WO2010103296A2

WO2010103296A2 - Improvements in and relating to sterilisation and/or decontamination

Info

Publication number: WO2010103296A2
Application number: PCT/GB2010/000471
Authority: WO
Inventors: James Robert Jennings; Geoffrey Bruce Randall
Original assignee: Steritrox Limited
Priority date: 2009-03-12
Filing date: 2010-03-12
Publication date: 2010-09-16
Also published as: WO2010103296A3; GB2468519A; JP5815415B2; KR101658401B1; KR20120004989A; JP2012520104A; GB2468519B; GB0904266D0

Abstract

A method of sterilisation, sanitisation and/or decontamination comprises the steps of producing a humidified environment having a relative humidity which is higher than ambient humidity; discharging ozone into the humidified environment; maintaining the ozone level at a concentration that will achieve the required degree of decontamination and sterilisation of the humid environment; reducing the relative humidity of the decontaminated and sterilised environment and passing the environment through a catalyst to reduce the concentration of ozone to a predetermined level.

Description

Improvements in and relating to sterilisation and/or decontamination '

This invention relates to a method of sterilisation and/or decontamination, including sanitation, and to apparatus for use with said method.

It is a requirement to sterilise and sanitise enclosed spaces, such as kitchen areas and hospital rooms, quickly and effectively in order to destroy potentially harmful microorganisms, such as bacteria and viruses, contaminating the air and surfaces therewithin, in an acceptable timescale.

The biocidal activity of ozone is widely known and appreciated, and it is also known that the provision of ozone in a humid atmosphere increases the biocidal effectiveness.

However, problems associated with the use of ozone as a biocide have been the relatively lengthy post-treatment process to ensure that the environment is safe for returning occupants, the use of potentially environmentally damaging chemicals during the process, the general ineffectiveness of the process in sanitising the environment, and the overall lack of simplicity in quickly setting up and using the apparatus.

The Applicant's previous application (EP 1500404, Steritrox Limited), demonstrated a method whereby the beneficial effect of ozone in a humid atmosphere could be utilised with the residual atmosphere being freed from harmful ozone within a useful timescale. The method involved the addition of an olefinic compound, such as butene-2 to the atmosphere in sufficient quantity to react with and remove all of the residual ozone. Whilst this process is efficient at providing a substantially sterile environment, it has now been recognised that the reaction between the residual ozone and the olefinic compound leads to the production of a range of compounds, some of which have harmful properties when present in the atmosphere above a certain concentration, commonly referred to as the Occupational Exposure Level (OEL). Without prejudice to the invention, the range of compounds may include, for example, acetaldehyde, acetic acid, formaldehyde, formic acid, methanol, propionaldehyde and the like. Furthermore, the large amount of water that has to be provided to achieve the required humidity has certain drawbacks.

The present invention seeks to provide a solution to these problems, in particular to provide a high degree of sterilisation and/or decontamination process and apparatus that enables a substantially sterilised area to be made safe of harmful products within an acceptable timescale.

According to a first aspect of the present invention, there is provided a method of sterilisation, decontamination and/or sanitation, the method comprising the steps of: a) producing a humidified environment having a relative humidity which is higher than ambient humidity; b) discharging ozone into the humidified environment; c) maintaining the ozone level at a concentration that will achieve the required degree of decontamination, sterilisation and/or sanitation of the humid environment; d) reducing the relative humidity of the decontaminated, sterilised and/or sanitised environment; and e) following the reduction in relative humidity of the environment, passing the substantially decontaminated, sterilised and/or sanitised environment through a catalyst to reduce the concentration of ozone to a predetermined level.

The water obtained during step d) may optionally be collected and re-used in the method for producing the humidified environment, thereby reducing the amount of water used by the process and removing the need to dispose of waste water.

The reduction in relative humidity may be achieved by one or more of a dehumidifying step, the passage of the environment through a water absorbent to remove water molecules and/or by heating the environment. Preferably, the method includes all these steps for reducing the relative humidity.

Preferably, a hydrocarbon containing a carbon-carbon double bond is then introduced into the environment to react preferentially with any residual ozone. Preferably, the hydrocarbon comprises a secondary olefin, cis or trans, including cyclic olefins. The decontaminated and sterilised environment may be recycled through the catalyst until the concentration of any harmful products falls to a safe level. The humidified environment is preferably around 90 % v/v at ambient temperatures and reduced to a minimum of about 30% prior to its passage through the catalyst. Preferably, the humidified environment has a partial pressure of water vapour of at least 5.00 torr but this will depend upon the temperature of the environment. For example, a cool environment having a temperature of around 6⁰C will preferably have a partial pressure of 6.00 torr and a warmer environment having a temperature of around 18⁰C will preferably have a partial pressure of around 13.9 torr.

Further preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 11 inclusive.

According to a second aspect of the present invention, there is provided a sterilisation, decontamination and/or sanitation apparatus for use with a method in accordance with the first aspect of the present invention, the apparatus comprising a humidifier unit, an ozone discharge unit, humidity reducing means, an ozone depletion catalyst and a controller by which the humidifier unit, humidity reducing means and/or ozone discharge unit are controllable based on predetermined conditions.

Optionally, the humidity reducing means may include recycling means to enable the water collected to be reused in the humidifier unit. Preferable and/or optional features of the second aspect of the invention are set forth in claims 12 to 20 inclusive.

The invention will now be more specifically described, by way of example only, with reference to the accompanying drawings, in which :

Figure 1 is a diagrammatic side elevational view of one embodiment of sterilisation and decontamination apparatus for carrying out the process of the invention; and Figure 2 is a diagrammatic front view of the apparatus shown in Figure 1;

The process and apparatus of the present invention use ozone at high humidity levels (generally in excess of 90% at ambient temperature) for the sterilisation and decontamination of an environment. However, the actual relative humidity will depend upon the temperature of the environment to be treated. The process and apparatus also includes an ozone depletion catalyst for reducing levels of the ozone and any unwanted by-products such as hydrogen peroxide to a safe level in minimal time, thereby reducing the time during which a room has to be kept unoccupied. However, it is unusual for catalysts to operate close to the dew point, particularly when water is not one of the reactants. This can result in the surface of the catalyst becoming covered by a film of water molecules, thus inhibiting the required reaction. Furthermore, the high humidity levels can leave a very damp feel to the environment after completion of the sterilisation/decontamination process. The present invention alleviates this problem by pre-treating the atmosphere to reduce its relative humidity, preferably to less than 30%, prior to its entry into the catalytic converter for the removal of ozone.

In one embodiment of the present invention, the relative humidity of the environment is reduced by heating the air prior to its entry into the catalyst vessel. This moves the reaction conditions further away from the dew point and thereby reduces the thickness of the absorbed film of water.

hi an alternative embodiment of the present invention, a dehumidifϊer is provided prior to the catalyst. This device does have additional benefits in that the condensed water extracted by the dehumidifier also contains some of the organic byproducts of the reaction, such as acetaldehyde, formaldehyde, acetic acid and formic acid. Any residual hydrogen peroxide is also partially removed by such means.

In yet a further embodiment of the present invention, water is removed by means of an absorption trap containing, for example, a molecular sieve or silica gel.

The accompanying drawings illustrate a preferred embodiment of the present invention which includes multiple means for reducing the humidity of the atmosphere, namely a dehumidifier unit, an absorption trap in the form of a molecular sieve and a heater. This particular combination has been found to be especially beneficial in reducing the levels of water present in the atmosphere to an acceptable level which thus helps to decrease the level of deactivation of the catalyst. The large amount of water required for the process means that an absorption trap alone, such as a molecular sieve, soon becomes saturated, requiring frequent replacement or regeneration of the sieve. In contrast, the provision of a dehumidifier removes the bulk water from the atmosphere whilst the absorption trap reduces the water levels further to a very low value thereby extending the potential life of the catalyst, prior to any regeneration stage. Heating the air prior to its entry into the catalyst not only helps to regenerate the trap but increases the rate of ozone decomposition on the catalyst.

An example of a sterilisation and decontamination apparatus 10 for carrying out the method of the present invention comprises a portable enclosure 12 which can be opened and which, in use, can generate a positive pressure within the interior to protect sensitive devices contained within the enclosure from the deleterious affects of the ozone. However, it is to be appreciated that alternative means could be provided to protect internal sensitive components from being damaged by the ozone. The enclosure 12 has wheels 14 and houses a humidifier unit 16 having a humidified air outlet 17, an ozone discharge unit 18 having an ozone discharge outlet 20, a dehumidifier 90, a moisture absorption unit 92, a heater 94, a vessel containing an ozone catalyst 70, an ozone catalyst fan 71, a hydrocarbon discharge unit 22 having a hydrocarbon discharge outlet 24, and a control unit 26.

The humidifier unit 16 in the illustrated example includes a humidifier 28, a humidistat sensor 30, a temperaure sensor 31 and a water reservoir 34. If an ultrasonic humidifier is used, a compressed air supply also needs to be provided, for example, in the form of a compressed air tank 32 or container housed within the enclosure 12. The compressed air tank is connected to the water reservoir 34 and the humidifier 28. Water droplets having a diameter of less than 5 microns, preferably 2- 3 microns, are introduced into the air to enhance the rate of evaporation of the water into the atmosphere.

The ozone discharge unit 18 includes an ozone generator 36, an ozone detector sensor 38, and an oxygen supply 56 for supplying oxygen to the ozone generator 36.

Oxygen is preferred to air for the generation of ozone because this avoids the formation of toxic oxides of nitrogen, increases the rate at which the required concentration of ozone is achieved and also increases the yield of ozone.

The dehumidifier unit 90, moisture absorption device 92 and heater 94 together form a humidity reducing means.

The ozone catalyst 70 is any suitable catalyst that is able to remove ozone from the atmosphere. The catalyst may be selected from a range of proprietary substances that are known to be active in the catalytic decomposition of ozone. Such catalysts may optionally contain platinum group metals, oxides of manganese, and other substances which may have a promoting effect.

The hydrocarbon discharge unit 22 includes a hydrocarbon supply 42 in the form of a tank or container containing a volatile unsaturated hydrocarbon, such as butene. Preferably, the butene is butene-2. However, the hydrocarbon can be any suitable hydrocarbon having a carbon-carbon double bond, for reasons which will become apparent hereinafter. The selection of hydrocarbon is based on its speed of reaction with ozone and the toxicology of its decay products.

The control unit 26 controls the apparatus 10 and is preset with at least one sterilisation and decontamination routine. The control unit 26 includes a controller 46 and a user interface 48 by which a user can input commands to the apparatus 10.

The apparatus 10 may include an on-board battery 50 and/or may be connectable to a mains power supply. In the case of the on-board battery 50, the battery is preferably rechargeable. If a mains-operated apparatus is provided, this may have a battery back-up system to enable the machine to failsafe in the event of a mains power failure.

The apparatus 10 will also typically include other safety features, such as safety sensors, and software routines to prevent start-up or initiate shut-down in the event of a system failure.

In use, the apparatus 10 is first located in the area which is to be sterilised and decontaminated. The power to the apparatus 10 is switched on, and the control unit 26 undertakes an initial safety check. If the safety check is not passed, the apparatus 10 does not operate and outputs a suitable indication using warning lights 52. During the process, safety checks are made continuously, and in the event of a system failure, the system defaults to a safe mode. The temperature of the humidified air is above the dew point of the environment, and thus condensation does not occur.

The controller 46 continues to monitor the ozone level, relative humidity through the humidistat sensor 30 and ambient temperature through the thermocouple. If after a predetermined interval of time, for example 10 minutes, the calculated relative humidity level and/or the required ozone level has not been reached, the controller 46 aborts the sterilisation and decontamination routine and provides a suitable indication.

Oxygen is supplied to the ozone generator 36, and ozone is generated. The generated ozone is then fed into the discharging humidified airstream. The controller 46 provides a suitable indication that the ozone generator 36 is operating, and monitors the ambient ozone levels through the ozone detector sensor 38.

Both the ozone and water vapour concentrations to be detected can be altered. However a typical setting is 25 ppm v/v or ozone and 13.6 torr. , Once the preset ozone and water vapour levels have been detected within the allotted interval, the controller 46 enters a timing phase, known as the "dwell time".

The dwell time can also be altered, for example, to one hour, and will depend on the degree and type of decontamination / sterilisation to be provided. For instance, contamination by spores or moulds, such as Clostridium difficile, generally require a longer dwell time than contamination by bacteria, such as listeria and methicillin resistant staphyloccocus aureus (MRSA).

During the dwell time, the ozone concentration and relative humidity are continuously monitored. If the ozone level falls below a predetermined threshold, the ozone discharge unit 18 is reactivated to replenish the ozone levels. If relative humidity level falls below the calculated value, the humidifier unit 16 is reactivated to restore the water vapour level.

Again, during the reactivation period, should either the ozone concentration or the relative humidity fail to reach the above-mentioned predetermined minima within a set time interval, for example 10 minutes, the controller 46 aborts the sterilisation and decontamination routine and outputs a suitable indication.

After the dwell time has elapsed, the controller 46 closes the compressed air . valve 54 and the oxygen supply valve 60, and the humidifier unit 16 and the ozone discharge unit 18 are switched off. A pump 71 then blows the atmosphere through the dehumidifier unit 90, the moisture removal unit 92 and the heater 94. This removes a substantial amount of water from the atmosphere which is then passed through the catalyst 70 to reduce the levels of ozone, the level of ozone being monitored continuously. When the concentration of the ozone has fallen to the required level, such as around 8 ppm v/v, an olefin is introduced by means of a hydrocarbon discharge valve 58 of the hydrocarbon discharge unit. 22. The concentration of ozone is continuously monitored and seen to fall to an undetectable level. The catalyst 70 may be continuously deployed until the concentration of ozone. falls below its OEL.

When the ozone detector sensor 38 detects that the ozone concentration levels are less than a predetermined value, for example 0.2 ppm or less, the controller 46 closes the hydrocarbon discharge valve 58 and outputs an indication that the sterilisation and decontamination routine is complete. The ozone level of 0.2 ppm, depending on the size of the area being sterilised and decontaminated, is usually achieved within 3 to 4 minutes. The apparatus may include a feedback ozone measurement system (not shown) to determine the quantity of hydrocarbon added to the environment thereby reducing the chance of overdosing the hydrocarbon input and associated potential toxicology issues.

If the ozone detector sensor 38 fails to indicate that the predetermined safe level of ozone has been reached within a predetermined time interval, for example within 10 minutes, the controller 46 outputs an indication warning of potentially hazardous ozone levels in the room. The controller may be programmed to allow a time interval to pass in excess of the standard half-life of ozone before announcing that the room may be re-occupied.

It is envisaged that the sterilisation and/or decontamination apparatus may be integrally formed as part of an area, or may be only partly portable. For example, the compressed air supply and/or oxygen supply could be integrally formed as part of the area to be regularly sterilised and decontaminated. Alternatively, components could be housed within the enclosure of the apparatus. In this case, the required supply could be linked to the apparatus via a detachable umbilical pipe. The machine may also consist of a main unit and a wirelessly connected remote controller wherein the required preset routine may be remotely initiated by a user from outside the area to be sterilised and/or decontaminated.

Although the oxygen supply is typically in the form of one or more oxygen tanks or cylinders, a commercially available oxygen concentrator can be used.

The apparatus uses an electric fan 72 as a gas movement device to circulate the humidified air, ozone and hydrocarbon. However, depending on the particular application, an air mover may be used instead of an electric fan.

The above-described apparatus utilises a method of producing an artificially high level of non-condensing humidity, and generating in-situ a high concentration of ozone.

The materials of the apparatus are resistant to the corrosive effects of ozone and the solvent effects of the hydrocarbon.

The condition of all the valves are monitored using integrally incorporated sensors connected to the controller. The valves failsafe to ah appropriate position, such as the closed position so that user safety is maintained at all times. The controller may also incorporate a tamper proof recording system to monitor use, time, date, operational success/failure and other parameters required to measure performance of the machine.

In a further embodiment of the present invention (not shown), water collected from the dehumidifier may be directed into the original water container, water reservoir or a separate container and reused in subsequent treatments. This has the added benefits of reducing the amount of water used in the process and the need to dispose of the waste water.

It is thus possible to provide a method for providing a degree of sterilisation and/or decontamination which is fast and effective and does not requirement frequent replacement of the ozone catalyst. Furthermore, the apparatus may be discrete and portable. The method can provide better than 99.99% effective sterilisation and decontamination of an area without an impact on the environment from harmful byproducts. Rapid re-use of a contaminated area can thus be realised.

The embodiments described above are given by way of examples only, and other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of sterilising, sanitising and/or decontaminating an enclosed environment, the method comprising the steps of: a) producing a humidified environment having a relative humidity which is higher than ambient humidity; b) discharging ozone into the humidified environment; c) maintaining the ozone level at a concentration that will achieve the required degree of decontamination, sterilisation and/or santitation of the humid environment; d) reducing the relative humidity of the decontaminated, sterilised and/or sanitised environment; and e) following the reduction in relative humidity of the environment, passing the decontaminated, sterilised and/or sanitised environment through a catalyst to reduce the concentration of ozone to a predetermined level.

2. A method as claimed in claim 1 further comprising the step of introducing a hydrocarbon having a secondary olefinic carbon-carbon double bond into the environment to react preferentially with the discharged ozone.

3. A method as claimed in claim 2 further comprising the step of recycling the decontaminated, sanitised and/or sterilised environment through the catalyst until the concentration of ozone and hydrogen peroxide falls to a safe- level.

4. A method as claimed in claim 1, 2 or claim 3 farther comprising the step of recycling water obtained from step d) and reusing the water in step a).

5. A method as claimed in any one of the preceding claims wherein the reduction in relative humidity is achieved by a dehumidifying step.

6. A method as claimed in claim any one of claims 1 to 4 wherein the reduction in relative humidity is achieved by passing the environment through a water absorbent to remove water molecules.

7. A method as claimed in any one of claims 1 to 4 wherein the reduction in relative humidity is achieved by heating the environment. .

8. A method as claimed in any one of claims 1 to 4 wherein the reduction in relative humidity is achieved by a dehumidifying step, followed by the passage of the environment through a water absorbent and heating of the environment.

9. A method as claimed in any one of the preceding claims wherein the level of ozone maintained in step c) is in the range 1-100 ppm v/v.

10. A method as claimed in any one of the preceding claims wherein step d) reduces the level of ozone to below the occupational exposure level (OEL).

11. A method as claimed in any one of the preceding claims, wherein the relative humidity is reduced to about 30% based on ambient conditions.

12. Sterilisation and decontamination apparatus for use with a method as claimed in any one of the preceding claims, the apparatus comprising a humidifier unit, an ozone discharge unit, humidity reducing means, an ozone depletion catalyst and a controller by which the humidifier unit, ozone discharge unit and/or humidity reducing means are controllable based on pre-determined conditions.

13. Apparatus as claimed in claim 12 further comprising recycling means for recycling water obtained by the humidity reducing means.

14. Apparatus as claimed in claim 12 or claim 13, wherein the humidity reducing means comprises a dehumidifier unit.

15. Apparatus as claimed in claim 12 or claim 13, wherein the humidity reducing means comprises a moisture absorption unit.

16. Apparatus as claimed in claim 15 wherein the moisture absorption unit comprises silica gel.

17. Apparatus as claimed in claim 15 wherein the moisture absorption unit comprises a molecular sieve.

18. Apparatus as claimed in claim 12 or claim 13, wherein the humidity reducing means comprises a heater.

19. Apparatus as claimed in claim 12 or claim 13, wherein the humidity reducing means comprises a dehumidifier unit, a water absorption unit and a heater.

20. Apparatus as claimed in any one of claims 12 to 19, further comprising sensors which monitor the relative humidity and the concentration of the ozone, both prior to and after its passage through the catalyst.