Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device, capable of efficiently and sufficiently decomposing PFAS present in water.SOLUTION: In one example, the water treatment method comprises: a removal step of removing a substance A inhibiting ultraviolet treatment in water W1 to be treated; and an irradiation step of irradiating the water W1 to be treated from which the substance A is removed in the removal step with ultraviolet rays. In another example, the water treatment method may further comprise, subsequent to the removal step, a concentration step of increasing the concentration of PFAS present in the water W1 to be treated from which the substance A is removed in the removal step to obtain PFAS-concentrated water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method and a water treatment device. [Background technology]

[0002] Among organic fluorine compounds, there are concerns about the environmental impact of compounds called PFAS, a general term for perfluoroalkyl and polyfluoroalkyl compounds, and it is said that more than 10,000 substances fall into the PFAS category. The two most common examples of PFAS are PFOS (perfluorooctane sulfonate) and PFOA (perfluorooctanoic acid). PFOS and PFOA are particularly difficult to break down in nature and in the body, and are known to accumulate in the environment, such as soil.

[0003] While some PFAS are buried in landfills or released into the atmosphere, the majority are said to be released into the hydrosphere via wastewater. This raises concerns about the impact of PFAS, which are difficult to decompose, on the aquatic environment. In April 2020, Japan established a provisional target value for the combined concentration of PFOS and PFOA in tap water of 50 ng / L or less. Each business is implementing water quality management and purification processes in compliance with this target value.

[0004] Several methods for treating PFAS in water have been proposed (for example, Patent Document 1). Patent Document 1 discloses that an aqueous solution containing fluorocarboxylic acids is irradiated with light including ultraviolet light in the presence of an oxygen-containing gas, thereby decomposing the fluorocarboxylic acids into fluorocarboxylic acids with fewer carbon atoms and fluoride ions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-154277 Summary of the Invention [Problem to be solved by the invention]

[0006] To apply the method described in Patent Document 1 to water treatment, oxygen-containing gas must be injected into the water to be treated under certain pressure conditions. However, it is difficult to dissolve the injected oxygen-containing gas uniformly in the water. The solubility of oxygen gas is also affected by temperature. As a result, PFAS cannot be sufficiently decomposed, and as shown in the examples in Patent Document 1, the PFAS decomposition rate is low.

[0007] The present invention provides a water treatment method and a water treatment device that can efficiently and sufficiently decompose PFAS in water. [Means for solving the problem]

[0008] The present invention has the following aspects. [1] A water treatment method for purifying water to be treated containing either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound by ultraviolet treatment, comprising: a removal step of removing a substance A that inhibits ultraviolet treatment from the water to be treated; an irradiation step of irradiating the water to be treated from which the substance A has been removed in the removal step with ultraviolet light; The water treatment method according to claim 1, [2] The substance A has a molar absorption coefficient of 1 L mol at the wavelength of light irradiated in the wavelength range of 150 nm to 410 nm. -1 cm -1 The water treatment method according to [1], comprising the above-mentioned substance. [3] The water treatment method according to [1] or [2], wherein the substance A includes a substance that consumes either or both of hydroxyl radicals and hydrated electrons. [4] The water treatment method according to any one of [1] to [3], wherein the irradiation step involves irradiating with ultraviolet light having a single wavelength within the range of 150 to 410 nm. [5] The water treatment method according to any one of [1] to [4], further comprising, after the removal step, a concentration step of increasing the concentration of either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds in the water to be treated from which substance A has been removed in the removal step, to obtain PFAS-enriched water. [6] In the concentrating step, the water to be treated is concentrated using an adsorbent that adsorbs either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound; The water treatment method according to [5], wherein the PFAS-treated water that has passed through the adsorbent is obtained after the concentration step is temporarily stopped. [7] The water treatment method according to [6], wherein in the concentration step, the PFAS-enriched water is obtained by supplying a regenerating liquid for regenerating the adsorbent to the adsorbent. [8] The water treatment method according to [6] or [7], wherein in the removal step, a regenerated solution for removing substance A is passed through the adsorbent to remove substance A using the adsorbent. [9] The water treatment method according to [8], wherein in the concentration step, a PFAS elution regenerant is supplied to the adsorbent as a regenerant for regenerating the adsorbent.

[10] In the concentrating step, one or both of the perfluoroalkyl compound and the polyfluoroalkyl compound are concentrated using a filtration membrane; The water treatment method according to any one of [5] to [9], wherein the PFAS-treated water that has permeated the filtration membrane is obtained while the concentration step is being carried out.

[11] In the concentration step, either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound are concentrated using a reverse osmosis membrane or a nanofiltration membrane; The water treatment method according to any one of [5] to

[10] , wherein a portion of the PFAS-enriched water is irradiated with ultraviolet light while the remainder of the PFAS-enriched water is re-enriched.

[12] The water treatment method according to any one of [5] to

[11] , wherein in the concentration step, the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the PFAS concentrated water is concentrated to at least twice the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the water to be treated.

[13] The water treatment method according to any one of [1] to

[12] , wherein a PFAS decomposition accelerator is premixed with the water to be treated from which the substance A has been removed in the removal step.

[0009]

[14] A water treatment device that purifies water to be treated containing either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds by ultraviolet treatment, a removal means for removing a substance A that inhibits ultraviolet treatment from the water to be treated; an irradiation means for irradiating the water to be treated from which the substance A has been removed by the removal means with ultraviolet light; A water treatment device comprising:

[15] The substance A has a molar absorption coefficient of 1 L mol -1 cm -1 The water treatment device according to

[14] , containing the above-mentioned substance.

[16] The water treatment device according to

[14] or

[15] , wherein the substance A includes a substance that consumes either or both of hydroxyl radicals and hydrated electrons.

[17] The water treatment device according to any one of

[14] to

[16] , wherein the removal means has an adsorbent that adsorbs either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound.

[18] The water treatment device according to any one of

[14] to

[17] , further comprising a concentration means for increasing the concentration of either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds in the water to be treated from which the substance A has been removed by the removal means, to obtain PFAS-enriched water.

[19] The water treatment device according to

[18] , wherein the concentrating means has an adsorbent that adsorbs either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound.

[20] The water treatment device according to

[19] , wherein the concentrating means obtains the PFAS-enriched water by supplying a regenerating liquid for regenerating the adsorbent to the adsorbent.

[21] The water treatment device according to any one of

[18] to

[20] , wherein the concentrating means has a filtration membrane that filters out either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound.

[22] The water treatment device according to

[21] , wherein the concentrating means uses the filtration membrane to separate the water to be treated into the PFAS-concentrated water and the PFAS-treated water that has permeated the filtration membrane.

[23] The filtration membrane is a reverse osmosis membrane or a nanofiltration membrane; The water treatment device according to

[21] or

[22] , further comprising a PFAS concentrated water return pipe that returns a portion of the PFAS concentrated water to the primary side of the concentrating means.

[24] The water treatment device according to any one of

[18] to

[23] , wherein a mixing means for mixing a PFAS decomposition accelerator with the PFAS concentrated water is disposed on the primary side of the irradiation means.

[25] The water treatment device according to any one of

[14] to

[24] , further comprising a tank storing a regenerated solution for removing substance A, which is used to remove substance A in the removal means.

[26] The water treatment device according to

[25] , further comprising a tank storing a PFAS elution regenerant for eluting either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the removal means.

[27] The water treatment device according to any one of

[14] to

[26] , wherein the irradiation means is an ultraviolet irradiation device having a UV-LED. [Effects of the Invention]

[0010] According to the present invention, a water treatment method and a water treatment device are provided that can efficiently and sufficiently decompose PFAS in water. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of a water treatment device. [Figure 2] FIG. 2 is a schematic diagram showing another example of the water treatment device. [Figure 3] FIG. 3 is a schematic diagram showing another example of the configuration of a water treatment device. [Figure 4] FIG. 4 is a schematic diagram showing another example of the configuration of a water treatment device. DETAILED DESCRIPTION OF THE INVENTION

[0012] "PFAS" refers to either or both perfluoroalkyl compounds and polyfluoroalkyl compounds, and is a general term for perfluoroalkyl compounds and polyfluoroalkyl compounds. "PFAS concentration" means the combined concentration of perfluoroalkyl and polyfluoroalkyl compounds.

[0013] The "primary side" refers to the upstream side in the direction of flow of the water to be treated and the treated water. The "secondary side" refers to the downstream side in the direction of flow of the water to be treated and the treated water. Therefore, the water to be treated and the treated water flow from the primary side to the secondary side. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0014] The water to be treated is not particularly limited as long as it contains PFAS. Examples of the water to be treated include groundwater, surface water, industrial wastewater, and domestic wastewater. In addition, the water to be treated may be concentrated water generated when water containing PFAS is treated with a separation membrane (nanofiltration membrane, reverse osmosis membrane, etc.), or recycled wastewater generated when water containing PFAS is treated with an ion exchange resin and then the ion exchange resin is regenerated.

[0015] The PFAS concentration in the treated water varies depending on the water source. The PFAS concentration in the treated water is not particularly limited, but may be, for example, 1 ng / L or more, 100 ng / L or more, 10,000 ng / L or more, or 1,000,000 ng / L or more. In groundwater, PFAS concentrations are often between 4 and 2000 ng / L.

[0016] In addition to PFAS, the treated water may also contain impurities such as organic matter, ammonia nitrogen, anions such as bicarbonate ions, carbonate ions, nitrate ions, sulfate ions, and chloride ions; cations such as iron ions, manganese ions, calcium ions, and magnesium ions; and bacteria.

[0017] The water treatment method and water treatment device of the present invention are characterized in that ultraviolet light is irradiated after removing substance A, which inhibits ultraviolet treatment from PFAS-containing water to be treated. Substance A typically includes a substance that absorbs in the wavelength range of the ultraviolet light used for ultraviolet irradiation and can reduce the transmittance of ultraviolet light through the water to be treated.

[0018] Examples of substance A include those having a molar absorption coefficient of 1 L mol at the wavelength of light irradiated in the wavelength range of 150 nm to 410 nm. -1 cm -1 More specifically, examples of substance A include aromatic compounds, organic compounds with unsaturated bonds such as humic acid and fulvic acid, inorganic compounds such as iron ions, manganese ions, and nitrate ions, and turbid substances such as soil.

[0019] In the water treatment method and water treatment device of the present invention, ultraviolet light is irradiated after removing substance A, which inhibits ultraviolet treatment from PFAS-containing water to be treated. This prevents the transmittance of ultraviolet light in the water to be treated from decreasing due to the presence of substance A. As a result, it is believed that the PFAS decomposition rate is improved.

[0020] Substance A also includes substances that consume hydroxyl radicals and hydrated electrons generated by ultraviolet irradiation. Examples of substances that consume hydroxyl radicals and hydrated electrons include organic substances such as humic substances, metal ions (iron ions, manganese ions, arsenic ions, etc.), and anions (carbonate ions, bicarbonate ions, sulfate ions, phosphate ions, soluble silica, chloride ions, nitrate ions, etc.).

[0021] In the water treatment method and water treatment device, the concentration of PFAS in the treated water from which substance A has been removed may be increased to obtain PFAS-enriched water. After increasing the PFAS concentration in the water through concentration, it is thought that the PFAS decomposition rate can be further increased by irradiating the PFAS-enriched water with ultraviolet light.

[0022] PFAS-enriched water with a high PFAS concentration can be obtained by concentrating treated water containing PFAS. The main methods are concentration using an adsorbent and concentration using a filtration membrane, but these examples are not limited to these.

[0023] In the case of concentration using an adsorbent, PFAS is adsorbed onto the adsorbent, resulting in a high concentration of PFAS on the surface and inside the adsorbent. The adsorbent is then regenerated by supplying a regenerating solution to the adsorbent, yielding PFAS-enriched water.

[0024] In the case of concentration using a filtration membrane, PFASs are separated on the primary side of the membrane, resulting in a high PFAS concentration on the primary side. At this time, PFAS-treated water from which PFASs have been removed is obtained on the secondary side of the membrane, and at the same time, PFAS-enriched water from which PFASs have been concentrated is obtained on the primary side of the membrane. Filtration membranes are not particularly limited, but examples include nanofiltration membranes and reverse osmosis membranes.

[0025] Hereinafter, several embodiments of the present invention will be described with reference to the drawings. However, the following description is for representative examples, and the present invention is not limited to the following description. The dimensional ratios in the drawings are for the convenience of explanation and may differ from the actual ones. In the following drawings, the same components are indicated by the same reference numerals, and descriptions of overlapping components may be omitted.

[0026] [First embodiment] (Water treatment equipment) 1 is a water treatment device 1A for purifying water W1 containing PFAS. The water treatment device 1A includes a water-to-be-treated pipe L1, a pump P1, a removal means 7, a concentration means 2 having an adsorbent, a PFAS-treated water pipe L2, a post-treatment means 5, a treated water pipe L6, a tank 4, a regenerated liquid pipe L3, a PFAS-concentrated water pipe L4, an irradiation means 3, a drainage pipe L5, a tank 9, a removal means regenerated liquid pipe L17, and a removal means drainage pipe L18.

[0027] The water to be treated pipe L1 is used to supply the water to be treated W1 to the concentrating means 2. A first end of the water to be treated pipe L1 is connected to a supply source of the water to be treated W1 (not shown), and a second end of the water to be treated pipe L1 is connected to the concentrating means 2. A pump P1 and a removal means 7 are provided in this order in the water to be treated pipe L1. The water to be treated W1 is supplied to the concentrating means 2 via the removal means 7 by the action of the pump P1.

[0028] The removal means 7 is for removing substance A, which inhibits ultraviolet treatment, from the water to be treated W1. The removal means 7 is provided midway through the water to be treated pipe L1 on the upstream side of the concentration means 2. The removal means 7 can remove substance A, which inhibits ultraviolet treatment, from the water to be treated W1. This makes it possible to prevent the transmittance of ultraviolet light in the water to be treated W1 from decreasing due to the presence of substance A. As a result, it is believed that the PFAS decomposition rate will improve in the irradiation means 3, which will be described later.

[0029] The removal means 7 is not particularly limited as long as it can remove radicals, hydrated electron-capturing components, and components that reduce ultraviolet transmittance. For example, an adsorbent can be used. The adsorbent may be the same as the adsorbent used in the concentration means 2 described below, or a different one may be used.

[0030] Tank 9 stores a regenerating liquid used to remove substance A and regenerate the adsorbent in removal means 7. The regenerating liquid is not particularly limited as long as it can desorb substance A adsorbed to the adsorbent in removal means 7 from the adsorbent. The regenerating liquid can be changed depending on the state of the water to be treated W1, the treatment conditions, and the type of adsorbent.

[0031] Examples of the regeneration liquid for regenerating the adsorbent of the removal means 7 include seawater and a regeneration liquid containing an ionic substance. Examples of the ionic substance include halide salts such as sodium chloride, potassium chloride, potassium iodide, sodium bromide, and ammonium chloride, oxoacid salts such as sodium sulfate, sodium nitrate, and ammonium sulfate, acids such as sulfuric acid and hydrochloric acid, and bases such as sodium hydroxide and ammonium hydroxide.

[0032] The regenerating liquid is preferably a substance that accelerates the subsequent ultraviolet reaction, such as the PFAS decomposition accelerator described below.

[0033] The removal means 7 is connected to a removal means regenerating liquid pipe L17 and a removal means drainage pipe L18. The adsorbent of the removal means 7 can be regenerated by supplying regenerating liquid stored in a tank 9 through the removal means regenerating liquid pipe L17. At this time, substance A is removed from the water to be treated W1. The waste liquid after regenerating the adsorbent of the removal means 7 can be drained through the removal means drainage pipe L18.

[0034] If the removal means 7 uses the same adsorbent as the concentration means 2, in addition to components that reduce ultraviolet transmittance and components that capture radicals and hydrated electrons, PFAS will also be adsorbed by the removal means 7, so the regenerant used in the removal means 7 must be different from the regenerant used in the concentration means 2. In this way, a system can be constructed in which PFAS can be eluted using only the regenerant used in the concentration means 2.

[0035] If an adsorbent different from the adsorbent used in the concentration means 2 is used in the removal means 7, PFAS will hardly be adsorbed by the removal means 7. In this case, since the PFAS in the water to be treated W1 is adsorbed by the concentration means 2, the regenerant used in the removal means 7 may be the same as the regenerant used in the concentration means 2. In that case, tank 9 and tank 4, which will be described later, may be shared as the same tank.

[0036] The concentrating means 2 concentrates the water to be treated W1 to obtain PFAS-concentrated water W3 having a concentrated PFAS concentration. In the water treatment device 1A, the concentrating means 2 has an adsorbent that adsorbs PFAS. Examples of adsorbents for the concentrating means 2 include organic ion exchangers, activated carbon, and inorganic ion exchangers. However, the adsorbent is not limited to these examples. Furthermore, one type of adsorbent may be used alone, or two or more types may be used in combination. In one example, the concentrating means 2 may be an ion exchange resin tower filled with an ion exchanger, or an activated carbon tower filled with activated carbon.

[0037] Only one ion exchange resin tower or activated carbon tower may be installed, or two or more towers may be installed, or an ion exchange resin tower and an activated carbon tower may be used in combination. When two or more ion exchange resin columns are installed and different resins are used for each ion exchange resin column, the resins may be regenerated with the same regenerant or with different regenerants depending on the characteristics of each type of resin. The PFAS-enriched water W3 generated from each column may be combined with the irradiation means 3.

[0038] Examples of backbone polymers for ion exchangers include styrene-based, (meth)acrylic, (meth)acrylamide-based, and cellulose-based polymers. From the perspective of non-electrostatic interaction, highly hydrophobic styrene-based polymers are desirable as backbone polymers. From the perspective of recyclability, less hydrophobic acrylic and acrylamide-based polymers are desirable.

[0039] The ion exchanger may be an anion exchanger or a cation exchanger, and it is preferable to use an anion exchanger as the ion exchanger. The anion exchanger may be either weakly basic or strongly basic, but from the viewpoint of adsorption, a strongly basic anion exchanger is preferred because it is easily adsorbed by electrostatic interaction, and from the viewpoint of regeneration, a weakly basic ion exchanger is preferred. Here, the "strongly basic anion exchanger" includes an anion exchanger having, as an ion exchange group, a quaternary ammonium group that remains dissociated even in alkaline conditions. The "weakly basic anion exchanger" includes an ion exchanger having a tertiary ammonium group as the ion exchange group.

[0040] Examples of the strongly basic anion exchanger include those having various ion exchange groups. Examples of the ion exchange group include trimethylammonium group, triethylammonium group, tripropylammonium group, tributylammonium group, hydroxyethyldimethylammonium group, dihydroxyethylmethylammonium group, etc. Among these, the trimethylammonium group is preferred as the ion exchange group from the viewpoints of maximizing the static exchange capacity, preventing an increase in the amount of organic matter due to leaching caused by the poor thermal stability of the ion exchange group, the generation of odors due to the ion exchange group, and the generation of formaldehyde due to the detachment and decomposition of the ion exchange group over long-term use.

[0041] Examples of anion exchangers include anion exchange resins and anion exchange fibers. When a strongly basic anion exchange resin is used as the anion exchange resin, the strongly basic anion exchange resin may be either type I or type II.

[0042] The anion exchanger may be a commercially available product. For example, commercially available ion exchange resins include Diaion HPA25M, HPA512L, SA10A, SA12A, SA20A, and PA308, as well as Relight JA810, JA800, and JA830 (Mitsubishi Chemical Corporation products), A860, A520E, and PFA694E (Purolite Corporation products), Lewatit A8071, Monoplus M500, M800, MP800, and TP-108 (Lanxess AG products). However, the ion exchange resin is not limited to these examples. One type of ion exchange resin may be used alone, or two or more types may be used in combination.

[0043] Activated carbon may be made of carbon with micropores (10 to 200 Å in diameter) that are produced by reacting carbonaceous materials such as coal and coconut shells with gases and chemicals at high temperatures. These micropores are structured like a network inside the carbon, and the walls of the micropores have a large surface area (500 to 2500 m). 2 / g), and substances such as PFAS are adsorbed onto its surface. Activated carbon is more than 90% carbon, some of which is in the form of compounds with oxygen and hydrogen. Ash is a component specific to the raw material and often contains Na, Si, K, Ca, Fe, etc.

[0044] Examples of activated carbon include powdered activated carbon smaller than 100 Mesh, granular activated carbon, fibrous activated carbon, and specially molded activated carbon (honeycomb, sheet, plate, etc.). Among these, granular activated carbon is preferred for water treatment applications. Examples of granular activated carbon include coconut shell charcoal, coal, and crushed charcoal.

[0045] Examples of commercially available activated carbon include Shirasagi WH2c, W2c, WH5c, W5c, LGK-100, and LGK-400 (products of Osaka Gas Chemicals Co., Ltd.), Kuraray Co., Ltd. GW, GW-H, GLC, and Filtersorb 400 (products of Kuraray Co., Ltd.), and PL-1S, PL-C1SK, PL-WPH, and PL-WPS (products of Dainen Co., Ltd.). However, activated carbon is not limited to these examples. One type of activated carbon may be used alone, or two or more types may be used in combination.

[0046] Tank 4 stores a regenerating liquid for regenerating the adsorbent of concentration means 2. The regenerating liquid is not particularly limited as long as it can desorb the PFAS adsorbed to the adsorbent of concentration means 2 from the adsorbent. The regenerating liquid can be changed depending on the state of the water to be treated W1, the treatment conditions, and the type of adsorbent.

[0047] The regeneration liquid for regenerating the adsorbent in the concentration means 2 may be a regeneration liquid containing an ionic substance or seawater, as long as it can desorb PFAS adsorbed by electrostatic interaction. Examples of ionic substances include halide salts such as sodium chloride, potassium chloride, potassium iodide, sodium bromide, and ammonium chloride, oxoacid salts such as sodium sulfate, sodium nitrate, and ammonium sulfate, acids such as sulfuric acid and hydrochloric acid, and bases such as sodium hydroxide and ammonium hydroxide.

[0048] PFAS adsorbed by non-electrostatic interactions are preferably eluted using a regenerant containing a nonionic substance. Examples of nonionic substances include alcohols such as methanol, ethanol, and isopropyl alcohol, and water-soluble organic solvents such as acetone. However, the regenerant is not limited to these examples. One regenerant may be used alone, or two or more may be used in combination.

[0049] It is desirable that the regeneration liquid does not contain any substances that inhibit UV treatment. Specifically, it does not contain any substances that absorb in the relevant UV wavelength range and reduce transmittance, and it does not contain any substances that consume hydroxyl radicals or hydrated electrons generated by accelerated oxidation or accelerated reduction reactions. For example, bicarbonate in accelerated oxidation reactions.

[0050] The regenerating liquid is preferably a substance that accelerates the subsequent ultraviolet reaction, such as the PFAS decomposition accelerator described below.

[0051] The regenerated liquid pipe L3 is used to supply the regenerated liquid in the tank 4 to the adsorbent in the concentrating means 2. A first end of the regenerated liquid pipe L3 is connected to the inside of the tank 4, and a second end of the regenerated liquid pipe L3 is connected to the concentrating means 2 so that the regenerated liquid can be supplied to the adsorbent. A valve V1 is provided in the regenerated liquid pipe L3. By opening and closing the valve V1, it is possible to switch between supplying and not supplying the regenerated liquid in the tank 4 to the concentrating means 2. The opening and closing of the valve V1 may be switched manually or may be automatically controlled by an electric signal.

[0052] In the water treatment device 1A, the PFAS concentration in the adsorbent increases as the PFAS is adsorbed onto the adsorbent in the concentration means 2. Thereafter, a regenerant for regenerating the adsorbent in the concentration means 2 is supplied from the tank 4 to the adsorbent in the concentration means 2, thereby obtaining PFAS-enriched water W3 in which the PFAS is concentrated.

[0053] The PFAS concentrated water pipe L4 is used to supply the PFAS concentrated water W3 from the concentrating means 2 to the irradiation means 3. A first end of the PFAS concentrated water pipe L4 is connected to the concentrating means 2, and a second end of the PFAS concentrated water pipe L4 is connected to the irradiation means 3. A valve V2 is provided on the PFAS concentrated water pipe L4. The supply of the PFAS concentrated water W3 to the irradiation means 3 can be switched on and off by opening and closing the valve V2. The opening and closing of the valve V2 may be switched manually, or may be automatically controlled by an electrical signal.

[0054] The irradiation means 3 is for irradiating the PFAS-concentrated water W3 with ultraviolet light. The PFAS in the PFAS-concentrated water W3 is decomposed by ultraviolet irradiation to obtain UV-treated water W5. In the water treatment device 1A, the UV-treated water W5 is discharged through a drainage pipe L5.

[0055] The wavelength of the ultraviolet light irradiated by the irradiation means 3 is not particularly limited, but is preferably 150 nm to 410 nm. When the wavelength of the ultraviolet light is equal to or greater than the lower limit, it is less likely to be absorbed by dissolved oxygen or water molecules, and the photoreaction is more likely to proceed. In addition, the luminous efficiency of the light source is less likely to decrease, improving energy efficiency. When the wavelength of the ultraviolet light is equal to or less than the upper limit, the light energy of the ultraviolet light itself is sufficiently high, and the efficiency of generating radicals and hydrated electrons is good.

[0056] The irradiation means 3 may or may not include visible light with a wavelength of 410 nm to 800 nm in addition to ultraviolet light, and is not particularly limited.

[0057] The ultraviolet light irradiated by the irradiation means 3 is not particularly limited, but is preferably ultraviolet light having a single wavelength in the range of 150 to 410 nm. Irradiating the PFAS-enriched water W3 with ultraviolet light of a single wavelength allows for more efficient and thorough decomposition of the PFAS in the PFAS-enriched water W3. The single wavelength is preferably 240 nm or longer, and more preferably 350 nm or shorter. When the single wavelength is equal to or greater than the lower limit, the light is less likely to be absorbed by dissolved oxygen or water molecules, facilitating the photoreaction. Furthermore, the light emission efficiency of the light source is less likely to decrease, improving energy efficiency. When the single wavelength is equal to or less than the upper limit, the light energy of the ultraviolet light itself is sufficiently high, resulting in good efficiency in generating radicals and hydrated electrons. It is desirable for the wavelength to match the absorption wavelength of the PFAS decomposition accelerator described below.

[0058] A mercury lamp or UV-LED light source having a single wavelength is suitable as the light source of the irradiation means 3. In a suitable example, the irradiation means 3 may irradiate ultraviolet light having a single wavelength in the range of 150 to 410 nm from a mercury lamp or UV-LED light source having a single wavelength.

[0059] Although not shown, a mixing means for mixing a PFAS decomposition accelerator with the PFAS concentrated water W3 may be disposed on the upstream side of the irradiation means 3. For example, a pipe for mixing the PFAS decomposition accelerator with the PFAS concentrated water W3 in the PFAS concentrated water pipe L4 may be connected to the PFAS concentrated water pipe L4. By mixing the PFAS decomposition accelerator in advance, the PFAS decomposition reaction can be accelerated. As a result, the PFAS decomposition rate by ultraviolet irradiation can be increased. In another example, a pipe for mixing the PFAS decomposition accelerator with the PFAS concentrated water W3 in the PFAS concentrated water pipe L4 may be connected to the regenerated liquid pipe L3.

[0060] The following three types of PFAS decomposition accelerators are preferred. PFAS decomposition accelerator 1: An accelerator that promotes the generation of radicals and hydrated electrons through ultraviolet light. PFAS decomposition accelerator 2: An accelerator that promotes the generation of radicals and hydrated electrons without UV irradiation. PFAS decomposition accelerator 3: One that can reduce side reactions that consume radicals and hydrated electrons.

[0061] When using the above-described PFAS decomposition accelerator 1, the PFAS decomposition accelerator is preferably one that has an absorption spectrum for ultraviolet light with a wavelength in the range of 150 to 410 nm. Examples of the PFAS decomposition accelerator include an oxidizing agent, a reducing agent, and a photocatalyst.

[0062] Examples of oxidizing agents include oxygen acids and salts thereof such as sodium hypochlorite and sodium persulfate, oxygen, ozone, hydrogen peroxide, and halogens such as chlorine. However, the oxidizing agent is not limited to these examples. One type of oxidizing agent may be used alone, or two or more types may be used in combination.

[0063] Examples of reducing agents for the PFAS decomposition accelerator 1 include sodium sulfite, potassium iodide, ferrous chloride, ferrous sulfite, sulfuric acid, and oxalic acid. However, the reducing agent is not limited to these examples. One reducing agent may be used alone, or two or more reducing agents may be used in combination.

[0064] When using an oxidizing or reducing agent for PFAS decomposition accelerator 1, the accelerated reduction reaction can be promoted by creating a reducing atmosphere using gases such as nitrogen or argon, or the accelerated oxidation reaction can be promoted using oxygen or the like.

[0065] As the photocatalyst, a heterogeneous photocatalyst such as TiO2 or Ga2O3, or a metal complex such as a metal complex may be used to promote radicals or hydrated electrons.

[0066] When the above-mentioned PFAS decomposition accelerator 2 is used, examples thereof include an oxidizing agent, a reducing agent, a metal ion, and a catalyst. An example of the oxidizing agent for PFAS decomposition accelerator 2 is hydrogen peroxide. An example of a reducing agent for PFAS decomposition accelerator 2 is potassium iodide.

[0067] When the above-mentioned PFAS decomposition accelerator 3 is used, examples thereof include alcohols and ethers such as methanol, ethanol, and isopropanol, aldehydes, organic acids, chelating agents such as EDTA, and natural organic substances such as NOM, but are not limited to these examples.

[0068] The PFAS decomposition accelerators 1, 2, and 3 may be used singly or in combination of two or more.

[0069] The PFAS decomposition accelerator may be solid, liquid, or gas. From the viewpoint of increasing the PFAS decomposition rate, solid or liquid is preferable. The solid PFAS decomposition accelerator is not particularly limited as long as it comes into contact with the liquid, but it may be dissolved or dispersed in the PFAS-enriched water W3. The decomposition accelerator may be fixed in the ultraviolet irradiation device and brought into contact with the liquid.

[0070] If necessary, the water treatment device 1A may further include a tank (not shown) for storing the PFAS decomposition promoter and a mixing tank (not shown) for mixing the PFAS decomposition promoter with the PFAS concentrated water W3.

[0071] The PFAS-treated water pipe L2 is used to supply the PFAS-treated water W2 that has passed through the concentration means 2 to the downstream treatment means 5. A first end of the PFAS-treated water pipe L2 is connected to the concentration means 2, and a second end of the PFAS-treated water pipe L2 is connected to the downstream treatment means 5.

[0072] The PFAS-treated water pipe L2 is provided with a valve V3. Opening and closing the valve V3 allows the supply of the PFAS-treated water W2 to the downstream treatment means 5 to be switched on and off. Because PFAS is removed by an adsorbent in the concentration means 2, the PFAS-treated water W2 passes through the concentration means 2 while concentration is temporarily stopped. The opening and closing of the valve V3 may be switched manually or automatically controlled by an electrical signal.

[0073] The downstream treatment means 5 is intended to convert the water quality of the PFAS-treated water W2 into a usable state. The downstream treatment means 5 may be appropriately selected depending on the water quality of the water to be treated W1 and the treated water W4, and is not particularly limited. Examples of downstream treatments include, but are not limited to, ion exchange treatment, coagulation treatment, oxidation treatment, sand filtration treatment, membrane filtration treatment, and sterilization treatment. Furthermore, one type of downstream treatment may be performed alone, or two or more types may be performed in combination. The treated water W4 flows through the treated water pipe L6 and can be used as drinking water, domestic water, industrial water, etc. Drinking water means water that meets the water quality standard items and standard values ​​(51 items).

[0074] (Water treatment method) Next, an example of a water treatment method using the above-described water treatment device 1A will be described.

[0075] First, the process of removing substance A will be described. In the process of removing substance A, substance A that inhibits ultraviolet treatment in the water to be treated W1 is removed. In the process of removing substance A, substance A in the water to be treated W1 is adsorbed by the adsorbent of the removal means 7. As a result, the concentration of substance A increases in the adsorbent of the removal means 7. Thereafter, by supplying a regenerating liquid to regenerate the adsorbent of the removal means 7, the wastewater in which substance A has been concentrated is discharged through the removal means drainage pipe L18. After the substance A removal step, the content of substance A in the water to be treated W1 is preferably as low as possible, and may be, for example, 1% by mass or less, or 0.1% by mass or less.

[0076] It is also useful to adjust the treatment conditions for the substance A removal process while directly monitoring the UV transmittance of the PFAS-enriched water W3. More specifically, the higher the UV transmittance of the relevant UV wavelengths of the PFAS-enriched water W3 and the higher the removal rate of components that capture radicals and hydrated electrons, the better. For example, the treatment conditions of the removal means 7 may be adjusted so that the UV transmittance and removal rate are 70% or higher, 90% or higher, or 95% or higher.

[0077] The treatment conditions for the substance A removal step include, for example, the selection of the adsorbent for the removal means 7 and the selection of the numerical range of the water flow rate (space velocity SV, linear velocity LV). To measure the ultraviolet transmittance of the PFAS-enriched water W3, an ultraviolet transmittance sensor may be installed in the PFAS-enriched water pipe L4, or a sample of the PFAS-enriched water W3 may be obtained and measured separately. When the ultraviolet transmittance of the PFAS-enriched water W3 falls below a threshold value (for example, less than 70%), it is preferable to regenerate or replace the adsorbent of the removal means 7.

[0078] Next, the concentration process will be described. During concentration, pump P1 is stopped. Then, valves V1 and V2 are opened, and valve V3 is closed. In the concentration process, PFAS in the water to be treated W1 is adsorbed onto the adsorbent. As a result, the PFAS concentration in the adsorbent of concentration means 2 increases. Then, a regenerant for regenerating the adsorbent of concentration means 2 is supplied from tank 4 to the adsorbent of concentration means 2, thereby obtaining PFAS-enriched water W3 in which PFAS is concentrated.

[0079] In the concentration step, the PFAS concentration in the PFAS-enriched water W3 is preferably at least twice the PFAS concentration in the water to be treated W1, more preferably at least 100 times, and even more preferably at least 1000 times. When concentrating using an adsorbent, PFAS can be concentrated to a higher concentration than when concentrating using a filtration membrane.

[0080] Next, the irradiation step will be described. PFAS-enriched water W3 is supplied to irradiation means 3. Then, in irradiation means 3, the PFAS-enriched water W3 is irradiated with ultraviolet light, thereby decomposing the high concentration of PFAS in the PFAS-enriched water W3 and producing UV-treated water W5. In water treatment device 1A, UV-treated water W5 is discharged through drainage pipe L5.

[0081] Before irradiating the PFAS-enriched water W3 with ultraviolet light, it is preferable to premix a PFAS decomposition accelerator with the PFAS-enriched water W3. By premixing the PFAS decomposition accelerator, the PFAS decomposition reaction can be accelerated. As a result, the PFAS decomposition rate by ultraviolet light irradiation can be increased.

[0082] The PFAS decomposition accelerator may be supplied to and mixed with the PFAS concentrated water W3 in the PFAS concentrated water piping L4. Alternatively, a mixing tank may be additionally installed, and the PFAS concentrated water W3 and the PFAS decomposition accelerator may be mixed in the mixing tank.

[0083] In the irradiation step, ultraviolet light having a single wavelength in the range of 150 to 410 nm is preferably irradiated onto the PFAS-enriched water W3. As described above, ultraviolet light having a single wavelength in the range of 150 to 410 nm does not contain excess ultraviolet light not utilized in the PFAS decomposition reaction. Therefore, it is possible to suppress the generation of chemical species such as ozone that may cause a decrease in the decomposition efficiency of PFAS. As a result, it is believed that the decomposition efficiency of PFAS is improved. The single wavelength is preferably 240 nm or more, more preferably 250 nm or more. Furthermore, it is more preferably 350 nm or less, and even more preferably 290 nm or less.

[0084] Next, the PFAS removal process will be described. Hereinafter, the PFAS removal process will be referred to as the "PFAS removal process" to distinguish it from the substance A removal process. In the water treatment device 1A, PFAS is removed from the water to be treated W1 using an adsorbent in the concentration means 2. By removing PFAS from the water to be treated W1, PFAS-treated water W2 is obtained.

[0085] In the PFAS removal process, pump P1 is operated. Then, valves V1 and V2 are switched from open to closed, and valve V3 is switched from closed to open. In this way, the water to be treated W1 is concentrated using an adsorbent that adsorbs PFAS in the concentration process, and after the concentration process is temporarily stopped, PFAS-treated water W2 is obtained, thereby completing the PFAS removal process.

[0086] (Mechanism of action) According to the embodiment described above, after removing substance A from the water to be treated containing PFAS, ultraviolet light can be irradiated. As already explained, substance A is a substance that inhibits ultraviolet treatment, and includes, for example, substances that consume hydroxyl radicals and hydrated electrons. Therefore, the presence of substance A can prevent a decrease in the transmittance of ultraviolet light through the water to be treated W1 and the amount of hydroxyl radicals and hydrated electrons produced by photoreaction. As a result, it is believed that the PFAS decomposition rate is improved in the irradiation means 3 described below.

[0087] [Second embodiment] The water treatment device 1B shown in FIG. 2 differs from the water treatment device 1A shown in FIG. 1 mainly in the following points. In the water treatment device 1B, the concentrating means 6 has a filtration membrane that filters out PFAS.

[0088] 2 is for purifying water W1 containing PFAS. Water treatment device 1B includes a water-to-be-treated pipe L1, a pump P1, a removal means 7, a concentration means 6 having a filtration membrane, a PFAS-treated water pipe L2, a post-treatment means 5, a treated water pipe L6, a tank 9, a PFAS-concentrated water pipe L4, an irradiation means 3, a drainage pipe L5, a removal means regenerated liquid pipe L17, and a removal means drainage pipe L18.

[0089] In the water treatment device 1B, the concentrating means 6 uses a filtration membrane to separate the water to be treated W1 into PFAS-concentrated water W3 and PFAS-treated water W2 that has permeated the filtration membrane. PFAS-treated water W2 from which PFAS has been removed is obtained on the secondary side of the filtration membrane, and at the same time, PFAS-concentrated water W3 from which PFAS has been concentrated is obtained on the primary side of the filtration membrane. In this way, by concentrating PFAS using the filtration membrane and obtaining PFAS-treated water that has permeated the filtration membrane while performing the concentration process, the PFAS removal process and the concentration process can be performed simultaneously.

[0090] The concentrating means 6 having a filtration membrane may be a nanofiltration membrane device or a reverse osmosis membrane device, and is not particularly limited. The material of the filtration membrane is also not particularly limited as long as it can separate and filter PFAS.

[0091] When a reverse osmosis membrane device is used as the concentrating means 6, it is preferable to add a PFAS concentrated water return pipe L7 that returns a portion of the PFAS concentrated water W3 to the primary side of the concentrating means 6, as in the water treatment device 1C shown in Figure 3. A first end of the PFAS concentrated water return pipe L7 is connected to the middle of the PFAS concentrated water pipe L4, and a second end of the PFAS concentrated water return pipe L7 is connected to the treated water pipe L1 on the secondary side of the pump P1. The PFAS concentrated water return pipe L7 allows a portion of the PFAS concentrated water W3 generated on the primary side of the reverse osmosis membrane to be supplied to the irradiation means 3 for ultraviolet irradiation, while the remainder of the PFAS concentrated water W3 is resupplied to the concentrating means 6 for reconcentration. This improves the recovery rate of the PFAS-treated water W2 that has permeated the reverse osmosis membrane.

[0092] The water treatment device 1B and the water treatment device 1C also have the same mechanism of action as the water treatment device 1A of FIG.

[0093] [Third embodiment] As in the water treatment device 1D shown in FIG. 4, substance A may be removed by passing two or more different types of regenerating liquid through the removal means 7.

[0094] 4 is for purifying water W1 containing PFAS. Water treatment device 1D includes a water-to-be-treated pipe L1, a pump P1, a removal means 7, a PFAS-treated water pipe L2, a post-treatment means 5, a treated water pipe L6, a tank 8, a regenerated liquid pipe L3, a PFAS-concentrated water pipe L4, an irradiation means 3, a drainage pipe L5, a tank 10, a PFAS-eluting regenerated liquid pipe L20, and a substance A removal drainage pipe L21.

[0095] Tank 8 stores a regenerated liquid for removing substance A, which is used to remove substance A and regenerate the adsorbent in removal means 7. There are no particular limitations on the regenerated liquid for removing substance A, as long as it can desorb substance A adsorbed to the adsorbent in removal means 7 from the adsorbent. The regenerated liquid for removing substance A can be changed depending on the state of the water to be treated W1, the treatment conditions, and the type of adsorbent.

[0096] Examples of the regenerating solution for removing substance A include seawater and a regenerating solution containing an ionic substance. Examples of the ionic substance include halide salts such as sodium chloride, potassium chloride, potassium iodide, sodium bromide, and ammonium chloride, oxoacid salts such as sodium sulfate, sodium nitrate, and ammonium sulfate, acids such as sulfuric acid and hydrochloric acid, and bases such as sodium hydroxide and ammonium hydroxide. As the regenerating solution for removing substance A, one type of ionic substance may be used alone, or two or more types may be used in combination.

[0097] According to the water treatment device 1D, in order to remove substance A from the water to be treated W1, a regenerated solution for removing substance A stored in a tank 8 can be passed through the adsorbent of the removal means 7. Here, the regenerated solution for removing substance A is selected so as not to elute PFAS from the adsorbent of the removal means 7.

[0098] According to the water treatment device 1D, substance A removal regenerated solution stored in tank 8 is passed through the adsorbent in removal means 7, thereby eluting substance A without eluting PFAS, and then the substance can be discharged. Substance A may be discharged from drainage pipe L5 without operating ultraviolet irradiation means 3, but to avoid contamination of the inside of the device by substance A, it may also be discharged from substance A removal drainage pipe L21. In the water treatment device 1D, the step of removing substance A can be carried out as described here.

[0099] A valve V12 is provided in the drainage pipe L21 for removing substance A. By opening and closing the valve V12, it is possible to switch between discharging and not discharging substance A. The opening and closing of the valve V12 may be switched manually, or may be automatically controlled by an electrical signal.

[0100] The concentration of the ionic substance in the regenerated solution for removing substance A is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass. When the concentration of the ionic substance in the regenerated solution for removing substance A is equal to or greater than the lower limit of the aforementioned range, the elution amount of substance A is further improved. When the concentration of the ionic substance in the regenerated solution for removing substance A is equal to or less than the upper limit of the aforementioned range, chemical costs can be reduced.

[0101] Tank 10 stores a PFAS elution regenerated liquid used to elute PFAS in removal means 7. The PFAS elution regenerated liquid is not particularly limited as long as it can desorb PFAS adsorbed to the adsorbent in removal means 7 from the adsorbent. The PFAS elution regenerated liquid can be changed depending on the state of the water to be treated W1, the treatment conditions, and the type of adsorbent.

[0102] In the water treatment device 1D after the removal process of substance A is completed, the PFAS elution regenerated solution stored in tank 10 can be passed through the adsorbent of the removal means 7. Here, the PFAS elution regenerated solution is selected to elute PFAS from the adsorbent of the removal means 7.

[0103] A valve V11 is provided in the PFAS elution regenerant liquid pipe L20 connected to the tank 10. The supply of the PFAS elution regenerant liquid can be switched on and off by opening and closing the valve V11. The opening and closing of the valve V11 may be switched manually or automatically controlled by an electrical signal.

[0104] According to the water treatment device 1D, the PFAS elution regenerated solution stored in the tank 10 is passed through the adsorbent in the removal means 7, thereby eluting and concentrating the PFAS in the removal means 7. The PFAS can then be decomposed using the irradiation means 3 and discharged. In the water treatment device 1D, the concentration step and irradiation step can be carried out as described here.

[0105] As the regenerant for PFAS elution, a nonionic substance is preferred, and it is more preferred to use a combination of an ionic substance and a nonionic substance. Examples of nonionic substances include alcohols such as methanol, ethanol, and isopropyl alcohol, and water-soluble organic solvents such as acetone. The ionic substance and nonionic substance used as the regenerating solution for PFAS elution may be used alone or in combination of two or more.

[0106] The concentration of the ionic substance in the regenerated solution for PFAS elution is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass. When the concentration of the ionic substance in the regenerated solution for PFAS elution is equal to or greater than the lower limit of the above-mentioned range, the amount of PFAS eluted is further improved. When the concentration of the ionic substance in the regenerated solution for PFAS elution is equal to or less than the upper limit of the above-mentioned range, chemical costs can be reduced. The concentration of nonionic substances in the PFAS elution regeneration solution should be selected based on the strength of the hydrophobic interaction between the adsorbent and PFAS.

[0107] In the water treatment device 1D, the regenerated solution for PFAS elution and the regenerated solution for substance A removal are supplied from different tanks 8 and 10, respectively. When removing substance A using two or more different regenerating solutions, if the hydrophobic interaction between the adsorbent and PFAS is weak, PFAS may be eluted during regeneration with the regenerating solution for removing substance A. In this case, PFAS cannot be properly treated, so it is preferable to use a styrene-based polymer, which has a strong hydrophobic interaction with PFAS, as the adsorbent for removal means 7.

[0108] [Other embodiment examples] Although one embodiment has been described above by showing one example embodiment, the present invention is not limited to the example embodiment disclosed in this specification and can be appropriately modified and implemented without departing from the spirit of the invention. The embodiment disclosed in this specification can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. [Example]

[0109] Hereinafter, the embodiments will be described in more detail with reference to examples, but the present invention is not limited to the following description.

[0110] [Example 1] Water treatment equipment 1A shown in FIG. 1 is used to purify water W1 containing PFAS. The PFAS concentration in the water W1 is 10 ng / L. Activated carbon or ion exchange resin is used as the adsorbent in the concentration means 2. A UV-LED light source that irradiates ultraviolet light having a single wavelength in the range of 255 to 320 nm is used as the ultraviolet light source in the irradiation means 3. The output of the UV-LED light source is 10 W.

[0111] In Example 1, PFASs in the treated water W1 are concentrated to obtain PFAS-enriched water W3 with a PFAS concentration of 10,000 ng / L. The PFAS-enriched water W3 is then irradiated with ultraviolet light from a UV-LED light source. In this test, the PFAS degradation rate due to ultraviolet irradiation is assumed to be constant at 30%. Therefore, the PFAS degradation rate per 1 W can be expected to be 10,000 ng / L × 0.3 ÷ 10 W = 300 ng / L.

[0112] [Example 2] Except for changing the PFAS concentration of the water to be treated W1 to 100 ng / L, PFAS is concentrated in the water to be treated W1 under the same conditions as in Example 1 to obtain PFAS-enriched water W3 with a PFAS concentration of 100,000 ng / L. Then, under the same conditions as in Example 1, ultraviolet light is irradiated onto the PFAS-enriched water W3 from a UV-LED light source. Assuming that the PFAS degradation rate due to UV irradiation in this test is constant at 30%, the PFAS degradation rate per 1 W can be predicted to be 100,000 ng / L × 0.3 ÷ 10 W = 3,000 ng / L.

[0113] [Example 3] Water to be treated W1 containing PFAS was purified using the water treatment device 1D shown in Figure 4. The PFAS concentration in the water to be treated W1 was 2000 ng / L. A styrene-based anion exchange resin was used as the adsorbent for the removal means 7. A 6 W low-pressure mercury lamp light source with an emission wavelength of 254 nm was used as the ultraviolet light source for the irradiation means 3.

[0114] In Example 3, the removal step was carried out by the removal means 7 of the water treatment device 1D. Specifically, substance A (carbonate ions, nitrate ions, and organic matter other than PFAS, such as humic substances and fulvic acid) and PFAS were adsorbed onto a styrene-based ion exchange resin, which was the adsorbent of the removal means 7, and removed from the water to be treated W1. To remove substance A adsorbed to the adsorbent, a regenerated solution for removing substance A (aqueous solution containing 10% by mass of NaCl) in tank 8 was passed through the regenerated solution pipe L3 to the removal means 7, and substance A was discharged from the wastewater pipe L21 for removing substance A. Thereafter, the passage of the regenerated solution for removing substance A was stopped.

[0115] Next, in the concentration step, the PFAS elution regenerated solution (aqueous solution containing 10% by mass of NaCl and 40% by mass of methanol) stored in tank 10 was passed through the adsorbent in removal means 7, thereby eluting and concentrating the PFAS adsorbed to the adsorbent in removal means 7. PFAS-enriched water W3, in which PFAS was concentrated, was passed through irradiation means 3, and ultraviolet light was irradiated in irradiation means 3. A 6 W low-pressure mercury lamp light source having an emission wavelength of 254 nm was used as the ultraviolet light source for irradiation means 3. As a result, by ensuring that inhibitors were removed in advance, the PFAS degradation rate reached 71%.

[0116] [Comparative Example 1] The PFAS-containing treatment water W1 was purified using the water treatment device 1D under the same conditions as in Example 3, except that a concentration process was performed in which the PFAS elution regenerated solution was passed through the adsorbent of the removal means 7, without performing a removal process in which the substance A adsorbed on the adsorbent was removed using the substance A removal regenerated solution. If the inhibitors were not removed beforehand, PFAS degradation was significantly inhibited, resulting in a 0% degradation rate. [Industrial Applicability]

[0117] According to the present invention, a water treatment method and a water treatment device are provided that can efficiently and sufficiently decompose PFAS in water. [Explanation of symbols]

[0118] 1. Water treatment equipment 2 Concentration means 3 Irradiation means 7 Removal means

Claims

1. A water treatment method for purifying water to be treated containing either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound by ultraviolet treatment, comprising: a removal step of removing a substance A that inhibits ultraviolet treatment from the water to be treated; an irradiation step of irradiating the water to be treated from which the substance A has been removed in the removal step with ultraviolet light; The water treatment method according to claim 1,

2. The substance A has a molar absorption coefficient of 1 Lmol at the wavelength of light irradiated in the wavelength range of 150 nm to 410 nm. －１ cm －１ The water treatment method according to claim 1 , wherein the water contains a substance selected from the group consisting of:

3. The water treatment method according to claim 1 , wherein the substance A includes a substance that consumes either or both of hydroxyl radicals and hydrated electrons.

4. 2. The water treatment method according to claim 1, wherein the irradiation step involves irradiating with ultraviolet light having a single wavelength in the range of 150 to 410 nm.

5. 2. The water treatment method according to claim 1, further comprising a concentration step after the removal step, in which the concentration of either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds in the treated water from which the substance A has been removed in the removal step is increased to obtain PFAS-concentrated water.

6. In the concentrating step, the water to be treated is concentrated using an adsorbent that adsorbs either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound; The water treatment method according to claim 5 , wherein the PFAS-treated water that has passed through the adsorbent is obtained after the concentration step is temporarily stopped.

7. 7. The water treatment method according to claim 6, wherein in the concentrating step, the PFAS concentrated water is obtained by supplying a regenerating liquid for regenerating the adsorbent to the adsorbent.

8. The water treatment method according to claim 6 , wherein in the removal step, a regenerated solution for removing the substance A is passed through the adsorbent to remove the substance A using the adsorbent.

9. 9. The water treatment method according to claim 8, wherein in the concentrating step, a regenerant solution for PFAS elution is supplied to the adsorbent as a regenerant solution for regenerating the adsorbent.

10. In the concentrating step, one or both of the perfluoroalkyl compound and the polyfluoroalkyl compound are concentrated using a filtration membrane; The water treatment method according to claim 5 , wherein the PFAS-treated water that has permeated the filtration membrane is obtained while the concentration step is being carried out.

11. In the concentrating step, one or both of the perfluoroalkyl compound and the polyfluoroalkyl compound are concentrated using a reverse osmosis membrane or a nanofiltration membrane; 6. The water treatment method according to claim 5, wherein the remainder of the PFAS concentrated water is re-concentrated while irradiating a portion of the PFAS concentrated water with ultraviolet light.

12. The water treatment method according to claim 5, wherein in the concentration step, the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the PFAS concentrated water is concentrated to at least twice the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the water to be treated.

13. The water treatment method according to any one of claims 1 to 12, wherein a PFAS decomposition accelerator is premixed with the water to be treated from which the substance A has been removed in the removing step.

14. A water treatment device that purifies water to be treated containing either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound by ultraviolet treatment, a removal means for removing a substance A that inhibits ultraviolet treatment from the water to be treated; an irradiation means for irradiating the water to be treated from which the substance A has been removed by the removal means with ultraviolet light; A water treatment device comprising:

15. The substance A has a molar absorption coefficient of 1 Lmol at the wavelength of light irradiated in the wavelength range of 150 nm to 410 nm. －１ cm －１ The water treatment device of claim 14, comprising a material that is one of the above.

16. The water treatment device according to claim 14 , wherein the substance A includes a substance that consumes either or both of hydroxyl radicals and hydrated electrons.

17. The water treatment device according to claim 14, wherein the removal means has an adsorbent that adsorbs either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds.

18. The water treatment device according to claim 14, further comprising a concentration means for increasing the concentration of either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds in the water to be treated from which the substance A has been removed by the removal means, thereby obtaining PFAS-concentrated water.

19. The water treatment device according to claim 18, wherein the concentrating means has an adsorbent that adsorbs either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds.

20. The water treatment device according to claim 19, wherein the concentrating means obtains the PFAS-concentrated water by supplying a regenerating liquid for regenerating the adsorbent to the adsorbent.

21. The water treatment device according to claim 18 , wherein the concentrating means has a filtration membrane that filters out either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds.

22. 22. The water treatment device according to claim 21, wherein the concentrating means separates the water to be treated into the PFAS-concentrated water and the PFAS-treated water that has permeated the filtration membrane using the filtration membrane.

23. the filtration membrane is a reverse osmosis membrane or a nanofiltration membrane; 22. The water treatment device according to claim 21, further comprising a PFAS concentrate return pipe for returning a portion of the PFAS concentrate to the primary side of the concentrating means.

24. 19. The water treatment device according to claim 18, wherein a mixing means for mixing a PFAS decomposition accelerator with the PFAS concentrated water is disposed on the primary side of the irradiation means.

25. The water treatment device according to claim 14 , further comprising a tank storing a regenerated solution for removing the substance A, which is used to remove the substance A in the removal means.

26. The water treatment device according to claim 25, further comprising a tank storing a PFAS elution regenerant solution for eluting either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the removal means.

27. The water treatment device according to any one of claims 14 to 26, wherein the irradiation means is an ultraviolet irradiation device having a UV-LED.

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