Note: Descriptions are shown in the official language in which they were submitted.
I
SYSTEM FOR SELECTIVE WASTE REMOVAL FROM AN AQUACULTURE UNIT
Field of invention
The present invention relates to a collection device for collecting sludge
such
as sunken particulate waste and for collection of sunken farmed organisms such
as
dead fish from an aquaculture cultivation unit positioned in a body of water.
The
present invention also relates to a use of said device for collection and
removal of
waste. Furthermore, the present invention relates to a method for collection
and
removal of waste from an aquaculture cultivation unit positioned in a body of
water.
Background of the invention
The annual production of salmonids in Norway was about 1.3 millions tons in
2012, 99 % being Atlantic salmon and trout. The production of salmon is at
present
mainly based on cage aquaculture in the sea, where salmon are cultivated in
large
net pen units. The intensive production entails different forms of waste
produced
during the production process such as dead fish (also referred to as "morts"),
faeces,
unconsumed feed etc. Even though often only recognized as waste, and a
potential
environmental threat, the discharges from sea farms also represent a largely
unexploited, potentially valuable source for nutrients.
The nutrient components deriving from salmon cage systems during
production of salmon can generally be divided into dissolved inorganic
nutrients,
dissolved organic nutrients and particulate nutrients. Dissolved inorganic
nutrients
such as ammonium and phosphate, are immediately taken up and consumed by
phytoplankton or macro algae in the body of water. Dissolved organic nutrients
comprise dissolved organic nitrogen and phosphorus, consisting of molecular
nutrient components forming complex chemical compounds from feces and feed.
These dissolved organic nutrients may be consumed by bacteria, thereby
entering
the microbial food web or they may aggregate to sink as "marine snow" in slow
processes to the sediment.
The particulate nutrients, including particulate organic nitrogen and
phosphorus, typically originate from feed pellets, small particles from feed
and
faeces as well as other particles from fouling on the cage.
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Smaller particles deriving from intensive sea based aquaculture are typically
suspended in the water column where they are consumed by filter feeders and
bacteria within days. Larger particles from aquaculture systems are either
consumed
by the fish or if not collected these particles sink rapidly to the sea floor
where they
accumulate in the sediments. When collected or accumulated the sunken
particles
appear as sludge.
In a study carried out in 2009, the Norwegian salmon industry used about
1 173 000 tons feed in intensive production of salmon. About 3 % of this feed
was
not consumed by the fish and represent feed losses discharged as waste from
the
farms. Based on a carbon budget analysis, 30 % of the feed is going to fish
biomass
and 48% to respiration, while 19% of the feed is faeces discharged as waste to
the
body of water. Feed losses, faeces, and other organic waste are mainly
discharged
as particles which sink down and accumulate on the sea bottom in the sediments
if
not collected. Discharged in these significant amounts during intensive
production in
net cages, the particulate waste is not only affecting the environment in
vicinity to
fish farms, but also represent a significant loss of biomass and nutrients
which may
be used for other purposes. For a later use of the sludge e.g. as a
fertilizer, a high
quality of the sludge product is necessary but also low costs for necessary
treatments to make its use economically feasible. This is not achieved with
the
methods for collection and treatment of the sludge known today.
In order to reduce problems with diseases and parasites, in particular salmon
lice, as well as escapes from net cage farms, different types of closed sea-
based
cultivation units have recently been developed and tested. These closed
systems are
typically more or less water tight cultivation units, e.g. made of tarpaulin,
plastic,
concrete or the like, which are used in stead of nets. Water is pumped into
these
containers to supply the fish with fresh water and oxygen. Particulate sunken
waste
such as faeces and feed losses are typically removed at the bottom of the
closed
cultivation unit together with the effluent water.
Today, combined waste collection and suction systems for sunken waste such
as for dead fish (also referred to as "morts") and larger particles
(unconsumed feed
pellets and faeces) are in use for fish farm cages. These systems are often
referred
to as "mort collection systems" by the industry as their main purpose is to
remove
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dead fish from the cage. A well known system, being in use in many salmon
farms, is
a collection head where dead fish are collected in a funnel formed head at the
bottom of the cage and sucked up to the surface once per day using an air
lifting
pump system (also called mammoth pump system). N0335174 B1 discloses such a
type of collection head typically used in salmon aquaculture. The disadvantage
of
this known system is that high amounts of water have to be used to lift the
fish up
from the bottom and that a subsequent separation of the different types of
waste, i.e.
dead fish and sludge, is ineffective and laborious.
N0339302 B1 discloses a waste collection system for collecting sunken waste
using a sucking head placed in the bottom of a sea cage. The system does not
open
for a separate lifting up of sludge and fish.
N0329813 B1 disclose a system for collection of dead fish from the bottom of
a sea cage, having a funnel formed collection device arranged at the bottom of
the
cage and a hose for sucking up the fish. Neither this system allows to remove
sludge
and fish separately.
Thus, there is a need for a universal and flexible collection and handling
system of waste, in particular of particulate organic waste such as faeces and
feed
losses from intensive sea-based aquaculture production such as from salmon
farming in net cages.
Summary of the invention
An object of the present invention is to overcome the problems and
disadvantages described above. In more detail, the present invention aims at
providing an effective system and a method for reducing the discharge of waste
from
water-based fish farming systems and an improved system for collecting and
handling of waste. In particular, it is an object of the present invention to
provide a
system and a method for collection and handling of sludge, feed remnants, and
other
small particulate organic and inorganic waste from aquaculture production.
Another object of the present invention is to provide a universal waste
collection system suitable for both open and closed farms systems placed in
the sea.
Another object of the present invention is to provide a system where both
small particulated waste from feed and faeces as well as dead fish can be
effectively
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collected, removed, and handled in the same device without affecting or
disturbing
the farmed fish.
Yet, another object of the present invention is to provide such a combined
system which is optimized in respect to the need of water for pumping and
waste
water treatment thereafter.
Yet another object of the present invention is provide a robust and flexible
waste collection system which is easy to install, remove, and adapt for
different
needs of waste collection.
Yet another object of the present invention is to obtain an improved sludge
product suitable for further use.
In particular, it is an object to provide a waste collection system which is
suitable/adaptable for use with fish of different size such as smolt and on-
grown
salmon.
The objects are achieved by a solution as defined in the independent claims,
while the dependent claims represent preferred embodiments.
Thus, in a first aspect the present invention relates to a collection device
for
collecting sludge such as sunken particulate waste and sunken farmed organisms
such as dead fish from an aquaculture cultivation unit positioned in a body of
water.
The device comprises
- a collection head at the bottom of the cultivation unit for collection of
sunken
sludge and sunken farmed organisms, the collection head comprises a funnel
formed top plate wherein the sunken sludge and organisms are collected in or
in vicinity to the lowest point of the funnel,
- a first removal system for sunken sludge, having a first inlet for
sludge and
small particles at the lowest point of the funnel-formed top plate, the first
inlet
being provided with a retaining system for holding back the farmed organisms,
and in that the first removal system further comprises a first pumping system
for removal of said sunken sludge from the first inlet,
- a second removal system for sunken farmed organisms accumulated on
the
top plate and a second pumping system for removal of the sunken organisms
from the top plate.
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The first and/or second pumping system can be an airlifting pump suitable to
transport the sludge and/or the organisms to the water surface.
The retaining system can comprise a locking element covering at least the
first
inlet located in the funnel formed top plate and leaving at least one opening
for
5 sludge discharge, said opening being smaller than the farmed organisms.
Preferably, the locking element is a locking disk.
The opening can be in form of a circumferential slot between the lower end of
the
locking element and an upper edge of the first inlet.
The one or more openings/slots of the first inlet can be adjusted in size
and/or
closed.
Preferably, a conduit is connected to the first inlet at the funnel formed top
plate,
the conduit being located inside the collection head and extending in a U-form
from
the first inlet a distance down into a bottom part of the collection head and
further up
to at least the upper surface of the top plate.
The second removal system can be arranged in a center area on the funnel-
formed top plate in close vicinity to the first removal system, wherein the
organisms
are preferably removed sideways/upwards from the funnel-formed top plate.
The second removal system preferably comprises
- a housing which is arranged on the top plate and has a second inlet for
organisms
on one side, the second inlet facing towards the center of the funnel-formed
top
plate,
- a passage through the housing, and
- an outlet on the top of the housing.
In a second aspect, the present invention relates to a method for collection
and removal of waste from an aquaculture cultivation unit positioned in a body
of
water. The method uses a device according to any of the preceding paragraphs
and
comprises the following steps:
- collecting sinking sludge on the top plate of the collection head,
- activating the first removal system for pumping said sludge collected on
the top plate with water to a receiving station above the water surface;
- deactivating the first removal system;
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- separating the water-sludge mixture to remove water and to
concentrate
the sludge.
Preferably, the method additionally comprises the following steps after
removal of sludge:
- activating the second removal system for pumping the organisms
accumulated on the top plate to the surface,
- deactivating the second removal system.
The sludge can be removed by a first airlift-pump, preferably with a capacity
of
5 - 20 m3 water per hour, more preferably with 10-15 m3 water per hour, most
preferably 10-12 m3 water per hour. The organisms can be removed by a second
airlift-pump, preferably with a capacity of about 120 to160 m3 water per hour,
more
preferred about 150 m3 water per hour.
The sludge may be removed several times per day, preferably at least once
every second hour, more preferably at least once every hour. The organisms are
preferably removed at least once per day.
A third aspect of the present invention relates to a use of the device as
defined above for collection and removal of waste from an open sea cage or
from a
closed cultivation unit, preferably for intensive aquaculture of fish, more
preferably
for a species selected from the group consisting of salmonids, codfish,
flatfish,
breams, basses, groupers.
Short description of diagrams
Embodiments of the invention will now be described, by way of examples
only, with reference to the following diagrams in which:
Figure 1 shows schematically a sea cage with a waste collection device
according to
a first embodiment of the present invention;
Figure 2 shows a view in perspective of a collection head according to the
first
embodiment of the present invention;
Figure 3 shows schematically a side view of the head disclosed in figure 2;
Figure 4 shows schematically a front view of the head disclosed in figure 2,
also
indicating the position of the section axis C-C;
Figure 5 shows schematically a section view through axis C-C of figure 4;
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Figure 6 shows schematically a top view of the device of figure 2, also
indicating the
position of the section axis A-A;
Figure 7 shows schematically a section view through axis A-A of figure 6;
Figure 8 shows schematically an enlarged view of the sludge removal system of
figure 7 (marked with "B" in figure 7).
Figure 9 shows schematically a side view a collection head according to a
second
embodiment of the present invention;
Figure 10 shows schematically a front view of the head disclosed in figure 9,
also
indicating the position of the section axis C-C;
Figure 11 shows schematically a section view through axis C-C of figure 10;
Figure 12 shows schematically a top view of the collection head of figure 9,
also
indicating the position of the section axis A-A;
Figure 13 shows schematically a section view through axis A-A of figure 12;
Figure 14 shows schematically a section view through axis C-C of figure 10 of
an
alternative cone-shaped collection head having downwards inclining V-formed
walls
extending from the backside of the house to the outward edge of the cones top
plate;
Figure 15 shows schematically a top view of the collection head of figure 14,
also
indicating the position of the section axis A-A.
Detailed description of embodiments
The following description of the exemplary embodiments refers to the
accompanying drawings. The same reference numbers in different drawings
identify
the same or similar elements. The following detailed description does not
limit the
invention. Instead, the scope of the invention is defined by the appended
claims. The
following embodiments are discussed, for simplicity, with regard to various
forms of
waste collection systems for a sea-based fish farm. It should be appreciated,
however, that the referenced collection system for sludge, dead fish, and
other waste
is also applicable and suitable for use in respect to any other type of
aquaculture
systems, requiring handling of waste. Reference throughout the specification
to "one
embodiment" or "an embodiment" means that a particular feature, structure, or
characteristic described in connection with an embodiment is included in at
least one
embodiment of the subject matter disclosed. Thus, the appearance of the
phrases "in
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one embodiment" or "in an embodiment" in various places throughout the
specification is not necessarily referring to the same embodiment.
In the description relative terms such as front, top, center, bottom, side,
lower,
upper, downward, upward, outward, sideward, vertical, and horizontal etc. are
all
related to the collection device when in upright position i.e. when mounted in
a farm
cage. Even though only exemplified for one side, it is to be understood that
some
features will correspondently also apply for the opposite side of the device.
In the context of the present invention an aquaculture cultivation unit refers
to
a farm or cage, most commonly a farm located in a body of water, typically a
sea-
based fish farm cage. The term includes open sea cages, typically net pens
(fish
cages), where the water can freely flow through the net from the outside into
the
cage with the farmed organisms. The term also includes closed systems where
the
farmed organisms are kept in a more or less water tight container, effectively
stopping a direct water exchange with the surrounding water and having an
external
water supply by one or more pumps. It may also include land-based systems.
By sludge is meant feed waste such as not ingested feed pellets,
disintegrated feed particles, excrement(s)/faeces from the farmed organisms,
particulated organic waste such as microalgae and macroalgae, dead plankton,
fouling organisms, and other small particulated waste typically found in an
open or
closed cage, sinking down to the bottom section of the cultivation unit. Said
sludge is
removed by the first removal system which is described in detail later on.
By sunken farmed organisms is meant aquatic organisms which are farmed or
kept in the aquaculture cultivation unit and which are dead (often called
"morts"),
almost dead or at least sick and are not swimming but sinking down to the
bottom of
the cage. The farmed organisms can typically be pelagic fish such as
salmonids,
codfish, breams, basses, groupers and the like. The sunken organisms are
removed
by the second removal system according to the present invention which is
described
later on. Even though disclosed as a collection and removal system for sunken
fish/aquatic organisms, the skilled person will understand that other type of
waste
may be removed by this system as long as the waste to be removed has suitable
characteristics e.g. dimensions.
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Figure 1 shows a side view of an aquaculture cage 1 having a surrounding net
or wall 2 extending downwards from the water surface 3 for enclosing the fish
or
aquatic organisms to be cultivated or kept in the unit, the net or wall 2
being mounted
to a floating ring-formed collar 4, which floats on the surface 3 of a body of
water.
Also shown in figure 1 is a (hand)rail 5 mounted on the collar, which is a
typical
equipment on todays fish cages. The enclosing net or wall 2 is typically more
or less
cylindrical in the upper section, while the bottom section is funnel-formed
i.e. the
diameter of the net/wall 2 inclines towards the center of the cage in the
lower section
of cage 1. It further shows a waste collection device 6 according to the
present
invention. The waste collection device 6 is for collection and accumulation of
sunken
(sedimented) sludge and sunken farmed organisms such as dead fish from the
cultivation unit 1. The waste collection device 6 comprises a collection head
10 fixed
in the center to the bottom section of the sea cage 1. The collection head 10
has a
bottom part 30 and a funnel-formed top plate 20.
The waste collection device as shown in figure 1 is provided with two separate
systems for removal of waste. A first removal system 40 is a sludge removal
system
for removal of sunken sludge accumulated on the top plate 20 of the collection
head
10. A second removal system 60 is for sunken organisms cultivated or kept in
the
cage and collected on the top plate 20 e.g. dead fish. Both waste types are
collected
and lifted up from the bottom section of the fish cage by an airlift pump
system each
to the water surface 3 and further to one or more stations for storage and/or
treatment of waste (not shown). For the transport to the surface, the waste
collection
device is provided with two different conduits extending from the collection
head 10
to the surface, being a conduit 12 for the sunken organisms, typically
provided with a
floating element 13, for transport of the organisms, and a sludge pipe 15 for
lifting up
the sludge by airlifting. Further shown in figure 1 are pipes 14, 16 for
pressured air
used for the two separate air lifting pump systems for sludge (first pump
system) and
for organisms (second pump system), respectively. The collection and transport
of
waste to the surface will be explained in more detail below.
Figure 2 shows schematically a perspective view of a collection head 10
according to one first exemplary embodiment of the invention. Figure 3 to 7
show
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side, front, top, and sectional views of the collection head embodiment of
figure 2.
Figure 8 shows an enlarged view of the sludge removal part of the collection
head.
Said collection head 10 is mounted in the bottom part of the sea cage 1, as
described above, which can be a closed cage e.g. a tarpaulin container without
or
with only minimal direct water exchange with the surrounding body of water or
an
opened net type of cage allowing a direct water exchange.
The collection head 10 of this first embodiment comprises a horizontally
extending; typically circular top plate section 20 on the top and a
cylindrical bottom
section 30 with a substantially planar bottom 32 (see e.g. Fig. 2, 3, 4 and
7). The
bottom section 30 comprises technical elements for the suction of sludge as
well as
ballast elements. The top plate 20 and the bottom part 30 of the collection
head 10
are preferably made as one part such as by moulding. If made of two parts, the
parts
can be fixed to each other by screws, clamps, welding, or other suitable
means. The
collection head is typically made of one or more materials which can withstand
longer periods in sea water such as plastic materials, fibre glass, non-
corrosive
metal compositions or combinations thereof. In a particular preferred
embodiment,
the collection head is moulded, typically casted in two moulds forms.
Preferably, it is
made of low density polyethylene.
For stabilization and reinforcement, the collection head can be provided with
reinforcements structures 66 such as shown in figure 2, 5, and 6. These can be
for
example steel elements extending from the top plate 20 a distance down into
the
bottom part 30 of the head 10.
The circular top plate 20 of the collection head 10 is funnel-formed allowing
the sunken waste to sink down towards the lowest point or lower section of
said
funnel in the top plate 20. Thus, the lowest point of the funnel is pointing
downwards
when the collection head 10 is mounted in the sea cage as shown in figures 2
and 7.
Typically, the funnel has its lowest point in a center area of the top plate,
but other
non-central arrangements of the funnel are neither excluded. The top plate 20
has a
first removal system 40 for collection of sunken/sedimented sludge and
transport to
the surface. The removal system 40 for sludge is typically arranged centrally
in the
funnel of the top plate and comprises a first inlet 42 for discharging of
small
particulate waste/sludge such as unconsumed feed particles and faeces through
a
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sludge conduit 44 arranged inside the collection head 10 under the top plate
20,
wherein the sludge conduit 44 is connected to said first inlet 42.
As shown in detail in figure 8, the first inlet 42 is provided with a
retaining
element 45 for fish, morts, or other aquatic organisms to be cultivated to
avoid that
these are accidentally sucked into said system. The retaining element 45 is
therefore
typically provided with one or several apertures or slots large enough to
allow water
and smaller particles to pass through, but holding back the aquatic organisms
to be
cultivated as well as dead fish/rnorts accumulated on the top plate 20 of the
collection head 10. Preferably, at least the first inlet 42 is covered by said
retaining
element 45 for fish which hinders that the fish can pass through but allows
removing
the collected sludge. This is achieved by a suitable locking element 46. The
locking
element 46 is shown in form of an adaptable locking disk which is arranged
above
the sludge conduit 44/ first inlet 42 such that a more or less circumferential
slot 48 is
left open between said disk and the edge of the conduit 44/ first inlet 42
allowing free
passage of said particulate waste/sludge through said circumferential slot and
into
the inlet 42 for sludge. This slot 48 is preferably adjustable in its
dimensions
depending on the size of fish being cultivated in the cage at any time and the
sludge
particles to be removed. This can be achieved by mechanically reducing or
enlarging
the distance between the inlet covering locking disk and the edge of the
conduit 44
i.e. the height of the slot 48 (see also figure 8). This can e.g. be done
manually or in
an automated matter.
In figure 8 it is shown an embodiment where the locking disk of the retaining
element 45 is fixed and adjustable by means of one or more screws 47. The
screw(s) 47 may be arranged on the side of the disk as shown in the figures.
In a
preferred embodiment, a threaded element/screw 47 is arranged in the center of
the
disk and engages with a suitable receiving element in the center of the first
inlet 42
(not shown). Other means well known to the skilled person may be used instead
such as clamps or the like. The possibility for an adjustment of the opening
dimension of the retaining element is an advantage since larger fish will be
fed with
larger pellets, producing larger faeces particles, meaning that larger
particles have to
be collected and transported through the first removal system 40 for sludge.
Preferably, the first removal system 40 can also be closed totally if needed.
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Preferably, the openings/slots/apertures 48 of the retaining element 45 for
the
sludge are adjustable from 4 to 11 mm depending on the pellets size used which
is
typically between 3 and 10 mm in dimension.
The conduit 44 below the first inlet 42 is formed as a U-formed pipe. This is
schematically illustrated in figure 7 which is a section view through the A-A
axis of
figure 6. The U-formed conduit 44 extends a distance downwards in the bottom
part
30 of the collection head 10, and turns thereafter more or less vertically up
through
the top plate 20 and at least to the top surface of the top plate 20. The U-
formed
conduit is preferably constructed without edges and corners to avoid
turbulences and
areas with no or reduced water flow through the conduit. The conduit 44 is
connected at its upper section 43 to the sludge pipe 15 extending from the
collection
head 10 to the water surface 3 for transport of the sludge to the water
surface 3 (see
also Figure 1) or preferably to a receiving station for sludge. The sludge
pipe 15 as
well as the conduit 12 can typically be a collapsible, flexible pipe made of a
plastic
material, such as PVC. Typically, the sludge pipe has a diameter of about 90
mm
while the conduit 12 has a diameter of about 200 mm. In a preferred embodiment
the
lower part, e.g. the first 6 meters, of the pipe 15 and of conduit 12 is a
spiral tube,
e.g. made of PVC, while the upper part extending to the surface, is a
collapsible flat
tube.
The first removal system 40 for sludge is typically provided with a first pump
system, e.g. a first air-lift pump system (also called "mammoth pump") as
shown in
figure 1, creating a suction force upwards by pressing compressed air into the
water
filled pipe system in the upwards oriented section 43 of conduit 44 or into
the sludge
pipe 15. Thereby a dragging force is created lifting up the water-sludge
mixture. For
this purpose, the first removal system 40 is provided with a pipe 16 for
compressed
gas, preferably compressed air. The inlet for the compressed air should be in
the
vertically raising upper section 43 of the conduit 44 or in the sludge pipe 15
extending to the surface. Preferably, the inlet for the compressed air is
inside or at
the collection head or in close vicinity to it. A compressor for the
production of
compressed air is typically placed above the water surface on a fleet or the
like (not
shown).
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13
Even though an air-lifting pump is a preferred solution, other pumping systems
maybe used instead such as an injector pump or the like.
Alternatively to the described disk locking arrangement as retaining element
45 for the inlet 42, a valve, sieve, or grid may be used to cover the inlet 42
and the
top of the sludge conduit 44 (embodiment not shown in figures) whereby the
openings/apertures are dimensioned to hold the fish/farmed organisms back,
while
allowing smaller particles to pass. Due to the risk of clogging of valves,
grids, and
sieves, the disk type of retaining element is generally a preferred solution.
An alternative solution for a locking element 46 can also be an element that
has inclining wall(s) such as a conical form, a substantially frusto-conical
form, a
substantially cupula form, a substantially pyramidal form, or a substantially
frusto-
pyramid form.
Being pumped up to the surface, the sludge and water mixture may be stored
in a suitable container or treated directly e.g. by passing the mixture
through a
suitable filter for separation of the particles/sludge from the water.
Typically, a filter
with apertures being 350 pm or less can be used for this purpose. Smaller
apertures
can be used if e.g. certain infectious stages of parasites such as salmon lice
shall be
filtrated out of the water. The water treatment may also comprise a
filtration,
centrifugation, purification and/or disinfection systems with several steps
and grades.
Suitable filters are known in the field such as from water treatment systems
e.g. in
slaughter houses for fish. The skilled person is well known with suitable
filter
apparatuses to be used for this purpose and these will therefore not be
described in
more detail.
Typically, the sludge from several cages can be collected and treated together
in one sludge receiving station. For practical reasons this can be done on a
floating
structure such as a vessel or a service fleet being in close vicinity to the
cage(s). If
the aquaculture site is located close to land, it maybe done on shore, e.g.
the waste
receiving and/or treatment station may be placed on land.
In a particular preferred embodiment as shown in figures 1 to 7, the waste
collection and collection head 10 additionally comprises a second removal
system 60
for sunken or dead fish/ aquatic organisms ("morts"). The second removal
system 60
is typically located in the center area on the top plate 20 in close vicinity
to the first
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removal system 40 for sludge. The second removal system 60 is known per se and
comprises a hollow housing 61 for passage of the sunken organisms through the
housing 61 (see e.g. figure 2). The housing 61 can be mounted on the top plate
or
can be an integrated part on the surface of the top plate 20. The passage
through
the housing 61 is typically in a L-form. The housing has two openings. One
opening
is a second inlet 62 for sucking in the sunken organisms/fish. This second
inlet 62 is
typically on one side of the housing 61 and is oriented towards the lowest
point of the
funnel-formed top plate 20 in the center area i.e. the area where both the
fish and
the sludge will naturally accumulate in the funnel when sunken down. Dead
fish/dead
aquatic organisms sink down on the funnel-formed top plate 20, accumulate at
the
lowest point in said center area of said plate 20 and are removed
sideward/upward
through the housing 61. Thus, the sunken fish are typically sucked in sideways
through said second inlet 62. The second opening 64 of housing 61 is an outlet
on
top of the housing 61 where the conduit 12 for the sunken organisms is
connected to
the housing 61 (see figure 1) for sucking and transporting of the organisms to
the
surface. Sucking forces are typically produced by a second pump system e.g. a
second air-lift pump system using compressed air being pressed through the
pipe 14
for pressurized air/gas into the housing 61 or into the conduit 12 in close
vicinity to
the collection head 10.
The second collection system 60 maybe provided with mechanical barriers or
elements (not shown) which hinder living (swimming) fish to enter the housing
61
through the inlet 62 or to be sucked up accidentally.
The removed organisms e.g. dead fish are transported through said conduit
12 to a receiving station for the organisms (not shown). Organisms from
several
cultivation units may be transported to the same receiving station.
The two different waste treatments systems typically operate with different
pumping capacities. The first removal system 40 for sludge typically pumps up
10-15
m3water per hour, preferably 10-12 m3per hour by airlifting. The second
removal
system 60 pumps up about 150 m3 water per hour by airlifting.
The conduits/pipes extending from the collection head to the stations for
waste collection can be at least in part collapsible when not in use during
active
pumping.
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The pipes 14 and 16 for compressed air used for airlifting of dead fish and
sludge may be attached to each other by permanent welding or other attachment
means such as clamping, sewing or the like. The injection of compressed air
can be
regulated by suitable valve systems e.g. magnetic valves and a suitable system
for
programmable logic controlling (PLC).
Thus, in a preferred embodiment of the present invention, such as also shown
in the exemplifying figures, the sludge is first transported downward from the
top
plate into the U-formed sludge conduit 44, before it is transported upward.
Since the
retaining element does not stop the sludge from entering the conduit 44, the
sludge
can also sink down in the conduit 44 by sedimentation during the periods
between
the active pumping of sludge. The dead fish/dead aquatic organisms are
preferably
sucked directly upward or sideward and upward as shown in the figures.
Even though shown in the figures that the conduit 44 is located inside the
bottom part 30 of the collection head 10, an alternative, even though less
preferred
embodiment, would be to arrange the conduit 44 laterally from the head plate
i.e.
only partly under the collection head 10.
The bottom part 30 can have several functions e.g. ballasting, mounting the
collection head to the cage and/or protecting the sludge conduit 44. However,
the
skilled person would understand that the collection head 10 may have other
shapes
and may essentially also only consist of the top plate 20 without the bottom
part. In
this case, the conduit would not be enclosed by the bottom part 30.
A main advantage of this 2-part system for waste handling is a reduced need
for handling large amount of water. While it is necessary to pump dead fish
with
rather large amounts of water, this is not necessary for the pumping of
sludge. In the
contrary, if the sludge is pumped together with the dead and/or sunken fish,
which is
practically possible and practiced by the prior art, then the sludge will be
mixed with
large amounts of water needed to pump up dead fish. If the sludge shall be
collected, it has to be separated from the pumping water after lifting it to
the surface
3. Considering the large amounts of water needed to lift up fish, this is both
an
expensive and difficult procedure making the handling and further use of the
sludge
for other purposes impractical or at least less attractive from an economical
point of
view.
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Another main advantage is that the different types of waste can be collected
in
the same area on the funnel-formed head plate 20 i.e. typically at the lowest
point of
the funnel formed top plate 20. This means that both sludge and large
particles such
as dead fish, can be collected in the same area, even though they can be
pumped
and handled separately. This is a great advantage from a practical point of
view as it
improves the quality of the sludge and makes the handling of the waste more
effective.
Another main advantage is that the sludge can be pumped up more frequently
i.e. in shorter intervals, resulting in a lower salt content in the sludge.
Tests carried
out show that a low salt content in the sludge is obtained if the sludge does
not
remain in the cage more than 2 hours. Thus, the sludge should be removed once
every second hour, or preferably once every hour. Longer periods in sea water
result
in an increase in salt content in the sludge, affecting its quality.
The present invention provides a solution to this problem by having a
separated system for transport of sludge and dead fish. Although, having two
separate systems for waste handling, one for sludge and one for dead fish, it
is
possible to make use of the same general collection head construction. Both
waste
handling systems can be arranged in the same head construction for collecting
the
waste and the required conduits/pipes to the surface can be arranged together
reducing the amount of equipment in the cage. However, as discussed above,
even
though collected together, it is an important issue that the removal and
pumping of
the different types of waste can be operated independently from each other to
avoid
that sludge is sucked into the dead fish system.
Typically, the first removal system 40 for sludge is operated once per hour
for
a couple of minutes (typically 5 to 10 minutes) to suck up the sunken sludge.
The
second removal system 60 for sunken/dead organisms is typically only operated
once per day for some minutes to remove e.g. dead fish. To avoid simultaneous
removal of sludge by the second removal system 60, the first removal system 40
is
preferably operated for a certain period before the second system 60 for
sunken/dead organisms is activated. Thereby the sunken accumulated sludge is
effectively removed from the top plate 20. When the sludge has been removed
from
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the top plate 20, the system 40 for pumping up the sludge can be inactivated
and the
second removal system 60 for sunken organisms can be activated.
Thus, an advantageous method according to the present invention for
collection and removal of sludge from an aquaculture cage in a body of water
comprises the steps of
- collecting the sludge on the funnel-formed top plate 20;
- activating the first removal system and pumping the sunken sludge
accumulated on the top plate 20 of the collection head 10 together with
water to the water surface, preferably with 10-12 m3 per hour by a first
pump system, e.g. a first airlift-pump for at least 5 minutes several times
per day, preferably once each hour;
- deactivating the first removal system 40;
- optionally, separating the water sludge mixture e.g. by filtration
to remove
water and concentrate the sludge.
Depending on the case, the sludge may also simply be released with the
water, or may be transferred to a tank for interim storage or for
sedimentation from
the water.
An advantageous and particularly preferred method according to the present
invention for collection and removal of sludge and sunken/dead organisms
farmed or
kept in an aquaculture farm/cage comprises the steps of
- collecting sedimenting/sinking sludge and organisms in or close to the
the
lowest point of the funnel-formed top plate 20;
- activating the first collection system 40 for sludge and pumping sunken
sludge accumulated on the top plate 20 with water to the surface,
preferably with 10-12 m3 water per hour by a first airlift-pump;
- deactivating the first removal system 40;
- activating the second removal system 60 and pumping dead/sunken
organisms accumulated on the funnel-formed top plate 20 with water to the
surface, preferably with about 150 m3 water per hour by a second airlift-
pump;
- deactivating the second removal system 60.
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The exact periods and optimal intervals for pumping as well as the ratio and
amount of water to be pumped may vary depending on the need for removal of
waste, the biomass to be removed, the size of fish, the type of cage etc.
These can
be adapted individually by the skilled person to the local requirements and
conditions.
Preferably, the systems for pumping up the sludge and sunken organisms/
fish 40,60 comprise separate pumps, i.e. preferably each system has an own
airlifting pump as described above. However, by using a suitable controlling
system
and valves, the same pump/compressor may be used to operate the two different
waste removal systems.
Removing the sludge several times per day, preferably once per 1-2 hours,
has the advantage that the sludge has a lower salt content which is an
advantage if
used later on e.g. as fertilizer or the like.
After being pumped to the surface, the dead fish/organisms will typically be
isolated from the transport water by a grid, sieve or the like. Thereafter,
the dead
fish/organisms can be treated further or disposed. For example, the dead fish
may
be grinded in a mill and optionally transferred to the sludge.
Even though described as a combination, the skilled person would understand
that the collection head 10 may also only be provided with the first removal
system
40 without having a dead fish collection system 60 in the same head. Other
equip-
ment for sucking dead fish may used in this case such as a temporarily
installed pipe
from a vessel down to the bottom section of the cage for pumping up dead fish.
Figure 9 shows schematically a side view of a collection head 10 according to
a second exemplary embodiment of the invention. Figure 10 to 13 show side,
front,
top, and sectional views of the collection head embodiment of figure 9. The
enlarged
view of the sludge removal system marked with "B" will be identical with the
system
shown and described for figure 8.
The main difference from the first embodiment shown in figure 1-8 and
described above is that the bottom part 30 of the collection head 10 in this
second
embodiment is cone-shaped, with sidewalls 31 inclining towards the center at
the
lower end of the bottom part 30. The other elements in this second embodiment
have corresponding constructions and functions as described above for the
first
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embodiment and will thus apply likewise for this embodiment. Preferred
variants,
methods, uses, and functions described for the first embodiment will thus
correspondingly apply for this second embodiment.
Typically, the cone of the bottom part 30 is designed to correspond to the
conical shape found in the bottom part of the net cage allowing a more or less
smooth and tight fit into the net walls in the bottom region of said net. To
be mounted
in an existing net, the conical shape of the bottom part of the collection
head will be
chosen according to the conical shape of said net in its bottom region. The
cone
shape, in particular when having a smooth fit inside the cone of the net cage
not only
has the advantage that existing net forms can be used but may also result in
lower
wear and tear forces between the net and the collection head 10 of the net
compared to a cylindrical form.
Figure 14 and 15 illustrate an alternative cone-shaped collection head only
differing from the cone-shaped collection head described above and shown in
figures
8 to 13 in that the top plate 20 on the back side of the housing 61, i.e. the
side facing
to the outer edge of the top plate and thus being on the opposite side of the
housing
inlet 62, has inclining V-formed walls 33 extending a distance downwards from
the
housing to the edge of the top plate 20. By these inclining V-shaped walls 33
it can
be avoided that dead fish accumulate on the backside of the housing 61. The V-
form
will guide dead fish along the sides of the housing 61 towards the center of
the
funnel-formed top plate 20 where they can be pumped and lifted through the
second
inlet 62 of the second collection system for dead fish. The section view A-A
indicated
in figure 15 of the collection head 10 will be identical with the system shown
for
figure 13.
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