JP2004202364A - Soil treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency in decomposition of organic pollutants and treat difficultly-decomposed substances at a low cost in the treatment of soil contaminated by the organic pollutants. <P>SOLUTION: In a soil treatment method, microorganisms are activated, and the components of the organic pollutants which can be decomposed by microorganisms are decomposed, and then the pollutants are further decomposed by using an oxidizing agent. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a low-cost soil purification method for decomposing soil to be treated containing organic pollutants with microorganisms and an oxidizing agent.
[0002]
[Prior art]
Conventionally, methods for decomposing and purifying organic contaminants in soil contaminated with organic contaminants include methods using an oxidizing agent or microorganisms. Potassium permanganate (Patent Literature 1), ozone (Patent Literature 2 and Patent Literature 3), Fenton's reagent using hydrogen peroxide and a metal catalyst (Patent Literature 4 and Patent Literature 5) and the like are conceivable as oxidizing agents. ing. On the other hand, in the soil purification method using microorganisms, a method of adding a nutrient source to activate the movement of the organic pollutant-decomposing bacteria living in the contaminated soil, or adding the grown organic pollutant-decomposing bacteria to the contaminated soil A way has been devised.
[0003]
Further, a purification method has been proposed in which a treatment with an oxidizing agent is performed to increase the decomposition rate of organic pollutants, followed by a treatment with a microorganism (for example, Patent Documents 4 and 5). These use hydrogen peroxide to decompose a part of the hardly decomposable organic matter, and then perform a decomposition treatment by a microorganism. Patent Document 6 proposes a decomposition treatment by a microorganism before and after the ozone treatment.
[0004]
However, each of the above-mentioned conventional methods has the following problems.
[0005]
(Problem 1) The treatment method using an oxidizing agent is considered to be effective for high-concentration and narrow-range pollution because the amount of the oxidizing agent used is proportional to the volume of the treated soil, but is costly for a wide range of pollution. Is high and is not suitable. On the other hand, the microbial treatment method is suitable for a wide range of pollution due to its low cost, but the decomposition rate of organic pollutants is slow, so it takes time, and the components of organic pollutants that can be decomposed are limited. Therefore, it is difficult to completely clean contaminated soil. Organic contaminants defined here refer to halogenated organic compounds and crude oil, etc.Particularly for crude oil, it is a mixture of various substances, from low molecular paraffin to high molecular asphaltene. A thing. It is difficult for microorganisms to decompose all of these, and in particular, halogenated organic compounds, polycyclic aromatic compounds, high molecular asphaltenes, and the like remain without being decomposed.
[0006]
(Problem 2) Generally, organic contaminants in the soil are adsorbed on the soil, so that even if an oxidizing agent is directly added, no reaction occurs, and a problem that decomposition efficiency is low occurs. In particular, in soils that have been continuously polluted for a long time, organic pollutants are strongly adsorbed, and even if an oxidizing agent is added in this state, it is considered that they are hardly oxidized. Even if the oxidizing agent is added to the organic contaminant as it is, it does not come into contact with the organic contaminant, so that the reaction efficiency is poor and almost no decomposition occurs. Therefore, the technique of Patent Document 4 can be applied only to organic substances having solubility in water. On the other hand, in order to solve this problem, a method of eluting organic contaminants from soil using a surfactant before treatment with an oxidizing agent has been devised (for example, Patent Document 5).
(Problem 3) In the method of adding microorganisms after treatment with an oxidizing agent, microorganisms usually form an ecosystem in the natural world. Therefore, even if new microorganisms are introduced into an already formed ecosystem, the microorganism is added to the system. It is difficult to survive.
[0007]
(Problem 4) The method of adding microorganisms after treatment with an oxidizing agent involves the use of an oxidizing agent even in the case of treating a mixture containing a large amount of organic substances such as crude oil, even when the mixture can be decomposed by microorganisms. It would be very inefficient and costly.
[0008]
[Patent Document 1]
JP 2001-276799 A, paragraphs [0017], [0027], [0032], etc.
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-325935, Claim 1, paragraph [0008], etc.
[Patent Document 3]
JP 2001-269658 A, Claim 1, paragraph [0006], etc.
[Patent Document 4]
JP-A-7-75772, Claims 5, paragraphs [0009], paragraphs [0010], [3], [4], etc.
[Patent Document 5]
JP 2001-269657 A, Claim 3, paragraph [0009], etc.
[Patent Document 6]
JP-A-2001-269658, claims 3, 4, paragraphs [0008], [0009], etc.
[Problems to be solved by the invention]
An object of the present invention is to provide a method for purifying soil contaminated with organic contaminants by combining chemical treatment with an oxidizing agent and microorganism treatment, (1) increasing the efficiency of decomposition of organic contaminants by microorganisms, and (2) oxidizing. It is an object of the present invention to provide a soil purification method for reducing the cost of organic pollutant decomposition by chemical treatment and (3) increasing the efficiency of a treatment method combining oxidizing agent treatment and microbial decomposition.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the method for remediation of soil contaminated with organic pollutants of the present invention according to the present invention comprises the steps of (1) decomposing a readily decomposable organic pollutant component by a microorganism, and This is a purification method in which an oxidizing agent is subjected to a chemical treatment until the microorganism becomes a usable low-molecular substance. As a result, it is not necessary to add an extra oxidizing agent to low-molecular substances that can be decomposed by microorganisms contained in the initial contaminating organic contaminants. By using, microorganisms can decompose hardly decomposable substances that could not be treated by microorganisms, and purification of contaminated soil by organic pollutants is realized.
[0016]
(2) Further, as described in claim 2, the organic pollutants adsorbed on the soil are eluted by using a surfactant, so that the contact efficiency between the oxidizing agent and the organic pollutants is increased, and the oxidation is efficiently performed. It is a method of decomposing. According to this method, the addition amount of the oxidizing agent can be reduced as much as possible. The surfactant is preferably Triton X-100 (a non-ionic surfactant; manufactured by Nakarai Tesque, Inc .; component: polyethylene glycol mono-p-isooctyl phenyl ether). Biological surfactants may be used.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. A nutrient source, such as phosphorus or nitrogen, is added to soil contaminated with organic contaminants, and stirring is performed to increase air permeability in the soil, thereby activating the movement of microorganisms present in the soil, and causing microorganisms to move. Decomposes degradable organic pollutants. It has been clarified that microorganisms can decompose aliphatic compounds having about 23 carbon atoms, and polycyclic aromatic compounds can decompose up to about four-membered rings. The surfactant may be added before or after the treatment of decomposition of organic pollutants by microorganisms, such as Triton X-100 or a microorganism-derived surfactant, but at least before the oxidizing agent is added. It is desirable. After the decomposition of the organic pollutants by the microorganism, the remaining organic pollutants are decomposed by using an oxidizing agent such as Fenton's reagent of hydrogen peroxide and ferrous iron, hydrogen peroxide, ozone, or the like. Then, after the decomposition treatment of the residual organic pollutant by the oxidizing agent, it is also preferable to add the nutrient again to perform the decomposition by the microorganism, or to repeat the decomposition by the microorganism and the decomposition treatment of the residual organic pollutant by the oxidizing agent.
[0018]
(Example)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
For 2 kg of soil contaminated with crude oil, the moisture content was kept at 17%, the temperature was kept at 20 ° C., and phosphorus and nitrogen were added as nutrient sources. FIG. 1 shows the result of measuring the oil concentration of this soil over two months. The crude oil concentration was measured by measuring the weight of the oil extracted with dichloromethane.
[0020]
As is clear from FIG. 1, in the system to which the nutrient source was added, a decrease in the oil content of about 30% of the initial value was observed after three months. On the other hand, the oil content was also reduced in the system without the addition of nutrients, which is thought to be due to the decrease in oil content and the decomposition bacteria that are easily volatilized. .
[0021]
FIG. 2 shows the results of measuring residual oil in soil treated by a combination of microbial treatment and oxidizing agent. In the treatment with microorganisms, the moisture content is kept at 17%, the temperature is kept at 20 ° C., phosphorus and nitrogen are added as nutrients, and the analysis is performed using soil one month later. The oxidizing agent treatment shows a comparison in which crude oil was decomposed using a hydrogen peroxide solution and a metal ion catalyst. In addition, a comparison is made for the case where the oil content in the soil is eluted with the surfactant during the treatment with the oxidizing agent. Specifically, 25 g of water was added to 25 g of crude oil-contaminated soil, Triton X-100 was added as a surfactant, so as to be 2% of the weight of the soil, and 0.1 M of iron sulfate and 2 M of hydrogen peroxide were added. The reaction was stirred for 24 hours. From the results shown in FIG. 2, the microbial treatment reduced the oil concentration by 27.5% compared to the original soil. Further, as a result of treating the soil with an oxidizing agent after the microorganism treatment, the oil concentration was reduced by 55%. On the other hand, in the treatment with the oxidizing agent, the oil concentration decreased only by 4% in the system to which the surfactant was not added, but the oil concentration decreased by 37.5% in the system with the surfactant. In addition, as a result of treating the soil with microorganisms after the oxidizing agent treatment, the degree of oil agriculture decreased by 47.4%. From the above results, it is found that the treatment combining the oxidizing agent treatment after the treatment with the microorganism is effective.
[0022]
FIG. 3 shows a diagram of the molecular weight distribution of the oil in the soil treated in FIG. 2 measured using FD-MS. From the results of FD-MS, it can be seen that the original soil before the treatment ((1) in FIG. 3) contains a large amount of substances having a molecular weight of about 600 and oils having a molecular weight of 200 to 2000. In the molecular weight distribution of the oil after microbial treatment ((2a) in FIG. 3), those having a molecular weight of 600 or less decreased, and the main molecular weight was shifted to the 800th. This indicates that microorganisms can decompose substances having a molecular weight of 600 or less and cannot decompose substances having a molecular weight higher than 600. On the other hand, the molecular weight distribution after the oxidizing agent treatment (FIG. 3 (3a)) shows almost no difference from the molecular weight distribution of the oil in the soil before the treatment, indicating that the oxidizing agent acts regardless of the molecular weight. From the above, it can be seen that when there is a substance having a molecular weight of 600 or less that can be treated by microorganisms, it is more efficient to treat with an oxidizing agent after treating with microorganisms. Further, when the oxidizing agent treatment is performed, the molecular weight distribution of the oil can be shifted to a lower molecular side (shift from (2a) to (2b) in FIG. 3). I can plan.
[0023]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, in soil purification contaminated with organic contaminants over a wide range, oil-contaminated soil can be purified more efficiently at lower cost.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing oil decomposition in contaminated soil by microorganisms. It is a measure of the amount of oil in the soil.
FIG. 2 is a view showing oil decomposition in soil by oxidizing agent treatment and microorganism treatment. This is a measurement of the amount of oil in the soil after the treatment with the combination of the oxidizing agent and the microorganism treatment.
FIG. 3 is a diagram of the molecular weight distribution of oil in soil by oxidizing agent treatment and microorganism treatment. FIG. 2 shows the oil treated in FIG. 2 whose molecular weight distribution was measured by FD-MS. (1) Molecular weight distribution of oil in soil in soil before treatment, (2a) Molecular weight distribution of oil in soil in microorganism-treated soil, (2b) Molecular weight distribution of oil in soil in oxidant-treated soil after microorganism treatment FIG. 3 (a) is a molecular weight distribution map of oil in soil in an oxidant-treated soil, and FIG. 3 (b) is a molecular weight distribution map of soil oil in a microorganism-treated soil after oxidant treatment.

Claims (2)

A soil purification method comprising: a step of subjecting soil contaminated with an organic substance to a microorganism treatment; and a step of subjecting the soil subjected to the microorganism treatment to an oxidizing agent treatment. The soil purification method according to claim 1, wherein a surfactant is added to the soil to be treated before at least one of the step of performing the microorganism treatment and the step of performing the oxidant treatment.

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