Water treatment process and installation 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 enclosure, and brought into contact with a bed of bubbles generated by a bubble generation device, at least a part of the amphiphilic molecules adhering to the surface of the bubbles, - a step of separating a floating phase located inside the enclosure from the surface of the aqueous effluent, the floating phase containing the bubbles associated with the amphiphilic molecules that have risen to the surface of the aqueous effluent.During the flotation stage, the aqueous effluent and the bubbles associated with amphiphilic molecules carried by the aqueous effluent pass through a retention system located inside the enclosure and held securely attached to it, comprising at least one retention material. Fig. 1.

Description

Title of the invention: Process and installation for water treatment by flotation incorporating a pollutant retention system. Field of the invention

[0001] The invention relates to water treatment processes by flotation incorporating a pollutant retention system. The process and treatment plant 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 process and treatment plant of the present invention are thus particularly suitable for removing amphiphilic molecules such as detergents, lipids, surfactants, and especially fluorinated molecules such as perfluoroalkyl and polyfluoroalkyl substances, from water. Prior state of the art

[0002] Human activity produces contaminated liquid waste (well water, drinking water, urban or industrial wastewater, wastewater from treatment plants, etc.) that must be treated before reuse or discharge into the environment. Contaminants present in this liquid waste include amphiphilic molecules, such as perfluoroalkyl and polyfluoroalkyl substances, also known by the acronym "PFAS." These molecules are organofluorine compounds with a hydrophobic alkyl chain that is wholly or partially fluorinated. Their structure consists of a fluorinated carbon chain with a functional group at its end. This functional group may be, in particular, a carboxyl group (-COOH), a carboxylate group (-COO-), a sulfonic acid group (-SO3H), or a sulfonate group (-SO3-).

[0003] PFAS constitute a family of over 4,700 emerging man-made compounds, the best-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, and textile stain repellents, due to their surfactant properties. PFAS can be released into the environment through many pathways, including air, soil, and water, and have been detected in water sources, soils, and biological samples.

[0004] PFAS thus constitute a problem as emerging organic contaminants, firstly because they are widely present in wastewater effluents and resources used for drinking water production worldwide, On the one hand, there is their stability in the environment, their potential for bioaccumulation, and their negative health effects. Due to growing concerns about the effects of PFAS on ecology and human health, regulations concerning them are becoming increasingly stringent. These regulations have led to the development of processes for their removal or concentration.

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

[0006] Flotation is a solid-liquid or liquid-liquid separation process which applies to aggregates and / or particles whose density is less than that of the liquid which contains them, these aggregates and / or particles being collected, in the end, 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 that contains them is naturally sufficient to allow their separation.

[0008] This separation can be improved by injecting a gas into the liquid to be treated. This is then referred to as "assisted" flotation. Finally, flotation is said to be "induced" when the density of the aggregates and / or particles is greater than the density of the liquid containing them. Their density is then artificially reduced by injecting a gas, leading to the formation of bubbles on the surface of which the aggregates and / or particles can bind together, forming clusters less dense than the liquid containing them.

[0009] There are also processes in which flotation is induced by floating particles, which are recirculated within the flotation chamber. The purpose of adding these floating particles is to limit, or even eliminate, the need for gas. This is the case, for example, in 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 to eliminate contaminants dissolved in the water to be treated, such as PFAS, in particular 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 an 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 bubble bed within 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 within the flotation chamber, and brought into contact with a bed of bubbles generated by at least one bubble-generating device, with at least some of the amphiphilic molecules adhering to the surface of the bubbles, - a separation step of a floating phase located inside the enclosure at the surface of the aqueous effluent, the floating phase containing the bubbles associated with amphiphilic molecules that have risen 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 carried by the aqueous effluent pass through a physico-chemical retention system located inside the enclosure at least in part, preferably totally, inside the bubble bed and kept attached to said enclosure, the physico-chemical retention system comprising at least one physico-chemical retention material capable of retaining at least a part of the amphiphilic molecules present in the aqueous effluent, at least a part of the amphiphilic molecules adhering to the surface of said bubbles being retained on a surface of the physico-chemical retention material and / or inside pores of said physico-chemical retention material.

[0014] The process according to the invention improves the separation of some of the amphiphilic molecules present in the liquid aqueous effluent. Indeed, some of the amphiphilic molecules, depending on their concentration in the system, will naturally form micelles that will rise in the floating phase to be separated. However, some molecules, particularly 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 act as a vector, i.e., a transport agent, for these molecules.Thus, all amphiphilic molecules present will pass through the chemical retention system in the form of micelles and / or hemi-micelles, adhering to gas bubbles, or simply transported by the aqueous effluent, allowing their retention on the surface and / or inside the pores of the physico-chemical retention material. There is then a displacement of some of the amphiphilic molecules from the liquid phase to a solid phase, which can facilitate their removal or subsequent treatment.

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

[0016] Typically, the process may further include a step c) of recovering the purified aqueous effluent (i.e., the treated water) during which the aqueous effluent purified is evacuated from the flotation chamber through a discharge pipe opening into the chamber below the physico-chemical retention system and outside the bubble bed.

[0017] Advantageously, at least one physico-chemical retention material can be in particulate form, in foam form, in gel form or in fiber form.

[0018] Advantageously, the at least one physico-chemical 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 at least one physico-chemical retention material. Thus, the bubbles formed can circulate within the pores of the latter and transport the amphiphilic molecules adhering to their surface into the pores for retention.

[0020] Advantageously, the process may include, at predetermined time intervals, a step of replacing at least a portion of at least one physico-chemical retention material. This step allows for the renewal, in whole or in part, of the physico-chemical retention material and thus maintains the overall retention capacity of the physico-chemical retention system.

[0021] Advantageously, the method may include at least one of the following features: - during the flotation stage, bubble generation is discontinuous in time, - during the flotation stage, bubbles are generated using a gas chosen from air, including ambient air, ozone, nitrogen, oxygen, chlorine, chlorine dioxide.

[0022] The discontinuous generation of bubbles over time can prevent an accumulation of bubbles in the installation.

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

[0024] Circulating the floating phase increases the efficiency of amphiphilic molecule removal by increasing their concentration in the aqueous effluent. This increased concentration promotes the formation of micelles within the aqueous effluent, thus facilitating their retention by the physicochemical retention system. Circulating the floating phase also reduces the energy required to generate bubbles and decreases the amount of chemical reagents, such as surfactants, coagulants, flocculants, and acids or bases for pH adjustment, thereby promoting the flotation of potentially added amphiphilic molecules.

[0025] Advantageously, at least a portion of the separated floating phase can be degassed in a storage tank before being returned inside the containment. This implementation is advantageous for batch reactor operation.

[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 facility.

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

[0028] The method may further include, in combination or not with the various 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 include at least one of the following features: - at least one chemical compound chosen from a flotation aid compound (surfactant), a flocculation aid compound, a coagulation aid compound and a pH modifying 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 inside the enclosure by the bubble generation device.

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

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

[0032] The invention also relates to a flotation treatment installation for 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, and at least one bubble generation device capable of generating a bubble bed within 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 chamber and maintained attached to said chamber, a physico-chemical retention system comprising at least one physico-chemical retention material capable of retaining at least a portion of the amphiphilic molecules present in said liquid aqueous effluent, said physico-chemical retention system being located at least in part, preferably totally, within a bubble bed generated within the liquid present in the flotation chamber 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 physico-chemical retention system may include at least one physico-chemical retention material in particulate, foam or gel form and at least one retaining device attached to the enclosure extending transversely to a direction of flow of the liquid inside the enclosure, the retaining device having a plurality of through passages whose dimensions are smaller than the dimensions of at least one physico-chemical retention material.

[0035] Alternatively or in combination, the physico-chemical retention system may include at least one physico-chemical retention material in the form of fibers and at least one retaining device attached to the enclosure and forming a support to which the fibers are fixed.

[0036] Advantageously, the installation may include at least one of the following features: - at least one purified aqueous effluent discharge pipe leading into the flotation chamber below the physico-chemical retention system, outside the bubble bed generated by the bubble generation device, - at least one recirculation line fluidly connecting at least one floating phase separation device to the flotation chamber, optionally at least one storage tank fluidly connected to said recirculation line between the separation device and the flotation chamber, - at least one storage capacity for a chemical compound fluidically 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 include, in combination with the various embodiments described, a system for controlling the quantity of floating phase, optionally degassed, returned to the enclosure, and / or the duration of injection of the floating phase, optionally degassed, into the enclosure. optionally based on at least one target concentration of at least one contaminant inside the enclosure. Definitions

[0038] The terminology used in this document is solely for the purpose of describing particular embodiments and is not intended to limit the disclosed subject matter. Although the following terms are assumed to be readily understood by a person with ordinary competence in the art, the following definitions are given to facilitate the explanation of the subject matter disclosed at present.

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

[0040] The acronym PFAS refers to all perfluoroalkyl substances and polyfluoroalkyl substances.

[0041] Perfluoroalkyl substances are molecules comprising 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 found in the environment. The fluorine atoms are attached to all possible bonding sites along the carbon chain of the tail, except for one bonding site on the last carbon where the head of the functional group is attached. The chemical formula of these substances can be written CnF2n+iR, where "CnF2n +i" defines the length of the perfluoroalkyl chain tail, "n" is >2, and "R" represents the head of the attached functional group.The functional group may 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 "PFAA") are among the most fundamental PFAS molecules. They are essentially non-degradable and currently constitute the most frequently detected class of PFAS in the environment. The PFAS class is divided into two main groups:

[0043] - Perfluoroalkylcarboxylic acids of formula CnF2n+iR, with R=- COOH, or perfluoroalkylcarboxylates with the formula CnF2n+iR, where 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, C7Fi5 COOH (designated by the acronym "PFOA").

[0044] - Perfluoroalkane sulfonic acids of formula CnF2n+iR, with R=-SO3H, Perfluoroalkyl sulfonates of the formula CnF2n+iR, 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, C8FnSO3 (designated by the acronym "PFOS").

[0045] Perfluoroalkane sulfonamides of formula CnF2n+iR, with R=-SO2-NH2, designated by the acronym "FASA", such as perfluorooctane sulfonamide (FOSA, C8Fn SO2NH2), are used as raw materials to manufacture perfluoroalkane sulfonamide substances that are used for surfactants and surface treatments. FOSAs can degrade to form PF AAs 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, 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 (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 CnF2n+i perfluoroalkyl group are potential precursor compounds that can be converted into PFAAs.

[0047] The expression "long-chain PFAS" generally refers to:

[0048] - to perfluoroalkylcarboxylic acids, PFCA, comprising eight carbon atoms or more (seven or more carbon atoms are perfluorinated),

[0049] - to perfluoroalkane sulfonates, PFSA, with six or more carbon atoms (six (carbon atoms or more 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 expression "short-chain PFAS" generally refers to:

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

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

[0054] - and for all other perfluoroalkyl and polyfluoroalkyl substances in 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 be composed of, one or more liquid aqueous effluents. The liquid aqueous effluent to be treated contains amphiphilic molecules, in particular amphiphilic molecules selected from perfluoroalkyl substances and polyfluoroalkyl substances, or any amphiphilic molecule capable of forming micelles, such as surfactants, soaps, detergents and emulsifiers.

[0057] Aqueous liquid effluents within the meaning of the 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 flue gas scrubbing water from incinerators, whether pre-treated or not. 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 processes, and especially 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 include a concentration of amphiphilic molecules, and in particular PFAS, of 0.2pg / L or more, preferably from 0.2pg / L to 200pg / L.

[0063] To facilitate the implementation of the process according to the invention, the effluent may further have a turbidity of no more than 5 NTU (Nephelometric Turbidity Units). The turbidity is measured with a turbidimeter, for example, one from the Hach brand.

[0064] Detailed description of the process

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

[0066] To this end, it comprises a flotation step implemented in a flotation chamber within which a physico-chemical retention system is fixedly maintained, comprising at least one physico-chemical retention material capable of retaining amphiphilic molecules present in the liquid aqueous effluent. The combination of flotation and at least one physico-chemical retention material improves the removal of amphiphilic contaminants.

[0067] By "physico-chemical retention," we mean the ability to retain a molecule by adsorption, absorption, ion exchange, and / or by steric retention (capture of molecules within pores according to the respective sizes of the molecules and pores). Physico-chemical retention, as defined in the present invention, thus allows the retention of molecules present in dissolved form in the liquid aqueous effluent to be treated.

[0068] The invention can in particular be implemented with any type of physico-chemical 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 physico-chemical retention material specifically adapted to the amphiphilic contaminant to be eliminated.

[0069] Typically, the process further includes 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 the direction of flow of the aqueous effluent within the flotation chamber.

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

[0071] Flotation step

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

[0073] The term "bubble bed" refers to an area of ​​the flotation chamber in which bubbles are predominantly present. This bubble bed extends to a height less than the total height of the chamber, at a distance from the liquid surface and the bottom of the chamber, and in particular at a distance from the floor generally present in flotation chambers. This area typically extends across the entire surface of the chamber transversely to a direction of flow of the aqueous effluent within the chamber. The floor is typically a horizontal wall with a plurality of openings allowing the liquid aqueous effluent to pass through it. The treated water is generally discharged from the chamber via one or more pipes opening into the chamber, below the floor.

[0074] During this flotation step, 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 commonly used in a flotation chamber may be used.

[0075] During this circulation, the aqueous effluent will pass through the bubble bed and come into contact with the bubbles. This contact of the liquid effluent with the bubbles will allow at least some of the amphiphilic molecules, particularly those that form micelles less readily (due to their intrinsic properties and / or the properties of the aqueous effluent), to adhere to the surface of the bubbles. Since these gas bubbles, associated with amphiphilic molecules, tend to rise to the surface of the liquid effluent, they will end up, at least partially, in a floating phase on the surface of the liquid effluent. It is thus understood that the gas bubbles act as carriers for some of the amphiphilic molecules.

[0076] Furthermore, during this flotation step, at least some of the amphiphilic molecules, particularly those that easily form micelles (due to their intrinsic properties and / or 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 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 carried by the aqueous effluent pass through a physicochemical retention system located inside the vessel and attached to it. This system comprises at least one physicochemical retention material capable of retaining at least some of the amphiphilic molecules present in the aqueous effluent. The physicochemical retention system is located at least partially, and preferably entirely, within the bubble bed of the flotation vessel. Thus, the physicochemical retention system does not extend over the entire height of the liquid inside the flotation vessel. In particular, it is located above and at a distance from the bottom of the flotation vessel to allow for the discharge of treated water away from the chemical retention system.

[0078] When bubbles pass through the physicochemical retention material, at least some of the amphiphilic molecules adhering to the bubble surfaces will be retained on the surface of the physicochemical retention material and / or within pores of the physicochemical retention material. The bubbles thus act as carriers for the amphiphilic molecules. Without being bound by any particular theory, this physicochemical retention can result from the adhesion of amphiphilic molecules associated with the bubbles to the internal and / or external surface of the bubbles, notably through adsorption, absorption, or ion exchange mechanisms. Since the aqueous effluent passing through the physicochemical retention system also contains amphiphilic molecules, whether or not they are formed into micelles, these amphiphilic molecules can also be retained on the surface of the physicochemical retention material and / or within pores of the physicochemical retention material.Furthermore, amphiphilic molecules formed into micelles that were not retained by the physico-chemical retention system end up in the floating phase and can then be separated in the usual way, or returned to the flotation step, as explained below.

[0079] Thus, amphiphilic molecules that readily form micelles (due to their intrinsic properties and / or the properties of the aqueous effluent), such as long-chain PFAS, will preferentially form micelles, some of which may be retained by the physicochemical retention system and others may accumulate on the surface of the aqueous effluent in the floating phase. This predominantly micelle configuration does not preclude some of these amphiphilic molecules from adhering to the surface of the bubbles without being micelled.

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

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

[0082] During the flotation step, bubbles are generated by the bubble-generating device. Typically, the bubbles are generated by means of a bubble-generating device that injects a gas-supersaturated liquid into the liquid aqueous effluent inside the flotation chamber. As the gas expands inside the flotation chamber, gas bubbles form and rise to the surface, carrying with them some of the amphiphilic molecules and forming a bubble bed. The liquid used is generally water (referred to as "white water") or an aqueous effluent, for example, the treated aqueous effluent exiting the flotation chamber.

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

[0084] The generation of bubbles can be obtained by the usual techniques used in flotation, for example by pressure dissolution (dissolving the gas in a liquid medium at higher pressure and then expanding the mixture), by rotational flow (introducing the liquid from the top into a cylindrical tank, the liquid flowing in a spiral downwards, with gas being drawn in at the bottom of the tank), by means of a static turbulent mixer, by means of an ejection nozzle or by means of a hammer mill.

[0085] In one embodiment, bubble generation can be discontinuous in time. Bubble generation is then intermittent. This can allow for the control of the transport of amphiphilic contaminants.

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

[0087] Preferably, the bubbles generated during the flotation step of the present invention are smaller in size than the bubbles used in conventional flotation processes. Ultrafine bubbles, with a diameter of at most 200 nm, preferably at most 100 nm, and more preferably at most 50 nm, will be used, which is much smaller than the diameter of the bubbles used in conventional flotation processes (on the order of 50 µm).

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

[0089] It will be possible to adjust the contact time between the effluent to be treated and the at least 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] By way of example, a contact time of aqueous effluent / retention material 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 according to 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 physico-chemical retention material and / or in the floating phase.

[0092] When the physico-chemical retention material is porous, it is advantageous to generate bubbles with 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 50 nm, while the porous retention material(s) have pores of at least 50 nm in size.

[0093] Depending on the nature of the amphiphilic molecules present, their micelle conformation can be favored by the properties of the aqueous effluent, namely its pH and / or its content of chemical compounds that aid flocculation (polymers) and / or its content of chemical compounds that aid coagulation and / or its content of chemical compounds that 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 (namely a surfactant), and a pH-modifying compound may be added to the aqueous effluent before it enters the chamber, 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 chamber by the generation device. of bubbles. These compounds can improve foam formation by promoting micelle formation, and promote the association of amphiphilic molecules with bubbles.

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

[0096] The coagulation aid compound may be a conventionally used coagulant (iron or aluminum salts). Alternatively, a salt of a cation may be used, for example, chosen from the following cations: Fe3+, La3+, Al3+, Ca2+, Fe2+, 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, Ci9H42BrN), tetra-n-butyl-ammonium bromide (TBAB, Ci6H36BrN), decyl-trimethyl-ammonium bromide (DTAB, Ci3H30BrN), n-octyl-trimethyl-ammonium bromide (OTAB, CnH26BrN).

[0098] The pH modifying compound can be an acid, for example an inorganic acid such as HCl, H2SO4 or other, or an organic acid (citric, acetic acid) 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] Physico-chemical retention system

[0101] The physico-chemical retention system used in the present invention allows the retention of at least some of the amphiphilic molecules present in the aqueous effluent. This system is installed inside the flotation chamber, at least partially, and preferably entirely, within the bubble bed generated during the flotation step.

[0102] Preferably, so that all of the aqueous effluent can pass through it, the physico-chemical retention system can extend over the entire surface of the enclosure transversely to a direction of flow of the aqueous effluent within the enclosure. The retention system can, for example, be arranged horizontally, typically over the entire surface of the enclosure so that all of the aqueous effluent passes through it.

[0103] Preferably, the physicochemical retention system is also located within the enclosure, away from a bottom wall of the enclosure and away 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 to a height of 100 cm or less.

[0104] In the area of ​​the enclosure comprising the physico-chemical 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 physico-chemical retention system is kept attached to the enclosure and includes at least one physico-chemical retention material.

[0106] By "physico-chemical 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 may, in particular, be trapped (steric retention) in pores of the physico-chemical retention material when it contains them.

[0107] The physico-chemical retention material has, in particular, the function of retaining amphiphilic molecules on its external surface and / or on its internal surface within pores, if present. Free amphiphilic molecules can be retained directly by the physico-chemical retention material as the aqueous effluent flows through the material, as can amphiphilic molecules formed into micelles. Amphiphilic molecules can also be transported on the surface of the physico-chemical retention material and / or within pores of the physico-chemical retention material by bubbles.These different mechanisms allow for better distribution of amphiphilic molecules on the surface (internal and / or external) of the physico-chemical retention material, thus extending the lifespan of the physico-chemical retention material, since this maximizes the physico-chemical retention surface area by optimizing the transport of amphiphilic molecules over the entire available surface of the physico-chemical retention material.

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

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

[0110] The physico-chemical 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 retaining device attached to the enclosure and forming a support to which the fibers are fixed. This retaining device can extend parallel to the direction of flow of the liquid effluent within the enclosure or transversely to this direction of flow. In the latter case, the retaining device has multiple through-holes for the passage of the fluid. The retaining device can, for example, be a plate, a grid, or a net to which the fibers are attached.

[0112] Where the physico-chemical retention material is in particulate form, foam, or gel, it may be retained by at least one retention device attached to the enclosure and extending transversely to a direction of flow of the aqueous effluent within the enclosure. Each retention device may have a plurality of through-holes whose dimensions are smaller than the dimensions of at least one retention material. This retention device may be a membrane, a net, a fabric, or even a sieve or grid.

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

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

[0115] The retention system may comprise one, two, or more physico-chemical retention materials and one or more retention devices selected according to the nature of the retention materials. For example, different materials may be mixed in particulate, foam, or gel form and / or layers of these materials may be arranged in particulate, foam, or gel form (each layer being separated, for example, by a retention device). Alternatively, at least one material may be provided in particulate form and at least one material in fiber, foam, or gel form, for example, arranged in layers.

[0116] Preferably, the physico-chemical retention system comprising at least one physico-chemical 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 physico-chemical 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 process includes, at specified time intervals, a step of replacing at least part of at least one physico-chemical retention material.

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

[0119] Advantageously, the spent physico-chemical containment material can then be destroyed, for example by incineration, or regenerated by thermal regeneration processes that also destroy amphiphilic molecules, or by destruction processes such as cavitation, oxidation, or the Fenton process. Destroying the spent physico-chemical containment material, for example by incineration, has the advantage of not generating polluted liquid effluent that would require further treatment.

[0120] The physico-chemical retention material can be selected 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) porous structure polymers, 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 physico-chemical retention material is typically chosen according to the type of amphiphilic molecules to be treated and can also be selected according to the composition of the aqueous effluent. The choice can be made based on existing literature or on laboratory tests. The quantity of retention material to be used can be chosen according to the flow rate of the liquid effluent to be treated and the quantity of amphiphilic contaminants to be removed.

[0122] Chemical retention materials usable in the present invention are described, for example, in document WO2022 / 018613. The main characteristics of the usable material families are recalled below.

[0123] (i) Cyclodextrin polymers and cyclodextrin polymers supported or unsupported on a solid substrate.

[0124] Cyclodextrins (hereinafter referred to as "CD") are a group of structurally related natural products formed during the bacterial digestion of cellulose. The cyclodextrins used in the present invention may include cyclodextrin derivatives. Cyclodextrin polymers consist of two or more Cyclodextrin macromolecules are covalently linked together using a crosslinking agent. These cyclodextrin macromolecules can be natural or synthesized cyclodextrins, and possibly 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 for removing long-chain PFAS through hydrophobic interaction, such as PFOS. Powdered activated carbon (PAC), superfine powder 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 organic clays (phyllosilicates to which at least one organic modifier has been added) and inorganic-organic clays, can 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 organic clays can be modified by at least one cationic modifier, in particular an organic cation.

[0130] (v) Porous structure polymers

[0131] Porous structure polymers, whether or not capable of ion exchange, include for example the Mycelx® polymer and anion exchange resins, in particular strongly basic anion exchange resins.

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

[0133] (vi) Biochar, activated or not

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

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

[0136] (vii) Carbon fibers

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

[0138] (viii) Polyacrylonitrile fibers

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

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

[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, may be used. Silica, and in particular macroporous silica typically having pores with a diameter greater than 50 nm, functionalized or not, may also be used.

[0144] Separation step

[0145] The process finally includes 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 amphiphilic molecules arranged in micelles that have risen to the surface of the aqueous effluent.

[0146] The separation step is implemented in a usual way by a separation device which may for example include a discharge pipe towards which the floating phase can be pushed generally by means of an overflow or scraping device provided for this purpose.

[0147] In one embodiment, at least part of the separated floating phase is returned inside the enclosure. Before being returned inside the flotation enclosure, the floating phase is preferably first degassed in a storage tank.

[0148] Recirculating the floating phase helps limit liquid discharges and also promotes micelle formation, since the concentration of amphiphilic molecules capable of forming micelles increases when the floating phase and aqueous effluent are added together. The foams from the floating phase can be recirculated as foam or as a liquid (after degassing).

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

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

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

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

[0153] One or more of the following controls may therefore be considered:

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

[0155] - the injection of a precise quantity of the floating phase (degassed or not) in a manner continuous operation, with the control system then only regulating the quantity injected.

[0156] - the injection of a precise quantity over a determined period of time (continuous or not) to the floating phase (degassed or not), the control system regulates both the quantity injected and the duration of injection.

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

[0158] The control system can thus be configured, in particular programmed, to implement control of the quantity of injected floating phase 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 includes one or more processors, for example a microprocessor, a microcontroller, or the like. It also includes output or input / output interfaces. These may be wireless communication interfaces (Bluetooth, Wi-Fi, or the like) or connectors (network port, USB port, serial port, FireWire® port, SCSI port, or the like). 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) into the chamber, 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 other. 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 is discharged during a recovery step (c) in an area near the bottom of the enclosure via at least one discharge pipe. It can be reused to generate bubbles, thereby reducing the energy consumption required to form 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. Step b) of separation can begin as soon as a floating phase is formed, during step a) of flotation.

[0163] Depending on the desired effluent quality, the treated aqueous effluent may be subjected again to flotation steps a) and separation steps b). This may be carried out in a separate flotation chamber or within the same chamber. The purified aqueous effluent can be used as drinking water, possibly after further purification treatment, or discharged into the environment. Drawing description

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

[0165] The [Fig. 1] represents the installation for treating a liquid aqueous effluent by flotation according to an 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 [Fig. 1], the treatment plant 1 comprises a flotation chamber 30 connected to an aqueous effluent supply line 20. The supply line 20 is equipped with a device for circulating the liquid within the flotation chamber, such as a pump. Depending on the size of the chamber, one or more supply lines and / or circulation devices may be used.

[0168] Optionally, the installation includes a storage tank 40 for a chemical compound such as a flocculation aid, a coagulation aid, a surfactant, or a pH-modifying compound. The storage tank 40 is fluidly connected to the flotation chamber 30, and in particular to the feed line 20, by a line 4L. Depending on the nature and number of chemical compounds to be added, one or more storage tanks 40 may be provided. The line 41 may be equipped with a valve or similar device for regulating the quantity of chemical compound added.

[0169] The flotation chamber 30 is generally divided into several parts, as shown in [Fig. 1]. However, the invention is not limited to a specific type of flotation chamber having a particular number of parts; any type of flotation chamber is usable. In general, the flotation chamber may include 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 bubbles are generated by the bubble-generating device comprising at least one inlet receiving the effluent to be treated, possibly exiting the coagulation / flocculation zone, and one outlet; and a flotation zone comprising at least one inlet connected to the outlet of the bubble-generating zone and at least one outlet for discharging the treated water and one outlet for discharging the floating phase.Typically, the physico-chemical retention system is located in the zone of . flotation. 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 supply line 20 feeds a first section 31 of the flotation chamber. In the embodiment shown, the first section 31 includes a mixer 32, which is particularly useful when a chemical compound has been added or when the floating phase is recirculated within the installation 1, in order to obtain a homogeneous mixture. This first section forms a coagulation and / or flocculation zone, which may be omitted depending on the nature of the effluent.

[0171] The aqueous effluent then flows into 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 includes a boundary wall 34b providing a passage to the bottom of the chamber for the fluid: the fluid thus flows downwards (towards the bottom of the chamber) when it enters the second part, then upwards (towards the surface of the aqueous effluent) until it leaves the second part 33. The second part 33 also includes a bubble-generating device 50 capable of generating a bubble bed within the liquid present in the chamber. Preferably, the bubble-generating device 50 is installed in the lower part of the chamber, in an area where the aqueous effluent flows towards the surface of the liquid present in the chamber.Depending on the dimensions of the enclosure, one or more bubble generation devices may be present in this second part, which forms a bubble generation zone.

[0172] The bubble generation device 50 here includes a supply line 51 within the flotation chamber of a gas-supersaturated liquid, supplied by means of 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 by a line 53 and receives, via a line 54, a portion of the treated (purified) aqueous effluent recovered from 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 bubbles generated. Optionally, a storage capacity 60 for a chemical compound, such as a flocculation and / or coagulation and / or flotation aid compound, fluidly connected to the line 54, may be present.

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

[0174] The third part 35 comprises a physico-chemical retention system 37 including at least one physico-chemical retention material. This system 37 is held securely within the enclosure. Preferably, the retention system 37 is installed within the zone 36b containing the bubbles, and advantageously entirely within the bubble bed, as shown in the figure. Optionally, depending on the nature of the physico-chemical retention material, a physico-chemical retention material extraction device 70 is installed to extract the spent physico-chemical retention material at predetermined time intervals. The spent physico-chemical retention material can then be regenerated thermally or using other processes such as cavitation, oxidation, centrifugation by desorbing amphiphilic molecules, or destroyed.

[0175] In the example shown, the physico-chemical retention system 37 comprises one or more physico-chemical retention materials in particulate form arranged in a bed 37a between two retaining devices 37b, 37c, for example, perforated plates or grids having through-holes smaller than the particles of the retention material(s). However, the invention is not limited to this embodiment. In particular, a single retaining device may be required: when the particulate physico-chemical retention material is denser than the liquid to be treated and naturally tends to settle, retaining device 37c may suffice. Conversely, if the particulate physico-chemical retention material is less dense and the effluent flow does not carry it to the bottom of the enclosure, retaining device 37b may suffice.Furthermore, the particulate material could be replaced, in part or in whole, by a material in the form of foam and / or gel, and / or by fibers attached to a retaining device similar to retaining devices 37b, 37c, arranged transversely to the direction of flow, or parallel to the direction of flow. Finally, these different embodiments can be combined with each other.

[0176] At the bottom of the third section 35 of the flotation chamber 30, a discharge pipe 38 for the treated (purified) aqueous effluent is installed. This discharge pipe 38 can be positioned between the bottom of the chamber and a floor (not shown) with openings allowing the effluent to pass through. It is thus located outside the bubble bed of zone 36b and the chemical retention system 37, below these lastly. Depending on the dimensions of the enclosure, one or more 38 drainage pipes 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 includes 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 includes a conduit 81 for the discharge of part of the floating phase.

[0180] Depending on the dimensions of the enclosure, one or more separation devices 80 may be present. Furthermore, the invention is not limited by a specific separation device, and any device suitable for 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 line 82 fluidly connecting the separation device 80 of the floating phase to the first part 31 of the flotation chamber 30. Optionally, a storage tank 83 fluidly connected to the recirculation line 82 is installed between the separation device 80 and the flotation chamber 30. Optionally, in this tank 83, the foam of the floating phase can reliquefy naturally or by forced reliquefaction using a centrifugation or ultrasonic process. The settled sludge is also advantageously extracted periodically from the bottom of this tank by a line 84. Depending on the dimensions of the chamber, one or more discharge lines 81 and / or recirculation lines 82 and / or storage tanks 83 may be provided.

[0183] A control system 90 connected to a valve 91 mounted on the recirculation line 282 allows control of the quantity of floating phase returned inside the enclosure, and / or the duration of its injection; in the absence of a degassing tank, this valve 91 can be mounted on the line 81. This control makes it possible to improve the efficiency of the process and the treatment plant 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

Demands

1. A method for 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 bubble bed (36b) within 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 within the flotation chamber (30), and brought into contact with the bubble bed (36b) generated by at least one bubble-generating device (50), at least some of the amphiphilic molecules adhering to the surface of the bubbles, - a step of separating a floating phase (36a) located within the flotation chamber (30) from the surface of the aqueous effluent, the floating phase (36a) containing the bubbles associated with the amphiphilic molecules rising to the surface of the aqueous effluent,said process being characterized in that, during the flotation step, the aqueous effluent and the bubbles associated with the amphiphilic molecules carried by the aqueous effluent pass through a physico-chemical retention system (37) located inside the flotation chamber (30), at least partially, preferably totally, inside the bubble bed (36b) and maintained attached to said chamber (30), the physico-chemical retention system (37) comprising at least one physico-chemical 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 physico-chemical retention material and / or within pores of said physico-chemical retention material, the at least one physico-chemical retention material comprising 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 at least one physico-chemical retention material.

2. A treatment method according to claim 1, characterized in that at least one physico-chemical retention material is in particulate form, in foam form, in gel form or in fiber form.

3. A method according to claim 1 or 2, characterized in that it comprises, at determined time intervals, a step of replacing at least a part of at least one physico-chemical retention material.

4. A method according to any one of claims 1 to 3, characterized in that it comprises at least one of the following features: - during the flotation step, the generation of bubbles is discontinuous in time, - during the flotation step, the bubbles are generated using a gas selected from air, ozone, nitrogen, oxygen, chlorine, and chlorine dioxide.

5. A method according to any one of claims 1 to 4, characterized in that at least a part of the separated floating phase is returned inside the enclosure (30).

6. A method according to claim 5, characterized in that at least a part of the separated floating phase is degassed in a storage tank (83) before being returned inside the enclosure (30), and optionally sludge deposited at the bottom of the storage tank (83) is removed.

7. A method according to any one of claims 1 to 6, characterized in that it comprises at least one of the following features: - at least one chemical compound selected from a flotation aid compound, a coagulation aid compound, a flocculation aid compound and a pH modifying compound is added to the aqueous effluent before it enters the enclosure (30), - at least one chemical compound selected 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).

8. A method according to any one of claims 1 to 7, characterized in that the amphiphilic molecules are selected from perfluoroalkylated substances and polyfluoroalkylated substances.

9. Installation (1) for the flotation treatment of 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, and at least one bubble-generating device (50) capable of generating a bubble bed (36b) within the liquid present in the flotation chamber (30), at least one separation device (80) for a floating phase on the surface of the liquid present in the flotation chamber (30), characterized in that it further comprises, within the chamber and maintained attached to said chamber, a physico-chemical retention system (37) comprising at least one physico-chemical retention material capable of retaining at least a portion of the amphiphilic molecules present in said aqueous liquid effluent, said physico-chemical retention system being located at least partially, preferably totally, within the bubble bed generated within the liquid present in the flotation chamber by the bubble-generating device (50), the at least one physico-chemical retention material comprising a plurality of pores and the bubble-generating device (50) being capable, during the flotation step,to generate bubbles whose dimensions are smaller than the dimension of at least one pore of at least one physico-chemical retention material.

10. Installation (1) according to claim 9, 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 retaining device (37b, 37c) attached to the enclosure extending transversely to a direction of flow of liquid inside the enclosure, the retaining device having a plurality of through passages whose dimensions are smaller than the dimensions of at least one physico-chemical retention material.

11. Installation (1) according to claim 9 or 10, characterized in that the physico-chemical retention system (37) comprises at least one physico-chemical retention material in the form of fibers and at least one retaining device attached to the enclosure and forming a support to which the fibers are fixed.

12. Installation (1) according to any one of claims 9 to 11, characterized in that it comprises at least one of the following features: - at least one discharge pipe (38) of 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 line (82) fluidly connecting at least one floating phase separation device (80) to the flotation chamber (30), optionally at least one storage tank (83) fluidly connected to said recirculation line (82) between the separation device (80) and the flotation chamber (30), - at least one storage capacity (40) for a chemical compound fluidically connected to the flotation chamber (30), - at least one storage capacity (60) of a chemical compound fluidly connected to the bubble generation device (50).

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