JP4098653B2 - 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 purification method and a purification body for contaminated ground contaminated with an organic compound and the like, and more particularly, contamination by sucking a raw solution from a pollution source in which the pollutant exists in a raw liquid state and a high concentration contaminated groundwater around it. The present invention relates to a ground purification method and a purification body.
[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. High density water-insoluble liquids (DNAPL) such as trichlorethylene are heavier than water and difficult to dissolve in water, so they tend to accumulate in the deep underground below the water table. In addition, DNAPL accumulated in the deep underground is gradually dissolved in the groundwater, and a highly contaminated groundwater zone is formed around it.
[0003]
As a method for positively removing a contamination source such as DNAPL accumulated in the deep underground, a groundwater pumping method is generally used. This method sucks and removes the DNAPL stock solution together with the groundwater. However, in such a method, even if the source of contamination is specified to some extent, only water with a density lower than that of the DNAPL stock solution is pumped out from the pumping well, and then groundwater is replenished from the surroundings. Only a lot will be pumped up. Therefore, the DNAPL stock solution cannot be efficiently aspirated and removed. If the groundwater pumping is performed for a long time, the DNAPL stock solution will gradually dissolve in water, so suction and removal are possible. However, the efficiency depends on the dissolution rate of the DNAPL stock solution, so a long time is required for suction and removal. As a result, there is a problem that the processing cost becomes enormous.
[0004]
On the other hand, Japanese Patent Application Laid-Open No. 11-169837 of Patent Document 1 discloses a method for purifying a contaminated ground, which is followed by a step of freezing the contaminated ground area, and then sucking in the soil gas from the ground and extracting the contaminated vapor. Yes. However, this purification method of contaminated ground is intended to purify contaminated ground above the groundwater level, and is not intended to purify contaminated ground below the groundwater level. The purpose of freezing the contaminated ground is to cause minute disturbances between the soil fine particles by freezing, and then to enhance the suction effect of gaseous pollutants present in the unsaturated ground. It is not intended to leave the contaminants, but to suck and remove them.
[0005]
[Patent Document 1]
JP-A-11-169837 (Claim 1, paragraph number 0010)
[0006]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to efficiently suck and remove undiluted pollutants existing in the soil below the groundwater level and surrounding high-concentration contaminated groundwater, thereby shortening the treatment time and the treatment cost. It is providing the purification method and purification body of a contaminated ground.
[0007]
[Means for Solving the Problems]
Under such circumstances, the present inventors have conducted intensive studies, and as a result, due to the difference in freezing point between water and DNAPL stock solution, DNAPL can be present as a liquid substance in the frozen ground, and the liquid substance in the frozen ground is aspirated. It has been found that if suction and removal is performed with a suction means such as a tube, it is extremely easy and efficient, and the processing time can be reduced and the processing cost can be reduced. Thus, the present invention has been completed.
[0008]
That is, the present onset Ming, the ground frozen tube at an appropriate pitch in Contaminated Land the presence of contaminants in the following soil groundwater level, the ground first suction body at an appropriate pitch between during該地cryotubes a purifier disposed step of respectively disposing the ground second suction member in the vicinity freezing tube該地, a freezing step of freezing the contaminated soil region, a first suction member in該地while keeping the frozen state A raw solution suction step for sucking liquid contaminants from, a step of thawing the contaminated ground region, and supply of air or water from the first suction body to the ground for the contaminated ground water of the thawed contaminated ground region. 2. Purification of contaminated ground in which contaminated groundwater is aspirated by sucking contaminated groundwater from the suction body or supplying air or water from the second suction body in the ground to suck contaminated groundwater from the first suction body in the ground A method is provided. According to the present invention, since the saturated ground below the groundwater level is frozen at a temperature below the freezing point and above the freezing point of the contaminant, DNAPL can be present as a liquid in the ground where the pore water is frozen. In addition, due to the spout effect caused by freezing, liquid substances such as pollutants other than pore water are pushed toward the first suction body in the ground, and the liquid contaminants are sucked easily and efficiently by the first suction body in the ground. Can be removed. For this reason, the purification processing time can be shortened and the processing cost can be reduced. In addition, after thawing the contaminated ground, the groundwater in which the contaminants around the undiluted solution are dissolved at a high concentration can be easily and efficiently sucked and removed by the first suction body in the ground. In addition, since there is contaminated groundwater around the freezing pipe after thawing, in particular, the contaminated groundwater is dissolved in a high concentration. This contaminated groundwater is easily and efficiently sucked from the underground second suction body arranged near the freezing pipe. Can be removed. Moreover, since air or water is supplied from one underground suction body and contaminated groundwater is sucked from the other underground suction body, the purification efficiency can be further enhanced by both the action of extrusion and suction.
[0012]
Further, the present invention is a purification body constructed in a contaminated ground in which contaminants exist in the soil below the groundwater level, between the underground freezing pipes arranged at an appropriate pitch, and the underground freezing pipe A first underground suction body for sucking liquid pollutants existing in the frozen ground, and a second underground for sucking liquid pollutants present in the frozen ground disposed near the underground freezing pipe. a suction member, the first suction member and the ground second suction member in該地is to provide a purifier in which also serves as a supplying member for supplying air or water. Further, the present invention, the ground first suction member and the ground second suction member is to provide the purifier is suction tube or 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 of the present invention will be described with reference to FIGS. 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 in a contaminated ground in which contaminants exist in the soil below the groundwater level (WL), and the underground freezing pipe 1 disposed at an appropriate pitch. And the underground first suction body 2 disposed at an appropriate pitch between the underground freezing tubes 1 and 1. 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 9 in which the purification body 10 of this example is constructed is not particularly limited as long as the pollutant 7 is present in a saturated ground below the groundwater level, and the ground is sandy, clay layer , Natural ground such as alternate layers and landfilled artificial ground. The contaminant 7 is not particularly limited, and examples thereof include a high density water-insoluble liquid (DNAPL) whose density is heavier than water, hardly soluble in water, and has a freezing point of −10 ° C. or lower. Specifically, trichloroethylene having a freezing point of −86 ° C., tetrachloroethylene having a freezing point of −22 ° C., dichloroethylene having a freezing point of −57 ° C., dichloroethane having a freezing point of −97 ° C., and the like. Since DNAPL is heavier than water and difficult to dissolve in water, it tends to accumulate in the deep underground part 71 below the groundwater surface, and when the saturated ground is frozen below the freezing point and above the freezing point of DNAPL, Exists in liquid form.
[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 first 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. Even when a columnar drain is used as the underground first 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 first suction body 2 is not particularly limited. However, as shown in FIG. 2, as shown in FIG. 2, in the contaminated ground region 8 and between the freezing tubes 1, that is, substantially between the adjacent freezing tubes 1. It is preferable to dispose at an intermediate position because the discharge effect caused by freezing can be easily and efficiently aspirated and removed from the pollutant stock solution other than pore water pushed away from the underground freezing tube 1.
[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 first suction body 2 are arranged at an appropriate pitch on the contaminated ground 9 where the contaminant 7 exists in the soil below the groundwater level. At this time, a ground refrigerator and a vacuum pump are also installed.
[0018]
Next, a freezing step is performed in which the contaminated ground region 8 below the groundwater level is frozen and the contaminant is held in a liquid state. 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 stock contaminant 7 can be present as a liquid in the frozen ground. In FIG. 1, a range 5 surrounded by a two-dot chain line is frozen soil, and a reference numeral 6 is an impermeable layer.
[0019]
In the freezing process, the heater 22 of the underground first suction body 2 is moved so that the water passage hole 23 and the hollow part of the hollow hollow tube 21 are not blocked by freezing. Further, in the freezing process, when the pore water in the ground is gradually frozen, a discharge phenomenon occurs. 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. As a result, the stock solution that is a contaminant is naturally collected in the first suction body 2 in the ground. In this state, the stock solution suction process is started. The heater 22 in the underground first 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 first 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 first suction body 2. In this case, a stock solution of contaminants is collected around the first suction body 2 in the ground, and 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 saturated ground below the groundwater level is frozen at a temperature below the freezing point and above the freezing point of the pollutant. DNAPL can be present as a liquid in the ground. Further, due to the discharge effect generated by freezing, liquid materials other than pore water are pushed to the underground first suction body 2 side, and the liquid materials can be easily and efficiently sucked and removed by the underground first suction body 2. . 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. Moreover, although the high concentration contaminated groundwater around the undiluted solution exists in the ground after thawing, this can be further removed by suction with the underground first suction body 2.
[0022]
Next, the contaminated ground purification method and purification body in the second embodiment will be described with reference to FIGS. FIG. 3 is a schematic cross-sectional view showing a state after the thawing of the purifier in the present embodiment, and FIG. 4 is a schematic plan view of the purifier in the present embodiment. 3 and 4, 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 purification body 10a in the second embodiment further includes the underground second suction body 3 in the vicinity of the underground freezing pipe 1 relative to the purification body 10 in the first embodiment. Thus, the suction efficiency of highly concentrated contaminated groundwater after thawing is increased.
[0023]
The underground second suction body 3 is the same as the underground first suction body 2 except that it is disposed in the vicinity of the underground freezing tube 1. The vicinity of the underground freezing tube 1 includes a form close to the underground freezing tube 1 to a form slightly apart from the underground freezing tube 1, but is a form close to the underground freezing tube 1. For example, it is preferable in that the efficiency of supplying water from the underground second suction body 3, extruding contaminated groundwater, and suctioning and removing from the underground first suction body 2 is improved.
[0024]
3 and 4 show a state after the thawing of the contaminated ground region. 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. 3 and 4 show a situation in which high-concentration contaminated groundwater around the stock solution exists in the ground 9 after thawing. In this case, the underground second suction body 3 in the vicinity of the underground freezing pipe 1 is used as a water supply body, and the underground first suction body 2 is used as a contaminated groundwater suction body. That is, if water is supplied from the underground second suction body 3 and high-concentration contaminated groundwater is sucked from the underground first suction body 2, a circulation path is formed, and the high-concentration contaminated groundwater is easily and efficiently used. Can be removed. In addition, the underground 2nd suction body 3 is connected to the ground water supply means not shown, and the arrow in FIG. 4 is a flow of contaminated groundwater. Moreover, it may replace with the water supplied to the underground 2nd suction body 3, and may use compressed air. Similarly, when compressed air is used, a channel for contaminated groundwater from the underground second suction body 3 to the underground first suction body 2 is formed.
[0025]
According to the purification method of the contaminated ground in the second embodiment, since air or water is supplied from the underground second suction body 3 and the contaminated groundwater is sucked from the underground first suction body 2, extrusion and suction are performed. The purification efficiency can be further enhanced by both actions. 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.
[0026]
Moreover, as a modification of the purification method of the contaminated ground in the second embodiment, the underground first suction body 2 is used as a water supply body, and the underground second suction body 3 is used as a contaminated groundwater suction body. You can also. That is, if water is supplied from the underground first suction body 2 and contaminated groundwater is sucked from the underground second suction body 3, a circulation path is formed in the same manner, and the contaminated groundwater is easily and efficiently supplied. Can be removed. In this case, in the case of freezing, contrary to the discharge effect, a water movement phenomenon on freezing where groundwater moves to the underground freezing pipe 1 can be used. 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 decreases further, water is replenished from the unfrozen part toward the frozen surface. Becomes easier to collect in the underground freezing tube 1. Therefore, after the thawing, the collected contaminated groundwater can be immediately sucked by the underground second suction body 3, and further, the purification efficiency is further improved because it is pushed out by the supply water. Also in the modification of the second embodiment, compressed air can be used in place of the water supplied from the underground first suction body 2.
[0027]
【Example】
EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention.
Example 1
(Production of simulated contaminated soil)
Simulated contaminated soil having the following composition was prepared and filled in the following bottomed cylindrical container. The filling amount was packed up to a thickness of 100 mm from the bottom of the container. The simulated contaminated soil has an outer diameter of 7 mm × inner diameter of 5 mm, the tip is closed with a filling adhesive, and suction pipes with a total of 36 pores with an inner diameter of 1 mm in two rows are arranged at intervals of 5 mm from the bottom to 90 mm. Set up. In addition, a constantan heater wire having a diameter of 0.1 mm was provided inside the suction tube to prevent the suction tube from being blocked by freezing of water droplets during suction. Furthermore, in order to prevent mixing of sand particles, the outer peripheral surface of the suction tube was wound with a nonwoven fabric.
[0028]
・ Simulated contaminated soil: Silica sand No. 5 with a density of 1.76 g / cm ³ (25 ° C.) and a fluorine-containing inert liquid with a freezing point of −43 ° C. and saturated with water No. 5 bottomed cylindrical container; Top opening container made of 100 mm acrylic resin and bottom plate made of 2 mm thick aluminum plate.
(Purification experiment)
-The entire simulated contaminated soil was frozen in a refrigerant bath adjusted to -15 ° C. In addition, the heater put in the suction tube was turned on. After confirming the reading of the temperature sensor installed at a depth of 2 cm from the surface of the simulated contaminated soil and freezing of floating water on the surface, the aspirator was activated and the suction tube was activated. As a result of suction for 30 minutes, 124 g of 180 g of the fluorine-based inert liquid added to the simulated contaminated soil was removed by suction.
[0030]
【The invention's effect】
According to the present invention, since the saturated ground below the groundwater level is frozen, DNAPL can be present as a liquid in the ground where the pore water is frozen. Further, due to the discharge effect caused by freezing, liquid materials other than the pore water are pushed to the underground first suction body side, and the liquid materials can be easily and efficiently sucked and removed by the underground first suction pipe. For this reason, the purification processing time can be shortened and the processing cost can be reduced.
According to the present invention, after thawing the contaminated ground, the groundwater in which the contaminants around the undiluted solution are dissolved at a high concentration can be easily and efficiently sucked and removed by the first suction body in the ground.
According to the present invention, since there is contaminated groundwater in which the pollutant is dissolved at a high concentration especially around the freezing pipe after thawing, the contaminated groundwater can be easily removed from the underground second suction body disposed near the freezing pipe. Efficient suction and removal.
According to the present invention, if air or water is supplied from one underground suction body and contaminated groundwater is sucked from the other underground suction body, the purification efficiency can be further improved by both the action of extrusion and suction. .
According to 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 showing a state after the thawing of the purifier in the second embodiment.
FIG. 4 is a schematic plan view of a purification body in a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Underground freezing pipe 2 Underground 1st suction body 3 Underground 2nd suction body 5 Frozen earth 6 Impermeable layer 7 Contaminant (stock solution)
8 Contaminated ground area 9 Contaminated ground 10, 10a Purified body 21, 31 Perforated hollow tube 22, 32 Heater 23, 33 Water hole W.L. Groundwater level

Claims (3)

Underground freezing pipes at an appropriate pitch on the contaminated ground where contaminants are present in the soil below the groundwater level , the first underground suction body at an appropriate pitch between the underground freezing pipes, and near the underground freezing pipe underground second suction body for sucking the purifier disposing step of disposing each a freezing step of freezing the contaminated soil region, the liquid contaminants from the first suction member in該地while keeping the frozen state A raw solution suction step , a step of thawing the contaminated ground region, and supplying the ground water in the thawed contaminated ground region by supplying air or water from the ground first suction body and the contaminated ground water from the ground second suction body A contaminated ground purification method characterized by performing a contaminated groundwater suction step of sucking or supplying air or water from the underground second suction body to suck contaminated groundwater from the underground first suction body . A purification body constructed on a contaminated ground in which contaminants exist in soil below the groundwater level, and an underground freezing pipe disposed at an appropriate pitch, and a frozen ground disposed between the underground freezing pipes A first underground suction body for sucking liquid contaminants existing therein , and a second underground suction body for sucking liquid contaminants disposed in the frozen ground near the underground freezing pipe , The purifying body, wherein the underground first suction body and the underground second suction body also serve as a supply body for supplying air or water . The purifying body according to claim 2, wherein the underground first suction body and the underground second suction body are suction pipes or columnar drains.

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