DK202370407A1

DK202370407A1 - A separation unit for a protein skimmer

Info

Publication number: DK202370407A1
Application number: DKPA202370407A
Authority: DK
Inventors: Røeggen Sigmund; Albrigtsen Rikard
Original assignee: Redox As
Priority date: 2021-01-11
Filing date: 2023-08-10
Publication date: 2023-08-15
Also published as: WO2022149989A1; CL2023001981A1; NO20210029A1; NO346901B1; CA3204722A1

Abstract

There is described herein a separation unit for a protein skimmer, the separation unit comprising: an inlet through which water and foam can pass into the unit, a first outlet for purified water, and a second outlet for foam; a tray across which water can flow between the inlet and the first outlet; and a plate positioned above the tray such that a leading edge of the plate sits at or below a level of the water surface in use, the plate being inclined at an acute angle to the direction of water flow across the tray so that foam floating on the surface of the water can be separated from the water surface and directed up the inclined plate to the second outlet. There is also described herein a filtration system for a fish tank comprising a protein skimmer and a method for providing a separation unit for a protein skimmer.

Description

DK 2023 70407 A1 1

A Separation Unit for a Protein Skimmer

The present invention relates to a separation unit for a protein skimmer, or a water purification apparatus. More particularly, the invention relates to an improved separation unit for a protein skimmer, the skimmer being suitable for use in an aquaculture system.

Recirculating Aquaculture Systems (RAS) are increasingly used in commercial fish or shellfish farming to reduce the need for a constant supply of clean water from a separate source. Land-based fish farming, in particular, has seen an increase globally over the past decades, where in Norway this applies especially to the farming of smolt and other fish for consumption. Fish farms may comprise a large number of holding tanks for fish or shellfish, each with fresh or salt water circulating from the holding tank, through a filtration system, and then back into the holding tank — again. The recirculating water may also be treated to increase levels of oxygenation, to remove CO, to adjust the pH to optimum levels, and to heat or cool the water to provide the ideal environment for maximum yield. The vast scales of these projects means that small changes in the environment, or minor improvements to the efficiency of filtration of the circulating water, can make a large difference in terms of profit. in such systems, proper treatment of the water or other liquids to remove {oxic substances is crucial. In environments where marine animals are densely packed together, levels of ammonia excreted by the fish, as well as other organic matter from excess feed, dead animals/fish, or other pollutants, can increase to levels which are damaging to the health of the animals if left unchecked. The water must therefore be properly filtered or treated to keep these levels within an acceptable range.

Biofiltration is often used to convert the ammonia, which itself can be toxic, to nitrites and/or nitrates using a particular type of bacteria. These latter substances are less harmful than ammonia, and can be removed in a process of denitrification.

Mechanical filters are also often employed. Within some of these fillers water is passed through material such as sand or plastic beads in order to remove larger particulate matter. Screens or rotating micro-screens can also be used for mechanical filtering. Alternatively, or in addition, larger particles of waste substances can be separated out by way of a settling tank. Here, denser particulate matter is

DK 2023 70407 A1 2 allowed to sink, under the action of gravity, to the bottom of the tank where it is removed from the system.

Mechanical filters work well for larger particulate waste matter, however they are inefficient or ineffective when it comes to removing dissolved substances and fine suspended solids within the water (for example, particles of an average size/diameter smaller than around 50um). Foam fractionation is therefore also often employed instead of, or as well as, other filtration methods in order to remove the smaller particulate waste matter.

Foam fractionation, also known as protein skimming, involves the formation of small, usually micron-sized, air bubbles within the water or other liquid passing through the filtration system. Most dissolved organic compounds (DOCs) within the waste water from a fish tank comprise molecules which are hydrophobic or have a hydrophobic part. This hydrophobic part is attracted to the air pocket formed by a bubble and the compounds tend to attach themselves to the surface of the bubbles so that the hydrophobic part is surrounded by air. Other particulate matter can then attach itself to the hydrophilic portion of the DOC molecule, which faces outwards from the surface of the bubble and extends into the surrounding water. As the bubbles rise to — the surface of the water, they bring with them the attached DOCs and particulate matter. The foam can then be 'skimmed off i.e. removed from the surface of the water within the filtration apparatus, to leave purified or partially purified water for recirculation to the fish holding tank. If substances to be removed do not have a hydrophobic portion then a surfactant may be added to treat the substances so that they will attach themselves to the bubble surfaces.

Protein skimmers are very often cylindrical in shape, and removal of the foam is usually by means of collection in a cup located directly above the water surface level in a main tank. The skimmed material can then pass either as foam or as a liquid out through a waste pipe for disposal.

NO-A-20040521, which is incorporated herein by reference in its entirety, describes a water purification system for a fish tank including a pump for circulating water through the system. Existing protein skimmers are generally bulky and tend not io be particularly efficient in terms of removing the foam and attached pollutants.

DK 2023 70407 A1 3

According to a first aspect of the present invention, there is provided a separation unit for a protein skimmer, the separation unit comprising: an inlet through which liquid and foam can pass into the unit, a first outlet for purified liquid, and a second outlet for foam; a tray across which liquid can flow between the inlet and the first outlet, and a plate positioned above the tray such that a leading edge of the plate sits at or below a level of the liquid surface in use, the plate being inclined at an acute angle to the direction of liquid flow across the tray so that foam floating on the surface of the liquid can be separated from the liquid surface and directed up the inclined plate towards the second outlet. In embodiments, the liquid is water, such as salinated or desalinated water. Obviously, the water or liquid entering the separation unit and potentially also the water leaving the separation unit will generally not be pure, and may contain contaminants, salt, and other additional materials.

The quality of the water or other liquid within commercial fish tanks or other systems can be improved by use of the above mechanism. The system is low cost, efficient, and can be adapted for use with smaller applications as well as large, land-based systems. Foam is skimmed off easily and quickly making full use of the momentum of the foam carried across the tray by the water/iauid currents.

The leading edge of the inclined plate refers to the edge of the plate closest to the inlet, or the edge which the liguid/water flowing from the inlet to the outlet across the tray reaches first. This is also the lowermost part or edge of the inclined plate. The plate therefore extends in a direction from the inlet to the outlet with its lowest edge closest to the outlet, is positioned with all or most of the tray above the level of the liquidiwater surface, and is angled in an upwards direction so that the leading edge, which the foam and liquid pass first as they travel from the inlet is positioned lower than the trailing edge, and closer to the tray base. The angle between the inclined plate and the vector representing the direction of travel of the liguid across the tray {or running from the inlet to the first outlet), measured in an upwards direction from this vector line, is less than 90 degrees. Foam is thus separated from the liquid surface at the leading edge of the inclined plate and travels up the plate, continuing in the same general direction away from the inlet but now following a sloping path relative to the flow direction of the liquid so that it rises upwards away from the liquid surface, to the second outiet. The purified liquid continues flowing under the plate to the first outlet. Water will be referred to below as the liquid to be purified, since this will most often be the case, but it should be noted that any liquid can be purified using the apparatus described herein.

DK 2023 70407 A1 4 in embodiments, the inclined plate is a flat sheet. A flat sheet will be the most effective in terms of maximising the amount of foam which can be carried away from the water/iquid surface within a particular time period. The plate may be curved or undulating rather than flat. A plurality of plates, possibly having different shapes or different sizes, may be located across the width of the tray carrying foam to the same outlet or to different outlets. The flat inclined plate may represent the upper surface of a wedge shape or another shape, or may represent the upper surface of a thin sheet of material, preferably having a thickness between 0.05 mm and 1 cm. in embodiments, the leading edge of the plate is positioned closer to the inlet and lower than the trailing edge so that the plate slopes upwards in the direction of water/liquid flow across the tray.

In embodiments, the angle between the inclined plate and direction of water/liquid flow across the tray is between 20° and 70°. In embodiments, the angle between the inclined plate and the direction of water/liquid flow is between 30° and 55°, preferably between 40° and 50°, and most preferably 45°. Where a flat-based tray is used, this angle will also correspond to the angle between the tray base and the inclined plate. in embodiments, in use, the base of the tray is angled between 0.5” and 10°, preferably between 1° and 10° from the horizontal in a downwards direction at the inlet. This creates a current drawing water/ligquid into the separation unit and across the tray helping to pull foam towards the inclined plate for removal. Preferably, the tray is angled between 2° and 5° from the horizontal in a downwards direction at the inlet, most preferably the tray is angled around 1°, around 2°, or around 3° from the horizontal in a downwards direction at the inlet. This slight downwards slope results in an optimum flow rate through the separation unit for efficient foam removal, whilst still allowing enough time for foam creation within the system. The optimum slope for the tray may be slightly different depending on the type of water or type of liquid being purified by the system (e.g. salt or fresh water). The horizontal in this case refers to a plane through the unit that will be parallel to a flat platform when the unit is placed with its base or supporting structure resting on such a platform in the correct orientation for use. The current that is created at least partly by the slope at — the first inlet, and which draws water/liguid into the separation unit, can also help to create foam due to the turbulence created at the inilet near to the water or liquid's surface. If the level of the water in the tank is set so as to substantially coincide with

DK 2023 70407 A1 the top of the inlet, or so as to sit above the top of the inlet, then this effect will be increased. in embodiments, the tray has a flat base extending between the inlet and the outlet. 5 The current across the tray from the inlet to the first outlet is created most efficiently and the flow rate for the water crossing the tray is the most stable if the tray is flat- based. The whole of the flat tray from the inlet to the first outlet may be angled downwards with respect to the horizontal, as mentioned above. The first outlet may, however, itself slope upwards with respect to the horizontal, and this will be described in more detail below. in embodiments, the inclined plate extends across the entire width of the tray. This will maximise the area for redirection/skimming off of the foam and will minimise the amount of foam left in the purified water or liquid which has flowed past the plate's leading edge. The length of the tray extends in the direction of water/liquid flow along the tray, and the width in a direction from side to side across the tray and perpendicular to the direction of water/iquid flow. in embodiments, the inlet and the first outlet are each rectangular openings or tubular regions of or immediately adjacent a closed-topped portion of the tray. in embodiments, the tray comprises a first enclosed portion adjacent the inlet, an open- topped portion, and a second enclosed portion adjacent the first outlet, and the inclined plate is located in the open-topped portion of the tray. This way the water/iquid is protected from material falling into the system from above across a large portion of the tray. The open-topped portion may also be protected by a hinged cover, which can be lifted to inspect the contents, for cleaning, or for repairs. in embodiments, the first outlet slopes upwards at an acute angle with respect to the direction of water/liguid flow across the tray or with respect to the base of the fray.

The upwardly sloping first outlet helps to regulate the water/liquid level within the tray. in embodiments, the separation unit comprises a sweeper having one or more paddies configured to travel in the direction of movement of the foam along atleast a portion of the path from the inlet to the second outlet to push the foam up the inclined plate. The sweeper contacts the foam and helps to lift, encourage, or push it up the inclined plate. The paddies may be flat or shaped, for example to include one or

DK 2023 70407 A1 6 more ridges or cupped portions to trap the foam.

The sweeper may contact the foam in the open-topped region of the tray. in embodiments, the sweeper comprises at least one paddle coupled to a rotating axle. in embodiments, the sweeper comprises two arms coupled to the rotating axle at one end and rotating with the axie, a rod coupled between the other ends of the arms, wherein the paddle is attached to and rotates with respect to the rod. in embodiments, the separation unit comprises a water wheel positioned beneath the first outlet such that water or liquid flowing from the first outlet contacts the wheel to cause it to tum. in embodiments, the water wheel is coupled to the axle of the sweeper by way of a transmission mechanism, such that when the water wheel turns, the axle of the sweeper is caused to turn. in embodiments, the transmission mechanism comprises a transmission belt extending between two gear wheels which are fixed to and rotatable with the water wheel and the axie of the sweeper respectively.

in embodiments, the separation unit comprises an adjustment mechanism for adjusting the angle of the inclined plate.

This way the separation unit can be easily adjusted to sult different systems, which may have different flow rates or may involve different types of fluid.

A shallower angle may suit systems where the foam is likely to be thicker and more sticky, or where the flow rate of water or liquid flow through the system is generally slower. in embodiments, the adjustment mechanism comprises an extendible element coupled to the inclined plate.

The element can be extended to raise the part of the inclined plate to which it is coupled.

If coupled to the trailing (highest) edge of the plate then extending the element will increase the angle of the plate. in embodiments, the extendible element comprises a threaded element, and the angle of the inclined plate is adjusted by turning the threaded element.

Here, the threaded element can be passed through a receiving opening, which may also be threaded, such as a nut, and turning one relative to the other can extend the adjustment mechanism to raise an edge of the inclined plate.

DK 2023 70407 A1 7 in embodiments, the separation unit comprises one or more spray nozzles for spraying and liquifying the foam as it travels between the trailing edge of the inclined plate and the second outlet. This improves the ease of removal of the foam from the system after it has travelled up the inclined plate. The second outlet can be located below the level of the trailing edge of the inclined plate so that the foam, once liguified, can run down to the outlet. The nozzles can be positioned on a frame, which may represent a hood under which the nozzles are fitted.

According to a second aspect of the present invention, there is provided a filtration system for a fish tank comprising a protein skimmer including the separation unit of the first aspect.

According to a third aspect of the present invention, there is provided a method for providing a separation unit for a protein skimmer comprising: providing a unit housing having an inlet through which liquid and foam can pass into the unit, a first outlet for purified liquid, a second outlet for foam; providing a tray within the housing and across which liquid can flow between the inlet and the first outlet; and positioning an inclined plate above the tray at an acute angle to the direction of liquid flow across the tray such that a leading edge of the plate sits at or below a level of the liquid surface in use and foam floating on the liquid surface can be separated from the liquid surface and directed up the inclined plate to the second outlet. The liquid may be water, such as salinated or desalinated water.

According to a fourth example, there is provided a separation unit for a protein skimmer, the separation unit comprising: an inlet through which liquid and foam can pass into the unit, a first outlet for purified liquid, and a second outlet for foam; a tray across which Houid can flow between the inlet and the first outlet; and a sweeper having one or more paddies configured to move with the foam along at least a portion of the path from the inlet to the second outlet to push the foam towards the second outlet. The inclusion of a sweeper helps to prevent build-up of the foam within the unit. The liquid may be water, such as salinated or desalinated water. in examples, the sweeper comprises at least one paddle coupled to a rotating axle.

DK 2023 70407 A1 8 in examples, the sweeper comprises two arms coupled to the rotating axle at one end and rotating with the axle, a rod coupled between the other ends of the arms, wherein the paddle is attached to and rotates with respect to the rod. in examples, the separation unit comprises a water wheel positioned beneath the first outlet such that water/liquid flowing from the first outlet contacts the wheel to cause if to turn. in examples, the water wheel is coupled to the axle of the sweeper by way of a transmission mechanism, such that when the water wheel turns, the axle of the sweeper is caused to turn. in examples, the transmission mechanism comprises a transmission belt extending between two gear wheels which are fixed to and rotatable with the water wheel and the axle of the sweeper respectively. in examples, the separation unit comprises a plate positioned above the tray such that a leading edge of the plate sits at or below a level of the water/liquid surface in use, the plate being inclined at an acute angle to the direction of water/liquid flow across the tray so that foam floating on the surface of the water/liquid can be separated from the water/liquid surface and directed up the inclined plate to the second outlet, In embodiments, the sweeper is configured to push foam up the inclined plate.

According to a fifth example, there is provided a separation unit for a protein skimmer, the separation unit comprising: an inlet through which liquid and foam can pass into the unit, a first outlet for purified liguid, a second outlet for foam; and means for liquifying the foam. In examples, the unit comprises a tray across which figuid can flow between the inlet and the first outlet iquification of the foam makes it easier fo remove from the system. in examples, the means for liauifying the foam comprise one or more spray nozzles for spraying and liguifying the foam as it travels between the inlet and the second outlet. In examples, the separation unit comprises means (such as a plate with a leading edge positioned at the water surface) for separating the foam from the water, and the liquification means are positioned to liquify the foam after it has been separated from the water surface.

DK 2023 70407 A1 9

Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein:

Figure 1 shows an example of a water purification unit including a protein skimmer for a fish tank;

Figure 2 shows a cross-section though a water purification unit;

Figure 3 illustrates an aquaculture tank with filtration system included;

Figure 4 shows a filtration system including protein skimmer, mechanical, and bio filters;

Figure 5A shows a plan view of a skimmer with additional rotating paddle;

Figure 5B shows a view from above of the skimmer shown in figure 4A;

Figure 5C shows a side view of the skimmer of figures 4A and 4B;

Figure 8 illustrates the foam separation mechanism within the separation unit;

Figure 7 illustrates another embodiment of the foam separation mechanism within the separation unit;

Figure 8 shows an isometric view of the separation unit of figure 7;

Figure SA shows a cross sections through a skimmer with the paddle in its upwards extended position during rotation,

Figure 9B shows a cross seclions through a skimmer with the paddie in its downwards extended position;

Figure SC shows a cross sections through a skimmer with the paddle at an angle of around 45° to the vertical;

DK 2023 70407 A1 10

Figure 10 illustrates the transmission mechanism for use of energy from the movement of water through the system to move a sweeper; and

Figure 11 shows a protein skimmer in situ.

A water purification system including a protein skimmer is ilustrated in figure 1. The skimmer within the purification unit functions to remove small particulate matter and dissolved organic compounds from the water, and can be used in any system where water circulates. As mentioned above, water is described as the liquid to be purified in the examples below, but the apparatus described is also useable for the purification of liquids other than water. The apparatus finds particular use in recirculating aguaculture systems, such as in certain fish farming apparatus including fish tanks, where a compact and efficient means for water filtration is required. The skimmer can be used with both salt and fresh water systems. The illustration in figure 1 represents part of the prior art, however the specific configuration of parts of the tank and skimmer (including the mechanism by which the foam is separated from the water within the separation unit), that are not shown in this figure, are new and are the focus of this patent application. Figure 1 is therefore included only to Hlustrate an example of how the protein skimmer, including the novel separation unit described below, may be integrated within a larger water purification system.

The water purification system includes a main tank 1 through which air is passed from an inlet 3 at the base of the tank to an outlet 5 at the top of the tank, and is pumped out using a vacuum pump. The tank may be used as a degassing tank, with the oxygen injection increasing the relative pressure of Oz in the water and forcing

CO out through a de-gassing outlet, such as the outlet 5. The pH of the water may be adapted at this stage, or prior to eniry into the tank, in order to improve de- gassing efficiency. Water, including dissolved organic compounds and particulate matter to be removed, enters the tank through inlet 7. In the example shown, ozone — is added to the water prior to entry into the tank in an ozonation unit 8. The addition of ozone has a number of advantages including increasing the efficiency of the skimming process by breaking down larger particles and making them easier to remove. Ozone may be added at the rate of between 20g and 100 g per hour, more preferably between 40g and 80g per hour, and most preferably around 65g per hour fora commercial fish tank of average size where around 100 kg of fodder is supplied per day. The ozonation unit and flow rate therethrough may be configured so that the

DK 2023 70407 A1 11 water spends a reasonable length of time, such as around 30 seconds, within the ozonation tank to ensure proper uptake of the ozone.

Figure 2 shows a cross section through the tank 1 and skimmer 2 in an example of a — water/liquid purification system including the new separation unit described below.

Water enters at the top of the tank 1 through the inlet and passes downwards to the base through one or more mechanical filler layers 69 comprising perforated screens.

Water drips through the screens one by one, during which process large particulate matter is captured and removed. Lower screens may comprise finer gratings or smaller perforations than those located higher up in the tank in order to remove smaller and smaller particulate matter in stages as the water passes through the tank. Four mechanical filters are shown in figure 2, although any number (or none at all) can be included, and these are orientated horizontally within the tank. Biofiltration may also be utilised within the tank or in a separate part of the system. A pool of walter sits at the base of the tank in use, and water that has passed through the lowest screen splashes as it hits the surface of this pool producing foam. This foam is carried into a separation unit 35 along with any dissolved organic compounds and particulate matter which have attached themselves to the bubbles making up the foam.

The apparatus is shown as part of a larger aquaculture system in figure 3. in this system water travels from a fish tank 21, through the protein skimmer 2 where it is purified by removal of particulate waste and DOCs, and then back into the fish tank as purified or partially purified water. Other water treatment systems 25 (for acidity — and/or temperature control, oxygenation, and so on) may be incorporated into the system between the fish tank outlet and the protein skimmer 2 as shown in figure 2, between the protein skimmer 2 and the inlet to the fish tank, or both. Water is circulated by way of a pump 23. The pump may be situated anywhere in the path of the circulating water, but will preferably be located at or close to the outlet from the fish tank as shown.

The water purification system may include additional mechanical 31 and/or biofilters 29 as shown in figure 4. Here the filtration apparatus 33 comprising the protein skimmer 2 and other filtration mechanisms (31; 29) is formed as a stand-alone unit — which can be easily attached as part of an existing aquaculiure system or another system. The stand-alone unit can comprise only the protein skimmer in some embodiments. The filtration unit shown in figure 4 comprises a housing and includes

DK 2023 70407 A1 12 a mechanical filter 31 at the rear of the unit, and a moving/fixed bed bio-filter 29 in the central region. The protein skimmer 2 is located at the front of the unit and can include the tank 1 where CO, may be de-gassed, and where at least some of the foam extracted at the separation unit of the skimmer may be formed. lf the tank 1 is used solely for degassing, then the protein skimmer will not include the tank but may comprise an additional mechanism (such as a venturi injector or a waterfall or weir- like structure) to induce bubble formation within the water before it passes through the inlet io the separation unit. Foam can also be produced within the separation unit or at the inlet due to turbulence created there, as described in more detail below. 16 Obviously, the locations of the different filters within the apparatus can be changed.

The protein skimmer 2 may be located at the rear or in the central region, for example, with the cutlets for foam and purified water at the back or side of the units.

The stand-alone unit may also only contain a protein skimmer such as the protein skimmer described below, with the mechanical and bio filters omitted. These can be included in the system of figure 3 as separate units or can be dispensed with in some cases.

The protein skimmer 2 may be preceded by an ozonation mechanism or ozonation unit & which adds ozone to the water prior to foam production. The addition of ozone can help to improve the efficiency of the process as explained above, particularly in situations where the level of fat in the waste water is high. Ozone oxidises waste products within the water, and this process produces CO. The excess CO» can then be removed by de-gassing from tank 1. The ozone causes particulate matter to flocculate into larger particles which are more easily attached to the bubbles and removed during the foam fractionation/protein skimming process. Another benefit of adding ozone to the water is that it can kill off pathogens.

Water leaves the main tank 1 at inlet 11 to the separation unit 35 of the skimmer.

Foam may be formed by mixing of the water within tank 1 as It splashes into a pool of water at the base of the tank as described above, by currents produced within the pool of water, and/or by mixing and bubble creation at or near to the inlet 11 or within the separation unit itself, or by a combination of two or more of the above mechanisms. Once formed, the foam tends to rise to the surface of the water. Within the separation unit, water and foam are separated from each other, after which purified water is removed through one or more first outlets 15 and foam is removed through one or more second outlets 41 as described in more detail below. The purified water passes from the first outlet 15 into conduit 17 which carries the clean

DK 2023 70407 A1 13 water away from the separation unit of the protein skimmer, and usually on to further treatment systems or back to the fish tank.

The positions and numbers of the various inlets and outlets, and the direction in which waste foam and clean water are carried away from the system are adaptable. in some cases, the inlet 11 to the separation unit may be located at another location within the tank 1 rather than near to the bottom as shown in the figures, but obviously locating the inlet 11 at the base of the tank improves mixing and foam generation in the base of the tank and at the inlet. Baffles or a grating may be included at the inlet to the tank or to the protein skimmer to help to create turbulence and generate more foam. The inlet 11 and the first outlet 15 for water may be elongate as shown. This maximises the water surface area for removal of the foam within the separation unit. The water and foam exit the tank 1 and enter the separation unit 35 through a rectangular shaped opening in the example shown. The — water/foam inlet and first outlet may, however, have any other shape. in a preferred example, water flows through the separation unit in a conduit which is elongate, and which may be closed-topped along some sections and open-topped along others (or which may be open topped along its whole extent). The end of this structure is visible as outlet 15 in figure 3. This conduit therefore forms a tray-like structure within the separation unit which will be at least partially filled with water in use. An overflow pipe for excess water may be included in the tank or within the separation unit. This functions to ensure that the depth of the water passing through the unit is maintained at a certain level for optimum performance.

The tray, across which water passes through the separation unit, may be angled very slightly downwards in a direction from the inlet 37 through which foam and water enter the unit to the start of an upwardly extending portion forming the first outlet 15 for purified water. The angle between the tray at the inlet and the horizontal may be between 0.5" and 10%, preferably between 1° and 10°, preferably between 2° and 5°, or between 1° and 3°. The angle may be around 1°, around 2°, or around 3°, for example. This angle may, in some cases, be adjustable, such as within the ranges described above, for example using an extendable foot underneath the separation unit. The angle of the tray helps to create a current through the inlet from the tank to the separation unit and across the tray. This current carries foam into and through the separation unit. The precise angle can depend on the type of water which the system is being used to purify. The use of salty water (such as seawater), for example, results in more efficient foam production. The speed of flow across the

DK 2023 70407 A1 14 separation unit can therefore be higher while still removing a minimum volume of foam than it could be were fresh water being purified, and the tray can be angled so as to slope downwards more steeply.

The tray may represent an elongated tube along at least a part of its length as mentioned above. The tray in an initial portion directly following the outlet from the tank, which is also the inlet to the separation unit, may represent an elongated tube {i.e. with a closed top). An open-topped section may foliow, and an upwardly extending lip may be formed at the edge of the roof of the tray where the closed portion ends, and the open-topped portion begins. Within the open-topped section the water flowing through can be seen from above if looking directly down onto the tray. After this comes another ciosed-topped tubular section which leads to the first outlet. Another similar lip may extend upwards from the roof of the tray also where the open-topped portion ends, and the second closed-topped portion begins. Both lips may extend along the entire width of the tray, providing an upwardly extending ridge along at least two sides of the opening formed in the roof of the tray.

Alternatively, a lip may be provided on along one side of the opening only, such as the outlet side closest to outlet 15. Between the two enclosed sections of the tray, in the open-topped portion, the foam is removed from the water flow as will be described in detail below. There may be no additional lips at the intersections between the open and closed topped sections of the tray in some cases.

Separation of the foam from the water as it passes across the tray is by way of an inclined plate which has a leading edge located at or just below the surface of the water. The plate is inclined at an acute angle to the direction of water flow such that the foam, once separated, continues to move in the same direction, which is a forwards direction with respect to water flow across the tray, encouraged by ihe build-up of foam behind, but rises upwards slowly away from the water surface. The water passes underneath the leading edge of the plate and continues its path across — the tray to the first outlet 15, but the foam is forced up the inclined plate and on to the second outlet 41. The inclined plate in this case is located just before the second enclosed portion of the tray. As mentioned, the edges of the roof of the tray where the open-topped portion begins and again where it ends may each comprise an upwardly extending lip, which may extend vertically a distance of between 2cm and 8cm, preferably around Sem. The water and foam therefore passes under the first (possibly) lipped edge of the first enclosed tray portion, travels across the open topped portion of the tray (where the foam rises to the top of the water or sits on the

DK 2023 70407 A1 15 top of the water and is carried along), meets a region of the inclined plate at or just above the leading edge, travels up the inclined plate, meets and is pushed over the second lip (if present) and continues along above the second enclosed section of the tray where it is directed towards an outlet 41 provided for foam.

Control of the water level can be provided at least partially by the overflow pipe which sits at the desired level of the water surface within the skimmer. If the flow rate through the tank is higher than expected, any excess water will run out of the system through the overfiow. The skimmer can be designed to handle a particular flow rate without the requirement of an overflow. For one size of skimmer like the one described herein, for example, a flow rate of around 25 cm?/s through the inlet to the tank results in the desired water level in the separation unit and an overflow pipe is not required. The overflow pipe can still be provided to allow for variations in flow rate, or to allow a higher flow rate io be used with the same system. The default — water level can also be adjusted in some embodiments by moving the position of the overflow pipe manually or automatically. An adjustable overflow pipe can be provided either in the wall of the tank, as shown in the figures, or within the separation unit itself.

The inclined plate need not be flat in shape. The plate (and therefore also in some cases the leading edge) can be curved or undulating, for example, forming one or more grooves up which the foam can preferentially travel. The plate may comprise the bottom portion of a tray or tube. What is important is that the foam is able to travel up the plate easily, away from the water surface, and over any additional lip — that might be present. To this end, an angle of between 5” and 85°, preferably between 10° and 80”, more preferably between 20° and 70°, more preferably between 20° and 60°, and most preferably around 45° between the direction of water flow across the tray and the plate is used. The angle between the direction of water flow and the plate refers to the angle between the direction of water flow and the — direction of flow of the foam just after it has started to move up the plate. The angle of the plate may or may not be constant across the plate in a direction from the leading to the trailing edge, but most often will be. The plate will usually be formed of a solid material such as a plastics material. The surface of the water may be slightly angled with respect to the base of the tray, as described above (although these will not be far off parallel because the slope of the tray is very slight). The water still passes across the tray from the inlet to the outlet, though, so the direction of water

DK 2023 70407 A1 16 fiow referred to herein refers to the direction parallel fo the base of the tray between the inlet and outlet in the region where the inclined plate is located.

The inclined plate may include vertically extending side portions or may extend across the entire width of a housing such that, in effect, vertically extending side portions are provided by the edge of the unit housing. These side portions or walls on the plate help to contain the foam on the ramp formed by the plate. The plate may in some cases include one or more perforations or openings in a region at the base to prevent any water build-up. If present, these can be sized so as to allow water but not foam through.

Before reaching the second outlet 41, and after passing over the lip (if present) at the top of the inclined plate, the foam may enter a collection unit 19 where it may sit for a time before being removed from the unit through the second outlet 41. inside the separation unit, only a small region of the pathway for water may be exposed on its upper surface. Here the leading edge of the inclined plate sits at or below the water surface. Once the water passes under the leading edge of the plate, it may pass within a second covered rectangular section of tubing which ends with outlet portion 15 (the second covered portion of the tray described above). The foam may be sprayed within the collection unit if present, or after reaching the top of the inclined plate, to liquify it and making it easier to remove from the system. The liguified foam can then easily flow from the area where it is sprayed and towards the second outlet 41. Usually the second outlet, which may comprise more than one outlet channel, will be positioned lower than the top of the inclined plate so that liquified foam can flow down to the outlet for removal.

The outlet 15 for purified water may be angled upwards slightly from a horizontal direction as shown in the figures. This upwardly extending outlet helps to maintain the water surface in the separation unit at a desired level. The incline also helps to prevent any excess foam from passing through the outlet with the purified water and allows the addition of a water wheel, which will be described below, as part of a compact configuration.

The water and foam pass from tank 1 through the inlet to the separation unit 35, which is shown in figures BA to 5C, 6, 7, and 8. Here, foam is separated from the purified water in a simple way which makes use of the momentum of the flow of water across a tray forming an elongated conduit within the unit. In its simplest form,

DK 2023 70407 A1 17 the separation unit 35 comprises an angied plate or surface 69 with a leading edge sitting at or below ihe level of the water surface in use. The plate is fixed or removably/movably fixed at an acute angle with respect to the direction of water flow from the water/foam inlet 37 to the unit towards the water outlet 15. This corresponds to a direction from the inlet to the first outlet, and usually also to a direction parallel to the base of the tray 73. The positioning of the plate may be adjustable, but the leading edge should always be at or near the surface of the water in use to be able to guide the foam, and substantially only the foam, up the incline formed by the plate to the second outlet. The tray itself may be a conduit or tube and may be closed- topped in some sections and open-topped in others.

The level of the water in use may be known fairly accurately based on the configuration of the system and the water flow rate, so that the plate can be positioned accurately prior to use. The water level may be kept stable with the help — of an overflow pipe in addition. If adjustment of the plate position is required then the coupling mechanism between the plate to the rest of the separation unit may allow the position of the plate to be adjustable, at least to some extent. One or both of the height of the plate leading edge and the angle of the plate may be adaptable by way of an adjustment mechanism, for example, but the plate should be able to be held fixed during use of the protein skimmer. The inlet for foam and water 37 may be located at a rear (upstream in use) face 39 of the unit and the outlet 15 for purified water at the front (downstream in use) face 42 of the unit, in which case the plate may be coupled to the unit housing such that it is angled or can be angled at an acute angle with respect to a plane extending through the inlet and the outlet for water and parallel with the direction along which water flows across the tray therebetween. The plate will be above the plane and extending with its leading edge lower than its trailing edge (with the edge of the plate that is closest to the inlet for water and foam, and under which the water passes first as it flows across the tray, lowermost).

The inclined plate 69 extends in the direction of water flow from the inlet 37 to the outlet 15 and is angled less than 90° with respect to this flow direction (in an anticlockwise direction from the water flow vector). The leading edge of the plate (the first part of the plate that the water reaches when flowing from the inlet 37 to the first outlet 15) will sit lower than the trailing edge during use to form the incline, such that foam floating on the water surface meets the leading edge, or a region of the sloping surface just above the leading edge, and travels up the inclined plate towards the

DK 2023 70407 A1 18 trailing or downstream edge. As the water passes the leading edge of the plate, the foam which sits on the surface of the water travels up the sloped plate and is thus separated from the purified water which continues to flow beneath the plate’s leading edge, beneath the rest of the plate, and on to the first outlet 15. There may be an upwardly extending lip at the railing edge of the inclined plate, as mentioned above, which the foam must travel over as it leaves the inclined plate and passes on to the outlet for foam. The embodiment shown in figure 6 includes such a lip, and the embodiment shown in figure 7 comprises an adjustable inclined plate with no lip, or fitted over the lip of figure 6. Of course, a lip could be added to the device of figure 7 atthe top of the adjustable slope if desired.

The housing of the separation unit 35 is substantially rectangular and may be wider than it is high, as shown in ihe figures. The first outlet 15 in this example is also wider than it is high, such that it forms a rectangulariy shaped tube. The water flows from the inlet to the outlet across a tray-like structure which may be open across at least a part of the top surface as shown. Foam is either carried into the inlet with the water as the water flows or is formed within the separation unit, and this foam passes up the sloping/inclined plate, and then exits the housing of the separation unit through a second outlet 41. The second outlet 41 may lead to a further housing or container where the foam can be collected for use or for later disposal. The foam may also simply be ejected from the system at the outlet.

The separation unit 35 is seen viewed from above in figure 5B. Here the water passes through the lower part of the unit which in this case is largely enclosed and is thus not visible from above. In the righimost section of the housing 43 shown in the figure which is closest to the inlet side of the unit, the foam moves up a flat, inclined ramp (representing the inclined plate, which rises out of the page in a direction towards the left of the unit). A sweeper 45 rotating on axle 47 helps to encourage the foam to move up the ramp and down into a foam collection unit 19 located in the leftmost part 49 of the unit. The sweeper mechanism is, however, optional. Travel of the foam up the slope is helped by the build-up of foam behind, and this may be enough to remove the foam effectively without the sweeper. From the foam collection unit, the foam can drop down into one of two channels 51 on either side of the collection unit which lead to one or more outlet pipes for the foam. As mentioned the foam may be liquified or partially liquified, such as by spraying with water jets or sprays, to encourage movement into the channels in any of the examples described herein. The positioning, shape, size, and number of the spray nozzles can vary to

DK 2023 70407 A1 19 suit specific requirements. Liquification may be assisted by the material used to spray the foam, which can act to dissolve the foam in some cases. The channels 51 can be omitted, with one or more outlets 41 being located in the side of the collection unit 19. One channel can also be included rather than two, or the channel may extend all of the way around at least three sides of the collection unit, or a part of the way around one or more sides. The presence of the channels 51 helps to encourage the foam towards the outlets, and to this end they can slope towards the outlets 41 as shown in figures 5A and 5C at least. Including two outlets for the foam increases flexibility. A hose or a similar mechanism can be used to wash foam out of the system through either one of the cutlets, although this, again, is optional.

The sweeper and/ or the spray mechanism for liguifying the foam can also be used with a separation unit without a sloping path for the foam. The foam can be separated via a flat plate, for example, lying at the level of the water surface in a horizontal plane, or the sweeper or the build-up of foam behind can simply push foam directly over an upwardly extending lip in the absence of the inclined plate.

Obviously, the level of the water then needs to be more stable for the mechanism to work well, it is much harder to move the foam along, and partially purified water is more likely to escape from the system. Including the inclined plate is advantageous for these reasons at least.

The foam separation mechanism within the unit is shown in more detail in figure 8.

Here the position of the inclined plate or ramp 69 with respect to the rest of the unit 35 in one example is clearly shown. The water passes across the tray 73 in a direction from right to left in figure 8 from inlet 37 to outlet 15. A cross-section — through the separation unit 35 shown, which allows the positions of the inclined plate 69 and lip 71 to be seen.

The water level within the separation unit should be constant, or substantially constant (with only small variations, due to rapid changes in flow rate from the tank for example). The water level may be such that it sits around 1 mm above the bottom edge of the first lip 75 (which the water passes under as II leaves the first enclosed tray portion) and around 6 mm above the leading edge of the inclined plate. These levels are marked in the figure and the water level is visible. This difference is due to the slight downward slope of the tray described above. The inclined plate 69 may be between 5 mm and 200 mm long, preferably between 100 mm and 200 mm long, and most preferably around 150 mm long, and may be around 10 mm higher at its upper end than at its leading edge. Each of the two lips may be around 5 cm high.

DK 2023 70407 A1 20

The lips help to ensure that no water can leave the system and the second lip additionally provides a barrier to prevent foam from travelling backwards down the inclined plate. Where the water travels under the edge of the roof of the tray (including the first upwardly extending lip) as it moves from the first enclosed tray portion to the open-topped portion, it may be dragged under the edge by currents, and this can result in additional foam formation which aids the performance of the skimmer. in some cases, most or all of ihe foam within ihe open-topped portion of the tray can be created via this mechanism. This effect is due to the fact that the tray comprises a closed portion 77 followed by an open topped portion 79 in the direction of water flow and the lowest part of the edge of the closed top portion sits at or just underneath (less than 5 mm below, preferably less than 2 mm below, most preferably around 1 mm below) the surface of the water in use so that turbulence is created as the water passes undemeath and out into the open-topped section.

Figure 7 shows another example configuration for the inclined plate 89 of the separation unit 35. Here, no lip is present at the top of the inclined plate and the sloping section formed by the plate longer than in the example of figure 6. The system is still generally configured so that the level of the water surface is kept around Omm to 10mm, preferably between 4mm and 8mm, and most preferably around 8mm above the leading edge of the plate (as for the example of figure 5).

The length of the inclined plate 89, measured in a direction from the leading to the trailing edge in this example is between 10cm and 50cm long, preferably between 20cm and 20cm. The sloping portion of figure 7 can be retrofitted to a separation unit, such as the one shown in figure 6, by fitting the inclined plate with a support bracket and adjustment mechanism (if present) onto the unit where the water passes into the second closed portion of the tray and on towards the outlet.

The angle of the plate can be adaptable by way of an adjustment mechanism, an example of which is shown in figure 7 as adjustment mechanism 70. Some example measurements are shown in mm in the figure, however these are intended as examples only and are not limiting different sizes and relative sizes can be used for the different parts depending on need. In the example shown in figure 7, the adjustment mechanism 70 includes a threaded screw 82 which passes through an opening or nut. One of the screw or nut is coupled to an upper or lower edge of the plate, and the other to the rest of the mechanism. in figure 7, the opening through which the screw passes is in a support bracket 81, and the upper end of the screw is coupled to, but can turn relative to, the adjustable inclined plate 69. Turning the

DK 2023 70407 A1 21 screw moves the upper (or lower in other examples) end of the slope towards or away from the support bracket to adjust the angle of the slope. In general, turning the screw 82 then increases or decreases the length of the screw between the inclined plate and a supporting section, adjusting the angle of the inclined plate. Any extendible element coupled to the inclined plate can be used as the adjustment mechanism, activated either remotely or manually. Other adjustment mechanisms can be envisaged, such as a ratchet-based or spring-based mechanism.

Allowing for some adjustment of the angle of the slope means that the system can be easily adapted to sult different flow rates for the water, different production rates for the foam, different positions of any overspill pipe to control the water level, and variation in the water content (e.g. salinity, concentration of particles to be removed), among other things.

Figure 7 is a cross-section through the separation unit shown in figure 8. In both figures, a spraying system 76 is visible above the end of the inclined plate. This is formed of a frame 85, which may be in the form of a hood or a curved plate coupled by a bolt connection above the tray. The frame supports one or more spray nozzles 80, here supported underneath the hooded section. These nozzles are configured to spray the foam with a substance which liquidizes it to make it easier to remove. A number of nozzles may be positioned along the width of the inclined plate to liquidize the foam just after it passes over the trailing or upper edge of the inclined plate. Here 4 nozzles are spaced along the unit, but there may be any number of nozzles, such as 110 20, preferably 2 to 10, most preferably 4, depending on the size of the unit, the consistency of the foam expected, and other factors.

The separation unit 35 may include a sweeper 45, as mentioned above, in order to improve the efficiency of the foam separation process. The sweeper 45 in one example comprises a moving paddle 53 which acts to sweep or encourage the foam through the system, and may act to sweep the foam up the inclined plate after it has encountered the plate and been separated from the surface of the water. The action of the sweeper in this case encourages the foam up the ramp formed by the inclined plate, over the upwardly extending lip if present at the trailing edge of the inclined plate, and into the foam collection unit 19 or directly to an outlet. The sweeper 45 may be in any form such as a brush, or may be formed as a number of separate elongated structures, but a particularly advantageous form for the sweeper is a solid, substantially flat, paddle 53 which provides a large surface area to contact the foam

DK 2023 70407 A1 22 and push it along more effectively. The sweeper may also be employed at an earlier or later stage in the foam's path through the separation unit, such as to push foam across the open-topped region of the tray or to push foam across the collection unit towards an outlet.

The sweeping action itself can be achieved in a number of ways, a preferred method being the coupling of the sweeper io a rotating axle 47. As the axle rotates, the sweeper also follows a circular path. in embodiments, the sweeper can be attached directly to the rotating axle to rotate with the axle, however more typically arms 55 are included at either end of the axle which rotate with the axle and which carry the rotating sweeper, in this case a flat paddle, at their ends by way of a rod 57. This can allow the sweeper to be more easily removed in case repair or replacement is required, or the size of the sweeper needs to be adjusted. This configuration also allows the paddie to be rotatable with respect io, and to hang from, the rod so that it — always extends substantially downwards in use.

Figures 9A-9C illustrate the relative movements of the axle 47, arms 55, and paddie 53 of the sweeper 45 during rotation of the axle. in figure BA, the arms extend in an upwards direction. The paddle, which is also able to rotate relative to the rod 57, extends downwards. The coupling of the paddie to the arms can be by any means that will allow rotational movement of the paddie. Here, the paddie is coupled along one side to the rod 57 by way of a number of rings within which the rod can turn. The rod is coupled to, and moves with, the arms (it may or may not be able to rotate, but preferably does not rotate relative to the arms). As the axle 47 rotates, the arms with the rod 57 at their ends sweep out a circular path and the paddle 53 is carried with the rod but rotates relative to it. The paddle will tend to extend in a downwards direction under the action of gravity, and so will act to sweep the foam as it passes the upper surface of the inclined plate.

In figure 8B, the arms 55 are orientated such that they extend downwards, with the paddie 53 hanging downwards therefrom. The paddle extends at least far enough downwards in this orientation to extend into the layer of foam which is moving up the inclined plate, or is about to start to travel up the inclined plate. Here the paddle hangs directly downwards, but it may be angled slightly if a iot of foam is present because of the reaction force provided by the foam. Obviously, to what extent the paddie tends to hang directly downwards during contact with the foam will depend on the weight of the paddle and can be adjusted as desired. In figure BC, the arms are

DK 2023 70407 A1 23 orientated at roughly 45° from the vertical and the paddle hangs directly downwards.

The paddie may include a brush or bristle-like structures extending along at least a portion of its lowermost edge to help with sweeping.

The paddle may be configured to extend to the anticipated level of the water surface when hanging directly downwards with the arms also oriented directly downwards in the orientation shown in figure 9B. The paddle may be configured to extend io the position of ihe leading edge of the inclined plate when hanging directly downwards with the arms also oriented directly downwards. This will provide the most effective sweeping action for the foam. Depending on the orientation and shape of the inclined plate, the paddle may move along contacting the inclined plate as it rotates further (from the orientation shown in figure 9B to that shown in figure 8C). This, also, may improve the sweeping action. in embodiments the ramp itself may be curved as the surface of part of a cylinder or tube such that the paddle hanging directly downwards justiouches or just reaches the surface of the plate throughout a portion of the rotation of the axle. This portion may be from 0° {paddle hanging directly downwards as in figure 9B) to between 30° and 50°, or preferably around 45° of one rotation of the axle (i.e. for around the first 1/8" of the full rotation of the axle, the sweeper may contact or extend to the level of the inclined plate). in such an embodiment, it may be — advantageous to include a heavy paddle which will hang substantially directly downwards whether or not foam is building up in front of it to reach the surface of the inclined plate.

A lighter paddle, on the other hand, and one which does not reach and contact the inclined plate or does so for a shorter portion of the rotation will require less energy to turn which may be desirable in some circumstances. At least the weight and size of the paddie, the position of the axle above the water level, and the configuration of the inclined plate itself can be adjusted to achieve an efficient sweeping motion for the foam with minimal energy output.

The axle 47 on which the paddle is mounted may be turned by way of a transmission mechanism which uses at least some of the energy from the flow of water through the system. Ultimately, this energy is provided by the pump 23 or another mechanism which circulates the water around the system. This pump may force the — water from a fish tank or another holding tank to the separation and/or filtration units and then back to the tank again. The energy of the water flow is captured using a water wheel 59 as shown in at least figures 5A to 5C and 9A to 9C. Water travels

DK 2023 70407 A1 24 through the separation unit where the foam is separated from the water surface and carried up the inclined plate as described above.

The water with the foam removed continues through the unit towards the first outlet 15. Where a water wheel is used, the water pours out of the outlet (i.e. over an edge of a tray or out of a tube) and on to the paddies of the water wheel, which causes the wheel to turn. The water wheel can be coupled to the axle of the sweeper by way of at least one transmission mechanism. This may comprise a transition belt running between two gear wheels which rotate with the axle and the water wheel respectively. There may be one or more gears and/or one or more additional belts included. When the water wheel turns, the axle is thus caused to rotate to operate the sweeper. The water then continues through the system and is carried as purified water back to the tank.

Figure 10 shows the transmission mechanism coupling the water wheel 59 to the axle 47 of the sweeper in one example. Here one additional gear wheel 81 is included, Two or more additional gear wheels may be included in some embodiments. The gear wheel 61 may provide a simple transmission and may be the same size as the gear wheel 63 coupled to the axle and/or the gear wheel 85 coupled io the water wheel. Different sized gears can alternatively be used to speed up or slow down the sweeping motion of the paddle (e.g. a smaller or larger gear wheel coupled to the paddie) if desired. The water wheel itself can also include a gear wheel of any size. This will depend largely on the speed of the water travelling through the system and how quickly the paddie needs to tum to optimize the sweeping motion given the weight, shape, and size of the different components of the separation unit.

The water wheel can be dispensed with in some examples, in which case the sweeper can be turned using another means such as a battery/mains power and a motor. Water with foam removed will then flow from the outlet 15 into to a conduit, and will continue its path through the system. The sweeper can also be omitted entirely in some examples, in which case the foam is carried up the inclined slope simply by the action of the water moving through the system and the tendency of the foam to build-up behind and force foam ahead to continue moving along in the — direction of water flow. in such a case it may be preferable io include a smaller upwardly extending lip or no lip at all at the tralling edge of the inclined plate to make it easier for the foam to pass through the separation unit.

DK 2023 70407 A1 25

The entirety of the separation unit may be contained within an additional outer housing for protection of the various parts and for prevention of contamination of the purified water. The separation unit may be contained within the same outer housing as the tank 1 and other parts of the system. Other filtration mechanisms may also be present within this housing as shown in figure 4. The separation unit, and in particular ihe open-topped portion of the tray within the separation unit may be enclosed within a hinged cover to allow access while protecting the internal paris and the water from contamination or damage.

Figure 11 illustrates a protein skimmer 2 including the separation unit 35 described above (including any of the variations and embodiments described), and mounted in situ within a larger system. The separation unit and tank 1 are mounted on a platform 67 and ihe water inlet pipe 7 to the tank 1 is visible at the top of the apparatus. The — water pipe in this case is bifurcated to form two separate inlets for better distribution of the water entering the tank. Any number of inlets may be included. Including more than one inlet through which water enters the tank can aid the filtration process within the tank. Water passes down through the tank and exits the tank at outlet located near to the base which leads to or is the same as the separation unit inlet, as described above. By this point a layer of foam may have formed on the surface of the water, and this is also carried into the separation unit.

The air outlet 5 from the top of the tank is also visible in the figure. Once the water has passed through the separation unit it flows over the water wheel 59, causing it to turn to actuate a sweeper, and on to outlet conduit 17 shown at the front of the apparatus. The water passing through this outlet will have much lower levels of dissolved organic compounds and particulate matter than the water flowing through inlet 7.

Claims

DK 2023 70407 A1 26 Claims

1. A separation unit for a protein skimmer, the separation unit comprising: an inlet through which liquid and foam can pass into the unit, a first outlet for purified liquid, and a second outlet for foam; a tray across which liquid can flow between the inlet and the first outlet; and a piate positioned above the tray such that a leading edge of the plate sits at or below a level of the liquid surface in use, the plate being inclined at an acule angle to the direction of liquid flow across the tray so that foam floating on the surface of the liquid can be separated from the liquid surface and directed up the inclined plate towards the second outlet.

2. A separation unit according to claim 1, wherein the inclined plate comprises a flat upper surface.

3. Å separation unit according to any of claims 1 and 2, wherein the leading edge of the plate is positioned closer to the inlet and lower than the trailing edge so that the plate slopes upwards in the direction of liquid flow across the tray. 4, A separation unit according to any of claims 1 to 3, wherein the angle between the inclined plate and the direction of liquid flow between the inlet and the outlet in use is between 20° and 70%.

3. A separation unit according to any of claims 1 to 4, wherein, in use, the base of the tray is angled between 0.5” and 10" from the horizontal in a downwards direction at the inlet.

6. A separation unit according to any of claims 1 to 5, wherein the tray has a flat base extending between the inlet and the outlet.

7. A separation unit according to any of claims 1 to 6, wherein the inclined plate extends across the entire width of the tray.

8. A separation unit according to any of claims 1 to 7, wherein the tray comprises a first enclosed portion adjacent the inlet, an open-topped portion, and a second

DK 2023 70407 A1 27 enclosed portion adjacent the first outlet, and the leading edge of the inclined plate is located in the open-topped portion of the tray.

9. A separation unit according to any of claims 1 to 8, wherein the first outlet slopes upwards at an acute angle with respect to the direction of liquid flow across the tray.

10. A separation unit according to any of claims 1 to 9, comprising an adjustment mechanism for adjusting the angle of the inclined plate.

11. A separation unit according to claim 10, wherein the adjustment mechanism comprises an extendible element coupled to the inclined plate.

12. A separation mechanism according to claim 11, wherein the extendible element comprises a threaded element, and the angle of the inclined plate is adjusted by tuming the threaded element.

13. A separation mechanism according to any of claims 1 to 12, comprising one or more spray nozzles for spraying and liquifying the foam as it travels between the trailing edge of the inclined plate and the second outlet.

14. A filtration system for a fish tank comprising a protein skimmer including the separation unit of any of claims 1 to 13.

153. A method for providing a separation unit for a protein skimmer comprising: providing a unit housing having an inlet through which liquid and foam can pass into the unit, a first outlet for purified liquid, and a second outlet for foam; providing a tray within the housing and across which liquid can flow between the inlet and the first outlet; and positioning an inclined plate above the tray at an acute angle to the direction of liquid flow across the tray such that a leading edge of the plate sits at or below a level of the liquid surface in use so that foam floating on the liquid surface can be separated from the liquid and directed up the inclined plate to the second outlet.