JP7660434B2 - Contaminated soil remediation method - Google Patents

Description

The present invention relates to a method for purifying contaminated soil, for example soil contaminated with harmful chemicals such as volatile organic compounds (VOCs).

A conventional technique for purifying soil with low permeability, where a purification agent is unlikely to diffuse even when injected, is to allow hydrogen to penetrate by molecular diffusion and biodegrade harmful chemicals by the reductive dechlorination reaction of dechlorinating bacteria. More specifically, for example, a rod with an injection device at its tip is inserted into a borehole formed in contaminated soil, and a microbial activator is injected to cut the soil, forming a mixed area such as a disk or cone shape where the soil and microbial activator are mixed, thereby generating hydrogen through the biodegradation reaction of the microbial activator. When the generated hydrogen penetrates by molecular diffusion, harmful chemicals can be biodegraded by the reductive dechlorination reaction of the dechlorinating bacteria (see, for example, Patent Document 1).

JP 2015-071126 A

When purifying a large area of soil by boring and forming mixing areas as described above, it is necessary to form multiple mixing areas, such as disk-shaped areas. In order to diffuse hydrogen throughout the entire area to be purified, it is inevitable that there will be areas where the hydrogen diffusion areas caused by multiple mixing areas, such as disk-shaped areas, overlap. This makes it difficult to improve work efficiency by reducing the number of borings and mixing areas.

The present invention was made in consideration of the above points, and aims to improve the work efficiency when purifying soil by molecular diffusion of hydrogen, etc.

In order to achieve the above objectives,
The present invention relates to
A method for remediating contaminated soil, comprising:
a borehole forming step of forming a borehole;
a region forming process in which an injection device is inserted into the borehole, and while rotating, water is injected at high pressure to cut a planar, slit-shaped region in the soil, and the purification agent is then injected and filled to form a mixed region in which the soil and the purification agent are mixed, and a diffusion region in which a predetermined substance diffuses molecularly around the mixed region;
having
The region forming step is characterized in that the plurality of diffusion regions formed have non-arcuate boundaries and are adjacent to each other and in contact with or overlap each other.

This makes it easy to keep the overlap between adjacent diffusion regions small, reduce the number of drilling operations, and improve the efficiency of the region formation process.

The present invention can improve the work efficiency when purifying soil by molecular diffusion of hydrogen, etc.

FIG. 1 is a perspective view showing a schematic example of an injection device. FIG. 2 is an explanatory diagram showing an example of a unit purification section within a site. FIG. 1 is an explanatory diagram showing an example of the shape and arrangement of purification areas for each borehole within a unit purification section. FIG. 11 is an explanatory diagram showing an example of detection of a mixed region. FIG. 13 is an explanatory diagram of a comparative example showing an example of the arrangement of purification regions when a unit purification section is purified by a plurality of disk-shaped purification regions.

The following describes in detail an embodiment of the present invention with reference to the drawings.

(Schematic configuration of the ejection device 102)
First, referring to FIG. 1, the schematic configuration of an injection device 102 used for purifying contaminated soil will be described. The injection device 102 is provided with a nozzle 102a for injecting jets J in a pair of radial directions that are point symmetrical with respect to the central axis of the injection device 102. The injection device 102 is attached to the tip of a boring rod 101 and inserted into a borehole that has been drilled in advance. While rotating at a constant speed, the injection device 102 injects water at high pressure to cut a planar, slit-shaped area in the soil, for example, like a disk S, and pressurizes and fills the slit with a microbial activator (purifying agent), thereby forming a mixed area in which the soil and the purifying agent are mixed. In addition, by controlling the rotation speed to a predetermined value according to the rotation angle, or by changing the injection speed, injection pressure, and injection flow rate of the high-pressure water, it is possible to form a mixed area such as a planar shape close to a square, as described in, for example, FIG. 12 of Japanese Patent Publication No. 5649052 and related parts thereof. Here, the above-mentioned "surface" does not mean a surface with a thickness of 0 as in mathematics, but means a shape with a thickness that is sufficiently thin compared to the size of the spread. The rotation may include an operation involving a rotational movement around a central axis, such as rotating while changing the rotation speed according to the rotation angle, intermittent rotation, or repeated forward and reverse rotation.

(Overview of purification process)
This section explains the purification of soil by molecular diffusion of hydrogen and other gases.

By using the above-mentioned injection device 102 to inject a microbial activator as a purification agent and form a mixed area in which it is mixed with the soil, it is possible to activate microorganisms present in the ground and generate hydrogen through a biodegradation reaction of the microbial activator. Such microbial activators can include, for example, at least one of nitrogen, phosphorus, and vitamin B12 (cobalamin), or sucrose fatty acid esters, glycerin, soybean oil, water, etc.

The hydrogen generated penetrates relatively easily through low-permeability layers due to molecular diffusion, and permeates around the mixed region, forming a diffusion region. There, microorganisms that exist in the soil and have the ability to biodegrade harmful chemicals (e.g., organic chlorine compounds), such as dechlorinating bacteria such as Dehalococcoides bacteria, become activated and grow, and the harmful chemicals (e.g., organic chlorine compounds) are biodegraded by reductive dechlorination reactions, purifying the soil.

(Specific examples of purification areas)
Specifically, for example, within a boundary 201 of a site to be purified as shown in Fig. 2, the presence or absence and the degree of contamination are determined for each 10m square unit purification section divided by 10m division lines 202, and purification is performed on the area determined as a contaminated soil area 203. Each contaminated soil area 203 is purified by carrying out a borehole formation process of forming 16 boreholes 303 as shown in Fig. 3, and a region formation process of forming a mixing region 301 in which soil and a purification agent are mixed, and a diffusion region 302 in which a predetermined gas diffuses molecularly around the above-mentioned mixing region.

The mixing area 301 is formed in a rectangular shape, such as a square shape, with the borehole 303 at the center, and is arranged vertically and horizontally. In addition, the diffusion area 302 is also formed in a roughly square shape by molecular diffusion of hydrogen and the like around the mixing area 301. Here, the meaning of the square shape of the mixing area 301 and the diffusion area 302 does not necessarily mean a geometrically accurate square, but means that each side is non-arc-shaped, that is, a shape closer to a straight line than an arc, as shown in, for example, FIG. 12 of the above-mentioned Patent Publication No. 5649052. As a result, multiple diffusion areas 302 are adjacent to each other through a non-arc-shaped boundary as shown by the two-dot chain line in FIG. 3, and the overlapping area is kept smaller than when the boundary of the diffusion area is arc-shaped, and the efficiency of the area formation process can be easily improved. In addition, it is easy to prevent or reduce the spread of the mixing area 301 outside the contaminated soil area 203.

Here, geometrically, the distance from each vertex to the portions between the vertices of the four adjacent mixing regions 301 is longer than the distance between the sides of each mixing region 301 and the sides of the diffusion region 302, so this distance from each vertex is considered to be the molecular diffusion distance. In this case, the molecular diffusion range of hydrogen, etc. between the sides of each mixing region 301 and the sides of the diffusion region 302 will exceed the planned area, but this will not result in the diffusion of contamination, and it is considered that purification by the diffusion region 302 can be performed sufficiently and appropriately throughout the entire contaminated soil area 203.

For example, when the mixing area is formed as a circular mixing area 501 as shown in FIG. 5, the area of each circular mixing area 501 is larger than the mixing area 301, but the overlap of the circular diffusion area 502 tends to be large, for example, in the part on the line connecting the centers of adjacent circular mixing areas 501, and the area of the circular mixing area 501 that extends outside the contaminated soil area 203 also becomes large, so the number of boreholes 503 (number of times drilling) tends to increase, and the amount of purification agent used tends to increase.

In contrast, by forming the mixing area 301 as described above so that it is divided by a straight (non-arc) boundary such as a square, it is easy to reduce the number of times drilling and other operations are performed within the contaminated soil area 203, and it is also easy to increase the efficiency of purification. Furthermore, if an area adjacent to the contaminated soil area 203 is not a contaminated soil area, it is also possible to prevent the soil from being cut or the purification agent from being mixed in such an adjacent area inadvertently.

(Other matters)
When a mixed area as described above is formed, in order to increase the accuracy of the extent of the area, the degree of activation of biodegradation and dechlorination reactions can be measured in advance using the soil to be purified, and the distance from the center of the borehole to the boundary of the diffusion area within a specified time can be estimated, and the arrangement pitch of the boreholes can be determined based on the estimated distance.

In addition, instead of the above estimation, or in addition to the estimation, the mixed region may be formed while monitoring the range of the mixed region. Specifically, for example, as shown in FIG. 4, a diffusion region outer edge detection unit 401 and a mixed region outer edge detection unit 402 consisting of a measurement tube, a vibration sensor, a microphone, etc. may be provided at the outer edge of the target diffusion region 302 or mixed region 301, more specifically, at the vertices and sides of each region, and it may be confirmed that the mixed region reaches the position of the mixture region outer edge detection unit 402 but does not reach the position of the diffusion region outer edge detection unit 401. Furthermore, such detection results may be fed back to automatically control the formation of the diffusion region.

As described above, in the purification process in which the diffusion regions are formed by molecular diffusion of gases such as hydrogen and the like to purify the soil, the mixing and diffusion regions are formed so that the multiple diffusion regions have non-arc boundaries and are adjacent to each other or overlap each other, particularly so that each mixing region is square or rectangular. This allows the diffusion regions to be adjacent to each other via non-arc boundaries, and the overlapping of the diffusion regions is smaller than when the boundaries of the diffusion regions are arc-shaped, making it easy to reduce the number of drillings and improve the efficiency of the region formation process. In addition, it is easy to prevent the mixing region 301 from spreading outside the contaminated soil area 203 (beyond the area to be purified), and to ensure that the diffusion region 302 is sufficiently formed within the contaminated soil area 203 (formed beyond the area to be purified).

The purification method in which the above-mentioned diffusion region is formed is not limited to the method of generating hydrogen using microorganisms, but the same effect can be obtained even when the purification agent itself, its components, reaction products, and other substances such as gases and liquids undergo molecular diffusion.

REFERENCE SIGNS LIST 101 Boring rod 102 Injection device 102a Nozzle 201 Boundary of site to be purified 202 10m division line 203 Contaminated soil area 301 Mixing area 302 Diffusion area 303 Borehole 401 Diffusion area outer edge detection unit 402 Mixing area outer edge detection unit 501 Circular mixing area 502 Circular diffusion area 503 Borehole

Claims (6)

A method for remediating contaminated soil, comprising:
a borehole forming step of forming a borehole;
a region forming process in which an injection device is inserted into the borehole and rotated while injecting water at high pressure to cut a slit-shaped area on the surface of the soil, and then a purification agent is injected and filled into the borehole to form a mixed region in which the soil and purification agent are mixed, and a diffusion region in which a predetermined substance diffuses molecularly around the mixed region in a direction along the planar slit-shaped area ;
having
The above-mentioned region formation process is carried out so that the multiple diffusion regions formed have non-arc-shaped boundaries and are adjacent to each other and adjacent to each other, either in contact or overlapping relation, and the multiple mixed regions formed are carried out so that they are neither in contact with each other nor overlapping each other, in accordance with a contaminated soil purification method. The method for remediating contaminated soil according to claim 1,
A method for remediating contaminated soil, wherein the mixing area is a rectangular area. The method for remediating contaminated soil according to any one of claims 1 to 2,
A method for purifying contaminated soil, characterized in that the purification agent is a microbial activator that generates hydrogen through a biodegradation reaction of microorganisms present in the ground, and the diffusion area is an area where the generated hydrogen diffuses molecularly. The method for remediating contaminated soil according to claim 3,
A method for remediating contaminated soil, characterized in that the distance from the center of the borehole to the boundary of the diffusion zone is estimated based on a measurement of the degree of activation of the biodegradation reaction using the soil to be remediated in advance, and the arrangement pitch of the boreholes is determined based on the estimated distance. The method for remediating contaminated soil according to any one of claims 1 to 4,
A method for remediating contaminated soil, characterized in that a detection means for detecting whether or not the purification agent has reached the borehole is located at a predetermined distance from the center of the borehole, and the soil is cut by spraying the purification agent. The method for remediating contaminated soil according to any one of claims 1 to 5,
A method for remediating contaminated soil, characterized in that the mixing area does not extend beyond the area of the soil to be remediated, and the diffusion area is formed to be larger than the area of the soil to be remediated.

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