Abstract:
A method and apparatus are described for killing or inhibiting growth of undesired microorganisms using ultraviolet radiation. A vortex turbulated flow of water is established within a vertical tube through which is transmitted ultraviolet radiation. In a preferred embodiment the dwell time of water within the tube may be varied to achieve optimum exposure. The method can be used to treat water alone or to treat objects suspended in water. In a particularly preferred embodiment freshly cut pieces of fruit may be treated.

Description:
This is a nationalization of PCT/NZ03/00073 filed Apr. 28, 2003 and published in English. 
     TECHNICAL FIELD 
     This invention relates to a method and apparatus for killing or inhibiting growth of undesired microorganisms with ultraviolet radiation. In one embodiment, the apparatus and method of the invention are used for treating undesired microorganisms on whole and cut fresh fruit and vegetables with ultraviolet radiation to enhance their shelf life. In another embodiment the method and apparatus are used to kill undesired microorganisms in waste water. 
     BACKGROUND ART 
     Ultraviolet radiation systems are known for the treatment of water. In one type of system an ultraviolet bulb or tube is mounted in a housing which is transparent to ultraviolet radiation. This is surrounded by a vertically oriented annular chamber containing water to be treated. In some embodiments the ultraviolet radiation is used to generate ozone to sterilise the water. In other embodiments the ultraviolet radiation provides the sterilisation directly. Representative patents of such technology are U.S. Pat. No. 4,141,830; US 4,273,660; US 6,099,799 and US 6,193,894. 
     It is also known from U.S. Pat. No. 6,015,229 to disinfect fluid by passing fluid flow through a uniform array of ultraviolet lamps having cross-sections perpendicular to the direction of fluid flow. Flow defecting delta wings are positioned to create pairs of vortices that either rotate in the same direction or in directions opposed to one another to assist in mixing the fluids while exposing them to ultraviolet radiation. 
     In U.S. Pat. No. 5,994,704 there is also described a flowthrough photochemical reactor using ultraviolet radiation. Deflectors are imposed in the flow path to create a turbulent flow to increase the uniformity of the fluid&#39;s exposure to photons radiating from a source within a tube. The flow path is substantially annular to that central source. 
     It would be desirable to provide a system to kill or inhibit growth of microorganisms suspended or dissolved in water by ultraviolet radiation. In order to ensure as complete a kill as is required the time of exposure of the microorganisms should be able to be controlled in a simple manner. 
     It is an object of this invention to go some way towards achieving this desideratum or at least to offer the public a useful choice. 
     SUMMARY OF THE INVENTION 
     Accordingly the invention may be said broadly to consist in a method for killing or inhibiting the growth of microorganisms in water which comprises:
         establishing a vortex turbulated flow of water containing said microorganisms through a vertically oriented ultraviolet light transparent tube which is open at both ends,   generating a flow of ultraviolet radiation into said tube and through said vortex flow, whereby said microorganisms are exposed to said ultraviolet radiation while passing down said tube, and   recovering said water after it has exited said tube.       

     Preferably said vortex is augmented by projecting a jet of water containing said microorganism substantially tangentially into said tube at or adjacent the top thereof. 
     Preferably the rate of flow of said jet is controlled so as to control the dwell time of said microorganisms in said tube. 
     In one alternative the strength of said ultraviolet radiation is varied while said microorganisms are exposed in said tube. 
     Preferably said microorganisms are on objects in said vortex turbulated flow. 
     Preferably said objects are recovered after they have exited said tube. 
     Preferably said objects are comestibles. 
     Preferably said comestibles are vegetables or fruit. 
     More preferably said comestibles are freshly cut fruit. 
     Preferably said comestibles have been permeated with a preserving agent before being placed in said vortex flow. 
     Preferably said comestibles are dried after exiting said tube. 
     Preferably said ultraviolet radiation has a wavelength of 200 to 280 nanometers. 
     Most preferably said ultraviolet radiation has a wavelength of 253.7 nanometers. 
     Preferably the temperature of said vortex flow when said microorganisms are exposed to said ultraviolet radiation is at about 42° C. 
     The invention may also be said broadly to consist in an apparatus for killing or inhibiting the growth of microorganisms in water or which comprises:
         a vertically oriented tube which is transparent to ultraviolet radiation, said tube having a top end and a bottom end,   means to supply water into said top end in a manner which establishes a vortex flow in said tube,   ultraviolet radiating means surrounding said tube adapted to radiate ultraviolet radiation through said tube and water containing said microorganisms therein, and   draining means from said bottom end of said tube.       

     Preferably said tube is constructed of a fluoropolymer. 
     In one alternative said means for supplying said water into said tube comprises a funnel having a spiral flow path therethrough. 
     In another alternative there is provided a tangential water jet to impart a controllable vortex turbulation within said tube in combination with said funnel. 
     In a still further embodiment there is provided a tangential water jet as the sole means for supplying said water containing said microorganisms. 
     Preferably said ultraviolet radiating means is a low pressure mercury vapour quartz tube. 
     Preferably said low pressure mercury vapour quartz tube radiates ultraviolet radiation at a wavelength of 253.7 nanometers. 
     Preferably there is a casing surrounding said ultraviolet radiating means, the inner face of said casing having reflecting means for reflecting ultraviolet radiation. 
     Preferably there is a temperature control system associated with said tube and said ultraviolet radiating means for controlling the temperature at which said ultraviolet radiation is radiated. 
     Preferably there is a temperature control means for controlling the temperature of said water flowing through said tube. 
     Preferably said draining means is a pipe. 
     Preferably there is provided an infeed tank upstream of said means to supply water into said tube. 
     Preferably there is a means for continuously feeding comestibles into said infeed tank. 
     Preferably there is a holding tank downstream of said draining means into which said draining means may discharge water and comestibles that have passed through said tube. 
     Preferably there are means to convey comestibles out of said holding tank. 
     Preferably there are means for recycling water from said holding tank to said infeed tank. 
     Preferably said means to recycle said water comprises a main tank, a pipe discharging water from said holding tank to said main tank, conduit means from said main tank to said infeed tank, a pump and a filtering system in said conduit means, the distal end of said conduit means returning water into said infeed tank. 
     The invention may also be said broadly to consist in an apparatus substantially as herein described with reference to  FIGS. 1 to 6 . 
     This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more fully understood by having reference to the accompanying drawings in which: 
         FIG. 1  is a side elevational schematic view of all the components associated with the treatment apparatus according to one embodiment of the invention. 
         FIG. 2  is a side elevation sectional view of a preferred embodiment of the ultraviolet treatment portion of the apparatus according to the invention. 
         FIG. 3  is a top plan view of a funnel for supplying water from the infeed tank into the top end of the treatment tube of the apparatus according to one embodiment of the invention. 
         FIG. 4  is a side elevation sectional view of an alternative embodiment of the portion of the apparatus shown in  FIG. 2 . 
         FIG. 5  is an isometric view, partly exploded, of the embodiment shown in  FIG. 4 . 
         FIG. 6  is side elevational view of another alternative embodiment of the invention which is particularly effective in treating waste water. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Construction of the Apparatus 
     The apparatus consists of an infeed tank  12 , a holding tank  16  and a main tank  21 . The ultraviolet radiation treatment part of the apparatus is housed in chamber  10 , the construction of which will be described in more detail with reference to  FIG. 2  below. Infeed tank  12  is provided with a cover  15  to keep out contamination. An infeed conveyor  11  is aligned with chute  26  to supply product (such as comestibles) into tank  12 . Within tank  12  is treatment fluid  33 . The treatment fluid may be water or water containing preservatives known to those skilled in the art. When the product is sliced fresh fruit a 1–7% (W/W) solution of calcium hydroxide may be used. 
     At the upstream end of infeed tank  12  there is a weir  25  over which fluid from pipe  24  is supplied into infeed tank  12 . 
     At the downstream end of tank  12  is a funnel  14 , the construction of which will be discussed in relation to  FIG. 3 . 
     The lower end of treatment chamber  10  is connected to an outlet pipe  18  which has two 180° bends and ends with its mouth open to discharge liquid into holding tank  16 . Holding tank  16  is also provided with a cover  15  to keep out contamination. The bottom of holding tank  16  is substantially v-shaped in cross-section to accommodate an outfeed conveyor  13 . Outfeed conveyor  13  is arranged above a further conveyor  17  to convey treated comestibles for further processing. 
     A pipe  19  is arranged as illustrated to discharge treatment fluid into main tank  21 . Main tank  21  has a return pipe  20  leading to a pump  22 . This in turn leads to a filtration system  23 . A further return pipe  24  connects to weir  25  to complete the circuit. 
     A peristaltic pump (not shown) injects super-saturated calcium makeup solution into main tank  21  as required. 
     The construction of the ultraviolet radiation chamber  10  is described with reference to  FIG. 2 . The chamber will be described starting with the central passage and moving radially outward. A tube  34  made from an advanced fluoropolymer which is transparent to ultraviolet radiation (AFP-840™) defines a passage  36  extending from funnel  14  to outlet pipe  18 . The tube  34  is held in position at either end by compression rings  32  and in between by compression bands  35 . The rings  32  are preferably stainless steel hose clips. Their purpose is to stop leakage. 
     In the annular chamber  39  surrounding tube  34  there are positioned a series of ultraviolet radiating tubes  30 . In the preferred embodiment these tubes are of a low pressure mercury vapour quartz type. The optimum ultraviolet radiation wavelength to achieve maximum germicidal activity is 253.7 nanometers. This is considered to be 100% efficient when the lamps&#39; surface temperature is 42.2° C. 
     The tubes  30  are held at either end in tube holders  29 . These are powered by a wiring loom  31 . 
     To the outside of the annular chamber  39  surrounding tube  36  is a cylindrical reflector shield  28 . Preferably the inner reflective surface  28  is brushed aluminium which is highly reflective to ultraviolet radiation. 
     The ultraviolet radiating chamber construction is completed by a cylindrical outside casing  27  which may be made of stainless steel. At the bottom of the chamber  10  is a base plate  38 . 
     From the bottom end of tube  34  there is a funnel-shaped portion  37  which joins the bottom end of passage  36  to the end of outlet pipe  18 . In the embodiment illustrated in  FIG. 2  there is a sleeve fitting  43  over an open end of pipe  18  leading to an extension of this pipe as shown in  FIG. 1 . 
     The funnel  14  leading from the edge of infeed tank  12  into the top of ultraviolet radiation chamber  10  is shown in plan view in  FIG. 3 . An opening though a side of infeed tank  12  through which an aqueous solution containing floating comestibles passes is provided above weir  42 . From weir  42  a downward sloping sluiceway  44  leads over a steeply sloping portion  45  down a scrolling portion  46  and into the top of passage  36 . A sloping side  48  completes the passageway from the top edge of funnel  14  down to the scrolling portion  46 . The funnel  14  constitutes a means for providing a feed of the cut comestibles and water through the tube into its first end in a manner which establishes a vortex flow over at least the part of its vertically oriented length of the tube. 
     In the embodiments illustrated in  FIGS. 4 and 5  the passageway  36  is shorter and has a greater diameter than that illustrated in  FIG. 2 . Otherwise the componentry and the construction is substantially the same. In addition there is provided an auxiliary tangential jet  40  which injects water into funnel-shaped portion  37  as shown by the arrow A in  FIG. 4 . The injection of this jet has an effect on the flow through rate of the vortex formed within passageway  36  as will be explained below. Jet  40  is connected to a source of high pressure water. 
     In the embodiment illustrated in  FIG. 6  infeed tank  12  is positioned to be at a slightly higher elevation than holding tank  16  so as to provide an appropriate head. A passage  36  from infeed tank  12  to holding tank  16  is defined, in the downstream direction, by a funnel  14  which joins a first AFP tube  34 , an elbow portion  54  followed by a second AFP tube  52  and an outlet  50 . 
     A weir  42  is provided in infeed tank  12  at the mouth of funnel  14 . Funnel  14  is of the type illustrated in  FIG. 3 . However, it is provided with a water jet  41  which is directed tangentially into funnel  14  adjacent the upper end of the first AFP tube  34 . The volume and velocity of water jet  41  can be controlled with, for example, a common water tap valve. 
     Three ultraviolet tubes  30  are illustrated. In this embodiment a casing (not shown) surrounds the total irradiating portion of the apparatus, that is both AFP tubes  34 , and to the outside of the outer ring of UV tubes  30 . 
     A second water jet  40  also directed tangentially into elbow  54  can optionally be provided. It too has a control valve in common with waterjet  41 . 
     Operation of the Apparatus 
     The overall operation of the apparatus will be explained with reference to  FIG. 1 . Comestibles, for example sliced apples, are placed on infeed conveyor  11  and fed down a chute  26  into the treatment fluid  33  in infeed tank  12 . Treatment fluid  33  contains preservatives. The preferred aqueous treatment solution will contain 1–7% W/W calcium hydroxide. 
     Inflow of recycled treatment fluid  33  over weir  25  causes a flow across infeed tank  12  and over weir  42  into the funnel  14 . As the fluid  33  containing the pieces of fruit travels down the scrolling pathway  46  it establishes a vortex which then swirls down passageway  36  through the ultraviolet radiation chamber  10 . 
     In the embodiment illustrated in  FIGS. 1 and 3  the flow rate of the turbulated vortex is not able to be varied. In the embodiments shown in  FIGS. 4 to 6  the speed of the turbulated vortex is able to be varied by the tangential injection of a jet of water within the main flow. The flow valves of the water jets  40  and  41  are able to control their flow rate. The faster the speed of the turbulated vortex, the longer is the residence time in the AFP tube or tubes. 
     The effectiveness of ultraviolet treatment depends on the length of exposure to the radiation, the wavelength of the radiation and the temperature at which the radiation is applied. The advantage of forming a vortex within passageway  36  is that it allows for a controlled dwell time in passage  36  during which it is exposed to the radiation. The pieces of fruit within the vortex may remain more or less stationary depending on the speed with which the vortex descends down the passage  36 . A vortex, effective in suspending the pieces within the radiation chamber momentarily, can be achieved by the use of an infeed funnel  14  as described with reference to  FIG. 3 . 
     The optimum temperature of 42.2° C. to achieve best disinfection using the particular tube described above can be achieved within the chamber by the heat generated by the ultraviolet tubes. Temperatures up to 50° C. can be employed. A thermostat and air conditioning may maintain the temperature at the desired level. 
     Once the treatment has been completed in ultraviolet radiation chamber  10  the pieces of fruit are discharged out pipe  18  into the holding tank  16 . The conveyor  13  travels in a clockwise direction. The upper lap of the conveyor  13  picks up pieces of fruit and discharges them onto a further conveyor  17 . From conveyor  17  they are taken for further treatment, usually involving drying and packaging. Because of the disinfection by exposure to ultraviolet radiation the pieces of fruit will then have an enhanced shelf life once they are packaged in sterile packaging. 
     Treatment fluid  33  in holding tank  16  will overflow into the top of pipe  19  and be discharged into main tank  21 . Make up treatment fluid  33  may be added to main tank  21  as required. 
     Pump  22  then pumps treatment fluid  33  through return pipe  20  in the direction of arrow B through a filtration system  23  and up pipe  24  over weir  25  where it completes the circuit by refilling infeed tank  12 . A means to recycle water from the holding tank  16  to the in-feed tank  12  includes the main tank  21 , the pipe  19  discharging water from the holding tank  19  to the main tank  21 , pipes  20 ,  24  forming conduit means from the main tank  21  to the in-feed tank  12 , a pump  22  and a filtering means  23  in the conduit means, the distal end of the conduit means returning water into the in-feed tank. 
     The method has been described in relation to pieces of cut fruit. However, it can be used for any form of comestible which can benefit from disinfection through ultraviolet radiation. 
     The embodiment illustrated in  FIG. 6  may be used in conjunction with tanks  12 ,  16  and  21  illustrated in  FIG. 1 . It offers compactness in height between infeed tank  12  and holding tank  16  while providing a residence time for UV radiation equivalent to that achieved if tubes  34  and  52  were end to end. The positioning of outlet  50  at the bottom of tank  16  also reduces the overall height of the apparatus. When the flow of treatment fluid  33  is stopped in infeed tank  2  the level of fluid in tube  34  is that of fluid in holding tank  16 . 
     The invention has been described with particular reference to the treatment of comestibles. During such treatment the UV radiation kills or inhibits the growth of microorganisms on comestibles. It is the microorganisms which cause the degradation of the comestibles. 
     The apparatus and method of the invention can also be used to kill or inhibit growth of microorganisms in waste water. A waste water treatment apparatus would not require means for recovery of comestibles and would be a continuous flow system rather than the closed loop system shown in  FIG. 1 . 
     Where the waste water is particularly cloudy a source of UV radiation of higher intensity may be used in addition to means to increase the dwell time in the treatment chamber. Additional tubes and loops additional to those illustrated in  FIG. 6  may be employed. Tangential water jets with higher velocity may be employed to increase the vortex turbulated flow rate. This increases the radial moments of force and decreases the axial moments of force along flow path  36 . This in turn means the waste water advances more slowly along flow path  36  and hence its dwell time in the chamber is increased. 
     Although the invention has been described through the use of a low pressure mercury vapour quartz ultraviolet radiating tube at its optimum temperature, other sources and conditions of ultraviolet radiation known to those skilled in the art may be used. 
     Other permutations and combinations of the invention will be apparent to those skilled in the art.