HK1189567B - Method for separating liquid from suspended matter in a sludge and device for same - Google Patents

Description

Method for separating liquid and suspended matter of slurry and device for implementing same

Technical Field

The invention relates to the use of a flow rate Q_EBBetween the liquid part of the slurry and the suspended matter in a continuous stream of V/hA line separation method.

The invention thus allows to remove almost all suspended substances so that they fall below a determined threshold.

The invention also relates to a sludge treatment plant for implementing such a method.

The invention finds particular, although not exclusive, application in the fields of mud dewatering and water clarification.

Surprisingly, the invention results from the use of very high energy in the liquid muddy medium, which will in particular allow to attack the colloidal structure within such waste liquid.

In fact, colloids are present in the solid sludge (in its organic fraction) but also in the water.

It is these colloids in particular that produce a cloudy colour, which makes separation between the liquid and solid phases and decolourisation of some water difficult.

Background

Several methods are known for separating suspended solid matter from waste liquid in which it is present.

The prior art for extracting water into a slurry is basically: compaction, which increases the solid composition content (weight percent of the total mixture) by about 5%; centrifuging or filtering, each of which increases the solid composition content by 18% -25%; finally, drying (by burning or spreading over a period of weeks) increases the solid composition content by 90% to 95%, and it is known for this that the solid composition weight content of the clarified sludge before treatment is generally between 0.1% and 1% of the total weight of the effluent.

All these known treatments of the prior art have some drawbacks, related either to the fact that drying is insufficient (compaction, centrifugation, filtration) or to the treatment (drying) time or to a large energy consumption (combustion).

It is also known (FR73.08654) a method for treating sludge residues, in which a sealed circuit comprising a tank is fed, in which circuit recirculation is carried out within a few tens of minutes by introducing an oxygen-containing gas into the circuit upstream of the tank.

The activated sludge is retained in the lagoon for a period of time sufficient to allow supersaturation with oxygen-containing gas, which is indicated to allow substantial elimination of suspended solids.

Such a method, in addition to being long, uses a sufficiently complex device that is the source of many blockages.

Disclosure of Invention

The present invention aims to provide a method and a device that better meet the practical requirements than previously known, in particular in that the invention will allow to obtain deep dewatering that is much higher than that obtained with the prior art, whether it is carried out alone or in combination with such techniques, and this is done in a very rapid manner, the use of the method according to the invention only requiring a few seconds before obtaining the result.

In particular, the method allows to obtain excellent results only for highly mineralized sludges (i.e. having a percentage of organic matter of less than 5% -15% with respect to 100% by weight of dry matter).

Whereas with less mineralized slurry, when the process is combined with a supplementary separation means (belt filter or centrifuge) arranged downstream of the apparatus, an optimal yield can be obtained, increasing the drying by more than 10%, for example by 25%.

The existing plant can thus be easily improved by adding one or more reactors for implementing the invention, which will later save for example the costs of transport and final incineration of the sludge.

Furthermore, the invention has a very low electrical consumption and uses few consumable substances (compressed air, additives).

Furthermore, the present method uses a simple device of very small volumetric size, easily transportable, which will therefore be able to be installed in inaccessible locations.

With the present invention, continuous operation is possible and this has less severe operating constraints.

Moreover, the treatment according to the invention does not produce any pollution, while completely using techniques which are in themselves much more economical than the techniques known in the field of liquid/solid separation (centrifuges, filter presses, belt filters, continuous oxidation recycling, etc.).

Finally, with the present invention, a new type of dewatered porous cake constituting usable residue is surprisingly obtained.

To this end, the invention proposes, in particular, a method for controlling the flow rate Q_EBMethod for separating suspended matter from a liquid fraction of a continuously fed stream of sludge, in which air is injected at a flow rate d, characterized in that the sludge stream is formed of at least two partial streams, which are injected one above the other into a closed housing having a volume V < V/20 for the passage of the sludge stream under pressure, air is injected into the housing which is maintained at a pressure greater than a defined value, and the suspended matter of the thus treated stream is then filtered or let to settle in a recovery vessel.

The closed housing is supplied and discharged at substantially the same flow rate or at the same flow rate for the continuous input and output of waste liquid.

The housing thus constitutes an interruption in the process flow line, and the waste liquid is not recirculated in a loop to the interior of the housing.

Advantageously, in the case of sedimentation, the solid fraction or the sludge cake sinks into the bottom part of the container, is separated from the liquid fraction, and the liquid fraction is continuously discharged.

A closed housing is understood to mean a tank or reactor with a defined closed volume, but of course it comprises an output member (usually a pipe) discharging a continuous flow once treated, and a continuous flow input member, at the same flow rate or substantially at the same flow rate.

The housing is thus a housing for the passage of a pressure flow.

The value V < V/20 is understood to be a small value or a nearly small value with a tolerance on the order of + -10% to 20%.

Advantageously, v.ltoreq.V/25 or v.ltoreq.V/30.

In an advantageous embodiment of the invention, particularly excellent results are achieved by combining several functions in the same housing of small dimensions by providing the following four functional areas.

A zone of slightly compressed air is introduced, in which zone the heaviest particles, which however can rise in the reactor and can be discharged together with the finest particles in the top part, are also suspended or prevented from settling.

-a hydraulic impingement zone, where the introduction of the liquid stream takes place.

A rise zone for a layer of gas of about 1, water of 0.1 and solids of 0.01 in weight quantities. In this zone, very intense stirring is made possible by supplying air of the recommended mass (flow rate and pressure).

A depressurization zone, which is regulated, for example, by a valve located at the top part of the reactor. In the case of this valve, the valve should allow the reactor to be maintained at a relative pressure of about 0.5 bar to 2 bar.

In an advantageous embodiment, one and/or the other of the following arrangements is/are furthermore used:

-injecting said flow into said housing with a volume V < V/20 through two identical openings located in the lower half of said housing, opposite to each other in a face-to-face relationship, air being injected below said openings, said flow being discharged continuously or intermittently in the top part, for example by means of a safety valve activated above a determined threshold;

with d > 1.5Q_EBE.g. greater than 5Q_EBGreater than 10Q_EBOr at 1.5 times Q_EBTo 15 times Q_EBThe flow between them is injected with air;

air is injected at moderate pressure. By "medium pressure" it is understood that it is between 1.4 bar and 2.5 bar, advantageously between 1.6 bar and 1.9 bar. Such pressure will furthermore generate large bubbles which will be able to disperse freely into the housing, better entering the environment;

the recovery tank is permanently drained due to overflow;

-v≤V/50；

-v≤V/100；

-flow rate Q_EBGreater than or equal to 15m³H, flow d is greater than or equal to 25Nm³A relative pressure in the shell greater than or equal to 0.8 bar;

-flow rate Q_EBGreater than or equal to 20m³H, flow d is greater than or equal to 50Nm³H, and the relative pressure in the shell is greater than 1.2 bar;

-continuously adding at least one liquid reagent to the interior of the housing at a flow rate q;

-adding said liquid agent in a proportion comprised between 0.05% and 0.1% of the dry matter ratio contained in the sludge. "dry matter ratio" is understood to mean the weight percentage of solids relative to the total weight percentage of the waste liquid;

-the liquid agent is an organic flocculant of the cationic type;

degassing the waste liquid at the outlet of the housing, using the gas obtained to feed the air jets at the bottom part.

-recovering the obtained mud cake, dewatering said mud cake by drying, pressing or centrifuging to obtain a solidified mud cake.

The invention also provides the product directly obtained by the process as described previously.

The invention also provides a solidified mud cake obtained by the method described above, characterized in that the solidified mud cake has a porosity between 5% and 15%.

The invention also provides an apparatus for carrying out the method as described above.

In addition, the invention also provides a flow Q_EBApparatus for separation between the liquid fraction of a slurry fed in continuous flow at V/h and suspended matter, comprising means for feeding air at a flow rate d, and a container for recovering and settling the suspended matter of the thus treated slurry flow, and means for continuously discharging the supernatant liquid fraction of the slurry flow to the outside of the container, characterized in that it comprises:

-a closed housing of volume V < V/20, comprising at least two identical, oppositely facing openings in the lower half of said housing,

-means for collecting the slurry and feeding the stream of slurry thus collected into the housing in at least two partial streams each injected through one of the openings,

a member for supplying air to the housing at a flow rate d, adapted to inject air under said opening, and

a component that discharges said flow continuously or intermittently, the pressure in the housing being greater than a determined threshold.

Advantageously, the device is arranged to discharge the flow at the top portion by means of a safety valve activated above said determined threshold.

It is also advantageous if the continuous discharge of the supernatant liquid fraction is formed by a gravity overflow.

In an advantageous embodiment, v.ltoreq.V/50.

Also advantageously, v.ltoreq.V/100.

The invention also provides a device in which means are provided to feed liquid reagent directly into the housing at a determined flow rate.

Drawings

The invention will be better understood on reading the description of the embodiments given below as non-limiting examples. The description makes reference to the accompanying drawings, in which:

figure 1 is a schematic diagram illustrating the principle of the treatment method according to the invention.

Figure 2 is a schematic diagram illustrating the operation of an embodiment of the device according to the invention.

Figure 3 is a view schematically illustrating the conversion of mud by using a device according to an embodiment of the invention.

Detailed Description

FIG. 1 shows the principle of a method for separation between liquid and solid of a slurry according to embodiments of the invention more particularly described herein.

In a reactor 1 formed by an oblong shell 2 elongated around an axis 3, with a small volume v, for example of about 50 litres, waste liquid is injected through two opposite nozzles 5, 6 symmetrical with respect to the shell axis 3 (arrow 4).

These nozzles are located at the bottom part of the housing, for example at a distance H from the housing bottom 7 of between one fifth and one third of the housing height H.

These two nozzles, situated opposite each other, allow a pressurized feed of a water flow of high load dry Matter (MS) (for example MS 10%/total weight τ), which causes a strong impact at the junction of the two flows in zone 8.

In other words, the pumping of external water (not represented) introduced into the shell of the small-size reactor 1 through two opposite nozzles allows the impact between these flows in the zone 8 to be caused by the outlet pressure of one or more feed pumps (not represented) depending on the water level of said feed pump upstream of the nozzles and the head loss of the circuit.

Typically, a pressure of 2 bar at the mouthpiece outlet 9 in the housing is readily achievable by using a commercial industrial pump and a circuit without excessive interruption (accident).

The pumping kinetic energy is then converted into impact energy, which is maximized by increasing the velocity of introduction into the shell due to the adjusted nozzle 9 outlet having a small, but compatible size with the maximum particle size of the sludge.

Furthermore, according to the embodiment of the invention described more particularly herein, a quantity of overpressure air (arrow 10) is introduced below zone 8.

By "overpressure" is meant a slight overpressure, which may be between relatively 0.1 bar and relatively 1 bar, for example relatively 0.8 bar, with respect to atmospheric pressure.

This air introduction takes place through an air distribution tube (ramp) 11, for example a tube formed by a serpentine or elongated circular duct, which allows to disperse the air bubbles through openings 12 distributed along said duct 13 onto the surface of the casing.

Air may also be brought through a nozzle in the bottom part.

The tube is located in zone 8 below the junction of the waste streams, for example between one tenth and one fifth of the height H of the housing, and produces large bubbles B, for example between 1mm-1cm in diameter.

This air introduction increases the energy level of the housing under overpressure relative to its treated waste outlet 14.

A functional region 16 is also obtained in the upper part 15 of the housing, in which region extremely turbulent mixing excited by brownian motion is achieved (dashed line 17).

In the bottom part 18 of the reactor, there is provided a discharge opening 19 for the too dense components not discharged from the upper part of the reactor, which are discharged sequentially, as is known in the art.

Air, water and sludge are discharged from the outlet 14 of the reactor to produce, after sedimentation, physically transparent water separated from the solid matter, which water has a very low solid matter ratio, in particular below 30mg/l, even below 10mg/l, whereas the initial solid matter ratio may be close to more than 500 mg/l.

The solid matter of the degummed body obtained there is more porous and can therefore be easily compacted. It can even be directly pelletizable on leaving the reactor, depending on its starting organic matter ratio.

The air is introduced into the pressure in the shell itself at a medium pressure, for example between 1.6 bar and 1.9 bar absolute, so that large bubbles can be generated therein in the environment, which will be able to enter the environment and be distributed randomly in the reactor to achieve the desired mixing.

Furthermore, at a high flow rate d, i.e. the flow rate Q of the incoming water_EB(in m)³1.5 to 15 times (in Nm)³The flow rate of/h) introduces air.

The gas withdrawn from the reactor leaves with water and sludge at booster flows, which can be recovered, treated and recycled as needed for reuse in the bottom part of the reactor.

It is noted that the presence of larger substances, of the sand, gravel, etc. type, increases the number of impacts and therefore improves the process.

As regards the shell pressure, it is arranged and/or adjusted to generate an ascending flow exiting from the altitude, optimizing the internal energy.

Such pressure is therefore determined according to the operating characteristics of the circuit (water level of the pump) but also according to the type of waste liquid and the flow rate of the treatment sought.

The final selected reactor size will also be determined by the skilled person on the basis of the basic knowledge and flow charts of engineers in the field of chemical engineering.

The pressure and output are ensured, for example, by a slide valve (vannesouppe) which releases the flow when a given pressure is exceeded.

Since the process according to the invention performs stirring of the three phases, solid, liquid and gas, it is necessary to perform a separation at the outlet taking into account degassing, a solid phase more dense than water and drainage.

In an advantageous embodiment, a coagulant (e.g. lime, ferric chloride) is additionally added.

This supplementary addition is carried out, for example, in the functional zone 16.

Thus, up to 20m can be treated using a reactor having a diameter of 55 litres and a nozzle having a diameter of 40mm for injection into the reactor³A slurry of/h.

Surprisingly, it was furthermore observed with the process of the invention that: when the pressure in the reactor is higher than 0.8 bar, the slurry is supplied at a flow rate Q_EBGreater than 15m³H, air flow d greater than 25m³At/h, an unusual separation is obtained with a maximum sludge settling rate, which after drying has a novel granular porous appearance, wherein the muddy water is formed, for example, by a sprinkled mud loaded with 5% MES derived from the biodegradation of swamp grass, clays, sand and various petroleum residues in trace state (< 1 ‰).

With a 55 litre reactor and a 40mm injection nozzle for injecting the waste liquid inside, extremely fast impact velocity values and particularly short residence times in the reactor were obtained [ see table I below ].

TABLE I

By means of the invention, it is thus possible to obtain deep dewatering which is much higher than that obtained by means of the prior art, and which takes place in a few seconds.

By way of example, the degree of improvement in drying Δ, which is obtained with the method according to the invention for a slurry from a FossurMer industrial clean-up station, which slurry has a low degree of mineralization (90% of organic substances) in the field of petrochemistry, is listed in table II below.

Comparison was made between a simple treatment by means of a belt filter (filter cloth, over which water and sludge are poured by pumping and conveyed between dewatering rolls) and the same belt filter after pretreatment with the method according to the invention.

For a determined MS load (in g/l) at the housing inlet, the relative pressure P (bar) inside the housing, the gas flow d (Nm) were varied for a housing volume v of 55l³H) mud flow rate Q_EB(m³Parameter of/h).

Furthermore, results are given according to the initial state of the slurry, i.e. fresh (without intermediate precipitation), less fresh (after one day of precipitation) or fermented (several days of anaerobic precipitation).

It can be seen that: the high gas flow (eight times the mud flow) and the high pressure in the housing (1.3 bar) increase the dryness by 48.8% (test N ° 10) for a sufficiently low initial load (8.2g/l MS), which is a demonstration of good efficiency of the colloid removal.

On average (see tests N ° 13 to 16), for a 32.4g/l loaded fresh sludge, for a gas flow rate 20 times the sludge flow rate and a pressure of relatively 1 bar inside the casing, the method according to the invention improves the dryness (dry Matter (MS) weight ratio of MS + liquid with respect to the total weight of the sludge) by 24% -36.4%, i.e. on average 30%.

TABLE II

Subsequently, examples of the results obtained with a single unit (without make-up treatment) and with make-up treatment (belt filter) for the sediments (highly mineralized sludge) are shown in table III.

The treatment with the invention alone compared to the treatment with the belt filter alone did not exceed an improvement of the dryness of 15-18%.

Here, excellent results are obtained even without additional treatment with filters or centrifuges.

TABLE III

In addition to a great saving of time in the treatment, a very low consumption of electricity, compressed air and/or additives is necessary.

Furthermore, the small volumetric size of the housing makes it easily transportable, allowing it to be installed in locations where access is difficult, all allowing continuous operation with great simplicity.

The treatment according to the invention does not produce any pollution and this is carried out with much more economical equipment than other treatment systems, such as centrifuges, filter presses, belt filters, etc., which are conceivable for separate liquid/solid separation operations.

A schematic representation of the operation of the apparatus 20 according to an embodiment of the invention more particularly described herein is shown in fig. 2.

The device 20 allows a flow rate Q_EBSeparation of the liquid and dry matter of the slurry fed at 21 in a continuous flow of V/h, the feed at 21 being subsequently divided into two portions for feedingA feed nozzle 22.

More precisely, the device 20 comprises a closed stainless steel casing E having a volume V less than V/20, for example for 1.5m³The flow rate Q/h is 55 liters for V/h, and the housing comprises at least two identical openings or nozzles 22 located opposite one another in the lower housing part 23, for example at a distance equal to one third of the housing height.

Said housing is constituted, for example, by a cylindrical sector 24 which ends, at the top and at the bottom, in two identical conical zones 25, for example with an apex angle of about 120 °.

Each end portion terminates itself in an upper tube 26, a lower tube 27. The lower pipe 27 is connected to an intermittent discharge pipe 28 equipped with a valve 29 for intermittently discharging suspended matter 30, which suspended matter 30 has settled in the bottom 27 of the housing.

The device 20 furthermore comprises a supply means 31 for supplying the housing with air 32 at a flow rate d below the opening 22.

This supply takes place, for example, by means of a rectilinear duct or pipe 33, of small diameter, for example 5cm in diameter, with a length approximately equal to the diameter of the cylindrical housing, which comprises regularly distributed nozzles 34 for outputting compressed air into the housing in a dispersed manner, so as to generate large bubbles that cause great agitation (circles 35).

A per se known component 36 for supplying a liquid reagent 37, such as a coagulant, is provided. Said means 36 are formed, for example, by a tank 38, the tank 38 being fed to the interior of the casing above the nozzle 22 in the turbulent zone by means of a metering pump 39 and a remote control valve 40.

The device 20 furthermore comprises a continuous discharge member 41 for continuously discharging the liquid that has entered the housing through a valve or flap 42, said valve or flap 42 opening above a certain pressure within the housing, for example 1.3 bar.

It is also possible that, without a valve, the downstream circuit itself constitutes the head loss necessary to maintain the relative overpressure of the casing.

The waste liquid 43 is then discharged at the top portion in order to reach a settling tank 44 known per se.

The settling tank 44 is formed, for example, by a cylindrical reservoir 45, and a discharge conduit 46 opens into the cylindrical reservoir 45 below the operating level 47 to limit turbulence.

As for the tank 44, this tank 44 is discharged by overflowing at 48 through a non-turbulent side sump portion 49, the side sump portion 49 being separated from the rest of the sump by a wall of a local (paredorait) opening.

The settled solid matter 50 is discharged at the bottom part 51 to be able to be disposed of later.

Fig. 3 shows a top view of the device 20 according to the invention from fig. 2, which allows a sludge cake 53 to be obtained from the sludge 52.

In the following description, like reference numerals will be used to refer to like elements.

The housing E is fed with the slurry or waste liquid 52 loaded with suspended matter through two oppositely situated nozzles 22 facing each other, wherein the slurry or waste liquid is passed through a pipe having a water height H₀At a flow rate Q of the pump 55_EBPumped into the environment 54. Thus, at each nozzle the flow rate is half, Q_EB/2。

The air 32 feed is through the nozzle 56 below the nozzle as previously described.

A reagent (coagulant such as ferric chloride or lime), known per se and adapted by the person skilled in the art according to the waste liquid to be treated, is continuously supplied from a tank 38 into the housing E via a metering pump 39.

The spent liquor, once treated in the housing as described above, is discharged at a top portion at 41 to obtain a defragmented degummed spent liquor as schematically shown in fig. 3.

The defragmented degummed waste liquid is then fed to a settling tank 45. After successive precipitations within a few seconds, an extremely clear water is observed at 58, which water is able to let 99%, even 99.5%, for example, of the light pass through it.

At 59, after possible additional compaction treatment at 60, a particularly interesting mud cake is obtained, which is aerated, solidified at the same time, with an excellent porosity of between 5% and 15%.

Such products obtained with the method according to the invention are new and will form materials for later use as humus, as raw materials in construction, etc.

The operation of the purge according to embodiments of the invention described more particularly herein will now be described with reference to figure 3.

Sludge 52 is drawn from the environment, such as a river 54 loaded with the sludge, by a pump 55.

In an embodiment, the sludge ratio, i.e. the mass percentage of dry matter, is for example between 3% and 10%.

The slurry is at a rate of, for example, 5m³/h-50m³Between/h, e.g. 15m³The flow rate/h is supplied to a housing E having a volume V of 100l, for example.

As described previously, the effluent is injected into the reactor through two nozzles 22 facing each other. At the same time, pass through the lower tube 33 of the reactor at a rate higher than, for example, 25Nm³The flow rate of/h is supplied with air.

The pressure inside the reactor is comprised between relatively 0.3 bar and relatively 1.5 bar, for example higher than relatively 0.8 bar, according to the water level of the waste liquid feed pumps and/or of one pump, and to the head loss generated by the casing itself and by the discharge valve 42 located in the top part of said casing.

The pressure inside the reactor can be regulated in particular by means of the upper valve or flap.

The waste liquid thus stirred and supplied with air is retained in the reactor for a period of time corresponding to the relative ratio between the flow rate, the volume and the pressure.

The waste liquid is thus retained for a residence time of e.g. several seconds, e.g. less than 1 minute, before being discharged.

This time can be even very short, since it is higher than 20m³The waste liquid flow rate/h can, for example, be in the housing for a period of less than 10 seconds.

As regards the slurry feed rate, which has a direct effect on the impact velocity according to the table generated previously, it is known that the contact and residence time in the pressure reactor also has an effect on the formation of flocs and on their settling rate.

Furthermore, the pressure influence and the air flow in the reactor are also factors which can be adjusted within the capabilities of the person skilled in the art depending on the results sought.

Once the slurries have been treated, they leave the reactor at a pressure corresponding to the flow pressure of the amount of fluid in the line 43 to a settling tank 45 where settling will take place in a manner known per se.

The water obtained as supernatant is of high purity and is itself continuously discharged at 58.

The sludge obtained in the bottom part of the settling tank is then discharged either continuously or discontinuously, according to a determined period of time, for example once a day.

The fact of re-discharging the sludge very quickly improves its quality, especially with respect to its good porosity.

The treatment carried out by means of the method and reactor according to the invention thus allows to obtain a porous and dewatered cake, the recovered sludge being empty, dry and operational. In contrast to three months in the context of the use of so-called conventional drying, a few hours is sufficient to obtain similar results, and with the present invention the characteristics of the sludge obtained are much better, since it is more easily recyclable.

As is self-evident, the invention is not limited to the more specifically described embodiments, as also follows from the foregoing. Rather, the invention includes all variants thereof, in particular those in which the openings may be pipes, nozzles, deep inside the housing, in order to minimize the distance between the openings and to increase the impact force.

Claims (19)

1. At a flow rate Q_EBMethod for separation between the liquid fraction of a slurry fed in continuous flow V/h, V being the volume, and suspended matter, in which air is injected at a flow rate d, characterized in that the slurry flow is formed by at least two partial flows, which are injected one above the other into a volume V for the passage of the slurry flow under pressure<In a closed V/20 housing, the air is at a flow rate d>1.5Q_EBIs injected into the casing maintained at a relative pressure greater than 0.1 bar, and then the suspended matter of the mud flow thus treated is filteredOr in a recovery vessel where the solid fraction or mud cake settles to the bottom part of the recovery vessel, separated from the liquid fraction that is continuously discharged.

2. Method according to claim 1, characterized in that the air is injected at a pressure between 1.4 bar and 2.5 bar.

3. Method according to any of the preceding claims, characterized in that the slurry flow is injected into the housing with a volume V < V/20 through two identical openings located opposite to each other in the lower half of the housing, below which openings air is injected, which slurry flow is discharged continuously or intermittently in the top part.

4. A method according to claim 1 or 2, characterized in that the supernatant liquid fraction of the sludge flow is permanently discharged from the recovery vessel by overflow.

5. The method according to claim 1 or 2, wherein V ≦ V/50.

6. The method of claim 5, wherein V ≦ V/100.

7. Method according to claim 1 or 2, characterized in that said flow rate Q is_EBGreater than or equal to 15m³H, the flow rate d is greater than or equal to 25m³H; and the relative pressure in the housing is greater than or equal to 0.8 bar.

8. Method according to claim 7, characterized in that said flow rate Q is_EBGreater than or equal to 20m³H, the flow rate d is greater than or equal to 50m³H, phase in the shellFor pressures greater than 1.2 bar.

9. A method according to claim 1 or 2, characterized in that at least one liquid reagent is continuously added to the interior of the housing at a flow rate q.

10. The method according to claim 9, characterized in that the liquid agent is added to the turbulence zone of the casing in a proportion comprised between 0.05% and 0.1% of the dry matter ratio contained in the slurry.

11. A method according to claim 1 or 2, characterised in that no flocculating agent is added in and/or upstream of the housing.

12. Method according to claim 1 or 2, characterized in that the waste liquid is degassed at the outlet of the housing, and the obtained gas is used to feed an air jet at the bottom part.

13. A method according to claim 1 or 2, characterized in that the obtained mud cake is recovered, and the mud cake is dewatered by drying, pressing or centrifuging to obtain a solidified mud cake.

14. At a flow rate Q_EBDevice for separating between the liquid fraction and the suspended matter of a slurry fed in continuous flow, V/h, V being the volume, said device comprising a flow rate d>1.5Q_EB-means for supplying air, and-a container for recovering and filtering or settling the suspended matter of the thus treated sludge flow, and-means for continuously discharging the supernatant part of the sludge flow outside the container, characterized in that the device comprises:

a closed housing of volume V < V/20, said housing comprising at least two identical openings in the lower half of the housing, in face-to-face opposition;

a member for collecting the slurry and feeding the thus collected stream of slurry into the housing in at least two partial streams each injected through one of the openings;

the flow rate d>1.5Q_EBA member for supplying air capable of injecting air into the housing below the opening; and

means for continuously or intermittently discharging said slurry stream, the relative pressure in said housing being greater than 0.1 bar.

15. The apparatus according to claim 14, characterized in that the sludge flow is discharged at the top part by a safety valve activated by a relative pressure exceeding 0.1 bar.

16. Device according to claim 14 or 15, characterized in that the means for continuously discharging the supernatant liquid fraction are formed by a gravity overflow.

17. The device according to claim 14 or 15, wherein V ≦ V/50.

18. The device of claim 17, wherein V ≦ V/100.

19. A device according to claim 14 or 15, characterized in that the device comprises means for feeding liquid reagent directly into the housing at a determined flow rate.