NO346901B1

NO346901B1 - A Separation Unit for a Protein Skimmer

Info

Publication number: NO346901B1
Application number: NO20210029A
Authority: NO
Inventors: Sigmund Røeggen; Rikard Albrigtsen
Original assignee: Redox As
Priority date: 2021-01-11
Filing date: 2021-01-11
Publication date: 2023-02-20
Also published as: CA3204722A1; DK202370407A1; CL2023001981A1; NO20210029A1; WO2022149989A1

Description

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 CO2, 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 to remove toxic 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 filters 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 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 50µm). 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 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 to be particularly efficient in terms of removing the foam and attached pollutants. WO-A-01/32562 describes a filtration system for a fish tank comprising a protein skimmer including a fractionation column and an aggregation tank for waste foam collection positioned directly above the fractionation column. US-A-2233448 describes a particle removal system for waste water comprising a flocculation section and a separation tank with a paddle for removing matter collecting at the base of the tank. NO325052B1 describes a protein skimmer including a first horizontal passage for water to flow through the system and tube directed rearwards up which foam created at the water surface can travel for removal. KR101655895B relates to a water cleaning system including two sub-tanks separated by an inclined partition. The bottom of the two tanks represents a protein skimmer in which foam rises to the surface of the water and is removed therefrom out of an opening in the side of the tank.

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 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 extending in the direction of water flow with the leading edge positioned lower than the trailing edge and 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 towards the second outlet.

The quality of the water within commercial fish tanks 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 currents.

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 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 angle between the inclined plate and direction of water flow across the tray is between 20° and 70°. In embodiments, the angle between the inclined plate and the direction of water 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 1° and 10° from the horizontal in a downwards direction at the inlet. This creates a current drawing water 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 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 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 into the separation unit, can also help to create foam due to the turbulence created at the inlet near to the water’s surface. If the level of the water in the tank is set so as to substantially coincide with 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. 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 flatbased. 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 which has flowed past the plate’s leading edge. The length of the tray extends in the direction of water flow along the tray, and the width in a direction from side to side across the tray and perpendicular to the direction of water 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 opentopped 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 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 flow across the tray or with respect to the base of the tray. The upwardly sloping first outlet helps to regulate the water level within the tray.

In embodiments, the separation unit comprises a sweeper having one or more paddles configured to travel in the direction of movement of the foam along at least 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 paddles may be flat or shaped, for example to include one or 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 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 embodiments, the separation unit comprises a water wheel positioned beneath the first outlet such that water flowing from the first outlet contacts the wheel to cause it to turn.

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 axle of the sweeper respectively.

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 water and foam can pass into the unit, a first outlet for purified water, a second outlet for foam; providing a tray within the housing and across which water 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 water flow across the tray such that the plate extends in the direction of water flow with the leading edge positioned lower than the trailing edge and sitting at or below a level of the water surface in use and foam floating on the water surface can be separated from the water surface and directed up the inclined plate to the second outlet.

According to an example, there is provided 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 sweeper having one or more paddles 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.

In examples, the sweeper comprises at least one paddle coupled to a rotating axle.

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 flowing from the first outlet contacts the wheel to cause it 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 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. In embodiments, the sweeper is configured to push foam up the inclined plate.

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 6 illustrates the foam separation mechanism within the separation unit; Figure 7A shows a cross sections through a skimmer with the paddle in its upwards extended position during rotation;

Figure 7B shows a cross sections through a skimmer with the paddle in its downwards extended position;

Figure 7C shows a cross sections through a skimmer with the paddle at an angle of around 45° to the vertical;

Figure 8 illustrates the transmission mechanism for use of energy from the movement of water through the system to move a sweeper; and

Figure 9 shows a protein skimmer in situ.

A water purification system including a protein skimmer is illustrated 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. The apparatus finds particular use in recirculating aquaculture 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 illustrate an example of how the protein skimmer, including the novel separation unit described below, may be integrated within 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 O2 in the water and forcing CO2 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 entry into the tank, in order to improve degassing 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 9. 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 for a 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 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 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 filter 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 water 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 aquaculture system. The standalone unit can comprise only the protein skimmer in some embodiments. The filtration unit shown in figure 4 comprises a housing and includes 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 CO2 may be de-gassed, and where at least some of the foam extracted at the separation unit of the skimmer may be formed. If 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 to 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. 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 outlets 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 9 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 CO2. The excess CO2 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 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 1° and 10°, preferably between 2° and 5°, and most preferably around 3°. This angle may, in some cases, be adjustable, 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 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 follow, 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 closed-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 opentopped portion, the foam is removed from the water flow as will be described in detail below.

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, encouraged by the 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 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 5cm. The water and foam therefore passes under the first 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 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 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 overflow. 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<3>/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 to 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 30° 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 flow referred to herein refers to the direction parallel to 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.

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 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 5A to 5C and figure 6. 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, the separation unit 35 comprises an angled plate or surface 69 with a leading edge sitting at or below the 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 closedtopped 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 and parallel with the direction along which water flows across the tray therebetween.

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. 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 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 trailing 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 housing of the separation unit 35 is substantially rectangular and may be wider than it is high, as shown in the figures. The first outlet 15 in this example are each also wider than it is high, such that it forms a rectangularly 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 rightmost 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 (which rises out of the page 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. From here, 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. 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 outlets.

The sweeper 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 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 6. 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 6 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 it 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. 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 the foam within the 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 underneath and out into the open-topped section.

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 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 to 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 paddle to be rotatable with respect to, and to hang from, the rod so that it always extends substantially downwards in use.

Figures 7A-7C illustrate the relative movements of the axle 47, arms 55, and paddle 53 of the sweeper 45 during rotation of the axle. In figure 7A, 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 paddle to the arms can be by any means that will allow rotational movement of the paddle. Here, the paddle 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 7B, the arms 55 are orientated such that they extend downwards, with the paddle 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 lot of foam is present because of the reaction force provided by the foam. Obviously, to what extent the paddle 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 6C, the arms are orientated at roughly 45° from the vertical and the paddle hangs directly downwards. The paddle 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 7B. The paddle may be configured to extend to the position of the 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 7B to that shown in figure 7C). 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 just touches 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 7B) to between 30° and 50°, or preferably around 45° of one rotation of the axle (i.e. for around the first 1/8<th >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 paddle, 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 7A to 7C. Water travels 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 paddles 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 8 shows the transmission mechanism coupling the water wheel 59 to the axle 47 of the sweeper in one example. Here one additional gear wheel 61 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 65 coupled to the water wheel. Different sized gears can alternatively used to speed up or slow down the sweeping motion of the paddle (e.g. a smaller or larger gear wheel coupled to the paddle) 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 paddle needs to turn 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 to include a smaller upwardly extending lip or no lip at all at the trailing edge of the inclined plate to make it easier for the foam to pass through the separation unit.

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 the open-topped portion of the tray within the separation unit may be enclosed within a hinged cover to allow access while protecting the internal parts and the water from contamination or damage.

Figure 9 illustrates a protein skimmer 2 including the separation unit 35 described above, and mounted in situ within a larger system. The separation unit and tank 1 are mounted on a platform 67 and the 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

1. A separation unit (35) for a protein skimmer (2), the separation unit comprising:

an inlet (37) through which water and foam can pass into the unit, a first outlet (15) for purified water, and a second outlet (41) for foam; characterised in that the separation unit comprises:

a tray (73) across which water can flow between the inlet (37) and the first outlet (15); and

a plate (69) 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 extending in the direction of water flow with the leading edge positioned lower than the trailing edge and 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 (69) towards the second outlet (41).

2. A separation unit (35) according to claim 1, wherein the inclined plate (69) comprises a flat upper surface.

3. A separation unit (35) according to any of claims 1 and 2, wherein the angle between the inclined plate (69) and the direction of water flow between the inlet and the outlet in use is between 20° and 70°.

4. A separation unit (35) according to any of claims 1 to 3, wherein, in use, the base of the tray (73) is angled between 1° and 10° from the horizontal in a downwards direction at the inlet (37).

5. A separation unit (35) according to any of claims 1 to 4, wherein the tray (73) has a flat base extending between the inlet (37) and the first outlet (15).

6. A separation unit (35) according to any of claims 1 to 5, wherein the inclined plate (69) extends across the entire width of the tray (73).

7. A separation unit (35) according to any of claims 1 to 6, wherein the tray (73) comprises a first enclosed portion adjacent the inlet (37), an open-topped portion, and a second enclosed portion adjacent the first outlet (15), and the leading edge of the inclined plate (69) is located in the open-topped portion of the tray (73).

8. A separation unit (35) according to any of claims 1 to 7, wherein the first outlet (15) slopes upwards at an acute angle with respect to the direction of water flow across the tray (73).

9. A separation unit (35) according to any of claims 1 to 8, comprising a sweeper (45) having at least one paddle (53) configured to move with the foam along at least a portion of the path from the inlet (37) to the second outlet (41) to push the foam through the unit.

10. A separation unit (35) according to claim 9, wherein the at least one paddle (53) is coupled to a rotatable axle (47).

11. A separation unit according to claim 10, wherein the sweeper (45) comprises two arms (55) coupled to the rotatable axle (47) at one end and rotatable with the axle, and a rod (57) coupled between the other ends of the arms (55), wherein the paddle (53) is attached to and is rotatable with respect to the rod.

12. A separation unit (35) according to any of claims 10 and 11, comprising a water wheel (59) positioned beneath the first outlet (15) such that when water flows from the first outlet (15) it contacts the wheel causing it to turn, wherein the water wheel is coupled to the axle (47) of the sweeper (45) by way of a transmission mechanism, such that when the water wheel turns, the axle (47) of the sweeper (45) is caused to turn.

13. A separation unit (35) according to claim 12, wherein the transmission mechanism comprises a transmission belt extending between two gear wheels (65; 63) which are fixed to and rotatable with the water wheel (59) and the axle (47) of the sweeper (45) respectively.

14. A filtration system for a fish tank comprising a protein skimmer (2) including the separation unit (35) of any of claims 1 to 13.

15. A method for providing a separation unit (35) for a protein skimmer (2) comprising:

providing a unit housing having an inlet (37) through which water and foam can pass into the unit, a first outlet (15) for purified water, a second outlet (41) for foam; characterised in that the method comprises:

providing a tray (73) within the housing and across which water can flow between the inlet (37) and the first outlet (15); and

positioning an inclined plate (69) above the tray (73) at an acute angle to the direction of water flow across the tray such that the plate (69) extends in the direction of water flow with the leading edge positioned lower than the trailing edge and sitting at or below a level of the water surface in use so that foam floating on the water surface can be separated from the water and directed up the inclined plate (69) to the second outlet (41).