REDUCTION OF PERFLUOROALKYLED AND POLYFLUOROALKYLED SUBSTANCES IN A FLUID

Abstract

The invention relates to the use of colloidal silica to reduce the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in a fluid. The invention also relates to a process for treating a fluid containing perfluoroalkyl and / or polyfluoroalkyl substances, said process comprising at least one step of contacting said effluent with colloidal silica and a step of recovering a fluid having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in the fluid before contact with the colloidal silica. Figure for the abstract: none

Description

Title of the invention: REDUCTION OF PERFLUOROALKYLED AND POLYFLUOROALKYLED SUBSTANCES IN A FLUID TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a process for treating per- and polyfluoroalkylated substances from a fluid containing said substances, the fluid will advantageously be of the water type, in particular drinking water, but also of the urban or industrial type, for example waters containing aqueous film-forming foam, leachates from floor washing or waste leachates. STATE OF THE ART

[0002] Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are chemicals manufactured for their oil and water resistance properties. Since the 1940s, PFAS have been used in a wide range of consumer products and industrial processes. As a result, PFAS are released into water, air, and soil. These PFAS are particularly difficult to remove from effluents using existing water treatment processes.

[0003] Water treatment can be implemented by various treatment methods using physical, chemical and / or biological means.

[0004] Physical and / or chemical water treatment steps can clarify the water. These steps are generally implemented according to a predetermined sequence. These treatment steps can be chosen, in particular, from the group including filtration, sedimentation (gravity separation), flotation, flocculation, coagulation, and combinations thereof. Chemical water treatment requires the use of chemical reagents, in particular coagulation agents or flocculating agents.

[0005] A well-known process for treating water, particularly surface water for drinking water treatment and urban or industrial wastewater for pollution control, consists of coagulating the water to be treated with a coagulating reagent, such as, for example, a trivalent metal salt, flocculating the organic matter contained in the coagulated water with a flocculating reagent, usually consisting of an organic polymer, and settling or filtering the flocs and other solid matter in a settling tank or through a filter. In the case of a settling tank, the sludge is extracted from the bottom of the tank, and the treated water is extracted via the overflow; whereas in the case of a filter, the filtered water is extracted from the other side of the filter, and the sludge / dirty water is extracted by backwashing through the filter overflow.

[0006] More specifically, an example of a technology implementing coagulation and flocculation steps involves adding coagulants and / or flocculants to raw water to obtain flocs. The coagulated and / or flocculated water can then be filtered through an ultrafiltration membrane, with the flocs forming a cake on the membrane's surface and the clarified water passing through it. Subsequently, the floc cake can be removed by backwashing the membrane and overflowing a dirty wash water tank.

[0007] The increasing load of PFAS-type organic contaminants observed in resources leads drinking water producers and effluent treatment companies to modify their treatment processes which are not adapted to the removal of these new PFAS-type pollutants.

[0008] There is therefore a need to improve the treatment of a fluid, such as water, to take into account, in particular, new contaminants such as PFAS. Summary of the invention

[0009] The invention relates to a process for treating a fluid containing perfluoroalkyl and / or polyfluoroalkyl substances, said process comprising at least one step of contacting said effluent with colloidal silica and a step of recovering a fluid having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances of the fluid before contacting the colloidal silica.

[0010] The process may include one or more of the embodiments described below.

[0011] According to one embodiment of the process of the invention:

[0012] a) the fluid is a liquid, in particular water and / or

[0013] b) the total concentration of perfluoroalkyl and polyfluoroalkyl substances in the fluid before treatment with colloidal silica is at least 20 ng / L; and / or

[0014] c) colloidal silica has a particle size ranging from 5 nm to 500 nm, preferably from 10 to 300 nm.

[0015] According to one embodiment, the process of the invention further includes a step of adjusting the pH of the fluid in order to regulate the pH of the fluid comprising the colloidal silica.

[0016] According to one embodiment, the process of the invention includes, before the step of contacting the colloidal silica, a step of concentrating the fluid, preferably by reverse osmosis or by foam fractionation.

[0017] According to one embodiment, the process of the invention further comprises an adsorption step by passing the fluid, upstream or downstream of the contacting step, through an adsorbent material such as ion exchange resins, modified clays, or activated carbon, preferably, this adsorption step being implemented downstream of the contacting step.

[0018] According to one embodiment, the process of the invention is chosen from a clarification process or a foam fractionation process.

[0019] According to a first embodiment, the process of the invention comprises:

[0020] a) A step of coagulation and flocculation of the fluid to be treated,

[0021] b) A step of settling the fluid comprising colloidal silica,

[0022] c) A fluid recovery step having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in the fluid before contact with colloidal silica,

[0023] said process comprising, upstream or downstream of the coagulation and flocculation step, a step of bringing the fluid into contact with colloidal silica implemented, preferably upstream of the coagulation and flocculation step.

[0024] According to a second embodiment, the process of the invention comprises:

[0025] a) A step of coagulation and flocculation of the fluid to be treated,

[0026] b) A step of admitting the fluid to be treated and white water into a part lower of a mixing zone included within a flotation zone,

[0027] c) A flotation step in a separation zone separate from the mixing zone,

[0028] d) A step of recovering clarified fluid having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances of the fluid before contact with colloidal silica,

[0029] e) optionally a recirculation step of all or part of the clarified water recovered in a lower part of the separation zone via a recirculation loop,

[0030] said process comprising a step of contacting the fluid with colloidal silica, said contacting step being implemented (i) upstream of the coagulation and flocculation step and / or (ii) downstream of the coagulation and flocculation step, and / or (iii) when step e) is implemented, in the recirculation loop of all or part of the clarified fluid.

[0031] According to a third embodiment, the process of the invention comprises:

[0032] - A step of introducing the fluid into an air-fed reactor thus forming a foam,

[0033] - A fluid recovery step having a reduced concentration of substances perfluoroalkylated and / or polyfluoroalkylated substances relative to the concentration of substances perfluoroalkylated and / or polyfluoroalkylated fluid before contact with colloidal silica,

[0034] said process comprising a step of bringing the fluid into contact with colloidal silica, said contacting being carried out upstream of the reactor or in the reactor.

[0035] According to this third embodiment, preferably, the process further comprises a step of adding a surfactant-type agent to the reactor.

[0036] The invention also relates to the use of colloidal silica to reduce the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in a fluid.

[0037] The use according to the invention may include one or more embodiments described below.

[0038] According to one embodiment, the fluid is a liquid, in particular water.

[0039] According to one embodiment, the total concentration of perfluoroalkyl substances and polyfluoroalkylates in the fluid before treatment with colloidal silica is at least 20 ng / L.

[0040] According to one embodiment, the colloidal silica has a median particle diameter ranging from 5 nm to 500 nm, preferably from 10 to 300 nm.

[0041] The process of the invention makes it possible to reduce the concentration of many PFAS in an aqueous fluid.

[0042] The colloidal silica used in the invention is particularly well suited for treating fluids with a high concentration of PFAS. Thus, colloidal silica can advantageously be used upstream of subsequent treatment on an adsorbent such as a resin or activated carbon, for example.

[0043] The invention is particularly simple to implement and can be easily integrated into existing water treatment systems. BRIEF DESCRIPTION OF THE FIGURES

[0044] [Fig. 1] represents an installation for implementing a treatment process according to the invention including clarification by decantation.

[0045] [Fig.2] represents an installation for implementing a treatment process according to the invention including clarification by flotation.

[0046] [Fig.3] represents an installation for implementing a treatment process according to the invention including foam fractionation. DETAILED DESCRIPTION OF THE INVENTION

[0047] The invention relates to the use of colloidal silica to reduce the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in a fluid.

[0048] The invention also relates to a method for treating a fluid containing perfluoroalkyl and / or polyfluoroalkyl substances, said method comprising at least one step of contacting said fluid with colloidal silica and one step of recovering a fluid having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances of the fluid before contacting colloidal silica.

[0049] In the context of the invention, the fluid having a reduced concentration of PFAS compared to the concentration of PFAS of the fluid before contact with colloidal silica is designated as "treated effluent".

[0050] Perfluoroalkylated and / or polyfluoroalkylated substances are called PFAS. Among the PFAS whose concentration can be reduced by means of the invention, the following substances may be cited for example: perfluorobutanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoro-n-undecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorobutane sulfonic acid, perfluoropentane sulfonic acid, perfluorohexane sulfonic acid, perfluoroheptane sulfonic acid, perfluorooctane sulfonic acid, perfluorononane sulfonic acid, N-ethyl-N-[(heptadecafluorooctyl)sulfonyl]glycine, perfluorooctane sulfonamide, 6:2-fluorotelomere sulfonic acid.

[0051] The fluids that can be treated by means of the invention can be water, in particular drinking water or water to be made potable, process water effluents, desalination unit effluents, industrial or municipal wastewater effluents, water containing aqueous film-forming foam (AFFF), leachate from floor washing or waste leachate.

[0052] Process water effluents can originate, for example, from surface water, groundwater, municipal treatment facilities, or a combination of these water sources.

[0053] The invention uses colloidal silica.

[0054] Colloidal silica is a liquid dispersion of microscopic, non-porous, amorphous silica particles in a liquid phase. These particles are stabilized, which prevents their aggregation and precipitation.

[0055] In the context of the present invention, colloidal silica differs from a silica gel. Colloidal silica differs from a silica gel in particular in that colloidal silica is a liquid suspension of fine particles, whereas silica gel is a solid mass formed by the aggregation (polymerization) of these particles.

[0056] Silica gels are generally applied to supports. Compared to silica gels, the application of colloidal silica in the treatment of PFAS will be easier since it does not require such supports.

[0057] According to one embodiment, the colloidal silica used in the invention can have a particle size ranging from 5 nm to 500 nm, preferably from 10 to 300 nm.

[0058] Typically, within the scope of the present invention, particle size refers to the median diameter D50 of the particles. It can be measured by any method known to those skilled in the art, for example by laser diffraction.

[0059] The colloidal silica used in the invention may be negatively or positively charged.

[0060] Advantageously, the pH of the fluid comprising the colloidal silica (in particular just after contact between the fluid and the silica) can be adjusted to move away from neutrality, for example a pH below 6 or above 8. This makes it possible to further improve the treatment efficiency of PFAS.

[0061] The treatment process of the invention may therefore optionally include a pH adjustment step, implemented for example by adding an acid or a base in order to achieve a pH different from neutrality for the mixture comprising the fluid and the colloidal silica.

[0062] According to one embodiment, the colloidal silica used in the invention has an acidic pH, typically less than or equal to 6, or a basic pH, typically greater than or equal to 8.

[0063] The inventors discovered that these pH values ​​for silica (different from a pH of 7) made it possible to significantly improve the proportion of PFAS removal.

[0064] The contacting of colloidal silica with the fluid to be treated can be implemented for example by adding colloidal silica into the fluid, either by an inline injection into the fluid or by an addition in a mixing zone comprising the fluid to be treated.

[0065] By way of example, colloidal silica can be added to the fluid to be treated at concentrations of 1 to 800 g / L, for example from 10 to 500 g / L.

[0066] Colloidal silica can be added to the fluid upstream or downstream of a water treatment process, or even during a step of a water treatment process.

[0067] According to one embodiment, colloidal silica is added to a fluid during a clarification process or during a foam fractionation treatment process.

[0068] At the end of the treatment process, a fluid with a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in the fluid before the treatment step may be obtained. This effluent may also be referred to as the "treated fluid".

[0069] According to one embodiment, the treatment process includes a preliminary step, implemented before the step of contacting the colloidal silica, of the concentration of the fluid to be treated. Thus, the colloidal silica will then be brought into contact with a concentrated fluid.

[0070] This concentration step makes it possible in particular to treat less flow upstream of contact with colloidal silica.

[0071] The fluid concentration step can be implemented, for example, by reverse osmosis or by foam fractionation.

[0072] According to a first embodiment, the treatment process of the invention is a clarification process. At the end of the treatment process, the treated fluid may also be referred to as "clarified fluid".

[0073] The clarification process may, for example, be a clarification process by decantation or by flotation.

[0074] According to one embodiment, the treatment process of the invention is a clarification process by decantation. According to this embodiment, the process of the invention may then comprise: a. A step involving coagulation and flocculation of the fluid to be treated, b. A step of settling the fluid containing silica, c. A fluid recovery step having a reduced PFAS concentration compared to the PFAS concentration of the fluid before contact with colloidal silica,

[0075] said process comprising, upstream or downstream of the coagulation and flocculation step, a step of bringing the fluid into contact with colloidal silica implemented, preferably upstream of the coagulation and flocculation step.

[0076] Colloidal silica does not naturally settle. Therefore, it will be advantageous within the framework of the invention to implement the contacting of the fluid and the colloidal silica upstream of the coagulation and flocculation step.

[0077] Thus, in this embodiment by decantation, the PFAS and the colloidal silica form sediments which can be evacuated into a separation zone in the lower part of the decantation zone.

[0078] The treated fluid will thus be advantageously recovered in the upper part of the settling zone.

[0079] Reference will be expressly made to [Fig. 1] illustrating an installation for implementing a treatment process according to the invention. This is an example of a treatment process by decantation.

[0080] The fluid to be treated, advantageously mixed with colloidal silica, enters via the inlet line 1 into a coagulation-flocculation reactor 2, optionally equipped with mixing means 3. This reactor can be divided into several successive basins, for example, a first coagulation basin (itself possibly equipped with a mixing means) followed by a second flocculation basin (itself possibly (be equipped with a mixing device). Also, a third basin can be provided between the first coagulation basin and the second flocculation basin to allow the injection of a flocculant and / or a polymer, for example. It is thus possible to provide injection devices to inject a coagulant and / or a flocculant into reactor 2.

[0081] It is also possible to provide, according to an embodiment not illustrated, two separate reactors, a first coagulation reactor, for example an in-line coagulation reactor, and a second flocculation reactor, for example a stirred tank flocculation reactor.

[0082] In the case where the colloidal silica is not mixed upstream of reactor 2 or in the case where the colloidal silica is also added in reactor 2, it is possible to provide a means of injecting colloidal silica into reactor 2.

[0083] After the coagulation and flocculation stage, the fluid enters the settling tank 4, which may or may not be equipped with settling fins 5, and which has means for discharging clarified water 6, as well as a separation zone 8 for settling sludge (containing, in particular, PFAS, colloidal silica, flocculants, and possibly other flocculated suspended matter). The settling tank 5 may also optionally include a scraper 7.

[0084] According to an embodiment not shown in [Fig. 1], it is possible to provide a recirculation circuit for at least part of the settling sludge (containing colloidal silica), which can then be reinjected into reactor 2, in particular upstream of the flocculation basin in the case of several basins in reactor 2.

[0085] According to one embodiment, the treatment process of the invention is a clarification process by flotation. According to this embodiment, the process for treating a fluid according to the invention may thus comprise, in addition to the step of contacting the fluid with colloidal silica, at least one step of flotation of a previously coagulated and flocculated fluid.

[0086] Flotation is a solid-liquid or liquid-liquid separation process in which sludge, whose density is lower than that of the liquid containing it, is collected from the upper surface of the liquid. This sludge can then be referred to as floated sludge. This sludge can then be removed (for example, by scraping) and separated from the fluid.

[0087] According to one embodiment, the fluid treatment process according to the invention is a clarification process by flotation and comprises: a. A coagulation and flocculation step of the fluid to be treated, during which one or more coagulating and flocculating agents are injected into the fluid to be treated before it is directed to the flotation zone, b. A step of admitting the fluid to be treated and white water into the lower part of a mixing zone, said mixing zone being included within a flotation zone. This admission is advantageously implemented in an upward flow. The white water is pressurized water that is then expanded in such a way that micro-bubbles of air form. The air bubbles thus formed allow all the particles suspended in the fluid to be treated, agglomerated with the air bubbles, to be brought back to the surface of the mixing zone. c. A flotation step in a separation zone distinct from the mixing zone (e.g., separated by a wall). These particles, agglomerated with air bubbles and including colloidal silica, can then be discharged from the upper part of the separation zone. d. A step for recovering clarified fluid having a reduced PFAS concentration compared to the PFAS concentration of the fluid before contact with colloidal silica, in the lower part of the flotation zone, for example by means of perforated pipes connected to pipelines, or by any other means, e. Optionally, a recirculation step of all or part of the clarified water recovered in the lower part of the separation zone via a recirculation loop, advantageously allowing the generation of white water (micro air bubbles) injected into the mixing zone,

[0088] said process comprising a step of contacting the fluid with colloidal silica, said contacting step being implemented i. upstream of the coagulation and flocculation step and / or ii. downstream of the coagulation and flocculation step, and / or iii. when step e) is implemented, in the recirculation loop of all or part of the clarified water, said recirculated clarified water being advantageously used for the production of white water.

[0089] The white water used in the process can be obtained either by pressurizing and then expanding water, for example through a diffusion nozzle, or using a white water pump. The white water pump draws in atmospheric air and, through a shearing system, creates microbubbles in water, for example, to produce white water.

[0090] For the purposes of the present invention, white water is water containing micro air bubbles.

[0091] Preferably, according to this embodiment, the water is pressurized to a pressure in the range of 3 to 8 bars.

[0092] Thus, within the framework of the invention, this embodiment makes it possible to create fine air bubbles enabling the flotation of PFAS and colloidal silica. The size of the bubbles can vary from approximately 50 to 150 pm.

[0093] Thus, in this flotation embodiment, PFAS and colloidal silica form floated sludges which can be discharged into a separation zone.

[0094] The treated water will thus be advantageously recovered in the lower part of the flotation zone.

[0095] Reference will be expressly made to [Fig. 2] illustrating an installation for implementing a treatment process according to the invention. This is an example of a flotation treatment process.

[0096] Thus, according to a particular embodiment, the process of the invention comprises a flotation treatment which consists of passing the water through an installation comprising at least: - a water inlet zone to be treated 31 previously coagulated and flocculated; - a mixing zone 32 of pressurized and then depressurized water with said water to be dealt with; - a flotation zone 35 separated from said mixing zone 32 by a wall 34; - a clarified water recovery zone 36 provided in the lower part of said flotation zone 35;

[0097] said mixing zone 32 housing at least one diffusion nozzle 40 of said pressurized water, said diffusion nozzle 40 extending in the vicinity of a floor 33, at least part of which has perforations 331, said floor 33 separating said inlet zone 31 and said mixing zone 32.

[0098] According to this embodiment, the process also consists of admitting into said mixing zone an upward current of said water to be treated through said perforated floor, and a current of said pressurized water by means of said or said diffusion nozzles so as to form air bubbles capable of bringing particles suspended in said water to be treated back to the surface of said mixing zone.

[0099] According to this embodiment, colloidal silica can for example be injected using an injection device into the arrival zone 31.

[0100] With reference to [Fig.2], the clarified water recovery zone 36 is connected to a pipe 37 which extends outside the flotation zone 35 towards a weir (not shown), or to any other means, which allows the clarified water obtained after flotation treatment to be collected.

[0101] According to the embodiment illustrated in [Fig. 2], vertical partitions 39 extend transversely and substantially vertically in the flotation zone 35. The height of these partitions 39 can be between 30 and 300 centimeters. These partitions 39 The partitions 39 are solid and can be arranged at regular or irregular intervals. For example, they can be spaced between 30 and 300 centimeters apart. Preferably, the closer the partitions 39 are to the wall 34, the smaller the distance between them. In other embodiments, the partitions 39 may be perforated. This has the advantage of improving the distribution of clarified water over the entire horizontal surface of the clarified water intake zone. Furthermore, these partitions 39 may be designed to be removable, particularly to facilitate maintenance of the system. In addition, these partitions 39 are preferably made of stainless steel. In alternative configurations, they may be made of plastic materials. This can be particularly advantageous when treating seawater.

[0102] As illustrated in [Fig.2], this wall 34 is essentially vertical in its lower part and has in its upper part an inclined portion 341 towards the flotation zone 35. The implementation of this inclined portion 341 makes it possible in particular to facilitate the passage of water from the mixing zone to the flotation zone (arrow J).

[0103] These diffusion nozzles 40 can be connected to pressurized water production means 42 via pipes 41.

[0104] These pressurized water production means can be connected on the one hand to the pipe 37 in which the clarified water circulates by a tube 43, and on the other hand to an air production source 44.

[0105] Several rows 45 of a plurality of diffusion nozzles 40 can be arranged in parallel.

[0106] A water treatment plant for implementing a flotation clarification process according to the invention may optionally include a scraper (not shown in [Fig. 2]). Such a scraper allows the sludge, including in particular PFAS and colloidal silica, present in the water, floating in the upper part of the mixing zones 32 and flotation zones 35, as well as air bubbles introduced into the structure outside the flotation zone (arrow I) to be removed by recovery means 46.

[0107] A water treatment installation for implementing a clarification process by flotation according to the invention may optionally also include means for resuming clarified water. These water resuming means typically comprise a chamber 36, the lower face 361 of which is perforated over at least a portion of its surface to allow clarified water to enter it.

[0108] According to a second embodiment, the treatment process according to the invention is a foam fractionation treatment process.

[0109] According to this embodiment, the process for treating a fluid according to the invention shall comprise: - A step involving the introduction of the fluid into an air-fed reactor, thus forming a foam, - A fluid recovery step with a reduced PFAS concentration compared to the PFAS concentration of the fluid before contact with colloidal silica,

[0110] said process comprising a step of bringing the fluid into contact with colloidal silica, said contacting being carried out upstream of the reactor or in the reactor.

[0111] Thus, within the framework of the invention, this embodiment makes it possible to create a foam containing PFAS. The foam will then be positioned in the upper part of the reactor so that the treated fluid can be recovered in the lower part of the reactor.

[0112] According to this embodiment, a surfactant may optionally be added to promote foam formation. The addition of a surfactant may be particularly advantageous for promoting the trapping of PFAS with short chains, for example, a chain length of less than 8 carbon atoms.

[0113] Reference will be expressly made to [Fig. 3] illustrating an installation for implementing a treatment process according to the invention. This is an example of a foam fractionation treatment process.

[0114] With reference to [Fig. 3], the fluid to be treated, containing colloidal silica 21, is introduced into an air-supplied reactor 24 20, typically at the bottom of the reactor 24. During treatment in the reactor, foam forms. This foam contains PFAS and colloidal silica. This foam 22 can be discharged from the top of the reactor 24, and the treated fluid 23 can be recovered via a lower part of the reactor 24.

[0115] The invention can thus be implemented to treat PFAS in fluids, in particular industrial or municipal waters or drinking water or water to be made potable.

[0116] In particular, the invention can be coupled with other techniques for treating pollutants in fluids, for example adsorbents, for example ion exchange resins, zeolites, modified clays or activated carbons.

[0117] The reduction of PFAS is particularly effective when PFAS concentrations are, for example, at least 20 ng / L or even at least 50 ng / L or at least 100 ng / L. Examples

[0118] In the examples, colloidal silica was brought into contact with water contaminated with PFAS, the water and colloidal silica mixture was centrifuged and filtered. This process reproduces on a laboratory scale the principle of two-phase separation of the fluid and the contaminant-laden silica. After filtration, treated water was collected on one side and sludge containing the silica and PFAS was collected on the other.

[0119] Table 1 below summarizes the results on PFAS removal under different implementation conditions (initial pH, type of colloidal silica, quantity of colloidal silica); the final pH is also indicated. The final pH corresponds to the pH of the mixture comprising the water to be treated and the colloidal silica.

[0120] The reduction corresponds to the proportion by mass of PFAS that has been treated in the water.

[0121] [Tables 1] Initial pH 5 7 10 7 7 Final pH 7.1 6.9 7.2 3.6 7.4 Colloidal silica Diameter (nm) 80 80 80 12 12 Charge negative negative negative positive negative Concentration (g / L) 100 100 100 50 100 PFAS reduction % 61 12 65 17 16

[0122] The results in Table 1 show that colloidal silica makes it possible to reduce the concentration of PFAS present in water.

Claims

Demands

1. A process for treating a fluid containing perfluoroalkyl and / or polyfluoroalkyl substances, said process comprising at least one step of contacting said effluent with colloidal silica and a step of recovering a fluid having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances of the fluid before contact with colloidal silica.

2. A process according to claim 1, wherein: a. the fluid is a liquid, in particular water and / or b. the total concentration of perfluoroalkyl and polyfluoroalkyl substances in the fluid before treatment with colloidal silica is at least 20 ng / L; and / or c. the colloidal silica has a particle size ranging from 5 nm to 500 nm, preferably from 10 to 300 nm.

3. A method according to any one of claims 1 to 2, further comprising a step of adjusting the pH of the fluid in order to regulate the pH of the fluid comprising the colloidal silica.

4. A method according to any one of claims 1 to 3, comprising, before the step of contacting the colloidal silica, a step of concentrating the fluid, preferably by reverse osmosis or by foam fractionation.

5. A method according to any one of claims 1 to 4, further comprising an adsorption step by passing the fluid, upstream or downstream of the contacting step, through an adsorbent material of the type ion exchange resins, modified clays, or activated carbon, preferably, this adsorption step being carried out downstream of the contacting step.

6. A method according to any one of claims 1 to 5, selected from a clarification method or a foam fractionation method.

7. A method according to any one of claims 1 to 6, comprising: a. A step of coagulation and flocculation of the fluid to be treated, b. A step of settling the fluid containing colloidal silica, c. A fluid recovery step having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in the fluid before contact with colloidal silica, said process comprising, upstream or downstream of the coagulation and flocculation step, a step of bringing the fluid into contact with colloidal silica implemented, preferably upstream of the coagulation and flocculation step.

8. A method according to any one of claims 1 to 6, comprising: a. A step involving coagulation and flocculation of the fluid to be treated, b. A step of admitting the fluid to be treated and white water into a lower part of a mixing zone included within a flotation zone, c. A flotation step in a separation zone distinct from the mixing zone, d. A step for recovering clarified fluid having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in the fluid before contact with colloidal silica, e. possibly a recirculation step of all or part of the clarified water recovered in a lower part of the separation zone via a recirculation loop, said process comprising a step of bringing the fluid into contact with colloidal silica, said contacting step being carried out (i) upstream of the coagulation and flocculation step and / or (ii) downstream of the coagulation and flocculation step, and / or (iii) when step e) is carried out, in the recirculation loop of all or part of the clarified fluid.

9. A method according to any one of claims 1 to 6, comprising:

10.

11.

12.

13.

14. - A step involving the introduction of the fluid into an air-fed reactor, thus forming a foam, - A fluid recovery step having a reduced concentration of perfluoroalkyl and / or polyfluoroalkyl substances compared to the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in the fluid before contact with colloidal silica, said process includes a step of bringing the fluid into contact with colloidal silica, said contact being implemented upstream of the reactor or in the reactor. A process according to claim 9, further comprising a step of adding a surfactant-type agent to the reactor. Use of colloidal silica to reduce the concentration of perfluoroalkyl and / or polyfluoroalkyl substances in a fluid. Use according to claim 11, wherein the fluid is a liquid, in particular water. Use according to claim 11 or 12, wherein the total concentration of perfluoroalkylated and polyfluoroalkylated substances in the fluid before treatment with colloidal silica is at least 20 ng / L. Use according to any one of claims 11 to 13, wherein the colloidal silica has a median particle diameter ranging from 5 nm to 500 nm, preferably from 10 to 300 nm.

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