sludge dewatering plant

Abstract

A sludge dewatering installation and a sludge dewatering process using such an installation, the installation comprising a sludge dewatering device (20) and at least one suction line (50, 60), wherein the first and second trays (21a, 21b) of the sludge dewatering device (20) define a chamber configured to receive sludge to be dewatered (B), wherein first and second electrodes are configured to establish an electric field within the chamber, wherein the chamber is provided with at least one discharge port configured to discharge a filtrate (Fa, Fb), wherein the chamber is provided with at least one suction port connected to said at least one suction line (50, 60), and wherein said at least one suction line (50, 60) comprises at least one pump (59) and at least one gas treatment unit (52, 62). Fig. 1.

Description

Title of the invention: sludge dewatering installation Technical field

[0001] The present disclosure relates to a sludge dewatering installation and a sludge dewatering method using such an installation. The latter make it possible to achieve a high level of dryness while maintaining limited energy consumption and industrial risks. Such a device can in particular be used to dewater sludge, that from treatment plants for example, with a view to incinerating it or burying it. Prior art

[0002] Sludge, such as that from wastewater treatment plants for example, is generally subject to dehydration followed by recovery, as an organic amendment (spreading) or by combustion (incineration), or by burial in a storage center. In the case of combustion, the dryness of the sludge reached at the end of the dehydration stage, that is to say the ratio of dry matter to the total mass of sludge, must be sufficient to allow self-maintenance of combustion: a dryness of 30 to 45% is thus preferred. Similarly, in the case of burial, certain national legislations require a minimum dryness rate before burial of the sludge, of the order of 40% for example. We therefore understand the importance of developing effective dehydration processes and devices, in particular when the sludge is of a type that is difficult to dehydrate, as is particularly the case with biological sludge in wastewater treatment plants.

[0003] Among the known processes, some aim to mechanically dehydrate the sludge: these may involve centrifugation or pressure filtration processes, in particular using a filter press or a belt filter. However, such processes are limited. For example, for sewage treatment plant sludge, they make it possible to achieve drynesses of only 15 to 40%; this maximum value of 40% is only achieved in rare cases with particularly effective devices and sludge that is particularly easy to treat (predominantly mineral, for example). Thus, for certain sludge, such as biological sewage treatment plant sludge, it is difficult to achieve a dryness of 30%, which may be insufficient depending on the fate of this sludge.

[0004] Other processes aim to thermally dehydrate the sludge: this involves heating the sludge in order to dry it. These processes are very effective: depending on the heating temperature and the duration of the treatment, it is possible to achieve dryness levels of around 90%. However, these processes are very energy-intensive. and consume at least 700 kWh per tonne of water eliminated (kWh / tEE), or even more, when a mechanical process generally consumes less than 20 kWh / tEE depending on the type of technology (filter press, belt filter or centrifuge).

[0005] Finally, electrically assisted mechanical dehydration processes, called electro-dehydration processes, aim to filter a volume of sludge under pressure, for example in a filter press, by also applying an electric field. This, added to the hydrolysis phenomenon that it creates, makes it possible to break the water-sludge bonds, facilitating the migration of water molecules in the opposite direction of the solid particles. Such electrical assistance therefore makes it possible to improve the dehydration of sludge and thus to gain a few additional dryness points. In particular, document FR 3 042 186 describes such an electro-dehydration device. However, such a process is faced with certain difficulties in the case of certain sludges.

[0006] In particular, the water hydrolysis reactions occurring in the sludge under the effect of the applied electric field are responsible for the production of gaseous dihydrogen H2 at the cathode and gaseous dioxygen O2 at the anode. Therefore, the simultaneous presence of these two gases in the electro-dehydration device can lead to the formation of an explosive atmosphere. In addition, depending on the nature of the sludge to be dehydrated, the occurrence of other electrolysis reactions can also lead to the formation of dangerous, toxic, explosive or corrosive gases for example, and in particular dichlorine Cl2 when the sludge contains chlorides. To evacuate these various dangerous gases, document FR 3 042 186 proposes injecting a purge fluid into the chamber of the electro-dehydration device in order to force the gases produced towards the filtrate evacuation orifices.

[0007] However, this solution simply shifts the problem by pushing the hazardous gases further downstream into the filtrate recovery channels. Thus, while such a solution is satisfactory for small dehydration units, it remains imperfect for larger dehydration units that generate large quantities of hazardous gases.

[0008] There is therefore a real need for a sludge dewatering installation and a sludge dewatering method which are free, at least in part, from the drawbacks inherent in the aforementioned known configurations. Statement of the invention

[0009] The present disclosure relates to a sludge dewatering installation, comprising a sludge dewatering device, comprising at least a first tray, provided with a first electrode, and at least a second tray, provided with a second electrode, and at least one suction line, in which the sludge dewatering device comprises at least a first tray, provided with a first electrode, and at least a second tray, provided with a second electrode, wherein the first and second trays define a chamber configured to receive a sludge to be dewatered, wherein the first and second electrodes are configured to establish an electric field within the chamber, wherein the chamber is provided with at least one discharge orifice, provided in the lower third of the chamber, configured to discharge a filtrate, wherein the chamber is provided with at least one suction port, provided in the upper third of the chamber, connected to said at least one suction line, and wherein said at least one suction line comprises at least one pump and at least one gas treatment unit.

[0010] Thus, thanks to such a configuration, said at least one pump generates a vacuum in said at least one suction line, which makes it possible to suck any dangerous gases produced in the chamber into a dedicated line. This therefore facilitates the evacuation of the latter and thus reduces the risks of accumulation of dangerous gases in the chamber. The durability of the device is thus preserved and the danger of the working environment is reduced for the operators.

[0011] Furthermore, since this is a dedicated suction line, the hazardous gases do not mix, or practically do not mix, with the filtrates discharged via a discharge line connected to said at least one discharge orifice. This facilitates any subsequent treatment of the filtrates while reducing the danger of the working environment downstream of the dehydration device.

[0012] Furthermore, since the dangerous gases are sucked into a dedicated line, they can be treated at the gas treatment unit to neutralize them or, at least, reduce their danger. The danger of the working environment as a whole is therefore reduced for operators. It is even possible, where appropriate, to recover gaseous by-products.

[0013] This device is therefore particularly effective in the context of an electro-dehydration process, such as that described for example in document FR 3 042 186.

[0014] In some embodiments, at least one tray is provided with a filter medium. Such a filter makes it possible to retain the solid matter of the sludge and to allow the water extracted from the sludge to pass through. Preferably, each tray is provided with a filter medium. This may in particular be a filter cloth.

[0015] In some embodiments, at least one plate is provided with at least one membrane configured to be deformed by a compression fluid, in particular compressed air or pressurized water. Such a membrane makes it possible to reduce the volume of the chamber and therefore to compress the sludge present in the chamber in order to mechanically extract part of the water contained in the sludge. Each tray can be equipped with such a membrane but preferably only one tray per chamber is equipped with it, preferably the tray equipped with the cathode.

[0016] In some embodiments, the installation comprises a booster configured to supply the membrane with compressed air.

[0017] In some embodiments, the installation comprises a pressurized water supply configured to supply the membrane with pressurized water.

[0018] In certain embodiments, the surface of at least one plate comprises reliefs forming flow channels. These reliefs may in particular take the form of grooves; they are preferably provided in front of the membrane but behind the corresponding electrode. These flow channels facilitate the evacuation of filtrates downwards, by gravity, and the evacuation of gases upwards, by suction.

[0019] In some embodiments, the installation comprises a power supply, for example an electric generator, a rectifier or a battery, configured to power the first and second electrodes.

[0020] In some embodiments, the device comprises a hydraulic cylinder configured to hold the first and second plates against each other and thereby seal the chamber.

[0021] In some embodiments, the device comprises a plurality of first trays and a plurality of second trays.

[0022] In some embodiments, said at least one discharge orifice is provided at the lower end of the filtration chamber.

[0023] In some embodiments, each tray is provided with at least one discharge orifice. This makes it easier to discharge the filtrate, with a discharge orifice being provided on each side of the chamber.

[0024] In certain embodiments, said at least one discharge orifice of the first tray is connected to a first discharge channel, configured to discharge a first filtrate, and said at least one discharge orifice of the second tray is connected to a second discharge channel, distinct from the first discharge channel and configured to discharge a second filtrate. This makes it possible to separate the filtrate recovered at the anode from that recovered at the cathode, these two filtrates not having the same chemical composition, in particular the same pH.

[0025] In some embodiments, said at least one suction port is provided at the upper end of the filtration chamber.

[0026] In some embodiments, each tray is provided with at least one suction port. This makes it easier to evacuate the gases produced, an orifice evacuation being provided on each side of the room.

[0027] In certain embodiments, said at least one suction orifice of the first plate is connected to said at least one suction line, constituting a first suction line, and said at least one suction orifice of the second plate is connected to a second suction line, distinct from the first suction line. This makes it possible to separate the gases produced at the anode from those produced at the cathode, these different gases not having the same chemical composition, in particular the same pH. This is particularly useful when certain gases would risk creating an explosive atmosphere in the event of mixing.

[0028] In some embodiments, said at least one gas treatment unit of the first suction line constitutes a first gas treatment unit and said second suction line comprises a second gas treatment unit. It is thus possible to treat these different gases in a differentiated manner, taking into account their expected chemical composition.

[0029] In some embodiments, at least one gas processing unit comprises at least one reactor.

[0030] In some embodiments, at least one reactor comprises a closed enclosure, a reactive liquid, a gas inlet opening into the reactive liquid and a gas outlet arranged above the level of the reactive liquid. The gas is thus forced to pass through the reactive liquid, the latter being provided to neutralize or, at least, reduce the danger of the gas. Preferably, the gas inlet is arranged at the bottom of the reactor; preferably, the gas outlet is arranged at the top of the reactor.

[0031] In some embodiments, the reactive liquid fills at least half of the enclosure, preferably at least 80% of the enclosure. These fill volumes are intended to encompass any elements suspended in the reactive liquid, such as solid media like those presented below.

[0032] In some embodiments, at least one reactor comprises a liquid inlet, opening into the enclosure, and a liquid outlet, arranged below the level of the reactive liquid. It is thus possible to renew the reactive liquid so that it can continue to react with the gas passing through the reactor over time. Preferably, the liquid inlet is arranged at the top of the reactor; preferably, the liquid outlet is arranged at the bottom of the reactor.

[0033] In some embodiments, at least one reactor comprises solid media suspended in the reactive liquid. These media make it possible to slow the progression of the gas upwards within the reactive liquid and therefore increase the contact time between the gas and the reactive liquid, which increases the quantity of gas actually treated. In addition, these media can be set in motion, including rotation, during the passage of the gas.

[0034] In certain embodiments, the total volume occupied by the media is between 20 and 70%, preferably between 25 and 55%, of the filling volume of the reactor. By "total volume occupied by the media", is meant here the total volume globally occupied by the media when they are poured in bulk into a container: it is therefore not the intrinsic volume of the media; on the contrary, this total occupied volume includes the volume of air, or of reactive liquid when the latter is present in the reactor, between each medium and, where appropriate, within each medium. By "filling volume of the reactor", is meant here the volume of the reactive liquid including the media in suspension. This volume range represents a good compromise making it possible both to effectively slow down the progression of the gas while leaving sufficient mobility of the media in the reactive liquid to ensure agitation of the latter.

[0035] In certain embodiments, the solid media have a divided structure, preferably comprising a plurality of through passages. These passages may in particular be parallel. Such a divided structure makes it possible to increase the contact surface between the gas and the liquid and to further slow down the progression of the gas, the gas bubbles being able to be temporarily retained by adsorption on the walls of the media, in particular in the through passages.

[0036] In certain embodiments, the solid media are supports of the type used in moving bed biofilm reactors (MBBR), preferably of the K3 or K5 type.

[0037] In some embodiments, each element of the solid media has a diameter between 10 mm and 30 mm, preferably between 20 and 28 mm.

[0038] In some embodiments, each element of the solid media has a density of between 0.9 and 1.3 kg / m3.

[0039] In some embodiments, at least some, and preferably all, of the solid media elements are made of plastic, for example, polyethylene.

[0040] In some embodiments, the first gas treatment unit comprises at least one reactor including a basic liquid. This is particularly suitable for neutralizing chlorine Cl2 and hydrogen sulfide H2S.

[0041] In some embodiments, the first gas treatment unit comprises a first reactor, including a basic liquid, and a second reactor, arranged downstream of the first reactor, including a basic liquid. The succession of two reactors makes it possible to increase the quantity of neutralized gas; it also makes it possible to use two different reactive liquids, having different chemical compositions and / or concentrations.

[0042] In some embodiments, the second gas processing unit comprises at least one reactor including an acidic liquid. This is particularly suitable for neutralizing ammonia.

[0043] In some embodiments, the second gas treatment unit comprises at least one reactor including a basic liquid. This is particularly suitable for neutralizing chlorine Cl2 and hydrogen sulfide H2S.

[0044] In certain embodiments, the second gas treatment unit comprises a first reactor, including an acidic liquid, and a second reactor, arranged downstream of the first reactor, including a basic liquid. Chaining an acidic then basic treatment makes it possible to treat gases of different natures present in the same suction line.

[0045] In certain embodiments, at least one basic liquid comprises sodium hydroxide NaOH. In particular, the NaOH concentration may be between 5 and 30%, preferably between 15 and 20%.

[0046] In some embodiments, at least one basic liquid comprises at least a portion of a filtrate from the dehydration device, preferably at least a portion of the second filtrate. This configuration offers the advantage of recovering at least a portion of the filtrates.

[0047] In some embodiments, at least one acidic liquid has a pH between 0.5 and 3, preferably between 0.5 and 1.5.

[0048] In some embodiments, at least one acidic liquid comprises sulfuric acid H2SO4.

[0049] In some embodiments, at least one acidic liquid comprises at least a portion of a filtrate from the dehydration device, preferably at least a portion of the first filtrate. This configuration offers the advantage of recovering at least a portion of the filtrates.

[0050] In certain embodiments, at least one reactor of the gas treatment unit of one of the suction lines is supplied with a liquid from a reactor of the gas treatment unit of the other of the suction lines. This configuration offers the advantage of recovering the effluents of at least one reactor.

[0051] In some embodiments, at least one suction line, and preferably each suction line, comprises a control valve downstream of the gas treatment unit of said suction line. Such a control valve makes it possible to control the output flow rate of the gas treatment unit and therefore to control the residual concentration of hazardous gas.

[0052] In some embodiments, at least one suction line, and preferably each suction line, comprises a flow meter downstream of the gas processing unit of said suction line.

[0053] In certain embodiments, the second suction line joins, downstream of its gas treatment unit, the first suction line, downstream of its gas treatment unit.

[0054] In certain embodiments, at least one pump is a vacuum pump. It may in particular comply with ATEX standards relating to explosive atmospheres.

[0055] In some embodiments, said at least one pump of said at least one suction line is disposed upstream of said at least one gas treatment unit of said at least one suction line.

[0056] In some embodiments, said at least one pump of said at least one suction line is disposed downstream of said at least one gas treatment unit of said at least one suction line.

[0057] In some embodiments, the pump of the first suction line is arranged downstream of the junction with the second suction line. A single, common pump can thus be used for both suction lines.

[0058] In some embodiments, a pump is provided on each suction line.

[0059] In some embodiments, the installation comprises a ventilation line including a ventilation device, in which said at least one suction line opens into the ventilation line downstream of the ventilation device. Such a ventilation line makes it possible to dilute the output of the suction line in order to reduce its residual danger, in particular when certain gases cannot be chemically treated.

[0060] In certain embodiments, the ventilation line is configured to dilute the gases from said suction line in the air flow driven by the ventilation device with a dilution factor of at least 100, preferably at least 500, more preferably at least 1000, possibly at least 1500. However, preferably, the dilution factor is between 1000 and 1500, more preferably between 1200 and 1300.

[0061] In certain embodiments, the ventilation line comprises at least one suction outlet provided in the installation room. This makes it possible to evacuate potentially polluted air from the room, in particular when it includes a portion of dangerous gases coming from the installation.

[0062] In certain embodiments, the ventilation line comprises an outlet opening outside the installation room. This allows any residual hazardous gases to be discharged from the room.

[0063] In certain embodiments, the installation comprises a reinjection device configured to reinject into the sludge, for example upstream of the chamber or directly into the chamber, at least a portion of at least one filtrate. This makes it possible to recycle a portion of the injected electrolytes. This also makes it possible to lower the pH in the room.

[0064] In some embodiments, the sludge to be dewatered is a biological sludge from a wastewater treatment plant. This type of sludge specifically contains a high proportion of bound water. However, naturally, the present disclosure could be applied to other types of sludge, in particular to industrial sludge.

[0065] The disclosure also relates to a sludge dewatering method, using an installation according to any one of the preceding embodiments, comprising the following steps: - admission of sludge into the chamber of the dehydration device, - setting up an electric field within the chamber, - evacuation of a filtrate via said at least one evacuation orifice, - suction in said at least one suction line of gases produced in the chamber, and - treatment of said gases in said at least one gas treatment unit.

[0066] The above-mentioned features and advantages, as well as others, will become apparent from reading the following detailed description of examples of embodiments of the proposed installation and method. This detailed description refers to the attached drawings. Brief description of the drawings

[0067] The attached drawings are schematic and are intended primarily to illustrate the principles of the disclosure.

[0068] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference signs. In addition, elements (or parts of elements) belonging to different embodiments but having a similar function are identified in the figures by numerical references incremented by 100, 200, etc.

[0069] [Fig.l] [Fig.l] is a diagram of an example installation.

[0070] [Fig.2] [Fig.2] represents a dehydration module of the installation of the [Fig.l].

[0071] [Fig.3] [Fig.3] is an anode side view of a tray of the installation of [Fig.l].

[0072] [Fig.4] [Fig.4] is a cathode side view of a tray of the installation of [Fig.l].

[0073] [Fig.5] [Fig.5] is a diagram of the processing units of the installation of [Fig.l]

[0074] [Fig.6] [Fig.6] is a photograph of a first example of solid media.

[0075] [Fig.7] [Fig.7] is a photograph of a second example of solid media.

[0076] [Fig.8] [Fig.8] is a graph representing the evolution of the Cl2 concentration in output of the processing units of the installation of [Fig.l]. Description of the embodiments

[0077] In order to make the description more concrete, an example of installation is described in detail below, with reference to the attached drawings. It is recalled that the invention is not limited to this example.

[0078] [Fig.l] illustrates an example of a dewatering installation 1 according to the invention. This installation 1 comprises a sludge supply line 10, a filter press 20, an electrical supply 13, a pressurized water supply 14, a first suction line 50, a second suction line 60 and a ventilation line 70.

[0079] The sludge feed line 10 comprises a conditioning tank 11 receiving at its inlet a sludge to be dewatered B. Adjuvants, including a flocculant Al and a coagulant A2, are added to the conditioning tank 11. A portion of the filtrates recovered at the outlet of the filter press 20, in particular anode-side filtrates Fa, can also be injected into the conditioning tank 11. The conditioning tank 11 comprises an agitator driven by an electric motor. The outlet of the conditioning tank 11 is connected to a booster pump 12 to supply the filter press 20 with sludge to be dewatered B.

[0080] The filter press 20 comprises a plurality of modules 20a composed of plates 21a, 21b pressed against each other by a hydraulic cylinder 29 so as to ensure sealing between the different plates 21a, 21b.

[0081] A module 20a is shown diagrammatically in [Fig.2]. It comprises three trays 21a, 21b defining two chambers 22 into which the sludge to be dewatered B is introduced. Each wall of the trays 21a, 21b, defining an edge of a chamber 22, is provided with an electrode 23a, 23b preferably taking the form of a grid: the lateral trays 21a are thus provided with an electrode forming the anode 23a and the central tray 21b is provided on each of its faces with an electrode forming the cathode 23b. In [Fig.2], the lateral trays 21a shown comprise only a single working face, that is to say a single face bordering a chamber 22 and equipped with an electrode 23a. Indeed, [Fig.2] represents only a single module 20a. However, as can be seen in [Fig.l], when the filter press 20 comprises several modules 20a, the so-called lateral plates 21a may, for reasons of compactness, comprise two active faces, each face then being configured in the manner described below.

[0082] The inner wall of each plate 21a, 21b is provided with a filter cloth 24 arranged in front of the electrode 23a, 23b in question. The main surface 25 of each lateral plate 21a, defining a first lateral edge of the chamber 22, has grooves 25a, the electrode 23a being arranged in front of these grooves 25a. Each central plate 21b is for its part provided, on each of its faces, with a deformable membrane 26, arranged behind the electrode 23b and defining a second lateral edge of the chamber 22; the membrane 26 also has grooves 26a on the side of room 22.

[0083] The membrane 26 may be inflated using pressurized water supplied from the pressurized water supply 14 in order to reduce the volume of the chamber 22 and therefore increase the pressure exerted on the mud B in order to assist the expulsion of the water present in the mud B.

[0084] [Fig.3] now represents a side plate 21a from the front, seen from a chamber 22 considered; [Fig.4] represents for its part a central plate 21b from the front, seen from the same chamber 22.

[0085] Each tray, lateral 21a and central 21b, comprises sections of conduit 41, 42, 43, 44 provided, from one tray to the other, in alignment with each other in the stacking direction in order to form, when the trays 21a, 21b are pressed against each other, continuous and sealed conduits passing through the filter press 20 from one end to the other in the stacking direction.

[0086] Each tray 21a, 21b thus comprises in a first upper corner sections of first conduit 41 forming, once assembled, a first conduit constituting a mud supply channel connected to the feed pump 12.

[0087] Each tray 21a, 21b further comprises in a first lower corner sections of second conduit 42 forming, once assembled, a second conduit constituting a first channel for evacuating the filtrates.

[0088] Each tray 21a, 21b further comprises in a second lower corner sections of third conduit 43 forming, once assembled, a third conduit constituting a second channel for evacuating the filtrates.

[0089] Each tray 21a, 21b further comprises in a second upper corner sections of fourth conduit 44 forming, once assembled, a fourth constituting a gas communication channel.

[0090] Each side plate 21a is then equipped with a mud feed passage 31 connected to its first conduit section 4L. Each central plate 21b also has a mud feed passage 31 connected to its first conduit section 4L. These mud feed passages 31 therefore allow the admission of mud B into each of the chambers 22 of the filter press 20.

[0091] Each lateral plate 21a is also equipped, at the lower end of the chamber 22, with a plurality of discharge orifices 32a, connected to its second conduit section 42, allowing the anode-side filtrates Fa to be discharged. Similarly, each central plate 21b is also equipped, at the lower end of the chamber 22, with a plurality of discharge orifices 32b, connected to a fourth conduit section 43, allowing the cathode-side filtrates Fb to be discharged. The anode-side filtrates Fa and the cathode-side filtrates Fb are therefore discharged separately. The presence of the grooves 25a, 26a, forming circulation channels behind the filter cloth 24 and the electrodes 23a, 23b, facilitates the flow of the filtrates Fa, Fb towards the discharge orifices 32a, 32b.

[0092] Each side plate 21a is also equipped, at the upper end of the chamber 22, with a plurality of suction ports 33a, each connected to a suction pipe 34a, making it possible to evacuate the gases on the anode side Ga. Similarly, each central plate 21b is also equipped, at the upper end of the chamber 22, with a plurality of suction ports 33b, each connected to a suction pipe 34b and to the fourth conduit section 44, making it possible to evacuate the gases on the cathode side Gb. The evacuation of the gases on the anode side Ga and the gases on the cathode side Gb is therefore carried out separately. The presence of the grooves 25a, 26a, forming circulation channels behind the filter cloth 24 and the electrodes 23a, 23b, makes it easier for the gases Ga, Gb to flow towards the suction ports 33a, 33b.In particular, these circulation channels being located behind the filter cloth 24 and the electrodes 23a, 23b, they can be maintained under depression relative to the sludge B thanks to the suction pump 59 which will be described below, which promotes the extraction of the gases Ga, Gb.

[0093] The suction pipes 34a of the side plates 21a, on the anode side, are all connected to a suction duct 51 of a first suction line 50. This suction duct 51 leads downstream to a first gas treatment unit 52. Similarly, the suction pipes 34b of the central plates 21b, on the cathode side, are all connected to a suction duct 61 of a second suction line 60. This suction duct 61 leads downstream to a second gas treatment unit 62.

[0094] These gas treatment units 52, 62 will now be described with reference to [Fig.5].

[0095] The first gas treatment unit 52 comprises a first reactor 53 and a second reactor 54, in series one after the other. Each reactor 53, 54 takes the form of a closed enclosure comprising a reactive liquid 53a, 54a and solid media 53b, 54b suspended in the reactive liquid 53a, 54a. The gas to be treated arrives via a gas inlet 53c, 54c opening at the bottom of the enclosure, passes through the reactive liquid 53a, 54a and escapes via a gas outlet 53d, 54d located at the top of the enclosure. In the present example, for each reactor 53, 54, the volume of the enclosure of the reactor 53, 54 is equal to 2 L; the filling volume, corresponding to the volume of the reactive liquid 53a, 54a including the suspended media 53b, 54b, is approximately equal to 90% of the volume of the reactor enclosure 53, 54, i.e. 1.8 L; and the total volume occupied by the media 53b, 54b represents approximately 30% of the filling volume, i.e. approximately 0.5 L.

[0096] [Fig. 6] represents a first example of media 91 which can be placed in one and / or the other of these reactors 53, 54. This first example of media 91 is conventionally known under the name K3. These media have a central axis which constitutes an axis of symmetry of order 6; their cross-sectional profile is invariant along this central axis. They comprise 19 axial passages distributed in a central passage and two concentric crowns. Their diameter is equal to 25 mm and their thickness is between 10 and 12 mm: they offer a total contact surface greater than 500 m2 per m3 of media. Preferably made of polyethylene, their density is between 0.95 and 0.98.

[0097] [Fig. 7] represents a second example of media 92 which can be placed in one and / or the other of these reactors 53, 54, possibly mixed with the first example of media 91. This second example of media 92 is conventionally known under the name K5. These media have a central axis which constitutes an axis of symmetry of order 4; their cross-sectional profile is invariant along this central axis. They comprise 64 axial passages distributed in four concentric rings. Their diameter is equal to 25 mm and their thickness is between 3 and 4 mm: they offer a total contact surface greater than 800 m2 per m3 of media. Preferably made of polyethylene, their density is between 0.95 and 0.98.

[0098] The anode-side gases Ga therefore pass through the first reactor 53, then the second reactor 54, then a control valve 55 and a flow meter 56. During their passage through the first and second reactors 53, 54, the anode-side gases Ga are treated as follows.

[0099] In the first reactor 53, the reactive liquid 53a, renewed regularly, is a basic liquid, comprising between 15 and 20% by mass of sodium hydroxide NaOH. The latter makes it possible to neutralize the chlorine gas according to the following reaction: Cl2 + 2 NaOH = NaCl + NaCIO + H2O.

[0100] In the second reactor 54, the reactive liquid 54a, renewed regularly, is also a basic liquid. It preferably comprises sodium hydroxide NaOH, at a level of 15 to 20% by mass, and a portion of the filtrates on the cathode side Fb. This new basification step makes it possible to complete the neutralization of the chlorine gas.

[0101] The second gas treatment unit 62 also comprises a first reactor 63 and a second reactor 64, in series one after the other. In a manner similar to the first gas treatment unit 52, each reactor 63, 64 takes the form of a closed enclosure comprising a reactive liquid 63a, 64a and solid media 63b, 64b suspended in the reactive liquid 63a, 64a. The gas to be treated arrives via a gas inlet 63c, 64c opening at the bottom of the enclosure, passes through the reactive liquid 63a, 64a and escapes via a gas outlet 63d, 64d located at the top of the enclosure.In the present example, for each reactor 53, 54, the volume of the reactor enclosure 53, 54 is equal to 2 L; the filling volume, corresponding to the volume of the reactive liquid 53a, 54a including the suspended media 53b, 54b, is approximately equal to 90% of the volume of the reactor enclosure 53, 54, i.e. 1.8 L; and the total volume occupied by the media 53b, 54b represents approximately 30% of the filling volume, i.e. approximately 0.5 L. The suspended media 63b, 64b may be the same as or different from those of the first processing unit 52.

[0102] The gases on the cathode side Gb therefore pass through the first reactor 63, then the second reactor 64, then a control valve 65 and a flow meter 66. During their passage through the first and second reactors 63, 64, the gases on the cathode side Gb are treated as follows.

[0103] In the first reactor 63, the reactive liquid 63a, renewed regularly, is an acidic liquid, the pH of which is less than 3; it can comprise a portion of the filtrates on the anode side Fa. The latter makes it possible to neutralize the ammonia NH3 according to the following reaction: NH3 + H+ = NH4+.

[0104] In the second reactor 64, the reactive liquid 64a, renewed regularly, is a basic liquid. It preferably comprises sodium hydroxide NaOH, a portion of the filtrates on the cathode side Fb and / or a portion of the effluents from the first reactor 53 of the first treatment unit 52. This reactor allows the neutralization of hydrogen sulfide H2S according to the following reaction: H2S + OH = HS + H2O. With the addition of NaCIO from the first treatment unit 52, this reaction can be completed according to the following reaction: HS + 4C1O = SO< + H+ + 4 Cl, which gives the following overall formula: H2S + 2OH + 4C1O = SOr + 4C1 + H2O.

[0105] At the outlet of the first and second treatment units 52, 62, the first and second suction lines 50, 60 merge into a common suction line connected to a common suction pump 59. In the present example, the first and second suction lines 50, 60 are configured to each have a flow rate of treated gas Ga', respectively Gb', of the order of 10 1 / min.

[0106] The treated gases on the anode side Ga' and the treated gases on the cathode side Gb' thus mix and are sent to the ventilation line 70. In the present example, the suction pump 59 is an explosion-proof type vacuum pump, i.e. complying with ATEX standards.

[0107] The ventilation line 70 comprises a plurality of suction vents 71, provided in the premises of the installation 1, connected to a ventilation device 72, here a fan. The outlet of the suction pump 59 is then connected downstream of the ventilation device 73 so as to dilute the treated gases Ga' and Gb' in the air taken from the premises by the suction vents 71. In this way, the dangerous gases which could not be chemically neutralized, such as methane CH4, carbon monoxide CO and dihydrogen H2j, are sufficiently diluted to present an acceptable level of danger. In addition, preferably, the outlet vent 73 of the ventilation line 70 opens outside the premises, preferably into the open air. The ventilation line 70 is sized to ensure a renewal rate vely greater than 8, that is to say capable of sucking 8 times the volume of the room in one hour. In the present example, the ventilation line 70 ensures a flow rate of 1500 m3 / h, which makes it possible to ensure a dilution factor of the treated gases Ga', Gb' of approximately 1250.

[0108] The operation of the dehydration plant will now be described in detail.

[0109] In the context of the present example, the sludge to be treated B is a digested sludge.

[0110] Mud B, the initial dryness of which is approximately 2% in this example, i.e. 20 g / L, is admitted into the filter press 20 using the feed pump 12 and fed into the filtration chambers 22 of the filter press 20 via the feed channel 41 and the feed passages 31. This sludge B may have undergone a prior chemical conditioning step during which certain chemical components are added to the sludge B in order to facilitate its treatment and dehydration: thus, in this example, a coagulation adjuvant Al, such as A12O3, and a flocculation adjuvant A2, such as the polymer Hydrex 6588, are added.

[0111] Then, during a filtration step, the booster pump 10 generates a mechanical pressure of 8 bar within the sludge B which is then filtered using the filter cloths 24. This step stops when the filtrate flow rate Fa, Fb discharged by the plates 21a, 21b reaches a predetermined low threshold. This step makes it possible to eliminate the free water present on the surface of the sludge flocs with less energy expenditure.

[0112] Once the sludge B has been filtered in the chambers 22 of the filter press 20, a single compression step is carried out within the filter press 20. The pressurized water supply 14 thus makes it possible to inflate the membranes 26 of the filter press 20 so as to compress the sludge B present in the chambers 22 until a pressure in the membranes 26 of the plate 21b of approximately 13 to 16 bar is reached.

[0113] This compression step alone makes it possible to extract a first part of the interstitial water present in the sludge B in the form of filtrates Fa, Fb evacuated through the evacuation orifices 32a, 32b of the plates 21a, 21b.

[0114] At the end of this compression-only step, the compression is maintained and the electrical assistance is triggered in order to initiate an electro-dehydration step.

[0115] The electrical rectifier 13 then imposes a current between the pairs of electrodes 23a, 23b of each chamber 22. Initially, the regulation is carried out at constant current. In this example, the current density is between 26 and 29 A / m2.

[0116] During this step, the water extracted from the sludge B is discharged in the form of filtrates Fa, Fb through the discharge orifices 32a, 32b of the plates 21a, 21b. Due to the electrolysis reactions taking place at each electrode, the anode-side filtrates Fa have an acidic pH, typically between 0.5 and 3, while the cathode-side filtrates Fb have a basic pH, typically between 11 and 14.

[0117] Furthermore, this step leads to the formation of Ga gas at the anodes 23a and Gb gas at the cathodes 23b. In particular, the electrolysis of water leads to the formation of oxygen O2 at the anode and hydrogen H2 at the cathode. In addition, depending on the chemical elements present in the sludge B, other electrolysis reactions can lead to the formation of other gaseous species, in particular dichlorine Cl2 and carbon monoxide CO at the anode and ammonia NH3, methane CH4, carbon monoxide CO and hydrogen sulfide H2S at the cathode.

[0118] However, these gases Ga and Gb are sucked respectively into the first suction line 50 and into the second suction line 60, by the suction orifices 33a, 33b of the plates 21a, 21b thanks to the depression caused by the suction pump 59.

[0119] The gases Ga, Gb thus sucked then each pass through their respective treatment unit 52, 62 and are then diluted in the ventilation line 70 before being discharged outside through the mouth 73.

[0120] The constant current regulation is maintained until the temperature near an anode 23a, measured using a thermocouple for example, reaches a first threshold value: when this condition is met, the current regulation is abandoned in favor of constant voltage regulation.

[0121] The constant voltage electrical assistance is then maintained until the temperature near an anode 23a reaches a second threshold temperature: when this condition is met, the electrical treatment is stopped and the compression of the membranes 25 is released.

[0122] The hydraulic cylinder 29 can then release the plates 21a, 21b of the filter press 20 so as to be able to remove the dehydrated mud cakes from the chambers 22 of the filter press 20.

[0123] These cakes can then be stored, or used as organic amendment or energy.

[0124] To ascertain the effectiveness of this device, the inventors carried out a series of measurements in the operating room, i.e. the room where the dehydration installation 1 is located. The measurement results are compared with the UK EH40 / 2005 Workplace Exposure Limit standard to assess the working conditions of the operator.

[0125] Table 1 below shows, over time, the average values ​​over three series of gas measurements during a cycle of application of the electrodes in the operating room and compares these with those of the short-term Exposure Limit (15 minutes) for chlorine and the Long-term Exposure Limit (8 hours) for the other gases.

[0126] [Tables 1] Time (min) 10 20 30 40 50 60 70 80 UK value EH 40 / 2005 Cl2 (ppm) 0.0 0.0 0.0 0.2 0.1 0.0 0.0 0.1 0.5 CO (PPm) 0 0 0 0 2.3 0 0 0.1 20 h2s (ppm) 0 0 0 0 0 0 0 0 5 nh3 (ppm) 0 0 0 0 0 0 0 0 25

[0127] We therefore note that the regulatory working conditions are well respected because the concentration of each gas in the room is lower than the standard.

[0128] [Fig.5] shows the evolution of the concentration of chlorine gas Cl2 during a cycle of application of the electric field (average value of 4 series of tests), represented by curve 81, and the evolution of the chlorine elimination efficiency during this same cycle, represented by curve 82. The initial concentration of chlorine gas Cl2, measured at the inlet of the treatment unit 52, was equal to 49.9 mg / m3.

[0129] It is thus noted that the removal efficiency of chlorine Cl2 is greater than 90% at the outlet of the treatment unit 52, that is to say at the outlet of the two reactors 53, 54 in series. The slight increase in the concentration of chlorine C12 over time is explained by the consumption of a portion of the reagents in the reactors 53, 54 during the tests. However, this effect can be countered by renewing the reactive liquid 53a, 54a of the reactors 53a, 54.

[0130] Concerning hydrogen sulfide H2S and ammonia NH3, their concentrations are much lower: they are in fact below the detection threshold of the measuring instrument, i.e. less than 1 mg / m3.

[0131] For gases that cannot be chemically treated, such as methane CH4, carbon monoxide CO and dihydrogen H2, Table 2 below shows the concentrations measured after mixing in ventilation line 70 (averaged over nine test series) and compares these concentrations with the flammability thresholds.

[0132] [Tables2] Gas CO h2 ch4 Average concentration (%vol) <0.02 <0.01 0.65 Minimum flammability threshold (%vol) 12 4 4.4

[0133] Table 2 above shows that the gas concentrations are all below the flammability thresholds: the safety standard is therefore respected.

[0134] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0135] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. Sludge dewatering installation, comprising a sludge dewatering device (20), comprising at least one first tray (21a), provided with a first electrode (23a), and at least one second tray (21b), provided with a second electrode, and at least one suction line (50, 60), in which the first and second trays (21a, 21b) define a chamber (22) configured to receive a sludge to be dewatered (B), in which the first and second electrodes (23a, 23b) are configured to set up an electric field within the chamber (22), in which the chamber (22) is provided with at least one discharge orifice (32a, 32b), provided in the lower third of the chamber (22), configured to discharge a filtrate (Fa, Fb), in which the chamber (22) is provided with at least one suction orifice (33a, 33b), provided in the upper third of the chamber (22), connected to said at least one suction line (50, 60),and wherein said at least one suction line (50, 60) comprises at least one pump (59) and at least one gas treatment unit (52, 62).,

2. Installation according to claim 1, in which the surface of at least one tray (21a, 21b) comprises reliefs (25a, 26a) forming flow channels.

3. Installation according to claim 1 or 2, wherein each tray (21a, 21b) is provided with at least one discharge orifice (32a, 32b), and wherein said at least one discharge orifice (32a) of the first tray (21a) is connected to a first discharge channel (42), configured to discharge a first filtrate (Fa), and said at least one discharge orifice (32b) of the second tray (21b) is connected to a second discharge channel (43), distinct from the first discharge channel (42) and configured to discharge a second filtrate (Fb).

4. Installation according to any one of claims 1 to 3, in which each tray (21a, 21b) is provided with at least one suction orifice (33a, 33b), in which said at least one suction orifice (33a) of the first tray (21a) is connected to said at least one suction line, constituting a first suction line (50), and said at least one suction port (33b) of the second plate (21b) is connected to a second suction line (60), distinct from the first suction line (50), and wherein said at least one gas treatment unit of the first suction line constitutes a first gas treatment unit (52) and said second suction line (60) comprises a second gas treatment unit (62).

5. Installation according to any one of claims 1 to 4, in which at least one gas treatment unit (52, 62) comprises at least one reactor (53, 54, 63, 64), in which at least one reactor (53, 54, 63, 64) comprises a closed enclosure, a reactive liquid (53a, 54a, 63a, 64a), a gas inlet (53c, 54c, 63c, 64c) opening into the reactive liquid (53a, 54a, 63a, 64a) and a gas outlet (53d, 54d, 63d, 64d) arranged above the level of the reactive liquid (53a, 54a, 63a, 64a), and in which at least one reactor (53, 54, 63, 64) comprises solid media (53b, 54b, 63b, 64b) suspended in the reactive liquid (53a, 54a, 63a, 64a).

6. An installation according to claim 5, wherein the solid media (53b, 54b, 63b, 64b) have a divided structure, preferably comprising a plurality of through passages.

7. Installation according to claim 4 and any one of claims 5 and 6, in which the first gas treatment unit (52) comprises a first reactor (53), including a basic liquid, and a second reactor (54), arranged downstream of the first reactor (53), including a basic liquid.

8. Installation according to claim 4 and any one of claims 5 to 7, in which the second gas treatment unit (62) comprises a first reactor (63), including an acidic liquid, and a second reactor (64), arranged downstream of the first reactor, including a basic liquid.

9. Installation according to claim 7 or 8, in which at least one basic liquid comprises at least a part of a filtrate (Fb) of the dehydration device (20).

10. Installation according to any one of claims 7 to 9, in which at least one acidic liquid comprises at least a part of a filtrate (Fa) of the dehydration device (20).

11. Installation according to claim 4 and any one of the re- indications 5 to 10, in which at least one reactor (64) of the gas treatment unit (62) of one of the suction lines (60) is supplied with a liquid from a reactor (53) of the gas treatment unit (52) of the other of the suction lines (50).

12. Installation according to claim 4 and any one of claims 4 to 11, in which the second suction line (60) joins, downstream of its gas treatment unit (62), the first suction line (50), downstream of its gas treatment unit (52), and in which the pump (59) of the first suction line (50) is arranged downstream of the junction with the second suction line (60).

13. Installation according to any one of claims 1 to 12, comprising a ventilation line (70) including a ventilation device (72), in which said at least one suction line (50, 60) opens into the ventilation line (70) downstream of the ventilation device (72).

14. Installation according to claim 13, in which the ventilation line (70) is configured to dilute the gases from said suction line (50, 60) in the air flow driven by the ventilation device (72) with a dilution factor of at least 100, preferably at least 500, more preferably at least 1000.

15. A method of dewatering sludge, using an installation (1) according to any one of the preceding claims, comprising the following steps: - admission of a sludge (B) into the chamber (22) of the dewatering device (20), - establishment of an electric field within the chamber (22), - evacuation of a filtrate (Fa, Fb) via said at least one evacuation orifice (32a, 32b), - suction in said at least one suction line (50, 60) of gases (Ga, Gb) produced in the chamber (22), and - treatment of said gases (Ga, Gb) in said at least one gas treatment unit (52, 62).

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