JP4715059B2 - Method for decomposing organochlorine compounds in soil and / or groundwater - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for decomposing organochlorine compounds in soil and / or groundwater in situ.
[0002]
[Prior art]
Soil and groundwater can be polluted by various harmful persistent substances. In particular, contamination with organic chlorine compounds such as tetrachloroethylene, trichlorethylene, and dichloroethylene is a serious problem.
[0003]
As a method for purifying soil and / or groundwater contaminated with pollutants such as organochlorine compounds in a short period of time, a treatment agent for decomposing the pollutants is supplied to the soil and / or groundwater, and the soil and / or groundwater Among them, a processing method for decomposing contaminants, a so-called in-situ processing method, has attracted attention as a new technology. The in-situ treatment method includes a microbial treatment method. In this microbial treatment, a microbial growth substrate is supplied as a treatment agent to soil and / or groundwater, and an organochlorine compound is produced by the action of microorganisms present in the soil and / or groundwater. Decompose contaminants such as
[0004]
In such a microbial treatment method, an organic chlorine compound having a high chlorine bond number is generally decomposed into a compound having a low chlorine bond number. For example, tetrachlorethylene is sequentially decomposed into ethylene via trichlorethylene, dichloroethylene, and vinyl chloride.
[0005]
[Problems to be solved by the invention]
However, in the conventional in-situ treatment method using microorganisms, even if a compound having 3 or more chlorine bonds such as tetrachloroethylene and trichlorethylene is decomposed into a compound having 2 chlorine bonds such as dichloroethylene, the number of chlorine bonds such as dichloroethylene is 2 or less. In some cases, the organic chlorine compound was not further decomposed into vinyl chloride or ethylene.
[0006]
The present invention solves the above-mentioned conventional problems, and in a method for decomposing organochlorine compounds in soil and / or groundwater by a microbial treatment method, an organochlorine compound having a small number of chlorine bonds is efficiently decomposed. It is an object of the present invention to provide a method for decomposing organochlorine compounds in soil and / or groundwater that can be rendered harmless.
[0007]
[Means for Solving the Problems]
The method for decomposing organochlorine compounds in soil and / or groundwater of the present invention (Claim 1) supplies a growth substrate of microorganisms to the soil and / or groundwater, and the organochlorine compounds in the soil and / or groundwater are transformed into microorganisms. a method of decomposing by the action, the growth substrates, as a processing agent for a silver / redox potential of the silver chloride electrode potential -100 to-50 m V, a method of supplying to the soil and / or groundwater The organic chlorine compound is one or more substances selected from the group consisting of tetrachloroethylene, trichloroethylene, dichloroethylene, vinyl chloride and dichloroethane, and the organic chlorine compound content in the soil is 0.05 to 5 mg / kg, the content of organochlorine compound in the groundwater is 0.1 to 10 mg / L, and the growth substrate is citric acid and / or citrate, The content of the growth substrate in the treatment agent is 10 to 1000 mg / L, and the liquid containing the growth substrate is passed through a column filled with metal iron and / or iron sulfide to cause metal iron and / or iron sulfide. By supplying the treating agent prepared by contacting to the soil and / or groundwater, the organochlorine compound having 2 or less chlorine bonds in the soil and / or groundwater is decomposed into vinyl chloride or ethylene. It is characterized by that.
[0008]
In the method for decomposing organochlorine compounds in soil and / or groundwater according to the present invention (claim 2), a microorganism growth substrate is supplied to the soil and / or groundwater, and the organochlorine compounds in the soil and / or groundwater are converted into microorganisms. A method for supplying the growth substrate to the soil and / or groundwater as a treatment agent having a redox potential of a silver / silver chloride electrode potential of −100 to −50 mV, The organochlorine compound is one or more substances selected from the group consisting of tetrachloroethylene, trichloroethylene, dichloroethylene, vinyl chloride and dichloroethane, and the organochlorine compound content in the soil is 0.05 to 5 mg / kg. The organochlorine compound content in the groundwater is 0.1 to 10 mg / L, the growth substrate is citric acid and / or citrate, The growth substrate content in the agent is 10 to 1000 mg / L, and the water and the growth substrate are brought into contact with the metal iron and / or iron sulfide by passing water through a column filled with metal iron and / or iron sulfide. By supplying the treating agent prepared by mixing to the soil and / or groundwater, the organic chlorine compound having a chlorine bond number of 2 or less in the soil and / or groundwater is decomposed into vinyl chloride or ethylene. It is characterized by doing.
[0009]
Organochlorine compounds are degraded by the action of microorganisms in the presence of growth substrates. This decomposition reaction proceeds under anaerobic conditions. For example, tetrachloroethylene is decomposed into ethylene via trichlorethylene, dichloroethylene, and vinyl chloride. In addition, dichloroethylene is directly decomposed into ethylene. However, in the conventional microbial treatment method, an organic chlorine compound having 3 or more chlorine bonds such as tetrachloroethylene or trichloroethylene is decomposed into a compound having 2 or less chlorine bonds such as dichloroethylene, whereas the number of chlorine bonds such as dichloroethylene is 2 The following organochlorine compounds may not be decomposed.
[0010]
The present inventor examined this cause and confirmed that the above-described phenomenon occurs when the microorganism is exposed to a condition where the oxidation-reduction potential is +100 mV or more. That is, when supplying the growth substrate to soil and / or groundwater in the microbial treatment method, the growth substrate is dissolved or diluted with water and injected into the soil and / or groundwater. If the growth substrate solution has a high redox potential, The oxidation-reduction potential of soil and / or groundwater also increases, the above phenomenon occurs, and the organic chlorine compound having a chlorine bond number of 2 or less remains in the soil and / or groundwater without being decomposed.
[0011]
In the present invention, the growth substrate is injected into soil and / or groundwater as a treatment agent having a redox potential of the silver / silver chloride electrode potential (hereinafter simply referred to as “ORP”) of −100 to −50 mV , The above phenomenon is prevented, and an organic chlorine compound having a chlorine bond number of 2 or less such as dichloroethylene can be reliably decomposed .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the method for decomposing soil and / or organic chlorine compounds in the groundwater of the present invention will be described in detail below.
[0013]
In the present invention, an organic chlorine compound to be processed is an organic chlorine compounds contained in soil and / or groundwater, degraded by microbial treatment as the type state, and are not capable of removing, tetrachlorethylene (PCE), trichlorethylene ( Organochlorine compounds such as TCE), dichloroethylene (DCE), vinyl chloride (VC), and dichloroethane (DCA ) are suitable as treatment targets. One kind of these organic chlorine compounds may be contained alone or two or more kinds may be contained in combination in the soil and / or groundwater.
[0014]
The content of these organic chlorine compounds in soil and / or groundwater, in the soil 0.05 to 5 mg / kg, in the ground water 0.1 to 10 mg / L is suitable for processing.
[0015]
The growth substrate of microorganisms comprising as an active ingredient of the treatment agent used in the treatment of the organic chlorine compounds, Ri growth substrates der capable decompose and remove the organic chlorine compounds by situ process using microorganisms, some have citrate the sodium salt, potassium salt, calcium salt, magnesium salt, a salt such as an iron salt. These growth substrates may be contained alone or in a combination of two or more in the treatment agent.
[0016]
Among these growth substrates, since it has a chelating ability for metal ions such as iron, it can prevent precipitation of metal ions and has a pH buffering ability in the vicinity of neutrality. Citric acid or its sodium salt or potassium salt is preferred.
[0017]
Suitable content of the growth substrate in the treatment agent used in the present invention, 1 0~1000mg / L, is prepared preferably Ri 50 to 300 mg / L der, treating agent as a growth substrate an aqueous solution of such concentration .
[0018]
In the microorganism treatment according to the present invention, since the treatment is performed using microorganisms present in soil and / or groundwater, it is not particularly necessary to supply microorganisms, but microorganisms having a high organochlorine compound decomposition activity are treated. It may be supplied by being contained in the agent, or may be treated by inoculating it by supplying it to soil and / or groundwater separately from the treatment agent.
[0019]
In the present invention, a treatment agent containing the growth substrate and having an ORP of −50 mV or less is used. When the ORP of the treatment agent is higher than +100 mV, the ORP of the soil and / or groundwater is increased, and the organic chlorine compound having a chlorine bond number of 2 or less cannot be decomposed.
[0020]
For this reason, in the present invention, the growth substrate solution obtained by dissolving or diluting the growth substrate is reduced, or the growth substrate is dissolved or diluted with reduced water, so that the OR P- 50 mV or less. A growth substrate-containing treatment agent is prepared.
[0021]
This reduction treatment can be performed, for example, by bringing a growth substrate solution or a growth substrate solution or diluted water into contact with metallic iron and / or iron sulfide. The metal iron or iron sulfide used here preferably has a large surface area, and can be formed into a porous shape or a fiber shape. The contact method is a column flow method , and the contact time can be about 10 to 20 minutes. According to such a reduction treatment, a treatment agent of about ORP + 100 mV to −100 mV can be prepared.
[0022]
In the method of the present invention, the growth substrate-containing treatment agent prepared as described above is supplied to the soil and / or groundwater and diffused in the soil and / or groundwater, and the microorganisms in the soil and / or groundwater are propagated. Then, the organochlorine compound in the soil and / or groundwater is decomposed using the action of microorganisms.
[0023]
The method of supplying the treatment agent to the soil and / or groundwater is a method of supplying the treatment agent to the soil and / or groundwater by a treatment agent supply facility such as a well or a seepage pit installed in the soil, and the treatment agent to the surface layer of the soil. For example, a method of supplying and allowing the treatment agent to settle and diffuse in the deep layer can be employed.
[0024]
In this way, the treatment agent supplied to the soil and / or groundwater diffuses into the soil and / or groundwater, and the organic chlorine compound contained in the soil and / or groundwater is decomposed and rendered harmless by the microbial reaction. Is done. In this case, organochlorine compounds having 3 or more chlorine bonds such as PCE and TCE are decomposed via organochlorine compounds having 2 or less chlorine bonds such as DCE and VC. In the present invention, ORP is −100 to −50 m. By using the treating agent of V, it becomes possible to efficiently decompose an organic chlorine compound having a chlorine bond number of 2 or less, preventing the residue of these organic chlorine compounds in soil and / or groundwater, Soil and / or groundwater can be reliably purified.
[0025]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.
[0026]
Example 1
To the tap water, sodium citrate was added as a growth substrate at 500 mg / L to obtain a growth substrate aqueous solution. The ORP of this aqueous growth substrate solution was +300 mV. The reduction treatment was carried out by passing the aqueous growth substrate solution through a column filled with metallic iron, and ORP was used as a growth substrate-containing treatment agent of −50 mV. The water residence time in the column was 10 minutes.
[0027]
100 mL of this growth substrate-containing treatment agent was placed in a vial, 50 mL of soil contaminated with PCE, TCE, DCE, VC and DCA was added, sealed, and cultured at 30 ° C.
[0028]
The headspace gas was analyzed by gas chromatography to examine changes in the organochlorine compound concentration, and the results are shown in FIG.
[0029]
Example 2
In Example 1, an experiment was performed in the same manner except that an iron sulfide packed column was used instead of the metal iron packed column, and the result is shown in FIG. The ORP of the growth substrate-containing treatment agent after the reduction treatment in the iron sulfide-filled column was −100 mV.
[0030]
Comparative Example 1
In Example 1, an experiment was performed in the same manner except that the reduction treatment was not performed and an ORP + 300 mV growth substrate aqueous solution was used, and the results are shown in FIG.
[0031]
The following is clear from FIGS.
[0032]
That is, in Comparative Example 1 using an ORP + 300 mV growth substrate aqueous solution, although PCE and TCE were decomposed, DCE (cis-DCE) was produced, and this DCE was decomposed into vinyl chloride (VC) or ethylene. However, DCE remained. In addition, the decomposition reaction of DCA did not occur. For this reason, the organochlorine compound could not be completely decomposed and removed.
[0033]
In contrast, in Example 1 using the ORP-50 mV growth substrate-containing treatment agent and Example 2 using the ORP-100 mV growth substrate-containing treatment agent, all organochlorine compounds were decomposed and converted to ethylene. It was done.
[0034]
From these results, it can be seen that by reducing the ORP by reducing the growth substrate solution, the organic chlorine compound can be efficiently decomposed and the residual organic chlorine compound having 2 or less chlorine bonds can be prevented.
[0035]
【The invention's effect】
As described above, according to the method for decomposing organochlorine compounds in the soil and / or groundwater of the present invention, by supplying the growth substrate-containing treatment agent of ORP -100 to -50 mV , the organic compound having a large number of chlorine bonds. Since not only chlorine compounds but also organic chlorine compounds with a small number of chlorine bonds can be efficiently decomposed and detoxified, the residue of these organic chlorine compounds can be prevented to ensure soil and / or groundwater Can be purified.
[Brief description of the drawings]
1 is a graph showing the results of Example 1. FIG.
2 is a graph showing the results of Example 2. FIG.
3 is a graph showing the results of Comparative Example 1. FIG.

Claims (2)

In a method of supplying a growth substrate of microorganisms to soil and / or groundwater and decomposing an organic chlorine compound in the soil and / or groundwater by the action of microorganisms,
A method of supplying the growth substrate to the soil and / or groundwater as a treatment agent having a redox potential of a silver / silver chloride electrode potential of −100 to −50 mV ,
The organochlorine compound is one or more substances selected from the group consisting of tetrachloroethylene, trichloroethylene, dichloroethylene, vinyl chloride and dichloroethane;
The organochlorine compound content in the soil is 0.05 to 5 mg / kg, the organochlorine compound content in the groundwater is 0.1 to 10 mg / L,
The growth substrate is citric acid and / or citrate, and the content of the growth substrate in the treatment agent is 10 to 1000 mg / L,
The treatment agent prepared by bringing the liquid containing the growth substrate into contact with metal iron and / or iron sulfide by passing water through a column filled with metal iron and / or iron sulfide is used as the soil and / or groundwater. The organic chlorine compound having a chlorine bond number of 2 or less in the soil and / or ground water is decomposed into vinyl chloride or ethylene by supplying to the soil and / or ground water, and the organic chlorine compound in the soil and / or ground water is decomposed . In a method of supplying a growth substrate of microorganisms to soil and / or groundwater and decomposing an organic chlorine compound in the soil and / or groundwater by the action of microorganisms,
A method of supplying the growth substrate to the soil and / or groundwater as a treatment agent having a redox potential of a silver / silver chloride electrode potential of −100 to −50 mV ,
The organochlorine compound is one or more substances selected from the group consisting of tetrachloroethylene, trichloroethylene, dichloroethylene, vinyl chloride and dichloroethane;
The organochlorine compound content in the soil is 0.05 to 5 mg / kg, the organochlorine compound content in the groundwater is 0.1 to 10 mg / L,
The growth substrate is citric acid and / or citrate, and the content of the growth substrate in the treatment agent is 10 to 1000 mg / L,
The treatment agent prepared by mixing water and a growth substrate in contact with metallic iron and / or iron sulfide by passing water through a column filled with metallic iron and / or iron sulfide, and the soil and / or Decomposing organochlorine compounds in soil and / or groundwater by decomposing organochlorine compounds having 2 or less chlorine bonds in the soil and / or groundwater into vinyl chloride or ethylene by supplying to groundwater Method.

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