GB2269303A

GB2269303A - Controlling bacterial growth

Info

Publication number: GB2269303A
Application number: GB9315252A
Authority: GB
Inventors: Christopher John Pendred
Original assignee: PENDRED NORMAN CO; Fractal Inc
Current assignee: PENDRED NORMAN CO; Fractal Inc
Priority date: 1992-07-24
Filing date: 1993-07-23
Publication date: 1994-02-02
Anticipated expiration: 2013-07-23
Also published as: EP0651657A1; GB9315252D0; GB2269303B; WO1994002180A1; AU4716293A; AU669558B2; GB9215743D0

Abstract

Method and apparatus for controlling bacterial growth in a fluid by treatment thereof with bactericidal radiation wherein the fluid, such as, water, is used as a coolant for a source (3) of radiation e.g. ultraviolet light but has a flow rate which is insufficient to maintain the source (3) at a sufficiently low working temperature for the generation of bacteriacidal radiation thereby, wherein the apparatus comprises a radiation source (3) which is capable of generating bactericidal radiation at a given working temperature or within a given working temperature range and is arranged to enable the fluid to be treated with bacteriacidal radiation and to effect cooling of the source (3) and where in the apparatus further comprises means (20) e.g. timer circuit, arranged to operate the radiation source intermittently to maintain its working temperature at a given temperature or within a given temperature range at which bacteriacidal radiation is generated thereby. The invention has particular application in humidification systems for serve-over, point-of-sale food and/or floral display cabinets.

Description

BACTERIAL CONTROL DESCRIPTION This invention relates to the control of bacterial growth in a fluid and to apparatus for exercising such control, the apparatus comprising a source of radiation for treating the fluid in which bacterial growth is to be controlled, with the fluid acting as a coolant for the source.

Throughout this specification, the word "control"1 and its various derivatives, is used in relation to bacteria to mean not only the inhibition of the growth of existing colonies of bacteria but also the destruction thereof, as the case may be.

Under normal operating conditions, the rate of flow of coolant fluid is sufficient to maintain the temperature of the radiation source at a given level or within a given range, whereby the wavelength of the radiation is such as to possess bacteriacidal properties. If the temperature of the radiation source changes during usage, for instance, due to a reduction in the flow rate of the coolant fluid being treated, such that there is insufficient cooling of the source to maintain it at the given temperature or within the given range of temperatures at which the radiation wavelength possesses bacteriacidal properties, then the wavelength of the radiation will change accordingly, such that it does not possess bacteriacidal properties.

As a consequence, control of bacterial growth and activity within the coolant fluid can be diminished seriously.

This invention is particularly suited for use in humidification systems associated with point-of-sale display cabinets or service cases containing food products, such as, meat, dairy products, fish, fresh vegetables and fruit and similar products, as well as fresh flowers, being displayed therein.

In known point-of-sale humidification systems of this type, such as, that disclosed in published British Patent Application No. 2258299A, a mixture of moisture and air, preferably, water vapour-saturated air, is injected into the atmosphere in which food and/or floral products are displayed at point-of-sale in the cabinet or service case. Bacterial growth can occur on components of the humidification system, such as, the moisture/air mixture injection nozzles. As a result, and particularly when the humidifying moisture/air mixture is injected at intermittent intervals into the associated atmosphere resulting in a substantial reduction in the rate at which water flows to the air mixer and injection nozzle, bacterial growth can extend upstream of the nozzle and into the very water supply itself.

Attempts have been made to overcome this problem, one being the use of a radiation source operating at a bacteriacidal wavelength employing the water supply of the humidification system as a coolant for the radiation source, namely, the type of arrangement discussed above. Unfortunately, however, such attempts have not been too successful in cases where the coolant water is fed at a greatly reduced flow rate to the air/water mixture and injection nozzles, that is to say, at a flow rate which is insufficient to maintain the working temperature of the source of radiation, in most cases an ultra-violet light source, at one at which the wavelength of the emitted radiation possesses bacteriacidal properties.As a result, the working temperature of the source rises and a consequential shift in the radiation wavelength occurs to such an extent that it no longer possesses bacteriacidal properties. Thus, control of bacterial growth within the humidification system is diminished and is eventually eliminated, resulting in a build-up of undesirable and, in certain circumstances, harmful, bacteria within the system. This can then be transmitted to the atmosphere of the point-of-sale display or service case and eventually to the displayed products themselves, causing contamination thereof.

Further, consequential overheating of the radiation source can enhance the growth of more bacteria, in that the water which should be cooling the source, is in fact becoming warmer itself.

It is an object of the present invention to overcome, or at least substantially reduce, the disadvantages associated with known apparatus for controlling bacteriacidal growth, particularly in humidification systems for food and floral products displayed at point-of-sale, as discussed above.

Accordingly, one aspect of the invention provides apparatus for controlling bacterial growth in a fluid by treatment thereof with bacteriacidal radiation, wherein the fluid is used as a coolant for a source of radiation but has a flow rate which is insufficient to maintain the source at a sufficiently low working temperature for the generation of bacteriacidal radiation thereby, wherein the apparatus comprises a radiation source which is capable of generating bacteriacidal radiation at a given working temperature or within a given working temperature range and is arranged to enable the fluid to be treated with bacteriacidal radiation and to effect cooling of the source, and wherein the apparatus further comprises means arranged to operate the radiation source intermittently to maintain its working temperature at a given temperature or within a given temperature range at which bacteriacidal radiation is generated thereby.

In accordance with another aspect of the invention, there is provided a method of controlling bacterial growth in a fluid by treatment thereof with bacteriacidal radiation, wherein the fluid is used as a coolant for a source of radiation but has a flow rate which is insufficient to maintain the source at a sufficiently low working temperature for the generation of bacteriacidal radiation thereby and wherein the radiation source is operated intermittently to maintain its working temperature at a given temperature or within a given temperature range at which it generates bacteriacidal radiation.

The radiation source is preferably one which generates ultra-voilet light, although other sources may be used depending upon the bacteria to be controlled. In most applications of the inventive apparatus and method, but not necessarily all, the coolant fluid is water.

The intermittently-operable radiation source can be operated at intervals, preferably regular intervals and preferably also for predetermined time periods, depending upon the flow rate of the coolant fluid.

However, such intermittent operation of the source may be controlled thermostatically, for example, in dependence upon the temperature of the source and/or the coolant fluid and, possibly, other associated parameters.

In accordance with a further aspect of the invention and for particular, but not exclusive, application in point-of-sale humidification systems for food and floral products, such as that described in the British Patent Application identified above, wherein a mixture of moisture and air is injected into the atmosphere in which the food and/or floral products are displayed, apparatus as defined above has the intermittently-operated radiation source located immediately upstream of an associated water/air mixture injection nozzle, to substantially reduce back contamination by bacteria of the coolant water supplied thereto. Preferably, this arrangement is associated with a serve-over, point-of-sale food service cabinet.

In order that the invention may be more fully understood, a preferred embodiment in accordance therewith will now be described by way of example and with reference to the accompanying drawing which is a sectional view of an ultra-voilet light source forming part of a humidification system for a serve-over pointof-sale food service cabinet.

Referring now to the drawing, part of a humidification system for a serve-over point-of-sale food service cabinet (not shown) comprises a water inlet aperture 1' in which is threadedly engaged a water inlet 1 communicating with the interior of a tubular water jacket 2 surrounding an ultra-voilet light source indicated generally at 3.

The lower end of the water jacket 2 has a water tight cap 9 through which insulated conductors 4, 5 for respective elements 6, 7 of the Wight source 3 extend.

The upper end of the water jacket 2 also has a water tight cap 8 in the side wall of which is provided a water outlet 10' in which is threadedly engaged a water outlet 10 connected to a nozzle 11 by a small bore pipe 12. Immediately upstream of the nozzle 11, another small bore pipe 13 is joined to the pipe 12 and is connected to an air supply (not shown).

With the exception of the inlet 1 and outlet 10 and associated components 11 to 13, the apparatus described above represents a prior art arrangement, whereby the W light source 3 surrounded by water in the jacket 2 is arranged to kill bacteria in that water which also acts as a coolant for the source as it flows continuously from the inlet aperture 1' to the outlet aperture 10' at a flow rate of, say, at least 2-3 litres per minute. Such cooling action by the continuously flowing water prevents the UV light source from overheating, thereby maintaining is working temperature substantially constant, so that it generates ultra-violet light at a bacteriacidal wavelength.

It has been found, however, that for applications with humidification systems of the type described above in which the flow rate of the coolant water is reduced substantially to, say, 0.03 litres per minute because of the frequency of the injections of the water/air mixture into the service cabinet atmosphere and the low conductance of the nozzle 11 and small bore pipes 12, 13, the ultra-violet light source 3 tends to overheat due to this very low rate of flow of the coolant water through the water jacket 2, thereby resulting in a change of wavelength of the ultra-voilet light to one which does not possess bacteriacidal properties. This effect causes the ultra-voilet light to become ineffective as far as bacterial control is concerned and, in fact, also causes the growth of more bacteria due to a consequential warming of the water due to overheating of the source.

Also, tests have shown that water contained in the pipes 12, 13 in the vicinity of the nozzle 11 and components upstream thereof tend to become contaminated by bacteria creeping back from the nozzle 11 which is situated in the atmosphere being humidified.

In accordance with the invention, therefore, a solution to this problem has been found by operating the ultra-violet light source 3 intermittently, to prevent its overheating, thereby maintaining the wavelength of the ultra-violet light at one which possesses bacteriacidal properties.

Thus, a timer circuit 20 is connected to the ultra-voilet light source 3 via its filament conductors 4, 5 for operating the W light source intermittently.

It has been found that operation of the W light source 3 for 2 minutes after every 20 minutes, namely, a 22 minute cycle, results in the effective control of substantially all bacterial growth in the coolant water flowing at a rate of 0.03 litres per minute. In this regard, microbiological tests on the apparatus have shown that the bacteria are greatly reduced in numbers and tests have also shown that the lamp does not overheat when used intermittently, thereby maintaining the bacteriacidal properties of the ultra-voilet light so generated. For example, with continuous operation of the source 3, 10,000 bacteria per millilitre of water have been detected, whereas, with the inventive arrangement using intermittent operation of the W source 3, bacteria kill rates of 99.9% have been achieved, resulting in bacteria populations as low as 150/ml or a total viable count of all bacteria of less than 10.

It is to be appreciated that this arrangement could be fitted into any part of the water supply for the humidification system, although its location immediately upstream of the injection nozzle 11 for the water/air mixture is preferred, because it controls back contamination of the water supply.

Also, the inlet 1 at the inlet aperture 1' and the outlet 10 at the outlet aperture 10' may be transposed, if operating conditions dictate.

Claims

1. Apparatus for controlling bacterial growth in a fluid by treatment thereof with bacteriacidal radiation, wherein the fluid is used as a coolant for a source of radiation but has a flow rate which is insufficient to maintain the source at a sufficiently low working temperature for the generation of bacteriacidal radiation thereby, wherein the apparatus comprises a radiation source which is capable of generating bacteriacidal radiation at a given working temperature range and is arranged to enable the fluid to be treated with bacteriacidal radiation and to effect cooling of the source, and wherein the apparatus further comprises means arranged to operate the radiation source intermittently to maintain its working temperature at a given temperature or within a given temperature range at which bacteriacidal radiation is generated thereby.

2. Apparatus according to claim 1, wherein the source of radiation is one which generates ultra-violet light.

3. Apparatus according to claim 1 or 2, wherein the source of radiation can be operated at intervals, preferably regular intervals, and/or for predetermined time periods, depending upon the flow rate of the coolant fluid.

4. Apparatus according to claim 1 or 2, wherein operation of the source of radiation is controlled thermostatically.

5. Apparatus according to any preceding claim, wherein the coolant fluid is water.

6. Apparatus according to claim 5, wherein the water forms a coolant jacket around the radiation source.

7. Apparatus for controlling bacterial growth in a fluid, substantially as hereinbefore described with reference to the accompanying drawing.

8. A method of controlling bacterial growth in a fluid by treatment thereof with bacteriacidal radiation, wherein the fluid is used as a coolant for a source of radiation but has a flow rate which is insufficient to maintain the source at a sufficiently low working temperature for the generation of bacteriacidal radiation thereby, and wherein the radiation source is operated intermittently to maintain its working temperature at a given temperature or within a given temperature range at which it generates bacteriacidal radiation.

9. A method according to claim 8, wherein the source of radiation generates ultra-violet light.

10. A method according to claim 8 or 9, wherein the source of radiation is operated at intervals, preferably at regular intervals, and/or for predetermined time periods, depending upon the flow rate of the coolant fluid.

11. A method according to claim 8 or 9, wherein operation of the radiation source is controlled thermostatically.

12. A method according to any of claims 8 to 11, wherein the coolant fluid is water.

13. A method according to claim 12, wherein the water provides a coolant jacket around the radiation source.

14. A method of controlling bacterial growth in a fluid substantially as hereinbefore described.

15. Apparatus for controlling bacterial growth in a fluid substantially as hereinbefore described with reference to the accompanying drawing.

16. In a point-of-sale humidification system of food and floral products, wherein a mixture of moisture and air is injected into the atmosphere in which food and/or floral products are displayed, apparatus according to any of claims 1 to 7 and having an intermittently-operated radiation source located immediately upstream of an associated water/air mixture injection nozzle, to substantially reduce back contamination by bacteria of the coolant water supplied thereto.

17. An arrangement according to claim 16 and associated with a serve-over point-of-sale food service cabinet.