium dioxide when exposed to ultraviolet radiation together with irrigation with water. As a result of the destructive effect of these particles on the vital organs of bacteria, they die.

The method is illustrated by graphical dependencies showing the effectiveness of various factors (UV radiation, photocatalysis and irrigation) and their combination on the content of microorganisms in the air.

Figure 1 shows the time dependence of the content of microorganisms in the room air when exposed to various factors: curve 1 - when air passes through the photocatalytic layer when exposed to UV radiation; curve 2 - when air passes through the photocatalytic layer without exposure to UV radiation; curve 3 - when air passes through the photocatalytic layer when exposed to UV radiation and continuous irrigation of the layer.

Figure 2 shows the time dependence of the content of microorganisms directly at the outlet of the reactor: curve 1 - when air passes through the photocatalytic layer with the UV lamp turned off; curve 2 - when air passes through the photocatalytic layer with the UV lamp and irrigation on.

The method was carried out as follows.

The effectiveness of disinfection was studied in a closed room (box) with a volume of 30 m ³ during artificial infection of the air with test organisms, which were used as Staphylococcus aureus strain 906. The infected air was pumped through a reactor with a photocatalytic nozzle in the form of a layer of quartz rings coated with them a coating based on titanium oxide, which was illuminated by a 40 W low-pressure mercury discharge lamp with a UV wavelength of 254 nm, placed in a quartz case. The energy of the activating UV radiation was 4.88 eV with a photocatalyst band gap of 3.2 eV. The layer was irrigated with water by dropping at a constant speed of 50 mg / cm ² sec.

The initial level of artificial air infection with test organisms was 10 ⁶ -10 ⁷ CFU / m ³ , which is typical for a high level of airborne contamination of the premises. Then, to simulate the constant presence of people, the air was additionally infected by spraying a culture of microorganisms at a level of 10 ⁵ CFU / m ³ . The air velocity through the photocatalytic reactor was 0.5-1 m ³ / s with a reactor capacity of 20 m ³ / h.

To assess the contribution to the disinfection efficiency of each factor separately (UV radiation, photocatalysis and irrigation), air samples were taken at the outlet of the reactor and the state of the air in the box was evaluated at regular intervals from air samples to determine the number of microorganisms in its volume. The obtained data on the dynamics of insemination are shown in tables 1-3 and figure 1, 2.

Table 1 No. p / p Time after infection, min The concentration of bacteria, CFU / m ³ one. 0 1.710 ⁷ 2. twenty 2.110 ⁵ 3. 40 3.1 · 10 ⁶ four. 60 2.6 · 10 ⁴

Table 1 presents data on the dynamics of changes in the seeding of the air environment of the box during artificial seeding in the background without exposure to UV radiation on the catalyst and irrigation. As you can see, the airborne contamination after spraying bacteria is set at 10 ⁷ CFU / m ³ , then gradually decreases to 10 ⁴ CFU / m ³ and then remains at this level.

table 2 No. p / p Time after infection, min The concentration of bacteria, CFU / m ³ one. 0 3.4 · 10 ⁶ 2. twenty 1.3 · 10 ⁴ 3. 40 4.210 ³ four. 60 3.110 ³

Table 2 shows data on the dynamics of the contamination of the air of the box when air is passed through the photocatalyst with the UV lamp on without irrigation. From table 2 it follows that when air is passed through a photocatalyst activated by UV radiation, an equilibrium concentration of bacteria of the order of 10 ³ CFU / m ^{3 is} established in the volume of the room. No viable microorganisms were found in air samples after exiting the reactor.

Table 3 No. p / p Time after infection, min The concentration of bacteria, CFU / m ³ one. 0 9.610 ⁶ 2. twenty 0 3. 40 0 four. 60 0

Table 3 shows the dynamics of the airborne contamination in the room during the irrigation of the photocatalyst together with its UV irradiation. After 20 minutes, microorganisms are not detected both in the volume of the room and at the outlet of the reactor, even with constant feeding of microorganisms. Moreover, this effect is achieved after 20 minutes, i.e. previously 2 times air exchange.

It was found that no microorganism remains in the water that has passed through the photocatalyst. As can be seen from table 4, bacterial samples taken in water after passing through the reactor after 20, 40 and 60 minutes are almost sterile.

Table 4 No. p / p Sample Name The concentration of bacteria, CFU / m ³ 2. Water from the reactor, 20 min 0 3. Water from the reactor, 40 min 0 four. Water from the reactor, 60 min 0

In addition, such water acquires additional bactericidal properties: when introduced into the water that has passed through the photocatalytic reactor, suspensions of microorganisms in a concentration of 10 ⁶ CFU / cm ³ within 5 minutes after the introduction of viable cells are not detected in the water, while in untreated water continuous growth of bacteria is observed.

The proposed method also allows disinfection of vertically and horizontally located surfaces of metal, linoleum and unpainted wood. On the surface before the start of the experiment, a suspension of microorganisms with a bacterial load (Staphylococcus aureus) of more than 10 ⁹ CFU / cm ^{2 was} applied.

The results on the effectiveness of disinfection of vertical and horizontal surfaces with additional spraying of bacteria and with the use of photocatalytic oxidation, activated by UV radiation in conjunction with the irrigation of the photocatalyst, are shown in Table 5. When exposed to all these factors, the contamination was reduced by 6-8 orders of magnitude.

Table 5 No. p / p Surface view Horizontal Vertical The concentration of bacteria (without treatment),
CFU / cm ² The concentration of bacteria (after treatment),
CFU / cm ² The concentration of bacteria (without treatment),
CFU / cm ² The concentration of bacteria (after treatment),
CFU / cm ² one. Metal <10 ⁹ 1.7 · 10 ³ <10 ⁹ 1.3 · 10 ² 2. Linoleum <10 ⁹ 0.8 · 10 ² <10 ⁹ 2.7 · 10 3. Painted tree <10 ⁹ 3.110 ² <10 ⁹ 2.310

The method was also carried out using a UV lamp manufactured by Philips with a radiation wavelength of 365 nm and a power of 40 W under similar conditions of infection of air in a closed room (box) with a volume of 30 m ³ .

The relevant data are presented in table 6. At the exit from the reactor, the level of contamination was 0 CFU / m ³ .

Table 6 No. p / p Time after infection, min The concentration of bacteria, CFU / m ³ one. 0 7.8 · 10 ⁶ 2. twenty 1.7 · 10 ² 3. 40 0 four. 60 0

The proposed combination of photocatalytic oxidation under the influence of UV radiation during irrigation of the photocatalyst with water gives a steady disinfection effect in the entire volume of the room and on its surfaces while maintaining the level of infection, despite the presence of infection sources. The effect of disinfection is determined by the effect of the photocatalytic process in the reactor on bacteria in the air, which results in the process of active oxidation of the membrane or internal organs of the bacterium by active radicals or ions.

The advantages of the proposed method in comparison with the known ones is the stable effect of disinfection in the entire volume of the room and maintaining a low level of air contamination even with constant sources of infection, as well as the efficiency of the method and the simplicity of its implementation.

Claims (1)

A method of disinfecting indoor air, which consists in passing air through a layer of a photocatalyst based on titanium dioxide when exposed to ultraviolet radiation with an energy greater than or equal to the band gap of the photocatalyst, characterized in that the photocatalyst layer is continuously irrigated with water.

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