JP7221257B2 - Groundwater purification method and underground structure - Google Patents

Description

The present invention relates to a groundwater purification method and an underground structure.

In recent years, a method using anaerobic microorganisms has been proposed as a method for purifying groundwater.
For example, there is a method described in Patent Document 1 as a method for purifying soil and groundwater contaminated with organochlorine compounds. In the method described in Patent Document 1, the soil and aquifer are excavated to fill the nutrient salt of the solid molding mainly composed of linear saturated monocarboxylic acid having 6 or more carbon atoms and the nutrient salt. Using the formed purification wall. The purification wall is installed so as to shield the downstream side of the groundwater that traverses the contaminated part of the soil and groundwater / its diffusion area, and the nutrient salt of the purification wall proliferates and activates the anaerobic microorganisms, A method for decomposing volatile organic compounds in the field is described.

Moreover, there is a method described in Patent Document 2 as a method for cleaning soil contaminated with organic chlorine compounds. In the method described in Patent Literature 2, a well provided upstream of a contaminated area of an aquifer is filled with a finely divided porous powder containing a sustained release nutrient salt. Then, anaerobic microorganisms are propagated in the porous powder in the well, and the porous powder containing nutrient salts and anaerobic microorganisms with sustained release properties is moved from the well to between soil particles in the contaminated area together with groundwater. Clean up contaminated soil by

Further, as a method for denitrifying nitrate nitrogen in waste water by biological treatment with sulfur denitrifying bacteria, a method described in Patent Document 3 has been proposed. In the method described in Patent Document 3, sulfur denitrification is performed in a packed bed obtained by mixing a granular or massive porous mixture containing calcium and/or magnesium carbonate and sulfur as main components with granular or massive Ryukyu limestone. The nitrate nitrogen contained in the waste water is denitrified by passing the waste water containing nitrate nitrogen through the packed bed on which the bacteria are supported and the sulfur denitrifying bacteria are supported.

JP 2005-279394 A Japanese Unexamined Patent Application Publication No. 2008-29929 JP 2014-223612 A

In recent years, contamination of ground water by nitrate nitrogen has become a problem. Further, the contamination of ground water by nitrate nitrogen often covers a wide area. Therefore, it has been demanded to provide a method for easily removing nitrate nitrogen from groundwater even if the contaminated area is extensive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a groundwater purification method capable of easily removing nitrate nitrogen from groundwater even if the contaminated area is wide.
Moreover, this invention makes it a subject to provide the underground structure used for the said groundwater purification method.

The inventor of the present invention has made intensive studies to solve the above problems.
As a result, the present inventors have found that a plurality of structures filled with a filler that dissolves eluted components including sulfur components into groundwater should be scattered in the contaminated area, and have arrived at the present invention.
That is, the present invention relates to the following matters.

[1] A space forming step of forming a plurality of spaces apart from each other in an underground aquifer layer inhabited by microorganisms that remove nitrate nitrogen from groundwater; A structure filled with a filler with a particle size of 5 to 20 mm that dissolves eluted components including sulfur components and calcium components into groundwater , and that dissolves sulfur components at a concentration of 1 to 50 mg / L. a structure forming step to form a structure, and the eluted component eluted from the filler into the groundwater in contact with each structure; and a purification step for activating the metabolism of nitrogen-removing microorganisms . and purifying a purification region extending fan-shaped in plan view from one of the plurality of structures to the downstream side in the direction of groundwater flow while maintaining the oxidation-reduction potential in a reduced state, and A region with a lower concentration of nitrate nitrogen than the concentration of nitrate nitrogen in the groundwater on the upstream side of the structure, which is not affected by the components eluted from the filling material, is generated in the purification region, and is affected by the components eluted from the filler. A region with a higher sulfate ion concentration than the sulfate ion concentration in the structure upstream groundwater without calcium ion concentration is generated in the purification region, and the calcium ion concentration in the structure upstream groundwater that is not affected by the components eluted from the filler material. A method for purifying groundwater , wherein a region having a higher calcium ion concentration is generated in the purification region .
[2] The method for purifying groundwater according to [1] , wherein the purification area is fan-shaped with a radius of 10 m or more and 100 m or less in plan view on the downstream side in the direction of groundwater flow.
[3] The groundwater purification method according to [1] or [2], wherein the oxidation-reduction potential of the groundwater in the purification region is -150 mV to -400 mV.
[4] Groundwater purification according to any one of [1] to [3], wherein the microorganisms include sulfur-oxidizing denitrifying bacteria that remove the nitrate nitrogen from the groundwater in an anaerobic atmosphere. Method.
[5] The method for purifying groundwater according to [4] , wherein the microorganisms further include sulfur-reducing bacteria that remove organic matter from the groundwater.

[6] In the structure forming step, the shortest distance between the outer surfaces of adjacent structures is 100% to 300% of the outer shape of each structure [1]- [5] The method for purifying groundwater according to any one of items.
[7] In the structure forming step, the plurality of structures are arranged in two or more rows to form a line connecting the centers of the plurality of structures forming the row and other adjacent rows. [1] to [6] , characterized in that the lines connecting the centers of the plurality of structures in which the The method for purifying groundwater according to any one of the items.
[8] The method for purifying groundwater according to any one of [1] to [7], wherein the groundwater in contact with the structure has a nitrate nitrogen concentration of 1 to 100 mg/L.
[9] The method for purifying groundwater according to any one of [1] to [8] , wherein the elution component contains an organic substance.

[10] A particle size of 5 to 20 mm that is spaced apart from each other in an underground aquifer layer inhabited by microorganisms that remove nitrate nitrogen from groundwater and that elutes eluted components including sulfur components and calcium components into groundwater. The filling material comprises a plurality of structures filled with a filling material that elutes a sulfur component at a concentration of 1 to 50 mg / L, and the eluted component eluted from the filling material into the groundwater in contact with the structures. has a function of purifying by activating the metabolism of microorganisms that inhabit the underground aquifer layer and remove nitrate nitrogen from the groundwater using the elution component, and passes through the structure Regarding the groundwater that has flowed out of the structure and the groundwater that has passed through the structure in contact with the surface of the structure, starting from one of the plurality of structures, in a plan view downstream in the direction of groundwater flow Regarding the purification area spreading in a fan shape, the nitrate nitrogen is purified from the nitrate nitrogen concentration in the groundwater on the upstream side of the structure, which is purified while maintaining the redox potential in a reduced state and is not affected by the components eluted from the filler. A region with a low sulfate ion concentration is generated in the purification region, and a region with a sulfate ion concentration higher than the sulfate ion concentration in the groundwater on the upstream side of the structure that is not affected by the components eluted from the filling material is generated in the purification region. characterized by having a function to purify while generating in the purification area a region having a higher calcium ion concentration than the calcium ion concentration of the groundwater on the upstream side of the structure that is not affected by the components eluted from the filling material. underground structure.
[11] The underground structure according to [10], wherein the purification area is fan-shaped with a radius of 10 m or more and 100 m or less in plan view on the downstream side in the direction of groundwater flow.
[12] The underground structure according to [10] or [11], which has a function of making the oxidation-reduction potential of groundwater in the purification area -150 mV to -400 mV.
[13] The underground structure according to any one of [10] to [12], wherein the eluted component contains an organic matter.
[14] The microorganism according to any one of [ 10] to [ 13], wherein the microorganism contains a sulfur-oxidizing denitrifying bacterium that removes the nitrate nitrogen from the groundwater in an anaerobic atmosphere. underground structure.
[15] The underground structure according to [14], wherein the microorganisms further include sulfur-reducing bacteria that remove organic matter from the groundwater.
[16] Any one of [ 10] to [ 15] , wherein the shortest distance between outer surfaces of adjacent structures is 100% to 300% of the outer shape of each structure. underground structure as described in paragraph 1.
[17] A plurality of structures are arranged in two or more rows, and a line connecting the centers of the plurality of structures forming a row and a line connecting the centers of the plurality of structures forming the adjacent row The line connecting the centers is spaced apart at regular intervals with a dimension of 100% to 500% of the outer shape of each of the structures [ 10] to [ 16] . underground structure.

In the method for purifying groundwater of the present invention, a filler having a particle size of 5 to 20 mm for eluting eluted components including sulfur components and calcium components into groundwater, wherein the filler is capable of eluting sulfur components at a concentration of 1 to 50 mg/L. The components eluted into the groundwater from each filled structure activate the metabolism of microorganisms that inhabit the underground aquifer layer and remove nitrate nitrogen from the groundwater using the components eluted. Therefore, according to the groundwater purification method of the present invention, the metabolism of microorganisms is promoted in a wide area downstream of each structure in the underground aquifer layer, the nitrate nitrogen in the groundwater is removed, and the groundwater is purified. Purified.

In addition, by using the method for purifying groundwater of the present invention, for example, compared with the case where contaminated water pumped up from an underground aquifer layer is passed through a packed bed carrying microorganisms that remove nitrate nitrogen, the amount of contamination is reduced. Nitrate nitrogen in groundwater can be easily removed even if the area is wide. In addition, in the method for purifying groundwater of the present invention, there is no need to form a large-scale structure unlike, for example, a case where a wall-like structure is provided by continuously forming structures in a plan view. can form an underground structure.

It is a plane schematic diagram for demonstrating an example of the underground structure of this embodiment. FIG. 3 is a plan view showing a columnar structure arranged in an underground aquifer layer in A city and its surrounding area; FIG. 3 is a plan view showing a columnar structure arranged in an underground aquifer layer in A city and its surrounding area;

Hereinafter, the method for purifying groundwater and the underground structure of the present invention will be described in detail. In addition, this invention is not limited only to embodiment shown below.
"underground structure"
FIG. 1 is a schematic plan view for explaining an example of the underground structure of this embodiment. The arrows in FIG. 1 indicate the direction of groundwater flow.
The underground structure 10 of this embodiment biologically purifies groundwater. An underground structure 10 shown in FIG. 1 includes a plurality of columnar structures (structures) 1a, 1b, 1c, 1d, 1e, 1f, and 1g. The columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g are arranged discontinuously and separated from each other in the underground aquifer layer.

Each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g may have any structure as long as the eluted component can be eluted from the filler 2 into the groundwater in contact with each columnar structure. Specifically, each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g is desirably permeable and has a structure through which groundwater can pass. may That is, each columnar structure may have a structure in which groundwater does not enter the interior and groundwater flows while contacting the surface of the structure.

The shape of each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g may be a columnar shape, and the planar shape and cross-sectional shape are not particularly limited. For example, the planar shape of each columnar structure may be circular as shown in FIG. 1, or may be elliptical, oval, rectangular, or the like. Also, the plurality of columnar structures may have different shapes, some of them may have the same shape, or, as shown in FIG. 1, all of them may have the same shape. Each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g shown in FIG. 1 has a cylindrical shape with a substantially uniform diameter from the top surface to the bottom surface.

The number of columnar structures forming the underground structure 10, the distance between adjacent columnar structures, and the arrangement of a plurality of columnar structures depend on the flow velocity of groundwater, the amount and distribution of nitrate nitrogen in the groundwater, and the topography of the place of installation. It can be determined as appropriate depending on the
For example, as shown in FIG. 1, a plurality of columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g are arranged in a row or in a direction intersecting with the direction of groundwater flow in a plan view and spaced apart at a predetermined pitch. A plurality of rows (two rows in FIG. 1) may be arranged side by side. When arranging a plurality of columnar structures in two or more rows, as shown in FIG. 1, the columnar structures forming adjacent rows are preferably arranged in a zigzag pattern.

Further, for example, as shown in FIG. 1, when all of the plurality of columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g are cylindrical with the same shape and are arranged at equal intervals, adjacent The shortest distance between the outer surfaces of the columnar structures is preferably 100% to 300% of the outer shape of each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f and 1g. Specifically, the shortest distance between the outer surfaces of adjacent columnar structures may be about 10 m.
Further, as shown in FIG. 1, all of the plurality of columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g are cylindrical with the same shape, and are spaced apart in two or more rows (two rows in FIG. 1). When arranged side by side, a line connecting the centers of multiple columnar structures forming a row (e.g., 1a, 1b, 1c, 1d) and multiple columnar structures forming adjacent rows It is preferable that the lines connecting the centers of the objects (eg, 1e, 1f, 1g) are spaced apart at regular intervals with a dimension of 100% to 500% of the outer shape of each columnar structure. Specifically, a line connecting the centers of a plurality of columnar structures forming a row and a line connecting the centers of a plurality of columnar structures forming an adjacent row are spaced apart by about 10 m. may be

Each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g is filled with a filling material 2 that dissolves eluted components including sulfur components into ground water. The filler 2 is preferably granular or lumpy. As the filler 2, for example, a porous material containing an eluted component may be used, or a porous base material impregnated with an eluted component and adhered thereto may be used. Further, as the filler 2, a material obtained by encapsulating an eluted component in a resin such as polyvinyl alcohol and processing it so as to be gradually eluted may be used. As the filler 2, only one kind may be used, or two or more kinds may be mixed and used. When two or more types of fillers 2 are used, for example, a filler that elutes a sulfur component and a filler that elutes an organic matter may be mixed and used.

Examples of the porous material containing an eluted component include a porous material that elutes elemental sulfur, which is a sulfur component, and the like. As a porous material from which elemental sulfur is eluted, there is, for example, a material obtained by mixing equal amounts of sulfur and a calcium component, solidifying the mixture, and adjusting the particle size to 5 to 20 mm.

The eluted component may contain a sulfur component, and may contain an organic substance.
The sulfur component contained in the eluted component includes, for example, elemental sulfur. When the eluted component is S (sulfur), the concentration of the eluted component in the filler is preferably 1 to 50 mg/L, more preferably 1 to 10 mg/L. When the concentration of the S (sulfur) component in the filler is 1 mg/L or more, the metabolism of microorganisms is further promoted in a wide area downstream of each columnar structure in the underground aquifer layer. Moreover, when the concentration of the S (sulfur) component in the filler is 50 mg/L or less, it is possible to prevent the eluted component from contaminating the underground aquifer.
Organic substances contained in the eluted components include saccharides, alcohols, organic acids, and the like.

"Groundwater Purification Method"
Next, an example is given and demonstrated about the groundwater purification method of this embodiment.
In the groundwater purification method of this embodiment, first, a plurality of spaces are formed in the underground aquifer layer so as to be separated from each other. The method for forming the space is not particularly limited, and can be formed by a known method, and can be appropriately determined according to the size and number of the spaces, the conditions of the place where the spaces are to be formed, and the like.
Next, the spaces are each filled with a filling material 2 for eluting an eluted component containing a sulfur component into the ground water. As a result, the plurality of columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g are spaced apart from each other (structure forming step).

Next, the components eluted from the filling material 2 into the groundwater in contact with the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g cause metabolism related to the denitrification reaction of microorganisms that remove nitrate nitrogen. Activate (cleaning process).
When each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g has water permeability, groundwater and each columnar structure are separated from each other by the groundwater passing through each columnar structure and the surface of each columnar structure. contact by moving in contact with When each columnar structure does not have water permeability, the groundwater and each columnar structure come into contact with each other as the groundwater moves in contact with the surface of each columnar structure.

In this embodiment, the microorganisms that remove nitrate nitrogen from groundwater are microorganisms that originally inhabit the underground aquifer layer, and use the eluted components eluted from the filler 2 . The function of removing nitrate nitrogen from groundwater by microorganisms may be a function obtained by only one type of microorganism, or a function obtained by combining a plurality of types of microorganisms with different characteristics. Specifically, microorganisms that remove nitrate nitrogen from groundwater include a combination of multiple species of bacteria, including sulfur-oxidizing denitrifying bacteria, which are autotrophic bacteria that commonly inhabit silt clay layers. . In addition to the sulfur-oxidizing denitrifying bacteria described above, the plurality of types of bacteria may include sulfur-reducing bacteria that reduce compounds such as sulfuric acid.

In order to remove nitrate denitrification from groundwater in an anaerobic atmosphere, the multiple types of bacteria described above are activated by keeping the redox potential of the groundwater in a reduced state of -150 mV to -400 mV. .

The sulfur-oxidizing denitrifying bacteria oxidize elemental sulfur, which is one of the sulfur components, which is poorly soluble in water, and convert it into a compound such as sulfuric acid, which is then eluted from the filling material 2 into groundwater as an eluted component. In addition, sulfur-oxidizing denitrifying bacteria extract oxygen molecules necessary for oxidation of sulfur components from nitrate nitrogen, and convert nitrate nitrogen into nitrogen gas. In this way, the sulfur-oxidizing denitrifying bacteria remove nitrate nitrogen from groundwater and use the energy of converting the nitrate nitrogen into nitrogen gas to act and proliferate. Therefore, the sulfur-oxidizing denitrifying bacteria proliferate more in places where the sulfur component eluted from the filling material 2 can be utilized more. For example, when each columnar structure 1a, 1b, 1c, 1d, 1e, 1f, and 1g has water permeability, sulfur-oxidizing denitrifying bacteria enter each columnar structure due to the inflow of groundwater into each columnar structure. It enters and proliferates in each columnar structure using the sulfur component eluted from the filler material 2 .

Compounds such as sulfuric acid produced by oxidation of sulfur components by sulfur-oxidizing denitrifying bacteria include sulfuric acid, thiosulfuric acid, sulfurous acid, and the like.
Compounds such as sulfuric acid eluted from the filler 2 flow downstream of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g by groundwater. In the downstream areas of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g, the groundwater continues to be reduced. For this reason, in the downstream area of each columnar structure, oxygen is removed from compounds such as sulfuric acid by sulfur-reducing bacteria that originally inhabit the area, and they are reduced to reducing sulfur compounds (S ^2- , thiosulfuric acid, sulfurous acid, etc.). be done.
The produced reducing sulfur compounds are used again for removal of nitrate nitrogen from groundwater by sulfur-oxidizing denitrifying bacteria.

Sulfur-reducing bacteria use organic substances when reducing compounds such as sulfuric acid to convert them into reducing sulfur compounds. For the reduction of compounds such as sulfuric acid by the sulfur-reducing bacteria, organic substances originally present in the soil where the sulfur-reducing bacteria live are used. When the filling material 2 elutes an elution component containing an organic matter, the organic matter eluted from the filling material 2 may be used as the organic matter utilized by the sulfur-reducing bacteria. Examples of organic substances used by sulfur-reducing bacteria include sugars, alcohols, organic acids, etc., and are determined according to the type of sulfur-reducing bacteria.

The effect of removing nitrate nitrogen in the groundwater obtained by the method for purifying groundwater of the present embodiment is the area of about 100 m downstream of each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g (hereinafter referred to as " It is also known as "purification area".).
The purification area is fan-shaped starting from one of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g (for example, 1a) and spreading downstream in the direction of groundwater flow. is preferred. Nitrate nitrogen in the groundwater can be removed over a wider area by expanding the purification area in a fan shape.
When the purification area spreads in a fan shape, the radius of the fan shape (the distance from the center of the columnar structure to the purification area on the downstream side) is preferably 10 m or more, more preferably 50 m or more, for example. When the radius of the sector is equal to or greater than the above lower limit, nitrate nitrogen in groundwater can be easily removed over a wider range. In addition, it is easy to reduce the number of columnar structures to be arranged. The upper limit of the radius of the sector is preferably 100 m or less, although the larger the better.
The radius of the sector can be adjusted by the groundwater flow rate, the amount of nitrate nitrogen in the groundwater, the type of the filler 2, the concentration of the sulfur component eluted from the filler 2, and the like.
In addition, the radius of the sector may be less than 10 m, or may be negative. Here, the fact that the radius of the fan shape is negative means that the purification area extends to the upstream side of the columnar structure in the direction of groundwater flow. An example of a negative sector radius is -5 m.

When the purification region spreads in a fan shape, the central angle of the fan shape is, for example, preferably 20 to 120°, preferably 40 to 90°. When the central angle of the sector is equal to or greater than the above lower limit, nitrate nitrogen in groundwater can be easily removed over a wider range. When the central angle of the sector is equal to or less than the above upper limit, it is easy to reduce the concentration of nitrate nitrogen in the direction of groundwater flow.
The central angle of the sector can be adjusted according to the type, shape, etc. of the columnar structure.

The groundwater purification method of the present embodiment is suitably used when the concentration of nitrate nitrogen in groundwater in contact with each of the columnar structures 1a, 1b, 1c, 1d, 1e, 1f, and 1g is 1 to 100 mg/L. and more preferably 1 to 20 mg/L.

In addition, when the elution component eluted from the filler 2 into the groundwater contains organic matter, the purification process is performed to remove the organic matter from the groundwater using the elution component (such as the above-mentioned sulfur-reducing bacteria) Metabolism of microorganisms. is sometimes activated. In this case, nitrate nitrogen is removed from groundwater, and organic matter is also removed.
In the method for purifying groundwater of the present embodiment, the oxidation-reduction potential of groundwater is -150 to An anaerobic condition of -400 mV is preferred.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the present invention is not limited only to the following examples.
FIG. 2 is a plan view showing a columnar structure 1 arranged in an underground aquifer layer in A City and its surrounding area. The columnar structure 1 shown in FIG. 2 was formed by the method shown below.

First, in the underground aquifer layer, a substantially oval space with a length of 3.7 m and a width of 1.5 m in a plan view and a height of 4.7 m is formed with the direction of flow of groundwater and the direction of the width being approximately parallel. bottom. Next, the space was filled with Batyllock (trade name: registered trademark, manufactured by Nippon Steel & Sumikin Engineering Co., Ltd.) adjusted to a particle size of 5 to 20 mm. Thus, a columnar structure 1 having water permeability was formed.
Bacillus rock is obtained by mixing equal amounts of sulfur and calcium components and solidifying them.
In the vicinity of the columnar structure 1 filled with bacillus, the concentration of calcium ions and bicarbonate ions eluted from the calcium component tends to increase.

Nitrate nitrogen contained in the groundwater sampled from the observation well was measured as the nitrate nitrogen concentration (mg/L) in the groundwater one year after the columnar structure 1 was formed. Observation positions (observation wells) for nitrate nitrogen concentrations in groundwater are indicated by circles in FIG. In addition, the numerical values written around the circles in FIG. 2 are the measured concentrations of nitrate nitrogen in the groundwater.
As shown in FIG. 2 , the concentration of nitrate nitrogen in the groundwater was lower in a wide area downstream of the columnar structure 1 than in the upstream area of the columnar structure 1 .

Next, FIG. 3 shows a plan view showing a region in which the number of observation wells in FIG. 2 is increased. Observation wells A1, A2, A3, A4, B, C2, C4, C5 in FIG. 3 represent the same observation wells as in FIG.
A virtual line P1 is a straight line connecting the observation well A2 and the center of the columnar structure 1 toward the downstream side of the groundwater flow direction. Observation wells A2, A4, B, C2 and C4 are located on imaginary line P1. The observation well C1 is positioned 20 m in the +X direction and 50 m in the +Y direction from the center of the columnar structure 1 . The observation well C3 is positioned 90 m in the +X direction and 50 m in the +Y direction from the center of the columnar structure 1 . The observation well C6 is positioned 90 m in the +X direction and 100 m in the -Y direction from the center of the columnar structure 1. As shown in FIG.

The shaded area in FIG. 3 represents the range (purification area) where the purification reaction is progressing. The purification region spreads in a fan shape with an angle θ as the central angle.
A virtual line Q1 is a tangent line connecting the observation well C3 and the outer edge of the columnar structure 1 nearer to the +Y direction.
A virtual line Q2 is a tangent line connecting the observation well C5 and the outer edge of the columnar structure 1 near the -Y direction.

The radius of the sector representing the cleaning area in FIG. 3 was 103 m.
The central angle of the sector representing the cleaning area in FIG. 3 was 58°.

Table 1 shows the nitrate nitrogen concentration (mg/L), sulfate ion concentration (mg/L), calcium ion concentration ( mg/L), hydrogen carbonate ion concentration (mg/L).

As shown in Table 1, in the observation well B located near the center of the columnar structure 1, the nitrate nitrogen concentration was low, and the sulfate ion concentration, calcium ion concentration, and bicarbonate ion concentration were high. This means that in the observation well B, the removal of nitrate nitrogen (purification reaction) by the filling material (bacillus rock) is progressing. In addition, it means that a sulfur component and a calcium component are eluted from the filler.
The concentration of nitrate nitrogen was higher than 2.0 mg/L in the upstream area (observation wells A1, A2, and A3) in the direction of groundwater flow from the columnar structure 1. In addition, the sulfate ion concentration was 5.0 mg/L or less in the upstream area of the groundwater flow direction from the columnar structure 1 . This means that the oxidation reaction of the sulfur component by the sulfur-oxidizing denitrifying bacteria is not progressing.
In observation well A4, the sulfate ion concentration, calcium ion concentration, and bicarbonate ion concentration were high. This means that the vicinity of the columnar structure 1 is likely to be affected by components eluted from the filler.
In observation wells C2, C4, and C5, the concentration of nitrate nitrogen was lower than that in the upstream area. This means that the purification reaction is progressing in the downstream area of the groundwater flow direction from the columnar structure 1 . In addition, in observation wells C2, C4, and C5, the sulfate ion concentration was higher than that in the upstream area. This means that the oxidation reaction of the sulfur component by the sulfur-oxidizing denitrifying bacteria is progressing.
In the observation well C6, the concentration of nitrate nitrogen was higher than that in the upstream area. This means that the effect of removing nitrate nitrogen by the columnar structure 1 is not obtained in the observation well C6.
The reason why the concentration of nitrate nitrogen is higher in the observation wells C1 and C3 than in the upstream area is considered to be due to the influence of the nitrate nitrogen-containing fertilizer being sprayed upstream of the observation wells C1 and C3.

As shown in FIG. 3 and Table 1, the concentration of nitrate nitrogen in the groundwater was lower in a wider region downstream than the columnar structure 1 compared to the upstream region of the columnar structure 1 .
In addition, the concentration of sulfate ions in the groundwater was higher in a wider area downstream than the columnar structure 1 compared to the upstream area of the columnar structure 1 .
From these results, it was found that the columnar structure 1 can easily remove nitrate nitrogen from groundwater even if the contaminated area is wide.

1, 1a, 1b, 1c, 1d, 1e, 1f, 1g... columnar structures (structures), 2...
Filler 10: Underground structure A1, A2, A3, A4, B, C1, C2, C3, C4, C5, C6: Observation well, P1, Q1, Q2: Virtual line.

Claims (17)

a space forming step of forming a plurality of spaces apart from each other in an underground aquifer layer inhabited by microorganisms that remove nitrate nitrogen from groundwater; A structure that forms a structure filled with a filler having a particle size of 5 to 20 mm that dissolves eluted components including sulfur components and calcium components into groundwater , and that dissolves sulfur components at a concentration of 1 to 50 mg/L. an object forming process;
The eluted components eluted from the filler into the groundwater in contact with each structure promote the metabolism of microorganisms that inhabit the underground aquifer layer and remove nitrate nitrogen from the groundwater using the eluted components. an activating purification step;
With regard to the groundwater that has flowed out of the structure after passing through the structure and the groundwater that has passed through the structure while being in contact with the surface of the structure, the flow of groundwater originates from one of the plurality of structures. Purification is performed while maintaining the oxidation-reduction potential in a reduced state for the purification region that spreads in a fan shape in plan view on the downstream side of the direction ,
creating a region in the purification region where the concentration of nitrate nitrogen is lower than the concentration of nitrate nitrogen in the underground water on the upstream side of the structure that is not affected by the components eluted from the filling material;
generating a region in the purification region having a higher sulfate ion concentration than the sulfate ion concentration in the groundwater on the upstream side of the structure that is not affected by the components eluted from the filling material;
A method of purifying groundwater, wherein a region having a higher calcium ion concentration than the calcium ion concentration of the groundwater on the upstream side of the structure, which is not affected by the components eluted from the filling material, is generated in the purification region while purifying the groundwater. 2. The method for purifying groundwater according to claim 1, wherein the purification area is fan-shaped with a radius of 10 m or more and 100 m or less in plan view on the downstream side in the direction of groundwater flow. 3. The method of purifying groundwater according to claim 1, wherein the oxidation-reduction potential of the groundwater in the purification area is -150 mV to -400 mV. The method for purifying groundwater according to any one of claims 1 to 3, wherein the microorganisms include sulfur-oxidizing denitrifying bacteria that remove the nitrate nitrogen from the groundwater in an anaerobic atmosphere. . 5. The groundwater purification method according to claim 4, wherein the microorganisms further include sulfur-reducing bacteria that remove organic matter from the groundwater. Claims 1 to 5 , characterized in that, in said structure forming step, the shortest distance between outer surfaces of adjacent structures is set to a dimension of 100% to 300% of the outer shape of each said structure. The method for purifying groundwater according to any one of . In the structure forming step, the plurality of structures are arranged in two or more rows, a line connecting the centers of the plurality of structures forming the rows, and the plurality of adjacent rows forming the other rows. 7. The line connecting the centers of the structures is spaced apart at regular intervals with a dimension of 100% to 500% of the outer shape of each structure. The method for purifying groundwater according to the item. The method for purifying groundwater according to any one of claims 1 to 7, wherein the concentration of nitrate nitrogen in the groundwater contacting the structure is 1 to 100 mg/L. The method for purifying groundwater according to any one of claims 1 to 8 , wherein the eluted component contains an organic substance. A filling material with a particle size of 5 to 20 mm that is spaced apart from each other in an underground aquifer layer inhabited by microorganisms that remove nitrate nitrogen from groundwater and that dissolves eluted components including sulfur and calcium components into the groundwater. comprising a plurality of structures filled with a filler that elutes a sulfur component at a concentration of 1 to 50 mg / L ,
The eluted components eluted from the filler into the groundwater in contact with the structure promote the metabolism of microorganisms that inhabit the underground aquifer layer and remove nitrate nitrogen from the groundwater using the eluted components. It has the function of activating and purifying,
With regard to the groundwater that has flowed out of the structure after passing through the structure and the groundwater that has passed through the structure while being in contact with the surface of the structure, the flow of groundwater originates from one of the plurality of structures. Purification is performed while maintaining the oxidation-reduction potential in a reduced state for the purification region that spreads in a fan shape in plan view on the downstream side of the direction,
creating a region in the purification region where the concentration of nitrate nitrogen is lower than the concentration of nitrate nitrogen in the underground water on the upstream side of the structure that is not affected by the components eluted from the filling material;
generating a region in the purification region having a higher sulfate ion concentration than the sulfate ion concentration in the groundwater on the upstream side of the structure that is not affected by the components eluted from the filling material;
The underground characterized by having a function to purify while generating in the purification area a region with a higher calcium ion concentration than the calcium ion concentration of the groundwater on the upstream side of the structure that is not affected by the eluted components from the filling material. Structure. 11. The underground structure according to claim 10, wherein the purification area is fan-shaped with a radius of 10 m or more and 100 m or less in plan view on the downstream side in the direction of groundwater flow. 12. The underground structure according to claim 10 or 11, having a function of making the oxidation-reduction potential of groundwater in the purification area -150 mV to -400 mV. The underground structure according to any one of claims 10 to 12, wherein the eluted component contains organic matter. The underground structure according to any one of claims 10 to 13 , wherein the microorganisms include sulfur-oxidizing denitrifying bacteria that remove the nitrate nitrogen from the groundwater in an anaerobic atmosphere. . 15. The underground structure of claim 14, wherein the microorganisms further include sulfur-reducing bacteria that remove organic matter from the groundwater. 16. The shortest distance between outer surfaces of adjacent structures is set to a dimension of 100% to 300% of the outer shape of each structure. underground structures. A plurality of structures are arranged in two or more rows, and a line connecting the centers of the plurality of structures forming a row connects the centers of the plurality of structures forming an adjacent row. 17. The underground structure according to any one of claims 10 to 16 , wherein the lines are spaced apart at regular intervals with a dimension of 100% to 500% of the outline of each said structure. .

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