AU2008213885B2

AU2008213885B2 - Water treatment

Info

Publication number: AU2008213885B2
Application number: AU2008213885A
Authority: AU
Inventors: William Bliss
Original assignee: WOBELEA Pty Ltd
Current assignee: WOBELEA Pty Ltd
Priority date: 2007-02-05
Filing date: 2008-02-05
Publication date: 2012-05-24
Anticipated expiration: 2028-02-05
Also published as: WO2008095230A1; NZ578890A; AU2008213885A1

Abstract

A system for treating turbid water in which the turbid water to be treated is caused to pass through a filter bed into a storage area, the water flow being such as to ensure a sufficient residence, time in the bed. The filter material is selected from the group comprising palagonite, pearlite, silica sand, vermiculite, carbon, lignite, zeolite, rockwool and synthetic filtering agents and is preferably palagonite. Preferably there are provided two containers, one within the other, the outer container being a tank or the like, the inner container having the filter material therein, meansto provide turbid water to the inner container and meansto permit water which has passed through the filter material to pass to the outer container for use. An apparatus for carrying out the system is also described.

Description

WO 2008/095230 PCT/AU2008/000122 -1 WATER TREATMENT Technical Area This invention relates to a system and apparatus for water treatment and it is specifically adapted for use with turbid water. It is also useful for other waters as will be described herein. Background to the Invention Much water from dams and rivers suffer from a degree of turbidity which can affect the quality of the water and can make it difficult to sterilise the water by ultraviolet sterilisation. For example, under the recognised turbidity unit, the FTU,-(Formazin Turbidity Unit), Melbourne tap water has a turbidity between 0 - 1, normal dam water may have a turbidity of the order of 80-120, and Murray River and other river waters may have an FTU of the order of 110. This turbidity is the result of number of factors and overall is comprised of a mixture of silt, organic material, germs and viruses suspended in the water.

WO 2008/095230 PCT/AU2008/000122 -2 It is generally unsatisfactory for use as potable water as there is often an off taste and the germs and viruses can be dangerous when imbibed by persons or animals. Where such water is to be drunk or used for other purposes, it is usual that it be sterilized either by chemical dosing or by UV treatment. Chemical dosing, whilst efficient can leave a taste and the water is still turbid and UV sterilization does not work effectively in turbid water. It has been known to use sand-bed filters to remove turbidity and any micro organisms from the water and provided the residence time in the filter is sufficient the resultant water will be clear and have only a very small micro organism count although, generally, viruses will pass through such filters. Sand filters have not been generally satisfactory in relatively small applications, but there have been filters using materials with better surface area per volume than sand which have been not unsatisfactory in smaller applications. Outline of the Invention The invention has a number of objects. Firstly, it is to provide a means of treating water which removes a substantial part of the turbidity there-from and provides water which is potable. The invention is specifically suitable for relatively small applications, those using up to a few thousand litres per day, but -3 can be applied to larger applications. A second object in one aspect of the invention is to provide such a filter using as a filtering material a product which is not being used in this area. 5 A third object is to provide a system in which the filtration can readily be effected and a fourth object is to provide such a system which can readily be used in conventional tanks or the like. to A system for treating turbid water in which the turbid water to be treated is caused to pass through a filter bed into a storage area, the water flow being such as to ensure a sufficient residence time in the bed. The filter material can be selected from the group comprising palagonite, is pearlite, silica sand, vermiculite, carbon, lignite, zeolite, rockwool and synthetic filtering agents.

-4 In one embodiment of the invention the water passing from the inner container to the outer container is first caused to pass to the exterior of the outer container whereby it is available for additional treatment. 5 A system of this type may have provision for chemical dosing, Ultra Violet irradiation or other form of sterilization or a mixture of these where the water has passed from the inner container, In one form of the invention, the inner container may comprise a water 10 impermeable flexible bag which can be passed to the interior of an existing tank or the like via the access manhole. Alternatively a water impermeable flexible bag may be used which can be supported by a cage which may be of metal, plastic or fibreglass mesh. 15 In a preferred form of the invention the filtration material is palagonite. Description of an Embodiment of the Invention In order that the invention may be more readily understood, there shall be 20 described particular arrangements of the invention in relation to the accompanying drawings and there shall then be discussed various modifications and applications of this.

In the drawing: Fig I shows a form of invention which can be Used in a domestic water storage tank or the like: 5 This embodiment illustration in Fig 1 is suitable for a domestic filstration system, or a small industrial system, which can filter rain water or, say, dam or river water, to provide sufficient potable water for a household. 10 in the specific embodiment we provide a 5,000 litre tank 10 and within the tank we provide an internal container or secondary tank 20, which may take one of several forms, as will be described hereinafter which has a capacity of the order of a 1,000 litres, 15 Within this secondary tank 20 there is placed a filtration material 21, which will be described further hereinafter, and the outlet 22 from the secondary tank may pass directly into the main tank through a valve which controls the flow rate. As illustrated it is preferred the outlet is brought out through the side wall 11 of the main tank where there can be located water treatment arrangements 12 if 20 required. These could include a chemical dosing system and/or an Ultra-Violet treatment system.

WO 2008/095230 PCT/AU2008/000122 -6 As will be discussed hereinafter the water quality which is obtained is extremely good and further treatment may not be required. This outlet may also- be useful for providing a point for back-wash, as will be discussed later. The output from the treating system 12 is then fed back at 13 into the main tank and thus clean filtered water can occupy up to 4,000 itres of the tank, after filtration has been completed, and this is readily available for use. The arrangement of the inner tank 20 and the filter material 21 is such as to control the quantity of water which can pass there-through and it has been found that if approximately 1000 litres an hour passes through this particular arrangement then the water quality will be as required. In general terms, the ration of filter volume to storage volume is of the order of 1:5 (the ratio mentioned for this embodiment). It will be appreciated that the total volume of water in the system at any time is effectively the volume of the system less the volume of the filter material which in this case may be only 250 litres. Thismeans that some 24,000 litres of water a day can be treated and this would normally be more than sufficient for a house-hold or even to some small commercial operations.

WO 2008/095230 PCT/AU2008/000122 -7 The filter material 21 that is preferred is crushed palagonite. Palagonite is a naturally occurring material and for these purposes has certain advantages over other types of material, such as other natural materials such as pearlite, vermiculite, carbon, lignite, zeolite, rockwool or sand. It has been found, somewhat surprisingly, that when palagonite is crushed to a desirable grain size (of the order of 0.8 to 2.0 mm, but see material herebelow), there are still a large number of vesicules in the individual grains which still provides a low weight per volume whereas at a comparable grain size, the other materials largely lose this quality. Thus, the lower bulk density results in a lighter media in a given volume. This attribute allows greater flow during the backwash cycle. Preferred grain sizes of the palagonite are between 0.5 and 2.5 mm with a specifically preferred size of between 0.8 and 2.0 mm. Notwithstanding this, from a practical point-of-view it would still be possible to apply the invention using other materials. In this application, the placing the secondary tank 20 within the main tank 10 has several practical advantages. The first is that the overall unit is compact which is generally desirable if being used in a domestic situation; the filter unit is -8 secure an relatively safe from physical damage and thirdly the filter temperate is maintained stable. In one preferred form of apparatus the secondary tank 20 may be in the form of 5 a water impermeable bag which is of a composite material such as one which has a terylene centre core with PVC outer-faces. As previously stated, a supporting mesh may be provided although if the system is arranged to keep the outer tank effectively full, then the water in this tank will support the bag. 10 The bag must be of a material which is impermeable to water and thus not allow turbid water to pass there through. The other main requirements for the bag are that it will have a substantial life when immersed in water and that it is substantially strong to hold the required volume of filter material. It would be unusual that this property would be relied upon as, normally, if the outer tank has 15 water therein the bag will, in fact, be largely supported by the water in the tank, The situation anticipated above would only occur if the outer tank was empty. The position of the outlet from the outer tank could be arranged so that under normal conditions, water would always be left in the tank to support the filter material. 20 In a specific form the bag may be of a height to extend from the floor of the tank to adjacent the upper end thereof and the bag may be physically attached to the tank by being tied to hooks or the like in the upper surface of the tank.

- 9 This arrangement is such that the bag in its empty and collapsed form can be passed through the normal man-hole 14 in the top of the tank and then held in position by being tied to the underside of the top of the tank. The filtration material can then be located therein and as this is granular it could be pumped 5 into the bag! At or adjacent the bottom of the bag there is the outlet 22 which may be a flexible hose or the like and it is preferred that this hose is connected at its free end to a connector arrangement which passes through the side wall of the outer io tank at 11, as previously described. Alternatively, the hose may itself be passed through the outer wall of the tank with a gland or the like provided at the junction. s In each case, a control valve to adjust filtration speed is in the line. The outlet hose is then connected as described earlier for further treatment of the water, such as a chemical dosing arrangement and/or a UV-sterilisation arrangement, 20 The system of this embodiment, as previously mentioned, may be provided with an connection at 12 which can enable backwashing of the filter material. A filter arrangement of this type can operate for a long period without any service, WO 2008/095230 PCT/AU2008/000122 -10 possibly six to twelve months in a domestic situation. However, once there is a noticeable reduction in effectiveness it would generally not be necessary to replace the filter material although, if sand is used there can be substantial caking and the top portion at least may have to be removed and replaced. Palagonite, and some of the other natural materials are light and it is necessary to effect optimum backwashing to pass sufficient water through the bed to cause it to fluidise and enable the attached material to be displaced therefrom and passed to waste. Backwashing can be effected in different'ways. In the first, a fire fighting pump or the like can be connected to the pipe 11 and the water is passed through the array 24 through the filter material 21. This water would be passed to waste, or for recycling. In the second, gravity backwashing is used. In this case water from the outer tank 10 Is connected by a three way valve 11 to the under drain assembly 24 and the inner tank above the filter material is connected to waste, preferably also through the three way valve so that the water in the outer tank enters the inner tank below the filter material, passes up through this, displacing the material resident on the filter material and passing this to waste. Using an arrangement WO 2008/095230 PCT/AU2008/000122 having the ratio described, there will be enough water available to provide a full backwash. The inlet to the bag may simply be an outlet from roof guttering or the like which would be so arranged that once the tank was full there would be a standard over flow or, if the tank is being fed from some other water source the inlet is simply onto the top of the bag, and this may be by means of a dispersed arrangement so that the inlet water passes over the total surface of the top of the filtration material. In this arrangement there may be a float valve 23 on the inlet or in the main tank so that when that tank reaches its desired level the float-valve causes the pump which is feeding the water into the tank to cease operating and as water is used then the float valve will again close the circuit and permit the pump to recommence, It will be appreciated that if the outer tank is full and water is not being used then incoming water will be resident in the filter material for very much longer than.their minimum period but this will have no adverse affects whatsoever. The outlet from the bag may well comprise a member located at or adjacent the lower surface of the bag which gathers water from over the area of the bag so that there is a continual movement of water, when being withdrawn from the bag, from all parts of the filter material so there are no pockets of water which remain undisturbed for long periods.

- 12 Whilst in the foregoing there has been discussed one particular arrangement where there can be an inner and outer tank and has specifically described the inner tank as being a bag to permit the system to be added to the existing tanks it would be possible to manufacture a composite tank in which both tanks are of s solid material with one located and held within the other or it could be possible to form the inner tank in ways other than that specifically described. In a second embodiment of the invention, illustrated in Fig 2 we provide two separate tanks, one of which 200 includes the filtration material 201 and the io other of which 100 the filtered water with the inlet water being passed to the surface of the tank through an inlet 202 which may disperse the water over the surface of the filter material which includes the filtration material and the outlet 203 of the tank feeding to the purified water tank 100. 15 In such an embodiment it can be preferred that the container holding the filtration material be located physically above the tank which will hold the potable water, In this case, the size of the tank is designed so that water placed on the upper surface thereof will percolate through the filter medium under gravity and its residence time in the tank will be sufficient to remove the required impurities. 20 -13 It was discussed earlier that palagonite is an extremely satisfactory material in this application because its physical formation is such that it can be crushed to a size which is suitable for the application and still retain the properties of large surface area to volume. 5 -14 Whilst generally there has been described in this specification the application of the invention for relatively low flows it is to be understood that this is simply a preferred system for a particular application. 5 If one was to supply a commercial application which may need to use thousands or tens of thousands of litres of water per day then it is possible to simply change the scale of the arrangement described and, where there are large quantities involved, to simply duplicate the system so that a number of units operate at the one time. 10

Claims

1. Apparatus for treating turbid water comprising two containers, one within the other, the outer container being a tank, the inner container being 5 elongated and, apart from having an inlet for turbid water at one end and an outlet conduit passing through the wall of the inner container at the other end, said inner container is impermeable to water and contains a homogeneous filter material therein; means to provide turbid water to said inlet and means to permit 10 water which has passed through the filter material to enter said outlet conduit and pass to said outer container.

2. Apparatus as claimed in claim 1 wherein said inner container is solid. 15

3. Apparatus as claimed in claim I wherein said inner container is a water impermeable flexible bag.

4. Apparatus as claimed in any one of the preceding claims wherein there is a restriction valve in said outlet conduit whereby the rate of flow of water 20 between the inner and outer containers can be controlled.

5. Apparatus as claimed in any one of the preceding claims wherein said outlet conduit passes out of said outer container to allow a further treatment process on the water passing through said outlet conduit prior 25 to being delivered to the inner container.

6. Apparatus as claimed in claim 5 wherein the additional treatment is chemical dosing or Ultra Violet irradiation, or, a combination thereof. 30

7. Apparatus as claimed in any one of the preceding claims wherein the homogeneous filter material is selected from the group consisting of palagonite, pearlite, silica sand, vermiculite, carbon, lignite, zeolite, rockwool and synthetic filtering agents. -16

8. Apparatus as claimed in claim 7 wherein the filter material is palagonite.

9. An apparatus as claimed in claim 8 wherein the grain size of the palagonite lies within the range of 0.5 to 2.5 mm. 5

10. An apparatus as claimed in claim 9 wherein the grain size of the palagonite lies within the range of 0.8 to 2.0 mm.

11. Apparatus as claimed in any one of claims 3 to 9 wherein there is a 10 reinforcing cage about the water impermeable flexible bag.

12. Apparatus as claimed in any one of the preceding claims wherein means are provided to enable backwashing of the filter material. 15

13. A system for treating turbid water whereby said turbid water is passed through apparatus as claimed in any one of the preceding claims.