Sludge dewatering device

Abstract

Sludge dewatering device that makes it possible to achieve a high degree of dryness while retaining a limited energy consumption and limited industrial risks, comprising at least one first plate (21a) equipped with a first electrode (23a), and at least one second plate (21b) equipped with a second electrode (23b), wherein the first and second plates (21a, 21b) define a chamber (22) configured for receiving a sludge to be dewatered (10a), wherein the first and second electrodes (23a, 23b) are configured for establishing an electric field within the chamber (22), wherein the chamber (22) is equipped with at least one discharge port (32, 34), provided in the bottom third of the chamber (22), configured for discharging a filtrate (15a, 16a), and wherein the chamber (22) is equipped with at least one injection port (33), provided in the top third of the chamber (22), configured for injecting the pressurized purge fluid (11a) into the chamber (22).

Claims

1. A sludge dewatering device, comprising a first plate equipped with a first electrode; a second plate equipped with a second electrode, at least one of the first plate and the second plate equipped with a filter; and a supply of a pressurized purge fluid, the pressurized purge fluid comprising a gas, wherein the first and second plates define a chamber configured for receiving a sludge to be dewatered, wherein the first and second electrodes are configured for establishing an electric field within the chamber, wherein the chamber is equipped with: at least one discharge port, provided in the bottom third of the chamber, configured for discharging a filtrate from the filter, and at least one pressurized purge fluid injection port, provided in the top third of the chamber, connected to the supply of pressurized purge fluid for injecting the pressurized purge fluid into the chamber, the at least one pressurized purge fluid injection port being connected to the at least one discharge port via the chamber.

2. The device as claimed in claim 1, wherein each of the first plate and the second plate is equipped with at least one of the discharge ports, and wherein each of the first plate and second plate is equipped with at least one of the pressurized purge fluid injection ports.

3. The device as claimed in claim 2, wherein said at least one discharge port of the first plate and said at least one discharge port of the second plate are connected to different discharge channels, and wherein said at least one pressurized purge fluid injection port of the first plate and said at least one pressurized purge fluid injection port of the second plate are connected to different injection channels.

4. The device as claimed in claim 1, further comprising: a supply of a second purge fluid, the second purge fluid being different from the pressurized purge fluid, wherein the first plate is equipped with the at least one pressurized purge fluid injection port, and wherein at least one of the first plate and the second plate is equipped with at least one second purge fluid injection port, provided in the top third of the chamber, connected to the supply of second purge fluid for injecting the second purge fluid into the chamber.

5. The device as claimed in claim 1, wherein the pressurized purge fluid supplied from the supply comprises the gas or a mixture of gases that is/are inert, nontoxic, nonflammable and unable to create an explosive zone in the presence of H.sub.2 or O.sub.2.

6. The device as claimed in claim 1, wherein the pressurized purge fluid supplied from the supply is moistened.

7. The device as claimed in claim 1, wherein the pressurized purge fluid supplied from the supply comprises at least one electrolyte.

8. The device as claimed in claim 7, wherein the at least one electrolyte supplied from the supply comprises a compound containing the element chlorine.

9. The device as claimed in claim 1, wherein the pressurized purge fluid supplied from the supply is sulfate-free.

10. The device as claimed in claim 1, wherein the pressurized purge fluid supplied from the supply comprises at least one acid.

11. The device as claimed in claim 1, wherein the pressurized purge fluid supplied from the supply comprises at least one base.

12. The device as claimed in claim 1, comprising at least one liquid/gas separator provided downstream of said at least one discharge port.

13. The device as claimed in claim 5, wherein the pressurized purge fluid supplied from the supply is selected from the following gases: N.sub.2, He, Ar, CO.sub.2, air or a mixture thereof.

14. The device as claimed in claim 7, wherein the pressurized purge fluid supplied from the supply comprises at least one electrolyte selected from the following species: NaCl, KCl, Na.sub.2SO.sub.4 or K.sub.2SO.sub.4.

15. The device as claimed in claim 10, wherein the pressurized purge fluid supplied from the supply comprises HCl.

16. The device as claimed in claim 11, wherein the pressurized purge fluid supplied from the supply comprises NaOH.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The appended drawings are schematic and aim primarily to illustrate the principles of the invention.

(2) In these drawings, from one figure (FIG) to the next, identical elements (or element parts) are identified by the same reference signs.

(3) FIG. 1 is an overall diagram of an example of a device according to the invention.

(4) FIG. 2 is a diagram of a module of the filter press of this example of a device.

(5) FIG. 3 is a perspective view of a plate of this filter press.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

(6) In order to make the invention more concrete, an example of a dewatering device is described in detail below, referring to the appended drawings. It is recalled that the invention is not limited to this example.

(7) FIG. 1 illustrates an example of a dewatering device 1 according to the invention. This device 1 comprises a filter press 20, a booster pump 10, a supply of a first purge fluid 11, a supply of a second purge fluid 12, an electric rectifier 13, a booster 14, a first liquid/gas separator 15 and a second liquid/gas separator 16.

(8) The filter press 20 comprises a plurality of modules 20a, 20b made up of plates 21a, 21b pressed against one another by a hydraulic jack 26 so as to ensure hermeticity between the various plates 21a, 21b. As can be seen in FIGS. 1 and 2, each plate 21a, 21b extends vertically.

(9) A module 20a is shown schematically in FIG. 2. It comprises three plates 21a, 21b defining two chambers 22 into which the sludge to be dewatered 10a is introduced. Each wall of the plates 21a, 21b, defining one edge of a chamber 22, is equipped with an electrode 23a, 23b preferably taking the form of a grid: the side plates 21a are thus equipped with an electrode that forms the anode 23a and the central plate 21b is equipped on each of its faces with an electrode that forms the cathode 23b.

(10) The internal wall of each plate 21a, 21b is equipped with a filter cloth 24 positioned in front of the electrode 23a, 23b in question. Each wall of the central plate 21b is additionally equipped with a membrane 25 positioned behind the electrode 23b in question.

(11) Each side plate 21a, also shown in FIG. 3, is equipped with a passage 31 for supplying sludge 10a connected to a first line segment 41 passing all the way through plate 21a at the periphery of the chamber 22. Each central plate 21b also has a sludge feed passage connected to a first line segment passing all the way through plate 21b at the periphery of the chamber 22. All the first line segments 41 are aligned so as to form, when the plates 21a, 21b are pressed against one another, a first sealed line forming a feed channel, connected to the booster pump 10 so as to supply the filter press 20 with sludge 10a.

(12) Each side plate 21a is also equipped, at the bottom end of the chamber 22, with a plurality of discharge ports 32, connected to a second line segment 42, for discharging the filtrates 15a on the anode side, and, at the top end of the chamber 22, with a plurality of injection ports 33, connected to a third line segment 43, for injecting a first purge fluid 11a on the anode side.

(13) Similarly, each central plate 21b is also equipped, at the bottom end of the chamber 22, with a plurality of discharge ports 34, connected to a fourth line segment 44, for discharging the filtrates 16a on the cathode side, and, at the top end of the chamber 22, with a plurality of injection ports 35, connected to a fifth line segment 45, for injecting a second purge fluid 12a on the cathode side.

(14) In addition, each side plate 21a is equipped with a fourth line segment 44 that is not connected to the chamber 22 but is aligned with the fourth line segments 44 of the other plates so as to form, when plates 21a, 21b are pressed against one another, a sealed fourth line forming a discharge channel, for discharging the filtrates 16a collected on the cathode side via the various central plates 21b and connected to the inlet of the second liquid/gas separator 16.

(15) In the same way, each side plate 21a is equipped with a fifth line segment 45 that is not connected to chamber 22 but is aligned with the fifth line segments 45 of the other plates 21a, 21b so as to form, when the plates 21a, 21b are pressed against one another, a sealed fifth line, forming a feed channel, connected to the second purge fluid supply 12 so as to supply the filter press 20 on the cathode side with second purge fluid 12a.

(16) Similarly, each central plate 21b is equipped with a second line segment and with a third line segment so as to form, with its neighbours, a second line, forming a discharge channel, for discharging the filtrates 15a collected on the anode side via the various side plates 21a and connected to the inlet of the first liquid/gas separator 15 and, respectively, a third line, forming an injection channel, connected to the first purge fluid supply 11 so as to supply the filter press 20 on the anode side with first purge fluid 11a.

(17) In addition, sixth line segments 46 are provided similarly in plates 21a and 21b so as to inject compressed air from the booster 14 into the membranes 25.

(18) The operation of the dewatering device will now be described in detail.

(19) Within the context of the present example, the sludge to be treated 10a is a biological sludge derived from a wastewater treatment plant. This type of sludge is derived from a membrane bioreactor operating directly on the screened raw water.

(20) The sludge 10a, the initial dryness of which is around 0.9% in this example, that is to say 9 g/l, is admitted into the device 1 by means of the booster pump 10 and is fed into the filtration chambers 22 of the filter press 20 via the feed channel 41 and the feed passages 31. This sludge 10a may have undergone a preliminary chemical conditioning step during which certain chemical components are added to the sludge 10a to facilitate the treatment thereof and the dewatering thereof: thus, in this example, a coagulation aid, such as FeCl.sub.3, and a flocculation aid, such as the polymer Flopam EM 640 TBD, are added.

(21) Next, during a filtration step, the booster pump 10 generates a mechanical pressure of 8 bar within the sludge 10a which is then filtered with the aid of the filter cloths 24. This step is stopped when the flow rate of filtrate 15a, 16a discharged by the plates 21a, 21b reaches a predetermined low threshold. This step makes it possible to remove the free water present at the surface of the sludge flocs with a lower energy expenditure.

(22) Once the sludge 10a has been filtered in the chambers 22 of the filter press 20, a step of compression alone is performed in the filter press 20. The compressed air booster 14 thus makes it possible to inflate the membranes 25 of the filter press 20 so as to compress the sludge 10a present in the chambers 22 until a pressure of about 11 to 12 bar is reached in the membranes 25 of plate 21b.

(23) This step of compression alone makes it possible to extract a first portion of the interstitial water present in the sludge 10a in the form of filtrates 15a, 16a discharged through the discharge ports 32, 34 of plates 21a, 21b.

(24) At the end of this step of compression alone, the compression is maintained and the electrical assistance is started in order to initiate an electro-dewatering step.

(25) The electric rectifier 13 then applies a current between the pairs of electrodes 23a, 23b of each chamber 22. Initially, regulation is carried out at constant current. In this example, a current of about 9 A is selected, or about 40 A/m.sup.2.

(26) During this step, the water extracted from the sludge 10 is discharged in the form of filtrates 15a, 16a through the discharge ports 32, 34 of the plates 21a, 21b.

(27) Then the first purge fluid 11a is injected into the chambers 22, on the side with the anode 23a, from the first purge fluid supply 11 and via the injection channel 43 and the injection ports 33. The second purge fluid 12a is also injected into the chambers 22, on the side with the cathode 23b, from the second purge fluid supply 12 and via the injection channel 45 and the injection ports 35.

(28) In this example, the first purge fluid 11a is gaseous molecular nitrogen N.sub.2 comprising water, Na.sub.2SO.sub.4 and NaOH; for its part, the second purge fluid 12a is gaseous molecular nitrogen N.sub.2 comprising water, NaCl and HCl. In an example like this, the purge fluids thus comprise a gas phase and a liquid phase, dispersed in the gas phase in the manner of a mist, in which the electrolytes are dissolved.

(29) In addition, the first and second purge fluids 11a and 12a are injected into the chambers 22 at an absolute pressure of 2 bar and at room temperature.

(30) Then the gases generated during this electro-dewatering step, for example molecular oxygen and molecular hydrogen resulting from the hydrolysis of water, are driven by the purge fluids 11a, 12a back to the discharge ports 32, 34 of the plates 21a, 21b, via which they are then discharged along with the liquid filtrates. More precisely, the gases generated at the anodes 23a are driven back to the discharge ports 32 of the plates 21a and are therefore discharge within the filtrates 15a via the discharge channel 42 to the first liquid/gas separator 15. For their part, the gases generated at the cathodes 23b are driven back to the discharge ports 34 of the plates 21b and are therefore discharged within the filtrates 16a via the discharge channel 44 to the second liquid/gas separator 16.

(31) In this example, the purge fluids 11a and 12a are injected continuously into the chambers 22 throughout the electro-dewatering step. However, in other examples, this injection could be carried out intermittently, so as to purge the chambers 22 completely at regular intervals.

(32) Each separator 15, 16 then separates, within the filtrates 15a, 16a, the gas phase 17a, 17b, containing, depending on the case, the first or the second purge fluid mixed with the gases produced during electro-dewatering, and the liquid phase 18a, 18b comprising essentially the water extracted from the sludge 10a and also a portion of the electrolytes injected into the chambers 22 and/or produced at the electrodes 23a, 23b during electro-dewatering. A reinjection device may then be provided for recovering at least a portion of these electrolytes and reintroducing them into the purge gases 11, 12 in order to inject them back into the chambers 22.

(33) Regulation at constant current is maintained until the temperature in the vicinity of an anode 23a, measured using a thermocouple for example, reaches 60° C.: when this condition is met, regulation of the current is abandoned in favor of regulation at constant voltage.

(34) The electrical assistance at constant voltage is then maintained until the temperature in the vicinity of an anode 23a reaches a second threshold value: when this condition is met, the electrical treatment is stopped and the compression of the membranes 25 is released.

(35) The hydraulic jack 26 may then release the plates 21a, 21b of the filter press 20 to allow removal of the dewatered sludge cakes from the chambers 22 of the filter press 20.

(36) These cakes may then be landfilled, or recovered as organic soil conditioner or as energy.

(37) The embodiments or examples of implementation described in the present disclosure are given by way of illustration and nonlimitingly, a person skilled in the art could easily, in view of this disclosure, modify these embodiments or examples of implementation, or envisage other ones thereof, while remaining within the scope of the invention.

(38) Furthermore, the various features of these embodiments or examples of implementation may be used alone or may be combined with one another. When they are combined, these features may be as described above or otherwise, the invention not being limited to the specific combinations described in the present disclosure. In particular, unless otherwise specified, a feature described in connection with an embodiment or example of implementation may be applied in a similar manner to another embodiment or example of implementation.