MXPA99006244A - Method for the physico-chemical treatment of effluents in particular surface water for consumption - Google Patents

Abstract

The invention concerns a method for the physico-chemical treatment of effluents in particular surface water for consumption, comprising successive steps of coagulation (A), flocculation (B) and decantation (C), a contact mass being introduced in the water coming from the coagulating step, hence during the flocculating step and this contact mass consists of part of the densified sludge derived from the decanting step and recycled in the flocculating step. This method is characterised in that it consists in injecting in the sludge recycling circuit (16) at least part of the polyelectrolyte ensuring the flocculation.

Description

PROCEDURE FOR TREATMENT Fl S I CO-QUIMI CO OF EFFLUENTS, ESPECIALLY OF SURFACE WATERS FOR CONSUMPTION DESCRIPTION OF THE INVENTION The present invention relates to a process for the efficient treatment of effluents, especially of surface water for consumption. It is known that the implementation of physiological chemistry procedures is common for most of the treatments applied to different types of water, and that these treatments consist essentially of the following: - a clarification of the surface waters intended for consumption or the industries; a clarification of urban, rain or industrial wastewater; - a decarbonatation; - a removal of phosphates, etc. In all cases, these types of physical-chemical treatments cover the following successive stages: - a coagulation: stage of neutralization of the colloid with a metal salt, with a trivalent compound of iron or aluminum in general, in order to form my ero - fio ass s (microfloc). This coagulation step can be carried out in one or more stages: - flocculation: stage of agglomeration and growth of the mycofors. This agglomeration step takes place thanks to the addition of a polymeric polymer (or polymer), downstream of the coagulation stage; - a settling: stage of separation of the flocs and interstitial water, which has as a consequence the formation of sludge on the one hand, and clarified water, on the other hand. For about thirty years, the state of the art related to a physical-chemical treatment of this type, has evolved considerably due to the application of two techniques: the flocculation by means of a contact mass, which has allowed to improve the quality of the flocs, reduce the volume of the reactors and improve the clarification. In fact, the mi c r o - f 1 or coagulation have a greater possibility to agglomerate and to grow (increase in size) the higher the density of the particles present in the reaction medium; The velocity of formation of the flocs is proportional to the amount of free particles in the suspension. - laminar decanting, carried out by introducing plates or inclined tubes, in the reactors. This technology has allowed to reduce the size of these decanters in a proportion of 50 to 70% - The current technological evolution points to the improvement - of the flocculation conditions, which are decisive in terms of the quality of the treated water and Nowadays, modern decanters use two types of contact masses in the flocculation reactor: 1.- Decanted and recirculated sludge: an example of this technique is the one described in document FR-A-2.553.082; 2.- Fine weights, such as micro-sands: an example of implementation of this technique, has been described in documents FR-A-1.411.792 and FR-A-2.627 .704 - The present invention relates to improvements introduced in the apparatus for decanting and recirculating the sludge, said improvements being such that said devices, while retaining their specificities and their advantages, operate at settling rates. Before describing these improvements, we will proceed to export the advantages and disadvantages of this known technique, based on "contact" masses consisting of sludge. In FIG. 1 of the attached drawings, a co-chemical treatment plant has been schematically represented, in which said technique is used. In this figure it has been outlined: in A, the coagulation reactor; in B, the flocculator and in C the decanter. In this case, these are well-known installations by the art man, so they will not be the object of a description. _ As can be seen in Figure 1, the contact mass, in the flocculation reactor, B, is constituted by the recirculation of a part of the sludge decanted in C, said part of the recycled sludge being introduced in the flocculator B through the conduit 16 and the recirculation pump, 18. The recirculated sludge flow represents between 0.5 and 4% of the treated flow. The recirculated sludge, the raw water and the po 1 ie 1 ec t ro 111 o, are placed in reciprocal contact in a zone of strong turbulence, the polymer being, as can be seen in this Figure 1, usually injected into the vicinity of propeller 10 of flocculator B. Excess concentrated sludge is extracted and evacuated. The advantages of this flocculation technique based on the sludge decanted and recirculated, as a contact mass, are the following: 1.- the contact mass is generated by the procedure itself, so it is available without limitation of quantity, according to the needs of the procedure; J 2 - in the flocculation reactor B, the mass of the sludge, due to the r e ction, is very high with respect to the material in suspension contributed by the raw water. Therefore, the system is insensitive to both the decreases and the significant increases in the material in suspension in the raw water; 3. -the contact mass offers "a specific surface or a special occupation, very important, thanks to its exposed structure and weak relative density, for example, 1 gram of flocculated sludge in a liter (average concentration in the reactor ) occupies, after a decantation of approximately 5 minutes, a volume equal to 100 ml.This specific surface or special occupation, very high, considerably increases the probability of contacts between the flocs and the very fine particles, the coagulated colloids and the micro-organisms, and therefore the probability of "trapping" these materials in suspension very efficiently, 4.- due to the continuous recirculation of the sludge always re f 1 or c Also, the extracted sludge is very concentrated (two to ten times more concentrated than the sludge of most of the devices), 5.- This technique allows to achieve speeds of t relatively high treatment. Thus, in the case of clarification of river water, the speeds obtained through the laminar modules of the decanter are between 10 and 25 ra3 / hour, which corresponds to decanting speeds UD (flow rate / surface area of In fact, these speeds are limited by the mass flow limit (Fml) of the flocculated suspension, expressed in kg of suspended matter that transits per square meter. Soil of the decanter and per hour (kg / m2 / h) The mass flow is the limiting factor that determines the theoretical limit value of decantation, Udl - This value is also linked to the concentration CR of the sludge in reactor B , expressed in kg / m3: Fml = CR x Udl In other words: Udl = Fml / CR - If the decanting rate UD applied to the decanter C is equal to or greater than Udl, there is an appraisal. terminator, but is unable to retain a mud bed.

Therefore, it must be verified that the mass flow applied in the decanter is less than ML, or that the decanting rate UD applied to the decantator is less than Udl. For example, in the "case of river water clarification, the bulk flow limit is generally lower or closer to 20 kg / m3h.The CR concentration required for good flocculation is" about 1 kg / m3. The settling limit speed Udl is then 20 m / h, so the speed UD applies to the decanter is less than 15 m / h, for safety reason e_s. 6.- It is frequent that the apparatuses of this type are followed by a filtration system.

This is the case of the filtration of river water. The filtration is characterized by the quality of the filtered water and the duration of the filtration cycle. (duration of operation at the end of which the filter becomes dirty, which means that it must be washed). With the recirculation type decanters of the sludge, the duration of the filtration cycle is usually greater than 24 hours.

In order to translate the aptitude of the decanted water to be filtered with correct filtration times, tests are carried out for the reagent of the decanted water. One of the trials that can be used is to measure the time required to filter 250 cm3 of decanted water through a 5 μm membrane and under a vacuum of 8.101 Pa. "~. Water filtration will be so much easier how much "this time is shorter. In the case of a decanter that works __with an UFD settling velocity equal to 15 m / h, the fi rst degree is approximately 30 seconds 7.- The increase of the decanting speeds UD, is possible , but at the price of an increase in the dose of po 1 ie 1 ectro 1 ito However, an excess of po 1 ie 1 ec t ro 1 i to reduce the fi lity of the water decanted (increases the time of the test), which in a filter results in a surface grocery and therefore a reduction in the duration of the filtration cycle The present invention aims to improve the technique discussed above, in view of the Increasing the settling velocities, without affecting the effectiveness of decanted water Therefore, the subject of the present invention is a process for the chemical treatment of effluents, especially surface water. . intended for consumption, which comprises the successive stages c coagulation, flocculation and decanting agents, introducing a contact mass in the water and stone of the coagulation stage, therefore during the stage of the cul de ion, • said contact mass being constituted by a Part of the densified sludge from the decantation and recycled stage in the flocculation stage, said process being characterized in that at least part of the po is injected into the recirculation circuit of the sludge 1 ie 1 ec t ro 1 ito that flocculation is guaranteed. The owner of the present has verified that this way of proceeding has the unforeseen and advantageous effect of increasing the massive flow limit, the settling velocity, the fi rity of the raw water and the concentration of the sludge. extracted. The process object of the present invention, defined in what precedes, can be implemented with a flocculation stage that resorts to a ballast in quality of contact mass. It is known that according to this technique, the contact mass is obtained by the addition, upstream of the flocculator, of a new or recycled ballast after its washing. The means for separating and regenerating the ballast that has to be recycled in the flocculator, are well known by the art man, so they will not be the object of a description. In the implementation of this technique, the ballast is usually constituted by sand, and the extractions carried out continuously at about 5% of the flow of water treated by the decanter.; these extractions, laden with sludge surrounding the sand, must be subjected to treatment in order to regenerate said sand; the sand, cleaned, is subsequently reinjected in the upstream of the flocculator, at the head of the installation. The residue generated by this cleaning of the 1st tre - sand, represents the excess sludge. Note that ballast-type devices existing and described in the literature, and especially in documents FR-P-1,411,792 and FR-A-2,627,704, comprise a ballast recycling, for obvious reasons related to the cost of The explotion. On the other hand, in all the documents in which this technology is described, it is made clear that the ballast is always "cleaned", that is, regenerated. In effect, the ballast "stuck" by the polymer, must present - a maximum adhesive surface for the precipitation flocs made chemically on the occasion of coagulation. Therefore, "an effective physical cleaning is essential to expose the maximum of the hooking surface." Ballast is often sand whose diameter is generally between 50 μm and 150 μm, generally referred to as "micro-sand". The Journal Water SRT-AQUA, volume 41, No. 1, pages 18-27, 1992, reveals a graph that relates the turbidity of the water produced, with the diameter of the ballast particles, which shows that this procedure It is effective to the extent that the sand particles do not exceed 150 μm, these results being better when using values in the environment of 50 to 100 μm.Note that the advantage of this flocculation technique with contact mass constituted by a fine ballast, resides essentially in the speed of the decantation, which can be higher in 20% to 200% 7 ~ c oh respect to the "speeds obtained through the flocculation procedures with contact mass constituted by sludge decanted and recirculated. For example, in the case of clarification of river water, the speeds obtained by laminar modules are between 25 and 50 m3 / m2.h, while the teams that resort to the flocculation procedure based on the mud as masj of contact, have limited speeds, of the order of approximately 15 to 30 m3 / m2 h The essential drawbacks of this technique, are essentially based on the fact that the ballast has to ensure two different f-unctions: an accelerated flocculation, thanks to the immentation of a contact mass with a high specific surface (or high specific occupation 1); _ - the acceleration of the decantation velocities, resulting from the addition of ballast to the flocs. These limits or drawbacks are attributable to the following factors: under mass conditions of equivalent contacts (by weight), the ballast has a contact surface, or percentage of special occupation, much weaker than the sludge. By way of example: - in the case of "flocculation with sludge", the concentration in the reactor is approximately 1 g / l, "and the volume occupied by the sludge after five minutes of decanting, it is approximately 10% of the initial volume; in the case of a "flocculation with ballast (for example, sand) ", the concentration of the ballast in the reactor must reach at least 5 g / 1, while the volume occupied by the mud after five minutes of decanting, is only approximately 1 % of the initial volume, the increase in the amount of ballast, desirable for obtaining a strong contact mass (and not for obtaining a high decantation speed), leads to increase the flow of recirculation to the system for the treatment of the extracted mud, treatment that consists of separating the "sand from the muds, with the effect of regenerating it. This operation is usually carried out by means of hydrocyclones, fed at high pressures, which operation is therefore very costly in terms of energy consumption. In fact, and in order to limit operating costs, the flow rate of recirculation is intentionally limited between 5 and 10% of the treated flow, and the ballast concentration in the reactor does not exceed 5 to 10 g / 1; this choice is incompatible with the possibility of optimizing flocculation. There are several techniques aimed at compensating for the contact mass deficit resulting from the operating conditions described above, such as: the implementation of an increase in flocculation energy (s) and they mention figures that can reach up to one hundred times the classical energy of flocculation), or: - the use of still finer ballast particles, which increase the specific surface (for example, particles whose diameter is between 10 and 50 μm), can not be taken into account, for reasons of energy cost on the one hand, and the difficulties of decantation and s ep ara ion between sands and flocs, on the other hand In summary: the performances of flocculation with ballast, are limited by three factors: the system is sensitive to sudden variations in pollution, due to the lack of availability of hooking sites on the ballast (the contact mass is limited to a maximum or of 5, 10 g / 1), the system is of lower performance under the conditions of the so-called "sensitive" pollutants (helminth eggs, microorganisms, my cores, traces of complex organic compounds, pesticides, ...); the weak concentration of the extracted sludge, resulting from the need to clean the ballast "as completely as possible: this concentration is at least 10 times weaker than 1 a ^ concentration in sludge-type apparatus such as contact mass , and frequently involve the installation of an additional equipment, downstream of the decanter, for the thickening of the extracted sludge The owner of the present proposes to combine a procedure such as that defined in what refers to, with a flocculation. with ballast, and at the same time the drawbacks and limits of the classical methods described above, and allowing this procedure to obtain a high speed decantation.Accordingly, according to a second aspect, the present invention relates to to a process for the co-chemical physiological treatment of effluents, in particular that of surface water intended for consumption, which It turns on the following successive stages: coagulation, flocculation and decantation, because, during the flocculation stage, a ballast is introduced into the mud whose function is to make the mud more heavy, because the contact mass used During this stage of flocculation, it is constituted by a part of the densified sludge coming from the decantation stage and continuously recycled in the flocculation stage, without washing operation, and because it is injected into the recirculation circuit of the At least one part of the po and the ecoto 1 that ensures the production. In this way, according to the invention, a ballast is implemented, used in a manner different from that of the "procedure" flocculation with ballast "described in the foregoing. According to the invention the ballast plays a unique role, that of increasing the weight, and the function, of flocculation of the contact mass is carried out by the recirculated sludge only, the ballast no longer constitutes a surface of adherence offered to the particles, but simply constitutes a -reactor of the weight that arrives "to be incorporated in the sludge recirculated towards the flocculation reactor; said recirculated sludge constitutes the contact mass. According to a feature of the present invention, the ballast is constituted by a material having a granulometry comprised between 50 and 500 μm, preferably between 100 and 300 μm. According to a preferred embodiment of the invention, this ballast is a dense mineral material (actual specific mass of the particles, comprised between 2 and 8 g / ml), especially sand, garnet or magnetite. According to the present invention, excessively densified, non-recycled sludges can be discarded without treatment, or they can be treated in order to recover the ballast; this treatment does not include a thorough cleaning of the ballast separated from the sludge. In case of discarding without treatment, the densified sludge has a better aptitude for decanting. According to the invention, ballast recovery is preferably carried out by gravitational decanting, either inside or outside the decanter; The recovered ballast is then recovered in the flocculation stage. Other characteristics and advantages of the present invention will come to light thanks to the following description, made with reference to the attached drawings, which illustrate an embodiment totally devoid of limiting character. In the drawings: Figure 1 is a schematic view illustrating the principle of the physico-chemical treatment process, known and described above, in which the contact mass used during the flocculation stage is constituted by decanted sludge and recirculated; - Figure 2 is a schematic diagram, similar to Figure 1; illustrates the process object of the present invention, with double injection of polyelectrolyte, and: Figure 3 illustrates the second aspect of the invention, in which the double injection of the polyelectrolyte and the addition of ballast are combined. As can be seen in Figure 2, the contact mass in the flocculator B, as well as in the known method illustrated in Figure 1, is constituted by a continuous recirculation of a part of the densified sludge, after decanting and thickening in the decanter C. The part of the sludge thus recycled is recirculated to the flocculator B, by the recirculation conduit 16, which opens into the flocculator 14, and the pump 18. According to a preferred embodiment , the recycled flow presents between -0.5 and 4% of the treated flow.

According to the invention, at least one part (polymer 2) of the polyelectrolyte necessary for flocculation is introduced into the recirculation circuit 16 of the sludge. The remaining part of the polyelectrolyte (polymer 1) is "" "introduced into the flocculation reactor B. As can be seen in Figure 2, this introduction of at least one part of the polyelectrolyte in the recirculated sludge, it can be effected upstream or downstream of the recirculation pump 18. Generally, this injection will be carried out upstream of the pump 18, so that it mixes recycled sludge + polyelectrolytes, will have the advantage of being - As a variant, the part of the polyelectrolyte introduced in the recirculated sludge can be mixed with the latter in a specific agitation reactor, installed in the recirculation duct, 16. Accordingly, with the In this invention, the primary injection of the polyelectrolyte (polymer 1) can be effected in the flocculation reactor B, in the vicinity of the propeller 10 of the latter, as illustrated in FIG. Figure 2, but can also be made in the supply conduit 12 of the water to be treated in the flocculator (agitation zone), upstream or downstream of the intake point 14, of the sludge recirculated through the conduit 16. according to the invention, the ratio between the dose of polyelectrolyte introduced into the flocculation reactor, B, (primary injection) and the dose injected into recirculation circuit 16 of sludge (secondary injection),. It can vary and be modified. The polymer formation injected in the recirculation of sludge, it can vary between 10% and "100% of the total flow of polymer, 10% is the dose of polymer necessary to obtain a significant increase in massive flow (greater than 10%)." According to the invention, it is possible to inject 100% of the polymer into the recirculation circuit of the sludge, in which case the massive flows are even more important (100 to 200 kg / m3h), but the quality of the water degrades somewhat. In fact, in this case there is no longer enough free polymer to achieve adhesion between the dense recirculated sludge and the myro - loculus coming from the coagulation of the raw water, in practice, depending on whether the desired objective is a high speed UD decantation (compactness of the civil work) or a quality treated water, the proportion of polymer injected into the recirculation circuit of the sludge, with respect to the set of the polymer injected in the stage of care, will vary between 10% and 100%, being the propo optimal runtime in the range of 20 to 70%. According to the present invention, it is possible to inject into the recirculated lobes a polymer different from that of 3S and injected into the flocculation reactor B. Thus, for example, it is possible to inject an anionic polymer into the flocculation reactor B , and a cationic polymer in the recirculated sludge According to the present invention, the recirculated sludge can be injected directly into the flocculator B, as illustrated in "Figure 2, or in the conduit 12 which ensures the bond between coagulator A and flocculator B. "The process object of the present invention can be applied to all types of water treatment, water clarification for consumption or for industry, water treatment __ industrial or urban (primary or tertiary, etc ...). several tests were carried out in the same experimental pilot installation equipped with a fi lter A, with a flocculator B and with a decanter C, whose decantation surface SD was equal to 2 m2 and with a circuit for the recirculation of The two, 16, which was provided with a recirculation pump 18 adapted flow.The capacity of this experimental pilot installation, was approximately 100 m3 / h. ~ In this way have been carried out two series- tests , with a surface water The polyelectrolyte dose has been the same in both cases - (0.8 g / m3), but slightly higher than usual, this "in order to increase the decanting speeds UD. In the fi rst series, 100% of the po ue i cetrolite has been injected into the flocculation reactor, B, in the vicinity of its propeller 10, while in the second series of tests, only 50% of the polyelectrolyte it has been injected in the vicinity of the flocculation propeller 10, and another 50% was injected into the circuit 16 for the re-circulation of the sludge. The experimental installation lotus was regulated and adjusted in such a way that all the other test conditions were otherwise identical. The most significant results have been recorded in the following table.

TABLE ESSAYS No. 1 ESSAYS No. 2 Gross Water River water Co a gul "ante (g / m3) 20 20 P o 1 i e le c ytrol 0.8 (in the 0.4 (in the (g / m3) ^ proximity of prox imity of propeller 10) propeller 10) 0.4 (in recirculation 16) Massive flow 50 100 limit Fml (kg / m2 / h) Concentration From the examination of the results shown in this table, it follows that the procedure object of the invention has the following advantages with respect to the prior art: 1) at the same dose of polymer, the massive flow is doubled, This has allowed testing of decanting speeds UD, in the decanter, or UL in the laminar regime, of double, and this to qualities of the treated water practically equal, translating this advantage into a reduction in the size "of the devices; Decanted water presents a better fi rity The duration of the fi rity test (30 seconds) is of the order of half and is equivalent to that obtained with the usual polymer doses ( approximately 0.4 g / m3) and with weaker treatment speeds (UD = 15 m / h instead of 50 m / h), this longer duration of the filtration cycle implies a reduction in the amount of the washes to be effected in the filters; The extracted sludge has an improved concentration of approximately 50%; this r-esultado contributes the sale to allow to reduce the size of the systems for the treatment of the sludge. It should be noted that in some cases in which "the adherence of the coagulation microspheres on the" dense mud of the recirculation "is carried out" poorly, it is possible, according to the invention, to provide a third In this case, this third injection point is preferably located in the transfer pipe 12 which ensures the connection between the coagulator A and the flocculator B, or in a specific reactor interspersed between the coagulator and the f 1 or cudor. In the implementation example illustrated in Figure 3, a ballast addition is carried out in the "flocculator B." In this second aspect of the invention, and depending on the purging index of the densified sludge evacuated in P2 and the cost of the ballast, the excess sludges can be purely and simply discarded, they are subjected to treatment in order to recover the ballast, however, it should be kept in mind that the treatment of the sludge, for the recovery of the sand, is different from the - flocculation by ballast (FR-P-1.411.792 and FR-A-2.627.704) Indeed, according to the invention, the sand is recovered without being cleaned, that is, without regeneration, and the treatment is effected on concentrated sludge, since it is not necessary to proceed to a clean cleaning of the sand in the separation phase According to Figure 3, the means provided according to the invention have been schematized in E to ensure the recovery of the ballast. Note that the low flow rate of sludge to be extracted, from 0.1% to 1% of the flow rate of the treated water (that is, from 5 to 50 times weaker than in the case of flocculation with ballast), It allows you to use more sophisticated and better performance separation techniques, among which "special mention should be made of: - separation by" hydrocyclones; - separation by air blowing; J - separation by elution (élutriation); - centrifugal separation; - separation by po-u-tr-sound, or the reduction of the energy cost of this separation station. "Since the ballast has only the function of simple weight increaser and not a contact mass function, the choice of The weight of the particles of this weight-increasing ballast, contrary to the case of flocculation by ballast, can be oriented with advantage towards larger diameters, so it is possible to use weight-enhancing particles having a diameter between 50 and 50.degree. and 500 μm and preferably, between 150 and 300 μm, while in the case of a flocculation with contact mass constituted by a ballast, the particle size of the latter must be less than 150 μm, and preferably be between 50 and 100 μm. This diameter of the ballast, in the process object of the invention, constitutes a fundamental characteristic for: - the increase of the decanting velocities if d = 100μm, decanting speed of the ballast = 30 m / h; ~ if d = 250μm, decanting speed of the ballast = 115 m / h - the ballast recovery of the 1 or extra do s.Stand that in some cases, if the ballast diameter is sufficient, face a simple gravitational separation, inside or outside the decanter, in order to recover and recycle the ballast.

The process according to the invention, with flocculation with contact mass constituted by recirculated densified sludge, has in particular the following advantages: 1.- It offers a very high percentage of special occupation of the material of hooking, and therefore a ti highly effective a depuration whose performances are stable, even if there is a considerable increase in the "gross water load", a high aptitude for the elimination of the so-called "sensitive (delicate) pollutions" (micro-particles, micro-organisms, traces of complex organic compounds, pesticides, helminth eggs, etc ...). 2 .- The ballast no longer plays the role of weight enhancer. Its average particle size can therefore be higher than that required for ballast flocculation (eg 250 μm instead of 100 μm) .This possibility offers two advantages: the decantation rates are considerably increased, the more the diameter of the weight enhancer - the ballast recovery is so much easier when its diameter is more important.

In some cases, if its diameter is sufficient, it is possible to resort to a simple gravitational separation inside the decanter, or outside it. "3.- It is not necessary to clean the recovered ballast, since there is no attempt to regenerate" clean "sites for coagulation / flocculation, which is why it is possible, and advantageous, to recover the ballast from highly concentrated sludge. It offers -the following advantages: - since the extracted sludge is concentrated in approximately ten times, it is possible to reduce proportionally the volume of the chamber of the first stage / thickener installed downstream of the tank, the sand recovery system, operates on volumes that are smaller in the same proportions (for example, in 10 times) and, also in this case, it is possible to proceed to a reduction in the size of the equipment and energy consumption 4.- The dissociation of the functions ballast-mud mass for flocculation, allows to think about the possibility of a low flow operation (between less than 20% to 80% of Qmax, depending on the case), ~ without addition or rec ballast ion, which "allows further reduction" even the costs of exploitation. 5.- The densification of sludge, obtained through the combination: double injection of polymer and addition of ballast, allows to design large-speed decanting equipment that have spectacular advantages with respect to • known facilities. The variant according to the invention can be combined with the injection, in the recirculation circuit of the sludge, of at least one part of the polyelectrolyte that ensures the f 1 or cu The tion, and the addition of ballast in The flocculator is mainly used in the case of the production of difficult to densify the polymer only or, especially in the case of an overflow in the installation.

Claims (22)

1. A procedure for the chemical treatment of effluents, especially in surface water for consumption, which includes the successive phases consisting of coagulation, (A), flocculation, (B), and de_c (C), where a contact mass is introduced into the water withdrawn from the "coagulation stage, therefore during the flocculation stage, said contact mass consisting on the one hand of the densified sludge coming from the decanting step and re-icing the flocculation stage, characterized in that at least part of the po 1 ie 1 ec t ro 111 or flocculation is injected into the sludge recirculation circuit.

2. A procedure for the chemical and chemical treatment of effluents, especially of surface water intended for consumption, comprising the successive stages consisting of coagulation, (A), flocculation, (B), and decantation, (C) according to claim 1, characterized in that during the flocculation stage a ballast is introduced into the sludge whose function is to make the latter heavier, because the contact mass used during this flocculation stage is constituted on the one hand by densified sludge from the decantation stage and continuously recycled in the flocculation stage, without any treatment, and because in the circulation area of the sludge is injected, at least a part of the polyelectrolyte that ensures flocculation .

3. The process according to any of claims 1 or 2, characterized in that the percentage of the polymer injected into the recirculated sludge, or secondary injection, varies from 10% to 100% of the total amount of polymer injected in the flocculation stage and in the recirculated sludge, depending on whether it is desired to favor the settling speed or the quality of the water, respectively. -

4. The process according to the rei indication 3, characterized in that the percentage of the secondary polymer - injected in the recirculated sludge, varies from 20 to 70% of the total amount - of polymer injected in the flocculation stage and in the recirculated sludge.

5. The process according to any of the preceding claims, characterized in that the secondary polymer injected into the recirculated sludge is different from the primary polymer which is injected into the reactor of the reactor (B).

6. The process according to the rei indication 5, characterized in that the polymer injected into the flocculation reactor (B), is an anionic polymer and the polymer injected into the recirculated sludge is a cationic polymer.

7. The procedure according to which 1 was of the preceding indications, characterized because the primary injection of polymer is carried out in the vicinity of the helix of d 1 dculation.

8. The process according to any of claims 1 to 6, characterized in that the primary injection of polymer is carried out in the transfer conduit, between the coagulation reactor (A) and the flocculation reactor (B).

9. The process according to claim 1, characterized in that the secondary polymer injection is carried out in the conduit, to recycle the recycled sludge in the fermentation reactor, (B) , downstream and / or upstream: of the recirculation pump.

10. The process according to any of claims 1 to 8, characterized in that the secondary polymer injection is carried out in a recirculated mixing reactor, which is interposed in the recirculation pipe. the recycled sludge

11. The method according to any of the preceding claims, characterized in that a third polymer injection point is provided.

12. The method according to claim 11, characterized in that said third injection point is positioned upstream of the primary polymer injection point, in the conduit for the transfer of the tributary between the coagulation reactor, (A), and the reactor of f 1 or "culation, (B).

13. The process according to the rei indication 11, characterized in that said third injection point is positioned in a specific reactor that is interposed between the coagulation reactor, (A), and the reactor of f 1 or cu, (B)

14. The process according to any of the preceding claims, characterized in that the injection of the recirculated sludge is carried out directly in the flocculation reactor (B).

15. The process according to any of claims 1 to 13, characterized in that the injection of the recirculated sludge is effected in the connection conduit between the coagulation reactor, (A), and the flocculation reactor, (B) ).

16. The process according to claim 2, characterized in that said ballast is constituted by a material having a granulometry comprised between 50 and 500 μm, preferably between 100 and 300 μm.

17. The process according to claim 16, characterized in that said ballast is a "dense mineral material (actual specific mass of the particles, between 2 and 8 g / ml), especially sand, garnet or magnetite.

18. The process according to any one of the preceding claims, characterized in that the flow rate of the densified sludge - constituting the contact mass, continuously recirculated, after decanting and thickening, towards the flocculation stage, It is between 0.5 and 4% of the treated effluent flow.

19. The process according to any of the preceding claims, characterized in that the part of excessively densified sludge, not recycled in the flocculation stage and extracted in the decanting stage, represents a purge flow rate of the order of 0, 1 to 1% of the flow of treated water.

The process according to claim 19, characterized in that excessively densified, non-recycled sludges are discarded without treatment.

21. The process according to claim 19, characterized in that the excessively densified, non-recycled sludge is subjected to treatment in order to recover the waste, this treatment not comprising any thorough cleaning of the ballast separated from the sludge.

22. The process according to claim 21, characterized in that the recovery of the waste e_s effected by means of a gravitational decanting, either in the interior, or in the "exterior, of the decanter, the ballast being recovered subsequently recycled in the stage of production. _