NO344634B1 - A displacement body system and method for supply of water to an onshore or offshore seafood farm - Google Patents

Description

The Technical Field of the Invention

The present invention relates to a system and a method for supply of water in particular to an onshore or marine or offshore floating aquaculture farm, wherein a closed water filled volume, such as a seafood tank or a cage, containing for example fish, is supplied with water from a water supplying source, supplying water from a water source in the vicinity of the aquaculture plant.

Background of the Invention

Seafood farming as per today is conducted either by highly polluting, static, open and usually circular shaped offshore cages, anchored to the seabed, requiring expensive sea/boat transport to and from the shore, or by onshore tanks where sea water is pumped into the plant with pumps dependent of expensive electricity and maintenance.

Pollution and bacterially infested water or water containing and spreading disease, parasites, such as salmon lice, has during the last years developed into a major problem. At the same time, there is an increasing focus on sustainable development of the aquaculture industry improving the fish welfare, inter alia by securing oxygen sufficiency in the water inside the aquaculture plant and preventing pollution to sea. There have been several attempts to develop techniques that will lower the production costs for onshore seafood farming (especially for salmon and trout), but so far nobody has succeeded.

It has also been proposed to arrange aquaculture plants onshore, for example associated with infrastructure such as roads, electrical power supply lines, water supply, and harbor facilities. There is a prejudice or at least large skepticism in the aquaculture industry against such solution, mainly because of:

- excessive energy requirements.

- there are several problems and large challenges associated with such type of plant, such as negative impact on the nature in the form of heavy construction work.

- added need for energy for supplying sea water into the onshore plant and following added cost.

- increase in biomass per volume in order to compensate for increased investment and to maintain level of profit. Such added biomass will according to the prevailing opinions in the industry also lead to increased risks for illness and lethality of the biomass.

- there also exits a skepticism relating to the large volumes of wastewater produced by such land-based plants.

- it is also believed that the investments for such land-based plants will be excessively high.

WO 1995/23259 relates to a sea water pipe system which comprises a sea pipe connected to an intake pipe at the onshore end and with inlet pipes at the offshore end. A grille is preferably secured over each inlet pipe to prevent solid matter from flowing into the sea pipe. As the incoming tide rises, seawater is drawn into intake pipe at tide level and flows into pond. A second pond is constructed adjacent pond to allow water to overflow from pond into pond. An outlet pipe may extend from pond to the sea with an outlet valve being used to prevent water from an incoming tide being drawn through outlet pipe into pond. The outlet valve may be opened at low tide to allow wastewater to drain from the ponds.

WO 2017/030445 relates to a method to displace water from a water filled, closed sea pen of sealed sea pen fabric. A grid shaped cage is positioned inside a volume of water inside a sea pen, and water is withdrawn from the sea cage through a pipe or hose, which is arranged inside the grid cage. In this manner, the sea pen fabric is squeezed up against the outside of the grid cage. An arrangement to displace and remove water from the water filled closed sea pen of water tight sea pen fabric is also provided.

US 9,380,766 relates to a recirculation aquaculture system configured for growing aquatic animals. The system includes an inlet conduit, a tank, a water treatment unit, a clarifier, and an outlet conduit. The tank is in fluid communication with the inlet conduit to receive water displaced from the inlet conduit. The tank also contains water and aquatic animals. The water treatment unit is arranged within the tank and includes algae capable removing aquatic animal waste from the water within the tank. The clarifier is in fluid communication with the tank to receive displaced water from the tank. The clarifier is also configured to remove solid waste from the displaced water. The outlet conduit is in fluid communication between the clarifier and the inlet conduit.

DE 10-2006/041405 relates to a process of treating water, wherein treatment water in a biotope zone by interaction with organisms undergoes a first treatment step and in a soil filter zone by intermittent flow through a porous substrate bottom of at least one bottom filter pool a second treatment step, characterized in that macro algae and/or mussels are used as organisms, which are fastened to support elements which substantially completely pass through a flow region of the treatment water perpendicular to the flow direction and in that the soil filter zone upstream or downstream of the biotope zone comprises a plurality soil filter basins, which are fed intermittently with the treatment water out of phase, wherein a total flow through the habitat zone is kept substantially constant.

Summary of the Invention

The principle relied on according to the present invention is the incompressible properties of water and use of gravity to lift water up from one level to a higher level.

It is an object of the invention to lift water in a continuing cyclic or discontinuous process by a displacing body, movably arranged and lowered into, or lifted up from a defined water filled volume in a resulting vertical direction. It is the lifting height being determined the height of the volume while the volume of water lifted in a sequence being governed by the difference in volume between the defined water filled volume and the volume of a displacing body lowered into or lifted from the defined volume of water. The volume of the movably arranged displacement body is smaller than the volume of the defined volume of water.

According to the present invention, “a defined volume of water” may for example be a tank, container, or a basin, hereinafter named “defined volume of water”.

“Resulting vertical direction” means either vertical movement or movement in an inclined direction out of or into the volume of the body of water.

“Continuous” used herein means repeated lowering and lifting the displacing body into or out of the defined volume of body in a continuous and repeating cycles.

Another object of the present invention is to transfer water from a lower level to a higher level and into an aquaculture plant, so as to provide a secure supply of oxygen rich water to the plant, free of any contamination.

Yet another object of the present invention is to provide a plant where a negative effect on the environment is eliminated, enabling removal of detrimental substances in a sustainable manner.

Another object of the invention is to provide a plant where as much energy as possible, supplied to the plant for lifting the water, is recovered.

Yet another object of the invention is to provide a system where the feces, pollutions, surplus food, and dead fish may be removed and taken care of in a closed system without polluting the sea.

Yet another object of the present invention is to provide an aquaculture plant and a method for providing full control of the water supplied to the plant and discharged from the plant, avoiding contaminating the plant with detrimental living organisms and enabling removal of pollution from the water discharged to the environment.

A further object of the present invention is to provide an improved aquaculture plant, for example for salmon, preventing, or at least substantially reducing the risk for supplying lice and other possible organisms (and/or polluted water with negative effects) infested water to the aquaculture plant.

Yet another object of the present invention is to produce 100% or as much as possible of electrical energy needed for the entire operation of the invention through/via an integrated aqua plant/water turbine producing such electricity which should be located downstream from the outlet in the bottom of each seafood tank. According to international calculation standards, the following formula may be suited for each seafood farm using present invention and constructed for the purpose of optimum result for creation of electricity:

Mass of water flow (kg) x gravitation (9,807 m/s²) x water fall height (m) x

turbine effect 0.86 = kw

Yet another object of the invention is to provide an improved way to replace the water in the onshore aquaculture plant in an efficient and more or less continuous manner, and still maintain strict control on the pollution created by the farming activity, such as removal of feces, surplus of feedings and dead organisms.

Yet another object of the invention is to prevent or at least substantially reduce the possibility of fish escaping from the plant, eliminating or at least substantially preventing lice and other possible organisms and/or polluted water with negative effect from entering the plant and reduced impact on the surrounding environment.

Yet another object is to provide a closed aquaculture system that may operate floating in the fjord or offshore where seawater is supplied to the system and where the system is configured to secure that no infested water is drawn into the plant and no pollution is allowed to escape to the surroundings. In order to recover as much energy from such plant, the bottom of the cage(s) should be at a level above the sea level and a generator should be included in the outlet pipe system at the bottom of the cage(s).

Yet another object of the invention is to eliminate or at least substantially reduce the risk for spreading detrimental organisms or polluting the environments with feaces and/or surplus food. Moreover, such object also includes obtaining the possibility of having control both with respect to the quality and suitability of water entering the system from the neighbourhood or leaving the plant to the surrounding.

According to the present invention the objects are achieved by a system and a method as further defined by the independent claims, while embodiments, variants or alternatives are defined by the dependent claims.

The system according to the present invention comprises a seafood tank, configured the serve as a cage for the marine organisms to be cultured. Such organisms may be salmon and/or any other type pf aquaculture sea food. Cleaned or filtered water, free of pollution and/or detrimental organisms is supplied to the seafood tank from a nearby water source. Moreover, the system comprises a chamber or a defined volume; a displacing body or volume configured to be lowered down into and lifted out of the chamber or the defined volume; a one way inlet valve connecting the chamber to the water source, controlling the inlet flow of water into the chamber of defined volume; and a chamber outlet connecting the chamber to the seafood tank, allowing flow of water from the chamber into the tank.

According to one embodiment of the system, the density of the displacing volume may preferably be in the range from 1 g/cm<3>s-3 g/cm<3>.

The shape of the displacing body may be complementary to the shape of the chamber. Moreover, the volume of the displacing body may correspond to the volume of the chamber.

According to an embodiment of the invention, the tank may be provided with a tank outflow channel, to which an electrical generator is connected using the exit water head as a driving source for producing and regaining energy from the water discharged from the cage.

The inlet valve applied may be a one-way valve, preventing water to flow back from the chamber into the water source. Such inlet valve may for example be a check valve, gate valve, ball valve or similar.

According to an embodiment, the chamber outlet may be an open channel extending a slanted downwards from the top of the chamber towards the top of the cage, allowing mixing the water as much as possible with oxygen from the air, allowing water to cascade down into the cage, i.e. oxygenizing the water as much as possible. At the end of the duct, the duct may be provided with means preventing water to be blown away due to the appearance of strong wind or wind gusts.

According to the invention, the displacing body may be raised and lowered along an inclined track. The displacing body and/or the complimentary wall(s) of the chamber may be provided with guiding devices and/or devices reducing possible friction between two adjacent surfaces. Such friction reducing devices may be rails, wheels, rollers or surface material producing reduced friction.

According to the present invention, a method for use of a system for water circulation in an onshore or off-shore or floating seafood farm is provided for supplying water from a connecting water source, comprising connecting a chamber containing a movable displacing body to a water source by means of a duct or pipeline system incorporating a one way valve, the duct having an inlet at the lower end of the chamber, connecting the upper end of the chamber with a cage for breeding marine organisms by means of an outlet duct, the method further comprising the steps of:

- opening an inlet valve of the chamber;

- filling the chamber with water, preferably to the same water level as the water source;

- closing the inlet valve of the chamber;

- lowering the displacing body into the chamber;

- directing a flow of displaced water through the chamber outlet; and - raising the displacing body out of the chamber for a new cycle.

The water source may be a lake, a river, a fjord, the sea in the close vicinity of the aqua plant

According to the invention, the lifting or supply of water may be a continuous cyclic process, i.e. supplying water to the cage in a continuous manner and allow water to be drained more or less simultaneously from the cage, for example also transporting out sediments produced. Alternatively, the lifting or supplying process may be a discontinued process, i.e. filling the cage, suspending the filling and after a predefined tie interval draining water from the cage and starting simultaneously up the water supplying process. The plant may for this purpose be supplied with oxygen measuring devices and/or water level measuring device, activating the water lifting process when too low oxygen content or too low water level in the cage is identified.

Even if only one cage is described, it should be noted that the plant may include a number of cages, assembled to a multi cage plant.

The maximum lifting height of the system is dependent of the height of the displacing body used. If the lifting height for a unit is limited for various reasons, two or more units may be used, the first unit lifting water to the second unit and so forth.

In the land-based plant, the water is lifted to a height, allowing used, but cleaned and filtered water to flow back to the sea due to gravity.

Brief Description of the Figures

The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an embodiment of the invention given with reference to the accompanying drawings.

In the following, embodiments of the present invention shall be described in more details, referring to the drawings, wherein:

Figure 1 shows schematically and in principle an embodiment of a land based aqua culture plant;

Figure 2a shows schematically, in a simplified manner, and in principle an embodiment of a marine, floating aquaculture plant where the cages are arranged on a floating barge 26, while Figure 2b shows schematically and in a simplified manner an embodiment according to the invention where the cages are floating on the sea level;

Figure 3 shows schematically a first step supplying water from a water reservoir or a water source to a closed cage;

Figure 4 shows schematically the next step where water is supplied to a chamber for subsequent transport to the closed cage;

Figure 5 shows schematically the step where a displacing body is forced down into the chamber for raising or lifting the water up to the closed cage;

Figure 6 shows schematically the first step in the next cycle for supplying more water to the closed cage;

Figure 7 shows schematically and party in perspective a section through the device supplying water to the closed cage;

Figure 8 to 10 show the system from another sides indicating schematically the closed cage; the system for transferring lifted water from the chamber to the closed cage; and the system for draining water and solids from the closed cage in a controlled manner;

Figure 11 shows an alternative embodiment where water is supplied into the chamber through its bottom;

Figure 12 shows an alternative embodiment where the water supplied, and the water drained are used for producing electricity; and

Figures 13 (a) - (d) show side views of displacing bodies having different inclined skewed surfaces.

Detailed Description of the Embodiments disclosed in the Drawings

Various aspects of the disclosure are described more fully hereinafter with reference to accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure intended to cover such an apparatus or method which in practices are using either structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.

The Figures depicts in a schematically way, the water source, the system for lifting water from the water source 12 to the closed cage 11 and a closed cage. According to the embodiments shown, the lifting device and the closed cage 11 are depicted as an integrated unit. It should be noted, however that the lifting device may be in the form of an independent unit, distanced more or less apart from the closed cage 11, the water being conveyed in hoses or ducts.

The lifting unit may be associated with any water source as in a fjord, open seawaters, natural lakes or ponds, as well as any manmade artificial water sources, such as lakes and ponds, while the closed cage is situated onshore. Alternatively, the lifting unit may be positioned on a barge or in other ways associated with a traditional floating aquaculture plant in any fresh or sea/salt water marine environment, the lifting unit delivering water to closed cages. The Figures shows schematically a principle layout of the invention, indicating the various water levels and the device for lifting water up from one level to another. According to the present invention, a closed aquaculture plant 10 is provided, comprising a number of closed cages 11 configured to be filled with water for cultivating aqueous organisms such as for example salmon. The plant 10 may preferably be built onshore in association with a water reservoir or a water source 12. Alternatively, the plant may be installed on a floating body (not shown), such as a barge. If the supplied water is seawater the intake should be provided with a filtering device, in order to prevent intrusion of detrimental organisms such as fish lice or salmon lice into the water supplied to the cage(s) 11. Moreover, the system comprises a chamber 13 or chambers 13 in series in water communication with the water source 12 through an inlet line 14. A one-way valve or a check valve (not shown) is installed in the inlet line 14, the one-way valve being of a type only allowing water to flow in one direction from the water source 12 to the chamber or cage 13.

Figure 1 shows schematically and in principle a land based aqua culture plant A, where a water lifting device 15 lifts water from the sea B and lifting the water to a closed cage system comprising several cages 11, of which only one cage 11 is shown. Embodiments of the device for lifting C the water will be described in further details below, referring to the Figures 3 to 11. According to the embodiment shown, two lifting devices C are shown, working in series. Moreover, the drain line 23 from the cage 11 is directed to a filtering or separation 29 where feces etc. and water is separated and where filtered water is directed through an exit line 28 to the sea B. A generator 25 is arranged at the outlet region of the exit line 28 just above sea level, the water entering the sea through an exit 27. In this way energy from the water head is recovered.

Figure 2a shows schematically, in a simplified manner, and in principle an embodiment of a marine, floating aquaculture plant 10 where the closed cages 11 (only one shown) are arranged on a floating barge 26. In principle the same functions as discussed above are included, i.e. closed cages 11, a water supplying device 13,15 with a deep water inlet line 24 and a discharge line at the top, supplying the displaced water to the closed cage 11. Other elements described below in respect to the Figures 3 to 13 may also be incorporated. According to the embodiment shown in Figure 2a, energy may be recovered by use of a turbine system 25’ as further discussed below. Details of to the cage 11 as such are not shown, since such details are of conventional nature and form no part of the invention. As indicated, water to the lifting device 13,15 is drawn from a depth exceeding the depth of the surrounding water source B’ where lice are not expected to be. Water is supplied continuously to the cages in the same way as in the onshore embodiment, described above and further detailed below for supply of more oxygen containing water as well as creating necessary water circulation to the closed cage. Moreover, feces and food surplus being filtered and collected according to this embodiment, similar to the onshore embodiment described herein.

Figure 2b shows schematically and in a simplified manner an embodiment according to the invention where the cages 11 are floating on the sea level. The Figure shows schematically and in principle a floating aqua culture offshore plant A’ comprising a cage configuration consisting of a number of closed cages 11, of which only one is shown. This embodiment of the plant is arranged with cages floating on the sea level. For such embodiment it is not possible to regain energy, since the supplied water, including feces and the like have to be pumped out of the cage(s).

Figures 3 to 6 relates to an aqua culture plant A, for example for breed salmon. The Figures show only one closed cage 11. It should be noted, however, that the aquaculture plant 10 may comprise a number of closed cages, for example configured in any well-known manner with respect to each other. For simplicity, only one closed cage is shown and the system for supplying water to the closed cage is shown in a simplified manner. It should also be noted that the closed cage may either be a tank resting on ground or a closed cage floating in water.

Figure 3 shows schematically a first step supplying water from a water reservoir or a water source 12 to a closed cage 11. In order to lift the water a displacing body 15 is used. The displacing body 15 is movably arranged in a vertical chamber 13. The displacing body 15 is provided with at least one inclined surface in order to reduce the energy required for moving the displacing body 15 vertically. The remaining three sides of the displacing body 15 may have vertical walls. The displacing body 15 is movably arranged in general vertical direction in the chamber 13 and the shape and dimensions of the chamber 13 are complementary to the shape and dimensions of the displacing body 15. The dimensions of the displacing body 15 are smaller than that of the chamber 13, providing a smaller, unobstructed volume, allowing displaced water to be forced upwards towards the top of the chamber. According to the embodiment depicted, the displacing body 15 may be provided with wheels (not shown or rails, arranged in vertical direction on the skewed surface of the displacing body. Alternatively, the corresponding skewed surface of the chamber wall may be provided with rails 18 or wheels. Instead of rails and/or wheels, other types of remedies may be used for reducing the friction action on the system, such as for example use of a vertical, preferably centrally arranged guide arranged in the chamber 13 and where the displacing boy 15 provided with a corresponding complimentary vertical hole.

At the end of the chamber 13, the chamber 13 is provided with an inlet duct or line 14 in fluid communication with the water source 12. A controllable valve, preferably a one-way valve or check valve 20 is arranged in the inlet duct or line 14. At the upper end of the chamber 13, a chamber outlet duct 19 or other types of communication means is arranged, securing that the water lifted up by the downwards movement of the displacing body 15. The movement upwards and downwards may be powered by a motor 25 (ref. Figure 12) and suitable traction devices (not shown).

In order to enable water to be transported from the water source 12 to the closed cage 11, the valve 20 in the duct 14 is opened, allowing water from the water source 12 to flow into the lower part of the chamber 15. The inlet line or duct 14 is positioned at such depth in respect to the water level of the water source that water will partly fill the chamber 13. During this stage the displacing body is in its upper, elevated position as indicated in Figure 3.

When the water surface inside the chamber 13 is at the same level as the water surface of the water source 12, the one-way valve is closed, whereupon the displacing body 15 is lowered down towards the bottom of the chamber 13, sliding with its skewed surface 17 in contact with the corresponding skewed surface wall of the chamber. When the displacing body 15 is lowered down through the water surface towards the bottom of the chamber 13, the displacing body 15 will occupy larger and larger part of the volume of the chamber, displacing and pressing the water upwards until it is allowed to enter the upper duct and flow into the closed cage 11. If a check valve is used in the duct 14, the valve is configured to close once a small over pressure is established in the water at the lower part of the chamber 13, closing the valve, this preventing the water to be pressed back into the water source through the inlet line or duct 14.

In order to move the displacing body 15 up or down, the displacing body 15 is associated with a lifting and lowering mechanism (not shown). The displacing body 15 and the corresponding adjacent side walls of the chamber or tank 13 may be provided with complimentary guiding devices (not shown), allowing as frictionless relative movement as possible.

When the displacing body 15 is forced completely down, substantially all the water present in the lower part of the chamber 13 at the initial stage of the cycle will be displaced upwards and lifted into the closed cage 11. This stage of the cycle is shown in Figure 5.

The valve 20 in the inlet line or duct 14 may now be open as the displacing body 15 is lifted up again, for example due to the external water pressure from the water column in the water source 12, forcing water through the duct 14, the valve 20 and into the lower part of the chamber 13, and once again allowing the water surface inside the chamber 13 to level out with the water surface of the water source 12. The displacing body 15 will now be lifted to a height just above the referenced water surface inside the chamber 13 as indicated in Figure 6, and the cycle may be repeated.

Figure 7 shows schematically and party in perspective a section through the device supplying water to the closed cage, seen from the opposite side of the skewed surfaces, while Figure 8 shows the unit seen from the opposite side. As indicated a chamber outlet duct 19 is arranged at the upper end of the unit, allowing the water lifted up by the displacing body 15 to flow to the closed cage 11. As shown in Figure 8, the closed cage 11 is provided with a drain 21 with a valve 22 and a drain line 23 for draining water and surplus food, feces and other solid particles when and if required. Figures 9 and 10 show the system from yet another sides indicating schematically the closed cage; the system for transferring lifted water from the chamber 13 to the closed cage; and the system for draining water and solids from the closed cage in a controlled manner.

Figure 11 shows an alternative embodiment where water is supplied into the chamber 13 through its bottom by means of a pipe taking water from a water depth in sea and/or fresh water free of any lice or other detrimental marine pollution and/or organisms. A valve 20 is arranged in the deep water inlet pipe 24, functioning in the same manner as the valve 20 described above in relation to the embodiment shown in Figures 3-7. In such case the bottom surface of the chamber 13 or the inlet opening should be arranged at a level below the external sea level to secure required and sufficient filling of the chamber 13.

Figure 12 shows an alternative embodiment where the water flow supplied through the chamber outlet duct 19 at the top of the chamber 13 and/or the water drained from the closed cage may serve as a source for producing electricity through an aqua plant turbine or generator system 25’ associated with the duct system 19, drain line 23. The electricity created by such aqua plant turbine 25’ is available to give the whole system either 100% or partially enough electricity for its operation and thus lower the operational costs.The water's path from the source / seafood tank and down to the level of the water turbine/aqua plant turbine represents position energy that can be obtained under the law:

mass (kg) x gravity (9,807 m / s²) x fall height (m) x turbine effect (0.86) = kw

The water source 12 may be the sea, a fjord, a lake, a river or any other suitable source of liquid required by the operator depending of what is intended or needed for production. If the aqueous organism is salmon above the smolt stage, the water source should preferably be seawater. The inlet 14 may be provided with a filter system or for example fine mesh net or nets of any desired size, shape and format as for example bio filters with mesh smaller than the size of lice, thus preventing lice or any other small organisms and/or pollution to come into the chamber 13.

Figures 13(a)-(d) show side views of displacing bodies having different inclined skewed surfaces. As indicated above, the purpose of the skewed surface is to reduce the friction imposed by the sliding contact between the skewed vertical surface in the chamber 13 and the complimentary skewed surface on the displacing body 15. By using rails/wheels or a roller system the imposed friction may be reduced or minimized. The various angles indicated vary between 55 ° (the leanest angle) to 73 ° (the steepest angle). The ideal angle of the skewed surface is considered to depend on effect of the motor used to pull the displacing body in upwards direction together with other factors such as the size of the chamber. The ideal angle of the skewed surface 17 (a) - (d) is considered to depend on effect of any applying factors as i.e. gravity forces on displacing body/proper volume of the displacing body, friction between moving/dynamic and static materials, construction materials used etc. in addition to the motor and/or any available source with any kind of supply power used to pull the displacing body in upwards direction together with other factors such as the size of the chamber 13.

The ideal angle of the skewed surface 17 (a) - (d) is to be proven and tested for each operator’s needs for this system as this can vary according to many individual factors. The water lifted may be discharged at a height above the design water level in the closed cage, so that a water cascade is formed, drawing additional air into the water in the cage.

In order to secure a constant water level inside the closed cage, the outlet from the cage is provided with a valve, allowing the water level inside the cage to be controlled. When opened, water and sediments, i.e. for example surplus of food, will be drained from the cage, for example to a collecting tank where the water is cleaned, and the sediments separated. The sediments may be drawn out together with the water, possibly assisted by means of a removing device arranged at the bottom of the cage, bringing the sediments towards the outlet.

A preferred feature of the present invention is to configure the walls of the chamber 13 and/or the outer surfaces of the displacing body 15 in a way reducing the resistance against downwards movement of the displacing body 15 due to increasing pressure and because of the water being incompressible. Such effect may be obtained by allowing the shape and volume of the displacing body 15 to be slightly smaller than that of the chamber 13. Alternatively or in addition, the displacing body 15 and/or the walls of the chamber 13 may be provided with recesses or ducts extending upwards along the entire length of the chamber wall(s) and/or one or more side walls of the displacing body 15, enabling water to escape out of the chamber 13 more or less without any pressure, when the displacing body 15 is lowered down into the chamber 13. Such recesses/ducts may be inclined or vertical and at the upper end connected to a water-guiding duct securing that the water lifted up is directed towards the outlet at the top of the chamber 13.

Claims (9)

1. Claims

   1 A system for supply of water in a seafood farm, wherein a closed cage (11) is supplied with water from a water source (12)

   c h a r a c t e r i z e d i n that the system comprises

   - a chamber (13),

   - a displacing body (15) adapted to be lowered into and raised out of the chamber (13),

   - an inlet (14) with valve (20) connecting the chamber (13) to the water source (12), controlling the inlet flow of water, the valve (20) being a one way valve; and - a chamber outlet duct (19) connecting the chamber (13) to the closed cage (11).
2. 2 A system according to claim 1, wherein the density of the displacing body (15) is in the range from 1 g/cm<3>- 3 g/cm<3>.
3. 3. A system according to claim 1 or 2, wherein the shape and dimensions of the displacing body (15) is complementary to the shape and dimensions of the chamber (13).
4. 4. A system according to one of the claims 1 to 3, wherein the volume of the displacing body (15) corresponds to the volume of the chamber (13).
5. 5. A system according to one of the claims 1 to 4, wherein the tank (11) has a drain (21) to which a turbine system (25’) is connected for production of electricity.
6. 6. A system according to one of the claims 1 to 5, wherein the inlet valve (20) is a check valve, gate valve or ball valve.
7. 7. A system according to one of the claims 1 to 6, wherein the chamber outlet duct (19) is an open channel extending between the chamber (13) and the water level of the tank (11).
8. 8. A system according to one of the claims 1 to 7, wherein the displacing body (15) is raised and lowered along an inclined track (18).
9. 9. A method for water circulation in an onshore or offshore seafood farm according to any of the preceding claims, wherein a seafood tank (11) is supplied with water from a connecting water source (12)

   c h a r a c t e r i z e d i n that the system further comprises

   - a chamber (13),

   - a displacing body (15) adapted to be lowered and raised in the chamber (13), - an inlet valve (20) connecting the chamber (13) to the water source (12), and - a chamber outlet duct (19) connecting the chamber to the tank (11), which method comprising at least the steps of:

   - opening an inlet valve (20) of the chamber (13);

   - filling the chamber (13) with water, preferably to a same water level as the water source (12);

   - shutting the inlet valve (20) of the chamber (13);

   - lowering the displacing body (15) into the chamber (13);

   - directing a flow of displaced water through the chamber outlet duct (19); and

   raising the displacing body (15) out of the chamber (13).