EP3648862A1

EP3648862A1 - Water treatment plant and corresponding method

Info

Publication number: EP3648862A1
Application number: EP18733605.2A
Authority: EP
Inventors: Abdelkader Gaid; Hervé Paillard; Philippe Sauvignet
Original assignee: Veolia Water Solutions and Technologies Support SAS
Current assignee: Veolia Water Solutions and Technologies Support SAS
Priority date: 2017-07-06
Filing date: 2018-06-25
Publication date: 2020-05-13
Also published as: US20200155972A1; FR3068615A1; FR3068615B1; WO2019007744A1; CA3067103A1; CN110891666A

Abstract

The invention relates to a water treatment plant which comprises means (38) for supplying the water to be treated, means (31) for supplying coagulant reagent (21), a flocculation-decantation device (1) which has means (32) for dispensing the flocculant reagent, means (33) for distributing ballast, means (39d) for extracting decantation sludge and means (9) for discharging water that has been treated, a line (8) for supplying coagulated water to the flocculation-decantation device (1), means (24) for separating the ballast contained in the ballasted sludge followed by means (36) for recycling the ballast back into said flocculation-decantation device (1), characterised in that said device (1) comprises an outer tank (2) that has a first hopper (4), and at least one inner tank (3) that has a second hopper (5) and is arranged inside said outer tank (2); the inner tank (3) receiving the flocculant and the ballast and comprising stirring means (10), wherein a peripheral space is disposed between the inner tank (3) and the outer tank (2); the second hopper (5) having an opening (6) which opens into the first hopper (4); and said first hopper (4) having an outlet that communicates with the means (34) for discharging ballasted sludge, wherein the means (9) for discharging water that has been treated are disposed in the upper portion of said outer tank (2). The invention also relates to a method for implementing a plant of this types.

Description

Installation for water treatment and corresponding method Field of the invention

The invention relates to the field of water treatment physicochemically.

More specifically, the invention relates to a technique for treating contaminated water, such as water for drinking, municipal and industrial waste water, rainwater or seawater, to reduce the content of suspended matter such waters, as well as their turbidity, algae concentration, organic matter content and color.

The invention finds particular application in the context of water treatment for its potabilization, but also in the treatment of municipal or industrial wastewater for purification.

Prior art

Among the physico-chemical water treatment techniques known to those skilled in the art, those implementing a coagulation step, a flocculation step and a settling step are very commonly used.

In order to increase the performance of these techniques, the flocculation step is assisted by adding a weighting material. In practice, weighted flocculation settling consists in adding a ballast, for example microsand, during the flocculation stage in order to increase the density of the flocs and to accelerate the settling rate. The ballast is usually recycled after separation of sludge.

Patent FR2627704B1 thus discloses a method for treating water comprising a coagulation step, a weighted flocculation step and a flocculation separation step by decantation. This technique includes ballast recycling carried out by hydrocycling sludge.

Such a method makes it possible to cut down the organic matter contained in the water, but it requires the provision of a coagulation reactor, a flocculation reactor and a decanter. The footprint of the corresponding facilities is therefore high, whereas these facilities are often required to be close to the effluents, not far away or in an urban environment where the space available for this type of installation is small and expensive.

As a result, there is a real need to reduce the footprint of these water treatment facilities.

In addition, the hydrocyclones used for ballast recycling are high energy consumers. In addition, their separation efficiency decreases with the diameter of the particles to be separated, which can lead to significant ballast losses. There is a real need to improve ballast recycling performance in this type of process.

Objectives of the invention

The object of the invention is to propose an installation for the treatment of water by flocculation and ballast flocculation settling at least some of the disadvantages of the prior art mentioned above.

In particular, an object of the present invention is to provide such an installation that can have a lower footprint than the prior art facilities with equivalent processing capacity.

Yet another object of the present invention is to provide such an installation, the use of which involves an improvement in liquid-solid separation performance.

Yet another object of the present invention is to propose such an installation that can be adapted to different treatment rates and / or different qualities of the waters to be treated.

Yet another object of the present invention is to describe such an installation which makes it possible to fight against ballast leakage during ballast recycling.

Yet another object of the present invention is to provide a method implementing such a water treatment plant.

Presentation of the invention

All or part of these objectives are achieved thanks to the invention which concerns a water treatment installation comprising:

means for supplying water to be treated,

means for feeding at least one coagulating reagent into said waters,

a flocculation-settling device provided with means for dispensing at least one flocculating reagent, means for dispensing at least one ballast, means for extracting sludge and means for discharging treated water, at least one pipe for supplying coagulated water into said flocculation-settling device,

means for separating said ballast contained in the weighted sludge followed by recycling means of said ballast thus cleaned towards said flocculation-settling device, characterized in that:

said flocculation-settling device comprises an outer vessel provided with a first hopper, and at least one inner vessel provided with a second hopper and provided inside said outer vessel;

said inner vessel receiving said flocculant and said ballast and being provided with stirring means, a peripheral space being provided between said inner vessel and said outer vessel;

said second hopper being provided with an opening opening into said first hopper; and,

said first hopper being provided with an outlet communicating with said weighted sludge removal means and said treated water outlet means being provided in the upper part of said outer vessel.

Thus, the installation according to the invention makes it possible to cut down at least one of the suspended solids content, the turbidity, the algae, the content of organic matter and the color in the water to be treated. The coagulation according to the invention which makes it possible to destabilize the colloidal particles is carried out in line or in the tank.

In addition, the flocculation-settling device makes it possible to group the weighted flocculation step and the decantation step, and thus significantly reduce the footprint of the installation. Flocculation occurs in the inner vessel equipped with a stirrer. In this part, the agitator puts intimate contact the ballast, the polymer and the coagulated water, which leads to the formation of aggregates (flocs) weighed down by the ballast.

By way of example, the stirring means in said flocculation-settling device is a paddle stirrer.

By virtue of this specific configuration of said flocculation-settling device and the appropriate opening of the hopper of the inner vessel, the flocculated water inside said inner vessel is guided towards the bottom of said hopper of said outer vessel where a decantation and thickening of ballasted flocs. We hear by "ballasted sludge" sludge mixed with ballast. The floc-free water is discharged overflow according to an upward flow of fluid in the peripheral space formed between said inner vessel and said outer vessel.

According to such features, it is no longer necessary to install slats in the space between said inner vessel and said outer vessel for settling.

In practice, said ballast has an actual density greater than 2.3 tons per cubic meter and is preferably selected from sand, ilmenite and garnet. The addition of ballast thus makes it possible to increase the density of the flocs and to accelerate the settling speed.

According to a variant of the installation of the invention, said means for separating said ballast contained in said weighted sludge include a pump and a separation device, said pump being able to bring said weighted sludge inside said separation device.

According to another variant, these means include means for injecting air into said weighted sludge and a separation device.

Such air injection means constitute an air lift by injecting air bubbles in a vertical sludge evacuation pipe. Such an air lift makes it possible to promote ballast entrainment by means of the bubbles and to clean the ballast thanks to the movements created by the bubbles generating an abrasion of the agglomerate formed around it, which makes it possible to separate the ballast from the rest of the ballast. sludge.

Preferably, said device for separating sludge and ballast comprises a blade mixer or similar device rotating at high speed associated with a small decanter. The high speed mixer allows the ballast to dissociate from the remainder of the sludge possibly already begun during transport by the air lift of the ballasted sludge towards the separation device. The small decanter collects in its lower part the ballast and in its upper part the floating sludge. Flotation of the sludge can be improved by providing an injection of fluid such as air. This sludge, separated from the ballast, is extracted to a specific treatment.

Communication between said inner vessel and said outer vessel is via the opening of said second hopper. This opening is designed to direct the flow towards the bottom of the hopper to accelerate settling. According to a particularly advantageous preferred aspect of the installation according to the invention, said opening of said second hopper is dimensioned to allow a fluid velocity passing therethrough which prevents its blockage and which limits the turbulence in the settling zone. For a given passage rate, the speed of passage of water through said opening is inversely promotional to the surface of the opening.

According to another advantageous variant according to the invention, said tanks each have a body of cylindrical shape, said bodies being provided essentially concentric. Thanks to such a cylindrical shape, the work is less expensive to build. This configuration in cylindrical shape also allows for better hydrodynamics.

In this regard, it will be noted that several inner tanks may be provided arranged side by side inside said outer vessel.

Preferably, the injection of water to be treated inside said inner vessel is carried out in a direction substantially tangential to the cylindrical wall of said inner vessel. This speeds up settling.

According to another advantageous variant according to the invention, said first hopper and / or said second hopper are / are in conical shape or in the form of an inverted pyramid with a square base. These structural forms make it possible to facilitate the settling of ballasted flocs. However, other forms could be used by adapting them to each specific situation.

According to another particularly advantageous variant according to the invention, said stirring means comprise a paddle stirrer and a guide-flow tube, the blades of the paddle stirrer being entirely present inside the internal space of the tube. flow guide, the axes of said flux guide tube and said agitator being aligned. Thus, when such an agitator is used, the water circulates inside the guide-flow tube from bottom to top and then in the peripheral zone surrounding the flux guide in an opposite direction.

This makes it possible to optimize the mixing of the waters with the flocculant and the ballast. A fraction of the mixture then flows to the second hopper.

According to another advantageous variant of the invention, said means for discharging the treated water include at least one peripheral trough in the upper part of said outer tub. Thus, the floc-free waters are discharged overflow after an upward flow in the space between said inner vessel and said outer vessel.

It will be noted that, according to the invention, the coagulant feed means may be designed to allow coagulation of water in a line or in a reactor. For a reactor coagulation provided upstream of the flocculation-decantation device, the coagulant supply means distribute the coagulant in a reactor preferably equipped with a stirrer.

The invention also relates to a method comprising a water coagulation step, a weighted flocculation step, a decantation step and a step of separating and recycling the settled weight to said weighted flocculation step,

characterized in that said weighted flocculation step and said decantation step are carried out in said flocculation-settling device by passing water in a circuit in which:

said waters, after said coagulation step, are brought inside said inner vessel in which a flocculating reagent and a ballast are provided;

the waters are flocculated inside said inner vessel;

the water flows from the inner vessel to said outer vessel;

the water is decanted in the space formed between said inner vessel and said outer vessel circulating from bottom to top;

the treated water is discharged into the upper part of said outer vessel; and, the sludge is extracted;

and in that the sludge ballast separation step is performed by injecting air into said weighted sludge without a hydrocycling step.

Thus, the method according to the invention makes it possible to create a hydrodynamic movement inside said flocculation-settling device by which hydraulic residence time and water flocculation are optimized and the concentration of the sludge increased. The method according to the invention does not implement a hydrocycling step. This makes it possible to reduce the energy consumption resulting from the separation and to reduce the leakage of ballast material. When the agitating means of the flocculation-settling device comprise a guide-flow as described above, said waters circulate inside the guide-flow from bottom to top and said water present between said inner vessel and said guide-flows flow from top to bottom.

Preferably, the residence time of the water inside said inner tank is between 2 minutes and 10 minutes. This residence time will depend on the nature of the waters to be treated but also the nature of the ballast used.

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 nonlimiting example, with reference to FIG.

Description of an embodiment of the invention

With reference to FIG. 1, the plant according to the invention shown schematically comprises a coagulation tank 20 and a flocculation-settling device 1.

Said coagulation tank 20 is provided with feed means 38 for treating water 500, means for dispensing 31 a coagulating reagent 21 and stirring means 12. By way of example, said stirring means 12 comprise a paddle stirrer, and the feed means 38 comprise a pump.

In practice, the coagulant reagent can be organic or mineral. It is advantageously chosen from aluminum sulphate, sodium aluminate, ferric chloride, ferric sulfate, ferrous sulfate, polyamines (epichlorohydrin or polyDADMAC ^®), melamine-formaldehyde resins, polyethyleneimines, and certain polymers cationized plants.

Said flocculation-settling device 1 comprises an outer tank 2 provided with a first hopper 4, and an inner tank 3 provided with a second hopper 5 and provided inside said outer tank 2. Said tanks 2 and 3 have each a body 2a and 3a of cylindrical shape, said bodies being provided essentially concentric. Said second hopper 5 is provided with an opening 6 opening into said first hopper 4. This opening 6 is dimensioned to be able to pass the flow of water without promoting turbulence. She allows to direct the flocculated floc-containing waters 26 to the bottom of the hopper 4 without being dispersed so as not to interfere with their settling.

Said flocculation-decantation device 1 is provided with a conduit 8 for supplying coagulated water, distribution means 32 for a flocculating reagent 22, means for dispensing a ballast 23, a delivery pipe 23 discharging 34 weighted sludge 24 and means 9 for discharging treated water which are for example chutes surrounding said outer tank 2. For example, said distribution means 31, 32 and 33 are conduits with distribution valves. By way of example, the flocculating reagent is chosen from water-soluble polymers of animal or vegetable origin, and water-soluble polyelectrolytes of high molecular weight and of different ionicities.

Said inner tank 3 receives the flocculant 22 and the ballast 23 and is provided with stirring means 10. The stirring means 10 comprise a paddle stirrer 14 and a guide-flow tube 13, the blades of the stirrer blades 14 being entirely present inside the internal space of the flux guide tube 13, the axes of said flux guide tube 13 and said stirrer 14 being aligned. A peripheral space is provided between said inner vessel 3 and said outer vessel 2. Said second hopper 5 is provided with an opening 6 opening into said first hopper 4.. Said first hopper 4 is provided with an outlet 7 communicating with the discharge pipe 34 of the weighted sludge 24.

Said discharge means 9 of treated water are provided in the upper part of said outer tank 2. For example, said means 9 for discharging treated water are chutes around the outer tank 2.

The installation also comprises means for separating the ballast contained in the weighted sludge 24 followed by recycling means 36 of said ballast thus cleaned towards said flocculation-settling device 1.

By way of example, said separation means include air injection means 11 in the form of bubbles in the pipe 34, allowing the formation of an air lift, and a separation device 39 of the ballast contained in the sludge. transported by this air lift. The separation device 39, in which the pipe 34 arrives, is equipped with a mixer 39a with blades rotating at a high speed followed by a small decanter 39b equipped with an air injection ramp 39c and 39d evacuation chute floated mud.

The use of an air lift not only allows the weighted sludge to be conveyed to the separating device but also initiates the separation of the ballast they contain and thus reduces the ballast loss caused by the separation.

According to the invention, the separation means do not include a hydrocyclone.

The operation of such an installation will now be described.

The waters to be treated 500 arrive in the coagulation reactor 20 where they receive a suitable dose of coagulant which is intimately mixed therewith. The coagulated water passes through the pipe 8 to the flocculation-settling device 1 in which are brought ballast 23 and flocculant 22. The water is intimately mixed with the ballast and flocculant through the agitator 10. The movement of the blades 14 creates a flow of water from bottom to top within the flow guide 13 and from top to bottom between the flow guide 13 and the inner vessel 3. This movement leads to optimize water flocculation. The water is then discharged through the opening 6 of the hopper 5 to the outer tank. The water then flows from bottom to top in the space between the inner vessel 3 and the outer vessel 2, space in which the flocs formed decant, accelerated thanks to the ballast they contain, to the hopper 5 in the lower part of the tank. which they accumulate. The sludge mixed with the ballast 24 are removed from the flocculation-settling device via the pipe 34. The recycling means 36 of the ballast contained in these sludge are connected to this pipe. Air 11 is injected by the means 35 into the sludge. The air lift created causes the sludge to the separation device 39. The separation of sludge ballast, which began with the air lift, is completed in the separation device 39. In this device, the agitator 39a rotating at high speed take off the sludge from the ballast. The sludge and the ballast are then separated in the clarifier 39b equipped with an air ramp 39c. The ballast 23 is rerouted to the settling flocculation device, while the floated sludge is discharged through the chute 39d to a specific treatment.

Claims

1. I nstallation for the treatment of water comprising:

water supply means (38) to be treated,

means for supplying (31) at least one coagulating reagent (21) into said waters, a flocculation-settling device (1) provided with means for dispensing (32) at least one flocculating reagent (22), distribution means (33) of at least one ballast (23), means for extracting sludge (39d) and means for discharging (9) treated water,

at least one pipe (8) for supplying coagulated water into said flocculation-settling device (1),

means for separating said weight (23) contained in the weighted sludge (24) followed by recycling means (36) of said ballast (23) thus cleaned towards said flocculation-settling device (1),

characterized in that

said flocculation-settling device comprises an outer vat (2) provided with a first hopper (4), and at least one inner vat (3) provided with a second hopper (5) and provided inside said vat outside (2);

said inner vessel (3) receiving said flocculant (22) and said ballast (23) and being provided with stirring means (10), a peripheral space being provided between said inner vessel (3) and said outer vessel (2);

said second hopper (5) being provided with an opening (6) opening into said first hopper (4); and,

said first hopper (4) being provided with an outlet communicating with said weighted sludge discharge means (34) (24) and said treated water outlet means (9) being provided in the upper part of said tank outside (2).

2. Installation according to claim 1, characterized in that said ballast has a real density greater than 2.3 tons per cubic meter and is preferably selected from sand, ilmenite and garnet.

3. I nstallation according to claim 1 or 2 characterized in that said means of separating said ballast (23) contained in said weighted sludge (24) includes a pump and a separating device (39).

4. Installation according to claim 1 or 2, characterized in that said means for separating said ballast (23) contained in said weighted sludge (24) include air injection means (35) and a separating device (39). ).

5. Installation according to one of claims 1 to 4 characterized in that said separating device (39) includes a blade mixer (39a) associated with a decanter (39b).

6. Installation according to one of claims 1 to 5 characterized in that said opening (6) of said second hopper (5) is dimensioned to allow a fluid velocity therethrough which prevents clogging and which limits turbulence in the area decantation.

7. Installation according to one of claims 1 to 6 characterized in that said tanks (2,3) each have a body (2a, 3a) of cylindrical shape, said bodies being provided essentially concentric.

8. Installation according to any one of claims 1 to 7 characterized in that said first hopper (4) and / or said second hopper (5) is / are of conical or inverted pyramid-shaped form with a square base.

9. Installation according to any one of claims 1 to 8 characterized in that said stirring means (10) comprise blades (14) mounted on a vertical axis and a cylindrical guide-stream (13) arranged around said blades ( 14).

10. Installation according to any one of claims 1 to 9, characterized in that said discharge means (9) include at least one chute (9) peripheral in the upper part of said outer vessel (2).

11. A method of water treatment implementing an installation according to any one of claims 1 to 10, said method comprising a water coagulation step, a weighted flocculation step, a settling step and a separation step and recycling of the ballast to said weighted flocculation step, characterized in that said weighted flocculation step and said decantation step are carried out in said flocculation-settling device by passing water in a circuit in which:

the waters are flocculated inside said inner vessel;

the water flows from the inner vessel to said outer vessel;

12. Method according to claim 11, characterized in that said waters circulate inside a guide-flow from bottom to top and said waters present between said inner vessel and said guide-flow circulate from top to bottom.

13. The method of claim 11 or 12, characterized in that the residence time of the water inside the flocculation-settling device is between 2 minutes and 10 minutes.