JP2000210683A - Soil and / or groundwater purification method - Google Patents

Abstract

(57) [PROBLEMS] To efficiently decompose organic chlorine compounds in soil and / or groundwater contaminated with organic chlorine compounds. SOLUTION: The soil contaminated with an organochlorine compound and / or
Alternatively, hydrogen peroxide is added to groundwater in the presence of divalent iron ions, and then permanganate is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently decomposing organochlorine compounds in soil and / or groundwater contaminated with organochlorine compounds.

[0002]

2. Description of the Related Art Organochlorine compounds have been used as solvents having excellent dissolving power, but their carcinogenicity has recently been pointed out, and their release into the environment has been restricted. However, contamination by organic chlorine compounds has not been solved yet, and soil and groundwater contamination by organic chlorine compounds such as trichloroethylene and tetrachloroethylene has become a major social problem.

[0003] Organochlorine compounds are relatively volatile and hardly soluble in water. Therefore, utilizing this property, as a method for treating soil and / or groundwater contaminated with organochlorine compounds, vacuum extraction by suction from the soil with a blower or the like, or once groundwater is pumped and then air stripping (aeration treatment). Then, a method of collecting the waste with an adsorbent such as activated carbon and treating it as waste has been performed.

[0004] However, the method based on activated carbon adsorption merely transfers the contaminants unless the contaminants are recovered and reused, and has not been a fundamental solution. In addition, when this is incinerated, toxic dioxins may be produced unless sufficient temperature control is performed. For this,
Research on methods of decomposing organic chlorine compounds by methods other than incineration to make them harmless has been actively conducted.For example, as a method of decomposing using the energy of ultraviolet rays, an exhaust gas containing an organic halogen compound is irradiated with ultraviolet rays. A method has been proposed in which irradiation treatment is performed to form an acidic decomposed gas, followed by washing with alkali and detoxification treatment.

[0005] However, in these methods, the treatment is performed after the pollutants in the soil are once removed from the soil or groundwater by a vacuum extraction method or a pumping / aeration method.
A great deal of processing cost is required for the vacuum extraction, water pumping and aeration, and in these methods, pollutants cannot be sufficiently removed in the later stage of purification, and purification efficiency is reduced.
Therefore, as long as such a method is continued, the contamination of the contaminated soil or the groundwater in the vicinity thereof with the low concentration of the organic chlorine compound will be continued. Contamination by such a low concentration of an organic chlorine compound, for example, in the case of trichlorethylene, the concentration of the contamination is reduced from the environmental standard value of 30 μg / L to 1
For a contamination of about 000 μg / L, no effective purification method has been proposed from a practical viewpoint.

[0006] In general, the contaminated soil is often in the vicinity of operating facilities or immediately below buildings in the premises of various factories. Therefore, when such contaminated soil is treated, the contaminated soil is often removed from the site. In other words, there is a strong demand for a treatment method that can perform a purification treatment in situ and has no harmful effects due to residual chemicals after treatment.

[0007]

Therefore, in addition to the above method, a method has been proposed in which hydrogen peroxide is directly injected into contaminated soil to decompose pollutants such as trichloroethylene. It is also known that organochlorine compounds can be decomposed and removed by permanganate.

[0008] According to such a processing method, the in-situ purification processing can be performed, and there is no problem of adverse effects due to residual chemicals after the processing.

[0009] Hydrogen peroxide generates radicals in the presence of divalent iron ions and rapidly decomposes organic chlorine compounds.
It easily reacts with substances in soil and groundwater and is easily decomposed on the surface of the soil.

[0010] Further, since permanganate is decomposed by soil at a lower rate than hydrogen peroxide, the rate of decomposition on the soil surface and wastefully consumed is relatively small, so that the range of influence of the treatment can be widened. It is excellent in that it can be used, but is wasted by the reaction with a reducing substance such as divalent iron ions. That is, when hydrogen peroxide and permanganate are used alone, a large amount of these are decomposed on the soil surface or reacted with a reducing substance, so that many of them are wasted and the processing efficiency is deteriorated. there were.

The present invention solves the above-mentioned conventional problems, and provides a soil and / or soil which can efficiently treat an organic chlorine compound in soil contaminated with the organic chlorine compound and / or groundwater.
Alternatively, an object of the present invention is to provide a method for purifying groundwater.

[0012]

Means for Solving the Problems Accordingly, the present inventors have:
Focusing on divalent iron ion, a typical reducing substance in soil and groundwater, oxidizes this to trivalent by the action of hydrogen peroxide and simultaneously decomposes contaminants. By adding these, it was found that the remaining contaminants could be completely decomposed without wasting them, and the present invention was completed.

That is, the present invention is characterized in that hydrogen peroxide is added to soil and / or groundwater contaminated with an organochlorine compound in the presence of divalent iron ions, and then permanganate is added. And

The decomposition mechanism of the organic chlorine compound in the present invention is as follows.

The previously added hydrogen peroxide is reduced as follows under the condition that divalent iron ions are present to generate a hydroxyl radical.

H ₂ O ₂ + Fe ²⁺ → OH. + OH ⁻ + Fe ³⁺ These radical species are very reactive and can oxidatively decompose almost all organic substances (Fenton reaction). At this time,
Divalent iron ions are oxidized to trivalent ions. Therefore, when hydrogen peroxide is added under the condition that divalent iron ions are present, the divalent iron ions are oxidized to trivalent and, at the same time, the organic chlorine compound is decomposed. For example, in the case of trichloroethylene (TCE), it is decomposed as follows.

C ₂ HCl ₃ + 6OH.fwdarw.2CO ₂ + 3HCl + 2H ₂ O Next, when a permanganate is added, the divalent iron ions are already mostly converted to trivalent by the action of hydrogen peroxide previously injected. Since it is oxidized, wasteful consumption of permanganate by divalent iron ions is suppressed, and the permanganate can efficiently react with the organic chlorine compound to decompose it.

Even if the added hydrogen peroxide and permanganate flow out of the area to be treated, the hydrogen peroxide and permanganate are gradually decomposed by the reaction with the reducing substances in the soil or groundwater and the catalytic action on the soil surface. Therefore, since the concentration decreases relatively slowly, it is very unlikely that these will remain in soil or groundwater for a long period of time and cause secondary pollution.

[0019]

Embodiments of the present invention will be described below in detail.

In the present invention, hydrogen peroxide is first added to soil and / or groundwater contaminated with an organochlorine compound in the presence of divalent iron ions, and then permanganate is added.

Here, the divalent iron ion must be present at a concentration of 1 mg / L or more in soil and / or groundwater contaminated with the organochlorine compound, and the concentration of the divalent iron ion is lower than this. And the reaction may not proceed smoothly. In a normal case, since divalent iron ions are naturally present at a concentration of about several ppm to 20 or 30 ppm, it is not necessary to particularly add divalent iron ions. However, when divalent iron ions are insufficient in soil and / or groundwater, divalent iron ions such as ferrous sulfide and ferrous chloride are added. In this case, the addition concentration of divalent iron ions is preferably as high as 1 ppm or more, but if it is too high, trivalent iron ions generated by oxidation precipitate in the form of iron oxyhydroxide or the like, so that the injection hole is closed. Therefore, it is preferable to add so that the concentration becomes about 10 ppm.

Hydrogen peroxide is preferably added in a chemical equivalent or slightly excess (for example, about twice equivalent) to the concentration of divalent iron ions in soil or groundwater.

In general, pollutants such as organochlorine compounds are hardly soluble in water and have a large specific gravity, so that they often remain in the lower part of the aquifer in the soil. Is dissolved in groundwater as divalent iron ions, so that the amount of hydrogen peroxide to be added can be determined practically by measuring the concentration of divalent iron ions in the groundwater.

If a large amount of hydrogen peroxide is added, the permanganate added later reacts with hydrogen peroxide,
Since permanganate is wasted, it is important that the amount of added hydrogen peroxide is not excessive. In normal cases, hydrogen peroxide varies depending on the degree of contamination of soil and groundwater, but as described above, it is almost equivalent to or slightly in excess of divalent iron ions in groundwater, and is contaminated with organic chlorine compounds. It is preferable to add it so that it may be about 1 to 100 ppm with respect to soil and / or groundwater.

By adding hydrogen peroxide at such a concentration in the presence of divalent iron ions, the reaction between hydrogen peroxide and divalent iron ions causes the divalent iron ions to become trivalent iron ions. At the same time, active hydroxyl radicals are generated, and these hydroxyl radicals efficiently decompose organochlorine compounds in soil or groundwater.

In addition, when adding hydrogen peroxide, an acid such as sulfuric acid is added to lower the pH of soil or groundwater to 2 to 6, thereby improving the decomposition efficiency of the organic chlorine compound. . This is due to the mechanism by which some of the iron ions oxidized from divalent to trivalent by hydrogen peroxide are reduced to divalent again by hydrogen peroxide under acidic conditions.
This is because active species such as hydroxyl radicals are efficiently generated from hydrogen peroxide, so that hydrogen peroxide is effectively used for decomposing organic chlorine compounds.

After the addition of the hydrogen peroxide, the permanganate is added. Since hydrogen peroxide rapidly reacts with divalent iron ions, permanganate may be added several hours after the addition of hydrogen peroxide, and may be added 1 to 10 hours after the addition of hydrogen peroxide. Is preferred.

The amount of permanganate to be added is not particularly limited, and may be at least the minimum amount necessary to almost completely decompose the organochlorine compound remaining in soil or groundwater. This addition amount is, based on the concentration of the organochlorine compound remaining in the soil or groundwater after the decomposition treatment with hydrogen peroxide as a reference, from 1 to 1 of the theoretical amount required to decompose the entire amount.
000 times.

The hydrogen peroxide is usually a hydrogen peroxide solution having a concentration of 0.01 to 5% by weight,
It is added to soil or groundwater as an aqueous solution having a concentration of 1 to 1% by weight. As the permanganate, potassium permanganate, sodium permanganate or the like is used.

The amount of hydrogen peroxide and permanganate to be added varies depending on the degree of contamination of the soil and / or groundwater contaminated with the organochlorine compound to be treated, but usually 100 to 1000 μg / L. In the case of soil or groundwater contaminated with a certain amount of organic chlorine compounds, hydrogen peroxide is added in an amount of 1 to 25 ppm, and then permanganate is added in an amount of 5 to 10 ppm.
The treatment is performed by adding about 0 ppm.

The object to be treated in the present invention is soil and / or groundwater contaminated with an organochlorine compound. Among the organochlorine compounds, the method of the present invention is particularly applicable to dichloroethylene (DCE) and trichloroethylene (TCE). And tetrachlorethylene (PCE).

In the method of the present invention, the treatment efficiency is reduced in the latter stage of the purification treatment by the purification method employing the above-mentioned vacuum extraction method or the pumping / aeration method which is currently put into practical use, and the low-concentration organic chlorine which cannot be completely removed is used. It is effective in treating soil and / or groundwater in which the compound remains.

Such a method of the present invention is particularly effective for in-situ treatment, but is not limited to in-situ treatment, and is carried out by excavating soil, purifying according to the present invention, and then backfilling. You can also.

In the case of performing in-situ purification treatment, specifically, a well is set up to a depth where contaminants exist, and an aqueous solution of hydrogen peroxide is injected using the well, and then permanganate is used. Although a method of injecting an aqueous solution of salt is adopted, it is also possible to improve the treatment efficiency by providing a pumping well other than an injection well to give a flow to groundwater in the soil.

In such a purification treatment, if the area to be purified is limited, a sufficient purification effect can be obtained by adding hydrogen peroxide and permanganate once each, If contaminants diffuse from the area to the area to be purified, it is necessary to repeat the addition of hydrogen peroxide and permanganate. In such a case, by monitoring the concentration of the organic chlorine compound in the purification target area, the addition of hydrogen peroxide and permanganate may be repeated until the concentration falls below the environmental standard value. When the addition of the hydrogen peroxide and the addition of the permanganate are repeated alternately a plurality of times, the time from the addition of the permanganate to the addition of the next hydrogen peroxide is about 12 hours to several days. It is preferable to set the interval. That is, this interval is equivalent to the time when the groundwater in the treatment area is approximately replaced, and varies depending on the flow rate of the groundwater in the treatment area and the presence or absence of a pumping well for forced circulation of the groundwater. Can be set within the above range.

[0036]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 and 2 and Comparative Examples 1 to 4 Residual chlorine was removed through an activated carbon column, and 10 mg / L (0.18 mM) was added to deaerated and nitrogen-purged tap water.
Iron (ferrous sulfate) and 1mg / L TCE
Was added to obtain a test solution (simulated contaminated groundwater). This was put in a vial bottle, sealed with an aluminum seal septum, hydrogen peroxide in the amount shown in Table 1 was added, and after 4 hours, potassium permanganate in the amount shown in Table 1 was added (however, Comparative Examples 1 and 2). In No. 2, no hydrogen peroxide was added. In Comparative Examples 3 and 4, potassium permanganate was not added.), And left at 20 ° C. And T remaining 24 hours after the addition of hydrogen peroxide
The CE concentration was measured by gas chromatography, and the results are shown in Table 1.

[0038]

[Table 1]

Comparative Example 5 The treatment was performed under the same conditions as in Example 1 except that the order of adding hydrogen peroxide and potassium permanganate was reversed. As a result, potassium permanganate is consumed by reacting with divalent iron ions,
In addition, since divalent iron ions were also oxidized to trivalent, the residual TCE concentration after 24 hours even after adding hydrogen peroxide was 0.1%.
At 85 mg / L, there was almost no change from the initial concentration.

Comparative Examples 6 and 7 In Examples 1 and 2, residual chlorine was removed by passing through an activated carbon column, and divalent iron ions (ferrous sulfate) were not added to deaerated and nitrogen-purged tap water. 1 mg / L TCE
The same treatment was carried out except that only the test solution (simulated contaminated groundwater) was added thereto, and the residual TCE concentration was measured. The results are shown in Table 2.

[0041]

[Table 2]

Example 3 10 mg / L (0.18 mM) was added to dewatered and nitrogen-purged tap water to remove residual chlorine by passing through an activated carbon column.
Iron (ferrous sulfate) and 1mg / L TCE
And 1 mg / L of cis-DCE were added to make a test solution (simulated contaminated groundwater). This test liquid was used for a particle size of about 0.45.
40 mL was added to a vial having a capacity of 160 mL containing 80 mL of sand of mm, and immediately sealed with an aluminum seal septum. 2m of hydrogen peroxide solution with 1000mg / L concentration
L was injected with a syringe and shaken under the conditions of 20 ° C. and 60 rpm. Further, after 4 hours, 2 mL of a 1000 mg / L aqueous solution of potassium permanganate was injected with a syringe, and shaking was continued under the same conditions.

Separately from the sample thus prepared, neither hydrogen peroxide nor potassium permanganate was added, and a sample prepared by the same procedure except for the above was used as a standard concentration sample of TCE and cis-DCE.

Two days after the addition of hydrogen peroxide, the headspace of each sample was chromatographed and the residual TCE and cis-DCE were determined by comparison with a standard concentration sample.
Was determined. As a result, the TCE concentration was 0.015 m
g / L, cis-DCE concentration was 0.008 mg / L.

Comparative Example 8 The same operation as in Example 3 was performed, except that potassium permanganate was not added. As a result, the concentrations of TCE and cis-DCE remaining two days after the addition of hydrogen peroxide were 0.43 mg / L and 0.24 mg / L, respectively.

Comparative Example 9 The same operation as in Example 3 was carried out except that no hydrogen peroxide was added. As a result, the concentrations of TCE and cis-DCE remaining two days after the addition of potassium permanganate were 0.53 mg / L and 0.30 mg / L, respectively.

Comparative Example 10 The same operation as in Example 3 was performed except that the order of adding hydrogen peroxide and potassium permanganate was reversed. As a result, TCE and ci remaining two days after the addition of potassium permanganate were added.
The concentrations of s-DCE were 0.65 mg / L and 0.5, respectively.
It was 7 mg / L.

[0048]

As described in detail above, the soil and / or
Alternatively, according to the groundwater purification method, it is possible to efficiently decompose the organic chlorine compound in soil and / or groundwater contaminated with the organic chlorine compound. The method of the present invention can be processed in situ, has no problem of cross-contamination due to residual chemicals, and has extremely large industrial utility.

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[Procedure amendment]

[Submission date] January 27, 1999 (1999.1.2
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

Here, the divalent iron ion must be present at a concentration of 1 mg / L or more in soil and / or groundwater contaminated with the organochlorine compound, and the concentration of the divalent iron ion is lower than this. And the reaction may not proceed smoothly. In a normal case, since divalent iron ions are naturally present at a concentration of about several ppm to 20 or 30 ppm, it is not necessary to particularly add divalent iron ions. However, in the case of insufficient divalent iron ions in the soil and / or groundwater, adding a divalent iron ion such as sulfate <br/> ferrous and ferrous chloride. In this case, the addition concentration of divalent iron ions is preferably as high as 1 ppm or more, but if it is too high, trivalent iron ions generated by oxidation precipitate in the form of iron oxyhydroxide or the like, so that the injection hole is closed. Therefore, it is preferable to add so that the concentration becomes about 10 ppm.

Claims (1)

[Claims] A soil contaminated with an organochlorine compound and / or
Alternatively, a method for purifying soil and / or groundwater, comprising adding hydrogen peroxide to groundwater in the presence of divalent iron ions, and then adding permanganate.