FR2502976A1 - METHOD AND APPARATUS FOR REGENERATING AND RECOVERING A LOADED ADSORBENT AND CLARIFYING WATER - Google Patents

Abstract

A process is described for regenerating and recovery of a loaded adsorption medium, in which: (a) the loaded adsorption medium is brought into contact, for a time sufficient for its regeneration, with an alkaline solution; (b) the suspension obtained of the adsorption medium in the alkaline solution is diluted with returned overflow liquid from one or both subsequent separation stage(s), to reduce the concentration of the adsorption medium in the suspension to at least a value at which unhindered settling occurs; (c) the suspension is separated into a first liquid overflow and a first solids effluent with the adsorption medium; at least a portion of the first liquid overflow is rejected and the remainder (of the first liquid overflow) which may still be present is returned to stage (b); (d) the first solids effluent from stage (c) is suspended with wash water and a returned second liquid overflow from the following separation stage; (e) the resulting suspension is separated into a second liquid overflow and a second solids effluent with the adsorption medium, and a portion of the liquid overflow is returned to stage (d) and the remainder (of the second liquid overflow) into stage (b), and (f) the second solids effluent containing the regenerated and washed adsorption medium is collected.

Description

 The present invention relates to a process for regenerating adsorbents, in particular those called "coagulants / adsorbents" used in the water clarification process described in the Australian patent of the Applicant No. 512 553 and in the Applicant's Australian patent application no. 40 032/78.

 The aforementioned patent describes how it is possible to remove suspended impurities and colored substances from water by contact with a "coagulant / adsorbent", which is a mineral material in finely divided particles of which the individual particles have a thin layer. hydroxylated surface having a positive zeta potential at the adsorption pH, that is to say at the pH of the water being treated. The aforementioned patent application shows that the implementation of this process is improved by adding a polyelectrolyte during the treatment.

 The coagulant / adsorbent which has become charged with impurities and colored substances during the treatment of the water is regenerated by a simple treatment with an aqueous solution of alkali. This removes impurities and colored substances from the surface of the coagulant / adsorbent, which pass into the alkali solution and can thus be separated from the coagulant / adsorbent. After washing, the adsorbent coagulant can be recycled for use in the water treatment process.

Since the coagulant / adsorbent must be in the form of very fine particles (less than 10 microns), the mineral materials preferred for the coagulant / adsorbent are magnetic or magnetizable materials, in particular magnetite, due to the relative ease with which such materials can be handled, for example by magnetic means, compared to non-magnetic particles of similar size
The commercial viability of the water clarification process described in the aforementioned patent depends largely on the success of the regeneration and the reuse of the magnetite used as coa # ulant / preferred adsorbent.

The aforementioned patent describes a process comprising an alkali regeneration in three phases, against the current, which uses magnetic separators and which has been successfully used in experimental treatments.

However, further development of the process in commercial facilities has shown several disadvantages of the existing recovery process. First, it is relatively lumpy for small scale applications; the regeneration train can represent around half of the total investment of the installation. Therefore, the existing clarification process is not economical for installations with a capacity of less than 10 M1 per day. In addition, the process produces a liquid effluent whose volume is not less than 5% of the total capacity of the installation, which is to be compared with the volume of effluent representing 1/2% to 1% of the capacity of the installation for a conventional flocculation process with alum.

This difference may result in additional costs to get rid of the effluent in the above patent procedure.

 The main object of the invention is to provide an improved recovery and regeneration process for the aforementioned coagulants / adsorbents, in particular for magnetite, which eliminates the problems which have just been indicated.

 During the Applicant's research into different methods for regenerating magnetite, the Applicant attempted to replace the magnetic separators used in the method of the aforementioned patent with simple settling tanks, but this has led to unsatisfactory results. . For the water-magnetite ratios that the Applicant has used with magnetic separators in stages of regeneration of the patent process (188 to 25% by weight of magnetite), the Applicant has found that, although a deposit occurs, much of the turbidity and color removed from the surface of the magnetite as a result of the alkali treatment remained trapped in the decanted solid bed instead of appearing in the supernatant, reducing the overall yield regeneration and washing steps and, therefore, the ability of the regenerated magnetite to effect clarification of the water when it was recycled according to the patent process.

 The Applicant attributed this behavior to the phenomenon which it called "hindered deposition", in which the boundary layers surrounding the adjacent particles react and modify the velocity gradients in the vicinity of the particles. Thus, adjacent particles unduly modify the interaction forces, and the deposition rate is considerably reduced compared to that of a single particle. The deposition rate of a particle no longer depends on the size of the particle, but only on the concentration of the other particles. in its immediate vicinity.

 Due to the relatively high solids concentration in the mud and the high velocity gradient in the boundary layer surrounding each particle, the colloidal particles in the interstitial liquid have a much higher probability of hitting the surface of a particle . As a result, the smaller particles of collordal matter become trapped in the interstices between the larger magnetite particles and are dragged down with them, which results in all of the solids being deposited as tablecloth, with a clear interface between the mud and the clear liquid phase. This is the main reason why the settling tanks are apparently not suitable in the present regeneration process.

 We have now discovered that the above problems can be solved by reducing the concentration of the mud to a level where the individual particles do not interact with each other and where unobstructed discrete deposition can occur. For the magnetite-water system, the Applicant has found that this occurs below a concentration of the mud of approximately 10% by weight of magnetite, and that, when working at concentrations of mud having this level, it it is possible to use decantation tanks in place of the magnetic separators of the process of the aforementioned patent of the Applicant.

 However, the fact of using settling tanks and such diluted sludge while retaining the flow diagram described in the aforementioned patent would require a very significant increase in the consumption of washing water and, consequently, the volume of effluent water to be removed.

 The Applicant has found that, by appropriately modifying the design of the regeneration and washing steps of the flow diagram, it is not only possible to avoid increasing the consumption of washing water, but to actually reduce this consumption, as well as the quantity of effluent to be removed, up to levels which are comparable to those which can be obtained in a conventional flocculation process with alum.

 This new flow diagram forms the basis of the present invention.

According to one aspect, the subject of the invention is a method of regeneration and recovery of a charged adsorbent (as defined below), characterized in that it comprises the following steps:
(a) the charged absorbent is placed in contact with an alkaline solution for a sufficient time to effect the regeneration of the adsorbent;
(b) diluting the resulting slurry of the adsorbent in the alkaline solution with a flow of recycled supernatant liquid coming from one of the following two separation stages or from these two stages, in order to reduce the concentration of adsorbent in the mud at least at the level where unhindered deposition can occur;
(c) the mud is separated to obtain a prer: #r flow ## nent of supernatant liquid and a first bottom flow of solids containing the adsorbent, and a part of the first flow of supernatant liquid is returned to the step (b), the rest being discarded;
(d) the first bottom solids flow from step (c) is transformed into a slurry by means of washing water and a second flow of recycled supernatant liquid coming from the following separation step;
(e) the mud thus formed is separated to obtain a second flow of supernatant liquid and a second bottom flow of solid matter, and a part of this second flow of supernatant liquid is returned to step (d) and the rest to step (b); and
(f) recovering the second bottom flow of solids containing the regenerated and washed adsorbent.

 Preferably, the separations carried out in steps (c) and (e) are carried out in settling tanks, but the advantages of the process can be obtained with other separation devices, for example with magnetic separators.

 The term "adsorbent" is used herein for convenience to refer to finely divided particle magnetite or any other suitable adsorbent used as a coagulant / adsorbent in the patent or application process of the aforementioned patent. The term "loaded" assumes that the coagulant / adsorbent has been used in the sludge clarification process.

 It will be obvious to those skilled in the art that the regeneration and recovery process according to the invention may also have other applications, namely applications associated with the clarification of water by methods other than those described in the patent and in the aforementioned patent application.

 The preferred duration for the regeneration stage (a) is approximately 10 minutes.

 As already indicated, the preferred adsorbent is magnetite, for which, in step (b) of the process, the concentration after dilution must be less than about 10% by weight.

 The subject of the invention is also a process for clarifying water which comprises the regeneration and recovery process defined above but which is also in accordance with the teachings of the aforementioned patent or patent application.

 The process of the invention will now be described in more detail in the description which follows, given with reference to the appended drawing, the single figure of which represents a flow diagram of a water clarification process comprising the process regeneration according to the invention.

 As shown in the flow diagram, raw water <A) and a regenerated coagulant / adsorbent (magnetite) are mixed in 1 and introduced into a contacting member 2, which can be a pipe, as described in the aforementioned Australian Patent No. 512,553, or any other suitable device. If desired, the polyelectrolyte (B) can be added to the mixture (in accordance with the abovementioned Australian patent application no. 40 032/78) when the latter leaves the contacting member 2, in point 3. The mixture then passes through a solid matter clarification apparatus 4 which can be of any suitable type, for example those described in the aforementioned patent. The clarified water (C) constituting the supernatant flow is extracted from the clarification apparatus 4.

 The bottom flow (D) of solids from the clarification apparatus 4 consists of a charged coagulant / adsorbent, that is to say associated with colloidal and other impurities which have been removed from the water. . This bottom flow passes to regeneration mixture 5, where it is mixed with diluted caustic soda to raise the pH to a level sufficient to release the coagulant / adsorbent from impurities (for example at a pH of about 10 to 11), and from there to another mixer 6, where it is mixed with supernatant liquid coming from one of the following two separation stages or from these two stages (lines E2 and G2), to reduce the material content solids at an appropriate level, less than 10% by weight in the case of magnetite. The mixture is then sent to a first settling tank 7. The supernatant flow (E) coming from this tank 7 is divided into two flows (E1 and E2), the first of which is sent to waste and the second to the mixer 6. The bottom stream (F) containing the coagulant / adsorbent passes to a second mixer 8, where it is mixed with washing water (I) and with a flow of supernatant liquid coming from the next separation step (line G1) . The mixture passes from the mixer 8 to the second settling tank 9.

 The flow of supernatant liquid (G) from the tank 9 is divided into two flows (G1) and (G2). The flow (G1) is sent to the second mixer 8, and the flow (G2) to the first mixer 6.

 The bottom flow (H) containing the washed and regenerated magnetite is recycled to be mixed in l with the raw water.

 It is obvious that the process conditions can be adjusted by varying the ratio between the flows (G1) and (G2) and (El) and (E2). These adjustments could go as far as the complete elimination of some of the flows (G1), (G2) or (E2).

 It will be noted that, in the present flow diagram, the charged magnetite coming from the clarification apparatus 4 is regenerated during a treatment in a single step with alkali (caustic soda). This differs from the flow diagram of the process according to the aforementioned patent, which uses a three-stage alkali regeneration.

 As in the prior method, there are two washing steps after regeneration, but these have been modified with regard to the use of wash water recycling loops. Thanks to this modification of the recycling of the washing water, the concentration of solids in the solid / liquid separation stages can be reduced to the point where a discrete, unhindered deposition of the solid phase can occur without it this results in an increase in the total demand for washing water. In fact, it has proved possible to reduce the consumption of washing water to surprisingly low levels (approximately lt of the capacity of the installation) with this new flow diagram.

The process of the invention provides significant advantages over the previous process, namely:
l. The magnetic separators can be replaced by settling tanks. For small-scale installations (less than 10 ml per day), this makes it possible to use simple and inexpensive clarification devices of the conical bottom type.

 2. The make-up water supply can be reduced to approximately 1% or less of the capacity of the installation. This not only reduces operating costs, but also greatly reduces the problems of effluent disposal.

 3. The total number of steps for regeneration and washing has been reduced from 5 to 3.

 Those skilled in the art will understand that one or more steps can be added to the above procedure. additional washing, if this is considered necessary.

 During studies based on tests in containers of the type described in the patent and in the aforementioned patent application, the performance of a coagulant / adsorbent constituted by magnetite has been studied over numerous treatment cycles. water, using water from the Yarra River (Victoria), and regeneration3 using mixing and deposition processes simulating the process of the present invention. After 37 cycles, the magnetite still had adequate performances as a coagulant / adsorbent, and these performances approached a constant state, that is to say that these performances before and after a regeneration step were almost unchanged. This indicates that the treatment / regeneration cycle could be repeated almost indefinitely.

 The invention is illustrated in more detail by the following examples.

Examples 1 to 3 relate to a series of experiments on a pilot installation carried out to study the regeneration and recovery of a coagulant / adsorbent constituted by magnetite, which had been used at a rate of 12.5 g / l for clear water from the river
Yarra (Victoria) with a turbidity of 60 NTU and a color of 43 Pt-Co units. When fresh magnetite was used to clarify this water according to the teachings of the aforementioned patent and patent application, the clarified water had a turbidity of 0.5 NTU and a color of 4 Pt-Co units.

Example 1:
The charged magnetite was regenerated as described in the aforementioned patent, with the exception that decantation tanks were used in place of magnetic separators. The magnetite concentration in the washing steps was 30% by weight, and the washing water flow rate was 3%, i.e. the volume of water used to wash the regenerated magnetite was 3% of the total volume of water produced during the clarification step.

The regenerated and washed magnetite was then used to treat another quantity of river water, after which the magnetite was regenerated again. After two of these cycles, the turbidity of the clarified water was found to have been 14 NTU and its color to be 9 units
Pt-Co, that is to say that the regenerated magnetite was clearly lower than the fresh magnetite to effect the clarification.

Example 2:
The procedure of Example 1 was repeated, except that the regeneration and recovery of the magnetite were carried out in accordance with the process of the present invention, the concentration of magnetite in the washing steps being 8% by weight. weight. After 35 cycles, the clarified water had a turbidity of 0.5 NTU and a color of 4 Pt-Co units, which shows that the performance of the regenerated magnetite was equal to that of the fresh magnetite.

Example 3:
The procedure of Example 2 was repeated, except that the wash water flow rate was reduced to 1%. After 35 cycles, the clarified water had a turbidity of 0.8 NTU and a color of 8 Pt-Co units, which shows that a significant reduction in the flow of washing water had only a minor effect on the quality of produced water.

Example 4:
We also examined the effect of the variation of the wash water flow on the quality of the clarified water in a pilot water clarification installation in which the regeneration of the charged adsorbent (magnetite) was carried out. the manner described in the aforementioned patent of the Applicant and in which magnetic drum separators were used to carry out the separation steps during the regeneration and washing of the magnetite. The concentration of magnetite in the washing steps was 30% by weight. It has been found that when the wash water flow rate is reduced from 5% to 1%, the turbidity of the produced water increases by 1.0 NTU 3 3.3 NTU.

Example 5:
The procedure of Example 4 was repeated in another water clarification installation using magnetic drum separators but in which the regeneration and washing steps were designed and implemented according to the teachings of the present invention. The concentration of magnetite in the washing steps was 8% by weight. When the wash water flow was reduced from 5% to 1%, the turbidity of the produced water increased from 0.9 NTU to only 1.3 NTU.

 This example, considered in combination with example 4, demonstrates the increased efficiency of the regeneration and washing procedure according to the present invention compared to that described in the aforementioned patent of the Applicant, even when using magnetic separators. . It also shows that the present invention makes it possible to reduce the flow of washing water to around 1% without significantly reducing the quality of the clarified water.

Claims (14)

- CLAIMS  1.- Method for regeneration and recovery of a charged adsorbent, characterized in that it comprises the following stages:  (a) the charged adsorbent is brought into contact with an alkaline solution for a sufficient time to effect the regeneration of the adsorbent;  (b) diluting the resulting slurry of the adsorbent in the alkaline solution with a flow of recycled supernatant liquid coming from one of the following two separation stages or from these two stages, in order to reduce the concentration of adsorbent in mud at least at the level where unhindered deposition can occur;  (c) the sludge is separated to obtain a first flow of supernatant liquid and a first bottom flow of solids containing the adsorbent, and at least part of the first flow of supernatant liquid is discarded, the rest possibly being returned in step (b);  (d) transforming the first bottom solids flow from step (c) into a slurry by means of washing water and a second flow of recycled supernatant liquid coming from the following separation step;  (e) the mud thus formed is separated to obtain a second flow of supernatant liquid and a second bottom flow of solid matter, and a part of this second flow of supernatant liquid is returned to step (d) and the rest to step (b); and  (f) recovering the second bottom flow of solids containing the regenerated and washed adsorbent.  2.- Method according to claim 1, characterized in that the duration of step (a) of regeneration is about 10 minures.  3.- Method according to one of claims 1 and 2, characterized in that the adsorbent is magnetite.  4.- Method according to claim 3, characterized in that the concentration of the magnetite sludge after dilution in step (b) is less than approximately 0 by weight.  5.- A process for clarifying water, in which water is brought into contact, optionally in the presence of a polyelectrolyte, with a coagulant / adsorbent consisting of a mineral material in finely divided particles, the individual particles of which have a thin hydroxylated surface layer which has a positive beta potential at the adsorption pH, and the water is separated from the coagulant / adsorbent to obtain the clarified water, characterized in that the coagulant / adsorbent is regenerated according to a process in accordance with claim 1.  6.- Method according to any one of the preceding claims, characterized in that one carries out at least one of the separations of steps (c) and (e) in a settling tank.  7.- Method according to any one of claims 1 to 5, characterized in that one carries out at least one of the separations of steps (c) and (e) in a magnetic separator.  8.- Method according to any one of the preceding claims, characterized in that the flow of washing water is less than 5%.  9.- Method according to claim 8, characterized in that the flow of washing water is about 1%.  10.- Apparatus for implementing a method according to claim 1, characterized in that it comprises:  (a) first mixing means (5) for transforming the charged adsorbent into mud using an alkaline solution in order to regenerate the adsorbent;  (b) second mixing means (6) for mixing the sludge coming from the first mixing kernels with a flow of supernatant liquid coming from one of the following two separation stages, or from these two stages, to reduce the solids content mud;  (c) first separating means (7) for separating the sludge from the sexends rx :: # ens mixers in order to obtain a first bottom flow of solids and a first flow of supernatant liquid;  (d) means for returning part of the first flow of supernatant liquid to the second mixer means (7) and for discarding the remaining liquid;  (e) third mixing means (8) for converting the first bottom flow of solids into mud using washing water and a second flow of supernatant liquid from the next step;  (f) second separator means (9) for separating the sludge from the third mixer means to provide a second bottom flow of solids containing the washed and regenerated adsorbent, and a second flow of supernatant liquid; and  (g) means for returning part of the second flow of supernatant liquid to the second mixer means (6) and for returning the remainder of this flow of supernatant liquid to the third mixer means (8).  11.- Apparatus for implementing a method according to claim 5, characterized in that it comprises:  (aa) means (1, 2) for mixing and contacting to bring the water to be treated into contact with a coagulant / adsorbent;  (bb) optionally, means (3) for introducing a polyelectrolyte into the mixture of water and of coagulant / adsorbent; and  (cc) primary separation means (4) for separating the treated water from the spent coagulant / adsorbent;  this in association with a device in accordance with claim 10 intended to receive the spent coagulant / adsorbent coming from the primary separation means and to recycle the regenerated coagulant / adsorbent and washed with means (1, 2) of mixing and contacting.  12.- Apparatus according to one of claims 10 and 11, characterized in that the means (d) and (g) comprise adjustment means for adjusting the proportions of the flows of supernatant liquid returned to the respective means.  13.- Apparatus according to any one of claims 10 to 12, characterized in that the separation means (c) and / or (f) comprise a settling tank (7, 9).  14.- Apparatus according to any one of claims 10 to 12, characterized in that the separation means (c) and / or (f) comprise a magnetic separator.