Field of invention

The present invention relates to an erosion control device and in particular although not exclusively, to a biodegradable erosion control mat configured to prevent undesirable release of plastic pollutant into an underwater environment.

Background

Riverbeds and sea floors are exposed continuously to currents, tides and general water flow continually shifting sediment and solids at the river and sea beds. When structures such as pipelines, cables, pillars and platforms are submerged in these environments, water is caused to flow around them increasing the local flow velocities. This in turn scours the surrounding bed and supporting sediment leading to erosion, destabilisation and potentially structural failure. One solution to the problem of scour is to deposit rocks, concrete or other remedial materials for additional support. However, such strategies can damage the structures, are expensive and are themselves susceptible to scour. An alternative approach is the development of what are commonly referred to as frond mats. Such devices typically comprise a substrate or bed from which extend an array of buoyant synthetic strands (fronds). These strands are, at least in part, designed to resemble natural riverbed or sea grasses and seaweeds. The fronds act to induce drag to the flowing water which causes suspended sediments to deposit and accumulate in the region of the mats forming a consolidated sediment bank. Scour of the support structures may be reduced also.

WO 88/05842 describes a series of frond mats deployed on the seabed to control scour and erosion around structures such as oil rigs and pipelines. Similarly, CA 02288350 describes a structure having multiple buoyant fronds extending from a polyurethane sheet securable to a flexible frame. Anchoring straps provide attachment of the frond mats to underwater structures and the like. US 5,575,584 describes a buoyant multi-layered thin film for placement at the seabed to attempt for the same anti-erosion function.

As is now widely recognised, river and marine plastic pollution is a significant global problem. Conventional erosion control mats that utilise flexible fronds are disadvantageous by being linked to the public perception of plastics in the ocean. Accordingly, what is required is an erosion control device that addresses the above problems.

Summary of the Invention

It is an objective of the present concept to provide erosion control apparatus and in particular erosion control matting for use on a river or sea bed configured to create viscus drag on the flowing water to prevent erosion as specific regions of the river or sea bed. It is further specific objective to provide an underwater soil erosion prevention device configured to degrade an in particular to fully break-down to basic elemental component (such as water, biomass and gas) after a predetermined lifetime. It is a further specific objective to provide biodegradable under water erosion control apparatus specifically configured for biodegradation with the aid of microorganisms.

It is a further specific objective to provide an underwater erosion prevention system manufacturable from synthetic or natural polymer materials and preferably from natural polymer materials generated from natural resources such plants, microorganisms and animals. Such natural source materials may be processed to generate polymers which may then be configured according to the present concept to be biodegradable with the aid of microorganisms. It is a further specific objective to provide plastic underwater erosion prevention apparatus configured to protect a designated site or region from erosion due to the flow of water for a predefined time and then to degrade fully into basic elemental components (water, biomass and gas) so as to leave no plastic and microplastic residue in the water (fresh water or marine environment). It is a further specific objective to provide erosion control matting that is convenient to install at a predetermined site so as to protect a submerged structure or river or sea bed region from erosion due to water current.

The objectives are achieved via an erosion control device, apparatus and system having a composite structure including in particular a substrate formed from a first material that supports/mounts a plurality of buoyant and flexible strands. Such strands according to conventional frond mat design may be tubular or formed as flat tape having some buoyancy characteristic such that with the device mounted underwater, the strands are configured to float and extend upwardly or outwardly from the substrate to resemble seaweed or seagrass. In accordance with the present concept, the material of the substrate and the flexible strands are specifically configured to be biodegradable in an underwater environment (including a fresh water and a marine environment) with such degradation occurring relatively slowly such that the apparatus persists with sufficient structural integrity and cohesion to be an effective erosion control device and matting for a predefined time period. According to a preferred implementation, the present erosion control device is configured to biodegrade slowly over the course of a minimum of one year, two years, three years, four years, five years or six plus years. According to a first aspect of the present concept there is provided an erosion control device comprising: a substrate comprising a first material; a plurality of buoyant and flexible strands positioned side-by-side and extending from the substrate, the strands comprising a second material; wherein the first and/or the second material is a polymeric material and comprises a biodegradation additive to effectuate a biodegradation of the first and/or the second material within an underwater environment.

Preferably, the second material is biodegradable at a rate such that the strands degrade over a period of at least one year in a marine environment. Optionally the material/device is configured to degrade at a rate so as to persist in the marine environment for one year, two years, three years, four years, five years or up to or over six years. Preferably, the material is biodegradable at a rate such that the strands degrade over a period of at least at least one year in a marine environment. Optionally, the material is biodegradable at a rate such that the strands degrade over a period of at least at least two years, three years, four years, five years or at least six years in a marine environment.

Optionally, the first and second materials may be the same or substantially the same material and may comprise a polymer material. Preferably, the first and second materials are different. Optionally, the second material is a polymer material and sourced from a natural feedstock. Optionally, the first material may comprise a polyester comprising the biodegradation additives. Optionally, the polyester comprises polycaprolactone.

Optionally, the second material may comprise a material being or derived from an organic natural and/or biological source material. Optionally, the first material may be sourced from sugar cane, cellulose, wood pulp, manila, cotton, hemp, jute, sisal. Optionally, the first material may comprise the biodegradation additive. Alternatively, the first material is formed from an organic or natural source material and may not comprise the biodegradation additive, for example where the first material comprises wood, cane, bamboo or other natural materials.

Optionally, the first and/or the second material is derived from an organic, natural and/or biological source material. Optionally, the first and/or the second material is derived from any one or a combination of the following set of sugar cane, cellulose, wood pulp, manila, cotton, hemp, jute, sisal. Optionally, the first and second material sourced from an organic, natural and/or biological source material may be processed to generate a semi-synthetic polymer material. Such a semi-synthetic material may comprise the biodegradation additive so as to effectuate a biodegradation of the first and/or second material.

Optionally, the second material is a semi-synthetic polypropylene sourced from sugar cane or sugar cane ethanol. Such a material may be regarded a bioplastic. Optionally, second material may be a fully synthetic polypropylene comprising the biodegradation additive.

Preferably, the biodegradation additive comprises a chemoattractant compound. The chemoattractant compound may alternatively be termed a positive chemotaxis. The present biodegradable additive comprising the chemoattractant compound is configured to attract microorganisms to the first and/or second material so as to enable the microorganism to adhere to the surface of the first and/or second material and metabolise the molecular structure. Optionally, the present device and apparatus and in particular the biodegradation additive does not comprise a microorganism as these are typically present within an underwater environment including a fresh water and a marine environment. The first and second materials of the present concept are biodegradable via interaction with a variety of different microorganisms that are effective to metabolise the first and second materials through natural microbial processes.

Optionally, the chemoattractant compound comprises one or more furanone compounds configured to act as a chemoattractant for bacteria and/or microorganisms. Optionally, the chemoattractant compound comprises 3,5-dimethylyentenyl-dihydro-2(3H)furanone, isomer mixtures thereof, emoxyfurane, emoxyfurane and N-acylhomoserine lactones. Example bacteria that are attracted to such compounds include C. violaceum.

Optionally, the chemoattractant compound may comprise a sugar and optionally a sugar that is not metabolised by a bacteria. Optionally, the chemoattractant compound comprises anyone or a combination of galactose, galactonate, glucose, succinate, malate, aspartate, serine, fumarate, ribose, pyruvate, oxalacetate and other L-sugar structures and D-sugar structures but not limited thereto. Example bacteria attracted to these sugars include, but are not limited to Escherichia coli, and Salmonella. Optionally, the biodegradation additive comprises an acid or an acid derivative.

Optionally, the acid or the acid derivative may comprise glutaric acid and/or a carboxylic acid compound with chain length from 5-18 carbons.

Optionally, the biodegradation additive comprises a microbe configured to digest the first and/or the second material. Optionally, the microbe may comprise psychrophiles, mesophiles, thermophiles, actinomycetes, saprophytes, absidia, acremonium, Altemaria, amerospore, arthrinium, ascospore, aspergillus, aspergillus caesiellus, aspergillus candidus, aspergillus carneus, aspergillus clavatus, aspergillus deflectus, aspergillus flavus, aspergillus fumigatus, aspergillus glaucus, aspergillus nidulans, aspergillus ochraceus, aspergillus oryzae, aspergillus parasiticus, aspergillus penicilloides, aspergillus restrictus, aspergillus sydowi, aspergillus terreus, aspergillus ustus, aspergillus versicolor, aspergillus/penicillium - like, aureobasidium, basidiomycetes, basidiospore, bipolaris, blastomyces, B. borstelensis, botrytis, Candida, cephalosporium, Chaetomium, cladosporium, cladosporium fulvum, cladosporium herbarum, cladosporium macrocarpum, cladosporium sphaerospermum, conidia, conidium, conidobolus, Cryptococcus neoformans, cryptostroma corticale, cunninghamella, curvularia, dreschlera, epicoccum, epidermophyton, fungus, fusarium, fusarium solani, geotrichum, gliocladium, helicomyces, helminthosporium, histoplasma, humicula, hyaline mycelia, memnoniella, microsporum, mold, monilia, mucor, mycelium, myxomycetes, nigrospora, oidium, paecilomyces, papulospora, penicillium, periconia, perithecium, peronospora, phaeohyphomycosis, phoma, pithomyces, rhizomucor, rhizopus, rhodococcus, rhodotorula, rusts, saccharomyces, scopulariopsis, sepedonium, serpula lacrymans, smuts, spegazzinia, spore, sporoschisma, sporothrix, sporotrichum, stachybotrys, stemphylium, syncephalastrum, thermononespore fusca, torula, trichocladium, trichoderma, trichophyton, trichothecium, tritirachium, ulocladium, verticillium, wallemia and yeast.

Optionally, the biodegradation additive comprises a compatibilising additive. Optionally, the biodegradation additive comprises a carrier resin. Optionally, the carrier resin comprises any one or a combination of the group of polydivinylbenzene, ethylene vinyl acetate copolymers, maleic anhydride, acrylic acid, a polyolefin. The carrier resin is configured to facilitate incorporation of the biodegradation additive to the first and second material. The carrier resin may be used in varying proportions and blended with the first and second materials as part of the blending of the biodegradable additive with the first and second material.

Optionally, the biodegradation additive comprises any one or a combination of a carbohydrate, starch or cellulose. In particular, polypropylene blended with a carbohydrate, starch or cellulose material has been demonstrated to be biodegradable via the facilitation of adhesion of microorganisms to the surface of the polymer material such that the microorganism can then metabolise the polymer structure.

Optionally, the chemoattractant compound comprises a sugar, a sugar derivative or a furanone. Optionally, the furanone comprises any one or a combination of 2(3H)- furanone, dihydro-4,5 dimethyl, 3,4,5-trimethyl-2(5H)-furanone.

Optionally, the biodegradation additive comprises a swelling agent. The swelling agent is configured to create space within the molecular structure of the first and/or second material particularly where the first and second materials comprise a polymer. The swelling agent has been noted to work synergistically with the chemoattractant compound to attract a colony of microorganisms into the expanded matrix of the polymer structures so that the microorganisms can break-down the chemical bonds and metabolise the plastic through natural microbial processes. Optionally, the swelling agent may comprise natural fibers, cultured colloids, organoleptic compounds, cyclo-dextrin, polylactic acid.

Optionally, the first and/or the second material comprises any one or a combination of the set of straight chain or branched chain addition polymers, copolymers, condensation polymers, aliphatic or aromatic based polymers, polyethylene, polypropylene, polyvinyl acetate, polylactic acid, a polyester, polycaprolactone, polyglycolic acid, polylactic-co- glycolic acid, polyvinyl chloride, polystyrene, polyterepthalate, and polyester, polyamide biodegradable. In a preferred embodiment, the first material comprises polypropylene and the second material comprises a polyester. The polypropylene and polyester may be fully synthetic materials or may be semi-synthetic, being derived from natural feedstocks such as sugar cane and cellulose. Optionally the first and/or second material comprises wood pulp, manila, cotton, hemp, jute, sisal or derivatives thereof.

Optionally, a concentration of the biodegradation additive within each of the first and/or the second material based on a respective total weight of each of the first and/or the second material containing the additive is in a range 0.1 to 2 wt%; 0.2 to 1.8 wt%; 0.4 to 1.6 wt%; 0.4 to 1.4 wt%; 0.4 to 1.2 wt%; 0.5 to 1.0 wt%; 0.5 to 0.7 wt%. Such a concentration has been found to provide a relatively slow degradation of the first and second materials via microbial activity over a sufficiently long period of time. In particular, the recited concentration is effective to maintain the structural strength, integrity and cohesion of the first and second materials to allow the present apparatus and device to persist in the underwater environment for a minimum or around six years. The present device is configured such that the microbial degradation results in the break-down of the apparatus including the detachment of the strands from the substrate. The substrate and the strands are configured via the incorporation of the biodegradation additive to continue to degrade fully due to the microbial processes so as to not add to fresh water and marine plastic pollutant including in particular microplastics suspended in the water.

Optionally, the substrate comprises a polyester base structure and the strands are attached to the base structure. Optionally, each of the strands have a first end attached to the substrate and a second end that is free and non-tethered.

Optionally, the substrate comprises seeds and/or spores of marine flora/vegetation. Optionally, the seeds and/or spores are integrated into or coated onto the first material. Optionally, the device further comprises a marine flora seed/vegetation support attached to the substrate, the support comprising the seeds and/or spores of marine flora/vegetation. Optionally, the support comprises a natural fibrous and/or woven material optionally comprising any one or a combination of Hessian, Jute, Burlap. Optionally, the support comprises a bag, pocket or pouch attached to the substrate and containing the seeds and/or spores of marine flora/vegetation. Optionally, the support comprises a textured material, such as a textured fabric, or material having an open matrix type structure into which the seeds can be incorporated and be retained whilst the substrate is introduced to and is situated within the marine environment. The seeds and/or spores provided at the substrate are advantageous, by forming part of the webbing matrix of the present frond mat, such that as the fronds biodegrade, natural marine flora grows in their place. Optionally, substantially all the substrates may comprise the seeds and/or spores of marine flora/vegetation. Optionally, selected regions of the device may comprise the seeds and/or spores of marine flora/vegetation.

Preferably, the seeds or spores are provided over substantially all or a majority of the substrate including in particular the regions of the substrate to which the strands (formed at the second material) extend. That is, the spores or seeds extend from at least one edge of the substrate and over/across an inner and/or central region of the substrate (between the edge or edges).

The distribution of the seeds and/or spores of marine vegetation over all or a majority of the substrate ensures that as the biodegradable strands degrade, the seeds and/or spores germinate and the marine vegetation grows in place of the degraded strands.

In one implementation, the strands are provided with the biodegradation additive at a concentration to provide biodegradation in one to two years, three to four years, at least five or at least six years. The substrate may or may not comprise the biodegradation additive and may be configured to persist in an underwater environment for at least five, ten or fifteen years.

Optionally, the erosion control device may comprise a substrate formed from a natural material or a material sourced from natural resources and strands of a second different material that are configured to biodegrade and to be replaced with marine vegetation germinated from the seeds and/or spores provided at the erosion control device prior to installation within the underwater environment.

According to a further aspect of the present concept there is provided a frond mat, frond matting, a frond sheet, layer or other structure comprising the device as described and claimed herein. Brief description of drawings

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a frond mat according to one aspect of the present concept.

Detailed description of preferred embodiment of the invention

Referring to figure 1, an erosion control mat 10 comprises a substrate 11 formed from the first material and an array of buoyant flexible strands 12 attached and extending outwardly from the substrate 11. Substrate 11 is a generally planar base and comprises a plurality of lengthwise extending frame sections 13 and a plurality of widthwise extending frame sections 14. Sections 13 and 14 form a grid, mesh, grate or other generally open planar structure. In particular, substrate 11 is formed from a first material having sufficient structural integrity and strength so as to provide a structural substrate to support and mount the array of flexible strands 12. Substrate 11 may be formed as a unitary structure or may be constructed from individual sections 13, 14 so as to form a modular system. Additionally, substrate 11 may comprise connection members (not shown) to allow multiple substrates 11 to be positioned side-by-side so as to form a tessellated modular arrangement adapted for a plurality of different size configurations extending over a required surface area or region at an underwater environment such as a river or sea bed. Such attachment members (not shown) may be provided at each lengthwise and/or widthwise side of substrate 11. Alternatively, substrate 11 may be configured to be cut to the required size by cutting at selected regions of the different sections 13, 14.

Accordingly, substrate 11 may be formed as a large layer or sheet or alternatively may be formed as a discreet and smaller unit as desired.

The flexible strands 12 according to the preferred embodiment are tubular in a lengthwise direction. Each strand 12 comprises a first end 15 that is attached to substrate 11 and a second end 16 that non-tethered. According to the specific embodiment, strands 12 are grouped into widthwise extending sections, with a plurality of strands attached and extending from each widthwise extending frame section 14. According to further embodiments, strands 12 may comprise a tape, cord or rope configuration.

In use, mat 10 is anchored at a desired underwater location using anchoring devices optionally secured into a sea or river bed. Alternatively, mat 10 may be secured to an underwater structure via rigid anchorage members or flexible attachments such as tape, cord, wire etc. Mat 10 may be considered to comprise a first layer formed by substrate 11 and a second layer formed by the flexible strands 12 so as to comprise a multilayer structure. Consistent with conventional frond mat configurations, strands 12 are configured to impart a viscous drag to water flowing over and around mat 10 so as to reduce the velocity of water flow at the region of the river or sea bed and in particular around designated regions and structures so as to mitigate erosion.

Example 1

In an example construction of mat 10, substrate 11 comprises a first material being polyester. Strands 12 comprise a second and different material being polypropylene. Both the substrate 11 and the strands 12 are configured to be biodegradable so as to degrade in an underwater environment (including a fresh water and a marine environment) slowly and over the course of a minimum of one year, and optionally to degrade over a period of a minimum of six years or more. Accordingly, the polypropylene strands 12 and the polyester substrate 11 (formed as webbing) comprises a biodegradable/biodegradation additive to effectuate the biodegradation by structural break-down of the polymer structures (of the substrate 11 and strands 12) with the aid of microorganisms present within the underwater environment. The present mat 11 is accordingly configured to biodegrade in both aerobic and non-aerobic environments, (as will be encountered in the underwater environment) and to degrade within environments of varying levels of UV and natural light exposure.

The polypropylene material of strands 12 may be manufactured from naturally sourced feedstock such as sugar cane. Alternatively, the polypropylene strands 12 may be manufactured from organic polymers and monomers so as to be fully synthetic or semisynthetic. Polyester substrate 11 preferably comprises polycaprolactone (polyester) sourced from natural feedstocks including for example plant matter.

Both the substrate 11 and the strands 12 comprise the biodegradation additive at an amount in a range 0.1 to 1.0 wt% based on a total weight of each of the substrate 11 and the strands 12, respectively. The biodegradation additive is blended with the respective first and second materials as part of a melt-flow processing and mixing step such that the biodegradation additive is incorporated fully within the first and second materials.

The biodegradation additive is selected from the EcoPure® range of additives available from Bio-Tech Environmental LLC, US. In particular, the polyester substrate material 11 and the polypropylene material of the strands 12 comprise EcoPure® FP01 at the above concentrations.

The biodegradable character of the mat 10 was assessed using current biodegradability standards and test methods for all plastic materials in marine and wastewater environments. Standard test ASTM D6691-09 was undertaken based on the synthetic material of the substrate 11 and strands 12 in an aerobic environment at 30°C. The measurement involved CO2 emission under static test conditions for a test duration of a maximum of three months. The validity criteria of the standard requires greater than 70% degradation for the reference materials. The tests confirmed greater than 70% of the first and second materials biodegraded in the test period.

Example 2

The material and configuration of mat 10 according to example 2 corresponds to example 1 as described. However, in addition, seeds and/or spores of marine vegetation are provided at the second material. In particular, the seeds and/or spores may be coated onto the substrate material and/or present within the substrate material. The seeds and/or spores are configured to germinate in an underwater environment such that as the strands 12 degrade, marine vegetation grows in place of the strands. Example 3

The material and configuration of mat 10 according to example 3 corresponds to example 2. However and in particular, substrate 11 comprises a natural material being for example a material sourced from natural feedstocks such as a natural fibrous and/or woven material. Optionally, the substrate may comprise Hessian, Jute or Burlap. The substrate may be provided with bags, pockets or pouches containing the seeds and/or spores of the marine vegetation. According to a further example, the substrate may comprise a synthetic core but coated with a natural fibrous and/or woven material such as Hessian, Jute or Burlap with the seeds and/or spores provided at the natural material coating of the substrate.