JP2001327955A - Decontamination method for contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the efficiency and lower the cost of the aerobic bioremediation of contaminated soil. SOLUTION: In the case of decontamination of contaminated soil, a substance possible to generate oxygen is added to the contaminated soil to carry out bioremediation by aerobic microorganism and purify the contaminated soil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying contaminated soil.

[0002]

2. Description of the Related Art Bioremediation, which utilizes the decomposition ability of various microorganisms to reduce or eliminate environmental pollutants derived from the accumulation of toxic waste and toxic chemicals, is one of the methods for cleaning contaminated soil. Attention has been paid to its use results worldwide.

[0003] Bioremediation technology has a long history as an ecosystem restoration technology such as the use of compost, activated sludge method, and methane fermentation method. Application to the purification of contaminated soil has been reported, and the types of harmful substances are diversified. At this time, microorganisms suitable for the decomposition are determined according to the type and amount of the pollutants, temperature, water quality, etc. As well as being clarified, various isolation and inoculation methods have been developed.

[0004] Such soil bioremediation can be broadly classified into an in situ treatment method and a transfer treatment method. When an aerobic microorganism decomposes pollutants, the in situ treatment method uses wells in contaminated ground. Air or oxygen, and in some cases, nutrients, etc., are blown into the air. Although this method has the advantage of low cost burden, there is a limit in efficiency. Therefore, the most effective method is to move the contaminated soil to another controlled place or reactor (treatment tank) for efficient treatment. In the moving method,
A land farming method that supplies oxygen (furthermore, nutrients such as nitrogen and phosphorus and other organic substances) to the soil while turning the excavated soil with a heavy machine. And a slurry method in which water is added to soil to form a slurry, and a decomposition microorganism and nutrients are added in a reactor or the like while oxygen is supplied.

[0005]

In the case of aerobic biological purification of contaminated soil, the transfer treatment method has a higher decomposition efficiency than the in-situ treatment method. Various processes such as a process of transferring excavated contaminated soil to a treatment plant, a sedimentation and storage process, a biological purification treatment process in a treatment plant, a process of moving treated soil to a reuse site, and a backfilling process are necessary. However, there is a problem in that moving large amounts of energy and costs is required when targeting sediment. Also proposed is a method in which excavated contaminated soil is moved to an open surface or a controlled place, where a number of porous pipes are buried in the contaminated soil and oxygen is supplied to the soil from these porous pipes. However, in this case, there is a problem that a device for supplying oxygen is required, and the pipe burial work and the removal of the pipe after purification are required, which increases the construction cost.

Accordingly, an object of the present invention is to solve these problems and to provide a more economical and efficient method for purifying contaminated soil by bioremediation while making use of the advantages of the in situ method and the transfer treatment method. is there.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides an aerobic method in which contaminated soil contains an oxygen-generating substance in purifying and reusing the contaminated soil. Bioremediation treatment was performed using microorganisms. In this case, an area separated from the surrounding ground by a layer of water-impermeable and air-impermeable is provided, and this area contains contaminated soil and oxygen-generating substances and is subjected to bioremediation treatment with aerobic microorganisms. , It can be purified with the minimum necessary amount of oxygen generating substance. This area can be a reuse zone for contaminated soil. Also, in some cases,
Without particularly providing the above-mentioned region, the oxygen-generating substance can be stored in situ in the contaminated soil and subjected to bioremediation treatment with aerobic microorganisms. In this case, it is possible to omit the area divided by the water-impermeable and air-impermeable layer,
The treated soil can be reused as it is at the treatment location. Here, the oxygen-generating substance is a peroxide such as hydrogen peroxide, potassium peroxide, sodium peroxide,
One or more selected from the group consisting of sodium hydrogen peroxide, magnesium peroxide and ammonium peroxide can be used.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for purifying contaminated soil according to the present invention can be applied to either the in-situ method or the transfer treatment method. First, an embodiment implemented by the transfer treatment method will be described.

When the present invention is carried out by the transfer treatment method, it is preferable that the contaminated soil is moved to a reuse position as it is, and bioremediation is performed in a state where the soil can be reused. At this time, it is preferable to form a reusable zone that is separated from the surrounding ground at the reusing position by a layer that is hardly permeable and hardly permeable (hereinafter, referred to as a hardly permeable hardly permeable layer). In other words, a region is provided that is separated from the surrounding ground by a poorly permeable and poorly permeable layer, and contaminated soil is accommodated in this region (reuse zone) together with an oxygen-generating substance and subjected to bioremediation treatment with aerobic microorganisms.

More specifically, as shown schematically in FIG. 1, a region (reuse zone) that is separated from the surrounding ground 1 at a position where the contaminated soil is reused via the hardly permeable and hardly permeable layer 2 Form 3 The area 3 is the GL of the surrounding ground 1 in the illustrated example.
The recess is open to the atmosphere having a certain depth from the outside, and a hardly permeable and hardly permeable layer 2 that borders the surrounding ground 1 is uniformly laid on the side and bottom surfaces of the hollow.

The material and thickness of the water-impermeable and air-impermeable layer 2 are appropriately selected depending on the contaminated soil to be treated. For example, a viscous soil layer or a water-impermeable sheet can be used. When bioremediation of contaminated soil is carried out in the form of solid phase, it can be a viscous soil layer. It can be a poorly permeable layer 2. A cohesive soil layer can be used when slurrying contaminated soil and performing bioremediation treatment.
The water-impermeable sheet alone can also serve as the water-impermeable and air-impermeable layer 2.

The thus formed region (reuse band) 3
Then, the contaminated soil 4 excavated from the contaminated area is carried in. At that time, the oxygen-generating substance 5 is also introduced. The oxygen-generating substance 5 is preferably dispersed in the contaminated soil 4, but in the embodiment of FIG. 1, a layer of the oxygen-generating substance 5 is laid beforehand at the bottom of the region 3, and then the contaminated soil 4 Is shown. That is, in the example of FIG. 1, the powdery oxygen-generating substance 5 is evenly spread on the bottom of the region 3,
Further, an embodiment in which the contaminated soil 4 is introduced by using the soil carrying device 6 is shown. As a result, the oxygen-generating substance is loaded into the lower part of the contaminated soil in a planar manner with a two-dimensional spread, and there is no direct mixing with the soil to be treated. Alienation can be prevented. During the bioremediation process,
Oxygen generated from the oxygen-generating substance in the lower layer rises while diffusing in the contaminated soil.

FIG. 2 shows an example in which the oxygen-generating substance 5 is contained in the area (reuse zone) 3 while being added to the contaminated soil 4. In this example, the oxygen generating substance 5 is mixed into the contaminated soil 4 of the carry-in device 6 from the addition device 7. Also in this case, the concentration of the oxygen-generating substance 5 in the contaminated soil 4 contained in the lower part of the region 3 is increased, and the concentration of the oxygen-generating substance 5 is reduced in the soil contained in the upper part. can do.

FIG. 3 shows that when the contaminated soil 4 is carried into the area (reuse zone) 3, the culture soil 8 containing a high concentration of microorganisms is used.
And an example of adding a nutrient source 9 of the microorganism. In the illustrated example, the high-concentration culture soil 8 in the hopper 10 is thrown into the loading device 6 through the control valve 11, and the hopper 1
The nutrients 9 in 2 are loaded onto the carry-in device 6 via the control valve 12, and the amount and time of these additions are adjusted by operating the control valves 11 and 12. Also in this example, the oxygen-generating substance is introduced into the contaminated soil 4 in parallel with or separately from the microorganism source and the nutrient source. The types of microorganisms for decomposing the pollutants and the nutrients for the microorganisms need to be appropriately selected according to the types and amounts of the contaminants in the contaminated soil.

FIG. 4 shows a state in which the contaminated soil 4 contained in the area (reuse zone) 3 as described above is subjected to bioremediation treatment in the zone, and is loaded in the lower part of the zone. The oxygen-generating substance 5 is decomposed, and the oxygen gas or oxygen-containing gas 1 generated by the decomposition is decomposed.
4 shows a situation where 4 spreads into the contaminated soil 4. At that time, if necessary, the surface of the treated soil is impermeable to water impermeable sheet 1
Cover with 5. The sheet 15 can prevent rainwater from entering and staying in the zone, and can easily store the generated decomposed oxygen in the zone.

FIGS. 1 to 4 show an example in which a treatment area 3 is formed separated from the surrounding ground by a water-impermeable and air-impermeable layer 2, and contaminated soil is purified in this area 3. Depending on the form and condition of the contaminated soil, the purification treatment according to the present invention can be performed in situ of the contaminated soil without providing such a poorly permeable and poorly permeable layer 2 in particular. That is, the oxygen-generating substance is contained in the contaminated soil in situ, and is subjected to bioremediation treatment with aerobic microorganisms. In this case, there is an advantage that the construction cost is reduced by omitting the water-impermeable and air-impermeable layer 2. Therefore, even if the yield of the oxygen-generating substance may be reduced by omitting the water-impermeable and air-impermeable layer 2, the purification treatment can be economically performed as a whole. In such an in-situ process,
Preferably, the oxygen-generating substance is contained in the middle or lower part of the contaminated soil.

As the oxygen-generating substance for the bioremediation treatment according to the present invention, peroxides such as hydrogen peroxide, potassium peroxide, sodium peroxide,
It is preferable to use sodium hydrogen peroxide, magnesium peroxide and ammonium peroxide. These should be selected according to the properties of the treated soil, the amount of treatment, and the microorganisms. When potassium peroxide or sodium peroxide, which generates oxygen, is used, the amount of oxygen generated can be adjusted by adjusting the amount of water in the contaminated soil. A device that releases oxygen at a high rate can continuously release oxygen for a relatively long time. In any case,
Since these peroxides do not leave harmful components in the soil even after decomposition, they can be left in the reused soil as they are.

If there is a possibility that the decomposition action may be alienated by decomposition of the peroxide, the peroxide can be filled in the lower layer of the soil to prevent an increase in the pH of the target soil.

The aerobic microorganism used to decompose pollutants in soil is appropriately selected according to the type of pollutant.
When the contaminants are petroleum compounds such as crude oil, heavy oil, diesel oil, gasoline, etc., fertilizers such as nitrogen and phosphorus are used to form an environment that promotes the growth of petroleum-degrading microorganisms in the contaminated soil in the reuse zone. It is also preferable to spray. When the present invention is applied to soil contaminated with hard-to-decompose organic chlorine-based compounds such as PCB, trichloroethylene, dioxins, and methylene chloride, which are said to be high-tech pollution, it is suitable for decomposing those compounds. It is desirable to inject microorganisms, for example P.sp.KK for PCB
It is known that the enzyme produced by S102 strain has a high resolution, and that white dirt bacteria have high resolution in dioxins. In addition, the present invention can be carried out by appropriately selecting microorganisms and nutrient sources according to the type of contaminants, such as pesticide contamination, preservative contamination, organic solvent contamination, and food preservation compound contamination.

In practicing the present invention, it is necessary to form a completely water-impervious layer when there is a risk of contaminating groundwater due to rainwater infiltration. In solid phase treatment, contaminated soil is stored in a reuse zone at a relatively low density without consolidation, allowing natural ventilation to reach the ground, and loading oxygen-generating substances in the lower part as much as possible. It is desirable to allow the decomposition gas to reach the lower layer. Also,
It is also preferable to form ridges in the re-use zone and to improve ventilation and drainage. A method of digging a hole in some places and embedding an oxygen-generating substance in the hole can also be adopted.

When the bioremediation treatment according to the present invention is carried out in a slurry phase, the poorly permeable and air-permeable layer is formed of a water-impervious layer. It is good to pour into the reuse zone which has the following layers. The water-blocking layer can also be formed by clayey soil. It is practical to set up a slurry tank separately from the reuse zone, add water to the excavated soil in this slurry phase to make appropriate slurry, and inject microorganisms and nutrient sources. In addition, an oxygen-generating substance can be added together with these injections. However, the oxygen-generating substance can be charged at the stage of containing the slurry in the reuse zone or after the slurry is contained. Bioremediation treatment in the slurry phase can also be applied to oil pollution purification.

[0022]

As described above, according to the present invention,
Since the bioremediation treatment is performed while the contaminated soil is moved to the reuse zone, and oxygen is supplied to the soil with an oxygen-generating substance, the soil returns to the natural state where it can be reused at the treatment position after the treatment. Since the growth of aerial microorganisms is carried out efficiently, the energy cost and running cost for soil purification can be reduced. Further, by loading an oxygen-generating substance such as a peroxide into the lower layer of the soil to be treated, decomposition and alienation due to an increase in pH can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a method for purifying contaminated soil according to the present invention.

FIG. 2 is a schematic sectional view showing another example of the method for purifying contaminated soil according to the present invention.

FIG. 3 is a schematic sectional view showing still another example of the method for purifying contaminated soil according to the present invention.

FIG. 4 is a schematic cross-sectional view showing a treatment state of a method for purifying contaminated soil according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Surrounding soil 2 Layer with poor water permeability and poor air permeability 3 Reuse zone 4 Contaminated soil 5 Oxygen-generating substance 6 Conveying device for contaminated soil 15 sheet

Claims (7)

[Claims] 1. A method for purifying contaminated soil, wherein the contaminated soil contains an oxygen-generating substance and is subjected to bioremediation treatment with aerobic microorganisms. 2. When purifying contaminated soil, an area is provided which is separated from the surrounding ground through a layer that is hardly permeable and hardly permeable, and contains contaminated soil and oxygen-generating substances in this area. A method for purifying contaminated soil, comprising performing bioremediation treatment with aerobic microorganisms. 3. The method according to claim 1, wherein the oxygen-generating substance comprises a peroxide. 4. The method according to claim 1, wherein the peroxide is at least one member selected from the group consisting of hydrogen peroxide, potassium peroxide, sodium peroxide, sodium hydrogen peroxide, magnesium peroxide and ammonium peroxide. Item 4. The method for purifying contaminated soil according to Item 3. 5. The water-impermeable and air-impermeable layer comprises a viscous soil layer or a water-impermeable sheet.
3. The method for purifying contaminated soil according to 1.). 6. The method for purifying contaminated soil according to claim 1, wherein the oxygen-generating substance is accommodated in the lower part of the contaminated soil in a planar state. 7. The method for purifying contaminated soil according to claim 1, wherein the surface of the contaminated soil containing the oxygen-generating substance is coated.