BACKGROUND OF THE INVENTION

[0001] This invention relates to the sterilisation of a liquid such as wine, beer, diesel, blood or milk. [0002] This invention is described hereinafter with particular reference to the sterilisation of milk but it is to be understood that this is exemplary only.

[0003] An opaque liquid such as milk is traditionally sterilised using a filtration or pasteurisation process. In the latter process the milk is heated to about 71 °C for 15 seconds and then cooled rapidly to about 4°C. The equipment required for pasteurisation of milk, on a large scale, is expensive calling for stainless steel structures, and is energy intensive.

[0004] As an alternative to pasteurisation ultraviolet radiation can be used to sterilise milk. However, UV radiation incident on an opaque liquid such as milk is reflected to a substantial extent and consequently the capability of the radiation to "penetrate" into a body of the milk is restricted. In order to address this characteristic use has been made of a quartz sleeve which separates the milk from radiation emitted by a mercury vapour tube. To some extent this approach is successful but the dosing intensity of the ultra-violet radiation, i.e. its fluence, is adversely affected by the particular configuration. The energy requirement for producing sufficient radiation is thus increased while a throughput of treated milk is reduced. A further factor is that the mercury vapour tube and the quartz sleeve are prone to breakage. [0005] An object of the present invention is to provide an alternative technique for sterilising an opaque liquid using ultra-violet radiation.

SUMMARY OF THE INVENTION

[0006] The invention provides, in the first instance, a method of sterilising a liquid wherein a stream of the liquid is exposed to ultra-violet radiation emitted from at least one light diffusing element.

[0007] The element functions to spread or disperse the light freely.

[0008] The light diffusing element may be elongate and extend in a first direction and the liquid stream may flow in the same direction i.e. the stream may be generally parallel to the light diffusing element.

[0009] In an alternative arrangement the liquid stream is caused to flow transversely to the light diffusing element.

[0010] Preferably the liquid is exposed, simultaneously or successively, to radiation from a plurality of light diffusing elements. [0011] Use may be made of a plurality of light diffusing elements which are parallel to one other and the stream may be caused to flow through interstices between adjacent elements.

[0012] In another arrangement the elements are in a mesh form and the stream is directed through mesh apertures formed by the elements. [0013] In another arrangement an aperture is partly blocked by an element and the stream is caused to flow through an unblocked part of the aperture.

[0014] In implementing the aforementioned techniques use may be made of an arrangement, provided either by the elements, by external structure or by a combination of the elements and external structure, to reduce the thickness of the stream which is exposed to the light diffusing element or elements. The ultraviolet radiation is capable of penetrating to some extent into a body of an opaque liquid, from a surface of the liquid upon which the ultra-violet radiation is incident. Thereafter, due to the opacity of the liquid the radiation is absorbed or reflected. If the thickness of the stream is sufficiently reduced then the effect of this phenomenon is contained or restricted and better use of the ultraviolet radiation is achieved.

[0015] In order to ensure that the liquid is exposed to a sufficient extent to achieve adequate sterilisation, the reduced thickness stream of the liquid is exposed for an extended period of time to the ultraviolet radiation. This may be achieved by reducing the flow rate of the liquid or by exposing the stream of the liquid continuously to one or more sources of ultraviolet radiation or by exposing a stream of the liquid to successive stages of ultraviolet radiation treatment.

[0016] The invention further extends to apparatus for sterilising a liquid which includes at least one light diffusing element, a source which injects ultra-violet radiation into the element, and an arrangement for directing a stream of the liquid into contact with the light diffusing element.

[0017] The light diffusing element may be elongate, and extend in a first direction and the stream of liquid may be caused to flow in the first direction i.e. essentially parallel to the light diffusing element. In a different arrangement the stream of liquid flows transversely to the light diffusing element.

[0018] Use is preferably made of a plurality of light diffusing elements which are arranged in any suitable configuration. An intention in this respect is to ensure that the liquid is exposed for a suitable period of time to the radiation from the light diffusing elements to ensure that sterilisation of the liquid is achieved to an acceptable standard.

[0019] The arrangement may be configured to reduce the thickness of each stream which is exposed to a light diffusing element. This may be done in different ways. In a first approach the liquid is caused to flow through an unblocked portion of an aperture which is partly blocked by a light diffusing element. The liquid then flows through a gap which is that part of the aperture not blocked by the light diffusing element. A plurality of apertures may be used in this way. The gap thus has a smaller cross sectional area than the aperture.

[0020] In one form of the invention the apparatus includes a vessel into which the liquid is directed, the vessel including a wall with a plurality of apertures, the at least one light diffusing element overlying each of the apertures whereby at each aperture at least one gap which is smaller in cross sectional area than the aperture is formed and through which a stream of the liquid can flow from the vessel.

[0021] The vessel may be of any suitable shape but conveniently is a tube one end of which is sealed. [0022] In another approach the liquid is caused to flow through apertures defined by a plurality of the light diffusing elements which are arranged in a mesh. The liquid stream may then flow transversely to a direction or directions in which the light diffusing elements extend.

[0023] The mesh form may be a substantially planar configuration or of any other suitable shape.

[0024] In one embodiment the apparatus includes a housing with a wall, a plurality of apertures in its wall, an inlet to the housing through which a liquid, to be treated, is directed into the housing so the liquid is caused to exit the housing through the plurality of apertures in a plurality of streams, and a plurality of light-diffusing elements which are exposed to the liquid streams. [0025] The elements may be adjacent respective apertures.

[0026] Each element may be positioned so that it is exposed to a plurality of the streams. Each stream may be incident on a respective element at a respective location.

[0027] Ultraviolet energy may be introduced into the elements in any suitable way, e.g. via suitable conductors which are connected to an ultraviolet source. [0028] Other configurations are possible. For example the light diffusing element or elements may be positioned inside a tube and extend longitudinally therein. The liquid may then flow in a stream in a space between a wall of the tube and an outer surface of the light diffusing element or elements. [0029] In another arrangement a plurality of the light diffusing elements are held in a longitudinally extending bundle and the liquid is caused to flow through interstices between adjacent elements. This configuration holds the benefit that the period of time for which the liquid is exposed to the ultra-violet radiation is determined by the flow rate and by the length of the bundle of light diffusing elements. By packing the light diffusing elements suitably tightly together, the liquid is caused to flow in a plurality of streams, each of reduced thickness, continuously along the lengths of the elements. If any of the ultra-violet radiation is reflected by the liquid, due to its opacity, then the reflected ultra-violet radiation is essentially contained within a housing within which the elements are mounted. [0030] Thus the liquid is preferably brought into direct and extended contact with outer surfaces of the light diffusing elements.

[0031] The liquid may be subjected to the radiation in one stage or in a plurality of successive stages. In each stage the frequency of the ultra-violet radiation may be the same or it may be varied to achieve a more effective treatment. Typically the radiation has a wavelength which is appropriate for the sterilisation of the specific liquid e.g. from 230nm to 280nm.

[0032] The element may have any suitable shape. For example each element may be in the form of an elongate rod, thread, strip, tube, or the like. Each element may be flexible, at least to some extent, or rigid.

[0033] For example each element may comprise a rod made from a material such as quartz, possibly a material of the type sold by Corning under the trademark Fribrance™, a fibre such as glass or plastic fibre which has light-emitting and dispersing properties and which, generally, is flexible, or a light-bearing or light-diffusing polymer such as PMMA (polymethyl methacrylate).

[0034] Although the invention finds particular application for the treatment of an opaque liquid, as discussed, its use is not confined to that type of liquid for liquids which are not opaque can also be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention is further described by way of examples with reference to the accompanying drawings in which: -

Figure 1 is a block diagram representation of apparatus for treating an opaque liquid with ultra- violet radiation according to one form of the invention,

Figures 2, 2(a) and 2(b) show aspects of a radiation device, configured to expose an opaque liquid to ultra-violet radiation, which forms a part of the apparatus of Figure 1 ;

Figure 3 shows a two-stage version of the configuration in Figure 2.

Figure 4 and Figure 5 depict aspects of a different configuration for exposing a liquid to radiation; Figure 6 and Figure 6(a) show another arrangement for use in the apparatus of the invention; Figure 7 shows how the apparatus in Figure 1 can be cleaned; and

Figure 8 shows another radiation emitting device.

DESCRIPTION OF PREFERRED EMBODIMENTS [0036] Figure 1 of the accompanying drawings illustrates in block diagram form an apparatus 10 for exposing an opaque liquid such as milk to ultra-violet radiation for sterilisation purposes. The apparatus 10 includes a source 12 of the liquid, e.g. milk 14, and a mechanism 16 for controlling a flow of one or more streams of the milk into contact with a radiation device 18 which embodies a plurality of light diffusing elements 20 in a suitable configuration.

[0037] The elements 20 obtain light at an ultra-violet frequency in the range of 230 to 280nm, from a plurality of light sources, for example light emitting diodes 22, which draw power 24 via a suitable control unit 26. This frequency is exemplary, and non-limiting.

[0038] The milk 14 is directed past the configuration 18 to a collection point 30.

[0039] The aforementioned process can be repeated in that power can be supplied via the control unit 26 to a second assembly of light emitting diodes 22A which emit radiation at an ultraviolet frequency in the range of 230 to 280 nm to a second configuration 18A of light diffusing elements 20A. Milk 14A drawn from the collection point 30 is supplied via a control arrangement 26A to the light diffusing elements 20A which diffuse UV radiation onto the milk and the treated milk 14B is then directed to a collection point 30A.

[0040] Each light diffusing element 20, 20A is elongate and has the characteristic that light injected at one end of the element travels along the element. Diffused light is radiated at a substantially constant rate, radially outwardly from the element. A reflective mirror or a second ultraviolet LED light source (not shown) can be connected to a remote end of the element so that, at the end, the quantity of light energy which is emitted in the axial direction of the element is, for practical purposes, zero.

[0041] Each element may for example be made from quartz formed into an appropriate shape, or comprise a flexible or rigid fibre made from a suitable grade of glass. [0042] The invention is based, inter alia, on the light diffusing characteristics of these fibres. The fibres are charged with ultraviolet energy at a selected wavelength typically in the range of 230 to 280 nm. The frequency of operation can be varied according to requirement and, for example, a particular frequency may pertain at one stage of the treatment process while a different frequency may be applicable in a subsequent stage of the treatment process. The invention is not limited in that respect.

[0043] Figure 2 illustrates a radiation device 18 with a helical configuration of the light diffusing elements. Milk 14 emerging from the source 12 flows at an appropriate pressure and flow rate into an interior of an elongate stainless steel tube 42. The tube 42 is surrounded by a stainless steel collector tube 44.

[0044] At an input end 46 of the tube 42, i.e. at the entry point for the milk 14 an annular gap 48 between the tubes 42 and 44 is sealed by a sealing ring 50.

[0045] The tube 42 at an end 52 remote from the source 40, i.e. at the right side shown in Figure 2, is closed. [0046] Following a helical pattern on the outer side of the tube 42 a plurality of holes 54 are formed, in succession, at equally spaced intervals 56 through a wall 58 of the tube. A flexible elongate light diffusing element 60 is wound in helical fashion around the tube 42 and is positioned so that it overlies in succession each of the holes 54.

[0047] Typically over a first region 64 which extends in an axial direction of the tube 42 a first light diffusing fibre 60 is employed. Over an adjacent following region 66 a second fibre 60A is used, and so on. The reason for this is that the ultra-violet energy which is injected into a fibre is diffused radially outwardly and consequently the maximum effective length of a fibre which can be employed and which can diffuse energy at a suitable intensisty is restricted. This effective length is dependent on the energy level of the ultra-violet radiation at the injection point and on the degree to which this energy is diffused in an axial direction per unit length of the fibre.

[0048] Ends of the fibres 60,60A etc. are connected to the respective light emitting diodes 22 so that ultra-violet energy can be injected into the fibres.

[0049] Figure 2(a) shows on an enlarged scale a part 72 of the fibre 60 overlying six holes 54.1 to 54.6 respectively. Figure 2(b) shows a fibre located over a hole. Each hole has a diameter 74. The diameter 76 of the fibre 60 is equal to or greater than the diameter 74. The fibre 60 is secured tightly in position, centrally overlying each hole 54.1 to 54.6. Due to the circular cross- section of the fibre, small gaps 78 are formed between a rim of each hole 54 and an opposing adjacent outer surface of the fibre 60. The milk is thereby forced to flow in a stream 80 of much reduced thickness through each of the gaps. The stream 80 is in intimate contact with an outer surface of the fibre 60 which constantly diffuses ultra-violet energy and consequently at each hole 54 diffused ultra-violet radiation is directly incident onto the milk stream. The degree of reflection of the radiation which otherwise would occur due to the opacity of the milk is much reduced and the capability of the radiation to reach or extend into the milk stream and thereby carry out its germicidal action is enhanced.

[0050] The ultra-violet radiation process of Figure 2 can be carried out in one or more stages. Figure 3 depicts a two-pass system which is based on a duplication of the arrangement shown in Figure 2.

[0051] Milk 14 is injected via a feed tube 84 into a first stage 86 which includes an inner tube 42A and an outer tube 44A configured generally in the manner shown in Figure 2. Milk 14C emerging from the first stage 86 is directed to a second stage 88 which has an inner tube 42B located concentrically inside an outer tube 44B. In each stage 86, 88 the respective inner tube has holes 54 which are overlaid by lengths of light diffusing fibres 60, generally in the manner described in connection with Figure 2. The light diffusing fibres 60 are energized via couplings 90 to assemblies of light emitting diodes 22 which are used in the manner which has been described. The technique shown in Figure 3 can be repeated so as to ensure that milk is treated effectively, with an acceptable germicidal action and at an adequate flow rate.

[0052] The techniques which have been described can be employed in different configurations and the invention is not limited to the particular embodiments which have been shown. [0053] For example Figure 4 depicts a mesh assembly 100 formed from a plurality of light diffusing fibres 102 and 04 which are arranged in two overlying arrays to define mesh apertures 106. Figure 5 shows successive mesh assemblies 100A, 100B, 100C which are mounted to suitable frames, not shown, which are inserted into a bore 110 of a stainless steel tube 1 12. These structures are typically constructed from subwavelength optical fibres through electrospinning or extrusion. These fibres, also known as optical fibre nanowires (OFN's) provide for the transmission of energy at the required ultraviolet wavelength. The fibres 102, 104 are connected to a control arrangement 116 which embodies components similar to those in Figure 2. Milk 120 to be treated is injected into the bore 10 and is forced to flow along the length of the tube 1 12. At each assembly 100A, 00B, 100C etc. the milk flows in a plurality of small streams through the various mesh apertures 106 and the streams are thereby directly exposed to ultraviolet radiation. At an emerging point from the tube 1 12 the milk is collected and, if necessary, is directed to treatment in a second phase or even, thereafter, to a third phase. [0054] Figure 6 illustrates in cross-section a tube 140 which is made from stainless steel. A tightly packed array 142 of elongate longitudinally extending light diffusing elements 144 is placed into a bore 146 of the tube. Figure 6(a) shows, on an enlarged scale, a number of the fibres 144. As the fibres are circular in cross-section small longitudinally extending passages 150 are formed between spaced apart surfaces of adjacent fibres 144. These passages 150 are generally parallel to the corresponding fibres. Consequently, when milk is injected into the bore 146 the milk is forced to flow through the passages 150 in a plurality of streams each of which has a small cross-section. Additionally, each stream of milk is exposed to radiation which is simultaneously and continuously diffused from a number of the adjacent fibres 44. [0055] The rate of milk flow, the energy which is injected into the fibres, and the rate at which diffusion of the injected energy takes place, are all factors which are controlled to ensure that the milk is effectively treated to achieve a desired germicidal action.

[0056] Figure 7 illustrates how a vessel 160, which contains light diffusing fibres, not shown, can be cleaned after milk has been processed. Normally the milk 162 is injected via a port 164 into the vessel 160. The treated milk flows from the vessel 160 via a discharge port 166 into a collecting pipeline 168.

[0057] Once a desired quantity of milk has been treated the inlet port 164 is sealed by means of a valve 70 and the collecting pipeline 168 is also sealed via another valve 172. A cleaning liquid, e.g. superheated steam 174, is directed via an inlet 180 to flow through the interior of the vessel 160 to a discharge port 182. The flow of the cleaning medium is typically in a reverse direction to that taken by the milk through the vessel. The material 184 emerging from the port 182 is directed to waste or to a subsequent treatment phase. [0058] Figure 8 shows another form 200 of the apparatus according to the invention.

[0059] The apparatus 200 includes a housing or casing 202 which is made from an hygienically- acceptable material such as glass, aluminum or stainless steel.

[0060] A stainless steel vessel or pipe 204 has an inlet 206 which projects through an aperture 208 at one end of the housing 202. An opposing end of the housing 202 has an outlet 212.

[0061] The pipe 204 has a plurality of elongate grooves 214 in a surface 218 of a wall of the pipe and a plurality of small apertures 220 are formed at spaced intervals along the length of each groove 214. Elongate light-diffusing quartz rods 222 are placed in the respective grooves 214 and are secured in position, overlying the respective series of apertures 220 in the corresponding grooves. The invention is not limited to the use of quartz. A suitable light-bearing, light-diffusing polymer e.g. PMMA or glass could be used. These particular materials are nonetheless exemplary and non-limiting.

[0062] Ends of the rods 222 are connected by means of flexible light conductors 228, e.g. fibres, to an appropriate ultraviolet source 232 e.g. of the kind described hereinbefore. [0063] A liquid such as milk 240 which is fed into the pipe inlet 206 can only exit the pipe 204 via the plurality of apertures 220 in the form of a plurality of streams which are thus caused to contact directly the quartz rods 222 which are constantly emitting diffused ultraviolet radiation. The milk is thus effectively subjected to ultraviolet radiation for sterilisation purposes.

[0064] The milk streams, from the apertures 220 are collected in the housing 202 and a consolidated flow 244 of the treated milk exits the housing 202 via the outlet 212 and can then be further processed. [0065] The invention has been described hereinbefore with reference to the treatment of milk. As stated this is exemplary only. Also, although the invention is designed to treat liquids which are opaque the use of the invention is not necessarily restricted in that respect and the principles of the invention can be used with liquids which are not opaque but which are light-transmissive.