GB2464686A

GB2464686A - Filtration system

Info

Publication number: GB2464686A
Application number: GB0819290A
Authority: GB
Inventors: Robert Bawden
Original assignee: PISCES ENGINEERING Ltd
Current assignee: PISCES ENGINEERING Ltd
Priority date: 2008-10-21
Filing date: 2008-10-21
Publication date: 2010-04-28
Also published as: GB0819290D0

Abstract

A system 10 and method for filtering water for use in an aquaculture system is disclosed. The system comprises a first conduit 16 for circulating a first water stream between a vessel 12 and a non-biological filter 14 and a second conduit 20 for circulating a second water stream between a biological filter 18 and the non-biological filter 14, wherein the second conduit is isolated from the first conduit. The vessel is used preferably to house fish and may be adapted to receive, freshwater, saltwater or seawater. One or both of the water streams may be heated and the second water stream may be of higher salinity than the first. A method of filtering water for use in an aquaculture system is also disclosed wherein removable lipids (36, Fig. 4) are introduced into the water to remove taint-forming compounds (34, Fig. 3), such as geosmin, from the water.

Description

FILTRATION SYSTEM

FIELD OF THE INVENTION

This invention relates to a method of filtering water for use in an aquaculture system and a system for filtering water for use in an aquaculture system.

BACKGROUND OF THE INVENTION

In recent years, world demand for fish has been increasing and it is expected that this will continue to grow in future. However, in many areas of the world, fish are becoming an increasingly scarce resource, this resulting for example from over-fishing and from complications surrounding environmental changes.

If fishing is to satisfy demand, catches must rise. However, many fish stocks cannot support the increased level of fishing to meet current or increased demand such that it is thought that many stocks will not survive unless solutions to this problem can be found.

The aquaculture industry has become a major global industry and is seen as a route to meet the shortfall. Aquaculture systems have traditionally been divided into two forms: intensive culture systems and extensive culture systems. As might be expected, intensive culture systems involve high levels of intervention when rearing the fish and obtain higher output efficiencies, though intensive culture systems typically have higher overheads, are relatively labour intensive and have greater impact on the environment. In contrast, extensive culture systems involve low levels of intervention and utilise the natural growing terms of the fish. Extensive culture systems typically have lower overheads, are less labour intensive and have less impact on the environment, though the output efficiencies obtained are less than intensive culture methods. Although there has been some growth in extensive culture systems, due to their low productivity these are unlikely to meet the required global demand.

Other culture systems include enclosed floating net type or offshore systems, and, although addressing some of the environmental concerns, these systems are typically capital expensive and carry a high level of risk.

Of particular interest to the aquaculture industry is the desire to provide efficient, cost effective aquaculture systems that have a low impact on the environment and, more recently, the aquaculture industry has been moving towards enclosed systems. Rather than taking large quantities of water from the environment, polluting it with waste excretions from the fish and discharging it back to the environment, with enclosed systems the fish holding unit has its own water treatment plant that purifies the waste water to enable it to be reused.

In the design of water purification systems for aquaculture, there are typically three main processes: nitrification (which involves the breakdown of nitrogenous wastes such as ammonia and nitrites to less harmful nitrates); de-nitrification (which involves the breakdown of nitrate to nitrogen gas, thereby removing the nitrogen from the water); and the breakdown of organic wastes from undigested faeces and uneaten food.

However, although the technologies required to achieve these processes have been proven, it has been found that the processes used for water purification result in the production of compounds that impart a muddy or earthy taint to the flesh of the fish. The resulting taint in the fish from these recirculation systems can render the fish at worst unsaleable or at best saleable at a much reduced price.

Water purification systems typically rely on the management of large bacterial colonies and nitrification, de-nitrification and waste breakdown typically employ bacterial activity, for example to metabolise the various wastes from the fish, thereby rendering these into more harmless forms. Although the de-nitrification process is one that typically takes place in zero oxygen conditions (anaerobic), an environment which the taint producing bacteria do not prefer, the other processes require an aerobic biofilter in which the taint producing bacteria can thrive.

In particular, it has been found that the taints in recirculation systems are due two chemicals, Geosmin and MIB (2-Methylisoborneol). These chemicals are produced by some species of bacteria (and/or cyanobacteria) that reside along with the water treatment bacteria in the water purification systems. Control over these taint forming compounds in recirculation systems has been attempted through the application of large quantities of ozone or other oxidising agents. However, ozone is a highly toxic gas, is expensive to use and adds to the complication of the system.

Furthermore, although ozone may be partially effective in destroying the taint-forming compounds, results are variable and unpredictable as the ozone may be used preferentially by other compounds in the water.

A typical prior art system is shown in Figure 1 and involves pumping fish culture water from a fish culture tank 1 through a variety of filters including a solids filter 2 and a biological filter 3 before returning the water to the fish culture tank 1. A variety of side stream processes may also be employed. For example, an oxygen generator/injector 4 and an ozone generator/injector 5 may be employed in an effort to reduce taint forming compounds to concentrations where their impacts on fish flavour are lessened. However, as described above, these processes greatly complicate the aquaculture system, increase overheads, increase the impact on the environment and have been found to produce unpredictable results. A pH buffer 6 may be used to manipulate the acidity of the water and de-nitrification processes (shown schematically by reference 7 in Figure 1) may be carried out on the water prior to returning the water to the tank 1.

In addition, there are a number of other important concerns facing recirculation systems. For example, biosecurity, that is the ability to prevent and overcome disease, is clearly an important issue. While recirculation-type systems have the advantage that they are well isolated from the environment such that there is far less chance of a disease outbreak occurring, where a disease outbreak does occur the enclosed recirculation system then becomes disadvantaged over one open to the environment. In addition, most of the treatment chemicals and antibiotics required to counter a disease outbreak will have a detrimental effect on the bacterial colonies in the biofilters and cause a catastrophic loss of fish if used. Furthermore, once a disease has entered into a recirculation system, it can be very difficult to remove this from the system without completely emptying and sterilising the entire system. This process will typically include the stérilisation of the biological filters, which can then take up to six months or more to become fully established and mature again.

Furthermore, the reliance of aquaculture on the bacterial colonies also causes much concern, particularly with regard to the possibility of a "crash" in part or all of the bacterial colony. Such a crash will often lead to a sudden change in water quality and may result in death of all of the fish.

Other problem areas include the need to make any changes to the system over extended periods of time to allow the bacterial colonies time to acclimatise. For example, the culture of bacterial species is greatly affected by temperature change, such that their use is somewhat limited where there is a decline in temperature, this due to reduced activity in the biological filter. This is especially so for temperate species as the efficiency and rate of acclimation of the bacteria is reduced with temperature.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method of filtering water for use in an aquaculture system, the method comprising: circulating a first water stream between a vessel and a non-biological filter; and selectively isolating the non-biological filter from the first water stream and circulating a second water stream between the non-biological filter and a biological filter.

According to a second aspect of the present invention, there is provided a filtration system comprising: a vessel; a non-biological filter coupled to the vessel, wherein a first water stream is adapted to be circulated between the vessel and the non-biological filter; and a biological filter coupled to the non-biological filter, wherein the non-biological filter is adapted to be isolated from the first water stream and a separate second water stream is circulated between the non-biological fitter and the biological filter.

Embodiments of the present invention permit use of a biological fitter to break down nitrogenous and organic compounds produced in the system while separating the biological filtration activity from the first water stream. Thus, in use, taint-forming compounds may be prevented from being introduced into the first water stream and the vessel.

The biological filter may be coupled to the non-biological filter and may be provided in parallel with the non-biological filter.

In particular embodiments, the vessel may be used to house fish, though it will be understood that the vessel may be used to house any other aquatic animal or organism and reference to the term fish should be taken to include any aquatic animal or organism. Thus, taint-forming compounds may be substantially prevented from interacting with the fish housed in the vessel.

As the first water stream is isolated from the second water stream, then the properties of the water in the first and second water streams may be manipulated or maintained to optimise filtration activity while maintaining the conditions in the vessel.

For example, the method may further comprise heating at least one of the first and second water streams and the system may comprise a heater for maintaining the water temperature in the first and second water streams. In particular embodiments, the heater may be operated to heat the water in the second water stream to maintain the second water stream at a higher temperature than the first water stream.

Beneficially, the ability to operate the biological filter at higher temperatures permits the biological filter to be operated at higher efficiency than if the biological filter were limited to the temperature range amenable to the fish housed in the vessel.

Furthermore, operation of the biological filter at higher temperatures and different salinities than the fish culture water provides environmental conditions in the biological filter which facilitate the elimination or prevention of pathogens that may otherwise survive and transfer to the fish culture water. Accordinglyr embodiments of the present invention may also substantially eliminate the problem of harbouring pathogens in the biological filter.

The vessel may be adapted to receive fresh water for housing freshwater species of fish and the method may further comprise circulating freshwater between the vessel and the non-biological filter via the first water stream. Alternatively, the first water stream may comprise saline water, for example brackish or seawater and the vessel may be used for housing brackish, saltwater or euryhaline species of fish.

In particular embodiments, the second water stream may comprise water of higher salinity than the first water stream. For example, the second water stream may comprise seawater or the like. Operation at higher salinity may assist in increasing the regeneration efficiency of the non-biological filter, operation at higher salinity favouring the growth and maintenance of the bacterial colonies present in the biological filter. In addition, as the non-biological filter is periodically exposed to each of the first and the second water streams, where the first and second water streams are of different salinity, the salinity experienced by the non-biological filter may vary over time. These changes in salinity of the water passing through the non-biological filter may substantially prevent or inhibit the growth of bacteria and other organisms in the non-biological filter, which may otherwise result in the formation of taint-forming compounds which could be passed to vessel via the first water stream.

The method may further comprise introducing chemicals into the first water stream. For example, antibiotics or medicinal products may be introduced into the first water stream, thereby facilitating treatment or prevention of disease in the fish housed in the vessel while substantially eliminating the possibility that the beneficial bacterial colonies in the biological filter will be exposed to these products. For example, this may assist in reducing the chance that the bacterial colonies will be compromised or that a crash in the bacterial population will occur.

Chemical therapeutants may be removed from the first water stream and in particular embodiment, chemical therapeutants may be removed from the first water stream by activated carbon or other suitable media, the use of this media being greatly increased in efficiency due to the lack of other organic compounds in the water, which can then be transferred to the second water stream.

Furthermore, in the event that the biological filter was compromised or where a crash occurs, as the first and second water streams are isolated there may be limited or no effect on the first water stream and thus the fish housed in the vessel.

The method may further comprise manipulating or maintaining the acidity of the second water stream. For example, the system may further comprise a pH buffer for manipulating or maintaining the acidity of the second water stream. This facilitates the provision of the optimum conditions for growing and maintaining the bacterial colonies in the biologicat filter while maintaining different optimum conditions in the fish culture water.

The method may further comprise removing nitrogenous compounds from the biological filter. In particular embodiments, the method may comprise transforming nitrates in the biological filter into nitrogen gas and the method may further comprise removing the produced nitrogen gas from the biological filter. De-nitrification may comprise a bacterial process using colonies of anaerobic bacteria. Where otherwise such a process may have a detrimental affect on water quality for the fish, in embodiments of the present invention where de-nitrification occurs in the second water stream, there is not adverse affect on the fish culture water. Furthermore, a carbon source, for example methanol or molasses, may be added to aid this process.

The non-biological filter may be of any suitable form. For example, the non-biological filter may comprise a zeolite filter or the like.

The system may comprise a plurality of non-biological filters and the method may comprise isolating one or more of the non-biological filters from the first water stream and circulating the second water stream between the, or each, of the isolated non-biological filters and the biological filter. Accordingly, where a number of non-biological filters are provided, each may be separately isolated from the first water stream and selectively coupled to the biological filter so water flow around the first water stream need not be interrupted.

The biological filter may be of any suitable form. For example, the biological filter may comprise an aerobic marine biofilter or the like, though any suitable filter including, for example, a fluidised media, submerged static bed, trickle static bed or activated sludge biological filter may be used where appropriate.

The system may comprise a single biological filter and the biological filter may be selectively coupled to the, or each, non-biological filter. For example, where a plurality of non-biological filters are provided, the biological filter may be selectively coupled to one or more of the non-biological filters at a time.

Alternatively, the system may comprise a plurality of biological filters. In particular embodiments, the biological filters may be provided in parallel.

The method may further comprise removing solids and/or particulate matter from the first water stream and the system may comprise a filter for removing solids and/or particulate matter from the first water stream. The solids filter may be of any suitable form. For example, the solids filter may comprise media beds, screens or membrane filters. In particular embodiments, the solids filter may partially or wholly comprise a settlement tank filter.

The system may comprise a filter for removing solids and/or particulate matter from the second water stream and the system may comprise a filter for removing solids and/or particulate matter from the second water stream. The solids filter may be of any suitable form and may, for example, comprise media beds, screens or membrane filters. In particular embodiments, the solids filter may partially or wholly comprise a settlement tank filter. Alternatively, or in addition, the solids filter may utilise organisms such as shellfish and/or plants.

The method may further comprise introducing lipids into at least one of the vessel and the first water stream for removing taint-forming compounds from the system.

It has been discovered that where lipids are introduced, the lipids bind with the taint-forming compounds. The method may further comprise removing the lipids from the vessel and/or the first water stream, thereby removing the taint-forming compounds from the water.

For example, lipids may be introduced into at least one of the vessel and the first water stream prior to operation of the filtration system and/or where a shut-down has occurred. Alternatively, lipids may be introduced into at least one of the vessel and the first water stream during operation of the filtration system.

In particular embodiments, lipids may be introduced to assist in the removal of geosmin and 2-Methylisoborneol from the vessel and/or the first water stream.

The lipids may be provided on or impregnated in a membrane and, in particular embodiments, the membrane may be provided in the first water stream and/or in the vessel. Beneficially, in use water passes across the static membrane, the taint-forming compounds attach themselves or being absorbed by the lipids.

Alternatively, or in addition, the lipids may be provided as a mixed or fluid state surface, The system may further comprise an agitator adapted to mix lipids with water in the vessel and/or the first water stream. Thus, in use, the taint-forming compounds suspended in the water attach themselves or are absorbed into the lipid.

Accordingly, embodiments of the present invention facilitate removal of taint-forming compounds from the vessel and/or the first water stream, where these are found in the first water stream.

According to a further aspect of the present invention, there is provided an aquaculture system comprising a filtration system according to the second aspect of the invention.

Further aspects of the present invention relate to the use of removable lipids to remove taint-forming compounds from water in an aquaculture system.

It should be understood that the features defined above in accordance with any aspect of the present invention may be utilised either alone or in combination with any other defined feature in any other aspect of the invention or as described below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a prior art filtration system; and Figure 2 is a diagrammatic representation of a filtration system according to the present invention; Figure 3 is a diagrammatic representation of a filtration system according to another embodiment of the present invention; and Figure 4 is a diagrammatic representation of a filtration system according to a another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 2 shows a diagrammatic view of a filtration system 10 according to an embodiment of the present invention. The filtration system 10 operates to filter water for use in an aquaculture system (hereinafter referred to a fish culture water) and, in use, substantially prevents ingress of taint-forming compounds into the fish culture water, The system 10 comprises a vessel or tank 12 for containing the fish culture water and a number of fish (not shown). In order to maintain the water quality of the fish culture water in the tank 12 and to maintain the health of the fish contained in the tank 12, it is necessary to remove solids and particulate matter, nitrogenous compounds (particularly ammonia) and organic solids such as faeces and unused feed stock from the fish culture water.

In use, fish culture water from the tank 12 is circulated between the tank 12 and a non-biological filter 14 via a conduit 16. In the embodiment shown, the conduit 16 takes the form of an open channel but it will be understood that any suitable conduit such as a closed channel, pipe or hose may be used. As shown, a number of non-biological filters 14 are provided (two non-biological filters 14a and 14b are shown in Figure 2), each of the filters 14a, 14b arranged to receive fish culture water from the tank 12. In the embodiment shown, the non-biological filters 14a, 14b consist of a one or more series of beds of zeolite material and, in use, the filters 14a, 1 4b operate on the fish culture water to remove ammonia from the fish culture water.

The zeolite also acts. as mechanical filter and retains organic and other solid particles. After passing through the filters 14a, 14b, the fish culture water is returned to the tank 12 via the conduit 16.

However, over time the filters 14a, 14b reduce in effectiveness such that the water quality in the tank 12 will begin to decline as the levels of ammonia increases and the filter bed begins to block as a result of build up of solids materials. Thus, when it is desired to clean one or more of the filters 14a, 14b, the flow of fish culture water to the filter to be cleaned (for example filter 14a as shown in Figure 2) is stopped (shown by reference X in Figure 2), the water being allowed to drain back to the tank 12.

Following this, when the filter 14a is substantially empty of fish culture water, the filter 1 4a is coupled to a biological filter 18 which is isolated from the culture water conduit 16. In the embodiment shown, the biological filter 18 consists of a marine aerobic biological filter (the biofilter) and, in use, the biofilter 18 is coupled to the filter to be cleaned 14a by a second, separate conduit 20 (shown by broken line in Figure 2). Water (hereinafter referred to a biofilter water) is circulated between the filter 14a and the blot ilter 18 via the second conduit 20.

As the biofilter water is distinct from the fish culture water, the properties of the biofHter water and the fish culture water can be selected and maintained to assist in their different functions: that is to provide conditions amenable to the rearing of the fish in the case of the fish culture water; and to grow and maintain the bacterial colonies in the biotilter to facilitate operation of the biofilter.

In the embodiment shown, the biofilter water circulating between the filter 14a and the biofilter 18 has a higher salinity than the fish culture water and can be operated with water temperatures that would otherwise not be used in the fish culture water. For example, in the embodiment shown the fish culture water is maintained at a temperature range of about 10 degrees Celsius to about 30 degrees Celsius while the biological filter water is maintained at a temperature range of about 35 degrees Celsius to about 40 degrees Celsius, though it will be understood that any suitable temperature ranges may be maintained.

Nitrogenous materials, particularly ammonia, and organic materials such as unused feed and faeces trapped in the filter 14a is thereby flushed into the second conduit 20 and, due to the chemical nature of the higher salinity water, a proportion of the ammonia is stripped from the filter 14a.

Furthermore, organisms, typically bacteria, in the biofilter operate to break down the nitrogenous compounds and organic wastes as they circulate between the filter 14 and the biofilter 18.

After a period of time, the flow of biofilter water around the second conduit 20 is stopped and the water is permitted to drain back to the biofilter 18.

When the filter 14a is substantially free of biofilter water, the filter 14a is reconnected to the first conduit 16 and fish culture water is again circulated between the respective filter 14a and the tank 12.

Thus, in use, the present invention facilitates use of a biological filter 18 to break down nitrogenous and organic compounds while separating the biological filtration activity from the fish culture water. Accordingly, any taint-forming compounds produced inthe biofilter 18 and the second conduit 20 will be retained in the biofilter 18 and the second conduit 20 and will be substantially prevented from being introduced into the fish culture water, where they may otherwise result in a taint in the fish housed in the tank 12.

Iii addition, the changes in salinity of water passing through the filters 14a, 14b also substantially prevents or inhibits the growth of bacteria and other organisms in the respective filter 14a, 14b, which may otherwise result in the transmission of taint-forming compounds in the fish culture water.

As each conduit 16;20 is isolated from the other conduit 20;16, then separate processes can be carried out on the water in each of the conduits 16, 20.

For example, as the biofilter 18 is isolated from the fish culture water, embodiments of the present invention address the issue of being able to use chemical and antibiotic treatments on the fish, where otherwise there was a risk of compromising or causing a crash of the bacterial colonies.

Furthermore, the salinity and temperature of the water in the secondary conduit 20 can be selected to assist in growth and maintenance of the bacterial colonies in the biotilter 18. As shown in Figure 2, a pH bufter 22 may be used to control the biofilter water acidity and de-nitrification processes (shown schematically by reference 24 in Figure 2) are carried out on the biofilter water.

In the embodiment shown, the system 10 also includes a filter 26 for removing solids and particulates from the fish culture water. As shown, the solids filter 26 is positioned between the tank 12 and the non-biological filters 14a, 14b via a conduit 28 and comprises a settlement tank 26 arranged to receive fish culture water from the tank 12. In alternative embodiments, a combination of a screen or membrane filter with a settlement tank.

In use, fish culture water is directed through the settlement tank 26 and particulate matter, which will be of higher density than the fish culture water, settles on the bottom in the settlement tank 26, where it can subsequently be removed. The fish culture water is returned to the conduit 16 and is then directed to the non-biological filters 14a, 14b.

Referring now to Figures 3 and 4, there is shown schematic views of filtration systems 30 (Figure 3) and 32 (Figure 4) according to alternative embodiments of the present invention. In use, the systems 30, 32 are used to remove taint-forming compounds 34, such as geosmin and 2-methylisoborneog, from fish culture water by introducing removable lipids 36 into the fish culture water.

In the embodiment shown in Figure 3, a lipid surface 38, for example, a membrane impregnated with lipids 36, or a floating layer of lipid is introduced into the fish culture water flow (shown by arrow 40) and through adsorption and/or absorption processes, the lipid surface 38 removes the taint forming compounds 34 from the fish culture water. It will be understood that the ability of the lipid surface 38 to retain the taint-forming compounds 34 is likely to diminish over time and, in use, the lipid surface 38 can be replaced or processed to remove the taint-forming compounds 34.

Referring now in particular to Figure 4, the lipids 36 (shown by white circles in Figure 4) are introduced directly into the fish culture water as droplets and/or particles. An agitator 42 operates to mixes the lipids 36 with the water column and the taint-forming compounds 34 in the water attach themselves to, or are absorbed into, the lipid droplets or particles 36. Following this, the lipid droplets and/or particles 36 can be removed to facilitate removal of the taint-forming compounds 34 from the fish culture water.

It should be understood that the embodiments described are merely exemplary of the present invention and that various modifications may be made without departing from the scope of the invention.

For example, though the present invention is described in relation to aquaculture, embodiments of the present invention may alternatively be used to produce potable water or water suitable for any other application.

In addition, scrubbers may be provided, the scrubbers used to clean the inside walls of the tank 12 of faeces and/or bacteria, algae and fungi.

Furthermore, it will be recognised that the techniques and components of the embodiments described above may be incorporated into any other embodiment. For example, the techniques and components of the second embodiment of the invention (described in reference to Figure 3) and/or the third embodiment (described in reference to Figure 4) may be incorporated into the first embodiment (described in relation to Figure 2) and vice-versa.

Claims

CLAIMS1. A method of filtering water for use in an aquaculture system, the method comprising: circulating a first water stream between a vessel and a non-biological filter; and selectively isolating the non-biological filter from the first water stream and circulating a second water stream between the non-biological filter and a biological filter.
2. A method of filtering water according to claim 1, comprising coupling the biological filter to the non-biological filter.
3. A method of filtering water according to claim 1 or 2, comprising coupling the biological filter in parallel with the non-biological filter.
4. A method of filtering water according to claim 1, 2 or 3, wherein the vessel is used to house fish.
5. A method of filtering water according to any preceding claim, further comprising heating at least one of the first and second water streams.
6. A method of filtering water according to any preceding claim, comprising circulating freshwater between the vessel and the non-biological filter via the first water stream.
7. A method of filtering water according to any of claims 1 to 5, comprising circulating saline water between the vessel and the non-biological filter via the first water stream.
8. A method of filtering water according to any of claims 1 to 5 or 7, comprising circulating seawater between the vessel and the non-biological filter via the first water stream.
9. A method of filtering water according to any preceding claim, wherein the second water stream is of higher salinity than the first water stream.
10. A method of filtering water according to any preceding claim, comprising selectively coupling the non-biological filter to the first and second water streams periodically to vary the salinity of the water passing through the non-biological filter.
11. A method of filtering water according to any preceding claim, further comprising the step of introducing chemicals into at least one of the vessel and the first water stream.
12. A method of filtering water according to any preceding claim, comprising introducing antibiotics or other medicinal products into at least one of the vessel and the first water stream.
13. A method of filtering water according to any preceding claim, further comprising the step of manipulating or maintaining the acidity of the water in the second water stream independently of the first stream.
14. A method of filtering water according to any preceding claim, further comprising the step of removing nitrogenous compounds from the biological filter.
15. A method of filtering water according to any preceding claim, further comprising the step of transforming nitrates in the biological filter into nitrogen gas.
16. A method of filtering water according to claim 15, further comprising the step of removing the produced nitrogen gas from the biological filter.
17. A method of filtering water according to any preceding claim, further comprising the step of removing at least one of solids and particulate matter from the first water stream.
18. A method of filtering water according to any preceding claim, further comprising the step of removing at least one of solids and particulate matter from the second water stream.
19. A method of filtering water according to any preceding claim, further comprising the step of introducing lipids into at least one of the vessel and the first water stream for removing taint-forming compounds from the system.
20. A method of filtering water according to claim 19, comprising introducing lipids into at least one of the vessel and the first water stream when the filtration system is non-operational.
21. A method of filtering water according to claim 19 or 20, comprising introducing lipids into at least one of the vessel and the first water stream when the filtration system is in operation.
22. A method of filtering water according to claim 19, 20 or 21, comprising introducing lipids to assist in the removal of geosmin and 2-Methylisoborneol from at least one of the vessel and the first water stream.
23. A method of filtering water according to any of claims 19 to 22, comprising introducing lipids into at least one of the vessel and the first water stream in a fluid state.
24. A method of filtering water according to any of claims 19 to 23, comprising removing the lipids from the system to remove the taint-forming compounds from the system.
25. A filtration system comprising: a first conduit for circulating a first water stream between a vessel and a non-biological filter; and a second conduit for circulating a second water stream between a biological filter and the non-biological filter, where the second conduit is iSolated from the first conduit.
26. A filtration system according to claim 25, further comprising a heater for maintaining the water temperature in at least one of the first and second water streams.
27. A filtration system according to claim 25 or 26, wherein the vessel is adapted to receive fresh water for housing freshwater species of fish
28. A filtration system according to claim 25 or 26, wherein the vessel is adapted to receive salt water for housing saltwater species of fish.
29. A filtration system according to claim 25 or 26, wherein the vessel is adapted to receive seawater.
30. A filtration system according to any of claims 25 to 29, further comprising a pH buffer for manipulating or maintaining the acidity of the water in the second water stream.
31. A filtration system according to any of claims 25 to 30, wherein the non-biological filter comprises a zeolite filter.
32. A filtration system according to any of claims 25 to 31, comprising a plurality of non-biological filters.
33. A filtration system according to any of claims 25 to 32, wherein the biological filter comprises an aerobic marine biological filter.
34. A filtration system according to any of claims 25 to 33, wherein the system comprises a plurality of biological filters.
35. A filtration system according to claim 34, wherein the biological filters are provided in parallel.
36. A filtration system according to any of claims 25 to 35, further comprising a filter for removing solids and/or particulate matter from the first water stream.
37. A filtration system according to claim 36, wherein the solids filter comprises a settlement tank filter.
38. A filtration system according to any of claims 25 to 37, further comprising a filter for removing solids and/or particulate matter from the second water stream.
39. A filtration system according to any of claims 25 to 38, further comprising a membrane comprising lipids for removing the taint-forming compounds from at least one of the vessel and the first water stream.
40. A filtration system according to any of claims 25 to 39, further comprising an agitator adapted to mix the lipids with the water in at least one of the vessel and the first water stream.41 An aquaculture system comprising a filtration system according to the second aspect of the invention.42. A method of filtering water for use in an aquaculture system, wherein removable lipids are introduced into the water to remove taint-forming compounds from the water.43. A water filtration system substantially as described herein and as shown in the accompanying Figures.44. A method of filtering water substantially as described herein.