In-situ remediation system for contaminated soil and in-situ remediation method for contaminated soil

Abstract

To provide an on-site remediation system for contaminated soil, and an on-site remediation method for contaminated soil, enabling the heating efficiency thereof to be improved.SOLUTION: An on-site remediation system for contaminated soil 1 is provided, including: one or more heating wells 10 heating at least a part of a treatment target region A1 where contaminated soil contaminated with contaminants is present; one or more sucking wells 20 located in the treatment target region A1 and sucking at least a part of fluid including the contaminants and generated by the heating treatment; and one or more water injection wells 30 located in or around the treatment target region A1 and injecting water having temperature higher than that of underground water, into the treatment target region A1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an in-situ purification system for contaminated soil and an in-situ purification method for contaminated soil.

Background Art

[0002] As a method for purifying contaminated soil contaminated with volatile organic compounds (VOCs) or the like, a method of excavating and removing it (excavation removal method) is known. However, in the excavation removal method, a large amount of contaminated soil has to be carried out and transported, which requires an enormous cost.

[0003] In response to such problems, for example, Patent Document 1 proposes an in-situ purification method for contaminated soil in which heat is applied to a treatment target area containing a pollutant, a part of the pollutant is vaporized and sucked, and removed from the treatment target area. According to the invention of Patent Document 1, it is intended to improve the removal efficiency of pollutants by in-situ heating and steam extraction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique of Patent Document 1, when sucking the vaporized pollutant, groundwater and heated steam are sucked, so the water head in the treatment target area decreases, and groundwater or the like flows in from the outside. For this reason, the underground temperature in the treatment target area drops significantly, and the heating efficiency decreases.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide an in-situ purification system for contaminated soil and an in-situ purification method for contaminated soil that can improve heating efficiency.

Means for Solving the Problems

[0007] To solve the above problems, the present invention has the following aspects. [1] Multiple heating wells that apply heat treatment to at least a portion of the area to be treated where contaminated soil contaminated with pollutants is present, A plurality of suction wells located within the area to be processed, which suck up at least a portion of the fluid containing the contaminants generated by the heat treatment, The system includes a plurality of injection wells located within or around the area to be treated, which inject water with a temperature higher than the groundwater flowing into the area to be treated into the area to be treated. In a plan view, the plurality of water injection wells are arranged on the same straight line as the plurality of heating wells, and the water injection wells and heating wells are arranged alternately on the straight line. In a plan view, the plurality of water injection wells are arranged in a staggered pattern within the horizontal interior region of the processing area. In plan view, the distance d1 between the heated wells is 1 to 6 m. In plan view, the distance d2 between the suction wells is 2 to 12 m. In a plan view, the distance d3 between the water wells is 1 to 6 m. The distance d4 in a plan view between the aforementioned water injection well and the heating well adjacent to the water injection well is 0.5 to 3 m. An in-situ remediation system for contaminated soil, wherein the distance d5 in a plan view between the injection well and the suction well adjacent to the injection well is 0.5 to 3 m. [2] The in-situ remediation system for contaminated soil according to [1], comprising a gas-liquid separator connected to the suction well. [3] The in-situ remediation system for contaminated soil according to [1] or [2], comprising a heat exchanger connected to the suction well. [4] The in-situ remediation system for contaminated soil according to [3], wherein the heat obtained from the heat exchanger is used as a heat source for the water injected from the water injection well.

[0008] [5] A heating step in which heat treatment is applied to at least a portion of the area to be treated where contaminated soil contaminated with pollutants is present, using multiple heating wells, A suction step in which at least a portion of the fluid containing the contaminants generated by the heat treatment is drawn up using a plurality of suction wells, The process includes a water injection step in which water with a higher temperature than the groundwater flowing into the treatment area is injected into or around the treatment area using multiple injection wells, In a plan view, the plurality of water injection wells are arranged on the same straight line as the plurality of heating wells, and the water injection wells and heating wells are arranged alternately on the straight line. In a plan view, the plurality of water injection wells are arranged in a staggered pattern within the horizontal interior region of the processing area. In a plan view, the distance d1 between the heated wells is 1 to 6 m. The distance d2 between the suction wells in a plan view is 2 to 12 m. The distance d3 between the water wells in a plan view is 1 to 6 m. The distance d4 in plan view between the aforementioned water injection well and the heating well adjacent to the water injection well is 0.5 to 3 m. A method for in-situ remediation of contaminated soil, wherein the distance d5 in a plan view between the injection well and the suction well adjacent to the injection well is 0.5 to 3 m. [6] The method for in-situ remediation of contaminated soil according to [5], wherein the heating temperature in the heating step is 60°C or higher. [7] The method for in-situ remediation of contaminated soil according to [5] or [6], wherein the contaminant is one or more selected from volatile organic compounds, oils, mercury, polychlorinated biphenyls, and dioxins. [8] A method for in-situ remediation of contaminated soil according to any one of [5] to [7], further comprising a heat exchange step of obtaining heat from the fluid after the suction step. [9] The method for in-situ remediation of contaminated soil according to [8], wherein the heat obtained in the heat exchange step is used as a heat source for the water injected in the water injection step. [Effects of the Invention]

[0009] According to the in-situ remediation system and method for contaminated soil of the present invention, heating efficiency can be increased. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing the configuration of an in-situ remediation system for contaminated soil according to the first embodiment of the present invention. [Figure 2]It is a plan view schematically showing the arrangement of wells of the in-situ purification system for contaminated soil according to the first embodiment of the present invention. [Figure 3] It is a cross-sectional view schematically showing the configuration of the in-situ purification system for contaminated soil according to the second embodiment of the present invention.

Embodiments for Carrying out the Invention

[0011] The in-situ purification system for contaminated soil of the present invention (hereinafter also referred to as the "in-situ purification system") has a heating well, a suction well, and an injection well. The in-situ purification system is a system that heats a treatment target area where contaminated soil exists to volatilize contaminants and purify the soil. The volatilized contaminants are sucked by the suction well. At this time, the groundwater level drops in a part of the treatment target area. Therefore, groundwater with a low water temperature (for example, 10°C) flows in from the outside of the treatment target area. The in-situ purification system injects warm water (for example, 25°C) instead of the inflowing groundwater to enhance the heating efficiency by the heating well. Hereinafter, the first embodiment of the in-situ purification system of the present invention will be described with reference to the drawings.

[0012] [First Embodiment] This embodiment is an in-situ purification system when the difference between the depth of the treatment target area and the depth of the semi-permeable layer (a stratum where groundwater hardly penetrates) is large. In this embodiment, groundwater flows in from below in the depth direction of the treatment target area and from the outer peripheral part in the horizontal direction of the treatment target area. Therefore, in the in-situ purification system of this embodiment, warm water is injected below in the depth direction of the treatment target area and into the outer peripheral part in the horizontal direction of the treatment target area.

[0013] ≪In-situ Purification System for Contaminated Soil≫ The in-situ purification system 1 in Figure 1 comprises a heating well 10, a suction well 20, an injection well 30, a heat exchanger 40, a gas-liquid separator 50, an exhaust gas treatment device 60, and a wastewater treatment device 70. The suction well 20 and the heat exchanger 40 are connected by piping L1. The heat exchanger 40 and the gas-liquid separator 50 are connected by piping L2. The gas-liquid separator 50 and the exhaust gas treatment device 60 are connected by piping L3. Piping L4 is connected to the exhaust gas treatment device 60. The gas-liquid separator 50 and the wastewater treatment device 70 are connected by piping L5. Piping L6 is connected to the wastewater treatment device 70. The arrows in the diagram indicate the direction of movement of thermal energy, water, and other fluids.

[0014] In this embodiment, as shown in Figure 1, the treatment area A1 requiring soil purification is separated underground by a watertight wall W. This prevents groundwater from flowing in from the horizontal outer periphery of the treatment area A1. Examples of the watertight wall W include a continuous wall made of steel sheet piles, a concrete wall, or a watertight wall made of water glass. The watertight wall W is driven into the ground in the depth direction, with its upper end reaching the ground surface and its lower end reaching a position deeper than the lower end of the water injection well 30. A groundwater level L is formed in the treatment area A1.

[0015] The heating wells 10 are used to apply heat treatment to contaminated soil that has been polluted with pollutants. Multiple heating wells 10 are provided within the treatment area A1. The heating wells 10 are arranged to extend downward in the depth direction from the ground surface. Examples of the heating well 10 include a cylindrical body having a heating device. Examples of the heating device include a heating heater that generates heat itself, an electrode that can heat the surrounding soil by applying electricity, and high-temperature steam. The cylindrical body may be provided with a plurality of small holes into which high-temperature steam can be injected.

[0016] The suction wells 20 are for removing contaminants from the soil by sucking up at least a portion of the fluid containing contaminants generated by the heating treatment by the heating wells 10. Multiple suction wells 20 are provided within the treatment area A1. The suction wells 20 are arranged to extend downward in the depth direction from the ground surface. Examples of suction wells 20 include cylindrical bodies with suction devices. Examples of suction devices include vacuum pumps and other devices that enable negative pressure. A vacuum pump, a blower, and a submersible pump can be combined to create negative pressure and serve as a suction device.

[0017] The injection wells 30 are for injecting water (hot water) that is hotter than the groundwater flowing into the treatment area A1 into the treatment area A1. Multiple injection wells 30 are provided within the treatment area A1. The injection wells 30 are arranged to extend downward in the depth direction from the ground surface. Examples of the water injection well 30 include a cylindrical body into which hot water can be injected into the treatment area A1. The cylindrical body preferably has heat insulating properties. The cylindrical body may be provided with a plurality of small holes through which hot water can pass. The cylindrical body may be provided with a heating device that can heat the water flowing through it.

[0018] As shown in Figure 2, multiple heating wells 10 are provided. The multiple heating wells 10 are arranged in a straight line in a plan view, forming the horizontal outer periphery of the treatment area A1. In a plan view, the multiple heating wells 10 are arranged in a staggered pattern within the horizontal interior of the treatment area A1. By arranging the multiple heating wells 10 in a staggered pattern, uniform heating treatment can be applied to the contaminated soil inside the treatment area A1. The spacing d1 between the heating wells 10 in a plan view is preferably 1 to 6 m, and more preferably 2 to 4 m. If the spacing d1 is greater than or equal to the lower limit, the number of heating wells 10 can be reduced. If the spacing d1 is less than or equal to the upper limit, the efficiency of the heating treatment can be increased, and the efficiency of removing contaminants can be further increased.

[0019] Multiple suction wells 20 are provided. In a plan view, the multiple suction wells 20 are arranged in a staggered pattern within the horizontal interior region of the treatment area A1. By arranging the multiple suction wells 20 in a staggered pattern, the fluid containing contaminants inside the treatment area A1 can be uniformly suctioned. The spacing d2 between the suction wells 20 in a plan view is preferably 2 to 12 m, and more preferably 3 to 8 m. If the spacing d2 is greater than or equal to the lower limit, the number of suction wells 20 can be reduced. If the spacing d2 is less than or equal to the upper limit, contaminants can be sufficiently suctioned, and the efficiency of contaminant removal can be further increased.

[0020] Multiple water injection wells 30 are provided. Multiple water injection wells 30 are arranged in a straight line in a plan view along the horizontal outer periphery of the treatment area A1. In this embodiment, the multiple water injection wells 30 are arranged on the same straight line as the multiple heating wells 10. In a plan view, the multiple water injection wells 30 are arranged in a staggered pattern within the horizontal interior area of ​​the treatment area A1. By arranging the multiple water injection wells 30 in a staggered pattern, hot water can be uniformly injected into the interior of the treatment area A1. The spacing d3 between the water injection wells 30 in a plan view is preferably 1 to 6 m, and more preferably 2 to 4 m. If the spacing d3 is greater than or equal to the lower limit, the number of water injection wells 30 can be reduced. If the spacing d3 is less than or equal to the upper limit, the heating efficiency can be further increased.

[0021] The distance d4 in a plan view between the water injection well 30 and the heating well 10 adjacent to the water injection well 30 is preferably 0.5 to 3 m, and more preferably 1 to 2 m. If the distance d4 is greater than or equal to the lower limit, the number of water injection wells 30 can be reduced. If the distance d4 is less than or equal to the upper limit, the heating efficiency can be further increased. The distance d5 in a plan view between the water injection well 30 and the suction well 20 adjacent to the water injection well 30 is preferably 0.5 to 3 m, and more preferably 1 to 2 m. If the distance d5 is greater than or equal to the lower limit, the number of water injection wells 30 can be reduced. If the distance d5 is less than or equal to the upper limit, the heating efficiency can be further increased.

[0022] The heat exchanger 40 is a device that cools the high-temperature fluid drawn in by the suction well 20. The heat exchanger 40 only needs to be able to cool the high-temperature fluid drawn in by the suction well 20, and examples include a plate heat exchanger, a coil heat exchanger, and a shell-and-tube heat exchanger through which a refrigerant is passed.

[0023] The gas-liquid separation device 50 is a device that separates a fluid containing contaminants, which has been drawn in by the suction well 20, into gas and liquid. The gas-liquid separation device 50 only needs to be able to separate a fluid containing contaminants into gas and liquid, and examples include a condenser equipped with a cooling function.

[0024] The exhaust gas treatment device 60 is a device that removes pollutants from the gas containing pollutants that has been separated by the gas-liquid separation device 50. Examples of exhaust gas treatment devices 60 include pressure vessels having adsorption tanks filled with adsorbent, and pyrolysis devices that can heat to high temperatures to thermally decompose the gas inside. The exhaust gas treatment device 60 may be used individually or in combination of two or more units.

[0025] The wastewater treatment device 70 is a device that removes contaminants from a liquid containing contaminants that has been separated by the gas-liquid separation device 50. Known water treatment devices can be used as the wastewater treatment device 70. Examples of water treatment devices include a filtration device having an adsorption tank filled with an adsorbent, an adsorption device having an adsorption tank filled with an adsorbent, a membrane separation device, a pressurized flotation device, a coagulation and sedimentation device, and an aeration device. The wastewater treatment device 70 may be used individually or in combination of two or more units.

[0026] Examples of pipe L1 include metal or resin pipes. Pipes L2 to L6 are similar to pipe L1. The materials of pipes L1 to L6 may be different or the same.

[0027] ≪In-situ remediation methods for contaminated soil≫ The present invention provides a method for in-situ remediation of contaminated soil (hereinafter also simply referred to as the "in-situ remediation method") which comprises a heating step, a suction step, and a water injection step. The in-situ remediation method of this embodiment will be explained using the in-situ remediation method using the in-situ remediation system 1 as an example.

[0028] First, at least a portion of the area to be treated A1 is subjected to heat treatment in the heating well 10 (heating step). The in-situ remediation method, by including a heating step, can desorb contaminants from the contaminated soil within the treatment area A1, or recover contaminants by vaporization from the contaminated groundwater. In the heating process, it is sufficient to heat-treat at least a portion of the area A1 to be treated. However, from the viewpoint of improving the efficiency of removing contaminants, it is preferable to heat-treat as wide an area of ​​the area A1 as possible, and more preferably to heat-treat the entire area A1.

[0029] Examples of pollutants include volatile organic compounds (VOCs), oils, mercury, polychlorinated biphenyls (PCBs), and dioxins. Examples of VOCs include benzene, toluene, and halogenated hydrocarbons (e.g., trichloroethylene). Examples of oils include hydrocarbons with 5 to 44 carbon atoms. Hydrocarbons with 5 to 18 carbon atoms can be recovered mainly as a gas. Even hydrocarbons with 19 or more carbon atoms can be recovered as a liquid by reducing their viscosity. These hydrocarbons may be saturated or unsaturated. These hydrocarbons may be linear, branched, or cyclic. Specific examples of these hydrocarbons include n-pentane, isopentane, n-hexane, and cyclohexane. Examples of mercury include metallic mercury, inorganic mercury, and organic mercury. Examples of inorganic mercury include mercury oxide, mercury sulfide, mercury chloride (Hg2Cl2, HgCl2), and mercury nitrate. Examples of organic mercury include alkyl mercury (e.g., methylmercury, ethylmercury) and phenylmercury (e.g., phenylmercury acetate).

[0030] Examples of PCBs include 3,3',4,4'-tetrachlorobiphenyl, 3,4,4',5-tetrachlorobiphenyl, 3,3',4,4',5-pentachlorobiphenyl, 3,3',4,4',5,5'-hexachlorobiphenyl, 2,3,3',4,4'-pentachlorobiphenyl, 2,3,3',4,4',5-hexachlorobiphenyl, and 2,3,3',4,4',5,5'-heptachlorobiphenyl. Examples of dioxins include 2,3,7,8-tetrachloropradioxin and 2,3,4,7,8-pentachlorodibenzofuran.

[0031] The in-situ remediation method of this embodiment is a so-called in-situ thermal desorption method. Examples of heating methods for the in-situ thermal desorption method include electric heater type, electric resistance type, and steam type. Among the heating methods for the in-situ thermal desorption method, the electric heater type is preferred because it allows for high heating temperatures, easy uniform heating of the soil, and can treat a wide variety of pollutants.

[0032] The heating temperature during the heat treatment is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. When the heating temperature is above the lower limit, the vaporization and decomposition of contaminants are promoted, and more contaminants can be removed. A higher upper limit for the heating temperature is preferable, but in reality, it is around 350°C. The heating temperature during the heat treatment process can be measured using a monitoring well (not shown) equipped with a thermocouple or temperature sensor.

[0033] The electric heating heater type described above is a method that heats the processing area A1 at a heating temperature of 100°C or higher. By heating the treatment area A1 at a heating temperature of 100°C or higher, the moisture contained in the soil pores is evaporated, expanding the pores between soil particles, and the desorbed contaminants can be carried away by the water vapor, thus allowing for more efficient removal of contaminants from the soil.

[0034] The suction well 20 is activated. For example, a vacuum pump (not shown) connected to the suction well 20 is activated to create negative pressure inside the suction well 20. Then, by activating a blower (not shown) and a submersible pump (not shown), the fluid containing contaminants is drawn into the suction well 20 (suction process). The in-situ remediation method, by including a suction step, can remove contaminants desorbed in the treatment area A1 from the soil.

[0035] The internal pressure of the suction well 20 during the suction process is not particularly limited, and may be, for example, 100 kPa or less (atmospheric pressure or less). If the internal pressure of the suction well 20 during the suction process is below the above upper limit, the desorption of contaminants attached to the soil is promoted, and contaminants can be removed more efficiently. The lower limit of the internal pressure of the suction well 20 during the suction process is not particularly limited, and may be, for example, 0.1 Pa.

[0036] Before, after, or simultaneously with the heating process, water with a higher temperature than the groundwater flowing into the treatment area A1 (hot water) is injected into the treatment area A1 via the injection well 30 (injection process). When a fluid containing contaminants is drawn in by the suction well 20, the groundwater level L in the treatment area A1 decreases, and groundwater flows into the treatment area A1 from outside the impermeable wall W. When groundwater flows into the treatment area A1, there is a concern that the temperature of the treatment area A1 will decrease, reducing the heating efficiency of the heating well 10. The in-situ remediation method has a water injection step, which allows hot water to be injected into the treatment area A1. Therefore, the decrease in temperature of the treatment area A1 due to the inflow of groundwater from outside the impermeable wall W can be prevented. As a result, the heating efficiency of the heating well 10 can be further increased. In the water injection process, for example, hot water can be injected into the area A1 to be treated by an injection pump (not shown) connected to the injection well 30.

[0037] The temperature of the water injected during the injection process should be higher than the temperature of the groundwater flowing into the treatment area A1. The temperature difference between the injected water and the groundwater is preferably 5°C or more, more preferably 10°C or more, and even more preferably 20°C or more. If the temperature difference between the injected water and the groundwater is greater than or equal to the lower limit mentioned above, the heating efficiency of the heating well 10 can be further increased. The upper limit of the temperature difference between the injected water and the groundwater is not particularly limited, and is, for example, 95°C. The temperature difference between the injected water and the groundwater can be measured using a monitoring well (not shown) equipped with thermocouples, temperature sensors, etc.

[0038] The temperature of the water injected in the water injection process is preferably 20°C or higher, more preferably 25°C or higher, and even more preferably 30°C or higher. If the temperature of the water injected in the water injection process is above the lower limit mentioned above, the heating efficiency of the heating well 10 can be further increased. From the viewpoint of further increasing the heating efficiency of the heating well 10, a higher temperature of the water injected in the water injection process is preferable. The upper limit of the temperature of the water injected in the water injection process is, for example, 99°C.

[0039] The amount of water injected during the water injection process is not particularly limited and can be adjusted according to the temperature of the incoming groundwater, the flow velocity of the groundwater, the soil type (permeability) of the soil in the treatment area A1, etc.

[0040] The water injected during the water injection process must meet the groundwater infiltration standards in terms of the concentration of contaminants; therefore, it is preferable that the water used is sourced from an external source, such as tap water. It is preferable that the water injected in the water injection process is heated using the heat obtained in the heat exchange process described later as the heat source. By using the heat obtained in the heat exchange process as the heat source to heat the water injected in the water injection process, energy required to heat the water can be saved, and the environmental burden can be reduced.

[0041] The fluid containing contaminants drawn in during the suction process is supplied to the heat exchanger 40 via piping L1 connected to the suction well 20. In this embodiment, fluids drawn in by multiple suction wells 20 are supplied to the heat exchanger 40. In the heat exchanger 40, the high-temperature fluid (e.g., 100°C or higher) is cooled to obtain heat (heat exchange process). The in-situ purification method of this embodiment has a heat exchange process, which allows the obtained heat to be used as a heat source to heat the water injected in the water injection process. It is preferable to use the heat obtained in the heat exchange process as a heat source to heat the water injected in the water injection process because it saves energy used to heat the water injected in the water injection process and reduces the environmental burden. The fluid cooled in the heat exchanger 40 is supplied to the gas-liquid separator 50 via the piping L2.

[0042] The fluid supplied to the gas-liquid separator 50 is further cooled and separated into a gas containing the contaminant and a liquid containing the contaminant (gas-liquid separation step). The in-situ purification method of this embodiment, by having a gas-liquid separation step, can separate the fluid containing the contaminant into gas and liquid, and can separate and remove the contaminant more efficiently. In the gas-liquid separation process, it is preferable to cool the fluid containing contaminants to 40°C or below. By cooling the fluid containing contaminants to 40°C or below, the amount of gas processed by the exhaust gas treatment device 60 can be reduced, and the efficiency of contaminant removal can be further improved. The gas containing contaminants obtained in the gas-liquid separation process is supplied to the exhaust gas treatment device 60 via piping L3. The liquid containing contaminants obtained in the gas-liquid separation process is supplied to the wastewater treatment device 70 via piping L5.

[0043] The gas containing pollutants supplied to the exhaust gas treatment device 60 comes into contact with an adsorbent. Upon contact with the adsorbent, the pollutants contained in the gas are adsorbed onto the adsorbent, and a clean treated gas is obtained (exhaust gas treatment process). The in-situ purification method of this embodiment, by having an exhaust gas treatment process, can separate and remove pollutants from the gas containing pollutants. When a pyrolysis device is used as the exhaust gas treatment device 60, the exhaust gas treatment process may be a method of treating pollutants by decomposing them into harmless substances through pyrolysis (pyrolysis treatment method). When the pyrolysis treatment method is used, the heat obtained from the exhaust gas treatment device 60 may be used as a heat source to heat the water injected in the water injection process via a heat exchanger (not shown) different from the heat exchanger 40.

[0044] The adsorbent is not particularly limited and examples include activated carbon such as bamboo charcoal, coconut shell charcoal, powdered activated carbon, and granular activated carbon, as well as zeolite and activated alumina. From the viewpoint of excellent adsorption capacity for pollutants, activated carbon is preferred as the adsorbent, and among them, granular activated carbon is more preferred because it facilitates the operation and management of the in-situ purification system 1.

[0045] The concentration of pollutants in the treated gas is preferably below the environmental standard, and more preferably below the limit of quantification. The concentration of contaminants in the treated gas can be measured, for example, by gas chromatography.

[0046] The treated gas obtained in the exhaust gas treatment process is discharged to the outside of the in-situ purification system 1 via piping L4.

[0047] The liquid containing contaminants supplied to the wastewater treatment device 70 comes into contact with an adsorbent. Upon contact with the adsorbent, the contaminants contained in the liquid are adsorbed onto the adsorbent, and clear treated water is obtained (wastewater treatment step). The in-situ purification method of this embodiment, by having a wastewater treatment step, can separate and remove contaminants from the liquid containing them. The adsorbent used in the wastewater treatment process is the same as the adsorbent used in the first exhaust gas treatment process.

[0048] From the viewpoint of reducing environmental impact, the concentration of pollutants in treated water is preferably below the discharge standard, more preferably below the environmental standard, and even more preferably below the limit of quantification. For example, a wastewater discharge standard for trichloroethylene (TCE) is 0.1 mg / L. For example, an environmental standard for TCE (Total Cholesterol Ethylene Glycol) is 0.01 mg / L. As for the limit of quantification, for example, if the contaminant is TCE, 0.005 mg / L is preferred, 0.002 mg / L is more preferred, and 0.001 mg / L is even more preferred. The concentration of pollutants in treated water can be measured, for example, in accordance with the method described in JIS K0125:2016, if the pollutants are VOCs.

[0049] Furthermore, if the pollutant is a VOC, the wastewater treatment device 70 may not perform treatment with an adsorbent, but instead transfer the VOCs in the liquid to the gas phase by aeration and discharge them at a level below the wastewater discharge standard. In this case, it is preferable to discharge the treated gas into the atmosphere at a level below the environmental standard in the exhaust gas treatment process.

[0050] The treated water obtained in the wastewater treatment process is discharged to the outside of the in-situ purification system 1 via piping L7.

[0051] According to the in-situ purification system 1 of this embodiment, the presence of an injection well 30 allows hot water to be injected into the treatment area A1. This prevents groundwater from flowing in from outside the impermeable wall W and prevents a decrease in the temperature of the treatment area A1. As a result, the heating efficiency of the heating well 10 can be further increased. According to the in-situ purification system 1 of this embodiment, the heat obtained in the heat exchanger 40 can be used as a heat source to heat the water injected in the water injection process. Therefore, energy required to heat the water injected in the water injection process can be saved, and the environmental burden can be reduced.

[0052] [Second Embodiment] This embodiment is an in-situ remediation system for cases where the difference between the depth of the area to be treated and the depth of the low-permeability layer is small, the flow velocity of groundwater around the area to be treated is small, and no impermeable wall is constructed on the horizontal outer perimeter of the area to be treated. In this embodiment, groundwater flows in from the horizontal outer perimeter of the area to be treated. Therefore, in the in-situ remediation system of this embodiment, hot water is injected on the horizontal outer perimeter of the area to be treated. In this case, it is preferable to inject the hot water from a point close to the ground surface of the area to be treated to a point close to the lower end in the depth direction of the area to be treated.

[0053] ≪In-situ purification system≫ Figure 3 shows a schematic diagram of an in-situ purification system according to the second embodiment of the present invention. Components identical to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0054] As shown in Figure 3, the in-situ purification system 2 of this embodiment includes a heating well 10, a suction well 20, an injection well 32, a heat exchanger 40, a gas-liquid separator 50, an exhaust gas treatment device 60, and a wastewater treatment device 70. The suction well 20 and the heat exchanger 40 are connected by piping L1. The heat exchanger 40 and the gas-liquid separator 50 are connected by piping L2. The gas-liquid separator 50 and the exhaust gas treatment device 60 are connected by piping L3. Piping L4 is connected to the exhaust gas treatment device 60. The gas-liquid separator 50 and the wastewater treatment device 70 are connected by piping L5. Piping L6 is connected to the wastewater treatment device 70. The arrows in the diagram indicate the direction of movement of thermal energy, water, and other fluids. The in-situ remediation system 2 of this embodiment differs from the in-situ remediation system 1 of the first embodiment in that it is applied to an area without a watertight wall W and has an injection well 32 instead of an injection well 30.

[0055] In this embodiment, the in-situ remediation system 2 does not have a watertight wall W around the treatment area A2. Therefore, when a fluid containing contaminants is drawn in by the suction well 20, the groundwater level L in the treatment area A2 drops, and groundwater flows in from the surrounding area A2. When groundwater flows into the treatment area A2, there is a concern that the temperature of the treatment area A2 will decrease, reducing the heating efficiency of the heating well 10. In this embodiment, the in-situ remediation system 2 has an injection well 32, which allows hot water to be injected into the treatment area A2. Therefore, it is possible to prevent the temperature of the treatment area A2 from decreasing due to the inflow of groundwater from the surrounding area A2. As a result, the heating efficiency of the heating well 10 can be further increased.

[0056] The injection wells 32 are for injecting water (hot water) that is hotter than the groundwater flowing into the treatment area A2 into the treatment area A2. Multiple injection wells 32 are provided around the treatment area A2. The injection wells 32 are arranged to extend downward in the depth direction from the ground surface. Examples of the water injection well 32 include a cylindrical body having multiple small holes through which hot water can pass. The cylindrical body preferably has heat insulating properties. The cylindrical body may be equipped with a heating device that can heat the water flowing through it.

[0057] The arrangement of the heating wells 10 is the same as that of the heating wells 10 in the first embodiment. The arrangement of the suction wells 20 is the same as that of the suction wells 20 in the first embodiment. The arrangement of the water injection well 32 is the same as the arrangement of the water injection well 30 in the first embodiment.

[0058] ≪In-situ remediation methods for contaminated soil≫ The in-situ purification method of this embodiment comprises a heating step, a suction step, and a water injection step. The in-situ remediation method of this embodiment is the same as the in-situ remediation method of the first embodiment, except that it uses the in-situ remediation system 2 to remediate contaminated soil.

[0059] According to the in-situ purification system 2 of this embodiment, the presence of an injection well 32 allows hot water to be injected into the treatment area A2. This prevents a decrease in the temperature of the treatment area A2 due to the inflow of groundwater from outside the treatment area A2. As a result, the heating efficiency of the heating well 10 can be further increased. According to the in-situ purification system 2 of this embodiment, the heat obtained in the heat exchanger 40 can be used as a heat source to heat the water injected in the water injection process. Therefore, energy required to heat the water injected in the water injection process can be saved, and the environmental burden can be reduced.

[0060] Although the in-situ remediation system and in-situ remediation method of the present invention have been described above, the present invention is not limited to the embodiments described above and can be modified as appropriate without departing from the spirit of the invention. For example, the in-situ purification system 1 of the first embodiment has a heat exchanger 40, but the in-situ purification system does not necessarily have a heat exchanger. However, it is preferable for the in-situ purification system to have a heat exchanger because it allows for effective use of the heat obtained from the heat exchanger and reduces the environmental burden. For example, the in-situ purification system 1 of the first embodiment has a heat exchanger 40, but the in-situ purification system may have heat exchangers other than the heat exchanger 40. Examples of heat exchangers other than the heat exchanger 40 include heat exchangers connected to an exhaust gas treatment device. By having heat exchangers other than the heat exchanger 40, the heat obtained can be utilized more effectively and the environmental burden can be further reduced. For example, the in-situ remediation system 1 of the first embodiment has a gas-liquid separator 50, but the in-situ remediation system does not necessarily have a gas-liquid separator. However, it is preferable for the in-situ remediation system to have a gas-liquid separator because it separates the fluid containing the pollutants into gas and liquid, allowing for more efficient separation and removal of the pollutants. For example, the in-situ remediation system 1 of the first embodiment has a wastewater treatment device 70, but the in-situ remediation system does not necessarily have a wastewater treatment device. However, it is preferable for the in-situ remediation system to have a wastewater treatment device because it can separate and remove contaminants from a liquid containing contaminants.

[0061] For example, the in-situ remediation system 2 of the second embodiment has water injection wells 32 around the area to be treated A2, but the in-situ remediation system may also have water injection wells inside the area to be treated. For example, in the in-situ purification system 1 of the first embodiment, a plurality of heating wells 10 are arranged in a straight line in a plan view along the horizontal outer periphery of the treatment area A1, and a plurality of heating wells 10 are provided in a staggered arrangement within the horizontal interior area of ​​the treatment area A1. However, the heating wells do not have to be arranged in a straight line when viewed from above; they may be arranged on the circumference of a circle or ellipse, or they may be arranged irregularly. Furthermore, within the internal region of the area to be treated, the heating wells may be arranged in a grid pattern, a honeycomb pattern, or they may be arranged irregularly when viewed from above. For example, in the in-situ purification system 1 of the first embodiment, a plurality of suction wells 20 are provided in a staggered arrangement in a plan view within the horizontal interior region of the treatment area A1. However, the suction wells may be arranged in a grid pattern, a honeycomb pattern, or irregularly in a plan view. For example, in the in-situ purification system 1 of the first embodiment, a plurality of water injection wells 30 are arranged in a straight line in a plan view along the horizontal outer periphery of the treatment area A1, and a plurality of water injection wells 30 are provided in a staggered arrangement within the horizontal interior area of ​​the treatment area A1. However, the water injection wells do not have to be arranged in a straight line when viewed from above; they may be located on the circumference of a circle or ellipse, or they may be arranged irregularly. Furthermore, within the internal region of the area to be treated, the water injection wells may be arranged in a grid pattern, a honeycomb pattern, or they may be arranged irregularly when viewed from above. For example, in the in-situ purification system 1 of the first embodiment, multiple water injection wells 30 are arranged on the same straight line as the multiple heating wells 10. However, the multiple water injection wells 30 may be arranged on the same straight line as the multiple suction wells 20, or they may be arranged irregularly. The number of heating wells, suction wells, and water injection wells is not limited to the number exemplified in the embodiments described above; there should be one or more for each treatment area. It is preferable that the suction wells be arranged to evenly cover multiple heating wells. It is preferable that the water injection wells be arranged so as to evenly cover multiple heating wells. It is preferable that the water injection wells be arranged so as to evenly cover multiple suction wells.

[0062] For example, in the first embodiment, the in-situ purification system 1 discharges the treated water obtained from the wastewater treatment device 70 outside the system, but the in-situ purification system may also use the treated water as water injected into the injection well. For example, the in-situ remediation system 1 of the first embodiment has a heating well 10 and a suction well 20, but the in-situ remediation system may have one well that serves as both a heating well and a suction well. For example, in the in-situ purification system 1 of the first embodiment, the heating well 10 is arranged to extend downward in the depth direction from the ground surface. However, the heating well may be positioned horizontally underground. For example, in the in-situ remediation system 1 of the first embodiment, the suction well 20 is positioned to extend downward in the depth direction from the ground surface. However, the suction well may be positioned horizontally underground. For example, in the in-situ purification system 1 of the first embodiment, the water injection well 30 is arranged to extend downward in the depth direction from the ground surface. However, the water well may be positioned underground so as to extend horizontally. [Explanation of symbols]

[0063] 1,2...In-situ purification system, 10...Heating well, 20...Suction well, 30,32...Injection well, 40...Heat exchanger, 50...Gas-liquid separation device, 60...Exhaust gas treatment device, 70...Wastewater treatment device, A1,A2...Treatment target area, W...Waterproof wall, L...Water level, L1~L6...Piping

Claims

1. Multiple heating wells that apply heat treatment to at least a portion of the area to be treated where contaminated soil containing pollutants exists, A plurality of suction wells located within the area to be processed, which suck up at least a portion of the fluid containing the contaminants generated by the heat treatment, The system includes a plurality of injection wells located within or around the area to be treated, which inject water with a temperature higher than the groundwater flowing into the area to be treated into the area to be treated. In a plan view, the plurality of water injection wells are arranged on the same straight line as the plurality of heating wells, and the water injection wells and heating wells are arranged alternately on the straight line. In a plan view, the plurality of water injection wells are arranged in a staggered pattern within the horizontal interior region of the processing area. In a plan view, the distance d1 between the heating wells is 1 to 6 m. In a plan view, the distance d2 between the suction wells is 2 to 12 m. In a plan view, the distance d3 between the water wells is 1 to 6 m. The distance d4 in a plan view between the aforementioned water injection well and the heating well adjacent to the water injection well is 0.5 to 3 m. An in-situ remediation system for contaminated soil, wherein the distance d5 in a plan view between the water injection well and the suction well adjacent to the water injection well is 0.5 to 3 m.

2. The in-situ remediation system for contaminated soil according to claim 1, further comprising a gas-liquid separation device connected to the suction well.

3. The in-situ remediation system for contaminated soil according to claim 1 or 2, comprising a heat exchanger connected to the suction well.

4. The in-situ remediation system for contaminated soil according to claim 3, wherein the heat obtained from the heat exchanger is used as a heat source for the water injected from the water injection well.

5. A heating process in which heat treatment is applied to at least a portion of the area to be treated where contaminated soil contaminated with pollutants exists, using multiple heating wells, A suction step in which at least a portion of the fluid containing the contaminants generated by the heat treatment is drawn up using a plurality of suction wells, The process includes a water injection step in which water with a higher temperature than the groundwater flowing into the treatment area is injected into or around the treatment area using multiple injection wells, In a plan view, the plurality of water injection wells are arranged on the same straight line as the plurality of heating wells, and the water injection wells and heating wells are arranged alternately on the straight line. In a plan view, the plurality of water injection wells are arranged in a staggered pattern within the horizontal interior region of the processing area. The distance d1 between the heating wells in a plan view is 1 to 6 m. The distance d2 between the suction wells in a plan view is 2 to 12 m. The distance d3 between the water wells in a plan view is 1 to 6 m. The distance d4 in a plan view between the aforementioned water injection well and the heating well adjacent to the water injection well is 0.5 to 3 m. A method for in-situ remediation of contaminated soil, wherein the distance d5 in a plan view between the water injection well and the suction well adjacent to the water injection well is 0.5 to 3 m.

6. The in-situ remediation method for contaminated soil according to claim 5, wherein the heating temperature in the heating step is 60°C or higher.

7. The method for in-situ remediation of contaminated soil according to claim 5 or 6, wherein the pollutant is one or more selected from volatile organic compounds, oils, mercury, polychlorinated biphenyls, and dioxins.

8. A method for in-situ remediation of contaminated soil according to any one of claims 5 to 7, further comprising a heat exchange step of obtaining heat from the fluid after the suction step.

9. The method for in-situ remediation of contaminated soil according to claim 8, wherein the heat obtained in the heat exchange step is used as a heat source for the water injected in the water injection step.

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