GB2563996A

GB2563996A - System for selective waste removal from aquaculture unit

Info

Publication number: GB2563996A
Application number: GB1807564.8A
Authority: GB
Inventors: Heffernan Liam
Original assignee: Lift Up As
Current assignee: Lift Up As
Priority date: 2017-05-11
Filing date: 2018-05-09
Publication date: 2019-01-02
Anticipated expiration: 2038-05-09
Also published as: GB201807564D0; NO20170781A1; CL2018001290A1; NO342765B1; CA3004215A1; GB2563996B

Abstract

A collection device 6 for collecting sludge such as sunken particulate waste and sunken farm organisms such as dead fish from an aquaculture cultivation unit 1 positioned in a body of water. The collection device 6 comprises a collection head 10 at the bottom of the cultivation unit 1 for collection of sunken sludge and sunken farmed organisms. The collection head 10 comprises a funnel formed top plate 20 wherein the sunken sludge and organisms are collected in or in vicinity to the lowest point of the funnel. A first removal system (40, Fig 6) for sunken sludge, having a first inlet (42, Fig 7) for sludge and small particles at the lowest point of the funnel formed top plate 20. The first inlet 42 being provided with a retaining system 45 for holding back farmed organisms and in that the first removal system further comprises a first pumping system for removal of said sunken sludge from the first inlet 42. A second removal system 60 for sunken farmed organisms accumulated on the top plate 20 and a second pumping system for removal of the sunken organisms from the top plate 20.

Description

SYSTEM FOR SELECTIVE WASTE REMOVAL FROM AN AQUACULTURE UNIT

Field of invention

The present invention relates to a collection device for collecting sludge such as sunken particulate waste and for collection of sunken farmed organisms such as dead fish from an aquaculture cultivation unit positioned in a body of water. The present invention also relates to a use of said device for collection and removal of waste. Furthermore, the present invention relates to a method for collection and removal of waste from an aquaculture cultivation unit positioned in a body of water.

Background of the invention

The annual production of salmonids in Norway was about 1.3 millions tons in 2012, 99 % being Atlantic salmon and trout. The production of salmon is at present mainly based on cage aquaculture in the sea, where salmon are cultivated in large net pen units. The intensive production entails different forms of waste produced during the production process such as dead fish (also referred to as “morts”), faeces, unconsumed feed etc. Even though often only recognized as waste, and a potential environmental threat, the discharges from sea farms also represent a largely unexploited, potentially valuable source for nutrients.

The nutrient components deriving from salmon cage systems during production of salmon can generally be divided into dissolved inorganic nutrients, dissolved organic nutrients and particulate nutrients. Dissolved inorganic nutrients such as ammonium and phosphate, are immediately taken up and consumed by phytoplankton or macro algae in the body of water. Dissolved organic nutrients comprise dissolved organic nitrogen and phosphorus, consisting of molecular nutrient components forming complex chemical compounds from feces and feed. These dissolved organic nutrients may be consumed by bacteria, thereby entering the microbial food web or they may aggregate to sink as “marine snow” in slow processes to the sediment.

The particulate nutrients, including particulate organic nitrogen and phosphorus, typically originate from feed pellets, small particles from feed and faeces as well as other particles from fouling on the cage.

Smaller particles deriving from intensive sea based aquaculture are typically suspended in the water column where they are consumed by filter feeders and bacteria within days. Larger particles from aquaculture systems are either consumed by the fish or if not collected these particles sink rapidly to the sea floor where they accumulate in the sediments. When collected or accumulated the sunken particles appear as sludge.

In a study carried out in 2009, the Norwegian salmon industry used about 1 173 000 tons feed in intensive production of salmon. About 3 % of this feed was not consumed by the fish and represent feed losses discharged as waste from the farms. Based on a carbon budget analysis, 30 % of the feed is going to fish biomass and 48% to respiration, while 19 % of the feed is faeces discharged as waste to the body of water. Feed losses, faeces, and other organic waste are mainly discharged as particles which sink down and accumulate on the sea bottom in the sediments if not collected. Discharged in these significant amounts during intensive production in net cages, the particulate waste is not only affecting the environment in vicinity to fish farms, but also represent a significant loss of biomass and nutrients which may be used for other purposes. For a later use of the sludge e.g. as a fertilizer, a high quality of the sludge product is necessary but also low costs for necessary treatments to make its use economically feasible. This is not achieved with the methods for collection and treatment of the sludge known today.

In order to reduce problems with diseases and parasites, in particular salmon lice, as well as escapes from net cage farms, different types of closed sea-based cultivation units have recently been developed and tested. These closed systems are typically more or less water tight cultivation units, e.g. made of tarpaulin, plastic, concrete or the like, which are used in stead of nets. Water is pumped into these containers to supply the fish with fresh water and oxygen. Particulate sunken waste such as faeces and feed losses are typically removed at the bottom of the closed cultivation unit together with the effluent water.

Today, combined waste collection and suction systems for sunken waste such as for dead fish (also referred to as “morts”) and larger particles (unconsumed feed pellets and faeces) are in use for fish farm cages. These systems are often referred to as “mort collection systems” by the industry as their main purpose is to remove dead fish from the cage. A well known system, being in use in many salmon farms, is a collection head where dead fish are collected in a funnel formed head at the bottom of the cage and sucked up to the surface once per day using an air lifting pump system (also called mammoth pump system). NO335174 B1 discloses such a type of collection head typically used in salmon aquaculture. The disadvantage of this known system is that high amounts of water have to be used to lift the fish up from the bottom and that a subsequent separation of the different types of waste, i.e. dead fish and sludge, is ineffective and laborious. NO339302 B1 discloses a waste collection system for collecting sunken waste using a sucking head placed in the bottom of a sea cage. The system does not open for a separate lifting up of sludge and fish. NO329813 B1 disclose a system for collection of dead fish from the bottom of a sea cage, having a funnel formed collection device arranged at the bottom of the cage and a hose for sucking up the fish. Neither this system allows to remove sludge and fish separately.

Thus, there is a need for a universal and flexible collection and handling system of waste, in particular of particulate organic waste such as faeces and feed losses from intensive sea-based aquaculture production such as from salmon farming in net cages.

Summary of the invention

An object of the present invention is to overcome the problems and disadvantages described above. In more detail, the present invention aims at providing an effective system and a method for reducing the discharge of waste from water-based fish farming systems and an improved system for collecting and handling of waste. In particular, it is an object of the present invention to provide a system and a method for collection and handling of sludge, feed remnants, and other small particulate organic and inorganic waste from aquaculture production.

Another object of the present invention is to provide a universal waste collection system suitable for both open and closed farms systems placed in the sea.

Another object of the present invention is to provide a system where both small particulated waste from feed and faeces as well as dead fish can be effectively collected, removed, and handled in the same device without affecting or disturbing the farmed fish.

Yet, another object of the present invention is to provide such a combined system which is optimized in respect to the need of water for pumping and waste water treatment thereafter.

Yet another object of the present invention is provide a robust and flexible waste collection system which is easy to install, remove, and adapt for different needs of waste collection.

Yet another object of the present invention is to obtain an improved sludge product suitable for further use.

In particular, it is an object to provide a waste collection system which is suitable/adaptable for use with fish of different size such as smolt and on-grown salmon.

The objects are achieved by a solution as defined in the independent claims, while the dependent claims represent preferred embodiments.

Thus, in a first aspect the present invention relates to a collection device for collecting sludge such as sunken particulate waste and sunken farmed organisms such as dead fish from an aquaculture cultivation unit positioned in a body of water. The device comprises - a collection head at the bottom of the cultivation unit for collection of sunken sludge and sunken farmed organisms, the collection head comprises a funnel formed top plate wherein the sunken sludge and organisms are collected in or in vicinity to the lowest point of the funnel, - a first removal system for sunken sludge, having a first inlet for sludge and small particles at the lowest point of the funnel-formed top plate, the first inlet being provided with a retaining system for holding back the farmed organisms, and in that the first removal system further comprises a first pumping system for removal of said sunken sludge from the first inlet, - a second removal system for sunken farmed organisms accumulated on the top plate and a second pumping system for removal of the sunken organisms from the top plate.

The first and/or second pumping system can be an airlifting pump suitable to transport the sludge and/or the organisms to the water surface.

The retaining system can comprise a locking element covering at least the first inlet located in the funnel formed top plate and leaving at least one opening for sludge discharge, said opening being smaller than the farmed organisms.

Preferably, the locking element is a locking disk.

The opening can be in form of a circumferential slot between the lower end of the locking element and an upper edge of the first inlet.

The one or more openings/slots of the first inlet can be adjusted in size and/or closed.

Preferably, a conduit is connected to the first inlet at the funnel formed top plate, the conduit being located inside the collection head and extending in a U-form from the first inlet a distance down into a bottom part of the collection head and further up to at least the upper surface of the top plate.

The second removal system can be arranged in a center area on the funnel-formed top plate in close vicinity to the first removal system, wherein the organisms are preferably removed sideways/upwards from the funnel-formed top plate.

The second removal system preferably comprises - a housing which is arranged on the top plate and has a second inlet for organisms on one side, the second inlet facing towards the center of the funnel-formed top plate, - a passage through the housing, and - an outlet on the top of the housing.

In a second aspect, the present invention relates to a method for collection and removal of waste from an aquaculture cultivation unit positioned in a body of water. The method uses a device according to any of the preceding paragraphs and comprises the following steps: - collecting sinking sludge on the top plate of the collection head, - activating the first removal system for pumping said sludge collected on the top plate with water to a receiving station above the water surface; - deactivating the first removal system; - separating the water-sludge mixture to remove water and to concentrate the sludge.

Preferably, the method additionally comprises the following steps after removal of sludge: - activating the second removal system for pumping the organisms accumulated on the top plate to the surface, - deactivating the second removal system.

The sludge can be removed by a first airlift-pump, preferably with a capacity of 5 - 20 m3 water per hour, more preferably with 10-15 m3 water per hour, most preferably 10-12 m3 water per hour. The organisms can be removed by a second airlift-pump, preferably with a capacity of about 120 to160 m3 water per hour, more preferred about 150 m3 water per hour.

The sludge may be removed several times per day, preferably at least once every second hour, more preferably at least once every hour. The organisms are preferably removed at least once per day. A third aspect of the present invention relates to a use of the device as defined above for collection and removal of waste from an open sea cage or from a closed cultivation unit, preferably for intensive aquaculture offish, more preferably for a species selected from the group consisting of salmonids, codfish, flatfish, breams, basses, groupers.

Short description of diagrams

Embodiments of the invention will now be described, by way of examples only, with reference to the following diagrams in which:

Figure 1 shows schematically a sea cage with a waste collection device according to a first embodiment of the present invention;

Figure 2 shows a view in perspective of a collection head according to the first embodiment of the present invention;

Figure 3 shows schematically a side view of the head disclosed in figure 2;

Figure 4 shows schematically a front view of the head disclosed in figure 2, also indicating the position of the section axis C-C;

Figure 5 shows schematically a section view through axis C-C of figure 4;

Figure 6 shows schematically a top view of the device of figure 2, also indicating the position of the section axis A-A;

Figure 7 shows schematically a section view through axis A-A of figure 6;

Figure 8 shows schematically an enlarged view of the sludge removal system of figure 7 (marked with “B” in figure 7).

Figure 9 shows schematically a side view a collection head according to a second embodiment of the present invention;

Figure 10 shows schematically a front view of the head disclosed in figure 9, also indicating the position of the section axis C-C;

Figure 11 shows schematically a section view through axis C-C of figure 10;

Figure 12 shows schematically a top view of the collection head of figure 9, also indicating the position of the section axis A-A;

Figure 13 shows schematically a section view through axis A-A of figure 12;

Figure 14 shows schematically a section view through axis C-C of figure 10 of an alternative cone-shaped collection head having downwards inclining V-formed walls extending from the backside of the house to the outward edge of the cones top plate; Figure 15 shows schematically a top view of the collection head of figure 14, also indicating the position of the section axis A-A.

Detailed description of embodiments

The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to various forms of waste collection systems for a sea-based fish farm. It should be appreciated, however, that the referenced collection system for sludge, dead fish, and other waste is also applicable and suitable for use in respect to any other type of aquaculture systems, requiring handling of waste. Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment.

In the description relative terms such as front, top, center, bottom, side, lower, upper, downward, upward, outward, sideward, vertical, and horizontal etc. are all related to the collection device when in upright position i.e. when mounted in a farm cage. Even though only exemplified for one side, it is to be understood that some features will correspondently also apply for the opposite side of the device.

In the context of the present invention an aquaculture cultivation unit refers to a farm or cage, most commonly a farm located in a body of water, typically a sea-based fish farm cage. The term includes open sea cages, typically net pens (fish cages), where the water can freely flow through the net from the outside into the cage with the farmed organisms. The term also includes closed systems where the farmed organisms are kept in a more or less water tight container, effectively stopping a direct water exchange with the surrounding water and having an external water supply by one or more pumps. It may also include land-based systems.

By sludge is meant feed waste such as not ingested feed pellets, disintegrated feed particles, excrement(s)/faeces from the farmed organisms, particulated organic waste such as microalgae and macroalgae, dead plankton, fouling organisms, and other small particulated waste typically found in an open or closed cage, sinking down to the bottom section of the cultivation unit. Said sludge is removed by the first removal system which is described in detail later on.

By sunken farmed organisms is meant aquatic organisms which are farmed or kept in the aquaculture cultivation unit and which are dead (often called “morts”), almost dead or at least sick and are not swimming but sinking down to the bottom of the cage. The farmed organisms can typically be pelagic fish such as salmonids, codfish, breams, basses, groupers and the like. The sunken organisms are removed by the second removal system according to the present invention which is described later on. Even though disclosed as a collection and removal system for sunken fish/aquatic organisms, the skilled person will understand that other type of waste may be removed by this system as long as the waste to be removed has suitable characteristics e.g. dimensions.

Figure 1 shows a side view of an aquaculture cage 1 having a surrounding net or wall 2 extending downwards from the water surface 3 for enclosing the fish or aquatic organisms to be cultivated or kept in the unit, the net or wall 2 being mounted to a floating ring-formed collar 4, which floats on the surface 3 of a body of water. Also shown in figure 1 is a (hand)rail 5 mounted on the collar, which is a typical equipment on todays fish cages. The enclosing net or wall 2 is typically more or less cylindrical in the upper section, while the bottom section is funnel-formed i.e. the diameter of the net/wall 2 inclines towards the center of the cage in the lower section of cage 1. It further shows a waste collection device 6 according to the present invention. The waste collection device 6 is for collection and accumulation of sunken (sedimented) sludge and sunken farmed organisms such as dead fish from the cultivation unit 1. The waste collection device 6 comprises a collection head 10 fixed in the center to the bottom section of the sea cage 1. The collection head 10 has a bottom part 30 and a funnel-formed top plate 20.

The waste collection device as shown in figure 1 is provided with two separate systems for removal of waste. A first removal system 40 is a sludge removal system for removal of sunken sludge accumulated on the top plate 20 of the collection head 10. A second removal system 60 is for sunken organisms cultivated or kept in the cage and collected on the top plate 20 e.g. dead fish. Both waste types are collected and lifted up from the bottom section of the fish cage by an airlift pump system each to the water surface 3 and further to one or more stations for storage and/or treatment of waste (not shown). For the transport to the surface, the waste collection device is provided with two different conduits extending from the collection head 10 to the surface, being a conduit 12 for the sunken organisms, typically provided with a floating element 13, for transport of the organisms, and a sludge pipe 15 for lifting up the sludge by airlifting. Further shown in figure 1 are pipes 14, 16 for pressured air used for the two separate air lifting pump systems for sludge (first pump system) and for organisms (second pump system), respectively. The collection and transport of waste to the surface will be explained in more detail below.

Figure 2 shows schematically a perspective view of a collection head 10 according to one first exemplary embodiment of the invention. Figure 3 to 7 show side, front, top, and sectional views of the collection head embodiment of figure 2. Figure 8 shows an enlarged view of the sludge removal part of the collection head.

Said collection head 10 is mounted in the bottom part of the sea cage 1, as described above, which can be a closed cage e.g. a tarpaulin container without or with only minimal direct water exchange with the surrounding body of water or an opened net type of cage allowing a direct water exchange.

The collection head 10 of this first embodiment comprises a horizontally extending; typically circular top plate section 20 on the top and a cylindrical bottom section 30 with a substantially planar bottom 32 (see e.g. Fig. 2, 3, 4 and 7). The bottom section 30 comprises technical elements for the suction of sludge as well as ballast elements. The top plate 20 and the bottom part 30 of the collection head 10 are preferably made as one part such as by moulding. If made of two parts, the parts can be fixed to each other by screws, clamps, welding, or other suitable means. The collection head is typically made of one or more materials which can withstand longer periods in sea water such as plastic materials, fibre glass, non-corrosive metal compositions or combinations thereof. In a particular preferred embodiment, the collection head is moulded, typically casted in two moulds forms. Preferably, it is made of low density polyethylene.

For stabilization and reinforcement, the collection head can be provided with reinforcements structures 66 such as shown in figure 2, 5, and 6. These can be for example steel elements extending from the top plate 20 a distance down into the bottom part 30 of the head 10.

The circular top plate 20 of the collection head 10 is funnel-formed allowing the sunken waste to sink down towards the lowest point or lower section of said funnel in the top plate 20. Thus, the lowest point of the funnel is pointing downwards when the collection head 10 is mounted in the sea cage as shown in figures 2 and 7. Typically, the funnel has its lowest point in a center area of the top plate, but other non-central arrangements of the funnel are neither excluded. The top plate 20 has a first removal system 40 for collection of sunken/sedimented sludge and transport to the surface. The removal system 40 for sludge is typically arranged centrally in the funnel of the top plate and comprises a first inlet 42 for discharging of small particulate waste/sludge such as unconsumed feed particles and faeces through a sludge conduit 44 arranged inside the collection head 10 under the top plate 20, wherein the sludge conduit 44 is connected to said first inlet 42.

As shown in detail in figure 8, the first inlet 42 is provided with a retaining element 45 for fish, morts, or other aquatic organisms to be cultivated to avoid that these are accidentally sucked into said system. The retaining element 45 is therefore typically provided with one or several apertures or slots large enough to allow water and smaller particles to pass through, but holding back the aquatic organisms to be cultivated as well as dead fish/morts accumulated on the top plate 20 of the collection head 10. Preferably, at least the first inlet 42 is covered by said retaining element 45 for fish which hinders that the fish can pass through but allows removing the collected sludge. This is achieved by a suitable locking element 46. The locking element 46 is shown in form of an adaptable locking disk which is arranged above the sludge conduit 44/ first inlet 42 such that a more or less circumferential slot 48 is left open between said disk and the edge of the conduit 44/ first inlet 42 allowing free passage of said particulate waste/sludge through said circumferential slot and into the inlet 42 for sludge. This slot 48 is preferably adjustable in its dimensions depending on the size offish being cultivated in the cage at any time and the sludge particles to be removed. This can be achieved by mechanically reducing or enlarging the distance between the inlet covering locking disk and the edge of the conduit 44 i.e. the height of the slot 48 (see also figure 8). This can e.g. be done manually or in an automated matter.

In figure 8 it is shown an embodiment where the locking disk of the retaining element 45 is fixed and adjustable by means of one or more screws 47. The screw(s) 47 may be arranged on the side of the disk as shown in the figures. In a preferred embodiment, a threaded element/screw 47 is arranged in the center of the disk and engages with a suitable receiving element in the center of the first inlet 42 (not shown). Other means well known to the skilled person may be used instead such as clamps or the like. The possibility for an adjustment of the opening dimension of the retaining element is an advantage since larger fish will be fed with larger pellets, producing larger faeces particles, meaning that larger particles have to be collected and transported through the first removal system 40 for sludge. Preferably, the first removal system 40 can also be closed totally if needed.

Preferably, the openings/slots/apertures 48 of the retaining element 45 for the sludge are adjustable from 4 to 11 mm depending on the pellets size used which is typically between 3 and 10 mm in dimension.

The conduit 44 below the first inlet 42 is formed as a U-formed pipe. This is schematically illustrated in figure 7 which is a section view through the A-A axis of figure 6. The U-formed conduit 44 extends a distance downwards in the bottom part 30 of the collection head 10, and turns thereafter more or less vertically up through the top plate 20 and at least to the top surface of the top plate 20. The U-formed conduit is preferably constructed without edges and corners to avoid turbulences and areas with no or reduced water flow through the conduit. The conduit 44 is connected at its upper section 43 to the sludge pipe 15 extending from the collection head 10 to the water surface 3 for transport of the sludge to the water surface 3 (see also Figure 1) or preferably to a receiving station for sludge. The sludge pipe 15 as well as the conduit 12 can typically be a collapsible, flexible pipe made of a plastic material, such as PVC. Typically, the sludge pipe has a diameter of about 90 mm while the conduit 12 has a diameter of about 200 mm. In a preferred embodiment the lower part, e.g. the first 6 meters, of the pipe 15 and of conduit 12 is a spiral tube, e.g. made of PVC, while the upper part extending to the surface, is a collapsible flat tube.

The first removal system 40 for sludge is typically provided with a first pump system, e.g. a first air-lift pump system (also called “mammoth pump”) as shown in figure 1, creating a suction force upwards by pressing compressed air into the water filled pipe system in the upwards oriented section 43 of conduit 44 or into the sludge pipe 15. Thereby a dragging force is created lifting up the water-sludge mixture. For this purpose, the first removal system 40 is provided with a pipe 16 for compressed gas, preferably compressed air. The inlet for the compressed air should be in the vertically raising upper section 43 of the conduit 44 or in the sludge pipe 15 extending to the surface. Preferably, the inlet for the compressed air is inside or at the collection head or in close vicinity to it. A compressor for the production of compressed air is typically placed above the water surface on a fleet or the like (not shown).

Even though an air-lifting pump is a preferred solution, other pumping systems maybe used instead such as an injector pump or the like.

Alternatively to the described disk locking arrangement as retaining element 45 for the inlet 42, a valve, sieve, or grid may be used to cover the inlet 42 and the top of the sludge conduit 44 (embodiment not shown in figures) whereby the openings/apertures are dimensioned to hold the fish/farmed organisms back, while allowing smaller particles to pass. Due to the risk of clogging of valves, grids, and sieves, the disk type of retaining element is generally a preferred solution.

An alternative solution for a locking element 46 can also be an element that has inclining wall(s) such as a conical form, a substantially frusto-conical form, a substantially cupula form, a substantially pyramidal form, or a substantially frusto-pyramid form.

Being pumped up to the surface, the sludge and water mixture may be stored in a suitable container or treated directly e.g. by passing the mixture through a suitable filter for separation of the particles/sludge from the water. Typically, a filter with apertures being 350 pm or less can be used for this purpose. Smaller apertures can be used if e.g. certain infectious stages of parasites such as salmon lice shall be filtrated out of the water. The water treatment may also comprise a filtration, centrifugation, purification and/or disinfection systems with several steps and grades. Suitable filters are known in the field such as from water treatment systems e.g. in slaughter houses for fish. The skilled person is well known with suitable filter apparatuses to be used for this purpose and these will therefore not be described in more detail.

Typically, the sludge from several cages can be collected and treated together in one sludge receiving station. For practical reasons this can be done on a floating structure such as a vessel or a service fleet being in close vicinity to the cage(s). If the aquaculture site is located close to land, it maybe done on shore, e.g. the waste receiving and/or treatment station may be placed on land.

In a particular preferred embodiment as shown in figures 1 to 7, the waste collection and collection head 10 additionally comprises a second removal system 60 for sunken or dead fish/ aquatic organisms (“morts”). The second removal system 60 is typically located in the center area on the top plate 20 in close vicinity to the first removal system 40 for sludge. The second removal system 60 is known per se and comprises a hollow housing 61 for passage of the sunken organisms through the housing 61 (see e.g. figure 2). The housing 61 can be mounted on the top plate or can be an integrated part on the surface of the top plate 20. The passage through the housing 61 is typically in a L-form. The housing has two openings. One opening is a second inlet 62 for sucking in the sunken organisms/fish. This second inlet 62 is typically on one side of the housing 61 and is oriented towards the lowest point of the funnel-formed top plate 20 in the center area i.e. the area where both the fish and the sludge will naturally accumulate in the funnel when sunken down. Dead fish/dead aquatic organisms sink down on the funnel-formed top plate 20, accumulate at the lowest point in said center area of said plate 20 and are removed sideward/upward through the housing 61. Thus, the sunken fish are typically sucked in sideways through said second inlet 62. The second opening 64 of housing 61 is an outlet on top of the housing 61 where the conduit 12 for the sunken organisms is connected to the housing 61 (see figure 1) for sucking and transporting of the organisms to the surface. Sucking forces are typically produced by a second pump system e.g. a second air-lift pump system using compressed air being pressed through the pipe 14 for pressurized air/gas into the housing 61 or into the conduit 12 in close vicinity to the collection head 10.

The second collection system 60 maybe provided with mechanical barriers or elements (not shown) which hinder living (swimming) fish to enter the housing 61 through the inlet 62 or to be sucked up accidentally.

The removed organisms e.g. dead fish are transported through said conduit 12 to a receiving station for the organisms (not shown). Organisms from several cultivation units may be transported to the same receiving station.

The two different waste treatments systems typically operate with different pumping capacities. The first removal system 40 for sludge typically pumps up 10-15 m3 water per hour, preferably 10-12 m3per hour by airlifting. The second removal system 60 pumps up about 150 m3 water per hour by airlifting.

The conduits/pipes extending from the collection head to the stations for waste collection can be at least in part collapsible when not in use during active pumping.

The pipes 14 and 16 for compressed air used for airlifting of dead fish and sludge may be attached to each other by permanent welding or other attachment means such as clamping, sewing or the like. The injection of compressed air can be regulated by suitable valve systems e.g. magnetic valves and a suitable system for programmable logic controlling (PLC).

Thus, in a preferred embodiment of the present invention, such as also shown in the exemplifying figures, the sludge is first transported downward from the top plate into the U-formed sludge conduit 44, before it is transported upward. Since the retaining element does not stop the sludge from entering the conduit 44, the sludge can also sink down in the conduit 44 by sedimentation during the periods between the active pumping of sludge. The dead fish/dead aquatic organisms are preferably sucked directly upward or sideward and upward as shown in the figures.

Even though shown in the figures that the conduit 44 is located inside the bottom part 30 of the collection head 10, an alternative, even though less preferred embodiment, would be to arrange the conduit 44 laterally from the head plate i.e. only partly under the collection head 10.

The bottom part 30 can have several functions e.g. ballasting, mounting the collection head to the cage and/or protecting the sludge conduit 44. However, the skilled person would understand that the collection head 10 may have other shapes and may essentially also only consist of the top plate 20 without the bottom part. In this case, the conduit would not be enclosed by the bottom part 30. A main advantage of this 2-part system for waste handling is a reduced need for handling large amount of water. While it is necessary to pump dead fish with rather large amounts of water, this is not necessary for the pumping of sludge. In the contrary, if the sludge is pumped together with the dead and/or sunken fish, which is practically possible and practiced by the prior art, then the sludge will be mixed with large amounts of water needed to pump up dead fish. If the sludge shall be collected, it has to be separated from the pumping water after lifting it to the surface 3. Considering the large amounts of water needed to lift up fish, this is both an expensive and difficult procedure making the handling and further use of the sludge for other purposes impractical or at least less attractive from an economical point of view.

Another main advantage is that the different types of waste can be collected in the same area on the funnel-formed head plate 20 i.e. typically at the lowest point of the funnel formed top plate 20. This means that both sludge and large particles such as dead fish, can be collected in the same area, even though they can be pumped and handled separately. This is a great advantage from a practical point of view as it improves the quality of the sludge and makes the handling of the waste more effective.

Another main advantage is that the sludge can be pumped up more frequently i.e. in shorter intervals, resulting in a lower salt content in the sludge. Tests carried out show that a low salt content in the sludge is obtained if the sludge does not remain in the cage more than 2 hours. Thus, the sludge should be removed once every second hour, or preferably once every hour. Longer periods in sea water result in an increase in salt content in the sludge, affecting its quality.

The present invention provides a solution to this problem by having a separated system for transport of sludge and dead fish. Although, having two separate systems for waste handling, one for sludge and one for dead fish, it is possible to make use of the same general collection head construction. Both waste handling systems can be arranged in the same head construction for collecting the waste and the required conduits/pipes to the surface can be arranged together reducing the amount of equipment in the cage. However, as discussed above, even though collected together, it is an important issue that the removal and pumping of the different types of waste can be operated independently from each other to avoid that sludge is sucked into the dead fish system.

Typically, the first removal system 40 for sludge is operated once per hour for a couple of minutes (typically 5 to 10 minutes) to suck up the sunken sludge. The second removal system 60 for sunken/dead organisms is typically only operated once per day for some minutes to remove e.g. dead fish. To avoid simultaneous removal of sludge by the second removal system 60, the first removal system 40 is preferably operated for a certain period before the second system 60 for sunken/dead organisms is activated. Thereby the sunken accumulated sludge is effectively removed from the top plate 20. When the sludge has been removed from the top plate 20, the system 40 for pumping up the sludge can be inactivated and the second removal system 60 for sunken organisms can be activated.

Thus, an advantageous method according to the present invention for collection and removal of sludge from an aquaculture cage in a body of water comprises the steps of - collecting the sludge on the funnel-formed top plate 20; - activating the first removal system and pumping the sunken sludge accumulated on the top plate 20 ofthe collection head 10 together with water to the water surface, preferably with 10-12 m3 per hour by a first pump system, e.g. a first airlift-pump for at least 5 minutes several times per day, preferably once each hour; - deactivating the first removal system 40; - optionally, separating the water sludge mixture e.g. by filtration to remove water and concentrate the sludge.

Depending on the case, the sludge may also simply be released with the water, or may be transferred to a tank for interim storage or for sedimentation from the water.

An advantageous and particularly preferred method according to the present invention for collection and removal of sludge and sunken/dead organisms farmed or kept in an aquaculture farm/cage comprises the steps of - collecting sedimenting/sinking sludge and organisms in or close to the the lowest point of the funnel-formed top plate 20; - activating the first collection system 40 for sludge and pumping sunken sludge accumulated on the top plate 20 with water to the surface, preferably with 10-12 m3 water per hour by a first airlift-pump; - deactivating the first removal system 40; - activating the second removal system 60 and pumping dead/sunken organisms accumulated on the funnel-formed top plate 20 with water to the surface, preferably with about 150 m3 water per hour by a second airlift-pump; - deactivating the second removal system 60.

The exact periods and optimal intervals for pumping as well as the ratio and amount of water to be pumped may vary depending on the need for removal of waste, the biomass to be removed, the size offish, the type of cage etc. These can be adapted individually by the skilled person to the local requirements and conditions.

Preferably, the systems for pumping up the sludge and sunken organisms/ fish 40,60 comprise separate pumps, i.e. preferably each system has an own airlifting pump as described above. However, by using a suitable controlling system and valves, the same pump/compressor may be used to operate the two different waste removal systems.

Removing the sludge several times per day, preferably once per 1-2 hours, has the advantage that the sludge has a lower salt content which is an advantage if used later on e.g. as fertilizer or the like.

After being pumped to the surface, the dead fish/organisms will typically be isolated from the transport water by a grid, sieve or the like. Thereafter, the dead fish/organisms can be treated further or disposed. For example, the dead fish may be grinded in a mill and optionally transferred to the sludge.

Even though described as a combination, the skilled person would understand that the collection head 10 may also only be provided with the first removal system 40 without having a dead fish collection system 60 in the same head. Other equipment for sucking dead fish may used in this case such as a temporarily installed pipe from a vessel down to the bottom section of the cage for pumping up dead fish.

Figure 9 shows schematically a side view of a collection head 10 according to a second exemplary embodiment of the invention. Figure 10 to 13 show side, front, top, and sectional views of the collection head embodiment of figure 9. The enlarged view of the sludge removal system marked with “B” will be identical with the system shown and described for figure 8.

The main difference from the first embodiment shown in figure 1-8 and described above is that the bottom part 30 of the collection head 10 in this second embodiment is cone-shaped, with sidewalls 31 inclining towards the center at the lower end of the bottom part 30. The other elements in this second embodiment have corresponding constructions and functions as described above for the first embodiment and will thus apply likewise for this embodiment. Preferred variants, methods, uses, and functions described for the first embodiment will thus correspondingly apply for this second embodiment.

Typically, the cone of the bottom part 30 is designed to correspond to the conical shape found in the bottom part of the net cage allowing a more or less smooth and tight fit into the net walls in the bottom region of said net. To be mounted in an existing net, the conical shape of the bottom part of the collection head will be chosen according to the conical shape of said net in its bottom region. The cone shape, in particular when having a smooth fit inside the cone of the net cage not only has the advantage that existing net forms can be used but may also result in lower wear and tear forces between the net and the collection head 10 of the net compared to a cylindrical form.

Figure 14 and 15 illustrate an alternative cone-shaped collection head only differing from the cone-shaped collection head described above and shown in figures 8 to 13 in that the top plate 20 on the back side of the housing 61, i.e. the side facing to the outer edge of the top plate and thus being on the opposite side of the housing inlet 62, has inclining V-formed walls 33 extending a distance downwards from the housing to the edge of the top plate 20. By these inclining V-shaped walls 33 it can be avoided that dead fish accumulate on the backside of the housing 61. The V-form will guide dead fish along the sides of the housing 61 towards the center of the funnel-formed top plate 20 where they can be pumped and lifted through the second inlet 62 of the second collection system for dead fish. The section view A-A indicated in figure 15 of the collection head 10 will be identical with the system shown for figure 13.

Claims

1. A collection device (6) for collecting sludge such as sunken particulate waste and sunken farmed organisms such as dead fish from an aquaculture cultivation unit (1) positioned in a body of water, characterized in that the collection device (6) comprises - a collection head (10) at the bottom of the cultivation unit (1) for collection of sunken sludge and sunken farmed organisms, the collection head (10) comprises a funnel formed top plate (20) wherein the sunken sludge and organisms are collected in or in vicinity to the lowest point of the funnel, - a first removal system (40) for sunken sludge, having a first inlet (42) for sludge and small particles at the lowest point of the funnel-formed top plate (20), the first inlet (42) being provided with a retaining system (45) for holding back the farmed organisms, and in that the first removal system further comprises a first pumping system for removal of said sunken sludge from the first inlet (42), - a second removal system (60) for sunken farmed organisms accumulated on the top plate (20) and a second pumping system for removal of the sunken organisms from the top plate (20).

2. Device according to claim 1 wherein the first and/or second pumping system is an airlifting pump suitable to transport the sludge and/or the organisms to the water surface (3).

3. Device according to claim 1 or 2, wherein the retaining system (45) comprises a locking element (46) covering at least the first inlet (42) located in the funnel formed top plate (20) and leaving at least one opening for sludge discharge, said opening being smaller than the farmed organisms.

4. Device according to claim 3, wherein the locking element (46) is a locking disk.

5. Device according to any of the claims 3 or 4, wherein the opening is in form of a circumferential slot (48) between the lower end of the locking element (46) and an upper edge of the first inlet (42).

6. Device according to any of the claims 3 to 6, wherein the one or more openings/slots (48) of the first inlet (42) can be adjusted in size and/or closed.

7. Device according to claim 1, comprising a conduit (44) that is connected to the first inlet (42) at the funnel formed top plate (20), the conduit (44) being located inside the collection head (10) and extending in a U-form from the first inlet (42) a distance down into a bottom part (30) of the collection head (10) and further up to at least the upper surface of the top plate (20).

8. Device according to any of the preceding claims, wherein the second removal system (60) is arranged in a center area on the funnel-formed top plate (20) in close vicinity to the first removal system (40), wherein the organisms are preferably removed sideways/upwards from the funnel-formed top plate (20).

9. Device according to any of the preceding claims, wherein the second removal system comprises - a housing (61) which is arranged on the top plate (20) and having a second inlet (62) for organisms on one side, the second inlet (62) facing towards the center of the funnel-formed top plate, - a passage through the housing (61), and - an outlet on the top of the housing (61).

10. Method for collection and removal of waste from an aquaculture cultivation unit positioned in a body of water characterized in that the method uses a device according to any of the claims 1 to 9 and comprises the following steps: - collecting sinking sludge on the top plate (20) of the collection head (10), - activating the first removal system (40) for pumping said sludge collected on the top plate (20) with water to a receiving station above the water surface (3); - deactivating the first removal system (40); - separating the water-sludge mixture to remove water and to concentrate the sludge.

11. Method according to claim 10, additionally comprising the following steps after removal of sludge: - activating the second removal system (60) for pumping the organisms accumulated on the top plate (20) to the surface (3), - deactivating the second removal system (60).

12. Method according to claim 10 or 11, wherein the sludge is removed by a first airlift-pump, preferably with a capacity of 5 - 20 m3 water per hour, more preferably with 10-15 m3 water per hour, most preferably 10-12 m3 water per hour and the organisms are removed by a second airlift-pump, preferably with a capacity of about 120 to160 m3 water per hour, more preferred about 150 m3 water per hour.

13. Method according to any of the claims 10 to 12, wherein the sludge is removed several times per day, preferably at least once every second hour, more preferably at least once every hour and wherein the organisms are removed at least once per day.

14. Use of the device according to any of the claims 1 to 9 for collection and removal of waste from an open sea cage or a closed cultivation unit, preferably for intensive aquaculture offish, more preferably for a species selected from the group consisting of salmonids, codfish, flatfish, breams, basses, groupers.