NL2007667C2

NL2007667C2 - Method and device for the purification of water.

Info

Publication number: NL2007667C2
Application number: NL2007667A
Authority: NL
Inventors: Wouter Lengkeek
Original assignee: Waardenburg Holding B V
Priority date: 2011-10-28
Filing date: 2011-10-28
Publication date: 2013-05-06

Description

P30930NL00/RLA

Title: Method and device for the purification of water Scope of the invention

The present invention relates to a method for the purification of water. The invention further 5 relates to a method for improving of visibility of water. The invention further relates to a method for the clarification of water. The invention also relates to a method for the reduction of algae and/or Cyanobacteria as well as the improvement of the growth of water plants . The invention further relates to a structure containing aquatic animals and to the use of the structure in the method of the invention.

10

Background to the invention

Many water bodies in the Netherlands have seasonal problems with blooms of algae and Cyanobacteria (in Dutch: ‘blauwalgen’, Examples: Oscillatoria, Aphanizomenon, Anabaena, Mycrocystis). In particular Cyanobacteria, are harmful for animals and humans and can 15 cause damage to local ecosystems. Cyanobacteria in general thrive in nutrient rich and warm water and the problem seems to increase globally due to human activities and global warming. Blooms of Cyanobacteria or algae especially occur when the ecological functioning of a water body is suboptimal: for instance when light conditions under water are to poor for water plant development due to low visibility. In these cases water plants grow 20 poorly and consume few nutrients, so more remains available for the algae and Cyanobacteria.

One possible management strategy to prevent blooms is to increase the visibility in a water body. Increasing visibility can be achieved by the removal of particles from the water column. This will allow for water plants to grow properly and thereby fixating nutrients. This 25 will prevent sufficient nutrient availability for Cyanobacteria and will prevent harmful blooms.

An effective way to increase water visibility is to increase the density of fresh water bivalves. Fresh water bivalves such as Dreissena polymorpha and Dreissena rostriformis buggensis (in Dutch: ‘driehoeksmossel’ and ‘quaggamossel’, respectively) are filter feeders which can 30 occur in high densities. They filter the water from organic and inorganic particles, digest edible particles and excrete indigestible particles clustered in pseudo faeces. These pseudo faeces are larger than the original particles and sink to the bottom. The bivalves thus filter the water of both edible and inedible particles and can increase visibility in water bodies substantially. A method is described in an article by Noordhuis et al., (H20, 1994, 27(6) ISO-35 160) wherein field tests have been performed to determine the capacity of these freshwater -2- bivalves in cleaning water. The freshwater bivalves were introduced in a pond by harvesting freshwater bivalves form one pond and introducing the bivalves in a second pond with a positive effect at about 350 bivalves per cubic meter. The water of the second pond became more clear. However, probably due to predation and seasonal fluctuation, the population did 5 not procreate. In one of the larger lakes in the Netherlands, the Veluwemeer, the experiment was repeated with a seeding population of young bivalves that were provided on a substantially solid, two-dimensional mat of willow branches with a thickness of at most 20 cm.. Again, the population did not flourish, probably partly due to predation, because the population of bivalves were predominantly present at the outside. It is known that water birds 10 such as pochards or scaups forage for bivalves up to depths of about 5 meters. Another detrimental effect of seeding water randomly with freshwater mussels is that the mussels are located on the bottom, usually in more oxygen-poor conditions whereas bivalves in general prefer locations that are oxygen-rich or are located at more at elevated levels from the bottom to profit more from feed-rich currents .

15 Despite the disappointing results, manually increasing local Dreissena spp. density is technically still an option by transporting the bivalves from one water body to another. However, in the Netherlands, Dreissena spp. bivalves are considered an important element of the ecosystem in every water body where they occur in high densities. Therefore, simply removing them from a water body is generally not allowed or bound to strict regulations, 20 hampering the successful application of this technique. Hence, there remains a need in the art to obtain populations of freshwater bivalves that can be used in the purification of water where the populations have a chance to thrive and that is in line with local regulations.

Summary of the invention 25 The present inventor has found that providing a structure that can be inoculated with bivalves in their seed/larvae and/or spat stage while protecting them from predators results in stable structures that are capable of accommodating a population of bivalves. Such a structure can be inoculated in one water body with seed/larvae and/or spat. Transferring the structure with the bivalves to another water body allows for the purification of the other water 30 body by the natural action of the bivalves.

Detailed description of the invention

Thus, in one aspect, the invention relates to a device for collecting and growing an aquatic animal, comprising an outside that extends (or encompasses) at least partially around an 35 inner cavity, wherein the outside has a plurality of openings into the inner cavity, wherein the inner cavity contains an inner structure and wherein the device further contains aquatic animals.

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An aquatic animal in the sense of the present invention is an animal that respires predominantly underwater. In the terms of the present invention, such an animal can be a bivalve such as a scallop, mussel, oyster, or clam. In a preferred embodiment, the aquatic animals are shellfish, preferably from the phylum Mollusc, more preferably the class bivalvia, 5 even more preferable fresh water bivalves, most preferable Dreissena polymorpha and/or Dreissena rostriformis buggensis. The device of the present invention provides a habitat structure such that the device provides a site within, on or around which the aquatic animals may live, reside, breed and/or be reared. The device is advantageously designed such that it meets the habitat requirements of the animals that are to be grown, reared or kept in the 10 device. One of the advantages of the present device is that, among others due to its structural features, it is capable of providing protection to the aquatic animals from predatory animals. The device according to the invention has an outside that extends or encompasses at least partially around an inner cavity. The device has a three-dimensional structure. The inner cavity is preferably substantially defined and limited by the dimensions of the outside. 15 The outside may extend around the entire inner cavity. For example, a device in the form of a hollow sphere may be considered to have one outside extending wholly around the inner cavity. An elongated tube profile open at both ends may have one outside extending around the inner cavity. A rectangular construct, for instance a block, may be seen as an outside substantially defined by one or more walls that enclose the inner cavity. The shape, size and 20 wall may hence vary considerably, depending on the application of the structure.

The outside has at least one opening into the inner cavity. The opening may be provided by the outside not completely encompassing the inner cavity or may be provided by for instance the presence of openings (holes) in the outside. For example in a tube, openings are provided by both open ends or by providing openings (holes) in the tube profile.

25 The openings serve to provide water and food to the aquatic animals contained in and on the device. The openings also serve to allow the aquatic animals to enter (inoculate) and exit through the openings. Preferably, the openings have a shape and dimension such that the aquatic animals may enter and exit at will, while at the same time predators such as fish and birds are substantially kept out of the structure. In certain embodiments, the openings 30 independently vary from about 5 millimetre to about 250 millimetre, preferably from about 10 millimetre to about 150 millimetre, more preferably from about 15 to about 100 millimetre and even more preferred form about 20 millimetre to about 50 millimetre. The shape of the openings is not critical and may be round, pyramidal, square, oblong etc. and the openings may each be of a different shape or size.

35 In one embodiment, the inner cavity contains a structure. Preferably, the structure is a three-dimensional structure and more preferably is not a substantial two-dimensional structure.

The three dimensional structure is preferably such that the predators have no access to the -4 - internal structure of the device and may have only limited access to the outside. The structure may serve to provide structural strength to the device. The structure may be suitable for housing the aquatic animals in the sense that they may attach to the inner structure and use the structure. The structure may be in the form of a (three-dimensional) 5 mesh or plates, wires, ropes etc. In certain embodiments, the outside and the inner structure may be from the same material or be indistinguishable from each other, for instance when a three-dimensional mesh material is used. The material can be a porous material, preferably in one piece, that has an outside made from mesh material and preferably an inner structure made from (preferably the same) mesh material. The material preferably has a structure that 10 provides it with a certain strength so it can maintain itself. An example thereof is a honeycomb structure. The outside is formed by the outside dimensions of the material and the inner structure by the inside of the mesh material. The openings are provided by the pores of the porous material. A material that has been used with good result is a filter material that is known from its application in aquaculture. An example is a porous 15 polypropylene material having a hexagonal mesh that extends in three dimensions, thus forming a porous body with pore diameters in the range of 5 mm to 50 mm. Such a material can for instance be obtained from Fleuren en Nooijen bv, Nederweert, The Netherlands.

The material from which the outside and/or the inner structure are made are preferably from a polymer material, preferably a thermoplastic polymer, wherein the polymer is selected from 20 the group consisting of polyolefins, polyesters, biodegradable polymers and mixtures thereof. In certain embodiments, the polymer is selected from the group consisting of polyolefins, polyesters, biodegradable polymers and mixtures thereof and wherein (a) the polyolefins are selected from the group consisting of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1) and mixtures thereof; 25 and/or (b) the polyesters are selected from the group consisting of polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate( PHA), Polyethylene terephtalate (PET), polybutylene terephtalate (PBT) and mixtures thereof; and/or (c) the biodegradable polymers are selected from the group consisting of polyvinyl 30 alcohol, starch polymers such as corn starch, potato starch, tapioca starch, high amylose starch and mixtures thereof.

The device may be weighed down, for instance using weights or ballast to position it into location underwater. Devices may be interconnected to provide for lines or rows of devices. The device according to the invention preferably maintains at least 80 % of its structural 35 integrity for at least about 12 to 36 months (although longer is preferred) in an aquatic environment, preferably a freshwater environment. When the structure is capable of disintegrating over time in the environment, for instance because it is made from a -5- biodegradable material, it is not necessary to remove it. This can be an advantage. On the other hand, a structure that is stable for a prolonged period of time facilitates the removal thereof after the device has served its purpose.

The device according to the invention can basically have any shape or form. In certain 5 embodiments, the device has a shape selected from the group consisting of rectangular, square, oblong, spheroid, tube.

In order to contain an adequate number of aquatic animals for the desired purpose (whether growing, rearing, filtering etc.), it is preferred that the device has certain dimensions. By providing the device with dimensions that are large enough for the aquatic 10 animals to enter whereas predators can only predate to a limited extent, the aquatic animals have a safe harbour to life and proliferate. At the same time, the dimensions are preferably such that the animals are in close enough contact with water and food. In practice, it has been found that such a structure is inhabited by aquatic animals, for up to 30 cm, preferably up to 15 cm. The depth may vary with the type of aquatic animal and may also vary with the 15 dimensions of the openings (larger openings facilitate deeper inhabitation). Deeper inhabitation is rare, (albeit not impossible, for instance in faster running waters), due to restraints to the migration of water (oxygen) and food. Hence there is a balance between the depth of inhabitation on one hand and oxygen and food supply on the other hand. To this end it is preferred that the device has dimensions that can accommodate these 20 requirements. In one embodiment, the device has a thickness or diameter that is more than 25 cm, measured over the smallest possible distance. In one embodiment, it is preferred that the device has dimensions such that the shortest distance from a point located in the inner structure to the outside is at least 10 cm, preferably at least 20, more preferably at least 25 cm. Larger distances are possible but are less preferred as they tend to result in uninhabited 25 regions or require larger openings which allows predators to penetrate deeper. For example, this would accommodate a rectangular three-dimensional (block type) structure of indeterminate width and/or length but a height of at least 20 or 30 cm. Or a tube structure of any length, but with a diameter of at least 20 or 30 cm. The device of the invention may also be used to make larger constructions by linking or stacking. For instance, a 3 by 3 stack of 30 blocks can be made with the middle one removed and positioned in either vertical or horizontal position. Good results have been obtained with structures of 0,9mx0,45mx0,3m weighing 3 kg of polypropylene mesh material. Preferably the inner structure is a regular structure and/or is distributed substantially even over the space encompassed by the outside. In other words there are preferably no ‘local’ concentrations of inner structures in 35 the space encompassed by the outside.

The structure of the material can also be defined by the percentage of void space, i.e. the percentage of the space encompassed by the outside and not occupied by the inner -6- structure. It is preferred that the structure is substantially hollow, i.e. is void. It is preferred that, of the non-inhabited structure, at least 75%, more preferably at least 85%, more preferably at least 90% is not occupied by the inner structure. Put differently, in a preferred embodiment, the inner structure is at most 25%, more preferably at most 15% and most 5 preferably at most 5% of the volume encompassed by the outside.

The material from which the outside and/or the inner structure are made may be provided with a surface that facilitates, promotes or enhances the attachment of the aquatic animals thereto. The surface may be physically treated, for instance by sanding or roughing, or may be chemically treated or coated to facilitate the attachment of aquatic animals.

10 The invention in a further aspect relates to a method for the purification, clarification and/or increasing the visibility of water that uses a structure that is based on the device of the present invention,. To that end the invention relates to a method for the purification, clarification and/or increasing the visibility of water comprising the steps of: (a) providing a structure for an aquatic animal; 15 (b) contacting the structure with a first aqueous environment; (c) allowing the structure to become inoculated with seed and/or larvae and/or spat from the aquatic animal (clutching); (d) optionally, allowing the seed to grow into aquatic animals, preferably attached to the structure; 20 (e) retrieve the inoculated structure from the first aqueous environment; (f) contact the inoculated structure with a second aqueous environment; and (g) allowing the seed/aquatic animals to purify/clarify/increase the visibility of the second aqueous environment.

Thus, the device as described herein above is brought into a first aqueous environment, 25 preferably an environment that contains, or at least is suspected to contain, aquatic animals, and/or their seed and/or larvae and/or spat.

The structure is allowed to become inoculated with the aquatic animals, and/or their seed and/or larvae and/or spat. Typically, this is achieved by submerging it in the water for a period of time (days or weeks) in the right season. The seed and/or larvae and/or spat 30 attach themselves to the outside and/or the inner structure. The young bivalves can be allowed to grow/develop on the structure for a period of time until they are grown enough to be retrieved from the first aqueous environment.

Retrieval of the inoculated structure can be achieved relatively easy when the device according to the invention is used. The device can simply be lifted from the bottom of the 35 water body by a crane or other devices, or brought to the surface by floating. The device is such that it can be transported over a distance and over a period of time without damaging the structure or the (young) aquatic animals. The device containing the aquatic animals -7- (whether very young or more grown), can be transported to another place. The other place can be a second aquatic environment (water body), but can also be the same aqueous environment but at a different location, for instance further up- or downstream or in case of a large lake or pond, at another position in the lake or pond. There is a preference to culture 5 the bivalves first (prior to moving), so large quantities can be introduced in water bodies without significantly damaging the population of bivalves elsewhere. Alternatively, the inoculated structures, after being retrieved from the first aquatic environment can be cultured elsewhere before being placed in the second aqueous environment. Aquatic environments or water bodies as used herein refer to lakes, ponds, rivers, streams etc.

10 Having placed the structure comprising the (partly grown) aquatic animals in the second aqueous environment, the aquatic animals can purify/clarify and/or increase visibility of the second aqueous environment. By their natural biological action as outlined herein before, the aquatic animals can now improve the visibility of the water, clarify the water, purify the water from, amongst others, algae, Cyanobacteria , inorganic particles and the like.

15 In a further aspect, the present invention relates to a method for the purification, clarification and/or increasing the visibility of water comprising the steps of: introducing a structure for an aquatic animal comprising aquatic animals into the water to be purified; and purifying, clarifying and/or increasing the visibility of water by the action of the 20 aquatic animals.

In this aspect of the invention, a structure or device can be already available and can be a construction as outlined herein elsewhere. The structure is already inoculated and/ or contains grown aquatic animals, essentially as outlined herein before. The structure is placed in the second aqueous environment, typically the aqueous environment in need of 25 purification, clarification for improvement in visibility.

In certain embodiments, after the goal has been achieved, the structure containing the aquatic animals may be removed from the second aqueous body and discarded or returned to the original location. Alternatively, the structure can be left in the second aqueous environment to further stimulate the growth of aquatic animals therein and with that the 30 further and continuous improvement of the quality of the water by the clarification, purification in increasing the visibility of the water.

Example

Dreissena spp. bivalves reproduce by spawning gametes in to the water column. The 35 fertilised gametes then go through a pelagic life stage (they float in the water column for a certain amount of time). After a while the young bivalves, referred to as ‘mussel spat’, find an empty spot on hard substratum to settle. In the right time of the year there is a large -8- overabundance of mussel spat, and by far most spat cannot find any suitable hard substratum and dies. Spat are very young shellfish, and the raw material of mussel farms. Mussel spat develop from a floating larval stage. The larvae attach themselves to weed or ropes and develop into miniature shellfish 0.3 mm long - about the width of a needle tip.

5 They move from site to site until they are 0.6 mm in length, when they attach themselves permanently to a settlement site.

A three dimensional synthetic structure (blocks of 0,9mx0,45mx0,3m weighing 3 kg of polypropylene filter material of Fleuren en Nooijen bv) has been placed in the water. This provided an optimal hard substratum for the mussel spat to settle. Mussel spat from the 10 water column attached to the structure and the structures grew full of young mussels.

Now the structures contained a high density of Dreissena spp bivalves. The young bivalves lived inside the three dimensional structure, where they were protected from predators such as fish and birds (coot (Fulica atra) and for instance, diving ducks (Aythyinae). Furthermore, they were elevated from the bottom. The elevated position protected the bivalves from 15 oxygen-poor conditions, that occur commonly in silt-rich water bottoms.

The structures with mussels were transported to a water body that needed treatment. The complete structures were hauled to the surface, transported and placed in the new water body. The bivalves stayed attached to the structures, which now served as ‘biological filters’. Also in the new water body the structures had an important function to protect the bivalves 20 from predators and keep them elevated from the bottom. Furthermore, if need be, the structures and the bivalves could easily be removed from the water body. The structures were provided in sufficient numbers such that they filtered the water and increased visibility rapidly. When this is timed in the beginning of spring, before Cyanobacteria bloom, they can prevent such blooms. It is found that the mussels are capable of reproducing in their new 25 environment and are also capable of tilting the eco-system such that after removal of the blocks, the water remained clear and no blooms occur.

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CLAUSES

1. Method for the purification, clarification and/or increasing the visibility of water comprising the steps of: (a) providing a structure for an aquatic animal, the structure comprising an outside that extends at least partially around an inner cavity, wherein the 5 outside has a plurality of openings into the inner cavity, wherein the inner cavity contains an inner structure, wherein the inner cavity is for at most 25 % occupied by the inner structure and/or has a shortest distance from a point located in the inner cavity to the outside of at least 10 cm; (b) contacting the structure with a first aqueous environment; 10 (c) allowing the structure to become inoculated with seed and/or larvae and/or spat from the aquatic animal; (d) optionally, allowing the spat to grow into larger aquatic animals, preferably attached to the structure; (e) retrieve the inoculated structure from the first aqueous environment; 15 (f) contact the inoculated structure with a second aqueous environment; and (g) purifying/clarifying/increasing the visibility of the second aqueous environment.

2. Method for the purification, clarification and/or increasing the visibility of water comprising the steps of: 20 (a) introducing a structure for an aquatic animal comprising aquatic animals into the water to be purified; and (b) purifying, clarifying and/or increasing the visibility of water by the action of the aquatic animals; the structure comprising an outside that extends at least partially around an inner 25 cavity, wherein the outside has a plurality of openings into the inner cavity, wherein the inner cavity contains an inner structure, wherein the inner cavity is for at most 25 % occupied by the inner structure and/or has a shortest distance from a point located in the inner cavity to the outside of at least 10 cm; 3. Method according to clause 1 or 2, wherein the water is fresh water.

30 4. Method according to clauses 1-3, wherein the purifying, clarifying and/or increasing the visibility of water comprises the reduction of particles in the water column (organic or inorganic ).

5. A device for collecting and growing an aquatic animal, comprising an outside that extends at least partially around an inner cavity, wherein the outside has a 35 plurality of openings into the inner cavity, wherein the inner cavity contains an - 10- inner structure, wherein the inner cavity is for at most 25 % occupied by the inner structure and/or has a shortest distance from a point located in the inner cavity to the outside of at least 15 cm; and wherein the device further contains aquatic animals.

5 6. Device according to clause 5, wherein the inner structure and/or the outside have a (three-dimensional) structure selected from the group consisting of mesh, plates, wires, ropes, tubes, boxes, balls, poles and combinations thereof 7. Device according to clause 5 or 6, wherein the outside and/or the inner structure independently have openings ranging from about 5 millimeter to about 25 10 centimetre.

8. Device according to clause 5-8, wherein the aquatic animals are shellfish, preferably from the phylum Mollusc, more preferably the class bivalvia, even more preferable fresh water bivalves, most preferable Dreissena polymorpha and/or Dreissena rostriformis buggensis 15 9. Device according to clause 5-8, wherein the outside and/or the inner structure are made from a polymer material, preferably a thermoplastic polymer, wherein the polymer is selected from the group consisting of polyolefins, polyesters, biodegradable polymers and mixtures thereof.

10. Device according to clause 9, wherein 20 (a) the polyolefins are selected from the group consisting of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1) and mixtures thereof; and/or (b) the polyesters are selected from the group consisting of polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (POL), polyhydroxyalkanoate( PHA), 25 Polyethylene terephtalate (PET), polybutylene terephtalate (PBT) and mixtures thereof; and/or (c) the biodegradable polymers are selected from the group consisting of polyvinyl alcohol, starch polymers such as corn starch, potato starch, tapioca starch, high amylose starch and mixtures thereof.

30 11. Device according to clauses 5-10, wherein the structure maintains at least 80 % of its structural integrity for about 12 to 36 months in an aquatic environment, preferably a freshwater environment.

12. Device according to clauses 5-11, wherein the shortest distance from a point located in the inner cavity to the outside is at more than 15 cm, preferably more 35 than 20 cm.

13. Device according to clauses 5-11, wherein the outside encloses the inner cavity.

-11 - 14. Device according to clauses 5-13, wherein the device has a rectangular, square, oblong, spheroid, tube shape.

Claims

A method for purifying, clarifying and / or increasing the transparency of the water comprising the steps of: (a) providing a structure for aquatic animals comprising an exterior enclosing an interior cavity, wherein the exterior has a plurality of openings to the inner cavity, the inner cavity having an inner structure, in which the inner cavity is at most 5% filled by the inner structure and / or a shortest distance from any point in the inner cavity to the outside of at least 10 cm ;; (B) contacting the structure with a first aqueous environment; (c) seeding the structure with seeds and / or larvae and / or breeding of the aquatic animals; (d) optionally, allowing the seed and / or larvae and / or brood to grow into aquatic animals, preferably attached to the structure; (e) removing the aquatic animal-grafted structure from the first aqueous environment; (f) contacting the aquatic grafted structure with a second aqueous environment; and (g) allowing the seed / aquatic animals to purify / clear / increase the transparency of the second aqueous environment.

A method for purifying, clarifying and / or increasing the transparency of the water comprising the following steps: (a) introducing a structure for an aquatic animal, comprising an exterior that extends at least partially around an internal cavity, wherein the exterior has a plurality of openings to the interior cavity, the interior cavity having an interior structure, wherein the interior cavity is at most 25% filled by the interior structure and / or a shortest distance from any point in the interior cavity to the outside of at least 15 cm, further comprising aquatic animals, in the water to be purified and (b) purifying / clarifying / increasing the transparency of the water to be purified by the seed / aquatic animals.

The method of claim 1 or 2, wherein the water is fresh water.

Method according to claims 1-3, wherein the purifying, clarifying and / or increasing the visibility of the water consists of the reduction of the floating particles in the water such as suspended matter, algae and / or cyanobacteria.

A device for collecting and growing aquatic animals, comprising an exterior enclosing an interior cavity, wherein the exterior has a plurality of openings to the interior cavity, the interior cavity having an interior structure, wherein the interior cavity is at most 25% is filled by the inner structure and / or has a shortest distance from any point in the inner cavity to the outside of at least 15 cm, and wherein the device further contains aquatic animals.

Apparatus as claimed in claim 5, wherein the inner structure and / or the outside independently of one another has a structure selected from the group consisting of mesh, plates, wires, ropes, tubes, balls, boxes, beams.

An apparatus according to claim 5 or 6, wherein the outside and / or the inner structure have openings independently of each other, which can vary from about 5 millimeters to about 25 centimeters.

8. Device as claimed in claims 5-7, wherein the aquatic animals are shellfish, preferably from the strain Molluscs, more preferably from the class Bivalves, even more preferably freshwater bivalves, and most preferably Dreissena polymorpha and / or Dreissena rostriformis buggensis.

9. Device as claimed in claims 5-8, wherein the outside and / or the inner structure are made of a polymeric material, preferably a thermoplastic polymer, wherein the polymer is selected from the group consisting of polyolefins, polyesters, biodegradable polymers and mixtures thereof.

The device of claim 9, wherein (a) the polyolefins are selected from the group consisting of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1) and mixtures thereof, and / or (b) the polyesters are selected from the group consisting of polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and mixtures thereof, and / or (c) the biodegradable polymers are selected from the group consisting of polyvinyl alcohol, starch polymers such as corn starch, potato starch, tapioca starch, amylose-rich starch and mixtures thereof.

The device of claims 5-10, wherein the structure retains at least 80% of the structural integrity for at least about 12 to 36 months in an aqueous environment, preferably a freshwater environment.

Device according to claims 5-11, wherein the shortest distance from a point in the inner cavity to the outside is at least 15 cm, preferably at least 20 cm.

The device of claims 5-12, wherein the outside encloses an internal cavity.

The device of claims 5-13, wherein the device has a rectangular, square, elongated, spherical, or tubular shape, or combinations thereof.