JP4135909B2 - Purification method for contaminated ground - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying contaminated ground for purifying soil contaminated with pollutants.
[0002]
[Prior art]
Pollutants that have penetrated into the ground due to various causes are detoxified by physicochemical treatment, the contaminated ground is removed by excavation, etc. It has been practiced in the past.
One of the conventional methods for remediating contaminated ground is a soil washing method. In this method, the contaminated ground containing pollutants is removed by excavation, the contaminated soil is washed by a ground washing plant, and the purified soil is returned to the ground again.
In addition, as shown in Non-Patent Document 1, a cavity is formed by cutting contaminated ground with a water jet, discharging contaminated mud water formed by mixing contaminated ground and water, and cutting with detoxified ground material. There is also a way to backfill.
[0003]
[Non-Patent Document 1]
Junichi Kawabata and three others, “Repair technology of contaminated ground using water jet”, Soil and Foundation, Japan Society for Geotechnical Engineering, October 2002, Vol. 50, No. 10 (No. 537), p. 25-27
[0004]
[Means for Solving the Problems]
In order to achieve the above object, a method for purifying contaminated ground according to the present invention is a method for purifying contaminated ground for purifying soil contaminated with pollutants, wherein the contaminated ground containing the pollutants is subjected to high pressure. by stirring with water, the ground test tube-like or ground flask-shaped suspension area is formed in situ, to form a raised water flow by continuing to supply continuously or intermittently to a low-pressure water from a region below Pollution suspension The method is characterized in that after maintaining the suspended state for a predetermined period, the supply of the low-pressure water is stopped to settle the soil particles, and the fine-grained soil settled on the upper portion is removed. Here, air that has been bubbled with a surfactant is supplied together with the low-pressure water from below the suspension region, and fine soil particles adsorbing the pollutants adhere to and float on the bubbles. Grain soil can be selectively collected and removed.
[0005]
OBJECT OF THE INVENTION
The present invention was made to solve the conventional problems as described above, and an object thereof is to provide a method for purifying contaminated ground, which can purify the ground by removing the minimum necessary contaminated soil and contaminants. To do. That is, it aims at providing the purification method of the contaminated ground which can reduce the effort and expense accompanying removal work by selecting the soil or material to remove.
In addition, an underground test tube or flask-like suspension area is temporarily created inside the ground, and part of or all of the purification treatment is performed in-situ to remove the contaminated ground. It aims at providing the purification method of the contaminated ground which can reduce return work.
Furthermore, it aims at providing the purification method of the contaminated ground which can be implemented cheaply without requiring a large-scale installation.
The present invention achieves at least one of these objects.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a method for purifying contaminated ground according to the present invention provides a method for purifying contaminated ground for purifying soil contaminated with pollutants, wherein the contaminated ground containing the pollutants is treated with high-pressure water. To form an underground test tube-like or underground flask-like suspension region in situ, and ascending water flow is formed by continuously supplying low-pressure water continuously or intermittently from below the suspension region as necessary. Thus, after maintaining the suspended state for a predetermined period, the supply of the low-pressure water is stopped to settle the soil particles, and the fine soil settled on the upper portion is removed. Here, air that has been bubbled with a surfactant is supplied together with the low-pressure water from below the suspension region, and fine soil particles adsorbing the pollutants adhere to and float on the bubbles. Grain soil can be selectively collected and removed.
[0007]
Further, in the purification method for contaminated ground for purifying soil contaminated with pollutants, the contaminated ground containing the pollutants is agitated with high-pressure water, and suspended in the form of underground test tubes or underground flasks. By forming a region and forming a rising water stream by continuously supplying low-pressure water continuously or intermittently from below the suspension region, while maintaining a suspended state for a predetermined period of time, activated carbon, catalyst, oxidizing agent, In-situ treatment of contaminated soil is performed by supplying a reducing agent, chemical treatment agent or biological treatment microorganism. Here, the chemical treatment agent is a chemical agent that detoxifies the contaminant by decomposing or stabilizing it by a chemical reaction, and the biological treatment microorganism is a contaminant such as bacteria. A detoxifying microorganism. Moreover, in order to form a physical environment necessary for the in-situ treatment of the contaminated soil, hot water, cold water, high-frequency vibration, or the like can be supplied.
[0008]
Furthermore, in the purification method for contaminated ground for purifying soil contaminated with pollutants, the contaminated ground containing the pollutants is agitated with high-pressure water and suspended in the form of underground test tubes or underground flasks. Forming a region, placing the positive electrode and the negative electrode at positions separated from the suspension region, and forming a rising water flow by continuously supplying low-pressure water continuously or intermittently from below the suspension region, In this method, the suspended state is maintained for a predetermined period of time, and contaminants accumulated around the electrode are removed. The positive electrode and the negative electrode are disposed, for example, above and below the suspension region, or on the right and left sides of the suspension region.
Moreover, in the purification method of the above-mentioned contaminated ground, the dispersing agent which separates fine-grained soil from coarse-grained soil or aggregated fine-grained soil can also be supplied with the said low pressure water.
[0009]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1
Embodiment 1 of the present invention will be described below with reference to the drawings.
[0010]
<I> Contaminated ground The contaminated ground 1 is a ground containing a pollutant.
There are cases where pollutants permeate the ground due to various causes. As a result, there is a risk of contaminating groundwater or volatilizing and affecting the human body. For this reason, it is necessary to make the contaminated ground 1 harmless or remove it. There are various types of pollutants, but they are roughly classified into pollutants such as heavy metals and volatile organic compounds.
The contaminated ground 1 may exist locally or may be spread over a wide range. Here, a method for purifying the locally contaminated ground 1 will be described as an example. When the contamination range is spread in the horizontal direction, it can be dealt with by repeating the method described later or by performing purification work in parallel at a plurality of locations.
[0011]
<B> Principle of purification The principle of purification according to the first embodiment of the present invention will be described.
Since the contaminants adhere to the surface of the soil particles, the contaminants can be efficiently removed by removing the soil particles having a large surface area per unit weight (or unit volume). The ground showing a typical particle size distribution will be described as an example. In sandy soil, the fine soil 31 having a small particle size, which is only 10% of the total weight, occupies 70% of the total surface area. Here, the fine-grained soil 31 refers to silt or clay. Moreover, the coarse-grained soil 32 means a part for sand and gravel. In particular, ultrafine particles called colloids having a particle size of about 0.001 mm (1 μm) or less are not round and scale-like, so that the specific surface area representing the surface area per unit weight (or unit volume) is very large. Therefore, reliably removing ultrafine particles greatly contributes to the reduction of the total surface area.
Sandy soil is highly permeable and easily contaminated by pollutants. However, the same is true for silty soil and clay that have low water permeability and poor permeability. Many of the contaminants can be removed.
Therefore, in the first embodiment of the present invention, it is possible to efficiently remove pollutants by selecting and removing only the fine-grained soil 31 and simultaneously suctioning and removing suspended water containing a large amount of pollutants. it can.
[0012]
<C> High-pressure water and low-pressure water The high-pressure water 21 is water supplied with high pressure applied by a high-pressure pump or the like. As an apparatus for supplying the high-pressure water 21, for example, there is a water jet.
The water jet includes a high pressure pump, a high pressure hose, a nozzle, and the like. The ground, concrete, or the like can be cut by spraying water pressurized to about 50 to 250 MPa with a high-pressure pump from a small-diameter nozzle. If necessary, the high-pressure water 21 can be mixed with a thickener or an abrasive to increase the cutting ability.
The low-pressure water 22 refers to pressure water that can form the rising water flow 23 in the ground. It is not always necessary to use a high-pressure pump because it does not expect to cut or agitate the ground.
[0013]
<D> Suspension area The suspension area refers to an area for bringing the contaminated ground 1 into the suspended state 3. The suspension region can be formed in a tube-shaped underground test tube, or an underground flask having a locally expanded lower portion. For example, when the width of the contaminated ground 1 is narrow or when the contaminated ground is distributed long in the depth direction, a suspended region is formed in the underground test tube (see FIG. 1). Moreover, when the contaminated ground 1 spreads locally deeply in the ground, a suspension region is formed in the shape of a ground flask (see FIG. 2).
The suspended state 3 is a state in which the ground agitated by the high-pressure water 21 is mixed with the supplied water, and the fine-grained soil 31 and the coarse-grained soil 32 constituting the ground are dispersed in the water and become cloudy. Say.
The ground in the suspended state 3 settles and deposits in order from the soil particles having a larger particle size over time.
In addition, in order to perform physical and chemical purification treatment on the ground in the suspended state 3, when the suspended state 3 is maintained for a long time, the low-pressure water 22 is continuously supplied from below, 23 must be formed to prevent sedimentation. Here, the supply of the low-pressure water 22 is not necessarily continuous, and may be intermittent.
[0014]
The suspended state 3 can be formed simply by stirring the ground with the high-pressure water 21. Even if the soil particles are simply allowed to settle after the supply of the high-pressure water 21 is stopped, the difference in the sedimentation speed due to the difference in the particle diameters. The fine-grained soil 31 and the coarse-grained soil 32 can be separated to some extent. However, as shown in FIG. 5, the fine-grained soil 31 is attached to the surface of the coarse-grained soil 32, and the fine-grained soil 31 and the coarse-grained soil 32 cannot be completely separated only by stirring for a short time. . For this reason, there are also many fine-grained soils 31 that settle together with the coarse-grained soil 32 in the lower layer. In addition, when a plurality of fine-grained soils 31 are combined to form a aggregated state and the apparent particle size becomes large, the coarse-grained soil 32 may settle.
Therefore, in the present invention, the slow rising water flow 23 is formed in the ground by continuously supplying the low-pressure water 22 from below for a long time. Then, it waits for the fine-grained soil 31 to separate from the surface of the coarse-grained soil 32 trapped in the rising water stream 23 and rise upward (see FIG. 5). Since the effective time for which the low-pressure water 22 is continuously supplied varies depending on the soil quality, it may be appropriately determined according to the soil quality.
Further, by supplying air in the form of bubbles with a surfactant together with the low-pressure water 22 from below the suspension region, the particles of fine-grained soil 31 adsorbing contaminants can be attached to the bubbles and floated up. it can. As a result, the fine-grained soil 31 can be selectively collected and removed.
[0015]
<E> Soil purification procedure (see Figs. 3 and 4)
First, while rotating the hollow tube 2 with a boring machine, the high-pressure water 21 is jetted from the vicinity of the tip to propel the hollow tube 2 into the ground. A cylindrical riser 5 is constructed on the ground with a steel plate or a steel pipe so that the water used for drilling and the muddy water in the suspended state 3 do not overflow.
The ground agitated while jetting the high-pressure water 21 is formed into a underground test tube as a suspension region (see FIG. 3A). When the contaminated ground 1 spreads deep in the ground, the contaminated ground 1 is cut and widened by injecting high-pressure water 21 from the vicinity of the tip of the hollow tube, for example, in the horizontal direction and rotating the hollow tube 2. A suspension region is formed (see FIG. 4A).
[0016]
After the contaminated ground 1 is stirred, the low-pressure water 22 is supplied in a state where the tip of the hollow tube 2 is disposed below the stirred suspension region. An ascending water stream 23 can be formed by supplying the low-pressure water 22 from below the suspension region (see FIGS. 3B and 4B). The suspended state 3 can be maintained by the rising water flow 23. The supply of the low-pressure water 22 is preferably continued until the fine-grained soil 31 is completely separated from the coarse-grained soil 32 or until the fine-grained soil 31 in the aggregated state is separated.
[0017]
After sufficiently maintaining the suspended state 3, the supply of the low-pressure water 22 is stopped, and the coarse-grained soil 32 and the fine-grained soil 31 are allowed to settle. When the coarse-grained soil 32 and the fine-grained soil 31 are sufficiently separated, the sedimentary layer of the coarse-grained soil 32, the sedimentary layer of the fine-grained soil 31, and the supernatant 33 composed of interstitial water and supplied water are arranged in this order. Deposits (see FIGS. 1 and 2).
[0018]
Then, the supernatant 33 in which the contaminant is dissolved and the fine-grained soil 31 are sucked and removed by a suction pump or the like (see FIGS. 3C and 4C). If the contaminated ground 1 is sandy soil or sand ground, since the weight or volume ratio of the fine-grained soil 31 is small, the discharge amount can be reduced. The cavity formed by removing the fine-grained soil 31 is backfilled by filling with uncontaminated earth and sand or a known backfill material. In the present invention, since the removal amount can be reduced by selective removal, the filling amount can also be reduced.
In addition, since the machine used is about the same as a boring machine used for geological surveys, it can be carried out in a small site and has little noise. Furthermore, since the purification can be performed at the same time while confirming the contaminated ground 1 by the boring survey, the cost and construction period can be reduced.
[0019]
Second Embodiment of the Invention
In the first embodiment described above, the method of separating the fine-grained soil 31 from the coarse-grained soil 32 by continuously supplying the low-pressure water 22 or air in addition to the low-pressure water 22 has been described. In the second embodiment, a method of reducing the harmfulness of the contaminated ground 1 or promoting separation of the fine-grained soil 31 and the coarse-grained soil 32 by adding another substance to the low-pressure water 22 will be described.
[0020]
<I> Reduction of harmfulness In the first embodiment, the method of removing the contaminants adhering to the fine-grained soil 31 together with the fine-grained soil 31 has been described.
In the second embodiment, activated carbon, a catalyst, an oxidizing agent, a reducing agent, a chemical treatment agent, or a biological treatment microorganism is added while the suspension region is in the suspension state 3, thereby reducing the harmfulness of the pollutant. Reduce. If some or all of the contaminated soil can be processed in-situ, the harmfulness of the discharged supernatant 33 and fine-grained soil 31 can be reduced, so the burden of processing the discharged material discharged on the ground can be reduced. Further, if the degree of improvement by in-situ processing is excellent, it is not necessary to discharge the fine-grained soil 31. Further, the harmfulness of pore water left on the ground together with the coarse-grained soil 32 can be reduced.
For example, activated carbon can adsorb gaseous volatile organic compounds (organic chlorine compounds, low boiling point petroleums, etc.). In addition, the contaminants can be chemically reacted with the catalyst to reduce the harmfulness. However, in this case, it is necessary to pay attention to the characteristics of the substance produced in the middle. Further, by adding an oxidizing agent or a reducing agent that causes an oxidation reaction or a reduction reaction to the pollutant, it is possible to reduce the harmfulness or to make a part of it harmless. For example, by mixing a reducing agent such as ferrous salt or sulfite with hexavalent chromium in the soil, it can be changed to trivalent chromium, thereby reducing toxicity and making it insoluble.
Further, the chemical treating agent refers to a chemical that detoxifies the contaminant by decomposing or stabilizing the contaminant by a chemical reaction.
The biological treatment microorganisms refer to microorganisms such as bacteria that render the pollutants harmless.
The above-mentioned additives may change in reaction rate and processing capacity depending on the physical environment such as the water temperature and stability of the suspension region. Therefore, in order to prepare a physical environment necessary for in-situ processing, it is preferable to apply hot or cold water, high-frequency vibration, or the like.
[0021]
<B> Dispersant A dispersant may be used to efficiently separate the fine-grained soil 31 from the coarse-grained soil 32 and the fine-grained soil 31. As the dispersant, for example, sodium silicate, caustic soda solution, hydrogen peroxide solution and the like can be used.
By using a dispersant, when the fine-grained soil 31 is electrically charged and firmly attached to the coarse-grained soil 32, or when the fine-grained soil 31 is bonded together in a cluster shape, the apparent particle size is increased. Separation can be facilitated.
It is preferable that the dispersant is also supplied together with the low-pressure water 22 and thoroughly mixed in the suspension state 3.
[0022]
Embodiment 3 of the Invention
In the third embodiment, an example using an electrical separation method will be described with reference to FIG.
<A> Electrode Installation In the third embodiment, the contaminated ground 1 is cut and stirred with a water jet or the like in the same manner as in the first embodiment.
Then, the positive electrode 41 and the negative electrode 42 are respectively arranged at positions separated from the suspension region. FIG. 6 shows an embodiment in which the positive electrode 41 is arranged on the upper side and the negative electrode 42 is arranged on the lower side. However, when the suspension region is formed like a submerged flask, the electrodes 41 and 42 are widened. You may arrange | position at the right end and left end of a part, respectively.
In addition, it can be arbitrarily determined which of the positive electrode 41 and the negative electrode 42 is disposed above. Usually, it can be determined by whether the contaminant to be removed is an anion or a cation.
[0024]
<B> When the contaminated ground 1 is brought into the suspended state 3 with the electrodes for collecting and removing pollutants, the pollutants also float. In order to maintain the suspended state 3, the low-pressure water 22 may be continuously supplied as in the first embodiment.
For example, when the pollutant is hexavalent chromium, a carbon rod is used as the positive electrode 41 and a reinforcing bar is used as the negative electrode 42, and a DC voltage is applied between the electrodes. Then, hexavalent chromium existing in the ground as anions accumulates around the positive electrode 41. By maintaining the suspended state 3 for a long time, contaminants can be accumulated from a wide range. Then, soil water containing contaminants accumulated around the positive electrode 41 is removed using a suction pump or the like.
When the pollutant is a cation such as heavy metal, the upper and lower electrodes can be exchanged. Further, it is possible to adopt a method of removing contaminants accumulated on the electrodes arranged below.
[0025]
【The invention's effect】
Since the contaminated ground purification method of the present invention is as described above, the following effects can be obtained.
<I> The level of purification of contaminated ground can be selected. That is, if the target purification level is set, the minimum contaminated soil and contaminants necessary to achieve the target may be selected and removed. For this reason, it is possible to reduce labor and cost for the removal work, the backfilling work, the purification process of the discharged matter, and the like.
<B> Since what can be removed can be selected, it is not necessary to provide a large-scale washing facility or purification device. For this reason, soil can be purified at low cost. It is especially suitable for places where the site is small and large machinery and equipment cannot be installed, such as the site of a small and medium-sized factory.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a ground state in which soil particles are settled in a suspension region of an underground test tube.
FIG. 2 is a cross-sectional view showing a ground state in which soil particles are settled in an underground flask-like suspension region.
FIG. 3 is a procedural diagram showing a method for purifying contaminated ground according to the present invention when an underground test tubular suspension region is formed. (A) Sectional drawing which showed the Example of the stirring operation | work of a contaminated ground. (B) Sectional drawing of the Example which is maintaining the suspension state. (C) Sectional drawing which showed the Example of the removal operation | work of a fine grain soil.
FIG. 4 is a procedural diagram showing a method for purifying contaminated ground according to the present invention when a submerged flask-like suspension region is formed. (A) Sectional drawing which showed the Example of the stirring operation | work of a contaminated ground. (B) Sectional drawing of the Example which is maintaining the suspension state. (C) Sectional drawing which showed the Example of the removal operation | work of a fine grain soil.
FIG. 5 is an explanatory diagram schematically showing the state of fine-grained soil and coarse-grained soil.
FIG. 6 is an explanatory diagram of an embodiment in the case of using an electrical separation method.
[Explanation of symbols]
1 ... contaminated ground 21 ... high pressure water 22 ... low pressure water 23 ... ascending water flow 3 ... suspended state 31 ... fine grained soil 32 ... coarse grained soil 41 ... positive electrode 42 ... negative electrode

Claims (6)

In the purification method of contaminated ground to purify soil contaminated with pollutants,
The contaminated ground containing the pollutant is agitated with high-pressure water to form an underground test tube or underground flask-like suspension region in situ .
By forming the increased water flow from the suspension area lower by continuing to supply continuously or intermittently to a low-pressure water, after maintaining the suspension over a predetermined period of time,
Stopping the supply of low-pressure water to settle the soil particles;
A method for purifying contaminated ground, comprising removing fine-grained soil deposited on the upper part. Along with the low-pressure water, air that is made into bubbles with a surfactant is supplied from below the suspension region, and the fine-grained soil adsorbing the pollutants is attached to the bubbles and floated up to raise the fine-grained soil. The method for purifying contaminated ground according to claim 1, wherein the soil is selectively collected and removed. In the purification method of contaminated ground to purify soil contaminated with pollutants,
The contaminated ground containing the pollutant is agitated with high-pressure water to form an underground test tube or underground flask-like suspension region in situ.
A rising water stream is formed by continuously or intermittently supplying low-pressure water from below the suspension region, so that the suspended state is maintained for a predetermined period of time and activated carbon, catalyst, oxidizing agent, reducing agent, chemical A method for purifying contaminated ground, characterized by performing in-situ treatment of contaminated soil by supplying a treatment agent or a microorganism for biological treatment. 4. The method for purifying contaminated ground according to claim 3, wherein a physical environment necessary for in-situ treatment of the contaminated soil is formed by supplying hot water, cold water, high frequency vibration or the like. In the purification method of contaminated ground to purify soil contaminated with pollutants,
The contaminated ground containing the pollutant is agitated with high-pressure water to form an underground test tube or underground flask-like suspension region in situ.
A positive electrode and a negative electrode are respectively arranged at positions separated from the suspension region, and a rising water flow is formed by continuously or intermittently supplying low-pressure water from below the suspension region, so that the suspension is suspended over a predetermined period. Maintain turbidity,
A method for purifying contaminated ground, comprising removing contaminants accumulated around the electrode. The method for purifying contaminated ground according to any one of claims 1 to 5, wherein a dispersing agent for separating fine-grained soil from coarse-grained or aggregated fine-grained soil is supplied together with the low-pressure water.

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