Method for treating dirty overflow water from a water treatment plant, and corresponding facility

Abstract

The invention relates to a method for treating dirty overflow water in order to separate suspended matter and insoluble granular material that is heavier than water. This method involves a degassing step (1), two steps of liquid-solid separation within a hydrocyclone (4) and a recirculation cylinder (5), and a step of recirculating the water to be treated, carried out by a hydroejector (3).

Description

[0001] DESCRIPTION

[0002] TITLE: Process for treating dirty overflow water from a water treatment system, and corresponding installation

[0003] TECHNICAL FIELD

[0004] The field of the invention is that of water treatment with a view to its purification or making it potable.

[0005] More specifically, the invention relates to the treatment of previously coagulated and potentially flocculated dirty water, originating from a water treatment system.

[0006] PREVIOUS ART

[0007] A well-known process for treating water, particularly surface water to be made potable and urban or industrial wastewater to be depolluted, consists of coagulating the water to be treated with a coagulating reagent, such as, for example, a trivalent metal salt, flocculating the organic matter contained in the coagulated water with a flocculating reagent, usually consisting of an organic polymer, and settling or filtering the flocs and other solid matter in a decanter or through a filter. In the case of the decanter, the sludge is extracted at the bottom of the decanter, and the treated water is extracted as a decanter overflow; while in the case of a filter, the filtered water is extracted from another side of the filter, and the sludge / dirty water is extracted by backwashing through the filter overflow.

[0008] More specifically, an example of technology implementing coagulation and flocculation steps consists of adding coagulants and / or flocculants to the raw water in order to obtain flocs. The water thus coagulated and / or flocculated can be filtered through an ultrafiltration membrane, the flocs forming a cake on the surface of the membrane, and the clarified water passing through it. Subsequently, the floc cake can be evacuated by backwashing the membrane and by overflowing a tank of dirty wash water.

[0009] Thus, dirty water is recovered from the overflow of the filtration system, by filter or membranes, this dirty water can then be thickened and / or dehydrated in post-treatment systems. However, such a process leads to high water losses and expensive and cumbersome post-treatment.

[0010] Another example of technology implementing coagulation and flocculation steps is proposed by the Actiflo® process, which also uses a ballast made of a fine, high-density granular material such as microsand, injected into or upstream of the flocculation zone, in order to increase the rate of floc formation by serving as a flocculation initiator, and also to increase the settling rate of the flocs formed during the flocculation phase by increasing their density. The ballasted sludge is extracted at the bottom of the decanter.

[0011] Microsand, with an average diameter of between approximately 20 and 300 micrometers, most often 80 and 200 micrometers, is the ballast or ballast used most frequently for reasons of availability and cost.

[0012] Ballast is usually, for economic reasons of reuse, separated from the sludge extracted from the settling tank and recycled into the process. Ballast losses are usually divided between losses through the treated water overflowing from the settling tank and losses with the sludge extracted from the tanks.

[0013] An injection of fresh ballast to compensate for ballast losses is planned.

[0014] Losses of ballast carried with the sludge are important to control, both to minimize expenditure on fresh ballast and to avoid degrading the quality of the sludge extracted.

[0015] The means used to separate the ballast from the extracted sludge and recycle this ballast in the process while minimizing ballast losses are generally chosen from static gravity separation techniques (such as decantation) or dynamic gravity separation techniques (such as centrifugation and cycloning), most often by hydrocycloning of the sludge / ballast mixture.

[0016] Ballast losses in the hydrocyclone overflow, the most frequently used means in practice for separating ballast from extracted sludge, are generally, for a given hydrocyclone geometry and operating conditions, approximately proportional to the concentration of ballast in the mixture entering the hydrocyclone.

[0017] In order to reduce these ballast losses, it has already been proposed in the state of the art to treat this overflow in a second hydrocyclone. Such use of two hydrocyclones connected in cascade is disclosed in particular in WO03053862A1.

[0018] However, this process leads to volumes of sludge at the outlet of the second hydrocyclone that still contain a significant proportion of water. This diluted sludge is therefore the source of water losses.

[0019] This sludge must therefore be thickened and dehydrated during post-treatment.

[0020] Such post-treatment increases the implementation costs of the process. The corresponding equipment also increases the footprint of the installations.

[0021] To limit water losses, the invention disclosed in W02011103651A1 known as Actiflo® HCS is also known. It relates to a ballasted flocculation-settling installation including a simplified system for recirculating part of the overflow from the hydrocyclone for separating the ballasted sludge. Part of the overflow from the hydrocyclone is returned, after degassing, to the suction of the sludge / ballast mixture extraction pump feeding the hydrocyclone. This regulated recirculation system makes it possible to reduce the volume of water extracted with the sludge and therefore to concentrate this sludge. It also makes it possible to reduce ballast losses. However, it cannot be used on all types of water and must be selected according to the load and flow rate of the water to be treated.

[0022] OBJECTIVES OF THE INVENTION

[0023] The objective of the invention is to propose a method making it possible to overcome these drawbacks of the prior art.

[0024] More specifically, the main objective of the invention is to propose a method for treating dirty overflow water from a water treatment system, making it possible to limit water losses.

[0025] Another objective of the invention is to reduce the volume of sludge produced by such a water treatment system.

[0026] Another objective of the invention is to propose a process which makes it possible to reduce the quantities of chemical products which have to be used in such a process and therefore to limit the ecological impact of the corresponding treatment.

[0027] Another objective of the invention is to propose a device for implementing such a method making it possible to limit the size of such a die. PRESENTATION OF THE INVENTION

[0028] These objectives, as well as others which will appear subsequently, are achieved by means of a method for treating dirty overflow water used to separate, on the one hand, treated water, and on the other hand, solid particles contained in the dirty overflow water, said solid particles being composed of suspended matter and / or an insoluble granular material heavier than water. This method comprises the following steps:

[0029] - a step of degassing the dirty overflow water;

[0030] - a step of supplying degassed dirty overflow water to a hydrocyclone via a hydroejector powered by an accelerator pump, the accelerator pump being capable of adjusting a flow rate and a pressure;

[0031] - a first stage of separation of suspended matter and / or granular material present in the degassed dirty overflow water, by hydrocycloning within the hydrocyclone;

[0032] - a step of recovering an overflow from the hydrocyclone, the overflow mainly comprising water and residual suspended matter;

[0033] - a second stage of separation of residual suspended matter from the water recovered from the hydrocyclone overflow, within a recirculation cylinder;

[0034] - a step of recirculation to the hydrocyclone of water comprising the residual suspended matter coming from the recirculation cylinder by suction by the hydroejector;

[0035] - a step of extracting clarified water from the recirculation cylinder;

[0036] - a step of continuous measurement of the flow rate at the inlet and outlet of said hydroejector, and at the outlet of the recirculation cylinder.

[0037] According to the invention, in order to be able to eliminate the suspended matter present at the overflow outlet of an upstream installation, the invention proposes to implement a method for treating this dirty overflow water comprising two stages of liquid-solid separation using a hydrocyclone and a recirculation cylinder, coupled with recirculation of the water at the outlet of the recirculation cylinder.

[0038] According to the present description, the term "recirculation cylinder" designates a cylinder comprising the following elements: a water supply close to one end of the cylinder (connected to the overflow of the hydrocyclone), a clarified water outlet positioned at the other end of the cylinder, a solid particle discharge positioned at the periphery of the cylinder between the supply and the cylinder outlet and connected to the hydroejector, and a centrifugation system.

[0039] The function of this recirculation cylinder is similar to that of a hydrocyclone in that the recirculation cylinder implements a vortex creating a centrifugation of the water contained in the cylinder, allowing liquid-solid separation. The centrifugal force created by the swirling flow in which the fluid rotates around an axis causes the ejection of solid particles at the periphery of the cylinder wall. The water discharged through a tangential outlet is loaded with solid particles. The clarified water is discharged at the center of the cylinder.

[0040] According to the present invention, the dirty overflow water therefore undergoes at least a first stage of liquid-solid separation (or hydrocycloning) in the hydrocyclone; then the overflow water from the hydrocyclone also undergoes at least a second stage of liquid-solid separation in the recirculation cylinder, the latter having a lower cut-off threshold than the hydrocyclone, and making it possible to separate the majority of the residual suspended particles which have not been separated from the water during the first stage of liquid-solid separation.

[0041] In order to limit water losses, the water containing the residual suspended particles recovered on the cylinder wall and separated from the clarified water during the second liquid-solid separation step is reintroduced during the hydrocyclone feed step via the recirculation loop. Thus, the water coming from the recirculation cylinder and containing suspended matter is sucked in by a hydroejector (a device using the Venturi effect to create suction), and is recirculated to the hydrocyclone in order to optimize its treatment and eliminate the residual suspended matter. Thus, this process makes it possible to optimize liquid-solid separation, in particular for extremely fine solid particles (suspended matter), while limiting water losses.

[0042] In addition, the implementation of continuous measurement of flow and pressure also makes it possible to monitor the proper functioning of the process.

[0043] Furthermore, in order to avoid any malfunction linked to the presence of air, the method describes the implementation of a degassing step upstream of the feed step.

[0044] According to a preferred characteristic of the invention, the method comprises a step of continuously measuring the flow rate of the accelerator pump and a step of continuously adjusting this flow rate as a function of the result of the measurement taken during the measurement step; the step of adjusting the flow rate of said accelerator pump being such that, for an inlet flow rate of said hydroejector of xm 3 / h, then the flow rate at the hydroejector outlet is between l.lx and l.5x m 3 / h, the flow rate at the underflow outlet of the hydrocyclone is less than 0.1x m 3 / h, the recirculation flow rate is between 0.1x and 0.5x m 3 / h, and the flow rate at the overflow outlet of the recirculation cylinder is between 0.9x and 0.95x m 3 / h.

[0045] In order to set up the recirculation loop for sucking up water containing residual suspended matter from the recirculation cylinder, the invention proposes maintaining a specific flow rate at each stage of the process. Thus, advantageously, optimization of the process according to the invention is enabled by the use of a variable speed accelerator pump and the implementation of a continuous flow rate measurement. Indeed, the process according to the invention has a very specific operating point, requiring continuous maintenance of adequate conditions. In particular, all the parameters implemented in this process are co-dependent (flow rate, pressure, characteristics of the hydroejector and hydrocyclones, etc.).Thus, in order to limit water losses and maximize the elimination of suspended matter, the method according to the invention proposes to regulate the flow rate during each stage of the process to obtain at the outlet of the recirculation cylinder a flow rate close to the flow rate at the inlet of the hydroejector, i.e. approximately equal to x m. 3 / h, and more precisely, a flow rate between 0.9x and 0.95x m 3 / h.

[0046] According to another characteristic of the invention, the method comprises a step of adding polymer to the degassed dirty overflow water upstream of said hydroejector and / or at the inlet of the recirculation cylinder.

[0047] Advantageously, the addition of polymer to the water to be treated improves the removal of suspended matter. Indeed, the addition of polymers to the dirty overflow water to be treated, before it reaches the hydroejector, allows the particles of suspended matter to agglomerate together, and thus increases the size of these particles, which facilitates their separation from the water during the various stages of liquid-solid separation.

[0048] This step of adding polymers can be carried out automatically depending on a rate of suspended matter at the inlet of the hydroejector, and / or at the inlet of the recirculation cylinder. According to an advantageous characteristic of the invention, the flow rate at the inlet of the hydroejector x is between 4 and 50 m 3 / h.

[0049] Thus, the method according to the invention advantageously makes it possible to control the flow rate and adapt it for optimizing the liquid-solid separation and recirculation steps of the water to be treated. In addition, compliance with a predetermined flow rate at the pump outlet makes it possible to maintain the conditions corresponding to the specific operating point (flow rates, pressure) of the process, and thus to optimize its efficiency, by limiting water losses and maximizing the elimination of suspended matter.

[0050] Preferably, the hydraulic residence time is between 2 s and 4 s within the hydrocyclone and within the recirculation cylinder.

[0051] Thus, respecting a specific hydraulic residence time makes it possible to optimize the separation of suspended matter from water during the liquid-solid separation stages.

[0052] According to a preferred variant, the hydrocyclone has a cut-off threshold of between 10 and 25 pm, and the recirculation cylinder has a cut-off threshold of between 5 and 15 pm.

[0053] This process therefore allows the removal of extremely fine particles (e.g. flocs), whose density is relatively close to that of water. These cut-off thresholds limit the use of chemicals due to their effectiveness on fine particles. Indeed, these two mechanical liquid-solid separation steps do not require the use of coagulants or flocculants to effectively separate extremely fine contaminants from water.

[0054] According to an advantageous characteristic, the water pressure at the outlet of said accelerator pump is between 2 and 5 bars.

[0055] This pressure is adapted to the water treatment, and is part of the specific parameters of the process, allowing to respect the specific operating point of the latter. Indeed, a pressure of 2 to 4 bars at the outlet of the accelerator pump, allows, after passage of the water in the hydroejector, to obtain a pressure of between 1.5 and 2.5 bars at the inlet of the hydrocyclone, due to the pressure losses induced by the Venturi effect (approximately 1 to 1.5 bar). Thus, the pressure obtained at the inlet of the hydrocyclone and the recirculation cylinder allows the implementation of cut-off thresholds allowing an optimal separation of suspended matter.

[0056] According to another preferred aspect of the invention, the hydroejector comprises a nozzle whose outlet diameter is between 1 / 5th and half of its inlet diameter.

[0057] In order to create a Venturi effect generating sufficient suction force to allow the recirculation of part of the water coming from the recirculation cylinder to the hydrocyclone, the process proposes to adjust the nozzle diameter in order to respect the specific operating point of the process. In particular, the pressure losses and the suction force depend on the inlet and outlet diameters of the hydroejector nozzle. Indeed, the smaller the outlet diameter is compared to the inlet diameter, the greater the pressure losses and the suction force will be, while for an outlet diameter relatively close to the inlet diameter, the pressure losses and the suction force are lower.

[0058] According to a preferred variant of the invention, the dirty overflow water comes from a hydrocyclone of a ballasted flocculation-decantation installation.

[0059] According to other variants, the dirty overflow water may also come from a filtration system, said filtration system belonging to the group comprising:

[0060] - sand filters;

[0061] - granular activated carbon filters; - ultrafiltration membranes;

[0062] - biological filters using biomass fixed on a granular support such as, for example, filters marketed under the registered trademark Biostyr;

[0063] - mechanical filters, Hydrotech type or others.

[0064] The invention also relates to a device for treating dirty overflow water in order to separate suspended matter and / or an insoluble granular material heavier than water for implementing a method as described above. The device comprises:

[0065] - degassing means at the inlet of said installation;

[0066] - an accelerator pump capable of adjusting flow and pressure;

[0067] - a hydroejector;

[0068] - a hydrocyclone fed by water from the hydroejector;

[0069] - a recirculation cylinder fed by water from the hydrocyclone overflow;

[0070] - means for measuring pressure and / or flow rate; the hydroejector being capable of recirculating part of the water coming from the recirculation cylinder towards the hydrocyclone.

[0071] According to a characteristic of the invention, the device comprises means for adding polymer provided upstream of the hydroejector and / or at the inlet of the recirculation cylinder.

[0072] According to a preferred characteristic of the invention, the recirculation cylinder is positioned horizontally.

[0073] Indeed, the device can be installed at the top of a prior art ballasted flocculation-decantation device, and be connected to the overflow of the hydrocyclone thereof, such a configuration making it possible to minimize the overall size of the assembly.

[0074] According to a preferred characteristic of the invention, the hydrocyclone and the recirculation cylinder each have a length of between 0.8 and 2m.

[0075] Thus, the device is relatively compact and space-saving, and can be placed in the upper part of a pre-existing installation of the prior art.

[0076] PRESENTATION OF FIGURES

[0077] Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and non-limiting example and described with reference to the drawings in which:

[0078] [Fig. 1] represents a device for treating dirty overflow water, according to an exemplary embodiment of the invention;

[0079] [Fig. 2] shows a ballasted flocculation-decantation installation equipped with such a device. DETAILED DESCRIPTION OF THE INVENTION

[0080] 1. Description of an embodiment of a device according to the invention

[0081] The device according to the invention is supplied with dirty water from a water treatment system. This water treatment system may, for example, be in the form of a ballasted flocculation-settling installation, a biofilter, an ultrafiltration membrane, a sand filter, or any other water treatment installation. Within the water treatment system, the water has previously undergone physicochemical treatments. The dirty water may thus have been coagulated and potentially flocculated and / or ballasted, before being filtered, and / or settled, and / or hydrocycloned. The dirty water feeding the device according to the invention can therefore come from the pressurized overflow 100 of a hydrocyclone of a ballasted flocculation-decantation installation, or from the overflow 100 (under pressure, or gravity) of backwashing of a filter (biofilter, ultrafiltration, sand filter, activated carbon, etc.)) or any type of separator used in a water treatment system.

[0082] With reference to Figure 1, the DISP device according to the invention comprises degassing means 1 for removing any air from the dirty water entering the device. This device also comprises an acceleration pump 2 acting as a driving force, this pump making it possible to bring the water coming from the degassing means to a Venturi effect hydroejector 3. The water is then conveyed to a hydrocyclone 4. In the underflow 41 of this hydrocyclone, granular material that can be used to ballast the flocs, as well as a large part of the suspended matter, are recovered in the form of sludge. The granular material serving as ballast can possibly be reused. In the overflow 42 of the hydrocyclone, pretreated water, containing only extremely fine residual suspended matter, is recovered. The water can potentially also contain residual granular material.This pre-treated water is conveyed to a recirculation cylinder 5 in which the residual particles are separated from the treated water by centrifugation thanks to the creation of a vortex. The particles are therefore found on the walls of the recirculation cylinder, then are sucked in by the Venturi effect by the hydroejector 3, connected to the wall of the recirculation cylinder. The residual suspended matter from the recirculation cylinder is thus mixed with the untreated dirty water from the degassing tank or column, within the hydroejector, then the mixture is conveyed to the hydrocyclone 4, etc. This recirculation loop therefore makes it possible to reprocess these residual suspended matter until optimal elimination of contaminants.

[0083] The flow rate within the device implemented by the method according to the invention varies depending on the step of the method. Thus, at the outlet of the accelerator pump, the flow rate is preferably between 4 and 50 m3 / h. Then, taking this feed flow rate as a reference and assigning it the value x, the feed flow rate of the hydrocyclone is advantageously between 1.1x and 1.5x, the underflow flow rate of the hydrocyclone is preferably less than 0.1x, the recirculation flow rate is advantageously between 0.1x and 0.5x, and finally, the outlet flow rate is preferably between 0.9x and 0.95x. It should be noted that the flow rate does not depend on the size of the nozzle 31, unlike the circulation speed.

[0084] It is possible to put several treatment lines according to the invention in parallel to treat a higher total flow rate. 2. Characteristics of the elements constituting the device according to an exemplary embodiment of the invention

[0085] 2.1. Sensors

[0086] Flow and pressure sensors 6 can be placed between each treatment stage. These sensors allow the direction of water flow to be checked (in case of malfunction), as well as the quantity of recirculated water. This allows the pressure at the device inlet to be adjusted to maintain optimal treatment conditions.

[0087] 2.2. Degassing means

[0088] Degassing means 1 are used to remove air or any gas potentially contained in the dirty water to be treated. These means are, for example, a tank, a reservoir or a degasser. They thus prevent any presence of air that could cause phenomena that cause malfunctions within the installation (for example, the phenomenon of pump cavitation).

[0089] Hydraulic means, such as vents or purgers, can also be implemented to ensure the absence of air and / or gas in the device. These means can be placed at any stage of the device's processing, in particular, at the liquid-solid separation stages. This makes it possible, among other things, to avoid cavitation phenomena (which can cause malfunctions, particularly at the level of the feed pump and the Venturi effect hydroejector).

[0090] 2.3. Accelerator pump

[0091] Accelerator pump 2 acts as the driving force and supplies the device with degassed dirty overflow water.

[0092] Accelerator pump 2 allows very fine control of flow and pressure parameters. This pump operates preferably in conjunction with sensors 6. This pump can be frequency-variable.

[0093] In the embodiment implemented by the inventor during his tests, the pressure delivered by the accelerator pump was 3 to 4.5 bars.

[0094] 2.4. Venturi effect hydroejector

[0095] The hydroejector 3 is powered by the accelerator pump 2, and also feeds into the recirculation cylinder 5. In fact, the pump provides the flow of degassed water necessary for the hydroejector to suck, by Venturi effect, part of the water contained in the recirculation cylinder (this water containing solid particles to be extracted from the water), the hydroejector being connected to the wall of the recirculation cylinder.

[0096] The hydroejector is composed of a nozzle 31 whose conical shape (combined with the flow rate generated by the accelerator pump) allows the creation of the Venturi effect. At the nozzle outlet (inlet side of the hydrocyclone) the outlet diameter is between 1 / 5th and half of the nozzle inlet diameter (accelerator pump side). This ratio must be respected because, if the outlet diameter is too small, the pressure drop would be too great, and if the diameter is too large, the Venturi effect would disappear. The nozzle outlet diameters used by the inventor during his tests were between 2 and 15mm. In addition, the angle formed by the nozzle also influences the Venturi effect.

[0097] The water circulation speed within the device is advantageously 0.5 to 2 m / s, except within the Venturi effect hydroejector, where the water is accelerated 4 to 25 times to obtain a speed of 2 to 50 m / s. The water circulation speed within the hydroejector 3 is adjustable and depends on the diameter of the nozzle 31. The circulation speed at the outlet of the hydroejector 3 is therefore between 0.5 and 2 m / s.

[0098] The passage of the water to be treated through the hydroejector induces a reduction in pressure. The smaller the nozzle diameter, the greater the pressure drop. Similarly, the higher the flow rate, the greater the pressure drop. In the embodiment implemented by the inventor during his tests, the pressure drops due to the Venturi effect were 1 to 1.5 bars.

[0099] The materials used to manufacture the nozzle (and all the elements of the device) must be abrasion resistant and suitable for the viscosity of the water.

[0100] The Venturi effect has a precise operating point to allow the suction of suspended matter from the recirculation cylinder. This suction depends on the pressure and flow rate provided by the accelerator pump, as well as the parameters inherent to the hydroejector (diameter, nozzle angle).

[0101] 2.5. Hydrocyclone

[0102] Hydrocyclone 4 separates and extracts the solid particles contained in the water to be treated coming from hydroejector 3. The heaviest particles are thus extracted via the underflow of hydrocyclone 4, while the overflow containing the finest particles (residual particles) is transferred to recirculation cylinder 5.

[0103] The solid particles extracted from the hydrocyclone underflow may include granular materials used as ballast. These granular materials can be recycled for reuse in stages upstream of the device.

[0104] The hydrocyclone used in the device has a cut-off threshold between 5 and 25 pm. This threshold depends on the flow rate, pressure, and hydraulic residence time.

[0105] The cut-off threshold of the hydrocyclone can be adapted to the separation of microsand particles and particles of equivalent density (10 to 25 pm), or to the separation of particles of lower densities (5 to 15 pm). Thus, this cut-off threshold, like the cut-off threshold of the recirculation cylinder, can be adapted according to the particles (density, size) contained in the water to be treated.

[0106] The hydrocyclone preferably measures between 0.8 and 2 m in length, with a hydraulic residence time of between 1 and 4 s, and a velocity within it of 0.5 to 1 m / s. The optimal performance for such a hydrocyclone is obtained for a hydraulic residence time of 4 s. Indeed, the longer the hydraulic residence time, the more efficient the liquid-solid separation. According to an exemplary embodiment, the hydrocyclone is similar to a hydrocyclone in a ballasted flocculation-decantation plant, but is more fusiform. The hydrocyclone can optionally be larger than 2 m, depending on the desired use. Thus, the hydraulic residence time can be increased and allow an improvement in the liquid-solid separation efficiency.

[0107] In an exemplary embodiment, the hydrocyclone is positioned vertically. In the embodiment implemented by the inventor during his tests, the hydrocyclone operated at a pressure of 1 to 1.5 bars. In particular, in the case of use of the device of the invention following a ballasted flocculation-decantation installation comprising a first hydrocyclone, it is necessary to work at higher pressures than for the first hydrocyclone of the ballasted flocculation-decantation installation.

[0108] 2.6. Recirculation cylinder

[0109] According to the present description, the term "recirculation cylinder" designates a cylinder comprising the following elements: a water supply close to one end of the cylinder (connected to the overflow of the hydrocyclone), a clarified water outlet positioned at the other end of the cylinder, a solid particle discharge positioned at the periphery of the cylinder between the supply and the cylinder outlet and connected to the hydroejector, and a centrifugation system.

[0110] The recirculation cylinder uses a vortex to centrifuge the water from the hydrocyclone overflow and separate the residual particles from the water. The particles then gather on the walls of the recirculation cylinder and are sucked in by the hydroejector 3.

[0111] The function of this recirculation cylinder is similar to that of a hydrocyclone in that the recirculation cylinder implements a vortex creating a centrifugation of the water contained in the cylinder, allowing liquid-solid separation. The centrifugal force created by the swirling flow in which the fluid rotates around an axis causes the ejection of solid particles at the periphery of the cylinder wall. The water discharged through a tangential outlet is loaded with solid particles. The clarified water is discharged at the center of the cylinder.

[0112] The recirculation cylinder 5 used in the device has a very fine cut-off threshold (of the order of 5 to 15 μm) adapted to the fineness of the residual suspended matter. This threshold depends on the flow rate, the pressure, and the hydraulic residence time. In addition, since the recirculation cylinder is positioned downstream of the hydrocyclone, it has a lower threshold than the latter. Indeed, since the hydrocyclone has carried out a first liquid-solid separation, only the finest particles remain present in the water transmitted to the recirculation cylinder. Consequently, in order to carry out a second effective solid-liquid separation, the cut-off threshold must be reduced.

[0113] Furthermore, to meet both the space constraint, while optimizing the treatment of suspended matter, in one embodiment, the inventor set the length of the recirculation cylinder to lm20. The hydraulic residence time within this recirculation cylinder is between ls to 4s, with optimal performance for 4s, like the hydrocyclone. According to this embodiment, the recirculation cylinder had a size similar to the hydrocyclone, however, another configuration, in which their size differs, is also possible. The recirculation cylinder was positioned horizontally.

[0114] The recirculation cylinder may be fitted with a vent or purge to allow the evacuation of air introduced during the liquid-solid separation stages. In fact, this air purge, carried out by a purger for example, prevents the accumulation of air at the high point which could cause a malfunction.

[0115] In the embodiment implemented by the inventor during his tests, the recirculation cylinder operated at a pressure of 1 to 1.5 bars. 2.7. Other elements

[0116] In a variant of the invention, an additional step of adding polymer 7 can be implemented downstream of the acceleration pump, or at the inlet of the recirculation cylinder. To further improve the performance of the device, an automatic addition could be implemented depending on the rate of suspended matter at the inlet of the device.

[0117] A coagulant addition step 7 can also be implemented upstream of the polymer addition step.

[0118] A diaphragm valve can be positioned downstream of the accelerator pump, which can optionally allow pressure adjustment.

[0119] 3. Description of a filtration installation equipped with a device according to the invention

[0120] According to one embodiment of the invention, the DISP device can be implemented at the outlet of a filter's backwash overflow, this overflow being able to be either under pressure or by gravity. Within the installation upstream of the device, the water is previously coagulated and potentially flocculated. It can also contain solid mineral particles such as sand or clay.

[0121] Thus, the dirty water can be backwash water from an ultrafiltration membrane, this ultrafiltration membrane allowing for example the filtration of raw water or pre-treated water. According to an exemplary embodiment, raw water (e.g.: lake water) is coagulated, before being conveyed to an ultrafiltration membrane. The suspended matter is thus coagulated and forms a cake by sticking to the ultrafiltration membrane. This cake is then detached by backwashing and is evacuated with the backwash water by the overflow of the dirty water tank, towards the device of the invention. Subsequently, the device according to the invention makes it possible to separate the water from the solid matter contained in the dirty overflow water, in order to limit water losses from the installation.

[0122] According to another embodiment, the dirty water may be backwash water from a sand or granular activated carbon filter, or backwash water from a biofilter (example Biostyr™).

[0123] 4. Description of a ballasted flocculation-decantation installation equipped with a device according to the invention

[0124] In relation to Figure 2, one embodiment of the invention comprises implementing the DISP device within a ballasted flocculation-settling installation. Such a ballasted flocculation-settling installation implements:

[0125] - an optional coagulation step of the suspended matter contained in the water to be treated, by adding coagulants 1000 to the water to be treated, forming agglomerates of particles;

[0126] - a step of flocculation of the suspended matter contained in the water to be treated, in a flocculation zone 2000, thus forming flocs;

[0127] - an addition of granular material serving as ballast for the flocs, in the flocculation zone 2000; - a decantation of the suspended matter, the flocs and the granular material, in a decanter 3000, thus forming a sludge;

[0128] - a supply of sludge to a first hydrocyclone 4000, the first hydrocyclone separating part of the solid particles (suspended matter, flocs and granular material) from the sludge;

[0129] - recovery of a sludge composed of the heaviest particles (largely granular material) in underflow 4001 of the first hydrocyclone, the granular material being recycled for reuse;

[0130] - recovery of a sludge composed of the lightest particles in overflow (100) from the first hydrocyclone, this sludge (or dirty overflow water) always containing suspended matter, flocs and potentially granular material.

[0131] The installation also comprises a DISP device according to the invention as described above in connection with Figure 1 (for simplicity, certain elements of the device as described in Figure 1 have been omitted in Figure 2), and implementing the following steps:

[0132] - degassing 1 of the dirty overflow water 100 from the first hydrocyclone 4000;

[0133] - supply of a hydroejector 3 with dirty water degassed by an accelerator pump 2;

[0134] - hydrocycloning of the water leaving the hydroejector 3, within a second hydrocyclone 4;

[0135] - recovery of granular material, flocs and suspended matter, in underflow 41 of the second hydrocyclone;

[0136] - centrifugation of the overflow water 42 from the second hydrocyclone 4, within a recirculation cylinder 5;

[0137] - recirculation 200 of the solid particles (granular material, flocs, suspended matter) by suction via the Venturi effect produced by the hydroejector 3, the water containing these solid particles being sucked by the hydroejector 3 into the recirculation cylinder 5, to be mixed, within the hydroejector 3, with the degassed dirty overflow water feeding the hydroejector. The mixture then continues its circulation within the DISP device to feed the second hydrocyclone 4, etc.

[0138] - recovery of clarified water 300 at outlet 51 of the recirculation cylinder, this water being able to be recycled at the head of the flocculation installation - ballasted decantation;

[0139] - continuous measurement and adjustment of the flow rate, to meet the following conditions: for an accelerator pump outlet flow rate of xm 3 / h, then the flow rate at the hydroejector outlet is between l.lx and l.5x m 3 / h, the flow rate at the underflow outlet of the second hydrocyclone is less than 0.1x m 3 / h, the recirculation flow rate is between 0.1x and 0.5x m 3 / h, and the flow rate at the overflow outlet of the recirculation cylinder is between 0.9x and 0.95x m 3 / h.

[0140] Underflow 41 from the second hydrocyclone can optionally be recycled if it contains, for example, residual activated carbon (used for the treatment of organic matter in the ballasted flocculation-settling plant) or carbonate ions if the ballasted flocculation-settling plant is used to remove water hardness. 5. Experimental results

[0141] Tests were conducted with dirty overflow water from a hydrocyclone in a ballasted flocculation-settling plant, with the dirty overflow water containing 0.91 g / L of suspended solids. The results of these tests are presented below. According to these results, the clarified water leaving the recirculation cylinder represents 90-95% of the water entering the DISP device. The tests also determined that at lower temperatures, efficiency was better due to the increased viscosity of the water.

[0142] For an internal diameter of 8 mm at the outlet of the Venturi nozzle: For an internal diameter of 10 mm at the outlet of the Venturi nozzle:

Claims

AMENDED CLAIMS received by the International Bureau on November 9, 2023 (09.11.2022) 1. A method for treating dirty water from a water treatment system (100) to separate, on the one hand, treated water, and on the other hand, solid particles contained in the dirty water, said solid particles comprising suspended matter and / or an insoluble granular material heavier than water, a method characterized in that it comprises the following steps: a step of degassing (1) said dirty water (100); a step of supplying degassed dirty water to a hydrocyclone (4) via a hydroejector (3) powered by an accelerator pump (2), said accelerator pump (2) being capable of adjusting a flow rate and a pressure; a first step of separating the suspended matter and / or the granular material present in said degassed dirty water, by hydrocycloning within said hydrocyclone (4);a step of recovering an overflow (42) of said hydrocyclone (4), said overflow of the hydrocyclone (4) mainly comprising residual suspended matter; a second step of separating by centrifugation the residual suspended matter from the water recovered in overflow of said hydrocyclone (4), within a recirculation cylinder (5), configured to separate by centrifugation residual suspended matter from the water recovered in overflow of said hydrocyclone and comprising, a supply of overflow water of said hydrocyclone at a first end of said cylinder, a clarified water overflow outlet positioned at a second end of said cylinder, a discharge of solid particles positioned at the periphery of said cylinder between the supply and the outlet of said cylinder and connected to the hydroejector, and a centrifugation system;a step of recirculating to said hydrocyclone (4) water comprising said residual suspended matter from said recirculation cylinder (5) by suction by said hydroejector (3); a step of extracting clarified water, at the overflow outlet (51) of said recirculation cylinder; a step of continuously measuring the flow rate at the outlet of said accelerator pump (2), the flow rate at the outlet of said hydroejector (3), and the flow rate at the overflow outlet of said recirculation cylinder (5).; 2. Method according to claim 1 characterized in that it comprises: a step of continuously adjusting said flow rate of said accelerator pump as a function of the result of the measurement recorded during said measuring step; said step of adjusting the flow rate of said accelerator pump being such that, for a flow rate at the outlet of said accelerator pump of xm 3 / h, then the flow rate at the hydroejector outlet is between l.lx and l.5x m 3 / h, the flow rate at the underflow outlet of the hydrocyclone is less than 0.1x m 3 / h, the recirculation flow rate is between 0.1x and 0.5x m 3 / h, and the flow rate at the overflow outlet of the recirculation cylinder is between 0.9x and 0.95x m 3 / h.

3. Method according to claim 1 or 2, characterized in that it comprises a step of adding polymer to the water downstream of said accelerator pump and / or at the inlet of said recirculation cylinder. AMENDED SHEET (ARTICLE 19) 4. Method according to one of claims 2 or 3, characterized in that said flow rate at the outlet of said accelerator pump (2) x is between 4 and 50 m 3 / h.

5. Method according to one of claims 1 to 4, characterized in that the hydraulic residence time is between 2 s and 4 s within said hydrocyclone (4) and said recirculation cylinder (5).

6. Method according to one of claims 1 to 5, characterized in that said hydrocyclone (4) has a cut-off threshold of between 10 and 25 pm, and said recirculation cylinder (5) has a cut-off threshold of between 5 and 15 pm.

7. Method according to one of claims 1 to 6, characterized in that it comprises adapting the pressure of the water at the outlet of said accelerator pump, said pressure at the outlet of said accelerator pump being between 2 and 5 bars.

8. Method according to one of claims 1 to 7, characterized in that said hydroejector (3) comprises a nozzle (31) whose outlet diameter is between 1 / 5th and half of its inlet diameter.

9. Method according to one of claims 1 to 8, characterized in that said dirty water comes from a hydrocyclone (4000) of a ballasted flocculation-decantation installation.

10. Method according to one of claims 1 to 8, characterized in that the dirty water comes from a filtration system, said filtration system belonging to the group comprising: sand filters; granular activated carbon filters; ultrafiltration membranes; biological filters using biomass fixed on a granular support; mechanical filters.

11. Device (DISP) for treating dirty water from a water treatment line in order to separate suspended matter and / or an insoluble granular material heavier than water for implementing a method according to one of claims 1 to 10, characterized in that it comprises: means (1) for degassing at the inlet of said device; an accelerator pump (2) capable of adjusting a flow rate and a pressure of the water from the degassing means; a hydroejector (3) powered by said accelerator pump; a hydrocyclone (4) powered by the water from the hydroejector; a recirculation cylinder (5) configured to separate by centrifugation residual suspended matter from the water recovered in overflow from said hydrocyclone, a wall of said recirculation cylinder being connected to said hydroejector;means (6) for measuring pressure and / or flow rate, arranged at the outlet of said accelerator pump, at the outlet of said hydroejector and at the overflow outlet of said recirculation cylinder; said hydroejector (3) being capable of recirculating part of the water coming from the recirculation cylinder (5) towards the hydrocyclone (4).; AMENDED SHEET (ARTICLE 19) 12. Device according to claim 11, characterized in that it comprises means (7) for adding polymer provided downstream of said accelerator pump, and / or at the inlet of said recirculation cylinder.

13. Device according to one of claims 11 or 12, characterized in that said hydrocyclone (4) has a cut-off threshold of between 10 and 25 pm, and said recirculation cylinder (5) has a cut-off threshold of between 5 and 15 pm.

14. Device according to one of claims 11 to 13, characterized in that said hydroejector (3) comprises a nozzle (31) whose outlet diameter is between 1 / 5 and half of its inlet diameter.

15. Device according to one of claims 11 to 14 characterized in that the recirculation cylinder (5) is positioned horizontally.

16. Device according to one of claims 11 to 15 characterized in that said hydrocyclone (4) and said recirculation cylinder (5) each have a length of between 0.8 and 2m. AMENDED SHEET (ARTICLE 19)

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