GB2146255A

GB2146255A - Pond filter

Info

Publication number: GB2146255A
Application number: GB08422559A
Authority: GB
Inventors: Malcolm Graham Goodson
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-09-07
Filing date: 1984-09-06
Publication date: 1985-04-17
Also published as: GB8323919D0; GB8422559D0

Abstract

A filtering and biological treatment water purification system for ponds, aquaria and swimming pools comprises pieces (8) of an expanded open-cell polymeric material which form a biological treatment bed through which the water passes after passing through a mechanical filter (5), also of open-cell polymeric material, for removal of suspended solids. As shown the mechanical filter comprises tubular cartridges (5) which may be closed at the top or open to provide by-pass passages when they clog. Alternatively two flat sheets of polymer may act as the mechanical filter. <IMAGE>

Description

SPECIFICATION Pond filter This invention relates to, for example, pond filters and aquarium filters and to other apparatus for treating relatively clean water. The invention also relates to a method of treating such water.

There is disclosed below a water purification system providing biological purification and filtration of water containing low levels of water contaminants for use in the treatment of water discharged from ponds or tanks containing fish, or water recycled from swimming pools. Such water is hereafter called "relatively clean water" and is to be contrasted with raw sewage and sewage after screening or settling, which latter water contains vastly higher concentrations of dissolved and suspended pollutants, and for the treatment of which techniques are required which form a separate branch of the art.For a more exact definition of the term "relatively clean water" as used in this specification, it is to be understood that the expression is intended to cover potable water and biologically or chemically purified sewage effluent in which the greater proportion of pollution content has been removed, suspended solids being at less than 50 milligrams per litre and/or the biochemical oxygen demand being less than 50 milligrams per litre, and/or the ammonia/nitrogen content being less than 30 milligrams per litre, Conventionally in aquaculture and swimming pool purification practise, purification is effected by passage of the flow being treated through a bed of gravel or sand. Flow through such medium is either by gravity or is pressurised by use of a water pump.The gravel or sand particles strain out the solids in the water and, in addition, where biodegradable organic or inorganic pollutants are present in the water, micro-organisms become established on the surfaces of the filter material and break down these pollutants thereby providing biological treatment also.

The efficiency of removal of solids and biological purification achieved in such filters is determined by the size of the filter medium, process pollutant removal efficiency increasing with decreasing particle size in the medium.

Unfortunately, the smaller the particle size the quicker the filter will become blocked by accomulated solids and growth of bacteria, with the result that filters constructed on gravity flow principles use large volumes of fairly coarse filter medium-average particle size of 5 millimetres or above. Alternatively, filters using a fine medium, for example 1-2 millimetre sand particles, require some form of flow pressurisation to obtain the required water throughput. Such filters offer short filter life between washing, for example 18 to 24 hours, and following blockage require back washing with a flow of water. The back washing process removes bacteria from the filter, and therefore such fine medium filters are unsuitable to provide biological water purification.

Consequently, filters of either of the above types are either expensive to construct, or costly to operate, or both, and the fine medium filters are unsuitable when biological purification is required.

It has been previously proposed that in industrial biological fermentation processes and in the primary treatment of sewage or industrial effluent, and indeed in other processes where biological material is grown from a source of nutrient, that a monofilament of stainless steel wire or of a plastic material may be knitted to form a fabric which is used in a fluidised bed technique for the treatment of heavily polluted waters, or for promoting biological growth from a source of nutrient.

This process includes as an essential ingredient the constant removal of the biological matter from the bed material as a result of attrition, which renders it unsuitable for the processes with which the present invention is concerned. Moreover, this prior proposal relates principally to the treatment of highly contaminated effluents which, as already noted, forms a distinct and separate branch of the art.

It has already been proposed that certain foam-like materials may be used in purification of water for aquaria and the like. However, these prior proposals suffer from the shortcoming that so far as biological purification of the water is concerned, the long term nature of this biological process leads to practical problems. For example, the build up of biological matter in the filter bed (itself a slow process) tends to cause blockage of the bed eventually, thereby preventing proper water flow through the bed and limiting the useful life of the bed.

It will be appreciated that it is no answer to this latter problem simply to wash the bed since this removes the biological matter and requires the user to go through the four to six week period of biological matter build-up before the water purification process can be fully effective once more.

An object of the present invention is to provide a method and apparatus for treating relatively clean water offering one or more improvements in relation to the shortcomings of the prior art as discussed above, or generally.

According to the invention there is provided a method and apparatus for treating relatively clean water as defined in the accompanying claims.

The invention also provides a method and apparatus for water treatment comprising any novel feature or concept or combination of novel features or concepts as disclosed herein.

In an embodiment of the invention described below there is provided a treatment bed comprising open cell expanded polymeric material which, due to its high porosity and voidage and small pore size, provides for good filtration and storage of filtered solids, and in addition provides a large volume within the treatment bed for the growth of micro-organisms to achieve biological breakdown of biodegradable pollutants.

Typically, at least 50% of the voids in the foam material should be open to provide the three dimensional passage of liquid and growth of bacteria, optimum results being obtained at substantially 100% open voids in the material. Void size can be varied to suit the characteristics of the water being treated but normally would lie in the range 0.25 to 2.0 millimetres principal dimension. The porosity of the material may be varied between the limits mentioned, 75% of open cells being preferred to 50% and 95% open cells representing only a minor departure from the optimum.

Whereas in the treatment of waters discharged from ponds or tanks containing fish, the gravel filter serves the dual role of solids filtration and biological purification, using the open cell expanded polymeric material described below, the advantage is provided of splitting these functions and thereby substantially reducing the size of the purification system required.

In terms of biological treatment efficiency the expanded polymer is around twenty times more effective than gravel. Used as a filter it is up to ten times more efficient.

Ideally, when used for biological treatment of water, the expanded polymer should be provided in a form which permits long usage without blockage, whilst providing the maximum surface area for the growth of bacteria and the maximum opportunity for contact between the water being treated and the bacteria responsible for treatment. This is achieved in the embodiment by using a treatment bed of pieces of expanded polymer comprising pieces of nominal dimensions 25 millimetres by 25 millimetres by 12 millimetres, although pieces having sizes up to 30 millimetres by 30 millimetres by 30 millimetres have been used in a similar environment with equal success. In cases where suspended solid material is evident in the flow of water to be treated to the extent that this would cause premature blockage of the treatment bed, a primary filter is desirable to prefilter the water.

This can be achieved by using a gravel prefilter if desired, or preferably by use of a prefilter employing the same expanded polymeric material as the biological treatment bed, this pre-filter being provided as an integral part of the purification system. Such a pre-filter can then take the form of a cartridge pre-filter or sheets of the expanded polymer may be used.

These matters are more fully described below.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a cross-sectional elevation of a water purification system incorporating cartridge-type primary filters and a biological treatment bed; Figure 2 shows a plan view of the assembly of Fig. 1; Figure 3 shows a lateral cross sectional view of the assembly of Figs. 1 and 2, on the line Ill-Ill therein; Figures 4 and 5 show modifications in which the water treatment assembly is mounted within a pond or the like, and in which it comprises sheets of expanded polymeric material in place of the cartridges as a pre-filter; and Figure 6 shows a perspective view of the expanded polymeric material.

As shown in Figs. 1 to 3, a water purification system comprises a container 1 inside a second container 2 and carried on supports 3.

The base of the inner container is drilled to take ten cartridge drainage tubes 4. For each drainage tube, a cylinder of open cell expanded polymeric material 5 is provided. Each such cylinder or cartridge 5 is of nominal dimensions 120 millimetres by 120 millimetres by 420 millimetres and is drilled longitudinally and centrally with a 30 millimetres bore hole and placed over its drainage tube 4 so as to be disposed in a vertical position inside the inner container 1.

The material of the cartridges 5 is an open cell expanded polyether which has been treated to produce a totally open cell structure. It is understood that such a structure is produced by a technique of introducing hydrogen or other combustible gas into the voids in the expanded polymer and thereupon igniting the combustible gas to produce an open cell structure. The material is totally porous and permits liquid flow through it in all directions so that when a localised blockage occurs in it, liquid can flow around the blockage quite readily. In the embodiment, the expanded polymer is fairly resilient, but its completely open cell structure makes its physical characteristics otherwise totally different from those of a sponge since the latter is of largely closed cell structure and tends to retain liquids in which it is immersed. The expanded polymer 5 of this embodiment retains very little liquid when removed from water, for example. The water drains out from the open cell latticetype structure immediately upon removal from the water.

Moreover, the polyether itself is one of the few polymers which is resistant to biological and chemical degradation in the environment under consideration. Most other polymers undergo slow degredation and solution and tend to release toxins into the water.

The water to be treated is fed by gravity or by pumping through spray bar 6 to discharge downwards onto a splash plate 7 via a series of spray holes in the spray bar. The spray bar arrangement is provided to achieve aeration of the incoming water flow, and is desirable to provide oxygen for the micro-organisms responsible for the biological purification function. In cases where solids filtration only is required the spray bar arrangement can be dispensed with and an alternative and less turbulent feed system can then be provided.

Water fed into the inner tank 1 enters the cartridges around their perimeters and flows through the cartridge material to the central tubular void. The differential water level across the walls of the cartridges will vary according to the degree of blockage of the foam and will increase according to the accumulation of filtered solids and the growth of micro-organisms within the expanded polymeric material.

Filtered water passes out of the cartridges 5 through the tubes 4 and discharges into the void underneath and between containers 1 and 2. Biological treatment and additional filtration is provided within this latter volume by the use of separable pieces 8 of the same expanded polymeric material as is used for the cartridges. The space below container 1 is largely filled with the pieces 8 and water issuing from the cartridges 5 passes around and through the pieces 8, before being collected by perforated drainage pipes 9 prior to discharge from the outer container. An outlet flow control valve 10 permits the adjustment of the water level in containers 1 and 2.

Initially these will be set to prevent overflow from container 2, following which, after the development of sufficient differential head across the cartridges, the valves will be used to control the outer submergence of the cartridges.

Blockage of the cartridges is identified by the overflow of water in container 1 over and down through the central bores in the cartridges, whereupon the cartridges are removed for cleaning. Cleaning is effected by washing individual cartridges in water.

In the embodiment of Fig. 4, the arrangement differs from that of Figs. 1 to 3 in that there is no inner tank 1 and the spray bar assembly 6,7 is removed, and the cartridge holding tubes 4 are fixed into a solid plate which is sealed onto and rests on the perimeter ledge of tank 2.

Referring to Fig. 4, the purification system comprises a rigid plate 10 resting on the perimeter ledges 12 of the tank 13. The plate 10 is fastened to the ledges 12 in such a way as to provide a leak proof seal around the perimeter ledges 12. The rigid plate 10 is drilled to take ten cartridge drainage/holding tubes 14. Cartridges 5 of the same expanded polymeric material and each of nominal dimensions 120 millimetres by 120 millimetres by 420 millimetres and drilled longitudinally and centrally with a 30 millimetres bore hole are placed over the cartridge tubes 14 and disposed in vertical attitudes within the tank 13. The upper ends of the cartridges are closed by either plugs 16 or by forming the cartridges with closed ends 7 (by forming the central bore so as not to extend through one end of the cartridge).Tank 13 may be situated either inside or external to the body of water requiring purification. In the former case, the assembly is submerged so that the static water level in the pond or pool etc. is above the top of the cartridges 15. In the external mode of use, tank 13 is connected to the pool or pond by a pipe or pipes 18 such that the cartridges are always fully submerged.

Biological treatment and additional filtration is provided in the voids beneath plate 10 filled with loose separable pieces of the same expanded polymeric material 19 as is used in the cartridges 15, and in the previous embodiment.

Perforated collection pipes 21 are provided at the base of the assembly, as in the previous embodiment, and water is drawn through the filter assembly by a water pump 22 and is returned to the pond or pool being treated.

Water is drawn through the purification system by suction from the pump 22. Water to be treated first enters the filter cartridges around their peripheries and flows through the walls of the cartridges into their central collection tubes from where it flows into the void under plate 10. The differential pressure across the cartridges will vary according to the degree of blockage of the cartridges.

Water entering the space containing the pieces 19 of expanded polymer passes around and through those pieces and is thereby biologically treated and purified before being collected through the collection pipe 21.

In Fig. 4, the water level for use of the apparatus in an external mode, is indicated at 23. The water level when the apparatus is used in its internal mode, such as when it is immersed in a pond, is indicated at 25.

In the embodiment of Fig. 5, the main difference from the previous embodiments lies in the fact that the cartridges are replaced by sheets 31 of the open cell expanded polyether which rests on a perforated plate 32. The arrangement is otherwise very similar to that described above.

In the above embodiments, the primary filters or pre-filters provided by the cartridges in the embodiments of Figs. 1 to 4 and by the sheets 31 in the embodiment of Fig. 5 serve to remove suspended solid matter from the water being treated. The pieces of the expanded polymer which are provided in all embodiments in the treatment bed at the base of the apparatus serve to support and permit to grow the bacteria which provide biological treatment and purification of the water.

By the provision of primary filters on the upstream side of the biological treatment bed, the latter is much less prone to blockage and can remain in use for periods of up to two or three years without requiring washing or the like. The pre-filters may need to be removed for washing at much shorter intervals such as every two or three weeks or thereabouts.

In this way, the bacteria and other biological matter which builds up in the pores of the expanded polymer in the treatment bed is preserved for a long period of use. On initial assembly of the apparatus. a period of four to six weeks may elapse before the biological treatment bed at the base of the apparatus has built up its complement of bacteria to provide fully effective biological purification of the water. Such a long build-up period would need to be repeated each time the treatment bed were washed after blockage, and the merit of avoiding this is therefore readily appreciated.

Moreover, by providing the treatment bed in the form of pieces of expanded polymer, as opposed to a single preformed piece, the flow through the treatment bed is much more uniform, blockage after an extended period of use is avoided, and even when the individual pieces of expanded polymer have become more or less completely blocked by bacterial growth, the water can still flow around the pieces and biological purification can proceed at their surfaces, and even by diffusion into their interiors.

The efficiency of filtration is related to the pore size of the filter material and to the surface area of the medium presented at 90 degrees to the path of flow of the water being treated. The efficiency of biological treatment is directly proportional to the weight of biologically active organisms contained within the filtration material.

The use of cartridges provides for a large flow surface area when compared with simple downward or upward flow through a bed of a medium in the same size of container. Open cell expanded polymeric material provides 98% porosity compared with 40/50% porosity in the case of a gravel or sand filter material. The expanded polymer in cartridge form therefore provides many times more surface area of filter within the same container than is available from the use of aggregate filtration medias. This advantage is particularly beneficial when there is a significant need for filtration or there is a specific requirement for the filter to be as compact as possible. In cases where there is a need for pre-filtration but this need is secondary to good biological treatment, then sheets of the polymer may be substituted for the cartridges.

The high porosity of the polymer permits good penetration of solids into the body of the polymer, with the result that long filter runs can be obtained between cleaning intervals, Because of the large voidage, high concentrations of biological organisms can be held within the expanded polymer both in the cartridges and in the loose pieces thereof in the biological treatment bed. As a result, the systems have volumetric biological treatment capacity many times greater than is attainable from conventional aggregate media filters.

Among modifications which could be made in the above embodiments while remaining within the scope of the invention are the following: 1. Other polymers may be found which could be used instead of the specified polyether. The latter is at present the only polymer known to the applicant to have the required characteristics of chemical resistance, non-toxicity, insolubility, etc.

2. As regards the pieces of expanded polymer, the preferred shape is rectangular with sizes of 25 millimetres by 25 millimetres by 12 millimetres and up to 30 millimetres by 30 millimetres by 30 millimetres, but sizes up to a 75 millimetre cube could be contemplated, and down to a 5 millimetre cube, and indeed other particle shapes would be acceptable in certain applications.

3. As regards the degree of filling of the space to contain the pieces of expanded polymer for the biological treatment bed, a fairly loose assembly of pieces may be provided.

depending on the application concerned. The advantages mentioned above are obtainable by virtue of the use of pieces of the material at packings thereof of up to a 50% overfill of the container followed by compaction.

4. As regards the cartridges, in the above embodiments the cartridges are provided in the form merely of blocks of the expanded polymeric material with a central bore and direct access of water to the external surface.

In certain applications it may be desirable to provide a perforated external wall or support and/or a perforated internal collection tube.

5. Provision could be made for partial or complete cleaning of the biological treatment bed when desired by means of an air supply delivered into the bed to cause turbulence in the particles so as to remove biological matter, after which the bed could be drained and backwashed.

Claims

1. A method of treating relatively clean water (as defined herein) comprising passing said water through a bed comprising open cell expanded polymeric material.

2. A method according to claim 1 wherein biodegradable organic or inorganic pollutants are passed into the bed to cause micro-organisms to become established on the surfaces of said polymeric material to cause said biologi cal treatment.

2. A method according to claim 1 wherein said open cell expanded polymeric material is in the form of separable pieces.

3. A method according to claim 2 wherein the average volume of said pieces lies in the range of 125 cubic millimetres to 421,875 cubic millimetres.

4. A method according to claims 2 or 3 wherein said pieces are generally rectangular in form.

5. A method according to claim 4 wherein two of the dimensions of said pieces lie in the range of from 20 to 40 millimetres and one dimension lies in the range from 10 to 40 millimetres.

6. A method according to any one of claims 2 to 5 wherein said pieces are arranged so that said water can flow around said pieces.

7. A method according to claim 6 wherein the quantity of pieces of said open cell expanded polymeric material provided in said bed is such that the degree of compression of said pieces on assembly into said bed causes a reduction of the combined volume of said pieces of less than 33.3%.

8. A method according to any one of the preceding claims wherein said water is passed through a primary filter to remove suspended solid matter before the water is passed through said bed.

9. A method according to claim 8 wherein said primary filter comprises said open cell expanded polymeric material.

10. A method according to any one of the preceding claims for treating the water of a pond or aquarium comprising the step of returning the water directly to the pond or aquarium from the bed.

11. A method according to claim 8 or claim 9 comprising the step of allowing the water to pass through the primary filter and the bed in sequence, the primary filter being arranged above the bed and water being removed from the base of the bed for recirculation.

12. A method according to any one of claims 8, 9 or 11 comprising the step of cleaning the primary filter at relatively short intervals (for example from a few days to a few weeks) and cleaning the bed at much longer intervals (for example up to 2 years).

13. Apparatus for treating relatively clean water (as defined herein) comprising a treatment bed comprising open cell expanded polymeric material.

14. Apparatus according to claim 13 wherein said polymeric material comprises a polyether.

15. Apparatus according to claim 13 or claim 14 wherein said polymeric material is in the form of separable pieces.

16. Apparatus according to claim 15 wherein the average volume of said pieces lies in the range from 125 cubic millimetres to 421,875 cubic millimetres.

17. Apparatus according to claim 15 or claim 16 wherein said pieces are generally rectangular in form.

18. Apparatus according to any one of claims 15 to 17 wherein said pieces are arranged so that water can flow around the pieces.

19. Apparatus according to claim 18 wherein the combined volume of said pieces of said bed is such that on assembly the reduction of their combined volume by compression is less than 33.3% of the total volume of said pieces.

20. Apparatus according to any one of claims 13 to 19 wherein said treatment bed comprises water supply means above the polymeric material and water removal means below said material.

21. Apparatus according to claim 20 wherein said water removal means comprises a perforated duct connectible to the suction side of a water pump.

22. Apparatus according to any one of claims 13 to 21 comprising a primary filter to filter the water before the water reaches the treatment bed.

23. Apparatus according to claim 22 wherein said primary filter comprises open cell expanded polymeric material.

24. Apparatus according to claim 23 wherein the polymeric material of the primary filter is arranged in a bed.

25. Apparatus according to claim 23 wherein the polymeric material of the primary filter is provided in the form of a filter element.

26. Apparatus according to claim 25 wherein said filter element is constructed so as to be submersible.

27. Apparatus according to claim 26 wherein the filter element comprises periph eral water inlet means and central internal water outlet means.

28. Apparatus according to claim 27 wherein the open cell expanded polymeric material itself provides said water inlet and water outlet means.

29. Apparatus according to claim 28 wherein the filter element is in the form of an upstanding cartridge element with a central water removal tube at the bottom of the element.

30. Apparatus according to any one of claims 25 to 29 comprising two or more of said filter elements connected to the treatment bed.

31. Apparatus according to claim 30 wherein the filter elements are mounted in a common vessel located above the treatment bed.

32. Apparatus according to claim 31 wherein the water is supplied to said common vessel in the form of a spray.

33. A filter element comprising a submersible assembly having a water collection tube and a body of open cell expanded polymeric material from which said tube collects filtered water.

34. A method of treating relatively clean water (as defined herein) substantially as described herein with reference to the accompanying drawings.

35. Apparatus for treating relatively clean water (as defined herein) substantially as described herein with reference to the accompanying drawings.

36. A filter element substantially as described herein with reference to the accompanying drawings.

1. A method of biologically treating relatively clean water (as defined herein) comprising passing said water through a bed comprising open cell expanded polymeric material.