JP4091482B2 - Purification method and purification body of contaminated ground by freezing and suction - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying contaminated ground contaminated with oils, volatile organic compounds, and the like, and more specifically, the suction of the stock solution from a source of contamination below the groundwater level where the pollutant exists in the stock solution state and the surrounding area. The present invention relates to a purification method and a purification body for contaminated ground that sucks contaminated pore water.
[0002]
[Prior art]
Volatile organic compounds such as trichlorethylene, which are used in large quantities in the cleaning process of semiconductor manufacturing plants, etc., may contaminate the soil or groundwater due to leakage, etc. There is a problem that the use of groundwater is restricted. When a high-density water-insoluble liquid (DNAPL) such as trichlorethylene enters the soil, it penetrates the unsaturated zone shallower than the groundwater level and temporarily stops at the boundary with the groundwater surface. And in the soil gap shallower than the groundwater level, a contaminated area where water, air and DNAPL coexist is formed. This is because DNAPL requires a large osmotic pressure to penetrate into the saturation zone. In addition, oils such as gasoline, kerosene, light oil and heavy oil are lighter in density than water, and therefore do not penetrate below the groundwater surface and contaminate the gaps and pore water in the unsaturated zone.
[0003]
As a method for actively removing contaminants such as DNAPL and oils accumulated in the soil shallower than the groundwater level, a soil gas suction method is generally used. In this method, an extraction well is provided in an unsaturated zone shallower than the groundwater level, and the pressure in the extraction well is reduced by a suction means such as a vacuum pump or a blower, and the material volatilized in the well is recovered on the ground. However, in such a method, the gap in the soil is compressed by the suction pressure in the extraction well, or the range covered by the suction pressure is limited. Especially in the soil far from the extraction well, the purification efficiency is greatly reduced. That is, the conventional soil gas suction method has a problem that although only a relatively large gap and its periphery are purified, it is hardly purified in other regions.
[0004]
As a solution to this problem, Japanese Patent Application Laid-Open No. 11-169837 of Patent Document 1 discloses a purification of contaminated ground that is followed by a step of freezing a contaminated ground area, and then sucking in soil gas from the ground and extracting contaminated vapor. A method is disclosed. However, this method of remediation of contaminated ground is to cause minute disturbance between the soil fine particles by freezing and thawing of the ground, and then to enhance the suction effect of gaseous pollutants present in the soil. It does not leave liquid contaminants in the interior, which are sucked and removed.
[0005]
[Patent Document 1]
JP-A-11-169837 (Claim 1, paragraph number 0010)
[0006]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to efficiently suck and remove the pollutant in the raw liquid state existing in the soil shallower than the groundwater level and the contaminated pore water around it, thereby reducing the processing time and the processing cost. It is providing the purification method and purification body of a ground.
[0007]
[Means for Solving the Problems]
In such a situation, the present inventors have conducted intensive studies, and as a result, due to the difference in the freezing point of water and DNAPL stock solution and the difference in the density of oils and water, the DNAPL and oils are liquid substances in the frozen ground below the groundwater level. If the liquid material in the frozen ground is sucked and removed by suction means such as a suction tube, it is extremely easy and efficient, and the processing time and processing cost can be reduced. The headline and the present invention were completed.
[0011]
That is, the present invention is a ground freeze tube at an appropriate pitch in Contaminated Land the presence of contaminants in the soil of the ground water level shallower than the ground attractant in an appropriate pitch between during該地cryotubes, 該地 A purification body disposing step for disposing an underground injection body in the vicinity of the intermediate freezing pipe, a freezing step for freezing the contaminated ground area, and a liquid pollutant is sucked from the underground suction body while maintaining the frozen state. Concentrating material suction step , step of thawing the contaminated ground region, and contaminant suction of sucking the remaining contaminants of the thawed contaminated ground region from the underground injection body by supplying air or water from the underground suction body And a pollutant suction step of sucking the remaining contaminants of the thawed contaminated ground area from the underground suction body by supplying air or water from the underground injection body . A purification method is provided. When the saturation level of the melted soil below groundwater is low, air is supplied and gaseous pollutants are sucked between the underground suction body and the underground injection body. If the supply of water and the suction of contaminated pore water are performed between the suction body and the underground injection body, the purification efficiency can be further enhanced by the action of both extrusion and suction.
[0012]
Further, the present invention is a purification body constructed in a contaminated ground where contaminants exist in soil shallower than the groundwater level, and between the underground freezing pipe disposed at an appropriate pitch and the underground freezing pipe comprising a ground suction member is arranged to suck the liquid contaminants present frozen in the ground, and a ground injectors for supplying air or water disposed near freezing tube該地 to the ground suction the body also serves as a supplying member for supplying the air or water, underground injection member is to provide a purifier you also serves as a suction member for sucking contaminants. Moreover, this invention provides the said purification body whose said underground suction body and underground injection body are a suction pipe or a columnar drain. According to the purification body of the present invention, the invention of the purification method can be reliably implemented.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the purification method and purification body of the contaminated ground in the first embodiment as a reference example of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view of a purification body in the present embodiment, and FIG. 2 is a schematic plan view of the purification body in the present embodiment. The purification body 10 according to the present embodiment is constructed on a contaminated ground in which contaminants exist in soil shallower than the groundwater level (W.L.), and is disposed in an appropriate pitch. The freezing pipe 1 and the underground suction body 2 disposed at an appropriate pitch between the underground freezing pipes 1 and 1 are provided. On the ground, a refrigerator (not shown), a refrigeration means such as a refrigerant circulation pump and piping, a suction means such as a vacuum pump, and a pollutant decomposition means are installed.
[0014]
The contaminated ground 4 on which the purification body 10 of the present example is constructed is not particularly limited as long as the contaminant 7 exists in the ground shallower than the groundwater level, and the ground is sandy, clay layer, alternating layer, etc. Natural ground or reclaimed artificial ground. Further, the contaminant 7 is not particularly limited. For example, the density is heavier than water, difficult to dissolve in water, and has a freezing point of −10 ° C. or lower, and the density thereof is higher than that of water. Light oils are listed. Examples of DNAPL include trichloroethylene having a freezing point of −86 ° C., tetrachloroethylene having a freezing point of −22 ° C., dichloroethylene having a freezing point of −57 ° C., and dichloroethane having a freezing point of −97 ° C. When DNAPL enters the soil, it penetrates the unsaturated zone below the groundwater level and stops once at the boundary 71 with the groundwater surface. And in the soil gap shallower than the groundwater level, a contaminated area where water, air and DNAPL coexist is formed. This is because DNAPL requires a large osmotic pressure to penetrate into the saturation zone. Examples of oils include gason phosphorus containing various components having a freezing point of −30 to −95 ° C., and kerosene containing various components having a freezing point of −10 to −30 ° C. Since oils are lighter in density than water, they do not penetrate below the groundwater surface, stay at the boundary 71 with the groundwater surface and contaminate pore water. Such DNAPL and oil pollutants are present in liquid form in the frozen ground when the saturated ground is frozen at a temperature below the freezing point and above the freezing point of the pollutant.
[0015]
The underground freezing pipe 1 freezes the contaminated ground region 8 and is disposed almost uniformly in the contaminated ground region 8. The underground freezing tube 1 is the same as that used in a known underground freezing method. As a known underground freezing method, a refrigerant called brine is cooled to −20 ° C. to −30 ° C. using a refrigerator, and this is sent to the freezing pipe 1 embedded in the ground with a circulation pump to cool the ground. Freezing method is mentioned. The number of underground freezing pipes 1 is appropriately determined according to freezing equipment capacity, frozen soil temperature, and the like. The contaminated ground region 8 includes at least a region (range of solid line in FIG. 2) where the stock solution 7 of contaminant is present, and in this example, refers to a region 8 surrounded by a two-dot chain line in FIG.
[0016]
The underground suction body 2 is a structure embedded in the ground connected to suction means such as a vacuum pump on the ground, and examples thereof include a suction pipe or a columnar drain. In this example, it is a perforated hollow tube 21 provided with a large number of water passage holes 23 on the side peripheral surface, and it is easy to suck contaminants from various places of the contaminated soil, and a heater 22 is provided in the hollow portion. Further, the water passage hole 23 is prevented from being blocked by freezing of water in the freezing step. Further, it is preferable that the periphery of the water passage hole 23 is covered with a non-illustrated nonwoven fabric or the like because clogging of the water passage hole 23 can be prevented. Also when a columnar drain is used as the underground suction body 2, it is preferable to provide an internal heater 22 or a nonwoven fabric. An example of the columnar drain is a plastic board drain. The arrangement position of the underground suction body 2 is not particularly limited. However, as shown in FIG. 2, as shown in FIG. 2, it is the contaminated ground region 8 and between the freezing pipes 1, that is, an almost intermediate position between the adjacent freezing pipes 1. It is preferable to dispose them in terms of the discharge effect caused by freezing, because the pollutant stock solution other than pore water pushed away from the underground freezing tube 1 can be sucked and removed easily and efficiently.
[0017]
In the first embodiment, a method for purifying the contaminated ground using the purification body 10 will be described below. A purification body arrangement | positioning process is performed after specifying a pollutant and a contamination ground area | region by a prior ground investigation. That is, the underground freezing pipe 1 and the underground suction body 2 are arranged at an appropriate pitch on the contaminated ground 4 where the contaminant 7 exists in the soil 4 shallower than the groundwater level. At this time, a ground refrigerator and a vacuum pump are also installed.
[0018]
Next, a freezing process is performed in which the contaminated ground region 8 shallower than the groundwater level is frozen and the pollutant is held in liquid form. The temperature of the frozen ground is determined by the freezing point of the pollutant, and is a temperature below the freezing point and above the freezing point of the pollutant. If the contaminated ground region 8 is such a frozen ground, the contaminated ground region can form a hard skeleton of the frozen ground in which the gap is not compressed, and the raw contaminant 7 is converted into a liquid matter in the frozen ground. Can exist. In FIG. 1, a range 5 surrounded by a two-dot chain line is frozen soil.
[0019]
In the freezing step, the heater 22 of the underground suction body 2 is moved so that the water passage hole 23 and the hollow portion of the hollow hollow tube 21 are not blocked by freezing. Further, in the freezing process, if the contaminated ground is a highly saturated ground, the discharge phenomenon occurs when the pore water in the ground is gradually frozen. This phenomenon is a phenomenon in which liquid substances other than pore water move away from the underground freezing pipe 1 during freezing and are found in nature. Thereby, the undiluted solution which is a pollutant naturally gathers in the underground suction body 2. In this state, the stock solution suction process is started. The heater 22 in the underground suction body 2 may be moved in the stock solution suction step.
[0020]
The stock solution suction step is a step of sucking the liquid contaminant 7 from the underground suction body 2 while maintaining the frozen state. When the suction means on the ground is moved, the stock solution of the pollutant is sucked from the water passage hole 23 of the underground suction body 2. In this case, a stock solution of contaminants is collected around the underground suction body 2 and the suction efficiency is improved. In FIG. 2, the arrows indicate the flow of the pollutant concentrate.
[0021]
According to the contaminated ground purification method and purification body in the first embodiment, the unsaturated ground shallow below the groundwater level is frozen at a temperature below the freezing point and above the freezing point of the pollutant. Can form a hard skeleton of frozen soil. For this reason, since the gap is not compressed and the suction force is not reduced, the range of influence per suction pipe is widened. Further, in the unsaturated ground, the pore water is in a frozen state, and the pollutant can be present as a liquid, so that the efficiency of sucking and collecting the pollutant is good. For this reason, the purification processing time can be shortened and the processing cost can be reduced. Also, the frozen ground is temporary and there is no concern of secondary contamination after thawing. Further, the contaminated pore water existing in the ground after thawing and the contaminant in the gap can be further removed by suction with the underground suction body 2.
[0022]
Next, a contaminated ground purification method and purification body according to a second embodiment, which is a reference example of the present invention, will be described with reference to FIGS. FIG. 3 is a schematic sectional view of the purification body in the present embodiment, and FIG. 4 is a schematic plan view of the purification body in the present embodiment. In this example, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof will be omitted, and different points will be mainly described. That is, the purifying body 10a in the second embodiment is different from the purifying body 10 in the first embodiment in that the underground injection body 3 is further disposed in the vicinity of the underground freezing pipe 1 and the ground. One end of the medium injection body 3 is connected to a ground air supply means (not shown). That is, in the stock solution suction step, air is injected from the underground injection body 3 into the frozen ground, and the liquid contaminant is sucked from the underground suction body 2. In addition, in FIG.3 and FIG.4, the arrow is a flow of contaminated groundwater. If the purification body 10a in 2nd Embodiment is used, there exists an effect similar to the purification body 10 in 1st Embodiment, and the collection | recovery efficiency of a liquid contaminant will further improve.
[0023]
Next, the contaminated ground purification method and purification body in the third embodiment will be described with reference to FIGS. FIG. 5 is a schematic cross-sectional view of the purification body in the present embodiment, and FIG. 6 is a schematic plan view of the purification body in the present embodiment. In this example, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof will be omitted, and different points will be mainly described. That is, the purifying body 10b in the third embodiment further disposes the underground injection body 3 in the vicinity of the underground freezing pipe 1 with respect to the purifying body 10 in the first embodiment. The suction efficiency of the contaminated pore water and the contaminant in the gap in the melted ground 9 after thawing is increased. The underground injection body 3 can be the same as that used in the second embodiment. Also in the third embodiment, the vicinity of the underground freezing tube 1 has the same meaning as the underground injection body of the second embodiment.
[0024]
5 and 6 show the state after the thawing of the contaminated ground area, and the contaminated pore water around the undiluted solution and the contaminants in the gap are present in the melted ground 9 after thawing (not shown). The thawing step is not particularly limited, and includes a method of thawing to stand at room temperature by natural standing, a method of rapid heating with a ground heating tube (not shown), or a method of thawing by flowing warm water into the underground freezing tube 1. Among these, the method of pouring warm water into the underground freezing tube 1 and thawing is preferable in that simple and quick thawing can be performed. In the pollutant sucking step, for example, when the melting ground 9 is highly saturated, the underground injection body 3 in the vicinity of the underground freezing pipe 1 is used as a water supply body, and the underground suction body 2 is used as the contaminated pore water suction body. In addition to supplying water from the underground injection body 3, the contaminated pore water is sucked from the underground suction body 2. Thereby, a flow path of the circulation system is formed, and the remaining contaminated pore water can be removed easily and efficiently. The underground injection body 3 is connected to a ground water supply means (not shown). In FIG. 4, arrows indicate the flow of contaminated groundwater.
[0025]
Further, when the degree of saturation of the melted ground 9 is low, the underground injection body 3 in the vicinity of the underground freezing pipe 1 is used as an air supply body, and the underground suction body 2 is a gaseous contaminant present in the soil gap. Used as a suction body, air is supplied from the underground injection body 3 and gaseous contaminants are suctioned from the underground suction body 2. Thereby, a circulation channel is formed, and the remaining contaminants can be removed easily and efficiently. In this case, the underground injection body 3 is connected to a ground air supply means (not shown).
[0026]
According to the method for purifying contaminated ground in the third embodiment, air or water is supplied from the underground injection body 3 and the contaminated pore water or gaseous contaminants in the gap is sucked from the underground suction body 2. The purification efficiency can be further enhanced by the action of both extrusion and suction. Especially when thawing while warming the underground freezing pipe, water and air can be supplied from the open gap in the ground close to the underground freezing pipe, shortening the construction period and smoothing the circulation, improving the purification efficiency To do.
[0027]
Further, as a modified example of the contaminated ground purification method in the third embodiment, the underground suction body 2 is used as a water supply body or an air supply body, and the underground injection body 3 is used as a contaminated pore water suction body or a gaseous state. It can also be used as a contaminant suction body. That is, if water is supplied from the underground suction body 2 and the contaminated pore water is sucked from the underground injection body 3, a circulation channel is similarly formed, and the contaminated pore water can be easily and efficiently removed. . In this case, in the case of freezing, the water movement phenomenon on freezing where pore water moves to the underground freezing pipe 1 can be used contrary to the discharge effect. This phenomenon is a natural phenomenon in which the pore water in the ground gradually freezes to form an ice layer called an ice lens, and when the temperature further decreases, water is replenished from the unfrozen part toward the frozen surface. Water easily collects in the underground freezing pipe 1. Therefore, after the thawing, the collected contaminated pore water can be immediately sucked by the underground injecting body 3, and further the purification efficiency is further improved because it is pushed out by the supply water.
[0028]
【The invention's effect】
In accordance with the purification method of the present invention, if a low saturation melting soil groundwater shallower, subjected to suction of the feed gaseous pollutants in the air between the ground attractant and ground injectors, melting of ground water shallower When the degree of saturation of the soil is high, the purification efficiency can be further enhanced by both the extrusion and suction actions if water is supplied and the contaminated pore water is sucked between the underground suction body and the underground injection body. As described above, according to the purification method of the present invention, it is possible to reliably purify and repair the contaminated ground below the groundwater level, which is present in three modes in which the contaminant is dissolved in the raw solution state, the gas state, and the pore water.
Moreover, according to the purification body of this invention, invention of the said purification method can be implemented reliably.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a purification body in a first embodiment.
FIG. 2 is a schematic plan view of a purification body in the first embodiment.
FIG. 3 is a schematic cross-sectional view of a purification body in a second embodiment.
FIG. 4 is a schematic plan view of a purification body in a second embodiment.
FIG. 5 is a schematic cross-sectional view showing a state after the thawing of the purifier in the third embodiment.
FIG. 6 is a schematic plan view of a purification body in a third embodiment.
[Explanation of symbols]
1 Underground freezing pipe 2 Underground suction body 3 Underground injection body 4 Contaminated ground 5 Frozen soil 7 Contaminant (stock solution)
8 Contaminated ground area 9 Melted ground 10, 10a, 10b Purified body 21, 31 Perforated hollow tube 22, 32 Heater 23, 33 Water passage hole 71 Boundary with groundwater surface W.L. Groundwater level

Claims (3)

Underground freezing pipes at an appropriate pitch on the contaminated ground where contaminants exist in the soil shallower than the groundwater level , underground suction bodies at an appropriate pitch between the underground freezing pipes , and ground in the vicinity of the underground freezing pipe A purification body disposing step for disposing a medium injection body, a freezing step for freezing the contaminated ground area, a stock solution aspirating step for sucking liquid contaminants from the underground suction body while maintaining the frozen state, and contamination A step of thawing the ground region, a contaminant suction step of supplying air or water from the ground suction body and sucking the remaining contaminants of the thawed contaminated ground region from the ground injection body, and A method for purifying contaminated ground, comprising performing a pollutant suction step of supplying air or water from the underground injecting body and sucking the remaining contaminants in the contaminated ground area from the underground suction body . A purification body constructed on a contaminated ground in which contaminants exist in soil shallower than the groundwater level, and an underground freezing pipe disposed at an appropriate pitch, and a frozen ground disposed between the underground freezing pipes An underground suction body for sucking liquid contaminants present therein, and an underground injection body that is disposed in the vicinity of the underground freezing pipe and supplies air or water. The underground suction body receives air or water. also serves as a supplier for supplying, underground injection body purifier characterized that you alternate the suction body for sucking contaminants. The purifying body according to claim 2, wherein the underground suction body and the underground injection body are suction pipes or columnar drains.

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