WO2003004420A1

WO2003004420A1 - Apparatus for inhibiting the growth of algae in water by uv radiation

Info

Publication number: WO2003004420A1
Application number: PCT/GB2002/003109
Authority: WO
Inventors: Ian Williams
Original assignee: Thames Water Utilities Ltd.
Priority date: 2001-07-06
Filing date: 2002-07-08
Publication date: 2003-01-16
Also published as: GB2391864A; GB0328910D0; GB0116593D0

Abstract

The invention relates to an apparatus, for inhibiting the growth of algae in water treatment works, comprising a housing (2) which houses in the embodiment two UV-lamps which emit radiation at 254 nm and is directed to the surface of water flowing out of a settlement tank to inhibit algae growth.

Description

APPARATUS FOR INHIBITING THE GROWTH OF ALGAE IN WATER BY UV RADIATION

The invention relates to an inhibitor, and particularly to an apparatus, a system and method for inhibiting the growth of algae in water treatment works.

It is generally accepted and understood that water treatment plant such as sewage works with final or settlement tanks, and sewage works with Humus tanks generally suffer from algae growth to varying degrees. In particular, algae grows between scum boards and V notch weirs on such final or settlement tanks. The amount of algae growth is dependent on several factors including temperature, effluent quantity and quality, and amount of light.

Algae is not only unsightly but can be picked up on the final effluent sample and recorded as solids. In settlement tanks, this algae growth builds up around the V notch weirs, inhibiting water flow thereby raising the liquid level in the tank, and making scum removal ineffective as scum removal systems usually rely on surface tension to draw scum. Moreover, on works with tertiary treatment, algae will blind the filters and reduce the throughput of effluent.

In settlement tanks, owing to the complex profile of the scum boards and V notches, it is difficult to clean them with a mechanical brush system. Manual cleaning at regular intervals is therefore at present the only way of cleaning scum boards and V notches, but this is very time consuming, and thus expensive, and can lead to "down-time" of the plant, leading to inefficient operation and increasing expense.

It is an object of the invention to seek to mitigate the above-mentioned disadvantages.

According to a first aspect of the invention there is provided apparatus for inhibiting the growth of algae in water treatment works, comprising an algae growth inhibitor characterised by being a source of radiation adapted to emit radiation at a frequency sufficient to inhibit growth of algae.

The source may comprise a UV source. This is a particularly effective way of inhibiting, or killing, algae.

The UV source may be positioned above the surface of a body of water to be irradiated, submerged in a body of water to be irradiated, or at or adjacent the surface of a body of water to be irradiated.

The source may be movable with respect to the body of water being irradiated, particularly by a movable carrier mounting the source and by the source being mounted on the carried for movement therewith to treat substantially the whole of a designated surface part of the body of water being irradiated.

The source may be reciprocable in a direction substantially transversely of the direction of movement.

The source may also be adjustable in position relative to a surface of the body of water being irradiated.

The source may be pivotally adjustable on a hinged mounting whereby to adjust the angle of incidence of emitted radiation on the surface of the body of water being irradiated.

Moreover, the source may be adjustable in height with respect to the surface of a body of water to be irradiated.

There may be a support for the source, and the source may be adjustable in three planes relative to the support, and in addition may be pivotally adjustable with respect to the support.

There may be a plurality of discrete sources, the or each of which may be adapted to emit radiation periodically or in a pulsed manner. The or each source may comprise a housing for the source, and the housing may have an opening for the emission of radiation.

The opening may be positioned such that radiation is emitted downwards, away from users.

The housing may comprise an inner surface of reflective material. This enhances efficient use of the UV-source.

The shape of the housing maybe adapted to reflect radiation towards the opening, for example the housing may be parabolic, to direct emitted UV radiation to a focussed position say at the surface of the body of liquid being treated, or just below it.

A method of inhibiting growth of algae in a water treatment plant characterised by irradiating a body of water with radiation of a frequency sufficient to inhibit growth of the algae, for example by providing a UV source, the wavelength of the UV being preferably about 254nm.

UV radiation as hereinbefore described provides an effective means of killing or inhibiting growth of algae, as well as being cheap and requiring little maintenance.

Apparatus for inhibiting the growth of algae in water treatment works is hereinafter described, byway of example, with reference to the accompanying drawings.

Figs 1A, IB and 1C show respective schematic transverse sections through a part of a settlement tank of a sewage treatment works embodying apparatus according to the invention; and

Fig. 2 shows an elevational view in the direction "A" in Fig. 1 A;

Fig. 3 shows to an enlarged scale an end view of an algae removal apparatus of Figs. 1 A, IB and 2 according to the invention; and Fig. 4 shows a side view of the apparatus of Fig. 2 attached to the underside of a bridge over a settlement tank of the kind shown in Figs. lA-lC.

As mentioned previously, algae can seriously inhibit operation of such works as described above.

Referring to the drawings, there is shown apparatus for inhibiting the growth of algae in water treatment works, characterised by an algae growth inhibitor which is a source of radiation adapted to emit radiation at a frequency sufficient to inhibit the growth of algae.

Apparatus 1 embodying the invention for inhibiting, and preferably killing, algae is particularly applicable in water treatment plants such as sewage works and moreover is particularly effective in final or settlement tanks 100.

In such settlement tanks, a mixture of treated (activated) sewage and effluent is allowed to settle whereby to achieve separation of solids and liquid. Some of the separated liquid can be recycled to upstream parts of the plant, while the remainder is returned to rivers, usually after a period of rest in a reservoir or after passage through a slow sand filter. Algae can be detected as solids in the liquid which may increase the solids' count to unacceptable levels and also can inhibit the operation of a slow sand filter, or indeed other plant downstream of the settlement tank 100. A typical settlement tank is one which essentially comprises a circular device 101 (Fig. 1A) with a conical bottom (not shown), the tank typically being some 15' (45.7m) high and 2.2m in diameter. The tank 100 has a central area (also not shown) in which the activated sludge and effluent mixture is introduced, the sludge settling to the bottom of the tank 100 where it passes through an outlet at the bottom. In order to enhance passage of the sludge through the outlet, there is a system of chains or brushes (not shown) which depend from abridge or bar 102 which processes roundthe tank 101, the chains or brushes extending from the bridge 102 into the tank 100 and engaging the separated sludge to urge it towards the central outlet. The circular device 101 is defined by an outer cylindrical wall 103 on which the bridge 102 is supported on a wheeled arrangement 104, the wheel or wheels 105 running round the upper surface of the wall 103, which is unobstructed to allow for passage of the wheel or wheels 105 therealong. The wheel or wheels 105 are driven by a suitable motor device in a housing 106, from which the bridge 102 extends to the centre of the tank 100.

Inwardly of the wall 103 there is a launder channel 107 defined by an internal wall 108 spaced from the wall 103 and having a downwardly (as viewed in the drawings extending from left to right) upper surface 109 from which extends upwardly, as viewed, a V-notch weir 110, (Fig. 2). Between the wall 108 and V-notch weir 110 there is a further channel 111 defined between the wall 108 and an inner circular wall or scum board 112. The board 112 extends above the surface 'S' of the liquid (water) in the settlement tank 100, and part way below the surface. Its purpose is to prevent scum on the surface from entering the channel 111. In particular it prevents scum being blown into the channel 111 by wind. The V-notch weir 110 is essentially an upstanding metal plate, extending round the whole tank 100 and having a series of V-notches 113 through which liquid in the channel 111 debouches in a relatively thin flow over the inclined surface 109 of the wall 108 (which, like the water wall is usually of concrete) into the launder channel 107. The floor of the launder channel is arranged to direct the liquid to a single outlet at one point on the periphery of the tank, whence it leaves the tank 100 for further (downstream) treatment.

The apparatus 1 comprises a housing 2 containing the source, of radiation, namely, in the embodiment, two 254nm wavelength, 1200 mm UV tube lamps 2'. The housing 2 comprises four rectangular side panels 2a, 2b, 2c, 2d joined together along their long edges to form a strip, and two pentagonal end panels, 2e, 2f attached on either side of the strip of side panels 2a, 2b, 2c, 2d to form an enclosure. The side panels 2a, 2b, 2c, 2d are joined to each other at an angle of 135° and two internal angles of 45 °. The housing 2 comprises an opening 3 to allow UV radiation from the two UV tube lamps to be emitted, and is made from aluminium which has been polished or otherwise treated internally so that it is UV reflective.

Fig. 2 shows the apparatus 1 attached to the underside of the bridge 102 over a settlement tank 100. Two brackets 5 are welded to the bridge 102, and the housing 2 is attached to the brackets 5 by bolts 6.

A micro switch (not shown) is fitted externally on the housing 2 for circuit isolation in case the housing 2 is removed without electrical isolation. The supply is taken from the bridge slip ring assembly or from the half bridge drive motor starter. Protection is provided by a 5 amp RCBO.

The two UV tube lamps are set up to provide 40 seconds of UV radiation every 35 minutes. This is a standard rotation time for a 22m diameter final tank.

On a trial over a period of three weeks it was found that the algae died off and broke away completely leaving the V notches 113 clean without removing the tank 100 from service. The small proportion of light escaping around the box also started to kill algae on other surfaces adjacent to the V notches. It was found that the UV radiation was effective at killing algae to a depth of 150mm below the surface level. Below that level, algae growth is in any case reduced due to lower natural light levels.

UV tubes require very little maintenance, and their tube life is generally between 6 and 24 months. The ranning costs are dependent on how many tubes are installed, but for a standard 4 foot (121.92cm) fluorescent tube they amount to £0.16 per day with savings being made on scum removal pump running hours and manual tank cleaning, as well as on preventing the tanks being out of service.

Referring now to Fig. IB, there is shown a second embodiment 200 in which the source 1 of UV radiation is submerged below the level of the liquid in the channel 111. The lamps 2' are shown as being directed upwardly, however, there could be an additional source which comprises one or more UV lamps 2' directed downwardly, so that algae inhibition can be effected at a greater depth. Thus there would be a source in the form of UV lamps in which UV radiation is incident on the liquid both in a direction towards and away from the liquid surface. In such a construction the housing 2 will be made water-tight, with the opening(s) being closed by a quartz cover or plate for transmission of the UV radiation.

Similarly, in a third embodiment 300 as shown in Fig. 1C, the source can be mounted to be essentially at the surface of the liquid in the channel 111, suitably mounted on the scum board 112, though it could be mounted on the wall 108 or V-notch weir 1.10.

It will be understood that various other modifications are possible. Thus, there may be a plurality of sources 1 spaced apart along the length of the bridge, mounted so that the UV radiation is directed to the surface of the body of liquid inboard of the scum board 110. Further, the housing 2 may be adjustable in three planes, namely in Figs 1A-1C for example, transversely of the length of the bridge 102 and hence along the length of the channel 111, longitudinally of the length of the bridge 102 and hence transversely of the length of the channel 111 and substantially vertically (and hence its height is adjusted with respect to the level of the surface of the liquidin the channel 111). The adjustment may be effected manually, by a simple nut and bolt arrangement, or may be effected automatically by a motor for example driving a rack and pinion arrangement. Moreover, angular adjustment of the housing 2 may be effected by a pivot mounting 114 between the housing 2 and the bridge 102, or other support for the housing 2. The angle of inclination of the housing 2, and thus of the opening 3, may be adjustable by a simple ball and socket arrangement which can be clamped in a required position for a desired attitude of the housing, this clamping being effected manually. Alternatively, the angular attitude can be adjusted by motor means such as a snail cam arrangement which can be activated to tilt the housing as required, and maintain it in the desired attitude, or it can reciprocate swingably continuously.

The housing 2 could be curved, housing one or more curved UV lamps 2', and the lamps, in all embodiments can be operated continuously, particularly in daylight hours, or intermittently, in which case there could be an arrangement of fibre optic fibres to provide an electronic "chopper" to provide for intermittent operation.

The respective housings 2' referred to herein and described with reference to the drawings can be removably mountable on the bridge 102 or other support, for enhancement of repair or replacement.

Moreover, it will also be understood that the housing 2 in each case can house one, or more than two, UV-tubes 2'.

It will also be understood too that while the preferred position of the apparatus 1 is over the channel 111 as shown in Figs. 1 A-1C, the apparatus could be located in other positions, for example over the inclined surface 109 of the wall 108, or indeed at the front end of a water treatment works rather than in a settlement tank.

The housing is also effective to protect the lamp(s) from the environment and ambient atmosphere, and also protect the user from direct viewing of the UV-radiation, as the housing confines the radiation and directs it to the water being, treated by irradiation. In all embodiments, the incident UV-radiation is incident generally on either a surface film of liquid as it exits the V-notch weir plate, or on the top layer of liquid on the wall 109 say, most algae formation generally occurring at the surface. Hence there is a high incidence of UV radiation in a small water volume, which inhibits, and can kill, algae formation. This delay in algae formation is beneficial in reducing solids content of the liquid (water) downstream of the settlement tank and reduces maintenance to the extent that one person per site can be dispensed with, so dramatically reducing costs of operation of say a sewage works.

Claims

1. Apparatus for inhibiting the growth of algae in water treatment works, comprising an algae growth inhibitor characterised by being a source of radiation adapted to emit radiation at a frequency sufficient to inhibit growth of algae.

2. Apparatus according to Claim 1, characterised by the source comprising a UV source.

3. Apparatus according to Claim 2, characterised by the UV source being positioned above the level of a body of water to be irradiated.

4. Apparatus according to Claim 2, characterised by the UV source being submerged in a body of water to be irradiated.

5. Apparatus according to Claim 2, characterised by the UV source being positioned at the level of the surface of a body of water to be irradiated.

6. Apparatus according to any of Claims 2 to 5, characterised by the source being movable with respect to the body of water being irradiated.

7. Apparatus according to Claim 6, characterised by a movable carrier mounting the source and by the source being mounted on the carrier for movement therewith to treat substantially the whole of a designated surface part of the body of water being irradiated.

8. Apparatus according to Claim 6, characterised by the source being reciprocal in a direction substantially transversely of the direction of movement.

9. Apparatus according to any of Claims 2 to 8, characterised by the source being adjustable in position relative to a surface of the body of water being irradiated.

10. Apparatus according to Claim 9, characterised by the source being pivotally adjustable on a hinged mounting whereby to adjust the angle of incidence of emitted radiation on the surface of the body of water being irradiated.

11. Apparatus according to Claim 9 or Claim 10, characterised by the source being adjustable in height with respect to the surface of a body of water to be irradiated.

12. Apparatus according to any of Claims 9 to 11, characterised by a support for the source, and by the source being adjustable in those planes relative to the support.

13. Apparatus according to Claim 12, characterised by being in addition pivotally adjustable with respect to the support.

14. Apparatus according to any of Claims 2 to 13, characterised by a plurality of discrete sources.

15. Apparatus according to Claim 14, characterised by the or each source being adapted to emit radiation periodically .

16. Apparatus according to Claim 15, characterised by the or each source comprising a housing for the source, and by the housing having an opening for the emission of radiation.

17. Apparatus according to Claim 16, characterised by the opening being positioned such that radiation is emitted downwards, away from users.

18. Apparatus according to Claim 16 or 17, characterised by the housing comprising an inner surface of reflective material.

19. Apparatus according to any of Claims 16 to 18, characterised by the shape of the housing being adapted to reflect radiation towards the opening.

20. A system inhibiting growth of algae in a tank or weir, in a water treatment plant the system being characterised.by apparatus according to any preceding claim and means for mounting the apparatus over a tank or weir.

21. A method of inhibiting growth of algae in a water treatment plant characterised by irradiating a body of water with radiation of a frequency sufficient to inhibit growth of the algae.

22. A method according to Claim 21, characterised by the radiation source being a UV source.

23. A method according to Claim 22, the wavelength of the UV being about 254nm.