Process for plastics separation

Abstract

A process comprising (a) shredding or chopping a mixture of plastics material and seaweed comprising air bladders, such that the seaweed air bladders are perforated, to form a shredded material, (b) c

Description

Technical Field The present invention is concerned with a process to separate out plastics 5 materials from organic matter, in particular to separate out plastics materials from seaweed having air bladders (pneumatocysts). In particular, the process involves shredding the seaweed to burst / perforate the air bladders thereby reducing its buoyancy. Plastic and other light weight contaminants, such as plastic film, can then be separated from the shredded organic matter by fluid-based separation. 10 Background to the Invention All around the world, plastics waste within the oceans tends to become congregated in particular coastal areas, forming “litter sinks”, for example through tidal motion or prevailing winds. For example, the west coast of Scotland, UK 15 exhibits “litter sinks”, at areas such as Arrochar and Lochgoilhead. Beaches in Cornwall, UK also receive large amounts of seaweed / plastics mix during stormy weather. In addition, in the ocean plastic materials can congregate in ocean gyres along with seaweed. For example, in the North Atlantic Ocean floating Sargassum muticum seaweed has become entangled with plastic marine debris. Plastic 20 pollution in the oceans and onshore is known to be a hazard and to cause damage to wildlife, for example through entanglement or through ingestion. Additionally, the plastics waste is highly unsightly and so negatively impacts tourism in coastal regions. If the plastics waste is simply left, the plastics materials degrade further into smaller pieces through tidal motion and UV radiation, eventually forming 25 microplastics. Microplastics are particles of 5mm diameter or less, many of which are not visible by the naked eye. Microplastics are extremely difficult to remove from the environment and are known to be damaging and toxic to marine wildlife. For this reason, it is preferable to remove plastic pollutants in macro-form prior to such degradation. However, one difficulty experienced in removing plastics waste 30 from coastal areas is the tendency for it to become entangled with algae (seaweed). It is particularly difficult to separate out the plastic from the marine algae, hindering efforts to recycle either or both plastic and seaweed. 07 10 22 Brown types of seaweeds in sheltered locations (such as litter sinks) can grow pneumatocysts or bladders containing the gases oxygen, nitrogen and carbon dioxide to aid buoyancy and help the seaweed reach sunlight to achieve photosynthesis when immersed in water. Many brown seaweeds possessing 5 bladders are found in sheltered coastlines, away from the open sea and face the opposite direction of prevailing winds. These are exactly the locations which form “litter sinks” along the coast and are focal areas where plastics waste becomes congregated. Common seaweeds found at these locations include Ascophyllum nodosum and Fucus vesiculosus. Ascophyllum nodosum also known as “knotted 10 wrack” or “egg wrack” is a common large brown seaweed that is dominant on sheltered rocky shores of the Northern Atlantic Ocean and contains large egg-like bladders at intervals along its fronds. The fronds of this species are typically between 0.5 and 2m in length and the algae is found on the middle of the shore, growing slowly with individual fronds aging up to 15 years. Fucus vesiculosus also 15 known as “bladder wrack” is a large brown seaweed also common to the middle shore on coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans. Under sheltered conditions this seaweed’s fronds have been known to grow up to 1.5m in length. It has a prominent midrib and possesses almost spherical air bladders. 20 Both Ascophyllum nodosum and Fucus vesiculosus are commonly found entangled with plastics waste in coastal regions of the United Kingdom. In other areas of the world, other seaweeds containing pneumatocysts (such as Sargassum spp.) are likewise found entangled with plastics waste located on the shore or in ocean. 25 Summary of the Invention The present invention provides a process for separating plastics materials entangled in organic matter, such as seaweeds, for example brown seaweeds comprising air bladders. The process comprises: 30 i) shredding a mixture of plastics waste and seaweed comprising air bladders to form a shredded material, whereby the shredding perforates air bladders within the seaweed; ii) combining the shredded material with water or brine and allowing the shredded plastics waste and seaweed to separate into two fractions; and 07 10 22 iii) removing the plastics waste and / or the seaweed from the water or brine. Optionally the shredded material can be mechanically agitated before being allowed to separate into the two different fractions. For example, the shredded 5 material can be stirred with a paddle or other suitable agitator. Optionally, the plastics material comprises or consists of plastics films, for example crisp packets, confectionary wrappers, plastic packaging and bags etc. 10 In general, the shredded seaweed material will sink and form a lower fraction within the fluid, whereas the shredded plastics material will float, and form an upper fraction on or close to the fluid surface. The present invention further provides a process of recovering beach-cast 15 seaweed material for downstream processing (for example to make fertiliser, animal feed or similar), wherein said seaweed is separated from plastics material by a process as described above. The present invention further provides a process of recovering beach-cast plastics 20 material for potential recycling, wherein said plastics material is separated from seaweed comprising air bladders by a process as described above. Brief Description of the Figures Figure 1: Scatter graph showing the output shredded material of knotted wrack 25 (KW) that initially floats (triangle marker); the material that still floats after agitation / submergence (circle marker) and a representative subsample of seaweed fragments that have sunk (square marker). The dotted line is to help show fragment geometry - fragments on the dotted line have equal length and width. Figure 2: Scatter graph showing the output shredded material of bladder wrack 30 (BW) that initially floats (triangle marker); the material that still floats after agitation / submergence (circle marker) and a representative subsample of seaweed fragments that have sunk (square marker). The dotted line is to help show fragment geometry - fragments on the dotted line have equal length and width. 07 10 22 Figure 3: Scatter graph that shows the bladderwrack (BW) and knottedwrack (KW) shredded material that floats after agitation. The dotted line indicates fragment geometry - fragments on the dotted line have equal length and width. Detailed Description of the Invention The process of the present invention is now described in further detail. The present invention relates to a process for separating plastic contaminants from organic matter, such as seaweeds, in particular brown sea weeds, for example brown seaweeds with air bladders. Exemplary seaweeds with air bladders include, but are not limited to, A. nodosum and F. vesiculosus. Large kelps such as Laminara hyperborea and Laminara digitata can sometimes have air bladders also. Other seaweeds with air bladders include Sargassum spp. The process of the present invention finds particular utility with beach-cast material (for example material which is deposited on a beach or shore at a high-water mark). Generally large quantities of mixed organic matter and plastic contaminants become beach-cast after spring tides (i.e. tides having a larger tidal range) and / or on tides where there is wind in the same direction as a flood (incoming) tide. Storm surges can also be responsible for causing larger quantities of mixed plastics contaminants and organic matter to be deposited on the shore line. The process of the present invention therefore finds particular utility as a means of treating coastal areas after such events by allowing beach-cast materials to be treated so that the separated plastics and organics materials can be recycled. The process of the present invention can also be used to separate plastics contaminants when entangled with seaweed within seawater, for example when forming part of an ocean “garbage patch”. In step (i) of the present invention the raw material is shredded to perforate at least some of the air bladders within the seaweed, that is, the raw material is at least partially chopped or shredded. For example, a force can be exerted on the material with a mechanical shredder. In this step, seaweed air bladders present within the raw material are destroyed or damaged (e.g. punctured). Puncturing the air 07 10 22 bladders of the seaweed reduces the buoyancy of the seaweed material. Generally at least 50%, for example at least 80% or at least 90% of the air bladders within the seaweed present within the raw material will be punctured by shredding step (i). Machinery and / or equipment that could be used to shred the seaweed and plastic 5 material in step (i) include (without limitation) high speed biomass shredders, food processors, macerators that shred and / or grind material, hammer mills that use a combination of hammer impacts to crush and shatter material, granulators that use high speed blades to reduce material to a fine output, wood chippers that has blades on a spinning disc that slices the material into chips, industrial grinders that 10 use abrasion to reduce material in size, or the like. Optionally a mechanical shredder having an angular velocity of up to WOOrpm can conveniently be used. Optionally a mechanical shredder having an angular velocity of at least 2000rpm, for example at least 3000 rpm, for example at least 3500rpm 15 can be used. In some embodiments, a mechanical shredder operating at over 3000 rpm may be suitable to increase the likelihood that the seaweed bladders are perforated. However lower rpm machines could still work and any material that was remained floating could simply be put through a shredding process again. This option will work well for a continuous process and may be further assisted using a 20 shredder having a screening basket or grate to automatically separate smaller material - since smaller material falls through the perforations in the grating and larger material is retained within the cutting chamber for shredding. It should be noted that there is no absolute requirement for the seaweed to be 25 reduced in size, merely for the buoyant air bladders to be punctured. However, it has been found that subjecting the whole mass of material (including the plastics contaminants) to the shredding step is a simple and efficient process to reduce buoyancy of the seaweed material. As an example, reducing knotted wrack to a size of 40mm or less results in the majority of the seaweed having sufficient 30 reduced buoyancy to cause the seaweed fragments to sink. In one embodiment the shredding step reduces the buoyancy of at least 70% (by weight) of the seaweed, i.e. after shredding at least 70% of the shredded seaweed 07 10 22 will sink. Optionally at least 80% by weight, 90% by weight or 95% by weight of the shredded seaweed will have reduced buoyancy after shredding. It is noted that seaweeds may vary in terms of the size and spacing of the air 5 bladders, Consequently, smaller-sized seaweeds may have smaller air bladders and may require a longer period of shredding to ensure puncture of a sufficient proportion of the air bladders. However, all that is required is to return any floating material including seaweed for further chopping or shredding. In practice, this can be achieved by returning any floating mass which still includes too large a 10 proportion of seaweed to a shredder or similar. The process of the invention removes plastics material from the seaweed, so that the seaweed fraction can be removed for use, for example as a feedstock for downstream processing (for example to make fertiliser, animal feed or similar). Depending upon the downstream process required, a small amount of contaminant plastics material 15 may be tolerated, so that there is no requirement for the seaweed fraction to be 100% pure. In one embodiment at least 50% (w / w) of the plastics material (wet weight, relative to the weight of plastics present in the initial mixture of plastics and seaweed) is removed by the process of the present invention, for example at least 70% (w / w) of the plastics material, 90% (w / w) - or even more - of the plastics 20 material relative to the wet weight of plastic present in the initial mixture of plastics waste and seaweed is removed by the process of the present invention. As a result of the shredding step (i), any plastic contaminants (and also any other components within the raw material) may also be reduced in size. However, unlike 25 seaweed with air bladders, the buoyancy of the plastic contaminants (predominantly film plastics) is not affected by the shredding process. Therefore, the plastic contaminant fragments can be separated from the shredded seaweed by fluid-based density separation in a tank or other suitable receptacle. 30 Optionally, the seaweed can be chopped or shredded sufficiently so that at least one air bladder in each piece of seaweed is punctured. Accordingly, the shredded raw material can then be added to water (i.e. fresh water) or brine (e.g. seawater), typically within a suitably-sized fluid-tight container, 07 10 22 such as tank. The organic matter will typically sink within the water or brine, whilst the plastic contaminants will float. The water or brine(for example fresh water) can be at ambient temperature. Generally, the temperature of water does not significantly impact on its density and 5 therefore use of water at ambient temperature avoids heating costs. Cold fresh water, for example water at a temperature of 7 to 10 °C can be used. In some embodiments, the water can be sea water. Conveniently the container will hold sufficient water or brine to ensure that there is 10 a clear separation of the two layers. Generally, the layers will be separated by at least 10cm, for example 15cm, for example 20cm, for example 30cm, for example 50cm or more. The container should be sized appropriately to facilitate separation of the two layers and to hold the volume of water or brine required. A separating distance of 15 to 25cm generally works well for the majority of embodiments. 15 In one embodiment, the shredded material can be mechanically agitated at the start of and / or during the water / brine-based density separation step. For example, paddles on the top of the tank surface can be used to submerge the seaweed material and to waterlog perforated bladders of the seaweed, thereby encouraging 20 the organic matter to sink in the water or brine. Alternatively, the shredded material can be stirred within the water or brine. Alternatively or additionally, the shredded material and water or brine mixture can be left for a period of time, for example for a period of 5 to 10 minutes. Optionally 25 the material can be left for a period of 15 minutes or more, for example 20 minutes or more, for example 30 minutes or more. In practice a period of 5 minutes has been found to be sufficient and shorter periods, for example 4 minutes or less or 3 minutes or less can also be sufficient for some embodiments. 30 Once the raw material has been separated into two fractions, the floating (plastic contamination, for example plastic film contamination) fraction can then be separated from the other materials. Alternatively, it may be convenient to separate the fractions by removal of the lower (seaweed) fraction. Any suitable known means to separate the fractions can be used. For example, separation can be 07 10 22 achieved using skimmer paddles, rakes, nets etc. that move across the top of the fluid surface, pushing any floating material to one end of the tank for collection. Alternatively or additionally, the sunken fraction (cleaned shredded mixed 5 seaweed) can be separated from floating plastic contamination by a physical barrier. The process of the present invention can be operated in a batch-wise manner or can be performed as a continuous process. As a continuous process, there may be 10 the ability to alter the mass of material being fed into the system per unit time, to alter the length of time the material is subjected to the shredding step and / or to alter the speed of any mechanical shredder or size of cut, to alter any optional mixing step, to alter any settlement step and to alter the rate of output of material. Optionally the continuous process may include a step allowing shredded material 15 to be returned for further shredding / chopping if required. Optionally, the container may include a moving conveyor system at the bottom of the container to remove seaweed which has sunk. Alternatively, the material can be removed periodically by a boom or similar. 20 The following examples are provided to further illustrate the invention but are not intended to limit the scope of the invention in any manner. Preferred or alternative features of each aspect or embodiment of the invention apply mutatis mutandis to each other aspect or embodiment of the invention 25 (unless the context demands otherwise). All documents referred to herein are incorporated by reference. Any modifications and / or variations to described embodiments that would be apparent to one of skill in art are hereby encompassed. Whilst the invention has been described herein 30 with reference to certain specific embodiments and examples, it should be understood that the invention is not intended to be unduly limited to these specific embodiments or examples. 07 10 22 Examples Example 1 A fresh seaweed sample containing no plastic contamination was shredded and 5 the percentage of seaweed fragments that floated or sank by weight and by species was measured. In addition, the sizes (lengths and widths) of the fragments that floated and the fragments were sank by species was analysed by image analysis. 10 A 250g fresh sample of beach-cast mixed species seaweed was taken and manually separated into different species types. The sample contained approximately 90g of F. vesiculosus and 160g of A. nodosum. The initial size of the beach-cast material was analysed and included sizes of up to 1,5-2m for both species. 40L of cold, fresh water was prepared and placed into a rectangular, clear 15 box container, approximately 60cm in length by 30cm width, with volume 84L. The water temperature was within the temperature range of 7-10 °C, using a thermometer. The separated seaweed materials were shredded using a Bosch Shredder AXT Rapid 2200, a high-speed, powerful shredder that uses a laser-cut blade reaching angular velocities of up to 3650rpm. The output shredded material 20   {A. nodosum) was collected in a bucket before being dropped into the container of water and the contents allowed to settle for 2 minutes. The distance between the two fractions was approximately 20cm. After two minutes an initial floating fraction of seaweed material from the container was then removed and weighed and the weight of the material which had sunk was calculated by simple subtraction. The 25 floating seaweed material was then placed onto a laminated sheet of paper and photographed with a ruler for a reference for sizing within the image; the lengths and widths of floating fragments could then be analysed. This initial floating fraction material was then collected and dropped back into the water container, a wooden block was then manually impacted on the floating fraction moving along the water 30 surface performing agitation and submerging the floating fraction replicating the effects of a skimmer on the water surface with paddles. Any material that still failed to sink after agitation and submergence was removed and placed on the laminated sheet and photographed for analysis of the lengths and widths of these fragments by image analysis. A random sample of sunken seaweed fragments was then 07 10 22 removed (since this fraction was in far greater amount than floating fraction) and placed on the laminated sheet. The trial was performed for >4. nodosum (knotted wrack). The material lengths and widths were then analysed and a scatter graph of the data was produced - see Figure 1. 5 Figure 1 illustrates that larger fragments of A. nodosum were more likely to sink after shredding. Therefore, the shredding process need not shred to a small size, since perforation of the air bladders causes the seaweed to sink, rather than any reduction in its size. Agitation of floating shredded fragments helped to sink some 10 resistant fragments e.g. those where bladders have been perforated rather than destroyed. This process encourages water into the bladder affecting the buoyancy. After agitation the amount of knotted wrack which sank was 98% by weight. The process described above was repeated for F. vesiculosus (bladder wrack) 15 using fresh cold water of approximately 7 to 10 °C. The initial floating material, final floating material after agitation / submergence and sunk material for bladder wrack was removed, weighed and the dimensions were determined by image analysis of photographs. The trial was performed twice for F. vesiculosus (bladder wrack). The results are shown in Figure 2. 20 From Figure 2, larger fragments of F. vesiculosus were more likely to sink after shredding. Therefore, the shredding process does not need to shred to a small size. In the agitation and submergence of bladder wrack, four of the largest fragments sank with a relatively small change in buoyancy of each fragment. 25 Larger fragments of seaweed have larger sized air bladders - hence puncturing a smaller proportion of the air bladders causes the fragment to sink. For the smaller seaweed fragments, a higher proportion of the (relatively small) air bladders need to be perforated to achieve the same effect. In general terms a seaweed fragment which is larger than 35mm in length and breadth would be considered to be a large 30 fragment. After agitation the amount of F. vesiculosus, which sank was more than 97% by weight, relative to the total weight of the material. 07 10 22 It is concluded from Figure 3 that small shredded seaweed material ranging up to over 30mm in length to 15mm in width containing bladders remain unperforated were the least likely to sink in water. 5 Example 2 As shown in Table 1, the trials were performed by using recovered seaweed material and adding contaminated material containing over 5% by weight. Up to 500g of seaweed material was used in one trial with various contaminated materials added to the trial material. This mixture of material was then shredded 10 and dropped into a clear, rectangular container filled with fresh water (sufficient to allow a separating distance between the fractions of at least 20cm), and allowed to settle for a period of up to 10 minutes. The plastic fraction that floated to the surface was removed and oven dried to measure the dry weight of the plastic material removed. The sunken fraction of seaweed and plastic was then agitated, 15 causing further plastics to rise to the surface of the water. This further plastics fraction was removed and oven dried to measure the dry weight of the plastic material. In the above trials no plastic contamination was found in the lower fraction at the bottom of the container and after the material had been agitated. 20 In Trial No. 3, a larger proportion of harder plastics such as bottle caps and cotton bud sticks were used. The container of water with shredded material in this trial was allowed to settle for over half an hour and it was noted that considerably higher initial floating plastic contamination weight that could be separated, namely over 85% in this trial compared to around 60% in the first 2 trials. 07 10 22 Table 1: 84L Trial method using different plastic contaminants and mixed seaweed types. Trial No. Contaminated Material to be Separated Abundance of Litter (%w / w‘) Initial Floating Contamination (g dry weight) Initial Floating Contamination (%w / w) Final Floating Contamination (g dry weight) Final Floating Contamination (%w / w) 1 Plastic films, threads, and rope 5.0 1.9 58 3.3 100 2 Plastic films, threads, bottle cap, cotton bud sticks and rope 4.6 4.6 61 7.5 100 3 Plastic films, threads, bottle caps, cotton bud sticks and rope 5.0 9.7 86 11.3 100 * fresh weight plastic to fresh weight seaweed “Floating contamination” refers to plastic which immediately rose the surface after the seaweed / plastic mix was dropped into the water within the container and the contents were allowed to settle. “Final Floating contamination” refers to was plastic which rose to the surface after the water in the container was agitated and moved 10 around. Example 3 A trial was performed using material found at a litter sink. This material comprised mixed species seaweed material that visibly contained plastic contamination. In this trial 500g of the material found at the litter sink 5 (seaweed contaminated with plastic material) was used. This material was shredded using a Bosch Shredder AXT Rapid 2200 and then dropped into a rectangular, clear box container (length approximately 60cm, width 30cm and with volume 84L) filled with 40L of cold, fresh water and the water was agitated by hand for a few minutes. The separating distance between the 10 fractions is approximately 20cm. The fresh weight of plastic that floated to the surface was removed and measured. No plastics contamination was seen in the sunken fraction after agitation. 07 10 22 The results are shown in Table 2. 15 Table 2 Contaminated Material to be Separated Abundance of Litter (%w / w‘) Final Floating Contamination (g fresh weight) Final Floating Contamination (%w / w) Plastic films, threads, rope 1.1 5.3 100 * fresh weig nt plastic to fresh weight seaweed 20 “Final Floating Contamination” refers to plastic which rose to the surface after the water in the container was agitated and moved around.

Claims

1. A process comprising:a. shredding a mixture of plastics waste and seaweed comprising5                air bladders to form a shredded material, whereby theshredding perforates air bladders within the seaweed;b. combining the shredded material with water or brine and allowing the shredded plastics waste and seaweed to separate into two fractions; and10             c. removing the plastics waste and / or the seaweed from the wateror brine.

2. The process as claimed in claim 1, wherein said seaweed comprising air bladders is selected from Ascophyllum nodosum and Fucus15 vesiculosus.

3. The process as claimed in either one of claims 1 and 2, wherein the water or brine is fresh water or sea water.20 4. The process as claimed in any one of claims 1 to 3 wherein the process further comprises mechanical agitation of the combination of the water or brine and shredded material.

5. The process as claimed in any one of claims 1 to 4 wherein the25 combination of water or brine and shredded material is allowed to settle for 5 minutes before the fraction containing the plastics waste is separated from the fraction containing the seaweed.

6. A process of treating beach-cast seaweed comprising air bladders, 30 wherein said seaweed is separated from beach-cast plastics admixed therewith by a process as claimed in any one of claims 1 to 5.CM CM7. A process of recycling beach-cast plastics material, wherein said plastics material is separated from beach-cast seaweed having air bladders admixed therewith by a process as claimed in any one of claims 1 to 5.

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