NL2006360C2

NL2006360C2 - Water tank and method for preserving shellfish.

Info

Publication number: NL2006360C2
Application number: NL2006360A
Authority: NL
Inventors: Jan Murre
Original assignee: Murre Techniek Holding B V
Priority date: 2010-03-09
Filing date: 2011-03-08
Publication date: 2013-03-12
Also published as: NL2006360A

Description

P30230NL01/KHO

Title: Water tank and method for preserving shellfish.

The present invention relates to a water tank and method for preserving shellfish. Shellfish encompasses clams, oysters, scallops, crabs, lobsters, shrimps etc.

JP5292852 discloses such a watertank. The disclosed watertank has a main body which can be filled with water. The main body has at an inner sidewall a support member for 5 a shelter for shellfish culture. A plurality of shelters may be placed above each other in the container. The water in the water tank is refreshed by a water supply system. The water supply system has a water supply pipe having branched water ejection pipes. The water ejection pipes eject water in a horizontal and vertical direction to generate a circulating water stream in the water tank main body. The circulating water stream is necessary to enable the 10 living of shellfishes over the whole surface of a shelter, to quickly discharge the feces and residual feed, etc. A drainage pipe is positioned at the bottom of the water tank to keep the water tank in a clean state. A siphon is connected to the drainage pipe.

One drawback of the disclosed water tank is that in use the water circulation is not satisfying. The amount of water which is necessary to achieve sufficient water circulation to 15 keep the clean state is too high.

It is an object of the present invention to at least partially eliminate the above mentioned drawbacks and/or to provide a useable alternative. In particular, it is an object of the invention to provide a water tank for preserving shellfish which provide a clean and healthy environment to store the shellfish.

20 According to the invention, this object is achieved by a water tank according to claim 1.

The water tank according to the invention is suitable to preserve shellfish. Shellfish encompasses clams, oysters, scallops, crabs, lobsters, shrimps etc. The shellfish may be stored in the water tank to keep the shellfish healthy and alive for a long period, e.g. at least 25 one week.

The water tank according to the invention comprises a tub. The tub has a bottom wall and at least one sidewall which walls define an inner storage space for shellfish. The storage space is to be filled with water such that the shellfish are underwater level.

The storage space is provided with at least one shelf for carrying shellfish inside the 30 storage space. The shelf is preferably positioned at a lower region of the tub under a water level.

2 A water supply is provided for refreshing water in the storage space. The water supply comprises a water inlet for filling the tub and a water discharge outlet for discharging water from the tub.

The water tank according to the invention is characterised in that the water tank 5 further comprises an oxygen containing gas supply. Preferably, the gas supply is a supply of oxygen enriched water. Water may be enriched with oxygen outside the tub. In particular, the oxygen containing gas supply is an air supply. Environmental air may be treated and supplied to the water tank. The gas supply extends at least partially inside the storage space. In comparison with a gas supply, a supply of oxygen enriched water is 10 advantageous, because the water supply may less disturb the low water temperature inside the inner storage space and a separate gas supply inlet may become redundant. The gas supply has a gas supply outlet which is positioned at a lower region of the storage space. Typically, the gas supply has a positive pressure in between a range of at least 0.1 bar and at most 0.75bar. Preferably, the gas supply has a positive pressure of at least 0.10 and at 15 most 0.20bar, in particular about 0.15bar. In particular, the airflow rate is about 1m3/hr for a tub having a storage space of about 1 m3.

During use the gas supply generates locally an upwards gas flow in the water filled storage space. Rising gas will move surrounding water upwards which causes a water flow in the water volume of the storage space. The occurring water flow and turbulence may 20 advantageously improve a discharge of contaminations, like feces and residual feed from the water. The rising gas contributes to the refreshing process of the watervolume. Advantageously, less water may be necessary to refresh the watertank. Dead zones may be prevented which improves the quality of the watervolume. The water flow may pass the shellfish which cleans the shellfish. Besides the water flow in the storage space, the 25 presence of the under water gas supply containing oxygen introduces oxygen in the water which may improve the under water environment for the shellfish. The occurring water flow in the tub distributes oxygen enriched water over the upper surface of the shelf. It has appeared that shellfish may achieve a longer lifetime when oxygen is introduced in the water.

30 In an embodiment of the water tank according to the invention, the tub of the water tank is stackable. The tub may have a bottom part, a side wall and an open upper part. The open upper part may have an inner contour which corresponds with an outer contour of the bottom part to make the tub stackable in a stable manner. The outer contour of the bottom part may fit within the inner contour of the open upper part. The tub has preferably a 35 rectangular outer contour, but may also have a rounded outer contour. The tub may e.g. be elliptically or circularly shaped. Typically, the tub has a storage space comprising a water volume of at most 5m3, in particular at most 2m3, but preferably at most 1m3. Preferably, the 3 bottom part of the tub is provided with at least one fork-lift recess to engage the tub with a fork-lift truck.

In an embodiment of the water tank according to the invention, the shelf is a sieve plate. The shelf may be a perforated plate. Preferably, the shelf covers substantially the 5 whole bottom wall to prevent shellfish falling aside the shelf. The shelf may be as large as the bottom wall of the tub. The shelf may be made of plastic, in particular HMPE, which is less susceptible to deterioration by seawater. Preferably, the shelf has a plurality of passageways for a through flow of water through the shelf. The passageways may have a cross section of at least 0.25cm2 in particular at least 0.5cm2. The passageways of the shelf 10 enable a through flow of water through the shelf. A water flow may be generated which flows through the passageways of the shelf. The passageways may be arranged in a regular pattern over the shelf. The passageways may e.g. be spaced from each other at a distance of at least 5 cm. This may advantageously result in an improved discharge of contaminations out of the tub.

15 In an embodiment of the water tank according to the invention, the shelf is spaced from the bottom wall to create a bottom space. The shelf may be positioned in a lower region of the tub. The shelf may be spaced at a distance of at least 1cm, in particular at least 3cm, but preferably at least 5cm from the bottom wall. The shelf may be supported by spacers to space the shelf from the bottom wall.

20 In an embodiment of the water tank according to the invention, the shelf is pivotally connected to the tub. The shelf may be pivotally connected to a side wall of the tub. Advantageously, the tub may be more easy to clean. The tub may be positioned upside down to empty the tub. The shellfish may e.g. be collected on a conveyor for further processing and to pack the shellfish for consumption. The tub may be kept in the upside 25 down position for a cleaning operation. The open upper part may be positioned downwards and a water jet may be used to clean the inside of the tub. The pivotally connected shelf may remain inside the tube and being suspended to the sidewall of the tub. Advantageously, at the same time the shelf is cleaned together with the tub. After the cleaning operation the tub can be turned back to be reused.

30 In an embodiment of the water tank according to the invention, the shelf comprises a first shelf part and a second shelf part. The shelf parts may be each half a part of the shelf. The first and second shelf part may each be pivotally connected to the tub. When the tub is turned upside down, the first and second shelf parts suspend downwards from the tub. The limited length of the shelf parts keep the shelf parts inside the storage space of tub 35 without extending out of the tub. Advantageously, the shelf does not disturb a proper handling of the tub during cleaning operations.

4

In an embodiment of the water tank according to the invention, the water supply of the water tank comprises a water supply inlet and a water discharge outlet. The water discharge outlet may be arranged at an edge at the open upper part to keep the water level in the tub at a constant value. The water tank includes at least one water discharge outlet in 5 an upper region of the tub. Water exits the water tank at the water discharge outlet.

The water supply inlet is provided to fill the tub with fresh water. Preferably, the water inlet is arranged at a lower region of the water tank and supplies water into the inner storage space in between a shelf and the bottom wall of the tub. The water inlet extends into the bottom space. Water is discharged under the shelf. Advantageously, herewith the water 10 tank may be arranged without a siphon.

In an embodiment according to the invention, the water supply inlet serves also to feed oxygen to the inner storage space. Supplied water is enriched with oxygen before the water is fed to the inner storage space. Preferably, the supplied water is enriched with substantially pure oxygen. A water supply conduit may be connected to an oxygen provider.

15 The water supply conduit is arranged outside the water tank and is connected to the water supply inlet. The water supply conduit may be connected by a venturi conduit to an oxygen tank or an oxygen generator. Due to the water flow, oxygen is sucked or pumped via the venturi conduit to the water flow and supplied to the inner storage space of the water tank.

It is advantageous to supply pure oxygen in stead of environmental air to the water 20 tank, because a smaller volume of gas is necessary to refresh the inner storage space. The smaller volume of gas will less affect the water temperature and less foam will be generated. The gas supply is incorporated in the water supply. Advantageously, no separate gas supply is necessary. Fewer components may be favourable to clean the water tank. Advantageously, in comparison with a gas supply, the enriched water supply does less 25 affect the water temperature at the inner storage space. Supplying oxygen enriched water may further decrease a generation of foam at the water surface.

Water is discharged from the water inlet under the shelf and flows upwards. An upwardly directed flow of water from the bottom wall is generated by fed water. The oxygen enriched water flows along shellfish which lie on the shelf. The rising water flow keeps the 30 shellfish fresh and alive. Contaminants like feces and residual feed flow upwardly away from the shellfish and are discharged through a water discharge outlet. The water discharge outlet is arranged at an upper region of the water tank. In particular, the water discharge outlet is an overflow opening adjacent an upper edge of the water tank. Floating generated foam can easily be discharged via the overflow opening.

35 At least two water tanks may be stacked, wherein water from each water tank is discharged to a water treatment station. Each stacked water tank is provided with its own water supply.

5

In an embodiment of the water tank according to the invention, the water tank is provided with an exit hole in a lower region of the water tank, in particular in the bottom wall. The exit hole is positioned in a lower region of the watertank under a shelf position. The exit 5 hole is a small through hole which is open during operation of the water tank. During operation, a relatively small continuous water flow leaves the tub through the exit hole. The exit hole serves as a safety hole. In case of interference, e.g. a blockage of a water supply to the water tank, the available water in the inner storage of the water tank will be discharged through the exit hole to empty the water tank. In such a case of malfunction of 10 the water tank, shellfish which lay on the shelf will get exposed to the environmental air which will keep the shellfish alive. Without the exit hole, during malfunction, the shellfish would be hold in stationary water and would use all available oxygen until they die. Thus, the safety hole prevents this undesired situation.

In an alternative embodiment, the water supply inlet may be arranged above the shelf 15 and the water discharge outlet may be arranged at a lower region of the water tank in between the shelf and the bottom wall. The arrangement of the water inlet and outlet may contribute to an improved water flow through the shelf.

Due to the available gas supply, the water supply does not need to have a high flow rate. Both the gas and water supply may contribute to the occurring water flow in the storage 20 space of the tub. Advantageously, the water supply may have a flow rate of at most 5 liter/minute, in particular at most 3 liter/minute. The water flow rate may be minimized to be just sufficient to refresh the water volume in the tub.

In an embodiment of the water tank according to the invention, the water supply comprises a cooling device to cool water. The water supply may be cooled to a temperature 25 of at most 15°C, in particular at most 10°C, but preferably to at most 5°C. The cooled water supply may extend the lifetime of the shellfish and keep the shellfish fresh for a longer time period.

In an embodiment of the water tank according to the invention, the water discharge outlet is connected to a siphon. The siphon may serve advantageously to control the water 30 level in the storage space in an easy manner. Preferably, the siphon is an internal siphon which is a siphon which is arranged inside the storage space. By arranging the siphon inside in stead of external the tub, the siphon is less susceptible to damages during use and transport of the tub. The siphon may comprise a first and second siphon tube which are directed upwards, substantially vertically, and in fluid communication connected at an upper 35 region of the tubes. The first siphon tube may include the water discharge outlet at a lower region, wherein the second siphon tube may have an external opening to discharge water out of the tub. The second siphon tube may be a straight tube which may extend upwards 6 from the bottom wall of the tub. The external opening may be arranged in the bottom wall of the tub. Herewith, stacked tubs may be fed with water from a most upper positioned tub. Water may be fed from the most upper positioned tub to lower positioned tubs via the external opening in the bottom wall. Advantageously, the amount of water supplies may be 5 reduced for a water tank with stacked tubs.

In an embodiment of the water tank according to the invention, the gas supply is an air supply. The air supply may be generated by a fan which may be arranged in the vicinity of the water tank. Advantageously, the supplied air may comprise about twenty percent oxygen which may dissolve in the water and may contribute to the health of the shellfish.

10 The air supply may provide an air flow rate at a positive pressure in a range of at least 0.10 to at most 0.75 bar, in particular at least 0.10 to at most 0.30bar, preferably in a range of at least 0.10 to at most 0.20bar, preferably 0.15bar. The gas supply may be connected to the tub at a side wall. The sidewall of the tub may comprise at least one quick release coupling piece to quickly connect and remove an air hose of the air supply to or from the tub.

15 Advantageously, a tub can be removed and replaced by another tub and quickly reconnected to the air supply.

In an embodiment of the water tank according to the invention, the tub comprises an air distributing member at the inside. The air distributing member may be an air conduit. The air conduit may extend at least partially sidewards in the storage space. The air conduit may 20 be arranged substantially horizontally in parallel with the bottom wall of the tub and substantially in parallel with the side wall. The air conduit may have vent-holes along its length. A vent-hole may be an elongated slit or a drilled through hole. The vent-holes may be equally spaced along the length of the air conduit. The vent-holes may be arranged at the underside of the air conduit to obtain an improved distribution of air over all of the vent-25 holes. Advantageously, the air conduit may be suitable to generate an air curtain inside the storage space in parallel with a side wall.

In an embodiment of the water tank according to the invention, the air distributing member may be connected to the tub by a quick release coupling piece. The quick release coupling piece may be connected at the inside of the side wall of the tub at a lower region. 30 The quick release coupling piece may be positioned just above or beneath the shelf. The quick release coupling piece may enable a quick removal of the air distributing member out of the tub. This may advantageously contribute to a reduction of efforts to clean and reinstall the tub.

In an embodiment of the water tank according to the invention, the air distribution 35 member may be positioned in between the shelf and the bottom wall of the tub. The air distributing member may at least partially be positioned in between the bottom wall and the shelf such that gaseous medium is vented beneath the shelf. The quick release coupling 7 piece may be positioned in between the shelf and the bottom wall of the tub. In case that the shelf is smaller than the bottom wall, vented air may pass aside the shelf. Alternatively, when the shelf substantially covers the whole bottom wall, the shelf may comprise at least one air passageway locally at the position of the air distributing member to let pass vented 5 air. The air passageway may comprise a pattern of air passageway holes. The air passageway is designed to reduce a resistance for the air in upwards direction. The cross section of the air passageway may be sufficient large to generate a strong upwards directed airflow which may cause the desired water flow or water circulation in the tub. The cross section of the air passageway may be sufficient small to prevent shellfish falling through the 10 air passageways.

Further, the invention relates to a watertank system for preserving shellfish. The water tank system may be installed on board of a vessel or at land e.g. in a shed. The water tank according to the invention may comprise a water treatment station to define a water tank system. The water tank system may comprise a plurality of tubs. The tubs may be 15 stacked on each other or placed side by side. The system may comprise at least one array of stacked tubs. A portal may be provided aside an array of tubs to provide access to the tubes for an operator. Stacked tubs may be provided with a common water supply. The common water supply may have a single water supply inlet at a most upper positioned tub, wherein a water overflow is provided to transfer water from an upper to a lower arranged 20 tub. Water may be discharged from the lowest positioned tub to a sewer. Advantageously, just relatively few water may be used to refresh a plurality of stacked tubs. The water flow rate may e.g. be about 2 liters/minute for three stacked tubs.

In an embodiment of the water tank system according to the invention, the water tank system may comprise a water treatment station. The water treatment station may comprise a 25 basin to purify water.

The basin may be filled with bacteria containing bodies which may circulate through the basing to catch and/or convert contaminations in the water. The circulation of the bacteria containing bodies may be caused by a pump, in particular an air pump. The positive pressure of the air pump may be about 0.25bar. The air pump of the water tank system may 30 be the same air pump or fan as used to generate an air flow in the tubs. Advantageously, only one air pump needs to be implied in the water tank system to fulfil several functions.

The basin may have a basin water inlet and a basin water outlet. In particular, the water basin inlet is a return inlet to recycle water which is used to refresh water in the tubs. The water basin inlet may be in fluid communication with the water discharge outlet 35 originating from a tub. The water basin outlet may be in fluid communication with a water supply inlet of a tub.

8

In an embodiment of the water tank system, the basin water outlet is fluid communication with a skimmer, wherein the water flow is further cleaned before the water is fed to a tub. Water from the basin may be fed into the skimmer, wherein the skimmer is arranged to skim and separate scum from the water. The water may be mixed with air and/or 5 ozone before entering the skimmer. An ozone unit may be provided to add ozone to passing water before the water is transferred to the skimmer.

In an embodiment according to the invention the water tank system comprises a cooling element which extends in the basin to cool the water to a temperature of at most 15°C, in particular at most 10°C and preferably at most 5°C. Processing shellfish with water 10 of such a temperature may increase the shellfish health and lifetime.

In an embodiment according to the invention the watertank system comprises an external water supply. The external water supply may originate from a water source in the ground. A water softening unit may be provided to soften water originating from the water source. The external water supply may alternatively been provided by pumping water from 15 the sea. The external water supply may be provided to keep the water level in the water tank system at a constant level. The flow rate of the water from the external water supply may e.g. be about 500liter / hour. A second water basin may be provided in fluid communication with the external water supply to collect water and serve as a buffer.

Further, the invention relates to a vessel comprising an on board water tank system 20 as described above. A vessel arranged with such an on board water tank system may process shellfish almost immediately after a harvest in stead of processing the shellfish later at the arrival at land. The watertank or water tank system according to the invention may comprise a vessel.The on board water tank system provides an opportunity to store shellfish in tubs which may be efficiently refreshed with water. The shellfish can almost directly from 25 the seawater be stored in a water tank according to the invention which may considerably increase the lifetime of the shellfish. The shellfish may be kept fresh for a longer period. Advantageously, the harvest of shellfish may be less dependent of processing capacity on land. A complex logistic plan to get the shellfish packed quickly may no longer be necessary. Especially during summer time, the watertank according to the invention may be 30 advantageous when relatively high water and air temperatures of about 20°C normally cause a fast decay of the shellfish. Cooled water may be used in the watertanks to keep the shellfish fresh.

Further, the invention relates to a method of processing shellfish in a water tank as defined in claim 26.

35 In an embodiment of the method according to the invention, the method further comprises a step of removing byssesthreads of shellfish by means of a brush mill. The brush mill may comprise a sieve with cutting members and a brush which is rotatable 9 connected with respect to the sieve. The sieve may have a cylindrical shape, wherein the brush is arranged in a center of the sieve. The brush may be used to wipe shellfish over the sieve and the cutting members to remove byssesthreads and possibly other undesired elements from the shellfish. Advantageously, the use of the brush mill may prevent tearing 5 off the undesired elements and may contribute to a neat process of the shellfish.

Further preferred embodiments are defined in the subclaims.

The invention will be explained in more detail with reference to the appended drawings. The drawings show a practical embodiment according to the invention, which may 10 not be interpreted as limiting the scope of the invention. Specific features may also be considered apart from the shown embodiment and may be taken into account in a broader context as a delimiting feature, not only for the shown embodiment but as a common feature for all embodiments falling within the scope of the appended claims, in which: 15 Fig. 1A shows a perspective view of an embodiment of a water tank according to the invention including an internal siphon;

Fig. 1B shows in a perspective view an alternative embodiment of a water tank according to the invention comprising an external siphon;

Fig. 1C shows in a perspective view two stacked water tanks as shown in Fig. 1B; 20 Fig. 1D shows in a cross sectional view a water flow in a storage space of a water tank according to the invention;

Fig. 2A shows in a detailed view in perspective a first embodiment of an air distributing member including a quick release coupling;

Fig. 2B shows in a detailed view in perspective a second embodiment of an air 25 distributing member including a quick release coupling;

Fig. 2C shows in a detailed view in perspective a first embodiment of a siphon;

Fig. 2D shows in a detailed view in perspective a second embodiment of a siphon;

Fig. 2E shows in a top view an alternative embodiment of the water tank according to the invention without siphon, wherein the water tank includes a water discharge outlet in 30 an upper region;

Fig. 2F shows in a cross sectional side view the water tank of Fig. 2E;

Fig. 3A shows in a schematic view an embodiment of a water tank system according to the invention; and

Fig. 3B shows in a schematic view an embodiment of a water tank system 35 according to the invention including a waterbuffer; 10

Identical reference numbers correspond with similar components in the shown embodiments.

Figure 1A and 1B show in a perspective view a water tank 10 according to the invention. The watertank 10 comprises a tub 11. The tub 11 is a plastic box. The tub 11 has 5 a bottom wall 111 and a side wall 112. The tub 11 has an open upper part 110. The side wall 112 and bottom wall 111 define an inner storage space 113 which can be filled with water.

Inside the tub 11 at the bottom wall 111, a shelf 12 is provided. The shelf 12, as shown in Fig. 1A, is positioned at a distance from the bottom wall. A bottom space is formed 10 under the shelf 12. The shelf 12 is suitable for carrying shellfish. The shelf 12 may be positioned releasably inside the storage space. Spacers 123 may be provided at the underside of the shelf 12 to keep the shelf at a distance from the bottom wall 111 and to form a bottom compartment, a bottom space. The spacers 123 may be fixed to the bottom wall of the tub 11 or to the shelf 12. The shelf 12 covers substantially the whole bottom wall 15 111.

The shelf 12 is provided with a plurality of water passage ways 121 for a through flow of water through the shelf. The passage ways 121 are through holes and equally spaced over the surface of the shelf 12. Locally, at one side of the shelf, the shelf 12 is provided with an array or air passage ways to let pass vented air. Vented air may pass the 20 air passage ways from beneath the shelf 12 in an upwards direction towards the open upper part of the tub 11. The array of air passage ways 122 is formed by an array of through holes which extend in parallel with a side wall 112 of the tub 11. Venting air through the air passage ways 122 will create an air curtain which will generate an air and water flow in upwards direction along the side wall 112.

25 The storage space 113 of the tub 11 may be filled with water. A water supply is provided to keep the shellfish on the shelf 12 fresh. A water supply is provided for refreshing water in the storage space 113. The water supply comprises a water inlet for refilling the tub and a water discharge outlet (134) for discharging water from the tub. A siphon 13 is provided to keep the water level in the storage space 112 stable.

30 In Fig. 1A, the siphon 13 is arranged inside the tub 11 and positioned close to the side wall 112. The arrangement of the siphon 13 is further shown in detail in figure 2C.

In Fig. 1B, the siphon 13 is arranged outside the tub 11 and positioned close to the side wall 112. The siphon 13 is an external siphon which means that the siphon is arranged outside the tub 11 .The arrangement of the siphon 13 is further shown in detail in figure 2D. 35 The water tank 10 further comprises a gas supply. The gas supply is provided to create a relatively strong upwards gas flow in the water filled storage space 113. A gas distributing member 14 is provided inside the tub 11. The gas distributing member 14 11 comprises an air conduit which extends through the side wall 112. In Fig. 1A, the air conduit extends towards a lower region of the tub 11. In Fig. 1B, the air conduit extends through the sidewall 112 of the box at a lower region. The end of the gas conduit at the lower region of the tub is open for venting gas into the storage space 113. A first and second embodiment 5 of the gas distributing member 14 are further shown in more detail in figure 2A and figure 2B.

The tub 11 of the water tank 10 is stackable as shown in Fig. 1C. To stack several tubs 11 in a stable manner, the tub 11 is provided with an enclosing inner contour at the open upper part 110. The tub 11 has a bottom part which fits in the inner contour of the 10 open upper part of a lower tub 11. The tub 11 is provided with at least one recess to engage the tub 11 with a fork-lift truck. The recess enables a safe and stable operation for stacking the tubs.

Figure 1D shows in a cross sectional view two stacked water tanks 10. A first upper tub 11 is arranged above a second lower tub 11. Both water tanks 10 are provided with a 15 siphon 13 and a gas supply 14. A water flow is indicated with arrows. A first arrow starts from the gas supply 14 and indicates a water flow which is caused by rising gas. The gas is vented at the underside of the gas supply 14 and subsequently moves up in an upward direction to the upper open part of the tub 11. The upper water tank 10 is provided with a water supply inlet 130 above the tub 11. A water discharge outlet 134 is provided at the 20 bottom wall 111 of the tub 11. The water discharge outlet 134 is in fluid communication with the siphon 13. Water may be transferred by the siphon 13 from the upper tub 11 to the lower tub. No separate water supply inlet is necessary to refresh the water volume in the lower tub 11.

The discharge of water from the tub 11 at the bottom of the storage space 113 25 contributes to a water flow from above the shelf 12 to beneath the shelf 12 such that the waterflow passes shellfish on the shelf.

Figure 2A and 2B show in a perspective view a first and second embodiment of the gas supply 14. The gas supply, in particular an air supply, comprises in the first embodiment as shown in 2A an inlet conduit 141 which extends in upwards direction when mounted 30 inside a storage space 113 of the water tank 10. The relatively long inlet conduit enables an easy installation of the gas supply when a tub is filled with water. An operator does not need to reach far into the storage space to mount or demount the gas supply. At a proximal end, the inlet conduit 141 is provided with a quick release piece 145. The quick release piece 145 enables a quick mounting and removal of the gas supply from the tub 11. At the distal end, 35 the air gas inlet conduit 141 is in fluid communication with a gas distributing member 142. The gas distributing member 142 is arranged in perpendicular with the inlet conduit 141. When mounted inside the storage space, the gas distributing member 142 extends 12 substantially parallel with the side wall 112 and the bottom wall 111 of the tub 11. The length of the gas distributing member 142 corresponds with a width dimension of the storage space 113. The gas distributing member 142 is provided with venting holes 143 over its length. The venting holes 143 are equally spaced. The venting holes 143 are arranged at the underside 5 of the gas distributing member 142 which may improve an equal distributing of supplied gas over the venting holes 143. Further, the gas distributing member 142 is closed at both ends by a cap 144. The cap 144 may be easily removed for a cleaning operation.

The gas supply, in particular an air supply, comprises in the second embodiment as shown in 2B an inlet conduit 141 which may extend through a sidewall of a tub when 10 mounted inside a storage space 113 of the water tank 10. The second embodiment of the gas supply represents a simple embodiment which is relatively cheap to manufacture. Advantageously, the gas supply may be easy installed. At a proximal end, the inlet conduit 141 is provided with a quick release piece 145. The quick release piece 145 enables a quick mounting and removal of the gas supply from the tub 11. At the distal end, the air gas inlet 15 conduit 141 is in fluid communication with a gas distributing member 142. The gas distributing member 142 is arranged in perpendicular with the inlet conduit 141. When mounted inside the storage space, the gas distributing member 142 extends substantially parallel with the side wall 112 and the bottom wall 111 of the tub 11. The length of the gas distributing member 142 corresponds with a width dimension of the storage space 113. The 20 gas distributing member 142 is provided with venting holes 143 over its length. The venting holes 143 are equally spaced. The venting holes 143 are arranged at the underside of the gas distributing member 142 which may improve an equal distributing of supplied gas over the venting holes 143. Further, the gas distributing member 142 is closed at a distal end by a cap 144. The cap 144 may be easily removed for a cleaning operation.

25 Figure 2C shows in a perspective view an embodiment of the siphon 13. The siphon 13 comprises a first and second siphon tube 131, 132. The siphon tubes are arranged in parallel and are at one end in fluid communication with each other by a coupling piece 133. The siphon tube 131 is arranged aside the second siphon tube 132. The first siphon tube 131 is provided at the open end with a water discharge outlet 134. The water discharge 134 30 is provided to discharge water from the storage space 113 of the tub 11. The first siphon tube 131 is connected to the second siphon tube 132 by a siphon flange 136 at the open end of the first siphon tube 131. The siphon flange 136 is provided to connect the siphon 13 inside the tub 11 with bolds. A gasket is provided at the underside of the siphon flange 136 to prevent leakages from the tub. The second siphon tube 132 has an external opening to 35 discharge water out of the tub 11. The external opening of the siphon 13 may be connected to a bottom opening of the tub 11. When several tubs 11 are stacked on each other, discharge water from an upper tub 11 may be transferred by the siphon 13 and the bottom 13 opening in the tub to a lower arranged tub 11. Herewith, the siphon 13 serves to discharge water and additionally serves as a supply of water to a next tub. Advantageously, one common water supply inlet at the upper arranged tub 11 may serve for a plurality of stacked tubs. In this drawing the coupling piece 133 is shown without a cover plate.

5 Figure 2D shows in a perspective view a second embodiment of the siphon 13. The siphon 13 comprises a first and second siphon tube 131, 132. The siphon tubes are arranged in parallel and are at one end in fluid communication with each other by a coupling piece 133. The siphon tube 131 is arranged aside the second siphon tube 132. The first siphon tube 131 is provided at the open end with a water discharge outlet 134 to discharge 10 water out of the tub 11. The water discharge 134 is provided to discharge water from the storage space 113 of the tub 11. The first siphon tube 131 is connected to a siphon flange 136 at the open end of the first siphon tube 131. The siphon flange 136 is provided to connect the siphon 13 to the tub 11. A gasket is provided at the siphon flange 136 to prevent leakages from the tub. The second siphon tube 132 has an external opening 135 to 15 discharge water out of the tub 11. The external opening of the siphon 13 may be extend under the bottom wall 111 of the tub 11. When several tubs 11 are stacked on each other, discharge water from an upper tub 11 may be transferred by the siphon 13 and the external opening 135 to a lower arranged tub 11. Herewith, the siphon 13 serves to discharge water and additionally serves as a supply of water to a next tub. Advantageously, one common 20 water supply inlet at the upper arranged tub 11 may serve for a plurality of stacked tubs.

Fig. 2E shows in a top view an alternative embodiment of the water tank according to the invention. Fig. 2F shows in a cross sectional side view the water tank of Fig. 2E. In the shown embodiment, the water tank 10 is arranged without a siphon 13. The water tank is a tub 11. The tub 11 has a bottom wall 113 and a side wall 112. The tub has an open upper 25 side which may be closed by a lid. A water supply is provided which has a water inlet 130 for filling the tub with fresh water. The water inlet 130 is arranged at a lower region of the water tank and discharges water in between a shelf 12 and the bottom wall 111 of the tub 11. Water is discharged under the shelf.

The water inlet 130 is incorporated with the gas supply 14. The water inlet 130 is 30 tubular. The water inlet 130 comprises a tube with a plurality of venting holes 143 in its circumference wall to equally feed water into the inner storage space 113. At a distal end, the tubular water inlet is closed by a cap 144. At a proximal end, the water inlet 130 is provided with a quick release coupling piece 145 to easily release the water inlet 130 from the tub e.g for cleaning purposes. The water inlet extends from a side wall to an opposite 35 side wall.The water inlet extends through a centre region of the water tank to distribute water equally at the bottom side of the water tank.

14

The shelf 12 above the water inlet 130 is provided with a plurality of passageways for a through flow of water through the shelf. The shelf is supported by spacers 123 to space the shelf from the bottom wall. The shelf is made of a perforated plate. The perforated plate has passageways which are regularly distributed over the plate. The shelf is pivotally 5 connected to the tub.

The water supply serves also to feed oxygen to the inner storage space. Supplied water is enriched with pure oxygen before the water is fed to the inner storage space. Thus, the gas supply is incorporated in the water supply. Water is discharged under the shelf and flows upwards. An upwardly directed flow of water from the bottom wall is generated by fed 10 water. The water tank includes at least one water discharge outlet 134 in an upper region of the tub. Water and generated floating foam exits the water tank 10 at the water discharge outlet 134.

The tub 11 is further provided with an exit hole 119 in the bottom wall. The exit hole 119 is a small hole which is open during operation. A relatively small continuous water flow 15 leaves the tub 11 through the exit hole.

At least two water tanks 10 may be stacked, wherein water from each water tank is discharged to a water treatment station. Each stacked water tank is provided with its own water supply.

Figure 3A shows in a schematic view a water tank system according to the 20 invention in a first embodiment. Fig. 3B shows a second embodiment of the water tank system. A plurality of stacked water tanks is shown at the left side of the view. The most upper arranged water tank 10 is provided with a water supply inlet 130 to refresh the water volume in the water tanks during operation. A second water supply inlet 139 is provided for filling the water tanks 10. The first and second water supply inlets 130, 139 are connected 25 by a water supply header 203. Water from the water tanks 10 may be discharged to a drain 138.

All watertanks 10 are connected to a gas supply 140. The gas supply 140 comprises a fan 149 to generate an air flow. The air flow has a positive pressure of about 0,15 bar and an air rate of about 6,25 m3/h.

30 The water tank system further comprises a water treatment station 20. The water treatment station 20 is in fluid communication with the stacked water tanks 10.

In Fig. 3A, the watertank system 20 comprises a first and second basin 241, 242 for collecting and cleaning water. The basin 241 may contain bacteria holding elements which may circulate through the basin. Water may be transferred from the basin 241 to the 35 header 203 via a conduit 201 and 202. The water treatment station 20 may comprise a skimmer 22 to separate sludge from the water. The sludge may be discharged to a sewer 222. The skimmer may comprise a cylindrical skimmer container having a skimmer inlet 15 which is connected to the first water supply conduit 201. The skimmer container may further have a first outlet to the sewer 222 and a second skimmer outlet which is in fluid communication with the second water supply conduit 202 to the header 203. The water may be returned to the basin 241 via a first discharge outlet 204 which is connected to the 5 header 203 and a second discharge conduit 205 which is connected to the drain 138.

The water treatment station 20 further comprises a cooling element 23. In Fig. 3A the cooling element 23 is positioned in the basin for cooling water. The water is cooled to a temperature of at most 15 °C, in particular at most 10 °C and more in particular at most 5 °C. Further the water treatment station 20 comprises an air conduit 25 which is branched into 10 two air conduits 251,252 for each basin 241,242. The air supply 25 may be connected to the fan 129. The air supply in the basins may provide a circulation of the bacteria containing elements in the water.

In Fig. 3B, the second basin 242 is removed and a waterbuffer 27 is introduced.

The water buffer 27 has a water buffer container 270 for containing water and a water buffer 15 inlet 271 and a water buffer outlet 272 which are connected to the container 270. The water buffer inlet is in fluid communication connected to the skimmer outlet. The water buffer outlet 272 is in fluid communication connected to the conduit 202 for supplying water to the water tanks 10. The water buffer 27 comprises a cooling element 23 for cooling water in the water buffer 27. Water may be pumped from the container 270 to and froh the cooling element 23. 20 The cooling element may be a heat transfer unit which may be arranged inside the container 270. In comparison with Fig. 3A, in Fig. 3B, the cooling element is moved from the basin 241 to the water buffer 27 which advantageously may provide a higher temperature efficiency. The water may be cooled just before the water is supplied to the water tanks 10. The water buffer comprises an air inlet 273 for introducing air into the water buffer to cause a water 25 circulation.

As shown in figure 3A and 3B, an injector 21 may be provided in the first water supply conduit 201. The injector may inject air and ozone 212 into supplied water. Injected air and ozone may contribute to the separation in the skimmer 22. Air may be supplied via air conduit 212 which may be connected to the fan 149.

30 Further the water treatment station 20 comprises a source water supply 26. The source water supply may retrieve water from sea or source water out of the ground. A treatment unit 262 e.g. a water softening unit may be provided to treat source water before the source water is supplied to a basin 24.

The shown water tank system may be installed at a land location, but may also be 35 arranged on a vessel, in particular a fishing boat, more in particular a shellfish boat.

Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes 16 may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Numerous variants are possible in addition to the embodiment shown. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.

5 Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the appended claims.

Thus, the invention provides a water tank for preserving shellfish. Due to the presence of an oxygen containing gas supply which causes a water flow, a great amount of 10 water may be saved for refreshing a water volume of the watertank. A water tank system according to the invention is provided which may be installed on board of a vessel or at land for processing shellfish. Advantageously, the shellfish may have an increased lifetime and may be kept fresh for a relatively long period.

Claims

A water tank for keeping crustaceans conditioned, comprising: • a tub with a bottom wall and at least one side wall defining an inner storage space for crustaceans, which storage space can be filled with water; • at least one step for keeping crustaceans within the storage space; 5. a water supply for refreshing water in the storage space comprising a water inlet for filling the tub and a water discharge outlet for draining water from the tub; An oxygen-containing gas supply extending at least partially into the storage space, wherein a gas supply outlet of the gas supply 10 is positioned on a lower portion of the storage space such that during use an upwardly directed gas stream is generated to cause a water flow in the storage space .

2. Water tank according to claim 1, wherein the oxygen-containing gas supply is integrated in the water supply to supply oxygen-enriched water to the inner storage space, in particular to supply substantially pure oxygen via a water supply line to the inner storage space.

3. Water tank according to claim 1, wherein the oxygen-containing gas supply is an air supply.

The water tank of claim 3, wherein the gas supply has a positive pressure within a range of at least 0.1 bar and at most 0.75 bar.

5. Water tank according to one of the preceding claims, wherein the step has several passages for a flow of water through the step.

6. Water tank according to one of the preceding claims, wherein the step is positioned at a distance from the bottom wall and is positioned in a lower part of the tub.

Water tank according to one of the preceding claims, wherein the step is hinged to the tub. -18-

A water tank according to claim 7, wherein the step comprises a first step part, wherein the first and second step part are each hingedly connected to the tub.

9. Water tank as claimed in any of the foregoing claims, wherein the water discharge outlet is arranged in an upper area of the water tank.

The water tank of claim 9, wherein the water drain outlet is an overflow opening near an upper edge of the water tank.

Water tank according to one of the preceding claims, wherein the water inlet is arranged at the bottom wall.

12. Water tank as claimed in any of the foregoing claims, wherein the water tank is provided with an exit hole which is arranged in a low-lying part of the water tank below the step.

Water tank according to one of the preceding claims, wherein the water supply comprises a cooling device for cooling supplied water.

A water tank according to any one of claims 1-8, wherein the water discharge outlet is arranged on a lower portion of the water tank between the step and the bottom wall.

15. Water tank according to claim 14, wherein the water discharge outlet is connected to a siphon to control the water level in the storage space, the siphon being an internal siphon arranged inside the storage space.

A water tank according to any one of the preceding claims, wherein the side wall of the tub comprises at least one quick coupling piece for coupling the gas supply. 30

A water tank according to any one of the preceding claims, wherein the tub comprises an air distribution member in the storage space.

18. Water tank according to claim 17, wherein the air distribution element comprises at least one air line which is arranged substantially parallel to the side and bottom wall of the tub. -19-

A water tank according to any one of the preceding claims, wherein the air distribution member is connected to the tub by a quick coupling piece.

20. Water tank according to claims 17-19, wherein the air distribution element 5 is positioned between the step and the bottom wall of the tub.

Water tank according to claim 20, wherein the step comprises at least one air passage which is positioned at a position of the air part member for passing blown off air. 10

A water tank system for keeping crustaceans conditioned, comprising at least one water tank according to one of the preceding claims.

23. Water tank system as claimed in claim 22, comprising at least two stacked tubs, wherein the stacked tubs are provided with a common water supply with a single water supply inlet at an upper positioned tank and a water overflow for transferring water from an upper to a lower situated tank. and a single water discharge outlet for draining water from the lowest tub to a drain. 20

A water tank system according to claim 22 or 23 comprising a water treatment station.

25. Water tank system according to claim 24, wherein the water treatment station 25 comprises at least one basin for purifying water.

The water tank system of any one of claims 22-25, wherein the water tank system comprises a single air-containing gas pump for supplying gas to at least one tub and the basin of the water treatment station. 30

27. Water tank system according to any of the claims 22-26, wherein the basin has at least one basin water inlet and a basin water outlet wherein the water basin inlet is in flow communication with the water discharge outlet that comes from a tub, and wherein the water basin inlet is in flow communication with a water supply inlet from a tub. -20-

The water tank system of any one of claims 24-27, wherein the water treatment station further comprises a skimmer for separating foam from the water.

The water tank system of any one of claims 24-28, wherein the water treatment station comprises a cooling element which extends into the basin or water buffer.

30. Ship, in particular a fishing boat, comprising a water tank according to one of the claims 1-21 or a water tank system according to one of the claims 22-29.

A method for keeping shellfish sustainable, wherein a water tank as defined in any one of claims 1-21 or a water tank system as defined in any one of claims 22-29 is used. 15

A method according to claim 31, wherein trapped crustaceans are stored in an on-board water tank according to any of claims 1-21 to disinfect the crustaceans on board and to remove pollution.

The method of claim 31 or 32, wherein the method comprises a step of cutting the bysses threads of the crustaceans using a brush mill.