WO2008037900A2

WO2008037900A2 - Device for purifying gaseous media and method implementing said device

Info

Publication number: WO2008037900A2
Application number: PCT/FR2007/001593
Authority: WO
Inventors: Valéry BONNET; Nicolas Keller; Marc Jacques Ledoux; Marie-Claire Lett; Sébastien Josset; Jérôme TARANTO; Valérie KELLER-SPITZER
Original assignee: Recyclanet; CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE Etablissement public à caractère scientifique et technologique; UNIVERSITE LOUIS PASTEUR Etablissement public à caractère culturel, scientifique et professionnel
Priority date: 2006-09-28
Filing date: 2007-09-28
Publication date: 2008-04-03
Also published as: FR2906473B1; FR2906473A1; WO2008037900A3

Abstract

The invention relates to a device for purifying a gaseous medium, said device comprising a reactor (9), at least one element (5) consisting of a tangential ventilator having blades provided with a photocatalytic coating (6) based on titanium oxide, for example, and associated irradiation means (7). The invention also relates to a method for purifying gaseous media using said device. The aim of the purification process is to inactivate and/or degrade chemical and/or biological species contained in the gaseous medium to be treated.

Description

DEVICE FOR PURIFYING GASEOUS MEDIA AND METHOD

IMPLEMENTATION

The present invention relates to the purification of gaseous media; it relates to the decontamination, as defined hereinafter, of gaseous media comprising chemical and / or biological species, in particular, as regards the latter, bacteria, viruses and spores.

There are in many areas gas flows carrying chemical and / or biological species that can be harmful or toxic to more or less long term. By way of example, air conditioning systems or air from air-cooled towers, which contain fine droplets of water in suspension (aerosols), which may contain harmful bacteria such as those of the genus Legionella, such as Legionella pneυmophila responsible for legionellosis. Another example of a contaminated gas flow is that of air circulating in hospitals, which is likely to carry viruses, bacteria and spores that can lead to nosocomial infections. More generally, the air present in any confined or densely populated environment is likely to carry, in greater or lesser amounts, biological species of bacteria, virus or spore type, which it may be desirable to eliminate and / or chemical species that should be degraded into products that are harmless to human or animal health.

Filtration systems for such gas streams have been proposed. These filtration systems generally generate a significant cost, especially insofar as the chemical and / or biological species that one seeks to trap are generally of very small size. In addition, these systems generally require frequent maintenance, whether it is a replacement of consumables or a cleaning of the device.

Other systems have been proposed based on the principle of photocatalysb. Briefly, photocatalysis is a process allowing the destruction of chemical and / or biological pollutants through the combined action a catalyst (generally titanium dioxide which is a metal semiconductor), also called photocatalyst, and an ultraviolet source whose role is to activate the catalyst on the surface of which will create charges (electrons and holes) which are the basis of pollutant destruction reactions. It is important to note that once these pairs of charges formed on the surface of the catalyst, more than 95% of them recombine and only less than 5% will participate in the reactions of destruction of pollutants, among the so-called photocatalytic systems , some use a fan whose blades are the support on which the photocatalyst is deposited and irradiated by one or more ultraviolet light sources. For example, the system described in US Pat. No. 5,919,422.

At present, to achieve the decontamination of such stale gaseous media, most of the solutions proposed are however relatively expensive and / or complex to implement, and their effectiveness is not always satisfactory.

An object of the present invention is therefore to provide a device for the decontamination of gas flow which is compact, effective for a wide range of flow rates, inexpensive and simple to implement.

This device allows particularly effective degradation and inactivation of chemical and biological agents even for large airflows.

Preferably, the element provided with a photocatalytic coating of the reactor is in motion. This movement can be either induced by the gas flow, or directly or indirectly by a motor. In this context, it may be in particular provided to articulate one or more elements provided with the photocatalytic coating on a drum driven in rotation by a motor. Preferably, the photocatalytic coating is deposited on all the faces of the mobile element. Indeed, the movement of the part then makes it possible to increase the exchange surface between the photocatalyst and the biological or chemical agents of the gaseous medium.

In the context of the device according to the invention, and according to the geometry and the positioning of the moving elements, the illumination surface can increase substantially, and allow a better efficiency of the device. Moreover, the presence of the aforementioned movable parts makes it possible to put the gas stream in contact with the photocatalyst, in particular by inducing a non-laminar or even turbulent regime within the reactor, which increases the likelihood of encounter between the chemical agents and / or biological and photocatalytic coating.

Preferably, the device according to the invention comprises a reactor of which at least a part of the surface is mobile and can change orientation. In this case, the device allows controlled periodic illumination, the semiconductor being photoactivated each time this surface is exposed to radiation and the photocatalytic coating thus activated can then be effective against chemical and / or biological agents.

According to a preferred embodiment, the mobile element or elements also ensure the suction of the gaseous medium in the reactor and its delivery. This embodiment makes it possible to reduce the complexity of the device as well as the losses of loads since it is no longer necessary to add an auxiliary fan. Moreover, the device can operate close to its nominal rotation value, which reduces its wear.

According to a preferred embodiment, the irradiation means activate a portion of the photocatalytic coating periodically and not continuously

(while it was logical to think in this case that the decontamination would be more important). This periodic irradiation mode is particularly advantageous because it ensures constant global photocatalytic activity while allowing the photocatalyst to periodically return to the base state. Such periodic partial irradiation of the photocatalyst can be obtained by rotating a cylindrical support carrying elements provided with photocatalytic coatings facing one or more fixed UV sources.

Also, a preferred embodiment of the invention consists of a device in which the movable elements are constituted by blades of a tangential fan, provided with said photocatalytic coating.

This embodiment has several advantages. First, fan-induced turbulence ensures a high probability of encounter between the contaminants and the photocatalytic surface. Therefore, this device can effectively treat a gas flow having a high flow rate of at least 5 m ³ / h. Then, it is no longer necessary, unlike other devices, to provide separate conduction means of the gas stream, it follows that the device comprises fewer elements and is therefore more reliable. In addition, this device is economical and easy to manufacture since it is sufficient to deposit the semiconductor on the blades of a tangential fan and then to associate a radiation source to achieve the device according to the invention.

Especially preferred is a device comprising:

a reactor comprising a drum that can be rotated by drive means, on which drum blades are provided on at least one of their faces with a photocatalytic coating, which drum forms with guiding an inlet adapted to the introduction of the gaseous medium and an outlet adapted to the evacuation of the gaseous medium, and

means for irradiating the photocatalytic coating arranged so as to at least partially irradiate the photocatalytic coating. By "decontamination" is meant a treatment for inactivating biological agents and / or degrading the chemical agents so as to lose all or part of their hazardous nature, resulting in a purification of the gaseous medium treated.

For the purposes of the present description, the term "chemical agents" is intended to mean gaseous or solid compounds presenting a danger for humans or the environment, in particular nitrogen compounds of the NO _x type, in particular

NOΣ, carbon monoxide (CO), and volatile organic compounds (also called VOCs) especially aromatic compounds (benzene, toluene, ethylbenzene, xylenes), aldehydes (formaldehyde, acetaldehyde) and / or halogenated compounds (especially chlorinated compounds). By "biological agents" is meant, within the meaning of the present description, entities of biological nature, generally of small size, typically between 0.01 μm (microns) and 10 μm (microns), and likely to be carried by a gas stream. Thus, the biological agents to be inactivated according to the method of the invention may in particular be bacteria (Legionella bacteria, such as Legionella pneumophila for example), viruses, spores, fungi, or even a mixture of such entities.

The term "inactivated biological agent" refers for its part, within the meaning of the present description, an agent of the aforementioned type having lost a biological activity, and in particular having lost its capacity of replication (or reproduction).

In particular, the term "inactivated bacterium", as used herein, a bacterium unable to develop a colony after culturing in a suitable medium. Thus, are considered especially as "inactivated bacteria":

- "dead" bacteria (typically bacteria in which no breathing phenomena are detected); and

- Bacteria that, although living, do not develop after culturing. For the purposes of the present invention, the term "semiconductor material" is intended to mean a material in which the electronic states have a band spectrum comprising a valence band and a conduction band separated by a forbidden band, and where the necessary energy to pass an electron from said valence band to said conduction band is preferably between 1.5 eV and 4 eV. As such semiconductor material, there may be mentioned titanium dioxide TiO _2, or alternatively other metal oxides such as WO3, ZnO or SnO _Σ or metal sulfides such as CdS, ZnS or WS ₂ or still other compounds such as GaAs, GaP, CdSe or SiC. According to the present invention, it is preferable to use titanium dioxide which leads to particularly satisfactory results. It is known that, in a semiconductor material of the aforementioned type, it is created, under the effect of appropriate radiation, electron / hole pairs (a "hole" being an electronic deficit in the valence layer left during the "jump" of an electron towards the conduction band), which gives the material pronounced oxidation-reduction properties which are used in photocatalytic applications.

The photocatalytic material such as titanium dioxide is sufficiently active to allow the degradation and / or inactivation of chemical and / or biological agents in a gaseous medium where said agents are however highly dispersed. In this context, it is particularly surprising to note that the device of the invention makes it possible, for example, effectively to treat highly diluted gaseous media, namely comprising less than 10 ^{~ 3} biological agents per cm ³ , or even less than 10 ^{" 4} biological agents per cm ³ .

The activity of a photocatalytic material is also sufficient to effectively treat gaseous media having high levels of chemical and / or biological agents, for example gaseous media containing more than 1 biological agent per cm ³ , and even more than 100 biological agents per cm ³ in most cases, and this even with large flows of gaseous flow for example of the order of 1 to 10 m ³ per hour. Thus, the device of the invention allows, as a rule, to effectively treat gaseous media typically containing between 10 "and 100 biological agents per cm ³ , for example between 5.10 ^{" 3} and 5 biological agents per cm ³ , and in particular diluted media containing between 10 ^-4 and 0.1 biological agents per cm ³ or concentrated media containing between 0.1 and 100 biological agents per cm ³ It is assumed that the degradation and inactivation of the chemical and / or biological agents is induced by the strongly oxidizing nature of the photocatalytic material and is initiated when these agents come into contact with the surface of the photoactivated semiconductor.

In the present invention, to further increase the efficiency of the aforementioned oxidation mechanisms, it may be advantageous to use, in conjunction with the photocatalytic material, other materials, especially materials having an oxidizing character or sorbent materials, such as finely divided carbon or silica or zeolites.

In this context, it is possible in particular to envisage materials based on a semiconductor such as titanium dioxide, which also contains compounds such as gold or silver in metallic form, for example in the form of particles. dispersed in the semiconductor material or deposited on its surface.

According to this particular embodiment, the mass ratio (additional oxidant / semiconductor) advantageously remains less than 5%, or even 3%, and it is typically between 0.5 and 2%. The presence of such additional oxidants is however not required, in the general case, to obtain an effective treatment.

The photocatalytic degradation is very selective, which means that any chemical agent and / or biological is in principle likely to be degraded by contacting a photoactivated semiconductor. In practice, it turns out that titanium dioxide for example has a very broad spectrum of decontamination.

Another advantage of the device is that the particularly effective photocatalytic degradation is obtained very simply and at low cost, insofar as it requires only irradiation with relatively low energy radiation. Thus, in the case of titanium dioxide for example, only a radiation energy of the order of 3 to 3.2 eV, that is to say of lengths of the order of 380 to 400 nm, is required . The energy required for the photoactivation can be further reduced if the semiconductor material is doped (for example by metals such as chromium or by compounds based on N, S or C) or else by using agents chromophores (anthracenes or anthracins for example), in combination with the semiconductor material. In this case, a very low activation energy may be sufficient to photoactivate the material, which may for example correspond to wavelengths greater than or equal to 500 nm, for example greater than or equal to 550 nm. The irradiation of the semiconductor is generally carried out under radiation whose wavelength range is in the near ultraviolet range, for example by means of sunlight or else with the aid of sodium or mercury vapor, for example lamps called "black light".

The radiation used to photoactivate the semiconductor in the method of the invention is generally not, per se, sufficient energy radiation to provide a germicidal effect. The radiation used to photoactivate the semiconductor materials according to the method of the invention thus generally have wavelengths greater than 254 nm, and typically greater than 320 nm, for example greater than or equal to 350 nm.

It should also be emphasized that no heating is required to carry out the photoactivation of the semiconductor, which makes it possible to carry out the process of the invention at ambient temperature, for example between 10 and 30 ^° C.

The exact nature of the semiconductor material used according to the invention is, as a rule, not decisive for obtaining the desired effect of inactivation of the biological agents.

Thus, in the case of titanium dioxide, for example, any commercial titanium dioxide can be used effectively in the process of the invention, which is still an advantage of the process.

Nevertheless, according to one embodiment leading to good results in terms of inactivation of biological agents, the titanium dioxide used according to the process of the invention is anatase form, preferably at least 50%. Thus, according to this embodiment, the titanium dioxide used may, for example, be essentially constituted (ie in general for at least 99% by weight, and preferably for at least 99.5% by weight, or even for at least 99.9% by weight) of anatase form.

The use of TiO ₂ in rutile form is also interesting, insofar as the TiO ₂ in this form is photoactivated by the spectrum of visible light. According to another advantageous embodiment, the titanium dioxide used comprises a mixture of anatase form and of rutile form, with an anatase / rutile proportion preferably between 50/50 and 99/1, for example between 70/30 and 90/10, and typically of the order of 80/20. Moreover, in particular to optimize the exchanges between the semiconductor material and the chemical and / or biological agents dispersed in the gas stream, it is most often advantageous for the semiconductor material used to have a specific surface area of between 20 and 500. m ² / g, preferably greater than or equal to 40 m ² / g, and still more advantageously at least equal to 100 m ² / g. The specific surface area referred to herein is the BET specific surface area measured by nitrogen adsorption according to the so-called Brunauer-Emmet-Teller technique. For this purpose, it is especially possible to use a semiconductor having as such a high specific surface, or else deposited on a finely divided or porous support (such as, for example, a silica support) having a high specific surface area.

As particularly advantageous titanium dioxide, it will be possible to use titanium dioxide marketed by the company Degussa under the name T \ O ₂ type P25.

The photoactivated semiconductor material that is used according to the invention may be in various physical forms, depending on the gaseous medium treated, and in particular depending on the volume of this medium and the rate at which it is desired to perform the treatment. In general, the semiconductor material may be used in any form adapted to its irradiation by wavelength radiation for its photoactivation and allowing the contact with the gaseous medium to be decontaminated.

In the device of the invention, the semiconductor material used is implemented in the immobilized state on the surface of a mobile element of the reactor, the gaseous medium to be treated being brought into contact with this modified surface. According to one particular embodiment, the surface on which the titanium dioxide semiconductor material is immobilized may be a surface on which a support of high specific surface area (for example a layer of silica) is deposited, the semiconductor material being immobilized on this support. According to one Another embodiment, the semiconductor material can be implemented in the form of a deposit obtained by depositing a film of a dispersion (for example an aqueous dispersion) of particles based on said semiconductor, on a surface and then drying the resulting film. The deposit based on semiconductor material is preferably a titanium dioxide deposit chosen from those preferred above. Thus, it is advantageously a titanium dioxide of anatase form or a rutile / anatase mixture and having a specific surface of between 20 and 500 m ² lg. This deposit may for example be obtained by depositing a film of a dispersion (for example an aqueous dispersion) of particles based on titanium dioxide semiconductor material on the surface of the reactor element, then drying the obtained film. This deposit can also be obtained by drying a film of a dispersion in a non-aqueous solvent or the semiconductor used is not soluble. In the case where the photoactivated semiconductor used is titanium dioxide, a deposition of titanium dioxide on the surface can be carried out by depositing a solution of titanate and by thermally treating the deposit thus obtained, thereby obtaining the TiC * ₂ formation from the titanate precursor.

The deposition of semiconductor material of the titanium dioxide type may be of a continuous or discontinuous nature, but it is preferably a continuous solid film distributed over the entire surface of the mobile element or elements of the reactor, in particular to optimize the exchange surface between the gas stream and the photoactivated titanium dioxide. Preferably, the deposit is present on all the faces of the mobile element that can be activated under the effect of the irradiation. Moreover, this deposit preferably has an average thickness of between 0.5 μm and 100 μm, for example between 1 and 20 μm, this thickness being typically of the order of 5 μm.

The irradiation means associated with the photocatalytic coating are generally radiation sources comprising photons of energy greater than 3 eV (preferably greater than 3.2 eV), for example one or more lamps emitting radiation comprising lengths of waves below 400 nm (for example below 300 nm), for example lamps with black light or visible light. According to a particular embodiment, the radiation source used may be sunlight.

According to one embodiment, these radiation sources are located outside the reactor. Where appropriate, to enable activation of the semiconductor, the reactor wall has openings or portions made of a material that is transparent to at least a portion of the effective radiation emitted by the sources, i.e. the reactor wall passes at least a portion of the radiation which has sufficient energy to activate the semiconductor. According to another particular aspect, the present invention also relates to a method adapted to the implementation of the aforementioned device.

In particular, the invention also relates to a method for decontaminating a gaseous medium, comprising the step of passing at least a portion of the gaseous medium to be decontaminated through the device as described. Such a method is particularly advantageous when the gaseous medium comprises biological agents, in particular bacteria and in particular Legionella bacteria such as Legionella pneumophila.

According to a particular embodiment of this process, the gaseous medium is in the form of an aerosol. In general, the process of the invention is conducted on a gaseous medium comprising harmful and toxic chemical or biological agents and / or pathogens. In this case, the inactivation most often consists of denuding the agents of their harmful, toxic or pathogenic nature, in particular by transforming the chemical agents or by inhibiting the replication capacity (reproduction) of the biological agents.

The "gaseous medium" in which the above-mentioned agents are dispersed is generally air, but it may possibly be another gas. Nevertheless, for optimum efficiency of the decontamination process, it is preferable that the gaseous medium contains oxygen. According to a particular embodiment, the gaseous medium is in the form of an aerosol which comprises fine liquid droplets, generally droplets of water, dispersed within the gaseous medium. The chemical and / or biological agents may then be present, wholly or partly, within these droplets.

Thus, for example, the treated gaseous medium may be an aerosol comprising air as dispersing gaseous medium and containing water droplets including aforementioned agents.

However, the chemical and / or biological species can also be simply dispersed as such within the gaseous medium.

Whatever the nature of the chemical and / or biological agents and the gaseous medium, the decontamination process of the present invention is carried out by contacting the gaseous medium with a photocatalytic material. Such a material exhibits catalytic activity when exposed to radiation. These materials generally comprise a semiconductor. The device and the method of the invention will now be described in more detail in the following description, made with reference to the accompanying drawing, in which: the single figure shows a schematic sectional side view of a device according to a preferred embodiment of the invention. The device 1 illustrated in the figure comprises a reactor 9 formed by a tangential fan, and irradiation means 7. The tangential fans are known as such and sold for example by the company EBM-PAPST. The reactor 9 comprises a drum 4 rotatably mounted and connected to drive means (not shown). The drum 4 is pierced with openings between which are articulated blades 5 bent and forming an angle with the surface of the drum when they are rotated. The blades 5 are coated on one or preferably on both sides with a semiconductor material 6, for example titanium dioxide. In the illustrated design of the device, the blades 5 of the tangential fan form moving elements provided with a photocatalytic coating. The reactor 9 further comprises an inlet 2 and an outlet 3 of the gas stream, formed by the drum 4 and the guide means 8. The guide means 8 are composed of a guide plate 8a (also called "profile") and a vortex tongue 8b and on which the titanium dioxide can also advantageously be deposited. The drum 4 being disposed in the inlet, and provided with openings, a part of the gas flow entering the device is sucked through the drum to be discharged at the outlet. The positioning and the geometry of the guiding means induce a degree of turbulence in the gas flow. The gas flow is thus strongly stirred in a turbulent flow near the semiconductor-coated blades 6. This stirring makes it possible to increase the probability of contact with a biological and / or chemical agent and makes it possible to reach a very high efficiency. . Advantageously, the guide means 8 are adjustable in order to allow the modification of the direction of suction and discharge of the gaseous flow of the reactor. The device 1 also comprises irradiation means 7, in the illustrated embodiment composed of two lamps. The lamps emit appropriate radiation to activate the photocatalyst, usually in the ultraviolet. This may include UV-emitting lamps ("black light" type) or lamps with visible light emission. Advantageously, the photocatalyst is activated under radiation in the UVA domain. The irradiation means 7 are arranged to expose at least partially the radiation photocatalytic deposit. In the figure, the irradiation means comprise a lamp composed of two tubes (also called "U-shaped lamp" or "compact lamp"), but in practice, the number of lamps can vary as well as their power.

The irradiation means 7 are preferably arranged near the mobile element (s) provided with a photocatalytic coating, optionally inside or outside the reactor. Due to the design of some fan components and to avoid disturbance of the airflow, the positioning of the lamp outside the fan is however preferred as part of the illustrated design. When the device 1 is turned on, the drum 4 is rotated, creating a suction zone at the inlet 2 of the device 1. The gas flow, illustrated by arrows in the figure, is then sucked by the inlet 2 and largely through the drum 4 before being discharged from the reactor through the outlet 3. The design of the device described has a number of advantages.

First, the device allows controlled periodic illumination of the photocatalytic surfaces of the reactor. Indeed, the alternating operation of the photocatalyst, which is successively illuminated and unlit, ensures a periodic return of the semiconductor in the non-activated state, without the need to interrupt the lamp, which would cause wear premature of it. However, a part of the photocatalytic surface remains always lit and therefore in operation, thus ensuring a decontamination constant over time and reliable.

Indeed, the rotation of the drum causes the blades successively in front of the lamp, a portion of the blades being at each moment illuminated and their photocatalytic coating thus activated. As the drum continues to rotate, the blade is driven away from the lamp, allowing the photocatalyst to return to the off state. As said above, this alternation between the activated state and the deactivated state decreases the recombination rate of the electron / hole charges, which optimizes the use of photons that are useful for pollutant degradation reactions.

Moreover, the presence of the photocatalyst on moving elements, in particular on the blades of a fan, makes it possible to increase the illumination area and thus the treatment efficiency of the device. Finally, in the device described, the movable elements and their arrangement also allow to ensure the intense mixing of the gas flow, and thus a good probability of contact between the agents and the photocatalytic surface.

The device 1 described is easy to manufacture. Indeed, tangential fans are commercially available. The impregnation is carried out directly without disassembling the fan. The photocatalyst is suspended in a liquid, typically in water, and is sprayed at the surface of the blades and means of guiding the fan using a compressed gas spraying system, the spray gun type, and finally dried.

More specifically, the deposition can be obtained by spraying with compressed air an aqueous dispersion of semiconductor particles, then drying the film obtained under compressed air only and possibly repeating these operations. Spray deposition is particularly easy and ensures a reproducible and repeatable deposit on both sides of the blades and on the guide means. The film typically has a thickness of the order of 5 μm (microns), this thickness being able to be modulated in particular by varying the initial concentration of the semiconductor particle dispersion and the number of deposition / drying cycles.

The device 1 can be used to decontaminate large gas flows, typically between 1 and 100 m ³ / h, and this with a very good efficiency, namely bactericidal activity greater than 90% as defined in the example in one example. single run.

Thus, at the outlet 2 of the device, a gas stream is generally recovered in which most of the biological and / or chemical agents are inactivated and / or degraded.

The device 1 may comprise, downstream of the outlet 3, means for diverting a part of the outgoing gas flow, associated with means of qualitative and / or quantitative analysis of the biological and / or chemical agents in the gas stream, similar to those that may be present upstream of entry 2.

The device may also comprise, downstream of the outlet 3, means allowing part or all of the outgoing gas flow to be redirected to the inlet 2 of the device, in order to further perfect the decontamination of the biological and / or chemical agents . Alternatively, several devices may be arranged in series or in parallel, where the gas flow to be treated would be divided into several parts.

The device of the invention is particularly effective for the decontamination of gaseous medium containing harmful biological and / or chemical agents, toxic or pathogenic. Various features and advantages of the invention will become apparent from the illustrative example set out below.

EXAMPLE

The aerosol treatment comprising Legionella pneumophila bacteria was carried out by means of a device as described in FIG. 1 having the following characteristics:

- diameter of the fan: 4.75 cm

- total length of the fan: 36.3 cm

- blade size: 30.3 cm x 1 cm (curvilinear) - 16 blades

this device is known under the name "tangential blower with EC motor", type QG 030-303 / 12, marketed by the company EBM-PAPST.

- titanium dioxide used: TiO _Σ P25 type marketed by Degussa, (titanium dioxide having a rutile ratio of forms / anatase 20/80) present in the reactor in the form of an average thickness of deposit approximately 5 μm and BET equal to 50 m ² / g.

- lamp used: 1 single-base compact lamp with UV radiation (actinic powder coating lamp 10 according to the manufacturer) with an electric power of 24 W PLL24W-10 (U-shaped model) ₁ sold by the Philips company, willing to near the reactor at a distance of less than 1 cm from the nearest blade edges.

Of aerosol were formed from an aqueous suspension of Legionella pneumophila comprising 2 10 ⁹ bacteria per ml of water, distributed between 1, 193 September ¹⁰ live bacteria per ml and about as dead bacteria (0.807 September ¹⁰ bacteria dead per ml). These aerosols were produced by injecting with a peristaltic pump the solution containing Legionella pneumophila in the flow through a Venturi type system.

In each case, the ratio of living bacteria to total bacteria (BV / BT) was quantified. This quantification was performed by proceeding as follows. Legionella pneumophila bacteria, regardless of their state, are recovered, after passing through the photocatalytic device (or during the whites produced), in a bubble column with a volume of approximately 9000 ml containing a recovery liquid (sterile water which can contain glycerol), with a volume of 1000 ml. 30ml of solution are removed and then filtered on a 2 cm ² surface filter, in order to recover all the bacteria. The bacteria on filters are then brought into contact with two dyes, a green dye (SYTO9 from Invitrogen) and a red dye (propidium iodide IP). Propidium iodide enters the bacterium only if the wall of the bacterium is damaged. The counting of bacteria on filters is carried out by the epifluorescence microscopy technique.

The bactericidal efficacy is then given by the ratio between the BV / BT value at the outlet and at the inlet of the reactor.

The conditions of the tests carried out and the results obtained are reported in Table I below.

Table I: inactivation of Legionella pneumophila bacteria contained in an aerosol

Claims

1. Device for purifying a gaseous medium, comprising a reactor (9), at least one element (5) provided with a photocatalytic coating (6) and irradiation means (7) associated, characterized in that said element (5) is formed by the blades of a tangential fan.

2. Device according to claim 1, wherein the irradiation means (7) activate a portion of the photocatalytic coating periodically.

3. Device according to one of claims 1 or 2, comprising:

- a reactor (9) comprising a drum (4) capable of being rotated by drive means, on which drum are arranged blades (5) provided on at least one of their faces with a coating photocatalytic device (6), which drum forms with guiding means (8) an inlet (2) adapted to the introduction of the gaseous medium and an outlet (3) adapted to the evacuation of the gaseous medium, and

- Irradiation means (7) of the photocatalytic coating arranged to irradiate at least partially the photocatalytic coating.

4. Process for purifying a gaseous medium, comprising the step of passing at least a portion of the gaseous medium to be purified through the device according to one of claims 1 to 3.

5. The method of claim 4, wherein the gaseous medium comprises biological agents.

6. The method of claim 5, wherein the gaseous medium comprises bacteria.

The method of claim 6, wherein the bacteria are of the genus Legionella.

The method of claim 7, wherein the bacteria are of the genus Legionella pneumophila.

9. The method of claim 4, wherein the gaseous medium comprises chemical species.

10. Process according to any one of claims 4 to 9, wherein the gaseous medium is in the form of an aerosol.