WO2000014020A1

WO2000014020A1 - Waste treatment by adding at least an alkaline reagent

Info

Publication number: WO2000014020A1
Application number: PCT/FR1999/002140
Authority: WO
Inventors: Eric Judenne; Marc Remy; Michel Sarrazin; Claude Maynard
Original assignee: Lhoist Recherche Et Developpement S.A.
Priority date: 1998-09-08
Filing date: 1999-09-08
Publication date: 2000-03-16
Also published as: PL346619A1; FR2782937B1; EP1115665A1; SK3112001A3; HUP0103971A2; NO20011166L; CZ2001833A3; NO20011166D0; FR2782937A1; AU5523199A

Abstract

The invention concerns a method for treating waste (D) by adding an amount of at least an alkaline reagent (R) comprising steps which consist in: continuously supplying the waste to be treated into a mixer (1); continuously adding to the treated waste a measured amount of at least an alkaline reagent; closely and continuously mixing for a specific time interval the waste and the alkaline reagent; and simultaneously transporting the resulting mixture through the mixer; then extracting said mixture from the mixer. The invention is characterised in that during the mixing step, the waste and the alkaline reagent are successively mixed at a first speed (V1), during a first retention time (t1), and at a second speed (V2) not greater then the first speed (V1), during a second retention time (12) longer than the time (t1).

Description

WASTE TREATMENT BY ADDING AT LEAST ONE ALKALINE REAGENT

The invention relates to a waste treatment method comprising the steps of continuously supplying the waste to be treated in a mixer, continuously adding to the waste to be treated a metered amount of at least one alkaline reagent, mixing thoroughly and continuously the waste and said at least one alkaline reagent during a given residence time and, at the same time, transporting the mixture thus obtained through the mixer, then continuously extracting the waste-alkaline reagent mixture from the mixer.

The invention also relates to a device for implementing this method comprising a mixer comprising a body pierced with a first opening for the introduction of the waste to be treated, with a second opening for the introduction of at least one alkaline reagent and a third opening for the extraction of the waste-alkaline reagent mixture, a means for intimately mixing the waste and said at least one alkaline reagent which is placed inside the mixer and which serves as a means of conveying the alkaline waste-reactant mixture in the direction of the mixer extraction opening.

At present, this process is particularly used for the treatment of waste of the residual sludge type. These generally come from sewage treatment plants treating urban or industrial wastewater, septic tanks and other similar installations for the treatment of wastewater. This process, which is commonly called liming, has the advantage of being economical and of meeting the requirements related to environmental protection by making it possible to obtain, depending on the objectives set (i.e. recycling at industrial or agricultural character or landfill for ultimate waste): biological stabilization of the mud by blocking its fermentation, its chemical stabilization (inerting) by precipitation of most of the metallic trace elements, its physical stabilization (structuring) through dewatering, its recovery (for example in agricultural spreading) by enrichment in calcium and magnesium and its hygienization by destruction of pathogenic micro-organisms (DEWANDRE et al. Liming of sludge. Water, industry, nuisances, 1994, 174, 46-48). Document WO 96/09991 describes such a method as well as an apparatus for its implementation. The process comprises the stages consisting in supplying mud continuously, mixing the mud with at least one alkaline additive (such as for example hydrated lime, quicklime, dolomitic lime or the like) in proportion to the mud, so that the reaction thus provoked increases the temperature of the mixture to a desired minimum level and increases the pH of the mixture to a desired minimum level, provide a pasteurization chamber having at least one opening inlet and at least one discharge opening, continuously bring the mud-alkaline additive mixture to the inlet opening of the pasteurization chamber, transport the mixture continuously through the pasteurization chamber without significant agitation of the mixture of so that it does not become more aqueous, the mixture being enclosed in the pasteurization chamber for a desired residence time and the pathogenic germs noci fs of the mud being substantially destroyed, and discharging the mixture through the discharge opening of the pasteurization chamber.

The apparatus for carrying out this process mainly comprises a mixer 40, in which the mud and the alkaline additive are mixed and in which the mixture obtained is transported, and a pasteurization chamber 50 in which the mixture is kept at a determined temperature for a determined period. More specifically, the mixer 40 consists of an elongated enclosure, disposed parallel to the ground, which is provided with two openings 41 and 46 for the respective introduction of the mud and the alkaline additive and an opening 43 of outlet of the alkaline mud-additive mixture. The mixing of the mud and the alkaline additive is ensured by two mixing screws 42, 44 which at the same time make it possible to bring the mixture obtained towards the opening of outlet 43 of the mixer 40. After passing through this opening, the mud-alkaline additive mixture enters the pasteurization chamber 50 through an opening 52 formed therein. The pasteurization chamber 50 consists of a closed enclosure 51 of elongated shape, preferably insulated, provided with a movable bottom 53 which is actuated by a motor 62 and on which the mud-alkaline additive mixture is transported in the direction of an opening 54 for discharging the mixture made in the enclosure 51. Heating elements 66 are arranged in the chamber 50 to allow the mud-lime mixture to reach the expected temperature when the heat released by the reaction produced in the mixer n is not enough.

The major drawback of this process lies in the significant heat losses generated from the moment when the mixing of the mud and the alkaline additive ceases, that is to say during the passage of the mud-alkaline additive mixture between the mixer 40 and the pasteurization chamber

50 and during its movement in the chamber 50. In addition, the presence of the heating elements 66 in the chamber 50 makes the process costly in energy.

Another drawback of this process, and of other sludge treatment processes in general, is that it requires a device specially designed for its implementation, which is not suitable for treating other waste. In particular, this type of device is not suitable for treating:

- sewage sludge and dredging from networks, canals, ports, coastline, etc.

- sludge from construction sites (drilling, tunnel, soil injection, etc.);

- sludge from industrial processes (quarries, steelworks, hydrocarbons, etc.) and agricultural (droppings, slurries, etc.); - polluted land (brownfields, black spots, etc.);

- earthy cuttings, such as for example trench cuttings. Such waste is certainly treated respectively using a liming process, but the steps of this process, as well as the devices for implementing this process, vary from one type of waste to another and from one desired treatment result to another. The main object of the present invention is therefore to provide a method and a device for treating waste, of the type defined respectively in the preamble of claim 1 and of claim 9, which are capable of treating efficiently, simply and economically, as well sludge, earth or cuttings as mentioned above, this in order to obtain a fixed result at the start of the treatment, such as obtaining a biological stabilization, chemical stabilization, physical stabilization or hygienization of the waste .

To this end, the method according to the present invention is characterized in that in step c), the mixing is carried out successively at a first speed, during a first residence time, and at a second speed which is lower or equal to the first speed, during a second residence time which is greater than the first residence time.

To this end, the device according to the present invention is characterized in that the mixer body comprises a first and a second compartment communicating with each other by an adjustable opening, through which extends the mixing means and in which the means of mixing operates respectively at a first speed, during a first residence time, and at a second speed, which is less than or equal to the first speed, during a second residence time which is greater than the first residence time.

Advantageously, the waste treated by the method according to the invention is chosen from the group comprising sludge from water treatment, sludge from cleaning and dredging, sludge from construction sites, sludge from industrial processes and agricultural, polluted land and earthy spoil.

According to a particularly advantageous embodiment of the invention, the method comprises: - before treatment, a calibration of the waste to be treated comprising a determination of at least one specific function for this waste, chosen from the specific functions relating the cohesion values, dry matter content and rate of alkaline reagent specific to it , the pH values and rate of alkaline reagent specific to it, the values of temperature, dry matter content and rate of alkaline reagent specific to it, the values of immediate bearing index, content of dry matter and rate of alkaline reagent specific to it, as well as the specific function relating the values of residence time and speed specific to the mixture of this waste with the quantity of said at least one alkaline reagent, as well as a selection of at least one predetermined value chosen from the values of cohesion, immediate bearing index, pH, temperature of the mixture and residence time in the mixer; - before or during step a), a measurement of at least one value chosen from the values of cohesion, immediate bearing index, pH and temperature of the waste;

- During step b), an assay of the amount of said at least one alkaline reagent, using said at least one specific function, to obtain one of said predetermined values for the mixture;

- during step c), an adjustment of said speeds, on the basis of at least one value chosen from the measured cohesion value, of measured immediate bearing index and of predetermined temperature, in order to respect the predetermined residence time value of the mixture. This process makes it possible to treat wastes whose properties are not known at the start of the treatment. By an easy-to-perform preliminary calibration, one or more successive measurements can establish one or more of the five standard curves of the waste which respectively illustrate its own cohesion function - dry matter, immediate bearing index - dry matter - alkaline reagent rate, pH - rate alkaline reagent, temperature - dry matter - alkaline reagent rate, and the residence time function - speed specific to the waste / alkaline reagent mixture. Depending on the result of treatment set by the user, one or more of these functions will then be used, which will allow simple account to be taken of variations in cohesion and / or immediate bearing index and / or pH and / or temperature and / or residence time corresponding to the waste / alkaline reagent mixture.

Other characteristics and advantages of the present invention will emerge during the description which follows of an embodiment given by way of nonlimiting example, with reference to the accompanying drawings in which: - Figure 1 shows d schematically an embodiment of the method according to the invention;

- Figure 2 is a side view of the device implementing the method according to the invention;

- Figure 3 is a top view of the device shown in Figure 2;

- Figure 4 is an enlarged perspective view of two blades arranged successively on one of the shafts arranged in the mixer of the device shown in Figure 2;

- Figure 5 is a sectional view, along the line V-V, of the mixer of the device of Figure 2, with a cutaway showing the opening for communicating the compartments of the mixer;

- Figure 6 illustrates the pH function - alkaline reagent rate established for several types of sludge given;

- Figure 7 illustrates the cohesion - dry matter function for a given type of sludge;

- Figure 8 illustrates the immediate index function - natural water - alkaline reagent rate for a plastic silt treated with quicklime;

With reference to FIGS. 1 to 3, a waste to be treated D, such as for example a residual sludge, coming for example from a hopper (not shown), is introduced continuously into the longitudinal body 1a, preferably insulated, a mixer 1, by means of a pipe 2 disposed at the head thereof. As can be seen in Figures 2 and 3, the mixer 1 is placed parallel to the ground by means of a base 3. At least one alkaline reagent R, for example from a silo 4, preferably quicklime with a particle size advantageously less than 5 mm (in particular 0, 05 mm to 3 mm), is continuously added to the waste D in the body 1 a of the mixer 1 by a line 5 which is preferably arranged near the line 2 so that the mixture of waste / alkaline reagent takes place as soon as the start of treatment. At the outlet of the silo 4, the added amount of alkaline reagent is metered by means of a metering device 6 (for example a system comprising a worm screw driven by a motor 6A). During a first residence time t1 which is a function of the physicochemical nature of the waste to be treated (cohesion or immediate bearing index, pH, etc.), the alkaline reagent and the waste are mixed in a first compartment A of the mixer 1, which has for example a length of 0.9 m. This mixing is carried out by means of a shaft 7 which is arranged in the central longitudinal axis X of the body 1 a of the mixer 1, inside the compartment A, and which is rotated by a motor M1 having a speed variable V1 preferably between 12.8 and 77 rpm. The shaft 7 comprises several blades 7a, for example five in number (FIG. 2), which are connected to the latter respectively by arms 8 fixed, for example bolted, to the shaft 7, perpendicular to the latter.

As can best be seen in FIG. 4, the blades 7a have a shape and a position which are particularly suitable for promoting the separation of the waste into fine particles, with the aim of facilitating intimate contact with the grains of alkaline reagent simultaneously dispersed. To this end, each blade 7a comprises two sections P and P 'of substantially triangular shape, which are arranged on either side of a line L of direction perpendicular to the arm 8. The sections P and P' are, in addition , symmetrical with respect to a plane containing the line L and it is made so that each blade 7a has its concavity turned towards the outside of the body 1a of the mixer 1. With reference to FIG. 2, the blades 7a follow one another on the 'shaft 7 with an angular offset of 90 °. As can best be seen in FIG. 4, one blade out of two 7a is equipped with a conveying element P "of substantially rectangular shape. This element, which is not compulsory, can also be fixed on all the blades, on one in three blades, etc. and have different dimensions. It all depends in fact on the nature of the waste to be treated. The element P "is fixed, for example bolted, on one side of a blade 7a out of two, being slightly inclined relative to the latter. In the embodiment shown in FIG. 4 where the waste to be treated has a pasty consistency, the element P "is fixed to the pan P 'of the blade 7a which is, relative to the pan P, the pan closest to the tail of the mixer 1. Thus arranged, each element P" allows to increase the thrust of the mixture towards the tail of the mixer 1. In the case where the mixture would have a fluid consistency, the elements P "will of course be fixed on the sides arranged closest to the head of the mixer 1, this is in other words, the sides P associated with one blade out of two 7a. By their shape and their arrangement on the shaft 7, the blades 7a have the advantage of being suitable for mixing, with at least one alkaline reagent, all the types of waste which have been mentioned above, without fear of being damaged, for example by a large stone which could be contained in a site excavation.

Once the time t1 has elapsed, the waste / alkaline reagent mixture is transported continuously, under the effect of the rotation of the shaft 7, in a second compartment B of the body 1a of the mixer 1, which is adjacent to compartment A, by an opening 9 as shown in detail in FIG. 5. Thanks to this opening, no heat loss can be generated when the mixture passes between the compartments A and B.

As can be seen in FIG. 5, the opening 9 is made at the level of the lower part of the body 1a of the mixer 1, in a wall 10 which separates compartment A from compartment B. The opening 9 has a shape of crown section which runs approximately three-quarters of the lower periphery of the body 1a of the mixer 1. In order to regulate the flow rate of the waste / alkaline reagent mixture inside the mixer 1, the opening 9 presents the advantage of being able to be partially closed at by means of a plate 11 of shape complementary to that of said opening. A guide rail (not shown), formed on more than half of the periphery of the body 1a of the mixer 1, makes it possible to slide the plate 11 along the opening 9. This operation is carried out manually by the user by appropriate means, prior to the treatment of the waste and / or during the treatment thereof.

Referring again to Figures 1 to 3, it is noted that compartment B has a greater length than that of compartment A, for example equal to 3.30 m. During a second residence time t2 greater than the residence time t1, the waste and the alkaline reagent advantageously continue to be mixed in compartment B, by means of a shaft 12 provided with blades 12a, for example thirteen in number, whose shape and arrangement are, in the embodiment shown here, identical to those of the blades 7a. The shaft 12, of smaller section than that of the shaft 7, crosses the two compartments A and B. It has a section

12b, devoid of blades, which is connected coaxially to the shaft 7 by suitable coupling means, known to those skilled in the art. The shaft 12 is driven in rotation independently of the shaft 7, by a motor M2 having a variable speed V2 of, for example, between 18 and 84 rpm. The fact of continuing the mixing of the waste / alkaline reagent in compartment B is of interest in the context in particular of obtaining a hygienization of said mixture, where the temperature, the pH and the residence time of the mixture must respectively reach predetermined levels. Thus, it is possible to maintain a good heat exchange between the waste and the alkaline reagent, without destructuring the mixture.

The temperature of the mixture is maintained under the effect of the agitation produced by the rotation of the shaft 12, the user varying the speed V2 of this shaft in small proportions so as not only to respect the predetermined residence time t2 for hygienization, but also to avoid destructuring the mixture. Such treatment of the waste therefore proves to be particularly economical since the presence of heating elements inside the body 1a of the mixer 1 is no longer justified. The economy is also notable from the point of view of the consumption of alkaline reagent. In fact, the user will more easily opt for a longer residence time t2 in favor of a smaller quantity of alkaline reagent.

The continuation of the waste / alkaline reagent mixture in compartment B also proves to be advantageous when the desired result of the treatment is physical stabilization, for example physical stabilization by adding lime to a mud from a site, where the mixture must reach a predetermined cohesion, in order to be able to keep this mud in a heap. Thanks mainly to the shape and arrangement of the blades 12a and the possibility of varying the speed V2 in small proportions, it is possible to further homogenize the mud / lime mixture in compartment B without destroying it.

In any event, whatever the final result of the treatment desired by the user (biological, physical, chemical stabilization or even hygienization), the speed V2 will always be adjusted so as to be less than or equal to the speed V1 in the major goal of avoiding the destructuring of waste.

When the mixture has reached one or more of the parameters chosen from pH, temperature, cohesion or immediate bearing index and residence time which are set by the user according to the final treatment result he wishes to obtain , the waste / alkaline reagent mixture is extracted by an evacuation chute 13 disposed at the tail of the mixer 1. This chute 13 has the advantage of having an adjustable passage section, in order to be able to decrease or increase as the case may be. residence time t2 of the mixture.

So that the user can easily access the interior of the body 1a of the mixer 1, in the case in particular of the servicing or maintenance of the latter, there are provided, as shown in FIG. 2, several doors access, for example four doors 14, 15, 16 and

17. The doors 14 and 16, fixed to the body 1a of the mixer 1 for example by bolts, respectively allow access from below. compartments A and B. The doors 15 and 17, for their part, preferably articulated with respect to the body 1a of the mixer 1, allow access from the sides of the compartments A and B, respectively at the location of the opening 9 and the tail of the body 1a of the mixer 1. With reference to FIGS. 1 to 3, an additional pipe 5 ′ is arranged in the vicinity of the pipe 5, in the case where the treatment of the waste requires an additional additive in addition to the reagent alkaline, this additive can for example be an inert additive. Several conduits 18 are arranged on the top of the body 1a of the mixer 1 so as to extract the fumes which are liable to be released during mixing in compartment A and or in compartment B. This makes it possible to avoid the creation of an atmosphere confined inside the body 1a of the mixer 1, which could have an unfavorable influence on the result of the treatment by causing significant differences between the measured values of the parameters- cohesion or index bearing immediate and / or pH and / or temperature and / or residence time of the mixture and the predetermined values of these parameters. In order to be able to measure the parameters (cohesion or immediate bearing index, pH, etc.) of the waste / alkaline reagent mixture during treatment, several nozzles 18 'are arranged on the body 1a of the mixer 1, in the lower part of that -ci, and are adapted to be connected respectively to measurement sensors (not shown). As can be seen in FIG. 1, a circuit for circulating the fumes can be provided. The latter consists of a pump 19 intended to extract the fumes, the inlet of which is connected to the discharge conduit 18 closest to the discharge chute 13 of the waste / alkaline reagent mixture. The outlet of the pump 19 is connected to the inlet of a mist treatment device 20. This comprises a first outlet 20a, at the level of which the condensates are collected. This also includes a second outlet 20b which is connected to the duct 18 arranged at the head of compartment B. Thus, the air resulting from the treatment of the mist can be recirculated in the compartment B. Obviously and if this proves necessary, the air can also be recirculated in compartment A, as shown in dotted lines in FIG. 1.

A particularly advantageous embodiment of the process according to the invention consists in very strictly controlling the parameters of the waste / alkaline reagent mixture, even if the properties of the latter tend to vary, with a view to correctly dosing the alkaline reagent to be added even from the start of the treatment.

A control of the “cohesion” parameter of a sludge from a treatment plant, in the context of obtaining its physical stabilization, has been described in document BE-A-09800524. The method according to the invention, which has the result of obtaining physical stabilization and / or chemical stabilization and / or biological stabilization and / or hygienization, depending on the type of waste to be treated, must make it possible to control, in in addition to the “cohesion” parameter, which will be designated subsequently by C, other parameters such as the “immediate bearing index”, “pH” parameters,

“Temperature” and “residence time” which will be designated subsequently by IPI, pH, Θ and t1 and / or t2 respectively. The IPI parameter covers substantially the same notion as the C parameter. Depending on the type of waste and the final objective (recycling or landfill) desired by the user, the latter will choose to control one or more other of these two parameters. The following table makes it possible to make the link between the result that the user seeks to obtain by the method according to the invention and the number and type of predetermined parameters.

In this process, either the properties of the waste are known, or, by preliminary laboratory tests, the waste to be treated is characterized. In the latter case, depending on the desired result of the process, the user will determine one or more specific functions for the waste. In the case of obtaining a biological stabilization, the user determines the direct function which exists between the pH of the waste and the level of alkaline reagent. FIG. 6 gives an example of a pH-rate function of alkaline reagent established for several types of sludge from treatment plants treated with lime. In the case of obtaining physical stabilization, the user determines, depending on the nature of the waste to be treated and the final objective of the treatment, that is the direct function which exists between the cohesion and the dry matter of the waste to be treated. , or the direct function which exists between the immediate bearing index, the dry matter of the waste to be treated and the level of alkaline reagent. FIG. 7 gives an example of a cohesion-dry matter function established for a dehydrated sludge coming from an urban water treatment plant. FIG. 8 gives an example of an index function carrying immediate-natural water content (which is the complement to 100% of the dry matter) -alcoholic reagent rate for a plastic silt treated with quicklime.

In the case of chemical stabilization, the user determines the function represented in FIG. 6.

In the case of hygienization, the user determines the direct function which exists between the temperature and the rate of alkaline reagent using the following equation I:

Δθ = ^{U5 l Pt} ' ^MS ' (I)

4.184 (1 - MS,) + C _ms MS, + 0.89 t _c MS, where Δθ is expressed in ° C, t _c is the rate of alkaline reagent expressed in% by mass relative to the dry matter of the waste, MSi is the dry matter content of the waste before treatment expressed in% by mass and determined by the function represented either in FIG. 7, or in FIG. 8, or by direct measurement,

C _ms is the specific heat of the waste expressed in KJ / kgMS, P is the proportion (expressed in%) of alkaline reagent likely to transform during mixing with the waste.

In addition to this function, the user determines the direct relation which exists between the residence times t1 and t2 and respectively the rotational speeds V1 and V2 of the shafts 7 and 12. This relation is obtained by the following equation II:

V _m * 60 t = k * - (II)

^Υ 0 '0 ^υ ^7/5 ^J T ^y \ ol where t is in minutes residence time, k is the specific coefficient depending on the cohesion index or immediate-bearing waste to be treated, obtained by calibration,

V _rm is the average filling volume of the mixer expressed in m ³ ,

Vι or 2 is the speed of rotation of the shafts 7 or 10 of the mixer 1 expressed in rpm. Measuring devices 21, 22, 23, 24 and 25 are intended to determine respectively before the treatment of the waste, the initial cohesion d, the initial immediate index IPIj, the pH initiai pHj, the initial temperature θι of the waste to be treated and the initial residence time t1j and / or t2j. The determination of cohesion can be made using a texturometer, a scissometer, a penetrometer or the like. The determination of the immediate bearing index is made by a device meeting the standard NFR 94078. The determination of the pH and the temperature is carried out by completely conventional devices, such as a pH meter and a thermometer respectively. Finally, the measurement of the residence times t1 and t2 is carried out using a tracer (for example the iron filings) which are passed through the body 1a of the mixer 1 and the duration of passage in the compartments A and B is measured.

A flow meter 26, as mentioned in document BE-A-09800524, continuously measures the flow of waste to be treated. A control device 27 also mentioned in this document, such as for example a computer, receives the information from the devices 21 to 25. This device has a memory, a definition or the like to represent the functions illustrated in FIGS. 6 to 8 and to store equations I and II. This memory also stores a third equation III which makes it possible to obtain the dry matter content from the cohesion - dry matter function of FIG. 7. Equation III is as follows:

100 ((S .. / S - ï) t _c = - - ^ - - - (III)

1 + (0.32. (P / 100)) - MS _obj 1100 where t _c is the rate of alkaline reagent expressed in% by mass relative to the dry matter,

P is the proportion (expressed in%) of alkaline reagent likely to transform during mixing with the waste, MSj is the dry matter content of the waste before treatment expressed in mass% and determined by the cohesion - dry matter function of the figure 7,

MS _ob j is the predetermined dry matter content of the waste / alkaline reagent mixture after treatment, expressed in% by mass. As a function of the desired dry matter MS _0t> j and as a function of the initial dry matter content MSj obtained by the function C = f (MS) (see FIG. 7) after measuring d, the control device 27 calculates at using the equation

III the level of alkaline reagent necessary to obtain the value MS _0b j.

In the case of biological stabilization, the user sets a predetermined value pH ₀ bj and from the function shown in Figure 6, the device 27 deduces therefrom an alkaline reagent rate t _CO bj = f (pHj, pH _0b j) - In the case of physical stabilization, the user fixes a predetermined value C _0b j or IP j, and from the functions represented in FIGS. 7 or 8 and from equation III, the apparatus 27 deduces therefrom a value of alkaline reagent rate

or IPI ₀ bj, O or IP). In the case of chemical stabilization, the user fixes a predetermined value pH ₀ bj, and on the basis of the function represented in FIGS. 6, the device 27 deduces therefrom a value of rate of alkaline reagent tcobpfφHj, pHobj).

In the case of hygienization, the user sets at most three predetermined values θ _0bj , t1 _0b j and / or t2 _0b j, and from equations I and II, the device

27 deduces therefrom a predetermined value of rate of alkaline reagent t " _COb j, as well as one and / or two predetermined values of speed of rotation V1 _{0 j} = f (t1 _0bj ) of the shaft 7 and / or V2 _0bj = f (t2 _0bj ) of tree 12.

Note that in the case where several results are desired by the user, for example physical stabilization and hygienization, it is done so that the apparatus 27 determines the maximum value among the predetermined values of rate of alkaline reagent, obtained for physical stabilization, and the predetermined values of alkaline reagent rate obtained for hygienization. The apparatus 27 controls the motor 6a which rotates the dosing screw 6, as a function of the dose of alkaline reagent required per kg of dry matter of waste to be treated and as a function of the flow rate of dry matter of waste to be treated. The apparatus 27 also controls the motors M1 and M2 as a function of the values V1 _0b j and V2 _0bj obtained by equation II. As shown in Figure 1, measuring devices

28, 29, 30, 31 and 32, which can be respectively of the same type as the apparatuses 21, 22, 23, 24 and 25, are intended to determine, at the outlet of the mixer 1, a value C _m of cohesion, a IPI value _m of immediate index, a pH value _m of pH, a value θ _m of temperature, a value t1 _m and / or t2 _m of residence time of the mixture of waste and alkaline reagent. These devices can, of course, also be adapted to carry out measurements during the treatment of the waste / alkaline reagent mixture. The devices 28 to 32 are not absolutely necessary but nevertheless make it possible to obtain a finer control of the parameters C or IPI, pH, θ and t1 and / or t2 to arrive with more efficiency and certainty at the predetermined values C _ob j or IPI _ob j, pH _o j, θ _ob j and t1 _0bj and / or t2 ₀ bj. The following table makes it possible to make the link between the result that the user seeks to obtain by the method according to the invention and the minimum number, as well as the type, of parameters to be checked.

Signals are sent respectively by these measuring devices to the control device 27 which controls the flow rate of alkaline reagent added in the mixer 1 and the speeds V1 and V2 of the motors M1 and M2. If the said values measured respectively by the apparatuses 28 to 32 deviate from the predetermined values by more or less a preset threshold value, the apparatus 27 determines, in the same manner as previously, values of the rate of alkaline reagent as a function of the measured values Cm or IPI _m , pH _m , θ _m . Based on these new rate values, the dose of alkaline reagent per kg of dry matter to be treated is then automatically modified by an appropriate factor, as are the speeds V1 and or V2.

It may happen that the user decides to control, in addition to the minimum parameters, additional parameters. For example, in the case of physical stabilization, the user may want to control, in addition to the C or IPI parameter, the pH parameter. Initially, the apparatus 27 then determines a first value of the alkaline reactant level which is function of d or IPI, and of C _m or IPI _m , as well as a second value of rate of alkaline reagent which is function of pHi and pH _m . Then, in a second step, the apparatus 27 determines the average of these two values to obtain a single level of alkaline reagent. According to a variant of the method according to the invention, when the measured values θ _m and C _m or IPI _m deviate respectively from the predetermined values θ ₀ bj and C _ob j or IPI _obj by more or less a preset threshold value, the device 27 controls the pump 19 and the motors M1 and M2, so as to regulate the fume extraction rate. According to another variant of the process according to the invention, an inert additive, such as calcium carbonate, can be added to the waste to be treated in the mixer 1, in addition to the alkaline reagent. This inert additive can be added to compartment A by line 5 ′ shown in FIGS. 1 to 3 or to compartment B by another line (not shown). In the same way as the alkaline reagent, the inert additive, coming for example from a hopper 33, can be introduced by a metering device 34 driven by a motor 34a whose speed of rotation is controlled by a control device 35 receiving signals from measuring devices, of the same type as the devices 21 to 25, and from the flow meter 26 and / or a secondary flow meter. As described above, the measured values C _m or IPI'm, θ'm, pH'm, t1 ' _m and / or t2' _m , relating to the waste / alkaline reagent / inert additive mixture, are determined respectively by the devices 28 to 32. Signals are sent respectively by these measuring devices to the device 35 for controlling the flow of inert additive. If the values measured respectively by the devices 28 to 32 deviate respectively from the predetermined values CO j or IPr _ob j, θ ' _obj , ρH' _ob j, t1 ' _ob j and / or t2' _ob j by more or less a threshold value preset, the inert additive flow control device automatically modifies the dose of inert additive per kg of dry matter to be treated by an appropriate factor, as well as the speed V2 of the motor M2.

As an alkaline reagent, lime, cooked dolomite, cement, fly ash, hydraulic binders, slag can be used. and mixtures thereof. As an inert additive to be used optionally simultaneously with the reagent or after use of the reagent, mention may be made of calcium, magnesium and potassium carbonates, said carbonates being in the form of ground rocks, grains or powder, sand, cellulosic fibers, paper fibers, crushed mineral rocks, silicates, aluminosilicates, crushed or grain phosphates, crushed or powdered or grain nitrates, iron filings, sawdust wood, etc. and mixtures thereof. The amount of additive used advantageously corresponds to less than 25% by weight of the amount of reagent used.

It goes without saying that the embodiment of the method according to the invention and of the device for its implementation which have been described above have been given by way of purely indicative and in no way limiting example, and that numerous modifications can be easily made by those skilled in the art without departing from the scope of the invention. Thus the method and the device, instead of being adapted only to the mixture of waste, could as well be suitable for the mixture of products such as materials, natural or manufactured products.

Claims

1. Process for treating waste (D) comprising the steps consisting of: a) continuously supplying a waste (D) to be treated in a mixer (1); b) continuously add to the waste to be treated a measured quantity of at least one alkaline reagent (R); c) mix the waste (D) and said at least one alkaline reagent (R) intimately and continuously for a given time and, at the same time, transport the mixture thus obtained through the mixer (1); d) continuously extracting the waste/alkaline reagent mixture from the mixer (1), characterized in that in step c), the waste/alkaline reagent mixture is carried out successively at a first speed (V1), for a first residence time (t1), and at a second speed (V2) which is less than or equal to the first speed (V1), during a second residence time (t2) which is greater than the residence time (t1).

2. Method according to claim 1, characterized in that the waste (D) is chosen from the group comprising sludge from water treatment, sludge from cleaning and dredging, sludge from construction sites, sludge from industrial and agricultural processes, polluted land and earthy spoil.

3. Method according to claim 1 or 2, characterized in that it comprises:

-before treatment, a calibration of the waste (D) to be treated comprising a determination of at least one specific function for this waste, chosen from the specific functions linking the values of cohesion (C), dry matter content (DM) and alkaline reagent rate (tc) specific to it, the pH values (pH) and alkaline reagent rate (t _c ) specific to it, the temperature values (Θ), dry matter content (MS) and rate of alkaline reagent (tc) specific to it, the index values immediate bearing (IPI), dry matter content (DM) and alkaline reagent rate (t _c ) specific to it, as well as the specific function linking the values of residence time (t1; t2) and speed (V1; V2) suitable for mixing this waste with the quantity of said at least one alkaline reagent, as well as a selection of at least one predetermined value (C ₀ bj-; IP bj; pH ₀ bj; θ ₀ bj; t1 _0b j ; t2 _{0 J} ) chosen respectively from the values of cohesion (C), immediate bearing index (IPI), pH (pH), temperature (Θ) of the mixture and residence time (t1; t2) in the mixer (1); - before or during step a), a measurement of at least one value (C-,;

IP; pHi; ©i) chosen from the values of cohesion (C), immediate bearing index (IPI), pH (pH) and temperature (Θ) of the waste;

- during step b), a dosage of the quantity of said at least one alkaline reagent, using said at least one specific function, to obtain at least one of said predetermined values (C ₀ bj, IPIobj; pH _ob j ,

Θobj) for mixing;

- during step c), an adjustment of said speeds (V1) and (V2), on the basis of at least one value chosen from the measured cohesion value (Ci), measured immediate bearing index (IPIi) and the predetermined temperature value (Θ _0b j), to respect the predetermined residence time value (t1 ₀ bj; t2 ₀ j) of the mixture.

4. Method according to any one of claims 1 to 3, characterized in that it comprises:

- during or after the treatment, a measurement of at least one value (C _m ; IPI _m ; pH _m ; Θ _m ; t1 _m ; t2 _m ) chosen from the values of cohesion (C), immediate bearing index ( IPI), pH (pH), temperature (Θ), residence time (t1; t2) of the mixture;

- a comparison between said at least one measured value (C _m ; IP; pH _m ; Θ _m ; t1 _m ; t2 _m ) of the mixture during or after treatment and respectively said at least one predetermined value (C ₀ bj; IPIobj; pH ₀ bj; θobj; t1 obj ^" , t2 ₀ bj) of this mixture; - depending on this comparison, a possible adjustment of the dosage of the added quantity of said at least one alkaline reagent to obtain at least one of said predetermined values (C ₀ bj; IPIobj! pHobjî β ₀ bj) of the mixture, as well as a possible adjustment of the speeds (V1; V2) to respectively obtain the predetermined residence time value (t1 _0b j; t2 _0b j) of the mixture.

5. Method according to any one of claims 1 to 4, characterized in that it comprises during step c):

- extraction of steam likely to be released; - regulation of the steam extraction flow rate following the comparison between the measured temperature value (Θ _m ) of the mixture during or after treatment and the predetermined temperature value (Θ _ob j) of this mixture after treatment and/or following the comparison between the dry matter content value (MS _m ) of this mixture during or after treatment, determined as a function of the measured cohesion value

(C _m ) or (IPI _m ) thereof, and the predetermined value of dry matter content (MSo _b j) of this mixture after treatment, determined as a function of the predetermined cohesion value (C ₀ bj) or ( IPIobj).

6. Method according to any one of claims 1 to 5, characterized in that it further comprises:

- in step b), the continuous addition to the waste to be treated of a measured quantity of at least one inert additive;

- before treatment, a calibration of the waste to be treated comprising a determination of a specific function between the cohesion values (C) or instantaneous lift index (IPI) of this waste and the inert additive rate values;

- during or after the treatment, a measurement of at least one value (C' _m , IPI'_m;pH'_m;Θ'_m;t'1_m;t'2 _m ) chosen from the cohesion values (C ), immediate bearing index (IPI), pH (pH), temperature (Θ), residence time (t1; t2) of the waste/alkaline reagent/inert additive mixture;

- a comparison between said at least one measured value (C'_m;IPI'_m;pH'_m;Θ'_m;t'1_m;t'2 _m ) of this mixture during or after treatment and respectively said at least one predetermined value (C' _ob j, IPIObj, pHOBj, ΘObj, t1 Obj, ^t2 '°bj) of this mixture after treatment,

- depending on this comparison, a possible adjustment of the dosage of the added quantity of said at least one alkaline reagent and/or said at least one inert additive to obtain at least one of said predetermined values (COb _j , IPIObj, pHOBj, ΘObj) of this mixture after treatment, as well as a possible adjustment of the speed (V2),

7 Method according to any one of claims 1 to 6, characterized in that the alkaline reagent is chosen from the group comprising lime, cooked dolomite, cement, hydraulic binders, slags, fly ash and mixtures of these

8 Method according to claim 6, characterized in that the inert additive is chosen from the group comprising calcium carbonate, magnesium carbonate, potassium carbonate, sand, cellulosic fibers, paper fibers, crushed rock, silicates, phosphates, nitrates, iron filings, sawdust, zeohtes, silica, alumina, sepiolite, aluminosilicates and their derivatives, activated carbon, carbon black, clay, electrostatic precipitator dust and mixtures thereof 9 Waste treatment device (D) comprising a mixer (1) comprising a body (1a) pierced with a first opening ( 2) for the introduction of the waste (D) to be treated, a second opening (5) for the introduction of at least one alkaline reagent (R) and a third adjustable opening (13) for extraction of the waste/alkaline reagent mixture, a means for intimately mixing the waste and said at least one alkaline reagent which is arranged inside the body (1a) of the mixer (1) and which serves as a means of conveying the waste/reagent mixture alkaline towards the extraction opening (13) of the mixer (1), characterized in that the body (1a) of the mixer (1) comprises at least a first and a second compartment (A, B) communicating with each other by an adjustable opening

(9), through which the mixing means extends and in which the mixing means operates respectively at a first speed (V1), during a first residence time (t1), and at a second speed (V2), which is less than or equal to the first speed (V1), during a second residence time (t2) which is greater than the first residence time (t1).

10. Device according to claim 9, characterized in that the mixing means consists of a first rotating shaft (7) provided with blades (7a), which is arranged in the central longitudinal axis (X) of the body (1a ) of the mixer (1) and which passes through the first compartment (A), as well as a second rotating shaft (12) provided, on part of it, with blades

(12a) similar to those of the first shaft (7), which passes through the first and second compartments (A, B) and which is coupled coaxially to said first shaft (7).

11. Device according to claim 10, characterized in that the blades (7a; 12a) of the shafts (7; 12) each have two sides (P, P') on either side of a perpendicular line (L). at the axis of the trees (7;12).

12. Device according to any one of claims 9 to 1 1, characterized in that the body (1 a) of the mixer (1) is provided with one or more conduits (18) for evacuating steam likely to be released during the waste/alkaline reagent mixture.

13. Device according to any one of claims 9 to 12, characterized in that the body (1a) of the mixer (1) is provided with one or more connections (18') intended to be connected respectively to one or more sensors (s) measurement.

14. Device according to any one of claims 9 to 13, characterized in that the body (1a) of the mixer (1) has an opening (5') for the introduction of an inert additive.