WATER TREATMENT PLANT AND CORRESPONDING METHOD

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.

Claims

1-13. (canceled)

14. A ballasted flocculation water treatment system for treating water containing suspended solids comprising: a line for directing the water into the system; a coagulant line configured to direct a coagulant into the water to form a coagulated water; a flocculating-settling device configured to receive the coagulated water and comprising: (i) an external tank including a first hopper and a treated water outlet; (ii) an internal tank disposed in the external tank and including a stirrer and a second hopper; (iii) a space defined between the internal tank and the external tank; (iv) a flocculant line configured to direct a flocculant into the internal tank; (v) a ballast line configured to direct a ballast into the internal tank; (vi) wherein the stirrer in the internal tank is configured to mix the flocculant, the ballast and the coagulated water and produce ballasted floc; (vii) said second hopper including an aperture that opens into the external tank and the first hopper and which is configured to direct ballasted floc from the second hopper into the external tank; (viii) a decantation zone in the external tank and formed at least partially below the internal tank and configured to separate the water from the ballasted floc; (ix) wherein the first hopper forms a settling zone where the ballasted floc from the internal tank thickens and settles to form a ballasted sludge; (x) said first hopper including an outlet configured to discharge the ballasted sludge from the first hopper; and (xi) a ballasted sludge discharge line operatively connected to the outlet of the first hopper and configured to discharge the ballasted sludge that exits the outlet of the first hopper.

15. The system of claim 14 including a ballast separator for receiving the ballasted sludge and separating ballast from the ballasted sludge whereby the separated ballast is recycled to the internal tank.

16. The system of claim 15 wherein the ballast separator comprises a blade mixer configured to engage the ballasted sludge and cause the ballast to disassociate from the ballasted sludge; and a decantation tank configured to collect the separated ballast in a bottom portion thereof and the resulting sludge in the top portion thereof.

17. The system of claim 14 including a ballasted sludge air lift configured to receive the ballasted sludge and configured to convey the ballasted sludge to a ballast separator.

18. The system of claim 14 wherein the stirrer comprises a blade stirrer; and wherein there is a flow guide tube disposed in the internal tank and wherein the blade stirrer and flow guide tube have axes that are aligned; and wherein the blade stirrer and flow guide tube are configured to circulate the water upwardly through the flow guide tube and then reverse the flow of the water such that it flows downwardly in the space defined between the internal tanks and the flow guide tube.

19. The system of claim 14 wherein the internal and external tanks include main bodies that are generally cylindrical and wherein the internal and external tanks are concentric.

20. The system of claim 14 including an air inlet formed in the ballasted sludge discharge line and configured to inject air into the discharge line and form an air lift that conveys the ballasted sludge through the discharge line to a ballast separator.

21. A method of treating water in a flocculating-settling device comprising: mixing a coagulant with the water to form coagulated water; directing the coagulated water to the flocculating-settling device which includes an external tank an internal tank contained in the external tank; directing the coagulated water into the internal tank; directing a flocculant and a ballast into the internal tank; with a stirrer contained in the internal tank, flocculating the water by mixing the water, the ballast and the flocculant to form a mixture containing ballasted floc; during the course of mixing the water, the ballast and the flocculant, directing the mixture upwardly through a flow guide tube, contained in the internal tank, and directing the mixture from the top of the flow guide tube downwardly through a space defined between the internal tank and the flow guide tube; directing the water in the internal tank downwardly through an aperture in a hopper that forms a lower part of the internal tank and into the external tank; wherein the water in the external tank then flows upwardly through the external tank and between the external tank and the internal tank to where the water is discharged from a top portion of the external tank; directing the ballasted floc through the aperture of the hopper of the internal tank into a hopper that forms a lower part of the external tank; settling the ballasted floc in the hopper of the external tank and in the process yielding a ballasted sludge in the hopper of the external tank; directing the ballasted sludge from the hopper of the external tank to a ballast separator and separating the ballast from the ballasted sludge to yield separated ballast and separated sludge; and recycling the separated ballast to the internal tank.

22. The method of claim 21 wherein the ballast separator comprises a blade mixer and the method includes engaging the ballasted sludge with the blade mixer and disassociating the ballast from the ballasted sludge; and collecting the separated ballast in a bottom portion of a decantation tank and removing the separated sludge from a top portion of the decantation tank.

23. The method of claim 21 including directing the ballasted sludge from the hopper of the external tank into a discharge line; and injecting air into the discharge line where the air mixes with the ballasted sludge and drives the ballasted sludge through the discharge line to the ballast separator.

24. The method of claim 21 including air lifting the ballasted sludge from the hopper of the external tank to the ballast separator.

25. The method of claim 21 wherein the flocculated water inside the internal tank is guided towards the bottom of the hopper of the external tank in which decantation and thickening of the ballasted floc occurs.

26. The method of claim 21 wherein the aperture of the hopper associated with the internal tank is sized to permit the water to pass therethrough at a speed that prevents clogging and limits turbulence in a decantation zone disposed generally below the internal tank.

Description

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

[0058] With reference to FIG. 1, the plant according to the invention represented diagrammatically comprises a coagulation vessel 20 and a flocculating-decantation device 1.

[0059] Said coagulation vessel 20 is provided with means 38 of carrying in water 500 to be treated, means 31 of distributing a coagulating reagent 21 and stirring means 12. For example, said stirring means 12 comprise a blade stirrer, and the leading in means 38 comprise a pump.

[0060] In practice, the coagulating reagent may be organic or inorganic. It will advantageously be chosen from among aluminium sulphate, sodium aluminate, ferric chloride, ferric sulphate, ferrous sulphate, polyamines (epichlorhydrin or Polydadmac), melamine-formol resins, polyethylenimines and some cationised plant polymers.

[0061] Said flocculating-decantation device 1 comprises an external vessel 2 provided with a first hopper 4, and an internal vessel 3 provided with a second hopper and placed inside said external vessel 2. Said vessels 2 and 3 each have a cylindrical-shaped body 2a and 3a, said bodies being essentially concentric. Said second hopper 5 is provided with an aperture 6 opening into said first hopper 4. This opening 6 is sized so that the water flow can pass through it without causing turbulence. It directs flocculated water containing floc 26 to the bottom of the hopper 4 without being dispersed, so as to not hinder decantation of the floc.

[0062] Said flocculating-decantation device 1 is provided with a coagulated water inlet duct 8, means 32 of distributing a flocculating reagent 22, means 33 of distributing a ballast 23, a discharge duct 34 for ballasted sludge 24 and means 9 of discharging treated water, for example such as gutters surrounding said external vessel 2. For example, said distribution means 31, 32 and 33 are conduits with distribution valves. For example, the flocculant reagent is chosen from among water-soluble polymers of animal or plant origin, and high molecular weight water-soluble polyelectrolytes with different ionic valences.

[0063] Said internal vessel 3 receives the flocculant 22 and the ballast 23 and is provided with stirring means 10. The stirring means comprise a blade stirrer 14 and a flow guide tube 13, the blades of the blade stirrer 14 being entirely located inside an internal space in the flow guide tube 13, the axes of said flow guide 13 and said stirrer 14 being aligned A peripheral space is formed between said internal vessel 3 and said external vessel 2. Said second hopper 5 is provided with an aperture 6 opening into said first hopper 4. Said first hopper 4 is provided with an outlet 7 communicating with the discharge conduit 34 carrying the ballasted sludge 24.

[0064] Said treated water discharge means 9 are provided near the top of said external vessel 2. For example, said treated water discharge means 9 are gutters around the external vessel 2.

[0065] The plant also comprises means for separating the ballast contained in ballasted sludges 24 followed by means 36 for recycling said ballast thus purified towards said flocculating-decantation device 1.

[0066] For example, said separation means include means 11 of injecting air in the form of bubbles into the pipe 34, to form an air lift, and a device 39 to separate the ballast contained in the sludge carried by this air lift. The separation device 39, into which the pipe 34 leads, is equipped with a blade mixer 39a rotating at high speed followed by a small decantation tank 39b fitted with an air injection manifold 39c and a floated sludge evacuation gutter 39d.

[0067] The use of an air lift not only carries ballasted sludge to the separation device but it also initiates separation of the ballast contained in it and thus reduces loss of ballast caused by the separation.

[0068] According to the invention, the separation means do not include a hydrocyclone.

[0069] Operation of such a plant will now be described.

[0070] Water 500 to be treated enters the coagulation reactor 20 in which an appropriate dose of coagulant is added to it and is intimately mixed with it. Coagulated water passes through the pipe 8 as far as the flocculating-decantation device 1 in which the ballast 23 and the flocculant 22 are added. The water is intimately mixed with the ballast and the flocculent using the stirrer 10. Movement of the blades 14 causes water circulation from bottom to top inside the flow guide 13 and from top to bottom between the flow guide 13 and the internal tank 3. This movement optimises flocculation of water. Water is then discharged passing through the opening 6 in the hopper 5 towards the external vessel. Water then transits from bottom to top in the space between the internal vessel 3 and the external vessel 2, space in which the floc formed will decante, accelerated by the ballast contained in them, towards the hopper 5 at the bottom of which they accumulate. Decanted sludge mixed with the ballast 24 is discharged from the flocculating-decantation device through the pipe 34. The means 36 of recycling the ballast contained in this sludge are connected to this pipe. Air 11 is injected through the means 35 into the sludge. The created air lift entrains sludge towards the separation device 39. Separation of ballast from the sludge that was started due to the air lift is completed in the separation device 39. In this device, the stirrer 39a rotating at high speed detaches sludge from the ballast. The sludge and the ballast are then separated in the decantor 39b equipped with an air manifold 39c. The ballast 23 is then transferred back to the flocculating-decantation device, while the floated sludge is discharged through the gutter 39d to a special treatment.