GB1592085A

GB1592085A - Fish rearing apparatus

Info

Publication number: GB1592085A
Application number: GB35971/77A
Authority: GB
Original assignee: Fisons Ltd
Current assignee: Fisons Ltd
Priority date: 1977-08-26
Filing date: 1977-08-26
Publication date: 1981-07-01
Also published as: IE47256B1; IE781715L

Description

(54) FISH REARING APPARATUS (71) We, FISONS LIMITED, a British Company, of Fison House, 9 Grosvenor Street, London W1X OAH, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method and a vessel for use therein and is an improvement or modification of the method and vessel described and claimed in our co-pending Application No 8814/76 (Serial No 1567171).

In our co-pending Application No 8814/76 (Serial No 1567171) we have described and claimed, inter alia, a method for rearing fish in a vessel having an elongated aeration chamber in which air is injected into the foot of the chamber and the air bubbles carry water with them up the chamber. In this way water is drawn from the vessel, is aerated in the chamber and is caused to flow upwardly through the chamber and aerated water is returned to the vessel. In order to achieve adequate flow of water through the chamber it is desirable that the bubbles from the air injection means interact with both side walls of the chamber for at least part of the submerged height of the chamber. We have now found that with the form of aeration chamber design described in our co-pending Application it is difficult to achieve bubble interaction with both walls of the chamber with an economically acceptable air flow rate and yet have a chamber which is sufficiently wide to clean and service the base of the chamber and the air injection means.

We have now devised a method and a form of tank construction which reduces this problem.

Accordingly, the present invention provides a method for aerating and circulating water in a vessel which comprises passing an oxygen-containing gas up a chamber located within the vessel, the chamber having an overall width (as hereinafter defined) of at least 40 cms and being provided with a removable wall whereby the effective width of -the chamber (as hereinafter defined) is less than 30 cms for at least part of its submerged depth, the chamber also being provided with a lower inlet adjacent the base of the vessel whereby water enters the chamber and an upper outlet whereby aerated water is returned to the vessel.

The invention also provides a vessel through which water is to flow which vessel is provided with an aeration chamber which chamber has a basal inlet adapted to permit flow of water from the vessel into the chamber, an upper outlet adapted to permit water to flow from the chamber into the vessel and means for passing oxygen-containing gas up the chamber; the chamber has an overall width (as hereinafter defined) of at least 40 cms and is provided with a removable wall whereby the effective width of the chamber (as hereinafter defined) is less than 30 cms for at least part of its height.

The invention also provides a fish farm comprising a series of land based tanks through which fresh and/or salt water is to be passed characterised in that at least one of the tanks is a vessel of the invention.

The vessel used in the invention may be of round, oval or rectangular plan and may be made from any suitable material, e.g. from wood, plastics or concrete; and is erected on land rather than being a cage or similar structure floating in the sea as has been used hitherto. The water flows through the vessel e.g. as a linear stream or circulates around the vessel, as occurs with a round or oval vessel, with part of the water being passed to waste and make up water being added to the vessel. Typically, the vessels for present use have a capacity of at least 10 cubic metres, preferably at least 50 cubic metres, of water.

The chamber provides an aeration zone outside the main flow of water in the vessel.

This has the advantages that: aeration may be carried out under conditions which would not be acceptable to fish if practised in the main flow of water; injection of gas into the chamber does not deleteriously affect the flow of water in the vessel; and the flow of aerated water back to the vessel can have the effect of increasing the overall volume flow rate of water in the vessel as compared to that achieved merely by flowing water once through the vessel.

The aeration chamber can form a construction attached to the side wall of the vessel, e.g. having one side wall common with a side wall of the vessel. However, it is preferred to form the chamber as a substantially central construction in the vessel around which the water flows. A particularly preferred form of construction for present use is an elongated vessel having a hollow aeration chamber running along substantially the centre of the vessel. The chamber is conveniently formed from the same materials as the vessel.

The internal width, i.e. the distance between the removable wall and its opposed fixed wall is less than 30 cms over at least part, e.g. at least 40 tp 80% of its submerged height.

This internal width of the chamber between the co-operating fixed wall and removable wall during operation of the vessel of the invention is termed herein the "effective width" of the chamber. It will be appreciated that not all height of a vertical section of the chamber need have this narrow effective width, but that part of the chamber (e.g. the lower levels) may have a greater width. However, it is preferred that the opposed walls of the chamber be substantially upright and that the chamber have a substantially uniform width along its length and throughout its depth. The effective width of the chamber must be less than 30 cms over at least a portion of the submerged depth of the chamber in order that the gas bubbles rising up the chamber can interact with one another and with two opposed walls of the chamber to cause water in the chamber to rise up the chamber without excessive gas pumping requirements. We prefer that the chamber has an effective width of from 10 to 25 cms.

The chamber is provided with a removable wall whereby the overall width of the chamber, that is the width of the chamber when the removable wall is removed, can be increased to at least 40 cms. This larger width enables an operator of the vessel to service the operating features of the chamber which would otherwise be very difficult if the chamber width was less. The removable wall may take the form of a baffle mounted within a wider chamber so as to partition off that narrower section up which gas is to be passed.

Alternatively, one side wall of the chamber may be removable. The removable wall may occupy the whole length of the chamber or may be provided as removable sections in an otherwise fixed wall. Conveniently the removable wall or wall sections are formed from plates (e.g. metal plates) or boards mounted in vertical retaining slots or other mounting means.

The internal partition may be a simple plate. However, it is preferred to use a partition with an effectively thick section, e.g. a brick wall or a pair of spaced plates, to reduce the volume of the chamber through which incoming water flows to reach the aeration zone. This will also reduce settling out of solids in the chamber.

The gas passed up the chamber is preferably air and is preferably fed into the chamber by means which inject air under pressure into the water, e.g. by means of an injector pipe with air holes or nozzles or by means of a porous block or cylinder, to provide a diffused stream of air bubbles over the length of the chamber. It is preferred that the aeration means provide air bubbles of less than 5 mm diameter, preferably less than 3 mm diameter distributed throughout the water in the aeration zone or chamber.

Ideally, the aeration increases the oxygen level from inlet to outlet of the zone or chamber by at least 0 5 ppm dissolved oxygen and it should provide at least 6 ppm dissolved O2 in the water leaving the chamber to enable fish to thrive in the vessel. Typically, the aeration means provides from 7 to 10 ppm dissolved O2 in the water. If desired, two or more aeration means can be used in parallel to provide the necessary interaction between the bubbles and the chamber walls for satisfactory circulation of water through the chamber.

The chamber is in fluid flow connection with the vessel by means of the inlet and outlet, e.g. by means of underflow or overflow of a common wall between the aeration chamber and the vessel or by openings in the wall. Water is removed from the vessel preferably at above the level at which solids are being deposited in the vessel. Thus, the inlet to the aeration chamber is typically 10 to 50 cms above the floor of the vessel. It is also preferred that the water be removed from a number of points in the vessel and returned at a number of points so as to provide a comparatively uniform flow through the aeration chamber. It is also preferred that all the aerated water should be returned directly to the vessel, i.e. it is not treated (e.g.

filtered) before it is returned, although some, e.g. up to 10%, of the aerated water may be diverted and not returned directly. It is preferred that the outlets be upstream of the inlets so that the flow of water through the chamber has the effect of supplementing the volume flow of water through the vessel.

With a central chamber this is conveniently achieved by having the outlets on the opposite side of the chamber to the inlets. The outlets are preferably located so that their lower lips are at or below the lowest expected level of water in the vessel and desirably are constructed to have a variable area and/or lower lip level so that the rate of flow of water through the aeration chamber may be controlled.

The invention is of especial application in the raising of fish in land based tanks to maturity in fresh and/or salt water; notably of farmed species of fish, e.g. trout, salmon, carps, mullet, catfish and eels. However, the invention is of especial application in the farming of anadramous fish, notably salmon, on land using fresh and/or sea water flowing through tanks.

A preferred form of tank for use in the invention and its operation will now be described by way of illustration only and with respect to the accompanying drawings in which- :- Figure 1 is a diagrammatic plan view of the vessel; Figures 2, is a diagrammatic vertical section through the vessel of Figure 1; and Figures 3 and 4 are diagrammatic vertical sections through alternative forms of vessel.

The assembly comprises an elongated tank 1, for example built from concrete blocks, and having an internal length of 40 metres and an internal width of 10 metres.

The ends of the tank are rounded and a central partition wall 2, 30 metres long, runs along the interior of the tank to form an oval pond 3. Central wall 2 contains an internal chamber 10 which is 15-20 cms wide, which acts as the aeration chamber. As shown in Figure 2 one side wall of chamber 10 is formed from a series of superimposed dam boards 11 which can be removed to permit access to the interior of chamber 10. Alternatively, as shown in Figure 3 internal chamber 10 may be wider than in Figure 2 (e.g. 1 to 1-5 metres wide) with an internal removable baffle 12 to reduce the overall width to an effective width of say, 15 cms.

As indicated earlier, the chamber 10 may be provided with a double baffle as shown in Figure 4. The second baffle 12l is located from 5 to 15 cms from the wall of chamber 10 to maintain a rapid flow of water through the hatched area of the chamber. The double hatched area in Figure 4 may be filled in, e.g.

when the baffles 12 and 121 are provided by a brick wall.

Clean water is supplied to the tank via an overhead supply line 4 having outlet holes on opposed sides for each side of the pond so as to cause water to circulate around the pond as shown arrowed. The base of the tank is provided with drainage channels 5 and 6 on each side of the central wall 2. The channels are located along the junction of the wall and the base of the tank on that section of the pond opposed to the point of introduction of the clean water. The drainage channels are thus located at the points in the pond where the circulation rate is slowest and most of the water borne solids are being deposited.

Alternatively, the base of the tank is sloped to aid movement of solids to the outer rim of the tank; drainage channels 5 and 6 then being located along the junction of the side walls and the base of the tank. The channels are desirably covered with a grid. Water from the channels flows off via lines 7 and 8 to waste, carrying most of the deposited solids with it.

Chamber 10 is provided at its base with an air injector 13 along its length. This is, for example, one or more lengths of pipe with holes in; a porous block or cylinder to which air is fed; or a more sophisticated injector with nozzles and the like. The injector may also take the form of a length of lay flat plastic tubing with fine holes along its length.

The tube will thus be self sealing when not in use. The injector is one which delivers bubbles less than 3 mm in diameter. The air injector is fed with air from a fan blower (not shown) which, in the case of a tank having the sizes given above, delivers 3 to 10 cubic metres, for example 4 cubic metres, of air per minute at 0'1 to 2 kg/cm2 gauge, for example 0'2-0'4 kg/cm2.

In operation, clean water is fed via line 4 to the pond 3. By virtue of the holes in line 4, approximately half the feed enters at X and the rest at T as arrowed. The pond 3 fills with water which circulates (in this case clockwise) under the influence of the incoming water.

Some water passes via channels 5 and 6 and lines 7 and 8 to waste. The desired level of water in pond 3 is maintained by a wier or dam board, not shown. Water has also entered chamber 10 via the inlet ports 14 and chamber 10 is full with water to the same level as pond 3. Typically, 250010,000 litres per minute of water are fed to line 4 (1250--5000 litres coming out at each of X and Y) and the water depth is 0'95 to 1-05 metres.

Air is blown into air injector 13 and streams of fine bubbles rise up within chamber 10 causing the water level in chamber 10 to rise and water overflows from outlet ports 15 to pond 3. The air streams also draw water into chamber 10 through inlet 14 and through the basal ports in baffles 12 and, when used, 121. This water is aerated and picks up oxygen as it passes up chamber 10 before it overflows through outlet ports 15.

In this way oxygen depleted water is drawn from the pond 3, is aerated in chamber 10 and returned to the pond by the action of the air injector 13. By adjustment of the air pressure and air flow rate, one may vary the rate of circulation of water through chamber 10. Typically, with the figures given above, the total rate of circulation is 15000-75000 litres per minute through chamber 10. Thus, in effect the total rate of flow of adequately oxygenated water containing from 7 to 10 ppm dissolved oxygen in the pond is now 17500--85000 litres per minute; of which 1500()75000 litres are circulating through chamber 10, 2500-10000 litres are fed via line 4 and 2500-10000 litres are being withdrawn through channels 5 and 6 and lines 7 and 8 to waste. This effective increase in circulation of adequately oxygenated water through the pond means that the tank 1 may support more fish for a given capacity than a tank without the chamber 10; that less water from an outside source is required to maintain a given flow, since chamber 10 provides a proportion of the water required; the increased effective flow rate leads to enhanced cleaning action; and the water is effectively used several times without the build up of noxious materials therein which would occur with conventional re-use systems; or a combination of these.

WHAT WE CLAIM IS: 1. A method for aerating and circulating water in a vessel which comprises passing an oxygen-containing gas up a chamber located within the vessel, the chamber having an overall width (as hereinbefore defined) of at least 40 cms and being provided with a removable wall whereby the effective width of the chamber (as hereinbefore defined) is less than 30 cms for at least part of its submerged depth, the chamber also being provided with a lower inlet adjacent the base of the vessel whereby water enters the chamber and an upper outlet whereby aerated water is returned to the vessel.

2. A vessel through which water is to flow which vessel is provided with an aeration chamber which chamber has a basal inlet adapted to permit flow of water from the vessel into the chamber, an upper outlet adapted to permit water to flow from the chamber into the vessel and means for passing oxygen-containing gas up the chamber; the chamber has an overall width (as hereinbefore defined) of at least 40 cms and is provided with a removable wall whereby the effective width of the chamber (as hereinbefore defined) is less than 30 cms for at least part of its height.

3. A method or vessel as claimed in claim 1 or claim 2 wherein the aeration chamber is located as a generally central construction within the vessel.

4. A method or vessel as claimed in any one of the preceding claims wherein the outlet from the chamber into the vessel is located upstream of the inlet to the chamber.

5. A method or vessel as claimed in claim 4 wherein the inlet and outlet are located on opposite sides of the chamber.

6. A method as claimed in any one of the preceding claims wherein water is circulated around a generally central aeration chamber in the vessel.

7. A method as claimed in any one of the preceding claims wherein fish are reared in the water in the vessel.

8. A method as claimed in claim 7 wherein the fish are anadromous fish.

9. A method as claimed in any one of the preceding claims wherein the aeration in the aeration chamber provides at least 6 ppm of dissolved O2 in the water leaving the chamber.

10. A method as claimed in claim 1 substantially as hereinbefore described.

11. A method for aerating water substantially as hereinbefore described with respect to and as shown in any one of the accompanying drawings.

12. A vessel as claimed in any one of claims 2 to 5 wherein the removable wall is provided as an internal partition within the chamber.

13. A vessel as claimed in claim 12 wherein two substantially parallel internal partition walls are used.

14. A vessel as claimed in any one of claims 2 to 5 and 12 and 13 wherein the opposed fixed wall and removable wall of the chamber are substantially parallel to one another both vertically and horizontally.

15. A vessel as claimed in any one of claims 2 to 5 and 12 to 14 wherein from 40 to 80 of the height of the chamber has an effective width of less than 30 cms.

16. A vessel as claimed in any one of claims 2 to 5 and 12 to 15 wherein the effective width of the chamber is from 10 to 25 cms.

17. A vessel as claimed in claim 2 substantially as hereinbefore described.

18. A vessel substantially as hereinbefore described with respect to and as shown in any one of the accompanying drawings.

19. A fish farm comprising a series of land based tanks through which fresh and/or salt water is to be passed characterised in that at least one of the tanks is a vessel as claimed in any one of claims 2 to 5 and 12 to 18.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. lines 7 and 8 to waste. This effective increase in circulation of adequately oxygenated water through the pond means that the tank 1 may support more fish for a given capacity than a tank without the chamber 10; that less water from an outside source is required to maintain a given flow, since chamber 10 provides a proportion of the water required; the increased effective flow rate leads to enhanced cleaning action; and the water is effectively used several times without the build up of noxious materials therein which would occur with conventional re-use systems; or a combination of these. WHAT WE CLAIM IS:

1. A method for aerating and circulating water in a vessel which comprises passing an oxygen-containing gas up a chamber located within the vessel, the chamber having an overall width (as hereinbefore defined) of at least 40 cms and being provided with a removable wall whereby the effective width of the chamber (as hereinbefore defined) is less than 30 cms for at least part of its submerged depth, the chamber also being provided with a lower inlet adjacent the base of the vessel whereby water enters the chamber and an upper outlet whereby aerated water is returned to the vessel.

8. A method as claimed in claim 7 wherein the fish are anadromous fish.

10. A method as claimed in claim 1 substantially as hereinbefore described.

15. A vessel as claimed in any one of claims 2 to 5 and 12 to 14 wherein from 40 to 80 ó of the height of the chamber has an effective width of less than 30 cms.

17. A vessel as claimed in claim 2 substantially as hereinbefore described.