WO2023095074A1

WO2023095074A1 - Process and apparatus for the purification of environmental air

Info

Publication number: WO2023095074A1
Application number: PCT/IB2022/061433
Authority: WO
Inventors: Adriano CEROCCHI; Vincenzo GUTTADAURIA; Lorena NAPPA
Original assignee: Over S.P.A.
Priority date: 2021-11-26
Filing date: 2022-11-25
Publication date: 2023-06-01
Also published as: IT202100030032A1

Abstract

The present invention relates to a process for the purification of environmental air which provides for exposing a flow of air to an electrostatic field and an electromagnetic field. The invention further relates to an apparatus comprising a body with a treatment zone (11) with a first stage (30) equipped with a device (32, 33) for generating an electrostatic field and a second stage (40) equipped with a device (41) for generating an electromagnetic field, a ventilation device (20), configured to generate a flow of air between an inlet (18) and an outlet (19) of the treatment zone (11) and a the control unit connected to the devices (32, 33, 41) for generating the electrostatic and electromagnetic fields and to the ventilation device (20).

Description

TITLE:

“PROCESS AND APPARATUS FOR THE PURIFICATION OF ENVIRONMENTAL AIR”

DESCRIPTION:

The present invention relates to a process and an apparatus for treating environmental air, in particular for purifying it.

Within the scope of the present invention, the expression “purification” refers to a treatment of the environmental air aimed at eliminating or at least significantly reducing microorganisms such as bacteria, viruses and fungi present in the air of an environment, as well as breaking down the amount of suspended solid particles, such as dust and the like.

In the prior art, various types of apparatus for filtering and purifying the air are known.

Among these, apparatuses equipped with electrostatic precipitator devices (or ESP) are quite widespread.

These electrostatic precipitator devices subject the environmental air to a very intense electric (or electrostatic) field in which an electric discharge (called “corona” effect discharge) is generated which generates ion-electron pairs. The ions are attracted to the negative (capture) electrode of the device, while the electrons tend to move towards the positive (discharge) electrode of the device. In this step, the ions produced collide with the suspended contaminant particles and give them an electric charge. The charged powder particles are then attracted towards the capture electrodes where, once in contact with them, they lose their charge and precipitate along the walls.

In addition to the recognized ability to reduce suspended solid particles, electrostatic precipitators also carry out an action of damage to the microorganisms present in the air.

The effects of high intensity electric fields on microorganisms such as bacteria and viruses are described in the literature.

The inactivation of microorganisms depends not only on the tensile strength of the cell membrane, but also on their shape and consistency. High voltage electric fields can therefore cause damage to the nucleic acids of the virus particles, thus reducing the efficiency of nucleic acid amplification.

When microorganisms are exposed to an electric current, or to an induced field, stress is generated on the cells themselves, changing their surface properties and even their shape.

Furthermore, an external electric field can modulate the membrane potential difference. The electric field-induced transmembrane potential difference is a complex function of the specific conductivities of the membrane, cytoplasm, membrane thickness, and cell size.

When the resulting transmembrane potential difference reaches threshold values close to 250 mV, the membranes become permeable. The permeabilized portion of the cell surface is a linear function of the reciprocal of the field strength.

When a cell is permeabilized, osmotic swelling can occur leading to the ingress of water vapour into the cell. This increase in cell volume can lead to membrane rupture.

In the literature there are several theoretical models on what happens in the cell and its membranes at the molecular level such as the visco-elastic model, the dielectric breakdown model and the “electroporation model”.

Several studies argue that it is unclear whether the inactivation of microorganisms is the result of structural damage resulting in the loss of essential cellular components or is attributed to metabolic dysfunction following exposure to an electrostatic field.

According to Mendis et al.⁽¹⁾, the lipid bilayer membrane can be idealized as a capacitor, whose plates are separated by a uniform elastic medium, where the applied voltage leads to a compressive electrical force which ultimately leads to a catastrophic collapse of the membrane.

The negative electrostatic field has a potentially stronger inactivating effect on microorganisms than the positive electrostatic field and it is speculated that it may have to do with the net charge of the microorganism. Studies by Mainelis et al.⁽²⁾ on airborne microorganisms also indicated that microorganisms carry a net negative electrical charge; in practice, a larger fraction of bacteria have more negative charges on their outer surface than positive charges. Furthermore, the same study showed that sensitive microorganisms in the air are less susceptible to damage imparted by additional negative charges than positive charges.

Exposure of microorganisms with a net negative charge to a negative electrostatic field can cause the reorientation of the charges, which would change their membrane potential.

Cells depend on their membrane potential for their basic metabolic activity. For this reason, it is probable that alterations in the potential induce damage to the cell. In general, inactivation depends on electrostatic field strength and, in some cases, on polarity, as well as on the treatment time.

Other studies^(3,4) theorize that mechanisms involving reactive species generated in the crowns contribute to the inactivation.

This is consistent with the observation that inactivation increased after the onset of corona discharge. The ESP used in this study produces a localized plasma (or region of ionized gas) in the immediate vicinity surrounding the stainless steel wire (the discharge electrode). These ions then attach to or interact with gas molecules creating the reactive species.

Reactive species present in corona discharges can lead to inactivation through sufficient damage to the protein or nucleic acid structure of microorganisms.

Direct damage to the coat protein, maturation protein, or portions of the coding regions on the RNA genome could make the virion non-infectious.

The types and amount of reactive species produced by corona are dependent on whether the ESP is operated with a negative or positive applied potential (i.e., negative or corona positive, respectively), which could affect inactivation efficiencies. In fact, the logarithmic reduction values obtained with the negative crown are statistically significantly higher than with the positive crown.

In addition to the apparatuses equipped with the aforementioned electrostatic precipitator devices, for the purification of the air, in particular for the elimination of the microorganisms dispersed therein, apparatuses are also known which use light radiations with wavelengths in the UV range.

Also in this case the effects that such radiations cause on microorganisms such as viruses, bacteria and fungi have been studied.

These effects are mainly divided into three categories: photo-induced reactions in DNA that inhibit the replication of microorganisms, the generation of reactive oxygen species within microorganisms that can damage the cell and damage to the membrane.

Regarding the first effect, UV promotes electronic transitions to excited states if the wavelengths are appropriate. This excitation can foster a bond change within a specific system.

In the case of DNA, it has been studied that the electronic transition due to the UV wavelength at 254 nm favours a structural change. Therefore, in that wavelength range the UV absorption will be extremely intense. The most important UV-induced photoreaction between and within Nas results in the covalent bonding of two spatially adjacent bases along a single DNA strand.

The variables that contribute to this phenomenon are temperature, exposure time, the ratio between lamp power, volume and relative humidity.

The amount of UV rays is defined by the following equation:

If the quantity (dose) is not sufficient (typically <2.1 Jem^-2) the bacteria can repair some of the DNA damage.

On the other hand, proteins (namely the main component of prokaryotic and eukaryotic cells and the viral capsid) are another target of photo oxidation.

Indirect photochemical damage consists of the absorption of light by sensitizers and the transfer of electrons to molecular oxygen (O2) dissolved in fluids.

Some studies® determined that UV treatment induced cell membrane damage which was evaluated by the use of the fluorescent dye propidium iodide (PI). Thus, UV-induced membrane damage may be a potential bactericidal inactivation mechanism.

As mentioned above, on the market there are devices for purifying environmental air which implement one of the two technologies described.

Both types, i.e. devices equipped with ESP devices or with UV radiation sources, however have limited and in some cases even insufficient reduction effectiveness, in particular as regards UV radiation devices.

These purifying apparatuses are generally used in closed environments of homes, offices, shops, clubs, etc. and, often, they are independent of the heating and cooling systems, since they are installed after the construction of these systems and in already furnished rooms.

For these reasons, the overall size is a determining factor in the choice of such devices, especially when they have to be placed in homes or offices.

For both technologies considered, the effectiveness of killing microorganisms present in the air increases as the exposure time of the treated air volume increases with respect to the electrostatic field generated by the ESP or to the electromagnetic field generated by the ultraviolet radiation sources.

Since these are devices that treat a flow of moving air, the exposure time, in turn, depends on the size of the device. With the same flow rate of treated air (the minimum value of which depends on the type of environment and its dimensions) and regardless of the conformation of the apparatus, in general it can be stated that an air treatment area with a greater extension in direction of movement of the air flow allows a greater ability to kill microorganisms.

However, considering the limitations mentioned above, the apparatuses of the prior art often offer a compromise between the two factors, reduction capacity and size, resulting in many cases to be ineffective.

In addition to the size of the apparatus, another non-negligible aspect for these apparatuses is their production cost and, therefore, the selling price.

In fact, even where large dimensions are not a problem, the production of an apparatus with a larger treatment zone implies the adoption of a greater number of raw materials and components with a consequent increase in costs.

In addition to this, by increasing the sources which generate the electrostatic and electromagnetic fields (electrodes and UV sources), the electrical energy consumption of the apparatus also increases proportionally.

In this context, it is an object of the present invention to propose a process and an apparatus for the treatment of environmental air which overcome the limits of the prior art.

In particular, the object of the present invention is to develop a process and an apparatus by means of which it is possible to purify the air of an environment by completely, or almost completely, eliminating both microorganisms such as viruses, bacteria, fungi and the like, as well as particulates and pollutants in suspension, potentially harmful to health.

Another object of the present invention is to propose a space-saving apparatus for treating environmental air which can be easily placed in any environment, even domestic.

A further object of the present invention is to provide a cost-effective and therefore accessible apparatus to a large number of both professional and private users with low environmental impact.

The above objects are achieved by a process for the purification of environmental air according to claim 1 and by an apparatus according to claim 7.

In detail, according to the invention, the process for the purification of environmental air comprising a first step which provides for preparing a confined treatment zone with at least one inlet and at least one outlet for a flow of moving air.

Said treatment zone typically comprises a volume delimited by one or more walls arranged so as to have two passages in communication with the environment, for the inlet and outlet of the flow of air, respectively.

According to the invention, the treatment zone comprises a first stage and a second stage. Said first and second stages are arranged between the inlet and the outlet of the treatment zone and communicate with each other. According to a preferred variant of the invention, the second stage is arranged downstream of the first stage in the direction of the flow of air between the inlet and the outlet. According to an alternative variant, the first stage and the second stage may be reversed with respect to the direction of the flow of air.

The process comprises a further step which provides for the generation, in the first stage of the treatment zone, of an electrostatic field and a subsequent step, or contextual to the previous one, which provides for generating, in the second stage of the treatment zone, an electromagnetic field through UV radiation.

The process according to the invention comprises a further step which provides for generating a flow of air between the inlet and outlet of the treatment zone. In detail, the flow of air entering the treatment zone comprises air to be purified taken from the environment where said treatment zone is located.

In particular, according to a first embodiment of the invention, wherein it is envisaged to guide the flow of air through the electrostatic field in the first stage and subsequently through the electromagnetic field in the second stage of the treatment zone.

According to an alternative embodiment of the invention, it is provided to guide the flow of air through the electromagnetic field in the second stage and, subsequently, through the electrostatic field in the first stage of the treatment zone.

During this step, the flow of air is then exposed in sequence first to the electrostatic field and then to the electromagnetic field, or vice versa.

Finally, the process provides for guiding the flow of air leaving the second stage towards the outlet of the treatment area.

The flow of purified air leaving the treatment zone is then reintroduced into the environment.

With the process of treating the air in an environment described above it is possible to obtain particularly high efficiency in the reduction of pollutants and inactivation of any microorganisms such as viruses, bacteria and fungi which may be present.

In fact, the applicant has surprisingly discovered that the exposure of these microorganisms both to an electrostatic field and to an electromagnetic field causes them very high cellular damage, greater than the sum of the effects generated by the two energy fields applied individually.

According to the first variant described, this effect is probably linked to the partial damage to the cells of the microorganism, caused by the electrostatic field, which allows the electromagnetic field to carry out a more effective action than that which would be obtained on intact cells.

In more detail, when the microorganism crosses the electric field, its membrane is partially damaged and/or has greater permeability. In an airborne medium, the increased permeability of the membrane causes cytoplasmic leakage since the density of molecules inside the cells is much greater than those present in the air. The damage to the membrane caused by the electromagnetic field can therefore be enhanced by the increased vulnerability of the microorganisms. Furthermore, due to cytoplasmic leakage, DNA and its capsid proteins are closer to the membrane and are therefore more subject to the action of the electromagnetic field.

Furthermore, still in the first variant where the flow first passes through the first stage and then the second, since said first stage is also configured to remove a considerable amount of suspended particulate from the air flow, the effectiveness of the electromagnetic field on the microorganisms is improved by virtue of the lower probability that the particulate will screen against microorganisms allowing the microorganisms to be fully and effectively exposed to electromagnetic radiation.

What has been verified by the Applicant by means of tests carried out with an air purification apparatus which implements the method of the invention (which will be described hereinafter) is that the use of said two energy fields allows decidedly higher thresholds of killing of microorganisms to be reached than the sum of the effects of the individual fields used alone, i.e. a synergistic effect is achieved between the effects of the two fields.

According to one aspect of the invention, the value of the electrostatic field adopted in the first stage is selected according to the geometric parameters of the first stage and the components used; more generally, the value of the electrostatic field is selected between a minimum value such as to be able to trigger the corona effect and a maximum value such as not to cause electric shocks.

In this way the effectiveness of reduction is maximized by limiting the formation of ozone, but also the dimensioning of the components of the purifying apparatus that implements the process and the energy consumption.

According to a preferred variant, the electrostatic field is generated by a device comprising capture electrodes and discharge electrodes arranged in the first stage of the treatment zone. Even more preferably, the discharge electrodes comprise an array of metal wires stretched along one or more parallel planes and arranged between two capture electrodes in the form of metal plates or sheets.

According to another aspect of the invention, the electromagnetic field in the second stage of the treatment zone is obtained with ultraviolet radiation having a wavelength of between 250 nm and 280 nm. This range allows effective sterilization to be obtained but also the destruction of any ozone present in the flow of air, including any ozone formed in the first stage by the electrostatic field.

Said ultraviolet radiation is generated by ultraviolet light sources disposed in the second stage. Said sources are preferably configured to uniformly irradiate the whole volume of the second stage through which the flow of air flows. For example, said sources may be distributed in a uniform manner along the perimeter zone which delimits the second stage or placed in the passage area of the flow of air and oriented so as to spread the radiation at 360°.

According to another aspect of the invention, the treatment zone comprises a channel which extends substantially linearly between the inlet and the outlet. In practice, the inlet and outlet are arranged at opposite ends of the treatment zone. In this way it is avoided that part of the freshly purified air coming out of the outlet of the treatment chamber and not yet mixed with the rest of the environmental air is taken from the room at the inlet.

Furthermore, the adoption of a straight channel maximizes the efficiency of action of the two stages since it favours a laminar flow of air without vortices, the latter, in fact, could reduce the effects of electrostatic and electromagnetic fields.

The first stage and the second stage are preferably placed consecutively with respect to each other, i.e. the flow of air leaving the first stage enters the second stage directly.

In this way, in addition to reducing the size of the treatment zone, the effects of the electromagnetic field on the microorganisms are optimized since maximum exposure thereof to is obtained without however producing ozone.

The average speed of the flow of air may vary according to the size of the treatment zone, in particular the extension of the two stages in the direction of the flow of air. Typically this speed is between 2 m/s and 5 m/s.

As already stated, the present invention also relates to an apparatus for purifying environmental air configured to implement the purification process described above.

According to the invention, the apparatus comprises a body which defines an internal volume in which a treatment zone is formed. Said body is provided with at least two openings, respectively an inlet and an outlet, which put the treatment zone in communication with the external environment.

According to a preferred embodiment, the treatment zone has the shape of a substantially straight conduit or channel delimited at the ends by the inlet and outlet respectively.

According to the invention, the treatment zone comprises a first stage equipped with a device for generating an electrostatic field and a second stage equipped with a device for generating an electromagnetic field.

The apparatus further comprises a ventilation device, configured to generate a flow of air between the inlet and the outlet of the treatment zone. More precisely, the ventilation device is configured to suction environmental air from the inlet and bring it towards the outlet crossing the first and second stages of the treatment zone.

According to one aspect of the invention, the device for generating the electrostatic field comprises a pair of metallic plates, which act as capture electrodes, between which a plurality of filiform electrodes, which act as discharge electrodes, are arranged.

The discharge electrodes are connected to a high voltage power supply while the metallic plates are preferably electrically grounded (at 0 V).

The supply voltage of the capture electrodes is selected according to the size of the capture electrodes, their distance and the distance between them and the discharge electrodes. As mentioned above, the power supply voltage is selected in such a way as to be able to trigger the corona effect without producing electric discharges and ozone.

For example, an optimal voltage range is between 5 KV and 10 KV.

According to another aspect of the invention, the device for generating the electromagnetic field comprises one or more sources of ultraviolet radiation, preferably with a wavelength between 250 nm and 280 nm, more preferably between 250 nm and 260 nm.

Said at least one source is preferably of the LED type. According to one embodiment of the invention, the source may comprise a lamp provided with a plurality of LEDs oriented at 360° around an axis transverse to the direction of the flow of air and surrounded by a reflecting surface. According to this variant, the source is located in a central area of the second stage, i.e. it remains immersed in the flow of air.

Alternatively, the source may comprise an array of LEDs arranged on a flat plate-like support, which may be applied to the internal walls delimiting the second stage.

According to another aspect of the invention, the ventilation device is located close to the outlet of the treatment zone. Said device, by pushing the air present in the treatment zone towards the outside through the outlet, generates a depression inside said treatment zone, which causes the environmental air to be suctioned in from the inlet.

Overall, the apparatus has a flattened shape, i.e. it has the dimensions of width and height more developed than the thickness. The limited thickness of the apparatus allows two advantages to be obtained. The first is that the apparatus can be easily applied to a wall without significantly interfering with the environment. This is particularly useful in environments such as homes, offices, schools or shops, since it is possible to equip the apartment with an external casing with a sophisticated design that can be combined with the furnishings of the environment.

The second advantage is that a treatment zone with a flat and thin conformation (where the inlet and outlet are generally arranged at the ends of the width, and in any case not of the thickness) allows for an equally flat and thin flow of air which allows both the electrostatic field generator and the electromagnetic field generator to work with maximum efficiency over the entire volume of the respective stage. The treatment zone, which preferably has said flat and thin conformation, has the ratio between the dimensions of the width, between the inlet and the outlet, or of the height, perpendicular to the width in a plane, and the dimension of the thickness is comprised, preferably, between 2 and 12, more preferably between 4 and 8.

The apparatus further comprises a control unit connected to the devices for generating the electrostatic and electromagnetic fields and to the ventilation device.

According to another aspect of the invention, the apparatus may further comprise at least one sensor indicative of the quality of the inlet air, for example a sensor which detects the quantity of particulate matter present in the flow of air.

According to a preferred variant, the control unit is connected to said sensor and is configured to control the devices for generating the electrostatic and/or electromagnetic fields, according to the value of the particulate matter (PM) measured by the sensor.

Further features and advantages of the present invention will become more apparent from the description of a preferred but non-exclusive exemplary embodiment of an apparatus for the purification of environmental air, as shown in the accompanying figures, in which:

- Figures la and lb are two front perspective views of the apparatus according to an embodiment of the present invention;

- Figure 2 is a front view of the apparatus of Figure 1 partially disassembled;

- Figure 3 is a sectional view of the apparatus of Figure 1.

With reference to the accompanying figures, the apparatus for the purification of air, indicated as a whole with reference numeral 1, comprises a box-shaped body 10 with an internal compartment 11. In the variant illustrated, the body 10 has a substantially parallelepiped shape with two main faces 12, 13, also referred to as the front face and rear face, and side faces 14-17. According to one embodiment of the invention, the apparatus is designed to be fixed to a vertical wall at one of the main faces, specifically the rear face 13. However, the apparatus 1 may possibly be placed on the ground, resting on one of the side faces or on the rear face.

The body 10 may optionally include decorative elements applied externally, such as for example covering panels, frames, etc., not shown in the figures, to make its appearance more pleasant and possibly coordinated with the furnishings, especially in the case where the apparatus is placed in domestic environments, in offices or in hotels.

In the illustrated example, the body 10 is formed by two semi-shell parts 10a, 10b joined on a plane parallel to the main faces 12, 13.

The internal compartment 11 is placed in communication with the outside through two passages (openings) 18, 19, hereinafter referred to respectively as inlet and outlet, obtained on two side faces 14, 16. Said compartment 11 corresponds to the treatment zone of the apparatus.

The flow of air to be treated is moved by a motor-ventilation unit 20 located at the outlet 19 suitable for generating a depression in the compartment 11 by suctioning environmental air from the inlet 18 and expelling it from the outlet 19, after having passed through the compartment 11 according to a direction F indicated by the arrow in the figures.

In the example illustrated, the motor-ventilation unit 20 comprises a motor 21 which drives a radial fan 22.

In the internal compartment 11 there are the first stage 30 and the second stage 40 for air treatment.

The first stage 30 is located downstream of the inlet 18 in the direction F of the flow of air. Said first stage 30 comprises a support element 31, for example a quadrangular frame, to which electrodes 32 are applied in the form of metal wires preferably arranged parallel and equidistant from each other. In more detail, the support element 31 and the electrodes 32 lie on a plane parallel to the flow F of the air in the compartment 11 and, preferably, parallel to the main faces 12, 13 of the body 10.

Typically the support element 31 and the electrodes 32 are arranged in the compartment 11 at an intermediate distance between the main faces 12, 13, i.e. roughly in the centre of the compartment in the direction of the thickness of the body 10.

The electrodes 32 are electrically connected to a high voltage power supply 35.

The first stage also comprises a pair of metallic plates 33, each fixed to a half -part 10a, 10b of the body 10, between which the support element 31 and the electrodes 32 are arranged (fig. 3). In practice, said plates 33 define a section of channel crossed by the flow of air which strikes the electrodes 32.

According to one embodiment, said plates 33 are parallel to each other and arranged facing each other at a distance between about 20 mm and 60 mm. This distance may possibly vary according to the overall dimensions of the body 10.

The plates 33 are electrically grounded.

The second stage 40 is located downstream of the first stage 30 in the direction F of the flow of air.

The second stage 40 comprises at least one or, preferably, two or more lamps 41 which emit ultraviolet light. Said lamps 41 are preferably of the LED type and comprise a plurality of LEDs arranged on a flat or cylindrical support. In the first case at least two lamps 41 are arranged facing each other and the flow of air flows between them. In the second case, as in the illustrated example, the lamps are arranged substantially in the centre of the body 10, in the sense of the thickness, so as to remain immersed in the flow of air and, by virtue of the cylindrical arrangement of the LEDs, they can uniformly irradiate the whole flow of air. According to the latter variant, the internal walls of the compartment 11 at the second stage 40 are preferably coated with a light-reflecting material so as to spread the ultraviolet radiation even more uniformly.

The flow of air leaving the second stage 40 is pushed by the motor-ventilation unit 20 towards the outlet 19.

The various components of the apparatus, for example the motor-ventilation unit 20, the high voltage power supply 35 and the lamps 41, are controlled by a control unit included in an electronic card 50 located in a housing 25 of the body 10, preferably separate from the compartment 11 where the two stages 30, 40 are located.

Said control unit may manage, for example, the rotation speed of the motor 21, the voltage supplied by the high voltage power supply 35 and the switching on or off of the latter and of the lamps 41.

The apparatus is also equipped with sensors 60 for monitoring the environmental air. Also said sensors 60, like the electronic board 50, are preferably located in an internal area of the apparatus separate from the compartment 11. In more detail, said sensors are placed in communication with the external environment at a side face 15 of the body transverse to the faces 14, 16 where the air inlet and outlet are obtained. In this way it is possible to monitor environmental air which is not mixed with the treated air freshly expelled from outlet 19.

As mentioned above, the applicant has carried out tests with an apparatus according to the present invention to evaluate the effectiveness of killing viruses, bacteria and fungi.

The apparatus used for the test corresponds to that described above with reference to the figures.

The first stage has a width (in the direction of the flow of air) of approximately 41 cm, a height of 33 cm and a thickness, understood as the distance between the plates, of 4 cm.

The second stage has a width of about 16 cm, a height of 33 cm and a thickness of 8 cm.

The supply voltage of the discharge electrodes used is 10 kV.

The LED lamps used have a wavelength of 254 nm.

The air flow rate leaving the apparatus during the test runs is 80 m3/h. The test was performed according to the protocol of the ISO 15714:2019 standard “Method of evaluating the UV dose to airborne microorganisms transiting in-duct ultraviolet germicidal irradiation devices”.

The procedures described below are performed with each of the following organisms: Serratia marcescens ATCC1388O, Bacillus subtilis ATCC6633 and Cladosporium sphaerospermum ATCC 11289. Serratia marcescens is a gram-negative bacterium belonging to the Enterobacteriaceae family which represents the microorganism with high susceptibility to UV radiation.

Bacillus Subtilis is a Gram-positive bacterium of the Bacillaceae family, which represents the low susceptibility microorganism.

Finally, Cladosporium sphaerospermum is a spore-forming fungus representing fungi with high resistance to UV rays.

The test organism is initially cultured on solid plated culture medium. From the colonies obtained on the plate, after appropriate dilutions, a microbial solution is obtained at the cfu/mU concentration desired for inoculation.

The microbial suspension is then introduced into the flow of air via an aerosol generator connected in the inlet area. The sampling of the microorganism is obtained by an air sampler (SAS) in the outlet area of the device; in this system the air is suctioned in at a fixed speed for variable times through a head with a series of small holes. The resulting laminar airflow is directed onto the surface of an agar plate containing microbial growth medium. The culture medium plates are then incubated.

The test as described above was performed three times for each of the operating conditions of the apparatus listed below: a) electrostatic field generator and activated UVC FED lamps; b) electrostatic field generator and UVC LED lamps deactivated;

It was verified that each result obtained has a relative difference of less than 50%, if not, the anomalous result is discarded.

The following Table 1 shows the bacterial inactivation values obtained with the apparatus in condition a) i.e. in operation:

Table 1

The applicant performed two further tests only with the microorganism Serratia marcescens, with the same test methods described above, but with the following operating conditions of the apparatus: a) electrostatic field generator activated and UVC LED lamps deactivated (Table 2); b) electrostatic field generator deactivated and UVC LED lamps activated

(Table 3);

Table 2

Table 3

As can be appreciated from the data resulting from the tests, the process for purifying the ambient air according to the present invention allows obtaining an even total effectiveness of killing microorganisms as regards viruses and bacteria.

As mentioned above, this is due to the combined and sequential action of the electrostatic field generator and UVC radiation sources.

This combination, in fact, allows obtaining a reduction efficacy that is in any case higher than the sum of the reduction values of the individual sources, as demonstrated by the data in Tables 2 and 3.

The applicant has also carried out tests with the apparatus having the same geometrical features but varying the parameters of the sources of the energy fields (toward theoretically worsening conditions) to evaluate the effectiveness of killing viruses, bacteria and fungi even in non-optimal conditions.

The tests were conducted with a supply voltage of the discharge electrodes equal to 5kV (lower limit for this geometry for the activation of the corona effect).

The UV-C LED lamps used in the previous tests were instead replaced with sources with emissions in the UV-A spectrum. Specifically, a lamp was used which emits radiation with a wavelength between 380 nm and 400 nm.

The air flow rate at the outlet of the apparatus during the test trials equal to 130 m3/h; a greater range, therefore speed, involves less exposure to energy fields. The tests were conducted on the microorganisms Bacillus subtlis and Cladosporium sphaerospermum.

Table 5 shows the inactivation percentages for Bacillus subtlis with a power supply of the discharge electrodes equal to 5 kV and a single UV-A lamp. Table 7 instead lists the percentages of inactivation for Cladosporium sphaerospermum with power supply of the discharge electrodes equal to 10 kV and UV-A lamps.

Table 4

Table 5

Table 6

Table 7

From the results obtained, despite the theoretically pejorative parameters adopted, it has been demonstrated that the combination of the energy fields allows achieving a reduction effectiveness that is in any case higher than the sum of the reduction values given by the single energy fields.

In detail, in Table 5 it is possible to note how proximity to the minimum limit for triggering the corona effect leads to a lowering of the inactivation performance of the electrostatic field but, however, that the combination of the two energy sources considerably increases the percentage of inactivation of the tested microorganism.

From Table 7, on the other hand, it can be seen that by virtue of the greater mass and difference of the external membrane of the Cladosporium sphaerospermum, the inactivation efficacy is mainly due to the electrostatic fields but only the union with the electromagnetic fields allows reaching the maximum inactivation efficiency.

The present invention has been described for illustrative and non-limiting purposes, according to some preferred embodiments. The man skilled in the art will be able to find several other embodiments and variants thereof, all falling within the scope of protection of the following claims. Bibliography ) Mendis et al. - IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 28, NO. 4, AUGUST 2000 ) Mainelis et al. - Electrical charges on airborne microorganisms - Aerosol Science 32 (2001) 1087) 1110 ) Danil Dobrynin et. Al. - Inactivation of bacteria using de corona discharge: role of ions and humidity - New J Phys. Author manuscript; available in PMC 2012 Mar 6.) Manuela Buonanno et al. - Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses Reports volume 10, Article number: 10285 (2020) Cite this article ) Marcela Schenk et al. - Inactivation of Escherichia coli, Listeria innocua and Saccharomyces cerevisiae by UV-C light: Study of cell injury by flow cytometry - LWT - Food Science and Technology, Volume 44, Issue 1, 2011.

Claims

23

CLAIMS A process for the purification of environmental air, comprising the following steps: a) preparing a confined treatment zone (11) with at least one inlet (18) and at least one outlet (19) for a flow of moving air; b) generating an electrostatic field in a first stage (30) of the treatment zone (11); c) generating an electrostatic field in a second stage (40) of the treatment zone (11); d) generating a flow of air between the inlet (18) and the outlet (19) of the treatment zone; e) guiding the flow of air through the electrostatic and electromagnetic fields in the first stage (30) and in the second stage (40) of the treatment zone (11); f) guiding the flow of air leaving the treatment zone (11). Process according to claim 1, wherein it is envisaged to guide the flow of air through the electrostatic field in the first stage (30) and subsequently through the electromagnetic field in the second stage (40) of the treatment zone (11). Process according to claim 1 or 2, wherein the electrostatic field is generated by a device comprising discharge electrodes (32) and capture electrodes (33) arranged in the first stage (30) of the treatment zone (11). Process according to any one of the preceding claims, wherein the electromagnetic field in the second stage (40) is obtained with ultraviolet radiation with a wavelength of between 250 nm and 280 nm. Process according to any one of the preceding claims, wherein the treatment zone (11) comprises a channel that extends substantially linearly between the inlet and the outlet. Process according to any one of the preceding claims, wherein the first stage (30) and the second stage (40) are positioned consecutive to one another, in other words the flow of air leaving one stage enters directly into the other. Process according to any one of the preceding claims, wherein the average speed of the flow of air in the treatment zone (11) is between 2 m/s and 5 m/s. Apparatus (1) for the purification of environmental air, comprising:

- a body (10) defining an internal compartment (11) in which there is a treatment zone, said body (10) having at least one inlet opening (18) and one outlet opening (19) which place the treatment zone (11) in communication with the outside environment;

- a first stage (30), in the treatment zone (11), equipped with a device (32, 33) for generating an electrostatic field;

- a second stage (40), in the treatment zone (11), equipped with a device (41) for generating an electromagnetic field;

- a ventilation device (20), configured to generate a flow of air between the inlet (18) and the outlet (19) of the treatment zone (11);

- a control unit connected to the devices (32, 33, 41) for generating the electrostatic and electromagnetic fields and to the ventilation device (20). Apparatus (1) according to claim 8, wherein the treatment zone (11) has the shape of a substantially straight conduit or channel delimited at the ends by the inlet (18) and the outlet (19) respectively. Apparatus (1) according to claim 9, wherein the treatment zone (11) has a flat, thin conformation where the ratio between the dimensions of the width between the inlet and outlet, or of the height, perpendicular to the width in a plane, and the dimension of the thickness is between 2 and 12. Apparatus (1) according to any one of the preceding claims, wherein the device for generating the electromagnetic field comprises one or more sources of ultraviolet radiation, with a wavelength of between 250 nm and 280 nm. Apparatus (1) according to any one of the preceding claims, wherein the device for generating the electrostatic field comprises a pair of metallic plates (33), which act as capture electrodes, between which are arranged a plurality of filiform electrodes (32) which act as discharge electrodes and wherein the discharge electrodes are connected to a high-voltage power supply (35) and the metallic plates are electrically earthed. 13. Apparatus (1) according to claim 12, wherein the power voltage of the capture electrodes (32) is regulated so as to trigger the corona effect without producing electrical discharges.

14. Apparatus (1) according to any one of the preceding claims, comprising at least one sensor (60) indicating the quality of the incoming air, the control unit being connected to said sensor and being configured to command the devices for generating the electrostatic and/or electromagnetic fields, as a function of the values measured by said at least one sensor.