JP2006326503A - Organic compound decomposing composition and decomposing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition capable of inexpensively and efficiently decomposing organic compounds polluting soil into harmless substances, and to provide a decomposing method. <P>SOLUTION: The organic compounds in the soil containing iron compounds are efficiently decomposed by using the composition having an organic compound decomposition property which comprises reducing agents such as alkali metal sulfites and water. The composition containing the reducing agents of equal moles or more to that of the iron compounds under the condition existing the iron compounds of equal moles or more to that of the organic compounds in the soil. The iron compound is preferably a ferrous compound. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composition and a method for decomposing volatile organic compounds, particularly volatile organic compounds contaminating soil and groundwater, at low cost and effectively.

  Volatile organic compounds such as trichloroethene and tetrachloroethene are widely used as cleaning agents and solvents for dry cleaning in the machinery and semiconductor industries due to their nonflammability, flame retardancy, and degreasing properties. I came. However, in recent years, contamination of soil or groundwater by these compounds has been confirmed, and removal / decomposition of volatile organic compounds that contaminate soil and groundwater is strongly desired because of the risk of harming human health.

Conventionally, soil gas suction, groundwater pumping, and soil excavation and removal methods have been proposed as methods for purifying soil contaminated with volatile organic compounds. In these methods, collected organic matter is removed in situ. Can not be disassembled in the environment, for technical reasons, for example, it is difficult to apply to soil contamination in the deep underground and where the building is located, and the cost is very expensive There was a problem.
Methods for purifying soil by decomposing volatile organic compounds separated from soil, etc. by the above purification methods, or by directly decomposing organic compounds in soil, etc. include combustion decomposition methods, thermal decomposition methods Methods, chemical decomposition methods, catalytic decomposition methods, microbial decomposition methods, and electrolysis methods are known.

Among them, a decomposition method using iron powder or the like has been proposed as a chemical decomposition method that is easy to use locally and can be reliably decomposed (Patent Document 1). However, in this method, in order to diffuse iron powder that is a water-insoluble solid into the ground together with water or mud water, it is directly injected during boring, or a rotary tool (reamer) is driven and stirred, Work to mix iron powder into the formation is necessary, and dedicated equipment such as boring is essential, and the work of injecting the decomposition agent at the same time as the boring requires many work restrictions and is expensive. become.
Moreover, the proposal which raises decomposition | disassembly and a purification | cleaning speed by combining iron powder etc. and a reducing substance is also made | formed (patent document 2, patent document 3). However, even in these methods, it is essential to use iron powder or the like that is a water-insoluble solid, and there is still a problem that work restrictions and costs are expensive.
On the other hand, a method of injecting a highly water-soluble sodium dithionite aqueous solution to decompose and purify contaminating volatile organic compounds in situ has also been proposed (Non-Patent Document 1). However, this compound has high reactivity such as self-degradability, and in the solid state as well as in the drug solution state, the water evaporates, and when the concentration is high, it can self-decompose and express the function of the purification drug. There was a drawback that it was difficult to handle.
JP 2000-135483 A Japanese Patent No. 3490247 JP 2004-74141 A JP-A-5-231086 Japanese Patent Laid-Open No. 9-1225859 JP 2003-337534 A 37th Geotechnical Research Presentation Summary Page 2357-2358 (July 2002)

The problem to be solved by the present invention is that, when purifying soil contaminated with volatile organic compounds, by using a stable drug that is aqueous solution and does not have self-degradability, etc., on the land where the contamination is confirmed. It is cheap, efficient, and reliable and reliable.
In addition, this composition is effective also when purifying the groundwater in a soil, and groundwater is also included in the word soil in this invention.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, the present invention relates to a composition for decomposing organic compounds in soil contaminated with organic compounds and a method for decomposing organic compounds in soil using the composition, and includes the following inventions: .
(A) A composition that decomposes an organic compound in soil containing a reducing agent and water as essential components.
(B) A composition in which the reducing agent is an alkali metal sulfite or an alkali metal hydrogen sulfite.
(C) A method for decomposing an organic compound in soil containing an iron compound using the composition.
(D) A method of decomposing organic matter in the soil using the composition after adding a water-soluble iron compound to the soil in advance.
(E) A method for decomposing an organic compound by adding an equimolar amount or more of the composition to an iron compound and an equimolar amount of the organic compound in the soil.
(F) A method for decomposing an organic compound, including a step of confirming that the soil is contaminated with an organic compound, a step of confirming that the soil contains an iron compound, and a step of applying the composition.

  According to the present invention, an expensive solution that has been a problem in the conventional method for purifying contaminated soil by applying a stable chemical that is aqueous solution, not self-degradable, etc., to soil contaminated with organic compounds. It is possible to reliably and efficiently decompose contaminating organic compounds while reducing the construction cost.

Examples of the organic compound to be decomposed in the present invention include chloroethene (vinyl chloride monomer), 1,1-dichloroethene, 1,2-dichloroethene, trichloroethene, tetrachloroethene, dichloromethane, carbon tetrachloride, 1,2 -Halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane and chlorobenzene, and aromatic hydrocarbons such as benzene, toluene and xylene Etc.
The above-mentioned halogenated hydrocarbons or aromatic hydrocarbons are typical organic compounds that contaminate soil, groundwater, etc. as a result of being used in large quantities on earth as a cooling medium for air conditioners or paint solvents in the past. It is said that there is.
From the viewpoints of carcinogenicity, hardly decomposability and the like, the organic solvent which is the subject of the present invention is preferably halogenated hydrocarbon.

  In the present invention, the presence of the iron compound is essential, but it may be an iron compound contained in the soil, or the iron compound may be added to the soil in advance, or may be added simultaneously with the present composition. When added in advance, it is necessary to use a water-soluble iron compound for ease of construction. Preferred iron compounds are ferrous compounds, and specific examples include ferrous chloride, ferrous sulfate, ferrous ammonium sulfate, and ferrous oxide. The amount of the iron compound is preferably an equimolar amount or more with respect to the organic compound to be decomposed, more preferably 5 times the molar amount or more with respect to the organic compound.

  As the alkali metal sulfite or the hydrogen bisulfite metal salt in the present invention, specifically, sodium sulfite, sodium hydrogen sulfite, or a compound in which these sodium is substituted with potassium can be used. Moreover, some of these compounds can also be mixed and used. The amount used is an equimolar amount or more with respect to the iron compound, and preferably an amount of 5 times the molar amount or more with respect to the iron compound.

  The composition of the present invention comprises the above-mentioned alkali metal sulfite or alkali metal hydrogen sulfite (hereinafter sometimes referred to as alkali metal sulfite) and water as essential components. The amount of alkali metal sulfite is 0.01 to 10% by mass based on the total amount of alkali metal sulfite and water. A more preferable amount of water used is such that the proportion of the alkali metal sulfite is 0.1 to 5% by mass.

  Although the decomposition mechanism of the present invention is not clear, only carbon dioxide and chlorine ions were confirmed as the decomposition products of trichloroethene, and it is assumed that this is different from the conventional reductive decomposition reaction of trichloroethene. The In the conventional reductive decomposition of trichloroethene, cis-1,2-dichloroethene, chloroethene and ethylene are detected as decomposition products, but such products are not observed in the present invention.

In the present invention, there is no limitation on the method of using the degradable composition of the present invention, but a method of spreading and infiltrating the soil is preferably employed. Specifically, a step of confirming that the soil is contaminated with an organic compound and a step of applying the composition having the organic compound decomposability are employed.
As a specific example of the process for confirming soil contaminated with organic compounds, sampling and measurement related to soil gas surveys stipulated in Ordinance No. 16 of the Ordinance of the Ministry of the Environment are conducted based on the Enforcement Rules of the Soil Contamination Countermeasures Law. In addition, the methods described in Patent Documents 4 to 6 are also possible.
The points to be surveyed are also determined based on the laws and regulations, taking into consideration the center point of the 10m grid and the center point of the 30m grid, the size of the entire land concerned, and the possibility of contamination spreading. As for the part where it is recognized that there is a high possibility that contaminated soil is concentrated, a 1m grid as described in Patent Document 6, a history of handling volatile organic compounds, immovable buildings and large-sized buildings Considering the existence of equipment, etc., it is possible to determine a specific point according to the actual situation.

  As a step of confirming that the iron compound is contained in the soil, a certain amount of soil can be collected and subjected to a normal inorganic analysis. In general, the soil contains about 0.1% by weight or more of an iron compound, but when it is less than 0.1% by weight, it is preferable to apply a water-soluble iron compound.

  As a specific example of the process of applying a composition having organic substance decomposability, a spot where contamination is detected by the above-mentioned investigation is selected, and a spot detected at a high concentration is mainly applied. If necessary, work around contaminated points and low-concentration points. If the flow of groundwater or the direction in which the contamination has spread is known, it is effective to install it upstream.

  The construction of the decomposable composition of the present invention may be applied by spreading and infiltrating the soil, or a method of inserting an injecting tube into the soil and injecting the decomposable composition through the injecting tube can be employed. More specifically, there is a method in which the decomposable composition is directly injected into the holes or wells used in the survey, especially in the hole where the high concentration of contamination is observed, or is sprayed and permeated around the hole including those holes. Adopted. A degradable composition may be added to the groundwater pumped around these survey holes, or the water treated in this way may be returned to the groundwater and circulated. It may be recovered together with water directly by soil gas suction, pumped water aeration, air sparging, or the like, or an organic compound once adsorbed on activated carbon or the like may be treated with a decomposable composition and decomposed. It is also possible to decompose organic compounds by mixing the degradable composition into the excavated contaminated soil.

When the organic compound is not sufficiently decomposed by the above-described treatment, or when the organic matter has been re-contaminated after being decomposed by the treatment, the degradable composition of the present invention can be applied to the soil. Re-investigation and re-construction are possible by the same method.
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
○ Example 1

In a 40 mL vial, take 0.04 g of ferrous chloride corresponding to 0.3 mmol and 0.16 g of sodium bisulfite corresponding to 1.5 mmol, add 20 g of distilled water, mix and dissolve, The organic matter-decomposable composition (hereinafter referred to as a drug) of the present invention was prepared by sealing with a silicone rubber septum coated with a fluororesin and an aluminum cap. A microsyringe was used to inject 5 μL of trichloroethene corresponding to 0.06 mmol, and the concentration of trichloroethene in the gas phase after shaking for 3 days in a 25 ° C. constant temperature bath was analyzed by headspace gas chromatography. When the analysis was performed by the method, the decomposition rate was defined and calculated from the blank analysis value when no drug was used, as in the following formula, and the result was 0.7.
In gas chromatography, cis-1,2-dichloroethene, chloroethene and ethylene were not detected. In addition, it was confirmed by the separate analysis method that the generation of carbon dioxide in the cracked gas and the increase of chlorine ions in the vial liquid phase were confirmed.
Decomposition rate = ((blank analysis value) − (analysis value after test)) / (blank analysis value)
○ Examples 2-8

The same operation as in Example 1 was performed except that the drugs listed in Table 1 were used. The results are shown in Table 1.
○ Comparative Examples 1-6

Trichloroethene was decomposed under the conditions described in Table 1, and the results are shown in Table 1 as the decomposition rate.
Example 9

In place of ferrous chloride of Example 1, 10 g of masa soil was added, 0.2 g of sodium bisulfite corresponding to 1.9 mmol was taken, 20 g of distilled water was added thereto, mixed, dissolved, and coated with a fluorine resin. Sealed with a silicone rubber septum and an aluminum cap. A microsyringe was used to inject 5 μL of trichloroethene corresponding to 0.06 mmol, and the concentration of trichloroethene in the gas phase after shaking for 3 days in a 25 ° C. constant temperature bath was analyzed by headspace gas chromatography. According to the analysis by the method, the decomposition rate was defined from the analysis value of the blank when no chemical was used, as shown in the following formula, and calculated to be 0.8.
In gas chromatography, cis-1,2-dichloroethene, chloroethene and ethylene were not detected. In addition, it was confirmed by the separate analysis method that the generation of carbon dioxide in the cracked gas and the increase of chlorine ions in the vial liquid phase were confirmed.
Separately, the ferrous content in the Masa soil used in the test was measured and found to be 0.13% by weight, corresponding to 0.2 mmol of ferrous compound, and a total amount of 0.2 mmol in the system. Of ferrous compounds.
Decomposition rate = ((blank analysis value) − (analysis value after test)) / (blank analysis value)
* 1. Masa soil: Weathered debris such as granite collected from the Chubu region.
○ Examples 10-14

The same operation as in Example 9 was performed except that the drugs and soil described in Table 2 were used. The results are shown in Table 2.
* 2. Kuroboku soil: collected from the hilly area of the Chubu region. When the ferrous content was measured, it was 0.65% by weight.
○ Comparative Examples 7-12

Trichloroethene was decomposed under the conditions described in Table 2, and the results are shown in Table 2 as the decomposition rate.
Example 15

A glass column having a diameter of 26 mm and a height of 300 mm is filled with 150 g of masa soil (corresponding to 3.5 mmol in terms of ferrous component), and 7.5 mg of trichloroethene corresponding to 0.06 mmol is added to water. What was melt | dissolved in 20g was added, and the simulation contaminated soil layer which assumed the point where pollution was detected by investigation was adjusted. Thereto, 80 g of a 5 wt% aqueous solution of sodium bisulfite dissolved in distilled water (corresponding to 38 mmol of sodium bisulfite) was added dropwise at a rate of 0.48 g / min, and the drug was infiltrated. Trichloroethene in the effluent after dropping the drug was also added, and the total amount of trichloroethene detected in the system was 1.5 mg. Further, as a blank for this test, the total amount of trichloroethene detected in the system after dropping only the same amount of distilled water to which no drug was added was 4.9 mg, the decomposition rate was calculated as in Example 1, and 0.7 It was confirmed that
Example 16

  A glass column having a diameter of 40 mm and a height of 300 mm is filled with 450 g of masa soil (corresponding to 10.5 mmol in terms of ferrous component), and 7.5 mg (0.06 mmol) of trichloroethene and tetrachloro are added thereto. A solution in which 3.2 mg (0.02 mmol) of ethene was dissolved in 20 g of water was added, and a simulated contaminated soil layer assuming a point where contamination was detected was adjusted. Thereto was added dropwise 215 g of a 3% by weight aqueous solution of sodium sulfite (equivalent to 38 mmol) and sodium hydrogen sulfite (equivalent to 15.5 mmol) dissolved in distilled water at a weight ratio of 15: 5 at a rate of 0.41 g / min. The drug was infiltrated. Trichloroethene or tetrachloroethene in the effluent after dropping the drug was also added, and the total amount detected in the system was 1.7 mg and 1.2 mg, respectively, and only the same amount of distilled water without adding the drug was dropped. The total amount of the trichloroethene or tetrachloroethene blank was 5.8 mg or 2.3 mg, respectively, and the respective degradation rates were 0.7 and 0.5.

According to the present invention, volatile organic compounds can be decomposed reliably and inexpensively, and soil contaminated with them can be economically and efficiently constructed and purified.

Claims (10)

The composition which decomposes | disassembles the organic compound in the soil which has a reducing agent and water as an essential component. The composition according to claim 1, wherein the reducing agent is an alkali metal sulfite or an alkali metal hydrogen sulfite. A method for decomposing an organic compound, comprising decomposing an organic substance in soil using the composition according to claim 1. The method for decomposing an organic compound according to claim 3, wherein the soil contains an iron compound. A method for decomposing an organic compound, comprising: adding a water-soluble iron compound to soil in advance; and decomposing organic matter in the soil using the composition according to claim 1. 3. The composition according to claim 1 or 2, wherein the composition contains at least an equimolar amount of the iron compound and at least an equimolar amount of the reducing agent with respect to the organic compound in the soil. 4. A method for decomposing organic compounds according to 4-5. The method for decomposing an organic compound according to any one of claims 4 to 6, wherein the iron compound is a ferrous compound. 8. The method for decomposing an organic compound according to claim 3, wherein the organic compound is a halogenated hydrocarbon compound. The method for decomposing an organic compound according to claim 3, comprising a step of confirming that the soil is contaminated with an organic compound, and a step of applying the composition according to claim 1 or 2. It includes a step of confirming that the soil is contaminated with an organic compound, a step of confirming that the soil contains an iron compound, and a step of applying the composition according to claim 1. The method for decomposing an organic compound according to any one of claims 4 to 8.