Removal method for per- and polyfluoroalkyl substances

Abstract

To provide a novel removal method for PFAS.SOLUTION: A method for removal of per- and polyfluoroalkyl substances in accordance with an aspect of the present invention includes a process of treating water or soil containing per- and polyfluoroalkyl substances with a base material and plant bodies actively attached to the base material. In the process, the per- and polyfluoroalkyl substances are decomposed by biodegradation.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for the removal of per- and polyfluoroalkyl compounds. [Background technology]

[0002] Per- and polyfluoroalkyl substances (PFAS) are a general term for fluorine compounds that contain at least one fully fluorinated methyl or methylene carbon atom, and more than 9,000 types of compounds are known. PFAS are used for applications such as water and oil repellents, surfactants, fire extinguishing agents, and coating agents for cooking utensils. However, due to their high environmental persistence and toxicity, some PFAS are subject to regulation by the Stockholm Convention on Persistent Organic Pollutants (POPs Convention). Concerns about water and soil contamination by PFAS are growing worldwide, and in Japan, they are currently positioned as items requiring monitoring for the protection of human health related to water pollution, and the guideline value (provisional) for the total value of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) is set to 50ng / L or less.

[0003] Conventionally, a method for removing PFAS has been known in which PFAS is adsorbed onto an adsorbent such as activated carbon (for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Du et al.,(2014)Journal of Hazardous Materials,274,443-454 Summary of the Invention [Problem to be solved by the invention]

[0005] When an adsorbent adsorbs a certain amount of PFAS, it can no longer adsorb any more (breaks through), so methods using adsorbents could not continuously remove PFAS. Although it is possible to continue removing PFAS by periodically replacing the adsorbent, this increases costs. Thus, there was room for improvement in conventional methods of removing PFAS.

[0006] Therefore, an object of the present invention is to provide a novel method for removing PFAS. [Means for solving the problem]

[0007] The present invention includes the following embodiments. [1] A method for treating water or soil containing per- and polyfluoroalkyl compounds with a substrate and a plant body attached to the substrate, A method for removing per- and polyfluoroalkyl compounds, wherein in the process of treating water or soil, the per- and polyfluoroalkyl compounds are decomposed by biodegradation. [2] The method according to [1], wherein the biodegradation is microbial decomposition. [3] The method according to [1] or [2], further comprising a step of treating the substrate and the plant body planted in the substrate with a solution containing nitrogen and phosphorus prior to the step of treating the water or soil, thereby attaching the plant body to the substrate. [4] The method according to [3], wherein the solution further contains potassium, iron, calcium and magnesium. [5] The method according to any one of [1] to [4], wherein the plant body is an emergent plant. [6] The method according to [5], wherein the emergent plant is Typha. [7] The method according to any one of [1] to [6], wherein the water containing per- and polyfluoroalkyl compounds has a sodium concentration of 0.1 mg / L or more. [8] The method according to any one of [1] to [7], wherein the water containing per- and polyfluoroalkyl compounds has a calcium concentration of 0.1 mg / L or more. [9] The method according to any one of [1] to [8], wherein the water containing per- and polyfluoroalkyl compounds has an electrical conductivity of 3 to 5000 mS / m.

[10] The method according to any one of [1] to [9], wherein the water containing per- and polyfluoroalkyl compounds has a pH of 2 to 12.

[11] The method according to any one of [1] to

[10] , wherein the water containing per- and polyfluoroalkyl compounds has an organic nitrogen concentration of 2000 mg / L or less. Effect of the Invention

[0008] According to the present invention, a novel method for removing PFAS is provided. According to the present invention, PFAS is removed by utilizing biodegradation such as decomposition by microorganisms, so that more continuous removal of PFAS can be expected compared to the conventional method of removing PFAS by adsorbent. Since such a method does not require frequent replacement and regeneration or disposal of the adsorbent, it is possible to reduce costs, is easy to maintain, and is environmentally friendly. In addition, according to the present invention, short-chain PFAS such as perfluorobutanoic acid (PFBA) and perfluorobutanesulfonic acid (PFBS), which are difficult to remove with activated carbon, can also be removed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a graph showing the removal rate of various PFAS in landfill leachate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A method for removing per- and polyfluoroalkyl compounds according to one aspect of the present invention includes a step of treating water or soil containing per- and polyfluoroalkyl compounds with a substrate and a plant body attached to the substrate (hereinafter also referred to as a "PFAS treatment step").

[0011] The per- and polyfluoroalkyl compounds (PFAS) are not particularly limited and may be one or more perfluoroalkyl compounds and / or polyfluoroalkyl compounds. The perfluoroalkyl compounds may be, for example, perfluoroalkyl carboxylic acids (PFCAs) or perfluoroalkyl sulfonic acids (PFSAs). PFCAs include, for example, perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorononanoic acid (PFNA), perfluorooctanoic acid (PFOA), and perfluorodecanoic acid (PFDA). PFSAs include, for example, perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), and perfluorooctane sulfonic acid (PFOS). The polyfluoroalkyl compounds may be, for example, fluorotelomers. Fluorotelomers include, for example, fluorotelomer carboxylic acids (FTCA), such as 5:3 FTCA, 7:3 FTCA, and fluorotelomer sulfonic acids (FTSA), such as 6:2 FTSA.

[0012] Examples of water containing PFAS include groundwater, rivers, lakes, oceans, and other environmental waters (water in the natural environment) containing PFAS, waste landfill leachate, and wastewater. The wastewater may be, for example, wastewater from military bases, airports, and the like, industrial wastewater, sewage, and the like. Examples of soil containing PFAS include soil in contact with the environmental water containing the PFAS, and soil from a final waste disposal site. The total PFAS concentration in the water may be, for example, 1 ng / L or more, 50 ng / L or more, 1 to 1000,000 ng / L, or 1 to 100,000 ng / L. The sodium concentration (element concentration) in the water may be, for example, 0.1 mg / L or more, 1 mg / L or more, 100 mg / L or more, or 0.1 to 15000 mg / L. The calcium concentration (element concentration) in the water may be, for example, 0.1 mg / L or more, 1 mg / L or more, 10 mg / L or more, or 0.1 to 5000 mg / L. The nitrogen concentration (element concentration) in the water may be, for example, 0.01 mg / L or more, 1 mg / L or more, 10 mg / L or more, or 0.01 to 20,000 mg / L. The total organic carbon concentration in the water may be, for example, 0.01 mg / L or more, 1 mg / L or more, 10 mg / L or more, or 0.01 to 20,000 mg / L. The electrical conductivity in the water may be, for example, 3 mS / m or more, 5 mS / m or more, or 3 to 5000 mS / m. The pH in the water may be, for example, 2 to 12, 5 to 11, or 5 to 9. The organic nitrogen concentration in the water is not particularly limited, and may be, for example, 0.01 mg / L or more, 0.1 mg / L or more, or 0.01 to 2000 mg / L, or 2000 mg / L or less, or 0.01 mg / L or less. The water or soil may further contain humic substances such as humic acid, fulvic acid, and humin.

[0013] The substrate is not particularly limited as long as the plant body can be attached to the substrate, and may be an inorganic or organic substrate. The substrate is preferably a substrate capable of retaining microorganisms. The substrate may or may not have the function of absorbing or adsorbing PFAS. As the substrate, one type of substrate may be used alone, or two or more types of substrates may be used in combination. The number of substrates may be one or more. As described later, from the viewpoint of retaining more microorganisms, the substrate is preferably one having a large specific surface area, and examples thereof include a porous substrate, a substrate having gaps, a plurality of granular substrates, and combinations thereof. In this specification, granular means a shape in which gaps may be generated between a plurality of substrates when a plurality of substrates are stacked. Examples of substrates include glass (preferably foamed glass), resin (preferably foamed resin), sand, soil (not containing PFAS, and distinguished from the above soil containing PFAS), gravel, zeolite, biochar, activated carbon, shells, and palm fiber.

[0014] The plant body is not particularly limited as long as it is a plant body that can be attached to a substrate, that is, a plant body that develops roots or rhizomes. Attaching to a substrate means that the roots and / or rhizomes develop and take root in the substrate so that the plant body can grow. From the viewpoint of more continuous PFAS removal, the plant body is preferably a perennial plant body and / or a plant body that is resistant to water or soil containing PFAS. A plant body that is resistant to water or soil containing PFAS means a plant body that can grow in water or soil containing PFAS. As the plant body, one type of plant body may be used alone, or two or more types of plant bodies may be used in combination. In addition, the number of plant bodies may be one (one plant) or multiple (multiple plants). The plant body may be, for example, a terrestrial plant (terrestrial plant) or an aquatic plant. The aquatic plant may be an emergent plant, a floating-leaf plant, a submerged plant, or a floating plant. Examples of emergent plants include Typha, Typha, and Reed. The plant body is preferably an emergent plant, more preferably Typha.

[0015] In the above PFAS treatment step, the time for treating the water or soil containing PFAS with the substrate and the plant body attached to the substrate may be, for example, a time for the amount of microorganisms held per 1 g of substrate to be 0.05 mg or more, preferably 0.1 mg or more, more preferably 1 mg or more. However, since a longer time is required to increase the amount of microorganisms held on the substrate, the treatment time may be a time for the amount of microorganisms held per 1 g of substrate to be 0.05 mg or less. The temperature for treating the water or soil containing PFAS may be, for example, 5 to 58°C, 15 to 50°C, or 20 to 45°C. The illuminance on the surface of the water or soil containing PFAS may be, for example, 20 lux or more, 200 to 300,000 lux, or 1000 to 200,000 lux. The product of daily illuminance and duration may be 20 lux·hours or more, 1,000 to 7,200,000 lux·hours, or 1,000 to 4,800,000 lux·hours.

[0016] The PFAS treatment step may be carried out directly at the source of water or soil containing PFAS. That is, for example, at the source of water or soil containing PFAS, a hole may be dug or enclosed to compartmentalize the treatment target area, and a substrate and a plant body attached to the substrate may be introduced into the area. Alternatively, a substrate and a plant body attached to the substrate may be introduced into the source of water or soil containing PFAS without compartmentalizing the treatment target area. Alternatively, water or soil containing PFAS may be collected in a container, and a substrate and a plant body attached to the substrate may be introduced into the container, or a substrate and a plant body attached to the substrate may be placed in a container, and water containing PFAS may be passed through the container. Examples of the container include a container, a reactor, a column, and a pot.

[0017] In the above PFAS treatment process, PFAS is decomposed by biodegradation. Biodegradation may be decomposition by microorganisms and / or decomposition by plants. There is a very high probability that microorganisms capable of decomposing PFAS are present in water or soil containing PFAS, and there is also a possibility that microorganisms capable of decomposing PFAS are present in plants. Such microorganisms accumulate and grow in the roots and / or rhizomes of the plant body and in the substrate due to the rhizosphere effect of the plant body, and PFAS is decomposed by the action of the microorganisms. Here, the rhizosphere effect means that the growth and activity of various types of microorganisms are promoted around the roots and / or rhizomes due to the influence of the roots and / or rhizomes of the plant body. Decomposition by the plant body may be, for example, decomposition by substances secreted from the roots or rhizomes of the plant body. Examples of such substances include decomposition enzymes and hydrogen peroxide. Note that PFAS is decomposed by biodegradation means that at least a part of the PFAS contained in the water or soil is decomposed by biodegradation, and it is not necessary that all PFAS is decomposed by biodegradation. In other words, in the above-mentioned PFAS treatment process, in addition to decomposition of PFAS by biodegradation, absorption or adsorption of PFAS by the plant body and / or substrate may also occur.

[0018] The PFAS removal method according to this aspect of the present invention preferably further comprises a step of treating the substrate and the plant body planted on the substrate with a solution containing nitrogen and phosphorus before the PFAS treatment step, thereby attaching the plant body to the substrate. Such a step is expected to allow the roots or rhizomes of the plant body to develop better, and the accumulation of the above-mentioned microorganisms and the secretion of substances from the roots or rhizomes to become more active. The solution containing nitrogen and phosphorus may further contain potassium, iron, calcium and magnesium as further elements. As the solution containing nitrogen and phosphorus, a commercially available product of a culture solution for the plant body can also be used. In addition, when the water containing PFAS contains nitrogen and phosphorus, water containing PFAS can also be used as the solution containing nitrogen and phosphorus. In this case, this step and the above PFAS treatment step are performed continuously. The time for treatment with the solution containing nitrogen and phosphorus is not particularly limited as long as the plant body is attached to the substrate, and may be, for example, one day or more, preferably 14 days or more, and more preferably 30 days or more. Alternatively, from the viewpoint of shortening the treatment time, the treatment time may be one day or less. EXAMPLES

[0019] 650g of granular foam glass was added to a pot with a diameter of 16 cm (top), 14 cm (bottom), and a height of 25 cm, and Typha was planted in the foam glass. 2L of synthetic culture solution was added to the pot and cultured for 34 days, and Typha was attached to the foam glass. The synthetic culture solution used contained 100mg / L of nitrogen (derived from ammonia and nitric acid), 120mg / L of phosphorus, 230mg / L of potassium, 3mg / L of iron, 100mg / L of calcium, and 20mg / L of magnesium as elements. The culture solution was drained from the pot, and 2L of landfill leachate containing PFAS was introduced into the pot and allowed to stand at 20 to 41°C for 21 days (Example, n=3). As a control, 2L of the same landfill leachate as in the Example was introduced into an empty pot and allowed to stand at 20 to 41°C for 21 days (n=3). During the test period, pure water in the same amount as the water lost by evapotranspiration was appropriately added to the pot. The landfill leachate was collected from a waste final disposal site and had the following properties at the time of pot introduction: Total PFAS concentration: 19,000ng / L Sodium concentration: 380mg / L Calcium concentration: 18mg / L Nitrogen concentration: 130mg / L Total organic carbon concentration: 85mg / L Electrical conductivity: 300mS / m Organic nitrogen concentration: 11mg / L pH: 7.9

[0020] After introducing the landfill leachate into the pots, a small amount of leachate was collected from the pots at 0 hours, 2 hours, 2 days, 7 days, 14 days, and 21 days, and the concentrations of 13 types of PFAS were measured. In the example pots, the concentration of each PFAS decreased over time. The removal rate of PFAS after 21 days was calculated for each pot according to the following formula. In the formula, the initial PFAS concentration is the PFAS concentration after 0 hours. Removal rate (%) = ((initial PFAS concentration) - (PFAS concentration after 21 days)) / (initial PFAS concentration) x 100 The average removal rate of PFAS after 21 days is shown in Figure 1. In the examples, all PFASs were removed at a removal rate of 50% or more.

Claims

1. The method includes a step of treating water or soil containing per- and polyfluoroalkyl compounds with a substrate and a plant body attached to the substrate, A method for removing per- and polyfluoroalkyl compounds, wherein in the process of treating water or soil, the per- and polyfluoroalkyl compounds are decomposed by biodegradation.

2. The method of claim 1 , wherein the biodegradation is microbial decomposition.

3. The method according to claim 1 or 2, further comprising the step of treating the substrate and the plant body planted in the substrate with a solution containing nitrogen and phosphorus prior to the step of treating the water or soil, thereby attaching the plant body to the substrate.

4. The method of claim 3 , wherein the solution further comprises potassium, iron, calcium and magnesium.

5. The method according to claim 1 or 2, wherein the plant body is an emergent plant.

6. The method according to claim 5 , wherein the emergent plant is Typha.

7. 3. The method of claim 1 or 2, wherein the water containing per- and polyfluoroalkyl compounds has a sodium concentration of 0.1 mg / L or greater.

8. 3. The method of claim 1 or 2, wherein the water containing per- and polyfluoroalkyl compounds has a calcium concentration of 0.1 mg / L or greater.

9. 3. The method according to claim 1 or 2, wherein the water containing per- and polyfluoroalkyl compounds has an electrical conductivity of 3 to 5000 mS / m.

10. The method of claim 1 or 2, wherein the water containing per- and polyfluoroalkyl compounds has a pH of 2-12.

11. 3. The method of claim 1 or 2, wherein the water containing per- and polyfluoroalkyl compounds has an organic nitrogen concentration of 2000 mg / L or less.

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