JP2001347280A - Method for cleaning ground water polluted with halogenated organic compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for rapidly decomposing halogenated organic compound in ground water at an existing position with combined chemical and biological decomposition using heterotrophic anaerobic microorganisms. SOLUTION: In a method for cleaning ground water polluted with a pollutant containing the halogenated organic compound, a water permeable reaction region containing a reducing agent of which the standard electrode potential to a standard hydrogen electrode at 25 deg.C is 300-2,400 mV and nutrients for soil microorganisms is formed in the ground and the pollutant in ground water is chemically and biologically decomposed during the passage of ground water through the reaction region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for in situ purification of soil or groundwater contaminated by pollutants containing halogenated organic compounds.

[0002]

2. Description of the Related Art In recent years, tetrachloroethylene, trichloroethylene, and 1,1,2 have been widely used as degreasing / cleaning agents for metal parts of electronic devices and cleaning agents for dry cleaning.
Soil and groundwater contamination by halogenated organic compounds such as 1,1-trichloroethane and dichloroethylene has been reported one after another. In particular, recently, dioxin discharged from incineration facilities, pollution by PCBs, and the like have been attracting attention. Since these halogenated organic compounds are not easily decomposed in the natural world and are poorly water-soluble, they easily accumulate in soil and permeate into groundwater in a contaminated area. Also,
Halogenated organic compounds are known to cause liver damage and have carcinogenic properties. Therefore, it is desired to decompose and render harmless organic compounds such as chlorinated organic compounds contained in soil and the like.

[0003] As a technique for decomposing halogenated organic compounds by a chemical reaction, reductive treatment of chlorinated organic compounds with metallic iron has been reported (Tetsuo Sanezaki, Treatment of groundwater contaminated with organochlorine compounds-low temperature by activated carbon adhering to metallic iron). Processing Technology, "PPM", 1995, 26, 5
No. 64-page 70). As a purification method of decomposing a halogenated organic compound using such metallic iron, a method of injecting metallic iron and high-pressure air into contaminated soil, reacting the halogenated organic compound with iron powder to make it inorganic, and detoxifying it. Has been reported (JP-A-8-257570). This method requires the installation of an air injection facility and, on the other hand, has a problem that the halogenated organic compound may be volatilized. Furthermore, since high-pressure air is used, a cost problem occurs, which is not practical.

When iron powder is in water, anode and cathode polarization occurs on the surface of the iron particles, and a dechlorination reaction occurs as a redox reaction. As a method for decomposing halogenated organic compounds in situ by using such a reaction, a permeable groundwater purification wall using iron has been reported (Tokuheihei 5-50152).
No. 0, JP-A-11-156351, Negishi et al.
Vol.27, No.1 (1999)). Such a permeable groundwater purification wall is an effective means in terms of cost because it does not require a plant facility on the ground such as an air injection facility and is maintenance-free. However, in such a permeable groundwater purification wall, since oxygen contained in groundwater comes into contact with the iron powder surface, the iron powder surface is covered with an oxide film, and the reducing activity is lost in a relatively short time. ,There's a problem.

Further, a method has been proposed in which groundwater is forcibly circulated by a pump or the like, and contaminants contained in the circulated groundwater are reduced by a reducing agent such as reduced iron (Japanese Patent Application No. 11-33403). This method requires maintenance of a circulation device and the like in order to force the groundwater to flow.

On the other hand, recently, as a method for purifying soil, groundwater, and the like contaminated with a halogenated organic compound, a microorganism treatment method (bioremediation) has attracted attention.
The microorganism treatment method is cost-effective and safe. However, in the microorganism treatment method, as described below, there is a problem that the treatment takes a long time and the types and concentrations of decomposable substances are limited.

As an example of the microorganism treatment method, there is known an aerobic decomposition treatment method of trichloroethylene using methane-utilizing bacteria, toluene / phenol-degrading bacteria, ammonia-oxidizing bacteria, and alkene-utilizing bacteria. However, this method
1) The decomposition reaction is unstable, 2) The range of substances to be decomposed is extremely narrow, and 3) High chlorinated substances such as tetrachloroethylene and carbon tetrachloride have the disadvantage that they have no decomposition action.

On the other hand, many anaerobic microorganisms can decompose highly chlorinated organic compounds such as tetrachloroethylene, trichloroethylene and carbon tetrachloride, and have wide application. However, 1) that the growth of microorganisms is very slow, 2)
It has disadvantages such as the production and accumulation of highly toxic intermediate metabolites during the anaerobic decomposition process (Hiroo Uchiyama and Osamu Yagi, Bioscience and Industry, 1994, Vol. 52,
No. 11, pages 879-884).

[0009] In order to decompose contaminants such as soil in situ by biodegradation by microorganisms and to purify groundwater, a method of directly mixing a large amount of nutrients for microorganisms with soil is known (International Application PCT). / JP / 95/363). However, such a method requires a large amount of civil engineering work, and it is not always easy to uniformly mix a nutrient source and soil. Furthermore, it is also assumed that the mixing conditions affect the decomposition rate of the halogenated organic compound. In particular, in order to purify contaminants having a volume of 1 m ³ or more, particularly 10 m ³ or more, a method of mixing is required.

As described above, it is considerably difficult to efficiently purify groundwater contaminated with halogenated organic compounds by performing chemical decomposition or biodegradation by microorganisms independently. Therefore, various methods have been proposed for decomposing halogenated organic compounds by synergistic effects of the chemical decomposition and the biodegradation by microorganisms in combination.

As a method combining chemical decomposition of a halogenated organic compound and decomposition by a microorganism, a natural substance having a dehalogenation catalysis and a microorganism treatment are combined to remove an organic chlorine compound contaminating soil and groundwater. Methods for removal have been reported (Nikkei Biotech) (Nikkei BP
Issued October 7, 1996, No. 361, No. 1
4 to 15). However, there is no description about specific natural substances and microorganisms.

As a method of purifying groundwater by decomposing soil and other contaminants in situ by chemical decomposition and biodegradation by microorganisms, a small amount of water is pumped downstream of the contaminated aquifer, and the pumped groundwater is purified. A method of dissolving a reducing agent and a nutrient source to promote the growth of pollutant-degrading microorganisms after subjecting the pollutant to purification treatment and re-injecting it into unsaturated soil or aquifer on the upstream side has been proposed. (Japanese Patent Application No. 11-15929)
No., Japanese Patent Application No. 11-158100). However, in this method, re-injection is not possible unless the pumped-up contaminated water is purified to a level below the permeation regulation concentration underground. Therefore, it is necessary to additionally provide a purification facility on the ground, and there is a problem that the cost increases.
In addition, the injected water may cause a phenomenon such as a diversion of the flow of the contaminated groundwater, and there is also a problem that the injected nutrient source may not sufficiently mix with the groundwater.

In view of the above-mentioned problems in the prior art, the present inventor combines the advantages of both the chemical decomposition of a halogenated organic compound and the decomposition by a microorganism, thereby contaminating the organic compound containing the halogenated organic compound. This has led to the development of a method and apparatus for purifying objects quickly in situ, without the need for ground facilities, and for a long period of time without maintenance.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to rapidly decompose contaminants, including halogenated organic compounds, in groundwater in situ by combining chemical degradation and biodegradation by heterotrophic anaerobic microorganisms. Is to provide a way to

[0015]

SUMMARY OF THE INVENTION The present invention is a method for purifying groundwater contaminated with contaminants containing halogenated organic compounds, wherein the standard electrode potential at 25 ° C. with respect to a standard hydrogen electrode is 300 mV to −2400 mV. A water-permeable reaction zone containing a certain reducing agent and a nutrient for soil microorganisms is formed in the ground, and while the groundwater passes through the reaction zone, the contaminants in the groundwater are chemically removed by the reducing agent. It is an object of the present invention to provide a purification method characterized by undergoing a decomposition reaction and a biodegradation reaction by soil microorganisms.

As used herein, the term "halogenated organic compound" refers to all organic compounds substituted with halogen, such as fluorinated organic compounds, chlorinated organic compounds, brominated organic compounds, iodinated organic compounds and fluorinated organic compounds. Point. In particular, aliphatic compounds such as tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, and dichloroethylene, which have become problems as sources of pollution of groundwater and soil,
And aromatic compounds such as pentachlorophenol, but are not limited thereto.

The pollutant is a polluting source of groundwater, and includes various organic compounds (for example, petroleum organic compounds such as benzene, toluene, xylene, ethylbenzene, etc.) as well as pollutants such as domestic wastewater and industrial wastewater. The following is a general description. The present invention is particularly effective in purifying groundwater mixed with one or more types of pollutants containing a halogenated organic compound.

The groundwater refers to water existing underground with respect to surface water, and is a concept including free-surface groundwater above an impermeable layer and pressurized groundwater below an impermeable layer.

When the standard electrode potential at 25 ° C. with respect to the standard hydrogen electrode is higher than 300 mV, the reducing agent used in the present invention is not preferable because sufficient reducing power cannot be obtained.
On the other hand, if the standard electrode potential is lower than −2400 mV, the reducing power is too strong, and there is a risk of generating hydrogen gas, which is not preferable. The standard electrode potential (E 電位) with respect to the standard hydrogen electrode at 25 ° C. is shown in Table 1 below.

[0020]

[Table 1]

As the reducing agent, a reducing agent which is in a solid state and is insoluble or hardly soluble in water can be preferably used.

Examples of the solid-state reducing agent (hereinafter also referred to as a solid reducing agent) include reduced iron, cast iron, iron-silicon alloy, titanium alloy, zinc alloy, manganese alloy, aluminum alloy, magnesium alloy, calcium alloy, titanium alloy. At least one reduction selected from the group consisting of silicon alloys, titanium-aluminum alloys, zinc-aluminum alloys, manganese-magnesium alloys, aluminum-zinc-calcium alloys, aluminum-tin alloys, aluminum-silicon alloys, and calcium-silicon alloys An agent can be preferably mentioned.

When reduced iron is used as the reducing agent in the solid state, adsorption of the halogenated organic compound occurs on the surface of the reduced iron, and at the same time, the difference in the conditions between the metal side and the environment side on the reduced iron surface causes the anode and the cathode to change. And a current flows, and accordingly, the anode has the following formula 1
As shown in (1), iron is eluted as iron ions, electrons flow into the cathode, and a reduction reaction occurs.

[0024]

(Equation 1)

When cast iron is used as a reducing agent, graphite contained in cast iron adheres to the surface,
This graphite acts as a cathode and iron acts as an anode. When an alloy is used as the reducing agent, according to the standard electrode potential of the metal element constituting the alloy,
Polarize to the anode and cathode. In the case of an alloy, the reducing atmosphere is more easily maintained, and the potential difference with the halogenated organic compound becomes larger, so that the dehalogenation reaction is promoted.

The reducing agent in the solid state may be in the form of granules such as sand or gravel, or in the form of powder, lump, or the like. It is necessary that the particles have a particle size that can ensure water permeability.

As the reducing agent, for example, sand, gravel, gravel or the like may be used together as the filler. That is, sand, gravel, gravel, and the like may be mixed with metal particles such as iron. In this case, for example, sand, gravel, gravel and the like become the main components of the reaction zone, the reaction zone retains water permeability, and the reducing agent is contained to such an extent that water permeability is not impaired.

Heterotrophic anaerobic microorganisms include methanogens (for example, genus Methanosarcina, Methanothrix
Genus, Methanobacterium, Methnobrevibacter), sulfate-reducing bacteria (eg, Desulfovibrio, Desulfotomacu
lum, Desulfobacterium, Desulfobacter, Desulf
ococcus), nitrate-reducing bacteria (eg, Bacillus, Lac
Genus tobacillus, Aeromonas, Streptococcus, Microc
occus), acid-producing bacteria (eg, Clostridium, Acet)
ivibrio, Baceroides, Ruminococcus), facultative anaerobic bacteria (eg, Bacillus, Lactobacillus, Aer
omonas, Streptococcus, Micrococcus) and the like. In particular, the genus Bacillus, Pseudomo
The genus nas, the genus Aeromonas, the genus Streprococcus, and the genus Micrococcus are preferred because they have an oxidized nitrogen reducing activity.

As the heterotrophic anaerobic microorganisms, those which naturally inhabit the soil can be used. Heterotrophic anaerobic microorganisms originally existing in the soil are proliferated and activated by the nutrient sources of the microorganisms dissolved in the groundwater from the solid nutrients placed in the ground. The activated microorganisms degrade pollutants, including halogenated organic compounds, in groundwater.

As a nutrient, a solid state (hereinafter, referred to as a nutrient)
Solid nutrients), as long as the nutrient sources of microorganisms (including both aerobic and anaerobic microorganisms) living in the ground are gradually dissolved in groundwater. Anything is acceptable. By "gradually dissolving" is meant that when the solid nutrient comes into contact with groundwater, the nutrients do not all dissolve in the groundwater but continue to dissolve little by little over a period of time. Therefore, a solid nutrient in which components dissolve at once when groundwater reaches the reaction zone is not preferred in the present invention. Preferred solid nutrients include, for example, solid organic matter such as compost, compost, excess sludge, bottom mud having a high organic matter content, organic waste, and ready-made solid nutrients. Commercially available solid nutrients include, for example, Hydrogen Release C, which releases hydrogen slowly.
ompound (HRC, registered trademark, REGENESI
S company) can be suitably used. The solid nutritional supplement is preferably in a granular form, but is not limited thereto. From the viewpoint of uniformly mixing the above-described solid reducing agent and, if necessary, the filler, it is desirable that the solid reducing agent and the filler have the same particle size. Besides, those in the form of powder, lump, rod, fiber, etc. can also be used.

The solid reducing agent and the solid nutrient are, for example, excavated in the ground so as to be orthogonal to the flow of groundwater,
It can be placed in it. By arranging a mixture of a solid reducing agent and a solid nutrient and optionally a filler in this groove, the reaction zone can be installed in the form of an underground wall. That is, the underground wall refers to an underground groove filled with such a mixture. Typically, a mixture of a solid reducing agent, a solid nutrient and, optionally, a filler is formed in the groove so that the groove does not collapse, and has a water permeability equal to or higher than that of the surrounding ground. It shows the nature. Further, the depth of the groove should be a depth capable of catching the contaminated groundwater flowing down, and is usually up to about 20 m, preferably up to about 10 m from the surface of the ground, but is not limited thereto. The length of the ditch is determined by the width of the contaminated groundwater stream. The thickness of the groove can be changed depending on the flow rate of groundwater, the concentration of pollutants, and the like, but is typically about 0.5 to 2 m.

[0032] Alternatively, the solid reducing agent and the solid nutrient can be placed, for example, by drilling an elongated hole in the ground. In this case, the part of the elongated hole in which the solid reducing agent and the solid nutrient and optionally the filler are arranged becomes a reaction zone in which the decomposition of the halogenated organic compound in the groundwater occurs. Here, the elongated hole typically refers to a deep hole such as a boring hole, but is a concept including a conduit, a well, and the like inserted and installed in the ground. The elongated holes may or may not be sealed at the top. The depth of the elongated holes is set to a depth that can capture the contaminated groundwater flowing down.
Therefore, it is usually up to about 50 m from the surface of the earth, preferably up to about 20 m. The diameter of the elongated holes can vary depending on the contact time of the groundwater with the reducing agent and nutrients, the size of the contaminated area, the contaminants and their concentration, but typically about 5 to 100 cm, preferably about 5 to 100 cm. 50cm,
More preferably, it is about 5 to 30 cm. Also, the diameter of the holes can be changed depending on the number of holes to be installed.

In addition to directly placing the mixture of the solid reducing agent, the solid nutrient and optionally the filler in the groove or slot, it is first filled into a conduit or well or container, and this conduit or well or container is then filled. It may be located in a groove or slot. Alternatively, a tube or container may be placed in the groove or slot, into which a mixture of the solid reducing agent, the solid nutrient and, optionally, the filler may be charged. In such a case, the tube or container should have at least a part of a strainer part composed of a large number of through holes. Alternatively, it is filled, for example in a cloth bag, so that the groundwater can pass through the gaps of the mixture of solid reducing agent, solid nutrient and optionally the filler and come into contact therewith, which is then filled with the channel or the elongate. It is also possible to place it in a hole. Installation of the mixture in the form of a tube or container in a groove or slot allows the solid reducing agent and the solid nutrient to be placed therein to be changed regularly or irregularly. In areas where groundwater needs to be purified in the long term, it is preferred to use such grooves or holes in the form of replaceable tubes or vessels.

The grooves can be installed in the groundwater saturated zone, preferably by a continuous underground wall construction machine, while the elongated holes can be installed in the groundwater saturated zone, preferably by large diameter boring. When a continuous underground wall construction machine is used, it is possible to adjust the width and thickness of the underground wall according to the size of the contaminated area. The continuous underground wall is
One or more can be installed. Boring holes are
One or a plurality of units may be installed.
They may be arranged in a row or in a plurality of rows. As described below, the arrangement of the boring holes can be changed according to the size of the contaminated area.

In the present invention, when groundwater enters the above-mentioned reaction zone, the solid nutrient is dissolved in the groundwater, and the dissolved component and the contaminant containing a halogenated organic compound in the groundwater are mixed with the reducing agent. Contact with. At this time, groundwater is decomposed until the pollutants including halogenated organic compounds in it reach a concentration that does not exceed the environmental standard value.
You need to contact for a sufficient time. The contact time between the groundwater in the groundwater and the reducing agent or nutrient can be adjusted by changing the size of the reaction zone in consideration of the flow rate of the groundwater and the like. For example, in a place where the flow rate of groundwater is high, the thickness of the wall in the flow direction of groundwater is large, and when the flow rate is low, the thickness of the wall in the flow direction of groundwater is small.

In addition, where the width of the contaminated groundwater area is wide, the width of the reaction area must be widened. Changing the width of the reaction zone can be achieved, for example, by constructing the reaction zone in the form of a long underground continuous wall or by arranging a plurality of boreholes over a desired width. In addition, side continuous walls may be provided at both ends of the reaction zone to ensure that the contaminated groundwater enters the reaction zone. The side continuous wall is provided to guide the groundwater to the reaction zone, and is preferably a waterproof wall made of a water-impermeable material. Examples of the impermeable water blocking wall include a wall constructed with a sheet pile, grout, or the like.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the purification method of the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows that the purification method of the present invention is performed.
It is a side view showing permeation of groundwater when a mixture of a solid reducing agent and a solid nutrient is installed in a groundwater saturated zone using a large-diameter boring machine or a continuous underground wall construction machine. A permeable reaction zone 2 filled with a solid reducing agent and a solid nutrient is provided in the downflow area of the groundwater 1 contaminated with the halogenated organic compound by the construction of a boring hole or an underground continuous wall to provide a natural groundwater flow. The contaminated groundwater is allowed to flow into the reaction zone 2.
When groundwater flows into the reaction zone, solid nutrients begin to melt,
Dissolves in groundwater. Since the anaerobic microorganisms in the ground are activated by the nutrient, the biodegradation reaction of the halogenated organic compound by the anaerobic microorganisms is promoted. On the other hand, since the halogenated organic compound also comes into contact with the solid reducing agent, it is reduced on the surface of the solid reducing agent as described above, whereby the organic compound is decomposed. That is, the halogenated organic compound in the groundwater is efficiently produced in the reaction zone 2 by the synergistic effect of the biodegradation reaction by the microorganisms activated with the dissolution of the nutrient and the chemical reaction by contact with the reducing agent. The decomposed and purified groundwater 3 is discharged downstream. This makes it possible to purify groundwater without causing depletion or land subsidence due to pumping, and it is possible to prevent the diffusion of pollution downstream. Also, the method does not include a forced groundwater transfer step, and the water contaminated by natural streams and nutrients are mixed and come into contact with the reducing agent in this state, so that a means for groundwater transfer is used. Need not be installed on the ground.

However, when it is assumed that the flow of the groundwater is extremely slow and does not flow into the reaction zone effectively, a means for forcibly moving the groundwater may be provided in the ground or on the ground. However, even in such a case, instead of forcibly pumping and treating contaminated groundwater to the ground and returning it to the underground again, the purpose is to effectively guide the contaminated groundwater to the reaction zone, Pumps and water injection pumps upstream of the contaminated area should be used.

FIG. 2 shows the state of mixing and the permeation of groundwater when a solid reducing agent and a solid nutrient are mixed with sand and gravel and installed in a groundwater saturated zone using a continuous underground wall construction machine or large-diameter boring. FIG. In the figure, 4 indicates particles of a solid nutrient, 5 indicates particles of a solid reducing agent, and 6 indicates gravel particles. When the contaminated groundwater flows in the direction of the arrow, the nutrient gradually dissolves from the solid nutrient 4 into the groundwater, resulting in groundwater containing the nutrient. The nutrient activates anaerobic microorganisms in the ground, and promotes the biodegradation reaction of halogenated organic compounds by the anaerobic microorganisms. On the other hand, when the halogenated organic compound comes into contact with the solid reducing agent 5, it undergoes a reducing action on the surface of the solid reducing agent and is chemically decomposed. That is,
Halogenated organic compounds contained in groundwater are synergistically produced by the biodegradation reaction of microorganisms activated with the dissolution of nutrients and the reduction reaction by the contacting solid reducing agent.
Decomposes efficiently and flows out of the reaction zone.

The surface of the solid reducing agent is usually oxidized by oxygen dissolved in groundwater, and may lose its activity at an early stage of the reaction due to an oxide film formed thereby. However, in the method of the present invention, since the nutrients of the microorganisms dissolve into the groundwater, the aerobic microorganisms living in the ground also consume dissolved oxygen in the groundwater when ingesting and digesting this nutrient source. Therefore, in the method of the present invention, oxygen hardly comes into contact with the surface of the solid reducing agent. Therefore, the formation of an oxide film on the surface of the solid reducing agent is suppressed, so that the initial decomposition rate can be maintained longer as compared with the purification method using only the reducing agent.

Although FIG. 2 shows a case where sand and gravel 6 are mixed as a filler as one embodiment, for example, a porous carrier or the like may be used as the filler. Examples of the porous carrier that can be used include zeolite, molecular sieve, activated carbon, and anthracite. Such gravel or porous carrier is preferably in a granular form, and the particle size depends on the degree of water permeability in the region where the reaction zone is to be formed, the number of heterotrophic microorganisms, or the strength of the ground. It should be changed accordingly.

The proportions of the solid reducing agent, the solid nutrient and the filler mixture are about 10 to 50% of the solid reducing agent, about 10 to 50% of the solid nutrient and about 0 to 80% of the filler based on the total volume of the mixture. %, Preferably about 20-30% solid reducing agent,
It can be, but is not limited to, about 20-30% solid nutritional supplement and about 40-60% filler. In particular, the proportion of the filler can be freely changed according to the water permeability of the region where the reaction zone is to be formed, the strength of the ground, and the supporting force of the mixture itself. In order to promote the formation of heterotrophic anaerobic microorganisms, the ratio of solid nutrition
It can be increased to about 0%.

Further, as a modification of the embodiment of FIG. 2, the solid nutrient is adsorbed on the gravel and the porous carrier itself,
It is also possible to mix and install the adsorbed gravel or the adsorbed porous carrier and the solid reducing agent.

FIG. 3 is a side view showing a state where the ground is excavated by an underground continuous wall construction machine when an underground continuous wall containing a solid reducing agent and a solid nutrient is installed. As shown in FIG. 3, a trench for the underground wall reaching the aquifer is excavated by an underground continuous wall construction machine, and a mixture of a solid reducing agent and a solid nutrient, and in some cases, a gravel or a porous carrier, Charge the particle filler.

FIG. 4 is a schematic diagram showing the state of permeation of groundwater when the installed underground continuous wall is viewed from above. When groundwater flows into the underground continuous wall according to the natural flow, the biodegradation reaction by the microorganisms activated with the dissolution of nutrients and the interaction of the reduction reaction by the reducing agent, as described above,
Halogenated organic compounds in groundwater are decomposed. As another aspect, it is also possible to install a plurality of such underground continuous walls in parallel. As still another aspect, groundwater forced moving means such as a water pump is installed on the downstream side of the underground wall,
It can also ensure that groundwater passes through the reaction zone.

FIG. 5 is a side view showing a state in which a plurality of boring holes containing a mixture of a solid reducing agent and a solid nutrient are provided, and a wide reaction zone is formed as a whole. The boring holes may be arranged in a line or over a plurality of lines. The width and thickness of the reaction zone can be adjusted by changing the number and arrangement of the boreholes.

FIG. 6 shows an example of a construction in which a plurality of boring holes are arranged in two rows, and a solid reducing agent, a solid nutrient and a filler are arranged in each of the holes to form a reaction zone. It is a schematic diagram which shows the permeation state of the groundwater when it sees from. As another embodiment, the boring holes can be arranged in one row, and furthermore, three or more rows can be arranged.

[0049]

According to the purification method of the present invention, chemical degradation by a reducing agent and biodegradation by microorganisms existing in the ground are combined to decompose contaminants contained in groundwater in situ. be able to. By the synergistic effect of both the chemical decomposition reaction and the biodegradation reaction by microorganisms, the formation of oxide film on the surface of the reducing agent can be suppressed, and the decomposition rate at the time of burying the underground wall can be maintained longer. It turned out to be possible. In addition, this method does not require a means for forcibly moving groundwater unlike the conventional method, so that it is possible to avoid noise and the like due to driving of a pump for water circulation and the like. This is a very acceptable and effective method from the viewpoint of Furthermore, since the natural groundwater is allowed to flow into the reaction zone depending on the natural flow, it is possible to significantly reduce the maintenance labor after burial.

[Brief description of the drawings]

FIG. 1 shows a solid reducing agent for performing the purification method of the present invention;
It is a side view showing permeation of contaminated groundwater when a mixture of solid nutrients is installed in a groundwater saturated zone by large-diameter boring or a continuous underground wall construction machine.

Fig. 2 Schematic representation of the state of mixing and permeation of groundwater when a solid reducing agent and a solid nutrient are mixed with sand and gravel and installed in a groundwater saturated zone using a large-diameter boring machine or a continuous underground wall construction machine. FIG.

FIG. 3 is a front view illustrating a state where an underground continuous wall including a solid reducing agent and a solid nutrient is installed.

FIG. 4 is a schematic diagram showing the state of permeation of groundwater when the installed underground continuous wall is viewed from above.

FIG. 5 is a front view showing a state in which a plurality of boring holes containing a mixture of a solid reducing agent and a solid nutrient are provided, and a wide reaction zone is formed as a whole.

FIG. 6 is a schematic diagram illustrating a permeation state of groundwater when an example in which a reaction region is formed by arranging a plurality of boring holes in two rows is viewed from above.

[Explanation of symbols]

 1: Contaminated groundwater 2: Reaction zone 3. Purified groundwater 4: Solid nutrient 5: Solid reductant 6: Filler (sand and gravel)

Continuation of the front page (72) Inventor Masami Kitagawa 11-1 Haneda Asahimachi, Ota-ku, Tokyo F-term in Ebara Corporation (reference) 2D049 EA14 GB01 4B065 AA99X BC41 CA55 4D004 AA41 AC07 CA18 CA37 CC07 CC11 DA03 DA20 4D040 AA01 4D050 AA02 AB44 AB45 BA01 BA02 CA17

Claims (4)

[Claims] 1. A method for purifying groundwater contaminated with a pollutant containing a halogenated organic compound, wherein a standard electrode potential at 25 ° C. with respect to a standard hydrogen electrode is 300 mV or more.
A water permeable reaction zone is formed in the ground containing a reducing agent at −2400 mV and a nutrient for soil microorganisms, and while groundwater passes through the reaction zone, contaminants in the groundwater are chemically The above-mentioned purification method, which is subjected to a decomposition reaction and a biological decomposition reaction. 2. The purification method according to claim 1, wherein the reducing agent is in an insoluble or hardly soluble solid state, and the nutrient is in a solid state that gradually dissolves in water. Method. 3. The reaction zone is formed by an underground continuous wall or a plurality of boring holes. In the reaction zone, a dissolved component of the nutrient and a halogenated organic compound in groundwater are mixed to form the reducing agent and the reducing agent. The purification method according to claim 1, wherein the cleaning method has a size enough to secure a contact time. 4. The method according to claim 1, wherein the reducing agent and the nutrient are filled in the underground continuous wall or the plurality of boring holes as a mixture thereof or a mixture with a coarse-grained material composed of gravel or a porous carrier. The purification method according to claim 1, characterized in that: