SYSTEM AND METHOD FOR RECOVERING TEXTILE MICROFIBERS FROM A DRAINAGE LIQUID BY DISSOLVED AIR FLOTATION

Abstract

The present invention relates to a system and a method for recovering microfibers contained in a liquid effluent (L) from a textile treatment device. The system comprises at least one device for dissolving a gas (2, 4, 10, 20, 30, 5) directly into at least a portion of the liquid effluent (L) by pressurization and a device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62) connected together. The device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62) further comprises means for collecting (60, 61, 62) the microfibers (MF) from the surface of the liquid effluent (L) contained within its enclosure (50). Figure 1 to be published

Description

Title of the invention: SYSTEM AND METHOD FOR RECOVERING TEXTILE MICROFIBERS FROM A AIR FLOTATION DRAIN FLUID technical field

[0001] The present invention relates to the field of the removal of microfibers contained in a drain fluid from a textile processing device, such as a washing machine, a laundry (industrial or not), a device for dyeing textiles, or a device for waterproofing textiles.

[0002] Plastic is ubiquitous in our daily lives, and our clothes are no exception, as approximately 60% of the fibers used in the global textile industry are made from plastics such as polyester, polyamide, or acrylic. Due to abrasion during washing, these synthetic fibers can break down into microfibers. It is generally accepted that plastic microfibers are fragments of synthetic fibers with a length between 1 µm and 5 mm. According to recent studies, more than 700,000 plastic microfibers can be released with each use of a domestic washing machine. Discharged into wastewater, they are only partially retained in wastewater treatment plants (WWTPs), and a portion therefore ends up in rivers and then the oceans.It is estimated that 500kT / year of plastic microfibers from washing machines are released into the aquatic environment worldwide, representing nearly 33% of estimated primary microplastic releases.

[0003] In addition to discharges into the aquatic environment, it is important to note that the majority of plastic microfibers retained in wastewater treatment plants end up in the sludge during the initial treatment stages. However, the main use of this sludge in France, and in most countries, is spreading on agricultural land to amend and fertilize the soil. These microfibers therefore also end up in the natural environment. A post-treatment solution at wastewater treatment plants to reduce plastic microfiber discharges into the oceans would only solve part of the problem. To be effective, plastic microfiber capture solutions must be deployed as close as possible to the emission sources, that is, at the outlet of textile washing systems.

[0004] Several studies have shown the presence of these microplastics in our food (fish, seafood, etc.) or in drinking water. The University of Newcastle in Australia, for example, estimated that a human being ingests an average of 5g of microplastics per week, the equivalent of a credit card. The consequences The effects on human health are still unknown, but it is already known that microplastics adsorb organic pollutants and metals (whose toxicity is proven) onto their surface and impair the growth and reproduction of certain living organisms.

[0005] Furthermore, on February 11, 2020, France enacted a law on combating waste and promoting the circular economy, in which Article 79 stipulates that new washing machines must be equipped with a plastic microfiber filter from January 1, 2025. France was thus the first country in the world to take regulatory measures on the issue of microfiber emissions from washing machines. An amendment was subsequently adopted, specifying that the professional sector will also be affected, and that solutions external to washing machines may be considered. Previous technique

[0006] We are familiar with application WO2017 / 173215A1, which describes a spherical plastic object that is placed in the drum of a washing machine with the clothes to be cleaned and captures the released fibers in situ thanks to numerous protrusions. However, the geometry of these protrusions is not currently designed to capture small objects such as microfibers, as the retention efficiency for microfibers longer than 100 pm is only 26%.

[0007] Patent application WO2021 / 197937A1 is also known, which relates to a system and a method for filtering microfibers contained in a liquid effluent from a textile treatment device. More specifically, this system comprises a granular medium arranged in a chamber, means for percolating the liquid effluent through the granular medium, means for discharging the liquid effluent beneath the granular medium, and means for connecting to means for regenerating the granular medium by gaseous fluidization. Thus, this system allows the granular medium to be regenerated, particularly in the event of clogging. However, the presence of long natural fibers and soiling can quickly clog the granular medium, and the regeneration frequency can become too high, especially in the professional sector where the washing rate does not allow for frequent interruptions of the filtration process.

[0008] Patent application WO20057820A1 is also known, which relates to a device and a method for recovering microplastic fibers by means of a hydrocyclone located upstream of a cartridge filtration system. Such a system requires operation with a liquid pump that can generate pressure drop (implying high power consumption), and a cleaning process. of the filter (requiring regular maintenance and consuming additional water). Furthermore, this process is limited by the nature or density of the material constituting the fiber. Indeed, this process can only recover fibers that have either a density lower than that of water (as in the case of polyethylene, for example) or the opposite (as in the case of PET), but cannot recover both simultaneously.

[0009] More particularly in the field of industrial laundries in France, the filtration technologies used are technologies known to those skilled in the art such as screening baskets, static curved screens, rotary screens or continuous chain self-cleaning screening.

[0010] Existing filtration methods used in laundries can be continuously regenerated, with solids isolated and recovered as waste, but their filtration mesh size is too large (between 500 µm and 1 mm) to effectively capture microfibers, which are small particles, most often less than 200 µm in length. However, it is not technically possible to significantly reduce the mesh size of these sieve-based technologies due to machining and / or clogging issues.

[0011] The present invention overcomes these drawbacks. More specifically, the present invention relates to a method and a system for recovering microfibers contained in a liquid effluent from a textile treatment device, by means of generating gas microbubbles obtained by expanding dissolved gas directly in the liquid effluent to be treated. In particular, generating gas bubbles directly in the liquid effluent allows a major portion of the microfibers attached to the microbubbles to rise to the surface, and moreover, in a rapid manner and without risk of fouling or clogging the system. Summary of the invention

[0012] The present invention relates to a system for recovering microfibers contained in a liquid effluent from a textile treatment device, said system comprising at least:

[0013] A) A device for dissolving a gas in said liquid effluent by pressurization, comprising a first enclosure, means for bringing at least a part of said liquid effluent into said first enclosure, means for bringing said gas, means for compressing said gas, and means for evacuating said at least a part of said liquid effluent comprising said dissolved gas;

[0014] B) A device for separation by dissolved gas flotation, comprising a second chamber, means for reducing the pressure of said gas, means for bringing said at least a portion of said liquid effluent comprising said dissolved gas into said second chamber, and means for collecting surface microfibers. the liquid effluent in said second enclosure and means for the evacuation of the clarified liquid effluent from said second enclosure.

[0015] According to one embodiment of the invention, said means for collecting said microfibers may include means for collecting by scraping, by suction or by overflow.

[0016] According to one embodiment of the invention, said second chamber of said device for separation by dissolved gas flotation may include at least one separator extending perpendicularly with respect to the base of said chamber and disposed between said means for bringing said at least a part of said liquid effluent comprising said dissolved gas into said second chamber and said means for evacuating the clarified liquid effluent from said second chamber.

[0017] According to one embodiment of the invention, said second chamber of said device for separation by dissolved gas flotation may comprise at least one separator in the form of a hollow cylinder, said hollow cylinder being arranged so that an opening of said means for bringing said at least a part of said liquid effluent comprising said dissolved gas into said second chamber is inside said hollow cylinder, and an opening of said means for evacuating the clarified liquid effluent from said second chamber is outside said hollow cylinder.

[0018] According to one embodiment of the invention, said device for separation by dissolved gas flotation may further include means for bringing another part of said liquid effluent into said enclosure of said device for separation by dissolved gas flotation.

[0019] According to one embodiment of the invention, a geometry of said first enclosure and said means for compressing the gas of said device for dissolving a gas in said liquid effluent by pressurization can be configured so that the volume fraction of said gas is between 0.1 and 10%, preferably between 0.5 and 5%.

[0020] The invention further relates to a method for recovering microfibers contained in a liquid effluent from a textile treatment device, said method being implemented by means of the system for recovering microfibers contained in a liquid effluent from a textile treatment device as described above, said method comprising at least the following steps:

[0021] a) at least a part of said liquid effluent from said textile treatment device is introduced into said first chamber of said device for dissolving a gas in said liquid effluent by pressurization, and, by means of said device for dissolving a gas in said liquid effluent by pressurization, said at least a part of said liquid effluent comprising a dissolved gas is produced in said first chamber;

[0022] b) at least a part of said liquid effluent comprising said dissolved gas is introduced into said device for dissolved gas flotation separation, and by means of said device for dissolved gas flotation separation, at least a part of said liquid effluent comprising the dissolved gas is depressurized and said microfibers are separated by flotation from at least said at least a part of said liquid effluent;

[0023] c) said microfibers present on the surface of said liquid effluent are collected in said second enclosure by means of said microfiber collection means of said device for separation by dissolved gas flotation;

[0024] d) the said clarified liquid effluent is evacuated from the said second enclosure, by means of the said means for the evacuation of the said clarified liquid effluent from the said device for separation by dissolved gas flotation.

[0025] According to one embodiment of the invention, at the end of step d), said clarified liquid effluent can be introduced into at least one filtration and / or separation device for microfibers contained in a liquid effluent.

[0026] According to one embodiment of the invention, said filtration and / or separation device can be chosen from a granular media filtration device, a membrane filtration device, a hydrocyclone filtration device, a flocculation filtration device or a decantation filtration device.

[0027] According to one embodiment of the invention, said granular medium filtration device may further include means for connecting to means for regenerating said granular medium by gaseous fluidization.

[0028] Other features and advantages of the system and method according to the invention will become apparent from the following description of non-limiting examples of embodiments, with reference to the figures attached and described below. List of figures [Fig 1]

[0029] Fig. 1 schematically illustrates a first implementation of the system for recovering microfibers contained in a liquid effluent according to the invention. [Fig 2]

[0030] Figure [Fig.2] schematically illustrates a second implementation of the system for the recovery of microfibers contained in a liquid effluent according to the invention. [Fig 3]

[0031] Fig. 3 schematically illustrates a third implementation of the system for recovering microfibers contained in a liquid effluent according to the invention. [Fig 4]

[0032] Figure 4 schematically illustrates a fourth implementation of the system for recovering microfibers contained in a liquid effluent according to the invention. Description of the implementation methods

[0033] According to a first aspect, the invention relates to a system for recovering microfibers contained in a liquid effluent from a textile treatment device.

[0034] According to a second aspect, the invention relates to a method for recovering microfibers contained in a liquid effluent from a textile treatment device, which can be implemented using the system for recovering microfibers contained in a liquid effluent from a textile treatment device according to the invention, or not.

[0035] The term "microfibers," or "textile microfibers," refers to particles originating from woven (or non-woven) or knitted materials composed of natural fibers (cotton, wool, etc.) and / or synthetic fibers (polyester, polyamide, acrylic, etc.), such as clothing or fabrics used in apparel or for any other application (e.g., sheets, curtains, etc.) in homes or industries. Microfibers, normally carried away in the drain water of a washing machine, are generally elongated, with diameters typically ranging from 0.1 to 50 microns. The fiber length can vary from a few diameters to several millimeters, depending on the nature and condition of the materials being washed.

[0036] The term "textile processing device" refers in particular to a textile washing device, for example, an individual washing machine (or washing machine), for domestic or commercial use, a set of washing machines (for example, in laundries), an industrial laundry (for example, a laundry facility), etc. But a textile processing device according to the invention generally includes any device that brings a textile into contact with a liquid, the liquid then being separated from the textile, such as a device for dyeing a textile, or a device for waterproofing a textile.

[0037] The term "liquid effluent from at least one textile treatment device" means the liquid from the draining of the textile treatment device, for example, the liquid after washing and / or rinsing and / or spinning in the case of a washing machine. It is hereafter referred to equivalently as "drain fluid". In conventional textile treatment systems, the microfiber load of liquid effluents is generally limited, with levels ranging from 0.1 to 1000 ppm by weight, typically between 1 and 500 ppm by weight. "Clarified liquid effluent" refers to liquid effluent from at least one textile treatment system that has been separated from at least some of the microfibers it contains.

[0038] The system for recovering microfibers contained in a liquid effluent from a textile treatment device according to the invention comprises at least: - A device for dissolving a gas in said liquid effluent by pressurization, comprising a first enclosure, means for bringing at least a part of said liquid effluent into said first enclosure, means for bringing said gas, means for compressing said gas, and means for evacuating said liquid effluent comprising said dissolved gas; - A device for separation by dissolved gas flotation, comprising a second enclosure, means for reducing said gas, means for bringing said at least a part of said liquid effluent comprising said dissolved gas into said second enclosure, means for collecting microfibers on the surface of the liquid effluent in said second enclosure and means for evacuating the clarified liquid effluent from said second enclosure.

[0039] Thus, the system according to the invention differs from the prior art in that it implements the principle of flotation to separate the microfibers contained in a liquid effluent from a textile treatment device. Furthermore, the system according to the invention is configured for dissolving a gas directly in at least a portion of the liquid effluent to be treated, this liquid effluent, including the dissolved gas, then being injected into a device for separation by dissolved gas flotation. In processes involving flotation in fields other than that of the invention, the gas is dissolved in a liquid (generally water; this is then referred to as white water) separate from the liquid effluent to be treated.Generating these microbubbles directly within the liquid effluent to be treated allows for better attachment of the microbubbles to the microfibers (because some of the bubbles will nucleate directly on the suspended fibers during expansion) and therefore a better efficiency of microfiber recovery and uptake.

[0040] Indeed, the flotation kinetics, that is to say the kinetics describing the local phenomena of bubble-microfiber interaction, is classically decomposed as the product of three probabilities: - A probability of collision between bubbles and microfibers, essentially dependent on the hydrodynamics of the system considered (aspect ratio) fiber length over diameter, bubble diameter, gas volume fraction, liquid properties (density, viscosity); - a probability of attachment of microfibers to bubbles, dependent on surface forces (wetting of microfibers, van der Waals force, electrostatic forces, etc...) and therefore on the physico-chemical properties of the chemical system considered and in particular the presence of surfactants in the continuous liquid phase. - a probability of detachment (quantifying the risk of detachment of microfibers from bubbles), dependent on surface forces and hydrodynamics, and in particular if the regime of the continuous liquid phase is turbulent or if the gas volume fraction ratio is too high (which can generate induced turbulence (“bubbles induced turbulence”) if the gas volume fraction ratio is too high (greater than 10%).

[0041] The Applicant has observed, through laboratory tests, that generating microbubbles directly within the liquid effluent to be treated increases the probability of microbubbles attaching to microfibers. Indeed, during the rapid expansion of gas in the effluent, the nucleation phenomenon occurs preferentially on microfibers. In the application of the invention, the probability of collision and attachment is increased by this nucleation phenomenon directly on the textile microfibers, thus providing improved capture and recovery efficiency at the microfiber surface.

[0042] Furthermore, the Applicant was able to observe that, by this same phenomenon, hydrophilic microfibers, either by nature or by treatment, are captured by the bubbles (by direct nucleation of the bubbles on the microfibers), whereas the probability of attachment between the bubbles and the hydrophilic particles would be much lower in a conventional flotation separation process (gas dissolved in water).

[0043] In addition, the system according to the invention makes it possible to do without the use of a circulation device (pump) and control means to generate white water.

[0044] Finally, the device according to the invention also has the advantage of being compact, and in particular of having a reduced footprint compared to flotation devices known in other fields of application, thus making it perfectly suited to the treatment of effluents from textile treatment devices.

[0045] Figure 1 schematically illustrates a first implementation of the system for recovering microfibers contained in a liquid effluent according to the invention. For this implementation, the entire liquid effluent to be treated, L, is compressed by a pump 10 to enter the chamber 30 of the device to dissolve a gas G by pressurization 2, 4, 5, 20, 30 through a liquid inlet 2. The chamber 30 is also connected to a compressed gas inlet 4. The gas G is Compressed by a compressor 20 supplied by a pipe 3, the pressurized chamber 30 allows the dissolution of gas G in the liquid effluent L to be treated. The liquid effluent, containing the dissolved gas LG, is depressurized by means of a depressurization unit 40 upstream of the chamber 50 of the device for separation by dissolved gas flotation 5, 6, 7, 40, 50, 60, allowing the generation of microbubbles MB and the rise of microfibers MF into the chamber 50. The chamber 50 of the device for separation by dissolved gas flotation 5, 6, 7, 40, 50, 60 is also equipped with a microfiber collection system 60 allowing these to be discharged via the discharge pipe 7. The clarified effluent LC is discharged from the chamber 50 via the discharge pipe 6.

[0046] Description of the device for dissolving a gas in the liquid effluent by pressurization

[0047] The device for dissolving a gas in the liquid effluent by pressurization is intended to receive at least a part of the liquid effluent from the textile treatment device.

[0048] According to the invention, it comprises at least one enclosure, means for bringing at least a part of the liquid effluent into the enclosure, means for bringing the gas, means for compressing the gas, and means for evacuating said at least a part of the liquid effluent comprising the dissolved gas.

[0049] According to one embodiment of the invention, the enclosure (also called saturator) of the device for dissolving a gas in the liquid effluent by pressurization can be cylindrical or parallelepiped in shape, preferably cylindrical.

[0050] Preferably, the enclosure can be formed from metal so as to allow resistance to pressure. Preferably, the enclosure can be formed from stainless steel.

[0051] According to an embodiment in which the gas and the liquid effluent are brought into contact in the enclosure in co-current (flow of liquid effluent and gas in the same direction) or counter-current (flow of liquid effluent and gas in opposite directions), the enclosure is preferably substantially elongated along the vertical axis.

[0052] Subsequently, the terms "upper" or "lower" part or wall are defined with respect to the median plane of the enclosure of the device for dissolving a gas in the liquid effluent by pressurization in the service position.

[0053] According to an embodiment in which the gas and the liquid effluent are brought into contact in the co-current enclosure, the openings of the means for supplying the gas and the means for supplying at least a portion of the liquid effluent into the enclosure may be arranged in an upper part of the enclosure, advantageously in the upper wall of the enclosure, and most preferably in a central part of this upper wall (for example, located in an area centered on the centroid of the upper wall, and whose radius may correspond (at 30% of the smallest dimension of the upper wall). An opening in a central part of the upper wall of the enclosure allows for better distribution of the liquid and gas, and thus better contact.

[0054] According to an embodiment in which the gas and the liquid effluent are brought into contact in the enclosure in a counter-current manner, the opening of the means for bringing at least a part of the liquid effluent (respectively the means for bringing the gaseous effluent) into the enclosure can be arranged in an upper (respectively lower) part of the enclosure, advantageously in the upper (respectively lower) wall of the enclosure, and most preferably in a central part of this upper (respectively lower) wall, for example located in an area centered on the center of gravity of the upper (respectively lower) wall, and whose radius can correspond to 30% of the smallest dimension of the upper (respectively lower) wall.An opening in the central part of the upper (or lower) wall of the enclosure allows for better distribution of the liquid (or gas), and thus better contact.

[0055] According to one embodiment of the invention, the liquid effluent is brought into contact with the gas via a gaseous gap. In this embodiment, the enclosure is preferably substantially elongated along the horizontal axis, and the opening of the means for supplying at least a portion of the liquid effluent into the enclosure is located in a lower part of the enclosure, while the opening of the means for supplying the gas is located in an upper part of the enclosure. Preferably, the enclosure in this embodiment can have a length of at least 20 cm (for a liquid effluent flow rate of 120 L / h), which is a sufficient length for gas / liquid contact.

[0056] According to one embodiment of the invention, the geometry of the enclosure and the gas compression means can be configured so that the gas volume fraction is between 0.1 and 10%, preferably between 0.5 and 5%. In particular, any geometry that increases the exchange surface area (addition of baffles, a film running down the walls, etc.) makes it possible to increase the amount of dissolved gas (up to the saturation point given by Henry's law). Those skilled in the art have full knowledge of the means for configuring the device to dissolve a gas in the liquid effluent by pressurization so that the gas volume fraction is between 0.1 and 10%, preferably between 0.5 and 5%.

[0057] According to a preferred embodiment, the opening of the means for bringing at least a portion of the liquid effluent into the enclosure can be located in an upper part of the enclosure. This makes it possible to create within the saturator a laminar or turbulent liquid jet, or even a liquid film falling through a pressurized gaseous space, down to a liquid guard located at the bottom of the saturator, the latter being necessary to ensure that the downstream supply pipes are constantly pressurized, i.e. filled with liquid effluent.

[0058] According to one embodiment of the invention, the opening of the means for bringing at least part of the liquid effluent into the enclosure may have a diameter of at least 8 mm to avoid any risk of clogging.

[0059] According to one embodiment, for a flow rate of 4L / min, an internal diameter of saturator of 150 mm and a liquid inlet orifice diameter of 10 mm, a drop height of at least 20 cm in a gaseous head at 7 bar and a temperature of around 20°C can make it possible to have a volume fraction allowing the recovery and collection by flotation of microfibers in a concentration of around 200 ppm in a liquid effluent from a textile treatment device.

[0060] Preferably, the device for dissolving a gas in the liquid effluent by pressurization includes means for controlling the liquid level in the enclosure (such as a valve controlled by a level sensor or a liquid line with a height equivalent to the desired level in the enclosure) and configured to obtain a gas head occupying at least 30%, preferably at least 50%, of the total height of the enclosure. This provides sufficient height for the liquid to be brought into contact with the gas and liquid.

[0061] The compression means of the device for dissolving a gas in said liquid effluent by pressurization can be any type of compressor known to those skilled in the art. According to one embodiment of the invention, the compression means are sized to allow a pressurization of between 2 and 20 bar, preferably 4 and 10 bar.

[0062] According to one embodiment of the invention, the gas can be air. In this way, the gas can simply be drawn from outside the flotation separation device according to the invention, thus avoiding the need for means to store the gas.

[0063] According to one embodiment in which the liquid effluent from the textile treatment device has a low pressure (for example, close to atmospheric pressure), this effluent can be pre-pressurized using a pump before being introduced into the device's enclosure to dissolve a gas in the liquid effluent by pressurization. This can be useful when the liquid effluent is collected, at the outlet of the textile treatment device, in a recovery tank. A pump can then pump the liquid effluent to be treated from this tank and send it to the saturator.

[0064] According to one embodiment, packing elements (loose or structured) can be arranged in the enclosure to allow for better gas / liquid contact. For example, Raschig rings, of the Ralu or Pall type, can be used. commercially with the companies RASCHIG GmbH and JAEGER PRODUCTS, Inc.

[0065] According to one embodiment of the invention, the means for evacuating the portion of the liquid effluent comprising the dissolved gas include at least one opening, disposed in a lower part of the enclosure, and a conduit for connecting the enclosure of the device for dissolving a gas in said liquid effluent by pressurization to the enclosure of the device for a separation by dissolved gas flotation described below.

[0066] Description of the device for separation by dissolved gas flotation

[0067] According to the invention, the device for separation by dissolved gas flotation comprises a chamber (also called a flotation column), means for expanding the gas, means for bringing said at least a part of the liquid effluent comprising the dissolved gas into the chamber, means for collecting microfibers on the surface of the liquid effluent and means for evacuating the clarified liquid effluent.

[0068] Thus, by means of the device for dissolved gas flotation separation, the liquid effluent containing the dissolved gas is reduced to a pressure lower than the gas's compression pressure, which will generate microbubbles that will rise to the surface. The bubbles obtained by such a device can be between 30 and 70 microns in size.

[0069] According to one embodiment of the invention, the means for supplying at least a portion of the liquid effluent comprising the dissolved gas may include a conduit connecting the opening of the means for supplying at least a portion of the liquid effluent comprising the dissolved gas from the means for dissolving a gas in the liquid effluent by pressurization to the opening of the means for supplying the device for separation by dissolved gas flotation.

[0070] According to the invention, the gas expansion means are arranged along the means for supplying at least a portion of the liquid effluent containing the dissolved gas, preferably near the opening provided in the device housing for separation by dissolved gas flotation. The expansion means may consist of a valve, preferably a needle-type regulating valve. Such valves make it possible to create a strong shear force and maintain a constant pressure differential regardless of variations in the effluent flow rate.

[0071] According to one embodiment of the invention, the enclosure of the device for dissolved gas flotation separation according to the invention may be cylindrical or parallelepiped in shape, preferably cylindrical. This geometry promotes a homogeneous rise of the gas microbubbles. Preferably, the enclosure may be formed made of glass or metal or any other material preferably limiting the accumulation of electrostatic charges that could interact with the microfibers.

[0072] Preferably, the enclosure may have a height of at least 10 cm, which is a sufficient height to allow the capture and re-emergence of microfibers by the microbubbles as will be demonstrated in the application example below.

[0073] Advantageously, the opening for the means for supplying at least a portion of the liquid effluent containing the dissolved gas is located in a lower part of the enclosure, preferably in a lower wall of the enclosure. It is clear that this increases the interaction time between the microbubbles and the microfibers, thereby increasing their probability of collision.

[0074] According to one embodiment of the invention, the enclosure of the device for separation by dissolved gas flotation may further include at least one separator (or a separating blade) extending perpendicularly with respect to the base of the enclosure and disposed between the inlet opening of at least a portion of the liquid effluent comprising the dissolved gas and the means for the evacuation of the clarified liquid effluent.

[0075] According to one embodiment of the invention, the separator can also be a hollow cylinder arranged so that an opening of the means for supplying at least a part of the liquid effluent including the dissolved gas is inside the hollow part of the cylinder (preferably in its center), and an opening of the means for evacuating the clarified liquid effluent from the second chamber is outside the hollow cylinder.

[0076] Figure 2 schematically illustrates this implementation of the system for recovering microfibers contained in a liquid effluent from a textile treatment device according to the invention. More specifically, Figure 2 incorporates the elements of Figure 1 (thus, the common elements will not be described again), to which is added a cylindrical separator 51 located in the chamber 50. The separator 51 physically separates the area containing the ascending microbubbles to which the microfibers are attached (the so-called "contact" area) from the area for recovering the clarified effluent (the so-called "draw-off" area). This separation significantly limits the possibility of mixing between the effluent to be treated and the clarified effluent, and thus increases the efficiency of microfiber recovery.

[0077] According to one embodiment of the invention, the device for separation by dissolved gas flotation may include means for injecting a flocculant agent located between the means for reducing the gas and the means for bringing at least a part of the liquid effluent comprising the dissolved gas into the enclosure.

[0078] According to one embodiment of the invention, the means for collecting microfibers can correspond to suction means, scraping means, or overflow collection means.

[0079] According to an embodiment in which the microfiber collection means correspond to scraping means, these may correspond to a rotary system equipped with semi-rigid blades powered by a motor. The blades may be partially immersed in water and may be designed to collect and push the microfibers located on the surface towards the walls of the flotation column. Geometric reducers may be installed along the walls of the enclosure so that the semi-rigid blades, upon encountering these geometric reducers, deform and compress, dry, and remove the microfibers from the enclosure. Advantageously, in this design, the liquid level in the enclosure can be kept constant so that the scraping system, which is located at a fixed height, is effective.The liquid level can be kept constant by means of regulation known to those skilled in the art, such as a valve controlled by a level sensor or a liquid leg of a height equivalent to the desired level height in the device enclosure for separation by dissolved gas flotation.

[0080] Figure 3 schematically illustrates a third implementation of the system for recovering microfibers contained in a liquid effluent from a textile treatment device according to the invention. More specifically, Figure 3 incorporates the elements of Figure 2 (thus the common elements will not be described again), to which are added a rotary system equipped with blades 61 and a motor 62 to power the rotary system equipped with blades 61.

[0081] According to one embodiment of the invention, the device for separation by dissolved gas flotation may further include means for bringing in another part of the liquid effluent, in which gas has not been dissolved.

[0082] Figure 4 schematically illustrates a fourth embodiment of the system for recovering microfibers contained in a liquid effluent from a textile treatment device according to the invention. More specifically, Figure 4 incorporates the elements of Figure 1 (thus the common elements will not be described again), to which are added a circuit comprising a pump 70 and two pipes 7, 8 to bring a portion of the liquid effluent L directly into the enclosure 50 of the device for separation by flotation with dissolved gas 5, 6, 7, 40, 50, 60, without passing through the device to dissolve a gas G by pressurization 2, 4, 5, 20, 30.

[0083] According to an embodiment in which the microfiber collection means correspond to gaseous suction means, the suction means may correspond to a water vacuum cleaner configured to suction the foam phase containing The microfibers are located on the surface of the liquid effluent. This has the advantage of allowing the same method to be used to compress the gas as to remove the microfibers, by adding, for example, a venturi-type device to create the vacuum necessary for the suction of the foam phase.

[0084] According to one embodiment, the means for collecting the microfibers may correspond to means by overflowing the foam, along an inclined plane before being collected.

[0085] According to one embodiment of the invention, the means for discharging the treated liquid effluent comprise at least one opening, disposed in a lower part of the enclosure. This opening allows the liquid effluent, including the clarified liquid effluent, to be discharged by simple gravity into the lower part of the enclosure. Advantageously, the opening of the means for discharging the clarified liquid effluent is provided in the lower wall of the enclosure of the system according to the invention, to prevent the treated liquid effluent from accumulating at the bottom of the enclosure.

[0086] The method according to the invention comprises at least the following steps:

[0087] 1) Dissolution of a gas in the liquid effluent by pressurization

[0088] 2) Depressurization of the liquid effluent including the dissolved gas and separation by flotation of microfibers from the liquid effluent

[0089] 3) Microfiber collection

[0090] 4) Discharge of the clarified liquid effluent

[0091] The process according to the invention can be applied continuously (i.e., all the above steps are carried out simultaneously) or discontinuously (i.e., the above steps are carried out sequentially). The process according to the invention can be implemented using the system for recovering microfibers contained in a liquid effluent from a textile treatment device as described above, or any other system.

[0092] 1) Dissolution of a gas in the liquid effluent by pressurization

[0093] During this step, at least a portion of the liquid effluent from said textile treatment device is introduced into said first chamber of said device for dissolving a gas in said liquid effluent by pressurization, and, by means of said device for dissolving a gas in said liquid effluent by pressurization, at least a portion of the liquid effluent comprising a dissolved gas is produced in said first chamber.

[0094] Thus, during this step, a gas is dissolved in at least a portion of the liquid effluent, using the device for dissolving a gas in the liquid effluent by pressurization according to the invention. The purpose of this step is to put in contact, within the enclosure, at least a part of the liquid effluent comprising microfibers with a pressurized gas.

[0095] According to one embodiment, the means for bringing at least part of the liquid effluent may include a recovery tank disposed under the textile treatment device in the case of gravity drainage (as generally encountered for professional washing machines) and a pump enabling the sending and pressurization of the liquid effluent to be treated towards the enclosure of the device to dissolve a gas in the liquid effluent by pressurization.

[0096] According to one embodiment of the invention, the pressure in the enclosure of the device for dissolving a gas in the liquid effluent by pressurization can be predetermined so as to obtain a quantity of gas dissolved in the liquid effluent to be treated sufficient (i.e. a gas volume fraction of at least 0.1% and at most 10%) to carry out the separation by flotation once the liquid effluent to be treated has been decompressed.

[0097] According to a discontinuous implementation of the process according to the invention, the effluent from the textile treatment device can be brought directly into the device to dissolve a gas in the liquid effluent by pressurization before being held under static pressure for a period of between 1 and 15 minutes.

[0098] 2) Depressurization of the liquid effluent including the dissolved gas and separation by flotation of microfibers from the liquid effluent

[0099] During this step, at least a portion of the liquid effluent including the dissolved gas is introduced into the device for dissolved gas flotation separation and, by means of the device for dissolved gas flotation separation, the liquid effluent including the dissolved gas is depressurized and the microfibers are separated by flotation from at least a portion of the liquid effluent.

[0100] In other words, the depressurization of the liquid effluent containing dissolved gas will lead to the generation of microbubbles. The microfibers will then attach to the microbubbles rising to the surface of the liquid effluent, and float on the surface. It should be noted that the synthetic fibers have a significant hydrophobic character, which will facilitate their attachment to the microbubbles.

[0101] After numerous trials, the Applicant was able to observe that the range of microbubbles obtained by the system according to the invention (30-70pm) is suitable for flotation separation of at least 70% by number of microfibers from a liquid effluent from a textile treatment device.

[0102] According to a discontinuous implementation of the process according to the invention, at the end of step 1), the portion of the liquid effluent containing the dissolved gas is decompressed and injected into the device chamber for separation by dissolved gas flotation, and then the injection of the liquid effluent containing the dissolved gas is stopped for a predetermined period. According to one implementation of the invention, the predetermined period This can be a function of the rise time of the bubble-microfiber bundles (between 3 cm / minute and 16 cm / minute). For example, the predetermined duration could be 7 minutes for a 20 cm high enclosure of a dissolved gas flotation separation device.

[0103] According to an embodiment of the invention in which the device for dissolved gas flotation separation comprises means for injecting a flocculant agent as described above, step 2) may include a substep for injecting at least one flocculant agent between the depressurization substep and the flotation separation substep. Injecting a flocculant agent at the point of injection of the depressurized liquid effluent ensures satisfactory mixing of the flocculant agent and the liquid effluent to be treated. A flocculant agent promotes the agglomeration of the smallest fibers, thereby facilitating their separation.For example, a flocculant can be used in the form of versatile cationic mineral salts such as aluminum sulfate or ferric chloride, activated silica, or natural organic polyelectrolytes (starches, alginate) or synthetic ones (high molecular weight polymers such as polycrylamides or polyvinylamines). The injection of a flocculant will preferably be carried out at a low concentration, generally between 1 and 100 ppm relative to the liquid effluent to be treated.

[0104] 3) Collection of microfibers on the surface of the liquid effluent

[0105] During this step, the microfibers present on the surface of the liquid effluent are collected within the device for separation by dissolved gas flotation according to the invention, using the microfiber collection means of the device for separation by dissolved gas flotation according to the invention.

[0106] This step can be facilitated by the application of the process according to the invention, which concerns the treatment of a liquid effluent from a textile processing device. Indeed, due to the general use of detergents (surfactants) in this application (although not necessarily in the case of textile dyeing), a foam phase will naturally form on the surface of the liquid effluent. This foam can then promote the aggregation of microfibers that have reached the surface of the liquid effluent, facilitating their collection. Furthermore, natural fibers will generally form flocs by becoming entangled with one another.

[0107] This step can be carried out using any collection method of the device for dissolved gas flotation separation, for example, collection means by scraping, suction, or overflow. Figure 3, already described, illustrates an implementation of collecting microfibers present on the surface of the liquid effluent by scraping means.

[0108] According to an embodiment in which the process according to the invention is carried out continuously, the liquid level in the enclosure can be regulated and kept constant to allow the recovery of microfibers by means of collection such as scraping, suction or overflow.

[0109] According to an embodiment in which the process according to the invention is implemented discontinuously, the scraping, suction or overflow type collection means can be implemented after an observation time corresponding to the time required for the bubble-microfiber couplings to rise. 4) Disposal of the clarified liquid effluent

[0110] During this step, the clarified liquid effluent (at least partially) of the microfibers is evacuated from the enclosure of the device for dissolved gas flotation separation, by means of the means for evacuating the clarified liquid effluent from the device for dissolved gas flotation separation according to the invention.

[0111] According to an embodiment of the invention in which the process according to the invention is carried out continuously, the means for evacuating the clarified liquid effluent are sized according to the means for bringing in the liquid effluent (and vice versa), so as to allow a constant volume of liquid effluent inside the flotation column according to the invention.

[0112] According to an embodiment in which the process according to the invention is carried out discontinuously, the means for discharging the clarified liquid effluent may include a pump and a valve located downstream of the enclosure of the device for dissolved gas flotation separation according to the invention. Alternatively, the means for discharging the treated liquid effluent may be configured to utilize a gravity flow of the clarified liquid effluent. In this case, they may, for example, be located at the base of the enclosure of the device for dissolved gas flotation separation according to the invention. According to this design, the means for discharging the liquid effluent from the device for dissolved gas flotation separation may include a valve to allow the controlled discharge of the filtered liquid effluent from the enclosure.

[0113] According to one embodiment, the process according to the invention may further comprise at least one additional step in which the clarified effluent from the microfiber recovery system according to the invention is injected into an additional separation and / or filtration device, such as, for example, a granular media filtration device, a membrane filtration device (microfiltration, ultrafiltration membrane, reverse osmosis), a hydrocyclone separation device (or a cyclone separation chamber), a flocculation separation device, or a sedimentation filtration device. This additional step, downstream of steps 1) to 4) described above, This can improve the overall recovery of microfibers contained in the liquid effluent to be treated. Conversely, prior separation of the microfibers contained in the liquid effluent to be treated via the microfiber recovery system according to the invention helps to limit fouling and / or clogging of filters located downstream (in particular granular and / or membrane filters).

[0114] Preferably, at least one additional microfiber filtration step can be implemented using a system described in patent application WO2021 / 197937 A1, which relates to a system and a method for filtering microfibers contained in a liquid effluent from a textile treatment device. More specifically, this system comprises a granular medium disposed of in a chamber, means for percolating the liquid effluent through the granular medium, means for discharging the liquid effluent beneath the granular medium, and means for connecting to means for regenerating the granular medium by gaseous fluidization. Thus, this system allows the granular medium to be regenerated, particularly in the event of clogging, and for the recovery of plastic microfibers from the gas stream.Thus, the microfiber recovery system according to the invention makes it possible to remove a majority (at least 50% and preferably at least 70% by number) of the microfibers contained in the drain fluid, and filtration through granular media further improves this separation rate, as will be demonstrated in the application example below. In this design, the granular media filtration step is implemented after the flotation separation steps in order to limit clogging of the granular media filter.

[0115] According to one embodiment of the invention, the process according to the invention may further include an additional step in which the clarified effluent from the outlet of the system according to the invention, or from the outlet of an additional separation and / or filtration device if necessary, is injected into a bacterial treatment device, for example by UV or ozonation.

[0116] Thus, the process and system according to the invention allow for efficient and rapid recovery of microfibers contained in a liquid effluent from a textile treatment device.

[0117] Furthermore, unlike flotation separation processes known in other application areas, the process according to the invention does not require a preliminary coagulation / flocculation step, which is carried out using polyacrylamide-type chemical additives and whose function is to create flocs before the flotation step (collision of bubbles with flocs). Indeed, in the case of water from a textile treatment device, the coagulation / flocculation step is not necessary because: - Natural fibers will naturally form clumps by intertwining with each other

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125] - Synthetic fibers have a significant hydrophobic character which will facilitate the attachment of bubbles to the fibers. Furthermore, some flotation processes used in other applications employ surfactants in an effluent conditioning step to create a foam phase on the separator surface, thus stabilizing the pollutant. In the case of wastewater from a textile treatment system, the presence of residual detergent (from washing) provides this fiber stabilization function. This foam also allows for the recovery of pollutants in a drier state than with a conventional overflow. Moreover, compared to the prior art known in the field of application, the process according to the invention has the advantage of not being subject to the problems of fouling or clogging which are classically encountered when the technical solution involves a mechanical filter. Finally, the process according to the invention makes it possible to capture a wide variety of fibers present in the effluent from the washing plant and is not limited by the nature or density of the material constituting the fiber (PET, PE, natural cotton, etc.), unlike a centrifugation treatment system (hydrocyclone for example). Furthermore, the invention relates to a textile treatment device comprising at least one system for recovering microfibers contained in a liquid effluent from a textile treatment device as described above, and in which said textile treatment device is in fluidic connection with said system for recovering microfibers contained in a liquid effluent from a textile treatment device. Examples The characteristics and advantages of the process and system according to the invention will become clearer upon reading the application example below. The process according to the invention was implemented on a liquid effluent from an industrial laundry. The properties of this feedstock are described in Table 1. More specifically, Table 1 describes the total suspended solids and the microfiber concentration of the effluent to be treated. Total suspended matter (>25 µm) mg / L 74 Microfiber concentration Nb / L 57,000 The process according to the invention was implemented under the following conditions: 100L of effluent to be treated were injected by a pump (flow rate of 4L / min) into a saturator (of 15 Liters) whose function is to dissolve air in the effluent to be treated. For The saturator was then pressurized with air at a continuous pressure of 7 bar. A gas head of approximately 30 cm in the saturator ensured sufficient saturation of the water.

[0126] The effluent from the saturator was then conveyed to the treatment column. For this, the effluent containing dissolved air exits the saturator, then passes through a so-called depressurization valve (located just below the treatment column), whose function and geometry ensure the depressurization of the effluent and the appearance of microbubbles, whose diameter is between 30 and 70 µm.

[0127] The effluent to be treated is injected through the base of the column, at its center. The effluent enters the treatment compartment (approximately 3 liters) where it is treated by microbubbles. The microbubbles and microfibers are captured from the water surface, and this supernatant is recovered by suction. The clarified liquid effluent flows back down through the peripheral ring, formed by the space between the treatment compartment (approximately 13 liters) and the flotation column. The clarified liquid effluent is then drawn off from the bottom and collected. Throughout the process, the liquid level is kept constant to allow for the recovery of microfibers (constituting the supernatant) by suction.

[0128] The flotation kinetics were measured using a camera capable of measuring the opacity (determining a gray level) of the surface of the liquid effluent in the column. As microfibers are captured on the surface of the liquid effluent, the surface becomes increasingly opaque over time, until it is completely obstructed by the microfibers. Appropriate image processing (measuring the obstruction over time) allowed for the determination of a kinetic period of approximately 200 seconds.

[0129] Table 2 gives the properties of the clarified effluent from the process according to the invention. More specifically, Table 2 describes the total suspended solids and the microfiber concentration of the effluent at the outlet of the process according to the invention.

[0130] [Tables2] Total suspended matter (>25 µm) mg / L 16 Microfiber concentration Nb / L 10,000

[0131] The efficiency of the flotation separation was estimated by comparing the properties of the liquid effluent to be treated (Table 1) and the clarified effluent from the system according to the invention (Table 2). Thus, the application of the flotation separation process reduced the suspended solids (> 25 µm) by weight by 78% and the number of microfibers by 82%, demonstrating the suitability of the process according to the invention for this type of effluent.

Claims

Demands

1. System for recovering microfibers contained in a liquid effluent (L) from a textile treatment device, said system being characterized in that it comprises at least: A) A device for dissolving a gas in said liquid effluent by pressurization (2, 4, 10, 20, 30, 5), comprising a first enclosure (30), means for bringing (2, 10) at least a part of said liquid effluent (L) into said first enclosure (30), means for bringing (4) said gas (G), means for compressing said gas (20), and means for evacuating (5) said at least a part of said liquid effluent comprising said dissolved gas (LG); B) A device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62), comprising a second chamber (50), means for reducing the pressure (40) of said gas,means for bringing (5) at least a portion of said liquid effluent comprising said dissolved gas (LG) into said second chamber (50), means for collecting (7, 60, 61, 62) microfibers (MF) on the surface of the liquid effluent (L) into said second chamber (50) and means for evacuating (6) the clarified liquid effluent (LC) from said second chamber (50), said second chamber of said device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62) comprises at least one separator (51) in the form of a hollow cylinder, said hollow cylinder (51) being arranged so that an opening of said means for bringing (5) at least a portion of said liquid effluent comprising said dissolved gas (LG) into said second chamber (50) is inside said hollow cylinder (51),and that an opening in said means for the evacuation (6) of the clarified liquid effluent (LC) from said second enclosure (50) is outside said hollow cylinder (51).

2. System according to any one of the preceding claims, wherein said means for collecting said microfibers (MF) (7, 60, 61, 62) comprise means for collecting by scraping (61, 62), by suction or by overflow.

3. A system according to any one of the preceding claims, wherein said device for separation by dissolved gas flotation further comprises means for supplying (7, 8, 70) another portion of said liquid effluent into said enclosure (50) of said device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62).

4. System according to any one of the preceding claims, wherein a geometry of said first enclosure (30) and said gas compression means (20) of said device for dissolving a gas in said liquid effluent by pressurization are configured so that the volume fraction of said gas is between 0.1 and 10%, preferably between 0.5 and 5%.

5. A method for recovering microfibers contained in a liquid effluent from a textile treatment device, said method being implemented by means of the system for recovering microfibers contained in a liquid effluent from a textile treatment device according to any one of the preceding claims, characterized in that said method comprises at least the following steps: a) at least a portion of said liquid effluent (L) from said textile treatment device is introduced into said first chamber (30) of said device for dissolving a gas in said liquid effluent by pressurization (2, 4, 10, 20, 30, 5), and, by means of said device for dissolving a gas in said liquid effluent by pressurization (2, 4, 10, 20, 30, 5), said at least a portion of said liquid effluent comprising a dissolved gas (LG) is produced in said first chamber (30);b) at least a portion of said liquid effluent comprising said dissolved gas (LG) is introduced into said device for dissolved gas flotation separation (5, 6, 7, 40, 50, 60, 61, 62), and by means of said device for dissolved gas flotation separation (5, 6, 7, 40, 50, 60, 61, 62), at least a portion of said liquid effluent comprising the dissolved gas (LG) is depressurized and said microfibers (MF) are separated by flotation from at least said at least a portion of said liquid effluent (L); (c) said microfibers (MF) present on the surface of said liquid effluent (L) are collected in said second chamber (50) by means of said collection means (60, 61, 62) of said microfibers (MF) of said device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62); (d) said clarified liquid effluent (LC) is discharged from said second chamber (50), by means of said discharge means (6); clarified liquid effluent (LC) from said device for separation by dissolved gas flotation (5, 6, 7, 40, 50, 60, 61, 62).

6. A method according to claim 5, wherein, at the end of step d), said clarified liquid effluent (LC) is introduced into at least one filtration and / or separation device for microfibers contained in a liquid effluent.

7. A method according to claim 6, wherein said filtration and / or separation device is selected from a granular media filtration device, a membrane filtration device, a hydrocyclone filtration device, a flocculation filtration device or a decantation filtration device.

8. A method according to claim 7, wherein said granular medium filtration device further comprises means for connecting to means for regenerating said granular medium by gaseous fluidization.