SK10812001A3 - Method for conditioning sludge - Google Patents

Abstract

A method for conditioning sludge, whereby lime and at least one flocculent organic component are added and the sludge is flocculated. The inventive method is characterised in that the added lime only increases the pH of the sludge to a value which is above the pH that causes degradation of the applied flocculent organic component when the flocculation has finished.

Description

The invention relates to a process for treating mud comprising adding lime and at least one organic flocculating agent to the mud and one mud flocculation.

BACKGROUND OF THE INVENTION

Mud according to the present invention is to be understood as any type of mud whose pH is weakly alkaline, neutral or even acidic and preferably in the range of pH 6-8. Regardless of classification, mud from urban and agricultural treatment stations can be mentioned. It is also possible to take into account dredging mud or other types of possibly acidic mud.

During waste water treatment, the mud is generally first decanted and then concentrated. Then the mud is flocculated and dehydrated to facilitate transport and further handling.

Several methods of flocculation of preferably thickened mud are known. They all use a flocculating agent. Among these, in particular four processes which use mixtures of iron and lime salts, mixtures of aluminum and lime salts, organic polyelectrolyte and organic polyelectrolyte in conjunction with iron or aluminum salts are used as flocculating agents.

The disadvantages of using iron or aluminum salts in conjunction with lime are a significant increase in the amount of dry matter of the mud to be flocculated (by 50 to

%) compared to a slight increase when using an organic flocculating agent (less than 1%). Iron and aluminum salts attack non-oxidizable steel and almost all metals on the one hand, but on the other hand these salts in solid form (releasing irritating and even toxic dust. Their use therefore requires special precautions with regard to the material used and poses a danger to humans, who work with them.

Contrary to what we get from FeCb and lime mixtures, the use of an organic flocculating agent does not increase the agricultural value of the treated mud and the utility properties (cohesiveness, ease of peeling, spreading ability) are unlikely due to too low dry matter content in flocculated, dehydrated mud. . Lime not treated with lime usually contains pathogenic germs and represents poor biological stability.

There have been efforts to avoid the disadvantages of these procedures. For example, consideration has been given to treating lime-disinfected mud with a certain copolymer which is capable of maintaining a flocculating effect at pH 12.

This treatment, however, has the disadvantage of using a completely special copolymer, which is therefore expensive. It further envisages separate addition of lime. The copolymer is added only when the pH reaches its maximum value of about 12, requiring two downstream processing operations (US-A-4.160.731).

On the other hand, the simultaneous use of the polymer as a flocculating agent and lime milk has been contemplated some time ago for mud flocculation (see WOLF P., et al. Avril 1993, pp. 46-48). This use is intended to maintain all the advantages of lime, i.e.. increase of agricultural value of mud, higher content of dry matter after dehydration, good utility properties, hygienic treatment of mud and its biological stability. When filtration is carried out under pressure, the addition of lime facilitates the passage of mud and reduces the extrusion time.

This proposal does not seem to have been used so far. Indeed, when the organic flocculants that are commonly used operate correctly at neutral or only slightly basic pH, this is not the case at higher pH than when calcium is added

Milk to mud for processing. At higher pH they are degraded very quickly and are therefore ineffective.

This degradation is an uncontrollable phenomenon which, as can be seen in the results obtained by Wolf P. et al., Causes:

i. The dry matter content obtained under these conditions is not reproducible.

ii. The dry matter content obtained is in many cases lower than if lime was added only after dehydration.

iii. The dry matter content obtained cannot be controlled by adjusting the amount of liming applied to the mud.

In a similar manner to that of Wolf et al., JP-A-04-040286 provides for the application of a water-soluble calcium compound to mud from fish grounds and the addition of a flocculating polymer before or after the application. Only the pH of the aqueous phase is taken into account, with the recommendation of neutralizing it with acid after addition of the basic calcium compound. In all of the examples, the treated mud is initially strongly alkaline and is neutralized upon application of the calcium compound prior to the addition of the flocculating polymer. The dry yields and the agricultural value of the mud obtained are not investigated. While the mud is neutralized, it again becomes highly susceptible to bacterial contamination and subsequent odor release.

SUMMARY OF THE INVENTION

It is an object of the present invention to remedy these drawbacks and to improve the mud treatment process so as to make it possible to obtain dehydrated and pure mud with particularly good and uniform performance and a high dry material yield by means of commonly used organic flocculating agents.

To solve this problem, the process described above was considered, in which the addition of lime does not result in an increase in pH above the value causing the degradation of the organic flocculating component.

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It has been shown that it is possible in an unexpected way, by simply sensitively controlling the evolution of the pH during flocculation, to obtain treated mud exhibiting any lime-mud properties, using ordinary organic flocculants with perfectly repeatable results.

According to one embodiment of the invention, the process comprises adding lime before or simultaneously with the organic flocculating component, and the added lime during flocculation results in an increase in the pH of the mud to a value lower than the pH causing said degradation and further flocculation after pH. Preferably, the added lime causes an increase in pH to less than 9 during flocculation.

Thus, it has been shown in an interesting way that the less reactive the lime, the more reproducible the results of flocculation. Moreover, the dry matter yields were also fully reproducible in the same way, and in particular in the same way. Although this phenomenon has not yet been fully understood, the prevailing view is that, despite what was to be expected, lime is less reactive. Thus, increasing the pH of the processable mud is greatly retarded and flocculation initiated with a conventional organic flocculating agent can proceed properly despite the presence of lime.

For the purposes of the invention, lime is a compound of formula I:

(1-x) MgO TyH ₂ O (I) where x reaches a value of 0.5 to 1 and y reaches a value of 0 to 1. The compound may optionally be enriched with at least one additive. The lime may be present as burnt or slaked powder or as a slaked suspension in the aqueous phase. The quicklime is produced as a burning product of limestone and / or dolomite material at a temperature of about 1000 ° C and contains calcium oxide (CaO) and / or calcium magnesium oxide (CaO.MgO). The slaked lime consists predominantly of calcium hydroxide (Ca (OH) ₂ ) and / or mixed Ca (OH) ₂ hydroxide. Mg (OH) ₂ and is formed by hydrating (or extinguishing) quicklime and / or hydrating calcium oxide. Lime and / or calcium-magnesium milk is usually obtained either by hydrating quicklime and / or calcium-magnesium oxide in excess of water or by converting the slaked lime into an aqueous suspension.

The reactivity of lime is evaluated in different ways depending on whether it is quicklime or slaked lime. The reactivity of quicklime is determined by T60, a parameter that corresponds to the time required to raise the temperature of the lime / water system to be extinguished to 60 ΦΟ, the lime extinguishing being carried out according to the protocol given in Din 1060 Part ηφ 3. τ ₆₃ determination of slaked lime reactivity. τβ3 corresponds to the time required to pass 63% of the lime mixed with the volume of water into the solution under the following conditions: a lime volume corresponding to 0,1 g of slaked lime is added to 700 ml of water. The mixture was then stirred and maintained at 25 ° C. The conductivity of the solution is recorded until the lime is completely dissolved. It should be understood that dissolution of lime increases the conductivity of the solution, and that there is a linear relationship between the amount of dissolved lime and the observed increase in conductivity. τε ₃ is then determined on the basis of the conductivity obtained by determining the time required to reach 63% of the final conductivity. It should be emphasized that the faster the lime dissolves, the lower the ₆₃ .

It is preferred that the time required to reach pH 9 after the addition of lime is at least 20 s.

For lime with retarded reactivity, various products can be used. For example, it is contemplated to use powdered or slurry lime whose particles have a d 50 of at least about 100 µm, preferably at least 200 µm, and most preferably at least 400 µm. d50 is the particle size from which half of the particle size distribution by volume consists of larger particles. For example, it is possible to use defilerized lime, which means lime in the form of a powder or suspension from which fines have been removed, especially those having dimensions less than 200 µm, and preferably dimensions less than 250 µm. Such lime can be obtained by sieving, cycloning or any other method designed to remove fine impurities.

Thus, it has been shown in an interesting way that the thicker the lime particles are, the more favorable the flocculation results are.

According to another embodiment of the invention, the added lime is burnt, for example lime having a T60 of 10 min, and which is available from Rheinkalk BmbH, Wulfrath, Germany.

According to yet another embodiment of the invention, quicklime comprises a liquid additive capable of agglomerating its smallest particles. Such a product is described, for example, in WO-98/23705. As a liquid additive of this kind, for example, but not limited to, compounds belonging to the group of mineral oils, polyolefins and mixtures thereof.

According to a preferred embodiment of the invention, the quicklime added contains an agent which retards hydration. Such lime can be prepared, for example, according to WO-98/02391. As the hydration retardant, for example, but not limited to, glycerol, glycols, lignosulfonates, amines, polyacrylates, alkali metal or alkaline earth sulphates, gypsum, sulfuric acid, phosphoric acid, sucrose, and theirs mixture. It is also contemplated, as described in WO98 / 02391, to add a very small amount of water to quicklime without additional additives or in addition to the previous ingredients and in a controlled manner that allows the formation of a surface reaction retarding the later extinguishing reaction.

According to an embodiment of the invention, the lime in the slaked form may have a dry matter content of greater than 20% and preferably greater than 40%. For example, it is possible to use a Ca (OH) 2 suspension as described, for example, in BE-A1006655.

According to another embodiment of the invention, the lime may be in slaked form containing agglomerated particles. Such a product is thus in powder form

I f · - Even a lumpy substance that is easy to transport and easy to handle. A product of this kind can be prepared, for example, according to the process described in BE-A-1006655 or also in the example below. Such an agglomeration result may take the form of an aggregate of calcium hydroxide micro-leaves.

According to yet another embodiment of the invention, the added lime is slaked, with the addition of an agent reducing its activity. Examples of such limiting agents include, but are not limited to, glycerol, glycols, lignosulfonates, amines, polyacrylates, alkali metal or alkaline earth sulphates, gypsum, sulfuric acid, phosphoric acid, sucrose, and the like. mixtures thereof.

Preferred conditions are the addition of the slaked lime in an amount where the liming rate is at least 10% by weight relative to the dry weight of the mud and most preferably at least 20% by weight, without these limits being considered to be critical.

The lime may be added to the mud before, during and / or after the organic flocculating agent. Thus, the embodiment of the invention gives users the possibility to choose the moment for adding lime. Thus, the addition of lime and the organic flocculating agent is most preferred, which is a difficult to anticipate finding, given the antagonistic properties of the lime and flocculating agent. It is therefore not necessary to make any changes to the existing technical arrangement for mud treatment. It is even possible to consider adding lime before using a completely conventional organic flocculating agent, unless there has been a significant increase in mud pH prior to its use. It is preferred that the use of the organic flocculating agent occurs within a maximum of 5 minutes after the addition of the entire amount of lime.

It is preferred that the mud to be treated be detected beforehand. After flocculation, separation of the solid and liquid phases of the mud according to the invention can be envisaged by all suitable and conventional means, for example by means of filter belts, pressure filters, centrifugation devices, and possibly later dehydration.

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It is very advantageous if this separation is carried out immediately after the flocculation has ended, i.e. approximately before the pH reaches the values causing the degradation of the organic flocculating agent. The liquid phase is thus separated at neutral to slightly basic pH and can be discarded without further treatment, possibly after slight neutralization. In the solid phase, on the other hand, there is an increase in pH, preferably up to very high values, which allow recovery of the treated mud.

As already mentioned, the selection of the organic flocculants according to the invention is not critical and those which are most commonly used for this purpose today can be used. Depending on the mud properties, nonionic, anionic or cationic organic flocculants are used alone or in admixture. Particularly contemplated are acrylamide or acrylamide copolymers, for example with carboxylic or sulfonic acid, dimethylaminoethyl acrylate or dimethylaminoethyldimethacrylate, dialyldimethylammonium chloride or acrylamidopropyltrimethylammonium chloride.

Further details and particularities of the embodiment of the invention are set forth in the claims.

It is important to note that the mud obtained after flocculation and dehydration carried out according to the invention has a high lime content and is well disinfected. It can therefore be used well for the recovery of agricultural land.

The invention also relates to mud treated using the process of the invention wherein the dry yield is positive with respect to the dry matter loaded into the mud during processing.

The invention will now be explained in more detail by way of examples, which are purely illustrative and not limiting.

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DETAILED DESCRIPTION OF THE INVENTION

Example 1 - Preparation of slaked lime with low reactivity from quicklime g calcium sulfate dihydrate (CaSO ₄ .2H ₂ O) is dissolved in 5 liters of water. In this solution, a suspension is then formed by stirring with 1 kg of quick lime, the T60 of which, as determined by the above method, lies between 1 and 5 minutes. During this operation, commonly known as extinguishing, the suspension temperature is maintained below 30 ° C. Once the lime slaking is complete, the calcium hydroxide slurry is filtered to yield slaked lime with low reactivity. τ ₆ 3 of the slaked lime shall be determined as above and the dry matter content shall be calculated according to. Degrémont, Mémento Technique de leau, éd. Du Cinquantenaire, 9® ed., Tome I, p 370, 1989. The granulometric distribution is determined using a Laser Coulter LS 230 granulometer and d50 is determined based on this distribution.

The T63 of this slaked lime is 1010 s, the dry matter content is 80.5% and the d50 is 748 pm. The particle size distribution is shown in black squares in the attached figure.

Example 2 - Preparation of slaked lime with high reactivity from quicklime

200 g of micronized Ca (OH) ₂ having a d 50 of about 3 µm is poured into 1 liter of water while stirring. The suspension is stirred for a further 5 minutes. The same parameter determination methods as in Example 1 are applied.

τ ₆ 3 of this sample is 15 s, dry matter content is 25% and d50 is 3,3 µm. The particle size distribution is shown in white squares in the attached figure.

Example 3 - Filtration of mud treated with a conventional cationic organic flocculating agent and low reactivity slaked lime added after the flocculating agent.

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An amount of thickened, cleaned mud corresponding to 20 g of dry matter is taken into a liter vessel. This mud sample is treated as follows:

Preparation of an aqueous solution containing a flocculating agent:

An aqueous solution of organic cationic flocculating agent (acrylamide copolymer) at a concentration of 0.3% by weight is prepared by slowly pouring 0.6 g of flocculating agent in powder form into 200 ml of water prepared in a 400 ml container. While pouring until a homogeneous solution is obtained, the solution is stirred with a magnetic stirrer.

flocculation:

ml of this aqueous flocculant solution is added to the mud with a syringe. The mixture of mud and flocculant is then mixed with a standard laboratory flocculator at time 6 at 300 rpm.

Liming:

After 15 to 20 seconds after the addition of the flocculating agent, lime prepared according to Example 1 is added to the just flocculated mud. The mixture thus obtained is stirred at 10 rpm at 200 rpm using a conventional laboratory flocculator.

At each step of the operation, the vessel is weighed to accurately determine the liming rate.

filtration:

The sample thus obtained is transferred to a filter cell and allowed to drip for 4 minutes. A pressure of 2 to 4 is then applied to the dripped mud by means of a piston

II bars at the time required to form a filter cake with a height of 3 to 5 mm. This cake is then collected to determine the dry matter content.

In order to evaluate the effect of liming on the dry matter content of the filter cake, in a second experiment, the same, thickened mud is flocculated and then filtered according to the protocol described above, only omitting the liming containing step. For the lime mud filter cake, 16.5% dry matter was obtained, while the lime mud filter cake contained 25.4% dry matter, representing a 17.2% relative dry yield. This dry yield was determined by reference to the dry matter which would be obtained if an equal amount of lime was added to the non-calcined mud after dehydration (S2 *).

S1x (100 +1)

S2 * = ------------------------ (II)

100 + (S1 x (t / 100)) where S1 content denotes dry matter in the filter cake of non-calcined mud, t is the ratio of slaked lime added expressed in% by weight relative to the dry matter contained in the concentrated mud.

The drip water fraction (X ₀ dypap) of lime mud is 0.51, while in the case of non-lime mud the fraction is 0.41. This fraction is obtained by dividing the drip volume by the total volume of water contained in the treated mud during the dehydration test. The drip water volume is understood as the volume of the filtrate obtained after 240 seconds of dripping.

Example 4 - Filtration of mud treated with a conventional cationic organic flocculating agent and multiple types of slaked lime with varying reactivity that were added after the flocculating agent.

A series of filtration of purified flocculated mud, which was limed with several types of slaked lime with varying reactivity, was carried out according to the procedure described in Example 3. Different types of slaked lime were obtained by sieving the slaked lime obtained according to Example 1 into different granulometric fractions. D50, t _P h = 9, X63 different types of ingested slaked limes are listed below, in Table 1. tph = 9 expresses the time needed for a given type of lime to increase the pH of treated mud to 9. Dry matter content of lime or lime obtained after filtration is indicated in this table by S1 and S2, respectively. Dry yields (SH = dry mass) using liming were determined using the method described above. Finally, the drip fractions are designated as X _O dkvap- It should be noted that the drip fraction of 0.6 was obtained for flocculated, non-calcined mud.

Table 1

sample 1 2 3 4 5 6 Grain size limits (pm) 20-45 45-80 80-200 200-400 400-1000 > 400 D50 (pm) 4 59 119 235 550 748 TPH = 9 (a) <5 20 36 53 80 551 T63 (S) 12 80 180 350 800 1010 S1 (%) 15.5 15.5 14.9 14.9 14.9 14.9 S2 (%) 17.5 20.8 21.4 22 22 22.4 SH yield (%) rel.) -17.3 2 8.9 12 12 14 Xodkvap 0.50 0.49 0.63 0.63 0.61 0.63

The table clearly shows that in samples 4 to 6 a high and almost constant dry matter content is achieved and in the case of dry yield and dripping, satisfactory values are already achieved in sample 3.

Example 5 - Filtration of treated mud using a conventional cationic organic flocculating agent and fine particle lime milk, which is added after the flocculating agent.

The concentrated purified lime was flocculated, limed and then filtered according to the protocol described in Example 3, except that liming was in this case performed with lime milk according to Example 2.

In order to evaluate the effect of liming on the dry matter content of the filter cake, in the second experiment the same mud was flocculated, then filtered according to the protocol described in Example 3, except that the liming step was omitted. The show yields and X-drops were determined as described in this example. For the non-calcined mud filter cake, a dry matter content of 16.4% was obtained, while the calcined mud filter cake had a dry matter content of 19.1%. This represents a relative loss of approximately 1111% in the dry state. The drip water fraction from lime mud was 0.47, while the non-calcined mud was 0.61.

Thus, it can be noted that the dripping has poor properties when very reactive lime is used, and thus deflocculation and, of course, dry loss, which is the opposite of the target, are likely to occur.

Example 6 - Filtration of treated mud using a conventional cationic organic flocculating agent and low reactivity slaked lime added before the flocculating agent.

A quantity of purified thickened mud corresponding to 20 g dry matter is placed in a 1 liter vessel. This mud sample is further processed according to the following procedure:

Preparation of an aqueous flocculating agent solution:

An aqueous flocculant solution is prepared as in Example 3.

Liming:

The slaked lime prepared according to Example 1 is added to the concentrated mud. The amount of lime added is adjusted so that the weight of the slaked lime corresponds to 40% of its original dry mass. The mixture thus obtained is stirred at 200 rpm using a conventional laboratory flocculator. At each step of the liming operation, the vessel is weighed to accurately determine the liming rate.

flocculation:

after addition of lime, 20 ml of an aqueous solution of the flocculating agent is added to the calcined mud with a syringe. The mixture of mud and flocculant is then mixed with a standard laboratory flocculator at time 6 at 300 rpm.

filtration:

Filtration is performed as described in Example 3.

In order to evaluate the effect of liming on the dry matter content of the filter cake, in a second experiment, the same, thickened mud is flocculated and then filtered according to the protocol described above, only omitting the liming containing step. For the non-calcined mud filter cake, 16.5% dry matter was obtained, while the lime mud filter cake contained 25.8% dry matter, representing a 19.3% relative dry yield. The drip water fraction from lime mud was 0.663, while the non-calcined mud fraction was 0.648.

Example 7 - Filtration of mud treated with a conventional organic flocculating agent and burnt lime, which is added simultaneously with the flocculating agent.

A quantity of purified thickened mud corresponding to 20 g of its dry mass is placed in a 1 liter vessel. This mud sample is further processed according to the following procedure:

Preparation of an aqueous flocculating agent solution:

An aqueous flocculant solution is prepared as in Example 3.

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Flocculation and liming:

Using a syringe, add 20 ml of an aqueous flocculant solution to the mud. At the same time, burnt lime (T60 = 28.8 min) is added with a mass corresponding to 30% of the original dry mud mass. The mixture of thickened mud, flocculating agent and lime is then stirred at time 6 at 300 rpm using a conventional laboratory flocculator.

filtration:

Filtration was performed as described in Example 3.

In order to evaluate the effect of liming on the dry matter content of the filter cake, in a second experiment the same, thickened mud is flocculated and then filtered according to the protocol described. above, only the liming-containing step is omitted. The dry yield was determined as described above, the slaked lime used being 38.9%.

For the lime mud filter cake, 15.3% dry matter was obtained, while the lime mud filter cake contained 20.9% dry matter, representing a 4.2% relative dry yield.

Example 8 - Filtration of mud treated with a conventional organic flocculating agent and quicklime with one additive. The lime is added after the flocculating agent.

A quantity of purified thickened mud corresponding to 20 g of its dry mass is placed in a 1 liter vessel. This mud sample is further flocculated and filtered according to the procedure described in Example 3.

During liming, however, slaked lime is not added to the thickened mud, but a certain amount of quicklime obtained by the process described in WO98 / 23705. The T60 of the lime thus obtained is 7.3 min. The amount of lime added shall be adjusted so that the weight of quicklime corresponds to 30% of the original dry mass. :. * 'e · r - · ι · mud. The mixture thus obtained is stirred at 10 s at 200 rpm using a conventional laboratory flocculator.

In order to evaluate the effect of liming on the dry matter content of the filter cake, in a second experiment, the same, thickened mud is flocculated and then filtered according to the protocol described above, only omitting the liming containing step. The dry yield was determined as described above, with the slaked lime ratio used being 38.9%.

For the lime mud filter cake, 15.3% dry matter was obtained, while the lime mud filter cake contained 20.4% dry matter, representing a 1.7% relative dry yield.

Example 9 - Filtration of mud treated with a solution of a conventional cationic organic flocculating agent and defilerized quicklime which is added simultaneously with the flocculating agent.

Filtration of purified mud, which was flocculated and calcined with quicklime, from which particles less than 250 µm in size were removed, was carried out as described in Example 7. In order to evaluate the effect of liming on the dry matter content of the filter cake, the second If the experiment is the same, the concentrated mud is flocculated and then filtered according to the protocol described above, except that the liming-containing step is omitted. The dry yield was determined as described above, the slaked lime used being determined to be 38.7%.

For the lime mud filter cake, 18.1% dry matter was obtained, while the lime mud filter cake contained 25.7% dry matter, representing 8.3% relative dry yield.

During the mud liming experiment, the pH of the mud before adding lime was 6.96. The pH of the calcined mud just prior to filtration was 8.8. The pH of the obtained filtrate was 9.8 and the pH of dehydrated calcined mud four hours after dehydration was approximately 12.5.

Example 10 - Filtration of mud treated with a solution of cationic organic flocculating agent and low reactivity slaked lime, which is added simultaneously with the flocculating agent.

Filtration of purified mud, which was flocculated and calcined with slaked lime with low reactivity, was carried out as described in Example 7. In order to evaluate the effect of liming on the dry matter content of the filter cake, the second experiment is the same, concentrated mud flocculated and then filtered according to the protocol described above, only the liming-containing step is omitted. The dry yield was determined as described above and the slaked lime content was determined to be 37.5%.

For the lime mud filter cake, 18.1% dry matter was obtained, while the lime mud filter cake contained 24.9% dry matter, representing a 5.8% relative dry yield.

During the mud liming experiment, the mud pH was 7.01 before lime addition. The pH of the calcined mud just prior to filtration was 9.2. The pH of the obtained filtrate was 9.5 and the pH of dehydrated calcined mud four hours after dehydration was approximately 12.6.

It is to be understood that the present invention is not limited in any way by the embodiments described above, and that many of the methods may be varied within the scope of the appended claims.

For example, it is contemplated to use a type of lime other than that described herein, the reactivity of which will be diminished in a manner other than that indicated in the preceding description.

Industrial usability

For example, the invention relating to a mud treatment method can be used to treat mud from urban and agricultural treatment stations, mud obtained by dredging or waste water treatment.

P1 / 10ri-Zool

Claims (21)

A process for treating mud, comprising adding lime and at least one flocculating agent to the mud and one mud flocculating, characterized in that the added lime does not cause an increase in the pH of the mud beyond a value causing degradation of the organic flocculating agent applied only after flocculation has ended. The method of claim 1, comprising adding lime before or simultaneously with the organic flocculating agent, and wherein the added lime exhibits a reactivity that causes the pH to rise below the pH causing the above degradation during flocculation, and stop flocculation further increase the pH above the above value. The process according to claim 2, characterized in that the added lime exhibits a reactivity which during flocculation causes the pH to rise to a value below 9. Method according to claim 3, characterized in that the time required to reach pH 9 after the addition of lime is at least 20 s. The process according to any one of claims 1 to 4, wherein the added lime is a composition corresponding to the formula &lt; x &gt; Ca ₍ O-x) MgO2H2O, wherein x has a value of 0.5 to 1 and y has a value of 0 to 1, optionally enriched with at least one additive. The process according to claim 5, characterized in that the added lime is in burnt or slaked powder form or in slaked form of a suspension in the aqueous phase. The method of any one of claims 1 to 6, wherein the added lime comprises particles having a d 50 of at least 50 µm. r Γ 49 ' Method according to claim 7, characterized in that the added lime comprises particles having a d 50 of at least 100 µm, preferably of at least 200 µm. The method according to any one of claims 1 to 8, characterized in that the added lime is burnt lime. The method of any one of claims 1 to 8, wherein the added lime is quicklime containing a liquid additive having the ability to agglomerate the smallest particles of the composition. The method according to any one of claims 1 to 8, wherein the added lime is quicklime containing a hydration retardant. The method according to any one of claims 1 to 8, characterized in that the added lime is slaked lime containing agglomerated base particles. A method according to any one of claims 1 to 8, characterized in that the added lime is a slaked lime containing an agent reducing its activity. A method according to any one of claims 1 to 8, characterized in that the added lime is slaked lime with a dry matter content higher than 20% by weight. A method according to any one of claims 1 to 6, characterized in that the added lime is defilerized lime. Method according to any one of claims 1 to 15, characterized in that the treatment mud belongs to the group comprising the treatment mud, dredged mud or acid mud. A method according to any one of claims 1 to 16, characterized in that it comprises separating the solid and liquid phases of flocculated and calcined mud. • · · f Γ 9 9 9 · * <r • t 9 9 9 r t r SJO Process according to claim 17, characterized in that the separation is carried out by filtration or centrifugation. Method according to one of claims 17 or 18, characterized in that the aforementioned separation is carried out approximately before the pH reaches the above-mentioned values causing degradation of the organic flocculating agent used, and that after separation the liquid phase has this pH and a solid phase. the pH increases above this value. Use of mud treated according to the method of any one of claims 1 to 19 for the recovery of agricultural soils. The treated mud obtained by the process according to one of claims 17 to 19, representing a positive dry yield with respect to the dry matter content introduced into the mud. ? In 10? F Z0Of 1/1 Particle diameter (μιη) Volume (%) <=> o p