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

Abstract

The present invention relates to a method for treating dirty overflow water so as to separate suspended solids and insoluble particulate matter heavier than water. The method comprises a degassing step 1, two solid-liquid separation steps inside a hydrocyclone 4 and a recirculation cylinder 5, and a recirculation step of the treated water carried out by a liquid ejector 3.

Description

[Technical Field]

[0001] The field of the invention relates to the field of water treatment for water purification or for making water potable.

[0002] More precisely, the invention relates to the treatment of pre-flocculated and optionally flocculated wastewater coming from water treatment plants. [Background technology]

[0003] A well-known method for treating water, particularly surface water, to make it potable, and for treating municipal or industrial wastewater to decontaminate it, consists of flocculating the water to be treated with a flocculating agent such as a trivalent metal salt, flocculating the organic matter contained in the flocculated water with a flocculating reagent / reactant, usually an organic polymer, and settling or filtering the flocs and other solids in a settling tank or through a filter. In the case of a settling tank, sludge is removed from the bottom of the settling tank and treated water is removed in the settling tank overflow, and in the case of a filter, filtered water is removed from one side of the filter and sludge and / or wastewater is removed by backwashing through the filter overflow.

[0004] More specifically, a technical example of carrying out the coagulation and flocculation steps consists of adding a coagulant and / or a floc-forming agent to raw water so as 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 through which the clean water passes. The floc cake can then be removed by backwashing the membrane and overflowing the dirty wash water into the tub.

[0005] In this way, wastewater is collected as an overflow of a filter or membrane filtration facility, and can then be concentrated and / or dewatered in a post-treatment system. However, such methods lead to high water losses and costly, large-footprint post-treatment.

[0006] As another technical example for carrying out the coagulation and flocculation steps, the Actiflo® process has been proposed, which uses ballast consisting of fine, dense granular material, such as fine sand, injected into or upstream of the flocculation zone to act as a flocculation initiator, thereby increasing the rate of floc formation and, through increasing their density, the settling rate of the flocs formed during the flocculation stage. The ballasted (lestee) sludge is removed from the bottom of a settling tank.

[0007] Fine sand, with an average diameter of approximately 20 micrometers to 300 micrometers, usually between 80 micrometers and 200 micrometers, is the most commonly used ballast due to availability and cost.

[0008] For economic reasons regarding reuse, ballast is usually separated from the sludge removed from the settling plant and recycled into the process.

[0009] Ballast losses are usually split between losses via treated water leaving as settling tank overflow and losses with sludge removed from the plant.

[0010] New ballast is injected to compensate for the loss of ballast.

[0011] Controlling the loss of ballast entrained in the sludge is important to minimize expenditure on new ballast and to avoid degrading the quality of the sludge being removed.

[0012] The means used to separate the ballast from the extracted sludge and recycle this ballast into the process by minimizing ballast losses are generally selected from static, gravity-driven separation techniques (e.g., sedimentation) or dynamic separation techniques (e.g., centrifugation and cycloning), mostly by hydrocycloning / hydrocyclonage of the sludge / ballast mixture.

[0013] The loss of ballast in the overflow of a hydrocyclone, which is the means most often used in practice to separate ballast from the extracted sludge, is generally roughly proportional to the concentration of ballast in the mixture entering the hydrocyclone, for fixed hydrocyclone geometry and operating conditions.

[0014] To reduce these ballast losses, the prior art has already proposed treating this overflow in a second hydrocyclone, and in particular US Pat. No. 5,623,999 discloses the use of two such hydrocyclones mounted in series.

[0015] However, this method results in a large amount of sludge at the outlet of the second hydrocyclone, which contains even more water, i.e., these diluted sludges are a source of water loss.

[0016] Therefore, these sludges need to be thickened and dewatered during post-treatment.

[0017] Such post-processing increases the cost of implementing the method, and the corresponding equipment increases the facility footprint.

[0018] Regarding limiting water loss, another known invention is disclosed in Patent Document 2, known under the name Actiflo® HCS. This relates to a facility for ballasted flocculation-settling / flocculation-decantation sludge treatment, which includes a simplified system for recycling a portion of the overflow from a hydrocyclone that separates the ballasted sludge. After degassing, a portion of the hydrocyclone overflow is returned to the suction side of the pump that extracts the sludge / ballast mixture and feeds the hydrocyclone. This regulated recirculation system reduces the amount of water extracted with the sludge, thereby concentrating the sludge. It also reduces ballast loss. However, this system cannot be used for all types of water and must be selected depending on the input volume and flow rate of the water to be treated. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] International Publication No. 03 / 053862 [Patent Document 2] International Publication No. 2011 / 103651 Summary of the Invention [Problem to be solved by the invention]

[0020] The object of the present invention is to provide a method that can overcome these drawbacks of the prior art.

[0021] More precisely, the main object of the invention is to provide a method for treating dirty overflow water coming from a water treatment plant, which makes it possible to limit water losses.

[0022] Another object of the present invention is to reduce the amount of sludge produced by such water treatment plants.

[0023] Another object of the invention is to provide a method that makes it possible to reduce the amount of chemical products that need to be used in such plants and thus limit the ecological impact of the corresponding processes.

[0024] Another object of the invention is to provide an apparatus for implementing such a method that makes it possible to limit the footprint of such a plant. [Means for solving the problem]

[0025] These objectives, as well as others that will become apparent hereinafter, are achieved using a method for treating dirty overflow water, which is used to separate, on the one hand, the treated water and, on the other hand, the solid particles contained in the dirty overflow water, said solid particles consisting of suspended solids and / or insoluble particulate matter that is heavier than water, said method comprising the following steps: degassing the dirty overflow water; - feeding the degassed dirty overflow water to a hydrocyclone via a liquid ejector fed by an accelerator pump, the accelerator pump being capable of adjusting the flow rate and pressure; a first separation step of suspended solids and / or particulate matter present in the deaerated dirty overflow water by hydrocyclone treatment inside a hydrocyclone; - collecting the overflow of the hydrocyclone, the overflow comprising mainly water and residual suspended matter; - a second separation step of residual suspended matter from the recovered overflow water of the hydrocyclone inside a recirculation cylinder; - recycling the water containing the residual suspension coming from the recycling cylinder into the hydrocyclone through suction by a liquid ejector; - withdrawing purified water at the outlet of the recirculation cylinder; - continuously measuring the flow rate at the inlet and outlet of the liquid ejector and at the outlet of the recirculation cylinder; Includes:

[0026] According to the invention, in order to be able to remove the suspended solids present at the overflow outlet of the upstream facility, the invention proposes to carry out a method for treating this dirty overflow water, comprising two solid-liquid separation steps using a hydrocyclone and a recirculation cylinder, coupled with the recirculation of water at the outlet of the recirculation cylinder.

[0027] According to this specification, the term "recirculation cylinder" refers to a cylinder having the following elements: a water supply inlet near one end of the cylinder (connected to the overflow of the hydrocyclone), a clean water outlet located at the other end of the cylinder, a solid particle discharge located on the outer edge of the cylinder between the supply and outlet and connected to a liquid ejector, and a centrifuge system.

[0028] The function of this recirculation cylinder is similar to that of a hydrocyclone, in that it creates a vortex that causes centrifugal separation of the water contained within the cylinder, allowing for solid-liquid separation. The centrifugal force caused by the turbulent flow of the fluid rotating around its axis causes the ejection of solid particles at the outer edge of the cylinder wall. The water discharged through the tangential outlet is mixed with solid particles. Clean water is discharged at the center of the cylinder.

[0029] Therefore, according to the present invention, the dirty overflow water is subjected to at least a first solid-liquid separation step (or hydrocyclone treatment) in a hydrocyclone, and then the overflow water of the hydrocyclone is subjected to at least a second solid-liquid separation step in a recirculation cylinder having a lower cut-off threshold than the hydrocyclone, so as to separate most of the suspended residual particles that were not separated from the water during the first solid-liquid separation step.

[0030] To limit water loss, the water containing suspended residual particles collected on the cylinder wall during the second solid-liquid separation step and separated from the purified water is reintroduced into the feeding step of the hydrocyclone via a recirculation loop. Thus, the water containing suspended matter coming from the recirculation cylinder is sucked by a liquid ejector (a device that creates suction using the Venturi effect) and recirculated to the hydrocyclone to optimize its treatment and remove the suspended matter. Therefore, this method allows for optimizing solid-liquid separation, especially for very fine solid particles (suspended matter), while limiting water loss.

[0031] Furthermore, by establishing continuous measurements of flow rate and pressure, the precise operation of the method can be controlled.

[0032] Furthermore, the method describes a degassing step upstream of the feeding step to avoid any malfunctions related to the presence of air.

[0033] According to a preferred feature of the invention, the method includes the steps of continuously measuring the flow rate of the accelerator pump and continuously adjusting said flow rate in response to the results of measurements made during the measuring step, the step of adjusting the flow rate of the accelerator pump comprising adjusting the flow rate at the inlet of the liquid ejector by xm 3 / h, the flow rate at the outlet of the liquid ejector is 1.1xm 3 / h~1.5xm 3 / h, and the flow rate at the underflow outlet of the hydrocyclone is 0.1 x m 3 / h, and the recirculation flow rate is less than 0.1xm 3 / h~0.5xm 3 / h, and the flow rate at the overflow outlet of the recirculation cylinder is 0.9 x m 3 / h~0.95xm 3 It is supposed to be between / h.

[0034] The present invention proposes to maintain a specific flow rate at each step of the method, so as to establish a recirculation loop and to be able to suck in the water containing the residual suspended matter coming from the recirculation cylinder. Therefore, advantageously, the use of a variable-speed accelerating pump and the establishment of a continuous measurement of the flow rate allow the optimization of the method according to the invention. More specifically, the method according to the invention has a very specific operating point, and the appropriate conditions must be continuously maintained. In particular, the set of parameters used in the method (flow rate, pressure, characteristics of the liquid ejector and the hydrocyclone, etc.) are interdependent. Therefore, in order to limit water losses and maximize the removal of suspended matter, the method according to the invention proposes to maintain a flow rate at the outlet of the recirculation cylinder close to the flow rate at the inlet of the liquid ejector, in other words approximately xm 3 / h, more precisely 0.9xm 3 / h~0.95xm 3 It is proposed to adjust the flow rate during each step of the method to obtain a flow rate between 1000 and 1000 kcal / h.

[0035] According to another feature of the invention, the method includes the step of adding a polymer to the degassed dirty overflow water upstream of the liquid ejector and / or at the inlet of the recirculation cylinder.

[0036] Advantageously, the addition of polymers to the water to be treated can improve the removal of suspended matter, more particularly by adding polymers to the dirty overflow water to be treated before it reaches the liquid ejector, it is possible to flocculate all particles of suspended matter, thus increasing their size, which will facilitate their separation from the water during the various solid-liquid separation steps.

[0037] This step of adding polymer can be carried out automatically depending on the content of the suspension at the inlet of the liquid ejector and / or at the inlet of the recirculation cylinder.

[0038] According to an advantageous feature of the invention, the flow rate x at the inlet of the liquid ejector is 4 m 3 / h~50m 3 / h.

[0039] The method according to the invention therefore advantageously makes it possible to control the flow rate and adapt it to the optimization of the solid-liquid separation step and the recirculation of the water to be treated. Furthermore, by observing a predetermined flow rate at the pump outlet, it is possible to maintain conditions corresponding to a specific operating point of the method (flow rate, pressure) and thus optimize its efficiency by minimizing water losses and maximizing the removal of suspended solids.

[0040] Preferably, the hydraulic residence time inside the hydrocyclone and inside the recirculation cylinder is between 2 and 4 seconds.

[0041] Therefore, by adhering to a specific hydraulic residence time, separation of the suspended matter from the water during the solid-liquid separation step can be optimized.

[0042] According to a preferred variant, the hydrocyclone has a cut-off threshold between 10 μm and 25 μm, and the recirculation cylinder has a cut-off threshold between 5 μm and 15 μm.

[0043] Thus, this method can remove very fine particles (e.g., flocs) that have densities relatively close to that of water. These cutoff thresholds allow for the use of chemical products limited by their effect on fine particles. More specifically, these two mechanical solid-liquid separation steps do not require the use of coagulants or flocculants to effectively separate very fine contaminants from water.

[0044] According to an advantageous feature of the invention, the pressure of the water at the outlet of the accelerator pump is between 2 bar and 5 bar.

[0045] This pressure is adapted to the treatment of water and is one of the specific parameters of the method that allows to maintain its specific operating point. More specifically, if the pressure at the outlet of the accelerator pump is 2-4 bar, after the water passes through the liquid ejector, a pressure of between 1.5 bar and 2.5 bar can be obtained at the inlet of the hydrocyclone due to the pressure loss (approximately 1 bar to 1.5 bar) induced by the Venturi effect. Therefore, depending on the pressure obtained at the inlet of the hydrocyclone and at the inlet of the recirculation cylinder, a cut-off threshold can be used that allows optimal separation of the suspended matter.

[0046] According to another preferred embodiment of the present invention, the liquid ejector includes a nozzle whose outlet diameter is between 1 / 5 and half of its inlet diameter.

[0047] The method proposes adjusting the nozzle diameter to maintain a specific operating point of the method, so as to create a Venturi effect that generates sufficient suction to recirculate a portion of the water coming from the recirculation cylinder back into the hydrocyclone. In particular, the pressure loss and suction force depend on the inlet and outlet diameters of the liquid ejector nozzle. More specifically, the smaller the outlet diameter is relative to the inlet diameter, the greater the pressure loss and suction force; and the closer the outlet diameter is to the inlet diameter, the lower the pressure loss and suction force.

[0048] According to a preferred variant of the invention, the dirty overflow water comes from the hydrocyclones of the ballasted flocculation sedimentation facility.

[0049] According to another variant, the dirty overflow water can also come from a filtration system, which -Sand filter, a granular activated carbon filter; an ultrafiltration membrane; biological filters using biomass fixed on granular carriers, such as the filters marketed under the trademark Biostyr®; a mechanical filter such as Hydrotech or others; It belongs to a group including

[0050] The present invention also relates to an apparatus for treating dirty overflow water so as to separate suspended solids and insoluble particulate matter heavier than water, so as to carry out the method described above. degassing means at the entrance of said facility; - an acceleration pump capable of adjusting flow rate and pressure; a liquid ejector; a hydrocyclone fed with water coming from a liquid ejector; a recirculation cylinder fed with water coming from the overflow of the hydrocyclone; - means for measuring pressure and / or flow rate; The liquid ejector is capable of recirculating part of the water coming from the recirculation cylinder to the hydrocyclone.

[0051] According to a feature of the invention, the device comprises polymer addition means located upstream of the liquid ejector and / or at the inlet of the recirculation cylinder.

[0052] According to a preferred feature of the invention, the recirculation cylinder is arranged horizontally.

[0053] More specifically, the device can be installed on top of a ballasted flocculation settling device from the prior art and connected to the overflow of its hydrocyclone, which configuration makes it possible to minimize the footprint of the assembly.

[0054] According to a preferred feature of the invention, the hydrocyclone and the recirculation cylinder each have a length between 0.8 m and 2 m.

[0055] The device is therefore relatively compact, has a small footprint, and can be placed on top of existing prior art facilities.

[0056] Other characteristics and advantages of the invention will appear more clearly on reading the following description of preferred embodiments, given purely by way of illustrative and non-limiting example and explained with reference to the drawings, in which: [Brief explanation of the drawings]

[0057] [Figure 1] 1 illustrates an apparatus for treating dirty overflow water according to one embodiment of the present invention. [Figure 2] FIG. 1 shows a ballasted flocculation sedimentation facility equipped with such an apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0058] 1. Description of one embodiment of the device according to the invention The device according to the invention is fed with wastewater from a water treatment plant, which can be, for example, in the form of a ballasted flocculation sedimentation plant, a biofilter, an ultrafiltration membrane, a sand filter, or any other water treatment plant. In the water treatment plant, the water has previously undergone physicochemical treatment. The wastewater can therefore be coagulated, potentially flocculated and / or ballasted, before filtration and / or sedimentation and / or hydrocyclone treatment. The wastewater fed to the device according to the invention can therefore come from the pressurized overflow 100 of a hydrocyclone of a ballasted flocculation sedimentation plant, or even from the overflow 100 (pressurized or gravity-driven) for backwashing of a filter (biofilter, ultrafiltration, sand filter, activated carbon, etc.) or of any type of separator used in the water treatment plant.

[0059] Referring to FIG. 1, the device DISP according to the present invention comprises a degassing means 1 for removing any air from the wastewater at the inlet of the device. The device further comprises an accelerator pump 2, which acts as a driving force, and which allows the water from the degassing means to be delivered to a Venturi-effect liquid ejector 3. The water is then sent to a hydrocyclone 4. In the underflow 41 of this hydrocyclone, particulate matter that can be used to ballasted the flocs and most of the suspended matter are recovered in the form of sludge. The particulate matter that serves as ballast can optionally be recycled. In the overflow 42 of the hydrocyclone, pretreated water containing only very fine residual suspended matter is recovered. The water may potentially also contain residual particulate matter. This pretreated water is sent to a recirculation cylinder 5, in which the residual particles are separated from the treated water by centrifugal separation through the creation of a vortex. The particles thus collect on the wall of the recirculation cylinder and are then sucked in by the Venturi effect by the liquid ejector 3 connected to the wall of the recirculation cylinder. Thus, the residual suspension coming from the recirculation cylinder is mixed inside the liquid ejector with the untreated wastewater coming from the degassing vessel or column, and the mixture is then sent to a hydrocyclone 4 or the like. This recirculation loop therefore allows this residual suspension to be reprocessed until optimum contaminant removal is achieved.

[0060] The flow rate inside the device implemented by the method according to the invention varies depending on the method step: at the outlet of the accelerator pump, the flow rate is preferably 4 m 3 / h~50m 3 / h. Substituting the value x based on this supply flow rate, the supply 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, unlike the recirculation rate, the flow rate does not depend on the size of the nozzle 31.

[0061] It is possible to arrange several treatment plants according to the invention in parallel to treat larger total flow rates.

[0062] 2. Characteristics of the elements constituting the device according to one exemplary embodiment of the present invention Sensors Flow and pressure sensors 6 can be placed between each processing step. These sensors allow the direction of water circulation (in case of malfunction) and the amount of recirculated water to be verified. This allows the pressure at the inlet of the device to be adapted to maintain optimal processing conditions.

[0063] 2.2. Degassing means The degassing means 1 can remove air or any gas potentially contained in the contaminated water to be treated. These means are, for example, a container, a tarp, or a degassing device. Therefore, the degassing means 1 can avoid the presence of any air that may cause malfunctions inside the facility (for example, the phenomenon of cavitation of pumps).

[0064] Hydraulic means such as vents or bleeders can also be used to ensure that no air and / or gas is present in the apparatus. These means can be placed in any processing step of the apparatus, particularly in solid-liquid separation steps. This can in particular avoid cavitation phenomena, which can cause malfunctions in feed pumps and Venturi-effect liquid ejectors in particular.

[0065] 2.3.Accelerator pump The acceleration pump 2 serves as a driving force and can supply deaerated dirty overflow water to the device.

[0066] The parameters of flow rate and pressure can be very precisely controlled by the accelerator pump 2. This pump preferably operates in conjunction with a sensor 6. This pump can be a variable frequency pump.

[0067] In the embodiment carried out by the inventor during his tests, the pressure delivered by the accelerator pump was between 3 bar and 4.5 bar.

[0068] 2.4.Venturi Effect Liquid Ejector The liquid ejector 3 is fed by an acceleration pump 2 and also supplies a recirculation cylinder 5. More specifically, the pump provides the flow rate of degassed water necessary for the liquid ejector to suck, by the Venturi effect, a portion of the water contained in the recirculation cylinder (this water contains the solid particles to be removed from the water), and the liquid ejector is connected to the wall of the recirculation cylinder.

[0069] The liquid ejector consists of a nozzle 31, whose conical shape (combined with the flow rate generated by the accelerator pump) allows for the creation of a Venturi effect. At the nozzle outlet (on the inlet side of the hydrocyclone), the outlet diameter is between one-fifth and one-half of the nozzle inlet diameter (on the accelerator pump side). This ratio must be maintained because if the outlet diameter is too small, the pressure loss will be too great, and if the diameter is too large, the Venturi effect will disappear. The nozzle outlet diameters used by the inventors during their testing ranged from 2 mm to 15 mm. Furthermore, the angle formed by the nozzle also affects the Venturi effect.

[0070] The circulation speed of the water inside the device is advantageously between 0.5 m / s and 2 m / s, except inside the Venturi effect liquid ejector, where the water is accelerated 4 to 25 times to obtain a speed of 2 to 50 m / s. The circulation speed of the water inside the liquid ejector 3 is adjustable and depends on the diameter of the nozzle 31. The circulation speed at the outlet of the liquid ejector 3 is therefore between 0.5 m / s and 2 m / s.

[0071] The passage of the water through the liquid ejector causes a pressure drop. The smaller the nozzle diameter, the greater the pressure drop. Similarly, the higher the flow rate, the greater the pressure drop. In the embodiments carried out by the inventors during their testing, the pressure drop due to the Venturi effect was 1 bar to 1.5 bar.

[0072] The materials used to manufacture the nozzle (and all elements of the device) must be wear resistant and compatible with the viscosity of water.

[0073] The Venturi effect has a precise operating point that allows the suction of the suspension coming from the recirculation cylinder, which depends on the pressure and flow rate provided by the accelerating pump, as well as the specific parameters of the liquid ejector (diameter, nozzle angle).

[0074] 2.5.Hydrocyclone The hydrocyclone 4 is capable of separating and removing solid particles contained in the water to be treated coming from the liquid ejector 3. At this time, the heaviest particles are removed via the underflow of the hydrocyclone 4, and the overflow containing the finest particles (residual particles) is transferred to the recirculation cylinder 5.

[0075] The solid particles removed from the underflow of the hydrocyclone may include particulate matter that serves as ballast and can be recycled for reuse in steps upstream of the device.

[0076] The hydrocyclone used in this device has a cutoff threshold between 5 μm and 25 μm, which depends on flow rate, pressure, and hydraulic residence time.

[0077] The cut-off threshold of the hydrocyclone can be adapted to the separation of fine sand particles and particles of similar density (10 μm to 25 μm) or to the separation of particles of lower density (5 μm to 15 μm). This cut-off threshold, like the cut-off threshold of the recirculation cylinder, is therefore adapted according to the particles (density, size) contained in the water to be treated.

[0078] Preferably, the hydrocyclone has a length between 0.8 m and 2 m, a hydraulic residence time between 1 and 4 seconds, and an internal velocity between 0.5 m / s and 1 m / s. Optimal performance for such a hydrocyclone is achieved with a hydraulic residence time of 4 seconds. More specifically, the longer the hydraulic residence time, the more effective the solid-liquid separation. According to one exemplary embodiment, the hydrocyclone is similar to the hydrocyclone of a ballasted flocculation sedimentation facility, but with a more spindle-shaped configuration. Depending on the desired application, the hydrocyclone can optionally be sized greater than 2 m. This allows for increased hydraulic residence time and improved yields in solid-liquid separation.

[0079] In one exemplary embodiment, the hydrocyclone is vertically oriented.

[0080] In the embodiment carried out by the inventor during his tests, the hydrocyclone functioned at a pressure of 1 bar to 1.5 bar. In particular, when the device of the present invention is used after a ballasted flocculation and sedimentation facility with a first hydrocyclone, it is necessary to operate at a higher pressure than for the first hydrocyclone of the ballasted flocculation and sedimentation facility.

[0081] 2.6.Recirculating Cylinder According to this description, the term "recirculation cylinder" refers to a cylinder including the following elements: a water inlet near one end of the cylinder (connected to the overflow of the hydrocyclone), a clean water outlet located at the other end of the cylinder, a solid particle discharge located on the outer edge of the cylinder between the inlet and the outlet and connected to a liquid ejector, and a centrifuge system.

[0082] The recirculation cylinder generates a vortex that allows centrifugal separation of the water coming from the overflow of the hydrocyclone and separation of the remaining particles from the water. The particles are therefore collected on the wall of the recirculation cylinder and are sucked in by the liquid ejector 3.

[0083] The function of this recirculation cylinder is similar to that of a hydrocyclone, in that it creates a vortex that causes centrifugal separation of the water contained within the cylinder, allowing for solid-liquid separation. The centrifugal force caused by the turbulent flow of the fluid rotating around its axis causes the ejection of solid particles at the outer edge of the cylinder wall. The water discharged through the tangential outlet is mixed with solid particles. Clean water is discharged at the center of the cylinder.

[0084] The recirculation cylinder 5 used in this device has a very fine (on the order of 5 μm to 15 μm) cutoff threshold adapted to the fineness of the residual suspension. This threshold depends on the flow rate, pressure, and hydraulic residence time. Furthermore, since the recirculation cylinder is located downstream of the hydrocyclone, it has a lower threshold than the hydrocyclone. More specifically, since the hydrocyclone performed the first solid-liquid separation, only the finest particles remain in the water sent to the recirculation cylinder. Consequently, the cutoff threshold must be lowered to perform an effective second solid-liquid separation.

[0085] Furthermore, to accommodate footprint constraints while optimizing suspension processing, in one embodiment, the inventors fixed the length of the recirculation cylinder at 1.20 m. Similar to a hydrocyclone, the hydraulic residence time inside this recirculation cylinder ranged from 1 to 4 seconds, with optimal performance achieved at 4 seconds. In this embodiment, the recirculation cylinder had a similar size to the hydrocyclone, although different configurations with different sizes are possible. The recirculation cylinder was oriented horizontally.

[0086] The recirculation cylinder may be equipped with a vent or bleeder to allow the escape of air introduced during the solid-liquid separation step. More particularly, this air bleed, for example by a bleeder, prevents the accumulation of air at high points that could cause malfunction.

[0087] In the embodiment carried out by the inventors during their tests, the recirculation cylinder functioned at a pressure of 1 bar to 1.5 bar.

[0088] 2.7.Other Elements In a variant of the invention, a supplementary step 7 of polymer addition can be carried out downstream of the accelerator pump or at the inlet of the recirculation cylinder. To further improve the performance of the device, automatic addition can be carried out depending on the concentration of the suspension at the inlet of the device.

[0089] A step 7 of flocculant addition may also be carried out upstream of the step of polymer addition.

[0090] A membrane valve may be placed downstream of the accelerator pump, which may optionally allow the pressure to be adjusted.

[0091] 3. Description of the filtration installation equipped with the device according to the invention According to one embodiment of the present invention, the device DISP can be implemented at the backwash overflow outlet of the filter, which overflow can be either pressurized or gravity-driven. In a facility upstream of the device, the water is pre-flocculated and optionally flocculated. The water can also contain solid mineral particles such as sand or clay.

[0092] Thus, the wastewater can be backwash water from an ultrafiltration membrane, which allows for the filtration of, for example, raw water or pretreated water. According to one exemplary embodiment, raw water (e.g., lake water) is flocculated before being sent to the ultrafiltration membrane. The suspended matter is then flocculated and adheres to the ultrafiltration membrane to form a cake. This cake is then removed by backwashing and discharged together with the backwash water through the overflow of the wastewater tank into the device of the present invention. The device of the present invention can then separate the water from the solids contained in the dirty overflow water so as to limit water losses in the facility.

[0093] According to another exemplary embodiment, the wastewater may be backwash water from a sand filter or granular activated carbon, or even backwash water from a biofilter (eg, Biostyr®).

[0094] 4. Description of the ballasted flocculation sedimentation facility equipped with the device according to the present invention Referring to Figure 2, one embodiment of the present invention involves implementing the device DISP within a ballasted flocculation and sedimentation facility. Such a ballasted flocculation and sedimentation facility comprises: - an optional step of adding (1000) a flocculant to the water to be treated, thereby flocculating suspended matter contained in the water to be treated, thereby forming particle aggregates; - forming flocs by flocculating suspended matter contained in the water to be treated in the flocculation zone 2000; - adding granular material in the flocculation zone 2000 to act as ballast for the floc; - settling the suspension, flocs and particulate matter in a settling tank 3000 to form sludge; - feeding sludge to a first hydrocyclone 4000, which separates a portion of the solid particles (suspensions, flocs and particulate matter) from the sludge; - recovering the sludge composed of the heaviest particles (mostly granular matter) in the underflow 4001 of the first hydrocyclone, the granular matter being recycled for reuse; - recovering the sludge composed of the lightest particles in the overflow 100 of the first hydrocyclone, this sludge (or dirty overflow water) still containing suspended matter, flocs and potentially particulate matter; The following will be implemented.

[0095] The facility further comprises an apparatus DISP according to the invention as described above in relation to FIG. 1 (for the sake of simplicity, some elements of the apparatus as described in FIG. 1 are omitted in FIG. 2), and which performs the following steps: - degassing (1) the dirty overflow water 100 of the first hydrocyclone 4000; - supplying the degassed wastewater to a liquid ejector 3 by an acceleration pump 2; - hydrocycloning the water at the outlet of the liquid ejector 3 inside a second hydrocyclone 4; - recovering particulate matter, flocs and suspended matter in the underflow 41 of the second hydrocyclone; - centrifuging the overflow water 42 from the second hydrocyclone 4 inside the recirculation cylinder 5; - recirculating (200) solid particles (granular matter, flocs, suspended matter) by suction via the Venturi effect created by the liquid ejector 3, by which the water containing these solid particles is sucked into the recirculation cylinder 5 so as to be mixed inside the liquid ejector 3 with the degassed dirty overflow water fed to the liquid ejector, the mixture then continuing its recirculation inside the device DISP to feed a second hydrocyclone 4 etc.; - recovering (300) purified water at the outlet 51 of the recirculation cylinder, which water can be recycled to the head of the ballasting flocculation settling facility; -The following conditions are met: the flow rate at the outlet of the accelerating pump is xm 3 / h, the flow rate at the outlet of the liquid ejector is 1.1xm 3 / h~1.5xm 3 / h, and the flow rate at the underflow outlet of the second hydrocyclone is 0.1 × m 3 / h, and the recirculation flow rate is less than 0.1xm 3 / h~0.5xm 3 / h, and the flow rate at the overflow outlet of the recirculation cylinder is 0.9 x m 3 / h~0.95xm 3 / h; and The following will be implemented.

[0096] The underflow 41 of the second hydrocyclone can optionally be recycled if it contains, for example, residual activated carbon (used for the treatment of organic matter in ballasted flocculation sedimentation plants) or carbonate ions if the ballasted flocculation sedimentation plant is used to remove water hardness.

[0097] 5. Experimental Results Tests were carried out using dirty overflow water coming from a hydrocyclone forming part of a ballasted flocculation sedimentation facility. This dirty overflow water had a suspended solids content of 0.91 g / L. The results of these tests are shown below. According to these results, the clean water at the outlet of the recirculation cylinder represents 90% to 95% of the water at the inlet of the device DISP. The tests also showed that at lower temperatures the yield was better due to the increased viscosity of the water.

[0098] [Table 1]

[0099] [Table 2]

Claims

1. A method for treating dirty overflow water (100) so as to separate, on the one hand, the treated water and, on the other hand, the solid particles contained in said dirty overflow water, said solid particles comprising suspended matter and / or insoluble particulate matter heavier than water, said method comprising the following steps: a step (1) of degassing the dirty overflow water (100); feeding the degassed dirty overflow water to a hydrocyclone (4) via a liquid ejector (3) fed by an accelerator pump (2) with adjustable flow rate and pressure; a first separation step of suspended solids and / or particulate matter present in the degassed dirty overflow water by hydrocyclonic treatment inside the hydrocyclone (4); recovering the overflow (42) of the hydrocyclone (4), said overflow from the hydrocyclone (4) comprising mainly residual suspended matter; a second separation step of residual suspended matter from the recovered overflow water from said hydrocyclone (4) inside a recirculation cylinder (5); recirculating the water containing the residual suspended matter coming from the recirculation cylinder (5) to the hydrocyclone (4) through suction by the liquid ejector (3); taking purified water at the outlet (51) of said recirculation cylinder; continuously measuring the flow rates at the inlet and outlet of the liquid ejector (3) and at the outlet of the recirculation cylinder (5); A method comprising:

2. continuously measuring the flow rate of the accelerator pump (2); continuously adjusting the flow rate in response to the results of the measurements made during the measuring step; Including, The step of adjusting the flow rate of the acceleration pump may include adjusting the flow rate at the inlet of the liquid ejector by xm ３ / h, the flow rate at the outlet of the liquid ejector is 1.1 x m ３ / h~1.5xm ３ / h, and the flow rate at the underflow outlet of the hydrocyclone is 0.1 × m ３ / h and the recirculation flow rate is less than 0.1 × m ３ / h~0.5xm ３ / h, and the flow rate at the overflow outlet of the recirculation cylinder is 0.9 x m ３ / h~0.95xm ３ 2. The method according to claim 1, wherein the temperature is between 1000 and 10000 s / h.

3. 3. A method according to claim 1 or 2, characterized in that it comprises the step of adding a polymer to the water upstream of the liquid ejector and / or at the inlet of the recirculation cylinder.

4. The flow rate x at the inlet (2) of the liquid ejector is 4 m ３ / h~50m ３ 4. The method according to claim 2 or 3, characterized in that the temperature is between 1000 and 2000°C.

5. A method according to any one of claims 1 to 4, characterized in that the hydraulic residence time inside the hydrocyclone (4) and the recirculation cylinder (5) is between 2 and 4 seconds.

6. 6. The method according to any one of claims 1 to 5, characterized in that the hydrocyclone (4) has a cut-off threshold between 10 μm and 25 μm and the recirculation cylinder (5) has a cut-off threshold between 5 μm and 15 μm.

7. 7. The method according to claim 1, wherein the pressure of the water at the outlet of the accelerator pump is between 2 and 5 bar.

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

9. The method according to any one of claims 1 to 8, characterized in that the dirty overflow water comes from a hydrocyclone (4000) of a ballasting flocculation sedimentation facility.

10. The dirty overflow water comes from a filtration system, which Sand filters and a granular activated carbon filter; an ultrafiltration membrane; a biological filter using biomass fixed on a granular support; A mechanical filter; 9. The method according to claim 1, wherein the compound belongs to the group comprising:

11. 11. A device for treating dirty overflow water (DISP) to separate suspended solids and / or insoluble particulate matter heavier than water, so as to carry out the method according to any one of claims 1 to 10, comprising: a degassing means (1) at the entrance of the facility; an accelerator pump (2) capable of adjusting the flow rate and pressure; a liquid ejector (3); a hydrocyclone (4) fed with water coming from the liquid ejector; a recirculation cylinder (5) fed with water coming from the overflow of the hydrocyclone; means (6) for measuring pressure and / or flow rate; It is equipped with 10. Apparatus, characterized in that said liquid ejector (3) is capable of recirculating part of the water coming from said recirculation cylinder (5) to said hydrocyclone (4).

12. 12. Device according to claim 11, characterized in that it comprises polymer dosing means (7) provided upstream of the liquid ejector and / or at the inlet of the recirculation cylinder.

13. 13. Apparatus according to claim 11 or 12, characterized in that the hydrocyclone (4) has a cut-off threshold between 10 μm and 25 μm and the recirculation cylinder (5) has a cut-off threshold between 5 μm and 15 μm.

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

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

16. Apparatus according to any one of claims 11 to 15, characterized in that the hydrocyclone (4) and the recirculation cylinder (5) each have a length between 0.8 m and 2 m.

Images