Purification method

Abstract

To provide a purification method that is a method for purifying contaminated soil and / or contaminated water containing an organic fluorine compound in an in-situ, and is excellent in purification efficiency.SOLUTION: A purification method that is a method for purifying contaminated soil and / or contaminated water containing an organic fluorine compound in an in-situ includes: injecting wash water to an injection well disposed in the in-situ; and pumping water from a pumping well disposed in the in-situ. The wash water contains micro-nano bubbles, and a temperature of the wash water is higher than a temperature of the in-situ.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a purification method. [Background technology]

[0002] Patent Document 1 discloses a method for purifying oil-contaminated soil in situ, which includes an oil recovery trench formation step of forming an oil recovery trench on the ground surface of the oil-contaminated soil area, a fine-bubble hot water injection step of injecting hot water containing fine bubbles into the oil-contaminated soil to increase the moisture content in the oil-contaminated area, and an oil separation step of causing the oil-contaminated water with the increased moisture content to flow into the oil recovery trench by the fine-bubble hot water, and then separating oil from the oil-contaminated water that has flowed in.

[0003] Patent Document 2 discloses a method for purifying underground soil, in which an activated liquid that activates pollutant-decomposing microorganisms or a purification liquid that decomposes pollutants, in which air bubbles are mixed in, is heated to a temperature higher than the groundwater temperature and injected into an injection well provided underground, thereby sending the activated liquid or purification liquid into the underground soil.

[0004] Patent Document 3 discloses an in-situ purification system for organic fluorine compounds, which is a system for in-situ purification of soil contaminated with organic fluorine compounds, and includes a soil heating device that heats the soil by applying an electric current to three or more electrode wells constructed in the soil to pass the electric current through the soil, and a decomposition treatment device that decomposes organic fluorine compounds contained in contaminated water vapor generated by heating by the soil heating device, the decomposition treatment device being a portable device that is installed on the ground and that decomposes 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-209599 A [Patent Document 2] International Publication No. 2018 / 087995 [Patent Document 3] Patent Publication No. 2022-030560 Summary of the Invention [Problem to be solved by the invention]

[0006] Due to their useful properties such as surface activity, heat resistance, and chemical resistance, organic fluorine compounds have been used in a wide range of applications in manufacturing and industry. In recent years, the ecotoxicity and human toxicity of organic fluorine compounds have been reported, and restrictions on the manufacture and use of organic fluorine compounds have been tightened worldwide. On the other hand, organic fluorine compounds are difficult to decompose, and there is an urgent need to develop technology to purify organic fluorine compounds that have already accumulated in the environment.

[0007] It is against the above background that the present disclosure has been made. An object of the present disclosure is to provide a method for in-situ purification of contaminated soil and / or contaminated water containing organic fluorine compounds, the method having excellent purification efficiency. [Means for solving the problem]

[0008] Specific means for solving the above problems include the following aspects.

[0009] <1> A method for in-situ remediation of contaminated soil and / or contaminated water containing organofluorine compounds, comprising: injecting wash water into the in-situ injection well; and pumping the water from an in-situ pumping well separate from the injection well; The cleaning water contains micro-nano bubbles, The temperature of the wash water is higher than the in-situ temperature. Purification methods. <2> The temperature of the cleaning water is in the range of 35°C to 50°C. <1> The purification method according to claim 1. <3> The cleaning water further contains at least one compound selected from the group consisting of organic solvents, anionic surfactants, cationic surfactants, and nonionic surfactants (excluding organic fluorine compounds). <1> or <2> The purification method according to claim 1. <4> removing organic fluorine compounds from the water pumped from the pumping well; and preparing the cleaning water using water from which the organic fluorine compounds have been removed. <1> ~ <3> 13. The purification method according to claim 12, <5> Removing organic fluorine compounds from the water pumped from the pumping well, Adjusting the temperature of the water pumped from the pumping well to an appropriate temperature; Supplying air bubbles to the water pumped from the pumping well; and collecting foam from the surface of the water pumped from the pumping well. <4> The purification method according to claim 1. <6> Adjusting the temperature of the water pumped from the pumping well to an appropriate temperature includes at least one of heating and keeping warm the water pumped from the pumping well; <5> The purification method according to claim 1. Effect of the Invention

[0010] According to the present disclosure, there is provided a method for in-situ purification of contaminated soil and / or contaminated water containing organofluorine compounds, the method having excellent purification efficiency. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of a purification method according to the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram showing another example of the purification method of the present disclosure. [Diagram 3] FIG. 1 is a schematic diagram showing an example of a foam separation method. [Figure 4] FIG. 2 is a schematic diagram showing another example of a foam separation method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The cleaning method of the present disclosure will be described below. These descriptions and embodiment examples are merely illustrative, and the scope of the cleaning method of the present disclosure is not limited to the illustrative examples.

[0013] In the present disclosure, a numerical range indicated using "~" includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

[0014] In the present disclosure, the term "step" includes not only an independent step, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0015] <Purification method> The purification method of the present disclosure is a method for purifying in situ contaminated soil and / or contaminated water contaminated with an organic fluorine compound. Examples of the contaminated water to be purified include groundwater and lake water.

[0016] The purification method disclosed herein includes injecting wash water into an injection well provided in situ and pumping the wash water from a pumping well provided in situ away from the injection well, wherein the wash water contains micro-nano bubbles and has a temperature higher than the temperature of the in situ.

[0017] In the purification method of the present disclosure, "higher than the temperature in situ" means a temperature higher than the "reference temperature," which is the soil temperature or water temperature in the purification target area before starting the purification method of the present disclosure. Contaminated soil exists, for example, in an area 5 to 20 m deep from the ground. In Japan, the soil temperature at this depth is in the range of approximately 15°C to 17°C. Therefore, when the purification target is contaminated soil, the "reference temperature" is generally a point in the range of 15°C to 17°C in Japan. Hereinafter, water with a temperature higher than the "reference temperature" will be referred to as "hot water."

[0018] The purification method of the present disclosure purifies contaminated soil and / or contaminated water by using warm water containing micro-nano bubbles as cleaning water, injecting the cleaning water into the original location, and then pumping the water. The purification method of the present disclosure is believed to have excellent purification efficiency due to the following mechanisms (1) to (5).

[0019] (1) The use of warm cleaning water increases the molecular mobility of the organic fluorine compounds, making it easier for the organic fluorine compounds to be detached from the object (e.g., soil) to which they are attached. (2) Since the cleaning water is warm water, the solubility of the organic fluorine compounds in the cleaning water is relatively high. (3) Many organic fluorine compounds have surface-active properties, and they gather at the gas-liquid interface of the micro-nano bubbles, stabilizing them. The organic fluorine compounds move with the flow of the cleaning water together with the micro-nano bubbles. (4) The surface tension of water is inversely correlated with the water temperature (i.e., the higher the water temperature, the lower the surface tension of the water). Therefore, when the cleaning water is warm, the organic fluorine compounds tend to gather at the gas-liquid interface of the micro-nano bubbles. (5) Because the rising speed of micro-nano bubbles is slow (for example, a bubble with a diameter of 10 μm in water rises only about 20 cm in one hour), the micro-nano bubbles can travel a long distance horizontally (i.e., far from the injection point) by being carried by the flow of the cleaning water.

[0020] The configuration of the purification method of the present disclosure will be described in detail below.

[0021] [Organofluorine compounds] The organofluorine compounds that the cleaning method of the present disclosure is intended to remove include all known organofluorine compounds and those that will be developed in the future. The organic fluorine compounds to be removed by the purification method of the present disclosure include PFAS (per- and polyfluoroalkyl substances). PFAS is a general term for perfluoroalkyl compounds and polyfluoroalkyl compounds. Representative compounds of PFAS include PFSAs (perfluorosulfonic acids) such as PFOS (perfluorooctane sulfonic acid) and PFHxS (perfluorohexane sulfonic acid), and PFCAs (perfluorocarboxylic acids) such as PFOA (perfluorooctanoic acid) and PFHxA (perfluorohexanoic acid).

[0022] The purification method of the present disclosure preferably comprises collecting soil and / or water from the in-situ site, analyzing the collected soil and / or water, and quantifying the in-situ concentration of organofluorine compounds. Here, the organofluorine compounds whose concentrations are quantified preferably include at least one selected from the group consisting of PFSAs such as PFOS and PFHxS, and PFCAs such as PFOA and PFHxA, and preferably include at least PFOS and PFOA.

[0023] [Cleaning water] The cleaning water is warm water containing micro-nano bubbles. In this disclosure, the term "micro-nano bubbles" encompasses air bubbles on the order of micrometers (microbubbles) and air bubbles on the order of nanometers (nanobubbles).

[0024] The micro-nanobubbles contained in the cleaning water may be only microbubbles, only nanobubbles, or a mixture of microbubbles and nanobubbles. From the viewpoint of purification efficiency, the diameter of the micro-nano bubbles when they are formed is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. The diameter of the micro-nano bubbles when formed is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more.

[0025] There is no restriction on the content of micro-nano bubbles in the cleaning water, and the content of micro-nano bubbles may be set according to the concentration of organic fluorine compounds at the in situ, the volume of the area to be purified, and the like. The content of micro-nano bubbles per 1 L of cleaning water may be set to, for example, 100 to 20000 mL / L, 500 to 15000 mL / L, or 1000 to 10000 mL / L.

[0026] The micro-nano bubble content of the wash water may be constant or variable during injection into the injection well, and may be constant or variable throughout the duration of the purification method of the present disclosure.

[0027] The method for preparing the cleaning water may be a method in which water containing micro-nano bubbles is heated, or a method in which micro-nano bubbles are formed using warm water. Examples of methods for forming micro-nano bubbles include a method in which a gas is fed into water or warm water through fine pores to form micro-nano bubbles, a method in which a supersaturated gas solution is injected into water or warm water and micro-nano bubbles are formed by reducing the pressure, a method in which a solid that dissolves to generate micro-nano bubbles is poured into water or warm water, a method in which water or warm water and a gas are mixed in a nozzle to form micro-nano bubbles by utilizing shear forces caused by turbulent flows, and a method in which a gas is fed into water or warm water while being stirred at high speed to form micro-nano bubbles. The raw gas for the micro-nano bubbles is, for example, air or carbon dioxide.

[0028] Examples of water or warm water for preparing the washing water include groundwater collected from the original location, tap water, and river water. The cleaning water may be artificially heated warm water or may be unheated warm water. For example, if tap water or river water is warm water, the cleaning water can be prepared using the tap water or river water without the need for heating.

[0029] From the viewpoint of improving purification efficiency, the temperature of the washing water is preferably 3° C. or more higher than the reference temperature, more preferably 5° C. or more higher, and even more preferably 8° C. or more higher.

[0030] From the viewpoint of improving purification efficiency, the temperature of the washing water is preferably 18° C. or higher, more preferably 20° C. or higher, even more preferably 25° C. or higher, still more preferably 30° C. or higher, and even more preferably 35° C. or higher. From the viewpoints of the stability of micro-nano bubbles and the heating cost of the raw water, the temperature of the washing water is preferably 80°C or less, more preferably 70°C or less, even more preferably 60°C or less, still more preferably 55°C or less, and even more preferably 50°C or less.

[0031] The temperature of the wash water may be constant or may fluctuate during injection into the injection well, and may be constant or may fluctuate throughout the duration of the purification method of the present disclosure.

[0032] In the purification method of the present disclosure, from the viewpoint of improving the purification efficiency of organic fluorine compounds, it is preferable that the cleaning water contains at least one compound selected from the group consisting of organic solvents, anionic surfactants, cationic surfactants, and nonionic surfactants (excluding organic fluorine compounds).

[0033] Organic solvents are highly miscible with organic fluorine compounds and have the effect of desorbing the organic fluorine compounds adhering to an object (eg, soil) from the object (eg, soil). Examples of the organic solvent include methanol, ethanol, propanol, butanol, acetone, acetonitrile, etc. The organic solvent may be used alone or in combination of two or more kinds.

[0034] The surfactant improves the stability of the micro-nano bubbles in the cleaning water. Examples of the anionic surfactant include sodium dodecyl sulfate, fatty acid salts, polyoxyalkylene alkyl ether acetates, alkyl sulfates, polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkylamide ether sulfates, monoglyceride sulfates, olefin sulfonates, alkanesulfonates, acylated isethionates, acylated amino acids, alkyl phosphates, and polyoxyalkylene alkyl ether phosphates. Examples of the cationic surfactant include benzalkonium chloride, benzethonium chloride, cetylpyridinium chloride, hexadecyltrimethylammonium bromide, and dequalinium chloride. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, glycerin fatty acid esters, propylene glycol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan tetraoleate, polyoxyethylene polyoxypropylene glycol, polyoxyethylene polyoxypropylene alkyl ethers, polyethylene glycol fatty acid esters, polyoxyethylene castor oil, polyglycerin fatty acid esters, and alkyl glycosides. The surfactant may be used alone or in combination of two or more kinds.

[0035] [Example of the purification method] The purification method of the present disclosure will be further described below with reference to the drawings. The embodiment described below is an example of the purification method, and the purification method of the present disclosure is not limited thereto.

[0036] FIG. 1 is a schematic diagram showing the configuration of an embodiment in which water is not circulated (referred to as the "first embodiment"). FIG. 2 is a schematic diagram showing the configuration of an embodiment in which water is circulated (referred to as the "second embodiment"). 1 and 2, the arrows indicate the flow of water.

[0037] The contaminated soil 6 is soil contaminated by organic fluorine compounds. The contaminated soil 6 is in an aquifer. In the first and second types, the contaminated soil 6 is purified by utilizing water flowing through the aquifer.

[0038] In the first and second forms, the cleaning solution injected into the injection well 1 is sent from the injection well 1 to the contaminated soil 6, and while flowing through the contaminated soil 6, it causes the organofluorine compounds to desorb from the contaminated soil 6. The organofluorine compounds desorbed from the contaminated soil 6 gather at the gas-liquid interface of the micro-nano bubbles contained in the cleaning solution, and move with the water flow together with the micro-nano bubbles.

[0039] The first form comprises injecting wash water into an injection well 1 and pumping it from a pumping well 2. The first form further comprises treating the groundwater pumped from the pumping well 2 with an organic fluorine compound removal device 5 to remove organic fluorine compounds, and discharging the groundwater from which the organic fluorine compounds have been removed. Note that the first form does not necessarily have to treat the groundwater pumped from the pumping well 2 with an organic fluorine compound removal device 5 to remove organic fluorine compounds, but it is preferable that it does. It is sufficient that the organic fluorine compound removal device 5 is capable of removing at least a portion of the organic fluorine compounds.

[0040] In the first embodiment, the wash water injected into the injection well 1 is prepared by heating tap water with a heater 3 and adding micro-nano bubbles to the heated tap water with a micro-nano bubble supply device 4. Here, river water may be used instead of tap water.

[0041] The second form includes injecting wash water into injection well 1 and pumping it from pumping well 2. The second form further includes treating the groundwater pumped from pumping well 2 in organic fluorine compound removal device 5 to remove organic fluorine compounds, and preparing wash water using a part or all of the water from which the organic fluorine compounds have been removed as a raw material. It is sufficient for organic fluorine compound removal device 5 to be able to remove at least a part of the organic fluorine compounds.

[0042] In the second embodiment, the wash water that is initially injected into the injection well 1 is prepared by either (i) or (ii) below. (i) Tap water is heated by a heating device 3, and the heated tap water is made to contain micro-nano bubbles by a micro-nano bubble supplying device 4. Here, river water may be used instead of tap water. (ii) Treating groundwater pumped from a pumping well 2 with an organic fluorine compound removal device 5 to remove organic fluorine compounds, heating the groundwater from which the organic fluorine compounds have been removed with a heating device 3, and adding micro-nano bubbles to the heated groundwater with a micro-nano bubble supplying device 4.

[0043] In the first and second embodiments, the amount of washing water injected is not limited. The amount of washing water injected per hour in each injection well 1 may be set to, for example, 0.1 to 50 L / min, 0.5 to 30 L / min, or 1 to 20 L / min.

[0044] The injection well 1 is installed in the area to be purified, at a depth that reaches the aquifer. A temperature sensor is placed inside the injection well 1, and the temperature of the washing water flowing through the injection well 1 is constantly or occasionally monitored. The washing water may be injected into the injection well 1 continuously or intermittently. The injection well 1 may be one or more.

[0045] The pumping well 2 is installed in the purification area at a location away from the injection well 1 and downstream of the groundwater flow from the injection well 1, at a depth that reaches the aquifer. A pump is placed on the top of the pumping well 2, and groundwater is pumped from the pumping well 2 by driving the pump. Pumping from the pumping well 2 may be performed continuously or intermittently. There may be one or more pumping wells 2.

[0046] In the first and second embodiments, a water impermeable wall may be provided surrounding the area to be purified, in which case the injection well 1 and the pumping well 2 are installed within the area surrounded by the water impermeable wall.

[0047] The heating device 3 is provided upstream of the injection well 1. A heating means such as a heater is disposed inside the heating device 3, and the heating means operates according to the temperature monitored by a temperature sensor installed inside the injection well 1. When the temperature monitored by the temperature sensor is isothermal or lower than a reference temperature, the heating means operates to heat the water. When the temperature monitored by the temperature sensor is higher than the reference temperature, the heating means does not need to operate, but may operate to raise the water temperature to a more suitable temperature.

[0048] The micro-nano bubble supplying device 4 is provided upstream of the injection well 1. The micro-nano bubble supplying device 4 may be provided upstream of the heating device 3, downstream of the heating device 3, or in parallel with the heating device 3.

[0049] A micro-nano bubble forming means is disposed inside the micro-nano bubble supplying device 4. The micro-nano bubble forming means is, for example, a means for feeding gas into water through fine pores, a means for stirring water at high speed while feeding gas into the water, or a means for mixing water and gas in a nozzle to generate a turbulent flow.

[0050] Upstream of the injection well 1, an organic solvent and / or a surfactant other than an organic fluorine compound may be added to the washing liquid.

[0051] The organic fluorine compound removal device 5 is a device that removes at least a portion of the organic fluorine compounds contained in the pumped groundwater, and is provided downstream of the pumping well 2. Methods for removing organic fluorine compounds from groundwater in the organic fluorine compound removal device 5 include, for example, rendering the organic fluorine compounds harmless, precipitating the organic fluorine compounds, vaporizing and degassing the organic fluorine compounds, and foam separation of the organic fluorine compounds.

[0052] In the first and second embodiments, examples of the foam separation method when the organic fluorine compound removal device 5 is a foam separation device include the following foam separation method (A) and foam separation method (B). From the viewpoint of excellent purification efficiency, the foam separation method (A) is preferred.

[0053] Foam separation method (A): A foam separation method comprising adjusting the temperature of pumped water to an appropriate temperature, supplying air bubbles to the pumped water, and recovering bubbles from the surface of the pumped water.

[0054] Foam separation method (B): A foam separation method comprising storing pumped water and recovering foam from the surface of the pumped water. The pumped water contains bubbles derived from the micro-nano bubbles in the washing water, and the foam separation method (B) utilizes the fact that these bubbles rise to the surface and form foam on the water surface. The foam contains concentrated organic fluorine compounds.

[0055] The foam separation method (A) will be described in detail below. In the following description, the "water to be treated" refers to the "water pumped from a pumping well."

[0056] <Foam separation method (A)> The foam separation method (A) is Adjusting the temperature of the water to be treated to an appropriate temperature (referred to as the "temperature adjustment process"); Supplying air bubbles to the water to be treated (referred to as the "air bubble supplying step"); and recovering foam from the surface of the water to be treated (referred to as the "foam recovery step").

[0057] The foam separation method (A) is not limited to the first and second embodiments described above, and can be applied to the purification method of the present disclosure. An example of an embodiment of the purification method of the present disclosure includes removing organic fluorine compounds from water pumped from a pumping well, and the removal of organic fluorine compounds from the water pumped from the pumping well is carried out by a foam separation method (A).

[0058] The mechanism by which the foam separation method (A) has excellent purification efficiency is presumed to be as follows. Since the surface tension of water is inversely correlated with the water temperature (i.e., the higher the water temperature, the lower the surface tension of water), the higher the temperature of the water to be treated, the more likely it is that organic fluorine compounds will gather at the gas-liquid interface of the bubbles. On the other hand, the higher the temperature of the water to be treated, the greater the mobility of the molecules around the gas-liquid interface of the bubbles, and the gas that constitutes the bubbles expands, making the bubbles unstable. The foam separation method (A) stabilizes bubbles and collects a large amount of organic fluorine compounds in the bubbles by adjusting the temperature of the water to be treated to an appropriate temperature, resulting in excellent purification efficiency.

[0059] In the foam separation method (A), the order of each step is not limited. In one embodiment, the temperature adjustment step is performed before the air bubble supplying step. In one embodiment, the temperature adjustment step is started before the air bubble supplying step and is continued during the air bubble supplying step. In one embodiment, the air bubble supplying step and the foam collecting step are performed in parallel. In one embodiment, the air bubble supplying step is stopped, and then the foam collecting step is continued. In one embodiment, the temperature adjustment step, the air bubble supply step, and the foam recovery step are continuously performed while circulating a part or all of the water to be treated. In one embodiment, a set of a temperature adjustment step, an air bubble supply step, and a foam recovery step is repeated multiple times.

[0060] Each step of the foam separation method (A) will be described in detail below.

[0061] [Temperature control process] The temperature adjustment step includes, for example, at least one of heating and keeping the water to be treated warm. The water to be treated is heated or kept warm by treating or leaving the water to be treated until it reaches an appropriate temperature.

[0062] Heating the water to be treated may be achieved by artificially heating the water to be treated, or by allowing the temperature of the water to be treated to rise naturally. For example, the water to be treated may be stored until the temperature of the water to be treated reaches an appropriate range. Keeping the water to be treated warm may involve artificially heating the water to be treated, or may involve carrying out foam separation while maintaining the temperature of the water to be treated within an appropriate range in a water tank having heat retention capabilities.

[0063] The temperature of the water to be treated is preferably as high as possible, from the viewpoint that the surface tension of water is relatively low and organic fluorine compounds tend to collect at the gas-liquid interface of the bubbles, and is preferably 18°C ​​or higher, more preferably 20°C or higher, even more preferably 25°C or higher, even more preferably 30°C or higher, and even more preferably 35°C or higher. From the viewpoint of bubble stability, the temperature of the water to be treated is preferably 80°C or less, more preferably 70°C or less, even more preferably 60°C or less, still more preferably 55°C or less, and even more preferably 50°C or less.

[0064] The temperature of the water to be treated may be constant or may vary while the foam separation method (A) is being carried out.

[0065] The temperature adjustment step preferably includes measuring the temperature of the water to be treated. An example of an embodiment of the temperature adjustment step includes measuring the temperature of the water to be treated, and treating or leaving the water to be treated depending on the temperature of the water to be treated determined by the temperature measurement. An example of an embodiment of the temperature adjustment process includes measuring the temperature of the water to be treated, and includes at least one of heating and keeping the water to be treated warm depending on the temperature of the water to be treated determined by the temperature measurement.

[0066] The water to be treated is water pumped from a pumping well and contains the wash water injected at the original site. The wash water is warm water, but the temperature of the water pumped from the pumping well is usually lower than that of the wash water and is approximately the same as the temperature at the original site. The temperature at the original site is in the range of approximately 15°C to 17°C for soil temperatures at a depth of 5 to 20 m below the ground in Japan. Therefore, the temperature adjustment step usually includes heating the water to be treated. Heating the water to be treated may be done by artificially heating the water to be treated, or by allowing the temperature of the water to be treated to rise naturally. For example, the water to be treated may be stored until the temperature of the water to be treated reaches an appropriate range.

[0067] [Air bubble supply process] The air bubbles may be supplied continuously or intermittently.

[0068] Examples of methods for supplying bubbles include a method of feeding gas into the water to be treated through micropores to form bubbles, a method of injecting a supersaturated gas solution into the water to be treated and forming bubbles by reducing the pressure, a method of introducing a solid that dissolves and generates bubbles into the water to be treated, a method of mixing the water to be treated and a gas in a nozzle and forming bubbles by utilizing the shear force caused by turbulence, a method of stirring the water to be treated at high speed while feeding gas into the water to be treated, etc. Water containing bubbles may be prepared using a relatively small amount of water other than the water to be treated and gas, and the water containing bubbles may be injected into the water to be treated. The source gas for the bubbles is, for example, air or carbon dioxide.

[0069] The size of the bubbles may be on the order of centimeters, millimeters, micrometers, or nanometers, or may be a mixture of these.

[0070] The air bubbles are preferably micro-nano bubbles. The micro-nano bubbles may be only microbubbles, only nanobubbles, or a mixture of microbubbles and nanobubbles. In the foam separation method (A), the diameter of the micro-nano bubbles when formed is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less, from the viewpoint of purification efficiency. In the foam separation method (A), the diameter of the micro-nano bubbles when formed is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more.

[0071] The amount of air bubbles to be supplied is not limited and may be set depending on the concentration of the organic fluorine compounds contained in the water to be treated, the volume of the water to be treated, the foam recovery speed, and the like. For example, when purifying water to be treated while continuously supplying it to a foam separation device, the supply amount of air bubbles (mL / min) per unit supply amount (1 L / min) of water to be treated may be set to 100 to 20,000 mL / min, 500 to 15,000 mL / min, or 1,000 to 10,000 mL / min. The amount of foam dispensed may be constant or may vary during the foam dispense step.

[0072] [Foam recovery process] Examples of the method for collecting the foam include a method of sucking the foam, a method of letting the foam flow out together with a part of the water to be treated, etc. Foam collection may be performed continuously or intermittently.

[0073] The collected foam contains concentrated organic fluorine compounds. It is desirable to detoxify the collected foam and dispose of it appropriately. The treated water, in which the concentration of organic fluorine compounds has been reduced through the foam recovery process, is, for example, discharged into a river or the sea, poured onto soil, or used as industrial water. The treated water in which the concentration of organic fluorine compounds has been reduced through the foam recovery step may be used as a raw material for the cleaning liquid used in the purification method of the present disclosure.

[0074] [Other processes] The foam separation method (A) preferably includes analyzing the water to be treated and quantifying the concentration of organic fluorine compounds contained in the water to be treated (organic fluorine compound quantification step). Here, the organic fluorine compounds whose concentrations are quantified preferably include at least one selected from the group consisting of PFSAs such as PFOS and PFHxS, and PFCAs such as PFOA and PFHxA, and preferably include at least PFOS and PFOA.

[0075] The organic fluorine compound quantitative determination step is preferably performed before the temperature adjustment step, the air bubble supply step, and the foam recovery step, and is preferably performed before the air bubble supply step is stopped.

[0076] The foam separation method (A) preferably includes adding at least one surfactant selected from the group consisting of anionic surfactants, cationic surfactants, and nonionic surfactants (excluding organic fluorine compounds) to the water to be treated (surfactant addition step). The surfactant improves the stability of air bubbles in the water and foam on the water surface.

[0077] Examples of the anionic surfactant include sodium dodecyl sulfate, fatty acid salts, polyoxyalkylene alkyl ether acetates, alkyl sulfates, polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkylamide ether sulfates, monoglyceride sulfates, olefin sulfonates, alkanesulfonates, acylated isethionates, acylated amino acids, alkyl phosphates, and polyoxyalkylene alkyl ether phosphates. Examples of the cationic surfactant include benzalkonium chloride, benzethonium chloride, cetylpyridinium chloride, hexadecyltrimethylammonium bromide, and dequalinium chloride. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, glycerin fatty acid esters, propylene glycol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan tetraoleate, polyoxyethylene polyoxypropylene glycol, polyoxyethylene polyoxypropylene alkyl ethers, polyethylene glycol fatty acid esters, polyoxyethylene castor oil, polyglycerin fatty acid esters, and alkyl glycosides. The surfactant may be used alone or in combination of two or more kinds.

[0078] In one embodiment of the foam separation method (A), the surfactant addition step is carried out before the air bubble supply step. In one embodiment of the foam separation method (A), the surfactant addition step is continued during the air bubble supply step.

[0079] [Example of foam separation method (A)] Next, the foam separation method (A) will be further described with reference to the drawings. The embodiment described below is one example of the foam separation method (A), and the foam separation method (A) is not limited thereto.

[0080] 3 and 4 are schematic diagrams showing an example of the foam separation method (A). A foam separation apparatus 10A shown in FIG. 3 is a foam separation apparatus including a treatment tank 12, a temperature adjustment device 14, an air bubble supply device 16A, and a foam recovery tank 18. The foam separation apparatus 10B shown in FIG. 4 is a foam separation apparatus including a treatment tank 12, a temperature adjustment device 14, an air bubble supply device 16B, and a foam recovery tank 18.

[0081] In the first and second embodiments described above, when the foam separation device 10A or 10B is arranged as the organic fluorine compound removal device 5, the foam separation devices 10A and 10B may each be provided with a mechanism for injecting warm water containing micro-nano bubbles prepared by the micro-nano bubble supply device 4 into the treatment tank 12 without providing the air bubble supply devices 16A and 16B, respectively.

[0082] The treatment tank 12 is a tank for storing the water to be treated 22. The water to be treated 22 may be poured into and discharged from the treatment tank 12 by a batch method or a flow method. The treatment tank 12 may be equipped with an agitation means for agitating the water to be treated 22, a heat-retaining jacket for maintaining the temperature of the water to be treated 22, a temperature sensor for measuring the temperature of the water to be treated 22, and the like.

[0083] The temperature adjustment device 14 is provided upstream of the water injection section of the treatment tank 12 as shown in FIGS. A temperature sensor and heating means are arranged inside the temperature adjustment device 14. The heating means operates or does not operate depending on the temperature of the water to be treated 22 monitored by the temperature sensor. If the temperature of the water to be treated 22 monitored by the temperature sensor is not appropriate, the heating means operates to heat the water to be treated 22. If the temperature of the water to be treated 22 monitored by the temperature sensor is appropriate, the heating means does not operate.

[0084] The air bubble supplying device 16A is provided at the bottom of the treatment tank 12 as shown in FIG. An air bubble generating means is disposed inside the air bubble supplying device 16A. The air bubble generating means is, for example, a means for feeding gas into water through fine pores. The air fed into the air bubble supplying device 16A becomes air bubbles 24 and is fed to the water 22 to be treated.

[0085] The air bubble supplying device 16B is provided at the bottom of the treatment tank 12 as shown in FIG. An air bubble forming means is disposed inside the air bubble supplying device 16B. The air bubble forming means is, for example, a means for mixing water and gas in a nozzle and forming air bubbles by utilizing shear force caused by turbulent flow, or a means for forming air bubbles by feeding gas into water and stirring the water at high speed. The water used by the air bubble forming means to form bubbles is a part of the water to be treated 22. Water containing air bubbles 24 is prepared inside the air bubble supplying device 16B, and the water containing air bubbles 24 is supplied to the water to be treated 22 stored inside the treatment tank 12. The water used by the bubble forming means to form bubbles may be tap water or a portion of the water drained from the treatment tank 12, but it is preferable that it be a portion of the water to be treated 22 from the viewpoint of not diluting the concentration of organic fluorine compounds in the water to be treated 22 stored inside the treatment tank 12.

[0086] The foam collection tank 18 is a tank that stores foam 26 collected from the water surface of the water to be treated 22. Inside the foam collection tank 18, a means for rendering the foam 26 harmless (for example, a high-temperature heating means) may be disposed.

[0087] Water to be treated 22 is poured into the temperature adjustment device 14, and its temperature is adjusted by the temperature adjustment device 14. The temperature-adjusted water to be treated 22 is poured into the treatment tank 12 and stored therein. Air bubbles 24 are supplied to the water to be treated 22 stored inside the treatment tank 12 from the air bubble supply device 16A or 16B. The air bubbles 24 supplied to the water to be treated 22 rise in the water to be treated 22. While the air bubbles 24 rise, organic fluorine compounds adhere to the gas-liquid interface of the air bubbles 24. The air bubbles 24 rise to the water surface of the water to be treated 22 and form foam 26. The foam 26 contains a high concentration of organic fluorine compounds. The foam 26 is collected from the surface of the water to be treated 22. The collected foam 26 is stored in the foam collection tank 18 and, preferably, is rendered harmless and then appropriately disposed of. The water to be treated 22 with the reduced concentration of organic fluorine compounds is discharged from the treatment tank 12 . The water to be treated 22 in which the concentration of organic fluorine compounds has been reduced may be used as a raw material for a cleaning liquid used in the purification method of the present disclosure.

[0088] A surfactant other than an organic fluorine compound may be added to the water to be treated 22. The surfactant may be added, for example, to the water to be treated 22 stored inside the treatment tank 12, to the water to be treated 22 upstream of the temperature adjustment device 14, or to the water to be treated 22 inside the temperature adjustment device 14.

[0089] A configuration may be adopted in which a plurality of foam separation devices 10A or 10B are connected together, and wastewater from a first foam separation device 10A or 10B is poured into a second foam separation device 10A or 10B. The water to be treated 22 is purified in stages while flowing from the most upstream foam separation device 10A or 10B to the most downstream foam separation device 10A or 10B. EXAMPLES

[0090] The purification method of the present disclosure will be specifically described below with reference to examples, but the purification method of the present disclosure is not limited to the following examples.

[0091] <Example 1> In order to clarify the effect of temperature on the purification of organofluorine compounds, soil washing was carried out according to the following steps (1) to (7).

[0092] (1) Soil confirmed to contain PFOA was collected from the in-situ site. (2) Approximately 380 g (approximately 200 mL) of the soil from (1) was packed into a glass column with an inner diameter of 30 mm and a length of 300 mm. Glass beads were packed into the upper and lower parts of the column to a length of 10 mm. (3) The column from (2) was placed in a thermostatic bath at a temperature of 20°C, 35°C, or 50°C. (4) Ion-exchanged water adjusted to the same temperature as the thermostatic bath was pumped from the bottom to the top of the column. The amount of water passed was about 1700 mL, which is equivalent to 8.8 times the soil volume and 35 times the soil pore volume, and the time required for water passage was 45 to 49 hours. (5) The columns were disassembled, the soil was removed, and the whole was mixed homogeneously, after which a small amount was taken for analysis. (6) The soil sampled for analysis was air-dried, the soil clods and aggregates were crushed, and then passed through a 2 mm mesh sieve. The soil that passed through the sieve was mixed with pure water at a weight-to-volume ratio of 10%, and shaken at room temperature and normal pressure at approximately 200 times per minute for 6 hours in a shaker. The supernatant after shaking was filtered through a filter with a pore size of 0.45 μm, and the filtrate was used as the test liquid. (7) The PFOA concentration in the test solution, i.e., the amount of PFOA leaching from the soil, was measured using a liquid chromatography tandem mass spectrometry (LC-MS / MS). The measurement results are shown in Table 1.

[0093] [Table 1]

[0094] Washing at 20°C reduced the amount of PFOA leaching from the soil to approximately 2.3%. Washing at 35°C reduced the amount of PFOA leaching from the soil to approximately 0.8%. Washing at 50°C reduced the amount of PFOA leaching from the soil to approximately 0.1%. The higher the temperature in the range of 20℃~50℃, the higher the PFOA removal rate.

[0095] <Example 2> In order to clarify the effect of temperature on foam separation of an organic fluorine compound, foam separation was carried out according to the following procedures (1) to (9).

[0096] (1) PFOS or PFOA was added to ion-exchanged water to prepare a PFOS solution and a PFOA solution with a concentration of 1 mg / L. The solution was further diluted with ion-exchanged water to prepare a PFOS solution and a PFOA solution with a concentration of 5 μg / L, which was used as the water to be treated. (2) Sodium dodecyl sulfate (SDS) was added to ion-exchanged water to prepare an SDS solution with a concentration of 10 g / L. (3) A heating device with a thermostat was installed in a square polypropylene tank. An overflow-type protein skimmer (Kamihata Fish Farm Co., Ltd., product name: Kaido Daruma) was fixed to the edge of the tank, and the protein skimmer's intake pipe was inserted into the tank, forming a circulating foam separation device in which water circulates between the tank and the protein skimmer. (4) 16 L of water to be treated was placed in the water tank. A heating device with a thermostat was operated to raise and maintain the temperature of the water to be treated in the water tank at 20°C, 35°C, or 50°C. (5) 10 mL of an SDS solution with a concentration of 10 g / L was added to the water to be treated in the tank, and the whole was stirred slowly without creating bubbles. (6) The protein skimmer was operated to start circulating the water to be treated and bubbling by supplying air. The circulation rate of the water to be treated was 6 L / min, and the amount of air supplied was about 2 L / min. (7) The entire amount of foam from the water surface of the protein skimmer was collected from 10 minutes to 30 minutes after the protein skimmer started operating. (8) The weight of the collected foam was measured, and after mixing until homogeneous, a small amount was taken for analysis. (9) The PFOS or PFOA concentrations in the foam samples were measured using a liquid chromatography tandem mass spectrometer (LC-MS / MS). The measurement results are shown in Table 2.

[0097] The "initial concentration in the treated water" in Table 2 refers to the PFOS or PFOA concentration measured by LC-MS / MS in the treated water sampled from the tank after (5) and before (6) above.

[0098] [Table 2]

[0099] The higher the temperature in the range of 20℃ to 50℃, the higher the PFOS concentration in the foam. The higher the temperature in the range of 20℃ to 50℃, the higher the PFOA concentration in the foam. The removal efficiency of organic fluorine compounds was higher at higher temperatures in the range of 20℃ to 50℃. [Explanation of symbols]

[0100] 1. Injection well 2. Pumping wells 3 Warming device 4. Micro-nano bubble supply device 5. Organic fluorine compound removal equipment 6. Contaminated Soil

[0101] 10 Foam separator 12 Treatment tank 14 Temperature control device 16A Air bubble supply device 16B Air bubble supply device 18 Foam collection tank 22 Untreated water 24 Bubbles 26 Foam

Claims

1. A method for in-situ remediation of contaminated soil and / or contaminated water containing organofluorine compounds, comprising: injecting wash water into the in-situ injection well; and pumping the water from an in-situ pumping well separate from the injection well; The cleaning water contains micro-nano bubbles, The temperature of the wash water is higher than the in-situ temperature. Purification methods.

2. The method of claim 1, wherein the temperature of the wash water is in the range of 35°C to 50°C.

3. 2. The cleaning method according to claim 1, wherein the cleaning water further contains at least one compound selected from the group consisting of organic solvents, anionic surfactants, cationic surfactants, and nonionic surfactants (excluding organic fluorine compounds).

4. removing organic fluorine compounds from the water pumped from the pumping well; and preparing the cleaning water using water from which the organic fluorine compounds have been removed. The purification method according to any one of claims 1 to 3.

5. Removing organic fluorine compounds from the water pumped from the pumping well, Adjusting the temperature of the water pumped from the pumping well to an appropriate temperature; Supplying air bubbles to the water pumped from the pumping well; and collecting foam from the surface of the water pumped from the pumping well. The purification method according to claim 4.

6. 6. The purification method of claim 5, wherein bringing the temperature of the water pumped from the pumping well to a suitable temperature includes at least one of heating and keeping warm the water pumped from the pumping well.

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