Contaminated soil remediation apparatus and contaminated soil remediation method

Abstract

The object of the present invention is to solve the problems of the conventional method, namely, to provide a contaminated soil remediation device and a contaminated soil remediation method that can remove PFAS from contaminated soil without the need for sand separation treatment. [Solution] The contaminated soil remediation apparatus of the present invention is an apparatus for remediating contaminated soil containing PFAS, and comprises a mixing tank and a cyclone. The mixing tank produces mixed soil by adding an adsorbent to contaminated soil that has not undergone classification treatment and mixing it, and the cyclone separates the adsorbent and fine particles from the mixed soil produced in the mixing tank. The cyclone raises the adsorbent and fine particles, on which PFAS has been adsorbed, in the center of the cyclone and then discharges them from the upper outlet.

Description

Technical Field

[0001] The present invention relates to a technology for purifying organofluorine compounds (hereinafter referred to as "PFAS") present in soil and groundwater. More specifically, the present invention relates to a contaminated soil purification apparatus that allows PFAS to be adsorbed onto an adsorbent by adding an adsorbent (for example, powdered activated carbon) to PFAS-containing soil (for example, excavated soil) and then treating the mixture with a cyclone, and a contaminated soil purification method using the same.

Background Art

[0002] PFAS refers to perfluoroalkyl compounds and polyfluoroalkyl compounds, and is a general term for a group of more than about 10,000 types of organofluorine compounds including representative perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). PFAS has both water-repellent and oil-repellent properties, is resistant to heat and chemicals, and hardly decomposes in the natural environment. It has been used in a wide range of fields such as water repellents, surface treatment agents, emulsifiers, fire extinguishing agents, and coating agents since around the 1940s. However, in recent years, PFAS has come to be regarded as problematic because it is persistent and bioaccumulative, and regulatory tightening is progressing particularly in Europe and the United States.

[0003] In recent years, public interest in PFAS has also been growing in Japan, as the presence of PFOS and PFOA in groundwater and public water areas has become apparent. PFOS and PFOA have been designated as monitoring-required items and guideline values have been established, while PFHxS has been designated as an investigation-required item. In addition, as of February 1, 2023, PFOS and PFOA were designated as specified substances under the Water Pollution Control Act, and measures in the event of an accident have been mandated. Furthermore, PFOS and PFOA will be upgraded to standard items for tap water quality in April 2026, and it is highly conceivable that standards for soil will be established in the near future.

[0004] On the other hand, in Japan, there are limited examples of remediation of soil and groundwater contaminated with PFAS compounds, and even overseas, most of the technology is still at the laboratory level. Recent newspaper reports have indicated that PFAS compounds have been found in domestic water sources and tap water, necessitating not only measures at water treatment plants but also investigations and countermeasures for the soil and groundwater sources that supply these substances. As a result, several technologies for remediating soil and groundwater contaminated with PFAS compounds have been proposed. For example, Patent Document 1 proposes a technology for remediating contaminated soil containing PFAS compounds by mixing it with an adsorbent. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-079109 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technology disclosed in Patent Document 1 involves generating a slurry by treating soil contaminated with PFAS in some way, separating sand particles (e.g., 75-500 μm) from the slurry, mixing it with an adsorbent having a particle size equivalent to that of the sand particles, and finally recovering the separated adsorbent as adsorbed material.

[0007] Conventional purification technologies, including those described in Patent Document 1, first involve separating fine particles from the slurry, as mentioned above, and then mixing in an adsorbent. In other words, the separation of sand is an essential step, and this requires equipment, manpower, and time.

[0008] The object of the present invention is to solve the problems of the conventional method, namely, to provide a contaminated soil remediation device and a contaminated soil remediation method that can remove PFAS from contaminated soil without the need for sand separation treatment. [Means for solving the problem]

[0009] The present invention focuses on the fact that by directly adding an adsorbent to unclassified contaminated soil and then treating it with a cyclone, pollutants migrate from the soil to the adsorbent, and the adsorbent and soil are classified, thereby purifying the soil. This invention is based on a novel idea.

[0010] The contaminated soil remediation apparatus of the present invention is an apparatus for remediating contaminated soil containing PFAS, and comprises a mixing tank and a cyclone. The mixing tank generates mixed soil by adding an adsorbent to contaminated soil that has not undergone classification treatment and mixing it, and the cyclone separates the sand from the mixed soil generated in the mixing tank and extracts the adsorbent and fine particles. The cyclone also rotates the mixed soil, pressing the sand down against the inner wall of the cyclone and then discharging it from the lower outlet, while the adsorbent and fine particles on which PFAS have been adsorbed are raised in the center of the cyclone and then discharged from the upper outlet.

[0011] The contaminated soil remediation device of the present invention may also be equipped with a first cyclone and a second cyclone. The first cyclone separates sand from the mixed soil and extracts fine particles. The second cyclone separates non-fine particles from the fine particles and extracts the adsorbent on which PFAS has been adsorbed and the fine particles. The first cyclone causes the sand to descend while pressing it against the inner wall of the cyclone and discharges it from the lower outlet, while the fine particles rise in the center of the cyclone and are discharged from the upper outlet. The second cyclone causes the non-fine particles (but with a particle size larger than the fine particles) of the fine particles to descend while pressing them against the inner wall of the cyclone and is discharged from the lower outlet, while the adsorbent and the fine particles of the fine particles rise in the center of the cyclone and are discharged from the upper outlet.

[0012] The contaminated soil remediation apparatus of the present invention may further include a sedimentation tank and a dewatering device. The sedimentation tank stores water containing adsorbent and fine particles discharged from the upper outlet, and the dewatering device removes water from the fine particles that have settled in the sedimentation tank.

[0013] The soil remediation method of the present invention is a method for remediating contaminated soil using the soil remediation apparatus of the present invention, and comprises a mixed soil generation step and a separation step. In the mixed soil generation step, a mixed soil is generated by adding an adsorbent to unclassified contaminated soil using the mixing tank of the soil remediation apparatus. In the separation step, the sandy component is separated from the mixed soil generated in the mixing tank using the cyclone of the soil remediation apparatus, and the adsorbent and fine particles are extracted. [Effects of the Invention]

[0014] The contaminated soil remediation apparatus and contaminated soil remediation method of the present invention have the following effects. (1) Compared to incineration at an off-site location, it is possible to purify contaminated soil containing PFAS at a lower cost and with reduced environmental impact. (2) For example, treated excavated soil does not need to be treated as industrial waste and can be reused as fill material, etc. (3) Although it is necessary to procure adsorbents such as powdered activated carbon, the equipment to be prepared can be conventional products, meaning that it can be implemented at low cost and easily. [Brief explanation of the drawing]

[0015] [Figure 1] A block diagram showing the main components of the contaminated soil remediation device of the present invention. [Figure 2] A schematic model diagram showing a cyclone with a lower outlet, an upper outlet, and an inlet. [Figure 3] A block diagram showing the main components of a contaminated soil remediation system equipped with a first cyclone and a second cyclone. [Figure 4] A flowchart showing the main steps of the contaminated soil remediation method of the present invention. Mode for Carrying Out the Invention

[0016] Examples of embodiments of the contaminated soil purification apparatus and contaminated soil purification method of the present invention will be described with reference to the drawings.

[0017] 1. Contaminated Soil Purification Apparatus First, the contaminated soil purification apparatus of the present invention will be described. The contaminated soil purification method of the present invention is a method for purifying PFAS-containing soil (hereinafter simply referred to as "contaminated soil") using the contaminated soil purification apparatus of the present invention. Therefore, the contaminated soil purification apparatus of the present invention will be described first, followed by the description of the contaminated soil purification method of the present invention. It should be noted that the "contaminated soil" targeted by the present invention is strictly "soil", and thus naturally does not contain large-diameter particles such as gravel.

[0018] FIG. 1 is a block diagram showing the main configuration of the contaminated soil purification apparatus 100 of the present invention. As shown in this figure, the contaminated soil purification apparatus 100 of the present invention comprises a cyclone 110 and a kneading tank 120, and may further comprise a sifter 130, a sedimentation tank 140, a dewaterer 150, a water treatment apparatus 160, and the like.

[0019] Hereinafter, a detailed description will be given for each main element constituting the contaminated soil purification apparatus 100 of the present invention.

[0020] (Sifter) The sifter 130 constituting the contaminated soil purification apparatus 100 is capable of extracting "contaminated soil" by removing gravel from target soil containing gravel, and for example, a vibrating sieve can be used. When the target soil contains no gravel, that is, when the target soil is contaminated soil as it is, the contaminated soil purification apparatus 100 can be configured without providing the sifter 130.

[0021] (Kneading Tank) The mixing tank 120, which constitutes the contaminated soil remediation device 100, mixes contaminated soil, water, and adsorbent. More specifically, contaminated soil and water are introduced into the tank of the mixing tank 120, and then the adsorbent is added and mixed. However, the contaminated soil introduced into the mixing tank 120 is assumed to be in a state that has not undergone any prior classification treatment (excluding the removal of gravel by the sieve 130). Various materials capable of adsorbing PFAS can be used as adsorbent, including activated carbon (including granular activated carbon and powdered activated carbon), ion exchange resin, mineral-based adsorbent, and special polymers. For convenience, the slurry-like substance produced by the mixing in the mixing tank 120 will be referred to here as "mixed soil."

[0022] (Cyclone) The cyclone 110, which constitutes the contaminated soil remediation device 100, is a device that classifies contaminated soil using centrifugal force, and various types of centrifuges can be used. As shown in Figure 2, the cyclone 110 has a lower outlet 111, an upper outlet 112, and an inlet 113, and the mixed soil introduced from the inlet 113 is separated and discharged from the lower outlet 111 and the upper outlet 112. More specifically, when the mixed soil generated by the mixing tank 120 is introduced from the inlet 113, the cyclone 110 swirls the mixed soil. As a result, the sandy portion of the mixed soil, which has a relatively high specific gravity, is pressed against the inner wall of the cyclone 110 and descends, and is finally discharged from the lower outlet 111.

[0023] On the other hand, the "fine particles" of the mixed soil, which have a relatively low specific gravity, and the adsorbent rise towards the upper outlet 112 while rotating spirally in the center of the cyclone 110, as shown in Figure 2, and are eventually discharged from the upper outlet 112. Here, the fine particles can be, for example, particles with a particle size of less than 75 μm.

[0024] Furthermore, as the cyclone 110 swirls the mixed soil, the PFAS contained in the mixed soil is adsorbed by the adsorbent, and although some of it may remain in the fine particles, there is almost no PFAS left in the sand discharged from the lower outlet 111. In other words, the PFAS is transferred to the adsorbent and fine particles by the cyclone 110, and the sand discharged from the lower outlet 111 becomes PFAS-free soil (hereinafter referred to as "treated soil"), and therefore it is sufficient to treat only the adsorbent and fine particles discharged from the upper outlet 112 as industrial waste.

[0025] The contaminated soil remediation device 100 may also be equipped with a cyclone 110 consisting of a first cyclone 110F and a second cyclone 110S. This first cyclone 110F separates sand from the mixed soil and extracts fine particles. More specifically, it swirls the mixed soil produced by the mixing tank 120, discharging the sand, which has a relatively high specific gravity, from the lower discharge port 111, and discharging the fine particles, which have a relatively low specific gravity, from the upper discharge port 112.

[0026] The second cyclone 110S separates "non-fine particulate matter" from the fine particulate matter and extracts "fine particulate matter." More specifically, it swirls the fine particulate matter (including the adsorbent) extracted from the first cyclone 110F, discharging the non-fine particulate matter, which has a relatively high specific gravity, from the lower outlet 111, while discharging the adsorbent and fine particulate matter, which have a relatively low specific gravity, from the upper outlet 112. The second cyclone 110S then transfers the PFAS contained in the fine particulate matter to the adsorbent and fine particulate matter, so the non-fine particulate matter discharged from the lower outlet 111 contains almost no PFAS. The non-fine particulate matter consists of particles with a particle size of 30 μm to 75 μm, while the fine particulate matter consists of particles with a particle size of less than 30 μm.

[0027] (Sedimentation tank) The sedimentation tank 140, which constitutes the contaminated soil remediation device 100, is a device that stores the adsorbent containing PFAS and fine particles (or microparticles) together with water, separated by the cyclone 110, and various thickeners can be used. The adsorbent and fine particles (or microparticles) stored here settle over time, and it is possible to increase the settling rate by adding a coagulating sedimentation agent.

[0028] (dehydrator) The dewatering unit 150, which constitutes the contaminated soil remediation system 100, is a device that removes water from the fine particles (or microparticles) and adsorbent that have settled in the sedimentation tank 140, and can utilize, for example, a filter press. Specifically, the fine particles (or microparticles) and adsorbent that have settled in the sedimentation tank 140 are fed into the dewatering unit 150, and the dewatering unit 150 essentially squeezes out the moisture from the microparticles and adsorbent. The fine particles (or microparticles) and adsorbent from which the water has been removed are then transported off-site for disposal as industrial waste.

[0029] (Water treatment equipment) The water treatment device 160, which constitutes the contaminated soil remediation device 100, is a device that treats the water (hereinafter simply referred to as "removed water") removed from the fine particles (or microparticles) and adsorbent by the dewaterer 150, and can be, for example, a water treatment device 160 having activated carbon. The removed water discharged by the dewaterer 150 may contain PFAS, and therefore it is preferable to remove the PFAS before discharging it from the system or to reuse it as injection water for the mixing tank 120. However, according to the contaminated soil remediation device 100 of the present invention, the adsorbent stored in the sedimentation tank 140 adsorbs the PFAS contained in the water, so the removed water does not contain PFAS, and therefore the contaminated soil remediation device 100 can be constructed without providing a water treatment device 160.

[0030] 2. Methods for remediating contaminated soil Next, the soil remediation method of the present invention will be explained with reference to Figure 4. The soil remediation method of the present invention is a method of remediating contaminated soil using the soil remediation device 100 described above. Therefore, explanations that overlap with those described for the soil remediation device 100 will be avoided, and the explanation will focus mainly on aspects specific to the soil remediation method of the present invention. In other words, anything not described here is the same as what was explained in "1. Soil Remediation Device".

[0031] Figure 4 is a flowchart showing the main steps of the contaminated soil remediation method of the present invention. When remediating contaminated soil using the contaminated soil remediation device 100 of the present invention, first, as shown in this figure, the contaminated soil, adsorbent, and water are mixed in the mixing tank 120 (Step 201 in Figure 4). More specifically, the contaminated soil and water are put into the tank of the mixing tank 120, and then the adsorbent is added and mixed to produce mixed soil. However, the contaminated soil put into the mixing tank 120 is in a state that has not undergone any prior classification treatment (excluding the removal of gravel by the sieve 130).

[0032] Once the mixed soil is generated in the mixing tank 120, the mixed soil is introduced into the cyclone 110. For example, if the cyclone 110 consists of a first cyclone 110F and a second cyclone 110S, the mixed soil is first introduced into the first cyclone 110F, and as the mixed soil is swirled, the sandy portion is discharged from the lower outlet 111 and the fine-grained portion is discharged from the upper outlet 112 (Step 202 in Figure 4). Next, the fine-grained portion (including adsorbent) extracted from the first cyclone 110F is introduced into the second cyclone 110S, and as the fine-grained portion is swirled, the non-fine-grained portion of the fine-grained portion is discharged from the lower outlet 111, and the adsorbent and fine-grained portion of the fine-grained portion are discharged from the upper outlet 112 (Step 203 in Figure 4).

[0033] The discharged adsorbent and fine particles are stored in a sedimentation tank 140 along with water, and the adsorbent and fine particles settle over time (Step 204 in Figure 4). Once the adsorbent and fine particles have settled at the bottom of the sedimentation tank 140, the settled adsorbent and fine particles are put into a dewaterer 150, which removes the water from the adsorbent and fine particles (Step 205 in Figure 4). The removed water obtained from the dewaterer 150 is then treated by a water treatment device 160 (Step 206 in Figure 4). Meanwhile, the water-free fine particles and adsorbent are transported off-site for disposal as industrial waste (Step 207 in Figure 4).

[0034] 3. Test Results The inventors of the present invention have conducted tests to confirm the effects of the present invention. The details and results of these tests are described below.

[0035] The test was conducted using the following procedure. First, the PFOA (soil elution) concentration of the prepared contaminated soil (particle size 212 μm or less) was measured. Next, an adsorbent (powdered activated carbon with a particle size of 1 to 30 μm) and water were added to the contaminated soil to create a slurry sample. This slurry sample (mixed soil) was then fed into a small cyclone and classified at the classification point of 30 μm. Finally, PFOA (soil elution) analysis was performed on the classified soil particles of 30 μm or larger (sandy + non-fine particle content) and compared with the target treatment concentration (50 ng / L).

[0036] Measurements of the contaminated soil before cyclone treatment revealed a PFOA (soil elution) level of 3,700 ng / L. In contrast, the PFOA level in the slurry sample treated with the cyclone was reduced to 12 ng / L, significantly below the target treatment concentration (50 ng / L). This confirms that, through the process of mixing the contaminated soil with an adsorbent and classifying it in cyclone 110, the PFOA adsorbed on the contaminated soil is adsorbed by the adsorbent and discharged from the upper outlet 112 along with particles smaller than 30 μm (fine particles). In other words, it was confirmed that PFOA is removed from the treated soil (soil larger than 30 μm) discharged from the lower outlet 111, making it possible to meet the purification target value (50 ng / L). [Industrial applicability]

[0037] The contaminated soil remediation apparatus and method of the present invention can be used at operational sites (or former operational sites) and illegal dumping sites where PFAS-type organofluorine compounds such as PFOS and PFOA are manufactured, used, discharged, or by-products. Considering that the present invention is extremely beneficial to improving the environment in Japan, it can be said that it is an invention that can be expected to make a significant contribution not only to industrial use but also to society. [Explanation of symbols]

[0038] 100 Contaminated soil remediation device of the present invention 110 (Cyclone of a contaminated soil remediation device) 111 (Cyclone) Lower Outlet 112 (Cyclone) Top Outlet 113 (Cyclone) Inlet 110F (of the cyclones) Cyclone 1 110S (of the Cyclones) Second Cyclone 120 (Mixing tank of the contaminated soil remediation equipment) 130 (Sieve for contaminated soil remediation equipment) 140 (Sedimentation tank of the contaminated soil remediation system) 150 (Dewaterer for contaminated soil remediation equipment) 160 (Water treatment equipment for contaminated soil remediation)

Claims

1. A device for purifying contaminated soil containing PFAS, A mixing tank that produces mixed soil by adding an adsorbent to the contaminated soil that has not undergone classification treatment and mixing it, The system includes a cyclone for separating sand from the mixed soil produced in the mixing tank and extracting the adsorbent and fine particles, The cyclone swirls the mixed soil, causing the sand to descend while pressing it against the inner wall of the cyclone, and then discharges it from the lower outlet. The adsorbent material on which the PFAS has been adsorbed, and the fine particles are raised in the center of the cyclone and then discharged from the upper outlet. A contaminated soil remediation device characterized by the following features.

2. A first cyclone separates the sand from the mixed soil and extracts the fine particles, The system comprises a second cyclone that separates the non-fine particles from the fine particles and extracts the adsorbent on which the PFAS is adsorbed and the fine particles from the fine particles, The non-fine particles are larger in diameter than the fine particles. The first cyclone causes the sand to descend while pressing it against the inner wall of the cyclone and then discharges it from the lower outlet, and the fine particles are caused to rise in the center of the cyclone and then discharged from the upper outlet. The second cyclone lowers the non-fine particulate matter while pressing it against the inner wall of the cyclone and then discharges it from the lower outlet, and raises the adsorbent and the fine particulate matter in the center of the cyclone and then discharges them from the upper outlet. The contaminated soil remediation device according to claim 1, characterized by its features.

3. A sedimentation tank for storing water containing the adsorbent and fine particles discharged from the upper outlet, The system further comprises a dewaterer that removes water from the fine particles that have settled in the sedimentation tank, The contaminated soil remediation device according to claim 1, characterized by its features.

4. A method for purifying contaminated soil containing PFAS using a contaminated soil remediation device, The contaminated soil remediation apparatus includes a mixing tank and a cyclone, A mixed soil production step involves using the aforementioned mixing tank to produce mixed soil by adding an adsorbent to the contaminated soil that has not undergone classification treatment, The system includes a separation step of using the cyclone to separate the sand from the mixed soil generated in the mixing tank and extract the adsorbent and fine particles, In the separation step, the mixed soil is swirled to press the sand against the inner wall of the cyclone as it descends and is then discharged from the lower outlet, while the adsorbent material on which the PFAS has been adsorbed and the fine particles are raised in the center of the cyclone and then discharged from the upper outlet. A method for remediating contaminated soil characterized by the following features.

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