JP2006026551A - Contaminated soil decontaminating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contaminated soil decontaminating method by which soil contaminated with organic chlorine compounds that are decomposable by anaerobic microorganisms is decontaminated at an original position. <P>SOLUTION: The method for decontaminating soil contaminated with the organic chlorine compounds that are decomposable by the anaerobic microorganisms at the original position comprises a process A in which a high molecular absorbent with a hydrophilic group is poured into the contaminated soil to cut off invasion of air into the contaminated soil and thereby the place is made to be in an anaerobic state and a process B in which an anaerobic microorganism decomposition accelerator for promoting decomposition of the organic chlorine compounds by the anaerobic microorganisms is poured into the contaminated soil. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for in-situ purification of soil contaminated with organochlorine compounds that can be decomposed by anaerobic microorganisms.

  Tetrachloroethylene, trichlorethylene, and dichloroethylene, which are organochlorine compounds, are used in the degreasing and washing of metals, washing in dry cleaning, refrigerants, etc., and have high industrial utility value, but cause liver damage and kidney damage for the human body. It becomes a harmful substance. Therefore, soil and groundwater contamination by these organochlorine compounds is a serious social problem.

  There are many technologies for decomposing these organochlorine compounds and purifying contaminated soil and groundwater, one of which is a method of purifying contaminated soil and groundwater by reductive dechlorination treatment by anaerobic microorganisms. is there. This is a method for purifying contaminated soil and groundwater by substituting chlorine of an organic chlorine compound with hydrogen using anaerobic microorganisms present in the contaminated soil and groundwater (for example, Patent Document 1 or 2). ).

Such reductive dechlorination treatment by anaerobic microorganisms means a saturation zone (in this specification, a zone in which groundwater exists in a saturated state and is in an anaerobic state to prevent air intrusion). It can only be applied to soils). This is because soil in an unsaturated zone (which means “a zone where groundwater exists in an unsaturated state and there is a gap in which air and the like exist”) is not easily anaerobic.
JP-A-10-216694 JP 2000-263032 A

  However, it is not easy to distinguish between saturated and unsaturated zones of contaminated soil because it is not easy to measure the particle size and water permeability at each point and stratum of the soil. It takes.

  In order to solve this problem, the present invention aims to purify contaminated soil by purifying soil contaminated with organochlorine compounds that can be decomposed by anaerobic microorganisms without distinguishing between saturated and unsaturated zones of the soil. It aims to provide a method.

  In order to solve the above problem, a contaminated soil purification method according to the present invention is a method for purifying soil contaminated with an organic chlorine compound decomposable by anaerobic microorganisms in situ, and a polymer having a hydrophilic group Injecting the absorber into the contaminated soil and blocking the entry of air into the contaminated soil, thereby making the place anaerobic, and the organochlorine compound of the anaerobic microorganism Injecting an anaerobic microbial degradation promoter for promoting degradation into the contaminated soil. In addition, you may perform the process A and the process B together by making the said polymer absorber contain the said anaerobic microbial degradation promoter, and inject | pouring into the said contaminated soil. The contaminated soil purification method may further include a step C of injecting an aqueous solution for swelling the polymer absorber into the soil into which the polymer absorber has been injected. Furthermore, in the contaminated soil purification method according to the present invention, the aqueous solution contains the polymer absorber and the anaerobic microbial degradation accelerator, and the mixture is injected into the contaminated soil. And step C may be performed together. Note that performing a plurality of steps together means that each step is performed completely or partially overlapping in time. However, a plurality of steps may be performed independently by a plurality of operations, but may be performed by a single operation. As an example of the latter, when performing the same operation using a plurality of different objects, the plurality of objects may be mixed and a plurality of steps may be performed in a single operation.

  In any of the above contaminated soil purification methods, the viscosity of the polymer absorber may be increased in advance before the polymer absorber is injected into the contaminated soil. Further, the viscosity of the aqueous solution may be increased in advance before the aqueous solution containing the polymer absorbent and the anaerobic microbial degradation accelerator is poured into soil.

  In any of the above contaminated soil purification methods, the anaerobic microbial degradation promoter provides the hydrogen necessary to promote reductive dechlorination that replaces chlorine in the organochlorine compound with hydrogen. A hydrogen donor is preferred, and the polymer absorber is preferably biodegradable.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a soil purification method that purifies soil contaminated with an organic chlorine compound that can be decomposed by anaerobic microorganisms in situ without distinguishing between a saturated zone and an unsaturated zone of the soil.

  Hereinafter, a preferred embodiment of the present invention will be described in detail. The objects, features, advantages, and ideas of the present invention will be apparent to those skilled in the art from the description of the present specification, and those skilled in the art can easily reproduce the present invention from the description of the present specification. it can. The embodiments of the present invention described below show preferred embodiments of the present invention, and are shown for illustration or explanation, and the present invention is not limited to them. It will be apparent to those skilled in the art that various modifications and variations can be made based on the description of the present specification within the spirit and scope of the present invention disclosed herein.

=== Contaminated soil purification method ===
In the method of purifying the unsaturated zone of soil contaminated with organochlorine compounds that can be decomposed by anaerobic microorganisms, the following steps are carried out.

  First, in the process A, the polymer absorber having a hydrophilic group is injected into the contaminated soil to block the intrusion of air into the contaminated soil, thereby making the place anaerobic. In this step, the polymer absorbent is injected into and around the area to be purified at the original position (in the present specification, “contaminated soil location”). If there is enough moisture in the soil, the injected polymer absorber absorbs the moisture in the contaminated soil and swells, blocking the intrusion of air in the swollen place and creating an anaerobic state .

  As a method of injecting the polymer absorber, there is a method of injecting the polymer absorber into the soil to be purified using a tiller or an excavator, etc., but the polymer absorber into the soil to be purified Any method may be used as long as it can be injected. Here, the polymer absorber is capable of absorbing water of several hundred to several thousand times its own weight, such as an absorbent polymer, for example, as a specific example of the polymer absorber And polyacrylic acid. Taking into account the recovery after soil remediation, those having the property of being biodegradable by microorganisms such as biodegradable plastics are more advantageous because they do not need to be recovered. The polymer absorber is preferably in a powder state such as sand or a solid state such as stone.

  Furthermore, in the process B, the anaerobic microbial decomposition promoter for accelerating | stimulating the decomposition | disassembly of the organochlorine compound by an anaerobic microorganism is inject | poured into the said contaminated soil. As a method of injecting, there is a method of injecting an anaerobic microbial degradation promoter into the soil to be purified using a tiller or excavator, etc., but an anaerobic microbial degradation promoter is introduced into the soil to be purified. Any method may be used as long as it can be injected. As an example of an anaerobic microbial degradation promoter, hydrogen is provided by a chemical reaction with a hydrogen donor or water that provides the hydrogen necessary to promote reductive dechlorination that replaces the chlorine and hydrogen of the organochlorine compound. Iron powder is mentioned. Examples of the hydrogen donor include an alcohol such as methanol or ethanol, a low molecular organic substance such as glucose or sucrose, a lower fatty acid such as acetic acid, propionic acid, lactic acid, or butyric acid, or a hydrogen donor compound (HRC) that is a polylactic acid ester. Hydrogen Release Compound) and the like are used.

  Step A and Step B may be performed in any order as long as both can be widely added to the range of purifying the contaminated soil with the polymer absorber and the anaerobic microbial degradation promoter. May be performed multiple times. Further, as described below, Step A and Step B may be performed together, or even when performed together, a single step may be additionally performed, and any step may be performed a plurality of times. Good. Even when the process is performed a plurality of times, the order and the number of processes are not limited.

  If necessary, process C is performed. In step C, an aqueous solution for swelling the polymer absorber is injected into the soil mixed with the polymer absorber. The case where it is necessary is a case where there is no moisture necessary for the polymer absorbent to swell in the place where the polymer absorbent is mixed. In that case, an aqueous solution is injected into the place where the polymer absorber is injected, and the polymer absorber absorbs the aqueous solution and swells, thereby blocking the intrusion of air in the swollen place and making an anaerobic state. Can be produced. In the anaerobic state thus produced, an anaerobic microbial degradation promoter is injected, and the anaerobic microorganisms decompose the organochlorine compound to purify the contaminated soil.

  Here, the aqueous solution is not particularly limited, for example, purified water such as tap water, industrial water, ground water, or distilled water, or a buffer solution in which a buffering agent is dissolved. However, an aqueous solution that does not adversely affect soil or microorganisms is preferable.

  The anaerobic microbial degradation promoter may be injected at any stage as long as it can be widely added to the range of the contaminated soil to be purified. For example, if the anaerobic microbial degradation promoter is water-soluble, the anaerobic microbial degradation promoter may be dissolved in the aqueous solution, and the aqueous solution may be injected into the place where the polymer absorber is mixed. If the anaerobic microbial degradation accelerator is sparingly soluble, mix the anaerobic microbial degradation accelerator into the contaminated soil in the same way as the polymer absorber, and then penetrate the aqueous solution into the area where the polymer absorber is mixed. You may let them.

  Before injecting the polymer absorbent into the contaminated soil, the viscosity of the polymer absorbent may be increased in advance. When the aqueous solution penetrates into the contaminated soil where the polymer absorber is mixed, if the polymer absorber is not viscous, the polymer absorber will swell only in situ even if it absorbs the aqueous solution. However, when the polymer absorber has a certain viscosity, when the polymer absorber absorbs the aqueous solution, the polymer absorber spreads while swelling on the spot. Therefore, since the aqueous solution does not penetrate into the contaminated soil and is absorbed by the polymer absorber, the penetration rate of the aqueous solution into the contaminated soil can be delayed, so the polymer absorber absorbs the aqueous solution. The time can be increased, or the aqueous solution can be prevented from penetrating outside the range to be purified. Furthermore, even when only the water in the place where the polymer absorber is injected is absorbed, the polymer absorber does not simply swell but swells due to the viscosity of the polymer absorber. spread. As described above, in order to efficiently expand the injected polymer absorber in the soil, it is preferable to increase the viscosity in advance. Any substance that increases the viscosity of the polymer absorber may be used, and examples thereof include polymer fine particles having a hydrophilic group.

  The above process A, process B, and process C may be performed in any order, and each process may be performed a plurality of times. Further, as described below, Step A, Step B, and Step C may be performed together, or even when performed together, a single step may be additionally performed, and any of the steps may be performed multiple times. You may go. Even when the process is performed a plurality of times, the order and the number of processes are not limited.

=== Contaminated soil purification method (when step A and step B are performed together) ===
In the above-described contaminated soil purification method, Step A and Step B were carried out independently. However, in order to simplify and increase the efficiency of the injection work of substances necessary for the purification of contaminated soil, these substances were injected at once. The contaminated soil purification method is described below.

  By injecting the polymer absorber and the anaerobic microbial degradation promoter in the contaminated soil purification method into the contaminated soil, the polymer absorber contains the anaerobic microbial degradation promoter and injecting it into the contaminated soil. Step A and Step B are performed together. When the polymer absorber is in liquid form, the polymer absorber can penetrate and penetrate into the contaminated soil by simply injecting the polymer absorber without injecting an aqueous solution. is there. In this case, it may exist in a liquid state before being injected into the contaminated soil, and may be solidified after being injected. For example, an anaerobic microbial degradation promoter is added to a polymer absorber (for example, an agar medium) having a property (thermoplasticity) that is solubilized when heat is applied. The thermoplastic polymer absorber containing the anaerobic microbial degradation accelerator is liquefied by adding heat, and the liquefied thermoplastic polymer absorber is injected into the area to be purified of the contaminated soil. The injected thermoplastic polymer absorbent permeates while being scattered in the area to be purified. At the same time, the contained anaerobic microbial degradation promoter is also diffused. As these penetrate, the thermoplastic polymer absorber is cooled and gradually hardens. Since the place where the polymer absorber is hardened blocks the intrusion of air, it becomes anaerobic. As another example, a polymer absorber that solidifies when a coagulant is added may be used. Mixing a liquid polymer absorber with an anaerobic microbial degradation accelerator and injecting it into the area to be cleaned of contaminated soil, then adding a coagulant to solidify the polymer absorber, the above thermoplastic polymer absorption As with the body, the area to be purified becomes anaerobic. Under the anaerobic condition thus produced, the anaerobic microorganisms can decompose the organic chlorine compound, so that the contaminated soil can be purified.

  The anaerobic microbial degradation promoter in this case may be solid or liquid as long as it is a substance that can be added to the polymer absorber. It is preferable that

  In addition, in the above-described polymer absorbent, when it is desired to control the penetration rate into the contaminated soil in the same manner as the above-described contaminated soil purification method, in order to increase the viscosity, polymer fine particles having a hydrophilic group may be added. Good.

=== Contaminated Soil Purification Method (When Step A, Step B and Step C are Performed Together) ===
In the above-described contaminated soil purification method, the process A and the process B are performed together, but the contaminated soil purification method in which the process C is also performed is described below. In the present invention, the polymer absorber and the anaerobic microbial degradation promoter are contained in the aqueous solution, and the aqueous solution is injected into the contaminated soil, so that the process A, the process B, and the process C are performed together.

  An aqueous solution containing a polymer absorber and an anaerobic microbial degradation accelerator is, for example, a polymer absorber and an anaerobic microbial degradation accelerator dissolved in an aqueous solution, which penetrates while diffusing in soil. An aqueous solution that gradually hardens. Therefore, a liquid or a liquid material having a property of solidifying in soil (for example, neutral silica sol subjected to oxidation treatment) is used, or a coagulant is injected after injecting the aqueous solution into the contaminated soil. As another example of an aqueous solution containing a polymer absorber and an anaerobic microbial degradation accelerator, a solution obtained by swelling a polymer absorber containing an anaerobic microbial degradation accelerator with an aqueous solution can be considered. In this case, the swollen polymer absorbent is mixed into the soil in a range to be purified using a tiller or an excavator. The mixed polymer absorber absorbs moisture in the contaminated soil and further swells, thereby blocking the intrusion of air in the swollen place and creating an anaerobic state. When water in the soil is insufficient, an aqueous solution may be newly supplemented in the place where the polymer absorber is mixed. Under the anaerobic condition thus prepared, the anaerobic microorganisms decompose the organochlorine compound using an anaerobic microbial degradation accelerator to purify the contaminated soil.

  In addition, in the aqueous solution containing the polymer absorber and the anaerobic microbial degradation accelerator, when it is desired to control the penetration rate to the contaminated soil in the same manner as the above-described contaminated soil purification method, Polymer fine particles having a functional group may be added.

=== Effect of using contaminated soil purification method ===
The conventional decomposition of organic chlorine compounds by anaerobic microorganisms has been performed without problems in the saturated zone, but the organic chlorine compounds have not been easily decomposed in the unsaturated zone because it is difficult to be in an anaerobic state. Therefore, when decomposing organochlorine compounds by conventional anaerobic microorganisms, it is necessary to distinguish the unsaturated zone and the saturated zone of the contaminated soil, which is not easy and takes time. However, by using the contaminated soil purification method of the present invention, it is not necessary to distinguish between the unsaturated zone and the saturated zone of the contaminated soil, and at the same time, both zones can be purified in situ, and the number of steps or days for the purification of the contaminated soil Can be reduced, which is useful.

  In addition, when the polymer absorbent used in the contaminated soil purification method of the present invention swells in the contaminated soil, in order to prevent air from entering, organochlorine compounds present in the swollen range do not flow out of the range. Therefore, the contaminated soil purification method also has an effect of suppressing the diffusion of organochlorine compounds.

  Furthermore, when the polymer absorbent used in the contaminated soil purification method of the present invention is one that is biodegraded by microorganisms itself, an anaerobic microbial degradation promoter is continuously supplied. It has the effect of creating an environment where you can always work. In addition, there is an effect of preventing the anaerobic microbial degradation promoter from flowing into the groundwater.

Claims (8)

A method for in situ purification of soil contaminated with organochlorine compounds degradable by anaerobic microorganisms,
Injecting the polymer absorbent having a hydrophilic group into the contaminated soil, and blocking the intrusion of air into the contaminated soil, thereby making the place anaerobic,
Injecting an anaerobic microbial degradation promoter for promoting the degradation of the organochlorine compound by the anaerobic microorganisms into the contaminated soil; and
Contaminated soil purification method characterized by including.   The contaminated soil purification method according to claim 1, further comprising a step C of injecting an aqueous solution for swelling the polymer absorber into the soil into which the polymer absorber has been injected.   The process A and the process B are performed together by containing the anaerobic microbial degradation accelerator in the polymer absorbent and injecting the polymer absorbent into the contaminated soil. Contaminated soil purification method.   Step A, Step B and Step C are performed together by containing the polymer absorber and the anaerobic microbial degradation promoter in the aqueous solution and injecting the solution into the contaminated soil. The contaminated soil purification method according to claim 2.   The method for purifying contaminated soil according to any one of claims 1 to 4, wherein the viscosity of the polymer absorber is increased in advance before the polymer absorber is injected into the contaminated soil. .   5. The contaminated soil purification according to claim 4, wherein the viscosity of the aqueous solution is increased in advance before the aqueous solution containing the polymer absorbent and the anaerobic microbial degradation accelerator is injected into the soil. Method.   2. The anaerobic microbial degradation promoter is a hydrogen donor that provides the hydrogen necessary to promote reductive dechlorination for replacing chlorine in the organochlorine compound with hydrogen. The contaminated soil purification method according to any one of -6.   The contaminated soil purification method according to claim 1, wherein the polymer absorbent is biodegradable.