JP2008272597A - Method for treating polluted soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a method for purifying polluted soil for a shorter period of time that is industrially expected, more shorten an execution period of purification including the decomposition and a decrease in concentration of a polluted substance, period of a secondary treatment after the purification as well as the treating period required for the purification that are expected, and the purification of complex pollution soil polluted with organic halides, oil, and the like that may be expected in the iron powder process. <P>SOLUTION: The method for treating a polluted soil polluted with an organic halide with an iron powder that additionally applies a heating means to the soil where the polluted soil and iron powder are mixed, and the temperature of the polluted soil is set at 40 to 120°C with the heating means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to the treatment of contaminated soil containing organic halogen compounds and other pollutants.

  Various purification methods have been proposed for contaminated soil contaminated with organic halogen compounds. An iron powder method that mixes zero-valent iron powder into contaminated soil and decomposes organic halogen compounds in the soil by the action of iron powder. A microbial method that decomposes organic halogen compounds in soil using the ability to decompose microorganisms. There is an oxidation method in which a Fenton reagent or the like is added to contaminated soil to decompose an organic halogen compound in the soil. The iron powder method is an excellent technique capable of reliably decomposing an organic halogen compound without contamination by iron powder or the like even after the contaminated soil is purified.

  Organohalogen compounds in the contaminated soil are locally concentrated or diffused thinly at various locations depending on the soil quality of the contaminated soil. It is attributed to the ease of flow of groundwater, rainwater, and organic halogen compounds depending on the soil. When contaminated soil and iron powder are mixed, the soil quality of the contaminated soil is uniform in the mixed region, but the homogeneity is not required in the iron powder method. The iron powder in the contaminated soil decomposes under the influence of the original soil, decomposes the organic halogen compounds, and purifies the contaminated soil. For this reason, in the iron powder method, the construction period for purification has been changed under the influence of the original soil quality. In addition, in addition to organic halogen compounds, contaminants such as oil may be combined in the contaminated soil. In the iron powder method, depending on the oil, it may be a factor inhibiting the decomposition. Patent Document 1 discloses a technique capable of shortening the purification period by improving the decomposition performance when mixing and purifying contaminated soil with iron powder.

Japanese Patent Application Laid-Open No. 11-235577

  As described above, a method for finishing the purification of contaminated soil in a shorter period of time is desired in the industry. Purification will not only detoxify and reduce the concentration of pollutants, but will not only be detoxified, but also the construction period, including not only the treatment period for purification but also the secondary treatment period after purification. It is hoped that it will end. In the iron powder method, it has been desired to be able to purify complex contaminated soil such as organic halogen compounds and oil.

  The inventor has found the present invention to solve the above problems. That is, when purifying contaminated soil using the iron powder method, the inventors have focused on finding the solution that has less influence on the mixed state of iron powder and soil, and iron powder in the contaminated soil.

A method for treating contaminated soil, characterized in that in the method for treating contaminated soil contaminated with an organic halogen compound with iron powder, heating means is added to the soil in which the contaminated soil and iron powder are mixed. It is preferable because the purification of contaminated soil is promoted.

The method for treating contaminated soil according to claim 1, wherein the temperature of the contaminated soil is set to 40 ° C to 120 ° C by the heating means. This temperature is suitable for purification in soil.

  The method for treating contaminated soil according to claim 1 or 2, wherein the heating means is steam blowing or electric heating. Suitable for heating to contaminated soil. The temperature distribution can also be controlled.

The method for treating contaminated soil according to any one of claims 1 to 3, wherein the heating means involves physical recovery such as pumping, suction, pumping and water injection, injection and suction. The control of temperature distribution is made more suitable, and it is possible to move and remove contaminants in the contaminated soil.

  In remediation of contaminated soil, the time required for remediation can be significantly shortened. Here, in order to solve the above problem, the purification rate was dramatically improved by mixing zero-valent iron underground and heating. As a result, the environment can be recovered in a short period of time, and effective use of the land desired by the industry is promoted.

  Organic halogen compounds contained in contaminated soil are targeted for substances that can be decomposed by iron powder. For example, there are TCE, PCE, cis-DCE and the like.

  The mixed state of the contaminated soil and iron powder is not particularly affected and may be a mixed state in a heterogeneous state. The soil may also be a mixed state of soils with completely different water permeability, such as a mixture of silt and sand. However, it is desirable that the contaminant is decomposed by the iron powder in the mixed state.

  The iron powder may be iron powder used in the iron powder method. When the concentration of the organic halogen compound is higher, or when it is desired to finish the purification in a shorter period of time, it is preferable to use iron powder having high decomposition performance. For example, iron powder containing 0.1% or more of carbon and having a specific surface area of 500 cm2 / g or more may be used. The average particle size of the iron powder is preferably about 100 to 500 μm. In the state mixed with soil, it is preferable because it absorbs heat from the heating means and promotes dispersion of heat. The mixing amount of the iron powder into the contaminated soil may be a mixing amount suitable for decomposition by the iron powder method. About 0.1-10 mass% may be sufficient with respect to contaminated soil (dry).

  For contaminated soil, the area to be purified is identified and iron powder is mixed with the contaminated soil. The mixing method may be an auger method using heavy machinery, excavation mixing using a back fore, an in-situ method in which the mixed soil remains in-situ, or a pile method in which piles are formed in adjacent places. The invention is applicable. What is necessary is just to set suitably the mixing method and preservation | save of a mixing state.

When it is confirmed that the contaminated soil and the iron powder are mixed, the pollutant is decomposed, and the concentration is reduced, heating means is added to the soil area where the contaminated soil and the iron powder are mixed.
The heating means introduces heat by steam (steam) blowing, electric heating, or the like to raise the ground temperature by 20 ° C. or more. Below 40 ° C, the effect is small, and above 130 ° C is economically disadvantageous.
It is desirable that the steam blowing position is a position where the steam passes through the contaminated soil region. Furthermore, it is desirable to install in the deepest part of the contaminated area. This is because as the steam rises from the blowing position toward the ground surface, the blowing area is expanded as deep as possible.
It is more effective to perform physical recovery actions such as pumping, suctioning, pumping and pouring, injection and suction, as well as warming. This is presumed that the purification period is shortened by synergistic contributions of an increase in the rate of chemical reaction by heating and an increase in the mobility of pollutants.
During construction at the site, the generation of hydrogen gas is significant, so a device for collecting hydrogen gas will be installed.
For the steam blowing, it is preferable to use a steam spray tube that has a strainer structure through which steam passes and sprays the steam horizontally in the ground, and can spray steam from the tip. It is desirable to install multiple steam inlets within the contaminated soil area.

Pseudo-contaminated soil was created as follows.
The soil quality of the pseudo-contaminated soil is dredged soil with sand and silt layers, the soil pH is about 9, and the groundwater level is 2m deep from the surface.
The contamination range was 5 m × 5 m × depth 10 m. In addition, it was partitioned with a sheet pile or the like so that the contamination did not diffuse.
Contaminants and concentrations were as follows: PCE 100 mg / kg (dry soil, soil elution value), TCE 15 mg / kg (dry soil, soil elution value), cis-DCE 3 mg / kg (dry soil, soil elution value), oil 390 mg / kg The initial concentration was defined as a mixed state of kg (dry soil, soil content value).

The iron powder method was carried out on this pseudo-contaminated soil. In the iron powder method, iron powder was mixed in the region with a heavy machine (auger). The soil after mixing was in situ. The iron powder containing 0.1% carbon and having an average particle size of 200 μm was used, and the amount added was 3% by mass relative to the soil (dry). In addition, in order to make a mixed state nonuniform, the addition amount of iron powder was varied at the time of mixing. As a result, the amount of iron powder added varied by 1 to 10%.
In this state, it was left to stand for about 75 days. Due to the decomposition of iron powder, the concentration of pollutants is as follows: PCE 1.5 mg / kg (dry soil, soil elution value), TCE 0.01 mg / kg (dry soil, soil elution value), cis-DCE 0.2 mg / kg (Dry soil, soil elution value), oil 390 mg / kg (dry soil, soil content value), and it was confirmed that the pollutants were decomposed.
Furthermore, it was left still for 15 days. Pollutants are being decomposed, but decomposition is slowing down.
Therefore, a heating means was implemented. The heating means was steam injection. Steam injection pipes equipped with injection ports were installed at four locations in the contaminated area so that steam can be sprayed from the tip of the pipe. There are four places where the steam pipes are installed when the area is viewed from the ground surface. In addition, a steam injection pipe was inserted so that the injection port was placed at a depth of 10 m from the ground surface (the strainer section was -9 to 10 m from the ground surface (GL)), and a pumping well was installed on each side. Steam was generated in the boiler and the injection was carried out for about 10 days. At this time, the total amount of injected steam was 28 m ³ (from boiler usage record).
The temperature of the soil in the contaminated area increased from 20 ° C. to 120 ° C. at the maximum before injection.
Results: PCE 0.01 mg / kg (dry soil, soil elution value) or less, TCE 0.001 mg / kg (dry soil, soil elution value) or less, cis-DCE 0.001 mg / kg (dry soil, soil elution value) Hereinafter, it was confirmed that oil was 250 mg / kg (dry soil, soil content value) and that the contaminants were decomposed and the soil was purified.
After the injection of the steam, the temperature of the soil during the treatment was measured after 96 hours. The measurement location is 60 cm in the horizontal direction from the center of the steam pipe, and the depth, which is the depth distance from the ground surface, is 11 points at intervals of 0 to 1 m in the range of 0 to 10 m, similarly 130 cm and 11 to 16 m. Temperature was measured by arranging six thermometers. In addition, the part of the depth of 10 m from the ground surface is a position where the steam is jetted and becomes the end of the steam injection pipe. The measurement results are shown in Table 1. As shown in Table 1, the temperature of the soil reaches the highest temperature at 117 to 120.5 ° C. at a depth of 4 to 5 m. In this way, by blowing steam through the steam injection pipe, it is possible to generate an arbitrary temperature distribution in the depth direction, and the temperature distribution can be controlled according to the contamination concentration and the purification method, so that purification is promoted and steam It is possible to reduce costs by suppressing wasteful use.

In this way, even complex contaminated soil can be purified in a short period of time. In this example, it was allowed to stand for 15 days after the first standing period of 75 days, but since the progress of purification was slow, if the steam blowing of the present invention was performed after the first 75 days, the standing period of 15 days was It turns out that it is unnecessary. In addition, after the purification process, no work is required except for removing the apparatus for blowing steam, so that the secondary process after the purification is unnecessary.

Claims (5)

A method for treating contaminated soil comprising treating a contaminated soil containing an organic halogen compound with iron powder, wherein heating means is added to a region where the contaminated soil and iron powder are mixed. The method for treating contaminated soil according to claim 1, wherein the temperature of the contaminated soil is set to 40 ° C to 120 ° C by the heating means. The method for treating contaminated soil according to claim 1 or 2, wherein the heating means is steam blowing or electric heating. The method for treating contaminated soil according to any one of claims 1 to 3, wherein the heating means involves physical recovery such as pumping, suction, pumping and water injection, injection and suction. The method for treating contaminated soil according to any one of claims 1 to 4, wherein the contaminated soil is soil including a silty layer.