Method for estimating removal rate of organic fluorine compound, method for treating water to be treated, and apparatus for treating water to be treated

Abstract

To provide a method for estimating a removal rate of an organic fluorine compound, capable of estimating the amount of organic fluorine compounds contained in water to be treated in real time and in a short time, a method for treating water to be treated, and an apparatus for treating water to be treated.SOLUTION: There is provided a method for estimating a removal rate of an organic fluorine compound, for estimating a trend in a removal rate of an organic fluorine compound in a foam separation treatment method for separating the organic fluorine compound contained in water to be treated from the water to be treated, in which when gas is fed into the water to be treated to which a surfactant has been added, a concentration of the surfactant in the water to be treated is measured, and a reduction rate of the organic fluorine compound in the water to be treated is predicted based on a relation between the surfactant and the organic fluorine compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for estimating a removal rate of an organic fluorine compound, a method for treating water to be treated, and an apparatus for treating water to be treated. [Background technology]

[0002] Currently, environmental pollution problems caused by perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), which are classified as fluorinated organic compounds (PFAS), are becoming apparent. PFOS and PFOA are used in large quantities and over a wide range of applications, such as in firefighting foams, and restrictions on these substances have begun both domestically and internationally. The principle of firefighting foam is to block the air needed for combustion with foam. Firefighting foams contain surfactants.

[0003] PFOS / PFOA, the main components of firefighting foam, and PFHxS, which has been used as an alternative, have a structure that has a "hydrophilic group" that has the property of being compatible with water and a "hydrophobic group" that has the property of being compatible with oil. These components behave as surfactants in water. Surfactants have the property of concentrating at the air-water interface. Taking advantage of this property, in the water treatment field, a method called "foam fractionation" is used in which air is pumped into water to generate multiple bubbles (air-water interface), and the surfactants concentrated at the interface are collected as foam.

[0004] For example, Patent Document 1 describes a system in which an air pipe is installed in an in-situ purification well, and a foam layer is formed on the groundwater surface by injecting air into the groundwater, and the foam is then collected in an aboveground gas-liquid separation tank by a foam collection device. In the technology described in Patent Document 1, whether foam separation is being performed properly is determined by directly sampling groundwater in the in-situ purification well and directly measuring the PFOS / PFOA / PFHxS concentrations.

[0005] However, the measurement method for PFOS / PFOA must comply with the notification issued by the Director-General of the Water and Air Environment Bureau of the Ministry of the Environment, "Environmental Water and Environment Bureau No. 2005281, Environment and Water Bureau No. 2005282, Appendix 2, Attachment 1 (May 28, 2020)" (see Non-Patent Document 1), and the pre-processing and analytical procedures are complicated, so the current situation is that measurements take several days (or several weeks at public analytical institutions).

[0006] It is also known that adding a surfactant (sodium dodecyl sulfate: hereinafter referred to as "SDS") as a "foaming agent" is effective in achieving effective foam generation and separation of the contained organic fluorine compounds (see Non-Patent Document 2).

[0007] Furthermore, in order to perform water treatment continuously, it is necessary to observe the water quality in real time. Patent Documents 2 and 3 disclose known treatment systems for water containing organic fluorine compounds. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2023-50657 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0322951 [Patent Document 3] Japanese Patent Application Laid-Open No. 2024-17890 [Non-patent literature]

[0009] [Non-Patent Document 1] Regarding the enforcement of environmental standards for the protection of human health related to water pollution (Notice), Kansui-Daisui-hatsu No. 2005281, Kansui-Daisui-hatsu No. 2005282, May 28, 2020 [Non-patent document 2] Effect of different co-foaming agents on PFAS removal from the environment by foam fractionation,Water Research (2023),Vol. 230-119532 Summary of the Invention [Problem to be solved by the invention]

[0010] In conventional PFOS / PFOA measurement methods, when purifying groundwater using foam separation, the groundwater to be treated contains almost no surfactant components, so even if air was blown directly into it, a stable foam could not be maintained above the groundwater surface. Furthermore, the inventions described in Patent Documents 2 and 3 do not include any means for checking the water treatment status for organic fluorine compounds.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide a method for estimating the removal rate of organic fluorine compounds, which can estimate the amount of organic fluorine compounds contained in the water to be treated in real time and within a short period of time, a method for treating the water to be treated, and an apparatus for treating the water to be treated. [Means for solving the problem]

[0012] The present invention has the following aspects. [1] A foam separation treatment method for separating organic fluorine compounds contained in water to be treated from the water to be treated, comprising: a method for estimating a trend in the removal rate of the organic fluorine compounds, the method comprising: a prediction step of measuring the concentration of the surfactant in the water to be treated when gas is fed into the water to be treated to which a surfactant has been added, and predicting the reduction rate of the organic fluorine compounds in the water to be treated based on the relationship between the surfactant and the organic fluorine compounds. [2] The method for estimating the removal rate of an organic fluorine compound according to [1], wherein the surfactant is sodium dodecyl sulfate. [3] A method for treating water to be treated, which separates organic fluorine compounds contained in the water to be treated from the water to be treated, comprising: a recovery step of adding a surfactant to the water to be treated, then feeding gas into the water to generate bubbles, concentrating the surfactant and the organic fluorine compound at the air-water interface of the bubbles to generate foam, and recovering the foam near the water surface of the water to be treated; A method for treating water to be treated, comprising a stopping step of measuring the concentration of the surfactant in the water to be treated and stopping the supply of gas to the water to be treated when the concentration of the surfactant in the water to be treated becomes zero. [4] A water treatment device for separating organic fluorine compounds contained in the water to be treated from the water to be treated, a storage means for storing the water to be treated; adding means for adding a surfactant to the water to be treated in the storage means; a bubble generating means for generating bubbles by feeding gas into the water to be treated in the storage means to which a surfactant has been added; a recovery means for recovering foam in which the surfactant is concentrated at the air-water interface of the bubbles; a measuring means for measuring the concentration of the surfactant in the water to be treated in the storage means; a prediction means for measuring the concentration of the surfactant in the water to be treated when gas is fed into the water to be treated to which the surfactant has been added, and predicting the reduction rate of the organic fluorine compounds in the water to be treated based on the relationship between the surfactant and the organic fluorine compounds. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for estimating the removal rate of organic fluorine compounds, which can estimate the amount of organic fluorine compounds contained in the water to be treated in real time and in a short time, a method for treating the water to be treated, and an apparatus for treating the water to be treated. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a diagram schematically illustrating a treatment apparatus for water to be treated according to an embodiment of the present invention. [Figure 2] FIG. 10 is a graph showing the change in concentration of sodium dodecyl sulfate in a test solution over time when gas is pumped into the test solution containing sodium dodecyl sulfate in an experimental example. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Method for estimating the removal rate of organic fluorine compounds] A method for estimating the removal rate of organic fluorine compounds according to one embodiment of the present invention is a foam separation treatment method for separating organic fluorine compounds contained in water to be treated from the water to be treated, and is a method for estimating the trend of the removal rate of the organic fluorine compounds, the method comprising: a prediction step of measuring the concentration of the surfactant in the water to be treated when gas is fed into the water to be treated to which a surfactant has been added; and predicting the reduction rate of the organic fluorine compounds in the water to be treated from the relational equation based on the relationship between the surfactant and the organic fluorine compounds.

[0016] "Decision process" The method for estimating the removal rate of organic fluorine compounds of this embodiment may include a determination step of investigating the relationship between the concentration of the surfactant and the concentration of the organic fluorine compounds in the water to be treated, which changes over time when gas is fed into water to be treated that contains a surfactant and an organic fluorine compound, and determining a relational equation showing the relationship between the concentration of the surfactant and the concentration of the organic fluorine compound.

[0017] The water to be treated contains organic fluorine compounds such as PFOS, PFOA, perfluorohexane sulfonic acid (PFHxS), etc. The content of organic fluorine compounds in the water to be treated is usually 50 ppt or more and 2000 ppt or less.

[0018] The surfactant may be a cationic surfactant or an anionic surfactant, with anionic surfactants being preferred due to their low toxicity. Examples of anionic surfactants include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, etc. Among these, sodium dodecyl sulfate is preferred because it is used as a foaming agent in commercially available toothpastes for home use, is biodegradable, and is highly safe.

[0019] The amount of surfactant added to the water to be treated (addition amount) is preferably 1 ppm to 50 ppm, more preferably 3 ppm to 20 ppm, and even more preferably 5 ppm to 10 ppm, based on the total mass of the water to be treated. If the amount of surfactant added is above the lower limit, stable foam that is difficult to disappear is generated. If the amount of surfactant added is below the upper limit, the treatment time by foam separation is shorter (about 1 hour).

[0020] When gas is fed into water to be treated that contains surfactants and organic fluorine compounds, the concentrations of the surfactant and the organic fluorine compounds in the water change over time. The concentrations of the surfactant and the organic fluorine compounds in the water to be treated after the gas is fed into the water to be treated are measured, and the changes in each concentration over time are investigated. This allows the relationship between the surfactant concentration and the organic fluorine compound concentration in the water to be treated, which change over time, to be investigated. A liquid chromatograph mass spectrometer (LC / MS / MS) can be used to measure the concentration of surfactants in the water to be treated. The concentration of organic fluorine compounds in the treated water can be measured using the method described in "Ministry of the Environment, Water and Air Environment Bureau (2020): Notice on the enforcement of environmental standards related to the protection of human health in relation to water pollution, Kansui-Daisui-hatsu No. 2005281, Kansui-Daisui-hatsu No. 2005282, May 28, 2020."

[0021] From the obtained relationship between the surfactant concentration and the organic fluorine compound concentration in the water to be treated, a relational expression showing the relationship between the surfactant concentration and the organic fluorine compound concentration is determined. The concentrations of surfactants and organic fluorine compounds in the water to be treated, which change over time, are proportional to each other, so that, for example, when the surfactant concentration is x and the organic fluorine compound concentration is y, the relational expression showing the relationship between the surfactant concentration and the organic fluorine compound concentration can be expressed as y = f(x). When the relational expression is a linear function, it can be expressed as y = kx (k is a constant, k ≠ 0).

[0022] "Prediction Process" In the prediction step, when gas is fed into the water to be treated to which a surfactant has been added, the concentration of the surfactant in the water to be treated is measured, and the reduction rate of the organic fluorine compounds in the water to be treated is predicted based on the relationship between the surfactant and the organic fluorine compounds. In the prediction step, the reduction rate of the organic fluorine compounds in the water to be treated is predicted, for example, from the above-mentioned relational expression.

[0023] That is, in the prediction step, for example, the concentration of surfactants in the water to be treated is measured, and the measurement results are applied to the above-mentioned relational expression to estimate the concentration of organofluorine compounds in the water to be treated. The reduction rate of organofluorine compounds in the water to be treated is predicted from the estimation results and the concentration of organofluorine compounds in the water to be treated before treatment.

[0024] According to the method for estimating the removal rate of organic fluorine compounds of this embodiment, when gas is fed into the water to be treated to which a surfactant has been added, the concentration of the surfactant in the water to be treated is measured, and the reduction rate of the organic fluorine compounds in the water to be treated can be predicted in real time and in a short period of time based on the relationship between the surfactant and the organic fluorine compounds.

[0025] [Treatment method for untreated water] A method for treating water to be treated according to one embodiment of the present invention is a method for treating water to be treated, which separates organic fluorine compounds contained in the water to be treated from the water to be treated, and includes a recovery step in which a surfactant is added to the water to be treated, and then gas is fed into the water to generate bubbles, the surfactant and organic fluorine compounds are concentrated at the air-water interface of the bubbles to generate foam, and the foam is recovered near the surface of the water to be treated; and a stopping step in which the concentration of the surfactant in the water to be treated is measured, and when the concentration of the surfactant in the water to be treated becomes zero, the feeding of gas into the water to be treated is stopped.

[0026] "Recovery process" In the recovery process, a surfactant is added to the water to be treated that contains organic fluorine compounds, and then gas is pumped into the water to generate bubbles. The surfactant and organic fluorine compounds are concentrated at the air-water interface of the bubbles to generate foam, and the foam is recovered near the surface of the water to be treated.

[0027] The water to be treated contains organic fluorine compounds, as in the above-mentioned method for estimating the removal rate of organic fluorine compounds.

[0028] As the surfactant, the same surfactants as those used in the method for estimating the removal rate of organic fluorine compounds described above can be used.

[0029] The amount of surfactant to be added to the water to be treated (addition amount) is the same as in the method for estimating the removal rate of organofluorine compounds described above.

[0030] The flow rate of the gas fed into the water to be treated is not particularly limited, but is preferably 1 L / min to 100 L / min, more preferably 5 L / min to 50 L / min, and even more preferably 10 L / min to 20 L / min. When the gas flow rate is equal to or greater than the lower limit, the treatment time by foam separation is shortened. When the gas flow rate is equal to or less than the upper limit, stable foam that is difficult to disappear is generated.

[0031] "Stopping process" In the stopping step, the concentration of the surfactant in the water to be treated is measured, and when the concentration of the surfactant in the water to be treated becomes zero, the supply of gas to the water to be treated is stopped. If it can be confirmed that the concentration of surfactant in the treated water has reached zero, it can be estimated that the concentration of organic fluorine compounds in the treated water has also reached zero, based on the relational equation showing the relationship between the concentration of surfactant and the concentration of organic fluorine compounds in the above-mentioned method for estimating the removal rate of organic fluorine compounds.

[0032] The method for measuring the concentration of surfactants in the water to be treated is the same as the method for estimating the removal rate of organofluorine compounds described above.

[0033] According to the method for treating water of this embodiment, it is possible to easily determine whether to stop treating the water to be treated, thereby eliminating waste in the treatment of the water to be treated and reducing treatment costs.

[0034] [Treatment equipment for treated water] The treatment device for water to be treated will now be described. As the treatment device for water to be treated, for example, the device shown in FIG. As shown in FIG. 1, the treatment device for water to be treated (hereinafter sometimes abbreviated as "treatment device") 1 includes a storage means 10, a bubble generating means 20, a recovery means 30, an addition means 40, a measurement means 50, and a prediction means 60.

[0035] The storage means 10 is for storing the water to be treated, which contains a surfactant and is to be treated by the treatment device 1. When the treatment device 1 is installed in situ, the storage means 10 is constructed in contaminated soil G containing the water to be treated W. When the treatment device 1 is installed in situ, the water to be treated W is groundwater. Here, the contaminated soil G may be, for example, soil containing groundwater (water to be treated W) containing PFAS such as PFOS and PFOA, which are surfactants.

[0036] When the treatment device 1 is installed in situ, the storage means 10 is an in-situ purification well. The storage means 10 is tubular. The cross-sectional shape of the storage means 10 perpendicular to the depth direction is not particularly limited, and examples thereof include a circle, a square, and the like. Furthermore, the inner diameter (diameter of the largest part) of the storage means 10 is not particularly limited. It depends on the number of in-situ purification wells to be installed, taking into account the ease of construction and purification efficiency of the in-situ purification wells, but it is preferably, for example, between 5 cm and 20 cm, and more preferably between 7.5 cm and 10 cm. If the inner diameter is equal to or greater than the lower limit, the collection means 30 can be easily installed in the in-situ purification well. If the inner diameter is equal to or less than the upper limit, drilling and construction of the in-situ purification well can be performed using conventional boring machines.

[0037] It is preferable that an upper lid 11 is provided at the upper end of the storage means 10 to cover the opening 10a of the storage means 10. By providing the upper lid 11, it is possible to maintain airtightness inside the storage means 10. By maintaining airtightness inside the storage means 10, the gas separated in the gas-liquid separation section 71 (described later) can be returned to the water to be treated W via the blower 22 (described later) and recycled for generating foam B.

[0038] The bubble generating means 20 is for sending gas such as nitrogen or air into the water to be treated W in the storage means 10 to generate bubbles. The air bubble generating means 20 has a plurality of air pipes 21 for sending air into the water to be treated W in the storage means 10, and a blower 22 for sending gas into the air pipes 21.

[0039] The multiple air supply pipes 21 are arranged within the storage means 10 along the depth direction of the storage means 10. As shown in Figure 1, the multiple air supply pipes 21 are composed of, for example, three air supply pipes 21A, 21B, and 21C of different lengths. The positions of the tips of the air supply pipes 21A, 21B, and 21C are different in the depth direction of the storage means 10. In Figure 1, the tip of the air supply pipe 21A is at the deepest position relative to the depth of the storage means 10. The tip of the air supply pipe 21B is at the second deepest position relative to the depth of the storage means 10. The tip of the air supply pipe 21C is at the shallowest position relative to the depth of the storage means 10. Gas sent out by the blower 22 is sent out from the tip of the air supply pipe 21 into the water W to be treated. The positions of the tips of the air supply pipes 21A, 21B, and 21C are different in the depth direction of the storage means 10, so that the diffusion range of the bubbles generated by the gas sent into the water W to be treated in the storage means 10 can be expanded over a wide range. This allows the bubbles B to be efficiently generated in the water W to be treated in the storage means 10.

[0040] The number of air pipes 21 is not particularly limited, and is adjusted appropriately depending on the amount of water W to be treated in the storage means 10 and the size of the storage means 10 (inner diameter, depth). The shape of the tip of the air supply pipe 21 is not particularly limited, and the size of the bubbles to be generated can be adjusted appropriately by changing the shape of the outlet and the amount of air to be supplied. The positions of the tips of the plurality of air supply pipes 21 are not particularly limited and are adjusted appropriately depending on the amount of water W to be treated in the storage means 10 and the size of the storage means 10 (inner diameter, depth). The inner diameter of the air supply pipe 21 is not particularly limited, and is adjusted appropriately depending on the amount of water W to be treated in the storage means 10 and the size of the storage means 10 (inner diameter, depth).

[0041] The material of the air pipe 21 is not particularly limited as long as it does not adsorb PFOS or PFOA contained in the water to be treated W or is not deteriorated by these substances.

[0042] The blower 22 may be, for example, a conventional turbo blower (backward-curved blade blower).

[0043] The recovery means 30 is for recovering foam B, in which surfactant is concentrated, by causing it to flow into the air-water interface of the air bubbles generated in the water to be treated W in the storage means 10. The collection means 30 has a foam collection section 31 for collecting and temporarily storing foam B. The foam collection section 31 has an opening 31a that is positioned near the water surface W1 of the water to be treated W and faces upward relative to the water surface W1. By positioning the opening 31a of the foam collection section 31 near the water surface W1 of the water to be treated W in the storage means 10 and facing upward relative to the water surface W1, foam B that has risen to the water surface W1 of the water to be treated W can be efficiently collected.

[0044] The foam collection section 31 has a strainer 32 near the opening 31a, and the opening 31a is preferably installed at a position slightly higher than the water surface W1. By having the strainer 32 near the opening 31a, the foam B can be collected in the foam collection section 31 through the strainer 32. In other words, the collection efficiency of the foam B can be improved.

[0045] The foam collection section 31 is made up of a cylindrical member having a bottom. The foam collection section 31 may be extendable along the depth direction of the storage means 10. The material of the foam collection section 31 is not particularly limited as long as it does not adsorb PFOS or PFOA contained in the water to be treated W or is not deteriorated by these substances.

[0046] It is preferable that the position of the opening 31a of the foam collection section 31 in the depth direction of the storage means 10 be adjustable in accordance with the water level of the water W to be treated within the storage means 10. To make the position of the opening 31a adjustable, for example, as shown in FIG. 1 , a water level measurement means 80 is used. The water level measurement means 80 has a water level indicator 81 and a water level sensor 82. The water level sensor 82 is placed in a groundwater level observation well 90 constructed in the contaminated soil G, separate from the storage means 10, near the storage means 10. The position of the opening 31a of the foam collection section 31 is adjusted to be slightly higher than the water level W1 in accordance with the position (water level) of the water surface W1 of the water to be treated measured by the water level measurement means 80. This allows even a small amount of foam B floating on the water surface W1 of the water to be treated W to be collected.

[0047] The water level indicator 81 may be, for example, a self-recording water level indicator that displays the electric signal sent from the water level sensor 82 as the water level in real time and can output it to an external device. The water level sensor 82 may be, for example, a water pressure sensor whose sensor body is submerged in water and has the function of converting changes in water pressure caused by fluctuations in the water level into an electrical signal and outputting it.

[0048] An example of a means for adjusting the position of the opening 31a of the foam collection section 31 in accordance with the position (water level) of the water surface W1 of the treated water W measured by the water level measuring means 80 is a mechanism that adjusts the position of the opening 31a main body by positive or negative power generated by the rotation of a motor or the like in accordance with the amount of fluctuation in the water level output from the water level meter 81.

[0049] The adding means 40 is for adding a surfactant to the water to be treated W in the storing means 10. It is preferable that the adding means 40 is capable of adjusting the amount of surfactant added according to the amount of the water to be treated W in the storing means 10. The adding means 40 is disposed near the storing means 10.

[0050] The measuring means 50 is for measuring the concentration of surfactant in the water to be treated W in the storage means 10. As the measuring means 50, for example, a liquid chromatograph mass spectrometer (LC / MS / MS) or the like can be used.

[0051] The prediction means 60 measures the concentration of the surfactant in the water to be treated W when gas is fed into the water to be treated W to which a surfactant has been added, and predicts the reduction rate of the organic fluorine compounds in the water to be treated W based on the relationship between the surfactant and the organic fluorine compounds. The prediction means 60 also has a function of stopping the feeding of gas into the water to be treated W from the bubble generation means 20 when the concentration of the surfactant in the water to be treated W becomes zero. The prediction means 60 is connected to the measurement means 50.

[0052] The processing device 1 preferably includes a gas-liquid separation means 70 . The gas-liquid separating means 70 includes a gas-liquid separating section 71 , a conduit 72 , and a circulation path 73 . The gas-liquid separation means 70 recovers the liquid L produced by liquefaction of the foam B in the foam recovery section 31 in the gas-liquid separation section 71 via a conduit 72. The gas-liquid separation section 71 also separates the recovered liquid L into the gas contained in the foam B and a surfactant concentrate containing the water to be treated W. The gas separated in the gas-liquid separation section 61 is then circulated to the bubble generation means 20 via a circulation path 73.

[0053] The treatment device 1 includes the bubble generating means 20 that generates bubbles by sending gas into the water W to be treated in the storage means 10, so that the diffusion range of the bubbles generated by the gas sent into the water W to be treated in the storage means 10 can be expanded over a wide range. This allows bubbles B to be efficiently generated in the water W to be treated in the storage means 10.

[0054] In addition, the treatment device 1 is provided with a recovery means 30 that recovers foam B, which is a concentrated form of surfactant, at the air-water interface of bubbles generated in the water W to be treated in the storage means 10, and the recovery means 30 is provided with a foam recovery section 31 that has an opening 31a that is positioned upward relative to the water surface W1 near the water surface W1 of the water to be treated, so that foam B that has risen to the water surface W1 of the water to be treated W can be efficiently recovered.

[0055] Furthermore, according to the treatment device 1, the measuring means 50 measures the concentration of surfactant in the water to be treated W in the storage means 10, and the prediction means 60 measures the concentration of surfactant in the water to be treated W when gas is fed into the water to be treated W, and based on the relationship between the surfactant and the organic fluorine compounds, the reduction rate of the organic fluorine compounds in the water to be treated W can be predicted in real time and in a short period of time. In addition, the prediction means 60 also has a function of stopping the feeding of gas into the water to be treated W from the bubble generating means 20 when the surfactant concentration in the water to be treated W becomes zero, making it possible to easily determine when to stop treatment of the water to be treated.

[0056] Hereinafter, a method for treating water to be treated using the treatment device 1 will be described in detail with reference to FIG. As shown in FIG. 1, a surfactant is added to the water to be treated W in a storage means 10 provided in contaminated soil G by an adding means 40. Gas is sent from blower 22 into multiple air pipes 21 into water W to be treated to which a surfactant has been added, and the gas is sent into the water W to be treated from multiple air pipes 21 with their tips positioned at different depths in the storage means 10 to generate bubbles, and the surfactant is concentrated at the air-water interface of the bubbles to generate foam B. The generated foam B rises to the water surface W1 of the water W to be treated in the storage means 10.

[0057] The size (outer diameter) of the bubbles generated in the water to be treated W by the gas sent into the water to be treated is smaller, making it easier for them to flow into the recovery means 30. However, the size of the bubbles generated depends on the amount of surfactant contained in the water to be treated W and the amount of air sent, so it is adjusted appropriately depending on the water quality of the water to be treated W to be treated in the storage means 10. Furthermore, the amount of bubbles generated in the water to be treated W, i.e., the amount of bubbles contained per unit volume of the water to be treated W, is not particularly limited and is adjusted appropriately according to the amount of water to be treated W to be treated in the storage means 10.

[0058] When sending gas into the water W to be treated, it is preferable to send the gas into the water W from air supply pipes 21A, 21B, 21 whose tips are located at different positions in the depth direction of storage means 10. This makes it possible to widely expand the diffusion range of bubbles generated by the gas sent into the water W to be treated in storage means 10. In other words, foam B can be efficiently generated in the water W to be treated in storage means 10.

[0059] When PFAS such as PFOS or PFOA is contained in the water to be treated W, surfactants are concentrated at the air-water interface of bubbles generated in the water to be treated W, forming foam B. As described above, PFOS and PFOA behave as surface-active substances, and therefore, when gas is pumped into the water to be treated W containing PFOS or PFOA, multiple bubbles (air-water interface) are generated. In the treatment method according to this embodiment, the bubbles containing surface-active substances such as PFOS or PFOA concentrated at the air-water interface are raised to the water surface W1 of the water to be treated W in the storage means 10 as foam B and are collected.

[0060] The gas to be fed into the water to be treated W is not particularly limited as long as it does not chemically react with or dissolve in the water to be treated W, and examples thereof include air and nitrogen.

[0061] The method of collecting the foam B by the foam collection section 31 of the collection means 30 involves arranging the opening 31a of the foam collection section 31 at a position slightly higher than the water surface W1 of the water to be treated W in the storage means 10, and allowing the foam B to flow from the opening 31a into the foam collection section 31. By arranging the opening 31a of the foam collection section 31 at a position slightly higher than the water surface W1 of the water to be treated W in the storage means 10, the foam B that has risen to the water surface W1 of the water to be treated W can be selectively and efficiently collected.

[0062] By generating bubbles in the water to be treated W and continuing to concentrate PFOS and PFOA at the air-water interface of the bubbles, the foam B temporarily stored in the foam collection section 31 liquefies in a short period of time to become liquid L. Therefore, the amount of liquid L generated by the liquefaction of the foam B gradually increases in the foam collection section 31. Note that when the foam B flows into the foam collection section 31 until the amount of stored liquid L exceeds the height of the tip of the conduit 72, the internal pressure of the storage means 10, to which the upper cover 11 is attached, increases due to the gas being pumped into the water to be treated W. Therefore, the liquid L generated by the liquefaction of the foam B is automatically pushed through the conduit 72 to the gas-liquid separation section 71 together with the gas pumped into the water to be treated W. The gas-liquid separation section 71 separates the collected liquid L into a surfactant concentrate containing the gas contained in the foam B and the water to be treated. Furthermore, the gas separated in the gas-liquid separation section 71 is circulated to the bubble generation means 20 via a circulation path 73. An upper lid 11 is provided to cover the opening 10a of the storage means 10, thereby maintaining airtightness within the storage means 10. This makes it possible to use the power of the blower 22 used in the bubble generation means to collect the foam B, and furthermore, the gas separated in the gas-liquid separation section 71 can be returned to the water W to be treated via the blower 22 and recycled to generate foam B. This makes it possible to reduce the amount of gas used.

[0063] Because the water level of the water W to be treated in the contaminated soil G fluctuates from moment to moment, it is preferable to adjust the position at which foam B is collected by the foam collection unit 31 in accordance with the water level of the water W to be treated. Specifically, for example, as shown in FIG. 1 , it is preferable to use a water level measurement means 80 to adjust the position at which foam B is collected by the foam collection unit 31 in accordance with the water level of the water W to be treated. In accordance with the amount of water level fluctuation measured by the water level measurement means 80, the position of the opening 31a of the foam collection unit 31 is adjusted so that it is at a position (height) slightly higher than the position (water level) of the water surface W1 of the water W to be treated, taking into account the positional relationship between the water level measurement value and the storage means 10. This makes it possible to collect even foam B that is slightly floating on the water surface W1 of the water W to be treated.

[0064] The concentration of the surfactant in the water to be treated W in the storage means 10 is measured by the measuring means 50. When the concentration of the surfactant in the water to be treated W measured by the measuring means 50 becomes zero, the supply of gas to the water to be treated W is stopped.

[0065] Furthermore, when gas is fed into the water W to be treated to which a surfactant has been added, the prediction means 60 measures the concentration of the surfactant in the water W to be treated, and predicts the reduction rate of the organic fluorine compounds in the water W to be treated based on the relationship between the surfactant and the organic fluorine compounds. This makes it possible to predict the timing to stop feeding gas into the water W to be treated based on the measurement results of the surfactant concentration in the water W to be treated by the measurement means 50.

[0066] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the embodiments are merely illustrative of the present invention. Therefore, the present invention is not limited to the configurations of the embodiments, and design changes within the scope of the present invention are also included within the scope of the present invention. Furthermore, for example, when multiple configurations are included in each embodiment, possible combinations of these configurations are also included, even if not specifically stated. Furthermore, when multiple examples or variations are disclosed in an embodiment as the present invention, possible combinations of configurations across these are also included, even if not specifically stated. Furthermore, configurations depicted in the drawings are also included, even if not specifically stated. Furthermore, when the term "etc." is used, it is used to mean that equivalents are included.

[0067] In the above-described embodiment, the storage means 10 is an in-situ purification well installed in situ, the treatment device 1 is an in-situ treatment device, and the surfactant is a PFAS such as PFOS or PFOA, but the present invention is not limited to this. The treatment device and treatment method of the present invention can also be suitably used when various surfactants contained in the treated water are separated from the stored treated water at a location other than the in-situ. [Example]

[0068] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples.

[0069] [Experimental Example] Sodium dodecyl sulfate (hereinafter abbreviated as "SDS") was added to 45 L of tap water so that the initial concentration was 5.5 mg / L to prepare a test solution containing sodium dodecyl sulfate. Gas (nitrogen gas) was pumped into the test liquid to generate bubbles, and the surfactant was concentrated at the air-water interface of the bubbles to generate foam. The generated foam was allowed to rise to the surface of the test liquid and collected. The concentration of SDS in the test solution was measured using a liquid chromatograph mass spectrometer (LC / MS / MS) from the start to the end of gas supply to the test solution. The results are shown in Figure 2. The results shown in Figure 2 indicate that the SDS concentration decreased to 50% in about 8 minutes after the start of gas injection into the test solution, and that SDS was largely removed from the test solution after about 37 minutes. Even when SDS and organic fluorine compounds are mixed in the test solution, it is thought that the concentration of the organic fluorine compounds removed will also decrease in proportion to the concentration of SDS removed. The test solution containing SDS, PFOS, and PFOA was treated using the method described above, and the concentrations of SDS, PFOS, and PFOA in the test solution were measured before and after treatment in the same manner as described above. The results are shown in Table 1.

[0070] [Table 1]

[0071] The results shown in Table 1 confirm that the concentrations of PFOS and PFOA decrease as the concentration of SDS decreases. Therefore, it was suggested that when gas is pumped into treated water to which SDS has been added, the concentration of SDS in the treated water can be measured, and the rate of decrease in the concentrations of PFOS and PFOA can be estimated based on the relationship between SDS and PFOS / PFOA. [Explanation of symbols]

[0072] 1 Processing equipment 10 Storage means 11 Top lid 20 Bubble generating means 21 Air pipe 22 Blower 30 Recovery Methods 31 Foam collection section 40 Means of addition 50 Measurement means 60 Prediction Methods 70 Gas-liquid separation means 71 Gas-liquid separation section 72 Conduit 73 Circulation route 80 Water level measurement means 81 Water level gauge 82 Water level sensor 90 Groundwater level observation well

Claims

1. 1. A foam separation treatment method for separating organic fluorine compounds contained in water to be treated from the water to be treated, comprising: a prediction step of measuring the concentration of the surfactant in the water to be treated when gas is fed into the water to be treated to which a surfactant has been added, and predicting the reduction rate of the organic fluorine compounds in the water to be treated based on the relationship between the surfactant and the organic fluorine compounds.

2. The method for estimating a removal rate of an organic fluorine compound according to claim 1 , wherein the surfactant is sodium dodecyl sulfate.

3. A method for treating water to be treated, which separates organic fluorine compounds contained in the water to be treated from the water to be treated, comprising: a recovery step of adding a surfactant to the water to be treated, then feeding gas into the water to generate bubbles, concentrating the surfactant and the organic fluorine compound at the air-water interface of the bubbles to generate foam, and recovering the foam near the water surface of the water to be treated; A method for treating water to be treated, comprising a stopping step of measuring the concentration of the surfactant in the water to be treated and stopping the supply of gas to the water to be treated when the concentration of the surfactant in the water to be treated becomes zero.

4. A water treatment device for separating organic fluorine compounds contained in the water to be treated from the water to be treated, a storage means for storing the water to be treated; adding means for adding a surfactant to the water to be treated in the storage means; a bubble generating means for generating bubbles by feeding gas into the water to be treated in the storage means to which a surfactant has been added; a recovery means for recovering foam in which the surfactant is concentrated at the air-water interface of the bubbles; a measuring means for measuring the concentration of the surfactant in the water to be treated in the storage means; a prediction means for measuring the concentration of the surfactant in the water to be treated when gas is fed into the water to be treated to which the surfactant has been added, and predicting the reduction rate of the organic fluorine compounds in the water to be treated based on the relationship between the surfactant and the organic fluorine compounds.

Images