GB2334873A

GB2334873A - Sterilisation device comprising a plurality of elliptical reflectors

Info

Publication number: GB2334873A
Application number: GB9902773A
Authority: GB
Inventors: Ian A Ramsay; Iain D Ogden
Original assignee: Minister of Agriculture Fisheries and Food UK
Current assignee: Minister of Agriculture Fisheries and Food UK
Priority date: 1998-02-10
Filing date: 1999-02-08
Publication date: 1999-09-01
Also published as: GB9802715D0; GB9902773D0

Abstract

An ultraviolet sterilisation device comprising a sample holder, a plurality of ultraviolet lamps 3, and a multiple elliptical reflector 1, the device arranged such that each lamp has an associated elliptical reflector and the elliptical reflectors are arranged to provide a common focus at which the sample holder 2 is positioned with the associated ultraviolet lamps being positioned at each of the remaining focii. The sample holder may accomodate an annular flow of a fluid to be sterilised. A potential may be applied to the inner wall 26 to the annular sample holder to attract deposits. A stirring device 6 may also be employed.

Description

Sterilization Device The present invention relates to apparatus for killing and/or controlling microorganisms present in samples such as water, physiological fluids, pharmaceutical formulations and foodstuffs including liquid foods or drinks such as milk and fruit juice and solid food surfaces and food processing surfaces. In particular, the invention relates to sterilisation apparatus to remove microorganisms such as bacteria and viruses from samples.

The use of ultraviolet light in a narrow waveband centred at about 254nm, as produced by mercury lamps, to sterilise water is well known. Industrial deployment of mercury uV lamps is widespread both in the production of potable water, such as by Strathmore Mineral Water Company, for example, and to a lesser extent in the treatment of waste water. DNA has a strong absorption peak at 257nrn. Since bacteria and viruses in the water contain DNA, they absorb mercury liv light strongly. This has several effects including severing (photocleavage) of the DNA chain causing most bacteria to be killed at relatively small doses (intensity x time) and some viruses to be killed, generally with greater difficulty, using higher doses.

Known mercury lamp sterilisation apparatus comprises one or more ultraviolet (iso) lamps which are inserted into one or more quartz tubes or some other housing. The liquid to be treated flows around the outside of the housing. In some arrangements, the liv lamp or lamps are submerged in a container through which the liquid to be treated flows.

A disadvantage of the arrangement where the lamps are placed in a housing with the fluid flowing around the outside of the housing is that deposits which absorb liv radiation tend to build up on the surface of the housing, blocking the passage of liv radiation to the sample.

The fluid flowing over the outside of the housing cools the surface of the housing and the temperature difference between the inside surface of the housing, which is heated by the liv lamps, and the external surface of the housing, which is cooled by the fluid flow, causes condensation of deposits onto the external surface of the housing. These deposits are then 'burnt" onto the surface of the housing by the UV lamps, preventing penetration of the liv radiation into the sample fluid.

The submerged lamp arrangement has the disadvantage that the lamps are costly and difficult to replace and rely on cooling from the sample flow which means that their output power is determined by the liquid flow rate. Furthermore, submerged lamps are difficult to clean.

The applicants have found that a sample can be irradiated with a greater intensity of liv radiation using low pressure mercury indium lamps, such as the NNI series of lamps from Heraeus Noblelight Limited, in a novel lamp/reflector arrangement. Other liv lamps may be mounted to advantage in the same type of lamp/reflector arrangement. As the lamps are placed on the outside of a sample holder or sample tube any fluid flowing through the tube or holder does not cool the surface of the tube to the same extent as in the prior art devices, reducing the level of deposits on the surface of the tube or holder. Furthermore, as the lamps are not submerged, they are cheaper and easier to replace and clean and can be force air cooled using simple fans. Thus, the lamps are cooled independently of the liquid flow and hence their output power is independent of the liquid flow rate. This means that the flow rate through the lamp/reflector arrangement can be faster, which results in a slower build up of deposits and hence the requirement for cleaning is less frequent.

Accordingly, the present invention provides a sterilisation device comprising a sample holder and a plurality of ultraviolet lamps, each lamp having an associated elliptical reflector wherein the elliptical reflectors are arranged to provide a common focus at which the sample holder is positioned and the associated ultraviolet lamps are positioned at each of the remaining focii.

This arrangement of elliptical reflectors and mercury lamps increases the intensity of UV radiation that can be applied to a particular size sample. Thus, a tightly fitting double elliptical reflector containing two mercury lamps in accordance with the invention, for example, is more efficient than the known systems comprising a single elliptical chamber containing a single mercury lamp of twice the power output. This is because the double elliptical reflector chamber can accommodate a larger sample holder at the common focus than could fit into the focal position of a single elliptical reflector chamber of the same ellipse size. A much larger single elliptical reflector chamber would be required to accommodate the same size sample holder. Thus, the total intensity ofUV radiation on the sample holder, which in a cylindrical geometry varies inversely with the distance from the lamps, will be considerably greater in the case of irradiation by two lamps in a tightly fitting double elliptical reflector compared to irradiation by a single lamp of twice the power output in the most tightly fitting single elliptical reflector that can accommodate a sample holder whose diameter is larger than the diameter of the lamps.

The sterilisation device of the invention is particularly suitable for sterilising liquid samples, for example potable water samples such as mineral water, spring water and packaged water.

They may also be used to sterilise pharmaceutical formulations, where the reactions taking place on irradiation do not have significant effects on the active reagents. The device may also be used to sterilise physiological samples such as blood and spinal fluid. Where the sample is a blood sample, it would be expected that the irradiation would have an adverse effect on the white blood cells in the sample. This may not prove a problem where the presence of white blood cells is unnecessary or even undesirable, for example where the blood is intended for transfusions. However, if this is a problem, the white blood cells may be separated from the sample prior to sterilisation, for example using known white cell filtration methods and returned to the sample post sterilisation. White blood cells are not present in spinal fluid so irradiation may be effected without the need for complex cell separation processes.

Where the sample is a liquid, a sample holder in the form of a tube is preferred so that the sample can be irradiated whilst flowing through the tube. This arrangement may also be used for powdered samples. An advantage of the sample tube arrangement is that cleaning is more easily effected (by the method used to clean rifle barrels) since any deposits will form on the inside wall of the sample tube. The ease of cleaning the apparatus is particularly significant when disinfecting liquids containing a high level of deposits, for example peaty water.

In a preferred embodiment of the invention, a stirrer is provided in the sample holder to ensure that all particles of the sample are irradiated sufficiently for sterilisation. The penetration depth of liv radiation in liquid foods such as milk or orange juice is too small to ensure sterilisation of the bulk of such a liquid. The stirrer ensures that each particle of such samples is in contact with the walls of the sample holder for sufficient time to allow sterilisation to take place.

The penetration depth of liv radiation in water is sufficient that a stirrer is not required.

However, where the sample holder comprises a tube through which the sample flows, it is desirable to induce a degree of turbulence into the flow prior to irradiation.

The applicants have shown that a double elliptical mercury chamber according to the invention sterilises aqueous solutions of E.coli, Listeria innocua and the bacterial spores Bacillus subtilis, reducing the initial count by five orders of magnitude at flow rates in excess of 1 litre per second.

When dealing with samples that absorb liv strongly, another method for achieving the same result as the stirrer described above, is to reduce the flow rate through the apparatus by including a constrictor of smaller diameter than the diameter of the sample tube in series with and downstream of the sample tube, conveniently just before the final outflow. This method is limited, however, because bacteria tend to congregate on the surface of a very narrow constrictor from which they can become detached and contaminate the fluid that has been disinfected. By reducing the flow rate through the zone in which the sample is irradiated, the sample is irradiated for a longer period allowing greater penetration of the liv radiation. The operation of the system can be further enhanced by using a stirrer in combination with such a constrictor.

Furthermore, either in addition or as an alternative to a stirrer, the sample holder may comprise a tube, baving inner and outer walls between which the liquid or powdered sample flows. The thin annulus of flowing sample ensures that the liv radiation penetrates throughout the depth of the sample. This arrangement may be achieved by inserting a solid rod of smaller cross section into the sample tube. The tube may be made from vitreosil, spectrosil or any other materials which transmit the liv radiation from the lamps. The solid rod is preferably made from stainless steel because of its corrosion resistance and proven use in the food industry. Alternatively, the sample tube could be made in the form of a hollow tube (i.e. with a hollow stainless steel rod as an insert). A stirrer arrangement could then be mounted in the annular flow path with the control means for the stirrer located in the hollow in the centre of the sample tube. The insert may be aligned and supported inside the sample tube by provision of a support spider located in the annular flow path or by adjusting three or four nylon or other plastic screws mounted radially at one or both ends of the tube.

By applying an electrical potential to the insert, either positive or negative with respect to the ground potential, one can attract unwanted deposits, that tend to block transmission of the liv radiation, preferentially on to the insert rather than on to the wall of the sample tube through which liv radiation is being transmitted. This is clearly advantageous in reducing the frequency of necessary replacement or cleaning of the sample tube.

Where the sample tube is provided with an insert, there are regions at the top and bottom of the annular sample flow path which, in the double elliptical reflector arrangement, are protected from receiving direct irradiation due to interception by the insert or inner wall of the tube. One solution to this problem is to mount protrusions at intervals along the top and bottom of the annular flow path to discourage flow from these regions or at least break up the flow so that no stream escapes the liv radiation.

A better solution is to use an insert in a triple, quadruple or greater elliptical reflector arrangement with 3, 4 or more mercury lamps. Considering a quadruple elliptical reflector, for example, if the square cross section joining the axes of the four lamps contains the diameter (or largest cross sectional dimension) of the sample tube, then no region of the sample tube can escape direct irradiation. It will be appreciated that multiple reflector arrangements may alen be used with other, more general, sample holder arrangements, to ensure even distribution of irradiation over the surface of the sample.

When the liquid is sufficiently clear that the penetration depth of liv is large enough to dispense with an insert, the quadruple elliptical reflector arrangement described above has the capacity to sterilise potable water at flow rates of up to 10 litres per second which meets or exceeds industrial requirements.

The elliptical reflectors may be made from polished aluminium, polished stainless steel or any metal plated with, for example, nickel or silver. Preferably, the elliptical reflectors are made from chemically treated and anodised Aluminium because sheet aluminium is easy to shape and gives a high liv reflectivity. This reflectivity remains constant because any reduction by oxidation is prevented by virtue of the anodising.

The present invention will now be described, by way of example, with reference to the accompanying drawings wherein: Figure 1 shows a cross section through a double elliptical reflector/lamp arrangement with an integral sample tube.

Figure 2 shows a sectional side view of the double elliptical reflector/lamp arrangement shown in figure 1 with integral cooling fan.

Figure 3 shows a cross section through a quadruple elliptical reflector/lamp arrangement.

Figure 4 shows a cross section through a double elliptical reflectorAamp arrangement having an annular flow path within a dual wall sample tube.

Figure 5 shows a section through a dual wall sample tube having a stirrer located in the annular flow path, powered by a motor located in the hollow centre of the sample tube.

Figure 6 shows a section side view through the dual wall sample tube shown in figure 5.

Referring to figures 1 and 2, a double elliptical reflector 1 is arranged around a sample tube 2 which is positioned at the common focus of the reflector. Two mercury lamps 3 are placed at the other two focii of the double elliptical reflector 1. A simple fan 4 provides forced cooling for the mercury lamps 3.

Referring to figure 3, a quadruple elliptical reflector l has a sample tube 2 at its common focus. Four mercury lamps 3 are positioned at each of the remaining focii of the reflector. The sample tube 2 and elliptical reflector l are chosen such that largest cross sectional dimension of the sample tube 2 is contained within the square cross section 5 joining the four mercury lamps 3.

Referring to figure 4, a double elliptical reflector 1 is arranged around a sample tube having an outer wall 2a and an inner wall 2b. The sample to be irradiated flows along the annular flow path between the walls 2a and 2b and is acted upon by radiation from the mercury lamps 3.

Preferably, the spacing between the walls 2a and 2b is chosen such that the radiation from the mercury lamps 3 penetrates through the depth of sample in the annulus.

Referring to figures 5 and 6, a motor 7 is located within a hollow, sealed insert 8 of a dual walled sample tube 2 having an outer wall 2a and an inner wall 2b (provided by the insert 8).

The motor is connected to a stirrer 6 which is located within the annular flow path between the walls 2a and 2b. One end of the stirrer 6 is connected to the motor drive shaft and the other end of the stirrer 6 is provided with a rotating support 9 which maintains the position of the stirrer 6 relative to the inner wall of the sample tube 2b. The insert 8 is held centrally in the sample tube 2 by means of a support spider 11 and three or four centring screws 10. The motor drive shaft and any electrical connections for the motor supply are sealed into the hollow insert and sample tube by known methods.

A sterilisation device according to the invention using low power liv lamps, such as hybrid mercury and indium lamps which produce maximum output of 254nm for minimum electrical input, is particularly useful in remote areas without permanent electrical supplies. The double elliptical design according to the invention has a power consumption of about 200W which can be provided by standard portable generators. In particular, the necessary electrical power can be provided by pedal-powered generators or solar cells. Flow of the sample through the device can be gravity fed, removing the need for a pump. Such a device, preceded by gravel or sand and charcoal filters, could be used to provide drinking water from poor quality water in remote areas such as third world countries.

Claims

CLAIMS 1. A sterilisation device comprising a sample holder and a plurality of ultraviolet lamps, each lamp having an associated elliptical reflector, wherein the elliptical reflectors are arranged to provide a common focus at which the sample holder is positioned and the associated ultraviolet lamps are positioned at each of the remaining focii.
2. A sterilisation device as claimed in claim 1 having two ultraviolet lamps and a double elliptical reflector.
3. A sterilisation device as claimed in claim 1 having at least 3 ultraviolet lamps and associated multiple elliptical reflector, the elliptical reflector being suitably sized and arranged to ensure that the surface area of a sample in the sample holder is contained within the cross section joining the axes of the ultraviolet lamps.
4. A sterilisation device as claimed in any of the preceding claims further comprising a stirrer located in the sample holder.
5. A sterilisation device as claimed in any of the preceding claims wherein the sample holder comprises a tube through which a sample can flow.
6. A sterilisation device as claimed in claim 5 wherein the tube has i;"l*r and outer walls between which the sample flows in a thin annulus.
7. A sterilisation device as claimed in claim 6 wherein an electrical potential is applied to the inner wall of the tube to attract ultraviolet absorbing deposits onto the inner wall.
8. A sterilisation device as claimed in claim 6 or claim 7 wherein the sample holder comprises a tube with a rod of smaller cross section inserted therein.
9. A sterilisation device as claimed in any of claims 6 to 8 wherein the centre of the tube is hollow.
10. A sterilisation device as claimed in claim 9 wherein the tube further comprises a stirrer having control means located within the hollow.
11. A sterilisation device as claimed in any of claims 5 to 10, further comprising means for controlling the rate of flow of the sample through the tube.
12. A sterilisation device as claimed in any of the preceding claims wherein the elliptical reflectors are made from polished, anodised aluminium.
13. A sterilisation device as claimed in any of the preceding claims wherein the ultraviolet lamps are mercury lamps.
14. A sterilisation device as hereinbefore described and as shown in any of the accompanying drawings.