JP2002159959A - Method and device for purifying underground polluted region - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device by which an underground polluted region polluted by chemicals, in particular by an organic chlorine compound, can be purified in a short period of time, at a low cost and with low energy consumption. SOLUTION: At first, underground water W is pumped up by a pumping means 2 from the underground polluted region X or from the vicinity thereof. Then, pumped-up underground water is subjected to purification treatment (such as aeration treatment of the pumped-up water and oxidation treatment) with a purifying means 4. Further, an oxidant (such as H2O2) is added to purified water by an oxidant adding means 6. Thereafter, purified treated water to which the oxidant is added is injected again into the underground polluted region or the vicinity thereof with an injection means 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for physicochemically purifying an underground contaminated area contaminated with a chemical substance, in particular, an organic chlorine compound.

[0002]

2. Description of the Related Art Organochlorine compounds such as trichloroethylene and tetrachloroethylene are widely used as cleaning agents in various factories and cleaning shops. However, these organochlorine compounds are suspected to be carcinogenic substances. Pollution of groundwater, soil, sediment, sludge, etc. by chlorine compounds has become a major social problem.

[0003] Conventionally, as a method for treating soil contaminated with an organic chlorine compound, a process for containing the contaminated soil, a process for excavating and containing the contaminated soil, and the like are mainly performed. As a method of treating groundwater contaminated with an organic chlorine compound, a pump-and-treat method that combines pumping aeration and activated carbon treatment is mainly performed. The pump and treat method is a method of purifying groundwater by transferring pollutant chemicals in the water into a gas phase by aerating air into pumped ground water, and then treating the gas phase with activated carbon.
The purified water is drained to the surface.

[0004]

However, the above-described methods for contaminating contaminated soil, excavating and contaminating contaminated soil, and pumping and treating contaminated groundwater are described above.
There have been problems in that it is not a technology for actively decomposing polluting chemical substances to make it harmless, that it requires enormous cost, energy and labor, and that the purification period is as long as 10 to 20 years.

The pump-and-treat method purifies the contaminated groundwater that has been pumped on the ground, and does not directly remove the contaminated source existing underground. There is a problem that the removal period of the polluting source becomes very long.

On the other hand, in recent years, a method for oxidizing an underground contaminated area in situ by injecting potassium permanganate or a solution of hydrogen peroxide and iron (Fenton's reagent) directly into a well has been developed. ing. However, in the above-mentioned method, since a high-concentration oxidizing agent is injected into the underground contaminated region, there is a problem that the handling of the oxidizing agent is difficult and a rapid exothermic reaction occurs in the ground due to the oxidizing agent. In addition, in the method of injecting hydrogen peroxide and an iron solution into the underground contaminated region, the clogged soil occurs near the injection well due to the reaction between the hydrogen peroxide and the iron solution, and the precipitated trivalent iron compound causes oxidation. There is a problem that the injection of the agent can be performed only for a short time of several hours or several days.

The present invention has been made in view of the above circumstances, and can purify an underground contaminated area contaminated with a chemical substance, particularly an organic chlorine compound, in a short period of time, at low cost, and with low energy. It is an object to provide a method and an apparatus.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies on an oxidation treatment method for purifying an underground contaminated area contaminated with an organic chlorine compound such as trichloroethylene and tetrachloroethylene. As a result, when the purified groundwater is purified, the oxidizing agent is added to the purified water, and then the purified water is injected into the underground again, the purified water cleans the contamination source in the underground contaminated area. At the same time, the oxidizing agent contained in the treated water oxidizes and decomposes the pollution source in the underground pollution area,
As a result, they found that the remediation of the underground contaminated area could be completed in a short time.

Further, the inventor of the present invention has a problem that, since a high concentration of oxidizing agent is conventionally injected into the underground contaminated area, it is difficult to handle the oxidizing agent, and the oxidizing agent causes a rapid exothermic reaction in the ground. However, when injecting purified water treated with an oxidant into an underground contaminated area, the oxidant is diluted with the purified water to a low concentration, so that a high concentration of oxidant is injected into the underground contaminated area. It has been found that the above disadvantage can be solved.

The present invention has been made based on the above findings, and is a method for purifying an underground contaminated area contaminated with a chemical substance. In addition, the present invention provides a method for purifying an underground contaminated region, which comprises adding an oxidizing agent to the purified water and then injecting the purified water again into or near the underground contaminated region.

[0011] The present invention also relates to a device for purifying an underground polluted area contaminated with a chemical substance, comprising a pumping means for pumping groundwater from or near the underground polluted area, and a purification process for groundwater pumped by the pumping means. Purifying means, an oxidizing agent adding means for adding an oxidizing agent to water purified by the purifying means, and an injection means for injecting the water to which the oxidizing agent is added by the oxidizing agent adding means into or near the underground pollution area. A purifying apparatus for an underground polluted area is provided.

Hereinafter, the present invention will be described in more detail. In the present invention, a treatment for purifying groundwater pumped from or near the underground contaminated region is performed. Although there is no particular limitation on the method of purifying groundwater, a pumping aeration method or an oxidation treatment method can be suitably used. The pumping aeration method is a method of aerating air from pumped groundwater to transfer contaminants in the water into the gas phase.

As the oxidation treatment method, a method of adding hydrogen peroxide to the pumped groundwater in the presence of ferrous iron ions is particularly preferable. When hydrogen peroxide is added to contaminated groundwater in the presence of ferrous ion, pollutant chemicals such as organic chlorine compounds are efficiently oxidized and decomposed by hydroxyl radicals generated by the reaction between ferrous ion and hydrogen peroxide. Is done.

In this case, as a method for making ferrous ions exist in the pumped ground water, there is a method of adding a ferrous ion supplying substance such as iron chloride, iron sulfate, iron oxide, iron powder or the like to groundwater. . However, if the pumped groundwater originally contains an appropriate amount of ferric ion, it is not necessary to add a ferrous ion supplying substance to the groundwater.

[0015] The purification treatment of adding hydrogen peroxide to the pumped groundwater in the presence of ferrous ions is suitably performed under the following conditions. This makes it possible to efficiently perform oxidative decomposition of contaminant chemicals in water by hydroxyl radicals. The pH can be controlled by adding a pH adjuster such as sulfuric acid to water. -PH of water: 2 to 6, more preferably 3 to 4-Hydrogen peroxide concentration in water: 1 to 500 mg / L, more preferably 5 to 50 mg / L-Divalent iron ion concentration in water: 1 to 200 mg / L L, more preferably 5 to 50 mg / L

In the present invention, after purifying the groundwater pumped as described above, an oxidizing agent is added to the purified water. Examples of the oxidizing agent include hydrogen peroxide, potassium permanganate, and sodium hypochlorite, but are not limited thereto.

When hydrogen peroxide is added as an oxidizing agent to the purified water, it is preferable to add divalent iron ions together with the hydrogen peroxide to the purified water. This way,
Hydroxyl radicals generated by the reaction between ferrous iron ions and hydrogen peroxide efficiently oxidize and decompose contaminant chemical substances (contamination sources) such as organic chlorine compounds present in the underground contaminated area.

In this case, as a method of adding ferrous ion to the purified water, a method of adding a ferrous ion supply material such as iron chloride, iron sulfate, iron oxide, iron powder, or the like to the purified water is mentioned. Can be However, when an appropriate amount of ferrous ion is originally contained in the purified water, it is not necessary to add a ferrous ion supply substance to the purified water.

The addition of hydrogen peroxide and ferrous ion to the purified water is suitably performed under the following conditions. This makes it possible to efficiently perform the oxidative decomposition of the polluting chemical substance present in the underground polluted region by the hydroxyl radical. The pH can be controlled by adding a pH adjuster such as sulfuric acid to the purified water. -PH of the purified water: 2 to 7, more preferably 3 to 6-Hydrogen peroxide concentration in the purified water: 0.005 to 5% by weight, more preferably 0.01 to 2% by weight-Purified water Divalent iron ion concentration: 1 to 5000 mg
/ L, more preferably 1 to 2000 mg / L

When adding divalent iron ions together with hydrogen peroxide to the purified water, a chelating agent can be added to the purified water together with the divalent iron ions. That is, if ferrous ions are added to purified water together with hydrogen peroxide, these reactions may cause hydroxyl radicals to be generated.
A trivalent iron compound is generated and precipitated, and the trivalent iron compound causes clogging of the soil near the injection well. On the other hand, if a chelating agent is added to the purified water together with ferrous ions, the ferrous ions combine with the chelating agent and do not rapidly react with hydrogen peroxide, and do not react with the ferrous ions and hydrogen peroxide. Will react gradually. As a result, clogging of the soil near the injection well with the trivalent iron compound is suppressed, continuous injection of the oxidizing agent, sustaining the oxidizing power of the oxidizing agent, and expanding the oxidizing treatment range with the oxidizing agent. It is possible to do. As a chelating agent, specifically, EDTA,
1-hydroxyethylidene-1,1-diphosphonic acid or the like can be used. The amount of the chelating agent added is 0.1.
Suitably, it is 1 to 10 mg / L.

In the case where ferrous ions are added to purified water together with hydrogen peroxide, hydrogen peroxide and hydrogen peroxide are added to the purified water.
Ferrous ions can be added alternately. That is,
If ferrous ions are added to the purified water together with hydrogen peroxide, soil clogging occurs near the injection well as described above. On the other hand, when a method (intermittent injection method) of alternately adding hydrogen peroxide and ferrous ion to purified water is adopted,
Divalent iron ions do not react rapidly with hydrogen peroxide, and divalent iron ions and hydrogen peroxide are in underground contaminated areas (contamination site of contamination)
And react. As a result, clogging of the soil near the injection well by the trivalent iron compound is suppressed,
Hydroxyl radicals can be generated at the site of contamination to efficiently oxidatively decompose contaminant chemicals.

In the present invention, after the oxidizing agent is added to the purified water as described above, the purified water is injected again into or near the underground contaminated area. This allows
The polluted source in the underground polluted area is washed by the purified water re-injected into the basement, and the pollutant in the underground polluted area is oxidized and decomposed by the oxidizing agent contained in the purified water.

The method and apparatus for purifying an underground contaminated area according to the present invention are suitably used for purifying an underground contaminated area contaminated with an organic chlorine compound, but the present invention is not limited thereto. In other words, in the method of adding ferric ion together with hydrogen peroxide to the purified water, organic substances are oxidatively decomposed by hydroxyl radicals, which are powerful non-specific oxidizing agents that react with most organic substances. Can be decomposed. Therefore, the method of adding ferric ion together with hydrogen peroxide to the purified water is not only a method of purifying an underground contaminated region with an organic chlorine compound, but also a method of adding an underground contaminated region with other organic substances such as oil, benzene, toluene, and xylene. It can also be applied to purification of wastewater. However, other methods of the present invention are also applicable to purifying underground contaminated areas with various contaminating chemicals.

[0024]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a view showing a first embodiment of an apparatus for purifying an underground pollution area according to the present invention. In FIG. 1, 2 is a pumping means, 4 is a purifying means, 6 is an oxidizing agent adding means, 8
Indicates injection means.

The pumping means 2 is for pumping groundwater W from or near the underground contaminated area X. The pumping means 2 of the present embodiment is buried underground and has a pumping well 10 for flowing groundwater into the inside through a screen of a pipe, a pumping pump 12 installed in the pumping well 10, and a pumping pump connected to the pumping pump 12. It has a pipe 14 and a groundwater storage tank 16 connected to the pumping pipe 14.

The purifying means 4 purifies groundwater pumped by the water pumping means 2. Purification means 4 of this example
Is provided with a pumping aeration tank 18, a pipe 20 for introducing groundwater in the groundwater storage tank 16 into the pumping aeration tank 18, and a pump 22. The pumping aeration tank 18 is for aerating the air 24 into the groundwater flowing downward in the inside thereof to transfer contaminant chemicals in the water into the gas phase.

The oxidizing agent adding means 6 adds an oxidizing agent to the water purified by the purifying means 4 in the mixing tank 26. The mixing tank 26 is connected with a pipe 28 for introducing the effluent from the pumping aeration tank 18, a hydrogen peroxide addition unit 30, and a sulfuric acid addition unit 32. Then, hydrogen peroxide (oxidizing agent) and sulfuric acid (pH adjusting agent) are added from the hydrogen peroxide adding means 30 and the sulfuric acid adding means 32 to the purified water introduced from the pipe 28. As an example of the treatment in the oxidizing agent adding means 6, there is an example in which hydrogen peroxide and sulfuric acid are added to the purified water so that the hydrogen peroxide concentration becomes 0.5% by weight and the pH becomes 3 to 4. It should be noted that ferrous ions and a chelating agent may be added to the purified water together with hydrogen peroxide.

The injection means 8 is for injecting the water to which the oxidizing agent has been added by the oxidizing agent adding means 6 again into the underground contaminated area X or its vicinity. The pouring means 8 of this example is buried underground and has a pouring well 34 for discharging water to the outside through a screen of a pipe, a pouring pipe 36 connected to the mixing tank 26 and discharging water into the pouring well 34, A water injection pump 38 interposed in the water injection pipe 36.

FIG. 2 is a view showing a second embodiment of the apparatus for purifying an underground polluted area according to the present invention. The apparatus of this example is the same as the apparatus of FIG. 1 except that the configuration of the oxidizing agent adding means 6 is different. Therefore, in FIG. 2, the same components as those of FIG. Omitted.

The mixing tank 26 of the oxidizing agent adding means 6 of this embodiment is connected with a hydrogen peroxide adding means 40, a sulfuric acid adding means 41 and an iron sulfate adding means 42. And the pipe 28
Means for adding hydrogen peroxide to the purified water introduced from
And hydrogen peroxide (oxidizing agent) from the iron sulfate addition means 42
And a ferrous sulfate solution (a ferrous iron ion supplying substance)
By the operation of 4, 46, it is intermittently added alternately. In addition, sulfuric acid (pH
The pH of the water is adjusted to 3 to 4 by adding the adjusting agent) to the water in the mixing tank 26 by operating the valve 45. This adjustment is performed while watching a pH monitor (not shown).

FIG. 3 is a view showing a third embodiment of the apparatus for purifying an underground polluted area according to the present invention. The apparatus of this example is the same as the apparatus of FIG. 1 except that the configurations of the purifying means 4 and the oxidizing agent adding means 6 are different. Therefore, in FIG. 3, the same components as those in FIG. The description is omitted.

The purifying means 4 of this embodiment has a reaction tank 56. The pipe 20 for introducing groundwater in the groundwater storage tank 16, the hydrogen peroxide addition means 50, the sulfuric acid addition means 52, and the iron sulfate addition means 54 are connected to the reaction tank 56. Then, in the reaction tank 56, hydrogen peroxide is added to the groundwater introduced from the pipe 20 in the presence of ferrous iron ions to perform a groundwater purification treatment (oxidation treatment). Examples of the processing in the reaction tank 56 include, for example,
From the hydrogen peroxide adding means 50, the sulfuric acid adding means 52 and the iron sulfate adding means 54 such that the hydrogen peroxide concentration in the water is 10 mg / L, the divalent iron ion concentration is 10 mg / L, and the pH is 3.5. There is an example in which hydrogen peroxide (oxidizing agent), sulfuric acid (pH adjusting agent), and an iron sulfate solution (a ferrous iron ion supplying substance) are added and reacted for 30 minutes.

A hydrogen peroxide adding means 50 is connected to the mixing tank 26 of the oxidizing agent adding means 6 of this embodiment. Then, hydrogen peroxide (oxidizing agent) is added from the hydrogen peroxide addition means 50 to the purified water introduced from the pipe 28. As an example of the treatment in the oxidizing agent adding means 6, the concentration of hydrogen peroxide in purified water is 0.5% by weight.
An example is given in which hydrogen peroxide is added such that It should be noted that ferrous ions and a chelating agent may be added to the purified water together with hydrogen peroxide.

FIG. 4 is a view showing a fourth embodiment of the apparatus for purifying an underground polluted area according to the present invention. The apparatus of this example is the same as the apparatus of FIG. 3 except that the configuration of the oxidizing agent adding means 6 is different. Therefore, in FIG. 4, the same components as those of FIG. Omitted.

The mixing tank 26 of the oxidizing agent adding means 6 of this embodiment is connected with a hydrogen peroxide adding means 50 and an iron sulfate adding means 54. Then, the hydrogen peroxide (oxidizing agent) and the iron sulfate solution (ferrous iron ion supplying material) are supplied to the purification treatment water introduced from the pipe 28 from the hydrogen peroxide adding means 50 and the iron sulfate adding means 54 through the valve 56. By the operation of 58, it is added alternately and intermittently.

In the apparatus shown in FIGS. 1 to 4, the pumping position A by the pumping means 2 is set to the downstream side of the flow F of the groundwater W, and the injection position B by the injection means 8 in purifying the underground pollution area X. It is set on the upstream side of the flow F of the groundwater W. In this way, the contaminated groundwater pumped on the downstream side is purified, the oxidizing agent is added to the purified water, and the purified water is injected on the upstream side. Therefore, it is possible to efficiently purify the underground pollution area. Therefore,
In the apparatus for purifying an underground polluted area according to the present invention, it is preferable that the pumping position by the pumping means is set downstream of the flow of groundwater, and the water injection position by the injection means is set upstream of the flow of groundwater.

[0037]

EXAMPLE The effect of purifying pumped ground water, adding an oxidizing agent to the purified water, and reinjecting it into the ground was examined. In this case, a column packed with soil contaminated with trichlorethylene (soil column: column diameter 2 cm, column length 40
cm) was prepared and tested under the following conditions to compare the purification periods.

Conditions simulating the case where only groundwater is pumped. As shown in FIG.
Then, clean ground water 74 is passed at a linear velocity of 14 cm / day,
The relationship between the purification period (water passage period) and the concentration of trichlorethylene in the column effluent water 76 was examined.

Conditions simulating the case of purifying the pumped ground water and re-injecting the purified water as it is into the ground, as shown in FIG. 5, a soil column 72 filled with contaminated soil 70.
Then, a mixed water of clean groundwater 74 and circulating water 80 which has been subjected to aeration (purification treatment) of the column effluent 76 in an aeration tank 78 is passed at a linear velocity of 70 cm / day, and a purification period The relationship between the water period) and the concentration of trichlorethylene in the column effluent water 76 was examined.

Conditions simulating the case of purifying the pumped ground water, adding an oxidizing agent to the purified water, and reinjecting it into the ground, as shown in FIG. 5, a soil column 72 filled with contaminated soil 70.
In addition, the clean groundwater 74 and the column effluent water 76 are aerated in an aeration tank 78, and the hydrogenated aerated water in the addition tank 82 has a hydrogen peroxide concentration of 1% by weight and a pH of 3. Circulating water 8 containing hydrogen peroxide and sulfuric acid
Water mixed with 0 was passed at a linear velocity of 70 cm / day, and the relationship between the purification period (water passage period) and the concentration of trichlorethylene in the column effluent water 76 was examined.

FIG. 6 shows test results during the cleaning period. FIG.
Therefore, in the case of only pumping groundwater (), after 120 days, the concentration of trichlorethylene (TCE) has not yet reached the environmental standard value, and the groundwater that has been pumped is purified and the purified water is used as it is. When re-injecting underground (), it takes about 40 days for the trichlorethylene concentration to fall below the environmental standard value. On the other hand, the groundwater pumped as in the present invention is purified, and an oxidizing agent is added to the purified water. In the case of re-injection into the underground, the concentration of trichlorethylene in the column effluent is as short as about 15 days, because trichlorethylene in the contaminated soil flows out in a short time and trichlorethylene is oxidatively decomposed by an oxidizing agent. It was confirmed that the purification period was significantly shortened because it was below the environmental standard value. From the above processing results, it can be seen that the present invention is extremely effective for the short-time decomposition treatment of the contaminated groundwater and the shortening of the purification period of the underground contaminated area.

[0042]

As described above, according to the present invention, an underground polluted area contaminated with a chemical substance, particularly an underground polluted area contaminated with an organochlorine compound, can be reduced in a short period of time at low cost and low energy. Can be purified. In addition, the method of the present invention in which ferrous ions are added to purified water together with hydrogen peroxide utilizes a radical reaction that can efficiently decompose various hard-to-decompose chemical substances. It is particularly effective in purifying the area, and its usefulness is extremely large. Furthermore, in the present invention, since the purified water is re-injected into the underground, an effect of preventing land subsidence can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an apparatus for purifying an underground pollution area according to the present invention.

FIG. 2 is a view showing a second embodiment of the apparatus for purifying an underground polluted area according to the present invention.

FIG. 3 is a view showing a third embodiment of the apparatus for purifying an underground contaminated area according to the present invention.

FIG. 4 is a view showing a fourth embodiment of the apparatus for purifying an underground polluted area according to the present invention.

FIG. 5 is a diagram illustrating a test method of a purification period in an example.

FIG. 6 is a graph showing the relationship between the purification period and the concentration of trichlorethylene in the column effluent in the purification period test of the example.

[Explanation of symbols]

 X Underground pollution area W Groundwater 2 Pumping means 4 Purification means 6 Oxidant adding means 8 Injecting means 10 Pumping well 14 Pumping pipe 16 Groundwater storage tank 18 Pumping aeration tank 26 Mixing tank 30 Hydrogen peroxide adding means 32 Sulfuric acid adding means 34 Water injection Well 36 Water injection pipe 40 Hydrogen peroxide / sulfuric acid addition means 42 Iron sulfate addition means 50 Hydrogen peroxide addition means 52 Sulfuric acid addition means 54 Iron sulfate addition means 56 Reaction tank

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 1/58 C02F 1/00 K 4D050 1/72 B09B 3/00 304K E02D 3/10 ZAB // C02F 1/00 F Term (Reference) 2D043 DA00 EB06 2E191 BA12 BB01 BC01 BD11 4D004 AA41 AB06 AC05 AC07 CA12 CA35 CA36 CB05 CB42 CB43 CB44 CC03 CC06 CC11 CC12 DA02 DA20 4D037 AA01 AB14 BA23 BB05 CA11 CA14 4D038 AA03 AB19 BB04 BB04 ABB03BB04 BD06 CA03 CA13

Claims (9)

[Claims] 1. A method for purifying an underground contaminated area contaminated with a chemical substance, comprising purifying groundwater pumped from or near the underground contaminated area, and adding an oxidizing agent to the purified water. A method for purifying an underground contaminated region, comprising injecting the purified water again into or near the underground contaminated region. 2. The method according to claim 1, wherein hydrogen peroxide is added as an oxidizing agent to the purified water. 3. The method according to claim 2, wherein ferrous ions are added to the purified water together with hydrogen peroxide. 4. The method according to claim 3, wherein a chelating agent is added to the purified water together with ferrous ions. 5. The method according to claim 3, wherein hydrogen peroxide and ferrous iron ions are alternately added to the purified water. 6. The method for purifying an underground polluted area according to claim 2, wherein a pH adjuster is added to the purified water together with hydrogen peroxide. 7. The method according to claim 1, wherein the method of purifying the pumped ground water is a pumping aeration method or an oxidation treatment method.
3. The method for purifying an underground contaminated area according to the above item. 8. The method according to claim 7, wherein the oxidation treatment is a method in which hydrogen peroxide is added to the pumped groundwater in the presence of ferrous iron ions. 9. An apparatus for purifying an underground polluted area contaminated with a chemical substance, comprising: a pumping means for pumping groundwater from or near the underground polluted area; and a purifying means for purifying groundwater pumped by the pumping means. Oxidizing agent adding means for adding an oxidizing agent to water purified by the purifying means, and injecting means for injecting the water to which the oxidizing agent is added by the oxidizing agent adding means into or near the underground pollution area. Purification equipment for underground polluted areas.