Methods and apparatus for the destruction and defluorination of perfluoroalkyl and polyfluoroalkyl substances (PFAS), fluorotelomers, and other persistent organic pollutants

Abstract

A process for destroying PFAS, comprising irradiating a solution containing one or more PFAS with UV radiation, the solution further containing one or more photosensitizers (preferably sodium iodide or potassium iodide), one or more bases that raise the pH of the solution above 13, and sulfite ions. Also described is a process for destroying persistent and recalcitrant organic pollutants, including PFAS, using a combination of oxidative and reductive destruction. Also described is a treatment system that applies a UV reduction process to the product of a UV oxidation process following the UV oxidation process.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of Provisional Application No. 63 / 353,879, entitled "Method and Apparatus for the Destruction and Defluorination of Per - and Polyfluoroalkyl Substances (PFAS), Fluorotelomers and Other Persistent Organic Pollutants," filed on June 21, 2022, which is hereby incorporated by reference in its entirety.

Background Art

[0002] Per - and polyfluoroalkyl substances (PFAS) are a class of synthetically prepared compounds that have been used in numerous consumer and industrial applications for decades. PFAS have several unique surface properties and can be both hydrophobic and oleophobic. As a result, PFAS are used as coating aids, lubricants, foaming agents, and various surface treatment agents. They have been found to be particularly useful as flame retardants in the form of aqueous film - forming foams (AFFFs). Also, some PFAS are known to bioaccumulate in plants and animals. There is increasing evidence that exposure to PFAS can also cause various health problems. Due to these concerns, various regulatory agencies around the world are beginning to establish strict limits on the presence of PFAS in food and water.

[0003] PFAS is a type of chemical substance containing perfluoroalkyl or polyfluoroalkyl groups. The definition and classification of perfluoroalkyl and polyfluoroalkyl substances (PFAS) have changed over time. The definition adopted here is the 2021 definition of the Organization for Economic Co-operation and Development (OECD), which expands the term and states that "PFAS are defined as fluorinated substances (with no H / Cl / Br / I atoms bonded) containing at least one fully fluorinated methyl or methylene carbon atom, i.e., any chemical substance having at least a perfluoromethyl group (-CF3) or a perfluoromethylene group (-CF2-), with some well-known exceptions, is a PFAS." Some of the most important examples of PFAS include perfluorosulfonic acids such as perfluorooctanesulfonic acid (PFOS), and perfluorocarboxylic acids (PFCA) such as perfluorooctanoic acid (PFOA). Fluorotelomers are fluorocarbon-based oligomers or telomers synthesized by telomerization (telomerization). Some fluorotelomers and fluorotelomer-based compounds are sources of environmentally persistent perfluorinated carboxylic acids such as PFOA.

[0004] The persistence, health issues, and regulatory status of PFAS have prompted significant research efforts to reduce their presence in the environment. Much of the early research focused on, for example, taking samples from drinking water. However, more recently, even stronger efforts have been made towards the destruction of these materials. One of the attributes of PFAS is their resistance to degradation in the environment. PFAS are not easily metabolized by organisms and do not decompose upon exposure to visible light or UV irradiation with wavelengths longer than typically seen under terrestrial conditions.

[0005] The two main modes of chemically mediated PFAS destruction are oxidation and reduction, respectively. Oxidative destruction is defined by the removal of electrons from the target species (i.e., PFAS) followed by decomposition, and reductive destruction is defined by the addition of electrons to the target species followed by decomposition. Oxidative and reductive destruction of PFAS can be achieved using various reagents (e.g., persulfate, hydrogen peroxide, nitrate, and other reagents for oxidation; or iodide, sulfite, and other reducing reagents) as well as input energy (e.g., ultraviolet light or sonication, among others). Due to the vast structural diversity of PFAS as a class, individual target PFAS vary in their level of sensitivity to oxidative or reductive destruction regimes, and only a limited number of sequential oxidation / reduction destruction processes have been reported in the past. Therefore, a "one-pot" approach that includes the use of ultraviolet light or sonication as an energy initiator is needed.

Summary of the Invention

[0006] The present disclosure is directed to an apparatus for destroying PFAS, comprising a reaction chamber housing one or more UV radiation sources, one or more ports for adding an oxidizing species or one or more reducing species, and one or more sensors for measuring one of the following: pH, oxidation potential or reduction potential of the solution (ORP sensor), fluoride concentration, UV intensity, conductivity, temperature, and pressure, and embodiments including this apparatus.

[0007] The present disclosure is also directed to a process for destroying PFAS, comprising irradiating a solution containing one or more PFAS with UV radiation, wherein the solution contains one or more sensitizers capable of absorbing the UV radiation, one or more bases with a pH above 13, and sulfite ions, and embodiments including this process.

[0008] The present disclosure also relates to a process for destroying ultra-short chain PFAS, which comprises irradiating a solution containing one or more ultra-short chain PFAS with UV radiation, wherein the solution contains one or more sensitizers capable of absorbing UV radiation, one or more bases such that the pH of the solution exceeds 13, and sulfite ions, and embodiments comprising this process are encompassed.

[0009] The following drawings are illustrative of embodiments and do not limit the scope of the invention. These drawings are not necessarily to scale and are intended to be used in conjunction with the following detailed description. Embodiments of the invention are described with reference to the drawings, in which like reference numerals can represent like elements.

Brief Description of the Drawings

[0010]

Figure 1

[0011]

Figure 2

[0012]

Figure 3

Modes for Carrying Out the Invention

[0013] The use of the term "destruction" herein refers to the decomposition of toxic chemicals or organic pollutants into harmless by-products.

[0014] The term "defluorination" herein refers to the cleavage of C-F bonds in C-F compounds such as PFAS or fluorotelomers.

[0015] Ultra-short chain PFAS can be any perfluorinated or polyfluorinated molecule having a chain length of three or fewer carbon atoms.

[0016] Reductive destruction methods have been shown to have excellent performance in the treatment of perfluorocarboxylic acids and perfluorosulfonic acids such as PFOA, PFOS and their short-chain related substances, as well as perfluoroethers such as HFPO-DA. However, reduction does not effectively treat fluorotelomer compounds such as 6:2 FTS.

[0017] Conversely, oxidative destruction methods have shown great effectiveness in the decomposition of fluorotelomers such as 6:2 FTS, which produce short-chain perfluorocarboxylate and perfluorosulfonate PFAS as decomposition by-products, but lack the ability to destroy the by-product short-chain perfluorocarboxylate and perfluorosulfonate compounds they produce.

[0018] The structures of representative PFAS are shown below.

[0019]

Chemical formula

[0020] This difference in performance between the reductive treatment method and the oxidative treatment method is shown in Graphs 1 and 2 below, which show destruction performance tests using the same aqueous film-forming foam (AFFF) contaminated waste stream. Graph 1, which is a reductive case, shows destruction of over 95% of PFPeA and PFHxA, i.e., two perfluorocarboxylate compounds in the matrix, but does not destroy any of the major 6:2 FTS fluorotelomer compounds.

[0021] Graph 1

[0022]

Number

[0023] In comparison, the oxidative case (shown in Graph 2 below) destroys over 90% of the initial 6:2 FTS fluorotelomer but leaves a significantly increased amount of the by-product short-chain carboxylate PFBA, PFPeA, PFHxA, and PFHpA due to the decomposition of 6:2 FTS and other undetected pre-oxidized PFAS compounds in the matrix.

[0024] Graph 2

[0025]

Number

[0026] Embodiments of the present disclosure improve the destruction of PFAS and its by-products across each of the above methods. For example, according to the present disclosure, in some embodiments, a complete destruction can be achieved by combining the above oxidative and reductive methods in sequence, first oxidizing the target matrix (as in Graph 2) and then reducing it (as in Graph 1).

[0027] As seen in Figure 1, according to an embodiment of this combined disclosed method, the effectiveness of the reduction treatment on the already oxidized PFAS stock in the form of the feedstock was demonstrated to be able to destroy at least 90% and up to 99.99% of the PFAS remaining in the solution after the preliminary oxidation.

[0028] According to some embodiments of the present disclosure, matrices affected by PFAS, such as AFFF - contaminated wastewater, can be oxidatively treated to decompose oxidation - sensitive compounds such as 6:2 FTS and other fluorotelomers into short - chain carboxylates or sulfonates that are difficult to oxidatively treat. Following the oxidation process, the wastewater can then be subjected to a reduction treatment, thereby destroying the remaining carboxylate and sulfonate compounds. This combined treatment according to embodiments of the present disclosure can effectively eliminate all PFAS in the matrix, thereby enabling safe disposal.

[0029] Example 1

[0030] For contaminated military wastewater (Graph 3 below), a continuous one - pot oxidation - reduction process on a 5 - liter scale in aqueous film - forming foam (AFFF) was carried out, reproducing the separate trials shown in Graphs 1 and 2 above. The time series shows the same trend that short - chain carboxylate compounds increase as 6:2 FTS and other PFAS components are oxidatively decomposed, and then the carboxylate compounds are rapidly destroyed when the process is switched to the reduction mode.

[0031] Graph 3

[0032]

Number

[0033] According to some embodiments of the present disclosure, it should be understood that PFAS - contaminated wastewater can be treated by the following methods, provided that the embodiments of the present disclosure are not limited thereto: First, an oxidation reagent including, but not limited to, hydrogen peroxide, sodium persulfate, metal nitrates (such as zinc nitrate, nickel nitrate, etc.), or titanium dioxide or other metal, metal oxide or non - metal nanoparticles (having a nanoparticle size in the range of about 1 - 500 nm) may be added to the PFAS wastewater at a concentration of about 0.001 ppt - 100,000 ppm. Next, a base including, but not limited to, hydroxide salts (such as sodium hydroxide, calcium hydroxide, ammonium hydroxide, etc.) and carbonates and bicarbonates (such as sodium bicarbonate) may be added to the reaction mixture. The addition of the base reagent can be in the concentration range of about 50 mM - about 1 M.

[0034] In particular, the addition of the base can be carried out before, during, or after the oxidation treatment. The concentration of the oxidation reagent can be in the range of about 0.1 mM - about 100 mM, and in some embodiments, preferably 2 - 10 mM. In some embodiments, then, the sample can be irradiated with light having a wavelength in the range of about 100 nm - about 500 nm, and in some embodiments, preferably about 180 - about 300 nm, for a time in the range of about 10 minutes - about 96 hours, and in some embodiments, preferably about 40 minutes - about 240 minutes.

[0035] Following this oxidation reaction, in some embodiments, the oxidation reagent can be quenched or removed from the solution. Next, a reducing reagent including, but not limited to, sodium sulfite, potassium iodide, indole derivatives, and other hydrated electron generating organic or inorganic reagents or catalysts is added to the reaction mixture, and light with a wavelength of about 150 nm to about 500 nm, in some embodiments preferably about 200 to about 300 nm, is irradiated for a time ranging from about 10 minutes to about 96 hours, in some embodiments preferably about 1 to about 4 hours. According to some embodiments, all remaining PFAS degradation by-products of the oxidation reaction can be destroyed by more than 92%. In some embodiments, the reducing reagent concentration can range from about 0.1 mM to about 200 mM, in some embodiments preferably about 2 to about 50 mM.

[0036] In some embodiments, the addition of the reagent may be performed in bulk, for example, at the initialization of the procedure or throughout the reduction process. In water that is significantly affected by co-contaminants such as nitrates, organic contents, or cationic metal species, for example, higher-order reagent addition (e.g., but not limited to, about 200 mM) can be used. This post-treatment matrix from which PFAS has been removed can then be safely discarded.

[0037] Graph 4 (shown below) shows the reductive destruction and defluorination of the flow of industrial waste affected by PFAS, including ultra-short chain PFAS, according to embodiments of the present disclosure. Ultra-short chain PFAS can be any perfluorinated or polyfluorinated molecule having a chain length of three or fewer carbon atoms. As can be seen, the above reduction procedure reaches a significant and impressive 96% reduction in the observed total organic fluorine (TOF) of the industrial waste sample affected by PFAS from an initial TOF concentration of 33,114 ppb (μg / L).

[0038] Graph 4

[0039]

Number

[0040] Table 1 presents the results obtained from the treatment of AFFF wastewater from a military facility using a 5-liter reactor according to Example 1. As can be seen, treatment for 2 - 4 hours results in 92 - 100% destruction of all PFAS compounds in a single pass.

[0041] Table 1

[0042] [Table 1]

[0043] Figure 2 shows the main steps involved in the combined redox treatment according to some embodiments of the present disclosure. Figure 3 shows an example of a batch or continuous reactor that can be used for the continuous UV redox treatment of PFAS-contaminated streams (water, wastewater, AFFF) according to some embodiments of the present disclosure. As can be seen, the treatment can be carried out in a batch or continuous reactor as shown in Figure 3. These systems include an opaque reaction tank or vessel (1) made of materials or other materials; one or more UV lamps (2) that emit in the wavelength range of about 100 - about 500 nm; an optional pH sensor (3); and a stirring system (4) including, but not limited to, an impeller, mixer, and / or stirrer for homogenization of the solution or reagent. Further, the system can have an inlet (A) for a PFAS concentrated solution or PFAS-contaminated stream, an effluent (B), an inlet (C) for an oxidizing reagent, an inlet (D) for a reducing reagent, and an acid / base inlet (E) for pH control. It should be understood that the positioning of the components of the system can be different from that shown.

[0044] The process of the invention disclosed herein can also be applied to other persistent organic pollutants including, but not limited to, aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and toxaphene.

[0045] Similarly, the processes of the present invention disclosed herein can be applied to other persistent water pollutants including, but not limited to, for example, 3,4,3',4'-tetrachlorobiphenyl, 2,4,5,2',4,5'-hexachlorobiphenyl, 2,3,7,8-tetrachloro-dibenzo[p]dioxin (TCDD), 1,1,1-trichloro-2,2-bis(4-chlorophenyl)-ethane (DDT), 1,2,3,4,5,6-hexachlorocyclohexane (lindane), and benzo[a]pyrene, chlordane, 2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol (dicofol), pentachlorophenol, Aroclor-1254, phenanthrene, biphenyl p-cresol, and 2-methylnaphthalene.

[0046] Embodiments of the present disclosure provide many advantages. As described herein, some embodiments of the present disclosure may use UV-based oxidation followed by UV-based reduction. Thus, such embodiments can use UV in both steps and be carried out near ambient temperature (without adding heat beyond that generated by the UV lamp). The result is a very high level of destruction up to 100% of fluoropolymers and 92 - 97% destruction of other PFAS. This also enables both steps of the process to be carried out in a single reactor since both steps of the process are based on UV photochemistry. Further, embodiments of the present disclosure may only require the addition of reagents twice, (1) at the start of oxidation and (2) then at the start of reduction, and can be carried out without continuously adding reagents during the process. Further, the process can be carried out quickly, such as in about 1 - 4 hours or less. Finally, the process requires less energy input by avoiding the use of high temperatures required by prior art thermal oxidation processes.

[0047] Embodiments of the present disclosure may also include an apparatus for destroying PFAS, comprising the following elements: 1) a reaction chamber containing one or more UV radiation sources; 2) one or more ports for adding oxidizing species or one or more reducing species; 3) optionally, one or more sensors capable of measuring one of the following: pH, oxidation or reduction potential of the solution (ORP sensor); fluoride concentration; UV intensity; conductivity; temperature and pressure; 4) optionally, a thermal jacket surrounding at least a portion of the reaction chamber that can be cooled or heated by a fluid.

[0048] Embodiments of the present disclosure may also include an apparatus for destroying PFAS, including a thermal jacket surrounding at least a portion of the reactor.

[0049] Embodiments of the present disclosure may also include an apparatus for destroying PFAS, comprising one or more sensors capable of measuring one or more of the following: pH, oxidation or reduction potential of the solution (ORP sensor); fluoride concentration; UV intensity; conductivity; temperature and pressure.

[0050] Embodiments of the present disclosure may also include an apparatus for destroying PFAS, comprising one or more sensors capable of measuring one or more of the following: pH, oxidation or reduction potential of the solution (ORP sensor); fluoride concentration; UV intensity; conductivity; temperature and pressure; and a thermal jacket surrounding at least a portion of the reactor.

[0051] Embodiments of the present disclosure may also include an apparatus for destroying PFAS, wherein the UV radiation source is one or more low-pressure mercury lamps.

[0052] Embodiments of the present disclosure may also include an apparatus comprising one or more sensors capable of measuring all of the following: pH, oxidation or reduction potential of the solution (ORP sensor); fluoride concentration; UV intensity; conductivity; temperature and pressure.

[0053] Embodiments of the present disclosure may also include a process for destroying PFAS, which consists of irradiating a solution containing one or more PFAS with UV radiation, wherein the solution comprises: 1) one or more sensitizers capable of absorbing UV radiation; 2) one or more strong bases such that the pH of the solution is > 13; and / or 3) optionally, sulfite ions.

[0054] Embodiments of the present disclosure may also include a process for destroying PFAS, which consists of irradiating a solution containing one or more PFAS and containing sulfite ions with UV radiation.

[0055] Embodiments of the present disclosure may also include, for destroying PFAS, that one or more strong bases are alkali metal hydroxides such that the pH of the solution is > 13.

[0056] Embodiments of the present disclosure may also include a process for destroying PFAS, wherein one or more strong bases are sodium hydroxide such that the pH of the solution is > 13.

[0057] Embodiments of the present disclosure may also include a process for destroying PFAS, wherein one or more strong bases are potassium hydroxide such that the pH of the solution is > 13.

[0058] Embodiments of the present disclosure may also include a process for destroying PFAS, which consists of irradiating a solution containing sulfite ions, wherein the sulfite species is the sodium salt of sulfurous acid.

[0059] Embodiments of the present disclosure may also include a process for destroying PFAS, which consists of irradiating a solution containing sulfite ions, wherein the sulfite species is the potassium salt of sulfurous acid.

[0060] Embodiments of the present disclosure may also include a process for destroying PFAS, wherein one or more strong bases are a mixture of sodium hydroxide and sodium carbonate such that the pH of the solution is > 13.

[0061] Embodiments of the present disclosure may also include a process in which the sensitizer capable of absorbing UV radiation is sodium iodide or potassium iodide.

[0062] Embodiments of the present disclosure may also include a process in which one or more strong bases are added so that the pH of the solution is > 13.2.

[0063] Embodiments of the present disclosure may also include a process for destroying PFAS, which consists of irradiating a solution containing sulfite ions at a concentration of 5 mM to 500 mM sodium iodide and 50 mM to 1 M sodium sulfite.

[0064] Embodiments of the present disclosure may also include a process in which a sensitizer capable of absorbing UV radiation is present at a concentration of 5 mM to 500 mM.

[0065] Embodiments of the present disclosure may also include a process for destroying ultra-short chain PFAS, which consists of irradiating a solution containing one or more PFAS with UV radiation. The solution may include the following: 1) one or more sensitizers capable of absorbing UV radiation; 2) one or more strong bases such that the pH of the solution is > 13; and / or 3) optionally, containing sulfite ions.

[0066] Embodiments of the present disclosure may also include a process for destroying PFAS, which consists of irradiating a solution containing one or more PFAS and containing sulfite ions with UV radiation.

[0067] Embodiments of the present disclosure may also include a process for destroying PFAS, in which one or more strong bases are alkali metal hydroxides so that the pH of the solution is > 13.

[0068] Embodiments of the present disclosure may also include a process for destroying PFAS, in which one or more strong bases are sodium hydroxide so that the pH of the solution is > 13.

[0069] Embodiments of the present disclosure may also include a process for destroying PFAS in which one or more strong bases are potassium hydroxide such that the pH of the solution is > 13.

[0070] Embodiments of the present disclosure may also include a process for destroying PFAS that consists of irradiating a solution containing sulfite ions, wherein the sulfite species is the sodium salt of sulfurous acid.

[0071] Embodiments of the present disclosure may also include a process for destroying PFAS that consists of irradiating a solution containing sulfite ions, wherein the sulfite species is the potassium salt of sulfurous acid.

[0072] Embodiments of the present disclosure may also include a process for destroying PFAS in which one or more strong bases are a mixture of sodium hydroxide and sodium carbonate such that the pH of the solution is > 13.

[0073] Embodiments of the present disclosure may also include a process in which the sensitizer capable of absorbing UV radiation is sodium iodide or potassium iodide.

[0074] Embodiments of the present disclosure may also include a process in which one or more strong bases are added such that the pH of the solution is > 13.2.

[0075] Embodiments of the present disclosure may also include a process for destroying PFAS that consists of irradiating a solution containing sulfite ions at a concentration of 5 mM to 500 mM sodium iodide and 50 mM to 1 M sodium sulfite.

[0076] Embodiments of the present disclosure may also include a process in which a sensitizer capable of absorbing UV radiation is present at a concentration of 5 mM to 500 mM.

[0077] Embodiments of the present disclosure may also include processes in which the PFAS to be destroyed includes trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), perfluoro-2-methoxypropionic acid (PMPA), or conjugate bases thereof.

[0078] Embodiments of the present disclosure may also include processes for the destruction and defluorination of PFAS in a water stream (PFAS concentrate, wastewater, effluent, AFFF resulting from a water treatment system) that involve applying a UV oxidation process to the PFAS to produce a product, and then applying a UV reduction process to the product of the UV oxidation process.

[0079] Embodiments of the present disclosure may also include processes for the destruction of persistent and recalcitrant organic contaminants other than PFAS in a water stream (PFAS concentrate, wastewater, effluent, AFFF resulting from a water treatment system) that involve applying a UV oxidation process to the contaminant to produce a product, and then applying a UV reduction process to the product of the UV oxidation process.

[0080] It should be understood that the present disclosure is not limited to the specific embodiments disclosed, but rather includes all combinations of the various disclosed elements, and any known or later-occurring variations thereof.

Claims

Claim 1 An apparatus for destroying PFAS, comprising: A reaction chamber housing one or more UV radiation sources; One or more ports for adding oxidizing species or one or more reducing species; and One or more sensors for measuring one of the following: pH, oxidation potential or reduction potential of the solution (ORP sensor), fluoride concentration, UV intensity, conductivity, temperature, and pressure. Claim 2 The apparatus according to claim 1, further comprising a thermal jacket surrounding at least a part of the reaction chamber, the thermal jacket being fillable with a heating or cooling fluid. Claim 3 The apparatus according to claim 1, wherein at least one of the UV radiation sources is a low-pressure mercury lamp. Claim 4 A process for destroying PFAS, comprising irradiating a solution containing one or more PFAS with UV radiation, the solution containing one or more sensitizers capable of absorbing the UV radiation, one or more bases having a pH above 13, and sulfite ions. Claim 5 The process according to claim 4, wherein the solution contains the sulfite ions. Claim 6 The process according to claim 4, wherein the base is an alkali metal hydroxide. Claim 7 The process according to claim 4, wherein the base is potassium hydroxide. Claim 8 The process according to claim 5, wherein the sulfite species is a sodium salt of sulfite. Claim 9 The process according to claim 5, wherein the sulfite species is a potassium salt of sulfite. Claim 10 The process according to claim 4, wherein the base comprises a mixture of sodium hydroxide and sodium carbonate. Claim 11 The process according to claim 4, wherein the sensitizer is capable of absorbing sodium iodide or potassium iodide of UV radiation. Claim 12 The process according to claim 4, wherein the base is added in an amount sufficient to establish a pH of the solution above 13.

2. Claim 13 A process for destroying ultra-short-chain PFAS, comprising: Irradiating a solution containing one or more ultra-short-chain PFAS with UV radiation, the solution containing one or more sensitizers capable of absorbing the UV radiation, one or more bases such that the pH of the solution is above 13, and sulfite ions. Claim 14 The process of claim 13, wherein the PFAS to be destroyed comprises trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), perfluoro-2-methoxypropionic acid (PMPA), or their conjugate bases.

15. The process of claim 13, wherein the one or more bases are an alkali metal hydroxide.

16. The process of claim 13, wherein the one or more bases are potassium hydroxide.

17. The process of claim 13, wherein the sulfite ion species is the sodium salt of sulfurous acid.

18. The process of claim 13, wherein the sulfite ion species is the potassium salt of sulfurous acid.

19. The process of claim 13, wherein the sensitizer capable of absorbing UV radiation is sodium iodide or potassium iodide.

20. The process of claim 13, wherein the one or more bases are added in an amount sufficient to establish a pH of the solution above 13.2.

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