JP2002200480A - Soil decontamination process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil decontamination process which is used for removing organic matter contained in soil to be treated, with microorganisms and enables uniform decontamination of the whole soil to be treated by widely distributing oxygen over the whole soil to be treated. SOLUTION: This process for removing organic matter contained in to-be- purified soil 1 with microorganisms has a suction stage for sucking out soil pore water in the to-be-treated soil 1 from it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a soil purification method, and more particularly to a soil purification method for removing organic substances contained in soil to be purified using microorganisms capable of decomposing the organic substances.

[0002]

2. Description of the Related Art Conventionally, using this kind of soil purification method,
When trying to decompose and remove organic matter from contaminated soil in a state where the soil gap is filled with moisture such as groundwater, the supply of oxygen from the ground surface is limited by the stagnation of the groundwater and the like, whereby the soil gap becomes in a state of lack of oxygen. It has been known that the activity of decomposing the organic matter by the microorganism is suppressed. Therefore, in order to solve the oxygen deficiency, a pipe or air diffuser for injecting air is buried inside or under the soil, and the air containing oxygen is supplied from the pipe into the soil.

[0003]

However, according to the above-mentioned conventional soil purification method, the bubbles containing oxygen released from the pipes and the air diffusers tend to move vertically upward due to their buoyancy. , Horizontal diffusion does not occur much. In addition, the air bubbles do not spread evenly over the soil gap, but tend to rise in the direction of the ground surface in a relatively large diameter soil gap where entry is easy. Therefore, even if air is supplied from inside or below the soil, the air bubbles pass only through a limited area (passage) vertically above the supply source, and oxygen is supplied uniformly over the entire soil to be purified. Therefore, there is a problem that it is difficult to efficiently decompose the organic matter by the microorganism.

[0004] Accordingly, an object of the present invention is to provide a method for removing organic substances contained in a soil to be purified by using a microorganism to remove oxygen from the soil to be purified by widely spreading oxygen in the soil to be purified. An object of the present invention is to provide a soil purification method for uniformly purifying the entire soil.

[0005]

According to a first aspect of the present invention, there is provided a soil purification method for achieving the above object by using microorganisms to remove organic matter contained in a soil to be purified using a microorganism. The method for purifying soil to be removed is characterized in that the method comprises a suction step of sucking soil pore water in the soil to be purified. Further, in the above-mentioned characteristic means, the suction step may be performed intermittently as described in claim 2.

Alternatively, as described in claim 3,
It may have a supply step of supplying oxygen supply water having a higher dissolved oxygen concentration than the soil pore water sucked in the suction step to the purification target soil, as described in claim 4, In the supply step, the oxygen supply water may be obtained by adding oxygen to the soil pore water, and the suction step and the supply step are performed intermittently as described in claim 5. The fine soil particles contained in the soil pore water may be separated from the soil pore water in the suctioning step, as described in claim 6, as described in claim 7. As described above, the method may include a microorganism addition step of adding the microorganism capable of decomposing the organic matter to the soil to be purified. And these effects are as follows.

First, when aiming at solving the above-mentioned problems, the inventors have set forth a soil in which the soil gap is saturated with water (hereinafter referred to as “soil”).
When air or oxygen was supplied to the saturated soil, the reason why the purification of the purification target soil did not proceed uniformly was considered, and the following hypothesis was made. That is, when supplying gas into the saturated soil, as described above, several gas (bubble) passages are formed, and portions other than the passages do not come into direct contact with the gas. Therefore, when gaseous oxygen is supplied to the saturated soil by aeration, sufficient oxygen is supplied to the soil near the passage, but the oxygen supply to the soil located away from the passage is dissolved in the soil pore water. The resulting oxygen is carried by the movement or diffusion of water. However, the diffusion rate of dissolved oxygen in water is very slow,
Further, generally, since the movement speed of the soil pore water in the saturated soil is very slow, it is almost in a state of staying there.Therefore, before reaching the soil existing in a place away from the path, microbial activity may occur. It is estimated that oxygen has been consumed. As a result, it would be very difficult to provide oxygen to the soil remote from the gas source with conventional methods.

[0008] Based on this hypothesis, if it is possible to secure a path for widely distributing a gas containing oxygen or a liquid rich in oxygen in the above-mentioned soil gap, oxygen will be transferred throughout the soil to be purified. Can be spanned. If oxygen can be spread over the entire soil to be purified, the microorganisms that decompose the organic matter present in the soil to be purified can be activated, so that the entire soil to be purified can be activated. Therefore, it is considered that the decomposition of the organic matter can be promoted to purify the soil to be purified. The inventors of the present invention have conducted intensive studies focusing on such points, and as a result, have come to the present invention.

That is, as described in claim 1,
In a soil purification method for removing organic substances contained in the purification target soil using microorganisms, if a suction step of sucking soil pore water in the purification target soil is provided, compared with the movement of soil pore water such as the groundwater, By suctioning the soil pore water so as to increase the suction speed, a negative pressure is generated based on the difference between the volume of the soil pore water sucked and the volume of the soil pore water that has entered from another area due to the movement, and Fluid (liquid, gas) in the gap between the soils to be purified
Can be promoted to flow from a distance toward the suction point. As a result, a flow can be created in the soil pore water, and soil pore water having a high dissolved oxygen content near the ground surface and in other regions can be moved to other regions. In addition, soil pore water with a large amount of dissolved oxygen passes through fine soil gaps and remote soil gaps where it was difficult to transport oxygen by the conventional method, and is supplied to areas where oxygen supply was difficult. Oxygen can be supplied promptly up to this point. In particular, since it is easy to move soil pore water in the horizontal direction, oxygen can be easily supplied to the deep part away from the ground surface and the area horizontally away from the suction point, Oxygen can be supplied to a region where it was difficult to supply oxygen by a method such as supply aeration.

For the reasons described above, the invention according to claim 1 of the present application is suitable for performing in situ bioremediation in a wide area. Alternatively, even in the case where the purification target is accommodated in a reactor or the like and the purification treatment is performed without performing the treatment in situ, the entire purification target soil contained in the reactor or the like may be similarly used. Oxygen can be supplied efficiently.

As the method of removing organic substances using microorganisms, the above-described method of activating organic substance decomposition by indigenous microorganisms by improving the oxygen supply and the method of externally adding microorganisms capable of decomposing organic substances to be decomposed are employed. can do.

Further, if the suction step is performed intermittently as described in claim 2, the negative pressure generated in the soil gap after the end of the suction processing is used to reduce the oxygen in the atmosphere. The rich air can be drawn in from the soil surface to the deep soil gap. At this time, the air becomes a carrier, and the gaseous oxygen itself contained in the air becomes
Since the pressure in the soil gap penetrates all over the soil gap until it reaches equilibrium with the atmospheric pressure, it is possible to easily supply oxygen to a deep soil gap away from the ground surface or a fine soil gap horizontally separated from the suction point. Can be.

Further, as described in claim 3, in the suction step, the soil pore water is extracted from the soil to be purified, and a negative pressure is formed in the soil gap, and the negative pressure is formed. By performing a supply step of supplying oxygen supply water having a higher dissolved oxygen concentration than the soil pore water sucked in the suction step to the purification target soil, the fluid is actively guided to the soil gap, It can be made easier to flow in the soil gap. still,
If the position where the suction step is performed and the position where the supply step is performed are the same position, the suction step and the supply step may be performed alternately. In this manner, in the suction step, after the soil pore water is drawn into the soil gap, oxygen-rich air is introduced into the soil gap to supply oxygen, and then the oxygen supply with a higher dissolved oxygen concentration is performed. Supply water,
The microorganisms in the soil to be purified can be activated. In this case, the labor for excavating a well or the like for performing the processing can be saved. If the position where the suction step is performed and the position where the supply step is performed are different positions, the suction step and the supply step may be performed alternately or simultaneously, but may be performed simultaneously. It is preferable that the fluid is likely to move in the soil gap.

Further, in supplying the oxygen supply water, in the supply step, oxygen is added to the interstitial water removed from the soil to be purified in the suction step. By obtaining the oxygen supply water as above, the soil pore water can be reused as the oxygen supply water. This eliminates the need to discard the interstitial water taken out of the purification target soil in the suction step, thereby reducing the construction and operation costs of the wastewater treatment facility. At the same time, it is not necessary to separately procure the oxygen supply water,
The cost for collecting and transporting the oxygen supply water can be reduced.

The supply of oxygen to the soil to be purified can be performed continuously, but if the amount of oxygen required for the decomposition of the organic matter is less than the amount of oxygen supplied by the continuous supply, As described in claim 5, the suction step and the supply step may be performed intermittently. Thereby, the processing required for oxygen supply can be saved, and the cost can be reduced. Note that it is preferable that the supply step be performed while the negative pressure in the soil gap generated by performing the suction step exists, because the movement of the oxygen supply water is promoted.

Here, when the organic matter to be removed is highly hydrophobic, it is difficult to dissolve in the interstitial water of the soil, and therefore, the ratio of the organic matter adsorbed on the surface of the fine soil particles is high. In such a case, as described in claim 6, when the fine soil particles contained in the soil pore water are separated from the soil pore water in the suction step, removal in the soil to be purified by microorganisms is performed. Apart from that,
The organic matter can be collected and collected outside the purification target soil. Then, the organic matter attached to the fine soil particles is separated from the soil to be purified in which microorganisms are present, and the microorganisms are brought into contact with the low-concentration organic matter to further reduce the organic matter from the soil to be purified in a short period of time. It can be removed to a concentration. In particular, when the object to be removed is an organic substance that is toxic to microorganisms, it is very effective in that the inhibition of organic substance decomposition activity by microorganisms can be suppressed.

In addition, as described in claim 7, the microorganisms which add microorganisms capable of decomposing the organic matter to the soil to be purified from the outside not only depend on the decomposition of the organic matter to be removed by indigenous microorganisms. By providing a process and promoting the decomposition reaction of the organic matter to be removed by the foreign microorganisms, the soil to be purified can be more efficiently purified. In this case, the microorganism to be added can be arbitrarily selected in relation to the organic substance to be decomposed. For example, microorganisms that have a high rate of decomposition of organic substances to be decomposed,
Microorganisms that are resistant to organic matter at a concentration that inhibits the growth of general microorganisms, and microorganisms that promote the decomposition of organic matter in cooperation with other microorganisms, etc., are preferred. Alternatively, they can be added sequentially according to the purification stage.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an in-situ remediation facility for implementing a soil purification method according to the present invention.

The soil 1 to be purified in which this facility is installed is:
The soil gap near the surface layer is the unsaturated soil 11 that is not saturated with moisture. In this region, oxygen supply in the soil gap is relatively easily performed. This unsaturated soil 1
In the lower layer of 1, there is a saturated soil 12 in which the soil gap is filled with groundwater. In this saturated soil 12 region, the movement of air in the soil gap hardly occurs due to the accumulation of water,
Organic substances are hardly decomposed by microorganisms.

The in-situ remediation equipment includes a collection unit 2 (for example, a pipe or a well having a large number of pores) provided with a water intake unit (not shown) in the saturated soil 12, And a supply section 3 (for example, a pipe or a well with a large number of pores) provided with an injection section (not shown), which are provided separately in the soil 1 to be purified. The collection unit 2 and the supply unit 3 are connected via a liquid storage tank 5 so as to allow gas-liquid circulation. The collection unit 2 and the storage unit 51 of the liquid storage tank 5 are connected by a collection pipe 21. By driving the pump P1, the interstitial water in the saturated soil 12 is sucked from the recovery unit 2 into the liquid storage tank 5. The storage section 51 and the supply section 3 are connected by a supply pipe 31, and the pump P2 is driven to recover the collected liquid 52 stored in the storage section 51.
(Soil interstitial water) is injected into the supply unit 3. In addition, the gas sucked together with the soil pore water from the recovery unit 2 is discharged from a gas vent hole 53 provided in the liquid storage tank 5.

Further, in the saturated soil 12 near the supply section 3, a ventilation section 4 into which air is injected from a pump P3.
(For example, a pipe having a large number of pores) is bored, and air (bubbles) is supplied to the saturated soil 12.

The same number of the recovery unit 2, the supply unit 3, and the ventilation unit 4 may be provided for the soil to be purified, but one of them may be provided at a higher ratio than the other. Often, these installation ratios and base numbers can be determined in consideration of soil quality, purification range, purification depth, and the like.

When the pump P1 of the above-mentioned in-situ remediation facility is driven, the soil pore water in the saturated soil 12 is transferred to the liquid storage tank 5 through the recovery pipe 21 to become a recovered liquid 52. As a result, the soil gap of the saturated soil 12 is in a reduced pressure state as compared with other regions, and water easily flows in from other regions. On the other hand, the recovered liquid 52 flows into the supply unit 3 from the liquid storage tank 5 through the supply pipe 31, and is in a pressurized state as compared with other regions, so that the recovered liquid 52 is distant from the supply unit 3. Easy to penetrate. Therefore, the recovery liquid 52 flows in a substantially horizontal direction from the supply unit 3 toward the recovery unit 2 as shown by an arrow in FIG. At this time, when air is supplied from the ventilation part 4 provided in the vicinity of the part 3, the water flow from the supply part 3 to the collection part 2
A recovery liquid 52 (oxygen supply water) having a higher dissolved oxygen concentration than the soil pore water recovered from the recovery unit 2 flows, and the oxygen supply water permeates over a wide range of the saturated soil 12. By doing so, the soil pore water flowing in the saturated soil 12 becomes an oxygen carrier and reaches every corner of the soil gap.
Can promote the growth and activity of the aerobic microorganisms present in the microorganisms, so that the decomposition of organic substances by the microorganisms is promoted.
The permeation range and speed of the oxygen supply water can also be adjusted by increasing the installation area of the water intake section and the injection section or by adjusting the installation length in the vertical direction.

The microorganisms may be indigenous, but the decomposition of the organic substances proceeds more efficiently by introducing a microorganism having a high ability to decompose the organic substances to be removed from the outside. As a method of introducing the microorganisms, it may be spread on the ground surface and wait for migration to the saturated soil 12,
It may be sent from the supply unit 3 and the ventilation unit 4 to the saturated soil 12 together with the recovered liquid 52 and air.

The supply of the oxygen supply liquid may be continuously performed to form a circulation cycle at all times. However, when the oxygen demand is not so high as to require continuous circulation. The operation cost can be reduced by intermittently circulating the soil pore water.

Further, the diameter of the particles passing through the water intake section is increased to some extent (for example, particles having a size of 75 μm or less are passed), and as shown in FIG. When collected in the tank 5, the supernatant 52 and the soil particles 54 are separated in the storage section 51, and only the supernatant 52 is supplied to the supply section 3 again, the organic matter adsorbed on the soil particles is decomposed by the microorganism. Can be removed from Thereby, by lowering the concentration of the organic matter in the soil to be treated, addition to microorganisms can be reduced, and microbial decomposition can be promoted.

The soil to be purified may be excavated and put into a reactor, or may be treated by installing a pipe at the site without excavation.
Further, when supplying the recovered liquid 52 to the saturated soil 12 again, supplying nutrients preferred by microorganisms that decompose the organic matter to be removed is more effective than the microorganisms.

It should be noted that the pump P1 is driven for a certain period of time to extract soil pore water in the saturated soil 12 from the collecting part 2 and then to stand for a certain period of time. Efficient oxygen supply can be performed. That is, after stopping the pump P1, the soil gap is in a reduced pressure state as compared with other areas, so that it becomes easier to receive fluid from other areas.
If the air is easier to move than the soil pore water that fills the saturated soil 12, oxygen-rich air from the above-ground portion flows into the soil gap after extracting the soil pore water over a wide range, Oxygen is supplied to the microorganism. Thereafter, the groundwater gradually penetrates from other regions of the saturated soil 12 to fill the soil gap with the groundwater. However, if the soil porewater is extracted again, oxygen can be supplied using the air as a carrier. .

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, exemplifying a case where an organic substance to be removed by purification is tar.

A soil to be purified containing tar artificially (tar-impregnated soil) was prepared, and a mixture 62 of this tar-impregnated soil and tar-degrading microorganisms was subjected to an experiment described below.

Example 1 400 of the mixture 62
g was collected and, as shown in FIG. 2, housed in a compacted manner in the storage section 61 of the column 6 having a storage section 61 with a volume of 260 mL. The accommodating portion 61 has 10-20
Sintered stainless steel filters 63, 63 having a pore size of μm
Is attached so that the tar-impregnated soil does not flow out of the storage section 61. Further, a water storage tank 7 provided with a gas vent hole 71 is provided, and the water storage tank 7 and the upper and lower ends of the storage section 61 are connected by water supply pipes 81 and 82, and the liquid supply pump P4 is used to connect the water storage pipes 7 and Forming an aqueous solution circulating path for circulating the aqueous solution, and connecting the water tank 7 and the lower end of the housing portion 61 to the water supply pipe 81.
Was connected to an air supply pipe 9 to form an oxygen supply path from the air pump P5. Thus, an in-situ bioremediation and experimental system simulating a non-slurry soil treatment system in which the soil to be purified was accommodated in a reactor was constructed.

In the aqueous solution circulation system, 0.1% K ₂ HPO ₄
And an aqueous solution containing 0.1% NH ₄ NO ₃ (hereinafter referred to as NP
By flowing the medium, the NP medium was infiltrated in the direction of moving from the lower part to the upper part in the storage part 61 of the column 6, and the soil gap of the tar-impregnated soil was filled with the NP medium.

By driving the liquid feed pump P4, the inside of the accommodation part 61 is moved from the lower part to the upper part by 0.01,
While supplying the NP medium at a flow rate of 0.05 or 0.1 mL / min, the air pump P5 is driven to drive the storage section at a flow rate of 10 mL / min from the air supply pipe 9 to the NP medium. Air was supplied from the lower part of 61 to the upper part. In this way, by simultaneously proceeding with the step of sucking the NP medium from the tar-impregnated soil and the step of supplying the oxygen-enriched NP medium, the NP medium serves as an oxygen carrier in the storage section 61 as an oxygen carrier. Will move.

The N discharged from the upper part of the housing 61
The P medium is once conveyed to and stored in the liquid storage tank 7 through the liquid supply pipe 82, and is again transferred from the liquid storage tank 7 to the liquid supply pipe 81.
And then supplied to the tar-impregnated soil. In addition, the gas discharged together with the NP medium from the upper part of the storage part 61 was discharged into the atmosphere from the vent hole 71.

When this operation was continued for 7 weeks, the residual concentration of tar in the tar-impregnated soil was determined by measuring the total PA as the main component.
H (polycyclic aromatic hydrocarbon; polycyclic ar
, and the concentration was monitored with time. The result is shown in FIG. The PA
The H concentration was measured as follows. The collected tar-impregnated soil was air-dried in a fume hood for at least two days. The tar-impregnated soil dried in the air is pulverized, and 2 mL of acetonitrile is added to 1 g of the tar-impregnated soil to obtain 60 g of the tar-impregnated soil.
And then centrifuged at 3000 rpm for 10 minutes.
Was analyzed.

Comparative Example 1-1 For comparison, the NP
After the medium was filled in the container 61, only air was supplied from the lower part to the upper part of the container 61 at a flow rate of 10 mL / min without circulating the NP medium. Shown in Where the air (bubbles)
Is left to float in the soil gap of the tar-impregnated soil, and the NP medium in the storage section 61 does not actively work as an oxygen carrier.

[Comparative Example 1-2] The results of the treatment by the slurry method are also shown in FIG. In this method, it is known that the diffusion of oxygen into the culture medium is promoted by stirring, so that oxygen can be easily supplied to the microorganism. The treatment by the slurry method was performed as follows. 12 g of the mixture of the above-mentioned tar-impregnated soil and tar-degrading microorganisms and 20 mL of the NP medium were placed in a 300 mL Erlenmeyer flask, sealed with a breathable cotton plug, and shaken at 30 ° C. and 175 rpm for 7 weeks. Cultured.

In the case where the NP medium was not circulated and the NP medium charged at the start of the experiment was kept, that is, when the supply of oxygen to the microorganism depended on the diffusion of oxygen into the NP medium, FIG. As shown in FIG.
The AH decomposition rate was as low as 10%, and the PAH decomposition rate was low (Comparative Example 1-1). In the case of the treatment by the slurry method (Comparative Example 1-2), as shown in FIG. 3, the total PAH concentration in the tar-impregnated soil rapidly decreased, and about 60% of the total PAH was decomposed four weeks after the start of the treatment. It had been. However, the slurry method uses a large amount of medium (solution)
Since it is suspended and aerated with stirring, it is very difficult to apply it to in situ bioremediation, and it is not suitable as a method for solving the problems of the present application.

On the other hand, as in Example 1, the NP medium having oxygen dissolved therein was supplied to every corner of the soil gap by forcibly circulating the NP medium together with air in the tar-impregnated soil. In this case, the total PAH decomposition rate after the treatment for 7 weeks reached 50%, indicating that the decomposition of the tar was greatly accelerated. Although the decomposition rate in the initial stage was slower than the treatment by the above-mentioned slurry method (Comparative Example 1-2), there was almost no difference in the decomposition rate from the slurry method after 7 weeks.
From these results, rather than supplying air directly to saturated soil as air bubbles, circulating oxygenated water increases the rate of decomposition of organic matter by living organisms, almost to the same level as treatment by the slurry method. It became clear that it could be purified. In Example 1, the circulation speed of the NP medium was 0.01, 0.05, 0.1 m
The treatment was carried out with each set to L / min, but there was almost no difference in the total PAH decomposition rate due to the difference in flow rate.

According to the above results, in the medium- to long-term purification process, by employing this method, the soil to be purified is not fluidized and stirred, and the soil purification is performed to the same degree as the slurry method. It is thought that it can advance.

Example 2 In the same manner as in Example 1, 400 g of the mixture 62 was compacted in
Sintered stainless steel filters 63 and 6 having a pore size of 0 μm
3 was attached to the upper and lower ends of the storage section 61 so that the tar-impregnated soil did not flow out of the storage section 61.
The NP culture medium is stored in the housing 61.
The soil gap was filled with the NP medium supplied from below. Thereafter, the NP medium was pulled out from the lower part of the storage section 61 using the liquid sending pump P4 to remove almost all the soil pore water, thereby filling the soil gap with air (suction operation). This allows the air to supply oxygen directly to the emptied soil gap. Thereafter, the extracted NP medium is again stored in the storage unit 61 by using the liquid sending pump P4.
To fill the interstices of the tar-impregnated soil with the NP medium (injection operation). (This injection operation simulates the infiltration of groundwater from another area.) When the above-mentioned suction operation and injection operation of the NP medium are not performed, the soil gap is filled with the NP medium. In this state, the air is pumped to 1 using the air pump P5.
It was fed at a flow rate of 0 mL / min. The above suction / injection operation
Times / day for 7 weeks, that is, the air can easily flow through many areas of the soil gap of the tar-impregnated soil, and oxygen is supplied once a day to the soil gap using air as an oxygen carrier. FIG. 4 shows the change over time in the total PAH concentration when supplied.

[Comparative Example 2-1] For comparison, the result of performing the same process as in Example 2 except that the supply of air was continued without performing the above-described suction and injection operations of the NP medium. Is shown in FIG.

[Comparative Example 2-2] As in Comparative Example 1-2,
FIG. 4 shows the results of treating the tar-impregnated soil by the slurry method for 7 weeks.

As shown in FIG. 4, when only the supply of air was continued without suctioning the soil pore water, the total PAH decomposition rate after the treatment for 7 weeks did not reach 10%, and the total PAH decomposition rate did not reach 10%.
The H decomposition rate was low (Comparative Example 2-1). On the other hand, when the slurry was treated by the slurry method, the total PAH concentration in the tar-impregnated soil rapidly decreased, and was reduced to about 6
0% of the total PAH was decomposed (Comparative Example 2-2).

Here, in the second embodiment in which air (oxygen) spreads in the soil gap by intermittently sucking / injecting the soil pore water from the gap of the tar impregnated soil,
After 7 weeks of treatment the total PAH degradation rate reaches 50%,
It has been clarified that the decomposition of the tar is greatly promoted, and the soil purification effect can be improved to a level close to the case where the slurry method is employed.

Example 3 In the same manner as in Example 1, 400 g of the mixture 62 was compacted in the storage portion 61 of the column 6. Here, in Example 3, instead of the sintered stainless steel filter having a pore size of 10 to 20 μm, a glass filter having a pore size of 20 to 40 μm was attached to the lower part of the column to hold the soil, Attaches a Teflon (registered trademark) filter with many holes of 1 mm in diameter,
The fine soil particles flowed out of the housing part 61 together with the NP medium.

The NP culture medium is supplied from the lower part of the storage part 61 into the storage part 61 to remove the soil gap from the N.
After filling with the P medium, the liquid sending pump P4 is driven,
0.0 from the lower part to the upper part in the accommodation portion 61.
While supplying the NP culture medium at a flow rate of 1 or 0.1 mL / min, the air pump P5 is driven to drive the air supply pipe 4 from the lower part of the column 6 at a flow rate of 10 mL / min with respect to the NP culture medium. Air was supplied to the top. The NP medium discharged from the upper part of the column is once carried to and stored in the liquid storage tank 7 through the liquid supply pipe 82, and is again sent from the liquid storage tank 7 to the storage section 61 through the liquid supply pipe 81. And fed to the tar impregnated soil. The gas discharged from the upper part of the storage part 61
Was released into the atmosphere from the gas vent hole 71 of the above. Further, the fine soil particles flowing out of the storage section 61 and flowing into the liquid storage tank 7 settle at the bottom of the liquid storage tank 7 and again return to the storage section 61.
Not to be supplied. As described above, while removing fine soil particles from the tar-impregnated soil, the suction and supply of the NP medium are performed at the same time, and the NP as an oxygen carrier is removed.
FIG. 5 shows the time course of the total PAH concentration in soil when the medium was circulated and continued for 7 weeks.

Comparative Example 3 For comparison, FIG. 5 also shows the result when only the air was supplied while the NP medium was kept without circulating.

As shown in FIG. 5, in Comparative Example 3 in which the NP medium was not circulated, the decomposition of PAH hardly progressed until 4 weeks from the start of the treatment, but about 40% after the treatment for 7 weeks. Had been disassembled. On the other hand, as in Example 3, when the NP medium was circulated while being aerated and fine soil particles were removed, four weeks after the start of the treatment,
PAH in the tar-impregnated soil had been completely decomposed, and the decomposition rate of tar had been greatly improved. Comparing the results of Example 3 with those of Examples 1 and 2, the total PAH concentration after the treatment of Example 3 was extremely low. By removing fine soil particles, It is clear that organic matter can be removed efficiently. Here, it was confirmed that the PAH that had disappeared from the tar-impregnated soil was partially adhered to the soil particles deposited in the water storage tank 7 and stayed there, and the other was decomposed by the tar-degrading microorganisms. Conceivable. still,
There was almost no difference in the decomposition rate due to the difference in the flow rate of the NP medium.

[Another Embodiment] Another embodiment will be described below. In the above embodiment, the case where the organic matter to be removed is tar is illustrated, but the soil purification method according to the present invention is not particularly limited as long as the removal target is an organic matter. Therefore, by using this method, by promoting oxygen supply to microorganisms present in the soil to be purified and capable of decomposing the organic matter to be removed, the decomposition of the organic matter is promoted, and the soil purification efficiency is improved. be able to. or,
In the above embodiment, the ventilation section 4 is connected to the saturated soil 1.
2, but provided to the purification target soil 1 by providing an aeration tank downstream of the recovery unit 2 or by supplying air to the recovery pipe 21 and the supply pipe 31 using an air pump. The recovered liquid can be enriched with oxygen to provide oxygen supply water. Further, in the above embodiment, microorganisms that decompose the organic matter to be removed are added to the soil to be purified from the outside to reinforce the function of indigenous microorganisms that naturally inhabit the soil to be purified. It can also be used to improve the efficiency of decomposing the organic matter by activating indigenous microorganisms that inhabit the soil to be purified. Further, in the above embodiment, the NP medium serving as a nutrient source of the microorganism was circulated, but the circulating fluid was appropriately changed in consideration of the nutritional requirement of the microorganism useful for decomposing the organic matter to be purified. can do. Alternatively, the liquid collected from the soil gap of the soil to be purified may be reused as it is, or the liquid may be replenished with nutrients and re-supplied.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of the present method.

FIG. 2 is a schematic diagram of a soil purification model system used in an example of the present method.

FIG. 3 is a graph showing the results of tar decomposition by the present method.

FIG. 4 is a graph showing the results of tar decomposition according to another embodiment of the present method.

FIG. 5 is a graph showing the results of tar decomposition according to another embodiment of the present method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Soil to be purified 2 Collection unit 3 Supply unit 4 Ventilation unit 5 Storage tank 11 Unsaturated soil 12 Saturated soil

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinichi Ueda 5-14-19 Ibukidai Higashicho, Nishi-ku, Kobe City, Hyogo Prefecture No. F-term (reference) 4D004 AA41 AB05 AC07 CA18 CC03

Claims (7)

[Claims] 1. A soil purification method for removing organic matter contained in a soil to be purified using a microorganism, comprising a suction step of sucking soil pore water in the soil to be purified. 2. The soil purification method according to claim 1, wherein the suction step is performed intermittently. 3. The soil purification method according to claim 1, further comprising a supply step of supplying oxygen supply water having a higher dissolved oxygen concentration than the soil pore water sucked in the suction step to the purification target soil. 4. The soil purification method according to claim 3, wherein, in the supply step, oxygen is added to the soil pore water to obtain the oxygen supply water. 5. The soil purification method according to claim 3, wherein the suction step and the supply step are performed intermittently. 6. The soil purification method according to claim 1, wherein in the suction step, fine soil particles contained in the soil pore water are separated from the soil pore water. 7. The soil purification method according to claim 1, further comprising a microorganism addition step of adding the microorganism capable of decomposing the organic matter to the soil to be purified.