NO346397B1 - A method for separating out fish sludge (faeces + pre-spill) from large hydraulic flows in accordance with breeding cages - Google Patents

Description

Patent application

Method and device for the enrichment of solid impurities from closed breeding cages.

The present application relates to a method for operating a closed rearing cage with tight walls and bottom for marine organisms, particularly fish, where water from a greater water depth is supplied at the upper part of the cage in a tangential direction to create a downward spiraling circular movement of the water mass through the cage and is withdrawn from the bottom of the cage, as the waste water is subjected to a separation of solid particles which are further processed, while a cleaner water fraction is led back to the free water mass at the cage, as stated in the introduction of claim 1.

There is also mention of a device at a cage for treating fish slime as stated in the introduction in device requirement 8.

The invention therefore relates to a new method and device for producing an enriched aqueous fish sludge from the bottom of a fish cage, where the enriched sludge is then subjected to cleaning treatment.

Fish sludge is a waste product from breeding cages, where the sludge includes faeces and feed residues (pellets) from fish that are kept and fed and which sinks into the body of water in a downward current towards an outlet at the bottom. In open cages, fish slime often flows with the water flow into the body of water outside the cage. Solid particles and sludge also sink to the bottom of the cage and are enriched in a funnel, as in closed cage systems.

With the present invention, it is thought that dead fish that sink down to the bottom of the cage are handled in a separate system for bringing them up for further processing on the surface.

A closed cage in the sea includes a tight canvas or a tank with rigid walls that can be both round, square or polygonal, as well as a tight bottom section, depending on the design, so that the mass of water inside the cage is separated from the water/sea outside. Closed cages are also arranged on land in the form of multi-shaped water tanks. Both of these designs, where waste water is taken out at the bottom, can be subjected to a water-waste treatment as according to the invention. The invention can also be used in connection with an open cage made of netting material where the bottom part comprises a funnel that collects downwardly sinking solid particles (fish slime).

In a closed cage, water is supplied (pumped) as a rule in or just below the water table in the surface, and preferably tangentially from several sides around the perimeter, so that the mass of water is set in a rotating spiral movement downwards towards the outlet at the bottom where it, together with sludge, is taken out for further treatment.

The water that is taken out at the bottom includes various waste substances such as faeces from the fish in the water body as well as uneaten feed pellets, as well as sinking dead fish, and this mix is sucked with a pump through a separate line to the surface.

During the treatment, various separation processes can be used which separate the solid substances such as dead fish and feed pellets, and a possible further enrichment of the sludge part so that faeces and other more or less solid particles (feed pellets) are separated. The purified water can usually be released back into the sea, possibly after further chemical water purification.

A disadvantage of the known solutions is that large quantities of water must be pumped up to the surface to be cleaned and then released back into the sea. New closed cages have become larger than before and hold larger volumes of water and thus a higher number of fish, accompanied by larger volumes of water that must circulate through the cage, be drawn upwards to the surface and cleaned and processed. Today, it is relevant for plants where the water flow can be up to 100,000 m<3 >per. hour

There is thus an increasing need for large hydraulic capacities (pump volumes) both to ensure sufficient oxygen supply to the fish in the cage, while at the same time getting rid of waste materials at a sufficient pace and in a form that ensures that there are no areas in the cage with long residence times for water. In such areas in the cage, a lack of oxygen can occur, which must be avoided. It is important that oxygen-rich water is supplied continuously, so that the oxygen is not used up without new addition. For flow-through plants which, for example, are to raise food fish or mail smolt, significant quantities of water are required to be circulated. One can imagine water flows in the order of 5,000 m<3>/hour and up to 100,000 m<3>/hour.

Regarding the state of the art, reference should be made to the following patent publications: German patent application DE 1990/9172, US patent applications US 2010/224136 and US 2006/102087 as well as to Japanese patent publication JP 2018/094543.

The former, DE 1990/9172, is perceived to represent the closest state of the art in relation to the present patent proposal. From here, it is known to carry out the cleaning of aqueous waste from the cage bottom by passing this through a hydrocyclone. The cage tanks according to the German patent are in a land-based facility and the various cleaning operations take place in units placed next to each other on a dry surface.

From the aforementioned publications, it is known to use various cleaning methods which include a cyclone, sedimentation and flotation, individually and in various combinations. However, no one combines as proposed in the present solution which, according to what follows, to place the hydrocyclone directly below the cage in the sea, where the cage outlet is fed directly into the cyclone inlet.

Disadvantage of the known technique.

Since it is most likely that in the long term it will not be permitted to release contaminated seawater into the water and sea, there is no way around this by having to use large energy resources to pump water to the surface in order to carry out a proper separation of solids and water purification.

In the future, when one has to operate with such large flows of water as mentioned above, it will require correspondingly large amounts of energy consumption to operate pumping plants to carry out the cleaning on the surface.

Purpose of the invention.

It is an aim of the invention to reduce the liquid flow that needs to be pumped up to the surface, to a volume level that is manageable in relation to what is found in treatment systems for sludge today, i.e. upwards limited to 200-300 m3/hour.

In continuation of this, there is an aim to reduce the energy consumption for pumping water.

It is also a purpose to be able to separate a cleaner portion of water from aqueous enriched fish sludge on the underside of the cage, without the need to pump up anything other than the particulate fish sludge.

Present invention.

The method according to the invention is characterized by the fact that the impure water that flows out at the bottom of the cage is led into and through a cyclone mounted in the bottom of the cage, and from which a heavier proportion of watery fish sludge is led out from the bottom of the cyclone for further handling on the surface, while a cleaner proportion of water is led out of the top section of the cyclone and into the water mass below the cage bottom. as stated in the characteristic in claim 1.

According to a preferred embodiment, aqueous enriched fish sludge is fed from the bottom of the cyclone through a hose to the surface for further treatment.

According to another preferred embodiment, aqueous enriched fish sludge is made to flow out of the bottom of the cyclone and into a separate buffer and sedimentation tank, from where enriched fish sludge is conveyed through the hose to the surface for further treatment.

Preferably, enriched fish sludge is pumped continuously or in batches from the buffer and sedimentation tank and upwards to the surface for further sludge cleaning.

It is particularly preferred that a portion of the water from the middle of the cage, which is leaner in terms of sludge content, is led from a central part of the cage at a distance above the cage bottom, directly downwards and out into the free water mass, while a second portion enriched with fish sludge at the bottom is led into the cyclone as indicated in the preceding claims 1-4.

According to yet another preferred embodiment of the method, a correct back pressure against the water flow is ensured by operating a pump, such as a propeller in the outlet so that the input speed is not too low and that the energy consumption is optimised.

Preferably, sinking dead fish are captured inside the cage in a separate system from which dead fish mixed with water are led through a separate hose/pipe upwards to the surface for further treatment, and optionally, dead fish are ground up and ensiled to form a storage-stable mass for further use.

The device according to the invention where a number of pipelines are arranged with inlets at a greater water depth and lead up to the upper part of the cage where the pipes are deflected and define tangentially directed outlets to create a spiral circular movement of the water mass down through the cage, is characterized by the outlet from the bottom of the cage is connected to the inlet of a hydrocyclone mounted in the bottom of the cage and the hydrocyclone includes a downwardly directed outlet for enriched watery fish sludge as well as an upper outlet for the outlet of the purified water portion to the free water mass outside/under the cage.

According to a preferred embodiment, the lower outlet from the cyclone is connected to a hose that leads up to the surface for further treatment of the accumulated aqueous enriched fish sludge.

The separator is thus a hydrocyclone with an inlet for the supply of impure water, a top outlet for cleaner water to the sea outside the cage and a bottom outlet for the enriched aqueous fish sludge portion.

Advantages of the invention.

A major advantage of the present invention is that you can use the energy that is already set up in the form of added water inside the cage. By directing this onto a separator in the bottom part of the cage, the particulate impurities (pellets-faeces) are separated together with an amount of liquid that is manageable compared to what is found in sludge treatment systems today, i.e. advantageously no more than 200-300 m<3>/ hour.

In relation to other methods, this invention thus makes it possible to allow significantly greater hydraulic capacity and thereby achieve a much higher water exchange in the cages, which in turn can enable better water quality and living conditions for the fish, and the biomass in the cage can be increased somewhat which again leading to improved operating margins. From an environmental point of view, the majority of the particles are removed, which also contain the majority of the phosphorus that is currently released from aquaculture facilities. The solid particles that cannot be captured with the cyclone are so small that they will follow into the water flow outside the cage without contaminating locally.

By using a hydrocyclone, which has no moving parts, and which has a high hydraulic capacity (just a matter of dimensioning), you want quickly after the fish have generated the sludge or quickly after the feed has been released into the cage and not eaten fish, separate this with the help of the cyclone so that the fish sludge has less residence time in the cage and thus dissolves to a lesser extent, which means that the clusters of particles will be easier to separate. All added water to the cage will pass just as quickly through the hydrocyclone at the bottom and thus all water is subjected to a purification. This is in contrast to alternative methods which are based on sedimentation and accumulation at the bottom of the cages.

The point of the present method is therefore that the water is made to rotate through the cage from top to bottom and continues in the same rotational movement into the top and inlet of the cyclone. A heavier portion of watery fish sludge is led out of the bottom of the cyclone for further processing, for example on the surface, while the cleaner water portion is led out of the top section of the cyclone and into the free water mass.

Consequently, none of the above-mentioned publications mentions such an arrangement of a herd cyclone for cleaning waste water from a closed cage. According to the closest technique set forth in the publication DE 1990/9172, the elements stand next to each other on a surface on land.

Background

The invention will be explained in more detail, with reference to the accompanying figures, in which.

Figures 1 show a vertical section of a cage with associated hydrocyclone connected at the bottom of the cage, as according to the invention.

Figure 2 shows a horizontal view along A-A in Figure 1 with the spiral water flow downwards through the cage, and the bottom outlet into the cyclone is situated in the center of the figure.

Figures 3 and 4 show respectively a vertical view and a perspective view of a hydrocyclone used according to the invention.

Figure 5 shows a horizontal view along B - B in Figure 1 of the rotating flow downwards through the hydrocyclone towards its outlet 34.

Figure 6 shows the design of a hydrocyclone with a buffer tank inserted below the cyclone as a buffer tank.

Figures 7.1 and 7.2 show, in vertical sections, 2 different conceptual solutions where the mass of water in the middle of the cage a little above the bottom can be led out to the mass of water outside, without being led through the cyclone.

Mention of preferred designs.

Figure 1 shows a vertical section of the invention, in the form of a farming cage 10 which floats upright in the sea 12 with its upper edge in the water surface 14, using suitable buoyancy bodies 16. The cage's walls 11 and bottom 13 are made of dense cloth and have a round shape downwards towards a bottom outlet 18 to which is connected a hydrocyclone 20 of known construction, see figure 4. A number of sensors 22 for measuring central parameters hang down into the sea/water mass 12 from the top of the cage. Hose for supplying feed is indicated at 23.

Water for the cage is fed into the upper part of the cage from greater water depths, such as from a depth of 20 meters, by means of a number of pipes 24 which are shown here running up the outside of the tight cage. The inlet to the cage is shown at 26 as the inlet nozzles are directed in a largely tangential direction into the mass of water 12 in the cage. Thus, a circulating spiral water flow is created and the water sinks downwards towards the outlet 18 and into the inlet 30 of the hydrocyclone 20 which is anchored to a bottom frame at the bottom of the cage 10. Dead fish that sink into the cage with the water flow are caught on a collection unit 17 comprising a grate, adjacent to the bottom outlet. Dead fish do not enter the hydrocyclone, but are taken out at the bottom from the unit 17 through a hose 19 to the surface for appropriate handling. Such handling could be that the dead fish is ensiled, which means that acid is added to watery ground fish mass to produce enzymatic breakdown in order to make the mixture storage-stable over a longer period of time.

In general, a hydrocyclone 20 as shown in Figures 3 and 4 is a filter or separation mechanism that uses centrifugal force to separate solids from liquids or liquids of different consistencies. It has a two-part chamber with an inner profile which is cylindrical 31 along its upper part and conically tapering 32 downwards along its lower half.

The hydrocyclone is provided with one entrance 33 and two exits 34 and 35 respectively. When the water sludge is led into the cyclone it rotates around the inside of the chamber and creates a centrifugal force which causes the solids to settle along the conical outer wall 32 and be separated from the water. Filtered, purified water is pushed upwards and out the upper outlet 35 into the free water mass 12 around the cage, while the portion of water enriched in solids is led out in the bottom 34. This flow pattern is shown in figures 3 and 5.

The aqueous enriched sludge from the bottom of the hydrocyclone 20 at 34 (Figure 3) can either be pumped directly up to the surface via a hose 37. However, it is preferred that the bottom sludge is collected in an underlying buffer tank 40, see Figures 1, 3, 4 and 6, which is again connected to the cleaning system on the surface with the hose 37. Thus, sludge can be pumped in batches instead of all the time up to the surface.

Two alternative designs are shown schematically in figures 7.1 and 7.2. For cases where really large amounts of water are to be circulated through the cage, for example up to 100,000 m<3>/h, the central body of water in the middle of the cage a little above the bottom is often already so depleted of sludge that it does not need to be cleaned through a hydrocyclone. In such cases, this volume of water can be continuously fed out to the water mass under the cage. For this, a wider, longer tube 50 with a larger diameter is mounted upright to the bottom structure of the cage. The pipe protrudes above the bottom 13 and into the body of water 12 inside the cage. Since the water in the middle of the cage has smaller amounts of mud and impurities than the mud mass that slides down along the inner wall, this water can be led directly out through the pipe to outside the cage.

A cyclone to clean all or part of the flowable water mass can be installed in many ways at the bottom of most aquaculture facilities constructed with dense fabric, flowable netting, steel and composite. The bottom section of the cage can also be designed so that a hydrocyclone unit can be easily mounted and detached from the bottom, and so that it can be lifted up to the surface inside the cage for necessary maintenance, while the cage can lie in the sea without being taken ashore.

With the invention, it has now been achieved that it is possible to remove a relatively small amount of sludge from large volumes of water.

Claims (1)

PATENT CLAIMS Requirements 1 Procedure for operating a closed rearing cage with tight walls and bottom for marine organisms, especially fish, where water from a greater water depth is supplied at the upper part of the cage in a tangential direction to create a downward spiraling circular movement of the water mass through the cage and is withdrawn from the bottom of the cage, as the waste water is subjected to a separation of solid particles which are further processed, while a cleaner water fraction is led back to the free water mass at the cage, characterized by the fact that the impure water that flows out at the bottom of the cage is led into and through a cyclone mounted in the bottom of the cage, and from which a heavier proportion of watery fish sludge is led out from the bottom of the cyclone for further handling on the surface, while a cleaner proportion of water is led out of the top section of the cyclone and into the water mass below the cage bottom. Requirement 2. Method in accordance with claim 1, characterized in that aqueous enriched fish sludge is led from the bottom of the cyclone through a hose to the surface for further treatment. Requirement 3. Method in accordance with claim 1, characterized in that aqueous enriched fish sludge is caused to flow out of the bottom of the cyclone and into a separate buffer and sedimentation tank, from which enriched fish sludge is carried through the hose to the surface for further treatment. Requirement 4. Method in accordance with claim 3, characterized by enriched fish sludge being pumped continuously or in batches from the buffer and sedimentation tank and upwards to the surface for further sludge cleaning. Requirement 5. Method in accordance with the preceding requirements, characterized in that a portion of the water from the middle of the cage, which is leaner in terms of sludge content, is led from a central part of the cage at a distance above the cage bottom, directly downwards and out into the free water mass, while a second portion enriched with fish slime at the bottom is led into the cyclone as according to claims 1-4. Requirement 6. Method in accordance with the preceding requirements, characterized in that a correct back pressure against the water flow is ensured when operating a pump, such as a propeller (5) in the outlet (35) so that the input speed is not too low and that the energy consumption is optimised. Claim 7. Method in accordance with the preceding requirements, characterized by sinking dead fish inside the cage being captured in a separate system from which dead fish mixed with water are led through a separate hose/pipe upwards to the surface for further treatment, and optionally ground up dead fish and ensiled to form a storage-stable mass for further use. Claim 8. Device at the outlet from the breeding cage for handling fish sludge as stated in claims 1-7, where a number of pipelines are arranged with inlets at a greater water depth and lead up to the upper part of the cage where the pipes are deflected and define tangentially directed outlets to create a spiral-shaped circular movement of the water mass down through the cage, characterized in that the outlet (18) from the bottom of the cage is connected to the inlet (33) of a hydrocyclone (20) mounted in the bottom of the cage and the hydrocyclone (20) comprises a downwardly directed outlet (34) for enriched aqueous fish sludge as well as an upper outlet (35) for the outlet of the purified water portion to the free water mass (12) outside/under the cage. Claim 9. Device in accordance with claim 8, characterized in that the lower outlet (34) from the cyclone is connected to a hose (37) which leads up to the surface for further treatment of the accumulated aqueous enriched fish sludge. Claim 10. Device in accordance with one of claims 8-9, characterized in that the lower outlet from the cyclone is connected to a sedimentation and buffer tank (40) which in turn is connected to a hose (37) which leads up to the surface for further treatment of fish sludge. Claim 11. Device in accordance with one of the preceding claims 8-10, characterized in that the bottom section of the cage comprises a channel (50) which forms a free connection between an area in the middle of the cage at a distance above the cage bottom and the free mass of water below the cage. Claim 12. Device in accordance with the preceding claims 8-11, characterized in that a separate hose/pipe to carry dead fish from the bottom of the cage upwards to the surface for further processing.