Water treatment method, and maintenance method and installation method for water treatment apparatus

Abstract

The present invention provides a water treatment method capable of sufficiently reducing the PFAS concentration of water permeated through a filtration membrane disposed on the secondary side of a PFAS adsorbent, and a maintenance method and an installation method for a water treatment apparatus.SOLUTION: In one example, a water treatment method includes an adsorption step of obtaining PFAS-treated water W3 using an adsorbent that adsorbs PFAS, a membrane treatment step of treating the PFAS-treated water W3 using a filtration membrane having a fluorine-containing raw material to obtain filtration membrane-treated water W4, and a maintenance step of regenerating or replacing the adsorbent and simultaneously washing or replacing the filtration membrane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water treatment method, and a maintenance method and an installation method for 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. Businesses are implementing water quality management and purification processes in compliance with this target value.

[0004] Incidentally, in conventional water treatment, a filtration membrane having a fluorine-containing material such as polyvinylidene fluoride is sometimes used (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-062623 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors came up with the idea of ​​treating the PFAS-treated water obtained after removing PFAS from water by adsorbing it onto adsorbents such as activated carbon or ion exchange resins using a filtration membrane made of a fluorine-containing material. However, the inventors' experimental results revealed that PFAS gradually accumulates in trace amounts in the equipment secondary to the adsorbent, and that the accumulated PFAS may gradually leak into the PFAS-treated water. PFAS that leaks from the adsorbent exhibits an affinity for fluorine-containing materials, so there is a risk that it will mainly accumulate in the filtration membrane, which contains fluorine-containing materials.

[0007] In this way, PFASs accumulated in the filtration membranes will gradually leak into the treated water, which could cause the PFAS concentration in the treated water to exceed the target value. If this happens, it will be impossible to reliably reduce the PFAS concentration in the water that passes through the filtration membranes.

[0008] The present invention provides a water treatment method that can sufficiently reduce the PFAS concentration in the permeate of a filtration membrane placed on the secondary side of a PFAS adsorbent, as well as a maintenance method and installation method for a water treatment device. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] A water treatment method for purifying water containing either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound, comprising: an adsorption step of obtaining PFAS-treated water using an adsorbent that adsorbs either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds; a membrane treatment process for treating the PFAS-treated water using a filtration membrane having a fluorine-containing material to obtain filtration membrane-treated water; a maintenance step of regenerating or replacing the adsorbent and simultaneously cleaning or replacing the filtration membrane; The water treatment method according to claim 1, [2] The water treatment method according to [1], further comprising a simulation step of predicting the timing of regeneration or replacement of the adsorbent and the filtration membrane based on the water quality of the PFAS-treated water or the filtration membrane-treated water. [3] The simulation step a calculation step of calculating a total adsorption amount S1 based on the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the raw water to be treated and the amount of water to be treated; a monitoring step of comparing and monitoring the total adsorption amount S1 with a saturation amount S2 of the adsorbent; a prediction step of predicting a time to regenerate or replace the adsorbent based on the total adsorption amount S1, the saturation amount S2, and treatment conditions; a transmitting step of issuing an instruction to regenerate the adsorbent or an instruction to replace the adsorbent before the total adsorption amount S1 exceeds the saturation amount S2; The water treatment method according to [2], comprising: [4] The water treatment method according to any one of [1] to [3], wherein the maintenance step uses an organic solvent to wash the filtration membrane.

[0010] [5] A maintenance method for a water treatment device, comprising: The water treatment device purifies water to be treated that contains either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound, The water treatment device includes: an adsorption means having an adsorbent that adsorbs either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds; and a membrane treatment means having a filtration membrane for treating PFAS-treated water obtained by removing either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds with the adsorbent; the filtration membrane comprises a fluorine-containing material; A maintenance method for a water treatment device, comprising a maintenance step of regenerating or replacing the adsorbent and simultaneously cleaning or replacing the filtration membrane. [6] The maintenance method for a water treatment device described in [5], further comprising a simulation step of predicting the timing of regeneration or replacement of the adsorbent and the filtration membrane based on the water quality of the PFAS-treated water or the filtration membrane-treated water. [7] The simulation step a calculation step of calculating a total adsorption amount S1 based on the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the raw water to be treated and the amount of water to be treated; a monitoring step of comparing and monitoring the total adsorption amount S1 with a saturation amount S2 of the adsorbent; a prediction step of predicting a time to regenerate or replace the adsorbent based on the total adsorption amount S1, the saturation amount S2, and treatment conditions; a transmitting step of issuing an instruction to regenerate the adsorbent or an instruction to replace the adsorbent before the total adsorption amount S1 exceeds the saturation amount S2; The maintenance method for a water treatment device according to [6], [8] The maintenance method for a water treatment device according to any one of [5] to [7], wherein the maintenance step uses an organic solvent to clean the filtration membrane.

[0011] [9] A method for installing a water treatment device, comprising: A method for installing a water treatment system, comprising adding an adsorption means having an adsorbent that adsorbs either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds to the primary side of a membrane treatment means having a filtration membrane made of a fluorine-containing material, and simultaneously cleaning or replacing the filtration membrane.

[10] The method for installing a water treatment device according to [9], wherein an organic solvent is used to clean the filtration membrane. [Effects of the Invention]

[0012] According to the present invention, there are provided a water treatment method capable of sufficiently reducing the PFAS concentration in the permeate of a filtration membrane placed on the secondary side of a PFAS adsorbent, as well as a maintenance method and installation method for a water treatment device. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a water treatment device. DETAILED DESCRIPTION OF THE INVENTION

[0014] The meanings of the terms are as follows: "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.

[0015] 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.

[0016] The treatment target of the water treatment device and water treatment method is not particularly limited as long as it contains PFAS. Examples of raw water include groundwater, surface water, industrial wastewater, and domestic wastewater. Other examples of raw water include concentrated water generated when PFAS-containing water is treated with a separation membrane (such as an ultrafiltration membrane or a reverse osmosis membrane), and reclaimed wastewater generated when PFAS-containing water is treated with an ion exchange resin and then the ion exchange resin is regenerated.

[0017] PFAS concentrations vary depending on the water source. The PFAS concentration in raw water is not particularly limited, but may be, for example, 0.5 ng / L or higher, 4 ng / L or higher, 50 ng / L or higher, 100 ng / L or higher, or 1000 ng / L or higher. In groundwater, PFAS concentrations are often between 4 and 2000 ng / L.

[0018] In addition to PFAS, the treated water may also contain impurities such as organic matter, ammonia nitrogen, anions such as bicarbonate ions, nitrate ions, sulfate ions, and chloride ions, cations such as iron ions, manganese ions, calcium ions, and magnesium ions, and bacteria.

[0019] 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.

[0020] [Water treatment equipment] The water treatment device 1 shown in Figure 1 is used to purify water to be treated that contains PFAS. The water treatment device 1 includes a pumping pipe L1 for pumping up well water W1 (an example of raw water) from a well 2, a raw water tank 4, a first oxidant addition means 5, a raw water tank pipe L2, a raw water pump 6, a sand filter tower 7, a sand filtration treated water pipe L3, an adsorption means 8, a PFAS treated water pipe L4, a second oxidant addition means 9, a membrane treatment means 10, a filtration membrane treated water pipe L5, and a treated water tank 11.

[0021] A first end of the pumping pipe L1 is connected to a pumping pump 3 installed in the well 2, and a second end of the pumping pipe L1 is connected to a raw water tank 4. Through the pumping pipe L1, well water W1 from the well 2 can be supplied to the raw water tank 4 by the action of the pumping pump 3.

[0022] The raw water tank 4 is for storing raw water (well water). The raw water tank 4 is provided with a first oxidizing agent adding means 5. An oxidizing agent such as sodium hypochlorite is supplied from the first oxidizing agent adding means 5 to the raw water in the raw water tank 4.

[0023] A first end of the raw water tank piping L2 is connected to the raw water tank 4, and a second end of the raw water tank piping L2 is connected to the sand filtration tower 7. A raw water pump 6 is provided in the raw water tank piping L2. Through the raw water tank piping L2, stored water W1' in the raw water tank 4 can be supplied to the sand filtration tower 7 by the action of the raw water pump 6.

[0024] The sand filter tower 7 is not particularly limited. Sand filter towers used in known water treatment devices can be used without any restrictions. One sand filter tower 7 may be used alone, or two or more sand filter towers 7 may be used in combination in parallel or in series.

[0025] When the well water W1 contains metal ions such as iron ions and manganese ions, the metal ions can be oxidized and precipitated by mixing an oxidizing agent with the first oxidizing agent adding means 5. These precipitates are filtered in the sand filter tower 7, and sand-filtered water W2 is obtained as the filtrate.

[0026] A first end of the sand filtration treated water pipe L3 is connected to the sand filtration tower 7, and a second end of the sand filtration treated water pipe L3 is connected to the adsorption means 8. The sand filtration treated water pipe L3 allows the sand filtration treated water W2 to be supplied to the adsorption means 8.

[0027] The adsorption means 8 is not particularly limited as long as it has an adsorbent that adsorbs PFAS. In the adsorption means 8, PFAS in the sand filtration treated water W2 is adsorbed by the adsorbent. The PFAS is removed by the adsorbent, thereby obtaining PFAS-treated water W3.

[0028] As the adsorption means 8, there can be used, without limitation, an activated carbon tower or an ion exchange resin tower used in a known water treatment device. One adsorption means 8 may be used alone, or two or more adsorption means 8 may be used in combination in parallel or in series.

[0029] Examples of adsorbents for the adsorption means 8 include organic ion exchangers, activated carbon, and inorganic ion exchangers. However, the adsorbents are not limited to these examples. Furthermore, one type of adsorbent may be used alone, or two or more types may be used in combination.

[0030] Only one ion exchange resin tower or activated carbon tower may be installed, or two or more towers may be installed. An ion exchange resin tower and an activated carbon tower may be used in combination. When two or more ion exchange resin towers are installed and different resins are used in each ion exchange resin tower, they may be regenerated with the same regenerating liquid, or they may be regenerated with different regenerating liquids depending on the characteristics of each type of resin.

[0031] Examples of backbone polymers for ion exchangers include styrene-based, (meth)acrylic, (meth)acrylamide-based, and cellulose-based polymers. From the viewpoint of non-electrostatic interaction-based adsorption of PFAS, highly hydrophobic styrene-based polymers are preferred. From the viewpoint of recyclability, weakly hydrophobic acrylic and acrylamide-based polymers are preferred.

[0032] Examples of ion exchangers include anion exchangers and cation exchangers. From the viewpoint of PFAS removal performance, it is preferable to use anion exchangers 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 anion exchanger is preferred. A strongly basic anion exchanger is an anion exchanger having, as an ion exchange group, a quaternary ammonium group that remains dissociated even in alkaline conditions. A weakly basic anion exchanger is an ion exchanger having a tertiary ammonium group as an ion exchange group.

[0033] Strongly basic anion exchangers include those having various ion exchange groups. Examples of the ion exchange groups include trimethylammonium groups, triethylammonium groups, tripropylammonium groups, tributylammonium groups, hydroxyethyldimethylammonium groups, and dihydroxyethylmethylammonium groups. Among these, trimethylammonium groups are preferred as the ion exchange group from the viewpoints of maximizing 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 groups, the generation of odors due to the ion exchange groups, and the generation of formaldehyde due to the detachment and decomposition of the ion exchange groups over long-term use.

[0034] 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.

[0035] The anion exchanger may be a commercially available product. Examples of 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.

[0036] Activated carbon is made of carbon with micropores (10-200Å in diameter) that are created by reacting carbon materials such as coal and coconut shells with gases and chemicals at high temperatures. These micropores are formed in a mesh-like pattern inside the carbon. The walls of the micropores in activated carbon have a large surface area (500-2500m²). 2 / g) and adsorbs substances such as PFAS onto the surface of the micropores. 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.

[0037] Types 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.

[0038] 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 FILTRASORB400 (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.

[0039] A first end of the PFAS-treated water pipe L4 is connected to the adsorption means 8, and a second end of the PFAS-treated water pipe L4 is connected to the membrane treatment means 10. A second oxidant addition means 9 is provided midway along the PFAS-treated water pipe L4. The PFAS-treated water pipe L4 can supply the PFAS-treated water W3 to which an oxidant such as sodium hypochlorite has been added to the membrane treatment means 10.

[0040] The membrane treatment means 10 has a filtration membrane made of a fluorine-containing material, such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0041] The membrane treatment means 10 is not particularly limited as long as it has a filtration membrane for treating the PFAS-treated water W3. Membrane treatment means used in known water treatment devices can be used without limitation. Examples of the filtration membrane of the membrane treatment means 10 include an ultrafiltration (UF) membrane and a microfiltration (MF) membrane. The membrane treatment means 10 may be used alone or in combination of two or more in parallel or series. Also, the membrane treatment means 10 may be used alone or in combination of two or more.

[0042] A first end of the filtration membrane-treated water pipe L5 is connected to the membrane treatment means 10, and a second end of the filtration membrane-treated water pipe L5 is connected to the treated water tank 11. The filtration membrane-treated water pipe L5 allows the filtration membrane-treated water W4, which is the permeate of the membrane treatment means 10, to be supplied to the treated water tank 11.

[0043] (Installation method) The installation method of the water treatment device 1 is not particularly limited as long as the adsorption means 8 is disposed on the primary side of the membrane treatment means 10. In order to introduce a PFAS purification treatment function to an existing water treatment device having the membrane treatment means 10, it is preferable to newly add the adsorption means 8 to the primary side of the membrane treatment means 10 and simultaneously clean or replace the filtration membrane of the membrane treatment means 10.

[0044] [Water treatment method] The water treatment method is a method for purifying water containing PFAS. The water treatment method includes an adsorption process in which PFAS-treated water is obtained using an adsorbent that adsorbs PFAS; a membrane treatment process in which the PFAS-treated water is treated using a filtration membrane made of a fluorine-containing material to obtain filtration membrane-treated water; and a maintenance process in which the adsorbent is regenerated or replaced while the filtration membrane is cleaned or replaced.

[0045] An example of a water treatment method will be described with reference to FIG. First, well water W1 from a well 2 is stored in a raw water tank 4. In the raw water tank 4, an oxidizing agent such as sodium hypochlorite is supplied to the well water W1 from a first oxidizing agent adding means 5. The precipitates in the stored water in the raw water tank 4 are filtered in a sand filter tower 7, and sand-filtered water W2 is obtained.

[0046] Next, the sand filtration treated water W2 is supplied to the adsorbent of the adsorption means 8. The PFAS in the sand filtration treated water W2 is removed by adsorption in the adsorption means 8, and PFAS-treated water W3 is obtained (adsorption step). The PFAS-treated water W3 is additionally replenished with the required amount of oxidizing agent such as sodium hypochlorite from the second oxidizing agent addition means 9.

[0047] Next, the PFAS-treated water W3 is supplied to the filtration membrane of the membrane treatment means 10. The PFAS-treated water W3 is treated by the filtration membrane of the membrane treatment means 10 to obtain filtration membrane-treated water W4 (membrane treatment process). The filtration membrane-treated water W4 is stored in the treated water tank 11. The filtration membrane-treated water W4 in the treated water tank 11 can be used as drinking water, domestic water, industrial water, etc. In this specification, drinking water means water that meets the water quality standard items and standard values ​​(51 items) and has a total PFOS and PFOA concentration of 50 ng / L or less, which is the water quality management target setting item.

[0048] In the process from well water W1 to membrane-treated water W4, PFAS in the raw water is mainly adsorbed by the adsorbent in adsorption means 8. Before the cumulative amount of PFAS adsorbed exceeds the adsorbent's saturation level, the adsorbent must be regenerated or replaced. In the maintenance process, the adsorbent in adsorption means 8 is regenerated or replaced, and at the same time, the filtration membrane in membrane treatment means 10 is cleaned or replaced.

[0049] In one example, when the PFAS concentration in the PFAS-treated water W3 exceeds a predetermined threshold, the adsorbent in the adsorption means 8 may be regenerated or replaced. The threshold may be 2 ng / L, 4 ng / L, 40 ng / L, or 50 ng / L. When the PFAS concentration in the PFAS-treated water W3 exceeds the threshold, the adsorbent in the adsorption means 8 may be regenerated or replaced, and at the same time, the filtration membrane in the membrane treatment means 10 may be cleaned or replaced.

[0050] In one example, when the cumulative amount of PFAS supplied by passing the PFAS-treated water W3 through the filtration membrane of the membrane treatment means 10 exceeds a predetermined threshold, the filtration membrane of the membrane treatment means 10 may be cleaned or replaced. The threshold is 0.1 mg / m 2 may be 1 mg / m 2 may be 10 mg / m 2 and may be 100 mg / m 2 When the cumulative PFAS supply amount exceeds the threshold, the filtration membrane of the membrane treatment means 10 may be cleaned or replaced, and at the same time, the adsorbent of the adsorption means 8 may be regenerated or replaced.

[0051] In some examples, the regeneration or replacement of the adsorbent in the adsorption means 8 and the cleaning or replacement of the filtration membrane in the membrane treatment means 10 are carried out simultaneously, but the decision to carry out these procedures may be based on an estimate from the adsorption state of PFAS in the adsorption means 8, or may be based on an estimate from the adsorption state of PFAS in the filtration membrane of the membrane treatment means 10.

[0052] The regenerating solution for the ion exchange resin is not particularly limited as long as it can desorb PFAS adsorbed by electrostatic interaction. Examples include solutions containing ionic substances and seawater. 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.

[0053] For PFAS adsorbed by non-electrostatic interactions, it is preferable to use a regeneration liquid containing a nonionic substance. Examples of nonionic substances include water-soluble organic solvents such as alcohols (e.g., methanol, ethanol, isopropyl alcohol) and acetone. However, the regeneration liquid is not limited to these examples. One type of regeneration liquid may be used alone, or two or more types may be used in combination.

[0054] The cleaning solution for the filtration membrane is not particularly limited, and any cleaning solution may be used depending on the fluorine-containing material. Examples include aqueous sodium hydroxide solution, aqueous sodium hypochlorite solution, aqueous sulfuric acid solution, and aqueous citric acid solution. In a preferred example, organic solvents are preferred as cleaning solutions for the filtration membrane because they can effectively remove PFAS accumulated in the filtration membrane containing the fluorine-containing material. Examples of organic solvents include, but are not limited to, ethanol and acetone.

[0055] In a preferred embodiment, the water treatment method may further include a simulation step. In the simulation step, the timing for regenerating or replacing the adsorbent and filtration membrane is predicted based on the water quality of the PFAS-treated water W3 or the membrane-treated water W4. If the adsorbent of the adsorption means 8 is an ion exchanger, the simulation step predicts the timing for regenerating the ion exchanger. If the adsorbent of the adsorption means 8 is activated carbon, the simulation step predicts the timing for replacing the activated carbon.

[0056] In a preferred example, the simulation process may include a calculation step of calculating a total adsorption amount S1 based on the PFAS concentration in the raw water to be treated and the amount of water to be treated; a monitoring step of comparing and monitoring the total adsorption amount S1 with the saturation amount S2 of the adsorbent; a prediction step of predicting the time to regenerate or replace the adsorbent based on the total adsorption amount S1, the saturation amount S2, and the treatment conditions; and a transmission step of issuing an instruction to regenerate or replace the adsorbent before the total adsorption amount S1 exceeds the saturation amount S2.

[0057] The total adsorption amount S1 is calculated as follows. Total adsorption amount S1 = raw water PFAS concentration × cumulative flow rate

[0058] The saturation amount S2 of the adsorbent is calculated using the following method 1 or method 2.

[0059] Method 1: Small-scale column test using actual raw water The water flow conditions are set to the same as those of the actual equipment. The water quality at the column outlet is measured over time. The water flow time at which the amount of PFAS can be detected is designated as T. Saturation amount S2 = Water flow rate × Water flow time T × PFAS concentration in actual raw water

[0060] Method 2: Calculation of equilibrium adsorption amount by equilibrium adsorption test using actual raw water Saturation amount S2 = Amount of adsorbent in actual equipment × Equilibrium adsorption amount

[0061] In the case of groundwater, fluctuations in water quality are minimal, so it is effective to monitor the quality of the treated water (filtration membrane treated water W4) by measuring the PFAS concentration in the raw water in advance. Because groundwater has little fluctuation in water quality, it is easy to predict when to regenerate or replace the adsorbent. For advance predictions, it is useful to obtain the relationship between the amount of raw water supplied and the PFAS concentration in the filtration membrane treated water W4 from the results of a column water flow test, or to perform simulations using the results of equilibrium adsorption tests. Water volume meters and water quality meters are also useful for monitoring water quality.

[0062] The simulation can be performed on-site or remotely, and each function can be performed by a program. Furthermore, instruments such as water quality meters and water flow meters required to perform the functions of the simulation means can be communicatively connected to the components of the water treatment device. For example, remote monitoring of the cumulative flow rate and PFAS concentration of each of the well water W1, sand filtration-treated water W2, and PFAS-treated water W3 is useful.

[0063] The treatment conditions include, but are not limited to, for example, linear velocity, space velocity, water flow rate, and water temperature.

[0064] The timing of issuing a command to regenerate or replace the adsorbent is not particularly limited. For example, the command to regenerate or replace the adsorbent is issued when the total adsorption amount S1, which is the cumulative amount of adsorption onto the adsorbent, becomes 70% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more of the saturation amount S2.

[0065] [Action and effect] In the water treatment method using the water treatment device 1 described above, the filtration membrane containing a fluorine-containing material is cleaned or replaced at the same time as the adsorbent in the adsorption means 8 is regenerated or replaced. Even if PFAS accumulates in the filtration membrane containing a fluorine-containing material, the filtration membrane can be restored to like-new condition at the same time as the adsorption means is regenerated or replaced. Therefore, the PFAS concentration in the permeate of the filtration membrane located on the secondary side of the PFAS adsorbent can be sufficiently reduced.

[0066] The above-described embodiment also includes an explanation of a maintenance method for the water treatment device 1. The maintenance method for the water treatment device is characterized by including a maintenance step of regenerating or replacing the adsorbent of the adsorption means 8 and simultaneously cleaning or replacing the filtration membrane having a fluorine-containing material. According to this maintenance method, even if PFAS accumulates in a filtration membrane made of a fluorine-containing material, the PFAS concentration in the permeate of the filtration membrane placed on the secondary side of the PFAS adsorbent can be sufficiently reduced.

[0067] [Other embodiment examples] Although the present invention has been described above by showing several exemplary embodiments, the present invention is not limited to the exemplary embodiments disclosed in this specification and can be appropriately modified and implemented without departing from the spirit of the invention. The embodiments 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]

[0068] The following examples will be used to further explain the present invention in detail, but the present invention is not limited to the examples.

[0069] [Raw water] Groundwater was used as the raw water. The PFOS concentration in the groundwater was 100ng / L and the PFOA concentration was 30ng / L. Therefore, the PFAS concentration in this groundwater was 130ng / L, which exceeds the standard value of 50ng / L.

[0070] [Water treatment equipment] The water treatment device 1 shown in Figure 1 was used. The details are as follows. Adsorbent: Kuraray's FILTRASORB400 (granular activated carbon from coal) Filtration membrane: Toray Industries "HFU-2020AN (UF membrane, material: PVDF)"

[0071] [Processing conditions] The conditions for treating groundwater in the examples and comparative examples are as follows. ·Linear velocity LV: 12[m / h] ·Space velocity SV:15[h -1 ]

[0072] [Example 1] After passing groundwater for 1,800 days, the granular activated carbon in the adsorption means 8 was replaced with new granular activated carbon, and the filtration membrane in the membrane treatment means 10 was replaced with a new filtration membrane. The PFOS, PFOA, and PFAS concentrations in the PFAS-treated water W3 and the filtration membrane-treated water W4 before replacement are shown in Table 1. After the replacement, groundwater was allowed to flow for one day. The PFOS and PFOA concentrations in the PFAS-treated water W3 and the filtration membrane-treated water W4 were then measured. The results are shown in Table 1.

[0073] [Comparative Example 1] After passing groundwater for 1,800 days, the granular activated carbon in the adsorption means 8 was replaced with new granular activated carbon. At this time, the filtration membrane in the membrane treatment means 10 was not replaced. The PFOS concentrations, PFOA concentrations, and PFAS concentrations in the PFAS-treated water W3 and the filtration membrane-treated water W4 before replacement are shown in Table 1. After the replacement, groundwater was allowed to flow for one day. The PFOS and PFOA concentrations in the PFAS-treated water W3 and the filtration membrane-treated water W4 were then measured. The results are shown in Table 1.

[0074] [Table 1]

[0075] In Example 1, when the activated carbon and filtration membrane were replaced simultaneously and groundwater was passed through for one day, the PFAS concentrations in the PFAS-treated water W3 and the filtration membrane-treated water W4 were reduced to less than 1.0 ng / L. In contrast, simply replacing the activated carbon as in Comparative Example 1 was able to reduce the PFAS concentration in the PFAS-treated water W3, but was unable to sufficiently reduce the PFOS concentration in the filtration membrane-treated water W4. [Industrial Applicability]

[0076] According to the present invention, there are provided a water treatment method capable of sufficiently reducing the PFAS concentration in the permeate of a filtration membrane placed on the secondary side of a PFAS adsorbent, as well as a maintenance method and installation method for a water treatment device. [Explanation of symbols]

[0077] 1. Water treatment equipment 2. Well 3. Water pump 4 Raw Water Tank 5. First oxidizing agent adding means 6 Raw water pump 7 Sand filter tower 8 Adsorption means 9. First oxidizing agent adding means 10 Membrane treatment means 11 Treatment tank

Claims

1. A water treatment method for purifying water to be treated containing either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound, comprising: an adsorption step of obtaining PFAS-treated water using an adsorbent that adsorbs either or both of the perfluoroalkyl compound and the polyfluoroalkyl compound; a membrane treatment step of treating the PFAS-treated water using a filtration membrane containing a fluorine-containing material to obtain filtration membrane-treated water; a maintenance step of regenerating or replacing the adsorbent and simultaneously cleaning or replacing the filtration membrane; The water treatment method according to claim 1,

2. 2. The water treatment method according to claim 1, further comprising a simulation step of predicting a time to regenerate or replace the adsorbent and the filtration membrane based on the water quality of the PFAS-treated water or the filtration membrane-treated water.

3. The simulation step includes: a calculation step of calculating a total adsorption amount S1 based on the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the raw water to be treated and the amount of water to be treated; a monitoring step of comparing and monitoring the total adsorption amount S1 with the saturation amount S2 of the adsorbent; a prediction step of predicting a time to regenerate or replace the adsorbent based on the total adsorption amount S1, the saturation amount S2, and treatment conditions; a transmitting step of issuing an instruction to regenerate the adsorbent or an instruction to replace the adsorbent before the total adsorption amount S1 exceeds the saturation amount S2; The water treatment method according to claim 2, comprising:

4. The water treatment method according to any one of claims 1 to 3, wherein the maintenance step uses an organic solvent to clean the filtration membrane.

5. A maintenance method for a water treatment device, comprising: The water treatment device purifies water to be treated that contains either or both of a perfluoroalkyl compound and a polyfluoroalkyl compound, The water treatment device comprises: an adsorption means having an adsorbent that adsorbs either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds; and a membrane treatment means having a filtration membrane for treating PFAS-treated water obtained by removing either or both of the perfluoroalkyl compounds and the polyfluoroalkyl compounds with the adsorbent; the filtration membrane comprises a fluorine-containing material; A maintenance method for a water treatment device, comprising a maintenance step of regenerating or replacing the adsorbent and simultaneously cleaning or replacing the filtration membrane.

6. 6. The maintenance method for a water treatment device according to claim 5, further comprising a simulation step of predicting a time to regenerate or replace the adsorbent and the filtration membrane based on the water quality of the PFAS-treated water or the filtration membrane-treated water.

7. The simulation step includes: a calculation step of calculating a total adsorption amount S1 based on the total concentration of the perfluoroalkyl compounds and the polyfluoroalkyl compounds in the raw water to be treated and the amount of water to be treated; a monitoring step of comparing and monitoring the total adsorption amount S1 with the saturation amount S2 of the adsorbent; a prediction step of predicting a time to regenerate or replace the adsorbent based on the total adsorption amount S1, the saturation amount S2, and treatment conditions; a transmitting step of issuing an instruction to regenerate the adsorbent or an instruction to replace the adsorbent before the total adsorption amount S1 exceeds the saturation amount S2; The maintenance method for a water treatment device according to claim 6, comprising:

8. The maintenance method for a water treatment device according to any one of claims 5 to 7, wherein the maintenance step uses an organic solvent to clean the filtration membrane.

9. A method for installing a water treatment device, comprising: A method for installing a water treatment system, comprising adding an adsorption means having an adsorbent that adsorbs either or both of perfluoroalkyl compounds and polyfluoroalkyl compounds to the primary side of a membrane treatment means having a filtration membrane made of a fluorine-containing material, and simultaneously cleaning or replacing the filtration membrane.

10. The method for installing a water treatment device according to claim 9 , wherein an organic solvent is used to clean the filtration membrane.

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