Media filter

Abstract

A water filter comprising a cylindrical pressure vessel for receiving multiple layers of particulate filter media. The filter also comprising an inlet through which water to be filtered is introduced to said vessel. The inlet comprising a conduit entering via a cylindrical side wall of the vessel and extending through the filter media until it reaches the central axis of the vessel. 90At the central axis the conduit bends and extends upwardly as a central portion thereof and at a location above the filter media the central portion branches out into at least two spaced- apart arms, each arm being providing with a jet outlet at its free end for introducing water to a body of water above the filter media in use. Each of the jet outlets having a substantially different radial spacing to the inner surface of said cylindrical side wall.

Description

[0001] MEDIA FILTER

[0002] TECHNICAL FIELD

[0003] This invention relates to a media filter for water filtration. In particular, the present invention is described with reference to a media filter having an improved inlet arrangement with a plurality of radially extending arms from a central pipe portion.

[0004] BACKGROUND

[0005] Media filters are used for a wide variety of water filtration including treatment for industrial, commercial, potable drinking and wastewater applications. They can be divided into gravity filters and pressure filters. A typical pressure-type media filter has a cylindrical pressure vessel fabricated in metal, and containing various layers of particulate filter material media which are graded according to size, with a fine layer at the top and the coarsest layer at the bottom. During normal use the water to be filtered flows downwardly through the pressure vessel from an inlet at the top to an outlet at the bottom. In a process known as “backwashing”, water flow can be reversed periodically to fluidise the filter media and thereby clean and regenerate it. Air scouring is commonly used following “backwashing”.

[0006] International Patent publication WO2017 / 055794 (Cuppies) describes and depicts in its Fig. 1 a known pressure-type media filter, having multiple graded layers of material, identified from the bottom up as pea gravel, coarse sand(grit), finer grit, and fine sand. It also describes how a range of filter media can be used including heat treated modified recycled glass, and high- performance filter media that enhances static electrical charge to improve filter efficiency. One such high performance filter media that can replace fine sand is the AFM® “activated filter media” disclosed in GB2521667 (Dryden Aqua Ltd). The known pressure-type media filter depicted in Fig. 1 WO2017 / 055794 has a single inlet pipe that enters the pressure vessel through its cylindrical side wall but is typically elbowed upwardly to provide an inlet opening above the topmost layer of filter media. As indicated in WO2017 / 055794, such prior art pressure-type media filters can at best filter down to a level of 15-20 micron. When operating at this filtration level the filter media tend to retain bacteria, fungal spores, and other microbes towards the end of the operating cycle, shortly before backwashing takes place. Due to a low flow rate environment, these microbes can proliferate and colonise the filter media and water. WO2017 / 055794 also describes various other prior art filters with different inlet arrangements and the various attempts to improve them.

[0007] One such improved form of filter disclosed therein is GB2461119 (Cuppies) dating back to 2009, where the main inlet is aligned along a tangent to the wall (see Fig. 4 prior art of WO2017 / 055794), which causes the body of water above the filter media to move in a circular path (a vortex) about the vertical as indicated by arrows. The moving water serves to continuously disturb and disperse the fine media forming the top layer of the filter, preventing bacterial colonisation, and so enabling the filter to be used for fine filtration at much higher flow rates than can be achieved with the earlier prior art. It also helps to ensure that flow through the filter bed is distributed across its area, thereby reducing contamination. The circular movement of the water tends to remove filter media from the periphery of the pressure vessel and deposit it closer to the centre of the vessel, where water velocity is lower, to create a domed profile on the filter media. This is undesirable, potentially enabling breakthrough of water to lower media layers which might reduce filter performance. To avoid this effect, the media filter of GB2461119 employs a "vortex bed stabiliser" (identified as 38 in Fig. 4 of WO2017 / 055794). This vortex stabilizer is a distribution head arranged on the axis of the pressure vessel above the filter media, which is supplied with water to be filtered and which has discharge holes oriented to project water horizontally in a direction which promotes the rotary motion of the water. Looking at Fig. 4 of WO2017 / 055794, it can be appreciated that the discharge holes lie in a circle and each project water along a respective direction which is a tangent to that circle. In this way conical build-up of the filter media is reduced.

[0008] To improve on this known prior art, the abovementioned WO2017 / 055794 described an improved pressure-type filter shown in Figs. 6 and 7 where the first inlet is arranged above the level of filter media and oriented in such a manner to cause the body of water above the filter media to rotate. This rotational motion serves to reduce biofouling. It also has a secondary inlet in the centre of the pressure vessel at or below the top surface of the filter media, to resist the unwanted build up and “coning” thereof. This prior art also describes how the water velocity as it enters the pressure vessel, and the resultant rotational velocity of the vortex in the pressure vessel, have a significant effect on overall filter performance. To enable this aspect of the filter's performance to be adjusted and optimised, it proposes the use of an interchangeable velocity adjuster that can be used for a range of low flow to high flow applications. This prior art was described with a pressure-type filter having a diameter of about 1200mm, and its design is not suited for larger sizes in the 1600-3000mm diameter range. Furthermore, typical diffusers tend to allow water through the centre first during backwash, and this causes an uplift in the central core of the media bed while the waste at the surface is driven downward around the perimeter into the media bed.

[0009] Another problem with WO2017 / 055794 (Cuppies) is that the efficacy and efficiency of filter media is significantly affected by the throughput of flow, which is also impacted on by the radial velocity required to maintain a vortex. This prior art 1200mm diameter media filter allows you to rotate filter media at a radial velocity of up to about 10,000 rpm. However, this prior art still suffers from poor performance at higher rotational speeds, particularly with the efficacy and efficiency of filter media, and is not ideal for use in larger filters, particularly where biofouling may still occur in “dead zones”, such as those that may occur above the inlet.

[0010] The present invention provides a water filter that overcomes at least one of the problems associated with the prior art.

[0011] SUMMARY OF INVENTION

[0012] In a first aspect the present invention consists of a water filter comprising: a cylindrical pressure vessel for receiving multiple layers of particulate filter media; an inlet through which water to be filtered is introduced to said vessel, said inlet comprising a conduit entering via a cylindrical side wall of said vessel and extending through said filter media until it reaches the central axis of said vessel, characterised in that at the central axis said conduit bends and extends upwardly as a central portion thereof and at a location above said filter media said central portion branches out into at least two spaced-apart arms, each arm being providing with a jet outlet at its free end for introducing water to a body of water above the filter media in use, each of said jet outlets having a substantially different radial spacing to the inner surface of said cylindrical side wall.

[0013] Preferably said jet outlet of said spaced apart arm closest to said cylindrical side wall being spaced therefrom in the distance range of 5-20% of the diameter of said pressure vessel, and the other said jet outlet on the other said spaced apart arm being spaced from the said cylindrical side wall being spaced therefrom about 15-40% of the diameter of said pressure vessel. Preferably water flow emanating from said jet outlets causes water contained in said vessel to rotate at high speed in a roughly circular path substantially about said central axis, thus causing a portion of the upper layer of said fluid media to be rotated and maintained in a vortex.

[0014] Preferably the uppermost layer of the fdter media is Grade 0 activated fdter media, and particles of this uppermost layer are rotated in said vortex at about 20,000 rpm.

[0015] Preferably a vortex stabilizer is disposed on said central portion of said conduit, said vortex stabilizer having a plurality of spaced apart tangential slots, and in use when a portion of the upper layer of said fluid media is rotated and maintained in a vortex, said vortex stabilizer is at or near flush with the flatbed of fdter media below the vortex, and water from said conduit exits said slots of said vortex stabilizer and maintains a substantially flat surface of said fdter media below.

[0016] Preferably each said jet outlet is oriented at least a few degrees upward from a horizontal axis passing through said respective arm. Preferably said at least a few degrees is two or three degrees.

[0017] Preferably a baseplate is disposed in said vessel below said fdter media, said base plate comprising a plurality of diffusers that allow water to pass therethrough in both directions, downwards during fdtration and upwards when being backwashed.

[0018] Preferably in one embodiment said at least two arms are two arms that are oriented in substantially opposed directions. Preferably the diameter of said vessel is in the range of 1200mm to 2000mm.

[0019] Preferably in another embodiment said at least two arms are three arms that are substantially equidistantly spaced apart from each other. Preferably the diameter of said vessel is in the range of 2000mm to 3000mm.

[0020] Preferably in a further embodiment said at least two arms are four arms, and each arm is spaced apart to an adjacent said arm at substantially ninety degrees. Preferably the diameter of said vessel is about 3000m.

[0021] In a second aspect the present invention consists of a water filter comprising: a cylindrical vessel for receiving multiple layers of particulate filter media, said cylindrical vessel having a diameter in the range of 1200mm to 3000mm; an inlet through which water to be filtered is introduced to said vessel, said inlet comprising a conduit entering via a cylindrical side wall of said vessel and extending through said filter media until it reaches the central axis of said vessel, characterised in that at the central axis said conduit bends and extends upwardly as a central portion thereof and at a location above said filter media said central portion branches out into a plurality of spaced-apart arms, each arm being providing with a jet outlet at its free end for introducing water to a body of water above the filter media in use, each of said jet outlets having a substantially different radial spacing to the inner surface of said cylindrical side wall, wherein water flow emanating from said jet outlets causes water contained in said pressure vessel to rotate at high speed in a roughly circular path substantially about said central axis, thus causing a portion of the upper layer of said fluid media to be rotated and maintained in a vortex.

[0022] Preferably the uppermost layer of the filter media is Grade 0 activated filter media, and particles of this uppermost layer are rotated in said vortex at about 20,000 rpm.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] Fig. 1 is a vertical plane sectional schematic view of a media filter for water filtration according to a first embodiment of the present invention.

[0025] Fig. 2 is a horizontal plane sectional schematic view through I-I of Fig 1.

[0026] Fig 3 is a schematic of the tangential flow emanating from the vortex stabiliser of the media filter depicted in Fig. 1

[0027] Fig. 4 is schematic plan view of the diffuser baseplate of the water filter depicted in Fig. 1

[0028] Fig. 5 is a sectional schematic of the diffuser baseplate arrangement of Fig 4.

[0029] BEST MODE OF CARRYING OUT THE INVENTION

[0030] The present invention is described with an embodiment of a media filter for water filtration. However, such a media filter is suitable for use with liquids other than water. As such throughout the specification any reference to “water” should be understood to include within its meaning “a liquid other than water”. Figs. 1 to 5 describe a first embodiment of a media filter 100 of the pressure-type suitable for filtration of water or other liquids. Whilst water will be referred to throughout this description, the filter may be used with another liquid.

[0031] It has a pressure vessel 102 which is substantially cylindrical but has domed upper and lower end walls 104,106, with an access cover 108 in the upper domed end wall 104. In this embodiment the diameter of pressure vessel 102 is about 2000mm. Pressure vessel 102 contains filter media 118, that may contain various layers with a fine layer at the top and the coarsest layer at the bottom. The finest layer in this preferred embodiment is a Grade 0 activated filter media such as marketed under AFM®. Water to be filtered enters pressure vessel 102 via inlet 114. The upper media level is shown by line 20.

[0032] Inlet 114 comprises a pipe (conduit) entering via cylindrical side wall 129 of pressure vessel 102 and extends through filter media 118 until it reaches the central longitudinal axis L of pressure vessel 102, at which point it bends and extends upwardly, as central pipe portion 114a. At a location above said filter media 118 (when filter not in use) central pipe portion 114a of inlet 114 branches out into two spaced-apart arms 112, 113, each of which is substantial extending horizontally towards cylindrical side wall 129 in opposite directions. As such at the point 25 on axis L, where arms 112, 113 branch out they are at 180 degrees to each other. Each arm 112,113 is provided with a jet outlet 116,117 at its free end for introducing water to a body of water above the filter media. As can be seen in Fig. 2, arms 112,113 are curved as they extend away from the central axis L, and their jet outlets 116, 117 are not equidistant from the central axis L. This ensures that inlet jets 116,117 are disposed (spaced away) at different radial distances to the inner surface of cylinder wall 129, and oriented in substantially opposed directions, and inlet jets are of different size and shape to each other.

[0033] The nozzles of inlet jets 116,117 are directed in such way to minimise water being directed to the cylinder wall 129.

[0034] In this embodiment where the diameter of the filter 100 is about 2000mm, jet outlet 116 on arm 112 is disposed substantially closer to the inner surface of cylindrical side wall 29, than the jet outlet 117 on arm 113 on the opposed side. In this embodiment the radial distance (spacing) Di of centre of jet outlet 116 to inner surface of cylinder wall 129 is about 100mm, whilst on the opposite side the radial distance (spacing) D2 of centre of jet outlet 117 to inner surface of cylinder wall 129 is about 300mm. These radial distances (spacing) Di and D2 may vary, however they must be substantially different to each other. In this embodiment Di at 100mm is 5% of the diameter of filter 100 and D2 at 300mm is 15% of the diameter of filter 100. What should be understood is that these radial distances (spacings) Di and D2 could vary over a range, say with Di being about 5-20% of the diameter of filter 100, and D2 being about 15-40% of the diameter of filter 100, and filter 100 will still operate fairly efficiently, so long as there is a substantial difference in spacings Di and D2.

[0035] In operation, the water flow emanating from jet outlets 116,117 causes water in pressure vessel 102 to rotate in a roughly circular path substantially about central axis L, which when viewed in Fig. 2, would be in anti-clockwise direction. This flow at high-speed flow causes the “upper layer” of filter media 118, namely the AFM® fine layer media to be rotated and maintained in a vortex. The internally disposed twin distribution arms 112,113 and their respective jet outlets 116,117 ensure even fluidisation of the Grade 0 AFM® media while maintaining a flat bed in the media 118 to provide an even bed. Most suspended solids removed are kept against the inner cylinder wall 129 above the media bed (media 118) as the surface Grade 0 is fluidised and rotates at a constant velocity irrespective of the volumetric inflow rate. This rotation at a constant velocity irrespective of the volumetric inflow rate, is something that does not occur in any of the earlier mentioned admitted prior art filters.

[0036] In this embodiment the Grade 0 AFM® media is rotated at a preferred constant high standard radial velocity of 20,000 rpm. This constant velocity is achieved by the varied positioning (spacing) relative to the inner surface of cylindrical wall 129, and different sized nozzles of jet outlets 116, 117 and orientation of inlet jets 116, 117 to each other. This significantly improves the generation of static charges (negative zeta potential) on the surface of the AFM® media particles which results in greater efficacy and efficiency. As a result of this increased filtration efficiency most of the solid waste and biological waste and oxidized organic and inorganic dissolved solids such as iron, are trapped in the upper portion of pressure vessel 102 and not in or on the surface (upper level) of the bed of media 118, thus inhibiting water throughflow and reducing volumetric efficiency. As a result, this also significantly reduces the amount of backwash water volume required as only the contaminated water in the top section of the vessel above the media flatbed is to be removed as compared with the prior art.

[0037] For any one nozzle size, the “radial velocity” of the vortex will vary depending on the throughput of water through media filter 100. As the preferred constant high standard radial velocity is about 20,000 m / h, the size of nozzles of jet outlets 116,117 can be selected for a certain range of flow throughput to keep the constant high standard radial velocity at about 20,000 rpm. This will be discussed later as the size of nozzles will vary for different sized filters.

[0038] The central pipe portion 114a comprises a vortex stabiliser 130 through which water exits and maintains a substantially flatbed surface of media 118 and assures a stable vortex is formed. Vortex stabiliser 130 has four or more tangential slots of about 1 to 5mm depth that allow for water to exit tangentially, as depicted by arrows in Fig 3. The sizing of the slots is calculated or varied to suit the density of the inflowing water to ensure sufficient distribution to maintain vortex stability When media filter 100 is not in use, where media 118 is settled and substantially stationary, vortex stabilizer 30 is about 10-30mm below the upper surface (media level) of the bed of filter media 118. However, when the filter 100 is in use a portion of the uppermost Grade 0 AFM® media is suspended and moving around in the vortex, thus causing vortex stabilizer 130 to be at or near flush with the bed of filter media 118 below the vortex.

[0039] In this embodiment at a diameter of 2000mm, media filter 100 with two radial inlet jets 116,117 of different lengths branched out at substantially 180 degrees one from the other gives demonstrable and measurable improvement in filter performance with consistent level of static charge, an even fluidisation of the bed, a maintained vortex stability, and no scouring of media in the bed at a flux rate of 25 to 60 m3 / hr / m2, all at the earlier mentioned high constant standard radial velocity of 20,000 rpm.

[0040] As can be seen from Fig 2, inlet jets are shown as having a bent-elbow form. In addition to this, orientation of inlet jets 116, 117 a few degrees above the horizontal, say five or less degrees, and preferably two to three degrees above the horizontal, helps stabilise the vortex and minimises the dead-zone above the inlet jets 116,117, and therefore minimises the risk of biofouling in this upper region of vessel 102. It should be noted that in Fig 1 for ease of reference, the bent elbow form nozzle 116 appears to be in line with the horizontal, but in actuality it is angled at two degrees above the horizontal to slightly point upwards. An elevation above five degrees results in scouring of the flat media bed and thus is detrimental to the filtration efficiency.

[0041] The high constant radial velocity helps determine the fluidisation of the top media of the bed of fluid media 118 and minimises the risk of biofouling within media filter 100. In primary mode the abovementioned media filter 100 operates as a suspended solids removal filter, and induces disinfection and oxidation to remove bacteria, pathogens and other dissolved contaminants and biological materials, which can:

[0042] • Remove twice the mass removed by a similar sized prior art sand filter.

[0043] • Remove total dissolve solids (TDS) of 4-24%.

[0044] • Remove particles of less than 0.45 micron with greater than 92% efficiency without flocculants or coagulants.

[0045] • Remove pathogens and bacteria to a level where recolonisation is substantially prevented.

[0046] • Produce output water clarity levels at 1-2 NTU.

[0047] • Produce output water quality in with an SDI < 5 suitable in most instances for inflow to reverse osmosis filters.

[0048] • Filter at three to five times the rate of an equivalent sized sand filter while using the less energy than a sand filter with the same volumetric treatment.

[0049] It can reduce backwash water losses by greater than 75% compared with a similar sized prior art sand filter.

[0050] This abovementioned embodiment allows recovery of water and concentrated resources if required.

[0051] The diffuser baseplate (filter plate) 140 is set some 50mm above the vertical element of the cylindrical part of the pressure vessel 102. The base plate 140 comprises a plurality of diffusers 150 to allow an even flow of water in both directions, downwards when filtering, and upwards when backwashing. The design of diffusers 150 allows even vertical flow both up and down to ensure media is not displaced by internal circulation. This allows faster backwash across the media 118 bed with less than 22.5% bed expansion at a flux rate between 20- 25m3 / hr / m2to prevent tunnelling through the other bigger heavier media below the top layer of Grade 0 AFM® media being lost during backwashing. Tundish 141 disposed at a location higher than arms 116, 117, allows for water to exit media filter 100 via outlet conduit 142 during backwash with minimal removal of filter media 118.

[0052] It should be noted that in prior art sand filters you cannot use Grade 0 AFM® media due to the backwash flux rates of 30 to 60m3 / hr / m2, as it would flush the media out. Grade 1 is the finest other media filters can use and it filters down to three microns at best. This is why media filter 100 allows for the use of Grade 0 AFM® and achieves filtration down to less than 0.45 micron. Because media filter 100 holds most of the removed materials in the top of pressure vessel 102, it is possible to flush out 85-90% of the removed waste during the first two to four minutes of backwash. Sand filters and sand filters using AFM® media instead of sand must flush out the whole of the vessel and this takes five to fifteen minutes with considerable water losses (four minutes at flux 22m3 / hr / m2 for media filter 100 is significantly less than ten minutes at flux of 45m3 / hr / m2 of the sand filter prior art).

[0053] The arrangement of media filter 100 requires less energy to backwash due to reduced frequency of backwash and reduced flux rate required to backwash. Sand filter flux rate for backwash 30 to 60 m3 / hr / m2 versus the backwash rate of 20 to 25 m3 / hr / m2 for media filter 100. This is significant as backwash water losses mean good energy and water are lost to the ability to claim high water recycling capability of media filter 100. Furthermore, media filter 100 also has a “green footprint” which is significantly smaller than a bank of sand filters. Smaller volumes of concentrated backwash are easier to dispose of and have less transport costs associated with disposal. In a growing number of instances, the separation or partitioning of inflow water into water output and concentrated removals backwash material, generates a recoverable resource from the backwash. For example, oil partitioned from water can be used a resource. In other words, media filter 100 acts as partitioning machine.

[0054] Media filter 100 can generate its own backwash supply of water from the filtrate out water because the water is of a suitable quality and disinfected and free of bacteria and organics materials. This means little external water is required to supply “backwash” water.

[0055] The abovementioned embodiment employing two branched arms 112,113 can be used in filters say of the range of 1600 mm to 2000 mm diameter. However, it is preferable to use a greater number of branched arms and associated inlet jets for larger diameter filters. For example, in a not shown further embodiment of a filter in the diameter range of 2000mm to 3000mm, three branched arms and their three respective inlet jets are branched out (spacedapart) equidistantly, namely substantially at one-hundred-and-twenty degrees (120°) to each other. In an even further not-shown embodiment of a 3000 mm diameter filter, four branched arms and their four respective inlet jets are branched out (spaced-apart) at substantially ninety degrees (90°) to each other. Like that of the above mentioned first embodiment, these not shown embodiments have their three or four branched arms and their inlet jets disposed (spaced away) at different radial distances to the inner surface of the cylinder wall, and oriented in substantially opposed directions, and the inlet jets are of different size and shape to each other. Furthermore, like that of the first embodiment, these inlet jets are preferably oriented upward a few degrees above the horizontal.

[0056] The design of media filter 100 combines the benefits of centrifugal fluidisation of light media and a static, flat bed of media. The centrifugal action fluidises the light (Grade 0 AFM®) media and enhances the static charge and surface area of media interacting with inflowing fluid. This results in a surface interaction of three hundred times or more than is available in a sand-based media. The consequence of the fluidisation and circulation at high speed allows for creation of hydroxyl radicals which oxidise and disinfect inflowing liquids.

[0057] The above-mentioned embodiment of the present invention has certain advantages which are as follows:

[0058] • Allowing removal of suspended solids down to below 0.45 micron and creating chemical transformations which allow for the removal of certain dissolved solids including some salts.

[0059] • Efficient removal or substantial reduction of:

[0060] -hydrophobic contaminants such as hydrocarbons (oil & fats) organics.

[0061] -microplastics in both hard and soft water.

[0062] -positively charged particles such as heavy metals (e.g. Iron, Manganese and Arsenic) without the use of coagulation and / or flocculation.

[0063] -Cryptosporidium oocysts.

[0064] -E. coli.

[0065] -Legionella;

[0066] • Filtration does not rely on biological load accumulation to enhance filtration effectiveness;

[0067] • Consistent high filtration performance can be achieved; and

[0068] • Air scouring is not required after backwashing.

[0069] Regardless of the size of the diameter of the media filter of the present invention, it has been found that optimal efficiency and efficacy is achieved when the high constant radial velocity of the vortex is maintained at about 20,000 rpm for various inflow rates. Optimal electrostatic charge is reached after three hours of continual operation. The following Table 1 shows how nozzles sizes will vary to keep that high constant radial velocity maintained at about 20,000 rpm for a range of filter diameter sizes over a range of inflow rates where water is being treated. Table 1 Filter Diameter and nozzle Sizing to maintain 20,000 rpm radial velocity

[0070] The optimal sizing of nozzles to maintain the vortex at constant radial velocity of about 20,000 rpm will also need to be varied should the density of the fluid vary from that of water, such as when water has considerable solids or oil therein. Because the abovementioned embodiments of the present invention, can be used more efficiently in larger diameter sizes than the prior art, it makes them suitable for use in the separation and recovery of light oils from water, as well as a potential primary process in the concentration collection of salt from sea water or as a first step in the desalination of water before reverse osmosis. Where the water being filtered requires enhanced removal of larger heavy metals, infusing an oxidant into the water entering the filter, for example oxygen, hydrogen peroxide or ozone, with “micro” or “nano” bubbles will increase the efficiency of removal of heavy metals in the infeed water as insoluble oxides. Such addition of oxidants in “micro” or “nano” bubble form can reduce the reliance on chemical additives for water treatment and remove tannins from the water. Similarly, a reductant may be infused into the inflow to address specific requirements.

[0071] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

CLAIMS1. A water filter comprising : a cylindrical pressure vessel for receiving multiple layers of particulate filter media; an inlet through which water to be filtered is introduced to said vessel, said inlet comprising a conduit entering via a cylindrical side wall of said vessel and extending through said filter media until it reaches the central axis of said vessel, characterised in that at the central axis said conduit bends and extends upwardly as a central portion thereof and at a location above said filter media said central portion branches out into at least two spaced-apart arms, each arm being providing with a jet outlet at its free end for introducing water to a body of water above the filter media in use, each of said jet outlets having a substantially different radial spacing to the inner surface of said cylindrical side wall.

2. A water filter as claimed in claim 1, wherein said jet outlet of said spaced apart arm closest to said cylindrical side wall being spaced therefrom in the distance range of 5- 20% of the diameter of said pressure vessel, and the other said jet outlet on the other said spaced apart arm being spaced from the said cylindrical side wall being spaced therefrom about 15-40% of the diameter of said pressure vessel.

3. A water filter as claimed in claim 1, wherein water flow emanating from said jet outlets causes water contained in said vessel to rotate at high speed in a roughly circular path substantially about said central axis, thus causing a portion of the upper layer of said fluid media to be rotated and maintained in a vortex.

4. A water filter as claimed in claim 3, wherein the uppermost layer of the filter media is Grade 0 activated filter media, and particles of this uppermost layer are rotated in said vortex at about 20,000 rpm.

5. A water filter as claimed in claim 3, wherein a vortex stabilizer is disposed on said central portion of said conduit, said vortex stabilizer having a plurality of spaced apart tangential slots, and in use when a portion of the upper layer of said fluid media is rotated and maintained in a vortex, said vortex stabilizer is at or near flush with the flatbed of filter media below the vortex, and water from said conduit exits said slots of said vortex stabilizer and maintains a substantially flat surface of said filter media below.

6. A water filter as claimed in claim 1, wherein each said jet outlet is oriented at least a few degrees upward from a horizontal axis passing through said respective arm.

7. A water filter as claimed in claim 6, wherein said at least a few degrees is two or three degrees.

8. A water filter as claimed in claim 1 wherein a baseplate is disposed in said vessel below said filter media, said base plate comprising a plurality of diffusers that allow water to pass therethrough in both directions, downwards during filtration and upwards when being backwashed.

9. A water filter as claimed in claim 1 wherein said at least two arms are two arms that are oriented in substantially opposed directions.

10. A water filter as claimed in claim 9 wherein the diameter of the pressure vessel is in the range of 1200mm to 2000mm.

11. A water filter as claimed in claim 1 wherein said at least two arms are three arms that are substantially equidistantly spaced apart from each other.

12. A water filter as claimed in claim 11 wherein the diameter of said vessel is in the range of 2000mm to 3000mm.

13. A water filter as claimed in claim 1 wherein said at least two arms are four arms, and each arm is spaced apart to an adjacent arm at substantially ninety degrees.

14. A water filter as claimed in claim 13, wherein the diameter of said vessel is about 3000m.

15. A water filter comprising : a cylindrical vessel for receiving multiple layers of particulate filter media, said cylindrical vessel having a diameter in the range of 1200mm to 3000mm; an inlet through which water to be filtered is introduced to said vessel, said inlet comprising a conduit entering via a cylindrical side wall of said vessel and extending through said filter media until it reaches the central axis of said vessel, characterised in that at the central axis said conduit bends and extends upwardly as a central portion thereof and at a location above said filter media said central portion branches out into a plurality of spaced-apart arms, each arm being providing with a jet outlet at its free end for introducing water to a body of water above the filter media in use, each of said jetoutlets having a substantially different radial spacing to the inner surface of said cylindrical side wall, wherein water flow emanating from said jet outlets causes water contained in said pressure vessel to rotate at high speed in a roughly circular path substantially about said central axis, thus causing a portion of the upper layer of said fluid media to be rotated and maintained in a vortex.

16. A water fdter as claimed in claim 15, wherein the uppermost layer of the fdter media is Grade 0 activated filter media, and particles of this uppermost layer are rotated in said vortex at about 20,000 rpm.

Images