Patent ID: 12246974

DETAILED DESCRIPTION OF THE DISCLOSURE

Described below are exemplary embodiments of PFAS removal systems and methods. As explained above, PFAS has been used in commercial products for decades due in part to their non-stick and stain-resistant characteristics. However, because PFAS have such long half-lives (i.e., due to the particularly strong carbon-fluoride bond), they have leached into soil column and accumulated in the groundwater to contaminate the environment over the years. This is particularly concerning due to the adverse health risks associated with PFAS (i.e., kidney damage, immune system impairment, increased cholesterol levels, changes in liver enzymes, decreased vaccine response in children, low birth rates and birth defects, increased risk of some cancers, and reproductive issues, just to name a few).

Many PFAS treatment systems and methods known in the art remove PFAS and form other toxic substances. Thus, these systems and methods just replace one toxic chemical (a PFAS) with another toxic chemical (e.g., sodium fluoride, lithium fluoride, iron fluoride). However, the PFAS removal systems and methods provided herein treat one or more PFAS with calcium oxide (CaO) to remove the one or more PFAS and form calcium fluoride, carbon dioxide, and water, instead. Each of these products (i.e., calcium fluoride, carbon dioxide, and water) are less toxic than the products of known PFAS treatment systems and methods (e.g., sodium fluoride, lithium fluoride, iron fluoride).

The systems and methods described herein are configured to remove PFAS from a contaminated stream. PFAS, as used herein, may include any one or more of the following substances: AFFF, perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), GenX, perfluorobutane sulfonic acid (PFBS), perfluoropentanesulfonic acid (PFPS), perfluorohexane sulfonic acid (PFHxS), perfluoroheptanesulfonic acid PFHpS), perfluorononanesulfonic acid (PFNS), or perfluorodecanesulfonic acid (PFDS).

PFAS streams that may be treated by the PFAS removal systems provided herein can include groundwater, collected fire suppression foam (e.g., AFFF), water from natural bodies of water (e.g., creeks, rivers), soil, sediments, concentrated PFAS aqueous streams, PFAS ion exchange resins regeneration waste streams, fire suppression solutions stored in structures (Hangars, etc.) and firefighting equipment.

Prior to removing the PFAS from the contaminated stream, the stream may be treated to remove other contaminates in the stream. This pretreatment may include for example, separation methods, concentration methods, filtration methods (e.g., granulated activated carbon), distillation methods, for removing excess water, soil, minerals, solvents, sediments, and/or debris from the contaminated stream. Pretreatment methods may also include dilution methods for diluting concentrated PFAS of a concentrated PFAS stream to a suitable concentration for removal (i.e., CaO treatment).

The pretreated stream including PFAS can then be fed to a furnace comprising a calcium oxide source to remove the PFAS from the stream and produce calcium fluoride. The waste stream from this removal process is calcium fluoride, water, and carbon dioxide. The calcium fluoride can be disposed at municipal landfills after demonstration (toxicity characteristic leaching procedure (TCLP) analysis) of not being a RCRA hazardous waste. The water and carbon dioxide can be released into the atmosphere. In some embodiments, the carbon dioxide can be passed through an aqueous solution of calcium oxide at room temperature to form calcium carbonate to be landfilled.

Provided below are PFAS removal systems and methods for removing PFAS from a contaminated stream. The PFAS removal systems provided include systems that include a PFAS separation system and systems that do not include a PFAS separation system. Each are described in detail below.

PFAS Removal Systems

Described herein are systems for removing PFAS from contamination sites by treating the PFAS of a contaminated stream with calcium oxide (CaO) to produce calcium fluoride, carbon dioxide, and water.FIG.1, which is described in detail below, depicts a system for removing a PFAS from a concentrated feed stream (i.e., a feed stream having a PFAS concentration suitable for calcium oxide treatment). In some embodiments, PFAS removal systems may include a PFAS separation system for separating PFAS from a dilute contaminated stream to form a concentrated PFAS stream that may then be treated with calcium oxide to remove the PFAS. For example,FIG.2depicts a system having both a PFAS separation system (i.e., to form a concentrated PFAS stream for calcium oxide treatment) as well as a PFAS removal system (i.e., for treating a PFAS contaminated stream with calcium oxide). Note that the PFAS separation system is optional and is dependent upon the PFAS source material (i.e., the PFAS concentration of the PFAS source material). Below, both a PFAS removal system without a PFAS separation system (i.e., that depicted inFIG.1) as well as a PFAS removal system including a PFAS separation system (i.e., that depicted inFIG.2) are described.

FIG.1illustrates a PFAS removal process, according to some embodiments. As shown inFIG.1, the input stream102comprises aqueous film-forming foam (AFFF) stockpile. AFFF is frequently used in the military to rapidly extinguish hydrocarbon fuel fires. However, over years of AFFF use, it has contaminated the environment and caused significant health concerns.

In some places, residual AFFF has been collected and contained in stockpiles. In these cases, the PFAS of the PFAS-contaminated stream (e.g., a stream comprising AFFF and water) does not need to be concentrated (i.e., by a PFAS separation system), since the concentration of the stockpile is suitable for calcium oxide treatment as-is. Accordingly, input stream102may already have a PFAS concentration suitable for PFAS removal (and not require concentration or other pretreatment). In some embodiments, input stream102may comprise any one or more PFAS. AFFF is only one example.

In some embodiments, the concentration of input stream102is 0.1-10, 1-8, or 1-5 wt. % PFAS. In some embodiments, the concentration of input stream102is less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt. % PFAS. In some embodiments, the concentration of input stream102is greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt. % PFAS.

As shown in the Figure, input stream102is fed into furnace104. In some embodiments, input stream102may be fed into furnace104using air. Furnace104may be a muffle furnace. Furnace104may also be any kiln or heated oven. Furnace104comprises CaO source106, such as a CaO cartridge. In some embodiments, a CaO cartridge may include CaO pellets that can allow for a fast and easy flow. However, a CaO cartridge comprising CaO pellets exclusively may result in a less than acceptable PFAS reaction (e.g., 90%). Thus, in some embodiments, a CaO cartridge may include CaO pellets mixed with silica sand. The CaO pellets mixed with silica sand may significantly increase the reactive surface area while still exhibiting an acceptable flow rate (e.g., 1-4 cubic feet per minute through a 4 inch inside diameter cartridge).

CaO source106is configured to react with the one or more PFAS of input stream102. In some embodiments, system100may comprise a single furnace104. In some embodiments, system100may comprise more than one furnace104, such as two, three, four, five, six, or more furnaces104. In some embodiments, two or more furnaces104may be connected in series. In some embodiments, two or more furnaces104may be connected in parallel. In some embodiments, three or more furnaces104may be connected in a combination of series and parallel.

In some embodiments, system100may be a batch process. In some embodiments, system100may be a continuous process. In some embodiments of a batch process, system100may be configured to process input stream102in quantities of 0.1-1,000, 50-500, or 100-500 L. In some embodiments, system100may be configured to process input stream102in quantities of less than or equal to 1,000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 50, 10, 11, or 0.5 L. In some embodiments, system100may be configured to process input stream102in quantities of greater than or equal to 0.1, 0.5, 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 L.

In some embodiments of a continuous process, input stream102may enter furnace104at flow rates of 0.1 to 10 or 2 to 5 gallons per minute (GPM). In some embodiments, input stream102may enter furnace104at flow rates less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 GPM. In some embodiments, input stream102may enter furnace104at flow rates greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 GPM.

Once the one or more PFAS have sufficiently reacted with CaO source106, some of the CaO is converted to calcium fluoride (CaF2). Other products of the PFAS-CaO reaction (i.e., water and carbon dioxide) are released from furnace104in outlet stream108. In some embodiments, these products are released into the atmosphere. In some embodiments, the carbon dioxide may be bubbled through a calcium hydroxide solution to capture the carbon dioxide and avoid the release of greenhouse gases. In some embodiments, about 0.25 pounds of carbon dioxide is generated for each pound of PFAS mineralized. In some embodiments, about 66 liters of carbon dioxide is generated at 25° C. per pound of PFAS mineralized.

In some embodiments, systems provided herein include methods of capturing residual PFAS in the event not all PFAS is converted to CaF2, water, and carbon dioxide. For example, one such method may include tank110. As shown in the Figure, tank110includes granular activated carbon and sodium hydroxide. In the event not all PFAS reacts and some remains, it can be collected in tank110and disposed of as toxic waste, or extracted and recycled through the system. In some embodiments, tank110may comprise an alcohol. In some embodiments, system provided herein may comprise more than one tank110. For example, one tank110may comprise an alcohol, and a second tank110may comprises a hydroxide (e.g., sodium hydroxide, calcium hydroxide).

In some embodiments, to effectively react the PFAS and CaO, furnace104may be heated to 200-1500, 400-1000, or 500-800 degrees Celsius. In some embodiments, furnace104may be heated to less than or equal to 1500, 1200, 1000, 800, 600, 500, 400, or 300. In some embodiments, furnace104may be heated to greater than or equal to 200, 300, 400, 500, 600, 800, 1000, or 1200 degrees Celsius. In some embodiments, furnace104may comprise heating coils to maintain the desired temperature throughout the duration of the reaction. In some embodiments, furnace104operates at atmospheric pressure.

As explained above, the PFAS of input stream102can react with CaO under certain conditions to produce water, carbon dioxide, and CaF2. For example, Table 1 below shows an example reaction, including the Gibbs free energy of each reactant, each product, and of the complete reaction.

ReactantsProductsTotal215715161ΔGC8HF15O2CaOO2CaF2CO2H2O(kJ/mol)ΔG−12,400−9049.50−17,634−6310.4−237−2731.9(kJ/mol)

In some embodiments, the energy required to operate the system and evaporate the regeneration waste is 300-1500 or 500-1000 Kcal/L of waste. In some embodiments, the energy required to operate the system and evaporate the regeneration waste is less than or equal to 1500, 1200, 1000, 800, or 500 Kcal/L of waste. In some embodiments, the energy required to operate the system and evaporate the regeneration waste is greater than or equal to 300, 500, 800, 1000, or 1200 Kcal/L of waste.

In some embodiments, the PFAS-CaO reaction may run to 80-100%, 85-99%, 90-99%, or 90-95% completion. In some embodiments, the PFAS-CaO reaction may run to less than or equal to 100%, 99%, 95%, 90%, or 85% completion. In some embodiments, the PFAS-CaO reaction may run to greater than or equal to 80%, 85%, 90%, 95%, or 99% completion.

FIG.2illustrates a system200comprising PFAS removal process214as well as a PFAS separation system212for concentrating the PFAS of a feed stream to form a concentrated PFAS stream suitable for calcium oxide treatment, according to some embodiments. Specifically, the process shown inFIG.2includes a PFAS separation system212for concentrating one or more PFAS of a contaminated stream to more effectively remove the one or more PFAS from the contaminated stream. Once the PFAS is concentrated by PFAS separation system212, it may be removed by PFAS removal system214. Each component of both the PFAS separation system212and PFAS removal system214are explained below.

As explained above and depicted inFIG.2, some systems described herein may include a PFAS separation system, such as PFAS separation system212ofFIG.2. In some embodiments, PFAS separation system212can include contaminated stream216, ion exchange system218, concentrated stream220, distillation system222, and dilution system224.

In some embodiments, contaminated stream216is obtained from groundwater. For example, PFAS can leech into a soil column and get washed down and dissolve into the groundwater. The PFAS then migrates with the groundwater in a contamination plume. To mitigate the contamination, wells can be installed near a downstream end of the contamination plume to extract contaminated groundwater and prevent it from migrating any further. To remediate a contamination plume, well can be installed closer to the contamination source area to pump the groundwater out from the source area and treated (e.g., using PFAS removal systems provided herein). Thus, contaminated stream216may be obtained from a well installed near a PFAS contamination source.

PFAS separation system212is configured to receive contaminated stream216(e.g., obtained from a contamination plume) comprising one or more PFAS and produce a concentrated stream220with the one or more PFAS, such that the PFAS concentration of concentrated stream220is greater than that of the input contaminated stream216. In some embodiments, the concentration of contaminated stream216is 1×10−7to 5×10−3wt. % PFAS. In some embodiments, the concentration of contaminated stream216is less than or equal to 5×10−3, 1×10−3, 1×10−4, 1×10−5, or 1×10−6wt. % PFAS. In some embodiments, the concentration of contaminated stream is greater than or equal to 1×10−7, 1×10−6, 1×10−5, 1×10−4, or 1×10−3wt. % PFAS. In some embodiments, contaminated stream216comprises contaminated groundwater. In some embodiments, contaminated stream216may comprise soil and sediment.

Separation system212is configured to concentrate the PFAS of contaminated stream216to achieve a concentrated stream202having a PFAS concentration suitable for CaO treatment (i.e., of PFAS removal system214). In some embodiments, PFAS separation system212may include one or more of a filtration process, ion exchange process, distillation process, a chromatography process, an evaporation process, an extraction process, a heating process, a solvent extraction process, and/or a concentration process.

In some embodiments, separation system212comprises ion exchange system218. Ion exchange system218may comprise resin. Ion exchange system218may comprise two input streams: contaminated stream216comprising PFAS and a regeneration substance stream. Ion exchange system218may comprises two output streams: a PFAS-free effluent stream and a PFAS-methanol stream220. A PFAS-free effluent stream is formed after the PFAS of input contaminated stream216exchanges with components of the resin. Methanol may be used as a regeneration substance to regenerate the resin and remove the PFAS from the resin. After regeneration, PFAS-methanol stream220is produced.

In some embodiments, separation system212may include one, two, three, four, or more ion exchange systems218. In some embodiments, two or more ion exchange systems212may be connected in series or in parallel. In some embodiments, three or more ion exchange systems212may be connected in a combination of series and parallel.

In some embodiments, PFAS separation system212may be a batch process. In some embodiments, PFAS separation system212may be a continuous process. In some embodiments of a batch process, PFAS separation system212may be configured to process input contaminated stream216in quantities of 0.1-1,000, 50-500, or 100-500 L. In some embodiments, PFAS separation system212may be configured to process input contaminated stream216in quantities of less than or equal to 1,000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 50, 10, 11, or 0.5 L. In some embodiments, PFAS separation system212may be configured to process input contaminated stream216in quantities of greater than or equal to 0.1, 0.5, 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 L.

In some embodiments of a continuous process, input contaminated stream216may enter ion exchange system218at flow rates of 2 to 20 gallons per minute (GPM) per ion exchange unit. In some embodiments, input contaminated stream216may enter ion exchange system218at flow rates of less than or equal to 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, or 3 GPM per ion exchange unit. In some embodiments, input contaminated stream216may enter ion exchange system218at flow rates of greater than or equal to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 GPM per ion exchange unit.

In some embodiments, PFAS-methanol stream220may be treated prior to removing the PFAS. For example,FIG.2includes distillation system222and dilution system224configured to distill the methanol of PFAS-methanol stream220and dilute the PFAS to a suitable concentration, respectively. A concentrated stream202is formed after the output PFAS stream of ion exchange218(e.g., PFAS-methanol stream220) has been treated by distillation system222and dilution system224.

Once the PFAS is concentrated (e.g., by PFAS separation system212ofFIG.2to form concentrated stream202), the contaminated stream (i.e., concentrated stream202) is treated by PFAS removal system214to remove the PFAS. In some embodiments, PFAS removal system can include inlet feed202, furnace204, CaO source206, outlet208, and residual PFAS collection210.

Concentrated stream202includes any or all of the features of input stream102described above with reference toFIG.1. For example, concentrated stream may have a concentration of 0.1-10, 1-8, or 1-5 wt. % PFAS. In some embodiments, the concentration of concentrated stream202is less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt. % PFAS. In some embodiments, the concentration of concentrated stream202is greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt. % PFAS.

After passing through PFAS separation system212, one or more PFAS may be removes by PFAS removal system214. PFAS removal system214may include concentrated stream202, furnace204, CaO source206, byproduct outlet208, and tank210.

Concentrated stream202may be routed to furnace204comprising calcium oxide (CaO) source, such as CaO source206. In some embodiments, furnace204may include any or all features of furnace104ofFIG.1. In some embodiments, CaO source206may include any or all features of CaO source106ofFIG.1.

In some embodiments, furnace204may be a muffle furnace, kiln, or gas furnace. In some embodiments, PFAS removal system214may comprise a single furnace204. In some embodiments, PFAS removal system214may comprise more than one furnace204, such as two, three, four, five, six, or more furnaces204. In some embodiments, two or more furnaces204may be connected in series. In some embodiments, two or more furnaces204may be connected in parallel. In some embodiments, three or more furnaces204may be connected in a combination of series and parallel.

In some embodiments, PFAS removal system214may be a batch process. In some embodiments, PFAS removal system214may be a continuous process. In some embodiments of a batch process, PFAS removal system214may be configured to process input stream202in quantities of 0.1-1,000, 50-500, or 100-500 L. In some embodiments, PFAS removal system214may be configured to process input stream202in quantities of less than or equal to 1,000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 50, 10, 11, or 0.5 L. In some embodiments, PFAS removal system214may be configured to process input stream202in quantities of greater than or equal to 0.1, 0.5, 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 L.

In some embodiments of a continuous process, the concentrated input stream202may enter furnace204at flow rates of 0.1 to 10 gallons per minute (GPM) per furnace unit. In some embodiments, concentrated input stream202may enter furnace204at flow rates less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 GPM per furnace unit. In some embodiments, concentrated input stream202may enter furnace204at flow rates greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 GPM per furnace unit.

Furnace204may be configured to heat concentrated stream202, allowing one or more PFAS of concentrated stream202to react with the CaO of CaO source206. Furnace204may be heated to any of the temperatures provided above with reference to furnace104ofFIG.1. After reacting, the CaO of CaO source206is replaced with calcium fluoride (CaF2). Periodically, CaO source206will need to be replaced, since the CaO is replaced with CaF2as more PFAS is treated and removed. In some embodiments, CaO source206may include a cartridge.

Byproducts of the PFAS-CaO reaction (described above with respect toFIG.1and shown in Table 1) are released from furnace204to the atmosphere and can include water and carbon dioxide. In some embodiments, PFAS removal system214can include a capture system such as tank210to capture any residual PFAS that does not react with the CaO of CaO source206. In some embodiments, tank210may comprise granular activated carbon and sodium hydroxide. Tank210may include any or all features of tank110ofFIG.1.

Methods of Removing PFAS from a Contaminated Stream

Also provided herein are methods of removing PFAS from a PFAS-contaminated stream. For example,FIG.3illustrates a method300of removing per- and polyfluoroalkyl substances (PFAS) from a contaminated stream, according to some embodiments. Described below are methods that include separating (i.e., concentrating) PFAS from a contaminated stream (i.e., at step304) and removing the PFAS from the contaminated stream (i.e., at step306).

At step302, method300includes collecting a contaminated stream (e.g., contaminated stream216ofFIG.2) comprising one or more PFAS. In some embodiments, the contaminated stream comprising one or more PFAS may include contaminated groundwater and/or contaminated soil. The contaminated stream may first be concentrated or separated. For example, the contaminated stream may be routed through a separation system (e.g., PFAS separation system212ofFIG.2) configured to produce a concentrated PFAS stream (e.g., concentrated stream202ofFIG.2).

At step306, the concentrated PFAS stream may be treated by a PFAS removal system (e.g., PFAS removal system214ofFIG.2, system100ofFIG.1). For example, the PFAS of the concentrated PFAS stream may be removed by heating the concentrated stream in the presence of calcium oxide, producing calcium fluoride, water, and carbon dioxide.

EXAMPLES

In a stainless-steel container, 50 milliliters of a 1000 mg/L solution of perfluorooctanoic acid (PFOA) in methanol was mixed with 51 mg calcium oxide (CaO). The container was placed in a 65 degrees Celsius water bath to remove the methanol, producing a 101 mg powdered mixture of CaO and PFOA.

To cause the PFOA to react with the CaO to produce calcium fluoride (CaF2), the container was placed in a muffle furnace at 400° C. The time durations tested for thermal treatment include 10, 20, 30 and 60 minutes. The maximum reaction pressure was less than 50 psig. A complete stoichiometric reaction yields residuals of 71 mg.

After the reaction, any unreacted PFOA was separated by rinsing the residuals with 100 mL methanol and separating the residuals from the methanol rinse using glass fiber filtration/and or centrifuge. The solids are treated with 100 ml of 0.1 N HCL to remove all CaO and leave behind CaF2which is dried at 150 C and weighed to confirm stoichiometric completion of the reaction. Both the filtrate and the residuals were stored in borosilicate glass vials at 4 degrees Celsius for GC/MS/MS confirmation analysis.

The foregoing description sets forth exemplary systems, methods, techniques, parameters, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments.

Although the description herein uses terms first, second, etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another.

For any of the structural and functional characteristics described herein, methods of determining these characteristics are known in the art.