Low-temperature thermal treatment of PFAS-contaminated wastes

Abstract

Thermal treatment is an approach for the end-of-life treatment or regeneration of material contaminated with per- and polyfluoroalkyl substances (PFAS). However, its effectiveness has been limited by the requirement for high temperatures (> 1000 °C), the generation of fluorinated products of incomplete destruction, and the necessity to scrub hydrofluoric acid in the flue gas. The subject technology utilizes common alkali and / or alkaline-earth metal reagents to enhance the mineralization of PFAS present in wastes. Reagents reduced PFAS, products of incomplete destruction, and hydrofluoric acid in the flue gas by reacting them with the reagent to form inorganic fluorine (e.g., calcium fluoride).

Description

135404.045300-ND25-022LOW-TEMPERATURE THERMAL TREATMENT OF PFAS-CONTAMINATED WASTESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present disclosure claims priority to U.S. Provisional Application 63 / 712,771, filed on October 28, 2024, and entitled “LOW-TEMPERATURE THERMAL REGENERATION OR TREATMENT OF GRANULAR ACTIVATED CARBON USING ADDITIVES”, and to U.S. Provisional Application 63 / 860,043, filed on August 8, 2025, and titled “LOW-TEMPERATURE FIXED BED TREATMENT PROCESS TO MINERALIZE PER AND POLYFLUORO ALKYL SUBSTANCES (PFAS) IN WASTES”, which are both incorporated herein by reference in their entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under ER2 1-1 1 07 awarded by the U.S. Department of Defense and contract W912HQ-21-C-0058 awarded by the U.S. Department of Defense. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates to treatment of contaminated materials and more particularly to thermal treatment processes for the mineralization of per- and / or polyfluoroalkyl substances (PFAS) in contaminated materials.BACKGROUND

[0004] PFAS comprise a diverse group of synthetic organic compounds known for their exceptional thermal, chemical, and biological stability, water and oil resistance, and surfactant properties. PFAS find application in various industrial and consumer products, such as aqueous film-forming foams (AFFFs), nonstick cookware, stain-resistant fabrics and carpets, some cosmetics, and water repellent clothing, among others. Due to their recalcitrance, PFAS are ubiquitous in the environment, and they have been detected in municipal wastewater, freshwaters, and treated drinking water.135404.045300-ND25-022BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Certain features of the subject technology are set forth in the appended claims. However, for the purpose of explanation, several embodiments of the subject technology are set forth in the following figures, where like reference numerals refer to the same or similar features in the various figures.

[0006] FIG. 1 is a system for low-temperature treatment, in accordance with one or more embodiments.

[0007] FIG. 2 is an example system for low-temperature treatment in which contaminated waste is passed through a furnace to thermally release PFAS into a gas phase and the released PFAS in the gas phase is then passed through a bed including a calcium-based reagent, in accordance with one or more embodiments.

[0008] FIG. 3 is an example system for low-temperature treatment in which a reagent is precombined with contaminated waste, in accordance with one or more embodiments.

[0009] FIG. 4 is an example system for low-temperature treatment in which contaminated waste is comminuted and combined with a reagent, in accordance with one or more embodiments.DETAILED DESCRIPTION

[0010] PFAS represent a group of over 10,000 fluorinated chemicals with high resistance to chemical, biological, and thermal degradation because of their strong carbon-fluorine (C-F) bonds. PFAS have been frequently used in a variety of consumer and industrial products, which has led to their ubiquitous occurrence in the environment and engineered systems. A major contributor to environmental contamination by PFAS is AFFFs. AFFFs are used to extinguish oil and gasoline related fires, and since the 1950s, military installations have been conducting frequent training exercises on firefighting training grounds. This has led to the widespread contamination of more than 600 military installations. Additionally, public airports, roadways, and sites impacted by large fuel fire accidents and AFFF usage have become contaminated with PFAS. The historical use of AFFF has led to the contamination of surrounding soil and freshwater.

[0011] The widespread use of PFAS in industrial and commercial products has also led to the prevalent contamination of environmental systems. PFAS can enter the environment through wastewater treatment plants (WWTPs) where PFAS ends up in the effluent or the135404.045300-ND25-022 biosolids of WWTPs. The effluent is discharged into a receiving body of water (e.g., stream), which then transports the PFAS throughout the environment. Biosolids are either land applied, landfilled, or incinerated. Land application of biosolids contaminated with PFAS has led to the widespread contamination of groundwater, surface waters, air, plants, food, and livestock. Biosolids that are landfilled are not destroyed end up in leachate that is sent back to a WWTP or leaks into the environment. The inability to land apply biosolids because of PFAS contamination has led to increased costs for utilities and farmers. For example, in Decatur, Alabama, the use of PFAS-contaminated biosolids led to the contamination of drinking water for over 100,000 people.

[0012] The US Department of Defense (DoD) and the Environmental Protection Agency (EPA) have recommended landfilling and incineration as potential methods in their interim guidance for handling PFAS-containing wastes. Incineration is already applied as a hazardous waste management approach and would arguably be a better approach for treating AFFF- impacted wastes because, in contrast to landfilling, it can destroy PFAS. Out of a total of 126 waste incinerators in the US, there are 27 hazardous waste incinerators capable of handling approximately 680 kilotons of hazardous waste and typically operate at temperatures up to 850 °C in the primary stage and approximately 1100-1200 °C in the afterburner. Nonetheless, the complete thermal destruction of PFAS (i.e., mineralization) requires very high operating temperatures (>1,000 °C) and inefficient destruction can release undesirable products of incomplete destruction (PIDs) in the flue gas, including potent greenhouse gases with a global warming potential that exceeds CO2 by 10,000s-fold. Consequently, the DoD has recommended exercising caution in employing thermal treatment for managing PFAS wastes until further information is acquired.

[0013] Several studies have provided evidence that using reagents (also referred to herein as “additives”) can enhance the thermal treatment of PFAS. Abou-Khalil et al., “Enhancing the Thermal Mineralization of Perfluorooctanesulfonate on Granular Activated Carbon Using Alkali and Alkaline-Earth Metal Additives” (2024), which is incorporated by reference herein, showed that various alkaline and alkali earth metal oxide additives decreased the temperature and time required to mineralize perfluorooctanesulfonate (PFOS) on granular activated carbon (GAC). Calcium hydroxide (Ca(OH)2) was the most efficient reagent tested, mineralizing >95% of PFOS at <500 °C in under 5 min while producing innocuous calcium fluoride (CaF2). Portland cement concrete (PCC) is composed of Ca(OH)2 with around 10-20% by weight.135404.045300-ND25-022Thus, the inventors of the present disclosure hypothesized that the natural presence of Ca(0H)2 in PCC will mineralize PFAS at low temperatures while minimizing the production of PIDs.

[0014] The present disclosure addresses the limitations discussed above by introducing a low-temperature thermal treatment process that utilizes calcium-based reagents, such as calcium hydroxide or calcium oxide, to enhance the mineralization of PFAS. This approach significantly reduces the temperature required for effective treatment to as low as 400 °C, while also minimizing the formation of harmful byproducts. The result is a cleaner, more energyefficient process for destroying PFAS and stabilizing the resulting waste for safe disposal or reuse. The disclosed processes utilize the catalytic properties of the calcium-based reagents, which react with PFAS or its thermally degraded products to form hydrofluoric acid (HF). The HF then reacts with the calcium-based reagent to form a stable product, calcium fluoride (CaF?), thereby eliminating the need for further air pollution controls. Furthermore, the disclosure incorporates optimized system configurations, including gas-solid contactors and pre-mixing strategies, to improve efficiency and scalability. By enabling rapid and thorough mineralization of PFAS in under 15 minutes, the described processes offer a technological improvement in the field of environmental remediation, providing a practical and scalable pathway for managing PFAS-contaminated wastes.

[0015] Turning now to the figures, FIG. 1 is a system 100 for low-temperature treatment, in accordance with one or more embodiments. The system 100 may be used to mineralize PFAS 102, such as PFOS, using calcium-based reagents (e.g., calcium hydroxide, calcium oxide) under controlled conditions. The system 100 may facilitate the thermal decomposition of PFAS and the subsequent capture of byproducts for efficient treatment and minimal environmental impact.

[0016] The system 100 includes one or more thermal treatment units 108 and / or one or more gas treatment units 112. Waste treatment may begin with waste preparation where PFAS- contaminated waste 104 is combined with one or more reagents to enhance the thermal mineralization process. The waste 104 may be or include activated carbon, soils, sediments, biosolids, biota, pavements, ion-exchange resins, reverse-osmosis concentrates, AFFFs concentrates, and / or any other solid or concentrated liquid wastes containing PFAS. For example, the waste 104 may be or include spent granular activated carbon, concrete, soil, sand, and / or gravel. In some embodiments, the waste 104 may be comminuted. For example, the waste 104 may be concrete blocks that are crushed and / or ground into smaller pieces.135404.045300-ND25-022

[0017] The reagents may be or include alkaline and / or alkali earth metal oxides. For example, the reagents may be calcium-based and include calcium hydroxide and / or calcium oxide. Other reagents may include magnesium oxide, magnesium hydroxide, calcium chloride, calcium carbonate, or sodium hydroxide. The reagent may be added in an amount sufficient to achieve a solid reagent-to-waste volume ratio of about 5% to 20%, sufficient to fill pore spaces and promote gas-solid contact during thermal release of PFAS 102. Thermal release refers to the liberation of PFAS or fluorinated intermediates from a condensed phase (e.g., solid, sludge, or liquid) into the gas phase upon heating. This includes, without limitation, physical volatilization, desorption from surfaces or pores, sublimation, or in-situ chemical transformation that yields volatile species. The term encompasses intact PFAS and partially decomposed intermediates that enter the gas phase because of thermal input.

[0018] The reagent may be added by mixing the reagent with the waste 104 sufficient to fill pore spaces and promote gas-solid contact during thermal release of PFAS 102, by injecting the reagent as fine particles into the gas feed 106 of the thermal treatment unit 108, by providing the reagent as a layer above the waste 104, and / or coating one or more interior surfaces of the thermal treatment unit 108 with the reagent. In some embodiments, the reagent is already naturally present in the waste 104. For example, the waste 104 may be Portland cement concrete that includes calcium oxide- and calcium hydroxide-based minerals. In some embodiments, the waste 104 or the reagent may release water during heating.

[0019] The waste 104 may be fed into a thermal treatment unit 108 via an inlet of the thermal treatment unit 108. The waste 104 may be fed continuously into the thermal treatment unit 108 using waste handling equipment such as belt conveyors, screw feeders, or hoppers.

[0020] The thermal treatment unit 108 may be a furnace, incinerator, kiln, rotary kiln, pyrolysis reactor, gasifier, fluidized-bed reactor, combustion chamber, and / or any other suitable thermal system capable of thermal treatment of PFAS-contaminated waste described herein. The thermal treatment unit 108 operates at treatment temperatures greater than 400 °C, such as between about 425 °C to 1000 °C, which is adequate to thermally release PFAS and initiate their decomposition.

[0021] At around 425 °C, the temperature is sufficient to thermally release all PFAS. Once in the gas phase, the PFAS and / or its fluorinated intermediate that may form from thermolytic destruction during release, will react with the reagent to cleave their strong carbon-fluorine (C- F) bonds to form a calcium fluoride (CaF2), which remains bound within the solid phase rather135404.045300-ND25-022 than subliming into the gas phase. The heating process thus separates the treated material into discharge byproducts including a solid phase, which includes mineralized fluorine in the form of calcium fluoride, and a gas phase, which includes the primary air, water, and / or trace combustion gases. In some embodiments, the waste 104 may be heated at the treatment temperature for less than 15 minutes.

[0022] Upon completion of the thermal reaction, the solid and / or gas phases are discharged from the thermal treatment unit 108. The solid phase is a stable material (e.g., ash) that retains nearly all of the fluorine as inorganic fluorine, confirming that overall destruction and removal efficiency (DRE) of the PFAS 102 in the waste 104 exceeds about 90% and the degree of mineralization of PFAS 102 exceeds about 85%. Mineralization refers to the conversion of organic fluorine in PFAS or PFAS-derived intermediates to inorganic fluorine species, specifically calcium fluoride or hydrofluoric acid, indicating complete chemical destruction rather than physical removal or partial decomposition. DRE refers to the percentage of PFAS mass destroyed and / or removed from the treated waste relative to its concentration in the feed stream, determined in accordance with standard thermal treatment performance metrics.

[0023] The discharged gas phase is minimal in hazardous content, as the calcium-based chemistry prevents the formation of hydrofluoric acid or other volatile fluorinated byproducts. Particularly, the discharged gas phase may include less than about 15% fluorinated products. In some examples, measurements of the gas phase may include no detectable hydrofluoric acid or PFAS destruction intermediates, demonstrating that the process confines the reactive fluorine to the solid phase. This thermal conversion thus produces a stable solid phase that safely retains fluorine and a clean gas phase suitable for standard scrubbing and emission control systems.

[0024] A gas feed 106, or primary air, may be introduced to the thermal treatment unit 108 via an inlet of the thermal treatment unit 108 (along with the waste 104) to carry the thermally released PFAS and its thermolysis products through the system 100. The gas feed 106 enables the efficient transfer of these products out of the treatment unit 108 and into the subsequent treatment stages, if any. The gas feed 106 may be controlled to maintain a consistent flow rate for uniform exposure to the thermal treatment conditions. The gas flow is set to ensure a residence time that is sufficient for the fine particle fraction of the waste 104 to reach treatment temperature before exiting the thermal treatment unit 108, and to ensure thermally released PFAS and intermediate products do not react with the walls of the thermal treatment unit 108135404.045300-ND25-022 or the transfer line 110, or in any part of the setup used (e.g., inlet, tubing, etc.). For example, the gas may flow at a rate of 1.5 L / min for a thermal treatment unit 108 having a volume of 5.1 L. The gas may be air (e.g., Ultra Zero grade Air, natural air) or N2 (e.g., Ultra High Purity grade Nitrogen).

[0025] In some embodiments, after passing through the thermal treatment unit 108, the gas feed 106 may be directed into one or more gas treatment units 112 of the system 100. A gas treatment unit 112 may be fluidly coupled to an outlet of the thermal treatment unit 108 via a transfer line 110 and may receive and process the gas phase effluent, which may include thermally released PFAS, PFAS products of incomplete destruction, hydrofluoric acid, and other gaseous byproducts. The gas treatment unit 112 may be maintained at a temperature between about 42 °C and 1000 °C, such as between about 400 °C and 600 °C. The gas treatment unit 112 may be independently heated using external heat sources, heating jackets, and / or other thermal control systems. Additionally or alternatively, the gas treatment unit 112 is heated passively through residual heat of the thermal treatment unit 108 transferred via the transfer line 110, wherein the hot gas feed and / or thermal radiation from the transfer line maintains the gas treatment unit 112 at the desired operating temperature.

[0026] The gas treatment unit 112 may be or include a gas-solid contactor. Gas-solid contactor refers to any apparatus, reactor, and / or zone configured to bring a PFAS-containing gas feed into contact with a solid reagent (e.g., the calcium-based reagent) under conditions that promote physical or chemical reaction. Examples of gas-solid contactors include fixed-bed reactors, fluidized-bed reactors, monolithic blocks, porous blocks, coated filters, moving-bed systems, chambers containing dispersed or supported solids, and / or the like. The gas treatment unit 112 may be integral with the thermal treatment unit 108 and / or positioned downstream as a separate unit.

[0027] For example, the gas treatment unit 112 may include a fixed-bed contactor or reactor containing a dispersed particulate, where a dispersed particulate refers to the reagent that is spatially distributed or otherwise arranged to provide accessible reactive surface area for gassolid interaction. The fixed bed may include the dispersed particulate reagent combined with packing materials such as silica (SiCF), ceramic supports, and / or other inert materials to provide structural integrity, enhance gas-solid contact, and reduce pressure drop. The particle size of the calcium-based reagents may range from fine powders (e.g., less than 100 pm) to larger granular forms (e.g., 1-10 mm), and it may be mixed with or layered separately from inert135404.045300-ND25-022 packing materials. As the gas phase flows through the fixed bed, the thermally released PFAS and its intermediates react with the calcium-based reagents to form a stable inorganic fluoride such as calcium fluoride (CaF2). Any residual hydrofluoric acid will also be neutralized, preventing its release into the atmosphere and reducing the need for neutralizing wet scrubbers. In some embodiments, greater than 75% of the hydrofluoric acid from the PFAS is captured as CaF2in the discharged waste.

[0028] In some embodiments, such as an experimental configuration shown in FIG. 1, the outlet of the gas treatment unit 112 may be connected to one or more wet scrubbers. The scrubbers may be filled with a liquid medium, such as a 0.1 M sodium hydroxide solution, to neutralize any acids, including hydrofluoric acid. The impingers may be maintained at ambient temperature or cooled using ice baths or other cooling systems to enhance the capture efficiency of gaseous species.

[0029] The system 100 may also include a transfer line 110 that fluidly couples an outlet of the thermal treatment unit 108 to an inlet of the gas treatment unit 112. The transfer line 110 may convey the gas phase effluent from the thermal treatment unit 108, where the gas phase includes thermally released PFAS, PFAS products of incomplete destruction, HF, and / or other volatile fluorinated species generated in the thermal treatment unit 108. In some embodiments, the transfer line includes stainless steel tubing, such as 316 stainless steel, ceramic tubing, and / or other thermally resistant materials suitable for handling corrosive gaseous species at elevated temperatures. The transfer line may have a diameter ranging from 0.125 inches to 6 inches, and a length ranging from 10 cm to 500 cm, though the system 100 is not limited with regard to the diameter and length of the transfer line.

[0030] To prevent condensation of thermally released PFAS and fluorinated intermediates within the transfer line 110, the transfer line may be maintained at an elevated temperature between about 100 °C and 1000 °C, such as between about 180 °C and 250 °C. In some embodiments, the transfer line 110 is actively heated using resistive heating elements, heating tape, and / or heat tracing systems wrapped around or embedded within the transfer line wall. In some embodiments, the transfer line 110 may be heated by residual thermal radiation from the thermal treatment unit 108, or through passive insulation that retains heat carried by the hot gas feed passing through the transfer line from the thermal treatment unit 108. Maintaining the transfer line at elevated temperatures ensures that PFAS, PFAS products of incomplete destruction, HF, and other volatile fluorinated species remain in the gas phase during transport,135404.045300-ND25-022 thereby preventing the formation of condensed-phase deposits on the inner walls of the transfer line that could lead to system fouling, reduced thermal destruction efficiency, or release of incompletely destroyed PFAS.

[0031] FIG. 2 is an example system 200 for low-temperature treatment in which a waste 104 containing PFAS 102 is treated in a thermal treatment unit 108 and the resulting thermally released PFAS or its intermediates are passed through a fixed bed including a reagent, in accordance with one or more embodiments. In this system 200, PFAS-contaminated waste 104 (e.g., granular activated carbon, biosolids, soil, concrete, sand, gravel) is inserted into a thermal treatment unit 108 (e.g., a low-temperature incinerator, rotary kiln, infrared heater, conductive heater, tube furnace). The thermal treatment unit 108 may be maintained at a temperature between about 400 °C and 600 °C, which provides sufficient energy to thermally release PFAS from the waste 104 into the gas phase. An air or oxygen-deficient gas feed 106, such as nitrogen, may flow through the thermal treatment unit 108 at a controlled flow rate, such as between 0.5 L / min and 10 L / min, to facilitate the transport of thermally released PFAS away from the waste 104 and the outlet of the unit 108.

[0032] The gas phase, now containing thermally released PFAS along with the gas feed 106, is conveyed from the thermal treatment unit 108 through a heated transfer line 110 to a gas-solid contactor configured as a bed reactor 202. The bed reactor 202 is maintained at a temperature between about 42 °C and 500 °C, which may be achieved through independent heating elements surrounding the bed reactor 202 or through passive heating from the thermal energy carried by the hot gas feed 106 from the thermal treatment unit 108. The bed reactor 202 comprises calcium-based reagents 204, such as calcium hydroxide and / or calcium oxide, which may be present as small particles and / or large particles. The calcium-based reagents 204 may be mixed with or layered alongside inert packing materials 206 such as silica, alumina, ceramic beads, and / or other thermally stable support materials that provide structural integrity to the bed reactor 202, to improve gas flow distribution and increase the surface area available for gas-solid contact. The bed reactor 202 may be packed or fluidized.

[0033] As the gas phase containing PFAS flows through the heated bed reactor 202, the elevated temperature of 42 °C to 500 °C, combined with the calcium-based reagents 204, promotes the thermal decomposition and mineralization of PFAS. During thermal decomposition and mineralization, the C-F bonds are broken and the PFAS are converted to hydrofluoric acid along with other mineralization products such as carbon dioxide and water135404.045300-ND25-022 vapor. The hydrofluoric acid produced from the mineralization of PFAS reacts with the calcium-based reagent 204 to form calcium fluoride, an inorganic, thermally stable, and environmentally benign solid compound. These reactions effectively capture the fluorine content from PFAS as a stable mineral phase within the bed reactor 202, preventing the release of PFAS or PFAS products of incomplete destruction to the atmosphere.

[0034] FIG. 3 is an example system 300 for low-temperature treatment in which a reagent 302 is pre-mixed with a waste 104 containing PFAS 102, in accordance with one or more embodiments. In this system 300, the PFAS-contaminated waste 104 is first combined with a calcium-based reagent 302 in either dry powder form or as a slurry to form a pre-mixed waste 304. The dry powder mixing approach involves physically blending the calcium-based reagent 302 with the PFAS-contaminated waste 104 using mechanical mixing equipment such as rotary mixers, tube rotators, ribbon blenders, or drum mixers. Additionally or alternatively, the slurry approach involves dispersing the calcium-based reagent 302 in water, alcohols, or other suitable liquid carriers to create a fluid suspension with reagent concentrations ranging from 5% to 50% by weight, which may then be sprayed onto, poured over, or otherwise applied to the PFAS-contaminated waste 104. The liquid carrier enables the calcium-based reagent 302 to penetrate into pore spaces and coat particle surfaces thereby ensuring better contact with the thermally released PFAS and the reagent 302.

[0035] The resulting pre-mixed waste 304 is inserted into the thermal treatment unit 108, such as a low-temperature incinerator. The thermal treatment unit 108 is operated at a temperature between about 400 °C and 600 °C under an air or oxygen-deficient gas feed 106, with gas flow rates ranging from 0.5 L / min to 10 L / min to maintain desired residence time. At these treatment temperatures, there is enough energy to thermally release PFAS from the premixed waste 304. The released PFAS reacts with the reagent 302 that fills the pore space or resides on top of the pre-mixed waste 304 to form calcium fluoride. The efficiency of mineralization increases with reagent 302 to waste 104 volumetric ratio, achieving efficiencies above 95%, while large ratios greater than 10% yield near-quantitative conversion of PFAS to calcium fluoride.

[0036] FIG. 4 is an example system 400 for low-temperature treatment in which PFAS- contaminated waste 104 is inserted or fed into the thermal treatment unit, which is heated between about 400 °C and 600 °C. During the thermal treatment of the waste, the reagent 402 in the form of fine powder is injected into the thermal treatment unit 108 through one or more135404.045300-ND25-022 inlets positioned to introduce the reagent 402. The injection may be performed by pneumatic feeders, screw conveyors, venturi injectors, and / or other similar powder handling equipment capable of delivering controlled quantities of reagent into the thermal treatment unit 108.

[0037] As the waste 104 is heated within the thermal treatment unit 108, PFAS is thermally released. The released PFAS or PFAS products of incomplete destruction now in the gas phase react with the injected calcium-based reagent 402 powder particles, suspended in the gas phase and heated to the treatment temperature, converting PFAS to calcium fluoride. The calcium fluoride, along with unreacted calcium-based reagent 402, subsequently settles or is carried with the gas feed 106 to downstream processes (e.g., cyclone, bag house). The gas feed 106, which may be air or an oxygen-deficient gas, flows through the thermal treatment unit 108 at controlled rates to facilitate dispersion of the injected powder and / or transport gaseous byproducts and particles to downstream collection equipment.

[0038] The optimal loading of calcium-based reagent 402 is volume dependent, meaning the required injection rate must be determined based on the volumetric capacity of the thermal treatment unit 108, the gas flow rate, the residence time of waste 104 and gas within the thermal treatment unit 108, and / or the concentration of PFAS being treated.

[0039] The present detailed description provides illustrative examples of methods, systems, and compositions related to the thermal treatment and mineralization of PFAS in contaminated waste materials, including GAC, PCC, and other PFAS-laden wastes. The disclosed subject matter pertains to the field of environmental remediation, specifically addressing the challenges associated with the destruction and mineralization of PFAS, which are known for their chemical, thermal, and biological stability and environmental persistence. The described methods utilize innovative low-temperature thermal treatment processes, enhanced by the use of alkali and alkaline-earth metal reagents, to achieve efficient PFAS mineralization while minimizing the formation of harmful byproducts such as hydrofluoric acid and PIDs.

[0040] The foregoing description is intended to provide illustrative examples of the disclosed subject matter and is not intended to limit the scope of the claims. Certain widely recognized methods, procedures, and components may not be described in detail to avoid obscuring the disclosed subject matter. The disclosed embodiments are representative of the described subject matter and do not cover all possible variations; various modifications, substitutions, and rearrangements of the described methods and systems may be made without135404.045300-ND25-022 departing from the spirit and scope of the disclosed subject matter. The claims are intended to encompass all such variations and equivalents.

[0041] While this disclosure has described certain embodiments, it is understood that the claims are not intended to be limited to these embodiments except as explicitly recited in the claims. On the contrary, the instant disclosure is intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the disclosure. Furthermore, in the detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, the present disclosure is not limited to the specific details set forth herein and can be practiced using one or more other embodiments. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure various aspects of the present disclosure. Additionally, in one or more embodiments, structures and components are shown in block diagram form to avoid obscuring the concepts of the present disclosure.

[0042] As used herein, the phrase “at least one of’ preceding a series of items, with the term “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (i.e., each item). The phrase “at least one of’ does not require selection of at least one of each item listed; rather, the phrase allows a meaning that includes at least one of any one of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refers to only A, only B, or only C; any combination of A, B, and C; and / or at least one of any of A, B, and C.

[0043] Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, one or more implementations, one or more implementations, an embodiment, the embodiment, another embodiment, one or more implementations, one or more implementations, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the present disclosure or that such disclosure applies to all configurations of the present disclosure. A disclosure relating to such phrase(s) may apply to all configurations or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples. A135404.045300-ND25-022 phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases.

[0044] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any implementation described herein as “exemplary” or as an “example” is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, to the extent that the term “include”, “have”, or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.

[0045] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein but are to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. Unless specifically stated otherwise, the term “some” refers to one or more. Headings and subheadings, if any, are used for convenience only and do not limit the subject disclosure.

Claims

135404.045300-ND25-022CLAIMSWhat is claimed is:

1. A method of mineralizing per- / poly-fluoroalkyl substances (PFAS) in waste, the method comprising: providing the waste with a calcium-based reagent; heating, in a thermal treatment unit, the waste to a treatment temperature between about 425 °C and about 1000 °C thermally releasing the PFAS from the waste and into a gas phase; and discharging the waste and the gas phase from the thermal treatment unit, wherein an overall destruction and removal efficiency (DRE) of PFAS in the waste exceeds about 90%, a degree of mineralization of PFAS exceeds about 85%, and the discharged gas phase includes less than about 15% fluorinated products.

2. The method of claim 1, wherein the thermal treatment unit comprises any one or more of a furnace, incinerator, kiln, rotary kiln, pyrolysis reactor, gasifier, fluidized-bed reactor, or combustion chamber.

3. The method of claim 1, wherein the calcium-based reagent is provided as any one or more of a dispersed particulate, coating, or porous solid structure that directly interfaces with the gas phase.

4. The method of claim 1, wherein heating the waste to the treatment temperature thermally releases any one or more of PFAS or PFAS degradation products to the gas phase, and the calcium-based reagent converts the any one or more of PFAS or PFAS degradation products to calcium fluoride (CaF2).

5. The method of claim 1, wherein providing the waste with the calcium-based reagent comprises mixing the calcium-based reagent with the waste at a reagent-to-waste volume ratio of about 5% to about 20%.135404.045300-ND25-0226. The method of claim 1, wherein providing the waste with the calcium-based reagent comprises introducing the calcium-based reagent as fine particles injected into a gas feed of the thermal treatment unit.

7. The method of claim 1, wherein providing the waste with the calcium-based reagent comprises providing the calcium-based reagent as a layer above the waste.

8. The method of claim 1, wherein providing the waste with the calcium-based reagent comprises coating interior surfaces of the thermal treatment unit with the calcium-based reagent.

9. The method of claim 1, further comprising, after heating the waste to the treatment temperature, transferring the gas phase to a gas-solid contactor via a transfer line, wherein the gas-solid contactor is heated at a temperature between about 42 °C and 1000 °C.

10. The method of claim 9, wherein the calcium-based reagent is provided at the gas-solid contactor, and the gas-solid contactor is heated by any one or more of an external heat source or residual heat of the thermal treatment unit via the transfer line.

11. The method of claim 9, wherein the transfer line is heated at a temperature between about 100 °C and 1000 °C to prevent condensation of thermally released PFAS.

12. The method of claim 1, wherein the calcium-based reagent is one or more of calcium hydroxide or calcium oxide.

13. The method of claim 1, wherein the waste is heated at the treatment temperature for greater than five minutes.

14. A thermal treatment unit for low-temperature mineralization of PFAS in waste, the thermal treatment unit comprising: an inlet receiving PFAS-contaminated waste and a calcium-based reagent;135404.045300-ND25-022 a heating zone heating the waste to a treatment temperature between about 425 °C and about 1000 °C thermally releasing the PFAS from the waste and into a gas phase; and an outlet discharging one or more of the waste or the gas phase from the thermal treatment unit, wherein an overall destruction and removal efficiency (DRE) of PFAS in the discharged waste exceeds about 90%, a degree of mineralization of PFAS exceeds about 85%, and the discharged gas phase includes less than about 15% fluorinated products.

15. The thermal treatment unit of claim 14, further comprising: a gas- solid contactor fluidly coupled with the outlet of the thermal treatment unit via a transfer line, wherein the gas phase is discharged to the gas- solid contactor via the transfer line, and the gas-solid contactor is heated at a temperature between about 42 °C and 1000 °C.

16. The thermal treatment unit of claim 15, wherein the calcium-based reagent is provided in the gas- solid contactor and the gas- solid contactor is heated by any one or more of an external heat source or residual heat of the thermal treatment unit via the transfer line.

17. The thermal treatment unit of claim 16, wherein the transfer line is heated at a temperature between about 100 °C and 1000 °C to prevent condensation of thermally released PFAS.

18. The thermal treatment unit of claim 14, wherein the calcium-based reagent is provided as any one or more of a dispersed particulate, coating, or porous solid structure that directly interfaces with the gas phase.

19. The thermal treatment unit of claim 14, wherein heating the waste to the treatment temperature thermally releases any one or more of PFAS or PFAS degradation products to the gas phase, and the calcium-based reagent converts the released any one or more of PFAS or PFAS degradation products to calcium fluoride (CaF2).135404.045300-ND25-02220. The thermal treatment unit of claim 14, wherein the waste is mixed with the calcium- based reagent at a reagent-to- waste volume ratio of about 5% to about 20%.

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