PFAS capturing method and system therefor, and PFAS-reduced water production method and system therefor

Abstract

In this PFAS capturing and processing system 10, a structural agent 1 that contains, as a main agent, a water-soluble cationic polymer flocculant (A) containing a carbon chain having a higher-order structure and a structural agent 2 that contains at least one of inorganic agents including polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride and contains, as a main agent, a water-soluble cationic polymer flocculant (B) containing positive charges and having a cationic value smaller than that of the water-soluble cationic polymer flocculant (A) are input from an input unit 22 into contaminated water containing a PFAS-containing aqueous mixture and stored in a reaction tank 21 of a structured reactor 20, a structure 1 is formed in the contaminated water, anionic PFAS are adsorbed to the structure 1, a structure 2, such as an iron cation or an aluminum cation, having a hydrophobic carbon chain is formed on the PFAS adsorbed to the structure 1, by using the structural agent 2, so as to be superimposed on the captured PFAS, and the PFAS are stably held in a sandwich shape and can be separated in water.

Description

PFAS capture method and system, PFAS reduced water production method and system

[0001] The present invention relates to a method and system for capturing organic fluorine compounds (hereinafter referred to as PFAS) in contaminated water containing an aqueous mixture containing PFAS, and a method and system for producing PFAS-reduced water.

[0002] PFAS has little bond reactivity or electrostatic affinity like ordinary chemical bonds, and its hard, stable structure is similar to that of highly persistent pesticides such as DDT. PFAS has been used as a foaming agent in fire extinguishers due to its stability, good storage properties, ease of movement, and ability to drastically reduce interfacial tension even with a small amount.

[0003] In practical terms, PFAS has been used in well-known non-stick frying pans, the inner lining of weapons, and as a mold release agent for molded products, taking advantage of its chemical stability due to its low reactivity with other substances.

[0004] Because PFAS are widely used in this way, they are dispersed into the environment, and there is a need for methods and systems to capture and treat them.

[0005] When an inorganic flocculant is added to a PFAS-containing aqueous mixture in an attempt to capture PFAS, the dispersed colloidal particles coalesce to form large aggregates, but PFAS is an ultrafine molecular particle with little interaction and high kinetic energy, so it is rarely incorporated into the aggregates and remains on the surface of the aggregates in a state where it can be quickly moved. Therefore, it was not possible to capture PFAS using a flocculant.

[0006] The detailed characteristics of this PFAS are as follows:

[0007] The properties of contaminated water containing PFAS-containing aqueous mixtures vary depending on the nature of the business operations at the source of the discharge, but PFAS itself does not change depending on the properties of the contaminated water.

[0008] That is, PFAS is stable even when the environment changes, and although it is a low-molecular-weight substance that is hydrophilic and lipophilic but does not dissolve in extremely large amounts in water or oil, it has strong surfactant properties and foaming properties even in small amounts.

[0009] Furthermore, PFAS is often dispersed transparently without accompanying solid matter, and since it has low surface tension, it moves to the surface of coexisting substances and disperses, so it hardly aggregates.

[0010] Therefore, even if an inorganic flocculant is added to a PFAS-containing aqueous mixture, PFAS exhibits properties that disperse colloids without forming any flocculated colloids.

[0011] In the case of activated carbon adsorption, in the presence of organic molecules and other PFAS, PFAS adsorbed on the adsorption sites of activated carbon easily desorb from the sites and are replaced by organic molecules or other substances. The reasons for this are known as follows:

[0012] The fluorine atoms bonded to the carbon skeleton of the PFAS molecule are larger than the hydrogen atoms of ordinary hydrocarbons, resulting in a twisted bond in the carbon chain, which severely restricts the movement of the carbon chain. Furthermore, the distance between the fluorine and the carbon chain (skeleton) is relatively short, and there is a large overlap of the electron orbitals, meaning that the strong bond results in little interaction with other molecular species. As a result, the structure of PFAS itself is such that the fluorine and carbon chains are slightly twisted due to electronic repulsion, resulting in little bonding strength with other chemical molecules.

[0013] Typical PFAS molecules include PFOS and PFOA, and although activated carbon adsorption has been described in many research papers as a common removal method for these, no technology has been found that can actually capture even a few percent of PFAS from contaminated water. Also, as mentioned above, when other organic matter comes close to the activated carbon adsorption method, the PFAS easily loses its adsorption area (adsorption site) to the organic matter, causing it to separate from the activated carbon, meaning that it is not actually adsorbed.

[0014] JP 2021-146326 A JP 2022-79109 A

[0015] The present invention aims to provide a method and system for capturing PFAS in contaminated water containing a PFAS-containing aqueous mixture, which is designed to adsorb at least 10% of PFAS to the interior and surface of the structure when the contaminated water containing PFAS is aggregated and structured, and a method and system for producing PFAS-reduced water.

[0016] As a result of extensive research, the inventors of the present invention have noticed that the fluorine in the stable composition of the fluorine-carbon bond in the skeleton of PFAS is easily negatively charged, and that the PFAS has molecular chains of high molecular weight hydrocarbons that are prone to hydrogen bonding as well as electric charges, making it easy to form higher-order structures such as structures in three-dimensional space. They then attempted to add to the contaminated water containing PFAS two structuring agents: 1, which is mainly composed of a water-soluble cationic polymer flocculant (A) containing a long carbon chain, and 2, which is mainly composed of a water-soluble cationic polymer flocculant (B) that contains at least one inorganic agent selected from the group consisting of polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, and that has a positive charge and a lower cationic value than the water-soluble cationic polymer flocculant (A).

[0017] This confirmed the following: That is, iron cations, aluminum cations, etc. with hydrophobic carbon chains are present on the surface of the high-order carbon chain structure, and these adsorb and capture the anionic PFAS. Furthermore, this captured PFAS is sandwiched between a polymeric cationic water-soluble polymer with flexible carbon chains, forming a stable structure in a flexible compound with carbon chains and cationic properties, and it can be separated in water. It was also confirmed that PFAS is easily released into water using other methods. Furthermore, because the high-order structure changes with pH adjustment, it was confirmed that a pH adjuster can also be used as a structuring agent.

[0018] In the following, structuring agents refer to substances with a function of forming higher-order structures, such as flocculants that form higher-order structures in contaminated water, cationic amino acids such as lysine, arginine, and histidine, proteins with quaternary cations, synthetic polymers with quaternary cations in the side chains, cationic surfactants, synthetic polyimine polymers, and pH adjusters. Inorganic agents containing inorganic cations, such as polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, are also substances that can move quickly around PFAS and are structuring agents that form part of the structure that restricts the movement of PFAS within or on the surface of three-dimensional higher-order structures.

[0019] The above-mentioned problems are solved by a PFAS capture method comprising the steps of: adding, to contaminated water containing a PFAS-containing aqueous mixture, structuring agent 1, the main component of which is a water-soluble cationic structuring agent A containing a carbon chain with a higher order structure; and structuring agent 2, the main component of which is a water-soluble cationic polymer flocculant (B), the water-soluble cationic polymer flocculant (B) comprising at least one inorganic agent selected from the group consisting of polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, and the cationic polymer flocculant (B) containing a positive charge and having a lower cationic value than the water-soluble cationic polymer flocculant (A), to form structure 1 in the contaminated water; and allowing anionic PFAS to be adsorbed onto structure 1; and the capture step further comprises forming structure 2, such as iron cations or aluminum cations, on the PFAS adsorbed onto structure 1 by structuring agent 2, in such a manner that structure 2 is superimposed around the periphery of the captured PFAS molecules, thereby stably holding the PFAS in a sandwich-like state and enabling it to be separated in water.

[0020] The above-mentioned problems are also solved by a method for producing PFAS-reduced water, characterized in that the method for capturing PFAS includes a pressurized flotation separation step of separating PFAS from contaminated water containing the structures 1 that have adsorbed the PFAS, and the pressurized flotation separation step forms a jet of pressurized ultrafine bubble-containing liquid in the contaminated water containing the structures 1 and 2 that stably hold the PFAS, thereby pulverizing the structures 1 and 2 and moving the PFAS adsorbed to the structure 1 together with the structure 2 to the surface of the ultrafine bubbles, whereupon the PFAS is surrounded by the ultrafine bubbles together with the pulverized structure 1 and separated to float to the top of the contaminated water as floating scum.

[0021] Furthermore, the present invention provides a PFAS capture treatment system for capturing PFAS in contaminated water containing a PFAS-containing aqueous mixture, comprising: an input section for inputting structuring agents 1 and 2 into the contaminated water stored in a liquid tank; a jet forming section for forming a jet of pressurized ultrafine bubble-containing liquid in the contaminated water after the input structuring agents 1 and 2 react with the contaminated water; and a floating scum removal device. The input section is equipped with a structuring agent 1 input device and a structuring agent 2 input device, and the structuring agent 1 input device is configured to input structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant containing a carbon chain with a higher order structure, into the stored contaminated water; and the structuring agent 2 input device inputs structuring agent 2, the main component of which is a water-soluble cationic polymer flocculant (B), the main component of which is a water-soluble cationic polymer flocculant (B) containing at least one of polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, which contains a positive charge and has a cationic value smaller than that of the water-soluble cationic polymer flocculant (A). The liquid tank is configured to form structures 1 using structuring agent 1 and structures 2 using structuring agent 2, and further, on the PFAS adsorbed by structuring agent 1, structuring agent 2 forms a higher-order structure of iron cations, aluminum cations, etc. with hydrophobic carbon chains, which is layered on the anionic captured PFAS, and structures 2 such as iron cations and aluminum cations sandwich the PFAS molecules to prevent their movement and stably hold them so that they can be separated in water. The jet forming unit is configured to form a jet of pressurized liquid containing ultrafine bubbles in the contaminated water containing structures 1 and 2 with PFAS adsorbed, to move the PFAS trapped in the higher-order structures by structures 1 and 2 to the surface of the ultrafine bubbles, and float and separate the PFAS from the contaminated water as floating scum. The floating scum removal device is configured to remove the floating scum from the surface of the contaminated water.

[0022] When PFAS is confined in Structures 1 and 2 and its mobility is restricted, a conventional polymeric anionic flocculant can be additionally used for flocculation purposes. This addition is also within the scope of the present invention. The use of a polymeric anionic flocculant without the higher-order structure of Structures 1 and 2 results in the PFAS being dispersed in water.

[0023] Furthermore, the present invention solves the above problem by providing a PFAS-reduced water production system, which is characterized in that the PFAS capture system is configured so that the remainder that floats and separates from the contaminated water as floating scum is extracted as PFAS-reduced water.

[0024] According to the present invention, a polymeric cationic water-soluble structuring agent 1 containing carbon chains with a higher-order structure and a similar structuring agent 2 with a lower cationic value than structuring agent 1 are added to contaminated water containing PFAS, and iron cations, aluminum cations, etc. accompanied by hydrophobic carbon chains are present on the surface of carbon chain structure 1, which is prone to forming a three-dimensional structure due to the polymeric cationic water-soluble structuring agent 1. These cations adsorb and capture the anionic PFAS, and the captured PFAS is then sandwiched between a polymeric cationic water-soluble polymer (structure 2) with flexible carbon chains composed of structuring agent 2, maintaining it in a sandwich-like form in a flexible compound with carbon chains and cationic properties, and separating it in water, thereby achieving the effect of capturing at least 10% of the PFAS in the contaminated water.

[0025] It was also confirmed that the present invention has the effect of stably retaining PFAS in water, separating it from the water, and making the remaining water drinkable if it is reduced to a level below the allowable limit as purified water.

[0026] FIG. 1 is a block diagram showing an outline of a PFAS capture system including a PFAS-reduced water production system for carrying out the PFAS capture method and PFAS-reduced water production method according to the present invention; FIG. 2 is a piping diagram showing a schematic representation of the main parts of the PFAS capture system; and FIG. 3 is a flow chart showing the PFAS capture method and PFAS-reduced water production method according to the present invention.

[0027] A PFAS capture system 10 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. A PFAS-reduced water production system 11 has a configuration similar to that of the PFAS capture system 10, except that the dehydration device 36 and the subcritical water treatment device 70 are removed.

[0028] The PFAS capture treatment system 10 is composed of a structured reaction apparatus 20 including a reaction tank 21, a pressurized flotation separation apparatus 30 including a circulation apparatus 40, a floated scum removal apparatus 34, a dehydration apparatus 36, an apparatus for producing a liquid containing ultrafine bubbles 50, and a subcritical water treatment apparatus 70.

[0029] The structuring reaction device 20 is provided with an input section 22 for inputting structuring agents 1 and 2 into the contaminated water containing the PFAS-containing aqueous mixture stored in a reaction tank 21 .

[0030] The pressurized flotation separation device 30 has a pressurized flotation separation tank 32 that stores the structure-containing contaminated water after reaction with the added structuring agents 1 and 2, and a circulation device 40 that forms a jet of pressurized ultrafine bubble-containing liquid in the contaminated water to circulate the contaminated water.

[0031] The floating scum removal device 34 is provided at the upper end of the pressure flotation separator 30 to remove the floating scum.

[0032] The feeding section 22 is equipped with a structuring agent 1 feeding device 22A and a structuring agent 2 feeding device 22B, and the structuring agent 1 feeding device 22A is configured to dissolve structuring agent 1, which is mainly a polymeric cationic water-soluble flocculant containing a highly structured carbon chain, in the stored contaminated water and feed it into the reaction tank 21.

[0033] The structuring agent 2 injection device 22B is configured to dissolve a positively charged structuring agent 2 consisting of at least one of polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, zinc chloride, etc. in the contaminated water and inject it into the reaction tank 21.

[0034] Next, a pressurized flotation separation device 30 according to an embodiment of the present invention, which uses a liquid containing ultrafine bubbles, will be described in detail with reference to FIG.

[0035] As shown in Figure 2, the pressurized flotation separation device 30 according to the embodiment includes a pressurized flotation separation tank 32 having an inlet 41 at one end, and a liquid containing ultrafine bubbles is mixed with the contaminated water to be purified and injected into the pressurized flotation separation tank 32 from the inlet 41, causing the structures 1 and dissolved components in the contaminated water to be adsorbed to the interface of the ultrafine bubbles and float up, where they are separated and extracted from the contaminated water, and the remaining contaminated water is discharged as treated liquid.

[0036] The pressurized flotation separation device 30 has the above-mentioned circulation device 40 that circulates a mixed liquid of contaminated water containing the structure 1 and a liquid containing ultrafine bubbles within the pressurized flotation separation tank 32, and a floating scum removal device 34 that removes the floating scum that has floated to the liquid surface of the liquid containing ultrafine bubbles within the pressurized flotation separation tank 32.

[0037] Here, in the examples, contaminated water containing structures 1 and 2 and a liquid containing ultrafine bubbles are described, but basically the liquid can be water, and depending on the properties of the contaminated water, it can also be a liquid other than water or a mixture of water and other liquids.

[0038] The circulation device 40 is composed of a swirl discharge pipe 40A, a swirl flow guide 40B, and a gap 40C. The swirl discharge pipe 40A is provided so as to protrude from the end (the left end in the figure) within the pressurized flotation separation tank 32, with its tip curved obliquely upward and its tip opening serving as the inlet 41. The swirl discharge pipe 40A has a curved pipe shape that sprays the mixed liquid of the contaminated water and the liquid containing ultrafine bubbles obliquely upward, and is further configured to spray the mixed liquid as a swirl flow into the pressurized flotation separation tank 32 by fixed fins (not shown).

[0039] The swirl flow guide 40B is a cylindrical body that is open at the top and bottom and surrounds the swirl discharge pipe 40A and guides the swirl flow discharged from the pipe obliquely upward, and is positioned to guide the swirl flow ejected from the inlet 41 obliquely forward. A gap 40C is provided between the lower end opening of the swirl discharge pipe 40A and the bottom of the pressurized flotation separation tank 32, so that the swirl flow that has circulated within the pressurized flotation separation tank 32 flows from the lower end opening toward the tip of the swirl discharge pipe 40A.

[0040] Furthermore, the pressurized flotation separation device 30 has a floating scum removal device 34 for removing the floating scum that has floated to the liquid surface in the pressurized flotation separation tank 32, and the remaining liquid after the floating scum has been removed is discharged as treated liquid from a discharge port 31B. The discharge port 31B is connected to a pressure pump 56 via an inlet pipe 52B in the apparatus 50 for producing a liquid containing ultrafine bubbles.

[0041] Ultrafine bubbles are added to the treated liquid from the pressurized flotation separation device 30 by the ultrafine bubble-containing liquid manufacturing device 50, and the liquid is separated by the bubble-containing liquid separation device 60 into a liquid containing large bubbles and a liquid containing ultrafine bubbles. The ultrafine bubble-containing liquid is pressurized and passed through the pressurized liquid pipe 66, and added to the contaminated water containing the structures 1 and 2 discharged from the reaction tank 21, and flows as a swirling flow into the pressurized flotation separation tank 32 from the inlet 41.

[0042] When the pressurized flotation separation device 30 is operated for a certain period of time or longer, sediment settles on the bottom of the pressurized flotation separation tank 32. This sediment is also sucked into the swirling flow guide 40B through the gap 40C and circulates within the pressurized flotation separation tank 32 together with the swirling flow from the swirling discharge pipe 40A.

[0043] In the pressurized flotation separation device 30 according to this embodiment, after the liquid containing ultrafine bubbles is injected into the contaminated water to which the structures 1 and 2 have been dissolved and added, a spiral flow is formed, and an upward spiral flow from the left end to the right end in FIG. 2 is formed by the swirling flow guide 40B.

[0044] On the other hand, a gap 40C is formed between the lower end of the swirling flow guide 40B and the bottom of the pressurized flotation separation tank 32, and the liquid in the pressurized flotation separation tank 32 is drawn in by the swirling flow through this gap 40C, forming a large circulating flow within the pressurized flotation separation tank 32.

[0045] In this circulating flow, structuring agents 1 and 2 bound to PFAS can incorporate minute particles carrying PFAS that happen to come into contact with them into a three-dimensional molecular structure (higher-order structure) and sorb them at the gas-liquid interface of the fine bubbles due to their hydrophobic effect. However, if ultrafine bubbles are not present, almost no adsorption occurs.

[0046] The floating separated material caused by the ultrafine bubbles inevitably comes into contact with the structuring agent 1 due to the wide interface of the ultrafine bubbles, and is taken in as electrically neutralized flocs, forming a stable floating material. It rises to the liquid surface as floating scum.

[0047] The floating scum is collected at the right end in FIG. 2 by the floating scum extractor 34, and then collected upward and discharged to the outside.

[0048] The discharged floated scum is dehydrated and solidified by the dehydration device 36 and stored in a container. The liquid generated by the dehydration is returned to the pressurized flotation separation tank 32.

[0049] In the above embodiment, the structured reaction device 20 is provided in the upstream stage of the pressurized flotation separation device 30, but the present invention is not limited to this and can also be applied to a case where the structured reaction device 20 is not provided and the input section 22 is provided in the pressurized flotation separation device 30.

[0050] In the examples, the liquid containing ultrafine bubbles used in the ultrafine bubble washing is produced by an apparatus 50 for producing liquid containing ultrafine bubbles. This apparatus 50 for producing liquid containing ultrafine bubbles comprises a gas-liquid mixer 52, a pressure pump 56, and a separator 60 for liquid containing bubbles.

[0051] The gas-liquid mixing section 52 is configured to mix gas formed by negative pressure into the pressurized liquid flowing in from the inlet pipe 52B in the ejector section 52A, and to send the gas-containing liquid from the discharge pipe 52C to the raw liquid supply pipe 54.

[0052] The pressurized gas bubble-containing water is supplied from the pressure pump 56 via a pressure pipe 58 to a gas bubble-containing liquid separation device 60, where the liquid containing ultrafine gas bubbles is supplied in a pressurized state.

[0053] The bubble-containing liquid separator 60 is composed of an accumulation-type pressurized liquid tank having a circular cross section, and is provided on the upper side of the tank. The liquid containing ultrafine bubbles is pumped through a pressure pipe 58 and flows into the tank through a pressurized liquid inlet port 61, forming a downward swirling flow along the inner circumferential surface of the tank.

[0054] The pressurized liquid flowing into the tank is made to form a swirling flow, and the liquid in the central portion of the swirling flow in the tank is discharged from a central liquid discharge port 63 provided at the center position of the upper end surface of the tank through an on-off valve 65 to the outlet side of the reaction tank 21, and the liquid in the outer portion of the swirling flow is discharged from a pressurized liquid discharge port 62 on the side surface of the lower part of the tank.

[0055] The swirling flow causes the liquid in the tank to have a relatively high specific gravity, including ultrafine bubbles, on the outside of the swirling flow, while the portion containing larger bubbles has a relatively low specific gravity and gathers in the center of the swirling flow, so that the portion of the liquid that has flowed into the tank that contains relatively large bubbles is discharged from the central liquid discharge port 63, and the remaining liquid containing a larger number of ultrafine bubbles is discharged from the pressurized liquid discharge port 62. This reduces the opportunity for fine bubbles to come into contact with and be enclosed by larger bubbles, making the fine bubbles less likely to break down.

[0056] In the liquid containing ultrafine bubbles, the size of most of the bubbles is 100 nm or less, but by passing the liquid through the gas-liquid mixing section 52 multiple times, the proportion of bubbles 30 nm or less increases. Also, bubbles smaller than 10 Å and bubbles 3 Å or more were confirmed, although not all of the bubbles were present. For example, this can be measured using zeolite, as described in Japanese Patent No. 6120427.

[0057] The liquid containing ultrafine bubbles passes through a pressure pipe 58 and is constantly filled in a tank-shaped separator 60 for liquid containing bubbles, and is discharged to the outside from a central liquid discharge port 63 and a pressurized liquid discharge port 62 in an amount corresponding to the inflow of the pressurized liquid.

[0058] The pressurized liquid supplied from the pressure pipe 58 through the pressurized liquid inlet port 61 into the pressurized liquid filling the gas bubble-containing liquid separation device 60 flows into the tank as a swirling flow directed obliquely downward along the inner surface of the tank that constitutes the gas bubble-containing liquid separation device 60.

[0059] As a result, a large downward counterclockwise swirling flow is formed inside the tank, and liquid with a low specific gravity containing relatively large bubbles collects in the center of the flow, while ultrafine bubble-containing liquid with a high specific gravity containing relatively small ultrafine bubbles collects along the inner circumferential surface of the tank. The former is discharged from the center liquid discharge port 63, and the latter is discharged from the pressurized liquid discharge port 62 and reaches the inlet through the pressurized liquid pipe 66.

[0060] If the amount of PFAS remaining in the wastewater discharged from the discharge port 31B of the pressurized flotation separation tank 32 is large, the wastewater may be returned to the reaction tank 21 via the untreated liquid return pipe 55, and the structuring agent 1 and the structuring agent 2 may be added again for treatment.

[0061] It is known that the smaller the size of micro bubbles, the slower their rising speed, and this mechanism utilizing the swirling flow promotes separation of large bubbles from small micro bubbles, resulting in a liquid with an increased proportion of ultrafine bubbles in the swirling flow flowing out of the pressurized liquid discharge port 62. Relatively large bubbles are separated from the group of ultrafine bubbles by centrifugal force during the swirling and rise, gathering near the center of the upper part of the tank and being efficiently discharged.

[0062] The relatively large bubbles that were separated accounted for about 5% of the total amount of bubbles including the ultrafine bubbles, but almost all of these were separated and removed.

[0063] Therefore, the liquid containing ultrafine bubbles discharged from the pressurized liquid discharge port 62 contains only a small amount of fine bubbles of 100 nm or less, 30 nm or less, or 10 Å or more, and contains a large proportion of ultrafine bubbles of 10 Å or less in size.

[0064] The above-mentioned mechanism of action prevents ultrafine bubbles from being lost due to coalescence with relatively large fine bubbles of 10 Å or more, which are present in small quantities, and allows the unique functions of ultrafine bubbles to be exerted in the subsequent stage.

[0065] The subcritical water treatment apparatus 70 is disclosed in, for example, Japanese Patent Application Laid-Open No. 2017-127845 and other publications and is well known, so a detailed description thereof will be omitted.

[0066] In the subcritical water treatment device 70, the material to be treated is brought to a subcritical state by high-temperature, high-pressure steam, and the organic structure that constitutes PFAS is hydrolyzed to a low molecular weight and detoxified. The fluorine contained in the PFAS is separated by the subcritical water treatment faster than the carbon chain can be decomposed, and it bonds with the aluminum component to become stable inorganic salts such as aluminum fluoride. This is then extracted as a slurry together with other decomposition products and transported.

[0067] Next, with reference to the flowchart of FIG. 3, a process for capturing PFAS in contaminated water containing a PFAS-containing aqueous mixture and producing PFAS-reduced water using a PFAS capture treatment system according to an embodiment will be described.

[0068] In step S101, PFAS-containing contaminated water is introduced into the reaction tank 21.

[0069] Proceeding to step S102, structuring agent 1 and structuring agent 2 are respectively added from structuring agent 1 adding device 22A and structuring agent 2 adding device 22B to the contaminated water in the reaction tank 21. The added structuring agents 1 and 2 and the contaminated water are stirred by the stirring device 22C to promote the reaction (step S103).

[0070] In step S103, when structuring agent 1, whose main component is a water-soluble cationic polymer flocculant (A) containing a carbon chain with a high-order structure, and structuring agent 2, whose main component is a water-soluble cationic polymer flocculant (B) containing at least one inorganic agent including polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, and which contains a positive charge and has a lower cationic value than the water-soluble cationic polymer flocculant (A), are added to the contaminated water containing the PFAS-containing aqueous mixture, structure 1 is formed by stirring while capturing PFAS in the contaminated water, and PFAS is further captured and stably captured by structuring agent 2.

[0071] In detail, the structuring agent 2 causes iron cations, aluminum cations, and other high-order carbon chains with aqueous carbon chains to be present on the surface of the structuring agent 1, which adsorb and capture the anionic PFAS, and then the captured PFAS is layered on top of the iron cations, aluminum cations, and other water-soluble cationic polymers with hydrophobic carbon chains adsorbed by the coagulation force of the iron and aluminum inorganic coagulants, sandwiching them together to form a stable sandwich structure that can be separated in water. In this state, in step S104, the contaminated water containing the structures 1 is moved to the pressurized flotation separation tank 32.

[0072] Proceeding to step S105, a liquid containing ultrafine bubbles is sprayed from the ultrafine bubble-containing liquid manufacturing device 50 into the contaminated water containing structures 1 and 2 in the pressurized flotation separation tank 32, and proceeding to the next step S106, the contaminated water is circulated in the pressurized flotation separation tank 32 by the circulation device 40, and the PFAS trapped in the higher-order structure of structures 1 and 2 is caused to adhere to the gas-liquid interface of the ultrafine bubbles, and is then floated to the liquid surface by the ultrafine bubbles (floated scum).

[0073] In the next step S107, the floating scum on the liquid surface is removed by the floating scum removal device 34 and sent to the dewatering device 36.

[0074] In step S108, the floated scum that has been sent is dehydrated and solidified by the dehydration device 36, and in the next step S109, the solidified scum is introduced into the subcritical water treatment device 70.

[0075] Proceeding to step S110, high-temperature, high-pressure steam is supplied from steam supply device 74 into pressure vessel 72 of the subcritical water treatment apparatus, creating a subcritical state, where the organic portion of the PFAS in the scum is hydrolyzed and detoxified. Specifically, the decomposition products of PFAS are separated into detoxified and stabilized fluorine compounds, such as fluorine inorganic salts (aluminum fluoride). In particular, if an aluminum component is present nearby, the aluminum component can be detoxified as a stable inorganic salt of aluminum fluoride.

[0076] After the detoxification is completed, the decomposition products are taken out from outlet 72B of subcritical water treatment apparatus 70 in step S111, and the treatment is completed.

[0077] Furthermore, once the floating scum is removed in step S107, the remainder becomes PFAS-reduced water with a reduced PFAS concentration. This is discharged from the outlet 31B of the pressurized flotation separation tank 32, and in step S112, is stored in the PFAS-reduced water tank 33 and discharged as appropriate, for example, as drinking water, thereby completing the process.

[0078] The remaining PFAS-reduced water is supplied as raw liquid from the raw liquid supply pipe 54 to the ultrafine bubble-containing liquid manufacturing device 50, and is also supplied together with the raw water to the reaction tank 21 via the untreated liquid return pipe 55.

[0079] [Experimental Examples] The types of structuring agents and test results of Test Example 1 (beaker test) of the present invention are shown in Tables 1 and 2, and the types of structuring agents and test results of Test Example 2 (field test) are shown in Tables 3 and 4.

[0080] As shown in Table 3, in Experimental Example 2, a water-soluble anionic polymer flocculant is used as an additional structuring agent. This is based on the inventor's discovery that, as described in the "Means for Solving the Problems" section, "when PFAS is confined in Structures 1 and 2 and its mobility is restricted, a conventional polymer anionic flocculant can also be used for flocculation purposes."

[0081] It should be noted that a pressurized flotation separator was used in Test Example 2, but not in Test Example 1. When a pH adjuster is used, it also serves as a part of the structuring agent 2.

[0082] The difference in the PFAS reduction rate is thought to be mainly due to the use of a pressurized flotation separator in Example 2, but not in Example 1. In other words, this shows that the effect is greater when a pressurized flotation separator is used.

[0083]

[0084]

[0085]

[0086]

[0087] Although there is a large difference in the PFAS reduction rate between the beaker experiment [Experimental Example 1] and the field experiment [Experimental Example 2], it is shown that the present invention can achieve a minimum of 30% and a maximum of 85.3%.

[0088] It may be possible to use it in the purification of contaminated water containing PFAS.

[0089] DESCRIPTION OF SYMBOLS 10... PFAS capture treatment system 11... PFAS reduced water production system 20... Structuring reaction device 21... Reaction tank 22... Feeding section 22A... Structuring agent 1 feeding device 22B... Structuring agent 2 feeding device 22C... Agitator 30... Pressurized flotation separation device 31B... Discharge outlet 32... PFAS reduced water tank 32... Pressurized flotation separation tank 34... Floated scum removal device 36... Dehydration device 40... Circulation device 40A... Swirling discharge pipe 40B... Swirling flow guide 40C... Gap 41... Inlet 50... Ultrafine bubble-containing liquid production device 52... Gas-liquid mixing section 52A... Ejector section 52B... Inlet pipe 52C... Discharge pipe 52D... Gas introduction pipe 52E... Gas introduction amount control valve 54... Raw liquid supply pipe 55... Untreated liquid return pipe 56... Pressure pump 58... Pressure pipe 60... Air bubble-containing liquid separation device 61... Pressurized liquid inlet port 62... Pressurized liquid discharge port 63... Central liquid discharge port 65... On-off valve 66... ​​Pressurized liquid pipe 70... Subcritical water treatment device F... Flow

Claims

1. A PFAS capture method comprising a capture step of adding, to contaminated water containing a PFAS-containing aqueous mixture, structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant containing a carbon chain with a high-order structure, and structuring agent 2, the main component of which is a water-soluble cationic polymer flocculant (B), the main component of which is a positively charged water-soluble cationic polymer flocculant (B) that contains at least one inorganic agent selected from the group consisting of polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, and having a lower cationic value than the water-soluble cationic polymer flocculant (A), to form structure 1 in the contaminated water and adsorb anionic PFAS onto structure 1; wherein the capture step further comprises using structuring agent 2 to form structure 2, such as iron cations or aluminum cations with hydrophobic carbon chains, on the PFAS adsorbed onto structure 1, in such a way that the structure 2 is layered around the periphery of the captured PFAS molecules, thereby stably holding the PFAS in a sandwich-like state and enabling it to be separated in water.

2. A PFAS capture method according to claim 1, characterized in that it includes a reinforcing step in which the PFAS is stably held in a sandwich-like state so that it can be separated in water, and a polymeric anionic flocculant is added as an additional structuring agent to make structures 1 and 2 even stronger structures.

3. A PFAS capture method according to claim 1, characterized in that it comprises a pressurized flotation separation process in which a jet of pressurized ultrafine bubble-containing liquid is formed in the contaminated water containing Structure 1 and Structure 2 which stably hold PFAS, and the PFAS trapped in the higher-order structure of Structure 1 and Structure 2 is moved to the gas-liquid interface of the ultrafine bubbles, and the PFAS is sorbed by the hydrophobic effect of the ultrafine bubbles together with the higher-order structure consisting of Structure 1 and Structure 2, and floats and separates to the top of the contaminated water as floating scum.

4. A PFAS capture method according to claim 2, characterized in that it comprises a pressurized flotation separation process in which a jet of pressurized ultrafine bubble-containing liquid is formed in the contaminated water containing structures 1 and 2 that stably hold PFAS, and the PFAS confined in higher-order structures by structures 1 and 2 is moved to the gas-liquid interface of the ultrafine bubbles, and sorbed by the hydrophobic effect of the ultrafine bubbles together with the higher-order structures consisting of structures 1 and 2, causing them to float and separate to the top of the contaminated water as floating scum.

5. A PFAS capturing method according to claim 3 or 4, characterized in that it comprises a scum capturing step of extracting the floated scum in the pressurized floatation separation step.

6. A PFAS capture method according to claim 5, comprising: a scum dehydration step of dehydrating the floated scum removed from the pressurized flotation separation tank in the scum collection step; and a hydrolysis step of introducing the dehydrated floated scum into a subcritical water treatment device and hydrolyzing it in a high-temperature, high-pressure subcritical atmosphere to reduce the molecular weight of the organic portion of the PFAS and detoxify it.

7. A PFAS capture method according to claim 3 or 4, characterized in that the capture step and the pressurized flotation separation step are carried out in the same liquid tank.

8. A PFAS capture method according to claim 3 or 4, characterized in that a re-capture step is provided in which the PFAS-reduced water after removing the floated scum in the pressurized flotation separation step is returned to the capture step and structuring agent 1 and structuring agent 2 are added again.

9. A method for producing PFAS-reduced water according to claim 1, comprising a pressurized flotation separation process for separating PFAS from contaminated water containing structure 1 that has adsorbed the PFAS, wherein the pressurized flotation separation process comprises forming a jet of pressurized liquid containing ultrafine bubbles in the contaminated water that contains structure 1 and structure 2 that stably hold PFAS, thereby pulverizing structure 1 and structure 2 and moving the PFAS adsorbed to structure 1 together with structure 2 to the surface of the ultrafine bubbles, surrounding the PFAS together with the pulverized structure 1 with the ultrafine bubbles, and causing it to float and separate to the top of the contaminated water as floating scum.

10. A method for producing PFAS-reduced water according to claim 9, further comprising a scum collection step for extracting the floating scum in the pressurized flotation separation step.

11. A method for producing PFAS-reduced water as claimed in claim 10, characterized in that a re-capture process is provided in which a portion of the PFAS-reduced water after removing the floating scum in the pressurized flotation separation process is returned to the capture process and structuring agents 1 and 2 are added again.

12. A PFAS capture system for capturing PFAS in contaminated water containing a PFAS-containing aqueous mixture, comprising: an injection section for injecting structuring agents 1 and 2 into the contaminated water stored in a liquid tank; a jet forming section for forming a jet of pressurized ultrafine bubble-containing liquid in the contaminated water after the injected structuring agents 1 and 2 react with the contaminated water; and a floating scum removal device; the injection section is equipped with a structuring agent 1 injection device and a structuring agent 2 injection device; the structuring agent 1 injection device is configured to inject structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant containing a carbon chain with a higher order structure, into the stored contaminated water; and the structuring agent 2 injection device is configured to inject structuring agent 2, the main component of which is a water-soluble cationic polymer flocculant (B), the main component of which is a water-soluble cationic polymer flocculant (B) containing at least one of polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, the main component being a positively charged substance with a cationic value lower than that of the water-soluble cationic polymer flocculant (A); The liquid tank is configured to form structure 1 using structuring agent 1 and structure 2 using structuring agent 2, respectively, and PFAS is adsorbed onto structure 1, which is then layered on top of the anionic captured PFAS, and structure 2, which is a higher-order structure of iron cations, aluminum cations, etc., sandwiches the PFAS molecules to prevent them from moving, stably holding them in place and making them separable in water; the jet forming unit is configured to form a jet of pressurized water containing ultrafine bubbles in the contaminated water containing structure 1 and structure 2, which sandwich the PFAS, and move the ultrafine bubbles trapped in the higher-order structures of structure 1 and structure 2 to the gas-liquid interface, thereby floating and separating them from the contaminated water as floating scum; and the floating scum extraction device is configured to extract the floating scum from the surface of the contaminated water.

13. A PFAS capture system as claimed in claim 12, characterized in that the feeding section is provided in a reaction tank that stores the contaminated water, a pressurized flotation separation device is provided that has a pressurized flotation separation tank that receives the contaminated water into which structuring agent 1 and structuring agent 2 have been added in the reaction tank, and the jet forming section and the floating scum removal device are provided in the pressurized flotation separation tank.

14. A PFAS capture system according to claim 12, characterized in that a pressurized flotation separation device is provided with a pressurized flotation separation tank for receiving contaminated water, the feeding section and the jet forming section are both provided in the pressurized flotation separation tank, and the jet forming section is configured to begin forming a jet of pressurized ultrafine bubble-containing liquid in the contaminated water in the pressurized flotation separation tank after the feeding of structuring agent 1 and structuring agent 2 from the feeding section of the feeding section has been completed.

15. A PFAS capture system according to claim 13 or 14, further comprising a dehydration device that dehydrates the floated scum collected from the pressurized flotation separation device, and a subcritical water treatment device, wherein the subcritical water treatment device is configured to hydrolyze the floated scum that has been collected by the floated scum removal device and then dehydrated by the dehydration device in a high-temperature, high-pressure subcritical atmosphere, thereby reducing the molecular weight of the organic portion of the PFAS and detoxifying it.

16. A PFAS capture system as claimed in claim 13 or 14, characterized in that an untreated liquid return pipe is provided which can return the PFAS-reduced water after the floating scum has been separated in the pressurized flotation separation device as untreated water into which structuring agent 1 and structuring agent 2 are fed from the feeding section.

17. A PFAS-reduced water production system according to claim 10, characterized in that the remainder that has risen and separated from the contaminated water as floating scum is extracted as PFAS-reduced water.

18. A PFAS-reduced water production system as claimed in claim 15, characterized in that an untreated water return pipe is provided that can return the PFAS-reduced purified water after separation of the floating scum in the pressurized flotation separation device as untreated water into which structuring agent 1 and structuring agent 2 are input from the input section.

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