Method for capturing PFAS, system therefor, method for producing PFAS-reduced water, and system therefor

Abstract

A PFAS capturing system 10 comprises: a structuring reaction apparatus 20 including a reaction tank 21; and a pressurizing floatation separation apparatus 30 including a circulation device 40. The present invention involves feeding, from a feeding unit 22 into contaminated water containing a PFAS-containing aqueous mixture stored in the reaction tank 21 of the structuring reaction apparatus 20, a structural agent 1 containing, as a main agent, a water-soluble cationic polymer flocculant (A) capable of forming a high-order structure including a carbon chain having a high molecular weight, and a structural agent 2 containing, as a main agent, a water-soluble cationic polymer flocculant (B) that includes at least one among inorganic agents including polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, and that includes a positive charge and has a cation value lower than that of the water-soluble cationic polymer flocculant (A), to form a structural body 1 in the contaminated water and adsorb PFAS, which is anionic, on the structural body 1. Further, on the PFAS adsorbed on the structural body 1, a structural body 2 of an iron cation, an aluminum cation, or the like having a hydrophobic carbon chain is formed and overlaid on the PFAS in a captured state by means of the structural agent 2 to stably hold the PFAS in a sandwiched manner to enable separation of the PFAS in water. Subsequently, in a pressurizing floatation separation tank 32 of the pressurizing floatation separation apparatus 30, a jet flow of pressurized ultrafine bubble-containing water is formed in the contaminated water to cause the contaminated water to circulate, and cause the structural body 1 and the captured PFAS to float by means of ultrafine bubbles. The same is removed as floating scum to produce a PFAS-reduced water as the remainder. As a result, at least 30% of PFAS that is contained in contaminated water and is hard to capture can be captured and separated.

Description

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

[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] Once PFAS has been separated, it must then be mineralized. Patent Document 3 discloses an invention relating to a method for decomposing fluorine-containing polymers and an apparatus for decomposing fluorine-containing polymers, and Patent Document 4 discloses an invention relating to a method for decomposing ion exchange membranes and an apparatus for carrying out the same. Both of the inventions described in Patent Documents 3 and 4 attempt to decompose PFAS using subcritical water in the presence of sodium hydroxide and / or sodium hydroxide, or in the presence of an alkali metal or alkaline earth metal hydroxide, but the decomposition is insufficient.

[0015] Japanese Patent Application Laid-Open No. 2021-146326 Japanese Patent Application Laid-Open No. 2022-79109 Japanese Patent No. 7258319 Japanese Patent Application Laid-Open No. 2024-156212

[0016] 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.

[0017] 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, whose main component is a water-soluble cationic polymer flocculant (A) containing a long carbon chain; and 2, whose main component is a water-soluble cationic polymer flocculant (B) that contains a positive charge and has a lower cationic value than the water-soluble cationic polymer flocculant (A), and that is composed of 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.

[0018] 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.

[0019] 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.

[0020] The above-mentioned problem is solved by the following steps: a first capturing step of adding a structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant (A) capable of forming a higher-order structure containing a high-molecular-weight carbon chain, to contaminated water containing a PFAS-containing aqueous mixture, stirring the mixture to precipitate a structure 1, and movably attaching the PFAS-containing aqueous mixture to the surface of the structure 1; and a second capturing step of adding a water-soluble cationic polymer flocculant (A) containing ... and a second capture step in which a structuring agent 2, the main component of which is a thionic polymer flocculant (B), is added and stirred after or simultaneously with the start of the first capture step to precipitate a structure 2 consisting of at least one of iron cations, aluminum cations and zinc cations having a hydrophobic carbon chain, and the surface of the structure 2 is attached to the PFAS-containing aqueous mixture attached to the structure 1, so that the PFAS-containing aqueous mixture is stably held in a sandwich state between the structure 1 and the structure 2, making it separable from water.

[0021] The above-mentioned problems are also solved by a PFAS-reduced water production method that utilizes the above-mentioned PFAS capture method, comprising a pressurized flotation separation step of separating PFAS from contaminated water containing structures 1 and 2 that have adsorbed the PFAS, wherein the pressurized flotation separation step forms a jet of pressurized ultrafine bubble-containing liquid in the contaminated water containing structures 1 and 2 that stably hold PFAS, and moves the PFAS trapped between structures 1 and 2 together with the structure consisting of structures 1 and 2 to the surface of the ultrafine bubbles, whereupon the PFAS is surrounded by the ultrafine bubbles together with structure 1, and separated to float to the top of the contaminated water as floating scum.

[0022] Furthermore, the above-mentioned problems are solved by a PFAS capture method characterized by comprising: a scum dehydration step in which the removed floated scum is dehydrated to form a dehydrated agglomerate; and a mineralization step in which the dehydrated agglomerate is hydrolyzed in a high-temperature, high-pressure subcritical atmosphere to promote mineralization by bonding of fluorine atoms separated from the organic carbon chains of the PFAS contained therein with iron, aluminum, and zinc present in the dehydrated agglomerate.

[0023] Furthermore, the present invention provides a PFAS capture 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 (A) capable of forming a higher-order structure containing a high-molecular-weight carbon chain, into the stored contaminated water. The structuring agent 2 input device is configured to input structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant (A) capable of forming a higher-order structure containing a high-molecular-weight carbon chain, into the stored contaminated water. The structuring agent 2 input device is configured to input structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant (B) that is positively charged and has a cationic value smaller 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, and PFAS is adsorbed onto structure 1, and structure 1 is placed on top of the anionic captured PFAS, and structure 2, which is a higher-order structure consisting of at least one of iron cations, aluminum cations, and zinc cations having hydrophobic carbon chains, sandwiches the PFAS molecules between structure 2, preventing their movement and stably holding them so that they can be separated 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 moves the PFAS trapped in the higher-order structures of structure 1 and structure 2 to the surface of the ultrafine bubbles, thereby floating and separating 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.

[0024] Furthermore, the above problem is solved by a PFAS capture system characterized by having an additional structuring agent injection device that adds a water-soluble anionic polymer flocculant as an additional structuring agent to the contaminated water, while stably holding the PFAS-containing aqueous mixture between structure 1 and structure 2 so that it can be separated in water.

[0025] 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.

[0026] 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.

[0027] According to the present invention, a cationic structuring agent 2 having a lower cationic value than a cationic structuring agent 1, whose main component is a water-soluble polymer flocculant with a higher structure containing carbon chains, is added to contaminated water containing PFAS, and iron cations, aluminum cations, etc., accompanied by hydrophobic carbon chains are present on the surface of the carbon chain structure 1, which is easily formed into a three-dimensional structure by the cationic water-soluble polymer structuring agent 1. These cations adsorb and capture the anionic PFAS, and the captured PFAS is then sandwiched between a cationic water-soluble polymer (structure 2) with flexible carbon chains, which is composed of structuring agent 2, and held in a sandwich-like form to form a stable structure in a flexible compound with carbon chains and cationic properties, and separated in water, thereby achieving the effect of capturing at least 10% of the PFAS in the contaminated water.

[0028] 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.

[0029] Furthermore, when the floating scum containing the captured PFAS is hydrolyzed in a subcritical atmosphere, some of the components of structure 2, such as iron and aluminum, which are located at nanoscale distances, have a high probability of bonding with the decomposed PFAS, thereby having the effect of mineralizing the PFAS.

[0030] 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.

[0031] 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.

[0032] The PFAS capture 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 dewatering apparatus 36, an ultrafine bubble-containing liquid manufacturing apparatus 50, and a subcritical water treatment apparatus 70.

[0033] 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 .

[0034] 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.

[0035] The floating scum removal device 34 is provided at the upper end of the pressure flotation separator 30 to remove the floating scum.

[0036] The input section 22 is equipped with a structuring agent 1 input device 22A, a structuring agent 2 input device 22B, and an additional structuring agent input device 22C, and the structuring agent 1 input device 22A is configured to dissolve structuring agent 1, which is mainly composed of a polymeric cationic water-soluble flocculant containing a carbon chain with a high order structure, in the stored contaminated water and input it into the reaction tank 21. The symbol 22D in Figure 2 indicates a stirring device for stirring the liquid in the reaction tank 21.

[0037] The additional structuring agent supply device 22C is configured to add a water-soluble anionic polymer flocculant as an additional structuring agent to the contaminated water after the structuring agent 2 is supplied to the reaction tank 21.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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).

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The floating separated material caused by the ultrafine bubbles inevitably comes into contact with the structuring agent 1 in part due to the wide interface of the ultrafine bubbles, and is taken in as electrically neutralized flocs, forming stable floating matter that rises to the liquid surface as floating scum.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] In subcritical water treatment apparatus 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 low molecular weight. However, the fluorine contained in PFAS is separated by the subcritical water treatment faster than the carbon chain is decomposed, and combines with aluminum, iron, or zinc components to become stable inorganic salts such as aluminum fluoride, which are extracted and transported as a slurry together with other decomposition products.

[0072] 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 capturing system according to an embodiment will be described.

[0073] In step S101, PFAS-containing contaminated water is introduced into the reaction tank 21.

[0074] Proceeding to step S102A, structuring agent 1 is added from structuring agent 1 addition device 22A to the contaminated water in reaction tank 21. A few minutes after or simultaneously with the addition of structure 1, the process proceeds to the next step S102B, where structuring agent 2 is added from structuring agent 2 addition device 22B to the contaminated water and stirred. Further, in step S103, the contaminated water after stirring is completed is moved within reaction tank 21, and an additional structuring agent is added from additional structuring agent addition device 22C to the contaminated water containing structures 1 and 2 and the higher-order structures of PFAS. The added structuring agent 1, structure 2, and additional structuring agent are stirred with the contaminated water by stirring device 22D, accelerating the structural reaction.

[0075] In the above steps S102A and S102B, 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 selected from the group consisting of 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 by structuring agent 2 for stable capture.

[0076] Specifically, structuring agent 2 causes iron cations, aluminum cations, and other high-order carbon chains present on the surface of structuring agent 1, which adsorb and capture the anionic PFAS. Furthermore, the captured PFAS is sandwiched and stably held by iron cations, aluminum cations, and other water-soluble cationic polymers adsorbed by the coagulation force of the iron and aluminum inorganic coagulants, making it separable in water. In this state, a water-soluble anionic polymer coagulant is added to reaction vessel 21 as an additional structuring agent from additional structuring agent feeder 22C. This addition strengthens the higher-order structure consisting of structures 1, 2, and PFAS, further suppressing separation of PFAS.

[0077] Next, in step S104, the contaminated water containing the higher-order structures is transferred to the pressurized flotation tank 32.

[0078] 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).

[0079] In the next step S107, the floating scum on the liquid surface is taken out by the floating scum take-out device 34 and sent to the dewatering device 36.

[0080] In step S108, the floated scum that has been sent is dehydrated and solidified by the dehydration device 36 to form a dehydrated aggregate, and in the next step S109, the dehydrated aggregate is introduced into the subcritical water treatment device 70.

[0081] Proceeding to step S110, high-temperature, high-pressure steam is supplied from a steam supply device into the pressure vessel of the subcritical water treatment device, thereby creating a subcritical state, and the organic portion of the PFAS in the dehydrated aggregate is hydrolyzed to lower molecular weight compounds. Next, the separated fluorine, which is a decomposition product of PFAS, combines with iron, aluminum, and zinc components to form inorganic, stabilized fluorine compounds including inorganic salts (aluminum fluoride). In particular, if an aluminum component is present nearby (at a nanoscale distance), a stable inorganic salt (inorganic substance) of the aluminum component and aluminum fluoride can be formed.

[0082] In the present invention, the iron component, aluminum component or zinc component in the structure 2 is present in close proximity to the PFAS, so that the bond is rapidly strengthened.

[0083] After the mineralization is completed, the decomposition products are taken out from the outlet of the subcritical water treatment apparatus 70 in step S111, and the treatment is completed.

[0084] 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, stored in the PFAS-reduced water tank 33 in step S112, and then discharged appropriately in step S113 to be used as, for example, drinking water, thereby completing the process.

[0085] 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.

[0086] In the above embodiment, the additional structuring agent is injected from the additional structuring agent injection device 22C into the contaminated water containing the structures 1 and 2 and the higher-order structures of PFAS, but the present invention is not limited to this, and if the strength of the higher-order structures of PFAS is sufficient, the injection of the additional structuring agent is not necessary. Furthermore, when the injection of the additional structuring agent is insufficient to fix the PFAS, a second reinforcing step may be provided in which a reinforcing agent of the same components as the additional structuring agent is injected into the contaminated water.

[0087] [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.

[0088] In Tables 1 and 3, "concentration / target value" refers to the target concentration of structuring agent relative to the amount of contaminated water (hereinafter referred to as raw water) used in the test. Therefore, in the test, for example, structuring agent 1 in an amount to give a concentration of 1 ppm, structuring agent 2-1 in an amount to give a concentration of 2.5 ppm, etc. were added to 500 cc of raw water in a beaker.

[0089] 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."

[0090] 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.

[0091] The difference in the PFAS reduction rate is thought to be mainly due to the fact that a pressurized flotation separator was used in Example 2, but not in Example 1. That is, when a pressurized flotation separator was used, the iron components, aluminum components, etc. contained in Structure 2 and located in close nano-sized proximity to the fluorine rapidly and with a high probability bonded with the fluorine to form stable inorganic salts, in contrast to the fluorine separated by the hydrolysis of PFAS.

[0092]

[0093]

[0094]

[0095] [Amendment under Rule 91 07.05.2025]

[0096] 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%.

[0097] It may be possible to use it in the purification of contaminated water containing PFAS.

[0098] 10... PFAS capture 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... Additional structuring agent feeding device 22D... Stirring device 30... Pressurized flotation separation device 31B... Discharge outlet 32... Pressurized flotation separation tank 33... PFAS reduced water tank 34... Floating 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 manufacturing 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...Pressurizing pump 58...Pressurized transport pipe 60...Gas bubble-containing liquid separator 61...Pressurized liquid inlet port 62...Pressurized liquid discharge port 63...Center liquid discharge port 65...Open / close valve 66...Pressurized liquid pipe 70...Subcritical water treatment device F...Flow

Claims

1. A first capture step of adding a structuring agent 1, the main component of which is a water-soluble cationic polymer flocculant (A) capable of forming a higher-order structure containing a high-molecular-weight carbon chain, to contaminated water containing a PFAS-containing aqueous mixture, stirring the mixture to precipitate a structure 1, and then movably attaching the PFAS-containing aqueous mixture to the surface of the structure 1; and a second capture step of adding a water-soluble cationic polymer flocculant (A) containing a positive charge and having a cationic value lower than that of the water-soluble cationic polymer flocculant (A), the second capture step comprising: a second capture step in which a structuring agent 2, the main component of which is a cationic polymer flocculant (B), is added and stirred after or simultaneously with the start of the first capture step to precipitate a structure 2 consisting of at least one of iron cations, aluminum cations, and zinc cations having a hydrophobic carbon chain, and the surface of the structure 2 is attached to the PFAS-containing aqueous mixture attached to the structure 1, so that the PFAS-containing aqueous mixture is stably held in a sandwich state between the structure 1 and the structure 2, making it separable from water.

2. A PFAS capture method as claimed in claim 1, characterized in that it includes a reinforcement step of adding a water-soluble anionic polymer flocculant as an additional structuring agent to the contaminated water after a second capture step has been carried out between the structure 2, stably holding the structure 1 and the PFAS-containing aqueous mixture and making them separable in water.

3. The PFAS capturing method according to claim 2, wherein the water-soluble anionic polymer flocculant used in the reinforcing step is a weak anion having an anion value of 1-10 mol %.

4. A PFAS capture method according to claim 2 or 3, characterized in that, following the reinforcing step, there is a second reinforcing step in which an additional reinforcing structuring agent having the same components as the additional structuring agent is introduced into the contaminated water and stirred.

5. 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 that stably hold PFAS, and the PFAS trapped between structure 1 and structure 2 is moved to the surface of the ultrafine bubbles together with the structure consisting of structure 1 and structure 2, where it is sorbed onto the ultrafine bubbles by the hydrophobic effect, and floats and separates to the top of the contaminated water as floating scum.

6. 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 structure 1 and structure 2 that stably hold PFAS, and the PFAS trapped between structure 1 and structure 2 is moved to the surface of the ultrafine bubbles together with the structure consisting of structure 1 and structure 2, where it is sorbed onto the ultrafine bubbles by the hydrophobic effect, and floats and separates to the top of the contaminated water as floating scum.

7. A PFAS capturing method according to claim 5 or 6, characterized in that it comprises a scum capturing step of extracting the floated scum in the pressurized floatation separation step.

8. A method for capturing PFAS according to claim 7, characterized by comprising: a scum dehydration step of dehydrating the removed floating scum to form a dehydrated agglomerate; and a mineralization step of hydrolyzing the dehydrated agglomerate in a high-temperature, high-pressure subcritical atmosphere to promote mineralization by bonding fluorine atoms separated from the organic carbon chains of the PFAS contained in the agglomerate with iron, aluminum, and zinc present in the agglomerate.

9. A PFAS capture method according to claim 5 or 6, characterized in that the first and second capture steps and the pressurized flotation separation step are carried out in the same liquid tank.

10. A PFAS capture method according to claim 5 or 6, characterized in that the PFAS-reduced water after removing the floating scum in the pressurized flotation separation process is returned to the first and second capture processes, and a re-capture process is provided in which structuring agent 1 and structuring agent 2 are added again.

11. A method for producing PFAS-reduced water that utilizes the PFAS capture method of any one of claims 1 to 3, comprising a pressurized flotation separation process for separating PFAS from contaminated water containing structures 1 and 2 that have adsorbed the PFAS, wherein the pressurized flotation separation process forms a jet of pressurized liquid containing ultrafine bubbles in the contaminated water that contains structures 1 and 2 that stably hold PFAS, and moves the PFAS trapped between structures 1 and 2, together with the structure consisting of structures 1 and 2, to the surface of the ultrafine bubbles, whereupon the PFAS is surrounded by the ultrafine bubbles together with structure 1, and separated to float to the top of the contaminated water as floating scum.

12. A method for producing PFAS-reduced water according to claim 11, further comprising a scum collection step for extracting the floating scum in the pressurized flotation separation step.

13. A method for producing PFAS-reduced water as claimed in claim 12, characterized in that a re-capture process is provided in which a portion of the PFAS-reduced water obtained after removing the floating scum in the pressurized flotation separation process is returned to the first and second capture processes, and structuring agents 1 and 2 are added again.

14. A PFAS capture system for capturing PFAS in contaminated water containing a PFAS-containing aqueous mixture, comprising: an injection section for injecting structuring agent 1 and structuring agent 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; and 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 (A) capable of forming a higher-order structure containing high-molecular-weight carbon chains, into the stored contaminated water; The structuring agent 2 feeding device is configured to feed into the contaminated water a structuring agent 2 which is composed of at least one inorganic agent including polyiron, ferric chloride, ferrous sulfate, ferric sulfate, polyaluminum chloride, aluminum sulfate, and zinc chloride, which contains a positive charge and is mainly composed of a water-soluble cationic polymer flocculant (B) having a cationic value smaller than that of the water-soluble cationic polymer flocculant (A); the liquid tank is configured to form a structure 1 using the structuring agent 1 and a structure 2 using the structuring agent 2, respectively, to adsorb PFAS onto the structure 1, and to layer it on the anionic captured PFAS, and to sandwich the PFAS molecules with the structure 2 which is a higher-order structure consisting of at least one of iron cations, aluminum cations, and zinc cations having a hydrophobic carbon chain, thereby preventing the movement of the PFAS molecules and stably holding them so that they can be separated in water; The jet forming unit is configured to form a jet of pressurized water containing ultrafine bubbles in the contaminated water including the structure 1 and the structure 2 sandwiching the PFAS, and to move the PFAS trapped in the higher-order structures of the structure 1 and the structure 2 to the surface of the ultrafine bubbles, thereby floating and separating the PFAS 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.

15. A PFAS capture system as claimed in claim 14, characterized in that it has an additional structuring agent injection device between structure 1 and structure 2 that stably holds the PFAS-containing aqueous mixture and makes it separable in water, and adds a water-soluble anionic polymer flocculant as an additional structuring agent to the contaminated water.

16. A PFAS capture system according to claim 14 or 15, 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.

17. A PFAS capture system according to claim 14 or 15, 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.

18. A PFAS capture system as claimed in claim 14 or 16, further comprising a dehydration device that dehydrates the floating scum generated by the jet of pressurized ultrafine bubble-containing water in the jet forming section and collected to form a dehydrated floc, and a subcritical water treatment device, configured to promote mineralization by bonding of fluorine atoms separated from the carbon chains of the PFAS contained in the dehydrated floc by hydrolyzing the dehydrated floc in a high-temperature, high-pressure subcritical atmosphere with iron, aluminum and zinc present in the dehydrated floc.

19. A PFAS capture system as claimed in claim 16, 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.

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

21. A PFAS-reduced water production system as claimed in claim 20, 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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