GB2572375A

GB2572375A - Ultraviolet fluid-treatment

Info

Publication number: GB2572375A
Application number: GB1804982.5A
Authority: GB
Inventors: Anthony Rudd Little Richard
Original assignee: Jenact Ltd
Current assignee: Jenact Ltd
Priority date: 2018-03-28
Filing date: 2018-03-28
Publication date: 2019-10-02
Also published as: GB201804982D0

Abstract

An ultraviolet (UV) fluid-treatment apparatus comprises a plurality of elongate, cylindrical UV lamps 4 mounted with their longitudinal axes generally horizontal, such that when fluid 3, 7 flows onto a first lamp the fluid is caused to form a film on the lamp surface, and to flow from the first lamp to a second lamp and form a film on a surface of the second lamp. The lamps may be arranged in a ladder-, lattice-, herringbone- or pyramid-like array (see figures 3-6). A divider (9, fig. 3) may divide and guide fluid flowing from the first lamp to the second lamp and from the first lamp to a third lamp. A fourth lamp may be provided at the same vertical level as the first lamp, with fluid flowing from the fourth lamp to a fifth lamp (see figures 5 & 6). The fluid may flow under gravity. The apparatus may include a housing 20 to which the lamps are attached. The apparatus is intended to promote a thin film of fluid flow across the surface of the lamps in order to assist treatment of fluids having low UV transmissivity such as milk or juices.

Description

ULTRAVIOLET FLUID-TREATMENT

The invention relates to an ultraviolet fluid-treatment apparatus and an ultraviolet treatment method. The treatment apparatus and method may in particular be suitable for applying ultraviolet light to fluids to disinfect said fluids.

Background of the Invention

It is well known, researched and quantified that UV light below 280nm (UVC) can be used for germicidal applications. Mercury vapour gas discharge lamps (whether powered directly with an electric current or energised by radio frequency (RF) or microwave radiation) and more recently UV LED arrays emit a peak at 254 nm, close to the optimal wavelengths which cause irreparable damage to the DNA strands in cells, such cells including bacteria, viruses and moulds. This damage causes the cells to be disabled, to cease to be able to reproduce, and to die.

Since as early as the 1930s, such mercury vapour lamps have been used for disinfection of air, water and surfaces. This technology forms the basis of products provided by various companies, such as Trojan Technologies, Hanovia and Wedeco’s systems for drinking and waste water disinfection, and Sanuvox, Sterilaire and JenAct’s products for air disinfection and breakdown of chemicals such as VOCs, which can also be achieved with UVC. US patents 3,182,191 and 3,562,520 of the Puretest Water Purifier Co disclose a typical format for a water disinfection system. A longitudinal UV lamp runs down the centre of a cylindrical chamber and water is passed through the chamber and around the lamp and is consequently exposed to UV light. It is vital that the UV light is unobstructed in its transmission to the water, and the US’191 and US’520 documents disclose internal cleaning systems to try to ensure that the UV light emitted by the lamp is not obstructed by any deposits on the lamp.

A problem with existing treatment systems is the efficient transmission of the DNAdamaging UVC light to the DNA strands which are to be destroyed. UVC is transmitted reasonably well by air, distilled water and drinking water, and consequently UVC is used extensively and efficiently in disinfection of these fluids. In addition, some wastewater is filtered to a sufficient extent, before being exposed to UV light, that UVC can be used to disinfect it sufficiently for release into the sea etc. In these cases, the transmissivity of the fluid is sufficient for an adequate amount of UVC energy to reach the DNA in the cells of the microorganisms to be permanently disabled or killed. However, there are many fluids that contain undesirable bacteria and other microorganisms which have low transmissivity to UVC (such as opaque liquids). Examples of such fluids include milks, juices, syrups, industrial cutting fluids, and foul wastes. Disinfection of milks, juices, syrups, etc. is required to permit human and animal consumption and also to preserve the fluids and extend their shelf lives, but the systems described above for treatment are inadequate for those fluids because of the fluids’ low transmissivity. Additionally, in some cases, it is desirable to use UVC light to deliver energy to chemical reactions, such as oxidation or cationic reactions (for example for treatment of chemical and oil industry residues). The transmissivity issues described above can also prevent the use of UVC light to deliver energy to chemicals which have low transmissivity or are opaque.

I n some cases, disinfection of liquids is achieved by pasteurisation or other heat treatments instead of exposure to UVC light. Such treatments involve raising a liquid to a set temperature for a time which kills any microbiological agents in the liquid. This process takes a considerable amount of energy and can also adversely affect the taste of drinks, etc. In addition, in the case of drinks, these often need to be subsequently chilled and thus further energy is required to reduce the temperature from the elevated high. Some products can be filtered to remove organisms of a certain size or elements of the liquid, such as fat, that contain certain harmful microorganisms. After removal, those products or elements can be heat treated separately and returned to the liquid. However, these processes are expensive and complex.

Mercury vapour discharge lamps are cheap and widely available and efficient at producing UVC and are well proven and preferred in the purification and treatment of water and air. These features make such lamps desirable for treatment of other fluids if solutions can be found to the problem of transmitting the UVC with sufficient energy to microorganisms throughout the fluid. Variously it is suggested that 90% of UVC is absorbed within 0.01 mm of milk or 98% of UVC is absorbed within 2 mm of juices (see WO2010125389A1 and US20090004050, discussed below).

Various solutions have been proposed to make UV treatment of lower-transmissivity fluids practical. WO2010125389A1, for example, discloses a chamber system with a restricted annular space around a UVC lamp and a series of elements with mixing stations between adjacent longitudinal elements. This is intended to create turbulent flow and therefore to increase the chance of all microorganisms coming into sufficient proximity of the UV source. However, consideration of the narrow annular space suggested by WO’389A1 and the volume of production in a commercial milk or juice operation suggests that such a system would have to be very extensive and therefore expensive.

CA2743380C and US8293185B2 disclose systems where static mixer elements are positioned around a lamp to create turbulent flow, again to try to increase the effectiveness by increasing the chance of all microorganisms coming into contact with the UVC element. These are also likely to be expensive if scaled to match commercial production volumes, and may not be able to provide a satisfactory level of certainty that the microorganisms in a fluid have come sufficiently close to the UVC element to achieve the intended disinfecting.

US5144146A discloses the concept of pulsing a UV source to obtain high peak intensities of UV (including UVC) - in one embodiment pulsing a conventional 10Ow source to achieve pulses of 3000w. It is claimed that such increased intensity allows the UVC to penetrate much further into the fluid to be disinfected and therefore the restrictions on flow because of limited transmission would be eased. US5900211 discloses such pulses typically being between 10 nanoseconds and 10 milliseconds. W02003021632A3 discloses microwaveexcited UV sources being pulsed in a liquid environment. The cost of power supplies currently available to permit pulsing are many times the cost of conventional ballast type power supplies for mercury discharge lamps and this has restricted their use.

US2009004050A1 discloses an alternative thin film solution where liquid is forced between contra-rotating UV transmissive discs a short distance apart and UV light exposes the consequent thin film of liquid. Mixing and UVC exposure are simultaneous but the system is complex, requires expensive and accurate manufacture and maintenance, and again offers limited flow relative to likely commercial volumes.

The present invention aims to provide a simple, relatively cheap solution to the problem of how to expose fluids (liquids or gases) containing microorganisms to UV disinfection or treatment.

Summary of the Invention

In accordance with a first embodiment of the invention, there is provided an ultraviolet (UV) fluid-treatment apparatus as claimed in claim 1. In accordance with a second embodiment of the invention, there is provided a method of treating a fluid using ultraviolet (UV) radiation as claimed in claim 17.

Preferably, the lamps include individual quartz tubes. The lamps are preferably arranged in such a way that when a suitable volume of fluid flows at a suitable rate along or close to the centre line of the top of the top lamp in the series the fluid will flow around the lamp, the diameter and/or surface material of which will be selected to suit the surface tension characteristics of the fluid so that the fluid forms a film on the surface of the lamp and then flows from the centre of the lamp to the centre line of the lamp below it, where the process is repeated over a ladder-, lattice-, herringbone- or pyramid-like structure until the fluid is released from the bottom lamp in the series to a collection trough and then flows to post process. Thus UVC exposure from simple, commercially available lamps can be combined with mixing powered by gravity or a pressure gradient, and exposure of the whole of the fluid in the form of a film on the surface of one or more of the UV lamps can be guaranteed. The system is easily scalable.

In an embodiment of the invention the flow from the bottom of the top lamp (or a suitable subsequent lamp in the series) is split by an angled divider so that the fluid pours onto the centre line of two separate parallel lamps beneath the upper lamp. This process could be repeated to allow slower flow or thinner films of fluid on the surfaces of the lamps. In cases where increased flow is required then there could be a number of ‘top lamps’ with a suitable matrix of lamps beneath.

Preferably, the lamp type or power density is chosen to allow temperature control which can be used to control the viscosity of the liquid being treated. Optionally the power density may be controllable separately for different lamps in the plurality of lamps, to allow the viscosity to be controlled differently in different parts of the apparatus. For example, it may be desirable to maintain the viscosity of the fluid at substantially the same value throughout the apparatus. Therefore, it may be desirable to control the power densities of the lamps so that lamps closer to the bottom of the apparatus have lower power densities than lamps closer to the top of the apparatus, as the temperature of the fluid may increase as it passes through the apparatus.

In an embodiment of the invention, the lamps can be electrodeless and operate in a cavity, such that the cost effectiveness of microwave energisation can be used and removal of lamps for cleaning/changing is easy.

Preferably, the UV fluid-treatment apparatus includes a chamber within which the plurality of lamps is located. Optionally, the inside of the overall chamber system may be reflective to maximise the use of any UVC not at first absorbed by the fluid.

In a further embodiment and if necessary for temperature control, cooling air can be passed through the annular spaces between the lamps and quartz tubes surrounding the lamps, if fitted. In a further embodiment, air passing through the annular space could, if by passing through the annular space it was partially converted to ozone, be fed back into the chamber for synergistic treatment of the liquid with ozone.

In any of the embodiments described above it is envisaged that the system would be easy to manufacture and maintain and could be completely enclosed in a watertight chamber with a pipe inlet at the top and a pipe outlet at the bottom. Unlike a conventional UV liquid treatment chamber, one access panel would allow access to all parts for cleaning and the system would operate at ambient pressure.

Brief Description of the Drawings

Figure 1 schematically illustrates, in cross-sectional view, an ultraviolet (UV) fluid-treating apparatus with a plurality of UV lamps arranged in a ladder-like structure;

Figure 2 schematically illustrates, in perspective view, the UV fluid-treating apparatus of figure 1;

Figure 3 schematically illustrates, in cross-sectional view, a UV fluid-treating apparatus with a plurality of UV lamps arranged in a pyramid-like structure;

Figure 4 schematically illustrates, in perspective view, the UV fluid-treating apparatus of figure 3;

Figure 5 schematically illustrates, in cross-sectional view, a UV fluid-treating apparatus with a plurality of UV lamps arranged in a lattice-like structure;

Figure 6 schematically illustrates, in perspective view, the UV fluid-treating apparatus of figure 5;

Figure 7 schematically illustrates, in cross-sectional view, a UV fluid-treating apparatus with a plurality of UV lamps arranged in a ladder-like structure and a reflective external structure; and

Figure 8 schematically illustrates, in cross-sectional view, a UV fluid-treating apparatus with a plurality of UV lamps arranged in a pyramid-like structure and a reflective external structure.

The present embodiments represent the best ways currently known to the applicant of putting the invention into practice, but they are not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only.

Detailed description

Figures 1 and 2 illustrate an ultraviolet (UV) fluid-treating apparatus comprising a series (12) of horizontally mounted, cylindrical, longitudinal, sleeved UVC lamps (4) (i.e. lamps emitting UVC radiation). The lamps (4) are arranged in such a way that when a suitable volume of liquid (3) is poured from a longitudinal slot (2) of an infeed system (1) at a suitable rate onto the centre line of the top of the top lamp (4) in the series (12), the liquid will flow around the lamp (4), covering the outer surface of the lamp (4). The diameter of the lamp (4) (and possibly other physical parameters of the lamp (4), such as a material covering the lamp’s external surface) will ideally be selected to suit the surface tension characteristics of the liquid so that the liquid forms a surface film (7) around the lamp (4) by flowing from the centre of the top of the circumference of the lamp (4) to the centre line of the bottom of the lamp (4). While the liquid is part of the surface film (7) around the lamp (4), the liquid is exposed to the UV radiation emitted by the lamp. After reaching the bottom of the lamp (4), the liquid drips, mixes and experiences turbulence (8) as it drops to the centre of the top of the lamp (4) beneath it. The process is repeated over the ladder-like structure (12) until the liquid (3) is released from the bottom lamp (4) in the series (12) to a collection trough (5) and then flows to post process (6). The thickness of the surface film is preferably optimally a thickness approximately equal to the distance that UVC radiation can penetrate into the liquid given the opacity of the liquid being treated. However, because the liquid will come into contact with a plurality of bulbs and the liquid will furthermore be mixed by the cascade nature of the system, the surface film can be thicker than the maximal depth of UVC penetration, as all of the liquid to be treated should come within the transmission dimension of a lamp during the liquid’s passage through the structure of the apparatus.

Figures 3 and 4 illustrate a UV fluid-treating apparatus comprising a series (14) of horizontally mounted, cylindrical, longitudinal, sleeved UV lamps (4). The lamps (4) are arranged in such a way that when a suitable volume of liquid (3) is poured from a longitudinal slot (2) of an infeed system (1) at a suitable rate along the centre line of the top of the top lamp (4) in the series (14) the liquid will flow around (7) the lamp (4). The diameter of the lamp (4) (and possibly other physical parameters of the lamp (4), such as a material covering the lamp’s external surface) will ideally be selected to suit the surface tension characteristics of the liquid so that the liquid forms a surface film around the lamp (4) by flowing from the centre of the top of the circumference of the lamp (4) to the centre line of the bottom of the lamp (4). After dropping from one lamp (4), the liquid is divided into two flows by an angled divider (also referred to as a dividing or splitting piece) (9). The flows continue downwards along surfaces of the divider (9) and at the lower edges (13) of the divider (9) the flows of liquid drip, mix and experience turbulence (8) as the liquid drops to the centres of the tops of further lamps (4) beneath them. The process is repeated over the illustrated pyramid-like or triangular/hexagonal lattice structure (14) until liquid (3) is released from one or more bottom lamps (4) in the series (14) to a collection trough (5) and then flows to post process (6). As illustrated in figures 3 and 4, there are several lamps (4) at the same vertical height at the bottom of the structure (14).

Figures 5 and 6 illustrate a UV fluid-treating apparatus suitable for greater flows of liquid. The illustrated UV fluid-treating apparatus comprises a series of horizontally mounted, cylindrical, longitudinal, sleeved UV lamps (4). The lamps (4) are arranged in such a way that when suitable volumes of liquid (3) are poured from a number of parallel longitudinal slots (15) of an infeed system (16) at suitable rates along the centre lines of top lamps (17) in the series, the liquid will flow around the top lamps (17). The diameters of the top lamps (17) (and possibly other physical parameters of the lamps (17), such as a material covering the lamps’ external surfaces) will ideally be selected to suit the surface tension characteristics of the liquid so that the liquid forms a surface film around the lamps by flowing from the centres of the tops of the circumference of the lamps to the centre lines of the bottoms of the lamps. After dripping off the bottoms of the lamps, the liquid is divided into multiple flows by angled dividing/splitting pieces (18). The flows continue downwards and at the lower edges (13) of the dividing pieces (18) the flows drip, mix and experience turbulence. The liquids drop to the centres of the tops of further lamps beneath them. The process is repeated over a lattice-like structure (19) of lamps until liquid is released from the bottom lamps in the series to a collection trough (5) and then flows to post process (6).

Fig 7 illustrates a UV fluid-treatment apparatus similar to the one illustrated in figures 1 and 2, i.e. comprising a series of horizontally mounted, cylindrical, longitudinal, sleeved UV lamps (4). The lamps (4) are arranged in such a way that when a suitable volume of liquid (3) is poured from a longitudinal slot (2) of an infeed system (1) at a suitable rate along the centre line of the top of the top lamp (4) in the series, the liquid will flow around the lamp. The diameters of the lamps (and possibly other physical parameters of the lamps (4), such as a material covering the lamp’s external surface) will ideally be selected to suit the surface tension characteristics of the liquid so that it forms a surface film around the lamp (7) and then flows from the centre of the top of the circumference of the lamp to the centre line of the bottom of the lamp. The liquid drips, mixes and experiences turbulence (8) as it drops to the centre of the top of the lamp beneath it. The process is repeated over a ladder-like structure until it is released from the bottom lamp in the series to a collection trough (5) and then flows to post process (6). An external structure (20) is provided, the surface of which directly facing the lamps (21) may be reflective to UV radiation and may also be used to contain and direct any liquid that might otherwise spray or fly from the ladder-like structure and therefore not be fully treated. In the illustrated embodiments, the gap (24) between the lamps (4) and the external structure (20) is set to ensure all liquid is kept within a transmissible distance of UV from the lamp.

Figure 8 illustrates a UV fluid-treatment apparatus similar to the one illustrated in figures 3 and 4, i.e. comprising a series of horizontally mounted, cylindrical, longitudinal, sleeved UV lamps (4). The lamps (4) are arranged in such a way that when a suitable volume of liquid (3) is poured from a longitudinal slot (2) of an infeed system (1) at a suitable rate along the centre line of the top of the top lamp (4) in the series the liquid will flow (7) around the lamps (4). The diameters of the lamps (and possibly other physical parameters of the lamps (4), such as a material covering the lamp’s external surface) will ideally be selected to suit the surface tension characteristics of the liquid so that the liquid forms a surface film around each lamp by flowing from the centre of the top of the circumference of each lamp to the centre line of the bottom of the lamp where the liquid is divided into two flows by an angled divider or dividing/splitting surface/piece (22). The flows continue downwards along the surfaces of the divider and at the lower edges of the divider they drip, mix and experience turbulence (8) as they drop to the centres of the tops of further lamps beneath them. The process is repeated over a pyramid-like structure of lamps until liquid is released from the bottom lamp in the series to a collection trough (5) and then flows to post process (6). Like in the embodiment of figure 7, an external structure (23) is provided, the surface of which directly facing the lamps (21) may be reflective to UV radiation and may also be used to contain and direct any liquid that might otherwise spray/fly from the ladder structure and therefore not be fully treated the gap (24) being set to ensure all liquid is kept within a transmissible distance of UV from the lamps. In the illustrated example, the angled dividers which split flows of liquid are provided by the external structure (23), but in other embodiments the dividers may comprise separate components.z

An external structure could also be provided in other embodiments, around different series of lamps. For instance, in some embodiments, an external structure may be provided around a triangular/hexagonal lattice having multiple lamps at the same vertical height at the top of the structure (such as the series of figures 5 and 6).

In the illustrated examples, the UV lamps are cylindrical, i.e. circular in cross section. Cylindrical lamps may be preferred as they are commonplace and can provide the necessary flow control (by appropriate choice of surface material and radius of curvature, as described above) for fluids which are to be poured over them. However, other cross sections of lamp may also be suitable for use in the illustrated treatment apparatus and treatment methods. For example, in some embodiments, lamps with an oval cross section, a tear-shaped cross section or a triangular cross section may be used. Additionally, there may be lamps having different cross sections within a plurality of lamps. For example, some embodiments may include one or more lamps with a circular cross section and one or more lamps with a triangular cross section. This may for example be advantageous if a triangular cross-section lamp can be used to split a flow of liquid into two flows of liquid, such that a separate divider is not required.

The embodiments illustrated in figures 5 and 6 show a plurality of UV lamps 4 in an equilateral triangular or hexagonal lattice. Other embodiments may have UV lamps in different lattice arrangements, such as (but not limited to) rhombic, square, rectangular or parallelogramic/oblique lattices.

In some embodiments, one or more of the lamps in a series may additionally or alternatively be mounted such that they are sloped relative to the horizontal, e.g. so that they form a “zig-zag” or “herringbone” pattern. In such an arrangement, liquid may flow along a first sloped lamp, the liquid being exposed to UV radiation from the lamp as the liquid flows along the lamp. The liquid may then drop off the end of the first lamp to a next lamp in the series which is sloped in the opposite direction relative to the horizontal, so that the liquid flows down the second sloped lamp. Such an arrangement may in some circumstances advantageously increase the likelihood that any given molecule of fluid passing through the UV fluid-treatment apparatus receives sufficient exposure to UV radiation to ensure adequate treatment of the fluid. In such “zig-zag” or “herringbone” embodiments, the lamps may alternatively be substantially flat or planar, such that the fluid flows down a substantially flat surface of a first angled planar lamp before dropping onto another lamp. This may permit larger volumes of fluid to be handled by the UV fluidtreatment apparatus.

In this document, the word “fluid” is intended to include (at least) liquids and gases. In the illustrated embodiments, a liquid (3) is described as flowing from an infeed system to one or more lamps and subsequently to a collection trough and post processing. This flowing of the liquid may advantageously happen under the action of gravity alone, meaning that no external power source is needed to create the flow of liquid. However, in other embodiments, a pressure gradient may be created with use of appropriate additional apparatus such as one or more pumps. This may enable the UV fluid-treatment apparatus to treat liquids or gases which are caused to flow from an infeed to the one or more lamps, the collection trough and post processing under the influence of the pressure gradient (possibly against gravity, if desired, though it may be preferable from an energyconsumption perspective to try to maximise usage of gravity’s influence).

In the above description, fluids are described as being poured or dropping onto “centre lines” and “tops” of lamps. It may be advantageous for the fluids to make initial contact with the tops/centrelines of the lamps, as that may help ensure an even and as-close-tocomplete-as-possible film of fluid around each lamp and therefore an even and maximised exposure of fluid to UV radiation from the lamp. However, in some embodiments, fluid may not initially make contact with the centreline. It may for example initially make contact with a lamp at a point offset from the centreline of the top of the lamp, in which case only part of the lamp will be coated with the fluid. In some embodiments, the apparatus may be arranged such that two separate flows of fluid are directed either side ofthe top centreline of a lamp, so that each side of the lamp is coated with fluid from a different flow.

The lamps in embodiments of the invention may all be connected (directly or indirectly) to 5 and/or contained within a housing which protects the lamps and any fluids flowing over the lamps as described in the above embodiments from external influences.

One or more sources of power may provide the lamps with power sufficient to allow the bulbs to produce UVC radiation.

Claims

1. An ultraviolet (UV) fluid-treatment apparatus, including:

a plurality of substantially horizontally mounted, cylindrical, longitudinal UVC lamps, the plurality of lamps being arranged such that when fluid flows onto the top of a first lamp in the plurality of lamps the fluid is caused to form a surface film of fluid on a surface of the first lamp as the fluid flows over the surface of the first lamp, and to flow from the first lamp to a second lamp in the plurality of lamps and form a surface film of fluid on a surface of the second lamp as the fluid flows over the surface of the second lamp.

2. A UV fluid-treatment apparatus as claimed in claim 1, wherein the plurality of lamps is arranged in a ladder-, lattice-, herringbone- or pyramid-like structure.

3. A UV fluid-treatment apparatus as claimed in claim 1 or claim 2, additionally including a divider arranged to divide fluid flowing from the first lamp and to guide fluid from the first lamp to the second lamp and from the first lamp to a third lamp in the plurality of lamps such that the fluid guided to the third lamp forms a surface film of fluid on a surface of the third lamp as the fluid flows over the surface of the third lamp.

4. A UV fluid-treatment apparatus as claimed in claim 1, claim 2 or claim 3, additionally comprising a fourth lamp arranged at substantially the same vertical level as the first lamp such that fluid is caused to form a surface film of fluid on a surface of the fourth lamp as the fluid flows over the surface of the fourth lamp, and to flow from the fourth lamp to a fifth lamp in the plurality of lamps and form a surface film on a surface of the fifth lamp as the fluid flows over the surface of the fourth lamp.

5. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein the apparatus is arranged such that fluid is caused to flow towards at least one final lamp in the plurality of lamps under gravity.

6. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein one or more of a diameter and a surface property of a lamp in the plurality of lamps are arranged in dependence upon surface tension characteristics of the fluid.

7. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein the longitudinal lamp has a circular cross-section.

8. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein a lamp in the plurality of lamps is enclosed within a quartz tube.

9. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein a lamp in the plurality of lamps is a low-pressure lamp.

10. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein a lamp in the plurality of lamps is a mercury vapour lamp.

11. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein a lamp in the plurality of lamps is an electrodeless lamp.

12. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein a lamp in the plurality of lamps is provided in a resonant cavity.

13. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein a power density of a lamp in the plurality of lamps is controlled in order to influence one or more of: the temperature of the lamp; and the viscosity of the fluid.

14. A UV fluid-treatment apparatus as claimed in any preceding claim, the apparatus being arranged to initiate or increase the speed of chemical reactions within the fluid by means of UVC output from the plurality of lamps.

15. A UV fluid-treatment apparatus as claimed in any preceding claim, wherein the plurality of lamps is arranged such that the fluid experiences turbulence and mixing due to the distance it flows downwards in free space as it flows from the first lamp to the second lamp.

16. A UV fluid-treatment apparatus as claimed in any preceding claim, comprising a housing to which the lamps in the plurality of lamps are attached.

17. A method of treating a fluid using ultraviolet (UV) radiation, the method comprising:

5 providing a plurality of substantially horizontally mounted, cylindrical, longitudinal

UVC lamps, the plurality of lamps being arranged such that when fluid flows onto a first lamp in the plurality of lamps the fluid is caused to form a surface film of fluid on a surface of the first lamp as the fluid flows over the surface of the first lamp, and to flow from the first lamp to a second lamp in the plurality of lamps and form 10 a surface film of fluid on a surface of the second lamp as the fluid flows over the surface of the second lamp;

providing power to the first and second lamps such that the first and second lamps emit UV radiation, to expose fluid on the surfaces of the first and second lamps to the UV radiation.