Process and plant for treating water by flotation incorporating a pollutant retention system

Abstract

The present invention relates to a process for treating a liquid aqueous effluent by flotation, the aqueous effluent containing amphiphilic molecules, the process comprising: - a flotation step during which the aqueous effluent is introduced and circulated inside the chamber, and brought into contact with a bed of bubbles generated by a bubble-generating device, at least some of the amphiphilic molecules adhering to the surface of the bubbles, - a step of separating a floating phase located inside the chamber at the surface of the aqueous effluent, the floating phase containing the bubbles combined with the amphiphilic molecules that have risen to the surface of the aqueous effluent. During the flotation step, the aqueous effluent and the bubbles combined with the amphiphilic molecules entrained by the aqueous effluent pass through a retention system located inside the chamber and kept firmly connected thereto and comprising at least one retaining material.

Description

Process and installation for water treatment by flotation integrating a pollutant retention system Field of invention

[0001] The invention relates to methods for treating water by flotation incorporating a pollutant retention system. The method and the treatment installation according to the invention are particularly suitable for removing amphiphilic molecules, containing a hydrophilic part and a hydrophobic part, from water to be treated. The method and the treatment installation of the present invention are thus particularly suitable for removing amphiphilic molecules such as detergents, lipids, surfactants, and particularly fluorinated molecules such as perfluoroalkyl and polyfluoroalkyl substances, from water. State of the prior art

[0002] Human activity produces contaminated liquid discharges (drilling water, drinking water, urban or industrial water, liquid discharges from treatment plants, etc.) that must be treated before they can be reused or released into the environment. The contaminants present in these liquid discharges include amphiphilic molecules, including perfluoroalkyl and polyfluoroalkyl substances, also known by the acronym "PFAS." These molecules are organofluorine compounds with a fully or partially fluorinated hydrophobic alkyl chain. Their structure is thus composed of a fluorinated carbon chain at the end of which is a functional group. This functional group can be a carboxyl group (-COOH), a carboxylate group (-COO-), a sulfonic acid group (-SO3H) or a sulfonate group (-SO3-).

[0003] PFAS are a family of over 4,700 emerging man-made compounds, the most well-known of which are perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonic acids (PFSAs). PFAS have been used since the 1940s in numerous industrial applications, such as firefighting foams, coatings, textile stain repellents, etc., due to their surfactant properties. PFAS can be released into the environment through many routes, including air, soil, and water, and have been detected in water sources, soils, and biological samples.

[0004] PFAS are therefore a problem as emerging organic contaminants, partly because they are widely present in wastewater effluents and resources used for drinking water production worldwide, and partly because of their environmental stability, bioaccumulation potential, and negative health effects. Due to growing concerns about the effects of PFAS on ecology and human health, regulations concerning them are increasingly important. This has led to the development of processes to remove or concentrate them.

[0005] Flotation processes have been considered in particular for the treatment of PFAS.

[0006] Flotation is a solid-liquid or liquid-liquid separation process which is applied to aggregates and / or particles whose density is lower than that of the liquid which contains them, these aggregates and / or particles being collected, ultimately, in the form of scum (floated sludge) on the upper surface of the flotation chamber.

[0007] Flotation is said to be “natural” when the difference in density between the aggregates and / or particles and the liquid which contains them is naturally sufficient to allow their separation.

[0008] This separation can be improved by blowing a gas into the liquid to be treated. This is called "assisted" flotation. Finally, flotation is called "induced" when the density of the aggregates and / or particles is greater than the density of the liquid that contains them. Their density is then artificially reduced by blowing a gas leading to the formation of bubbles on the surface of which the aggregates and / or particles can unite, forming clusters that are less dense than the liquid that contains them.

[0009] There are also processes in which flotation is induced by floating particles, which are recirculated inside the flotation chamber. This addition of floating particles aims to limit, or even eliminate, the supply of gas. This is the case, for example, of the processes described in documents US6890431B1 and FR2934582A1. The process described in document FR2934582A1 can in particular be implemented without the addition of gas.

[0010] However, these processes may prove unsuitable or insufficient for eliminating contaminants dissolved in the water to be treated, such as PFAS, particularly regardless of the length of their carbon chain.

[0011] There is therefore a need to improve the removal of amphiphilic molecules, and in particular PFAS, from aqueous effluent. Summary

[0012] The present invention relates to a method for treating a liquid aqueous effluent by flotation in a flotation chamber equipped with at least one bubble generating device capable of generating a bed of bubbles inside the liquid present in the chamber, the aqueous effluent containing amphiphilic molecules, the method comprising: - a flotation step during which the aqueous effluent is introduced and circulated inside the flotation chamber, and brought into contact with a bed of bubbles generated by the at least one bubble generating device, at least a portion of the amphiphilic molecules adhering to the surface of the bubbles, - a step of separating a floating phase located inside the chamber at the surface of the aqueous effluent, the floating phase containing the bubbles associated with the amphiphilic molecules raised to the surface of the aqueous effluent.

[0013] Furthermore, according to the invention, during the flotation step, the aqueous effluent and the bubbles associated with the amphiphilic molecules entrained by the aqueous effluent pass through a physicochemical retention system located inside the enclosure at least in part, preferably totally, inside the bed of bubbles and held integral with said enclosure, the physicochemical retention system comprising at least one physicochemical retention material capable of retaining at least a portion of the amphiphilic molecules present in the aqueous effluent, at least a portion of the amphiphilic molecules adhering to the surface of said bubbles being retained on a surface of the physicochemical retention material and / or inside pores of said physicochemical retention material.

[0014] The method according to the invention makes it possible to improve the separation of a portion of the amphiphilic molecules present in the liquid aqueous effluent. Indeed, a portion of the amphiphilic molecules, depending on their concentration in the system, will naturally form micelles which will rise in the floating phase to then be separated. However, certain molecules, in particular those with short carbon chains, will not naturally form micelles, making their separation by flotation difficult. Their adhesion to the surface of the gas bubbles formed then allows their transport to the surface of the aqueous effluent. In other words, the bubbles serve as a vector, i.e. a transport agent, for these molecules.Thus, all the amphiphilic molecules present will pass through the chemical retention system in the form of micelles and / or hemi-micelles, adhering to the gas bubbles, or simply transported by the aqueous effluent, allowing their retention on the surface and / or inside the pores of the physicochemical retention material. There is then a displacement of a part of the amphiphilic molecules from the liquid phase to a solid phase, which can facilitate their evacuation or subsequent treatment.

[0015] Furthermore, by controlling the size of the generated bubbles, the contact time between the physicochemical retention material and the liquid aqueous effluent can be modified, which can promote the retention of amphiphilic molecules by the physicochemical retention material.

[0016] Typically, the method may further comprise a step c) of recovering the purified aqueous effluent (i.e. the treated water) during which the purified aqueous effluent is discharged from the flotation chamber via a discharge pipe opening into the chamber below the physicochemical retention system and outside the bubble bed.

[0017] Advantageously, the at least one physicochemical retention material may be in particulate form, in foam form, in gel form or in fiber form.

[0018] Advantageously, the at least one physicochemical retention material may comprise a plurality of pores, for example pores of determined dimensions.

[0019] In this case, during the flotation step, bubbles can be generated whose dimensions are smaller than the dimension of at least one pore of the at least one physicochemical retention material. Thus, the bubbles formed can circulate inside the pores of the latter and transport the amphiphilic molecules adhering to their surface inside the pores for the purpose of their retention.

[0020] Advantageously, the method may comprise, at determined time intervals, a step of replacing at least part of the at least one physicochemical retention material. This step makes it possible to renew all or part of the physicochemical retention material and thus maintain the overall retention capacity of the physicochemical retention system.

[0021] Advantageously, the method may comprise at least one of the following characteristics: - during the flotation step, the generation of bubbles is discontinuous over time, - during the flotation step, the bubbles are generated using a gas chosen from air, in particular ambient air, ozone, nitrogen, oxygen, chlorine, chlorine dioxide.

[0022] Discontinuous generation of bubbles over time can prevent bubble accumulation in the installation.

[0023] Advantageously, at least part of the separated floating phase can be returned to the interior of the enclosure.

[0024] Circulating the floating phase increases the removal efficiency of amphiphilic molecules by increasing their concentration in the aqueous effluent. This increase in concentration will promote the formation of micelles within the aqueous effluent and thus promote their retention by the physicochemical retention system. Circulating the floating phase also reduces the energy requirement for generating bubbles and reduces the amount of chemical reagents, such as a surfactant, a coagulant, a flocculant, an acid or base for pH adjustment, promoting the flotation of amphiphilic molecules that may be added.

[0025] Advantageously, at least part of the separated floating phase can be degassed in a storage tank before being returned to the interior of the enclosure. This implementation is advantageous for discontinuous operation of the reactor.

[0026] In particular, the sludge deposited at the bottom of the storage tank can then be removed. Extracting the sludge from the bottom of the storage tank can improve flotation. The extracted sludge can be sent to a sludge treatment plant.

[0027] Advantageously, the separated floating phase, optionally degassed, can be returned, in part or in full, inside the enclosure, continuously or not over time, until at least one target concentration of at least one contaminant is obtained inside the enclosure. This target concentration can correspond to a concentration beyond which a given contaminant naturally forms aggregates.

[0028] The method may further comprise, in combination or not with the different embodiments of the invention, a control of a quantity of floating phase, optionally degassed, returned, inside the enclosure, and / or of a duration of injection of the floating phase inside the enclosure, in particular as a function of at least one target concentration of at least one contaminant inside the enclosure.

[0029] Advantageously, the method may comprise at least one of the following characteristics:- at least one chemical compound chosen from a flotation aid compound (surfactant), a flocculation aid compound, a coagulation aid compound and a pH modification compound (acid or base) is added to the aqueous effluent before it enters the enclosure,- at least one chemical compound chosen from a flotation aid compound, a flocculation aid compound and a coagulation aid compound is introduced into the enclosure by the bubble generation device.

[0030] The addition of a chemical flotation aid compound and / or a chemical coagulation aid compound and / or a chemical flocculation aid compound and / or a chemical pH modification aid compound can promote the formation of micelles by amphiphilic molecules.

[0031] Advantageously, the amphiphilic molecules can be chosen from perfluoroalkyl substances and polyfluoroalkyl substances.

[0032] The invention also relates to an installation for the treatment by flotation of a liquid aqueous effluent containing amphiphilic molecules, the installation comprising a flotation chamber, at least one device for circulating the liquid within the flotation chamber, at least one bubble generation device capable of generating a bed of bubbles inside the liquid present in the flotation chamber and at least one device for separating a floating phase on the surface of the liquid present in the flotation chamber.According to the invention, the installation further comprises, inside the enclosure and held integral with said enclosure, a physicochemical retention system comprising at least one physicochemical retention material capable of retaining at least a portion of the amphiphilic molecules present in said liquid aqueous effluent, said physicochemical retention system being located at least in part, preferably totally, inside a bed of bubbles generated within the liquid present in the flotation enclosure by the bubble generation device.

[0033] The method according to the invention can in particular be implemented by the installation according to the invention.

[0034] The physicochemical retention system may comprise at least one physicochemical retention material in particulate, foam or gel form and at least one holding device secured to the enclosure extending transversely to a direction of circulation of the liquid flow inside the enclosure, the holding device having a plurality of through passages whose dimensions are smaller than the dimensions of the at least one physicochemical retention material.

[0035] Alternatively or in combination, the physicochemical retention system may comprise at least one physicochemical retention material in the form of fibers and at least one holding device secured to the enclosure and forming a support to which the fibers are fixed.

[0036] Advantageously, the installation may comprise at least one of the following characteristics: - at least one discharge pipe for the purified aqueous effluent opening into the flotation chamber below the physicochemical retention system, outside the bubble bed generated by the bubble generation device, - at least one recirculation pipe fluidly connecting the at least one device for separating the floating phase to the flotation chamber, optionally at least one storage tank fluidly connected to said recirculation pipe between the separation device and the flotation chamber, - at least one storage capacity for a chemical compound fluidly connected to the flotation chamber, - at least one storage capacity for a chemical compound fluidly connected to the bubble generation device.

[0037] The installation may also comprise, in combination with the various embodiments described, a system for controlling a quantity of floating phase, optionally degassed, returned to the interior of the enclosure, and / or a duration of injection of the floating phase, optionally degassed, to the interior of the enclosure, optionally as a function of at least one target concentration of at least one contaminant inside the enclosure. Definitions

[0038] The terminology used herein is for the sole purpose of describing particular embodiments and is not intended to limit the subject matter disclosed. Although the following terms are expected to be well understood by a person of ordinary skill in the art, the following definitions are set forth to facilitate the explanation of the subject matter currently disclosed.

[0039] All technical and scientific terms used herein, unless otherwise defined below, have the same meaning as commonly understood by a person of ordinary skill in the art. References to techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations of such techniques or substitutions for equivalent techniques that would be apparent to a person skilled in the art. In describing the subject matter now disclosed, it will be understood that a number of techniques and steps are disclosed. Each of these has an individual advantage and each may also be used in conjunction with one or more, or in some cases all, of the other techniques disclosed.

[0040] The acronym PFAS refers to the group of perfluoroalkyl substances and polyfluoroalkyl substances.

[0041] Perfluoroalkyl substances are molecules containing a fully fluorinated (perfluorinated) alkyl group. Their basic chemical structure is a carbon chain (or tail) of two or more carbon atoms associated with a polar functional group (or head): acid (carboxylic, sulfonic, sulfinic, phosphonic, phosphinic, etc.), sulfonamide, iodide, aldehyde, etc. The most common functional groups are carboxylates or sulfonates, but other forms are also detected in the environment. Fluorine atoms are attached to all possible bonding sites along the carbon chain of the tail, except for a bonding site on the last carbon where the head of the functional group is attached. The chemical formula of these substances can be written C n F 2n+1 -R, where "C n F 2n+1" defines the length of the tail of the perfluoroalkyl chain, "n" is >2, and "R" represents the head of the attached functional group. The functional group can contain one or more carbon atoms, which are included in the total number of carbons when naming the compound.

[0042] Perfluoroalkyl acids (commonly referred to by the acronym "PFAAs") are among the most fundamental PFAS molecules. They are essentially non-degradable and are currently the most frequently detected class of PFAS in the environment. The PFAA class is divided into two main groups:

[0043] - Perfluoroalkylcarboxylic acids of formula C n F 2n+1 -R, with R=-COOH, or perfluoroalkylcarboxylates of formula C n F 2n+1-R, with R=-COO-, designated by the same acronym "PFCA", are degradation products of polyfluoroalkyl substances, such as fluorotelomer alcohols (designated by the acronym "FTOH"). The most frequently detected PFCA is perfluorooctanoic acid, C7F 15 COOH (designated by the acronym “PFOA”).

[0044] - Perfluoroalkane sulfonic acids of formula C n F 2n+1 -R, with R=-SO3H, or perfluoroalkyl sulfonates of formula C n F 2n+1 -R, with R=-SO3 - , designated by the same acronym PFSA, are also terminal degradation products of certain polyfluoroalkyl substances, such as perfluoroalkyl sulfonamidoethanols (designated by the acronym "FASE"). The most frequently detected FASE is perfluorooctane sulfonate, C8F 17 SO3 - (designated by the acronym “PFOS”).

[0045] Perfluoroalkane sulfonamides of formula C nF 2n+1 -R, with R=-SO2-NH2, designated by the acronym "FASA", such as perfluorooctane sulfonamide (FOSA, C8F 17 SO2NH2), are used as raw materials to manufacture perfluoroalkane sulfonamide substances which are used for surfactants and surface treatments. FOSA can degrade to form PFAAs such as PFOS.

[0046] Polyfluoroalkyl substances are distinguished from perfluoroalkyl substances by the fact that they are not fully fluorinated. Instead, they have an atom other than fluorine (usually hydrogen or oxygen) attached to at least one carbon atom, but not all carbon atoms, while at least two or more of the remaining carbon atoms in the tail of the carbon chain are fully fluorinated. The carbon-hydrogen bond (or other non-fluorinated bond) in polyfluoroalkyl molecules creates a "weak" point in the carbon chain that is susceptible to biotic or abiotic degradation. Therefore, many polyfluoroalkyl substances that contain a perfluoroalkyl group C n F 2n+1 are potential precursor compounds that could be transformed into PFAAs.

[0047] The term “long-chain PFAS” generally refers to:

[0048] - perfluoroalkylcarboxylic acids, PFCAs, containing eight or more carbon atoms (seven or more carbon atoms are perfluorinated),

[0049] - perfluoroalkane sulfonates, PFSA, with six or more carbon atoms (six or more carbon atoms are perfluorinated),

[0050] - and for all other perfluoroalkyl and polyfluoroalkyl substances, to PFAS having a carbon chain of six or more carbon atoms.

[0051] The term “short-chain PFAS” generally refers to:

[0052] - perfluoroalkylcarboxylic acids containing seven or fewer carbon atoms (six or fewer carbon atoms are perfluorinated),

[0053] - perfluoroalkane sulfonates with five or fewer carbon atoms (the five or fewer carbon atoms are perfluorinated),

[0054] - and for all other perfluoroalkyl and polyfluoroalkyl substances to PFAS having a carbon chain of five carbon atoms or less. Detailed description

[0055] Liquid aqueous effluent

[0056] The effluent treated by the present invention may comprise, or consist of, one or more liquid aqueous effluents. The liquid aqueous effluent to be treated contains amphiphilic molecules, in particular amphiphilic molecules chosen from perfluoroalkylated substances and polyfluoroalkylated substances, or any amphiphilic molecule capable of forming micelles, such as surfactants, soaps, detergents and emulsifiers.

[0057] Aqueous liquid effluents within the meaning of said invention include raw water, urban effluents, industrial effluents and discharges from drinking water treatment plants.

[0058] Raw water within the meaning of said invention includes any water intended for the production of drinking water, such as groundwater or surface water.

[0059] Urban effluents include wastewater, leachate, and waste truck wash effluents. Wastewater includes urban wastewater, namely domestic wastewater from households, municipal wastewater from public, commercial, and institutional facilities, and possibly industrial wastewater (a by-product of industrial or commercial activities).

[0060] Industrial effluents include liquid waste and / or wastewater discharged from industrial activities, including leachate and pre-treated or untreated incinerator flue gas wash water. Leachate is the result of water percolating through domestic, agricultural, or industrial waste stored in a landfill.

[0061] Urban or industrial effluents include, in particular, liquid discharges from water treatment systems, particularly drinking water. These liquid discharges include, in particular, concentrates from reverse osmosis units, concentrates from nanofiltration units, eluates from the regeneration of ion exchange resins, and eluates from chemical regeneration units for adsorbent materials such as activated carbon.

[0062] The aqueous effluent to be treated may in particular comprise a concentration of amphiphilic molecules, and in particular PFAS, of 0.2µg / L or more, preferably of 0.2µg / L to 200µg / L.

[0063] To facilitate the implementation of the method according to the invention, the effluent may also have a turbidity of at most 5 NTU (Nephelometric Turbidity Unit). The turbidity is measured with a turbidimeter, for example of the Hach brand.

[0064] Detailed description of the process

[0065] The method according to the invention makes it possible to eliminate amphiphilic molecules and in particular PFAS, from a liquid aqueous effluent, in particular as previously defined, this elimination combining the flotation purification technique, the generation of bubbles serving as vectors for the amphiphilic molecules and the physicochemical retention of the amphiphilic molecules by a suitable physicochemical retention material.

[0066] For this purpose, it comprises a flotation step implemented in a flotation chamber inside which is fixedly held a physicochemical retention system comprising at least one physicochemical retention material capable of retaining the amphiphilic molecules present in the liquid aqueous effluent. The combination of flotation and at least one physicochemical retention material makes it possible to improve the elimination of amphiphilic contaminants.

[0067] By "physicochemical retention" is meant the capacity to retain a molecule by adsorption, absorption, ion exchange and / or by steric retention (capture of molecules inside the pores according to the respective sizes of the molecules and pores). Physicochemical retention within the meaning of the present invention thus allows the retention of molecules present in a dissolved state in the liquid aqueous effluent to be treated.

[0068] The invention can in particular be implemented with any type of physicochemical retention material, including non-floating materials, held in the reactor at the level of the bubble bed by a holding device, serving as a separator / fixer depending on the nature of the material, flotation being obtained by the generation of gas bubbles, which makes it possible to choose a physicochemical retention material specifically adapted to the amphiphilic contaminant to be eliminated.

[0069] Typically, the method further comprises a step of discharging the purified aqueous effluent (depleted in amphiphilic molecules) from the flotation chamber. This discharge of the treated water is generally carried out continuously, typically at an area located downstream of the retention system relative to a direction of circulation of the aqueous effluent flow inside the flotation chamber.

[0070] In particular, this evacuation can be carried out by means of an evacuation pipe opening inside the flotation enclosure, below the physicochemical retention system (and consequently outside it), and outside the bed of bubbles generated by the bubble generation device when the latter is operating.

[0071] Flotation stage

[0072] The flotation step is carried out in a flotation chamber equipped with at least one bubble generation device for generating a bed of bubbles within the aqueous effluent inside the chamber. When carrying out this step, the bed of bubbles is generally located at a distance from the bottom of the flotation chamber and the level of the liquid inside the chamber. In other words, the bed of bubbles does not extend over the entire height of the liquid contained inside the flotation chamber.

[0073] The term "bubble bed" is used to mean an area of ​​the flotation chamber in which bubbles are predominantly present. This area, forming a bubble bed, extends over a height less than the total height of the chamber, away from the surface of the liquid and the bottom of the chamber, in particular away from the floor generally present in flotation chambers. This area generally extends over the entire surface of the chamber transversely to a direction of circulation of the aqueous effluent flow inside the chamber. The floor is typically a horizontal wall provided with a plurality of orifices allowing the liquid aqueous effluent to pass through it. The treated water is generally discharged from the chamber via one or more pipes opening inside the chamber, under the floor.

[0074] During this flotation stage, the aqueous effluent is introduced into the flotation chamber and circulated within it by a circulation device. For example, a pump or any other device normally used in a flotation chamber could be used.

[0075] During this circulation, the aqueous effluent will thus pass through the bed of bubbles and be brought into contact with them. The contact of the liquid effluent with the bubbles will allow at least some of the amphiphilic molecules, in particular those which form micelles least easily (due to their intrinsic properties and / or the properties of the aqueous effluent), to adhere to the surface of the bubbles. These gas bubbles associated with amphiphilic molecules tend to rise to the surface of the liquid effluent, they will find themselves, at least in part, in a floating phase on the surface of the liquid effluent. It is thus understood that the gas bubbles serve as vectors for some of the amphiphilic molecules.

[0076] Furthermore, during this flotation step, at least some of the amphiphilic molecules, in particular those which easily form micelles (due to their intrinsic properties and / or the properties of the aqueous effluent), will also form micelles which will aggregate and form foams which will tend to rise to the surface of the liquid, and to end up, at least in part, in the floating phase.

[0077] During the flotation step, the aqueous effluent and the bubbles associated with the amphiphilic molecules entrained by the aqueous effluent will pass through a physicochemical retention system located inside the enclosure and maintained integral with it, and comprising at least one physicochemical retention material capable of retaining at least a portion of the amphiphilic molecules present in the aqueous effluent. The physicochemical retention system is located at least in part, and preferably completely, inside the bubble bed in the flotation enclosure. Thus, the physicochemical retention system also does not extend over the entire height of the liquid present inside the flotation enclosure. In particular, it is located above and at a distance from the bottom of the flotation enclosure in order to allow evacuation of the treated water outside the chemical retention system.

[0078] When the bubbles pass through the physicochemical retention material, at least some of the amphiphilic molecules adhering to the surfaces of the bubbles will thus be retained on the surface of the physicochemical retention material and / or inside pores of the physicochemical retention material. The bubbles thus serve as a vector for the amphiphilic molecules. Without wishing to be bound by a theory, this physicochemical retention may result from the adhesion of the amphiphilic molecules associated with the bubbles to the internal and / or external surface of the bubbles, in particular by an adsorption, absorption or ion exchange mechanism. Since the aqueous effluent passing through the physicochemical retention system also contains amphiphilic molecules, whether or not shaped as micelles, these amphiphilic molecules may also be retained on the surface of the physicochemical retention material and / or inside pores of the physicochemical retention material.Furthermore, the amphiphilic molecules in the form of micelles which have not been retained by the physicochemical retention system are found in the floating phase and can then be separated in the usual manner, or returned to the flotation stage, as explained below.

[0079] Thus, amphiphilic molecules that easily form micelles (due to their intrinsic properties and / or the properties of the aqueous effluent), such as long-chain PFAS, will primarily form micelles that can be partly retained by the physicochemical retention system and partly accumulate on the surface of the aqueous effluent in the floating phase. This predominantly micelle configuration does not exclude the possibility that some of these amphiphilic molecules adhere to the surface of the bubbles without being shaped into micelles.

[0080] Amphiphilic molecules that do not easily form micelles (due to their intrinsic properties and / or the properties of the aqueous effluent), such as short-chain PFAS, will primarily adhere to gas bubbles that can bring them to the physicochemical retention material and can thus be partly retained by the physicochemical retention system and partly accumulate on the surface of the aqueous effluent in the floating phase. Some of these amphiphilic molecules will nevertheless also be able to form micelles.

[0081] Thus, the method according to the invention makes it possible to optimize the elimination of amphiphilic molecules, and in particular PFAS, regardless of the propensity of these molecules to form micelles. It is in particular possible to select the at least one physicochemical retention material of the physicochemical retention system according to the nature of the amphiphilic molecules present in order to optimize their retention. For this purpose, it is in particular possible to provide two or more different physicochemical retention materials in the physicochemical retention system.

[0082] During the flotation stage, the bubbles are generated by the bubble generation device. Typically, the bubbles are generated by means of a bubble generation device which will inject, into the liquid aqueous effluent inside the flotation chamber, a liquid supersaturated with gas. Under the effect of the expansion of the gas inside the flotation chamber, gas bubbles form by rising to the surface of the flotation chamber, carrying with them some of the amphiphilic molecules and forming a bed of bubbles. The liquid used is generally water (this is then referred to as "white water") or an aqueous effluent, for example the treated aqueous effluent leaving the flotation chamber.

[0083] The gas used to saturate the injected liquid may be selected from air, ozone, nitrogen, oxygen, chlorine, and chlorine dioxide. Preferably, air is used.

[0084] Bubble generation can be achieved by the usual techniques used in flotation, for example by dissolution under pressure (dissolution of the gas in a liquid medium at higher pressure then expansion of the mixture), by rotational flow (introduction of the liquid from above into a cylindrical tank, the liquid flowing in a spiral downwards, with gas suction in the lower part of the tank), by means of a turbulent static mixer, by means of an ejection nozzle or by means of a hammer mill.

[0085] In one embodiment, the generation of bubbles may be discontinuous over time. The generation of bubbles is then intermittent. This may allow the transport of amphiphilic contaminants to be controlled.

[0086] In step a), the bubbles (i.e. gas-filled cavities) generated may be fine bubbles with a diameter of less than 100 µm, microbubbles with a diameter of 1 µm to 100 µm, or ultrafine bubbles with a diameter of at most 1 µm. Fine bubbles, microbubbles and ultrafine bubbles are as defined in ISO 20480-1:2017. The diameter of a bubble corresponds in particular to the diameter of a sphere of the same volume as the bubble.

[0087] Preferably, the bubbles generated during the flotation step of the present invention are smaller than the bubbles used in conventional flotation processes. Thus, ultrafine bubbles will preferably be used, having a diameter of at most 200nm, preferably at most 100nm, more preferably at most 50nm, much smaller than the diameter of the bubbles used in conventional flotation processes (of the order of 50µm).

[0088] The size of the bubbles can be measured by laser scattered light measurement.

[0089] It may be possible to adjust the contact time between the effluent to be treated and the at least one retention material of the retention system and / or between the aqueous effluent and the bubbles, for example by adjusting the flow rate of the aqueous effluent and / or the size of the bubbles.

[0090] For example, an aqueous effluent / retention material contact time of at least 5 minutes, preferably at least 10 minutes, advantageously at least 30 minutes, typically at most 60 minutes may be provided.

[0091] The bubble size and contact time can be adjusted depending on the effluent to be treated, and in particular the quantity and type of amphiphilic molecule to be separated to promote the retention of amphiphilic molecules in the physicochemical retention material and / or in the floating phase.

[0092] When the physicochemical retention material is porous, it is advantageous to generate bubbles having a diameter smaller than the dimension of at least one pore of the porous material. For example, during the flotation step, the bubbles generated may have a diameter of less than 50nm, while the porous retention material(s) has pores of at least 50nm in dimension.

[0093] Depending on the nature of the amphiphilic molecules present, their conformation into micelles can be favored by the properties of the aqueous effluent, namely its pH and / or its content of chemical compounds to aid flocculation (polymers) and / or its content of chemical compounds to aid coagulation and / or its content of chemical compounds to aid flotation (surfactants).

[0094] Thus, in one embodiment, during the flotation step, at least one chemical compound selected from a coagulation aid compound, a flocculation aid compound, a flotation aid compound (i.e., a surfactant), and a pH-modifying compound may be added to the aqueous effluent before it enters the enclosure and / or at least one chemical compound selected from a flotation aid compound, a flocculation aid compound, and a coagulation aid compound may be introduced into the enclosure by the bubble-generating device. These compounds may enhance foam formation by promoting the formation of micelles, and promote the association of amphiphilic molecules with the bubbles.

[0095] For example, the pH can be adjusted and controlled depending on the type of amphiphilic molecules to be treated.

[0096] The coagulation aid compound may be a conventionally used coagulant (iron or aluminum salts). A salt of a cation may also be used, for example chosen from the following cations: Fe 3+ , There 3+ , Al 3+ , That 2+ , Fe 2+ , K + .

[0097] The surfactant may advantageously be an anionic or cationic surfactant, with a charge opposite to a charge of an amphiphilic molecule to be removed. For example, cationic surfactants may be used to remove PFOA, for example chosen from cetyl-trimethyl-ammonium bromide (CTAB, C 19 H 42 BrN), tetra-n-butyl-ammonium bromide (TBAB, C 16 H 36 BrN), decyl-trimethyl-ammonium bromide (DTAB, C 13 H 30 BrN), n-octyl-trimethyl-ammonium bromide (OTAB, C 11 H 26 BrN).

[0098] The pH-modifying compound may be an acid, for example an inorganic acid such as HCl, H2SO4 or other, or an organic acid (citric, acetic acids) or a base, for example LiOH, NaOH, CsOH, Ba(OH)2, Na2O, KOH, K2O, CaO, Ca(OH)2, MgO, Mg(OH)2, preferably NaOH.

[0099] When the chemical compound is introduced into the enclosure by means of the bubble generation device, it can for example be mixed with the gas-supersaturated liquid.

[0100] Physicochemical retention system

[0101] The physicochemical retention system used in the present invention allows the retention of at least part of the amphiphilic molecules present in the aqueous effluent. This system is installed inside the flotation chamber, at least in part, and preferably totally, within the bed of bubbles generated during the flotation step.

[0102] Preferably, so that the entire aqueous effluent can pass through it, the physicochemical retention system may extend over the entire surface of the enclosure transversely to a direction of circulation of the flow of the aqueous effluent inside the enclosure. The retention system may for example be arranged horizontally, typically over the entire surface of the enclosure so that the entire aqueous effluent can pass through it.

[0103] Also preferably, the physicochemical retention system is arranged within the enclosure, at a distance from a bottom wall of the enclosure and at a distance from the liquid level inside the enclosure. In other words, the physicochemical retention system does not rest on the bottom of the enclosure. The physicochemical retention system may extend over a height of 100 cm or less.

[0104] In the area of ​​the enclosure comprising the physicochemical retention system, this direction of circulation of the aqueous effluent flow is typically from left to right as well as from top to bottom.

[0105] The physicochemical retention system is held integral with the enclosure and comprises at least one physicochemical retention material.

[0106] By "physicochemical retention material" is meant a material capable of retaining a molecule of interest, here an amphiphilic molecule, by adsorption, absorption, ion exchange and / or steric retention. Molecules can in particular be trapped (steric retention) in pores of the physicochemical retention material when it has any.

[0107] The physicochemical retention material has the function of retaining amphiphilic molecules on its external surface and / or on its internal surface inside pores if it has any. Free amphiphilic molecules can be retained directly by the physicochemical retention material as the aqueous effluent flows through the retention material, as can amphiphilic molecules in the form of micelles. Amphiphilic molecules can also be transported onto the surface of the physicochemical retention material and / or inside pores of the physicochemical retention material by bubbles.These different mechanisms make it possible to better distribute the amphiphilic molecules on the surface (internal and / or external) of the physicochemical retention material and thus to extend the lifetime of the physicochemical retention material since this makes it possible to maximize the physicochemical retention surface by optimizing the transport of the amphiphilic molecules over the entire available surface of the physicochemical retention material.

[0108] The physicochemical retention material can be porous and have a plurality of pores. In this case, it is most often in particulate form, for example in the form of powder or grains. The porosity of the retention material can be chosen according to the amphiphilic molecules to be removed, the size of the micelles likely to form and / or the size of the bubbles.

[0109] The physicochemical retention material may have nanopores (dimensions less than 2 nm), mesopores (from 2 to 50 nm) or macropores (dimensions greater than 50 nm). In one embodiment, the pore size may be greater than 50 nm.

[0110] The physicochemical retention material can be in particulate form, in foam form, in gel form or in fiber form.

[0111] In the case where it is in the form of fibers, the material can be held by at least one holding device secured to the enclosure and forming a support to which the fibers are fixed. This holding device can extend parallel to the direction of circulation of the liquid effluent flow inside the enclosure or transversely to this direction of circulation. In the latter case, the holding device has a plurality of through passages for the passage of the fluid. The holding device can for example be a plate, a grid or a net to which the fibers are fixed.

[0112] In the case where the physicochemical retention material is in particulate form, in the form of foam or gel, it can be held by at least one holding device integral with the enclosure extending transversely to a direction of circulation of the flow of the aqueous effluent inside the enclosure, each holding device having a plurality of through passages whose dimensions are smaller than the dimensions of the at least one retention material. This holding device can be a membrane, a net, a fabric or even a sieve or a grid.

[0113] The holding device may then form a pocket containing the material in particulate, foam or gel form. Alternatively, two holding devices extending transversely to the direction of circulation of the effluent flow and spaced apart from each other along this direction may be provided, the material in particulate form extending between the two. Alternatively, depending on the buoyancy of the physicochemical retention material, a single transverse holding device may be provided, either to prevent the material from settling at the bottom of the enclosure or to prevent the material from rising to the surface of the liquid.

[0114] When in particulate form, the physicochemical retention material can have a particle size of 0.1 mm to 1 cm.

[0115] The retention system may comprise one, two or more physicochemical retention materials, and one or more retention devices chosen according to the nature of the retention materials. For example, it may be possible to mix different materials in particulate, foam or gel form and / or to arrange layers of these materials in particulate, foam or gel form (each layer being, for example, separated by a retention device). It may also be possible to provide at least one material in particulate form and at least one material in the form of fibers, foam or gel, for example arranged in layers.

[0116] Preferably, the physicochemical retention system comprising at least one physicochemical retention material is installed partly, and preferably entirely, within a bed formed by the bubbles to promote the contact time between the two.

[0117] The physicochemical retention material thus retains the amphiphilic molecules present in the aqueous effluent passing through it. Since its retention capacity is limited, it is preferable to replace it regularly. Thus, in one embodiment, the method comprises, at determined time intervals, a step of replacing at least a portion of the at least one physicochemical retention material.

[0118] Depending on the nature of the physicochemical retention material and the holding device(s), some or all of the physicochemical retention material may be replaced. When a physicochemical retention material is in particulate form, it may be extracted via a pipe, with another pipe allowing the introduction of fresh material.

[0119] Advantageously, the used physicochemical retention material can then be destroyed, for example by incineration, or regenerated by thermal regeneration processes which also allow the destruction of amphiphilic molecules, or by destruction processes such as cavitation, oxidation, the Fenton process. The destruction of the used physicochemical retention material, for example by incineration, has the advantage of not generating polluted liquid effluent which would require subsequent treatment.

[0120] The physicochemical retention material may be chosen from (i) a cyclodextrin polymer, in particular a porous cyclodextrin polymer, supported or not on a solid substrate, (ii) activated carbon, in particular granulated or powdered activated carbon, (iii) organic clays, in particular those positively charged, (iv) inorganic-organic clays, in particular positively charged, (v) polymers of porous structure, capable or not of ion exchange, (vi) biochar or activated biochar, (vii) carbon fibers, (viii) polyacrylonitrile fibers, (ix) zeolites, (x) silica, in particular macroporous silica, (xi) a combination of two or more of the aforementioned materials.

[0121] The physicochemical retention material is typically chosen based on the type of amphiphilic molecules to be treated and may also be selected based on the composition of the aqueous effluent. The choice may be made based on existing literature or based on laboratory tests. The quantity of retention material to be used may be chosen based on the flow rate of liquid effluent to be treated and the quantity of amphiphilic contaminants to be removed.

[0122] Chemical retention materials that can be used in the present invention are, for example, described in document WO2022 / 018613 incorporated by reference. The main characteristics of the families of materials that can be used are recalled below.

[0123] (i) Cyclodextrin polymers and cyclodextrin polymers supported or not on a solid substrate.

[0124] Cyclodextrins (hereinafter referred to as "CDs") are a group of structurally related natural products formed during bacterial digestion of cellulose. The cyclodextrins used in the present invention may include cyclodextrin derivatives. Cyclodextrin polymers consist of two or more cyclodextrin macromolecules covalently linked together using a crosslinking agent. These cyclodextrin macromolecules may be natural or synthesized CDs, and optionally their derivatives.

[0125] (ii) Activated carbon

[0126] Activated carbon is a material consisting essentially of carbonaceous matter with a porous structure. It can be produced in a known manner by pyrolysis of precursors of natural origin (wood, bark, coconut shells, coal, peat, cotton, organic materials of various origins, etc.) or of synthetic origin (polyacrylonitrile (PAN), aramid fibers, etc.), this pyrolysis step being followed by a chemical or physical activation step. Activated carbon is generally effective in removing long-chain PFAS by hydrophobic interaction such as PFOS. Powdered activated carbon (PAC), superfine powdered activated carbon (SAC) or granular activated carbon (GAC) can be used for the removal of PFAS and other amphiphilic molecules.

[0127] (iii) Organic clays / (iv) inorganic-organic clays

[0128] Clay minerals are phyllosilicates with a natural layered structure in which negatively charged structures or sheets are held together by monovalent (sodium, potassium, lithium, etc.) or divalent (calcium, magnesium, barium, etc.) cations or other inorganic cations located in anionic galleries between the sheets. These cations can be exchanged by other organic / inorganic cations.

[0129] In the present invention, modified clays, including organoclays (phyllosilicates to which at least one organic modifier has been added) and inorganic-organic clays, may be used for the removal of amphiphilic molecules such as PFAS, for example PFOS or PFOA. Preferably, to improve the efficiency of PFAS removal, the organoclays may be modified with at least one cationic modifier, in particular an organic cation.

[0130] (v) Polymers with porous structure

[0131] Polymers with a porous structure, capable or not of ion exchange, include for example the Mycelx® polymer and anion exchange resins, in particular strongly basic anion exchange resins.

[0132] The anion exchange resins have a polymer matrix that can be selected from polyacrylic polymers, polystyrene polymers, polystyrene-divinylbenzene (PS-DVB) copolymers. Advantageously, strongly basic anionic resins can be chosen for the removal of PFAS, particularly short-chain PFAS. In addition, the functional group can preferably be hydrophobic for the efficiency of PFAS removal.

[0133] (vi) Biochar, activated or not

[0134] Biochar can also be used for the removal of amphiphilic molecules, including PFAS. The biochar may be pyrolyzed biomass biochar, biomass biochar produced by hydrothermal carbonization, or a combination thereof. The biomass may be selected from agricultural crop waste, forestry waste, algae, animal or human waste, industrial waste, municipal waste, anaerobic digester waste, plant material grown for biomass production, or a combination thereof.

[0135] The biochar may comprise a metal salt powder or granule. The metal salt may comprise iron, aluminum, calcium, magnesium, manganese, zinc, copper, or a combination thereof, and in some examples, the metal salt comprises ferrous or ferric cations, ferrate anions, or a combination thereof. In particular embodiments, the metal salt comprises ferric chloride.

[0136] (vii) Carbon fibers

[0137] Carbon fibers can also be used for the removal of amphiphilic molecules, including PFAS. Carbon fibers are fibers with a diameter generally between about 5 and 10 micrometers and are composed primarily of carbon. Their length is typically less than 150 µm.

[0138] (viii) Polyacrylonitrile fibers

[0139] Polyacrylonitrile (PAN) fibers are fibers made from a polymer that is part of the acrylic family. This polymer is used in particular for its adsorption properties of various compounds contained in aqueous effluents.

[0140] These fibers can optionally be functionalized, for example to make their surface cationic. For example, PAN fibers can be used whose surface is functionalized by an amidoxime group (-CNH2NOH).

[0141] The average diameter of PAN fibers, functionalized or not, is typically 500 to 600nm.

[0142] (ix) Zeolites and (x) silica

[0143] Zeolites are aluminosilicates with a porous structure. Zeolites of natural or synthetic origin, generally synthetic, with specific pore sizes can be used. Silica can also be used, particularly macroporous silica, typically with pores with a diameter greater than 50 nm, whether functionalized or not.

[0144] Separation stage

[0145] The process finally comprises a step of separating the floating phase present on the surface of the aqueous effluent located inside the enclosure, namely at the interface between the aqueous effluent and the air. The floating phase contains the bubbles associated with the amphiphilic molecules as well as the amphiphilic molecules arranged in micelles which have risen to the surface of the aqueous effluent.

[0146] The separation step is usually carried out by a separation device which may, for example, comprise a discharge pipe towards which the floating phase can generally be pushed by means of an overflow or scraping device provided for this purpose.

[0147] In one embodiment, at least a portion of the separated floating phase is returned to the interior of the enclosure. Before being returned to the interior of the flotation enclosure, the floating phase is preferably pre-degassed in a storage tank.

[0148] Recirculation of the floating phase limits discharges in liquid form and also promotes the formation of micelles since the concentration of amphiphilic molecules capable of forming micelles increases by adding the floating phase and the aqueous effluent. The foams from the floating phase can be recirculated in the form of foams or in the form of liquid (after degassing).

[0149] During this recirculation of the foams, sludge may settle at the bottom of the storage tank. This sludge can then be evacuated, which prevents suspended matter that has accumulated in the flotation chamber from being reintroduced inside the chamber and disrupting flotation.

[0150] It may be possible to control the quantity of floating phase reinjected inside the flotation chamber and / or its injection duration in order to reach and / or maintain at least one target concentration of at least one contaminant inside the chamber.

[0151] For this purpose, the quantity of floating phase, optionally degassed, injected inside the enclosure and / or the duration of this injection (injection continuously or not over time) can be regulated. This can in particular be implemented by means of a control system, at least one valve controlling the injection of the floating phase (degassed or not) inside the enclosure, and optionally at least one sensor for measuring contaminant concentrations.

[0152] The target concentration typically corresponds to a critical micellar concentration beyond which a chemical contaminant tends to flocculate naturally. When the contaminant is a biological contaminant, this target concentration corresponds to a concentration beyond which microorganisms tend to form aggregates naturally. These target concentrations can be determined by tests and / or simulations.

[0153] We can therefore consider one or more of the following controls:

[0154] - an injection of the entire floating phase (degassed or not), the control system then only regulating the injection duration (which can be continuous over time or not),

[0155] - the injection of a precise quantity of the floating phase (degassed or not) continuously, the control system then only regulating the quantity injected,

[0156] - the injection of a precise quantity for a determined duration (continuous or not) of the floating phase (degassed or not), the control system regulating both the quantity injected and the duration of injection.

[0157] In all cases, the control system may be programmed to increase the quantity injected and / or the injection duration when the concentration of at least one contaminant is lower than the target concentration, or conversely, reduce the quantity injected and / or the injection duration when the concentration of at least one contaminant is higher than the target concentration for this contaminant.

[0158] The control system can thus be configured, in particular programmed, for the implementation of the control of the quantity of floating phase injected and / or the injection duration, for example based on models or simulations. This is, for example, an automated data integration and conversion system.

[0159] The control system typically comprises one or more processors, for example a microprocessor, a microcontroller or other. It also comprises output or input / output interfaces. These may be wireless communication interfaces (Bluetooth, WIFI or other) or connectors (network port, USB port, serial port, Firewire® port, SCSI port or other). These input and / or output interfaces may form means of communication, optionally bidirectional, between the control system, the valve(s) controlling the injection of the floating phase (degassed or not) inside the enclosure, and possibly one or more sensors.

[0160] The control system may also include storage means which may be random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), flash memory, external memory or the like. These storage means may, among other things, store received data, measured values, calculated values, a database, models, and one or more computer programs.

[0161] The treated (purified) aqueous effluent, for its part, is discharged during a recovery step c) into an area close to the bottom of the enclosure via at least one discharge pipe. It can be reused to generate the bubbles, which reduces the energy consumption for forming the bubbles.

[0162] Steps a) and b) (and c)) of the process according to the invention are typically carried out continuously. Steps a) and c) are typically carried out simultaneously. The separation step b) can begin as soon as a floating phase is formed, during the flotation step a).

[0163] Depending on the desired effluent quality, the treated aqueous effluent may be subjected to flotation steps a) and separation b) again. This can be carried out in another flotation chamber or in the same chamber. The purified aqueous effluent can be used as drinking water, possibly after undergoing additional purification treatments, or discharged into the environment. Description of the drawings

[0164] The invention will be better understood with reference to the single figure, which shows an exemplary embodiment of the invention.

[0165] The represents the installation for treating a liquid aqueous effluent by flotation according to one embodiment of the invention.

[0166] In the figure, the arrows represent the direction of circulation of the aqueous effluent flow inside the flotation chamber.

[0167] With reference to the, the treatment installation 1 comprises a flotation chamber 30 connected to a supply pipe 20 for an aqueous effluent. The supply pipe 20 is equipped with a device 21 for circulating the liquid within the flotation chamber such as a pump. Of course, depending on the size of the chamber, one or more supply pipes and / or circulation devices are conceivable.

[0168] Optionally, the installation comprises a storage capacity 40 for a chemical compound such as a flocculation aid compound, a coagulation aid compound, a surfactant or a pH modification compound. The storage capacity 40 is fluidically connected to the flotation chamber 30 and in particular to the feed pipe 20 by a pipe 41. Depending on the nature and number of chemical compounds to be added, one or more storage capacities 40 may be provided. The pipe 41 may be equipped with a valve or the like for regulating the quantity of chemical compound added.

[0169] The flotation chamber 30 is generally separated into several parts, as shown. The invention is however not limited to a specific type of flotation chamber having a particular number of parts, any type of flotation chamber being usable. In general, the flotation chamber may comprise an optional coagulation and / or flocculation zone comprising at least one inlet through which the effluent to be treated enters and at least one outlet, a zone in which the bubbles are generated by the bubble generation device comprising at least one inlet receiving the effluent to be treated, possibly leaving the coagulation / flocculation zone, and an outlet, and a flotation zone comprising at least one inlet connected to the outlet of the bubble generation zone and at least one outlet for discharging the treated water and an outlet for discharging the floating phase.Typically, the physicochemical retention system is located in the flotation zone. Depending on the nature of the effluent to be treated, the coagulation and / or flocculation zone may be omitted.

[0170] In the example shown, the feed pipe 20 feeds a first part 31 of the flotation chamber. In the embodiment shown, the first part 31 comprises a mixer 32, useful in particular in the case where a chemical compound has been added or in the case where the floating phase is recirculated within the installation 1, to obtain a homogeneous mixture. This first part forms a coagulation and / or flocculation zone which can be omitted depending on the nature of the effluent.

[0171] The aqueous effluent then circulates in a second part 33 of the flotation chamber, typically separated from the first part 31 by a wall 34a extending from the bottom of the chamber. The second part 33 comprises a delimiting wall 34b providing a passage with the bottom of the chamber for the fluid: the fluid thus circulates downward (toward the bottom of the chamber) when it enters the second part, then upward (toward the surface of the aqueous effluent) until it leaves the second part 33. The second part 33 also has a bubble generation device 50 capable of generating a bed of bubbles inside the liquid present in the chamber. Preferably, the bubble generation device 50 is installed in the lower part of the chamber, in an area in which the aqueous effluent circulates toward the surface of the liquid present in the chamber.Depending on the dimensions of the enclosure, one or more bubble generation devices 50 may be present in this second part which forms a bubble generation zone.

[0172] The bubble generation device 50 here comprises a supply line 51 within the flotation chamber of a gas-supersaturated liquid using a device 52 capable of supersaturating a liquid with gas, which may be located outside or inside the flotation chamber 30. The device 52 is supplied with gas via a line 53 and receives via a line 54 a portion of the treated (purified) aqueous effluent recovered at the outlet of the flotation chamber 30. The device 52 is adjusted and controlled according to the liquid effluent flow rate, the type of gas injected and the desired size of the generated bubbles. Optionally, a storage capacity 60 of a chemical compound such as a flocculation and / or coagulation and / or flotation aid compound, fluidically connected to the line 54 may be present.

[0173] The flotation chamber 30 finally comprises a third part 35 forming a flotation zone in which the aqueous effluent circulates towards the bottom of the chamber. This third part is separated from the second part by a delimiting wall 34c extending from the bottom of the chamber. In this third part 35, at the surface of the liquid effluent, a floating phase 36a is formed comprising the bubbles as well as amphiphilic molecules shaped as micelles brought to the surface. Under this floating phase 36a, the liquid present comprises a zone 36b (represented by hatching in the figure) in which the bubbles are located, this zone 36b thus forming the bed of bubbles generated by the bubble generation device 50.

[0174] The third part 35 comprises a physicochemical retention system 37 comprising at least one physicochemical retention material. This system 37 is held securely inside the enclosure. Preferably, the retention system 37 is installed within the zone 36b in which the bubbles are located, and advantageously entirely in the bed of bubbles, as shown in the figure. Optionally, depending on the nature of the physicochemical retention material, a device 70 for extracting the physicochemical retention material is installed to extract the used physicochemical retention material at determined time intervals. The used physicochemical retention material can then be regenerated thermally or using other processes such as cavitation, oxidation, centrifugation by desorbing the amphiphilic molecules, or destroyed.

[0175] In the example shown, the physicochemical retention system 37 comprises one or more physicochemical retention materials in particulate form arranged in a bed 37a between two holding devices 37b, 37c, for example perforated plates or grids having through passages of smaller dimension than the particles of the retention material(s). The invention is however not limited to this embodiment. In particular, a single holding device can be provided: when the particulate physicochemical retention material is denser than the liquid to be treated and naturally tends to sediment, holding device 37c can be used. Conversely, if the particulate physicochemical retention material is less dense and the effluent flow does not carry it towards the bottom of the enclosure, holding device 37b can be used.In addition, the particulate material could be replaced, in part or in full, by a material in the form of foam and / or gel, and / or in the form of fibers attached to a holding device similar to the holding devices 37b, 37c, arranged transversely to the direction of flow, or else arranged parallel to the direction of flow. Finally, these different embodiments can be combined with each other.

[0176] At the bottom of the third part 35 of the flotation chamber 30, a discharge pipe 38 for the treated (purified) aqueous effluent is installed. This discharge pipe 38 may be arranged between the bottom of the chamber and a floor (not shown) having passages allowing the effluent to pass through. It is thus located outside the bubble bed of the zone 36b and the chemical retention system 37, under the latter. Depending on the dimensions of the chamber, one or more discharge pipes 38 may be provided.

[0177] The treated aqueous effluent is then discharged into the environment, further treated, and / or partly reused by the bubble generation device 50.

[0178] Finally, the installation 1 comprises a device 80 for separating a floating phase on the surface of the liquid present in the flotation chamber 30.

[0179] The separation device 80 here comprises a pipe 81 for discharging part of the floating phase.

[0180] Depending on the dimensions of the enclosure, one or more separation devices 80 may be present. The invention is furthermore not limited by a specific separation device, and any device capable of separating a floating phase in a flotation enclosure may be used (scraping device, overflow device, etc.).

[0181] This floating phase can be eliminated or advantageously recycled in the process as described below.

[0182] In the example shown, the installation 1 thus comprises a recirculation pipe 82 fluidly connecting the separation device 80 of the floating phase to the first part 31 of the flotation enclosure 30. Optionally, a storage tank 83 fluidly connected to the recirculation pipe 82 is installed between the separation device 80 and the flotation enclosure 30. Optionally, in this tank 83, the foam of the floating phase can reliquefy naturally or forcibly using a centrifugation process or by ultrasound. The sedimented sludge is also advantageously extracted periodically at the bottom of this tank by a pipe 84. Depending on the dimensions of the enclosure, one or more discharge pipes 81 and / or recirculation pipes 82 and / or storage tank 83 can be provided.

[0183] A control system 90 connected to a valve 91 mounted on the recirculation pipe 282 makes it possible to control the quantity of floating phase returned to the interior of the enclosure, and / or the duration of its injection. In the absence of a degassing tank, this valve 91 can be mounted on the pipe 81. This control makes it possible to improve the efficiency of the process and of the treatment installation insofar as it can make it possible to reach more quickly, or more reliably, concentrations of chemical contaminants higher than critical micellar concentrations and / or concentrations of biological contaminants higher than concentrations at which these contaminants naturally flocculate.

Claims

A method of treating a liquid aqueous effluent by flotation in a flotation chamber (30) equipped with at least one bubble-generating device (50) capable of generating a bed of bubbles (36b) inside the liquid present in the flotation chamber (30), the aqueous effluent containing amphiphilic molecules, the method comprising:- a flotation step during which the aqueous effluent is introduced and circulated inside the flotation chamber (30), and brought into contact with the bed of bubbles (36b) generated by the at least one bubble-generating device (50), at least a portion of the amphiphilic molecules adhering to the surface of the bubbles,- a step of separating a floating phase (36a) located inside the flotation chamber (30) from the surface of the aqueous effluent, the floating phase (36a) containing the bubbles associated with the amphiphilic molecules raised to the surface of the aqueous effluent,said method being characterized in that, during the flotation step, the aqueous effluent and the bubbles associated with the amphiphilic molecules entrained by the aqueous effluent pass through a physicochemical retention system (37) located inside the flotation enclosure (30), at least in part, preferably totally, inside the bed of bubbles (36b) and held integral with said enclosure (30), the physicochemical retention system (37) comprising at least one physicochemical retention material capable of retaining at least a portion of the amphiphilic molecules present in the aqueous effluent, at least a portion of the amphiphilic molecules adhering to the surface of said bubbles being retained on a surface of the physicochemical retention material and / or inside pores of said physicochemical retention material., Treatment method according to claim 1, characterized in that the at least one physicochemical retention material is in particulate form, in foam form, in gel form or in fiber form. Treatment method according to claim 1 or 2, characterized in that the at least one physicochemical retention material comprises a plurality of pores and, during the flotation step, bubbles are generated whose dimensions are smaller than the dimension of at least one pore of the at least one physicochemical retention material. Method according to any one of claims 1 to 3, characterized in that it comprises, at determined time intervals, a step of replacing at least part of the at least one physicochemical retention material. Method according to any one of claims 1 to 4, characterized in that it comprises at least one of the following characteristics: - during the flotation step, the generation of bubbles is discontinuous over time, - during the flotation step, the bubbles are generated using a gas chosen from air, ozone, nitrogen, oxygen, chlorine, and chlorine dioxide. Method according to any one of claims 1 to 5, characterized in that at least part of the separated floating phase is returned to the interior of the enclosure (30). Method according to claim 6, characterized in that at least part of the separated floating phase is degassed in a storage tank (83) before being returned to the interior of the enclosure (30), and optionally sludge deposited at the bottom of the storage tank (83) is evacuated. Method according to any one of claims 1 to 7, characterized in that it comprises at least one of the following characteristics: - at least one chemical compound chosen from a flotation aid compound, a coagulation aid compound, a flocculation aid compound and a pH modification compound is added to the aqueous effluent before it enters the enclosure (30), - at least one chemical compound chosen from a flotation aid compound, a flocculation aid compound and a coagulation aid compound is introduced into the enclosure (30) by the bubble generation device (50). Method according to any one of claims 1 to 8, characterized in that the amphiphilic molecules are chosen from perfluoroalkylated substances and polyfluoroalkylated substances. Installation (1) for treating by flotation a liquid aqueous effluent containing amphiphilic molecules, the installation comprising a flotation chamber (30), at least one device (21) for circulating the liquid within the flotation chamber, at least one device (50) for generating bubbles capable of generating a bed of bubbles (36b) inside the liquid present in the flotation chamber (30), at least one device (80) for separating a floating phase on the surface of the liquid present in the flotation chamber (30), characterized in that it further comprises, inside the chamber and held integral with said chamber, a physicochemical retention system (37) comprising at least one physicochemical retention material capable of retaining at least a portion of the amphiphilic molecules present in said liquid aqueous effluent, said physicochemical retention system being located at least in part, preferably totally,inside the bed of bubbles generated within the liquid present in the flotation chamber by the bubble generation device (50)., Installation (1) according to claim 10, characterized in that the physico-chemical retention system (37) comprises at least one physico-chemical retention material in particulate, foam or gel form and at least one holding device (37b, 37c) integral with the enclosure extending transversely to a direction of circulation of the liquid flow inside the enclosure, the holding device having a plurality of through passages whose dimensions are smaller than the dimensions of the at least one physico-chemical retention material. Installation (1) according to claim 10 or 11, characterized in that the physicochemical retention system (37) comprises at least one physicochemical retention material in the form of fibers and at least one holding device secured to the enclosure and forming a support to which the fibers are fixed. Installation (1) according to any one of claims 10 to 12, characterized in that it comprises at least one of the following characteristics:- at least one discharge pipe (38) for the purified aqueous effluent opening into the flotation chamber (30) below the chemical retention system (37), outside the bubble bed (36b) generated by the bubble generation device (50),- at least one recirculation pipe (82) fluidly connecting the at least one device (80) for separating the floating phase to the flotation chamber (30), optionally at least one storage tank (83) fluidly connected to said recirculation pipe (82) between the separation device (80) and the flotation chamber (30),- at least one storage capacity (40) for a chemical compound fluidly connected to the flotation chamber (30),- at least one storage capacity (60) for a chemical compound fluidly connected to the bubble generating device (50).

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