JPH11169837A - Decontamination method for contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To crack the contaminated groud region as widely as possible by freezing the region and sucking the intrasoil gas from the ground to extract the contaminated vapor. SOLUTION: A gas or liq. pressure injection line 2 using a compressor 1, etc., is prepared in the contaminated soil region 8 to be restored previously set according to information of the boring test, etc. A freezing pipe 5 for supplying a refrigerant and a pressure injection pipe 2 or further a suction pipe 6 connected to a suction pump 7 are built in a well bored in the region. An antifreeze (aq. calcium chloride soln.) called a brine is cooled to -20 to -30 deg.C and introduced into the freezing pipe 5 through a circulating pump to cool the ground. The frozen ground is then naturally thawed to ordinary temps. or heated and rapidly thawed, and the gas in the soil is sucked to extract the contaminated vapor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the restoration of soil and groundwater contaminated with hydrocarbons, halogenated hydrocarbons and the like.

[0002]

2. Description of the Related Art In recent years, hydrocarbons such as aromatic hydrocarbons, paraffins and naphthenes, and trichloroethylene (T
Environmental pollution by organic chlorinated compounds such as CE), tetrachloroethylene (PCE), tetrachloroethane, and polychlorinated biphenyl has become a problem, and there is a concern about the effects on health and ecosystems. Therefore, it is strongly desired to establish a technique for preventing the spread of pollution and restoring the polluted environment. Various methods have been known and attempted as soil remediation methods for removing soil from polluted soil to return the soil to its original state. For example, repairs are performed mainly on physical and chemical methods such as a vacuum extraction method, a solar drying method, an aeration treatment method, and an oxidation treatment method, and a purification method using microbial decomposition is also being attempted.

However, when contaminants are volatile such as TCE and PCE, the vacuum extraction method is very effective, and many actual examples have been reported. Although many improvements have been devised for the vacuum extraction method, one example is to improve the steam exchange capacity by generating cracks (soil crushing) in the ground. As such a method, a method using water pressure (US Pat. No. 4,442,895) or a method using gas pressure (US Pat. No. 5,032,042) are known.

[0004]

The above-described crack forming method aims at cracking the widest possible range, but the crack density and the forming range can be increased by simply injecting gas or liquid under pressure as usual. Has limitations.

[0005] An object of the present invention is to provide a novel method for purifying contaminated soil that has solved the above-mentioned problems.

[0006]

The above object is achieved by the following means.

That is, the present invention provides a method for purifying contaminated soil, which comprises extracting a contaminated vapor for sucking gas in the soil from the ground, following the step of freezing the contaminated ground area, or a method for purifying contaminated ground area. And a method of purifying contaminated soil, characterized by extracting contaminated steam for sucking gas in the soil from the ground after the step of freezing the ground and the step of thawing the frozen ground. In addition, after adding a step of freezing the contaminated ground region and a step of generating a crack in the ground by applying pressure to the ground, extracting contaminated steam for sucking gas in the soil from the ground. The present invention provides a soil purification method.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

As will be described later, in the civil engineering work, a freezing method is known. In a ground containing fine components, freezing and expansion occur due to freezing, and dehydration and consolidation occur during thawing. Such changes in the ground are unfavorable phenomena in civil engineering work and are issues to be overcome. However, in pollution purification, the generation of minute cracks in soil is very convenient for promoting gas exchange such as suction.

[0010] That is, by temporarily freezing the retained water between the soil particles by freezing the ground and then pre-treating the step of removing the cooling water, disturbance such as freezing and swelling is caused between the soil particles and the soil in which the gas phase is diffused. And promoting the release of pollutants by agitation of retained water between soil particles by freezing and thawing.

In the area of ground excavation, an auxiliary method of freezing the ground using brine or liquid nitrogen is generally employed in a shield method or the like. In addition, a technique of undisturbed ground sampling by ground freezing is adopted. As described above, freezing the ground itself is a technique that has already been sufficiently put into practical use in civil engineering work.

The present invention is completely different in purpose and effect from such a conventional frozen ground. That is, in the conventional civil engineering method, the purpose is to shield the ground by freezing, or to preserve the in-situ ground without disturbing it.
In the present invention, a small disturbance is caused between the soil particles by temporarily freezing the retained water between the soil particles by the ground freezing and then performing the pre-treatment of the thawing process.

Although the effect of sucking contaminants is improved by the thawing treatment, it is very effective to further enhance this effect by forming cracks in the ground after thawing. Crack formation can be performed by inserting an air or water injection pipe to a desired formation site and pressurizing the air or water. It is also possible to sequentially select crack formation sites by using an injection tube having a double packer and expand the formation layer.

As described above, in order to remove contaminants from the treated stratum by suction after freezing and thawing, or after crack formation, the usual vacuum extraction method is used as it is. Can be done with

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

A pressurized injection system 2 of gas or liquid by pressurization of a compressor 1 or the like is prepared in a contaminated soil restoration area 8 set in advance based on information such as a boring survey. The freezing pipe 5 for supplying the refrigerant, the pressure injection pipe 2, and the suction pipe 6 connected to the suction pump 7 are respectively built in the well drilled in the restoration area 8.

For freezing the soil, a brine method can be used in which an antifreeze (aqueous calcium chloride solution) called brine is cooled to -20 to -30 ° C, and this is sent to a freezing tube by a circulation pump to cool the ground. The brine whose temperature has risen due to the freezing of the ground can be continuously frozen by returning to a freezing system including a compressor, a condenser, and a cooler and cooling again.

In addition, liquid nitrogen (vaporization temperature -196
C) is prepared in a cylinder or tank truck, and liquid nitrogen can be used by directly pouring liquid nitrogen into a freezing tube and cooling by the heat of vaporization of nitrogen.

Each method is a freezing method adopted in civil engineering work, and the same equipment can be diverted, which is convenient.

In the thawing step, either of a method of thawing naturally and leaving it at room temperature and a method of rapidly thawing in a heating step may be used. Although not shown in FIG. 1, it is also effective to similarly install a heating tube to accelerate the thawing process. In addition, other than the method of freezing the ground using a freezing tube or the like, a method of freezing the ground is not limited because a refrigerant may be directly added or sprayed.

Although the method of the present invention does not particularly specify the type of contamination, it is very effective for contaminants existing in the water phase between soil particles or between particles. Such examples include, but are not limited to, volatile organic chlorine-based compounds such as trichloroethylene, tetrachloroethylene, and dichloroethylene, or oil and petroleum hydrocarbons, aromatic hydrocarbons, and the like.

The formation of a soil crack by pressurized injection is easy by pressurizing water or air from an injection pipe. Further, if a double injection pipe having a packer 11 capable of setting the pressure depth and an injection hole 12 formed of a rubber sleeve is used, the pressure injection position can be conveniently selected.
The amount of water or air to be injected and the injection pressure may be set in accordance with the soil properties of the ground to be injected under pressure and the desired pressure injection region.

Hereinafter, the present invention will be described in detail with reference to Examples.
They do not limit the invention in any way.

[0024]

EXAMPLE (Test tank) As shown in FIG. 2, a cylindrical test tank 17 (drum: radius about 300 mm, height about 850 m)
m), a gravel layer 19 is provided in the lower layer (0.1 m), and a mixed soil of fine sand and silt (mixing ratio; fine sand: silt = 8: 2) having 10 ppm of trichlorethylene is filled thereon,
This was the contaminated soil layer 18 of the model. Simultaneously with the filling of the soil, a freezing tube 14 into which liquid nitrogen is poured, a pressure injection tube 15 having four lateral sides opened and covered with a rubber sleeve, and a suction tube 16 having a tip covered with a stainless steel mesh are included. , The freezing part, the injection part, and the suction part were built so as to be in the center of the test tank. The upper part of the test tank is provided with a gravel layer 19 and covered. The lid is provided with a valve for removing the internal pressure, and is opened at the time of freezing or injection of the bacterial solution. Except that the freezing tube 14 is not set up, a tank exactly the same as the above-mentioned test tank is prepared and used as a control tank.

After the test soil is frozen by flowing liquid nitrogen through the freezing tube of the test tank, the soil is thawed by standing. Also,
In both tanks, compressed air was repeatedly sent from a pressure injection tube. (Measurement) Soil gas was sucked from the suction tube of both the test tank and the control tank by a pump at a flow rate of 10 liters per minute. A trap was provided in the middle of the suction, the soil gas was sampled, and the concentration was measured over time. Table 1 shows the results. (Test results)

[0026]

[Table 1]

[0027]

According to the present invention, when a step of freezing a contaminated ground area, a step of thawing the frozen ground, and a step of generating a crack in the ground by applying pressure to the ground, the gas in the soil from the ground is obtained. The efficiency of extracting contaminated vapor by sucking air has increased, and it has become possible to realize more efficient purification and shorten the construction period.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of an embodiment of the present invention.

FIG. 2 is a sectional view of a test tank used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Compressor 2 Pressure injection system (Pressure injection pipe) 3 Pressure injection pipe 4 Supply device 5 Freezing pipe 6 Suction pipe 7 Suction pump 8 Repair area 9 Cracking 10 Sleeve pipe 11 Packer 12 Injection hole 13 Injection pipe 14 Freezing Pipe 15 Pressure injection pipe 16 Suction pipe 17 Test tank 18 Contaminated soil layer 19 Gravel layer

Claims (3)

[Claims] 1. A method for purifying contaminated soil, comprising: following a step of freezing a contaminated ground region, and thereafter extracting contaminated steam for sucking gas in the soil from the ground. 2. A method for purifying contaminated soil, comprising: a step of freezing a contaminated ground area; a step of thawing the frozen ground; and then extracting contaminated steam for sucking gas in the soil from the ground. 3. The method according to claim 1, further comprising a step of freezing the contaminated ground area and a step of generating a crack in the ground by applying pressure to the ground, and extracting contaminated vapor for sucking gas in the soil from the ground. Purification method of contaminated soil.