Sludge dewatering facility and method

Abstract

The present invention relates to a sludge dewatering facility and a sludge dewatering method using such a facility, the facility comprising a sludge dewatering device (20) and at least one suction line (50, 60), wherein first and second plates (21a, 21b) of the sludge dewatering device (20) define a chamber configured to receive sludge (B) to be dewatered, wherein first and second electrodes are configured to establish an electric field in the chamber, wherein the chamber is provided with at least one discharge port configured to discharge filtrate (Fa, Fb), wherein the chamber is provided with at least one suction port connected to the at least one suction line (50, 60), and wherein the at least one suction line (50, 60) includes at least one pump (59) and at least one gas treatment unit (52, 62).

Description

Technical Field

[0001] This invention relates to a sludge dewatering facility and a sludge dewatering method using such a facility. These methods allow for high dryness levels while maintaining limited energy consumption and industrial risk. In particular, such a system can be used to dewater sludge, such as sludge from wastewater treatment plants, for incineration or landfill purposes. Background Technology

[0002] Sludge, such as that from wastewater treatment plants, is typically dewatered and then reused as an organic amendment (spreading), incinerated, or disposed of in landfills. In the case of incineration, the sludge dryness level achieved at the end of the dewatering step (i.e., the ratio of dry matter to total sludge mass) must be sufficient to allow for self-sustaining combustion: therefore, a dryness level of 30 to 45% is preferred. Similarly, in the case of landfilling, some national regulations require a minimum dryness level of the sludge before it is landfilled, for example, around 40%. Therefore, it is clear why developing effective dewatering methods and equipment is important, especially when sludge is difficult to dewater, such as biological sludge typically from wastewater treatment plants.

[0003] Among known methods, some aim to mechanically dewater sludge: these can include centrifugation or pressure filtration, particularly using filter presses or belt filters. However, such methods have limitations. For example, sewage sludge only achieves a dryness level of 15 to 40%; the maximum of 40% is only achieved in very rare cases, using particularly efficient equipment and particularly easy-to-handle sludge (e.g., predominantly mineral-rich). Therefore, for some sludge, such as biological sewage sludge, achieving a dry solids content of 30% may be insufficient depending on the intended use of the sludge.

[0004] Other methods aim to thermally dewater the sludge: this involves heating the sludge to dry it. These methods are very efficient: depending on the heating temperature and treatment duration, a dryness level of approximately 90% can be achieved. However, these methods are very energy-intensive, consuming at least 700 kWh (kWh / tWR) per tonne of water removed, or even more in some cases, while mechanical methods typically consume less than 20 kWh / tWR, depending on the type of technology (filter press, belt filter, or centrifuge).

[0005] Finally, the purpose of electro-assisted mechanical dewatering methods (referred to as electro-dewatering methods) is to filter a volume of sludge under pressure, such as in a filter press, while simultaneously applying an electric field. This field, combined with the hydrolysis it creates, disrupts the water-sludge bond, allowing water molecules to migrate in the opposite direction to the solid particles. Therefore, this electro-assisted method improves sludge dewatering and increases dryness by several percentage points. Specifically, this electro-dewatering device is described in document FR3042186. However, this method encounters certain difficulties when processing some types of sludge.

[0006] Specifically, under the influence of an applied electric field, the hydrolysis reaction of water in the sludge is responsible for producing hydrogen (H2) at the cathode and oxygen (O2) at the anode. Therefore, the simultaneous presence of these two gases in an electrostatic dewatering unit can lead to the formation of an explosive atmosphere. Furthermore, depending on the properties of the sludge to be dewatered, other electrolytic reactions may occur, potentially leading to the formation of harmful, toxic, explosive, or corrosive gases, such as chlorine (Cl2), when the sludge contains chlorides. To remove these various harmful gases, document FR3042186 proposes injecting a purge fluid into the chamber of the electrostatic dewatering unit to force the generated gases toward the filtrate discharge port.

[0007] However, this solution merely diverts the problem by pumping the harmful gases further downstream into the filtrate recovery channel. Therefore, while this solution is satisfactory for small dehydration units, it remains insufficient for large dehydration units that generate large amounts of harmful gases.

[0008] Therefore, there is indeed a need for a sludge dewatering facility and method that does not at least partially lack the inherent disadvantages of the aforementioned known constructions. Summary of the Invention

[0009] This disclosure relates to a sludge dewatering facility, including a sludge dewatering device comprising a filter press having at least one first plate with a first electrode and at least one second plate with a second electrode.

[0010] At least one suction line, First and second plates define a chamber configured to receive sludge to be dewatered. First and second electrodes are configured to establish an electric field within the chamber. The chamber has at least one discharge port located in the lower third of the chamber and configured to discharge filtrate. The chamber also has at least one suction port located in the upper third of the chamber, connected to the at least one suction line, and the at least one suction line includes at least one pump and at least one gas treatment unit, which includes at least one reactor. At least one reactor includes a closed shell configured to contain a reactive liquid, the closed shell being equipped on one hand with a gas inlet configured to open inside the closed shell, particularly into the reactive liquid, and on the other hand with a gas outlet disposed above the gas inlet, particularly above the liquid level of the reactive liquid. The closed shell is constructed to include a solid medium suspended in a reactive liquid.

[0011] Therefore, due to this configuration, at least one pump generates a vacuum in at least one suction line to allow any harmful gases generated in the chamber to be drawn into a dedicated line. This facilitates the venting of these gases and reduces the risk of their accumulation within the chamber. Thus, the system's durability is maintained, and the operator's working environment is less hazardous. Preferably, at least one pump is located downstream of the gas processing unit to ensure that the gas to be treated is effectively drawn into the closed housing for processing, subsequently effectively extracted from the housing for venting, and, if necessary, delivered to a specific location. The gas processed in the gas processing unit is not stored therein. A pump upstream of the gas processing unit would not be effective for the above configuration.

[0012] Furthermore, because it is a dedicated suction line, harmful gases do not mix with, or barely mix with, the filtrate, which is discharged via a separate exhaust line connected to at least one exhaust outlet. This facilitates any subsequent treatment of the filtrate while reducing hazards in the working environment downstream of the dehydration unit.

[0013] Furthermore, because hazardous gases are drawn into dedicated pipelines, they can be treated at the gas handling unit to neutralize them, or at least reduce their hazard. Therefore, the overall level of danger in the working environment is reduced for the operator. Where appropriate, gaseous byproducts can even be recovered.

[0014] Due to the reactor configuration described above (a closed shell with a gas inlet and outlet), the gas to be treated is forced to pass through a reactive liquid contained within the closed shell, which is designed to neutralize or at least reduce the harmful properties of the gas. Preferably, the gas inlet is located at the bottom of the reactor; preferably, the gas outlet is located at the top. The treated gas inside the shell is then discharged to the outside of the shell.

[0015] Therefore, this device is particularly effective in the context of electro-dehydration methods, such as those described in document FR3042186.

[0016] In some embodiments, at least one plate is provided with a filter medium. This filter retains solids from the sludge while allowing water extracted from the sludge to pass through. Preferably, each plate is provided with a filter medium. This can particularly be a filter cloth.

[0017] In some embodiments, at least one plate is provided with at least one membrane, which is configured to deform by a compressed fluid, particularly compressed air or pressurized water. This membrane reduces the volume of the chamber and thus compresses the sludge present in the chamber to mechanically extract some of the water contained in the sludge. Each plate may be provided with such a membrane, but preferably, only one plate is provided per chamber, preferably a plate with a cathode.

[0018] In some embodiments, the facility includes a blower configured to supply compressed air to the membrane.

[0019] In some embodiments, the facility includes a pressurized water source configured to supply pressurized water to the membrane.

[0020] In some embodiments, the surface of at least one plate includes raised features forming flow channels. These features may, in particular, be in the form of grooves; they are preferably located in front of the membrane but behind the respective electrodes. These flow channels facilitate the downward discharge of filtrate by gravity and the upward discharge of gas by suction.

[0021] In some embodiments, the facility includes a power source, such as a generator, rectifier, or battery, configured to supply power to the first and second electrodes.

[0022] In some embodiments, the device includes a hydraulic cylinder configured to keep the first and second plates abutting each other and thus ensure the sealing of the chamber.

[0023] In some embodiments, the device includes a plurality of first plates and a plurality of second plates.

[0024] In some embodiments, the at least one discharge port is located at the lower end of the filter chamber.

[0025] In some embodiments, each plate is provided with at least one discharge port. The presence of discharge ports on each side of the chamber facilitates the removal of filtrate.

[0026] In some embodiments, at least one discharge port of the first plate is connected to a first discharge channel configured to discharge a first filtrate, and at least one discharge port of the second plate is connected to a second discharge channel, which is separate from the first discharge channel and configured to discharge a second filtrate. This allows the filtrate collected at the anode to be separated from the filtrate collected at the cathode, since the two filtrates do not have the same chemical composition, particularly the same pH.

[0027] In some embodiments, the at least one suction port is located at the upper end of the filter chamber.

[0028] In some embodiments, each plate is provided with at least one suction port. This makes it easier to discharge the generated gas using exhaust ports located on each side of the chamber.

[0029] In some embodiments, at least one suction port of the first plate is connected to at least one suction line constituting the first suction line, and at least one suction port of the second plate is connected to a second suction line separate from the first suction line. This allows the gas generated at the anode to be separated from the gas generated at the cathode, since these different gases do not have the same chemical composition, especially the same pH. This is particularly useful when certain gases, if mixed, would produce an explosive atmosphere.

[0030] In some embodiments, at least one gas processing unit of the first suction line constitutes a first gas processing unit, and the second suction line includes a second gas processing unit. This allows for the differentiated processing of these different gases, taking into account their expected chemical composition.

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

[0032] In some embodiments, at least one reactor includes a liquid inlet and a liquid outlet leading to the outer shell, preferably arranged below the level of the reactive liquid. This allows the reactive liquid to be replenished, enabling it to continue reacting with the gas passing through the reactor over time. Preferably, the liquid inlet is located at the top of the reactor; preferably, the liquid outlet is located at the bottom of the reactor.

[0033] In some embodiments, at least one reactor comprises a solid medium suspended in a reactive liquid. This medium slows the upward flow of gas within the reactive liquid, thus increasing the contact time between the gas and the reactive liquid, and consequently increasing the amount of gas actually processed. Furthermore, the medium can be programmed to move, including rotate, during gas passage.

[0034] In some embodiments, the total volume occupied by the medium is 20 to 70%, preferably 25 to 55%, of the reactor fill volume. The term "total volume occupied by the medium" refers to the total volume occupied by the medium when it is poured into the container in bulk; it is not the inherent volume of the medium; rather, this total occupied volume includes the volume of air, or, where applicable, the volume of the reactive liquid between and within each medium when reactivity is present in a liquid reactor. The term "reactor fill volume" refers herein to the volume of the reactive liquid including the suspended medium. This volume range represents a good trade-off, effectively slowing gas flow while allowing sufficient medium mobility within the reactive liquid to ensure proper agitation.

[0035] In some embodiments, the solid medium has a partition structure, preferably comprising multiple throughpasses. These passages may, in particular, be parallel. This partition structure increases the contact surface between the gas and the liquid and further slows down the gas flow (to increase the gas handling time within the closed housing), as bubbles can be temporarily retained by adsorption onto the medium walls, especially in the throughpasses.

[0036] In some embodiments, the solid medium is a support for a moving bed biofilm reactor (MBBR) type, preferably type K3 or K5.

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

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

[0039] In some embodiments, at least some, preferably all, of the solid media are made of plastic materials, such as polyethylene.

[0040] In some embodiments, the first gas processing unit includes at least one reactor comprising a base liquid. This is particularly suitable for neutralizing chlorine (Cl2) and hydrogen sulfide (H2S).

[0041] In some embodiments, the first gas processing unit includes a first reactor containing an alkaline liquid and a second reactor containing an alkaline liquid disposed downstream of the first reactor. The sequence of the two reactors increases the amount of neutralized gas; it also allows the use of two different reactive liquids with different chemical compositions and / or concentrations.

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

[0043] In some embodiments, the second gas treatment unit includes at least one reactor containing an alkaline liquid. This is particularly suitable for neutralizing chlorine (Cl2) and hydrogen sulfide (H2S).

[0044] In some embodiments, the second gas treatment unit includes a first reactor containing an acidic liquid and a second reactor, the second reactor being arranged downstream of the first reactor and containing an alkaline liquid. Performing alkaline treatment after acid treatment allows for the treatment of gases with different properties present in the same suction line.

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

[0046] In some embodiments, at least one alkaline liquid comprises at least a portion of the filtrate from the dehydration unit, preferably at least a portion of the second filtrate. This configuration provides the advantage of recovering at least some of the filtrate.

[0047] In some embodiments, at least one acidic liquid has a pH of 0.5 to 3, preferably 0.5 to 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 the filtrate from the dehydration unit, preferably at least a portion of the first filtrate. This configuration provides the advantage of recovering at least some of the filtrate.

[0050] In some embodiments, liquid from a reactor in a gas processing unit of another suction line is supplied to at least one reactor in a gas processing unit of one of the suction lines. This configuration provides the advantage of recovering effluent from at least one reactor.

[0051] In some embodiments, at least one suction line, preferably each suction line, includes a control valve downstream of the gas treatment unit of the suction line. This control valve allows control of the outlet flow rate of the treated gas in the gas treatment unit, and thus control of the residual concentration of harmful gases.

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

[0053] In some embodiments, the second suction line engages downstream of the first suction line in the gas processing unit.

[0054] In some embodiments, at least one pump is a vacuum pump. It may specifically comply with ATEX standards related to explosive atmospheres.

[0055] In some embodiments, the at least one pump of the at least one suction line is located downstream of the at least one gas processing unit of the at least one suction line.

[0056] In some embodiments, the pump for the first suction line is located downstream of the junction with the second suction line. Therefore, particularly for energy efficiency and architectural simplification, the two suction lines can use a single, shared pump.

[0057] In some embodiments, a pump is disposed on each suction line, particularly downstream of the at least one gas processing unit on the at least one suction line.

[0058] In some embodiments, the facility includes a ventilation duct with a ventilation device, wherein the at least one suction duct leads to a ventilation duct downstream of the ventilation device. This ventilation duct allows dilution of the suction duct outlet to reduce its residual hazard, particularly when certain gases cannot be chemically treated in the gas handling unit. Therefore, the treated air-gas mixture limits flammable or explosive gases below flammable or explosive thresholds, thereby ensuring the safety of the facility.

[0059] In some embodiments, the ventilation duct is configured to dilute the gas from the suction duct in an airflow driven by the ventilation device with a dilution factor of at least 100, preferably at least 500, more preferably at least 1000, and possibly at least 1500. However, preferably, the dilution factor is between 1000 and 1500, more preferably between 1200 and 1300.

[0060] In some embodiments, the ventilation ductwork includes at least one suction outlet located in a room within the facility. This allows potentially contaminated air to be exhausted from the room, particularly when it contains a proportion of harmful gases originating from the facility.

[0061] In some embodiments, the ventilation duct includes an outlet opening outside the room in the facility. This removes any remaining harmful gases from the room.

[0062] In some embodiments, the facility includes a reinjection device configured to reinject at least a portion of at least one type of filtrate into the sludge, for example, upstream of the chamber or directly into the chamber. This allows for the recovery of some of the injected electrolytes. It also helps to lower the pH in the chamber.

[0063] In some embodiments, the sludge to be dewatered is biological sludge from a wastewater treatment plant. This type of sludge particularly contains a high proportion of bound water. However, this specification can naturally be applied to other types of sludge, especially industrial sludge.

[0064] This disclosure also relates to a sludge dewatering method using the facility according to any one of the foregoing embodiments, comprising the following steps: - Allow sludge to enter the chamber of the dewatering unit. - Establish an electric field within the cavity. - Discharge the filtrate via the at least one discharge port. - The gas generated in the chamber will be drawn into at least one suction line. - By introducing the gas to be treated into the closed shell of the at least one reactor, the gas is treated in the at least one gas processing unit within a reactive liquid containing a solid medium suspended in the reactive liquid, and - The gas treated in this way is discharged from the closed shell of the at least one reactor.

[0065] The characteristics of the various embodiments of the facility briefly described above also apply to the methods described above, and will not be repeated. The above-described characteristics and advantages, as well as other characteristics and advantages, will become apparent from the following detailed description of illustrative embodiments of the proposed facility and methods. This detailed description refers to the accompanying drawings. Attached Figure Description

[0066] The accompanying drawings are schematic and are primarily intended to illustrate the principles of this disclosure.

[0067] In these figures, the same elements (or parts of elements) are identified by the same reference numerals from one figure to the next. Furthermore, elements (or parts of elements) belonging to different embodiments but having similar functions are identified by reference numerals incremented by 100, 200, etc.

[0068] [ Figure 1 ] Figure 1 This is an illustration of an exemplary facility.

[0069] [ Figure 2 ] Figure 2 It shows Figure 1 The dehydration module of the facility.

[0070] [ Figure 3 ] Figure 3 yes Figure 1 A side view of the anode plate of the facility.

[0071] [ Figure 4 ] Figure 4 yes Figure 1A cathode side view of the facility's plate.

[0072] [ Figure 5 ] Figure 5 yes Figure 1 A diagram of the processing unit of the facility.

[0073] [ Figure 6 ] Figure 6 This is a photograph of the first example of a solid medium.

[0074] [ Figure 7 ] Figure 7 This is a photograph of a second example of a solid medium.

[0075] [ Figure 8 ] Figure 8 It means Figure 1 A graph showing the evolution of Cl2 concentration at the outlet of the treatment unit in the facility. Detailed Implementation

[0076] To make the explanation more concrete, an example of the facility is described in detail below with reference to the accompanying drawings. It should be noted that the invention is not limited to this example.

[0077] Figure 1 An example of a dewatering facility 1 according to the present invention is shown. The facility 1 includes a sludge supply line 10, a filter press 20, a power supply 13, a pressurized water source 14, a first suction line 50, a second suction line 60, and a ventilation line 70.

[0078] The sludge supply line 10 includes a conditioning tank 11 that receives the sludge B to be dewatered as input. Additives including flocculant A1 and coagulant A2 are added to the conditioning tank 11. A portion of the filtrate recovered from the filter press 20, particularly the filtrate from the anode side Fa, can also be injected into the conditioning tank 11. The conditioning tank 11 includes an agitator driven by an electric motor. The outlet of the conditioning tank 11 is connected to a supply pump 12 to supply the sludge B to be dewatered to the filter press 20.

[0079] The filter press 20 includes multiple modules 20a, which consist of plates 21a and 21b pressed together by hydraulic cylinders 29 to ensure a seal between the different plates 21a and 21b.

[0080] Figure 2 Module 20a is schematically shown. It includes three plates 21a and 21b that define two chambers 22 into which sludge B to be dewatered is introduced. Each wall of the plates 21a and 21b defining the edges of the chambers 22 is provided with electrodes 23a and 23b, preferably in the form of a grid: thus, the side plate 21a is provided with electrodes forming anodes 23a, and the central plate 21b is provided with electrodes forming cathodes 23b on each of its surfaces. Figure 2 The side plate 21a shown has only one working surface, that is, only one surface that connects to the chamber 22 and is equipped with the electrode 23a. In fact, Figure 2 Only one module, 20a, is shown. However, as... Figure 1 As can be seen, when the filter press 20 includes several modules 20a, for the sake of compactness, the plate referred to as the side plate 21a may include two active faces, and each face is then constructed in the manner described below.

[0081] Each plate 21a, 21b has a filter cloth 24 positioned in front of the electrodes 23a, 23b on its inner wall. The main surface 25 of each side plate 21a defining a first side edge of the chamber 22 has a groove 25a, with the electrode 23a located in front of these grooves 25a. Each center plate 21b has a deformable membrane 26 on each of its surfaces, positioned behind the electrode 23b and defining a second side edge of the chamber 22; the membrane 26 also has grooves 26a on the side of the chamber 22.

[0082] Membrane 26 can be expanded using pressurized water supplied from pressurized water source 14 to reduce the volume of chamber 22 and thus increase the pressure applied to sludge B to help drain water present in sludge B.

[0083] Figure 3 The side plate 21a located at the front when viewed from the considered chamber 22 is now shown; Figure 4 Also shown is the central plate 21b located in front when viewed from the same chamber 22.

[0084] Each side plate 21a and center plate 21b includes conduit segments 41, 42, 43, and 44, which are configured to be aligned with each other in the stacking direction from one plate to another so as to form a continuous and sealed conduit through the filter press 20 from one end to the other in the stacking direction when the plates 21a and 21b are pressed against each other.

[0085] Therefore, each plate 21a, 21b includes a first conduit section 41 in the first upper corner, which, once assembled, forms a first conduit constituting a mud supply channel connected to the supply pump 12.

[0086] Each plate 21a, 21b also includes a second conduit section 42 in the first lower corner, which, when assembled, forms a second conduit constituting a first channel for discharging filtrate.

[0087] Each plate 21a, 21b also includes a third conduit 43 portion at the second lower corner, which, when assembled, forms a third conduit constituting a second channel for discharging filtrate.

[0088] Each plate 21a, 21b also includes a fourth conduit section 44 in the second upper corner, which, when assembled, forms a fourth conduit section constituting a gas communication channel.

[0089] Subsequently, each side plate 21a is provided with a sludge supply channel 31 connected to its first conduit section 41. Each center plate 21b also has a sludge supply channel 31 connected to its first conduit section 41. These sludge supply channels 31 thus allow sludge B to enter each chamber 22 of the filter press 20.

[0090] Each side plate 21a is also equipped with multiple discharge ports 32a at the lower end of the chamber 22. These discharge ports are connected to its second conduit section 42 to allow filtrate to be discharged from the anode side Fa. Similarly, each center plate 21b is also equipped with multiple discharge ports 32b at the lower end of the chamber 22, which are connected to the fourth conduit section 43 to allow filtrate to be discharged from the cathode side Fb. Thus, filtrate is discharged from the anode side Fa and filtrate is discharged from the cathode side Fb, respectively. The presence of grooves 25a and 26a forming circulation channels behind the filter cloth 24 and electrodes 23a, 23b facilitates the flow of filtrate Fa, Fb to the discharge ports 32a, 32b.

[0091] At the upper end of chamber 22, each side plate 21a is also equipped with multiple suction ports 33a, which are connected to suction pipes 34a to allow gas to be discharged from the anode side (Ga). Similarly, each center plate 21b at the upper end of chamber 22 is also equipped with multiple suction ports 33b, which are connected to suction pipes 34b and the fourth conduit section 44 to allow gas to be discharged from the cathode side (Gb). Thus, gas is discharged from both the anode side (Ga) and the cathode side (Gb). The presence of grooves 25a and 26a forming circulation channels behind filter cloth 24 and electrodes 23a, 23b facilitates the flow of gas Ga and Gb toward suction ports 33a, 33b. In particular, these circulation channels are located behind filter cloth 24 and electrodes 23a, 23b, and they can be maintained under negative pressure relative to sludge B by suction pump 59 (described below), which promotes the extraction of gas Ga and Gb.

[0092] The suction pipes 34a (anode side) of side plate 21a are all connected to the suction pipe 51 of the first suction line 50. This suction pipe 51 leads downstream to the first gas processing unit 52. Similarly, the suction pipes 34b (cathode side) of center plate 21b are all connected to the suction pipe 61 of the second suction line 60. This suction pipe 61 leads downstream to the second gas processing unit 62.

[0093] Now refer to Figure 5 These gas processing units 52 and 62 are described.

[0094] The first gas processing unit 52 includes a first reactor 53 and a second reactor 54 connected in series. Each reactor 53, 54 is in the form of a closed shell, containing reactive liquids 53a, 54a and solid media 53b, 54b suspended in the reactive liquids 53a, 54a. The gas to be treated is introduced into the shell through gas inlets 53c, 54c that open at the bottom of the shell. It passes through the reactive liquids 53a, 54a and exits through gas outlets 53d, 54d located at the top of the shell (discharging the treated gas from the shell). In this embodiment, for each reactor 53, 54, the volume of the shell of the reactor 53, 54 is equal to 2L; the filling volume corresponding to the volume of the reactive liquids 53a, 54a including the suspended media 53b, 54b is approximately 90% of the volume of the shell of the reactor 53, 54, that is, 1.8L; and the total volume occupied by the media 53b, 54b accounts for approximately 30% of the filling volume, that is, approximately 0.5L.

[0095] Figure 6 A first example of a medium 91 suitable for use in one or both of these reactors 53 and 54 is shown. This first example of medium 91 is generally referred to as K3. These media have a central axis constituting a sixth-order axis of symmetry; their cross-sectional profile is constant along this central axis. They comprise 19 axial channels distributed as a central channel and two concentric rings. They have a diameter of 25 mm and a thickness of 10-12 mm: they provide a total contact surface area greater than 500 square meters per cubic meter of medium. They are preferably made of polyethylene, and their density is between 0.95 and 0.98.

[0096] Figure 7 A second embodiment of medium 92, which can be used in any of these reactors 53 and 54, is shown, optionally mixed with the first embodiment of medium 91. This second example of medium 92 is generally referred to as K5. These media have a central axis constituting a fourth-order axis of symmetry; their cross-sectional profile is constant along this central axis. They comprise 64 axial channels arranged in four concentric rings. They have a diameter of 25 mm and a thickness of 3-4 mm: they provide a total surface area greater than 800 square meters per cubic meter of medium. They are preferably made of polyethylene, and their density is between 0.95 and 0.98.

[0097] The gas on the anode side Ga thus passes through the first reactor 53, then through the second reactor 54, and then through the regulating valve 55 and the flow meter 56. During their passage through the first and second reactors 53 and 54, the gas on the anode side Ga is treated as follows.

[0098] In the first reactor 53, the periodically replenished reactive liquid 53a is an alkaline liquid comprising 15-20% by mass sodium hydroxide (NaOH). This allows for the neutralization of chlorine gas according to the following reaction: Cl2 + 2 NaOH = NaCl + NaClO + H2O.

[0099] In the second reactor 54, the periodically replenished reactive liquid 54a is also an alkaline liquid. It preferably contains 15-20% by mass sodium hydroxide (NaOH) and a portion of the filtrate from the cathode side (Fb). This additional alkalization step completes the neutralization of chlorine gas.

[0100] The second gas processing unit 62 also includes a first reactor 63 and a second reactor 64 connected in series. Similar to the first gas processing unit 52, each reactor 63, 64 is in the form of a closed shell, which includes reactive liquids 63a, 64a and solid media 63b, 64b suspended in the reactive liquids 63a, 64a. The gas to be treated enters through gas inlets 63c, 64c that open at the bottom of the shell, passes through the reactive liquids 63a, 64a, and exits through gas outlets 63d, 64d located at the top of the shell (exhausting the treated gas from the shell). In this embodiment, for each reactor 53, 54, the volume of the shell of reactor 53, 54 is equal to 2L; the filling volume corresponding to the volume of the reactive liquids 53a, 54a including the suspended media 53b, 54b is approximately 90% of the volume of the shell of reactor 53, 54, that is, 1.8L; and the total volume occupied by the media 53b, 54b accounts for approximately 30% of the filling volume, that is, approximately 0.5L. The suspension media 63b and 64b may be the same as or different from those of the first processing unit 52.

[0101] Therefore, the gas on the cathode side Gb passes through the first reactor 63, then through the second reactor 64, and then through the control valve 65 and the flow meter 66. During their passage through the first and second reactors 63 and 64, the gas on the cathode side Gb is processed as follows.

[0102] In the first reactor 63, the periodically updated reactive liquid 63a is an acidic liquid with a pH less than 3; it may include a portion of the filtrate from the anode side Fa. The latter allows for the neutralization of ammonia NH3 according to the following reaction: NH3 + H + = NH4 + .

[0103] In the second reactor 64, the periodically refreshed reactive liquid 64a is an alkaline liquid. It preferably contains sodium hydroxide (NaOH), a portion of the filtrate (Fb) from the cathode side, and / or a portion of the effluent from the first reactor 53 of the first processing unit 52. This reactor allows for the neutralization of hydrogen sulfide (HS) according to the following reaction: H2S + OH - =HS - + H2O. Since NaClO is added from the first processing unit 52, the reaction can be completed according to the following reaction: HS - + 4ClO - = SO4² - + H + + 4Cl - It provides the following formula: H2S + 2OH - + 4ClO -= SO4² - + 4Cl - + H2O.

[0104] At the outlets of the first and second processing units 52, 62, the first and second suction lines 50, 60 are merged into a common suction line connected to a common suction pump 59, which optimizes the energy consumption associated with the gas suction function. In this example, the first and second suction lines 50, 60 are configured to deliver processed gas flow rates Ga', Gb', respectively, of approximately 10 l / min.

[0105] The treated gas on the anode side Ga' and the treated gas on the cathode side Gb' are thus mixed and sent to the ventilation line 70. In this example, the suction pump 59 is an explosion-proof vacuum pump, that is, it conforms to ATEX standards.

[0106] Ventilation duct 70 includes multiple suction inlets 71 located in the room of facility 1, connected to a ventilation device 72, in this case, a fan. The outlet of suction pump 59 is then connected downstream of ventilation device 73 to dilute the treated gases Ga' and Gb' in the air drawn from the room through the suction inlets 71. This ensures that harmful gases that cannot be chemically neutralized (such as methane CH4, carbon monoxide CO, and hydrogen H2) are sufficiently diluted to an acceptable hazardous level. Furthermore, preferably, the outlet 73 of ventilation duct 70 leads to the outside of the room, preferably to outdoor air. The ventilation duct 70 is sized to ensure an air exchange rate greater than 8, meaning it can draw in 8 times the room volume of air per hour. In this example, ventilation duct 70 provides a flow rate of 1500 m³ / h, which ensures a dilution factor of approximately 1250 for the treated gases Ga' and Gb'.

[0107] The operation of the dehydration equipment will now be described in detail.

[0108] In the context of this example, the sludge B to be processed is digested sludge.

[0109] In this example, sludge B with an initial dryness of approximately 2%, or 20 g / L, is allowed to enter the filter press 20 using the feed pump 12 and is supplied to the filter chamber 22 of the filter press 20 via feed channels 41 and 31. The sludge B may undergo a pre-treatment chemical conditioning step, during which certain chemical components are added to the sludge B to facilitate its treatment and dewatering: thus, in this example, a coagulation aid A1 (such as Al2O3) and a flocculant A2 (such as polymer Hydrex 6588) are added.

[0110] Subsequently, in the filtration step, the supply pump 10 generates a mechanical pressure of 8 bar within the sludge B, which is then filtered using filter cloth 24. This step stops when the filtrate flow rates Fa and Fb discharged from plates 21a and 21b reach a predetermined low threshold. This step allows for the removal of free water present on the surface of the sludge flocs with minimal energy consumption.

[0111] Once sludge B has been filtered in chamber 22 of filter press 20, a compression-only step is performed within filter press 20. Pressurized water source 14 thus allows membrane 26 of filter press 20 to expand in order to compress sludge B present in chamber 22 until a pressure of approximately 13 to 16 bar is reached in membrane 26 of plate 21b.

[0112] This compression step allows the extraction of the first portion of interstitial water present in sludge B in the form of filtrate Fa and Fb discharged through the discharge ports 32a and 32B of plates 21a and 21b.

[0113] At the end of the compression step alone, compression is maintained and electric assistance is triggered to begin the electro-dehydration step.

[0114] Subsequently, the rectifier 13 applies a current between the electrode pairs 23a, 23b of each chamber 22. Initially, this is regulated to a constant current. In this example, the current density is between 26 and 29 A / m².

[0115] In this step, water extracted from sludge B is discharged as filtrate Fa and Fb through discharge ports 32a and 32B of plates 21a and 21b. Due to the electrolysis reaction occurring at each electrode, filtrate Fa on the anode side typically has an acidic pH between 0.5 and 3, while filtrate Fb on the cathode side typically has an alkaline pH between 11 and 14.

[0116] Furthermore, this step results in the formation of gaseous Ga at the anode 23a and gaseous Gb at the cathode 23b. Specifically, 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 sludge B, other electrolysis reactions can lead to the formation of other gaseous substances, particularly chlorine (Cl2) and carbon monoxide (CO) at the anode, and ammonia (NH3), methane (CH4), carbon monoxide (CO), and hydrogen sulfide (H2S) at the cathode.

[0117] However, due to the vacuum generated by the suction pump 59, these gases Ga and Gb are drawn into the first suction line 50 and the second suction line 60 through the suction ports 33a and 33b of plates 21a and 21b, respectively.

[0118] The drawn-in gases Ga and Gb pass through their respective processing units 52 and 62, and are then diluted in the ventilation duct 70 before being discharged through the outlet 73.

[0119] Maintain constant current regulation until the temperature near anode 23a, as measured by, for example, a thermocouple, reaches a first threshold: when this condition is met, abandon current regulation to facilitate constant voltage regulation.

[0120] Subsequently, a constant voltage is maintained for electrical assistance until the temperature near the anode 23a reaches the second threshold temperature: when this condition is met, the electrical treatment is stopped and the compression of the membrane 25 is released.

[0121] Subsequently, hydraulic cylinder 29 can release plates 21a and 21b of filter press 20 so that dewatered sludge cake can be removed from chamber 22 of filter press 20.

[0122] These cakes can then be stored or used as an organic amendment or energy source.

[0123] To evaluate the effectiveness of the device, the inventors conducted a series of measurements in the operating room, specifically in the room where the dehydration facility 1 is located. The measurement results were compared with the workplace exposure limits of standard UK EH40 / 2005 to assess the operator's working conditions.

[0124] Table 1 below shows the variation of the average values ​​of three series of gas measurements over time during one application cycle of the electrodes in the operating room, and compares these values ​​with the short-term exposure limit (15 minutes) of chlorine and the long-term exposure limit (8 hours) of the other gases.

[0125] Table 1

[0126] Therefore, it should be noted that the prescribed working conditions were well observed because the concentration of each gas in the room was below the standard.

[0127] Figure 5 The evolution of gaseous chlorine (Cl2) concentration during the cycle with the applied electric field (average of four series of tests) is shown by curve 81, and the evolution of chlorine removal efficiency during the same cycle is shown by curve 82. The initial concentration of gaseous chlorine (Cl2) measured at the inlet of treatment unit 52 was 49.9 mg / m³. 3 .

[0128] Therefore, it should be noted that the chlorine (Cl2) removal efficiency is greater than 90% at the outlet of treatment unit 52 (that is, at the outlets of the two reactors 53 and 54 connected in series). The slight increase in chlorine (Cl2) concentration over time can be explained by the consumption of some reagents in reactors 53 and 54 during the test. However, this effect can be offset by refreshing the reactive liquids 53a and 54a in reactors 53a and 54.

[0129] Regarding hydrogen sulfide (H₂S) and ammonia (NH₃), their concentrations are much lower: they are actually below the detection threshold of the measuring instruments, that is, less than 1 mg / m³. 3 .

[0130] 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 across nine test series), and these concentrations are compared to flammability thresholds.

[0131] Table 2

[0132] Table 2 above shows that all gas concentrations are below the flammability threshold, thus meeting safety standards.

[0133] Although the invention has been described with reference to specific embodiments, it will be apparent that modifications and changes can 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 embodiments shown or mentioned may be combined in additional embodiments. Therefore, the specification and drawings should be regarded as illustrative rather than limiting.

[0134] It is equally evident that all features described in the reference method can be individually or in combination transferred to the apparatus, and conversely, all features described in the reference apparatus can be individually or in combination transferred to the method.

Claims

1. A sludge dewatering facility, comprising a sludge dewatering device (20) including a filter press, said filter press having at least one first plate (21a) provided with a first electrode (23a) and at least one second plate (21b) provided with a second electrode, and At least one suction line (50, 60). The first plate (21a) and the second plate (21b) define a chamber (22) configured to receive sludge (B) to be dewatered. The first electrode (23a) and the second electrode (23b) are configured to establish an electric field within the chamber (22). The chamber (22) is provided with at least one discharge port (32a, 32b), which is located in the lower third of the chamber (22) and is configured to discharge filtrate (Fa, Fb). The chamber (22) is provided with at least one suction port (33a, 33b), which is located in the upper third of the chamber (22) and connected to the at least one suction line (50, 60). The at least one suction line (50, 60) includes at least one pump (59) and at least one gas processing unit (52, 62), the gas processing unit including at least one reactor (53, 54, 63, 64). The at least one reactor (53, 54, 63, 64) includes a closed shell configured to contain a reactive liquid (53a, 54a, 63a, 64a). The closed shell is equipped with gas inlets (53c, 54c, 63c, 64c) configured to open inside the closed shell, particularly into the reactive liquid (53a, 54a, 63a, 64a), and with gas outlets (53d, 54d, 63d, 64d) disposed above the gas inlets, particularly above the level of the reactive liquid (53a, 54a, 63a, 64a). The closed shell is configured to include solid media (53b, 54b, 63b, 64b) suspended in the reactive liquids (53a, 54a, 63a, 64a).

2. The facility according to claim 1, wherein, The surface of at least one plate (21a, 21b) includes irregularities (25a, 26a) forming flow channels.

3. The facility according to claim 1 or 2, wherein: - Each plate (21a, 21b) is provided with at least one discharge port (32a, 32b), and - The at least one discharge port (32a) of the first plate (21a) is connected to a first discharge channel (42) configured to discharge a first filtrate (Fa), and the at least one discharge port (32b) of the second plate (21b) is connected to a second discharge channel (43) separated from the first discharge channel (42) and configured to discharge a second filtrate (Fb).

4. The facility according to any one of claims 1 to 3, wherein: - Each plate (21a, 21b) is provided with at least one suction port (33a, 33b). - The at least one suction port (33a) of the first plate (21a) is connected to the at least one suction line constituting the first suction line (50), and the at least one suction port (33b) of the second plate (21b) is connected to a second suction line (60) separate from the first suction line (50), and The first suction line includes at least one gas processing unit constituting a first gas processing unit (52), and the second suction line (60) includes a second gas processing unit (62).

5. The facility according to claim 4, wherein, The first gas processing unit (52) includes a first reactor (53) and a second reactor (54), the first reactor (53) being configured to contain an alkaline liquid, and the second reactor (54) being arranged downstream of the first reactor (53) and configured to contain an alkaline liquid.

6. The facility according to claim 4 or 5, wherein, The second gas processing unit (62) includes a first reactor (63) and a second reactor (64), the first reactor (63) being configured to contain an acidic liquid, and the second reactor (64) being arranged downstream of the first reactor (63) and configured to contain an alkaline liquid.

7. The facility according to claim 5 or 6, wherein, At least one alkaline liquid comprises at least a portion of the filtrate (Fb) from the dehydration device (20).

8. The facility according to any one of claims 5 to 7, wherein, At least one acidic liquid contains at least a portion of the filtrate (Fa) from the dehydration device (20).

9. The facility according to any one of claims 4 to 8, wherein, At least one reactor (64) in the gas processing unit (62) of one of the suction lines (60) is configured to be supplied with liquid from a reactor (53) in the gas processing unit (52) of the other suction line (50).

10. The facility according to any one of claims 4 and 5 to 9, wherein, The second suction line (60) connects downstream of its gas processing unit (62) to the first suction line (50) downstream of its gas processing unit (52), and The pump (59) of the first suction line (50) is located downstream of the junction with the second suction line (60).

11. The facility according to any one of claims 1 to 10, comprising a ventilation duct (70), said ventilation duct including a ventilation device (72), wherein, The at least one suction line (50, 60) leads to the ventilation line (70) downstream of the ventilation device (72).

12. The facility according to claim 11, wherein, The ventilation duct (70) is configured to dilute the gas from the suction duct (50, 60) in the airflow driven by the ventilation device (72) with a dilution factor of at least 100, preferably at least 500, more preferably at least 1000.

13. The facility according to any one of the preceding claims, wherein, At least one suction line, and preferably each suction line includes a control valve (55, 65) downstream of the gas processing unit of the suction line.

14. The facility according to any one of the preceding claims, wherein, At least one reactor includes a liquid inlet and a liquid outlet, the liquid inlet opening into the closed housing, and the liquid outlet being arranged above the liquid inlet and particularly below the level of the reactive liquid.

15. The facility according to any one of the preceding claims, wherein, The solid media (53b, 54b, 63b, 64b) have a partition structure, preferably including multiple through channels.

16. A sludge dewatering method, using the facility (1) according to any one of the preceding claims, comprising the following steps: - Allow sludge (B) to enter the chamber (22) of the dewatering device (20), - An electric field is established within the chamber (22). - The filtrate (Fa, Fb) is discharged via the at least one discharge port (32a, 32b). - The gas (Ga, Gb) generated in the chamber (22) is drawn into at least one suction line (50, 60). -The gas (Ga, Gb) is processed in at least one gas processing unit (52, 62) within a reactive liquid containing a solid medium suspended in the reactive liquid by introducing the gas to be treated into the closed shell of at least one reactor (53, 54, 63, 64), and - The treated gas is discharged from the closed shell of the at least one reactor (53, 54, 63, 64).

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