MIXING DEVICE, PARTICULARLY FOR A SLUDGE TREATMENT SYSTEM

Abstract

The present invention relates to a mixing device for a liquid solution having a longitudinal axis (X) comprising a first part (A) and a second part (B) connected to each other, the first part (A) comprising a housing including a side wall, a first end wall and a second end wall, the side wall having the shape of a logarithmic spiral, a feed orifice (106) in the side wall, a central orifice in one of the end walls through which the first part (A) is connected to the second part (B), vanes (120) extending substantially radially around the central connection orifice (110) and fixed to the first and second end walls,and in which the second part (B) has the form of a tube with longitudinal axis (X) connected by a first longitudinal end (X) to the central connection port (110) and having a second longitudinal end comprising the discharge port (118). [Fig.2],

Description

Title of the invention: MIXING DEVICE, IN PARTICULAR FOR A SLUDGE TREATMENT SYSTEM TECHNICAL FIELD AND PRIOR ART

[0001] The present invention relates to a mixing device, in particular for a sludge treatment system, in particular resulting from the extraction of materials from pipes and wells by water injection and pumping.

[0002] When you want to unblock a blocked pipe, pressurized water is injected into it, which dissolves the materials, thus forming sludge, which is then sucked up and collected in a tank.

[0003] This type of device is generally installed on a sanitation vehicle which has a water tank and a sludge collection tank. Generally, the sludge is filtered to separate the larger solid particles from the water. The water is then returned to the water tank for reuse.

[0004] In order to improve water recycling, it is known to inject a flocculating agent into the sludge, to agglomerate the remaining solid particles and facilitate their separation. The separation of the agglomerated solid particles and the water is then obtained by means of a filtration system.

[0005] The flocculant is generally injected directly into the sludge tank. However, the mixing is not done correctly and the generation of flocs is not done correctly, which does not allow the sludge to be treated effectively. Statement of the invention

[0006] It is therefore an aim of the present application to provide an improved mixing device, in particular for mixing a flocculation agent and sludge.

[0007] In the present application, "sludge" means the mixture of solid materials and water.

[0008] The aim stated above is achieved by a device for mixing an at least partly liquid solution ensuring the generation of a vortex within the mixer in order to obtain the intimate mixing of the components contained and / or transported by the liquid solution, for example between a flocculation agent and the sludge, allowing the generation of flocs and the agglomeration of flocs between them.

[0009] Particularly advantageously, the mixing device comprises inlet blades to generate a vortex in a tube in which the mixing takes place and the free end of which is preferably conical, further promoting the agglomeration of flocs by ensuring the bringing together of the particles. The flocs are then more easily separable from the liquid solution.

[0010] The mixing device is advantageously integrated into a sludge treatment system comprising a circuit for circulating the sludge to be treated, a reservoir of at least one flocculation agent, means for injecting said agent into the circuit, the mixing device being arranged downstream of the injection means.

[0011] Very advantageously, the system comprises at least one static mixer in which the flocculating agent is injected.

[0012] The present invention then relates to a mixing device for a liquid solution having a longitudinal axis, comprising a first part and a second part connected to each other, the first part comprising a casing comprising a side wall, a first end wall and a second end wall, the side wall having the shape of a logarithmic spiral, a supply orifice in the side wall, a central connection orifice in one of the end walls by which the first part is connected to the second part, blades extending substantially radially around the central connection orifice and fixed to the first and second end walls. The second part has the shape of a tube with a longitudinal axis connected by a first longitudinal end to the central connection orifice and comprising a second longitudinal end comprising the discharge orifice.

[0013] Preferably, the blades have a curved shape relative to a plane orthogonal to the end walls.

[0014] Very advantageously, the at least first end wall has a shape such that the section of the channels delimited between two blades and the first and second end walls decreases in the direction of the longitudinal axis.

[0015] The first end wall preferably has a generally conical interior shape.

[0016] The first end wall very advantageously comprises an extension along the longitudinal axis extending into the second part, having a free end in the shape of a drop.

[0017] Another subject of the present application is a sludge treatment system using a flocculant, comprising a circuit intended to circulate sludge to be treated, means for injecting a liquid solution of flocculant into said circuit. Said circuit comprises at least one mixing device downstream of the injection of the flocculant into said circuit according to the invention.

[0018] In a preferred example, the sludge treatment system comprises at least a first static mixer upstream of the mixing device.

[0019] The first static mixer is for example mounted in a duct and comprises an axis aligned with the axis of the duct, said first static mixer comprising a central core and blades extending radially from the central core, said blades being curved so as to generate a vortex around the longitudinal axis.

[0020] Advantageously, the system also comprises a static plate mixer at the injection of the flocculation agent into the circuit, the means for injecting a flocculant being advantageously configured to inject the liquid flocculant solution into the static plate mixer.

[0021] In an exemplary embodiment, the sludge treatment system according to the invention comprises means for injecting a coagulant upstream of the first static mixer.

[0022] Advantageously, the sludge treatment system comprises a system for premixing a flocculating agent with water so as to form the liquid flocculant solution, the premixing system advantageously comprising a water supply inlet, a flocculating agent supply inlet and a mixing circuit.

[0023] The present invention also relates to a sludge treatment installation comprising a water tank, a sludge tank, a sludge treatment system according to the invention, at least one cyclone separator, an inlet of the treatment system circuit being connected to the outlet of the sludge tank and the outlet of the treatment system circuit being connected to the cyclone separator.

[0024] The sludge treatment installation advantageously comprises a turbidimeter downstream of the cyclone separator and / or at a drain outlet of the water tank, and / or means for ultraviolet disinfection of the water at the drain outlet.

[0025] The present invention also relates to a sanitation vehicle comprising an installation according to the invention, means for injecting water into an area to be cleaned so as to form sludge, and means for sucking up the sludge. Brief description of the drawings

[0026] The present application will be better understood with the aid of the description which follows and the attached drawings in which: - [Fig.l] is a schematic representation of an exemplary embodiment of a sludge treatment installation capable of implementing a mixing device according to the invention, - [[Fig.2]] is a side view of an example of a mixing device according to the invention, - [[Fig.3]] is a sectional view along plane AA of the mixing device of [Fig.2], - [[Fig.4]] is a longitudinal sectional view of the mixing device of [Fig.2], - [[Fig.5]] is a side view of an example of a static mixer that can be implemented in the treatment system according to the invention, - - [[Fig.6]] is a front view of another example of a static mixer that can be implemented in the treatment system according to the invention, - [Fig.7] is a side view of the static mixer of [Fig.6], - [[Fig.8]] is a schematic representation of another example of an embodiment of a sludge treatment installation capable of implementing a mixing device according to the invention, - [[Fig.9]] is a schematic representation of a premixing system of the treatment system according to the invention, - [[Fig.l]0] is a front view of another example of a static mixer that can be implemented in the processing system according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS

[0027] The mixing device according to the invention will be described more particularly in its application to the treatment of sludge, more specifically for mixing a flocculation agent with the sludge. But it will be understood that the invention can be applied to any at least partly liquid mixture which requires contacting the components transported by the liquid solution, for example in the case of chemical reactions it may be required to obtain intimate contact, for example when catalysts are used.

[0028] In [Fig. 1], a schematic representation of a sludge collection installation can be seen comprising a sludge treatment system into which the mixing system according to the invention can be integrated.

[0029] The installation is intended to collect solid materials, for example contained in pipes, wells or the like. In general, these solid materials at least partially block the pipe or well. In order to facilitate the suction of these solid materials, water is injected into the area to be cleared and the water and the solid materials forming sludge are sucked up.

[0030] The installation comprises a sludge tank 1, a water tank 2, a water injection system 6 in the area to be cleaned, for example a CA pipeline, in order to facilitate the suction of the sludge and suction means 4 for the mixture of water and sludge contained in the pipeline.

[0031] The water injection system 6 comprises a high pressure pump 7.

[0032] The water tank has an outlet 2.1 for using water for the treatment system and an outlet 2.2 for discharging water and supplying the high-pressure pump which will be described later. The outlet 2.1 is equipped with a valve 3.

[0033] The valves are preferably pneumatic valves controlled either from a control panel by the user or automatically by a control unit which manages the different cycles autonomously. Alternatively, solenoid valves can be implemented.

[0034] In the example shown, the installation comprises a single tank whose internal volume is separated in two by a wall 8, thus forming the sludge tank 1 and the water tank 2.

[0035] The wall 8 can be movable, allowing the volume of the two reservoirs to be adjusted according to the volume of their contents.

[0036] The installation includes a sludge treatment system for separating the water from the solid matter and thus recycling the water so that it can be reused, for example to continue unblocking the pipes without having to fill the water tank.

[0037] The installation includes a circuit Cl intended to treat the sludge.

[0038] The circuit Cl is connected at the input to a discharge outlet 9 of the sludge tank. 1 and output to at least one separator 14.

[0039] The circuit comprises a pump 12 intended to circulate the sludge in the circuit, the cyclone-type separator 14 intended to separate the water from the solid matter. The circuit C1, at the outlet of the cyclone separator 14, comprises a branch connected to the sludge tank to return the solid matter thereto and a branch connected to the water tank to return the water thereto. The circuit C1 comprises a first portion C1.1 between the inlet of the circuit and the pump 12, a second portion C1.2 between the pump and the cyclone separator, a third portion C1.3 between the cyclone separator and the sludge tank and a fourth portion C1.4 between the cyclone separator and the water tank.

[0040] Preferably, a filtration system 20, for example of the filter drum type, is provided at the discharge outlet 9 of the sludge tank 1 to ensure a first filtration of the sludge so as to retain the largest particles in the sludge tank.

[0041] The treatment system S is configured to improve the separation of solid matter from water. For this purpose, it comprises means for injecting a flocculating agent into the sludge in order to cause the solid particles to agglomerate together and facilitate their separation. The use of flocculating agents for sludge treatment is well known and will not be described in detail.

[0042] The system comprises a circuit C2 connected at the inlet to the circuit C1 by a three-way valve 22 allowing the sludge to be directed towards the portion C1.1 or towards the circuit C2, and at the outlet to the circuit C1 upstream of the pump 12 by a three-way valve 24 connected at the inlet to the circuit C1 by a three-way valve 22.

[0043] The system comprises means 25 for injecting a flocculation agent into the circuit C2, comprising a flocculant reservoir 27 and a pump 29 and a mixing device DM.

[0044] Circuit C2 comprises a device DM for mixing the flocculant and the sludge.

[0045] In Figures 2 to 4, an example of a DM mixing device according to the invention comprising a feed inlet El for sludge and flocculant and a discharge outlet SI connected to the three-way valve 24.

[0046] The mixing device DM comprises a first part A intended to generate a whirlpool or vortex and a second part B in which the intimate mixing between the flocculant and the sludge takes place, causing the generation of flocs and their agglomeration.

[0047] The device extends along the X axis, which is intended to be preferably oriented vertically.

[0048] The first part A comprises a casing comprising an outer wall 104 in the form of a logarithmic spiral around the axis X and two longitudinal end walls 107, 108. The first part A comprises a supply orifice 106, preferably oriented laterally so that the flow is injected into the first part tangentially to the outer side wall.

[0049] The first part comprises in a central zone of its lower end wall 108 a connection orifice 110.

[0050] The second part B comprises a casing 112 comprising a cylindrical casing of revolution of axis X connected by a longitudinal end 114 to the connection orifice 110. The other longitudinal end 116 comprises an evacuation orifice 118 and preferably has a frustoconical shape.

[0051] The first part A comprises blades 120 distributed around the connection orifice 110 and oriented so as to generate a vortex in the fluid arriving from the supply orifice 106 and discharging through the connection orifice 110 towards the second part B. Furthermore, the blades 120 impose a radial speed on the fluid, which limits the appearance of an air pocket in the center of the second part B, in which the fluid could circulate towards the first part A and not towards the discharge orifice 118.

[0052] The blades 120 are advantageously distributed uniformly around the X axis. The blades are also advantageously curved relative to a vertical plane. Flat blades are not outside the scope of the present invention.

[0053] The blades extend between the two longitudinal end walls 107, 108 so as to limit channels between them.

[0054] Each blade 120 has an outer radial end 120.1 receiving the fluid at the inlet and an inner radial end 120.2 bordering the connection orifice 110 and discharging the fluid towards the second part B.

[0055] The blades are preferably dimensioned such that the absolute velocity of the fluid is tangential to the blades, in order to reduce the pressure drop during the guidance of the fluid operated by the blades.

[0056] Preferably, the shape of the blades and the shape of the longitudinal end face are such that the section of each channel decreases in the direction of the X axis, so as to compensate for the reduction in flow rate while maintaining a constant fluid speed, which makes it possible to reduce pressure losses.

[0057] In the example shown, the upper longitudinal end wall 107 has a generally conical internal shape oriented towards the second part B so as to provide between two blades a channel narrowing in the direction of the axis X. This shape makes it possible to limit the cavitation phenomenon.

[0058] In the example shown and preferably, the upper longitudinal end wall 107 extends into the second part B by a longitudinal extension 107.1 substantially in the shape of a drop. This shape makes it possible to limit the rise of air in the first part.

[0059] The operation of the DM mixing device will now be described.

[0060] The fluid comprising the sludge and the flocculant is injected into the mixing device. DM through the supply port 106. The fluid encounters the vanes 120 and is guided by them toward the outlet. Each vane 120 sees the same fluid pressure and projects the fluid toward the connection port 110 at substantially the same speed.

[0061] The fluid, upon emerging into the second part B, flows forming a vortex which rotates around the axis X and along the axis X towards the discharge outlet 118. This vortex causes intimate mixing between the sludge and the flocculant, generating the appearance of flocs which agglomerate with each other as they travel towards the discharge outlet. Furthermore, the truncated cone shape of the discharge outlet causes the streamlines and therefore the flocs to move closer to each other, which further improves the generation of flocs of larger dimensions.

[0062] Thanks to the shape of the blades 120, the flow speed remains substantially constant throughout the mixing device, which reduces the pressure losses within the mixing device. Furthermore, in the advantageous example shown, the risks of cavitation phenomena occurring are reduced, which limits the deterioration of the blades.

[0063] Preferably, the circuit C2 comprises a static mixer upstream of the mixing device DM. This static mixer may be of the helical type 28 as shown schematically in [Fig.5]. The helical static mixer receives the flocculant and sludge mixture. It is configured to ensure separation of the flow and its regrouping, as well as rotation of the flow around the axis of the pipe. The arrows F symbolize the flows in the static mixer. The static mixer 28 comprises fins 28.1 arranged in the flow duct and shaped so as to ensure separation of the flow, its rotation and its regrouping.

[0064] Preferably, the static mixer is such that it generates an axial vortex in the conduit, an example of which is shown in Figures 6 and 7 and is designated by the reference 128.

[0065] The static mixer is mounted in a longitudinal duct 129. The static mixer extends along an axis Y which coincides with that of the duct, and comprises a central core 130 and blades 132 extending radially from the core 130 and has a curved shape so as to generate a vortex in the fluid around the axis Y. The central core 130 induces a radial velocity in the fluid, which has the effect of facilitating the generation of flocs.

[0066] The central body 130 advantageously has tapered longitudinal ends so as to limit the effect of the central body on the circulation of the fluid.

[0067] This static mixer is fed with a mixture of sludge and flocculant, it promotes the creation of flocs which will then be agglomerated using the DM mixing device.

[0068] In [Fig.8] another example of a processing system in which the DM mixing device can be used can be seen.

[0069] The system is mounted between the inlet of circuit C1 and pump 12, as a bypass of portion C1.1 of circuit 10.

[0070] According to the invention, the treatment system comprises connected at the inlet to the circuit C1 by a three-way valve 22 allowing the sludge to be directed towards the portion C1.1 or towards the circuit C2, and at the outlet to the circuit C1 upstream of the pump 12 by a three-way valve 24 connected at the inlet to the circuit C1 by a three-way valve 22 allowing the sludge to be directed towards the portion C1.1 or towards the circuit C2, and at the outlet to the circuit C1 upstream of the pump 12 by a three-way valve 24. Control of the valves 3, 22 and 24 makes it possible either to isolate the circuit C2 and to circulate the sludge in the portion C1.1, or to circulate the sludge in the circuit C2, or to circulate water in the circuit C2 or in the circuit C1 for rinsing them.

[0071] This example is in no way limiting and a processing system without the possibility of short-circuiting the circuit C2 does not depart from the scope of the present invention.

[0072] Circuit C2 comprises means for mixing the flocculant and the sludge to optimize the effectiveness of the flocculation agent.

[0073] The injection means 25 for injecting a flocculation agent comprise a flocculant reservoir 27 and a pump 29 connected to the circuit C2. Very advantageously, the injection means 25 comprise a system SP for ensuring premixing of the flocculation agent with water before its injection into the circuit C2. Preferably, the water comes from the water reservoir 2. For this, a pipe 23 connects the water reservoir to the outlet of the flocculant reservoir 27 and a pump 30 ensures the conveyance of the water to the premixing system SP. Alternatively, a system using a water reservoir separate from the water reservoir 2 does not depart from the scope of the present invention.

[0074] This step is referred to as “premixing” because it takes place before mixing the flocculating agent with the sludge. The mixture obtained at the outlet of the premixing system is a liquid flocculant solution and will be referred to as “flocculant” for reasons of simplicity.

[0075] In a particularly advantageous manner, the SP premixing system comprises at least one coil receiving the flocculation agent and the water at the inlet.

[0076] In [Fig.9], a schematic representation of a preferred embodiment of the SP premixing system can be seen.

[0077] The premixing system comprises an alternation of straight portions and coils, and one or more changes of section. In this example, the premixing device comprises three straight sections D1, D2 and D3 connected by two coils S1 and S2. The coils generate vortices. The inventors found that this alternation of straight portions and coils significantly improved the mixing of the flocculating agent in the water.

[0078] The number of straight portions and coils is in no way limiting and is chosen, for example, as a function of the desired premix efficiency, the space available and the quantity of flocculation agent to be premixed.

[0079] Advantageously, the inlet of the device comprises one or more elbows 31 and one or more changes in section, in particular downstream of the injection of water and flocculation agent, further improving the premixing.

[0080] The injection device also has the advantage of ensuring continuous premixing of the flocculation agent with the water, and continuous injection into the circuit C2, which makes the sludge treatment faster. Such a system avoids having to stop the installation in order to fill a tank containing the water and flocculation agent mixture, as is done in existing installations.

[0081] The mixing system comprises at least one first static mixer and advantageously two first static mixers in series.

[0082] The first static mixers can be chosen from the plate static mixer, the helical static mixer 28 ([Fig.5]) and the axial vortex generating static mixer 128 (Figures 6 and 7).

[0083] In a preferred example, the injection means inject the flocculant at the static mixer plate 26, hereinafter referred to as the “diaphragm” for simplicity. “At the diaphragm” is understood to mean in or just after the diaphragm. Preferably, the injection means are integrated into the diaphragm, more particularly the injector(s) 26.1 are integrated into the diaphragm plate as shown diagrammatically in [Fig. 10].

[0084] In [Fig. 10], a front view of an example of diaphragm 26 can be seen. which can be implemented in the present invention. It generates strong turbulence downstream, which causes an initial dilution of the flocculant in the sludge.

[0085] The action of the diaphragm 26 and the static mixer 28 or 128 significantly improves the homogeneity of the mixture. Now the action of the flocculant which is to ensure an agglomeration of the particles between them is particularly effective when the mixture is homogeneous. This therefore results in obtaining a homogeneous mixture quickly between the sludge and the flocculant, and an improved action of the latter.

[0086] The number of elements allowing the separation of the flow, its rotation and its grouping is chosen according to the installation, in particular according to the volume to be treated, in order to achieve a homogeneous mixture. This agglomerate of particles is called "floc".

[0087] The system also comprises a DM mixing device downstream of the second static mixer.

[0088] Alternatively, the system comprises two first static plate mixers in series or two first static mixers 28 or 128 in series. Alternatively, the first static mixer is a mixer 28 or 128 and downstream of the first static mixer, it is a static plate mixer and the injection of the flocculant takes place between them.

[0089] In a particularly advantageous manner, the treatment system also comprises means 40 for injecting a coagulating agent into the circuit upstream of the injection of the flocculant.

[0090] The injection means 40 comprise a coagulant reservoir 42, an injection pump 44 and an injection tube 43 which connects the reservoir to the circuit C2 upstream of the diaphragm 26. Very advantageously, the circuit C2 also comprises at least a second static mixer at which the coagulant is injected. The second static mixer preferably comprises a diaphragm 46. Preferably, the coagulant is injected into the diaphragm 46, in a similar manner to the diaphragm 26, improving the dilution of the coagulant in the sludge. Alternatively, the coagulant is injected just downstream of the diaphragm 46.

[0091] Also advantageously, a helical static mixer or one generating an axial vortex 48 is provided in front of the diaphragm 46, further improving the homogeneous mixing between the sludge and the coagulant.

[0092] The coagulant comprises, for example, metal salts, generally iron or aluminum salts, for example A1C13, making it possible to eliminate or at least reduce the colloidal repulsions between the particles, which facilitates the formation of flocs under the action of the flocculant.

[0093] The diaphragm 46 may be similar to the diaphragm 26.

[0094] The helical static mixer 48 may be similar to the helical static mixer 48. licoidal 28.

[0095] Alternatively, the system comprises two second static plate mixers in series, two second helical static mixers in series. Alternatively, the second helical static mixer is upstream of the second static plate mixer and the injection of the flocculant takes place between them.

[0096] Also advantageously, the installation comprises means for monitoring and treating the recycled water 49 comprising for example a turbidimeter 53 which measures the turbidity of the water.

[0097] The water tank comprises a discharge outlet 2.2, a valve 51 for closing the outlet 2.2, a filter 52 and the turbidimeter 53.

[0098] For example, the filter 52 is such that it retains particles larger than 5 μm. The filter 52 is preferably a backwash filter.

[0099] Advantageously, the means 49 comprise a water treatment device, for example an ultraviolet disinfection lamp 54. The ultraviolet treatment makes it possible to make the water contained in the water tank comply with the requirements for being discharged into a drainage system.

[0100] In the example shown, a circuit C3 for short-circuiting the turbidimeter 53 and the water treatment device is provided between the valve 51 and an additional valve 58 which is provided between the water treatment device 52 and the ultraviolet lamp 54.

[0101] A turbidimeter 56 is advantageously arranged on the portion C1.4 at the outlet of the cyclone separator. Very advantageously, it may be provided to check the turbidity of the recycled water to adjust the quantity of flocculant and / or coagulant to be injected into the circuit C2. Preferably, an electronic control unit automatically ensures the adjustment of the injection of the flocculant and possibly the coagulant according to the turbidity measurement. The quantities injected are for example managed by the control of the pumps, which makes it possible to limit the quantity of flocculant and possibly the coagulant to the necessary quantities.

[0102] An example of operation of the installation will now be described.

[0103] Water taken from the water tank 2 is injected into a pipe to be evacuated CA, the sludge thus formed is sucked up and collected in the sludge tank 1.

[0104] The valve 22 is controlled so as to connect the sludge tank 1 with the circuit C2, the pump 12 is activated so as to circulate the sludge in the circuit C2. Simultaneously, the pumps 29 and 30 are activated to inject the flocculant and the water into the premixing system SP, the solution thus produced is injected into the diaphragm 26. The pump 44 is also activated to inject the coagulant into the diaphragm 46.

[0105] The sludge is mixed first with the coagulant, then secondly with the flocculant, which causes the formation of flocs. The sludge containing the flocs is then injected into the agglomeration device, which has the effect of agglomerating the flocs together.

[0106] The sludge is then conveyed to the cyclonic separator 14 which ensures separation of the water, which is returned to the water tank 2, and the solid particles P', which are discharged into the sludge tank 1.

[0107] By controlling valves 3, 22 and 24, it is possible to ensure rinsing of circuit C2 by circulating water from the water tank to the cyclone separator 14.

[0108] It is also possible to back-rinse the filter 20 by controlling the valves so that the water circulates from the water tank directly to the outlet of the mud tank.

[0109] Alternatively, the entire treatment system may be arranged between the pump 12 and the cyclone separator 14. According to another alternative, the treatment system is arranged between the cyclone separator 14 and the water tank.

[0110] Alternatively, the flocculant injection means 25 can inject the flocculant directly into the sludge tank and / or directly into the water tank.

[0111] It will be understood that the sludge treatment system is a system in its own right which can be integrated during manufacture into a treatment plant or manufactured independently and connected to a plant as required.

[0112] The sludge treatment installation comprising a treatment system according to the invention may be fixed or mobile, for example mounted on a sanitation vehicle.

[0113] It will be understood that certain elements of the installation of [Fig.8] can be integrated into the installation of [Fig.l], for example the means for injecting the coagulant and / or the plate mixer without this being limiting.

Claims

Claims

1. A mixing device for a liquid solution having a longitudinal axis (X) comprising a first part (A) and a second part (B) connected to each other, the first part (A) comprising a casing comprising a side wall (104), a first end wall and a second end wall, the side wall (104) having the shape of a logarithmic spiral, a feed orifice (106) in the side wall, a central orifice in one of the end walls by which the first part (A) is connected to the second part (B), vanes (120) extending substantially radially around the central connection orifice (110) and fixed to the first and second end walls,and wherein the second part (B) has the form of a tube of longitudinal axis (X) connected by a first longitudinal end (X) to the central connection orifice (110) and comprising a second longitudinal end comprising the discharge orifice (118).,

2. A mixing device according to claim 1, wherein the blades have a curved shape relative to a plane orthogonal to the end walls.

3. Mixing device according to claim 1 or 2, wherein the at least first end wall has a shape such that the section of the channels delimited between two blades and the first and second end walls decreases in the direction of the longitudinal axis.

4. A mixing device according to claim 3, wherein the first end wall has a generally conical interior shape.

5. A mixing device according to claim 4, wherein the first end wall has an extension along the longitudinal axis (X) and extending into the second portion, having a drop-shaped free end.

6. Sludge treatment system using a flocculant, comprising a circuit (C2) intended to circulate sludge to be treated, means (25) for injecting a liquid solution of flocculant into said circuit (C2), in which said circuit (C2) comprises at least one mixing device (DM) downstream of the injection of the flocculant into said circuit (C2) according to one of the preceding claims.

7. Sludge treatment system according to claim 6, comprising at least a first static mixer upstream of the device of blend.

8. A sludge treatment system according to claim 7, wherein the first static mixer is mounted in a conduit and has an axis aligned with the axis of the conduit, said first static mixer having a central core and vanes extending radially from the central core, said vanes being curved so as to generate a vortex about the longitudinal axis.

9. Sludge treatment system according to one of claims 6 to 8, also comprising a static plate mixer (26) at the injection of the flocculation agent into the circuit (C2), the means for injecting a flocculant being advantageously configured to inject the liquid flocculant solution into the static plate mixer (26).

10. Sludge treatment system according to one of claims 6 to 9, comprising means for injecting a coagulant upstream of the first static mixer.

11. 11. Sludge treatment system according to one of claims 6 to 10, comprising a system for premixing a flocculating agent with water so as to form the liquid flocculant solution, the premixing system advantageously comprising a water supply inlet, a flocculating agent supply inlet and a mixing circuit.

12. 12. Sludge treatment installation comprising a water tank (2), a sludge tank (1), a sludge treatment system according to one of claims 6 to 11, at least one cyclone separator (14), in which an inlet of the circuit (C2) of the treatment system is connected to the outlet of the sludge tank and the outlet of the circuit of the treatment system is connected to the cyclone separator (14).

13. 13. Sludge treatment installation according to claim 12, comprising a turbidimeter downstream of the cyclone separator and / or at a drain outlet of the water tank, and / or means for ultraviolet disinfection of the water at the drain outlet.

14. 14. Sanitation vehicle comprising an installation according to the preceding claim, means for injecting water into an area to be cleaned so as to form sludge, and means for sucking up the sludge.

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