WO1987001010A1

WO1987001010A1 - Holding tanks

Info

Publication number: WO1987001010A1
Application number: PCT/AU1986/000242
Authority: WO
Inventors: Michael Graeme Hanrahan
Original assignee: Michael Graeme Hanrahan
Priority date: 1985-08-20
Filing date: 1986-08-20
Publication date: 1987-02-26
Also published as: JPH0728629B2; AU595542B2; AU6282886A; JPS63501472A

Abstract

Apparatus for use in maintaining aquatic animals in a state of hibernation. The apparatus is of the type comprising a holding tank (200) to contain the water environment, a horizontal, perforate partition (507) above the floor of the tank, a particulate filter bed (508), (509) supported on the partition and extending to the walls, the filter bed bearing a culture of denitrifying bacteria, and a water conditioning circuit. The water conditioning circuit has two sections, a first circuit having a circulation pump (206), a water cooling device (213), an activated carbon filter (214) and a water-returning spray assembly (208) and a second circuit incorporating a skimmer assembly (211). The first circuit is to draw water to be conditioned from beneath the partition and to turn the conditioned water to the tank. The skimmer is a vertical tube, open at its upper end, the upper end being near the surface of water contained in the tank, the lower end being in communication with the first circuit upstream of the pump and the carbon filter via a conduit, the skimmer assembly being isolatable from the first circuit by a valve located on the conduit.

Description

"HOLDING TANKS" TECHNICAL FIELD OF THE INVENTION

THIS INVENTION relates to an apparatus for and method of storing, maintaining, revitalising, hibernating and/or breeding aquatic organisms.

BACKGROUND ART Various apparatus have been devised for the keeping of aquatic organisms, such as the valuable, edible marine crustaceans which are kept alive up until the time of cooking, typically in a restaurant. Typical problems which have bedevilled prior art holding tanks, aquaria etc. are corrosion, waste management, aeration and temperature control. These problems affect the lifetime of the apparatus, the quality and presentation of the, for example,

Crustacea, the carrying capacity of the tank and metabolic rate of the organisms respectively.

Refrigeration equipment of known types are not readily applied to the task of temperature control in a salt water environment, where corrosion of elements necessarily in contact with water occurs quickly, resulting in breakdowns and unreliability and in the release of toxic metallic ions into the aqueous environment of the tank. The standard waste management and aeration systems, with air-pump activated filter mechanisms and bubble systems are not capable of maintaining high population densities in a holding tank when it is required to keep marine animals in a state whereby their market quality is maintained.

In the prior art of live crustacean export, a "quick chill" process is used, wherein the body temperature of, for example, Tasmanian crays is rapidly lowered and then the animals are packeted in styrene containers for air freight. Mortality rates are commonly in excess of 40%. OUTLINE OF THE INVENTION It is an object of the invention to provide a holding tank system which overcomes the problems of the prior art systems. It is a further object of the invention to provide an apparatus and method capable of producing live, chilled crustacea for export with 95% survival.

The invention aims at providing a holding tank system which is able to handle large population densities whilst being readily sealed for application either with a restaurant in mind, needing to handle only small quantities of marine animals, or with the bulk supplier to a wholesale or export market in mind, who requires a holding tank able to handle bulk quantities of live seafood which is to be maintained live for distribution in that condition.

DETAILED DESCRIPTION OF THE DRAWINGS

Accordingly, there is provided an apparatus for use in maintaining aquatic animals in a state of hibernation, said apparatus being of the type comprising

(a) a holding tank having a floor portion and wall portions said tank being adapted to contain the water environment; (b) a horizontal, perforate partition maintained in spaced relationship above said floor portion and extending to closely within the inner peripheries of said wall portions;

(c) a particulate filter bed supported on said partition and extending to said wall portions, said filter bed bearing a culture of denitrifying bacteria; and

(d) a water conditioning circuit; characterized in that said water conditioning circuit comprises:

(i) a first circuit comprising circulation pump means, water cooling means, activated carbon filter means and water returning spray means, the said first circuit being adapted to draw water to be conditioned from beneath said partition and to return the conditioned water to the tank via said spray means, and (ii) a second circuit comprising a skimmer assembly consisting of a substantially vertical tube means, open at its upper end, said upper end being near, the surface of water contained at its operative level in the tank, its lower end being in fluid communication with the said first circuit upstream of said pump means and said carbon filter means via conduit means, said skimmer assembly being isolatable from said^' first circuit by valve means located on said conduit means. More specific objects and advantages of the present invention will hereinafter become apparent. The holding tank of the present invention is refrigerated so as to lower water temperatures and put stored marine creatures into a state of hibernation, in which state their oxygen demand is considerably reduced since their metabolic rate decreases. Typical water temperatures are about 10°C for marine animals from temperate zones, and about 13°C for marine creatures taken from tropical waters. It is desirable that all system components contacting the tank water should be a non-corrodable material, and typically PVC or epoxy type piping is employed. Advantageously the piping is insulated to prevent condensation as well as heat losses. In order to facilitate servicing, disconnectable unions are preferably used in conjunction with all components so that faulty components may be replaced with a minimum of effort.

In providing for refrigeration, the type of refrigeration unit which will be employed in any particular application is determined largely by the volume of water which is to be maintained at a lowered temperature.

Clearly, with the refrigeration unit evaporator necessarily in contact with the salt water of the tank, special consideration needs be given to the protection of the evaporator from marine corrosion. In a capillary system, typically.60 feetof electro¬ static process epoxy coated copper pipe is used as the evaporator coil. What ever the type of evaporator, the same coating process is performed as is outlined below in greater detail.

The evaporator is typically constructed from a length of copper tube coiled in^' a serpentine manner in a plurality of banks of windings, each serpentinely coiled in a horizontal plane, each bank being arranged in a vertical stack with the banks being parallel to one another. When fitted in the housing, the flow of water in at the bottom and upwardly through the banks of coils ensures an efficient heat exchange.

To ensure against corrosion of the coils, the evaporator coils are coated with an epoxy resin applied as follows. The copper coils are first treated with an abrasive grit blast to Class 3 G.50. They are then dip coated with E-Vac Epoxy liquid primer followed by an electrostatic spray coat of Dulux Powderkote Epoxy Res.in which is cured for 45 minutes at 350°F.

In constructing the housing, a 250 mm or 320 mm standard PVC pipe length may be hot air welded to PVC end plates. In smaller holding tanks using capillary systems, the control system may be a thermostat. With larger holding tanks the control on a DX unit is a thermostat for temperature control and HP/LP for safety.

The aeration of the tank and return of conditioned water to the tank are simultaneously achieved by the action of the spray means, which directs the returning water back into the tank in the form of one or more jets. As water is injected back into the main body through an air space of typically 25 mm and more, the main water body is densely filled with tiny air bubbles from one end to the other. Injection under pressure causes air to be entrained with the water jets to be streamed into the main water body where the air bubbles diffuse throughout the whole water volume. In larger tanks, more than one injection system may have to be employed at separate surface points, but in the smaller systems, a single manifold across one end of the tank is found to be sufficient. The breaking of the surface in the above set out method also effects a rapid removal of carbon dioxide.

The filter bed material to be preferred is shellgrit of particle size generally between 0.5 mm and 2.0 mm. This material is part of the natural marine environment and has proved suitable for mounting cultures of naturally occuring marine denitrifying bacteria. The vertical flow of highly aerated water down through the filter bed is effective to produce a dense denitrifying bacterial flora much denser than bacterial colonies of prior art filter beds populating the surfaces of the filter bed particles and feeding upon the waste products of the stored marine creatures. The superior aeration method in combination with a shellgrit bed filter and the resultant superior bacterial growth, provides an efficient combined filter mechanism enabling the volume of water in the tank to be swept through the filter bed many times each hour, typically between 4 and 7.5 times per hour.

The filter bed is established at the tank_^ base, above a perforated, flat inverted tray, which serves to maintain a water body in a space beneath, from which water is pumped so as to draw water from the tank down through a filter medium supported on the tray surface. The tray is typically of a non corrosive PVC material, which^* doesn't interfere with the salt balance in the tank water. A structured shellgrit bed is established naturally above the tray usually overlaid with nylon mesh, with a finer shellgrit bed on the tray overlaid with a more coarse shellgrit. The vertical flow down through the filter bed carries waste products, such as faeces, into the filter bed, and they and dissolved nitrates and ammonia wastes, are nutrients to be consumed by the highly aerated bacterial super culture, which, soon after setting up, populates the large surface area of the particulate filter bed. The fast flow rate of highly aerated water which is achieved in practice creates a bacterial super culture which is not normally seen in the more usual air displacement pumping systems.

The apparatus of the invention employs a protein skimmer. This device may be of a rather • simple construction, with, a tube led to just below the level of the water in the holding tank. As this level may vary, a height adjustment is readily provided by employing a telescopic construction. When protein is required to be removed, as when a visible scum is seen on the surface of the water in the holding tank, a shut off valve on the protein skimmer line, which is normally shut off or nearly so in normal operation, is fully opened. With the skimmer tube opening properly set just below the water level, the rapid rate of ingestion of surface water will cause surface floating scums to stream with the pumped water through the skimmer inlet so that the surface water is cycled, with all scum removed, in a matter of seconds. As set out elsewhere, the surface water collected by the surface skimmer tube, is fed to an activated carbon filter for cleaning.

Use of an all glass construction provides a 360° view of fish life, and typically toughened glass is employed. With a double glazed system, a thicker inner sheet is employed. In a holding tank being 1290 mm x 500 mm and 1160 mm high, 6 mm inner and 4 mm outer sheets of toughened glass are used. In a tank being 1870 mm x 500 mm x 1160 mm high, 10 mm inner and 6 mm outer sheets of toughened glass are used.

Preferably an acrylic or other safe plastic transparent sheet material is used as a lid to the tank, and the lighting system used is preferably of the colour rendition variety of fluorescent lamps developed for aquaria. These lamps promote vegetative growth and highlight colourings in marine creatures.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment thereof and wherein:- Fig. 1 is a schematic layout of a refrigeration unit for use in the holding tank system of the present invention;

Fig. 2 illustrates the flow cycle in a holding tank system in accordance with the invention;

Fig. 3 illustrates the characteristics of a protein skimmer as might be employed in the holding tank system of Fig. 2;

Fig. 4 illustrates the characteristics of an aerator as can be employed in the holding tank system of Fig. 2;

Fig. 5 illustrates a structure which may be adopted in assembling a holding tank in accordance with the principles of the invention; Fig. 6 illustrates the components of a protein filter cartridge;

Figs. 7a and 7b show the components of an evaporator of a typical refrigeration unit adapted for use in a holding tank in accordance with the present invention; Fig. 8 shows an alternate refrigeration unit to be employedwith larger holding tanks;

Fig. 9 shows the layout of a protein box to be employed in larger holding tanks; and

Fig. 10 shows a layout for a larger holding tank in accordance with the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Fig. 1 shows schematically, the components of a basic refrigeration unit suitable to provide refrigeration for smaller holding tanks. This system is found to be appropriate for holding tanks of a size suited to operation in a restaurant, typically with approximately 90 gallon capacity. The refrigeration cycle in this embodiment employs a capillary expansion system. In Fig. 1, the output of compressor 100 is led to condensor 102, via line 101, and from there via lines 103 and 105 through drier 104 to capillary unit 106 which feeds evaporator 107. The return line 108 to the compressor 100 connects to the evaporator output to complete the cycle.

In Fig. 2 is shown the various components employed in maintaining a body of water 201, in a tank 200, in suitable condition. Tank 200 is provided with a bed of shellgrit to act as a filter, with a water chamber 203 beneath, from which water is led by pipe 204 via refrigeration unit 213 and T-connector 205 to pump 206. Pump 206 feeds purified water via line 207 to spray jets at 208, which direct a spray 209 of water onto the surface of water body 201 in tank 200, so as to break the surface and aerate the tank at 210.

A protein skimmer 211 is employed to remove surface scum which is drawn off with surface water via pipe 212 and filter 214 to join the main flow through pump 206 and back to the tank. Ball valves 215 control the flow and drain cock 216 provides a drainage point.

Fig. 3 shows the components of a typical protein skimmer.

In Fig. 3, tank 300 has a vertical pipe 301 passed through the base thereof in a sealed manner at 302. Any of the known techniques for providing a seal may be used at this point. To enable a height adjustment, a length of pipe 303 is provided within pipe 301, to be slidable vertically thereinwith an O-ring seal between the pipes to seal the pipes one to the other.

Fig. 4 illustrates the operation of an aerator where a tank 400 holding a body of water 401 has the return line 402 from the water conditioning systems led, preferably through the bottom thereof to reduce the need for external lines, to an overhead manifold 403 with a plurality of water jets 404 breaking the water surface in the tank so as to aerate the water indicated at 405. Fig. 5 illustrates the components used in constructing a holding tank. Double glazed panelling is employed with inner and outer panels

502 and 501, sealed to a base sheet 500. The inner and outer panels 502 and 501 are sealed at

503 by a glass bar so as to enclose a closed volume of air 504, and a body of dessicant such as silica gell 506 is employed to dry the air in the space and prevent condensation. An inverted PVC tray 507 supports a multilayered shellgrit bed formulated from fine 508, and coarse 509, materials. The tank may be illuminated by an overhead light 510 beneath a reflective shield 511 typically constructed from PVC sheet material.

In Fig. 6 is shown the components employed in setting up a protein filter cartridge. A housing 601 is provided with an inlet 602 and outlet 603. The inlet 602 leads water into housing 601 into a compartment 605 filled with activated carbon. Compartment 605 is divided off from a central passageway leading to outlet 603 by a perforated wall such as may be formed by a perforated PVC pipe. The perforations serve to allow water to flow therethrough whilst retaining the activated carbon in compartment 605. The cartridge is conveniently constructed with a screwed lid at 606 so that the cartridge may be opened, emptied, and recharged whenever the activated carbon is required to be changed. In-order to enable this, the inlet and outlets are preferably connected to the inlet and outlet lines by disconnectable junctions with valves which may be closed to cut off the lines prior to disconnection. As with other components employed with the holding tank, the filter cartridge is constructed from non-corrodable materials. The presently set out filter structure is suited to the smaller, restaurant type tanks. In larger holding tanks, larger activated carbon filters may be required so as to handle larger volumes of waste.

Figs. 7a and 7b show the components of an evaporator which may be used in the present invention. Fig. 7a is an end view of the front end of the evaporator unit which is shown in side view in Fig. 7b.

The evaporator is housed in a container conveniently constructed using a cylindrical pipe section 700 between end plates 701 and 702. End plate 701 is provided with inlet 708 and outlet

709 to an evaporator coil within the housing, and inlet 711 and outlet 710 for the water to be cooled. A thermostat probe 706 is inserted through end plate 701 and this is connected via capillary line 705 to thermostat control 704. A support plate 703 may be fitted over the unit so as to become a convenient place at which to mount a condensing unit.

Fig. 8 shows the components of a refrigeration system which is suited to greater capacity holding tanks. In the DX system of Fig. 8, compressor 801, condenser 802, and evaporator 803 are connected in the usual way with sight glass 805 and drier 804 in the circuit. TX valves are utilised at 806. . Either a dual TX or

TX-distributor may be used at this point depending on the size of the .system.

Fig. 9 shows the layout of a protein filter which can be used for large holding tanks. A box 900 is split into two compartments 901 and 902 by a baffle 903 which reaches almost to the bottom of the box to retain a charge of activated carbon 904 in compartment 901. Water to be cleaned is fed in at inlet 905 to compartment 901, to diffuse downwardly through the activated carbon bed 904 beneath baffle 903 to compartment 902 and out via outlet 906.

In Fig. 10 are shown the basic components of a large holding tank comprising a partitioned double tank 950 and 951 together with partitioned separate protein filter boxes 952 and 953 and partitioned filter beds 954 and.955. A bank of evaporators is shown at 956 and pumps at 957. Twin sprayers are shown at 958 and 959 in each of the twin holding tank volumes by which the cleaned refrigerated water is fed back to the tank. Because of the size of the tank, and the amount of shellgrit that would be required to provide an adequate filter across its bottom, the filter beds are provided separately. Water from the holding tank is led out a number of bottom outlets which may be meshed, perforated pipe ends. The filter beds are of the above described structure with a super culture established in a layered shellgrit bed above a water volume beneath, with water flows downwardly through the filter bed. The refrigeration system of Fig. 10 is preferably set up with two condensing units, four evaporators and four pumps.

Whilst the above has been given by way of illustrative example of the invention, many modifications and variations may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein defined in the appended claims.

Claims

1. An apparatus for use in maintaining aquatic animals in a state of hibernation, said apparatus being of the type comprising

(a) a holding tank having a floor portion and wall portion said tank being. adapted to contain the water environment;

(b) a horizontal, perforate partition maintained in spaced relationship above said floor portion and extending to closely within the inner peripheries of said wall portions;

(i) a first circuit comprising circulation pump means, water cooling means, activated carbon filter means and water returning spray means, the said first circuit being adapted to draw water to be conditioned from beneath said partition and to return the conditioned water to the tank via said spray means, and

(ii) a second circuit comprising a skimmer assembly consisting of a substantially vertical tube means, open at its upper end, said upper end being near the surface of water contained at its operative level in the tank, its lower end being in fluid communication with the said first circuit upstream of said pump means and said carbon filter means via conduit means, said skimmer assembly being isolatable from said first circuit by valve means located on said conduit means.

2. An apparatus according to Claim 1 wherein said water cooling means comprises one or more water jacket assemblies each having inlet means and outlet means, said water jacket assembly containing the evaporator of a refrigeration plant.

3. An apparatus according to Claim 2 wherein the temperature of the water in the said jacket is controlled by controlling means operating on the said refrigeration plant.

4. An apparatus according to any of Claims 2 and 3 wherein said water jacket assembly is of substantially cylindrical cross section, said water jacket being closed at both ends by substantially circular end portions; the two end portions being provided with the said inlet and outlet means respectively, to provide fluid communication between said water jacket and said first circuit.

5. An apparatus according to any one of Claims

2 to 4 wherein said evaporator comprises a substantially serpentine capilliary evaporator of metallic construction, said evaporator being further characterized by being coated with a polymeric material.

6. An apparatus according to Claim 5 wherein said polymer material is an epoxy resin.

7. An apparatus according to any one of Claims 1 to 6 wherein said activated carbon filter means comprises a'housing having inlet and outlet means to provide fluid communication with said first circuit, said housing being adapted to receive an activated carbon cartridge therein, whereby fluid in passage through said housing is filtered thereby.

8. An apparatus according to any one of Claims 1 to 6 wherein said activated carbon filter means comprises a housing having inlet and outlet means to provide fluid communication with said first circuit. said housing containing activated carbon.

9. An apparatus according to any one of Claims 1 to 8 wherein said spray means comprises one or more substantially tubular manifolds, said manifolds being provided with one or more apertures, said apertures being so disposed as to direct pressurized water in a jet at the surface of the water contained in said holding tank, said manifolds being disposed above the said operative level and being in fluid communication with said first . circuit.

10. A method of hibernating aquatic organisms in an aquatic environment comprising lowering the metabolic rate of the said organisms by reducing the temperature of the said environment.

11. A method according to Claim 10 wherein the temperature of the aquatic environment is reduced to 10 to 13°C.

12. A method of maintaining aquatic organisms in a hibernated state said method comprising maintaining an aquatic environment containing said organisms at a temperature conducive to hibernation.

13. A method according to Claim 12 wherein said temperature is from 10 to 13°C.

14. A method according to any one of Claims. 10 to 13 wherein the apparatus as claimed in Claim 1 is used.

15. An apparatus as claimed in any one of Claims 1 to 9 substantially as hereinbefore described with reference to the accompanying drawings.