Alkaline-thermal degradation process and system for perfluoroalkyl and polyfluoroalkyl substances present in polluted soil.

Abstract

- Alkaline-thermal process and system for the degradation of perfluoroalkyl and polyfluoroalkyl substances present in contaminated soil. - The process (P) for the alkaline-thermal degradation of PFAS substances comprises, in particular, an incorporation step (E1) for incorporating an alkali compound and optionally an adjuvant into the contaminated soil, a heating step (E2) for heating the contaminated soil containing the alkali compound and the adjuvant to a degradation temperature between 100°C and 350°C, the heating step (E2) being carried out at ambient pressure, and an extraction step (E3) for extracting the gases generated during the heating step (E2), as well as preferably a treatment step for the extracted gases (E4). This process (P) makes it possible to achieve the degradation of PFAS substances on a large scale, at reduced cost, and in a relatively simple and highly efficient manner. Figure for the abstract: Fig. 2

Description

Title of the invention: Alkaline-thermal degradation process and system for perfluoroalkyl and polyfluoroalkyl substances present in polluted soil. technical field

[0001] The present invention relates to a process and a system for the alkaline-thermal degradation of perfluoroalkyl and polyfluoroalkyl substances present in polluted soil. State of the art

[0002] It is known that per- and polyfluoroalkyl substances, referred to below as PFAS (for "per- and polyfluoroalkyl substances"), also called "perennial pollutants," are very stable and mobile in the environment, causing widespread contamination on a global scale. The impact of some of these PFAS substances on health (for example, perfluorooctane sulfonate (PFOS) or perfluorooctanoic acid (PFOA)) has led to the establishment of threshold concentrations in some countries, particularly for drinking water.

[0003] Studies on the degradation of PFAS substances are currently booming in the scientific community, both academic and industrial. In particular, thermal processes, applied to polluted water as well as soils, are being studied.

[0004] Furthermore, one envisaged technique, which was initially studied in the field of water treatment, is a HALT process (for "Hydrothermal Alkaline Treatment"), which represents a hydrothermal degradation technique for PFAS compounds. The envisaged process is carried out in a closed reactor, with a rise in both temperature (up to 400 °C) and pressure (up to 25 MPa), in the presence of sodium hydroxide.

[0005] However, this envisaged process is not applicable on a large scale, in particular for the following reasons: - the small volume of polluted soil that can be treated in a closed reactor (for pressure build-up), which limits the treatment flow rate; - the large dose of caustic soda used in the tests presented; and - a high cost, especially compared to other PFAS degradation techniques.

[0006] In the case of degradation by incineration, the temperatures required for the degradation of PFAS substances are generally in the range of 800°C to 1000°C.

[0007] There is therefore a need for a process enabling the degradation of PFAS substances on a large scale, at reduced cost, and efficiently. Description of the invention

[0008] The present invention aims to satisfy this need. It relates to an alkaline-thermal degradation process of perfluoroalkyl and polyfluoroalkyl substances (or PFAS substances) present in polluted soil.

[0009] According to the invention, said process comprises at least the following steps: - an incorporation step, implemented by at least one incorporation device, to incorporate at least one alkaline compound into the polluted soil; - a heating step, implemented by at least one heating device, to heat the polluted soil containing the alkali compound to a so-called degradation temperature, the degradation temperature being between 100°C and 350°C, and preferably between 180°C and 300°C, and the heating step being implemented at ambient pressure; and - a gas extraction step, implemented by at least one extraction device, to extract the gases generated during the heating step.

[0010] Thus, the entire process (and in particular the heating step) is carried out at ambient pressure (i.e., in a non-pressurized environment), with extraction of the gases (generated by the degradation and potentially harmful), that is, without using a closed reactor, which eliminates any limitation on the volume of contaminated soil treated. Furthermore, and surprisingly, the degradation process is particularly effective with a heating step performed at relatively low temperatures and with a reduced concentration of the alkali compound, thereby reducing costs and simplifying process implementation.

[0011] Therefore, thanks to the invention, we have a process for achieving a degradation of PFAS substances on a large scale, at reduced cost, and in an efficient and relatively simple way (by simple heating at ambient pressure).

[0012] In the context of the present invention, the following definitions apply: - by "contaminated soil", soil or any other material, including soil located in or excavated from a site, including waterlogged soil, that is contaminated by PFAS substances; and - by "alkaline-thermal degradation", a degradation which is carried out both by an alkaline action (via the incorporation of an alkaline compound into the polluted soil to be treated) and a thermal action (namely heating up to a degradation temperature).

[0013] Advantageously, the incorporation step uses as an alkali compound at least one of the following alkalis: sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium oxide (CaO), calcium hydroxide (Ca(OH)2).

[0014] Furthermore, advantageously, at the incorporation stage, the alkali compound is incorporated in one of the following forms: - in liquid form; - in solid form.

[0015] In a particular embodiment, the incorporation step includes a mixing operation of the polluted soil and the incorporated alkaline compound, particularly when incorporated in solid form.

[0016] Advantageously, at the incorporation stage, the alkali compound is incorporated into the polluted soil in a proportion of between 0.01 and 0.5 kilogram of alkali compound per kilogram of polluted soil, and preferably in a proportion of between 0.01 and 0.1 kilogram of alkali compound per kilogram of polluted soil.

[0017] Furthermore, in a preferred embodiment, at the incorporation stage, at least one adjuvant to catalyze the degradation reaction is incorporated into the polluted soil. Such an adjuvant is intended, in particular, to react with the degradation by-products of PFAS substances, in order to promote the degradation of the parent compounds by eliminating the by-products.

[0018] Advantageously, the incorporation step uses as an adjuvant: CaCO3, NaHCO3, MgO2, Na2O, K2O, FeC13, FeO(OH), Fe(OH)3, A1(OH)3, A1C13, ZnCO3 or aluminium silicates.

[0019] Furthermore, advantageously, the heating step is implemented using a heating device comprising at least some of the following heating elements: - electric heating elements; - heating elements powered by an energy source using a fuel (liquid or gaseous).

[0020] Furthermore, in a first embodiment, said process is implemented at a treatment site, for example a treatment area (on site or off site) or a treatment center, to which the polluted soil has been brought during a preliminary step (after its excavation).

[0021] Furthermore, in a second embodiment, said process is implemented in-situ, that is to say at the place where the polluted land is located, for example on an industrial site.

[0022] Furthermore, in a particular embodiment, the degradation process also includes a treatment step, implemented by at least one treatment device, to treat the gases extracted in the extraction step. The degradation process may also include a control step as specified below.

[0023] The process further includes a preliminary step to possibly transport the polluted soil and to set up the devices which are used for the implementation of the degradation process.

[0024] The present invention also relates to an alkaline-thermal degradation system for perfluoroalkyl and polyfluoroalkyl substances (or PFAS substances) present in polluted soil.

[0025] According to the invention, said system includes in particular: - at least one incorporation device configured to incorporate at least one alkali compound into the polluted soil; - at least one heating device configured to heat the polluted soil containing the alkali compound to a so-called degradation temperature, the degradation temperature being between 100°C and 350°C (and preferably between 180°C and 300°C) and the heating being carried out at ambient pressure; and - at least one extraction device configured to extract the gases generated during the heating carried out by the heating device. Brief description of the figures

[0026] The accompanying figures will clearly illustrate how the invention can be implemented. In these figures, identical reference numerals designate similar elements.

[0027] Fig. 1 is a schematic view of a particular embodiment of a degradation system.

[0028] The [Fig.2] is the synoptic diagram of a particular embodiment of a degradation process.

[0029] Fig. 3 is a schematic view of a treatment site on which a degradation process is implemented using a degradation system according to a first embodiment.

[0030] Fig. 4 is a schematic view of a site whose soil includes polluted land, in which a degradation process is implemented using a degradation system according to a second embodiment. Detailed description

[0031] System 1, illustrating the invention and represented schematically on [Fig. 1], is intended to carry out an alkaline-thermal degradation of PFAS substances (for "per- and polyfluoroalkyl substances" in English, i.e. per- and polyfluoroalkylated substances) present in polluted (or contaminated) soil, for example in polluted soil.

[0032] Such polluted soil (contaminated by FAS substances which are persistent environmental contaminants), such as the polluted soil TA, TB shown in Figures 3 and 4, can be present on various types of sites, including industrial sites, fire training or fire sites (with the use of AFFF foams), wastewater treatment sites, waste storage or management sites, ...

[0033] In general, system 1 comprises, as very schematically represented in [Fig. 1]: - an incorporation device 2 configured to incorporate at least one alkali compound into the polluted soil TA, TB; - a heating device 3 configured to heat the polluted soil TA, TB containing the alkali compound to a so-called degradation temperature. The degradation temperature is between 100°C and 350°C (and preferably between 180°C and 300°C) and the heating is carried out at ambient pressure; and - an extraction device 4 configured to extract the gases generated during the heating implemented by the heating device 3.

[0034] The heating device 3 comprises conventional heating elements. Any type of heating element suitable for heating the polluted soil to the desired degradation temperature may be considered. By way of illustration, the heating device 3 may comprise at least some of the following heating elements: - electric heating elements including, for example, electric resistors which are supplied with electric current; - heating elements powered by an energy source using a common fuel (or combustible).

[0035] The heat source(s) (electrical, fuel or other type) used by the heating device 3 can in particular be used to heat a fluid which is circulated in pipes embedded in the polluted ground.

[0036] Furthermore, in a preferred embodiment, the system 1 also includes a treatment device 5 for treating the gases extracted by the extraction device 4, as specified below.

[0037] Furthermore, system 1 also includes a control device 6 to control system 1 and its operation, and in particular to control the temperature in the polluted soil, generated by the heating device 3.

[0038] System 1, as described above, is suitable for implementing a process P for the alkaline-thermal degradation of PFAS substances present in polluted soil.

[0039] This process P comprises, as shown in [Fig.2]: - an incorporation step El, implemented by the incorporation device 2, to incorporate at least one alkali compound into the polluted soil; and - a set EE of steps comprising a plurality of steps E2 to E5, which are implemented (at least partially) simultaneously, and this after the implementation of the incorporation step EL

[0040] This set of EE steps includes, in particular: - a heating step E2, implemented by the heating device 3, to heat the polluted soil (including the alkaline compound that was incorporated in the step Incorporation step E1) up to the degradation temperature, at which the polluted soil is heated and maintained throughout this heating step E2; and - an extraction step E3, implemented by the extraction device 4, to extract the gases generated during the heating step E2.

[0041] Heating the polluted soil, combined with the action of at least the alkaline compound, will degrade the PFAS substances present in the polluted soil and produce gases, in particular gases formed (at least in part) by the products generated by the degradation of said PFAS substances. These gases, which may contain harmful substances, are extracted from the polluted soil (in extraction step E3) to prevent their dispersion into the surrounding air. These extracted gases can then be treated in a treatment step E4.

[0042] In a particular embodiment, the set EE of steps of the process P (of alkaline-thermal degradation) also includes such a treatment step E4, implemented by the treatment device 5, to treat the gases extracted in the extraction step E3, as well as a control step E5 specified below.

[0043] The process P further comprises a preliminary step E0 intended in particular to prepare the polluted soil to be treated and to set up the various devices of system 1, in order to then be able to implement the set EE of steps.

[0044] The different stages of the process P are now described in more detail.

[0045] In the incorporation step El, operators therefore incorporate, using the incorporation device 2, at least one alkali compound into the polluted soil. Preferably, they incorporate as an alkali compound at least one of the following alkalis: sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium oxide (CaO), calcium hydroxide (Ca(OH)₂).

[0046] The proportion (in particular the mass ratio) of alkali incorporated varies depending on the type of alkali used and the concentration of PFAS in the soils to be treated. In a particular embodiment, the alkali compound is incorporated into the polluted soil in a proportion of between 0.01 and 0.5 kilograms of alkali compound per kilogram of polluted soil, and preferably in a proportion of between 0.01 and 0.1 kilograms of alkali compound per kilogram of polluted soil.

[0047] Thus, a relatively small amount of alkali compound is sufficient to implement the P process of alkali-thermal degradation, which reduces the cost and facilitates implementation.

[0048] In a first embodiment, the alkali compound is incorporated in liquid form in the incorporation step EL

[0049] To this end, in a particular embodiment, the alkali compound, for example sodium hydroxide, is dissolved in a liquid, preferably water, and This liquid is then injected by usual means (as part of the incorporation device) into the polluted soil.

[0050] The injection of the alkali compound in this liquid form can be carried out either in a gravity mode via injection means (wells, drains, ...), or under pressure via direct injection or via an injection device, for example sleeved tubes.

[0051] Furthermore, in a second implementation of this incorporation step El, the alkali compound is incorporated in solid form.

[0052] To do this, one of the following common techniques can be used: in-situ soil mixing, injection of sludge or particulate gel with the solid alkaline compound.

[0053] In a particular embodiment, the incorporation step El also includes a mixing operation during which the mixture of polluted soil and alkaline compound incorporated therein is mixed.

[0054] To achieve this, conventional mixing techniques are used. Such mixing is particularly carried out when the alkali compound is incorporated in solid form.

[0055] Regardless of the method of incorporation used, the incorporation device 3 includes standard means (not described further) for implementing this incorporation.

[0056] Furthermore, in a preferred embodiment, at the incorporation step E1, operations also incorporate at least one additive into the polluted soil. This additive is intended to catalyze the degradation reaction taking place in the polluted soil.

[0057] Such an adjuvant is intended, in particular, to react with the degradation by-products of PFAS substances, in order to promote the degradation of the parent compounds by disappearance of the by-products, and thus promote the alkaline-thermal degradation implemented by the P process.

[0058] To do this, the adjuvant can, for example, be mixed with the alkali compound when the latter is dissolved in water (or in another liquid) for injection in liquid form.

[0059] In the case of an adjuvant incorporated in solid form, it can be added and mixed with the alkali compound (before its incorporation) when the latter is incorporated in solid form.

[0060] By way of illustration, at least one of the following adjuvants may be used: CaCO3, NaHCO3, MgO2, Na2O, K2O, FeC13, FeO(OH), Fe(OH)3, A1(OH)3, A1C13, ZnCO3 or aluminium silicates.

[0061] However, in a particular embodiment, at least one of the following three adjuvants is preferably used: A1C13, MgO2 and NaHCO3, which are particularly effective.

[0062] The proportion (in particular the mass ratio) of adjuvant incorporated varies depending on the type of adjuvant used. In one particular embodiment, the adjuvant is incorporated into the polluted soil in a proportion of between 0.005 and 0.1 kilogram of adjuvant per kilogram of polluted soil.

[0063] In the context of the present invention, the entire process P, and in particular the heating step E2, is carried out at ambient pressure. Consequently, no closed device (or reactor) is required for the implementation of process P, which reduces the cost and simplifies the implementation of said process P and, above all, allows the process P to be implemented on a large scale, i.e., on significant volumes of polluted soil.

[0064] As indicated above, the heating step E2, implemented using the heating device 3, is intended to heat the polluted soil (initially at ground temperature) to the degradation temperature and to maintain the polluted soil at this degradation temperature during the implementation of the alkaline-thermal degradation process P.

[0065] This degradation temperature is between 100°C and 350°C, and preferably it is between 180°C and 300°C.

[0066] Preferably, the extraction step E3 is implemented as soon as gas is generated by the heating carried out in the heating step E2. In this extraction step E3, the gases generated during the heating step E2 are extracted from the polluted soil.

[0067] By way of illustration, at this extraction step E3, which is implemented by the extraction device 4, the extraction can be carried out according to one of the following methods: - the gases formed are extracted by suction of hot air, using a conventional suction system forming part of the extraction device 4; - the gases formed are extracted by a "venting" type process.

[0068] Typically, a "venting" type process generally includes the following operations: - an extraction well installation. Wells or pipes are installed in the ground at different depths to allow the extraction of gas; - the application of pressure or vacuum. Air can be injected into the ground to help push back the generated gases, or a pump can be used to create a vacuum and draw the gases to the surface; and - the extracted gases are collected.

[0069] Regardless of the extraction method used, the extraction device 4 includes standard means (not described further) for carrying out this extraction.

[0070] Furthermore, in a particular embodiment, the set EE of steps in process P (alkaline-thermal degradation) also includes the step of treatment E4, implemented by the treatment device 5, to treat the gases extracted at the extraction stage E3.

[0071] The extracted gases are treated to remove contaminants, including by-products generated by the degradation of PFAS substances and possible thermal desorption (volatilization) of smaller PFAS substances, as well as any other compound extracted by the increase in temperature (organic matter or other pollutants), before being released into the atmosphere or reused in a particular application.

[0072] To this end, by way of illustration, the gases extracted by a "venting" type process are treated by the treatment device 5 according to the pollutants present in the gas, and for example by condensation, by oxidation, by gas scrubbing or by filtration on activated carbon.

[0073] Similarly, by way of illustration for gases extracted by suction of hot air, the pollutant vapors are treated by the treatment device 5 which is also adapted to the type of pollutant targeted and which can, for example, implement cooling and condensation of vapors, gas scrubbing or adsorption on activated carbon.

[0074] Regardless of the treatment method used, the treatment device 5 includes standard means (not described further) for implementing this treatment.

[0075] The treated gases, from which the harmful contaminants have been sufficiently removed, can then be safely released into the atmosphere around the treatment area. For certain applications, they can also be reused, either immediately or after storage and possibly transport.

[0076] Furthermore, in a particular embodiment, the EE assembly of the P (degradation) process also includes a control step E5.

[0077] This control step E5 aims to control the process P during its implementation and in particular to measure the temperature of the polluted soil and to ensure that it is at the degradation temperature.

[0078] To measure the temperature of the polluted soil at the control step E5, the control device 6 may, in particular, include thermocouples installed at different points in the polluted soil.

[0079] The entire process P (and in particular the heating step E2) is carried out at ambient pressure, with extraction of potentially harmful gases generated by the degradation, i.e., without using a closed reactor, which eliminates any limitation on the volume of contaminated soil treated. Furthermore, and surprisingly, the degradation process P is particularly effective with the heating step E2 performed at temperatures that are not particularly high (especially compared to the thermal degradation temperature of PFAS substances) and with a concentration of reduced alkali compound, which helps to reduce the cost and facilitate the implementation of the P process.

[0080] Therefore, system 1 and process P make it possible to carry out alkali-thermal degradation of PFAS substances on a large scale, at reduced cost, and in an efficient and relatively simple manner.

[0081] System 1 and process P, as described above, can be used in numerous applications and in a variety of situations. In particular, they can be implemented in different embodiments, and especially in different locations. Thus, they can notably be implemented at a treatment site. They can also be implemented in-situ, that is, directly at the location of the contaminated soil, for example, at an industrial site.

[0082] In a first embodiment, the process P is implemented (using system 1) at a treatment site, for example, on-site treatment area or in a treatment center (such as an off-site platform), to which the polluted soil has been brought in a preliminary step E0, after its excavation.

[0083] In an example of this first embodiment, shown in [Fig.3], the treatment is carried out in a heated stack treatment center 8.

[0084] In this particular embodiment, in the preliminary step E0, the polluted soil TA is excavated in the usual way from where it is located and is transported to the treatment center 8. Then, this polluted soil TA is placed on a sealed surface 9.

[0085] The incorporation step El can then be carried out. In this case, the contaminated soil TA can, for example, be mixed with the alkaline compound and the additive. The alkaline compound and the additive can be applied in liquid or solid form according to one of the methods described above.

[0086] The pile 10 is then constructed in the usual way with the installation in particular of: - of usual heating elements 11, represented by black dots on the [Fig.3], which are part of the heating device 3; - air injection elements 12, represented by circles with a dot, and air extraction elements 13, represented by circles with a cross, which are part of the extraction device 4; and - thermocouples 14, represented by thick-lined circles, which are arranged for example near the heating elements 11 and which are part of the control device 6 (to monitor the temperature at the control stage E5).

[0087] Such a pile 10 (covered by a surface element 7) generally has an average size of 500 to 2000 m3. It is thus possible to treat a very large volume of polluted soil with a single implementation of the process P.

[0088] The number of heating elements 11 of the heating device 3, and their location and spacing within the stack 10, are determined based, in particular, on the conductivity and heat capacity of the contaminated soil TA, as well as the heat source of the heating device 3. The heating elements 11 can be powered by gas (burners), electricity, or any other energy source, as described above. The heat generated by the heating elements 11 of the heating device 3 in heating stage E2 is transferred to the contaminated soil TA by conduction and / or convection and / or irradiation at the hot spots created around the heating elements IL

[0089] Furthermore, in the extraction step E3, the gases formed are extracted by suction of hot air, via the air extraction elements 13 of the extraction device 4.

[0090] These gases (or vapors) containing pollutants are then treated, in treatment step E4, using a treatment device (not shown), which is adapted to the targeted pollution and which can, for example, implement one of the following common methods: cooling and condensation of vapors, gas scrubbing or adsorption on activated carbon, ...

[0091] Furthermore, in a second embodiment shown in [Fig.4], the process P is implemented (using system 1) in situ, i.e. on site 15 where the polluted soil TB is located, for example on an industrial site including buildings 16 and installations 17.

[0092] In this second embodiment, in the preliminary step E0, the soil 18 (containing the polluted soil TB) is left in place. In the example shown in [Fig.4], the soil 18 comprises vertically, from top to bottom, different zones, namely: - an unsaturated zone ZI; - a Z2 zone, in which the TB polluted soil to be treated is located (which may be in a saturated zone and / or an unsaturated zone); and - a saturated zone Z3.

[0093] In the preliminary step E0, various elements of system 1 are put in place, including: - standard structures 19, equipped with heating elements 20 which are brought into the Z2 area to be treated. These structures 19 and these heating elements 20 are part of the heating system 3; - gas extraction elements 21 which are part of the extraction device 4 and which are intended to extract gases from the unsaturated zone Zl, and in particular gases generated by the degradation of PFAS substances in polluted soil TB (or by thermal desorption of low molecular weight PFAS substances or other pollutants), which are found in this unsaturated zone Z; - water extraction elements 22 that terminate in the saturated zone Z3 and are intended to extract water from this saturated zone Z3; and - thermocouples 23, which are arranged for example near some of the heating elements 21, which are part of the control device 6 and are intended to measure the temperature (in order to be able to monitor the temperature at the control step E5).

[0094] These different elements of system 1 are installed by drilling in this example of embodiment.

[0095] To do this, these different elements, and in particular the structures 19 of the heating device 3 and the gas extraction elements 21 of the extraction device 4, are arranged in the ground 18 according to the geology, the target areas to be treated and the accessibility on the site 15.

[0096] In the incorporation step E1, the injection of the alkali compound and the adjuvant (prepared in liquid form) can be carried out either by gravity via injection means (wells, drains, etc.) or under pressure via direct injection or injection devices, such as sleeved tubes. The incorporation of the alkali compound and the adjuvant can also be carried out via other injection devices such as in-situ soil mixing, the injection of slurries or particulate gel, with solid compounds.

[0097] Furthermore, in extraction step E3, the soil gases 18 are extracted by the extraction device 4, for example via a venting process as described above. These gases (or vapors) containing pollutants are then treated, in treatment step E4, using a treatment device (not shown) which is adapted to the pollutants present in the extracted gases and which can, for example, implement one of the following common methods: condensation, oxidation, gas scrubbing, carbon filtration, etc.

[0098] System 1 and process P, as described above, which employ alkaline-thermal degradation (obtained by heating combined with the addition of an alkaline compound), are particularly effective. They have notably been tested in the laboratory on polluted soil contaminated with between 1,200 pg / kg and 2,330 pg / kg of twenty PFAS substances, and this: - initially, thermal desorption at 300°C without the addition of an alkaline compound resulted in reductions of 66% on the twenty PFAS substances at 2 days, 85.6% at 7 days, and 92.9% at 20 days; and - in a second step, with the addition of sodium hydroxide NaOH (allowing the polluted soil to have a pH greater than 13) at 300°C, the observed reductions were greatly improved with, from 2 days of treatment, 97.2% reduction in the polluted soil, then 99.8% over 7 days and 99.98% over 20 days.

Claims

Demands

1. Alkaline-thermal degradation process of perfluoroalkyl and polyfluoroalkyl substances present in polluted soil, characterized in that it comprises at least the following steps: - an incorporation step (E1), carried out by at least one incorporation device (2), to incorporate at least one alkali compound into the polluted soil (TA, TB); - a heating step (E2), carried out by at least one heating device (3), to heat the polluted soil (TA, TB) comprising the alkali compound to a so-called degradation temperature, the degradation temperature being between 100°C and 350°C and the heating step (E2) being carried out at ambient pressure; and - an extraction step (E3), carried out by at least one extraction device (4), to extract the gases generated during the heating step (E2).

2. The process according to claim 1, characterized in that the incorporation step (El) uses as an alkali compound at least one of the following alkalis: sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide.

3. A process according to any one of claims 1 and 2, characterized in that at the incorporation step (El), the alkali compound is incorporated in one of the following forms: - in liquid form; - in solid form.

4. A process according to any one of the preceding claims, characterized in that at the incorporation step (El), the alkali compound is incorporated into the polluted soil (TA, TB) in a proportion of between 0.01 and 0.5 kilogram of alkali compound per kilogram of polluted soil (TA, TB).

5. A process according to any one of the preceding claims, characterized in that at the incorporation step (El), at least one adjuvant for catalyzing a degradation reaction carried out is incorporated into the polluted soil (TA, TB).

6. A method according to any one of the preceding claims, characterized in that the heating step (E2) is implemented using a heating device (3) comprising at least some of the following heating elements (11, 20): - electric heating elements; - heating elements powered by a fuel-based energy source.

7. A method according to any one of the preceding claims, characterized in that the degradation temperature is between 180°C and 300°C.

8. A process according to any one of the preceding claims, characterized in that said process (P) is implemented: - on a treatment site (8), to which the polluted soil (TA) has been brought during a preliminary step (E0); or - in-situ.

9. A process according to any one of the preceding claims, characterized in that it comprises a treatment step (E4), implemented by at least one treatment device (5), for treating the gases extracted in the extraction step (E3).

10. Alkaline-thermal degradation system of perfluoroalkyl and polyfluoroalkyl substances present in polluted soil, characterized in that it comprises: - at least one incorporation device (2) configured to incorporate at least one alkali compound into the polluted soil (TA, TB); - at least one heating device (3) configured to heat the polluted soil (TA, TB) comprising the alkali compound to a so-called degradation temperature, the degradation temperature being between 100°C and 350°C and the heating being carried out at ambient pressure; and - at least one extraction device (4) configured to extract the gases generated during the heating carried out by the heating device (3).

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