JP7072780B2 - Plastic piece collection method and collection system - Google Patents

Description

The present invention relates to a method and system for recovering plastic pieces, and more particularly to a method and system for recovering plastic pieces that can be efficiently recovered from soil even if the plastic pieces have a higher density than water. ..

The outflow of microplastics into the ocean and rivers has been regarded as a problem, and the content of plastic pieces contained in the soil at the bottom of the water is being investigated. In order to understand the content of plastic pieces, it is necessary to separate and collect the plastic pieces from the soil. Conventionally, the soil collected from the bottom of the water is sieved to remove fine-grained soil (mainly silt and clay) with a relatively small particle size from the soil, and coarse-grained soil (mainly) with a relatively large particle size remaining on the sieve. The plastic pieces in the gravel) are visually identified and the plastic pieces are collected manually. However, it is difficult to visually distinguish a plastic piece from coarse-grained soil having a particle size equal to or larger than that of the plastic piece, and it takes a lot of time and effort to recover the plastic piece.

As a method for separating plastic waste, a method of collecting plastic floating on the water surface using a water tank has been proposed (see Patent Document 1). However, in this sorting method, plastic pieces having a density higher than that of water remain at the bottom of the aquarium. Therefore, plastic pieces having a density higher than that of water cannot be efficiently recovered.

Japanese Patent Application Laid-Open No. 2003-126727

An object of the present invention is to provide a method and a recovery system for recovering plastic pieces that can be efficiently recovered from soil even if the plastic pieces have a density higher than that of water.

In order to achieve the above object, the method for recovering plastic pieces of the present invention is a method for recovering plastic pieces contained in soil, wherein the muddy water obtained by dehumidifying the soil is separated by a cyclone type centrifuge. Using, coarse-grained deposits containing more coarse-grained sediment with a relatively large particle size discharged from the underflow outlet of the centrifuge, and the plastic pieces discharged from the overflow outlet of the centrifuge. It is characterized in that it is classified into fine-grained sediments containing a larger amount of fine-grained soil having a relatively small particle size, and the fine-grained sediments are filtered to separate and recover the plastic pieces from the fine-grained sediments. ..

The plastic piece recovery system of the present invention is a plastic piece recovery system for recovering plastic pieces contained in soil, in which a cyclone type centrifuge and muddy water obtained by dehumidifying the soil flow into the centrifuge. The muddy water is discharged from the underflow outlet of the centrifuge, and the coarse-grained sediment containing a larger amount of coarse-grained soil having a relatively large particle size and the overflow outlet are discharged. The plastic pieces are classified into fine-grained deposits containing a larger amount of fine-grained earth and sand having a relatively small particle size, and the fine-grained deposits are applied to the filter, whereby the plastic pieces are applied to the filter. The feature is that it is configured to be captured.

According to the present invention, the muddy water obtained by dehumidifying the soil is subjected to a coarse-grained sediment containing a larger amount of coarse-grained sediment (mainly gravel) having a relatively large particle size by using a cyclone-type centrifugal separator, and a plastic piece. And it is classified into fine-grained sediments containing more fine-grained soil (mainly silt and clay) with relatively small grain size. Since the plastic pieces have a lower density than the coarse-grained earth and sand having a particle size of the same or higher in the soil, the plastic pieces are discharged together with the fine-grained earth and sand from the overflow outlet of the centrifuge. On the other hand, coarse-grained earth and sand having a particle size equal to or larger than that of the plastic piece has a relatively high density, and is therefore discharged from the underflow outlet of the centrifuge. As described above, by using the cyclone type centrifuge, the plastic piece and the coarse-grained earth and sand can be efficiently separated even if the plastic piece has a density higher than that of water. The fine-grained sediment discharged from the overflow outlet has a low content of coarse-grained sediment having a particle size equal to or higher than that of the plastic piece, so by filtering the fine-grained sediment, the plastic piece can be easily separated from the fine-grained sediment. Can be separated. As a result, even plastic pieces having a higher density than water can be efficiently recovered from the soil.

It is explanatory drawing which illustrates the embodiment of the plastic piece recovery system of this invention. It is explanatory drawing which illustrates the internal situation of the cyclone type centrifuge of FIG. 1 in the vertical cross-sectional view.

Hereinafter, the method and system for recovering the plastic pieces of the present invention will be described based on the embodiment shown in the figure.

The plastic piece recovery system 1 of the present invention exemplified in FIGS. 1 and 2 is used for recovering the plastic piece P contained in the bottom of the water or the soil on land. The plastic piece P is a so-called microplastic, which is a fine piece or fine particle of a plastic material having a particle size of 5 mm or less. Soil contains plastic pieces P that are denser than water, such as polystyrene (about 1.03 g / cm ³ ), nylon (about 1.14 g / cm ³ ), and acetate (about 1.28 g / cm ³ ). May be.

The recovery system 1 includes a cyclone type centrifuge device 2 (hereinafter referred to as a centrifuge device 2), an inflow means 3 for flowing mud water S from which soil has been dehumidified into the centrifuge device 2, and a filter 9. Further, in this embodiment, the connecting pipe 8 connecting the storage container 7 for coarse grain deposits arranged below the underflow outlet 2b of the centrifuge device 2 and the overflow outlet 2c of the centrifuge device 2 and the filter 9 is connected. And a storage container 10 for fine-grained deposits arranged below the filter 9.

The inflow means 3 of this embodiment has a storage tank 4 in which the muddy water S is stored, a mud feed pipe 5 connecting the storage tank 4 and the centrifuge device 2, and a compressor 6 connected to the storage tank 4. It is composed of. The upper opening of the storage tank 4 is provided with an upper lid that can seal the storage tank 4, and the air supply pipe of the compressor 6 is connected to the upper lid. A discharge port from which muddy water S is discharged is provided at the bottom of the storage tank 4. Further, at the bottom of the storage tank 4, an inclined plate 4a inclined downward from the inner peripheral surface of the storage tank 4 toward the discharge port is provided. One end of the mud feed pipe 5 is connected to the discharge port of the storage tank 4, and the other end of the mud feed pipe 5 is connected to the inflow port 2a provided on the side of the centrifuge device 2.

As shown in FIG. 2, the inside of the centrifuge 2 has a truncated cone shape in which the inner diameter of the lower portion is smaller than the inner diameter of the upper portion. A descending vortex that flows downward along the inner wall of the centrifuge device 2 by the muddy water S flowing in at high speed from the inflow port 2a provided in the upper part of the centrifuge device 2 by the inflow means 3, and the centrifuge device 2. The structure is such that an ascending vortex that flows upward is generated in the center of the wall.

When the muddy water S flows in from the inflow port 2a, the coarse-grained sediment Sa containing a larger amount of coarse-grained earth and sand (mainly gravel) having a relatively large particle size and a high density in the muddy water S is inside the centrifuge device 2. It is greatly affected by the centrifugal force caused by the generated descending vortex. Therefore, the coarse-grained sediment Sa descends while swirling along the inner wall together with the descending vortex, and is discharged from the underflow outlet 2b provided below the centrifuge device 2. On the other hand, the plastic piece P has a relatively low density as compared with coarse-grained earth and sand having a particle size of the same or more contained in the soil. Therefore, the fine-grained sediment Sb containing more fine-grained earth and sand (mainly silt and clay) having a relatively small particle size and a low density as the plastic piece P has a smaller influence of centrifugal force due to the descending vortex. Therefore, the fine-grained deposit Sb containing the plastic piece P rises with the rising vortex in the center and is discharged from the overflow outlet 2c provided above the centrifuge device 2.

The size of the grain size of the earth and sand that is the boundary to be classified by the centrifuge 2 (hereinafter referred to as the classification boundary particle size of the earth and sand) is a plastic piece whose particle size of the fine-grained earth and sand discharged from the overflow outlet 2c is the target of recovery. It is set to be smaller than the particle size of P. Since the particle size of the plastic piece P contained in the soil is about 5 mm or less, the classification boundary particle size of the earth and sand by the centrifuge 2 is, for example, 0.01 mm or more and 2 mm or less, more preferably 0.02 mm or more and 1 mm or less. Is set to.

The classification boundary particle size of the earth and sand by the centrifuge 2 can be changed by changing the size of the centrifuge 2 itself, the size of the inflow port 2a, the inflow rate of the muddy water S flowing into the centrifuge 2, and the like. In the inflow means 3, the inflow speed of the muddy water S into the centrifuge device 2 can be adjusted by changing the magnitude of the air pressure applied to the inside of the storage tank 4 by the compressor 6.

As the filter 9, for example, a sieve having a mesh-shaped wire mesh or the like is used. The size of the mesh of the filter 9 is set to be larger than the particle size of the fine-grained earth and sand discharged from the overflow outlet 2c and smaller than the particle size of the plastic piece P to be collected. Specifically, the size of the mesh of the filter 9 is set to, for example, 0.01 mm square or more and 1 mm square or less, more preferably 0.02 mm square or more and 0.075 mm square or less. A vibration mechanism that vibrates the filter 9 can also be provided.

Next, a method of recovering the plastic piece P from the soil using this recovery system 1 will be described below.

The soil collected from the bottom of the water or the like is demudified to create a mud water S having fluidity, and the mud water S is stored in the storage tank 4. At this time, the viscosity and density of the muddy water S are adjusted by adjusting the water content of the soil. The viscosity of the muddy water S is adjusted within a range in which the muddy water S can be classified by the centrifuge device 2.

The density of the muddy water S can be appropriately set according to the density of the plastic piece P to be collected. For example, a plastic piece P having a density of 1.0 g / cm ³ or more and 1.3 g / cm ³ or less such as polystyrene or nylon is used. When the object is to be collected, the density of muddy water S may be adjusted to 1.0 g / cm ³ or more and 1.5 g / cm ³ or less, more preferably 1.0 g / cm ³ or more and 1.3 g / cm ³ or less. .. The density of the muddy water S may be set to be, for example, 1% or more higher than the density of the plastic piece P to be collected.

The density of the muddy water S can also be adjusted by adding an additive that increases the density of the muddy water S without changing the viscosity of the muddy water S so much. That is, it is preferable to use an additive that can maintain the viscosity of the muddy water S within a preset allowable range so as not to substantially increase the viscosity. Specifically, the allowable range of the viscosity (mPa · s) of the muddy water S after adding the additive is more preferably + 5% or less of the initial viscosity (mPa · s) of the muddy water S before adding the additive. Use an additive that can ensure this permissible range by setting it to + 3% or less. Examples of the additive include barium sulfate, magnesium hydroxide, calcium hydroxide and the like. It is preferable to use an additive that raises the pH value of muddy water S.

Next, the muddy water S is made to flow into the centrifuge device 2 by the inflow means 3. In this embodiment, the upper opening of the storage tank 4 is covered with an upper lid to seal the storage tank 4, and the air pressure inside the storage tank 4 is increased by the compressor 6, so that the mud water S stored in the storage tank 4 is used. Is flowed into the inflow port 2a of the centrifuge 2 through the mud feeding pipe 5.

The muddy water S flowing in from the inflow port 2a has a coarse-grained sediment Sa containing a larger amount of coarse-grained earth and sand having a relatively large particle size, a plastic piece P, and fine particles having a relatively small particle size by the centrifuge device 2. It is continuously classified into fine-grained sediment Sb containing more earth and sand. Then, the coarse-grained deposit Sa is discharged to the underflow outlet 2b, and the fine-grained deposit Sb containing the plastic piece P is discharged to the overflow outlet 2c.

The coarse-grained sediment Sa discharged from the underflow outlet 2b is collected in the coarse-grained sediment storage container 7. On the other hand, the fine-grained deposit Sb containing the plastic piece P discharged from the overflow outlet 2c is discharged onto the filter 9 through the connecting pipe 8. Then, the fine-grained sediment Sb is classified by the filter 9, so that the plastic piece P having a relatively large particle size is captured by the filter 9, and the fine-grained earth and sand having a relatively small particle size pass through the eyes of the filter 9. It collects in the storage container 10 for fine-grained deposits. Since only the plastic piece P remains on the filter 9, the plastic piece P can be easily recovered.

As described above, in the present invention, paying attention to the fact that the density of the plastic piece P is smaller than the density of coarse-grained sediment having the same or higher particle size, the muddy water obtained by dehumidifying the soil using the centrifuge 2 is used. S is classified into coarse-grained sediment Sa containing more coarse-grained sediment and fine-grained sediment Sb containing more coarse-grained sediment P and fine-grained sediment. As a result, even if the plastic piece P has a higher density than water, the plastic piece P contained in the soil and the coarse-grained earth and sand can be efficiently separated. Since the fine-grained sediment Sb discharged from the overflow outlet 2c of the centrifuge 2 has a low content of coarse-grained sediment having a particle size equal to or higher than that of the plastic piece P, the fine-grained sediment Sb is filtered. The plastic piece P can be easily separated from the fine-grained deposit Sb. As a result, even a plastic piece P having a density higher than that of water can be efficiently recovered from the soil.

Most of the plastic pieces P are contained in the coarse-grained sediment Sa stored in the coarse-grained sediment storage container 7 and the fine-grained sediment Sb stored in the fine-grained sediment storage vessel 10 after classification. It will be in a state where it is not included. Therefore, the coarse-grained sediment Sa and the fine-grained sediment Sb after classification can be returned to the bottom of the water where the soil was collected, or can be used as construction materials or other materials.

The density of muddy water S is 1.00 g / cm ³ or more and 1.50 g / cm ³ or less, more preferably 1.00 g / cm ³ or more and 1.30 g / cm ³ or less, and further preferably 1.05 g / cm ³ or more 1. When adjusted to 20 g / cm ³ or less, the plastic piece P having a density of polystyrene, nylon, etc. of 1.00 g / cm ³ or more and 1.30 g / cm ³ or less is easily discharged from the overflow outlet 2c of the centrifuge device 2, and the plastic. Coarse-grained earth and sand having a particle size equal to or larger than that of the piece P is likely to be discharged from the underflow outlet 2b. Therefore, it is advantageous to increase the recovery rate of the plastic piece P.

When creating the muddy water S, if an additive that increases the density of the muddy water S while maintaining the viscosity of the muddy water S within a preset allowable range is added, the density of the muddy water S is ensured while ensuring the fluidity of the muddy water S. Can be increased, so that the density of muddy water S can be adjusted accurately. Therefore, it is advantageous to increase the recovery rate of the plastic piece P.

Furthermore, if additives such as barium sulfate, magnesium hydroxide, and calcium hydroxide that increase the pH value of muddy water S are used, even if the target soil is acidic soil or acidic sulfate soil, it will be contained in the soil. It is possible to suppress the growth of sulfate-reducing bacteria and the generation of hydrogen sulfide. Therefore, the plastic piece P can be recovered in a safer environment even in acidic soil or acidic sulfate soil.

Further, by adding an additive that increases the pH value of muddy water S, the pH values of the coarse-grained sediment Sa and the fine-grained sediment Sb after classification can be increased, so that the coarse-grained sediment Sa and the fine-grained sediment are deposited. By returning the minute Sb to the soil at the bottom of the water, the growth of sulfate-reducing bacteria and the generation of hydrogen sulfide contained in the soil can be suppressed. Therefore, it also contributes to improving the soil environment.

When the inclined plate 4a is provided on the bottom of the storage tank 4, the plastic piece P is less likely to remain on the bottom of the storage tank 4, and the plastic piece P is likely to flow into the mud feeding pipe 5. Therefore, it is advantageous to increase the recovery rate of the plastic piece P.

The configuration of the inflow means 3 is not limited to this embodiment, and various other configurations can be used. For example, a mining means such as an underwater robot for mining the soil at the bottom of the water is connected to the inflow means 3, the soil mined by the mining means is demudged by water adjustment, and the muddy water S is centrifuged through the inflow means 3. It can also be configured to sequentially send to the inflow port 2a. Further, for example, the coarse-grained sediment Sa and the fine-grained sediment Sb remaining after the plastic piece P is collected may be directly returned to the bottom of the water without being temporarily accumulated.

Further, for example, a plurality of centrifuge devices 2 having different sizes of the centrifuge device 2 itself and the inflow rate of the muddy water S flowing into the centrifuge device 2 are connected to classify the muddy water S into a plurality of stages. This makes it possible to classify and collect plastic pieces P having different densities and particle sizes.

In the embodiment exemplified above, the filter 9 is connected to the overflow outlet 2c of the centrifuge device 2 via the connecting pipe 8, but the filter 9 does not have to be continuous with the overflow outlet 2c. That is, after stocking the fine-grained deposit Sb containing the plastic piece P discharged from the overflow outlet 2c in a storage container or the like, the stocked fine-grained deposit Sb is filtered through the filter 9 to collect the plastic piece P. You can also.

A simulated soil in which 20 spherical plastic pieces were mixed with clay was prepared, and the simulated soil was demudded to prepare four types of muddy water samples whose viscosity and density were adjusted. Then, an experiment was conducted in which plastic pieces were recovered from each muddy water sample using the recovery systems illustrated in FIGS. 1 and 2. The main experimental conditions and experimental results are shown in Table 1. “UF (pieces)” in Table 1 indicates the number of plastic pieces discharged from the underflow outlet of the centrifuge, and “OF (pieces)” indicates the number of plastic pieces discharged from the overflow outlet of the centrifuge. Shown, "remaining tank (pieces)" indicates the number of plastic pieces remaining in the storage tank.

As shown in Table 1, in all muddy water samples, 15 or more of the 20 plastic pieces contained in the simulated soil were discharged to the overflow side, and the recovery rate of the plastic pieces by the recovery system was 75%. That was all. From this experimental result, it can be seen that by using the recovery system, even a plastic piece having a higher density than water can be recovered from the soil with a high recovery rate.

1 Recovery system 2 Cyclone centrifuge 2a Inlet 2b Underflow outlet 2c Overflow outlet 3 Inflow means 4 Storage tank 4a Inclined plate 5 Mud pipe 6 Compressor 7 Coarse sediment storage container 8 Connection pipe 9 Filter 10 Fine granules Sediment storage container S (soil demudified) Mud water Sa Coarse sediment Sb Fine sediment P Plastic piece

Claims (5)

In the method of collecting plastic pieces that are contained in the soil,
Using a cyclone-type centrifuge, the muddy water obtained by dehumidifying the soil is discharged from the underflow outlet of the centrifuge to form a coarse-grained sediment containing a larger amount of coarse-grained sediment having a relatively large particle size. The plastic pieces discharged from the overflow outlet of the centrifuge are classified into fine-grained sediments containing more fine-grained earth and sand having a relatively small particle size, and the fine-grained sediments are filtered to form the fine-grained sediments. A method for collecting plastic pieces, which comprises separating and collecting the plastic pieces from a minute. The method for recovering a plastic piece according to claim 1, wherein when the muddy water is prepared, an additive for increasing the density of the muddy water is added to the soil while maintaining the viscosity of the muddy water within a preset allowable range. The method for recovering a plastic piece according to claim 2, wherein the additive for increasing the pH value of the muddy water is added. The method for recovering a plastic piece according to any one of claims 1 to 3, wherein the density of the muddy water is adjusted to 1.0 g / cm ³ or more and 1.5 g / cm ³ or less. In a plastic piece recovery system that collects plastic pieces contained in soil
It has a cyclone type centrifuge, an inflow means for flowing mud water from which the soil has been dehumidified into the centrifuge, and a filter.
The coarse-grained sediment containing more coarse-grained earth and sand having a relatively large particle size discharged from the underflow outlet of the centrifuge, and the plastic pieces discharged from the overflow outlet and the relatively particle size of the muddy water. It is characterized in that the plastic pieces are captured by the filter by being classified into fine-grained sediments containing a larger amount of small fine-grained sediment and the fine-grained sediments being applied to the filter. Plastic piece collection system.

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