Treatment method for water to be treated

Abstract

The present invention provides a method for treating water that can decompose organic fluorine compounds contained in the water to be treated. [Solution] A method for treating water to be treated, comprising a decomposition step of passing an electric current through water to be treated W1a containing an organofluorine compound and an electrolyte, and having an electrical conductivity of 6.0 mS / cm or higher, to decompose the organofluorine compound in the water to be treated W1a. The treatment method can be used to decompose organofluorine compounds in contaminated water W1A that is contaminated with organofluorine compounds such as perfluorooctanesulfonic acid and perfluorooctanoic acid.

Description

Technical Field

[0001] The present invention relates to a method for treating treated water.

Background Art

[0002] Organic fluorine compounds are used in a wide range of applications such as fire extinguishing agents, waterproofing, oil resistance, and fluorine-coated frying pans. Among organic fluorine compounds, perfluoroalkyl compounds and polyfluoroalkyl compounds are collectively called "PFAS". Among PFAS, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are used in various applications. Due to concerns about the health effects of organic fluorine compounds, the Ministry of Health, Labour and Welfare has classified PFOS and PFOA as water quality management target items for tap water in 2020, and set a provisional target value of 50 ng / L or less for the combined value of PFOS and PFOA.

[0003] Organic fluorine compounds are known to be hardly decomposable. In Patent Document 1, as a method for treating treated water containing hardly decomposable substances, a water treatment method including (a) a step of adsorbing and concentrating hardly decomposable substances by an adsorbent; and (b) a step of decomposing hardly decomposable substances by a physicochemical method has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the method using an adsorbent has problems such as the need to treat and dispose of the waste adsorbent adsorbed with organic fluorine compounds.

[0006] Currently, there is no established technology for treating contaminated water containing perfluorinated compounds, especially contaminated water containing perfluorinated compounds at low concentrations.

[0007] Under these circumstances, the present invention aims to provide a method for treating water that can decompose organofluorine compounds contained in the water to be treated. [Means for solving the problem]

[0008] The inventors of this invention have conducted extensive research to solve the above problems and have found that the following invention is suitable for the above purpose, leading to the present invention. That is, the present invention relates to the following invention.

[0009] <1> A method for treating water to be treated, comprising a decomposition step of passing an electric current through water to be treated, which contains an organofluorine compound and an electrolyte and has an electrical conductivity of 6.0 mS / cm or higher, to decompose the organofluorine compound in the water to be treated. <2> The method decomposes organic fluorine compounds in contaminated water, which is water contaminated with organic fluorine compounds, wherein the water is tap water, and the method includes an electrical conductivity adjustment step in which the contaminated water and an electrolyte are mixed before the decomposition step to adjust the water to be treated to have an electrical conductivity of 6.0 mS / cm or higher, and the decomposition apparatus that performs the decomposition step is an electrodialysis membrane apparatus comprising an anode, a cathode, and a desalination chamber and a concentration chamber formed by alternately arranging an anion exchange membrane and a cation exchange membrane between the anode and the cathode, and in the decomposition step, the organic fluorine compounds in the water to be treated are decomposed and desalination is performed. <1> The processing method described above. <3> In the electrical conductivity adjustment step, the electrical conductivity is adjusted using the concentrated liquid discharged from the electrodialysis membrane apparatus in the decomposition step. <2> The processing method described above. <4> The method is to decompose organofluorine compounds in contaminated water, which is water contaminated with organofluorine compounds, wherein the water is not tap water and has an electrical conductivity of less than 6.0 mS / cm, and after performing an electrical conductivity adjustment step in which the contaminated water and an electrolyte are mixed to adjust the water to be treated to have an electrical conductivity of 6.0 mS / cm or higher, the decomposition step is performed. <1> The processing method described above. <5> The method is for decomposing organofluorine compounds in contaminated water, wherein the water has an electrical conductivity of 6.0 mS / cm or higher and a calcium concentration of more than 200 mg / L, and before the decomposition step, a calcium removal step is performed to remove calcium ions from the contaminated water and prepare a low-concentration calcium solution with a calcium concentration of 200 mg / L or less, and the low-concentration calcium solution is used as the water to be treated in the decomposition step. <1> The processing method described above. <6> The water is leachate discharged from the final disposal site and / or excess water discharged from the offshore disposal site. <4> or <5> The processing method described above. <7> The water to be treated is sewage and / or industrial wastewater from a factory that handles organic fluorine compounds. <1> The processing method described above. <8> The disassembly apparatus that performs the disassembly step is a diaphragm-type electrolyte circulation electrolytic apparatus or a diaphragm-free electrolytic apparatus. <4> from <7> The processing method described in any of the following. <9> The water is one or more selected from the group consisting of groundwater, river water, spring water, lake water, reservoir water, well water and subsurface water. <2> from <4> The processing method described in any of the following. <10> The concentration of the organofluorine compound in the treated water is 50 ng / L or more and 20,000 ng / L or less. <1> from <9> The processing method described in any of the following. <11> The organofluorine compound is perfluorooctanesulfonic acid and / or perfluorooctanoic acid. <1> from <10> The processing method described in any of the following. <12> The electrolyte is NaCl, <1> from <11> The processing method described in any of the following. [Effects of the Invention]

[0010] According to the present invention, there is provided a method for treating treated water that can decompose organic fluorine compounds contained in the treated water.

Brief Description of Drawings

[0011] [Figure 1] It is a flowchart showing an example of the treatment method according to the present invention. [Figure 2] It is a diagram showing an example of a treatment system for implementing the treatment method shown in FIG. 1. [Figure 3] It is a flowchart showing another example of the treatment method according to the present invention. [Figure 4] It is a diagram showing an example of a treatment system for implementing the treatment method shown in FIG. 3. [Figure 5] It is a flowchart showing another example of the treatment method according to the present invention. [Figure 6] It is a diagram showing an example of a treatment system for implementing the treatment method shown in FIG. 5. [Figure 7] It is a flowchart showing another example of the treatment method according to the present invention. [Figure 8] It is a diagram showing an example of a treatment system for implementing the treatment method shown in FIG. 7. [Figure 9] It is a schematic diagram for explaining a partial configuration of the apparatus used in the decomposition test II of the examples.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the following content unless the gist thereof is changed. In this specification, when the expression "~" is used, it is used as an expression including the numerical values or physical property values before and after it. In FIGS. 1 to 9, the same reference numerals are given to common parts, and duplicate explanations are omitted.

[0013] <Method for Treating Treated Water> The present invention relates to a method for treating treated water (hereinafter sometimes referred to as "the treatment method of the present invention"), which includes an organic fluorine compound and an electrolyte, and has a decomposition step of decomposing the organic fluorine compound in the treated water by applying an electric current to the treated water having an electric conductivity of 6.0 mS / cm or more.

[0014] The inventors of the present invention have found that by setting the electric conductivity of the treated water containing an organic fluorine compound to 6.0 mS / cm or more and applying an electric current, the organic fluorine compound contained in the treated water can be decomposed, and the concentration of the organic fluorine compound can be sufficiently reduced. Further, in the treatment method of the present invention, without using a method for promoting oxidation such as blowing ozone, hydrogen peroxide, or oxygen or irradiating ultraviolet rays during electrolysis, only by performing electrolysis with an electrodialysis membrane device, a diaphragm-type electrolytic solution circulation type electrolyzer, or a diaphragmless electrolyzer, it has been found that the concentration of the organic fluorine compound can be sufficiently reduced. When the electric conductivity of the treated water during energization is less than 6.0 mS / cm, it is difficult to sufficiently decompose the organic fluorine compound.

[0015] According to the treatment method of the present invention, the organic fluorine compound in the treated water can be decomposed. Further, as described above, in the adsorption method using an adsorbent, treatment of the waste adsorbent is required, but since the treatment method of the present invention decomposes the organic fluorine compound, a secondary treatment is unnecessary.

[0016] The treatment method of the present invention can be used for purifying contaminated water contaminated with an organic fluorine compound. Specific examples of the contaminated water include groundwater, river water, spring water, lake water, stored water, well water, underflow water, leachate, surplus water, sewage, and factory wastewater discharged from factories handling organic fluorine compounds in which organic fluorine compounds are mixed. Examples of the organic fluorine compound include perfluoroalkyl compounds and polyfluoroalkyl compounds, and among them, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are mentioned.

[0017] The concentration of organic fluorine compounds in contaminated water varies depending on the type, but the treatment method of the present invention is preferably used for contaminated water with an organic fluorine compound concentration of 20,000 ng / L or less, and more preferably for contaminated water with an organic fluorine compound concentration of 50 ng / L or more and 20,000 ng / L or less. Furthermore, it can be used for contaminated water with organic fluorine compound concentrations of 60 ng / L or more, 80 ng / L or more, 100 ng / L or more, 10,000 ng / L or less, 5,000 ng / L or less, 3,000 ng / L or less, 1,000 ng / L or less, etc.

[0018] If the contaminated water has an electrical conductivity of 6.0 mS / cm or higher, it can be used as is for treatment. If the contaminated water does not contain electrolytes or has an electrical conductivity lower than 6.0 mS / cm, an electrolyte is added, and the treated water is used. The electrolyte is not particularly limited, but since calcium salts and potassium salts may cause scale formation, sodium salts are preferred, and sodium chloride (NaCl) is more preferred due to its safety and ease of handling.

[0019] The electrical conductivity of the water to be treated is preferably 8.0 mS / cm or higher, more preferably 10.0 mS / cm or higher, and even more preferably 15.0 mS / cm or higher. An electrical conductivity of 50.0 mS / cm or higher is also acceptable, and it may be 200.0 mS / cm or lower, or even 100.0 mS / cm or lower. Electrical conductivity can be measured using known electrical conductivity meters such as AC 4-electrode type, AC 2-electrode type, or electromagnetic induction type.

[0020] The treated water should ideally have a pH in the range of 6 to 9.

[0021] Furthermore, applying the treatment method of the present invention to leachate treatment eliminates the need for biological treatment processes (BOD oxidation, nitrification, denitrification, re-aeration), sedimentation and coagulation, and activated carbon treatment. It can also be applied to wastewater treatment at marine disposal sites, eliminating the need for proper treatment and biological treatment processes, thereby reducing the need for biological sludge acclimation, and enabling economical treatment by reducing construction costs and maintenance personnel for biological treatment facilities. In addition, the electricity used for electrolysis is less than the electricity used for blowers, pumps, etc., used in biological treatment, thus reducing the environmental burden.

[0022] The processing method of the present invention will be described in more detail below with reference to Figures 1 to 8.

[0023] [Implementation Method 1] The treatment method 1 shown in Figure 1 is an example of the treatment method of the present invention and comprises an electrical conductivity adjustment step (101) and a decomposition step (201). Treatment method 1 decomposes organic fluorine compounds in contaminated water W1A. Contaminated water W1A is water from a water source (i.e., water used as raw water for the water supply) that is contaminated with organic fluorine compounds. The treated water W1B after treatment is returned to the water source. Specifically, this includes water from water sources such as groundwater, river water, spring water, lake water, reservoir water, well water, and subsurface water, and treatment method 1 can be applied to the treatment of water containing organic fluorine compounds such as perfluorooctanesulfonic acid and perfluorooctanoic acid. Since water from water sources basically does not contain electrolytes, in treatment method 1, the electrical conductivity adjustment step (101) is performed before the decomposition step (201).

[0024] (Electrical conductivity adjustment process (101)) The electrical conductivity adjustment step (101) is performed before the decomposition step (201), and is a step in which the contaminated water W1A and an electrolyte are mixed to adjust the treated water W1a to have an electrical conductivity of 6.0 mS / cm or higher. In the electrical conductivity adjustment step (101), NaCl is used as the electrolyte. The electrolyte may be mixed with the contaminated water W1A in a solid state, or the solid may be dissolved in water to form an electrolyte aqueous solution which may then be mixed with the contaminated water W1A.

[0025] Furthermore, as described later, in the decomposition step (201), a concentrated solution containing concentrated electrolytes is discharged. In treatment method 1, it is preferable to use this concentrated solution as at least a portion of the electrolyte aqueous solution to adjust the electrolyte concentration of the contaminated water W1A. By using the concentrated solution, the amount of electrolyte used for adjusting electrical conductivity and the amount of concentrated solution to be discarded can be reduced.

[0026] (Decomposition process (201)) The decomposition process (201) is a process in which an electric current is passed through the water to be treated W1a to decompose the organic fluorine compounds in the water to be treated W1a. An electrodialysis membrane apparatus is used as the decomposition device to decompose the organic fluorine compounds in the water to be treated W1a and desalinate it, thereby obtaining treated water. When the water to be treated W1a is treated with the electrodialysis membrane apparatus, desalinate water is discharged from the desalination chamber. As the water to be treated W1a is passed through the desalination chamber, the organic fluorine compounds are decomposed and electrolytes are removed, so the desalinate water discharged from the desalination chamber can be discharged directly to water sources that have electrolyte concentration regulations (chloride ions of 200 mg / L or less).

[0027] The energizing conditions are set appropriately according to the configuration of the disassembly device, but as an example, the voltage is 9-15V, the current is 1.0-4.4A, and the current density is 0.04A / cm². 2 The above and 0.08 A / cm 2 The above can be applied. The processing time (residence time in the device) can be, for example, 50 to 150 minutes or 60 to 120 minutes.

[0028] Figure 2 shows a treatment system S1, which is an example of a system capable of carrying out treatment method 1. Treatment system S1 comprises a raw water tank 10, an electrolyte concentration adjustment tank 12, a water to be treated storage tank 14, an electrodialysis membrane device 20, a concentrated liquid storage tank 40, and an electrode liquid storage tank 30.

[0029] The raw water tank 10 is a tank for storing contaminated water, and the electrolyte concentration adjustment tank 12 is a tank for adjusting the electrical conductivity of the contaminated water to 6.0 mS / cm or higher (preferably 10.0 mS / cm or higher). In the treatment system S1, the raw water tank 10 stores the contaminated water W1A while also being able to supply a portion of the contaminated water W1A to the electrolyte concentration adjustment tank 12. The electrolyte concentration adjustment tank 12 is supplied with contaminated water W1A from the raw water tank 10 and concentrated liquid 41 from the concentrated liquid storage tank 40. The amount of contaminated water W1A and concentrated liquid 41 supplied to the electrolyte concentration adjustment tank 12 is controlled by controlling the discharge amount of contaminated water W1A from the raw water tank 10 and the discharge amount of concentrated liquid 41 from the concentrated liquid storage tank 40. Furthermore, the water to be treated W1a, whose electrolyte concentration has been adjusted in the electrolyte concentration adjustment tank 12, is configured to be transferred to the water to be treated storage tank 14.

[0030] The water to be treated W1a is stored in the water to be treated storage tank 14 and supplied to the electrodialysis membrane dialysis machine 20. The water to be treated storage tank 14 is connected to the supply port of the desalination chamber 25 of the electrodialysis membrane dialysis machine 20 via piping, and is configured to supply the water to be treated W1a to the desalination chamber 25. In addition, the water to be treated storage tank 14 is connected to the piping L1 through which the desalination water discharged from the desalination chamber 25 passes via switching means V1 and piping L2, and is configured so that the desalination water can be returned to the water to be treated storage tank 14 by controlling the switching means V1.

[0031] The concentrate storage tank 40, which stores the concentrate 41, is connected via piping to the supply port and discharge port of the concentration chamber 26 of the electrodialysis membrane apparatus 20, respectively, so that the concentrate 41 can be circulated between the concentrate storage tank 40 and the concentration chamber 26 of the electrodialysis membrane apparatus 20. The concentrate storage tank 40 is also configured to supply a portion of the concentrate 41 to the electrolyte concentration adjustment tank 12. As the concentrate 41, an aqueous solution of NaCl or an aqueous solution of KCl can be used, with an aqueous solution of NaCl being preferred.

[0032] The electrode solution storage tank 30, which stores the electrode solution 31, is connected via piping to the supply port of the electrode chamber 27 of the electrodialysis membrane apparatus 20, and is also connected via piping to the outlet of the electrode chamber 28, to which the electrode solution 31 discharged from the electrode chamber 27 is supplied, thus enabling the circulation of the electrode solution 31 between the electrode chamber 27, the electrode chamber 28, and the electrode solution storage tank 30. As the electrode solution 31, an aqueous solution of Na2SO4, an aqueous solution of NaCl, an aqueous solution of NaOH, etc., can be used, with an aqueous solution of Na2SO4 being preferred.

[0033] The electrodialysis membrane apparatus 20 is a device for decomposing organic fluorine compounds in water W1a to be treated and for desalination. The electrodialysis membrane apparatus 20 comprises a treatment tank having an anode 21, a cathode 22, a desalination chamber 25 and a concentration chamber 26 formed by alternately arranging anion exchange membrane 23 and a cation exchange membrane 24 between the anode 21 and the cathode 22, and a power supply (not shown) for applying a voltage between the anode 21 and the cathode 22.

[0034] There are no particular restrictions on the anode 21 and cathode 22, and known electrodes such as titanium, platinum, and titanium-platinum electrodes can be used. For the cation exchange membrane, a membrane in which anionic groups such as sulfonic acid groups are immobilized on a porous polymer and the membrane is negatively charged can be used, and for the anion exchange membrane, a membrane in which cationic groups such as ammonium groups or amino groups are immobilized on a porous polymer and the membrane is positively charged can be used.

[0035] The desalination chamber 25 is a compartment separated by an anion exchange membrane 23 on the anode side and a cation exchange membrane 24 on the cathode side, while the concentration chamber 26 is a compartment separated by a cation exchange membrane 24 on the anode side and an anion exchange membrane 23 on the cathode side. The widths of the desalination chamber 25 and concentration chamber 26 are approximately 1 to 2 cm each. The desalination chamber 25 is the flow path for the water to be treated (1 Wa), and the water to be treated (1 Wa) stored in the water to be treated storage tank 14 is supplied to the desalination chamber 25. Furthermore, the flow path through which the desalination water discharged from the desalination chamber 25 flows can be switched by a switching means V1, allowing it to be discharged to a water source through pipes L1 and L3, or returned to the water to be treated storage tank 14 through pipes L1 and L2. The concentration chamber 26 is the flow path for the concentrated liquid 41. The concentrated liquid 41 is supplied to the concentration chamber 26, passes through the concentration chamber 26, and is then returned to the concentrated liquid storage tank 40, thus circulating.

[0036] Furthermore, the treatment tank has an electrode chamber 27 between the anode 21 and the desalination chamber 25 on the anode side, and an electrode chamber 28 between the cathode 22 and the desalination chamber 25 on the cathode side. Electrode chambers 27 and 28 are flow paths for the electrode liquid 31. Electrode chambers 27 and 28 and the electrode liquid storage tank 30 are connected to form a circulating path in which the electrode liquid 31 leaves the electrode liquid storage tank 30, passes through electrode chamber 27, passes through electrode chamber 28, and returns to the electrode liquid storage tank 30, allowing the electrode liquid 31 to circulate between the electrode liquid storage tank 30, electrode chambers 27 and 28.

[0037] The power supply (not shown) is a means for applying a voltage between the anode 21 and the cathode 22. The power supply may be a constant current power supply or a constant voltage power supply. It may also be equipped with an ammeter and a voltmeter, and the voltage may be adjusted as appropriate.

[0038] In the electrical conductivity adjustment step (101), the amounts of contaminated water W1A and concentrated liquid 41 are controlled and supplied to the electrolyte concentration adjustment tank 12, where they are mixed to adjust the water to be treated W1a so that the electrical conductivity is 6.0 mS / cm or higher (preferably 10.0 mS / cm or higher). At this time, NaCl may be added separately as needed to adjust the electrical conductivity. A certain amount of the water to be treated W1a is transferred to the water to be treated storage tank 14. The NaCl concentration of the water to be treated W1a is preferably 0.5% by mass or higher, more preferably 0.8% by mass or higher, and even more preferably 0.8 to 3.5% by mass.

[0039] In the decomposition process (201), the water to be treated 1Wa stored in the water to be treated storage tank 14 is supplied to the desalination chamber 25, and the concentrated liquid 41 stored in the concentrated liquid storage tank 40 is supplied to the concentration chamber 26. Furthermore, the electrode liquid 31 is circulated, and a voltage is applied between the anode 21 and the cathode 22 to energize the water to be treated 1Wa. As a result, as the water passes through the desalination chamber 25, the organofluorine compounds in the water to be treated 1Wa are decomposed, and electrolytes (cations and anions) move out of the desalination chamber 25, resulting in the discharge of desalination water with a lower electrolyte concentration than the water to be treated 1Wa. Also, as the water passes through the concentration chamber 26, the electrolyte concentration of the concentrated liquid 41 increases due to the cations and anions that have moved from the desalination chamber 25. The desalination water is then discharged outside as treated water W1B through the piping L3, or returned to the water to be treated storage tank 14, where the decomposition process is repeated.

[0040] The concentration of organofluorine compounds in the treated water W1B is preferably 50 ng / L or less, more preferably 10 ng / L or less, and even more preferably 5 ng / L or less. The concentration of chloride ions in the treated water W1B is also preferably 200 mg / L or less. If the chloride ion concentration is higher than the above, it is preferable to return the desalinated water discharged from the desalination chamber 25 to the treated water storage tank 14 multiple times and treat it again in the electrodialysis membrane device 20 in order to sufficiently reduce the chloride ions. That is, it is preferable to circulate the treated water W1a through the electrodialysis membrane device 20 multiple times. On the other hand, since the treatment efficiency decreases as the number of repetitions (number of times the water is returned to the treated water storage tank 14) increases, it is preferable to have 2 or 3 repetitions.

[0041] [Implementation Method 2] The treatment method 2 shown in Figure 3 is an example of the treatment method of the present invention and comprises an electrical conductivity adjustment step (102) and a decomposition step (202). Treatment method 2 decomposes organofluorine compounds in contaminated water W2A. Contaminated water W2A is water that is not from a water supply source, is contaminated with organofluorine compounds, and has an electrical conductivity of less than 6.0 mS / cm. Specifically, it is water that is not from a water supply source, such as groundwater, river water, spring water, lake water, reservoir water, well water, and subsurface water, and treatment method 2 can be applied to the treatment of water that contains organofluorine compounds such as perfluorooctanesulfonic acid and perfluorooctanoic acid.

[0042] (Electrical conductivity adjustment process (102)) The electrical conductivity adjustment step (102) is performed before the decomposition step (202), and is a step in which the contaminated water W2A and the electrolyte are mixed to adjust the treated water W2a to have an electrical conductivity of 6.0 mS / cm or higher. The electrolyte E2 is NaCl. Depending on the installation conditions, the electrolyte E2 may be mixed with the contaminated water W2A in a solid state, or the solid may be dissolved in water to form an electrolyte aqueous solution which may then be mixed with the contaminated water 2WA. Industrial salt may be used for the electrolyte E2, or seawater may be used.

[0043] (Decomposition process (202)) The decomposition step (202) is a step in which an electric current is passed through the water to be treated W2a using a diaphragm-type electrode liquid circulation electrolytic device or a non-diaphragm electrolytic device as the decomposition device to decompose the organic fluorine compounds in the water to be treated W2a. The electric current can be applied under the same conditions as in the decomposition step (201). The concentration of organic fluorine compounds in the treated water W2B obtained by decomposing the organic fluorine compounds in the decomposition step (202) is preferably 50 ng / L or less, more preferably 10 ng / L or less, and even more preferably 5 ng / L or less.

[0044] Figure 4 shows a treatment system S2, which is an example of a system capable of carrying out treatment method 2. Treatment system S2 comprises a raw water tank 10, an electrolyte concentration adjustment tank 12, a water to be treated storage tank 14, an electrolytic device 50, and an electrode solution storage tank 30.

[0045] In the treatment system S2, contaminated water W2A is stored in the raw water tank 10. In the electrolyte concentration adjustment tank 12, electrolyte E2 is added to the contaminated water W2A supplied from the raw water tank 10 to adjust the water to be treated W2a. Electrolyte E2 is added to the electrolyte concentration adjustment tank 12 in solid or aqueous solution form. The water to be treated W2a is transferred from the electrolyte concentration adjustment tank 12 to the water to be treated storage tank 14.

[0046] The electrolytic device 50 is a diaphragm-type electrode liquid circulation electrolytic device that decomposes organic fluorine compounds in the water to be treated W2a. The water to be treated storage tank 14 is connected to the supply port of the reaction chamber 55 of the electrolytic device 50 via piping, so that the water to be treated W2a can be supplied to the reaction chamber 55. The water to be treated storage tank 14 is also connected to the piping L4 through which the water discharged from the reaction chamber 55 passes, via a switching means V1 and piping L2, so that by controlling the switching means V1, the water discharged from the reaction chamber 55 can be returned to the water to be treated storage tank 14.

[0047] The electrolytic apparatus 50 comprises a reaction vessel having an anode chamber 56 with an anode 51, a cathode chamber 57 with a cathode 52, and a reaction chamber 55 formed between the anode chamber 56 and the cathode chamber 57, and a power supply (not shown) for applying voltage. The reaction chamber 55 is a flow path through which the water to be treated W2a flows, and the reaction vessel is a reaction vessel in which the inside of the flow path through which the water to be treated W2a flows is not partitioned by an ion exchange membrane (diaphragm). In other words, the reaction vessel of the electrolytic apparatus 50 is a three-chamber type reaction vessel consisting of an anode chamber 56, a cathode chamber 57, and a reaction chamber 55.

[0048] The anode chamber 56 and the cathode chamber 57 are each compartments covered by a diaphragm 53 made of conductive thin-film plastic. A platinum electrode or the like can be used for the anode 51. A titanium electrode or the like can be used for the cathode 52.

[0049] The anode chamber 56 and the cathode chamber 57 serve as pathways for the electrode liquid 31. The anode chamber 56, the cathode chamber 57, and the electrode liquid storage tank 30 are connected to form a circulating path in which the electrode liquid 31 leaves the electrode liquid storage tank 30, passes through the anode chamber 56, passes through the cathode chamber 57, and returns to the electrode liquid storage tank 30, thereby allowing the electrode liquid 31 to circulate between the electrode liquid storage tank 30, the anode chamber 56, and the cathode chamber 57.

[0050] The reaction chamber 55 is the compartment between the anode chamber 56 and the cathode chamber 57. The width of the reaction chamber 55 is approximately 0.5 to 1 cm. When the water to be treated W2a passes through the reaction chamber 55, it is energized, which decomposes the organofluorine compounds contained in the water to be treated W2a.

[0051] The power supply (not shown) for the electrolytic device 50 is a means for applying a voltage between the anode 51 and the cathode 52, and may be a constant current power supply or a constant voltage power supply. It may also be equipped with an ammeter and a voltmeter, and the voltage may be adjusted as appropriate.

[0052] In the electrical conductivity adjustment step (102), the contaminated water W2A and electrolyte E2 are mixed in the electrolyte concentration adjustment tank 12 to adjust the water to be treated W2a so that the electrical conductivity is 6.0 mS / cm or higher. Preferably, the electrical conductivity of the water to be treated W2a is 10.0 mS / cm or higher. A certain amount of the water to be treated W2a is transferred to the water to be treated storage tank 14.

[0053] In the decomposition process (202), the water to be treated W2a is passed from the water to be treated storage tank 14 to the reaction chamber 55 of the electrolytic device 50 to decompose the organic fluorine compounds in the water to be treated W2a. Specifically, the electrode solution 31 is circulated between the electrode solution storage tank 30, the anode chamber 56, and the cathode chamber 57, and while applying a voltage between the anode 51 and the cathode 52, the water to be treated W2a is supplied to the reaction chamber 55, thereby decomposing the organic fluorine compounds in the water to be treated W2a within the reaction chamber 55. The water discharged from the reaction chamber 55 is either discharged outside as treated water W2B through the piping L3, or returned to the water to be treated storage tank 14, where the decomposition process is repeated.

[0054] In addition, during the decomposition process (202), the water discharged from the reaction chamber 55 may be returned to the treated water storage tank 14 and treated again. However, the treatment efficiency decreases as the number of repetitions (the number of times the water is returned to the treated water storage tank 14) increases. Therefore, when performing the treatment multiple times, it is preferable to repeat the process two or three times.

[0055] [Implementation Method 3] The treatment method 3 shown in Figure 5 is an example of the treatment method of the present invention and comprises a calcium removal step (303) and a decomposition step (203). Treatment method 3 decomposes organic fluorine compounds in contaminated water W3A. Contaminated water W3A is water contaminated with organic fluorine compounds, with an electrical conductivity of 6.0 mS / cm or higher and a calcium concentration of more than 200 mg / L. Specifically, it is water such as leachate (infiltration water) discharged from final disposal sites for waste, leachate discharged from landfill sites for waste, and excess water discharged from marine disposal sites, and treatment method 3 can be applied to the treatment of water containing organic fluorine compounds such as perfluorooctanesulfonic acid and perfluorooctanoic acid.

[0056] (Calcium removal process (303)) The calcium removal step (303) is performed before the decomposition step (203) and involves removing calcium ions from the contaminated water W3A to prepare a low-concentration calcium solution with a calcium concentration of 200 mg / L or less.

[0057] For example, in final disposal sites, ash such as incinerator residue and fly ash is landfilled, and since the ash contains salt removed by desalination agents, the leachate from such disposal sites contains electrolytes and has an electrical conductivity of 10.0 mS / cm or higher. Also, when ash is not landfilled and salt is contained in the slag or sludge, the electrical conductivity of the leachate is 15.0 mS / cm or higher. Thus, the leachate contains inorganic salts such as chloride ions and calcium ions caused by fly ash. High concentrations of inorganic salts such as calcium ions can cause a decrease in electrical conductivity due to scale buildup on electrodes and blockage of piping equipment due to scale buildup. Therefore, in treatment method 3, in order to prevent scaling, calcium ions are removed from the contaminated water W3A and a low-concentration calcium solution with a calcium concentration of 200 mg / L or less is prepared. Since the low-concentration calcium solution has an electrical conductivity of 10.0 mS / cm or higher, it can be used as is as the water to be treated W3a in the decomposition process (203).

[0058] (Decomposition process (203)) The decomposition step (203) is a step in which an electrolytic device 50 is used as a decomposition device to pass an electric current through the water to be treated W3a (low-concentration calcium solution) to decompose the organofluorine compounds in the water to be treated W3a. The decomposition step (203) is the same as the decomposition step (202), except that the water to be treated W3a is used instead of the water to be treated W2a, and the preferred embodiment is also the same.

[0059] Figure 6 shows a treatment system that is an example of a system capable of implementing treatment method 3. Treatment system S3 comprises a raw water tank 10, calcium removal equipment 60, a water to be treated storage tank 14, an electrolytic device 50, and an electrode solution storage tank 30.

[0060] The treatment system S3 is configured such that contaminated water W3A stored in the raw water tank 10 is treated in the calcium removal equipment 60, then transferred to the treated water storage tank 14, and the treated water W3a stored in the treated water storage tank 14 is treated in the electrolytic device 50. The treatment system S3 has the same configuration as the treatment system S2, except that it is equipped with the calcium removal equipment 60 instead of the electrolyte concentration adjustment tank 12. The calcium removal equipment 60 removes calcium ions from the treated water W3A and prepares a low-concentration calcium solution (treated water W3a) with a calcium concentration of 200 mg / L or less. The calcium removal equipment 60 can be equipment used in the field of leachate treatment, such as equipment that adds a precipitating agent X1 to precipitate calcium ions and removes the precipitated calcium sludge X2.

[0061] Furthermore, leachate (infiltration water) discharged from disposal sites and excess water discharged from marine disposal sites typically have an electrical conductivity of 10.0 mS / cm or higher, or 15.0 mS / cm or higher, but may be diluted by rainfall, etc., and their electrical conductivity may decrease. For this reason, a concentration adjustment tank may be provided between the calcium removal equipment 60 of the treatment system S3 and the water to be treated storage tank 14. If the electrical conductivity of the low-concentration calcium solution is less than 6.0 mS / cm, an electrolyte concentration adjustment process is performed to adjust the water to be treated by adding an electrolyte. If the electrical conductivity of the low-concentration calcium solution is less than 6.0 mS / cm, an electrolyte concentration adjustment process is performed in which the low-concentration calcium solution obtained in the calcium removal process is mixed with an electrolyte, and then the decomposition process is carried out.

[0062] Furthermore, while the processing system S3 uses an electrolytic device 50 as a decomposition device, an electrodialysis membrane device 20 may be used instead of the electrolytic device 50. When using the electrodialysis membrane device 20, it is preferable to remove calcium ions from the contaminated water W3A in the calcium removal step (303) and prepare a low-concentration calcium solution with a calcium concentration of 100 mg / L or less.

[0063] [Implementation Method 4] The treatment method 4 shown in Figure 7 is an example of the treatment method of the present invention and includes a decomposition step (204). Treatment method 4 decomposes organic fluorine compounds in contaminated water W4A. Contaminated water W4A is water contaminated with organic fluorine compounds, with an electrical conductivity of 6.0 mS / cm or higher and a calcium concentration of less than 200 mg / L. Specifically, it is water such as sewage and wastewater from factories that handle organic fluorine compounds, such as fluorine processing plants, and treatment method 4 can be applied to the treatment of water containing organic fluorine compounds such as perfluorooctanesulfonic acid and perfluorooctanoic acid. When such contaminated water W4A is to be treated, the contaminated water W4A can be used directly in the decomposition step as the water to be treated. The decomposition step (204) is the same as the decomposition steps (202) and (203), except that contaminated water W4A is used as the water to be treated, and the preferred embodiments are also the same.

[0064] Treatment method 4 can be implemented using a treatment system S4, as shown in Figure 8, which includes a raw water tank 10, a water to be treated storage tank 14, an electrolytic device 50, and an electrode solution storage tank 30. Treatment system S4 is the same as treatment systems S2 and S3, except that the contaminated water W4A stored in the raw water tank 10 is supplied to the water to be treated storage tank 14.

[0065] The processing methods of the present invention and the systems capable of implementing them have been described above using processing methods 1 to 4 and processing systems S1 to S4 as examples. However, the processing methods of the present invention are not limited to these, as long as the objectives of the present invention can be achieved. For example, in processing systems S2 to S4, which carry out processing systems 2 to 3, a diaphragm-type electrode liquid circulation electrolytic device equipped with an anode chamber 56, a cathode chamber 57, and a reaction chamber 55 is used as the electrolytic device. However, the electrolytic device is not limited to this, and a diaphragm-free electrolytic device may also be used in which the anode and cathode are arranged in the reaction chamber and the anode and cathode react directly with the water to be treated within the reaction chamber. [Examples]

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless its essence is changed.

[0067] <Disassembly Test I> As the experimental apparatus, we used Astom's tabletop electrodialysis machine (Ashilizer® EX3B). The experimental apparatus is equipped with an AC 4-electrode type electrical conductivity meter, and the electrical conductivity of the water to be treated was automatically measured using this conductivity meter.

[0068] The following water samples were prepared, and each was passed through the experimental apparatus, and electrolysis was performed under the following conditions. (Water to be treated) Water to be treated A: Raw water (taken from groundwater, PFOS and PFOA concentrations of 830 ng / L) Water to be treated B-E: Water obtained by adding NaCl to water to be treated, resulting in the electrical conductivity shown in Table 1. (Experimental conditions) • Processing volume: 800mL • Electrode plates: Titanium and platinum • Current: 1.1A~4.4A (current fluctuation) Voltage: 9~15V

[0069] Organic fluorine compounds in the treated water after electrolysis were quantified using solid-phase extraction-liquid chromatography-mass spectrometry (solid-phase extraction-liquid chromatography-mass spectrometry as defined in Target 31 of the Examination Methods for Water Supply Management Target Setting Items, Appendix 4 of the "Regarding the Establishment of Ministerial Ordinances Concerning Water Quality Standards and Partial Amendments to the Enforcement Regulations of the Water Supply Act, etc., and Points to Note in Water Supply Management" (Kensuihatsu No. 1010001, October 10, 2003)). The limit of quantification was 5 ng / L, and the provisional standard value is 50 ng / L or less. The results are shown in Table 1.

[0070] [Table 1]

[0071] <Disassembly Test II> As shown in Figure 9, the ion exchange membrane of the experimental apparatus used in decomposition test I was removed, and a rubber plate with an opening in the center was placed as a partition plate to make the width of the reaction chamber 1 cm, and the decomposition test was carried out. Using treated waters D and E, electrolysis was performed under the same conditions as in decomposition test I. As a result, similar to decomposition test I, the amount of PFAS / PFOS was below the limit of quantification. [Industrial applicability]

[0072] According to the present invention, various types of water that may contain organofluorine compounds can be treated. [Explanation of Symbols]

[0073] 1, 2, 3, 4 Processing methods 10 Raw water tank 12 Electrolyte concentration adjustment tank 14. Storage tank for treated water 20 Electrodialysis Membrane Machine 21, 51 Anode 22, 52 anode 23 Anion exchange membrane 24 Cation exchange membrane 25 Desalination room 26 Concentration chamber 27, 28 Electrode chamber 30 Electrode solution storage tank 31 Electrolyte 40 Concentrated liquid storage tanks 41 Concentrate 50 Electrolyzer 53 Diaphragm 55 Reaction Chamber 56 Anode chamber 57 Cathode Chamber 60 Calcium Removal Equipment L1, L2, L3, L4 piping V1 Switching method W1A, W2A, W3A, W4A contaminated water Water to be treated: W1a, W2a, W3a W1B, W2B, W3B, W4B treated water

Claims

1. A method for treating water to be treated, comprising a decomposition step of passing an electric current through water to be treated, which contains an organofluorine compound and an electrolyte and has an electrical conductivity of 6.0 mS / cm or higher, to decompose the organofluorine compound in the water to be treated.

2. This product decomposes organofluorine compounds in contaminated water, which is water contaminated with organofluorine compounds. The aforementioned water is water from a tap water source. Prior to the decomposition step, there is an electrical conductivity adjustment step in which the contaminated water and an electrolyte are mixed to adjust the water to be treated to have an electrical conductivity of 6.0 mS / cm or higher. The decomposition apparatus for performing the aforementioned decomposition process is an electrodialysis membrane apparatus comprising an anode, a cathode, and a desalination chamber and a concentration chamber formed by alternately arranging an anion exchange membrane and a cation exchange membrane between the anode and the cathode. The treatment method according to claim 1, wherein the decomposition step involves decomposing the organofluorine compound in the water to be treated and performing desalting.

3. The processing method according to claim 2, wherein in the electrical conductivity adjustment step, the electrical conductivity is adjusted using the concentrated liquid discharged from the electrodialysis membrane apparatus in the decomposition step.

4. This product decomposes organofluorine compounds in contaminated water, which is water contaminated with organofluorine compounds. The water in question is not water from a tap water source, and has an electrical conductivity of less than 6.0 mS / cm. The treatment method according to claim 1, comprising: performing an electrical conductivity adjustment step to adjust the water to be treated to have an electrical conductivity of 6.0 mS / cm or higher by mixing the contaminated water with an electrolyte; and then performing the decomposition step.

5. This product decomposes organofluorine compounds in contaminated water, which is water contaminated with organofluorine compounds. The water in question has an electrical conductivity of 6.0 mS / cm or higher and a calcium concentration of more than 200 mg / L. Prior to the aforementioned decomposition step, there is a calcium removal step to remove calcium ions from the contaminated water and prepare a low-concentration calcium solution with a calcium concentration of 200 mg / L or less. The treatment method according to claim 1, wherein the low-concentration calcium solution is used as the water to be treated in the decomposition step.

6. The treatment method according to claim 5, wherein the water is leachate discharged from a final disposal site and / or excess water discharged from a marine disposal site.

7. The treatment method according to claim 1, wherein the water to be treated is sewage and / or factory wastewater from a factory that handles organic fluorine compounds.

8. The processing method according to any one of claims 4 to 7, wherein the disassembly apparatus that performs the disassembly step is a diaphragm-type electrolyte circulation electrolytic apparatus or a diaphragm-free electrolytic apparatus.

9. The treatment method according to any one of claims 2 to 4, wherein the water is one or more selected from the group consisting of groundwater, river water, spring water, lake water, reservoir water, well water, and subsurface water.

10. The treatment method according to any one of claims 1 to 7, wherein the concentration of the organofluorine compound in the water to be treated is 50 ng / L or more and 20,000 ng / L or less.

11. The treatment method according to any one of claims 1 to 7, wherein the organofluorine compound is perfluorooctanesulfonic acid and / or perfluorooctanoic acid.

12. The treatment method according to any one of claims 1 to 7, wherein the electrolyte is NaCl.

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