In-situ organic fluorine compound purification system and in-situ organic fluorine compound purification method

Abstract

To provide an in-situ purification system capable of decontamination of soils and underground waters contaminated with organofluorine compounds such as PFOS and PFOA, and a purification method using the same, solving problems of conventional arts.SOLUTION: An organofluorine compound in-situ purification system is a system for in-situ decontamination of soils contaminated with organofluorine compounds and is assembled with a soil warming device and a decomposition treatment device. The soil warming device is a device for warming soils by applying voltage to 3 or more of electrode wells constructed in soils for feeding electric current to the soils. The decomposition treatment device is a portable type to be installed on a ground, and is a device for decomposition of organofluorine compounds by blowing ozone gas to contaminated water prepared by cooling contaminated water vapor and irradiating the contaminated water with UV light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technology for in-situ purification of contaminated soil and groundwater, and more specifically, to a technology for purifying soil and groundwater contaminated with organofluorine compounds (PFCs), such as perfluorooctanesulfonic acid and perfluorooctanoic acid, by utilizing an electric heating method, which is a soil heating technology, as well as physical recovery and chemical decomposition. [Background technology]

[0002] Due to their properties of water repellency, oil repellency, and chemical stability, organic fluorine compounds have been used in a variety of applications, including water repellents, surface treatment agents, emulsifiers, fire extinguishing agents, insecticides, and coating agents for cooking utensils. However, due to their properties, organic fluorine compounds are hardly decomposed in nature, and their environmental persistence and bioaccumulation have been viewed as problems. In particular, perfluorooctane sulfonic acid (hereinafter referred to as "PFOS") and perfluorooctanoic acid (hereinafter referred to as "PFOA"), which have eight carbon atoms, have been shown to exhibit significant persistence, accumulation, and toxicity, raising concerns about their harmfulness to humans and living organisms.

[0003] Therefore, at the 4th Conference of the Parties to the Stockholm Convention on Persistent Organic Pollutants (POPs Convention) in 2009, it was decided to add PFOS and its salts to Annex B (substances whose manufacture, use, import and export should be restricted). In response to this, in Japan, PFOS and its salts have been designated as Class I Specified Chemical Substances under the Law Concerning the Examination and Regulation of Manufacture, etc. of Chemical Substances (the so-called "Chemical Substances Control Law"), and as Class I Designated Chemical Substances under the Law Concerning Reporting, etc. of Releases of Specified Chemical Substances into the Environment and Promotion of Improvements to Their Management (PRTR Law), and in principle, the manufacture, import, use, etc. of PFOS and its salts are prohibited.

[0004] Meanwhile, at the 9th Conference of the Parties to the POPs Convention (2019), it was decided to add PFOA and related substances to Annex A (substances whose manufacture, use, import and export should be prohibited), and in Japan they are designated as Type 2 Monitoring Chemical Substances under the Chemical Substances Control Law.

[0005] PFOS and PFOA are hardly decomposed in the environment, so for example, if these substances leak from a manufacturing plant, they may remain in the environment for a long time, and may pollute rivers and groundwater. It has also been reported that people who drink tap water from rivers and other sources for a long time are more likely to develop kidney cancer, thyroid disease, and ulcerative colitis. For this reason, there is a movement in the field of water supply to focus on PFOS and PFOA in water quality management. At present, the World Health Organization (WHO) has not set target values ​​or guideline values ​​for PFOS and PFOA in drinking water, but Europe and the United States have set their own target values. In Japan, at the "2nd Water Quality Standards Sequential Revision Review Meeting for FY2019" held by the Ministry of Health, Labor and Welfare, it was agreed that the provisional target value for PFOS and PFOA in tap water quality would be 50 ng / L in total, and it was announced that this would be applied from April 1, 2020.

[0006] Thus, while efforts are being made to combat PFOS and PFOA in the area of ​​water supply, there have been no notable efforts made in the areas of soil and groundwater contamination. So However, soil contamination by PFOS, which is contained in foam fire extinguishing agents, has become a problem in Okinawa Prefecture, and it is easy to predict that in the future, attention will be focused on the purification of PFOS and PFOA in the field of soil and groundwater contamination.

[0007] By the way, the general methods for in-situ purification of contaminated soil and groundwater include physical, chemical, and biological methods. However, in cases of contamination with organofluorine compounds such as PFOS and PFOA, none of these methods are effective due to the properties of the substances. For example, physical methods involve recovering organofluorine compounds contained in soil gas or groundwater by gas suction or pumping, but organofluorine compounds have low volatility, making their recovery difficult by gas suction, and their solubility in water is also low, so the effect of pumping is limited. In particular, when PFOS or PFOA has penetrated into the pores of the soil, their mobility at room temperature is very low, so recovery by pumping is even less likely.

[0008] Chemical methods involve the use of chemicals to decompose organic fluorine compounds, but because organic fluorine compounds are chemically stable and do not decompose in the environment, accelerated oxidation methods are necessary for their decomposition. For this reason, although there is a track record of decomposition using "ozone + hydrogen peroxide" in the field of water treatment (waterworks), there are many challenges to applying ozone to in-situ purification of soil and groundwater, such as the technical difficulty of supplying high concentrations of ozone underground and the fact that ozone itself is harmful.

[0009] Biological methods utilize the action of microorganisms to decompose organofluorine compounds, but organofluorine compounds are biologically stable and are not easily decomposed by microorganisms either aerobic or anaerobic, and there is no track record of their use in the field of water treatment. Similarly, the application of biological treatment to in-situ purification of soil and groundwater is not realistic.

[0010] When physical, chemical, or biological methods cannot be used individually to effectively purify contamination, a combination of these methods may be an effective solution. For example, Patent Document 1 proposes a purification technology that decomposes 1,4-dioxane by injecting persulfate into heated soil, etc. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2018-34086 A Summary of the Invention [Problem to be solved by the invention]

[0012] The technology disclosed in Patent Document 1 utilizes an electric heating method, and therefore can efficiently raise the soil temperature to a predetermined temperature (for example, 40 to 90°C) and can stably maintain the predetermined temperature. As a result, 1,4-dioxane can be effectively decomposed by the injected persulfate. However, the technology disclosed in Patent Document 1 is a technology for decomposing 1,4-dioxane, and is not a technology for purifying soil or groundwater contaminated with organofluorine compounds, which have completely different physical and chemical properties from 1,4-dioxane.

[0013] The object of the present invention is to solve the problems inherent in the past, that is, to provide an in-situ remediation system capable of purifying soil and groundwater contaminated with organofluorine compounds such as PFOS and PFOA, and a remediation method using the same. [Means for solving the problem]

[0014] The present invention is characterized by the fact that, as the soil temperature rises, water vapor is generated, the volume of water expands, and the viscosity of water decreases, which improves the movement of the water itself, thereby increasing the recovery efficiency of organic fluorine compounds contained in the interstitial water. Furthermore, by increasing the temperature of the soil or groundwater, chemical reactions are promoted, which allows the decomposition of organic fluorine compounds that could not be decomposed by conventional methods (or minutes This invention focuses on the fact that it can simultaneously solve problems (which usually require a long time to solve) and is based on an entirely new idea.

[0015] The in-situ organic fluorine compound purification system of the present invention is a system for purifying soil contaminated with organic fluorine compounds in-situ, and is equipped with a soil heating device and a decomposition treatment device. The soil heating device is a device that heats the soil by applying an electric current to three or more electrode wells constructed in the soil and passing it through the soil, and the decomposition treatment device is a device that decomposes the organic fluorine compounds contained in the contaminated water vapor generated by heating the soil heating device. The decomposition treatment device is a portable type that is installed on the ground, and decomposes the organic fluorine compounds by blowing ozone gas into the contaminated water that has been cooled from the contaminated water vapor and irradiating it with ultraviolet light.

[0016] The in-situ organic fluorine compound purification system of the present invention can also be configured to blow ozone gas into contaminated water whose temperature has been adjusted to a predetermined level, while irradiating it with ultraviolet light.

[0017] The in-situ purification system for organic fluorine compounds of the present invention can also be configured to decompose organic fluorine compounds by blowing ozone gas and hydrogen peroxide into the contaminated water.

[0018] The in-situ organic fluorine compound remediation system of the present invention may further include a groundwater pumping device. This groundwater pumping device pumps up contaminated groundwater (groundwater contaminated with organic fluorine compounds) from a countermeasure well constructed in the soil. In this case, the decomposition treatment device treats the contaminated water containing the cooled contaminated water vapor and the contaminated groundwater.

[0019] The in-situ organic fluorine compound purification system of the present invention may further include a removal device that treats the treated water discharged from the decomposition treatment device to remove inorganic fluorine.

[0020] The in-situ remediation system for organic fluorine compounds of the present invention may also be equipped with a soil heating device and an agent injection device. The agent injection device is a device that injects persulfate dissolved in room temperature water into heated soil or groundwater.

[0021] The method for in-situ purification of organic fluorine compounds of the present invention is a method for purifying soil contaminated with organic fluorine compounds in situ using the in-situ purification system for organic fluorine compounds of the present invention, and is a method including a soil heating step and a decomposition treatment step. In the soil heating step, the soil is heated by applying an electric current to three or more electrode wells constructed in the soil to pass through the soil, and in the decomposition treatment step, the organic fluorine compounds contained in the contaminated water vapor generated by heating in the soil heating step are decomposed. In the decomposition treatment step, a portable decomposition treatment device installed on the ground is used to blow ozone gas into the contaminated water that has been cooled from the contaminated water vapor, and irradiate it with ultraviolet light to decompose the organic fluorine compounds.

[0022] The method for in-situ purification of organic fluorine compounds of the present invention can also be a method for decomposing organic fluorine compounds by blowing ozone gas and hydrogen peroxide into contaminated water.

[0023] The method for in-situ remediation of organic fluorine compounds of the present invention may further include a groundwater pumping step, in which contaminated groundwater is pumped up from a well constructed in the soil. In this case, the decomposition treatment step treats the contaminated water, which contains the cooled contaminated water vapor and the contaminated groundwater.

[0024] The in-situ purification method for organic fluorine compounds of the present invention can also be a method in which treated water obtained after treatment in the decomposition treatment step (after the organic fluorine compounds have been decomposed) is returned to the soil.

[0025] The in-situ remediation method for organic fluorine compounds of the present invention may also be a method comprising a soil heating step and an agent injection step, in which persulfate dissolved in room temperature water is injected into the heated soil or groundwater to chemically decompose the organic fluorine compounds. Effect of the Invention

[0026] The in-situ organic fluorine compound remediation system and in-situ organic fluorine compound remediation method of the present invention have the following effects. (1) By heating the soil, the groundwater temperature rises, which in turn generates steam, expands in volume, and reduces the viscosity of the water, improving the movement of the water itself and increasing the solubility of organic fluorine compounds. As a result, by collecting the steam and groundwater, the organic fluorine compounds contained in them can also be efficiently collected. (2) In the field of water treatment, PFOS and PFOA can be treated by large-scale treatment facilities such as tap water sources, but in the field of soil and groundwater contamination, where contaminated sites are scattered, such concentrated measures are difficult. Therefore, the present invention uses a portable decomposition treatment device. In other words, by making the decomposition treatment device portable, it is possible to flexibly and efficiently perform purification treatment on scattered contaminated sites. Furthermore, by treating groundwater in a heated state, the treatment time can be shortened. (3) In the case of injecting an aqueous solution of persulfate into soil or groundwater, there is no need to heat the agent itself (it dissolves at room temperature), so losses due to self-decomposition of persulfate can be reduced. On the other hand, reactivity increases in the heated earth, so the amount of agent can be reduced compared to when it is carried out at room temperature. Furthermore, it can also decompose organic fluorine compounds that do not decompose at room temperature. (4) The electrical heating method does not require a high-temperature heat medium such as a thermal conduction (heater), and there are no localized high-temperature areas underground, so polyvinyl chloride pipes (heat-resistant rigid polyvinyl chloride pipes, depending on the heating temperature) can be used as the material for the chemical injection well. (5) Since an electrical heating method is used in which the soil itself is heated by Joule heat, it is easy to control the temperature. Therefore, it is easy to raise the soil temperature to the desired temperature, and the entire soil can be heated uniformly. (6) Electric heating methods have better thermal efficiency than heating methods that use thermal conduction (heaters), and therefore can reduce the power consumption required for heating. (7) When the heated treated water is re-entered underground, heat loss caused by pumping is reduced, and the temperature of the soil and groundwater can be maintained with less electricity. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a block diagram showing a schematic diagram of the main configuration of a physical treatment type in-situ purification system for organic fluorine compounds. [Diagram 2] FIG. 1 is a cross-sectional view showing a schematic diagram of a soil heating device that uses an electrical heating method. [Diagram 3] FIG. 1 is a plan view showing electrode wells arranged in a plane to form a triangle. [Figure 4] FIG. 1 is a block diagram showing a schematic diagram of the main configuration of a chemical treatment type in-situ purification system for organic fluorine compounds. [Diagram 5] FIG. 1 is a flow diagram showing the flow of main steps of an in-situ organic fluorine compound purification method using a physical treatment type in-situ organic fluorine compound purification system. [Figure 6] FIG. 1 is a flow diagram showing the flow of main steps of an in-situ organic fluorine compound purification method using a chemical treatment type in-situ organic fluorine compound purification system. [Figure 7] This is a test result diagram showing the decomposition effect of a physical treatment type in-situ purification system for organic fluorine compounds. [Figure 8] This is a test result diagram showing the decomposition effect of a chemical treatment type in-situ purification system for organic fluorine compounds. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] An embodiment of the in-situ organic fluorine compound remediation system and the in-situ organic fluorine compound remediation method of the present invention will be described with reference to the drawings. Note that the in-situ organic fluorine compound remediation method of the present invention is a method for remediating soil, etc., using the in-situ organic fluorine compound remediation system of the present invention, and therefore the in-situ organic fluorine compound remediation system of the present invention will be described first, and then the in-situ organic fluorine compound remediation method of the present invention will be described.

[0029] 1. In-situ purification system for organic fluorine compounds The in-situ organic fluorine compound remediation system of the present invention purifies soil and groundwater contaminated with organic fluorine compounds such as PFOS and PFOA in-situ, and has one feature of decomposing organic fluorine compounds after heating the soil using an electric heating method. The in-situ organic fluorine compound remediation system of the present invention can be broadly divided into two types in terms of the method of decomposing organic fluorine compounds, that is, one that decomposes organic fluorine compounds on the ground (hereinafter, for convenience, referred to as a "physical treatment type in-situ organic fluorine compound remediation system") and one that decomposes organic fluorine compounds in the soil (hereinafter, for convenience, referred to as a "chemical treatment type in-situ organic fluorine compound remediation system"). Each embodiment will be described in order below.

[0030] (Physical treatment type in-situ purification system for organic fluorine compounds) 1 is a block diagram showing a schematic diagram of the main components of a physical treatment type in-situ organic fluorine compound purification system 100a. As shown in the figure, the physical treatment type in-situ organic fluorine compound purification system 100a includes a soil heating device (electrode well 111 and power supply device 112) and a decomposition treatment device 120, and can also include a gas suction device 130, a groundwater pumping device 140, etc. Below, each of the main components that make up the physical treatment type in-situ organic fluorine compound purification system 100a will be described in detail.

[0031] A soil heating device heats the soil in a target area to a specified temperature and to maintain that temperature. Although a method of heating the soil is known that uses thermal conduction (heater), the present invention employs an electric heating method, which is a type of electrical resistance heating method. This electric heating method has the following features: it can heat the soil evenly because it heats the soil itself, and it is easy to control the temperature; clay layers, which have a high current flow rate (low electrical resistance), are easier to heat; and it has excellent thermal efficiency, so it is possible to reduce the power consumption required to heat the soil compared to thermal conduction (heater).

[0032] FIG. 2 is a cross-sectional view showing a soil heating device 110 that uses an electric heating method. As shown in this figure, the soil heating device 110 includes an electrode well 111 constructed in the soil of the target range and a power supply unit 112 installed on the ground. The electrode wells 111 are formed of a steel casing, and by applying a three-phase AC voltage to the casing of each electrode well 111 by the power supply unit 112, a current flows between the electrode wells 111, and as a result, Joule heat is generated in the soil in between, that is, the soil can be heated. Therefore, each electrode well 111 may be installed at three or more locations so as to surround the soil of the target range, and may be arranged to form a plurality of triangles as shown in FIG. 3, for example. Note that the four triangles shown in FIG. 3 are each an equilateral triangle with one side of about 3.5 m, but the electrode wells 111 can be arranged in various shapes without being limited to this.

[0033] Even if the temperature of the soil is raised to 40 to 90°C by an electric heating method or the like, PFOS, PFOA, etc. will not volatilize, and of course they will not decompose. Therefore, conventional technical common sense does not lead to the technical idea of ​​heating the soil to purify PFOS, PFOA, etc. However, the inventors of the present invention came up with the idea of ​​recovering PFOS, PFOA, etc. together with water vapor and groundwater, and came up with the technical idea of ​​heating the soil to recover groundwater. PFOS, PFOA, etc. contained in the pore water of the soil hardly move at normal temperatures, but when the soil temperature rises, water vapor is generated, the volume of water expands, and the viscosity of water decreases, which improves the mobility of the groundwater (pore water) itself, and by recovering this groundwater, the PFOS, PFOA, etc. contained therein can be efficiently recovered. In addition, the solubility of PFOS, PFOA, etc. also increases with increasing temperature, so PFOS, PFOA, etc. can be efficiently recovered in this respect as well. Furthermore, even if PFOS or PFOA exists in the form of a liquid, the fluidity increases, allowing for efficient recovery.

[0034] As described above, the electric heating method allows easy temperature control, and therefore the soil temperature can be raised to a target temperature and maintained at the target temperature. The temperature at which the soil is raised or maintained (hereinafter referred to as the "planned temperature") should be determined in advance based on the type of soil and the normal soil temperature. As a result of various tests conducted by the inventors of the present invention, it has been found that PFOS, PFOA, etc. can be efficiently recovered by setting the planned temperature in the range of 40 to 90°C.

[0035] In order to fully recover PFOS, PFOA, etc., the soil is heated by the soil heating device 110 at a planned temperature for a planned period (for example, several weeks to several months). However, it is quite conceivable that the actual temperature of the heated soil or groundwater may differ from the predicted (or analyzed) temperature. Therefore, it is also possible to apply the actual temperature to the electrode well 111 while observing it. In this case, as shown in FIG. 3, it is preferable to construct a temperature observation well 160 between each electrode well 111 and observe the temperature of the soil or groundwater using this temperature observation well 160. Note that the temperature observation well 160 can also be configured so that the temperature measurement portion is installed at each depth (for example, every 1 m), in which case it is preferable to grasp the depth distribution of the temperature.

[0036] Water vapor containing PFOS, PFOA, etc. (hereinafter, for convenience, referred to as "contaminated water vapor") generated by the soil heating device 110 heating the soil is collected through a well. For example, as shown in FIG. 1, the contaminated water vapor can be collected through a countermeasure well CW constructed in the contaminated target area (hereinafter, simply referred to as the "target area"), or the contaminated water vapor can be collected using an electrode well 111 instead of the countermeasure well CW, or of course, the contaminated water vapor can be collected using both the countermeasure well CW and the electrode well 111. Note that while the soil is heated by the soil heating device 110, the electric heating method used in the present invention does not require a high-temperature heat medium like thermal conduction (heater), so a relatively inexpensive and easily procured polyvinyl chloride pipe (a heat-resistant rigid polyvinyl chloride pipe depending on the heating temperature) can be used as the countermeasure well CW.

[0037] In collecting contaminated water vapor, it is possible to collect the naturally rising water vapor through a vent pipe, or to collect the water vapor by sucking it up using a gas suction device 130. This gas suction device 130 can utilize various conventional vacuum pumps, etc., and is preferably placed on the ground as shown in Figure 1, and sucks up the contaminated water vapor through the vent pipe.

[0038] The physical treatment type in-situ organic fluorine compound purification system 100a can also be configured to include a groundwater pumping device 140 in addition to the gas suction device 130. This groundwater pumping device 140 pumps up (pumps) the "groundwater containing PFOS, PFOA, etc. (hereinafter, for convenience, referred to as "contaminated groundwater")" heated by the soil heating device 110 through a countermeasure well CW constructed in the soil. As the groundwater pumping device 140, a ground-mounted self-priming pump can be used, or if the head is insufficient, a submersible pump installed in the countermeasure well CW as shown in FIG. 1 can be used. However, since a three-phase AC voltage is applied to the countermeasure range to heat the soil, if a submersible pump is used, a motor-driven pump that is prone to malfunction due to the three-phase AC voltage should be avoided, and a compressed air-operated or bladder-type pump should be used.

[0039] The contaminated water vapor collected above ground (or the contaminated water vapor and contaminated groundwater if a groundwater pumping device 140 is provided) is sent to a decomposition treatment device 120 installed above ground, and PFOS, PFOA, and other substances contained in the contaminated water vapor are decomposed by this decomposition treatment device 120. It is advisable to adopt a portable decomposition treatment device 120. As mentioned above, in the field of water treatment, intensive treatment can be carried out using large-scale treatment facilities, but in the field of soil and groundwater contamination, where contaminated sites are scattered, such intensive measures are difficult. If the decomposition treatment device 120 is portable, it can be easily transported and installed (i.e., repurposed), and purification treatment can be carried out flexibly and efficiently at scattered contaminated sites.

[0040] When decomposing PFOS, PFOA, etc., in the decomposition treatment device 120, the collected contaminated water vapor (or the contaminated water vapor and the contaminated groundwater) is liquefied by natural cooling or forced cooling, and the liquid (hereinafter, for convenience, referred to as "contaminated water") is subjected to chemical treatment. Specifically, ozone gas is blown into the contaminated water stored in a water tank or the like, and ultraviolet light (UV: UltraViolet) is further irradiated. At this time, PFOS, PFOA, etc. can be decomposed even if ozone gas and ultraviolet light are applied to the contaminated water at room temperature, but the inventors of the present invention have found that contaminated water at a medium-high temperature (40 to 50°C) is more effective. Therefore, it is preferable to set a predetermined medium-high temperature in advance, heat the cooled contaminated water to the medium-high temperature, or cool the collected contaminated water vapor or contaminated groundwater to the medium-high temperature, blow in ozone gas, and irradiate ultraviolet light.

[0041] The decomposition treatment device 120 may also perform chemical treatment using ozone gas and hydrogen peroxide instead of ozone gas and ultraviolet light. In this case, the collected contaminated water vapor or contaminated groundwater is liquefied by natural or forced cooling, and ozone gas and hydrogen peroxide are blown into the contaminated water.

[0042] The treated water in which PFOS, PFOA, etc. have been decomposed by the decomposition treatment device 120 can be discharged outside the target area (for example, a public water area, etc.) as shown in Fig. 1, or can be condensed and circulated within the target area via the control well CW or electrode well 111. In this case, depending on the conditions of the contaminated site, it is advisable to treat the water in an inorganic fluorine treatment device (hereinafter referred to as a "fluorine removal device") and then discharge the treated water outside the target area, or circulate the treated water within the target area. In this case, the fluorine removal device is naturally provided downstream of the decomposition treatment device 120.

[0043] (Chemical treatment type in-situ purification system for organic fluorine compounds) 4 is a block diagram showing a schematic configuration of the main components of a chemical treatment type in-situ organic fluorine compound remediation system 100b. As shown in this figure, the chemical treatment type in-situ organic fluorine compound remediation system 100b includes a soil heating device 110 (electrode well 111 and power supply device 112) and an agent injection device 150.

[0044] The chemical treatment type in-situ organic fluorine compound remediation system 100b heats the soil using the soil heating device 110 described above, and injects a chemical into the soil or groundwater that has been heated to a predetermined temperature (for example, 40 to 90°C), thereby decomposing PFOS, PFOA, etc. For example, when persulfate is injected as a chemical into heated soil or groundwater, thermally activated persulfate is generated by various reactions such as sulfate radicals in a thermally activated state, and this thermally activated persulfate promotes the decomposition of PFOS, PFOA, etc.

[0045] As shown in FIG. 4, the chemical injection device 150 injects a chemical into soil or groundwater, and is composed of a chemical adjustment tank and a pressure transfer means (such as a pump) for sending the chemical from the adjustment tank. The chemical is a solution of persulfate in water at room temperature (15 to 25°C) (persulfate aqueous solution), and examples of the persulfate used here include sodium persulfate, potassium persulfate, and ammonium persulfate. The reason that the water in which the persulfate is dissolved is at room temperature is that since persulfate does not undergo reactions such as thermal activation at room temperature, dissolving it in room temperature water can prevent the generation of thermally activated persulfate or self-decomposition before it reaches the soil or groundwater, or in other words, dissolving it in room temperature water can send it to the soil or groundwater in the form of persulfate.

[0046] The chemicals pumped by the chemical injection device 150 can be injected into the soil or groundwater through a well. For example, as shown in FIG. 4, the chemicals can be injected through a countermeasure well CW constructed in the target area. Although the soil is heated by the soil heating device 110, the electric heating method used in the present invention does not require a high-temperature heat medium like thermal conduction (heater), so a relatively inexpensive and easily procured polyvinyl chloride pipe (a heat-resistant hard polyvinyl chloride pipe depending on the heating temperature) can be used as the countermeasure well CW. Therefore, the conventional "multi-point injection method using an injection pipe made of polyvinyl chloride pipe (a heat-resistant hard polyvinyl chloride pipe depending on the heating temperature)" can also be adopted. In this case, there is no need to use a steel material for the countermeasure well CW, so there is no concern about metal corrosion due to persulfates.

[0047] Even after the chemical injection, the soil temperature is maintained by the soil heating device 110. As explained in the physical treatment type in-situ organic fluorine compound purification system 100a, the temperature at which the soil is heated and the planned temperature to be maintained may be determined in advance based on the type of soil and the normal ground temperature. As a result of various tests conducted by the inventors of the present invention, it has been found that setting the planned temperature in the range of 40 to 90°C effectively generates thermally activated persulfuric acid, which allows PFOS, PFOA, etc. to be efficiently decomposed. In this case, too, it is preferable to construct a temperature observation well 160 between each electrode well 111 as shown in FIG. 3, and use this temperature observation well 160 to observe the temperature of the soil and groundwater.

[0048] By continuously applying the agent to the soil, the soil and groundwater are maintained at the planned temperature (e.g., 40 to 90°C), and the agent that reaches the soil or groundwater also raises its temperature. As a result, thermally activated persulfate is produced through various reactions, such as sulfate radicals in a thermally activated state, and this thermally activated persulfate promotes the decomposition of PFOS, PFOA, etc.

[0049] 2. In-situ purification method for organic fluorine compounds Next, the method for in-situ purification of organic fluorine compounds of the present invention will be described with reference to the drawings. The method for in-situ purification of organic fluorine compounds of the present invention is a method for purifying soil, etc., using the in-situ purification system for organic fluorine compounds described so far. Therefore, the description overlapping with the description of the in-situ purification system for organic fluorine compounds will be avoided, and only the description specific to the method for in-situ purification of organic fluorine compounds of the present invention will be described. In other words, the description not described here is the same as that described in "1. In-situ purification system for organic fluorine compounds". The method for in-situ purification of organic fluorine compounds of the present invention can be broadly divided into a method using a physical treatment type in-situ purification system 100a for organic fluorine compounds and a method using a chemical treatment type in-situ purification system 100b for organic fluorine compounds, and the physical treatment type and the chemical treatment type can be used together. Below, the embodiments of the case using the physical treatment type in-situ purification system for organic fluorine compounds and the case using the chemical treatment type in-situ purification system for organic fluorine compounds will be described in order.

[0050] (Method using a physical treatment type in-situ purification system for organic fluorine compounds) Fig. 5 is a flow diagram showing the flow of the main steps of the in-situ organic fluorine compound purification method using a physical treatment type in-situ organic fluorine compound purification system 100a. As shown in this figure, first, a control well CW and an electrode well 111 are constructed at appropriate positions within the target area (Step 11 in Fig. 5). This control well CW can be excavated using various conventional construction methods, and various materials including polyvinyl chloride pipes (heat-resistant rigid polyvinyl chloride pipes) can be used.

[0051] Like the countermeasure well CW, the electrode well 111 can be excavated using various conventional construction methods. The electrode wells 111 should be arranged in three or more locations so as to surround the soil of the target area (for example, to form multiple triangles as shown in FIG. 3). After the countermeasure well CW and the electrode well 111 are constructed, a portable decomposition treatment device 120 is installed on the ground, and a temperature observation well 160 is constructed as necessary.

[0052] Once the countermeasure well CW and the electrode well 111 are constructed and the decomposition treatment device 120 is installed, a three-phase AC voltage is applied to the casing of each electrode well 111 by the power supply unit 112 to raise the temperature of the soil (Step 12 in FIG. 5). If a temperature observation well 160 is installed, it is advisable to use the temperature observation well 160 to observe the temperature of the soil and groundwater while raising the temperature of the soil.

[0053] When the soil is heated, the gas suction device 130 collects the contaminated water vapor generated as a result of the temperature increase, and when the groundwater pumping device 140 is provided, the groundwater pumping device 140 collects the heated contaminated groundwater (Step 13 in FIG. 5). The collected contaminated water vapor and contaminated groundwater are cooled to become contaminated water (Step 14 in FIG. 5), and are chemically treated by the decomposition treatment device 120 to decompose PFOS, PFOA, etc. (Step 15 in FIG. 5). In this decomposition treatment device 120, chemical treatment can be performed using ozone gas and ultraviolet light, or chemical treatment can be performed using ozone gas and hydrogen peroxide. When chemical treatment is performed using ozone gas and ultraviolet light, it is preferable to blow ozone gas into the contaminated water while irradiating it with ultraviolet light, while keeping the water at a predetermined medium-high temperature.

[0054] The treated water obtained after being treated by the decomposition treatment device 120 in the decomposition treatment step (after the organic fluorine compounds have been decomposed) is condensed and circulated within the target area through the control well CW or electrode well 111 (Step 16 in FIG. 5). Alternatively, the treated water may be discharged outside the target area (for example, a public water area). In this case, depending on the conditions of the contaminated site, it is preferable to circulate the treated water within the target area after treating it with a fluoride removal device, or to discharge the treated water outside the target area after making it comply with the fluorine discharge standard. Condensing the heated treated water underground is preferable because it reduces heat loss and allows the temperature of the soil and groundwater to be maintained with less electricity.

[0055] The soil is heated by the soil heating device 110 at the planned temperature for a planned period (e.g., several weeks to several months), and when the PFOS, PFOA, etc. in the contaminated water are decomposed by the treatment device 120, the application of the three-phase AC voltage by the power supply device 112 is stopped (Step 17 in FIG. 5). Note that, before stopping the application by the power supply device 112, it is advisable to confirm by inspection or the like that the organofluorine compounds within the target area have been sufficiently purified.

[0056] (Method using a chemical treatment type in-situ purification system for organic fluorine compounds) Figure 6 is a flow diagram showing the flow of the main steps of the in-situ organic fluorine compound purification method using a chemical treatment type in-situ organic fluorine compound purification system 100b. As shown in this figure, first, a control well CW and an electrode well 111 are constructed at appropriate positions within the target area (Step 21 in Figure 6). This control well CW can be excavated using various conventional construction methods, and various materials including polyvinyl chloride pipes (heat-resistant rigid polyvinyl chloride pipes) can be used.

[0057] Like the countermeasure well CW, the electrode well 111 can be excavated using various conventional construction methods. The electrode wells 111 should be arranged in three or more locations so as to surround the soil of the target area (for example, to form multiple triangles as shown in FIG. 3). After the countermeasure well CW and the electrode well 111 are constructed, a chemical injection device 150 is installed on the ground, and a temperature observation well 160 is constructed as necessary.

[0058] Once the control well CW and electrode well 111 are constructed and the chemical injection device 150 is installed, a three-phase AC voltage is applied to the casing of each electrode well 111 by the power supply device 112 to raise the temperature of the soil (Step 22 in FIG. 6). If a temperature observation well 160 is installed, it is advisable to use the temperature observation well 160 to observe the temperature of the soil and groundwater (Step 24 in FIG. 6) while raising the temperature of the soil.

[0059] Once the soil has been heated by the soil heating device 110, the chemical is injected into the soil and groundwater by the chemical injection device 150 (Step 23 in FIG. 6). Note that even after the chemical injection, the soil temperature is maintained by the soil heating device 110.

[0060] The soil is heated by the soil heating device 110 at the planned temperature for a planned period (for example, several weeks to several months), and the chemical is injected by the chemical injection device 150. When PFOS, PFOA, etc. contained in the soil and groundwater are decomposed, the application of the three-phase AC voltage by the power supply device 112 is stopped (Step 24 in FIG. 6). Note that, before stopping the application by the power supply device 112, it is advisable to confirm by inspection or the like that the organofluorine compounds within the target area have been sufficiently purified.

[0061] (Test Results) Figure 7 shows the test results confirming the decomposition effect of the physical treatment type in-situ organic fluorine compound purification system 100a. As shown in this figure, it was confirmed that PFOS and PFOA were decomposed in both cases of chemical treatment using ozone gas and hydrogen peroxide and chemical treatment using ozone gas and ultraviolet light for contaminated water containing PFOS and PFOA. It was also found that the effect was further improved by extending the treatment time and increasing the amount of sodium persulfate added.

[0062] Figure 8 shows the test results confirming the decomposition effect of the chemical treatment type in-situ organic fluorine compound purification system 100b. As shown in this figure, it was confirmed that PFOS and PFOA are decomposed when sodium persulfate is injected into contaminated water at medium to high temperatures (40°C, 60°C). Although not shown in Figure 8, it has been found that the effect is further improved by setting the soil temperature to 60°C and injecting sodium persulfate multiple times (with an interval of about two weeks between injections). [Industrial Applicability]

[0063] The in-situ organic fluorine compound purification system and in-situ organic fluorine compound purification method of the present invention can be used at operational sites (or former operational sites) and illegal dumping sites where organic fluorine compounds such as PFOS and PFOA are manufactured, used, discharged, or by-produced. Considering that the present invention is extremely beneficial for improving the environment in Japan, it can be said to be an invention that can be expected to not only be used industrially but also to make a great contribution to society. [Explanation of symbols]

[0064] 100a: A physical treatment type in-situ purification system for organic fluorine compounds according to the present invention 100b Chemical treatment type in-situ purification system for organic fluorine compounds according to the present invention 110 Soil heating device (for in-situ purification of organic fluorine compounds) 111 (Soil heating device) electrode well 112 Power supply (for soil heating equipment) 120 Decomposition treatment equipment (for in-situ physical treatment of organic fluorine compounds) 130 Gas suction device (for physical treatment type in-situ purification system for organic fluorine compounds) 140 Groundwater pumping device (for physical treatment type in-situ purification system for organic fluorine compounds) 150 Chemical injection device (for in-situ purification system of chemical treatment type organic fluorine compounds) 160 Temperature monitoring well (for in-situ purification of organic fluorine compounds) CW Control Well

Claims

1. A system for in-situ remediation of soil contaminated with organofluorine compounds, comprising: A soil heating device that heats the soil by applying an electric current to three or more electrode wells constructed in the soil and passing the electric current through the soil; a decomposition treatment device that decomposes organic fluorine compounds contained in the contaminated water vapor generated by heating the soil heating device, The decomposition treatment device is a portable type installed on the ground, and decomposes organic fluorine compounds by blowing ozone gas into the contaminated water obtained by cooling the contaminated water vapor and irradiating it with ultraviolet rays. An in-situ purification system for organic fluorine compounds.

2. The decomposition treatment device blows ozone gas into the contaminated water adjusted to a predetermined temperature and irradiates it with ultraviolet light.

2. The in-situ purification system for organic fluorine compounds according to claim 1.

3. A system for in-situ remediation of soil contaminated with organofluorine compounds, comprising: A soil heating device that heats the soil by applying an electric current to three or more electrode wells constructed in the soil and passing the electric current through the soil; a decomposition treatment device that decomposes organic fluorine compounds contained in the contaminated water vapor generated by heating the soil heating device, The decomposition treatment device is a portable type installed on the ground, and decomposes organic fluorine compounds by blowing ozone gas and hydrogen peroxide into the contaminated water obtained by cooling the contaminated water vapor. An in-situ purification system for organic fluorine compounds.

4. The facility is further equipped with a groundwater pumping device for pumping up contaminated groundwater contaminated by organic fluorine compounds from a countermeasure well constructed in the soil, The decomposition treatment device performs treatment on the cooled contaminated water including the contaminated water vapor and the contaminated groundwater.

4. The in-situ purification system for organic fluorine compounds according to claim 1.

5. The present invention further includes a fluorine removal device that treats inorganic fluorine in the treated water discharged from the decomposition treatment device.

5. The in-situ purification system for organic fluorine compounds according to claim 1.

6. 1. A method for in-situ remediation of soil contaminated with organofluorine compounds, comprising: A soil heating step of heating the soil by applying an electric current to three or more electrode wells constructed in the soil; A decomposition process for decomposing organic fluorine compounds contained in the contaminated water vapor generated by heating in the soil heating process, In the decomposition treatment step, a portable decomposition treatment device installed on the ground is used, and ozone gas is blown into the contaminated water obtained by cooling the contaminated water vapor, and ultraviolet light is irradiated to decompose the organic fluorine compounds.

1. A method for in-situ purification of organic fluorine compounds comprising the steps of:

7. 1. A method for in-situ remediation of soil contaminated with organofluorine compounds, comprising: A soil heating step of heating the soil and groundwater by applying an electric current to three or more electrode wells constructed in the soil; A decomposition process for decomposing organic fluorine compounds contained in the contaminated water vapor generated by heating in the soil heating process, In the decomposition treatment step, a portable decomposition treatment device is installed on the ground, and ozone gas and hydrogen peroxide are blown into the contaminated water obtained by cooling the contaminated water vapor to decompose the organic fluorine compounds.

1. A method for in-situ purification of organic fluorine compounds comprising the steps of:

8. The method further includes a groundwater pumping process for pumping up contaminated groundwater contaminated with organic fluorine compounds from a control well constructed in the soil, In the decomposition treatment step, the cooled contaminated water including the contaminated water vapor and the contaminated groundwater is treated.

8. The method for in-situ purification of organic fluorine compounds according to claim 6 or 7.

9. In the decomposition treatment step, the treated water obtained after decomposing the organic fluorine compounds is returned to the soil. The method for in-situ purification of organic fluorine compounds according to any one of claims 6 to 8.

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