GB2181424A - Zeolite impregnated open-cell foam - Google Patents

Abstract

A filter, useful in purification of aquarium or pond water, comprises a reticulted foamed plastics material incorporating particles of a zeolite. The material may be adapted to host nitrifying bacteria, the zeolite absorbing ammonia when the bacteria are not sufficiently active. Other uses are in gas-separation as plant growth medium and odour control. <IMAGE>

Description

SPECIFICATION Zeolite impregnated open-cell foam This invention relates to the impregnation of open-cell foam with Zeolite, the material so produced then being capable of selectively adsorbing certain molecules from gases and liquids giving it a potentially wide field of use.

Without limiting the potential fields of use, this application relates in particular to the selective removal of ammonium by this material from water arising from tanks containing fish.

Ammonia is the principle by-product of fish metabolism and is highly toxic to fish. Failure to maintain the ammonia concentration in fish tank water below certain critical values can result in high mortalities, disease, or poor growth. Methods of controlling the level of ammonia in aquaculture systems are as follows: 1. Dilution 2. Conversion of toxic ammonia to less toxic nitrate by biological purification systems utilising nitrifying bacteria.

3. Removal of ammonia chemically using Zeolite.

Dilution techniques are not normally economically practicable in commercial warmwater aquaculture systems due to the high cost of replacing the displaced warm water. Similar considerations also preclude adoption of this remedy for domestic aquaria and ponds, and for fish display systems in general.

Biological methods of ammonia removal are widely used in both commercial and domestic aquaculture. Such systems invariably utilise a fixed medium of high specific surface which supports the growth of vast numbers of biological organisms including the nitrifying bacteria. The advantage of biological systems is that provided the pH of the water to be purified is maintained within a certain range for the survival of the nitrifying bacteria such systems are very reliable. The principal disadvantage of biological systems is that they can take up to 12 weeks to fully mature biologically.

Extreme care must be exercised during the maturation period not to overload the purification system with fish, requiring frequent monitoring of water quality, particularly with respect to ammonia, nitrite and pH. Whilst this presents no real problem in commercial fish farming establishments where the expertise is available for monitoring and controlling maturation, this is rarely the case with the hobbyist fishkeeper. Use of biological purification systems for domestic fishponds and aquaria can therefore, in the early stages, often lead to heavy fish mortalities.

Zeolites are natural volcanic rocks which have weathered over millions of years. Chemically they may be classed as "Alumino Silicate" being made up basically from oxygen, aluminium and silica, arranged in a particular interconnecting lattice structure rather like a "honeycomb". The channels connecting the honeycomb holes are extremely small in diameter so that only molecules of diameter smaller than the channels can pass into the honeycomb structure of the Zeolite. Molecules of caesium, strontium, potassium, water, ammonia, sodium, calcium, for example are smaller than the channels and thus are able to pass into the structure. Synthetic Zeolites are also available. The capacity of a particular Zeolite for removing a particular chemical is related to the precise nature of the Zeolite and the circumstances of use.All Zeolites eventually become exhausted in their capacity to remove a particular chemical or chemicals, exhaustion being signified by "breakthrough" of that chemical in the effluent water i.e. a significant reduction in pollutant removal efficiecy.

However a particularly useful feature of Zeolites is their characteristic of being able to reversibly adsorb/desorb the chemical(s) removed by washing with water containing another chemical, usually salt. This cleansing process is normally performed just after the point of breakthrough and is called "regeneration".

Careful and constant monitoring of the effluent water quality is therefore important with the use of Zeolites, and is particularly critical when used in connection with fish culture units when a sudden uncorrected breakthrough of ammonia can cause heavy fish mortalities.

Zeolites are therefore rarely used as the sole method of ammonia removal in recirculation aquaculture. They are mainly used as a temporary substitute for biological treatment during tank medication, or as a secondary treatment process during the period of maturation of the biological purification system.

Open-cell polymeric material, also known as, open-cell foams or reticulated plastics, are now widely used for biological purification and mechanical filtration for both commercial and domestic aquaculture. (Ref-my U K Patent Application GB 2146255 A). Fig. 1 shows a perspective view of the open-cell polymeric material, the internal structure of which is further illustrated by Fig. 2 which is a microphotograph of the material.

Whilst due to the high specific surface and high voidage of the material it is many times more efficient than other biological purification medias in terms of both mechanical filtration and biological treatment, nonetheless, in common with all other medias, up to 12 weeks may elapse before the media is biologically mature.

According to the present invention there is provided, an open-cell polymeric material impregnated, with Zeolite particles together with a method of using same. When incorporated in an aquaculture water purification system such material is therefore immediately capable of removing highly toxic ammonia excreted by the fish by virtue of the Zeolite particles, and will continue to act in this way until the adsorption capacity of the Zeolite becomes exhausted.

Incorporation of a sufficient quantity of Zeolite into the open-cell foam will ensure that the natural build-up of nitrifying bacteria occurs before the ammonia adsorption capacity of the Zeolite is reached. This aspect obviates close monitoring of the water quality with respect to ammonia during the maturation period and is therefore particularly advantageous to the amateur and hobbyist fishkeeper, when using the material for purification of water from ponds and aquaria.

There are many possible methods of impregnating the foam with Zeolite particles, but the most promising at present appears to be through the use of proprietry commercial adhesives. Important aspects of which, particularly for application in aquaculture, are that the adhesive should be non-toxic and not water soluble. In addition there should be minimal surface blinding of the particles by the adhesive.

According to another aspect of the invention there is provided a device for filtering water in aquaria, consisting of a sheet of open cell foam. The lower surface of the foam is not flat. It provides flow channels for filtered water to be drawn from under the foam to points of evacuation from where the filtered water is returned to the main water body of the aquarium. The underside of the foam may be dimpled or corrugated or formed in many other analogeus ways. Fig. 3 is a photograph of the underside of the foam formed to give a dimpled effect.

The sheet of foam is placed on the floor of the aquarium and may be covered by a layer of gravel or coarse sand. Water being filtered by the foam may be drawn through the sheet of foam by means of an air lift commencing from the flow channels or by means of mechanical pump which may be of the submersible or external type.

In another aspect of the invention there is provided an alternative method of filtering aquarium water using particles of open-cell foam. The particles would normally be of size 25 millimetres x 25 millimetres x 12 millimetres but any principal dimension up to 30 millimetres would be satisfactory. The particles are placed in a container situated either internal or external to the aquarium. Water to be filtered is arranged to pass upwards or downwards through the bed of particles using a pumping means.

Yet another aspect of the invention for filtering aquarium water is provided by an opencell foam cartridge. The cartridge may be of circular, square, or convoluted cross section or of any other external cross section providing a high peripheral area. The cartridge may be installed in a container internal or external to the aquarium or merely placed inside the aquarium. The cartridge is provided with a horizontal hole sealed at the end opposite to the point of withdrawal of water. Water to be filtered is caused to flow through the walls of the cartridge by a pumping means into the horizontal hole and is then returned to the main body of the aquarium. A perforated or slotted drainage pipe may be placed in the horizontal hole.

These aspects of the invention are not limited only to the use of open-cell foam impregnated with Zeolite, neither are they limited to the filtration of aquarium water.

Other uses of the material are also apparent: 1. As a molecular gas sieve for removing gases such as ammonia, hydrogen sulphide, carbon monoxide, carbon dioxide, sulphur dioxide, steam, oxygen, nitrogen, formaldehyde, and others from a complex gas stream. The power of the Zeolite to adsorb water, particularly without damage to the Zeolite, renders the material excellent as dessicants.

2. The high ion-exchange capacity of certain Zeolites offers benefits through the use of the material in controlling specific cationic levels in water pollution, agriculture and many other areas.

3. Too much nitrogen supplied to emerging crops can be toxic and lead to the "burning" of the root system. The correct type of Zeolite in the foam will allow the material to be used as part of a plant growth medium which will prevent root burning and improve growth by reducing the loss of nitrogen fertilizer.

4. Zeolite impregnated foam can be used as an effective odour control medium removing offensive ammonia fumes from public toilets, stables, and other animal production units.

5. Zeolite has been proven effective in the removal of phosphate and nitrate from water.

Both are considered plant nutrients and can initiate and sustain heavy algal blooms in outdoor pond systems. Use of Zeolite impregnated foam will remove nitrate and phosphate and help to prevent the unsightly green water conditions created by algal bloom.

6. Nothing in this application is to be interpreted as excluding coverage of the above uses of the invention.

Claims (11)

1. A filter comprising a reticulated foamed plastics material, and a plurality of particles of a zeolite carried by said material.

2. A filter as claimed in claim 1, wherein said material is adapted to host nitrifying bacteria.

3. A filter as claimed in either claim 1 or claim 2, wherein the zeolite is selected to absorb, inter alia, ammonia.

4. A filter as claimed in any one of the preceding claims, wherein the zeolite is adhered to the material.

5. A filter as claimed in any one of the preceding claims, wherein the material is shaped as a sheet, one major surface of which is profiled to form flow channels for the liquid being filtered.

6. A filter as claimed in any one of claims 1 to 4, wherein the material is shaped as a plurality of cuboids, said cuboids being retained within a container.

7. A filter as claimed in claim 6, wherein the container is located within a body of liquid to be filtered.

8. A filter as claimed in claim 6, wherein the liquid to be filtered is passed through the container.

9. A filter substantially as described herein with reference to any one of the Figures of the accompanying drawing.

10. A water purification system comprising a filter as claimed in any one of the preceding claims.

11. An aquarium comprising a filter as claimed in any one of the preceding claims.