Process and installation for water treatment by flotation with recirculation of the floating phase

Abstract

A process for treating a liquid aqueous effluent by flotation in a flotation chamber equipped with a bubble-generating device capable of generating a bubble bed within the liquid present in the chamber, the aqueous effluent containing contaminants capable of forming aggregates, the process comprising: - a flotation step during which the aqueous effluent is introduced and circulated within the flotation chamber, and brought into contact with a bubble bed generated by the bubble-generating device, at least a portion of the contaminants forming aggregates and / or at least a portion of the contaminants being transported by the bubbles, - a step of separating a floating phase located within the chamber from the surface of the aqueous effluent, the floating phase containing the aggregates and / or the bubbles associated with the contaminants rising to the surface of the aqueous effluent.said process being characterized in that at least a part of the separated floating phase is returned inside the enclosure. Fig. 1,

Description

Title of the invention: Method and installation for water treatment by flotation with recirculation of the floating phase. Field of the invention

[0001] The invention relates to water treatment processes by flotation incorporating recirculation of the floating phase. The process and treatment plant according to the invention are particularly suitable for removing contaminants capable of forming aggregates from water to be treated. The process and treatment plant of the present invention are thus particularly suitable for removing photosynthetic microorganisms, hydrophilic and / or amphiphilic molecules such as detergents, lipids, surfactants, and in particular fluorinated molecules such as perfluoroalkyl and polyfluoroalkyl substances, from water. Prior state of the art

[0002] Human activity produces contaminated liquid discharges (well water, drinking water, urban or industrial wastewater, liquid discharges from treatment plants, etc.) that must be treated before they can be reused or discharged into the environment. The contaminants present in these liquid discharges include contaminants capable of forming aggregates. These contaminants can be biological contaminants, particularly photosynthetic microorganisms such as microalgae, and / or chemical contaminants, particularly dissolved molecules, such as hydrophilic and / or amphiphilic molecules, the latter including perfluoroalkyl and polyfluoroalkyl substances, also known by the acronym "PFAS." PFAS are organofluorine compounds with a hydrophobic alkyl chain that is wholly or partially fluorinated.Their structure consists of a fluorinated carbon chain at the end of which is a functional group. This functional group can be, in particular, a carboxyl group (-COOH), a carboxylate group (-COO-), a sulfonic acid group (-SO3H) or a sulfonate group (-SO3-).

[0003] Flotation processes are commonly used in the field of water treatment.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] However, these processes may prove unsuitable or insufficient to eliminate contaminants dissolved in the water to be treated, and in particular of the PFAS type, especially regardless of the length of their carbon chain, or to eliminate contaminants of the photosynthetic microorganism type.

[0009] There is therefore a need to improve the removal of contaminants capable of forming aggregates, and in particular hydrophilic and / or amphiphilic dissolved molecules, and / or photosynthetic microorganisms, from an aqueous effluent. Summary

[0010] 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 contaminants capable of forming aggregates, the method comprising: - a flotation step during which the aqueous effluent is introduced and circulated within the flotation chamber, and brought into contact with the bubble bed generated by at least one bubble generation device, with at least some of the contaminants forming aggregates and / or at least some of the contaminants being transported by 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 aggregates and / or bubbles carrying the contaminants that have risen to the surface of the aqueous effluent, said process being characterized in that at least a part of the separated floating phase is returned inside the enclosure.

[0011] According to the invention, circulating the floating phase, namely returning all or part of the floating phase to the flotation chamber, increases the efficiency of removing contaminants capable of forming aggregates by increasing their concentration in the aqueous effluent. This increased concentration promotes the formation of aggregates within the effluent and thus facilitates their separation. Circulating the floating phase also reduces the energy required to generate bubbles and the amount of chemical reagents that need to be added. These chemical reagents include, for example, a surfactant, a coagulant, a flocculant, or an acid or base for pH adjustment, which promote the flotation of dissolved molecules, particularly amphiphilic and / or hydrophilic molecules, and / or promote the formation of contaminant aggregates.

[0012] The process according to the invention improves the separation of some of the contaminants capable of forming aggregates present in the liquid aqueous effluent. Indeed, contaminants capable of forming aggregates, depending on their concentration in the system, will naturally form aggregates that will rise in the floating phase to be subsequently separated. However, some contaminants will not naturally form aggregates, making their separation by flotation difficult. This is the case, for example, with amphiphilic contaminants containing short carbon chains. 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 can serve as a vector, i.e., a transport agent, for these contaminants. Furthermore, biological contaminants can also be transported by the bubbles to the surface of the aqueous effluent.Thus, the majority, if not all, of the contaminants present will be displaced either in the form of aggregates, and in particular micelles and / or hemi-micelles depending on their nature, by adhering to the gas bubbles, or simply transported by the aqueous effluent, or transported by the aqueous effluent and / or by the bubbles, in the form of aggregates or not, allowing their separation at the level of the floating phase.

[0013] Typically, the process may further include a step of recovering the purified aqueous effluent (i.e. the treated water) during which the purified aqueous effluent is discharged from the flotation chamber by at least one discharge pipe opening into the chamber outside the bubble bed, generally below the latter.

[0014] Advantageously, at least a portion of the separated floating phase can be degassed in at least one storage tank before being returned inside the enclosure.

[0015] Optionally, when at least one storage tank is present, sludge deposited at the bottom of at least one storage tank can 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.

[0016] Advantageously, the method may include at least one of the following features: - at least one chemical compound chosen 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, - 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 at least one bubble generation device.

[0017] The discontinuous generation of bubbles over time can also prevent an accumulation of bubbles in the installation.

[0018] Advantageously, the contaminants may include biological contaminants, optionally photosynthetic microorganisms.

[0019] Advantageously, alternatively or in combination, the contaminants may include chemical contaminants, in particular dissolved in the aqueous effluent, optionally amphiphilic molecules and / or hydrophilic molecules.

[0020] Advantageously, the chemical contaminants may include amphiphilic molecules selected from perfluoroalkyl substances and polyfluoroalkyl substances.

[0021] 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.

[0022] 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.

[0023] Advantageously, during the flotation step, the aqueous effluent and the bubbles carrying the contaminants carried by the aqueous effluent can 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 contaminants present in the aqueous effluent, at least a part of the contaminants carried by said bubbles being retained on a surface of the chemical retention material and / or inside pores of said chemical retention material.

[0024] This embodiment is particularly advantageous when the contaminants include chemical contaminants, especially those dissolved in the aqueous effluent to be treated.

[0025] The use of a physico-chemical retention system, through which the aqueous effluent containing contaminants passes, as well as contaminants transported by bubbles, and in particular adhering to the surface of the bubbles, makes it possible to further reduce the quantity of contaminants present in the aqueous effluent and improve its purification. Typically, at least one physico-chemical retention material is capable of retaining at least some of the dissolved molecules present in the aqueous effluent, in particular at least some of the amphiphilic and / or hydrophilic molecules present.

[0026] 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 contaminants, and in particular chemical contaminants, by the physico-chemical retention material.

[0027] Typically, the process may further include a step c) of recovery of the purified aqueous effluent (i.e. the treated water) during which the purified aqueous effluent is discharged from the flotation chamber by a discharge pipe opening into the chamber, outside the bubble bed, in particular below the physico-chemical retention system when present.

[0028] Advantageously, at least one chemical retention material may be in particulate form, in foam form, in gel form or in fiber form.

[0029] Advantageously, the at least one physico-chemical retention material may comprise a plurality of pores, for example pores of determined dimensions.

[0030] 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 contaminants, particularly those adhering to their surface, into the pores for retention.

[0031] Advantageously, the process may include, at predetermined time intervals, a step of replacing at least a portion of at least one chemical retention material. This step allows for the complete or partial renewal of the physico-chemical retention material and thus maintains the overall retention capacity of the physico-chemical retention system.

[0032] The invention also relates to a flotation treatment installation for a liquid aqueous effluent containing contaminants, 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 bubble bed inside the liquid present in the flotation chamber, at least one device for separating a floating phase on the surface of the liquid present in the flotation chamber, characterized in that it further comprises at least one recirculation line 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 at least one recirculation line between the at least one separation device and the flotation chamber.

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

[0034] Advantageously, the installation may include, within the enclosure and maintained attached to said enclosure, a physico-chemical retention system comprising at least one physico-chemical retention material capable of retaining at least a portion of the contaminants 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 enclosure by at least one bubble generation device.

[0035] The physico-chemical retention system may comprise 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 liquid flow within the enclosure, the retaining device having a plurality of through passages whose dimensions are smaller than the dimensions of the at least one physico-chemical retention material.

[0036] 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.

[0037] 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 and outside the bubble bed generated by at least one bubble generation device, optionally below the physico-chemical retention system, - at least one storage capacity for a chemical compound fluidically connected to the flotation chamber, - at least one chemical compound storage capacity fluidly connected to at least one bubble generation device, - a system for controlling the quantity of floating phase, optionally degassed, returned to the containment, and / or the duration of injection of the floating phase, optionally degassed, into the containment, optionally based on at least one target concentration of at least one contaminant inside the containment. 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] Photosynthetic microorganisms are microorganisms capable of using the photonic energy of light to synthesize organic molecules through the mechanism of photosynthesis. Photosynthetic microorganisms include microalgae and bacteria.

[0041] Hydrophilic molecules have an affinity for water. A hydrophilic molecule (or part of a hydrophilic molecule) is typically electrically polarized. It dissolves readily in polar liquids, such as water, and less readily in nonpolar liquids, such as oil.

[0042] Amphiphilic molecules are molecules that possess a water-soluble (hydrophilic) portion and a fat-soluble (lipophilic) portion. The hydrophilic portion can be polar or ionic, while the lipophilic portion is nonpolar. PFAS are amphiphilic molecules.

[0043] The acronym PFAS refers to all perfluoroalkyl substances and polyfluoroalkyl substances.

[0044] 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.

[0045] 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 PFAA class is divided into two main groups: Perfluoroalkylcarboxylic acids (PFCAs), with the formula CnF2n+rR (R=-COOH) or perfluoroalkylcarboxylates (CnF2n+iR, R=-COO), are degradation products of polyfluoroalkyl substances, such as fluorotelomere alcohols (FTOH). The most frequently detected PFCA is perfluorooctanoic acid, C7Fi5COOH (PFOA). Perfluoroalkane sulfonic acids with the formula CnF2n+rR, where R=-SO3H, or perfluoroalkyl sulfonates with the formula CnF2n+iR, where 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, C8Fi7SO3 (designated by the acronym "PFOS").

[0046] Perfluoroalkane sulfonamides of formula CnF2n+iR, with R=-SO2-NH2, designated by the acronym "FASA", such as perfluorooctane sulfonamide (FOSA, C8Fi7 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.

[0047] 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.

[0048] The expression "long-chain PFAS" generally refers to: - to perfluoroalkylcarboxylic acids, PFCA, comprising eight or more carbon atoms (seven or more carbon atoms are perfluorinated), - to perfluoroalkane sulfonates, PFSA, with six or more carbon atoms (six or more carbon atoms are perfluorinated), - and for all other perfluoroalkyls and polyfluoroalkyl substances, to PFAS having a carbon chain of six or more carbon atoms.

[0049] The expression "short-chain PFAS" generally refers to: - to perfluoroalkylcarboxylic acids comprising seven or fewer carbon atoms (six or fewer carbon atoms are perfluorinated), - to perfluoroalkane sulfonates of five or fewer carbon atoms (the five or fewer carbon atoms are perfluorinated), - and for all other perfluoroalkyl and polyfluoroalkyl substances containing PFAS with a carbon chain of five carbon atoms or less. Detailed description

[0050] Liquid aqueous effluent

[0051] 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 contaminants capable of forming aggregates, which may be biological contaminants. optionally photosynthetic microorganisms, and / or chemical contaminants, including those dissolved in the aqueous effluent, optionally hydrophilic and / or amphiphilic molecules, including amphiphilic molecules selected from perfluoroalkyl substances and polyfluoroalkyl substances, or any amphiphilic molecule capable of forming aggregates, including micelles and / or hemi-micelles, such as surfactants, soaps, detergents and emulsifiers.

[0052] Photosynthetic microorganisms may include microalgae and / or bacteria. Examples of photosynthetic microorganisms, living in fresh or salt water, that may be present in the aqueous effluent include, but are not limited to, cyanobacteria, chlorophytes, charophytes, diatoms, euglenophytes, dinoflagellates, cryptophytes, xanthophytes, chrysophytes, phaeophytes, rhodophytes, and pyrrhophytes, alone or in mixtures.

[0053] Hydrophilic molecules may include molecules generated by photosynthetic microorganisms, particularly microalgae, and / or micropollutants of industrial or agricultural origin (pesticides, pharmaceuticals, etc.). Examples of molecules generated by photosynthetic microorganisms include, but are not limited to, geosmin, 2-methylisoborneol (MIB), and toxins. The best-known toxins are microcystins (MC), cylindrospermopsins (CYN), nodularins (NOD), anatoxins (ATX), saxitoxins (STX), lyngbyatoxins, aplysiatoxins, and their derivatives.

[0054] Aqueous liquid effluents within the meaning of the said invention include raw water, urban effluents, industrial effluents and discharges from drinking water treatment plants.

[0055] Raw water within the meaning of said invention includes any water intended for the production of drinking water, such as groundwater, surface water or salt water.

[0056] 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).

[0057] 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.

[0058] Urban or industrial effluents include, in particular, liquid discharges from water treatment processes, and especially drinking water. These liquid discharges include including concentrates from reverse osmosis units, concentrates from nanofiltration units, eluates from the regeneration of ion exchange resins, eluates from chemical regeneration units of adsorbent materials such as activated carbon.

[0059] The aqueous effluent to be treated may include, in particular, one or more of the following characteristics:

[0060] - a quantity of photosynthetic microorganism cells greater than 2 millions per liter of aqueous effluent, as measured according to standard NF EN 15204, 2006,

[0061] - a volume of photosynthetic microorganisms greater than 0.65 mm3.L', such that measured according to standard NF EN 16695, 2015.

[0062] - a chlorophyll-a concentration of 14 pg.L', as measured according to the NF standard EN 16161,2012,

[0063] - a concentration of chemical contaminants, and in particular of molecules hydrophilic and / or amphiphilic molecules, and in particular PFAS, of 0.02pg / L or more, preferably from 0.02pg / L to 200pg / L.

[0064] 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.

[0065] Detailed description of the process

[0066] The process according to the invention makes it possible to eliminate contaminants capable of forming aggregates, and in particular chemical contaminants, especially dissolved in the aqueous effluent, and / or biological contaminants such as photosynthetic microorganisms, from a liquid aqueous effluent, especially as previously defined, this elimination combining the flotation purification technique, the generation of bubbles serving as vectors for the contaminants, and more particularly for chemical contaminants, and the recirculation of the floating phase in the flotation chamber.

[0067] To this end, it includes a flotation step, implemented in a flotation chamber comprising at least one recirculation line fluidly connecting at least one floating phase separation device to the flotation chamber, followed by a step of separating the floating phase located inside the chamber from the surface of the aqueous effluent, at least part of the floating phase separated via at least one separation device being returned inside the chamber via at least one recirculation line.

[0068] The combination of flotation and recirculation of the floating phase inside the flotation chamber improves the removal of contaminants capable of aggregating.

[0069] Typically, the process further includes a step of removing the purified aqueous effluent (depleted of contaminants) from the flotation chamber. This removal of the treated water is generally carried out continuously, typically at an area located downstream of the bubble bed generated inside the chamber, relative to the direction of flow of the aqueous effluent within the flotation chamber. When a physicochemical retention system is present, this removal is typically carried out downstream of it.

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

[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 at least one circulation device. For example, a pump or any other device commonly used in a flotation chamber may be used.

[0075] During this circulation process, the aqueous effluent will thus pass through the bubble bed and come into contact with the bubbles. The contact of the liquid effluent with the bubbles will allow at least some of the contaminants, and particularly the chemical contaminants, especially those that form least easily, to be removed. Aggregates (due to their intrinsic properties and / or the properties of the aqueous effluent) adhere to the surface of the bubbles. Furthermore, at least some contaminants, particularly biological contaminants, can be carried by the bubbles. These gas bubbles, associated with and / or transporting contaminants, tend to rise to the surface of the liquid effluent, and thus, at least partially, end up floating on the surface. It is therefore clear that the gas bubbles act as vectors for some contaminants.

[0076] Furthermore, during this flotation stage, at least some of the contaminants, and in particular chemical contaminants but also biological contaminants, especially those which easily form aggregates (due to their intrinsic properties and / or the properties of the aqueous effluent), will also form aggregates which will aggregate and form foams which will tend to rise to the surface of the liquid, and to be found, at least in part, in the floating phase.

[0077] In one embodiment, during the flotation step, the aqueous effluent and the bubbles carrying the contaminants entrained by the aqueous effluent pass through a physicochemical retention system located inside the vessel and secured to it, and comprising at least one physicochemical retention material capable of retaining at least some of the contaminants present in the aqueous effluent. The physicochemical retention system is located at least partially, and preferably entirely, within the bubble bed in the flotation vessel. Thus, the physicochemical retention system does not extend over the entire height of the liquid present inside the flotation vessel. In particular, it is located above and at a distance from the bottom of the flotation vessel to allow the treated water to be discharged away from the chemical retention system.

[0078] When bubbles pass through the physicochemical retention material, at least some of the contaminants, and particularly at least some of the chemical contaminants, especially those 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 a vector for the contaminants. Without being bound by any particular theory, this physicochemical retention can result from the adhesion of the contaminants associated with the bubbles to the internal and / or external surface of the physicochemical retention material, notably through a mechanism of adsorption, absorption, or ion exchange.Since the aqueous effluent passing through the physico-chemical retention system also contains contaminants, whether or not they are formed into aggregates, these contaminants can also be retained on the surface of the physico-chemical retention material and / or within the pores of the physico-chemical retention material. Furthermore, Contaminants formed into aggregates that were not retained by the physico-chemical retention system are found in the floating phase and are then separated in the usual way, and partly returned to the flotation stage.

[0079] Thus, contaminants, particularly chemical contaminants, and especially hydrophilic and / or amphiphilic molecules that readily form aggregates (due to their intrinsic properties and / or the properties of the aqueous effluent), such as long-chain PFAS, will primarily form aggregates that may be partially retained by the physicochemical retention system and partially accumulate on the surface of the aqueous effluent in the floating phase. This predominantly aggregated configuration does not preclude some of these contaminants from adhering to the surface of the bubbles without being formed into aggregates.

[0080] Contaminants, particularly chemical contaminants, and especially hydrophilic and / or amphiphilic molecules, which do not readily form aggregates (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 physico-chemical retention material. They can thus be partially retained by the physico-chemical retention system and partially accumulate on the surface of the aqueous effluent in the floating phase. Some of these contaminants may nevertheless also form aggregates.

[0081] Contaminants such as biological contaminants may form aggregates and / or be transported by bubbles and thus accumulate on the surface of the aqueous effluent in the floating phase.

[0082] By "physico-chemical retention," we mean the ability to retain a molecule by adsorption, absorption, ion exchange, and / or steric retention, preferably at least by adsorption, absorption, and / or ion exchange, and optionally by steric retention. 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.

[0083] 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 and / or hydrophilic contaminant to be eliminated.

[0084] Thus, in this embodiment, the process according to the invention makes it possible to optimize the removal of contaminants, and in particular amphiphilic and / or hydrophilic chemical contaminants, such as PFAS, regardless of the propensity of these chemical contaminants to form aggregates, and in particular micelles and / or hemi-micelles. It is possible to select at least one physicochemical retention material for the physicochemical retention system based on the nature of the chemical contaminants present in order to optimize their retention. Two or more different physicochemical retention materials can be used in the physicochemical retention system for this purpose. When the wastewater to be treated contains biological contaminants, particularly photosynthetic microorganisms such as microalgae and / or bacteria, the physicochemical retention system can be configured to exclude these biological contaminants. For example, one or more fiber-based retention materials could be used for this purpose.

[0085] Regardless of the embodiment, during the flotation step, the bubbles are generated by at least one bubble-generating device. Typically, the bubbles are generated by means of at least one 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 of the flotation chamber, carrying with them some of the contaminants, particularly chemical contaminants, 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.

[0086] The gas used to saturate the injected liquid can be chosen from air, ozone, nitrogen, oxygen, chlorine, and chlorine dioxide. Preferably, air is used.

[0087] 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.

[0088] In one embodiment, bubble generation can be discontinuous in time. Bubble generation is then intermittent. This can allow for the control of contaminant transport, particularly chemical contaminants.

[0089] During step a), the bubbles (i.e., gas-filled cavities) generated can be fine bubbles with a diameter less than 100 pm, microbubbles with a diameter from 1 pm to 100 pm, or ultrafine bubbles with a diameter of at most 1 pm. The fine bubbles, microbubbles, and ultrafine bubbles are such that as defined according to 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.

[0090] Preferably, the bubbles generated during the flotation step of the present invention are smaller in size than the bubbles used in conventional flotation processes. Preferably, ultrafine bubbles will be used, with a diameter of at most 200 nm, preferably at most 100 nm, and more preferably at most 50 nm, which is much smaller than the diameter of the bubbles used in conventional flotation processes (on the order of 50 µm).

[0091] The size of the bubbles can be measured by a laser light scattering measurement.

[0092] It will be possible to adjust the contact time between the aqueous effluent to be treated and the bubbles, and / or between the aqueous effluent to be treated and the minimum retention material of the retention system when present, for example by adjusting the flow rate of the aqueous effluent and / or the size of the bubbles.

[0093] The contact time between the aqueous effluent to be treated and the bubbles depends on the circulation speed of the aqueous effluent inside the enclosure, this speed being for example 10 to 30 m / h.

[0094] By way of example, a contact time of at least 5 minutes between aqueous effluent and retention material may be provided, preferably at least 10 minutes, advantageously at least 30 minutes, typically at most 60 minutes.

[0095] The bubble size and contact time can be adjusted according to the effluent to be treated, and in particular the quantity and / or type of contaminants to be separated to promote the migration of contaminants to the floating phase, and / or the retention of contaminants in the physico-chemical retention system when present.

[0096] When the physico-chemical retention system is present and 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.

[0097] Depending on the nature of the contaminants present, whether chemical or biological contaminants, their conformation into aggregates 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).

[0098] 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 its entry into The bubble-generating device may introduce into the chamber, and / or at least one chemical compound selected from a flotation aid, a flocculation aid, and a coagulation aid. These compounds may enhance foam formation by promoting aggregate formation and facilitating the association of chemical contaminants with the bubbles.

[0099] For example, the pH can be adjusted and controlled according to the type of chemical contaminants to be treated.

[0100] 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+.

[0101] The surfactant may advantageously be an anionic or cationic surfactant, with a charge opposite to a charge of a hydrophilic and / or amphiphilic molecule to be removed. For example, cationic surfactants may be used to remove PFOA, for example, selected 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).

[0102] 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 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.

[0103] When the chemical compound is introduced into the enclosure by means of at least one bubble generation device, it can for example be mixed with the gas-supersaturated liquid.

[0104] Physico-chemical retention system

[0105] The physico-chemical retention system used in an embodiment of the present invention allows for the retention of at least some of the contaminants, and in particular chemical contaminants, 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] The physico-chemical retention system is kept attached to the enclosure and includes at least one physico-chemical retention material.

[0110] By "physico-chemical retention material" is meant a material capable of retaining a molecule of interest, here an amphiphilic and / or hydrophilic 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.

[0111] The physico-chemical retention material has, in particular, the function of retaining chemical contaminants on its external surface and / or on its internal surface within pores, if present. Free chemical contaminants can be retained directly by the physico-chemical retention material as the aqueous effluent flows through the retention material, as can chemical contaminants formed into aggregates, particularly micelles and / or hemi-micelles. Chemical contaminants 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 chemical contaminants 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 by optimizing the transport of chemical contaminants over the entire available surface of the physico-chemical retention material.

[0112] 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 chemical contaminants to be removed, the size of the aggregates likely to form, and / or the size of the bubbles.

[0113] 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.

[0114] The physico-chemical retention material can be in particulate form, in foam form, in gel form or in fiber form.

[0115] When in fiber form, 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 a plurality of 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 fixed.This embodiment is particularly advantageous when the effluent to be treated contains photosynthetic microorganisms, and in particular microalgae and / or bacteria, as these are little or not retained by the retention system, which makes it possible to limit or eliminate clogging and / or pressure build-up in the retention system due to the retention of these microorganisms and thus reduce maintenance operations on the retention system.

[0116] 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.

[0117] 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.

[0118] When in particulate form, the physico-chemical retention material can have a particle size of 0.1 mm to 1 cm.

[0119] 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). It may also be provided 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.

[0120] 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.

[0121] The physico-chemical retention material thus retains the chemical contaminants present in the aqueous effluent passing through it. Since its retention capacity is limited, it is preferable to replace it regularly. Therefore, in one embodiment, the process may include, at predetermined time intervals, a step of replacing at least a portion of at least one physico-chemical retention material.

[0122] 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.

[0123] 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.

[0124] 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) polymers with a 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.

[0125] The physico-chemical retention material is typically chosen according to the type of chemical contaminant (in particular hydrophilic and / or amphiphilic molecules) to be treated and may also be selected according to the composition of the aqueous effluent. The choice may be made based on existing literature or on laboratory tests. The quantity of material The retention system to be used can be chosen based on the flow rate of liquid effluent to be treated and the amount of chemical contaminants to be removed.

[0126] 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.

[0127] (i) Cyclodextrin polymers and cyclodextrin polymers supported or unsupported on a solid substrate.

[0128] Cyclodextrins (hereinafter referred to as "CDs") 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 covalently linked together using a crosslinking agent. These cyclodextrin macromolecules may be natural or synthesized CDs, and optionally their derivatives.

[0129] (ii) Activated carbon

[0130] 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 and / or hydrophilic molecules.

[0131] (iii) Organic clays / (iv) Inorganic-organic clays

[0132] 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.

[0133] 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 hydrophilic and / or amphiphilic molecules such as PFAS, for example PFOS or PFOA. Preferably, to improve the efficiency of the removal of PFAS, organic clays can be modified by at least one cationic modifier, in particular an organic cation.

[0134] (v) Porous structure polymers

[0135] 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.

[0136] 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.

[0137] (vi) Biochar, activated or not

[0138] Biochar can also be used for the removal of hydrophilic and / or 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.

[0139] 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.

[0140] (vii) Carbon fibers

[0141] Carbon fibers can also be used for the removal of hydrophilic and / or 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.

[0142] (viii) Polyacrylonitrile fibers

[0143] 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.

[0144] 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.

[0145] The average diameter of PAN fibers, functionalized or not, is typically 500 to 600nm.

[0146] (ix) Zeolites and (x) silica

[0147] 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.

[0148] Separation step

[0149] 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 bubbles associated with contaminants, in particular chemical contaminants, contaminants transported by the bubbles, as well as contaminants, in particular biological and / or chemical contaminants, arranged in aggregates that have risen to the surface of the aqueous effluent.

[0150] The separation step is implemented in a usual manner by at least one separation device which may, for example, include at least one discharge pipe towards which the floating phase can be pushed generally by means of one or more overflow or scraping devices provided for this purpose.

[0151] In addition, at least part of the separated floating phase is returned inside the enclosure. Before being returned inside the flotation enclosure, the floating phase may preferably be pre-degassed in at least one storage tank.

[0152] Recirculating the floating phase helps limit discharges in liquid form and also promotes aggregate formation, since the concentration of contaminants capable of forming aggregates increases when the floating phase and the aqueous effluent are added together. The foams from the floating phase can be recirculated as foam or as liquid (after degassing).

[0153] During this recirculation of the floating phase, sludge may settle at the bottom of the storage tank(s). This sludge can then be removed, which prevents the suspended solids that have accumulated in the flotation chamber from being reintroduced into the chamber and disrupting the flotation process.

[0154] 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 achieve and / or maintain at least a target concentration of at least one contaminant inside the chamber.

[0155] To this end, 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.

[0156] 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 aggregate naturally. These target concentrations can be determined by testing and / or simulations.

[0157] One or more of the following controls may therefore be considered:

[0158] - 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),

[0159] - 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.

[0160] - 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.

[0161] In all cases, the control system can be programmed to increase the amount 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 amount injected and / or the duration of injection when the concentration of at least one contaminant is greater than the target concentration for that contaminant.

[0162] 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.

[0163] 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 outputs can 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.

[0164] 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.

[0165] 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.

[0166] 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 forms, during step a) of flotation.

[0167] 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 in the same chamber. The purified aqueous effluent may be used as drinking water, possibly after further purification treatments, or discharged into the environment. Drawing description

[0168] The invention will be better understood with reference to the figures, which show two exemplary embodiments of the invention.

[0169] The [Fig. 1] represents a liquid aqueous effluent treatment installation by flotation according to a first embodiment of the invention.

[0170] Fig. 2 represents the installation for treating a liquid aqueous effluent by flotation according to a second embodiment of the invention.

[0171] In the figure, the arrows represent the direction of flow of aqueous effluent inside the flotation chamber.

[0172] 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 21 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.

[0173] 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 41. 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.

[0174] 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(s) 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.Depending on the nature of the effluent to be treated, the coagulation and / or flocculation zone may be omitted.

[0175] 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 an optional mixer 32 for improving the homogeneity of the mixture of the aqueous effluent with the recirculated floating phase, and optionally the added chemical compound(s). This first section forms a coagulation and / or flocculation zone which can be omitted depending on the nature of the effluent.

[0176] 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, here substantially vertically. The second part 33 includes a boundary wall 34b, here substantially vertical, 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 has a bubble generation device 50 capable of generating a bed of bubbles within 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 in which the aqueous effluent flows towards the surface of the liquid present in the enclosure. 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.

[0177] The bubble generation device 50 here includes 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 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, at least one 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.

[0178] 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 aggregates of contaminants that have risen to the surface. Below this floating phase 36a, the liquid 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.

[0179] 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, below it. Depending on the dimensions of the chamber, one or more discharge pipes 38 may be provided.

[0180] The treated aqueous effluent is then discharged into the environment, further treated, and / or partly reused by the bubble generation device 50.

[0181] 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.

[0182] The separation device 80 here includes a conduit 81 for the discharge of part of the floating phase.

[0183] Depending on the dimensions of the enclosure, one or more separation devices 80 may be present. The invention is further not limited by a separation device specific, and any device suitable for separating a floating phase in a flotation chamber can be used (scraping device, overflow device, ...).

[0184] This floating phase is at least partly recycled in the process as described below.

[0185] The installation 1 thus includes a recirculation line 82 fluidly connecting the floating phase separation device 80 to the first section 31 of the flotation chamber 30. When this first section 31 is omitted, the recirculation line 82 can open into the second section 33. 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 means 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.

[0186] 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 chemical contaminant concentrations higher than critical micellar concentrations and / or biological contaminant concentrations higher than concentrations at which these contaminants naturally flocculate more quickly, or more reliably.

[0187] The treatment installation 1 shown in [Fig.2] differs from that shown in [Fig.1] only by the presence of a physico-chemical retention system 37. The same elements are thus designated by the same references.

[0188] In the example shown, 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 in which the bubbles are located, and advantageously entirely within the bubble bed, as shown in [Fig. 2]. 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.

[0189] 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 holding devices 37b, 37c, for example, perforated plates or grids having through-holes smaller than the particles of the retention material(s). The invention is not, however, limited to this embodiment. In particular, a single holding device may be provided: when the particulate physico-chemical retention material is denser than the liquid to be treated and naturally tends to settle, the holding 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, the retention device 37b can suffice.

[0190] The particulate material could also be replaced, in whole or in part, 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.

[0191] When the aqueous effluent to be treated includes microorganisms, it is preferable to use one or more retention materials in the form of fibers attached to a retaining device which extends parallel or transversely to the direction of flow (generally vertical direction).

Claims

Demands

1. A process for treating a liquid aqueous effluent by flotation in a flotation chamber equipped with at least one bubble-generating device (50) capable of generating a bubble bed within the liquid present in the chamber (30), the aqueous effluent containing contaminants capable of forming aggregates, the contaminants being photosynthetic microorganisms or perfluoroalkyl substances and / or polyfluoroalkyl substances, the process comprising: - a flotation step during which the aqueous effluent is introduced and circulated within the flotation chamber (30), and brought into contact with a bubble bed generated by at least one bubble-generating device (50), at least a portion of the contaminants forming aggregates and / or at least a portion of the contaminants being transported by the bubbles,- a step of separating a floating phase (36a) located inside the enclosure from the surface of the aqueous effluent, the floating phase (36a) containing the aggregates and / or bubbles carrying the contaminants that have risen to the surface of the aqueous effluent, at least a part of the separated floating phase (36a) being returned inside the enclosure, the process being characterized in that it comprises control of the quantity of said floating phase, optionally degassed, returned inside the enclosure, and / or of a duration of injection of the floating phase, optionally degassed, inside the enclosure, optionally as a function of at least one target concentration of at least one contaminant inside the enclosure.

2. A method according to claim 1, characterized in that at least a part of the separated floating phase is degassed in at least one storage tank (83) before being returned inside the enclosure, and optionally sludge deposited at the bottom of at least one storage tank is removed.

3. A method according to claim 1 or 2, 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 coagulation aid compound to flocculation, and a pH modifying compound 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 at least one bubble-generating device.

4. A method according to any one of claims 1 to 3, characterized in that it comprises at least one of the following features: - the separated floating phase, optionally degassed, is returned, in part or in whole, inside the enclosure, continuously or not over time, until at least a target concentration of at least one contaminant is obtained inside the enclosure.

5. A method according to any one of claims 1 to 4, characterized in that, during the flotation step, the aqueous effluent and the contaminant-carrying bubbles carried by the aqueous effluent pass through a physico-chemical retention system (37) located inside the enclosure, at least partly, 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 portion of the contaminants present in the aqueous effluent, at least a portion of the contaminants carried by said bubbles being retained on a surface of the physico-chemical retention material and / or inside pores of said physico-chemical retention material.

6. Processing method according to claim 5, characterized in that at least one physico-chemical retention material is in particulate form, in foam form, in gel form or in fiber form.

7. A method according to any one of claims 5 or 6, characterized in that it comprises, at specified time intervals, a step of replacing at least a part of at least one physico-chemical retention material.

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