JP2012035181A - In situ purification method of contaminated soil and groundwater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an in situ purification method of contaminated soil and groundwater which can efficiently increase the dissolved oxygen amount in an aerobic decomposition region.SOLUTION: A suction well 1 is arranged in a contaminated region R contaminated with volatile organic compounds, and a first injection well 2 and a second injection well 3 are arranged respectively in one contaminated region R1 and the other contaminated region R2 so as to put the suction well 1 between them. By first circulation S1 of groundwater W generated by supplying the groundwater W from the first injection well 2, making the groundwater flow through the contaminated region R1, and sucking it by the suction well 1, an anaerobic decomposition region P1 where the volatile organic compounds are decomposed by activated anaerobic microorganisms is formed in the contaminated region R1. By second circulation S2 of the groundwater W generated by supplying the groundwater W from the second injection well 3, making the groundwater flow through the contaminated region R2, and sucking it by the suction well 1, an aerobic decomposition region P2 where the volatile organic compounds are decomposed by activated aerobic microorganisms is formed in the contaminated region R2. Fine bubbles are formed in the ground water W in the second circulation S2.

Description

  The present invention relates to a contaminated soil and contaminated groundwater in-situ purification method that purifies soil and groundwater contaminated with volatile organic compounds such as tetrachloroethylene and trichlorethylene in situ by microorganisms.

Conventionally, methods for purifying soil and groundwater contaminated with volatile organic compounds (volatile organic chlorinated compounds) such as tetrachloroethylene and trichlorethylene have been proposed and implemented.
For example, Patent Document 1 discloses that an anaerobic decomposition region is provided on one side of a pumping well disposed in a contaminated region contaminated with a volatile organic compound and an aerobic decomposition is provided on the other side in order to carry out efficient microbial decomposition. A purification treatment method has been proposed in which a region is formed and the groundwater circulation in the in-situ microbial treatment is divided into two systems.
In this method, the nutrient solution is injected into the first injection well disposed in the anaerobic decomposition region and the microorganisms are activated to keep the anaerobic decomposition region in an anaerobic atmosphere. In addition, the aerobic decomposition region is brought into an aerobic atmosphere by circulating groundwater in which oxygen is forcibly dissolved by aeration (aeration) or the like in the second injection well disposed in the aerobic decomposition region. keeping.
And since the groundwater inject | poured from each injection well circulates and is collected by a pumping well, the environment where anaerobic atmosphere and aerobic atmosphere coexist is formed in the pumping well vicinity.

JP 2008-200598 A

However, in the purification method described in Patent Document 1, the amount of dissolved oxygen in the aerobic decomposition region is increased by aeration of the groundwater circulated in the second injection well, but in the conventional aeration, saturated dissolved oxygen is increased. It is physically difficult to dissolve oxygen in an amount (for example, about 9 mg / L at 20 ° C.) or more.
Dissolving a large amount of oxygen in the aerobic decomposition region keeps the aerobic atmosphere in the aerobic decomposition region for a long time and can perform reliable purification treatment. There is a desire for a purification method that can be increased beyond the amount.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an in-situ purification method for contaminated soil and contaminated groundwater that can efficiently increase the amount of dissolved oxygen in the aerobic decomposition region. And

  In order to achieve the above object, an in-situ purification method for contaminated soil and contaminated groundwater according to the present invention is a method for in situ purification of soil and groundwater contaminated with volatile organic compounds by microorganisms, A pumping well is disposed in a contaminated area contaminated with volatile organic compounds, and a first injection well is disposed on one contaminated area side and a second injection well is disposed on the other contaminated area side. The first circulated groundwater pumped up from the pumping well by supplying from the first injection well and flowing through the one contaminated well, to the one contaminated area, the activated anaerobic microorganisms and the volatile An anaerobic decomposition region for decomposing organic compounds is formed, and a second circulation of the groundwater supplied from the second injection well and circulated through the other contaminated region and pumped up in the pumping well. Forming an aerobic degradation region in the other contaminated region for decomposing the volatile organic compound with activated aerobic microorganisms, and generating fine bubbles in the groundwater in the second circulation. .

In the present invention, in the second circulation, fine bubbles are generated in the groundwater circulated from the pumping well to the second injection well. Since fine bubbles have a larger amount of dissolution than ordinary bubbles, the amount of dissolved oxygen in groundwater can be increased. In addition, fine bubbles can be present in the groundwater for a long time because the rising speed in water is slower than that of normal bubbles. And since a lot of oxygen exists in groundwater of an aerobic decomposition area for a long time, the aerobic state of an aerobic decomposition area can be maintained favorably for a long time.
Here, the fine bubbles usually indicate bubbles called microbubbles (particle size of about 50 μm to 1 μm) or nanobubbles (particle size of 1 μm or less), and the normal bubbles are usually millibubbles (particle size of several mm). ˜50 μm)).

  According to the present invention, since fine bubbles are generated in the groundwater in the second circulation, more oxygen than the saturated dissolved oxygen amount can be dissolved in the groundwater, and oxygen can exist in the groundwater for a long time. Since the aerobic state of the aerobic decomposition region can be maintained well for a long time, the aerobic decomposition region can be reliably purified in a short time and the purification effect can be maintained for a long time. Can

It is a figure which shows an example of the purification processing apparatus used for the contaminated soil and the contaminated groundwater in-situ purification method by embodiment of this invention. It is a figure which compares dissolved oxygen concentration.

  Hereinafter, the in-situ purification treatment method for contaminated soil and contaminated groundwater according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. The present embodiment relates to an in situ purification method for contaminated soil and contaminated groundwater, in which soil and groundwater contaminated with volatile organic compounds are purified in situ by microorganisms.

  As shown in FIG. 1, a purification treatment apparatus (purification treatment facility) A used in the in-situ purification treatment method for contaminated soil and contaminated groundwater according to the present embodiment is disposed in a contaminated region R contaminated with a volatile organic compound. A pumping well 1, a first injection well 2 disposed on the one contaminated region R1 side with the pumped well 1 interposed therebetween, and a second injection well 3 disposed on the other contaminated region R2 side with the pumped well 1 interposed therebetween. And is configured. Further, the pumping well 1 is provided with a slit portion 1a for allowing the surrounding groundwater W to permeate inside at the lower end side thereof, and the groundwater is driven through the slit portion 1a by driving of a pumping pump 1b installed therein. It is configured to collect W and pump it to the ground. On the other hand, the first injection well 2 and the second injection well 3 are provided with slit portions 2a and 3a on the lower end side, respectively, and the ground water W pumped up by the pumping well 1 is the first injection well 2 and the second injection well. 3, the groundwater W can be returned to the ground through the slit portions 2 a and 3 a when supplied to the inside of each. In FIG. 1, the pumping well 1, the first injection well 2, and the second injection well 3 are illustrated as being provided one by one. A plurality of two injection wells 3 may be provided.

Furthermore, in the purification treatment apparatus A of the present embodiment, the pipe 4 connected to the pump 1b of the pump well 1 is bifurcated on the ground, and one branch pipe 5 is connected to the nutrient solution addition tank 6 and the other is added. The branch pipes 7 are respectively connected to the fine bubble generation tank 8. Further, the nutrient solution addition tank 6 and the first injection well 2, the fine bubble generation tank 8 and the second injection well 3 are connected via pipes 9 and 10, respectively.
The nutrient solution addition tank 6 is a tank for adding nutrients such as nitrogen nutrient sources, carbon nutrient sources, organic acids, inorganic salts, and vitamins to the groundwater W sent from one branch pipe 5. is there.

  The fine bubble generating tank 8 is a tank that generates fine bubbles in the groundwater W sent from the other branch pipe 7 and includes a fine bubble generating device (not shown). The principle of generating fine bubbles in the fine bubble generating apparatus is a known principle such as a pressure dissolution method, a swirl method, or a static mixer method. Note that the number of fine bubbles, the particle size distribution, and the like vary depending on the generation principle. The fine bubble water in which fine bubbles are generated in such a fine bubble generation tank 8 contains more oxygen than oxygen saturated water.

  Fig. 2 shows two types of microbubble water 1, microbubble water 2, oxygen-saturated water and degassed water, which were collected by leaving them for 5 minutes or more to remove millibubbles after being manufactured by the pressure dissolution method and swirl method, respectively. It shows the result of measuring the dissolved oxygen concentration (JISK0102). The temperature condition during this measurement was about 25 ° C. As can be seen from FIG. 2, the dissolved oxygen concentration of oxygen-saturated water is 10.2 mg / L, but both types of microbubble water contain 1.2 to 1.3 times as much oxygen as oxygen-saturated water. ing.

  Further, in such fine bubble water, fine bubbles are characterized in that the rising speed is slower than that of normal bubbles (millibubbles) and the amount of dissolution is large. In addition, normal bubbles rise in water and burst at the surface of the water, while microbubbles that are microbubbles shrink in water and eventually collapse and disappear, and nanobubbles exist in water for a long time. Yes. For this reason, the fine bubbles are uniformly supplied over a wide range to form an aerobic atmosphere at an early stage, and this aerobic atmosphere can be maintained for a long time. Further, since radicals are generated when the microbubbles are crushed, contaminants (volatile organic compounds) can be decomposed by the radicals.

  When the contaminated soil and the contaminated groundwater are purified by the purification apparatus A configured as described above, the pumping pump 1b inserted into the pumping well 1 is driven, and the surroundings through the slit portion 1a of the pumping well 1 are driven. Pumping groundwater W to the ground while collecting water. When the groundwater W is pumped up from the pumping well 1 in this way, a groundwater flow T1 flowing from the first injection well 2 side toward the pumping well 1 is generated in one contaminated region R1, and in the other contaminated region R2, A groundwater flow T2 flowing from the second injection well 3 side toward the pumping well 1 is generated.

  In the present embodiment, the groundwater W collected from one contaminated area R1 and the groundwater W collected from the other contaminated area R2 are mixed in the pumping well 1 and pumped to the ground. A part of the groundwater W pumped up to the ground is sent to the nutrient solution addition tank 6 through one branch pipe 5, and the nutrient solution is added in the nutrient solution addition tank 6. The groundwater W to which the nutrient is added in this way is supplied to the first injection well 2 through the pipe 9, and is returned to the ground again from the slit portion 2a of the first injection well 2. The returned groundwater W containing the nutrient is passed through the one contaminated region R1 by the groundwater flow T1 flowing through the one contaminated region R1 and collected in the pumping well 1 again. Thereby, in the one contamination area | region R1 side between the pumping wells 1, the pumping well 1 to the nutrient solution addition tank 6, the nutrient solution addition tank 6 to the first injection well 2, and the first injection well 2 to one side. A first circulation S1 of the groundwater W that circulates again to the pumping well 1 through the contaminated region R1 is formed.

  And by the 1st circulation S1 of the groundwater W formed in this way, while the groundwater W containing a nutrient passes sequentially one pollution area | region R1, indigenous microorganisms are activated and oxygen in soil and groundwater is consumed. In addition, an anaerobic decomposition region P1 in which indigenous anaerobic microorganisms are activated is formed on one contamination region R1 side.

  On the other hand, in the groundwater W pumped up in the pumping well 1 and sent to the fine bubble generating tank 8 through the other branch pipe 7, fine bubbles are generated in the fine bubble generating tank 8, and the amount of dissolved oxygen increases. Is done. And the groundwater W in which dissolved oxygen concentration became high in this way is supplied to the 2nd injection well 3 via the piping 10, and is returned in the ground again from the slit part 3a of this 2nd injection well 3. FIG. The returned groundwater W having a high dissolved oxygen concentration passes through the other contaminated region R2 by the groundwater flow T2 flowing through the other contaminated region R2, and is collected in the pumping well 1 again. As a result, the pumping well 1 is interposed between the pumping well 1 to the fine bubble generating tank 8, the microbubble generating tank 8 to the second injection well 3, and the second injection well 3 to the other contamination area R 2. A second circulation S2 of the groundwater W that circulates again to the pumping well 1 through the contaminated region R2 is formed.

  Then, by the second circulation S2 of the groundwater W thus formed, the groundwater W having a high dissolved oxygen concentration sequentially passes through the other contaminated region R2, and the indigenous microorganisms are activated, and the other contaminated region R2 side is activated. In this case, an aerobic degradation region P2 in which native aerobic microorganisms are activated is formed.

  For example, when the first circulation S1 and the second circulation S2 are formed in the contaminated region R contaminated with tetrachloroethylene (volatile organic compound) and the groundwater W is circulated, the anaerobic decomposition region formed in the first circulation S1. At P1, it is decomposed into trichlorethylene and thus cis-1,2-dichloroethylene by a dechlorination reaction by an anaerobic microorganism in which tetrachloroethylene is activated. Further, the volatile organic compound thus decomposed into trichlorethylene and thus cis-1,2-dichloroethylene is pumped from the pumping well 1 together with the ground water W by the first circulation S1. Then, the groundwater W containing trichlorethylene and thus cis-1,2-dichloroethylene is sent to the second circulation S2, and flows from the second injection well 3 to the aerobic decomposition region P2. As a result, the volatile organic compound decomposed to trichlorethylene and thus cis-1,2-dichloroethylene by the anaerobic microorganism in the anaerobic decomposition region P1 is chlorinated by the dechlorination reaction by the aerobic microorganism activated in the aerobic decomposition region P2. It is decomposed into carbon dioxide via vinyl.

  Here, in this embodiment, the groundwater W pumped up by the pumping well 1 is the groundwater W in the first circulation S1 that has passed through the anaerobic decomposition region P1, and the groundwater W in the second circulation S2 that has passed through the aerobic decomposition region P2. Are mixed in the pumping well 1. Then, the water is pumped up to the ground and distributed to the first circulation S1 and the second circulation S2 by one branch pipe 5 and the other branch pipe 7. For this reason, a part of the volatile organic compound decomposed to the trichlorethylene and thus cis-1,2-dichloroethylene through the anaerobic decomposition region P1 again passes through the anaerobic decomposition region P1 by the first circulation S1. It will be circulated. However, by continuously pumping up the groundwater W in the pumping well 1 and distributing it to the first circulation S1 and the second circulation S2, all of the tetrachlorethylene in the contaminated region R is passed through the anaerobic decomposition region P1 and the aerobic decomposition region P2. Passes through and gradually decomposes to carbon dioxide and is rendered harmless. Thereby, the contaminated soil and contaminated groundwater contaminated with tetrachlorethylene in the entire contaminated region R are reliably purified. At this time, by measuring the concentration of volatile organic compounds in the groundwater W pumped up in the pumping well 1, the degree of purification of the contaminated soil and the contaminated groundwater can be confirmed.

  Therefore, in the in situ purification method for contaminated soil and contaminated groundwater of the present embodiment, the anaerobic decomposition region P1 is formed on the one contaminated region R1 side by the first circulation S1 of the groundwater W. Thereby, a volatile organic compound can be decomposed | disassembled by the anaerobic microorganisms activated in this area | region P1. Further, an aerobic decomposition region P2 is formed on the other contaminated region R2 side by the second circulation S2 of the groundwater W. As a result, the volatile organic compound that has not been decomposed until it is detoxified in the anaerobic decomposition region P1 flows along with the groundwater W to the aerobic decomposition region P2, so that the volatile organic compound is surely obtained by the aerobic microorganism. Can be broken down until detoxified.

  Then, by generating fine bubbles in the ground water W circulated in the second injection well 3 using the fine bubble generating tank 8, it is possible to dissolve more oxygen than the saturated dissolved oxygen amount in the ground water W. it can. Accordingly, oxygen can be present in the groundwater W for a long time, and the aerobic state of the aerobic decomposition region P2 can be maintained well for a long time, so that the purification process in the aerobic decomposition region P2 is efficiently performed. be able to.

As described above, the embodiment of the in-situ purification method for contaminated soil and contaminated groundwater according to the present invention has been described. However, the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the scope of the present invention. is there.
For example, in this embodiment, by returning groundwater W added with nutrients from the first injection well 2 to the ground, an anaerobic decomposition region P1 in which indigenous anaerobic microorganisms are activated is formed, An aerobic decomposition region P2 in which indigenous aerobic microorganisms are activated is formed by returning groundwater W having an increased dissolved oxygen concentration from the second injection well 3 to the ground. Anaerobic microorganisms are added to the groundwater W supplied to the well 2, or aerobic microorganisms are added to the groundwater W supplied to the second injection well 3, and these groundwaters W are in one contaminated area R1 and the other contaminated area R2. The anaerobic microorganisms may be supplied to the anaerobic decomposition region P1 and the aerobic microorganisms may be supplied to the aerobic decomposition region P2.

    In the present embodiment, the nutrient water is only added to the groundwater W pumped up in the pumping well 1 and returned from the first injection well 2. For example, the pumped-up groundwater W is sent to a deaeration device or the like. The ground water W with the dissolved oxygen concentration lowered may be returned from the first injection well 2. Accordingly, the anaerobic decomposition region P1 can be reliably formed by the first circulation S1, and the anaerobic microorganism can be reliably activated to decompose the volatile organic compound.

    Furthermore, in this embodiment, the groundwater W that has passed through the anaerobic decomposition region P1 and the aerobic decomposition region P2 is pumped up while being mixed in the pumping well 1, but the groundwater W that has passed through the anaerobic decomposition region P1, The groundwater W that has passed through the aerobic decomposition region P2 may be pumped up to the ground while being divided. In this case, it is possible to send all the groundwater W that has passed through the anaerobic decomposition region P1 to the fine bubble generation tank 8 and to send all the groundwater W that has passed through the aerobic decomposition region P2 to the nutrient solution addition tank 6. That is, the groundwater W can be circulated by one-system circulation connecting the first circulation S1 and the second circulation S2. In this case, all the volatile organic compounds decomposed to trichlorethylene and thus cis-1,2-dichloroethylene in the anaerobic decomposition region P1 can be sent to the aerobic decomposition region P2 in the next step. The purification process can be performed more efficiently than in the present embodiment.

    Further, in the present embodiment, the description has been made so that the fine bubble generating tank 8 of the second circulation S2 is used only for generating fine bubbles in the groundwater W. However, in the fine bubble generating tank 8, the fine bubbles are added to the groundwater W. And at least a part of the volatile organic compound contained in the groundwater W is volatilized and diffused in the gas phase in the fine bubble generating tank 8. For this reason, for example, an purification tank A is constructed by connecting an adsorption tank containing an adsorbent such as activated carbon to the gas phase of the fine bubble generation tank 8 to generate fine bubbles and to change the gas phase of the fine bubble generation tank 8 to You may make it collect a volatile organic compound volatilized in the gaseous phase with an adsorbent by sending to an adsorption tank. In this case, volatile organic compounds can be decomposed by underground microorganisms to purify contaminated soil and contaminated groundwater, and at the same time, volatile organic compounds can be removed from groundwater W pumped up on the ground. Therefore, the purification process can be performed more efficiently.

    Further, in the present embodiment, the volatile organic compound that contaminates the soil and groundwater has been described as being tetrachloroethylene (including trichloroethylene and cis-1,2-dichloroethylene). For other volatile organic compounds such as 1-trichloroethane, dichloromethane, carbon tetrachloride, 1,1-dichloroethylene, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,3-dichloropropene, benzene, By applying the in-situ purification method of the contaminated soil and contaminated groundwater of the present invention, it is possible to perform the purification treatment in the same manner as in this embodiment. In addition, for example, in the case of complex pollution in which heavy metals such as mercury, selenium, hexavalent chromium, cadmium, lead and arsenic coexist with these volatile organic compounds, the groundwater W pumped in the pumping well 1 The groundwater W, which has been insolubilized and removed other pollutants such as heavy metals, is returned to the ground from the injection wells 2 and 3 to decompose other volatile organic compounds while removing other pollutants. Can be processed.

DESCRIPTION OF SYMBOLS 1 Pumping well 1b Pumping pump 2 1st injection well 3 2nd injection well 6 Nutrient addition tank 8 Fine bubble production tank A Purification processing equipment (purification processing equipment)
P1 Anaerobic decomposition region P2 Aerobic decomposition region R Contamination region R1 One contamination region R2 The other contamination region S1 First circulation S2 Second circulation T1 Groundwater flow T2 Groundwater flow W Groundwater

Claims (1)

A method of purifying soil and groundwater contaminated with volatile organic compounds in situ by microorganisms,
A pumping well is disposed in a contaminated area contaminated with the volatile organic compound, and a first injection well is provided on one contaminated area side and a second injection well is provided on the other contaminated area side. Arranged,
By the first circulation of the groundwater supplied from the first injection well and circulated through the one contaminated area and pumped up in the pumped well, the volatile organic compound is activated by activated anaerobic microorganisms in the one contaminated area. While forming an anaerobic decomposition region to decompose,
By the second circulation of the groundwater supplied from the second injection well, circulated through the other contaminated area and pumped up in the pumped well, the volatile organic compound is activated by activated aerobic microorganisms in the other contaminated area. Forming an aerobic degradation zone to decompose,
An in-situ purification method for contaminated soil and contaminated groundwater, wherein in the second circulation, fine bubbles are generated in the groundwater.

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