WO2025054446A1

WO2025054446A1 - In situ method of degradation of fluoro-organic compounds

Info

Publication number: WO2025054446A1
Application number: PCT/US2024/045576
Authority: WO
Inventors: Brant A. SMITH; Brianna Desjardins; Josephine MOLIN; Lennart KLEINFELDT
Original assignee: Evonik Corporation
Priority date: 2023-09-08
Filing date: 2024-09-06
Publication date: 2025-03-13

Abstract

There is presented an in situ method of degradation of a fluoro-organic compound in an aqueous environment comprising at least soil and groundwater, the method comprising at least the steps of: (a) adding a sorptive media to the aqueous environment, the sorptive media being one or more of the group comprising: carbon, reactive organic and zero valent metal; (b) allowing the fluoro-organic compound to fix onto the sorptive media over a time period of greater than 24 hours; (c) providing an oxidant being reactive to the sorptive media; and (d) adding the oxidant to the aqueous environment to contact the sorptive media in situ at an oxidant concentration of ≥0.4M, and to initiate degradation of the fluoro-organic compound on the sorptive media when the temperature of the sorptive media is at least 65°C, so that one or more fluoro-degradation products are formed. The method relates to the in situ degradation of volatile and semi-volatile organic compounds, pesticides and other recalcitrant organic compounds in soil and groundwater, and includes soil remediation.

Description

IN SITU METHOD OF DEGRADATION OF FLUORO-ORGANIC COMPOUNDS

The present invention relates to an in situ method of degradation of fluoro-organic compound contamination using an oxidant, such as a peroxygen compounds such as persulfates or peroxides The method is useable for in situ degradation of fluoro-organic compounds in soils, sediments, groundwater, process water and wastewater, and especially relates to the in situ degradation of per- and polyfluoroalkyl substances (PFAS) and other recalcitrant organic compounds in soil and groundwater. A method of soil remediation is also described.

Background

The presence of contaminants in a variety of media is a well-documented and extensive environmental problem around the world, resulting from the use and release of various chemicals into the environment. These contaminants are often toxic, carcinogenic or are otherwise detrimental to humans or the environment. In addition, these contaminants are also often hydrophobic and resistant to natural degradation pathways resulting in their physical accumulation and/or bioaccumulation. The presence of organic compounds in soil can also lead to contamination of aquifers resulting in potential public health impacts and degradation of groundwater resources for future use.

Several methods have been developed and employed to treat such contaminants, including chemical oxidation, chemical reduction, and bioremediation. These transformative reactions have been successful in treating a wide assortment of contaminants but are typically limited to aqueous phase oxidative or reductive reactions This has led to difficulties in treating lower solubility and hydrophobic contaminants, including a wide array of semi volatile organic compounds (SVOCs), chlorinated dioxins, polychlorinated biphenyls (POBs), pesticides, energetic compounds, some volatile organic compounds (VOCs), and emerging contaminants such as per- and polyfluoroalkyl substances (PFAS). Thermal treatments have been identified as being able to degrade these contaminants of concern at temperatures of several hundred to over a thousand degrees Celsius. These methods are often difficult and costly to implement as they require significant energy to heat the matrix to the desired temperature and often require heating above the boiling temperature of water.

Chemical oxidation, either applied in situ or ex situ of the subsurface or waste stream, is an approach to treat a range of contaminants with strong oxidizing chemicals, with the goal of complete mineralization, or conversion to carbon dioxide and water. Examples of such treatment include WO 2005/081996, US6019548 and US7576254. Other emergent organic compounds are now also being considered as contaminants that need treatment and remediation, in particular fluoro-organic compounds due to the strong fluorine-carbon bonds therein. Among these fluoro-organic compounds, Per- and Polyfluoroalkyl substances (PFAS) are now considered to be of particular concern. PFAS are defined as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/CI/Br/l atom attached to it): that is, with a few noted exceptions, any chemical with at least a perfluorinated methyl group (-CF3) or a perfluorinated methylene group (-CF2-).

PFAS have so far proven to be extremely difficult to treat, typically requiring highly energetic systems based on very high temperatures and pressures: see for example Environ. Sci. Technol. 2021, 55, 3283-3295. In situ destructive mechanisms have focused on the destruction of PFAS using temperatures of several hundred degrees Celsius, which under ambient conditions, would require the evaporation of water.

Other methods for treating PFAS have focused on non-destructive phase change mechanisms, such as sorption, filtration or ion exchange. Ex-situ destructive mechanisms also exist, but are highly energetic or not achieving full remediation and degradation.

One object of the present invention is to provide an improved method for the in situ degradation of fluoro-organic compounds.

Summary

According to one embodiment of the present invention, there is provided an in situ method of degradation of a fluoro-organic compound in an aqueous environment comprising at least soil and groundwater, the method comprising at least the steps of:

(a) adding a sorptive media to the aqueous environment, the sorptive media being one or more of the group comprising: carbon, reactive organic and zero valent metal;

(b) allowing the fluoro-organic compound to fix onto the sorptive media over a time period of greater than 24 hours;

(c) providing an oxidant being reactive to the sorptive media; and

(d) adding the oxidant to the aqueous environment to contact the sorptive media in situ at an oxidant concentration of S0.4M to initiate degradation of the fluoro-organic compound on the sorptive media when the temperature of the sorptive media is at least 65°C, so that one or more fluoro-degradation products are formed. Optionally, the time period of step (b) is more than 1 day such as 2-7 days, 10 days, two weeks, 3-10 weeks or longer, including 2-12 months, 1 year or more than 1 year.

Optionally, the time period for step (b) is more than 7 days, including more than 1 week or 4 weeks or 8 weeks.

Optionally, the sorptive media is either: a carbon being one or more of the group comprising: natural carbon, peat, coal, charcoal, biochar and activated carbon; or a zero valent metal being one or more of the group comprising: iron, zinc, silver, magnesium, nickel, aluminum and copper; or a reactive mineral being one or more of manganese dioxide, titanium dioxide, iron oxide and iron sulfide.

Optionally, the sorptive media has a particle size in the range 1 m to 2000 pm, optionally in the range 1 pm to 150 pm, and optionally in the range 5 pm to 100 pm. Such a material can be more easily added to the aqueous environment, either directly or indirectly.

Optionally, adding the oxidant in step (d) is by injection into the aqueous environment, or by soil mixing. Injection methods are known in the art, and soil mixing can be carried out using known machinery and methods, including augers and the like. The method required for step (d) may also relate to the method of provision of the oxidant in step (c). Where the oxidant is in solution, or mixed with a carrier material, this can assist to establish the contact between the oxidant and the sorptive media. Methods of adding oxidants into an aqueous environment are known, and include injecting under pressure to result in the subsurface migration of the oxidant, establishing contact via soil mixing, or other means, natural or induced, including advection, diffusion and dispersion.

Optionally, the fluoro-organic compound is fixated on the soil prior to step (a). Thus, step (b) involves the transfer of the fluoro-organic compound away from its fixation to soil and towards its fixation onto the sorptive media. The transfer may involve a transfer medium or conveyor or mechanism, such as water such as the groundwater in, around, or passing through the aqueous environment. The transfer can be a slow process, hence the requirement in step (b) for a time period of greater than 24 hours, typically longer than 24 hours, including weeks, months and possibly more than 1 year.

Step (d) requires the temperature of the sorptive media to be at least 65°C. Only at this temperature can the subsequent reaction between the oxidant and the sorptive media be sufficient to cause the degradation of the nearby and fixed fluoro-organic compound on the sorptive media. The inventors have found that a temperature of at least 65°C for the sorptive media is a minimum temperature needed to start degradation of fixed nearby fluoro-organic compound(s), taking into account the materials and other process parameters of the method of the present invention.

In one embodiment of the present invention, attaining a temperature of at least 65°C for the sorptive media occurs inherently upon contact of the selected oxidant and the selected sorptive media, as they naturally exothermically react. As such, any external heating energy may not be required.

In another embodiment of the present invention, attaining a temperature of at least 65°C for the sorptive media requires the method to further comprise the step of heating the aqueous environment. As such, external energy is required. Such additional heating can be provided to the aqueous environment prior to step (c), prior to step (d), prior to both steps (c) and (d), with step (d), or after step (d), or combinations of same.

In another embodiment of the present invention, attaining a temperature of at least 65°C for the sorptive media occurs with a combination of the contact of the selected oxidant and the selected sorptive media, along with the step of heating the aqueous environment. Such additional heating can be provided to the aqueous environment prior to step (c), prior to step (d), prior to both steps (c) and (d), with step (d) ,or after step (d), or combinations of same,

In the present invention, calculation of the heat energy provided by the contact of the oxidant selected, the sorptive media selected, and the nature, concentration, etc. of the fluoro- organic compound(s) to be degraded, can determine, optionally by small scale site testing or laboratory testing, what amount of additional heating may be required to be provided to the aqueous environment to allow the temperature of the sorptive media to become at least 65°C.

Optionally, the method comprises the temperature of the sorptive media at any point or time during step (d) to be at least 65°C, and optionally in the range 65°C to 150°C. Optionally such temperature is in the range 70°C to 95°C, and including 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, and 95°C. Where the conditions for the method of the present invention are not standard conditions (i.e. not atmospheric pressure), the temperature may be adjusted accordingly. Optionally, step (d) starts at ambient temperature or a lower raised temperature, and as the reaction in step (d) initiates degradation of the fluoro-organic compounds, the temperature of the sorptive media rises to be at least 65°C, and possibly >65°C, >70°C, >75°C, >80°C, >85°C, >90°C, and >95°C.

Optionally, the temperature of the sorptive media is maintained at a raised, i.e. above ambient, temperature throughout the degradation of the fluoro-organic compound

Optionally, the raised temperature required to degrade the fluoro-organic compound is wholly or substantially self-sustaining once initiated, by contacting sufficient oxidant with the sorptive media over time

Optionally, the method maintains that an environmental temperature in step (d) that does not require evaporating water in the aqueous environment of step (d).

Optionally, the pH during step (d) can be pH7 or above, such as pH 0.0, pH > 10.5, pH >11.0, pH>12.0 or pH >13.0.

The pH values, measurements and ranges stated herein relate to the ‘apparent pH’, being the pH value determined by measurement with a pH-electrode employing a pH meter calibrated with an aqueous buffer solution of a known pH for measuring dilute aqueous solutions. Variations between apparent pH and ‘real pH’ are known to exist.

The oxidant may be provided in any suitable form able to be added to the aqueous environment. The oxidant may be provided partly or fully in solution, such as pre-dissolved in a suitable solvent. One suitable solvent is water. The oxidant may be admixed with a carrier material. The oxidant may be admixed with a suitable solvent or carrier material on site, and/or shortly or immediately before adding to the aqueous environment. Such oxidants such as hydrogen peroxide are provided in solution, ready for use.

Optionally, the oxidant concentration in a liquid carrier substance such as water, can be >0.4 M (Molar), or >0 5 M, or >0.8 M, or >1 M, or >1.5 M, or >2 M.

In one embodiment of the present invention, during step (d) of the method, the temperature of the sorptive media is in the range 70°C to 95°C, the pH is >11 , and the oxidant concentration is >0.8 M.

In another embodiment of the present invention, the method further comprisesactively raising or lowering the pH during step (d). The present invention provides a method of balancing the reaction conditions to best achieve degradation of the particular fluoro-organic compound(s) being targeted for degradation. The inventors have found that conditions favorable to degrading fluoro-organic compounds in the invention requires a combination of the specific temperature at the time and point of reaction in step (d) to be elevated compared to typical Standard State conditions (25°C), aqueous pH, and elevated oxidant concentration. These three parameters can be varied with one another to best achieve degradation of the fluoro-organic compound(s) Such variance can be through active intervention, or passively by allowing the reaction to achieve the desired change(s), such as a raised or increasing temperature as a result of an exothermic reaction occurring. With suitable pre-trials, the user can work out the best combination of sorptive media temperature, aqueous pH and oxidant concentration during step (d) to achieve the best or optimal degradation, possibly also taking account of the aqueous environment of concern.). This is demonstrated and discussed in more detail hereinafter.

Optionally, the molar ratio of oxidantsorptive media at the surface of the sorptive media is >0.25:1 , such as >0.35:1, >0.5:1 , >0.75:1, >1 :1 , >2:1, >4:1, >6:1 , >10:1 or higher, and including being in the range 0.25-2.5:1 or 0.5-5:1 or 1-10:1.

Optionally, the sorptive media is a carbon, optionally activated carbon.

Optionally, the sorptive media is mixed with or coated onto one or more of the group comprising: silica sand, sand, gravel, soil, zeolite, aluminum oxide, iron oxide, sediment or other matrix Optionally, the sorptive media mixed with or coated with one or more of the group stated hereinbefore is activated carbon.

Optionally, the sorptive media is a zero valent metal, mineral or reactive organic that is mixed with or coated onto one or more of the group comprising: silica sand, sand, gravel, soil, zeolite, aluminum oxide, iron oxide, sediment or other matrix.

Optionally, the fluoro-organic compound is one or more of the group comprising: a Per- and Polyfluoroalkyl substance (PFAS), a Perfluorosulfonic acid (PFSA), a Perfluoro oxide dimer, fluoropolymers, perfluoroalkanes, perfluoroalkenes, Perfluorocarboxylic acid (PFCA), and a chlorofluorocarbon.

Optionally, the fluoro-organic compound is a PFAS being one or more of the group comprising: perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutane sulfonic acid (PFBS), perfluorobutanoic acid (PFBA), and hexafluoropropylene oxide dimer acid (HFPO-DA). Optionally, the oxidant is one or more of the group comprising: a persulfate, a peroxide, and mono-persulfate.

Optionally, the oxidant is one or more of the group comprising: sodium persulfate, potassium persulfate, ammonium persulfate, sodium mono-persulfate, potassium mono-persulfate, magnesium peroxide, calcium peroxide and hydrogen peroxide.

Optionally, the sorptive media is activated carbon, the fluoro-organic compound is PFOS, and the oxidant is a persulfate.

Optionally, the sorptive media has a sorption capacity for each fluoro-organic compound or set of fluoro-organic compounds and sufficient sorptive media will be used to sorb the fluoro- organic compound mass.

Optionally, sufficient oxidant is used to react with the surface area of the sorptive media fixing the fluoro-organic compound.

Optionally, the degradation of fluoro-organic compounds results in the formation of fluoro- organic compounds with a shorter carbon chain length and/or lower molecular weight than the original fluoro-organic compound. Optionally, the degradation of the fluoro-organic compound results in the formation of volatile organofluorine (VOF) compounds. Optionally, these organofluorine degradation products include fluoroalkanes and fluoroalkenes including fluoromethane, fluoroethane, and fluoroethene. Optionally the fluorine degradation products include inorganic fluoride compounds such as sulfur hexafluoride, hydrogen fluoride, calcium fluoride, potassium fluoride, or sodium fluoride.

Optionally, the method further comprises adding an alkali to assist in one or more of: increase the reaction between the oxidant and the sorptive media, offset acid formed during the reaction, affect the temperature at which the fluoro-organic compound is thermally degraded, and affect the fluoro-organic compound degradation end products formed. In this way, the pH of step (d) can be maintained at a pH >10.0, pH > 10.5, pH >11.0, pH>12.0 or pH >13.0 as discussed above.

Optionally, the alkali is one or more of the group comprising: sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium tripolyphosphate, sodium phosphate, sodium silicate, potassium silicate, calcium carbonate, potassium carbonate, sodium carbonate Portland cement, blast furnace slag and calcium oxide. Optionally, at least two moles of alkali are added per mole of oxidant if the oxidant is a dipersulfate and one mole of alkali per mole of oxidant if the oxidant is a monopersulfate.

An added alkali can help to offset any acid formed from the decomposition of carbon materials. An added alkali can help to offset any alkali that is consumed by the formation of metallic oxy-hydroxides. pH values can be determined using monitoring of the relevant environment of step (d), and adding further alkali if required to maintain the pH; or, optionally, using tests to determine the alkali before the application and dosing sufficient alkali prior to or during step (d).

Any added alkali may also affect the temperature at which fluoro-organic compound degradation is initiated in the environment of concern. For example, the thermal decomposition of certain fluoro-organic compounds can start at a lower temperature in presence of an alkali, and thus be easier to initiate under alkali conditions.

Optionally, when alkali is added to the present invention, the degradation of the fluoro-organic compound results in the formation of fluoride or a fluoride containing compound, such as hydrogen fluoride, calcium fluoride, sodium fluoride, potassium fluoride, or a fluoro-gas such as sulphur hexafluoride, VOF, or fluorine gas.

Optionally, the alkali affects the degradation end product when treating PFAS compounds.

Optionally, the sorptive media comprises a carbon, and the fluoro-organic compound is allowed to partition onto the carbon before adding the oxidant. Where the sorptive media comprises carbon, the reaction of the oxidant and the sorptive media causes a combustion reaction with the carbon and fluoro-organic compound.

Optionally, the reaction of the oxidant and the sorptive media is an exothermic reaction that in and by itself is sufficient to cause the thermal degradation of the fluoro-organic compound. The exothermic energy released when combining the oxidant and sorptive media to react exceeds the rate at which such initial heat energy can dissipate into the environment, allowing the temperature of the fluoro-organic compound to further increase above an activation energy level or threshold, that then allows the degradation to continue.

If necessary or desired, additional heat energy is provided to the sorptive media to attain a temperature of at least 65°C as discussed hereinabove, so that the subsequent energy released by the reaction of the oxidant and the sorptive media causes the thermal degradation of the fluoro-organic compound in the same manner

Optionally, the oxidant is dissolved in water, either pre-mixed or on site, and the water of the oxidant-water mixture transports the oxidant to the sorptive media.

Optionally, the method of the present invention does not require the presence of a zero valent metal, such as ZVI, for treating certain fluoro-organic compounds such as PFAS.

Optionally, the fluoro-organic compound is PFOS, and the method of the present invention results in at least 50%, 60%, 70%, 80% or higher degradation of the PFOS mass or reduction in concentration.

Optionally, the oxidant concentration in a liquid carrier substance such as water, is so.4 M (Molar), or so.8 M, or S1 M, or S1.5 M, or S2.0 M.

Optionally the persulfate concentration, in particular the persulfate anion concentration, in a liquid carrier substance such as water, is >75 g/L, or >100 g/L, or >200 g/L, or >300 g/L, or >400 g/L or S500 g/L

Optionally the peroxide concentration in a liquid carrier substance such as water, is S10 g/L, or S20 g/L, or S50 g/L, or S100 g/L or >150 g/L, or >200 g/L. In one embodiment, the present invention comprises a method for the degradation of a fluoro-organic compound in an aqueous environment that includes soil, sand, clay, silt, aquifer water, sediment or other matrix.

According to another aspect of the present invention, there is provided a method of soil remediation comprising at least the steps of an in situ method of degradation of a fluoro- organic compound as defined herein.

Optionally, the method of soil remediation is to remediate a fluoro-organic compound being one or more of the group comprising: a Per- and Polyfluoroalkyl substance (PFAS), a Perfluorosulfonic acid (PFSA), a Perfluorocarboxylic acid (PFCA), fluorinated dimer acid, fluorinated polymer, fluorinated alkane, fluorinated alkene, and a chlorofluorocarbon.

Optionally, the method of soil remediation is to remediate a fluoro-organic compound being a PFAS being one or more of the group comprising: perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutane sulfonic acid (PFBS), perfluorobutanoic acid (PFBA), and hexafluoropropylene oxide dimer acid (HFPO-DA).

Optionally, the method of soil remediation of the present invention is an in situ method of degradation of a fluoro-organic compound as defined herein.

Optionally, the methods of the present invention described herein comprise the following steps, some in any order:

- adding activated carbon to soil containing one or more fluoro-organic compounds such as a PFAS in an in situ aqueous environment,;

- waiting for the fluoro-organic compound(s) to partition to the activated carbon and be sorbed thereonto so as to be fixed to the activated carbon;

- dissolving a persulfate in water, optionally to achieve a persulfate: activated carbon molar ratio of S2:1 ;

- optionally heating the aqueous environment;

- adding the persulfate mixture to the soil to contact the activated carbon with the persulfate, -testing and/or calculating the best balance of temperature of the sorptive media, pH and oxidant concentration, to degrade the fluoro-organic compound, as long as the temperature of the sorptive media is at least 65°C, and the oxidant concentration at the sorptive media is S0.4M; and

-optionally adding alkali to the environment.

Optionally, the present invention further includes the step of monitoring, detecting, analysing for, or otherwise identifying either the remainder of the fluoro-organic compounds being targeted for degradation, or one or more fluoro-degradation products such as fluoride, or a fluoro-gas emission, or both. This includes direct or indirect monitoring, detecting or analysing, using various methodologies known in the art

Detailed description of the invention

The present invention relates to an in situ method of degradation of a fluoro-organic compound in an aqueous environment. The method can comprise the step of adding a sorptive media to the aqueous environment, the sorptive media being one or more of the group comprising: carbon, reactive organic and zero valent metal. The method can comprise the step of allowing the fluoro-organic compound to fix onto the sorptive media over a time period of greater than 24 hours. The method can comprise the step of providing an oxidant being reactive to the sorptive media. The method can comprise the step of adding the oxidant to the aqueous environment to contact the sorptive media in situ at an oxidant concentration of >0.4M. The method initiates degradation of the fixed fluoro-organic compound on the sorptive media when the temperature of the sorptive media is at least 65°C, so that one or more fluoro-degradation products are formed.

The present invention provides a method of treating by in situ remediation environmental fluoro-organic compounds, also termed ‘contaminants of concern’, present in various environments, locations and situations, such as in soil, sediment, sorptive waste, air, gas, groundwater, process water, surface water, or wastewater,. In the present invention the contaminant is fixed onto a sorptive media, and the method comprises contacting the contaminant with an oxidant reactive with the sorptive media, such that the heat released from the reaction of the oxidant and sorptive media is sufficient to thermally degrade, or to exceed the activation energy required for contaminant auto-decomposition, or to otherwise degrade, the contaminant fixed to the sorptive media as it is in very close proximity.

The present invention also provides a method of soil remediation of fluoro-organic compounds comprising, consisting of or consisting essentially of, the steps of in situ method of degradation of a fluoro-organic compound in an aqueous environment described herein.

Conventional thermal treatments that only heat the entire environment to temperatures that initiate degradation of fluoro-organic compounds have been shown to be effective in some ex situ applications, but they are cost prohibitive, and face several further operational expenditure issues in trying to achieve the same thermal temperatures required for in situ applications

The present invention particularly relates to an in situ method of degrading recalcitrant environmental contaminants of concern contained in physical media, by reacting an oxidant with a sorptive media in quantities sufficient to raise the temperature and initiate degradation of the contaminants, while not requiring the evaporation of water in the environment concerned, such as the surrounding water. Therefore the method does not require the whole environmental temperature to be above 100°C, (the boiling point of water at standard conditions including at 1 atm), or does not require the environmental temperature to be above a slightly higher temperature such as 150°C, under non-standard conditions, for example due to a pressure existing or built up in some sub-surface conditions.

According to one embodiment of the present invention, there is provided an in situ method of degradation of a fluoro-organic compound in an aqueous environment comprising at least soil and groundwater, the method comprising at least the steps of: (a) adding a sorptive media to the aqueous environment, the sorptive media being one or more of the group comprising: carbon, reactive organic and zero valent metal;

(c) providing an oxidant being reactive to the sorptive media; and

(d) adding the oxidant to the aqueous environment to contact the sorptive media in situ at an oxidant concentration of S0.4M, and to initiate degradation of the fluoro-organic compound on the sorptive media when the temperature of the sorptive media is at least 65°C, so that one or more fluoro-degradation products are formed.

The present invention is based on the physical triangulation of the fluoro-organic compound, the reactive sorptive media and the oxidant, at the time the sorptive media and oxidant react. The localized reaction between oxidant and the sorptive media is sufficiently exothermic to release heat energy that creates a raised temperature at or above the decomposition temperature of the fluoro-organic compound fixed on the sorptive media. In this way, the heat energy released by the reaction between oxidant and the sorptive media creates a localized temperature spike, or “spark”, so that the entire environment further around the sorptive media does not require to all be at an elevated temperature to start and/or continue degradation of the fluoro-organic compound.

The initial heat increase and the fluoro-organic compound are in close enough proximity so that the thermal degradation of the fluoro-organic compound is at least started thereby. The fluoro-organic compound has been ‘fixed’ on the sorptive media. Thus, in the present invention, compounds that have high Koc (organic carbon sorption coefficients) are more easily treated.

In this way, the present invention can be carried out at the location of the aqueous environment of the fluoro-organic compound, without the need to relocate the fluoro-organic compound to another location in order to achieve its degradation Hence, the present invention provides a method of direct and in situ soil remediation, without requiring extensive machinery, transportation and cost, for relocating of tons or tonnes of contaminated soil to another place of treatment.

Certain fluoro-organic compounds require the temperature of the sorptive media, and thereby inherently the fluoro-organic compound fixed thereon, to be above a certain threshold, based on other process parameters. This temperature can be considered as the environmental or background temperature. The heightened sorptive media temperature affects bond energy, with increased temperatures making it easier to break those bonds. For example, treatment efficacy of PFOS sorbed onto activated carbon in the present invention begins as the sorptive media temperature increases above 65°C. But the present invention does not require the background temperature to be above the boiling point of water, which would otherwise dramatically increase the energy input required in the aqueous environment.

A higher temperature of the sorptive media also assists to provide a higher overall spark temperature to initiate the fluoro-organic compound degradation, and the longevity of the degradation, which can help offset the endothermic nature of breaking chemical bonds.

Raising or elevating the background or environmental temperature when required, (i.e the temperature of the sorptive media, and thereby the temperature of the nearby and fixed fluoro-organic compound), can be achieved by many means and methods, such as applying heat via thermal conduction, electric resistive heating, application of steam, using wires, pipes or a piping system, injection of hot water, etc., to the aqueous environment, using one or more methods known in the art.

The contact of the oxidant and the sorptive media can also partly or fully raise the temperature of the sorptive media and the fixed fluoro-organic compound to initiate degradation thereof on the sorptive media. In this way, the reaction can become self- sustaining, so that thereafter, the temperature required to continue the degradation of the fluoro-organic compound can be maintained as long as the rate at which the heat of reaction being released is greater than the rate the heat dissipates into the environment. This can depend on many factors, in particular but not limited to the supply of oxidant, and the presence of unreacted sorptive media.

Step (b) involves fixing the fluoro-organic compound onto the sorptive media. The fluoro- organic compound(s) can be in various other media such as in water, groundwater, surface water, wastewater, air, a gas, or partitioned on soil, silt, clay, sediment, rock, or natural organic matter and the like In step (b) the sorptive media is added to the environment containing the fluoro-organic compound, and sufficient time is allowed for the fluoro-organic compound to partition onto the sorptive media. The duration of time needed will vary depending on the situation For fluids, such as water, and gases, the sufficient time can be hours. For soils and sediments, a sufficient time can be days to weeks If used as a permeable reactive barrier, the sorptive media may be allowed to intercept contaminated water or groundwater for months to years during step ( b).

The exact duration of step (b) will be determined based on the intended location and application and compounds, and could be completed when a breakthrough or saturation of the sorptive media has occurred, or at or after a pre-determined time. Typically, the sorptive media is a solid media such as carbon and activated carbon. Some compounds have the ability to partition onto other surfaces such as metals and minerals. The sorptive media may also be a media able to dissolve or other dissipate or disassemble over time in the environment of concern.

The term “fluoro-organic compound” as used herein includes being one or more fluoro- organic compounds, i.e. mixtures of fluoro-organic compounds.

The term “fixed” as used herein relates to any form of conjugation between the fluoro-organic compound and sorptive media, including sorption, absorption, adsorption, complexing, coordination, electrostatic and hydrophobic interactions, and the like, wherein the fluoro- organic compound is no longer free and randomly distributed in the aqueous environment but concentrated on or around the sorptive media.

The term “in situ” as used herein relates to the fluoro-organic compound being degraded in the aqueous environment, and adding the sorptive media and oxidant- to the location of the fluoro-organic compound. That is, there is no re-location of the fluoro-organic compound required to another place to achieve the degradation thereof. It is possible for the fluoro- organic compound to be in motion in the aqueous environment prior to being fixed onto the sorptive media. For example, the fluoro-organic compound could be part of a fluid flow, such as water flow such as groundwater, process water, purge water or wastewater, through an environment, prior to fixation to the sorptive media. Indeed, the present invention extends to using the sorptive media as a sorption wall or barrier deliberately placed in the path of a fluid flow containing fluoro-organic compounds.

The term “groundwater” as used herein includes any fluid flow through ground. The ground may be soil, sand, gravel, silt, clay, earth or sediments, or man-made materials, or combinations of same. The term “groundwater” generally relates to the mobile fraction of the ground, including mobile part of any unsaturated zone, vadose zone, capillary zone, etc.

The present invention requires the favorable partitioning of the fluoro-organic compound from its environment onto the fixed media. Partition rates of fluoro-organic compounds and key contaminants onto various fixed media are known in the art, (for example see Kabiri, Shervin et al; (2023) Science of the Total Environment 875, “Physical and chemical properties of carbon-based sorbents that affect the removal of per- and polyfluoroalkyl substances from solution and soil"), and are not further discussed herein. This includes equilibrium partitioning of hydrophobic compounds onto media such as carbon, such as biochar, activated carbon, et al, especially in aqueous situations or locations such as soil, wastewater, process waters etc. Optionally, the present invention further includes the step of monitoring, detecting, analysing for, or otherwise identifying, either the remainder of the fluoro-organic compounds being targeted for degradation, or one or more fluoro-degradation products such as fluoride, fluoroalkane, fluoroalkene, or a fluoro-gas emission, or combination thereof. This includes direct or indirect monitoring, detecting or analysing, using various methodologies known in the art such as mass-balance of the fluoro-organic compounds being targeted, over time.

The formation of one or more fluoro-degradation products can be confirmed, detected, measured or otherwise identified, either directly or indirectly. For example, the concentration or amount of the fluoro-organic compounds being targeted for destruction could be analysed, and a conclusion of the progress of the method of degradation therefrom drawn.

The detection of degradation products such as fluoride or a fluoro-gas can be detected by any suitable detector or analyser known in the art: many are commercially available

For example, a sample of aqueous environment can be taken for analysis, for example in a laboratory, using fluoro-compound detection or marking techniques known in the art. The detection of such products confirms the degradation of the fluoro-organic compound by the method of the invention.

Fluoro-degradation products include the formation of fluoro-organic compounds with a shorter carbon chain length than the original fluoro-organic compound. Thermal degradation of fluoro-organic compounds will typically include the formation of volatile organofluorine (VOF) compounds including fluoromethane, fluoroethane, and fluoroethene or inorganic fluoride compounds such as sulfur hexafluoride, hydrogen fluoride, calcium fluoride, potassium fluoride, or sodium fluoride

Several mechanisms have been reported (Wang 2022) for thermolytic destruction of PFAS including cleavage of intramolecular bond through transition states, direct homolytic cleavage, radical reactions, hydrolysis, and oxidation.

Optionally, the aqueous environment during step (d) could be made an alkaline pH during the reaction of the oxidant and sorptive media and subsequent thermalytic degradation of the fluoro-organic compounds. A higher pH can be designed for and used to offset acid formed during the reactions, has been observed to decrease the decomposition temperature of fluoro-organic compounds and preferentially results in the formation of hydrogen fluoride, sodium fluoride, potassium fluoride, calcium fluoride and other fluoride compounds during thermalytic decomposition. Alkaline pH values include pHSIO.O, pH>10.5 pH>11 .0, pH>12.0, and pH>13.0 with increasing alkali content and pH benefiting the described reactions.

Sorptive media allows for fluoro-organic compounds to exist in sufficiently close proximity so as to have the temperature of the fluoro-compound increased to the point it is degraded at the time the sorptive media and oxidant react with one another.

Optionally, the interactions between the fluoro-organic compounds and the sorptive media that result in the conjunction of the sorptive media and fluoro-organic compound could include adsoption, absorption, hydrophobic interactions, micelle formation, hemi-micelle formation, electrostatic interactions, Van der Waals forces, magnetic attraction, polar forces, complexation or coordination between the compounds.

As such, the term “sorptive media” as used herein includes any suitable media able to form a fixed conjugation between the fluoro-organic compound and sorptive media.

Sorptive media carbon can be one or more of the group comprising: natural carbon, peat, coal, charcoal, biochar and activated carbon.

Activated carbon includes granular, powder, micron and nano-scale activated carbons. Activated carbon (AC) is a commercially available product available in several forms. A variety of natural carbon sources such as coal, coconut husk, wood, and paper or wood waste can be converted to a charcoal carbon material. The charcoal carbon material is then typically activated as the result of processes that increase the surface area of the carbon available for sorption processes and chemical reactions. Organic compounds, including fluoro-organic compounds, have an affinity to partition onto carbon. The equilibrium of a compound between water and carbon is known as the organic carbon partitioning coefficient (Koc). Published values for fluoro-organic compounds are known, for example at pfas- 1 itrcweb.org/fact-sheets/.

Activated carbon is commercially available in several sizes, including nano-scale, powder activated carbon (PAG), and granular activated carbon (GAC). Larger sizes of carbon can be mechanically altered to form finer particle sizes. Activated carbon can be agglomerated into a variety of shapes using a binder material, impregnated with other materials such as zero valent metals, or have its surface chemistry altered, such as being treated with amine groups to enhanced sorption of fluoro-organic compounds. Sorptive media zero valent metal can be one or more of the group comprising: iron, zinc, silver, magnesium, nickel, aluminum and copper.

Sorptive media reactive mineral can be one or more of manganese dioxide, titanium dioxide, iron oxide and iron sulfide. Reactive minerals include reduced minerals, as well as iron oxide minerals including magnetite

The sorptive media can be added to or combined with materials such as sand, gravel, silica sand, aluminum oxides, iron oxides, soils, sediments, sludges, or other materials.

Step (b) of the present invention involves the fluoro-organic compound partitioning onto the sorptive media or otherwise closely associating itself enough with the sorptive media to be thermally degraded in step (d). Sorptive media can have different capacities for each fluoro- organic compound or comingled fluoro-organic compounds, which can also be influenced by other compounds often found in groundwater, natural, process or other water environments, the dissociation energy required to remove the fluoro-organic compound from its existing environment, such as already being fixed onto soil, etc., particles. The sorption capacity of the sorptive media to be used may be tested with the specific fluoro-organic compound, and/or specific soils and/or water, for the specific application of the present invention to determine the sorption capacity of the fluoro-organic compound with the sorptive media.

Using this value with appropriate safety factors, the mass of sorptive media needed to sorb a given mass of fluoro-organic compound can be determined. Safety factors include over compensating the mass of sorptive media to account for uneven distribution of the fluoro- organic compound, preferential water flow, unideal distribution of the sorptive media, or other factors specific to the application.

In step (d) of the present invention, the oxidant is dosed into the aqueous environment based on the amount of the sorptive media that the oxidant is expected to contact. It is the reaction that ensues from the contact between the oxidant and sorptive media that results in the energy released that further raises the temperature of the fluoro-organic compound to the point that it is thermally degraded. As the oxidant is expected to react with the portions of the sorptive media it contacts, the oxidant mass is based upon the mass of sorptive media to be contacted which will be directly proportional to the surface area of the sorptive media exposed and available to react with the oxidant. The amount of oxidant may need to accommodate for reaction with any compounds other than the sorptive media in the aqueous environment. The degradation reaction in step (d) of the present invention between the sorptive media and oxidant can be aided by a balance of increased oxidant concentration, pH, including optionally an alkali pH (pH >10.0, pH >10.5, pH >11.0, pH >12.0, or pH>13.0), and increased environmental temperature of the combination of the elements of the present invention as a system (sorptive media, oxidant and fluoro-organic compound). These parameters can be tested, calculated and optimized, to result in a sufficiently exothermic reaction between oxidant and sorptive media to result in thermal degradation of the particular fluoro-organic compound of concern, alongside the nature of the sorptive media and oxidant.

For example, using a carbon as the sorptive media provides a combustion-like process with a persulfate, with the carbon being exothermically oxidized to carbon dioxide in a reaction with the oxidant. The optimal initial environmental or system temperature is between 65°C and 150°C depending on other system conditions such as pressure and more specifically between 70°C and 90°C for the destruction of fluoro-organic compounds. The exothermic reaction between the oxidant and sorptive material can initiate at a lower temperature and be used to raise the temperature into the range that is best suited for destruction of fluoro- organic compounds.

The initial or background temperature of the sorptive media at step (d) can have several effects, including: increasing the kinetics of the reaction between the sorptive media and oxidant, loosening the bonds of the fluoro-organic compound to be degraded, and increasing both the ultimate spark temperature and longevity of the spark in the environment; resulting in more effective treatment of the fluoro-organic compound. As an example, minor amounts of degradation end products of some PFAS compounds were observed at 65°C, so that a lower environmental temperature can initially be considered depending on other factors, whereas significant treatment of other PFAS compounds such as PFOS was observed when the environmental temperature was increased closer to 100°C, such as at 90°C.

Meanwhile, the method of the present invention against some fluoro-organic compounds was more vigorous in increasingly alkali conditions compared to environments that were more acidic.

In particular, the present invention allows a user to consider a combination of initial environmental temperature, the pH, and the concentration of the oxidant, to suit the in situ degradation environment, and the conditions of the fluoro-organic compound being targeted by the method. The user can conduct preliminary experimentation or in situ trials of process options before commercial operation. The present invention allows the user to select the most suitable process conditions to suit the particular fluoro-organic compound being targeted.

The nature of the “degradation” of fluoro-organic compounds as used herein includes any transformation, decomposition, treatment, or otherwise change in the chemical structure of the fluoro-organic compound.

Optionally, the sorptive media is provided in the method with, or supported by, a support substance or material. For example, a sorptive media of activated carbon can be mixed with silica sand. A support substance or material can assist locating the sorptive media in a suitable location able to allow fixing of the fluoro-organic compound therewith vis-a-vis the environment of the method of the present invention. For example, any water flow around the fluoro-organic compound may affect the placement or location of the sorptive media, so that a supporting substance or material assists resistance of movement of the sorptive media with any water flow therearound.

The fluoro-organic compounds treatable by the present invention particularly include Perfluoroalkyl and Polyfluoroalkyl substances (PFAS). PFAS compounds include perfluoroalkyl carboxylic acids (PFCAs) such as perfluorononanoic acid (PFNA), perfluorooctanoic acid (PFOA), and perfluorobutanoic acid (PFBA), perfluoroalkane sulfonic acids (PFSAs) such as perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS) and perfluorobutane sulfonic acid (PFBS), fluoropolymers, fluoroalkanes, fluoroalkenes, and hexafluoropropylene oxide (HFPO) dimer acids and their ammonium salts, such as compounds known by the tradename “GenX.”

Terms and acronyms as used herein include:

“PFAS”: Per and PolyFluorinated Alkyl Substances.

“PFSA”: Perfluorinated sulfonic acids.

“PFOS”: perfluorooctane sulfonic acid.

As such, PFAS is the broad definition, PFSA is a subgroup in that definition, and PFOS is a specific compound.

“PFOA”: Perfluorinated carboxylic acids.

“PFOA”: perfluorooctanoic carboxylic acid.

As such, PFAS is a broad definition. PFOA is a subgroup in that definition, and PFOA is a specific compound. Optionally, the fluoro-organic compound treatable by the present invention is a Perfluoroalkyl substance or a Polyfluoroalkyl substance (PFAS).

The present invention is particularly suitable for treating PFAS. Other proposals for treating PFAS have focused on non-destructive phase change mechanisms, such as sorption, filtration or ion exchange. Ex-situ destructive mechanisms also exist, but are still highly energetic. PFSA compounds, including PFOS, are not known to significantly react with radicals, such as hydroxyl or sulfate radicals or the superoxide radical anion prevalent in other remedial technologies at temperatures near 25°C, whereas the present invention achieves complete transformation of PFSA compounds to gaseous terminal end products, such as volatile organic fluorides (VOFs), fluoride, and or sulfur hexafluoride.

As such the present invention provides a method where thermal decomposition of PFAS compounds and other contaminants can occur in an aqueous environment such as in water, allowing for treatment of subsurface contamination found in soils, groundwater, fractured bedrock as well as other matrixes with high water content using a combustion like process with dissolved oxidants reacting with the sorptive media.

Optionally, the oxidant is one or more of the group comprising: a persulfate, a peroxide and a mono-persulfate.

Optionally, the sorptive media is activated carbon, the fluoro-organic compound is PFSA or PFOS, and the oxidant is a peroxide.

Optionally, the oxidant:sorptive media surface area molar ratio is >0.25:1, >0 35:1 , >0.5:1 , >0.75:1 , >1 :1, >2:1, >4:1 , >6:1, >10:1 or higher, such as being in the range 0.25-2.5:1 or 0 5- 5:1 or 1-10:1.

Optionally, the oxidantsorptive media surface area molar ratio is in the range 0.25-2.5:1 or 0 4-4:1 or 2.5-25:1. Optionally, the w/w sodium persulfate: activated carbon ratio is S5:1 , S8: 1 , ^10: 1 , S2O:1 or higher.

Optionally, the w/w hydrogen peroxide: activated carbon ratio is >0.7: 1 , >1:1, >1 5:1 , >3:1 or higher.

In the present invention, the oxidant is intended to dominate the amount of sorptive media, so that there is sufficient degradation of the fluoro-organic compound that results in one or more end products being formed. These can include various fluorides including volatile organic fluorides (VOFs), fluoroalkanes and fluoroalkenes such as fluoromethane, fluoroethane, and fluoroethene as well as inorganic fluorinated compounds such as sulfur hexafluoride, fluoride, hydrogen fluoride, calcium fluoride, sodium fluoride, potassium fluoride and/or other fluorinated fluoro-organic compounds. Many of these degradation products evolve as gases, but others could be precipitates or dissolved in the aqueous phase.

The present invention particularly assists in reducing or mitigating the spread of hydrophobic environmental fluoro-organic compound contaminants of concern, by having those contaminants contact a sorptive media, such as activated carbon or biochar, resulting in an equilibrium partitioning where the hydrophobic fluoro-organic compound favorably partitions onto the sorptive media. Such a method can reduce the hydrophobic contaminant concentrations in ground, potable, drinking, process, and waste waters, resulting in an accumulation of those contaminants on the sorptive media.

The present invention also assists in treating fluoro-organic compounds on sorptive media already known to sorp or fix such fluoro-organic compounds, but not further treated. Some environments have used sorptive media to simply ‘soak up’ fluoro-organic compounds from the environment, prior to relocation of the now ‘contaminated’ sorptive media.

It is a feature of the present invention that the method does not require the fluoro-organic compound to be in an aqueous phase to be treated, as is required by conventional methods such as bioremediation, in situ chemical reduction, and in situ chemical oxidation. Instead, the present invention is able to treat the fluoro-organic compounds in close proximity to the reaction between the sorptive media and oxidant. As the fluoro-organic compounds have partitioned onto or in close proximity to the surface of the sorptive media, when the reaction between the sorptive media and oxidant occurs, the fluoro-organic compound is destroyed by the heat generated during the reaction, possibly in combination with the radicals generated by the decomposition of the oxidant. In particular, the close proximity of the fluoro-organic compound to the point of reaction allows for thermal destruction of the fluoro-organic compound in any aqueous environment, including being submerged in water, negating the need for conventional thermal decomposition methods to first volatilize the water.

When using a persulfate (either mono- or dipersulfate) as the oxidant, acid is generated and can result in very acidic conditions. The overall rate of treatment, and this acid generation, can be offset with the addition of one or more alkali to the method of the invention. Alkalis include one or more of the group comprising: sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium tripolyphosphate, sodium phosphate, sodium silicate, potassium silicate, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, Portland cement, blast furnace slag, calcium oxide or a combination thereof.

In order to offset any acid evolution from the persulfate as discussed above, the alkali can be provided at 2 moles of hydroxide per mole of persulfate applied to the method.

Any added alkali can also affect the rate of reaction between the oxidant and sorptive media In most persulfate reactions, a combination of the kinetics and heat released by the reaction increases as the environment exceeds pH=10 and increases with increasing pH. If faster or rapid kinetics of reaction and oxidation are desired, sufficient alkali could be added to adjust the pH accordingly. Added alkali also results in the preferential formulation of fluoride end products including fluoride, calcium fluoride, sodium fluoride, hydrogen fluoride, or potassium fluoride. For example, in some cases, to maintain the pH for the duration of the reactions treating fluoro-organic compounds to be in the range 10 to 14, optionally a pH >13.0, pH>12.0, pH>11.0, pH>10.5, and pH>10.0.

In situ contacting of the sorptive media with an oxidant reactive to the sorptive media in step (a) may require one or more different methodologies. Optionally, the oxidant is provided to the sorptive media via or with or supported by a carrier material. The carrier material may be a fluid such as a gas, or a liquid such as water, able to pass through or across one or more other substances, such a topsoil layer, prior to engagement with sorptive media having affixed thereto a fluoro-organic compound.

Suitable methods for contacting the the sorptive media with an oxidant in the subsurface include going into the environmental subsurface, and include soil mixing, liquid injection, recirculation, and slurry emplacement. Soil mixing can include rotating drum mixers, buckets, augers, jet grouting and other mechanical mixers. Liquid injection can be through fixed wells with screens, open wells, screens or other orifices in tooling or by other devices that allow sorptive media or oxidant in a liquid or slurry to be injected into a targeted interval of the subsurface. Slurry amendments can be applied under pressure via tooling with larger open orifices to allow for the flow of the particle size of the sorptive media. If the particle size of the sorptive media is small enough then the oxidant may behave similarly enough to a liquid to use those methods.

Step (d) of the method of the present invention involves contacting the sorptive media with an oxidant reactive to the sorptive media. The contacting may be carried out by the same or similar methods as described herein in relation to step (a), including but not limited to injection or pouring the oxidant into or onto the surface of the environment comprising the sorptive media after step (b), optionally with active mixing if required. Soil mixing in step (d) can be carried out using any suitable method and/r machinery.

The present invention comprises attaining a temperature of the sorptive media during step (d) at or above 65°C, or at or above 70°C, or at or above 75°C, or at or above 80°C, or at or above 85°C, or at or above 90C, compared to a temperature nearby, such as ambient temperature or a local soil temperature.

Optionally, the temperature of the sorptive media can be raised with the addition of direct heat, electric resistive heating, steam, and/or by a chemical reaction if the rate of that energy is released by the chemical reaction is greater than the rate at which the energy is dissipated into the environment resulting in targeted temperature of the sorptive media at time of reaction degrading fluoro-organic compounds

The energy required to initiated degradation of the fluoro-organic compounds can be calculated from known degradation data of the fluoro-organic compound, or simple laboratory testing of the fluoro-organic compound. The user is aware of the fluoro-organic compound to be degraded, and can therefore calculate suitable oxidant and sorptive media combination(s) that achieve the initial temperature rise required for such fluoro-organic compound.

Optionally, the method further comprises adding an alkali to increase the reaction between the oxidant and sorptive media resulting in the degradation of the fluoro-organic compound. As the alkali needs to be present during step (d), the alkali may be added in combination with the sorptive media, or in combination with the oxidant, or both.

Optionally, the alkali is one or more of the group comprising: sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium tripolyphosphate, sodium phosphate, sodium silicate, potassium silicate, calcium carbonate, magnesium carbonate, sodium carbonate, potassium carbonate, Portland cement, blast furnace slag and calcium oxide. Typically such alkali is added in solid form, as a solid slurry, or dissolved in water.

The skilled person can see that step (b) of the method can be based on the environment of the fluoro-organic compound to be treated. In some embodiments, the fluoro-organic compounds are already static in an environment. In some embodiments, the fluoro-organic compounds are flowing through an environment. In some embodiments, the fluoro-organic compounds are removable from an environment. In some embodiments, the fluoro-organic compounds are housed in an environment. In some embodiments, the fluoro-organic compounds are bermed in an environment.

Application of the present invention could take place in any variety of tanks, vessels, bermed areas, or volume capable of holding the material to be treated and the sorptive media. The present invention could also be used to treat vapor phase contaminants. For example, the sorptive media could be held loosely in a container that allows for the flow of contaminated gases or the sorptive media could be adhered together.

Optionally, the present invention is carried out in an environment having the fluoro-organic compound flowing in water or groundwater through soils/rock/sediments, such that step (b) is sorbing aqueous phase contaminant onto a sorptive media, such as in a permeable reactive barrier, for subsequent treatment by step (d).

The present invention is implemented where step (b) is carried out in situ soil, and the sorptive media is mixed into the soil and allowed to contact with the soil for sufficient time for the fluoro-organic compounds to partition onto the sorptive media for subsequent treatment by step (d). Optionally where the soil is in the saturated zone. Optionally where the soil is in the vadose zone. Optionally where the soil is in the capillary fringe.

Optionally, step (b) is carried out in a tank or vessel, where the fluoro-organic compounds are fixed onto the sorptive media in that tank or vessel. Optionally where the tank or vessel contain water for subsequent treatment by step (d). Optionally where the tank or vessel contain a gas.

Optionally where step (b) and step (d) are conducted in the same space.

The following working scenarios and Examples both illustrate and exemplify the present invention, and also show how the present invention allows a user to consider a combination of initial or background environmental temperature, the pH, and the concentration of the oxidant, to suit the degradation environment and conditions of the fluoro-organic compound being targeted by the method. The user can conduct the same or similar preliminary trials of process options. For example, as is confirmed in the data below, the degradation of PFAS requires a higher initial temperature of the sorptive media.

Scenario 1:

Powder activated carbon (PAG) is emplaced into a soil matrix as a component with a permeable silica sand. PFSA compounds, including PFOS, PFHxS, and PFBS, in the soil matrix partition into the activated carbon material through transport mechanisms such as advection and diffusion of the groundwater.

After a suitable period of time, a concentrated sodium persulfate solution is applied to the sand that contains the activated carbon.

A persulfate is dissolved into water at a concentration of 100g/L to 500 g/L and injected into the sand containing the activated carbon containing the PFSA compounds. If deemed necessary by testing, the alkalinity can be added based on 2 moles of sodium hydroxide per mole of sodium persulfate and assuming 25% of the activated carbon is oxidized to form carbon dioxide that becomes carbonic acid, to be confirmed in a laboratory study. The reaction is allowed to proceed and increases to an elevated temperature. More efficient treatment occurs when the environmental temperature has reached approximately 80°C using for example electrical resistive heating, application of steam, or hot water. The temperature can be measured using any suitable temperature-measuring device, such as a thermocouple, thermometer, et al, in a manner known in the art.

Assistance to aid the sorptive media reaching a desired in situ location can be provided by various methods, including using direct push technology (DPT) or similar equipment to create a fracture in the material having the fluoro-organic compound contaminants, such as subsurface soils. As a fracture is forming, the fracture can be (continuously) filled with sand containing activated carbon. The media can be approximately 0.5 to 20% activated carbon with the remainder a permeable sand.

Some embodiments may also include adding a viscosifier to aid in the injection of the sorptive media, optionally in the form of a slurry. Multiple fractures can be created in the location of the PFSA contamination using suitable equipment. The center and each end of the fracture can be fitted with a well specifically screened to target the individual fracture. PFAS is allowed to migrate to the carbon in the subsurface over a period of time, until the PFAS is breaking through or nearing the point of saturation. The same injection points or wells installed for targeting each fracture can now be used to recirculate the persulfate solution, which can contain approximately 10x the mass of sodium persulfate to the mass of activated carbon in the fracture. The concentration of sodium persulfate and rate of recirculation is controlled to maintain an environmental temperature around the sorptive media of approximately 65°C in the fracture, with care to not exceed 90°C. To achieve this, hot water can be recirculated through the fractures to preheat the sand fractures to an appropriate temperature that allow the exothermic reaction between the oxidant and sorptive media, to help achieve and maintain 65°C.

Water can be flushed into the environment to help remove any residual, unused or remaining sodium persulfate solution, (which, being acidic, can be neutralized with an alkali above ground). Other embodiments could include adding the alkali with the sodium persulfate during the recirculation.

Detection of a fluorine degradation product such as fluorine or a fluoro-gas can be detected by any suitable detector known in the art: many are commercially available.

Alternatively or additionally, a sample of the degradation environment can be taken for other or more detailed analysis, for example in a laboratory, again using fluoro-detection techniques known in the art to look for either the level of PFAS being targeted or a fluorodegradation compound, or both.

Scenario 2:

As a result of a very high partitioning coefficient between organic carbon commonly found on soils and water, PFAS compounds including GenX, PFOA, and PFOS, tend to partition onto soils very tightly resulting in source areas with elevated contaminant concentrations that primarily reside on site soils.

In this arrangement, activated carbon is mixed into the subsurface using soil mixing technology. The soils have water added, to at least achieve 70 percent of the water holding capacity, or specific yield, of the soils in the unsaturated zone.

After sufficient time for the PFAS compounds to partition onto the activated carbon, the environment is either flooded with a hydrogen peroxide solution, or an alkaline persulfate slurry is applied via soil mixing, or a blend thereof. A blend of hydrogen peroxide, sodium persulfate and potassium persulfate may achieve a more desired rate of reaction to control the evolution of heat during soil mixing.

If the expected exothermic energy released from the persulfate-activated carbon reaction is not sufficient to achieve 65 °C, then steam can be used to preheat the subsurface, or applied with the persulfate to achieve a reasonable temperature that would allow the exothermic reaction to achieve 65 °C but not exceed 90 °C. The persulfate can be applied in the prescribed range to oxidize the activated carbon as well as account for non-target demand associated with the soil.

Scenario 3:

A sediment is contaminated with a mixture of contaminants including pesticides, chlorobenzenes, and PFAS compounds. The sediment slurry is continuously mixed and is brought up to an environmental temperature of 75 °C. The methods used to increase the temperature of the environment could include conventional heating elements, steam, hot water or sufficient reagents so that the exothermic reaction is sufficient to achieve the desired temperature.

The reagents include an oxidant such as sodium persulfate and a zero valent metal such as zero valent iron.

After the desired initial environment temperature is achieved, the reactive reagents are added to the environment in sufficient quantities so that the oxidant is at least 10 times the mass of contaminant or at least 10 times the mass of zero valent iron, whichever quantity is more. The temperature of the environment may increase but maintained to a temperature lower than the boiling temperature of water. Such steps could include adding cool water, ice, or a temperature control environment that involves temperature control pipe environments usually with cool water based solutions pumped through the pipes. The environment is then allowed to react until all the persulfate is consumed or that the contaminant treatment objectives are achieved.

Scenario 4:

Gases contaminant with PFAS compounds flowthrough activated carbon combined with calcium peroxide. After the PFAS compounds achieve either breakthrough, saturation, or otherwise the site goal is achieved. The solution is sufficiently moistened to approximately 60% of the water holding capacity of the carbon, and heated to 70°C. The reaction from calcium peroxide with the activated carbon then results in the destruction of the sorbed PFAS compounds. The temperature of the environment would be allowed to increase but steps are recommended to maintain the temperature lower than the boiling temperature of water The sorptive media is then allowed to react until all the peroxide is consumed or that the contaminant treatment objectives are achieved.

Example 1 : PFAS Treatment

PFOA and PFOS were dissolved in an aqueous environment to approximately 23,000 and 12,000 ng/L, respectively.

Four different sorptive media were used. Activated carbon (AC, 60 g/L), zero valent iron (ZVI; 30 g/L), pyrite (60 g/L), and elemental copper (30 g/L), were added to the aqueous environment, which was then brought up to 70°C (prior to contact with the oxidant, the temperature was subsequently allowed to increase to approximately 100°C as a result of the reaction after adding the oxidant).

Sodium persulfate was added to each environment to an approximate concentration of 500 g/L. The persulfate and the reactants were allowed to contact each other for approximately 24 hours. After this time, the aqueous phase from each environment and the activated carbon was collected and sent out for analysis.

The results in Table 1 show significant reduction of PFOA and PFOS in each environment

For example, the environment with sodium persulfate and activated carbon showed a 99.1% reduction of PFOA and 83.7% reduction of PFOS.

Table 1

In a similar test shown in Table 2 below, additional sorptive media were tested in an environment with a higher level of PFOS. These additional sorptive media included zero valent aluminum (ZV-AI), zero valent zinc (ZVZ), and biochar, a form of carbon. These tests had an initial temperature of 50 °C and were held in a water bath to control the temperature. The environment started at near neutral pH, but the pH was allowed to decrease as the reaction proceeded The amount of persulfate was 200 g/L, and the persulfate mass was 20 times greater than biochar and 8.3 times greater than the mass of metals

Table 2

The results in Table 2 show significant reduction of PFOS in each system.

Example 2: PFOS Treatment

The complete destruction of PFOS into all phases was evaluated by spiking PFOS onto activated carbon. The test environment was treated with sodium persulfate. The environment started at 50°C, and stayed within 50°C and 90° C for the duration of the test. Gases were captured in a water trap for the duration of the experiment. After 24 hours of contact time, samples from the water trap, liquid, and solid phases from the reactor, and the organic solvent used to rinse of the container to assess the potential for PFOS remaining in the reactor were all collected and sent to the lab for analysis Table 3 shows the reduction in PFOS mass summing the mass found into various phases, i.e. water phase, solid phase, and a solvent rinse of the reactor, after treatment by the present invention and comparing it to baseline mass found in the system. Assessing the various phases identified that the majority of residual PFOS after treatment still resided in partitioned onto the activated carbon, but that there was a significant reduction in PFOS mass which is attributed to destruction of PFOS.

Table 3

Example 3: Fluorinated Product detection

End products from the treatment of PFAS compounds were identified and were consistent with those found from direct thermal treatment of PFAS described in the art by Watanabe, Nobuhisa; et al; J Mater Cycles Waste Manag (2016) 18:625-630 “Residual organic fluorinated compounds from thermal treatment of PFOA, PFHxA, and PFOS adsorbed onto granular activated carbon (GAC)". The degradation products identified by Watanabe 2018 included organo-fluorinated gases and other fluorinated gases. End products of this treatment at neutral to acidic pH values include volatile organic fluorides (VOF) compounds, sulfur hexafluoride (SF6) and other fluorinated gases. Their presence was detected from test conditions using a spectrophotometer with the adsorption of certain wavelengths of infrared light.

The initial environment temperature and concentration of sodium persulfate were varied as shown in Table 4 below. The environment included PFAS sorbed onto activated carbon, which was held at the specified environment temperature in T able 4, and had 20: 1 weight ratio of persulfate to activated carbon. The detector registered as a detection less than 1% of the PFAS converted to sulfur hexafluoride or other fluorinated gas or gases. The detector was a qualitative detector that had a detection limit of 5 ppm of sulfur hexafluoride. The detections in Table 4 are in terms of the general response of the detector, non-detected (ND), Low, Moderate, and High as well as whether or not the fluorinated gases were first detected 1 hr or 24 hrs after the reaction was initiated. Table 4

The fluorinated gas response and kinetic increased with the water bath temperature and oxidant concentration with a high response detected after 1 hour of reaction time for system with 200 g/L or greater persulfate concentrations and held at water bath temperatures of 50°C or greater.

Additional fluorinated gas data evaluating different sorptive media and oxidant was collected and is presented in Table 5. These tests were performed with 200 g/L of oxidant and the reactors were held in a water bath at 50°C.

Table 5

The data in Table 5 indicates that fluorinated carbon gases are the end product of PFOS degradation under alkali to acidic conditions. The data in Table 5 further demonstrates the decomposition of PFOS by hydrogen peroxide, monopersulfates, biochar, and zero valent metals including iron, zinc, silver, magnesium, nickel, and aluminium.

Example 4: Fluoride Data

As identified by Hao, Shilai; Choi, Youn-Jeong; Wu, Boran; Higgins, Christopher; Deeb, Rula; and Strathmann; Environ. Sci Technol. 2021 , 55, 3283-3295 “Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam”, under alkali conditions, the end product of thermal decomposition of PFAS compounds was fluoride, which was previously not detected in PFAS samples treated with a persulfate at an acidic pH.

To further confirm this, PFOS was spiked onto activated carbon in another treatment, and then added to sand to create a sorptive media-silica sand matrix. The matrix was added to water to create a reactive environment, with the temperature maintained at the temperature specified in Table 6 below. The solution was varied up to 200 g/L sodium persulfate. Aqueous fluoride compounds (‘Fluoride’) and pH were measured in the aqueous solution after 24 hours of reaction time.

Table 6

The evolution of fluoride at pH 14 and volatile fluorinated gases at lower pH values are consistent with Wang et al 2022, Hao et al 2021 and Watanabe et al 2018 listed above, respectively, with respect to destruction of PFAS compounds by thermal degradation.

The present invention provides a method where thermal decomposition of PFAS compounds and other contaminants can occur both in aqueous environment, and in particular in water, allowing for treatment of subsurface contamination found in soils, groundwater, fractured bedrock as well as other matrixes with high water content using a combustion like process with dissolved oxidants.

Hitherto, the thermal decomposition of PFAS compounds, including PFSAs, has previously only been found possible at extreme temperatures and in the absence of water, or in the presence of water, but at pressures much higher than typically found in natural environments. The present invention provides a method where thermal decomposition of PFAS compounds and other contaminants can occur in aqueous environments, including water per se, allowing for treatment of subsurface contamination found in soils, groundwater, fractured bedrock as well as other matrixes with high water content using a combustion like process with dissolved oxidants

Claims

1 An in situ method of degradation of a fluoro-organic compound in an aqueous environment comprising at least soil and groundwater, the method comprising at least the steps of:

(c) providing an oxidant being reactive to the sorptive media; and

(d) adding the oxidant to the aqueous environment to contact the sorptive media in situ at an oxidant concentration of >0.4M, and to initiate degradation of the fluoro-organic compound on the sorptive media when the temperature of the sorptive media is at least 65°C, so that one or more fluoro-degradation products are formed.

2 A method as claimed in claim 1, further comprising the step of heating the aqueous environment so that the sorptive media is at least 65°C.

3 A method as claimed in claim 1 or claim 2, wherein the time period of step (b) is more than 1 week or 4 weeks or 8 weeks.

4 A method as claimed in any one of the preceding claims, wherein the sorptive media is either: a carbon being one or more of the group comprising: natural carbon, peat, coal, charcoal, biochar and activated carbon; or a zero valent metal being one or more of the group comprising: iron, zinc, silver, magnesium, nickel, aluminum and copper; or a reactive mineral being one or more of manganese dioxide, titanium dioxide, iron oxide and iron sulfide.

5 A method as claimed in claim 3 wherein the sorptive media has a particle size in the range 1 pm to 150 pm, optionally in the range 5 pm to 100 pm.

6 A method as claimed in any one of the preceding claims, wherein adding the oxidant in step (d) is by injection or soil mixing.

7 A method as claimed in any one of the preceding claims, wherein the fluoro-organic compound is fixated on the soil prior to step (a).

8 A method as claimed in any one of the preceding claims, wherein the temperature of the sorptive media for step (d) is in the range 65°C to 150°C.

9 A method as claimed in any one of the preceding claims wherein the pH during step (d) is pH is >10 or pH > 10.5, or pH >11.0, or pH>12.0, or pH >13.0.

10. A method as claimed in any one of the preceding claims wherein the molar ratio of oxidantsorptive media at the surface of the sorptive media is so.25:1

11. A method as claimed in any one of the preceding claims, further comprising actively raising or lowering the pH during step (d).

12. A method as claimed in any one of the preceding claims, wherein the fluoro-organic compound is one or more of the group comprising: a Per- and Polyfluoroalkyl substance (PFAS), a Perfluorosulfonic acid (PFSA), a Perfluorocarboxylic acid (PFCA), fluorinated dimer acid, fluorinated polymer, fluorinated alkane, fluorinated alkene, and a chlorofluorocarbon.

13. A method as claimed in claim 12, wherein the fluoro-organic compound is a PFAS being one or more of the group comprising: perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutane sulfonic acid (PFBS), perfluorobutanoic acid (PFBA), and hexafluoropropylene oxide dimer acid (HFPO-DA).

14. A method as claimed in any one of the preceding claims, wherein the oxidant is one or more of the group comprising: a persulfate, a peroxide, and mono-persulfate.

15. A method as claimed in claim 14, wherein the oxidant is one or more of the group comprising: sodium persulfate, potassium persulfate, ammonium persulfate, sodium monopersulfate, potassium mono-persulfate, magnesium peroxide, calcium peroxide and hydrogen peroxide.

16. A method as claimed in any one of the preceding claims, wherein the sorptive media is activated carbon, the organic compound is PFOS, and the oxidant is a persulfate.

17. A method as claimed in any one of the preceding claims, further comprising adding an alkali to assist in one or more of: increase the reaction between the oxidant and the sorptive media, offset acid formed during the reaction and affect the fluoro-organic compound degradation end products formed.

18. A method as claimed in claim 17, wherein the alkali is one for more of the group comprising: sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium tripolyphosphate, sodium phosphate, sodium silicate, potassium silicate, calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, Portland cement, blast furnace slag and calcium oxide.

19. A method as claimed in any one of the preceding claims, for the degradation of a fluoro-organic compound in an aqueous environment that includes soil, sand, clay, silt, aquifer water, sediment or other matrix.

20. A method of soil remediation comprising at least the steps of an in situ method of degradation of a fluoro-organic compound as defined in any one of claims 1 to 19

21. A method of soil remediation as claimed in claim 20 wherein the fluoro-organic compound is one or more of the group comprising: a Per- and Polyfluoroalkyl substance (PFAS), a Perfluorosulfonic acid (PFSA), a Perfluorocarboxylic acid (PFCA), fluorinated dimer acid, fluorinated polymer, fluorinated alkane, fluorinated alkene, and a chlorofluorocarbon.

22. A method as claimed in claim 21 wherein the fluoro-organic compound is a PFAS being one or more of the group comprising: perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutane sulfonic acid (PFBS), perfluorobutanoic acid (PFBA), and hexafluoropropylene oxide dimer acid (HFPO-DA).