Pellet detection in sludge

Abstract

A system for feed monitoring in an aquaculture farm for breeding aquatic animals, the system comprising a removal system for removing bottom waste from a cage arranged to contain the farmed animals. A

Description

The invention relates to a system for feed monitoring in an aquaculture farm according to the preamble of the independent patent claims. Background The annual production of salmonids in Norway was about 1.6 million tons in 2021, the salmonids mainly being Atlantic salmon and trout. The production is at present mainly based on fish farming plants in the sea, where salmon are cultivated in large fish cages, but the use of land based fish farming is constantly increasing. The intensive production results in different forms of waste being produced during the production process such as dead fish (also referred to as “morts”), faeces, unconsumed feed etc. Even though these are often only recognized as waste and a potential environmental threat, the discharge from sea farms also represents a largely unexploited, potentially valuable source of nutrients. A fish farming plant typically comprises a number offish cages and a common installation, such as a barge, holding common equipment. The fish cage may be an open cage having a bag of net, a closed cage or a semi closed cage. The choice of cage depends on the location site and the preference of the fish farmer, among other things. The common installation may be based onshore, but frequently the plant is located too far from the shore, and a barge is used. Such a barge is referred to as a main barge or feeding barge, and comprises equipment for controlling the whole plant, in addition to the feeding. A number of pipes, tubes and wires run from the main barge to each of the fish cages, for instance to be used for feeding, removal of waste and for carrying electrical power to lights, cameras, and other equipment on the fish cages. When the plant is running, and fish are in the net cages, some fish will die and these will be collected at the bottom of the fish cage together with uneaten feed, faeces and other waste. All of this waste together, which is collected at the bottom of the net cage, will hereinafter be referred to as "bottom waste". In order to maintain the optimal conditions in the fish cage, the bottom waste including the dead fish must be removed as soon as possible, and several devices have been developed in order to perform this removal for fish cages at sea. One such device has been developed by Lift Up AS, and comprises a pipe running from the surface of the water to a collector at the bottom of the fish cage, wherein a mammut pump is used to lift the bottom waste, including the dead fish, out of the cage. The pipe may be connected to a boat or a common barge of the plant as described above, and the system for waste removal may be connected to several fish cages. There are also known systems removing the dead fish separately from the rest of the bottom waste. For land-based and closed fish cages, the bottom waste may also be removed together with excess water. During Norwegian production of salmon, about 1,6 million tons of feed are used for production of about 1,25 million tons of salmon. The fish utilize the feed effectively compared to other animals, but some of the nutrients will still not be utilized by the fish because they are not digested. Further, some of the feed is not eaten, and the bottom waste from land-based fish farming may contain about 50 % uneaten feed. In order to avoid the uneaten feed being released to the environment, it is important to collect it and remove it from the cage. The industrial feed for salmon and trout comprises a number of ingredients and some heavy metals. In addition to the benefits of removing uneaten feed due to the nutrients, it is a clear advantage to also prevent these metals from being released into the environment. Salmon food contains of phosphor, zinc, iron, and magnesium, which the fish use to develop their bone structure. Normally 2 to 3% of food will be wasted in a fish farm, and it is important for the fish farmer to keep track of this. The feed is expensive, and uneaten feed represents a direct economic loss for the farmer. The feed is normally provided in the form of pellets, which may dissolve after some time in water. Too much uneaten feed in the waste may indicate that too much feed is being supplied, and too little uneaten feed in the waste may indicate that not enough feed is being provided to the fish in the fish cage. Therefore, there is a need to estimate the amount of uneaten feed, in order to regulate the feeding. Based on the above, there is a need to create a system for estimating the amount of uneaten feed. As the feed is expensive, there is a need to consider the development of appetite, in order to avoid excess feeding. Further, there is a need to create a system which may be installed at a feed barge, boat or the similar, which may be far from shore. Even further, it should preferably be possible to install the system in an existing fish farming plant, regardless of whether the plant has open, closed or semi closed fish cages. The objects and needs mentioned above are met by a system and a method according to the independent claims. Further advantageous features are provided in the corresponding dependent claims. The invention relates to a system for feed monitoring in an aquaculture farm for breeding aquatic animals, the system is comprising: - a removal system for removing bottom waste from the bottom of a cage arranged to contain the animals to be farmed, - a dewatering apparatus for dewatering the bottom waste, - a surface for distributing the dewatered bottom waste evenly, - at least one detector configured to capture an image of an area of the surface with the bottom waste distributed thereon, - a processor coupled to the detector, and configured to process the image to estimate a number of pellets in the image. As the farmer / operator will be informed of the number of uneaten pellets in the bottom waste, he may be using the information to regulate the feeding. Further, with such a system the farmer will be able to keep track of historical data from the feeding as well fresh data. The system will count every uneaten pellet and from that make a report the farmer can present to the government and use it to optimize the business. The processor may comprise or be coupled to a storage unit and may be configured to generate reports for present and historical data regarding the number of pellets in the bottom waste. Based on these reports it is possible to compare the amount of uneaten pellets with weather conditions and temperature, to optimize future feeding. The system may preferably further comprise a control unit, controlling and coordinating the different parts of the system. When the system is being used on a plant having more than one cage, the control unit may also inform the detector and / or processor from which cage the bottom waste is being removed, and thus the processor may be able to identify how many pellets are not eaten in each cage, both at present but also historically. Capturing an image of an area refers to the detection of a signal from the area of the surface. A number of smaller images can be captured and processed to map a larger region of the surface. The detection can, for example, be the detection of reflected electromagnetic or acoustic radiation from the area. The system for feed monitoring may comprise a distribution device for distributing the dewatered bottom waste evenly on the surface. This device may comprise a conveyor system which causes the surface to rotate as part of a conveyor belt into and out of a pool of the bottom waste. The distribution device may alternatively comprise a spray nozzle, a sweeper, or similar. The at least one detector may be at least one a camera or sensor. The camera may be an optical camera and can include one or more lenses selected to image an area of a desired size. The lens may be selected to image an area which extends all of the way across the width of the surface from side to side, and this may be a wide-angle lens. The system for feed monitoring may be coupled to a feeding mechanism for supply of feed pellets to the animals in the cage. The system for feed monitoring may include the feeding mechanism. The system may include a separation mechanism for removing dead fish and other large objects from the bottom waste. Such a separation mechanism may preferably arranged before the dewatering apparatus, and dewatered sludge, including uneaten pellets and smaller particulate matter, with the dead fish and large objects removed, passes from dewatering apparatus and is subsequently distributed on the surface. The separation mechanism may comprise one or more filters. A series of filters with increasingly small grid size may be used to remove increasingly small objects from the bottom waste. The filters will be coarse enough that uneaten pellets can pass through the separation mechanism and be distributed onto the surface. The system may be used in an aquaculture farm at sea, or on shore. If the farm is on shore the cage surrounding the organisms may be a tank or a pond, and if the farm is at sea, the cage may be a closed, open or semi closed fish cage. Closed, open and semi closed fish cages are well known to a skilled person. A feeding mechanism, to be used with the system according to the invention, comprises a feeder configured to add feed pellets to the cage. The feeder may be configured to add the feed pellets above or below the surface of the water, as a mixture of feed pellets and air or a mixture of feed pellets and water or even seawater. The preferred choice of feeder will depend on features of the aquaculture farm as such, and which feeders may be suitable in different situations will be obvious to a skilled person. The feeding mechanism may be arranged to feed one cage only, several cages simultaneously, or several cages one at a time. The feeding mechanism may be manually or automatically regulated in order to adjust the amount of feed to be supplied. The amount of feed to be supplied to a given cage depends generally on the aquatic animal in the cage, the size and number of animals in the cage, but also on a number of other parameters such as the time left before slaughter or how much time has passed since the fish was put into the sea. As mentioned above, bottom waste is created in a cage containing aquatic animals, and will sink to the bottom of the cage. The bottom waste will include excess feed, that is uneaten feed pellets. The removal system should preferably remove the bottom waste while the feed is still in the shape of a pellet in order to avoid the nutrients and contents of the pellet leaching out into the environment of the cage as the pellet dissolves. Further, if excess feed is removed while still in pellet form, the amount of feed may be quantified by counting a number of pellets. Depending on a number of factors, for instance the amount of uneaten pellets, the number and size of the fish in the cage, the time period for removal of bottom waste may be adjusted. The system may remove bottom waste once every hour, throughout the entire growth period of the fish, usually being 10-15 months. In the system according to the present invention, the removal system for removal of bottom waste should thus be configured to pump the waste gently, for instance by using an airlift pump / mammoth pump or a vacuum pump. The removal system may be arranged separately for each cage, or several cages may use the same removal system. It may also be possible to have a removal system which can be temporarily fitted to a cage, installing the removal system in one cage, removing sludge from that cage, and then uninstalling the removal system from the cage, before installing it in the next cage. The removal system may lead the bottom waste from each of the cages to a common processing site. Regardless of the type of removal system being used, the bottom waste extracted from the cage will contain a lot of water. Handling and storing of bottom waste is expensive, and for this reason it is desirable for the amount or volume of the waste to be reduced. This is generally achieved using a dewatering apparatus. Any suitable dewatering apparatus may be used. The dewatering apparatus may comprise several filters, for instance a coarse filter for removal of bigger articles, such as seaweed or fish arranged first, followed by a screw conveyor and / or drum filter and then a filter mesh or cloth of a given mesh size. After the coarse filter, sludge including uneaten pellets remains. The system according to the invention further comprises a surface onto which the sludge can be distributed evenly after dewatering. Once the sludge is dewatered, it may be distributed in a thin layer on the surface. By "thin layer" it is herein meant a layer thinner than the smallest size of the pellet, such that a pellet will protrude from the layer. If a pellet has a diameter of 3 to 9 mm, and a length of around 7 mm, a thin layer should not be thicker than 2 mm. The surface is preferably flat meaning that it is not concave or convex. The surface may be any flat surface such as a plate, a transparent plate, a glass plate, or a part of a conveyor band. Further, the surface may be a part of the dewatering apparatus, for instance it may comprise a screen or sieve. If the surface comprises a screen or sieve, the openings in the material should be smaller than the size of the pellet, possibly smaller than 1 mm, and may be between 350 and 500 microns in size. The screen may be formed of a cloth material. In an preferred embodiment, the dewatering apparatus comprises a rotation band filter, and the surface onto which the sludge is evenly distributed may be the band filter. The rotation band filter may be arranged to be sloping, having the lower end in a pool of sludge. The sludge will then be evenly distributed onto the band filter as the band filter rotates out of the pool. Between the dewatering apparatus and the surface, a distribution device may be arranged to distribute the sludge evenly over the surface. Such a distribution device may be a nozzle or may work by passing the sludge through an outlet, such as a trumpet-like outlet, onto the surface in order to distribute this evenly. Sludge may be removed from several cages and processed on the same site. A system according to the invention may be used to process bottom waste from many cages simultaneously or one at a time, depending on what it is desired to monitor. If estimates for each cage are desired, then sludge must be removed and processed from one cage at the time. A control unit may be used to control from which cage the bottom waste is removed, and to communicate this to the detector and / or processor in order to identify the number of uneaten pellets from each cage . A detector is configured to capture images of the bottom waste (by this time usually sludge including uneaten feed pellets) on the surface. The detector can be any device which is positioned and configured to obtain images of a region of the layer of sludge located on the surface. The detector may detect acoustic radiation, or electromagnetic radiation such as radio waves or visible light. The detector may be at least one camera. The wavelength of light imaged by the detector will most often be in the visible range (i.e. an optical camera), but detectors sensitive to other wavelength ranges, such as radio wavelengths, can be used. The detector must be able to produce images which can be processed in such a way that pellets in the image are distinguishable from the surrounding material of the thin layer. In an image taken with a camera that is sensitive to optical wavelengths, for example, the colour of the pellet and / or shadows formed by the protrusion of the pellet above the thin layer of sludge may be used by the processor to detect the pellet. If other wavelengths in the electromagnetic spectrum are used, the pellet may absorb / reflect radiation in the selected wavelength differently than the surrounding sludge and may be discernible in the images as a result. An infra-red camera may be an option, for example, if pellets absorb heat more or less efficiently than the surrounding sludge material. If a camera is used, this may comprise a lens which is sufficiently wide to allow the whole width of the surface or belt to be imaged at once. The detection system may include a radiation source for illuminating the area of the sludge layer to be imaged. The radiation source may emit radiation in the wavelength range to which the detector is sensitive. If the detector is an optical camera, for example, a visible light source may be arranged to illuminate the area to be imaged, either from above or from below. The light source may be usable at certain times, such as during the night, with sunlight providing the required illumination during the day. In some cases, the detector may be set up to receive reflected radiation and to quantify an intensity of the light received from the area being imaged. A layer of sludge containing a higher density of pellets may reflect more or less light of a certain wavelength / wavelength range, and the intensity measure can in this way provide an estimate of the number of pellets within the area. The images collected at the detector may comprise a series of still images taken periodically, or may represent video footage from which images for processing can be extracted. The processing software can operate continuously to provide estimates of a number of pellets present within the imaged area, and how this changes over time. In most cases, the surface on which the sludge, including pellets, is distributed will be configured to move, and the imaged area will be fixed, so that the layer of sludge containing pellets is carried through the imaged area. The image will therefore be constantly changing, and the processor can be configured to re-estimate a number of pellets in the image at intervals during operation of the system to provide a measure of how the number of pellets within the area changes over time. Rather than detecting electromagnetic radiation, the detector may be configured to detect acoustic radiation and a source may be arranged to emit acoustic radiation towards the area of the surface to be reflected towards the detector. A layer of sludge in which a higher density of pellets is contained may reflect the acoustic radiation in a different way, and this effect can allow a number of pellets on an area of the surface to be quantified. Images obtained with the detector can be processed using object detection techniques which allow the pellets to be identified reliably in a 2D (or even 3D) image. This may be done, for example, by picking out their outline in the image, or by identifying regions representing shadows on the sludge layer cast by the pellets or silhouettes of the pellets if these are illuminated from below. Machine learning techniques can be used to improve the function of the processor in detecting and counting pellets over time. Training data may then represent images taken with the detector in which pellets have been counted manually or in another way. The detector may comprise a single device, such as a sensor or camera, or may comprise a number of devices arranged to image the surface from different angles or to image different parts of the surface. Including two detectors for imaging from different angles may be useful if the processor works by identifying shadows or outlines of the pellets. Including two different viewing angles for the same area of the surface can improve reliability of the system because pellets which are more difficult to detect in one image may be more clearly demarcated in another. Similarly, two or more radiation sources, such as two or more light sources can be arranged to illuminate the imaged area from different angles. This will tend to create more shadows, and will result in shadows being present on different sides of the pellets, which may make the pellets more easily discernible by the processing software. The invention further relates to a method for estimating a number of uneaten feed pellets in bottom waste from a cage in an aquaculture farm, wherein the method comprises the following steps: i) removing bottom waste from the cage, ii) dewatering the bottom waste, iii) distributing the dewatered bottom waste in a thin layer on a surface iv) capturing at least one image of an area of the layer on the surface using a detector, v) processing the image using a processor to identify pellets in the image of the area, and vi) counting, by the processor, the number of identified pellets in the image. Step i) may be performed with well-known removal systems, for removing the bottom waste form the bottom of a cage and to processing site. Bottom waste may be removed from several cages to the same processing site, either simultaneously or one by one. The system for removing bottom waste may be a system removing bottom waste including larger articles such as dead fish, or a system excluding larger articles. If dead fish is included, a step for removing larger articles such as dead fish may be included before the dewatering in step ii). Even if the system for removing bottom waste does not include removal of larger articles, a step for coarse filtering may be performed before the dewatering. Step ii) may be performed in several steps by a dewatering apparatus, wherein dewatered bottom waste from one step is considered as wet bottom waste in the following step. In step iii), once the bottom waste is considered to be sufficiently dewatered it is distributed onto the surface in a thin layer. Sufficiently dewatered may refer to a reduction in water content of 5-10%. For example, material entering the dewatering stage may comprise around 1% dry material and 99% water, and this may be dewatered to a material comprising 90% or less water (10% or more dry material). The distribution of the dewatered material may be performed by a distribution device, such as a nozzle or similar. The surface may be a sieve or filtering cloth of the dewatering apparatus. The layer should be sufficiently thin in relation to the size of the feed pellet to allow an uneaten pellet to protrude from the bottom waste, i.e. for a part of the pellet to protrude above the layer of bottom waste on the surface. As mentioned above, dead fish and larger objects in the bottom waste will usually already have been removed by this stage, so that the material being distributed comprises sludge including uneaten feed pellets. Step ii) and iii) may be combined in that the dewatering apparatus comprises a surface wherein the sludge is distributed. This may for instance be a rotary band filter, wherein the filter is the surface. The system and method according to the invention may be used to breed any aquatic animals, preferably fish such as salmonids or cod, more preferably salmon or trout. The invention will in the following be described by way of exemplary embodiments and accompanying drawings. 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 an open fish farm typically deployed in the sea. However, it should be appreciated that the system and device is also applicable and suitable for use in respect of any other type of aquaculture system requiring handling of water and sludge. 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, centre, bottom, side, lower, upper, downward, upward, outward, sideward, vertical, and horizontal etc. are all related to the device when in upright position i.e. when mounted in a fish cage ready for use. Examples Embodiments of the present invention will now be described, with reference to the following schematic figures wherein: Fig. 1 shows a fish farming plant having several fish cages and a common removal system for removal of sludge, Fig. 2 shows a part of a dewatering apparatus, and Fig. 3 shows an image taken of dewatered sludge on a surface. The same reference numbers in different drawings identify the same or similar elements. The figures are for illustration purposes only, and the different parts may necessarily not be in scale to each other. Figure 1 shows a well-known fish farming plant, comprising ten fish cages 1, and two main pipes 2 for transporting waste from each cage to a main barge 3. At each cage 1 a pipe running from the bottom of each cage is connected to the main pipe 2 for bottom waste at a connection comprising a Y-pipe 4. The pipe running from the bottom of each cage, the Y-pipe and the main pipe are a part of a removal system for removing bottom waste from the bottom of a cage arranged to contain the animals to be farmed. Figure 2 shows a dewatering apparatus for dewatering the bottom waste, shown as a rotary band filter, meaning a conveyor 10 having a belt 11. The rotary band filter is arranged sloping in a container 12, wherein one end 10a of the conveyor is inserted inside the container, and a second end 10b is protruding above and beyond the container. The container 12 is shown transparent for clarity. The bottom waste removed from the bottom of each cage, is guided into the container 12, by the removal system. The bottom waste may be filtered in a coarse filter (not shown) before entering the container, to remove larger elements such as dead fish. The bottom waste / sludge creates a pool inside the container, and the wavy line at the upper end of the container indicates the level of sludge in the container. The end 10a of the conveyor being in the container, should be inserted into the pool of sludge / waste. In the shown embodiment, the belt 11 is a filter having openings, wherein the water may flow through the belt and either back into the container or being removed from the container. When the conveyor 10 is running, the waste will adhere to the belt 11 and be transported out of the container 12 while being dewatered. In this way, the belt 11 act as a surface, and as one end 10a of the conveyor is inserted into the pool of waste / sludge, evenly distribution of the waste is achieved when the band rotates out of the pool. This way of arranging a rotary belt filter is well known for a skilled person. Above the belt 11 of the conveyor 12, it is arranged a detector 13 to capture an image of an area of the belt. In Figure 2, the area being capture is indicated by a beam 14. The detector is coupled to a processor 15, which is configured to estimate a number of pellets in the image. The detector is arranged at a distance from the pool of sludge / waste, to ensure that the waste is sufficiently dewatered and that the layer of waste is sufficiently thin to make the pellets protrude from the surface. The optimal position of the camera will depend on a number of factors. The system may further comprise one or more radiation sources, such as one or more lights sources to illuminate the area. This is not shown in the figures. Once the dewatered waste is transported to the end 10b of the conveyor protruding above and beyond the container, the waste is removed from the belt, before the belt returns to the pool. The removal of waste may be by a scrape, water or air flow or any other suitable way. In one example, the waste entering the the container had a dry material content of 1%, and the material leaving the container had a dry material content of 10%, which is a dewatering of about 9-10 %. A possible image captured by the camera 13 is shown in Figure 3. The layer of dewatered waste / sludge 20 is shown as a grey background, and the pellets 21 are shown as protruding particles. The processor 15 configured to estimate a number of pellets in the image, may further be configured to compare the number of estimated pellets to a given range, and to send a signal to an operator if the estimate number is outside of the set range. This will give the operator a possibility to regulate the feeding in the cage wherefrom the bottom waste is removed. When there is a need to estimate a number of uneaten feed pellets in bottom waste from a cage, the method according to the invention comprises the following steps i) removing bottom waste from a cage, by using the removal system 2, 4, ii) dewatering the bottom waste by flowing the waste into the container 12, and running the rotary band filter (10, 11), iii) distributing the dewatered bottom waste in a thin layer 20 on a surface, the surface is the filter belt 11 of the rotary band filter, by running the rotary band filter 10, 11, iv) capturing at least one image of an area of the layer 20 using the detector 13, v) processing the image using the processor 15 to identify pellets 21 in the image of the area, and vi) counting, by the processor 15 the number of identified pellets 21 in the image. The shown and described system may be integrated in a bigger system relating to monitoring and controlling the whole fish farming plant. The sludge should be removed from the cage after feeding, but before the pellets dissolve and become a part of the sludge. Once the operator receives a signal from the processor 15, he / she may regulate the feeding of the cage until the number of pellets in the sludge return within the set range. As the fish in the cages may not respond identically, the system must analyse the sludge from each cage separately, and the operator must know which cage the analysed sludge is coming from.

Claims

1. System for feed monitoring in an aquaculture farm for breeding aquatic animals, the system is comprising- a removal system for removing bottom waste from the bottom of a cage arranged to contain the animals to be farmed,- a dewatering apparatus for dewatering the bottom waste,- a surface for distributing the bottom waste evenly,- at least one detector configured to capture an image of an area of the surface with the bottom waste distributed thereon,- a processor coupled to the detector, and configured to estimate a number of pellets in the image.

2. System according to claim 1, characterized by further comprising a coarse filter for removing dead fish from the bottom waste prior to the dewatering apparatus.

3. System according to any one of claim 1 and 2, characterized by further comprising a distribution device for distributing the dewatered bottom waste evenly on the surface.

4. System according to any one of claims 1 -3, characterized in that the surface on which the bottom waste is evenly distributed, is a part of the dewatering apparatus.

5. System according to claim 4, wherein the dewatering apparatus comprises a rotation band filter, wherein the surface for distributing the bottom waste, is the filter band.

6. System according to any one of claims 1-5, wherein the processor is further configured to compare the number of estimated pellets to a given range, and to send a signal to the operator if the estimated number is outside of the set range.

7. System according to any one of claims 1-6, wherein the detector is a camera.

8. System according to any one of claims 1-7, wherein the detector is arranged above the surface.

59. Method for estimating a number of uneaten feed pellets in bottom waste from a cage in an aquaculture cage, wherein the method comprises the following steps: i) removing bottom waste from a cage, ii) dewatering the bottom waste,10 iii) distributing the dewatered bottom waste in a thin layer on a surfaceiv) capturing at least one image of an area of the layer on the surface using a detector,v) processing the image using a processor to identify pellets in the image of the area, and15 vi) counting, by the processor, the number of identified pellets in the image.

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