WO2018019924A1

WO2018019924A1 - Electrodialysis device for desalinating water with a high concentration of dissolved salts

Info

Publication number: WO2018019924A1
Application number: PCT/EP2017/068971
Authority: WO
Inventors: Giuseppe LUISE
Original assignee: Luise, Marco; LUISE, Silvia
Priority date: 2016-07-28
Filing date: 2017-07-27
Publication date: 2018-02-01
Also published as: IT201600079225A1

Abstract

An electrodialysis device (10) for desalinating water with a high concentration of dissolved salts, which comprises, between two heads (11, 12), two opposite electrode chambers (13, 14), between which are arranged a plurality of reaction chambers of two alternate types, first chambers (17) for ion enrichment, and second chambers (18) for ion depletion, each chamber of a first type being open onto a laterally adjacent chamber of the second type by interposition of an ion-conducting membrane (19, 20), the first chambers (17) being interconnected by plumbing to each other and to the heads so as to define a first plumbing circuit (21) for the transit of a first water flow (22), with ion enrichment, the second chambers (18) being interconnected by plumbing to each other and to the heads so as to define a second plumbing circuit (23) for the transit of a second water flow (24), with ion depletion, there being plumbing means (25) for the exchange of the first and second water flows (22, 24) from the first plumbing circuit (21) to the second plumbing circuit (23) and vice versa, each electrode chamber (13, 14) being served by a corresponding independent plumbing circuit (26, 27); the electrodialysis device (10) also comprises: - a first plumbing service circuit (28) for the first plumbing circuit (21), for ion enrichment, and for the electrode chambers (13, 14), - and a second plumbing service circuit (37) for the second plumbing circuit (23), for ion depletion.

Description

ELECTRODIALYSIS DEVICE FOR DESALINATING WATER WITH A HIGH CONCENTRATION OF DISSOLVED SALTS

The present invention relates to an electrodialysis device for desalinating water with a high concentration of dissolved salts.

Nowadays an electrodialysis machine is known, and is the subject matter of Italian patent no. 0001409789 with priority date of 15/2/2012 in the name of Silvia Luise and Marco Luise, for desalinating water with a high concentration of dissolved salts, characterized in that it comprises, between two heads, two opposite electrode chambers, which contain electrodes having opposite polarities, between which are arranged a plurality of reaction chambers of two alternate types, first chambers for ion enrichment, and second chambers for ion depletion, each chamber of a first type being open onto a laterally adjacent chamber of the second type by interposition of an ion-conducting membrane; such first chambers are interconnected by plumbing to each other and to the heads so as to define a first plumbing circuit for the transit of a first water flow, with ion enrichment, while the second chambers are interconnected by plumbing to each other and to the heads so as to define a second plumbing circuit for the transit of a second water flow, with ion depletion; the electrodialysis machine also comprises plumbing means for the exchange of first and second water flows; each electrode chamber is served by a corresponding independent plumbing circuit.

Such electrodialysis machine offers a greater and higher flow of ions between the electrodes, and therefore offers greater efficiency than conventional apparatuses, by virtue of washing the ion-conducting membranes, which is achieved by exchanging the first and second flows, and by virtue of some details that increase the turbulence of the water flow in the reaction chambers.

Furthermore, in such electrodialysis machine the functionality of the ion-conducting membranes can be easily restored without resorting to costly chemical additives.

Such electrodialysis machine is capable of ensuring the functionality of the electrodes, by virtue of the independent electrode chambers and of ion-conducting screening membranes which are arranged especially in them.

Such an electrodialysis machine has an hourly productivity rate that is much higher than conventional apparatuses, and is capable of treating brackish waters with a high degree of salinity, approximately 55,000 microSiemens per centimeter, in order to reduce the saline content thereof as desired.

Such electrodialysis machine is described as operating with plumbing means of service which involve four pumps, of which three are arranged to draw water from a source of water with high salinity, such as for example a body or a tank of water with a particularly high saline content, and two of which are dedicated to the electrode chambers, and one pump is arranged to draw from a tank of water to be desalinated.

Such plumbing service means, although functional, are relatively costly and cumbersome, in particular due to the presence of the pumps and of the corresponding connecting pipes.

The aim of the present invention is to provide an electrodialysis device for desalinating water with a high concentration of dissolved salts, which is capable of overcoming the above mentioned drawbacks of the conventional electrodialysis machine.

Within this aim, an object of the invention is to provide an electrodialysis machine in which the plumbing service means are simpler and more compact.

Another object of the present invention is to provide an electrodialysis device that is capable of making desalinated water available more rapidly than the conventional electrodialysis machine.

Another object of the present invention is to provide an electrodialysis device that is automated and easily manageable without particular necessities for intervention by an operator.

This aim and these and other objects which will become better evident hereinafter are achieved by an electrodialysis machine for desalinating water with a high concentration of dissolved salts according to claim 1.

Further characteristics and advantages of the invention will become better apparent from the description of a preferred, but not exclusive, embodiment of the electrodialysis device structure according to the invention, which is illustrated by way of non-limiting example in the accompanying drawings wherein:

- Figure 1 is a diagram of the electrodialysis device according to the invention;

- Figure 2 is a perspective view of a supporting frame of an electrodialysis device according to the invention;

- Figure 3 is a schematic plan view of a first part of an electrodialysis device according to the invention;

- Figure 4 is a schematic plan view of a second part of an electrodialysis device according to the invention;

- Figure 5 is a schematic plan view of a third part of an electrodialysis device according to the invention;

With reference to the figures, an electrodialysis device for desalinating water with a high concentration of dissolved salts according to the invention is generally designated with the reference numeral 10.

The electrodialysis device 10 comprises, between two heads 11 and 12, two opposing electrode chambers 13 and 14 that contain corresponding electrodes 15 and 16 having opposite polarities, between which a desalination assembly 10a is arranged which comprises a plurality of reaction chambers of two alternate types, first chambers 17 for ion enrichment, and second chambers 18 for ion depletion, each chamber of a first type being open onto a laterally adjacent chamber of the second type by interposition of an ion-conducting membrane 19 and 20. The first chambers 17 are interconnected by plumbing to each other and to the heads so as to define a first plumbing circuit 21 for the transit of a first water flow 22 with ion enrichment, while the second chambers 18 are interconnected by plumbing to each other and to the heads so as to define a second plumbing circuit 23 for the transit of a second water flow 24, with ion depletion, i.e. water that is being desalinated.

There are plumbing means 25 for the exchange of the first and second water flows 22, 24 from the first plumbing circuit 21 to the second plumbing circuit 23 and vice versa.

Each electrode chamber 13 and 14 is served by a corresponding independent plumbing circuit 26 and 27.

For the purposes of clarity of disclosure, the reference numeral 10a designates the desalination assembly, which comprises the reaction chambers 17 and 18 which are arranged between the heads 11 and 12.

The peculiarity of the electrodialysis device 10 according to the invention consists in that it comprises:

- a first plumbing service circuit 28 for the first plumbing circuit 21, for ion enrichment, and for the electrode chambers 13 and 14, which comprises:

- a branch 29 for drawing water from a source of saline solution 30 for the water flow with ion enrichment 22, provided with a first service pump 31 ,

- a branch 32 for delivery to the first plumbing circuit 21 and to the electrode chambers 13, 14, with corresponding solenoid valves 33, 34, 35 for sorting and pressure control of the flows,

- a branch 36 for return from the first plumbing circuit 21 and from the electrode chambers 13, 14 to the source 30,

- and a second plumbing service circuit 37 for the second plumbing circuit 23, for ion depletion, which comprises:

- a branch 38 for delivery to the second plumbing circuit 21, with a second pump 43 and with corresponding solenoid valves 39, 40 for sorting and pressure control of the flows,

- a branch 41 for return from the second plumbing circuit 23 to a process tank 42 for containing the water being treated.

In particular, in the first plumbing service circuit 28, the delivery branch 32 comprises a first line 44, with a first solenoid valve 33, for the first plumbing circuit 21, and a second line 45, with two parallel branches, with a second solenoid valve 34, for the circuits 26 and 27 respectively of the two electrode chambers 13 and 14; such two lines, first 44 and second 45, are in parallel.

The delivery branch 32 comprises a third line 46, also in parallel with the two first and second lines 44 and 45, with a corresponding solenoid valve 35 for filling the process tank 42.

The return branch 36 similarly comprises a first line 47 for return of the first plumbing circuit 21 and a second line 48, which is in parallel with the first line, for return of the circuits 26 and 27 of the electrode chambers 13 and 14.

The first plumbing service circuit 28 also comprises a first manually actuated valve 50, which is arranged on the branch for drawing water 29, upstream of the first pump 31 , a second manually actuated valve 51 , which is arranged on the return branch 36 downstream of the two return lines, the first line 47 for return of the first plumbing circuit 21 and the second line 48, in parallel with the first, for return of the circuits 26 and 27 of the electrode chambers 13 and 14, and a third manually actuated valve 52, which is arranged on a connecting line 54 which connects the branch for drawing water 29 to the return branch 36.

The first manual valve 50 is arranged downstream of the connection between the branch for drawing water 29 and the connecting line 54.

The manually actuated valves 50, 51, 52 are designed to select between ordinary operation of the electrodialysis device 10 and operation "on standby", which is described in more detail below.

In particular, in the second plumbing service circuit 37, the delivery branch 38 comprises a first line 60, with a first solenoid valve 39, for the second plumbing circuit 23, and a second line 61, in parallel with the first line 60, with a corresponding second solenoid valve 40, for draining the process tank 42, once the treatment has been completed, into a tank, not shown for the sake of simplicity, for the accumulation of desalinated water, available to a user device.

The return branch 41 from the second plumbing circuit 23 to the process tank 42, at the drainage outlet in the process tank 42, has a scrubbing/degassing unit 62, which is adapted to facilitate the separation from the water flow of any gas that has formed inside the desalination assembly 10a.

The aforementioned plumbing means 25 for the exchange of the first and second water flows from the first plumbing circuit 21 to the second 23 and vice versa should be understood as being of known type, for example as described in the previously-cited Italian patent no. 0001409789; the plumbing means 25 comprise a series of conduits that are connected to each other by the interposition of distribution valves that are adapted to automatically select the incoming and outgoing flows from the first 21 and second 23 plumbing circuits that are defined in the desalination assembly 10a.

The electrodialysis device 10 according to the invention comprises an electronic control unit 80.

Operation of the electrodialysis device 10 according to the invention is the following.

All the steps of operation are executed and controlled by a central electronic control unit 80, which is described in more detail below.

In a first step of operation of the electrodialysis device 10 according to the invention it is put into operation; in such step of putting into operation the manual valves 50 and 51 are open and the manual valve 52 of the connecting line 54 is closed.

The branch for drawing water 29 is arranged to draw from a source 30 which can be constituted by a water body, by a well, by a storage and settling tank or by other, similar sources or reservoirs.

In the case of a tank, it is kept under internal pressure using an optional auxiliary pumping system, if necessary, provided by the user.

Upstream of the branch for drawing water 29 filtration means are also installed, which should be understood as being of conventional type and are not shown for the sake of simplicity, for the pretreatment of the saline solution sent by the first pump 31 to the first plumbing circuit 21 and to the electrode chambers 13 and 14.

When the signal to start is received, the electronic control unit 80 opens the third solenoid valve 35 of the third line 46 of the first service circuit 28, for filling the process tank 42, and actuates the first pump 31, with the first and second solenoid valves 33 and 34 closed.

The process tank 42 is filled until the saline solution introduced reaches a level that is preset by way of an adapted floating limiter, which is not shown in the figures and should be understood as being of conventional type.

When the floating limiter reports reaching the preset level of saline solution in the process tank 42, the control unit 80 stops the first pump 31 and closes the third solenoid valve 35.

A second step of operation involves switching the solenoid valves of the plumbing means 25 of exchanging the flows between the first plumbing circuit 21 and the second plumbing circuit 23, so that the flow of salt water, suitable for ion enrichment, transits the first plumbing circuit 21, in a first cycle, which is termed a "direct cycle".

A third step of operation involves starting the desalination process, by continuously recirculating the water in the process tank 42 in the second plumbing circuit 23 of the desalination device 10.

In such third step, the electronic control unit 80 opens the solenoid valves 33 and 34 of the first service circuit 28, so that the saline solution flows from the source 30 to the first plumbing circuit 21 and to the electrode chambers 13 and 14, and activates the first pump 31 , and simultaneously the electronic control unit 80 opens the solenoid valve 39 of the first line 60 of the second service circuit 37 and activates the second pump 43, in order to allow the circulation in the second plumbing circuit 23 of the solution being desalinated, i.e. with ion depletion, contained in the process tank 42.

The first plumbing circuit 21 drains to the supply source 30 by way of the first line 47 for return of the first service circuit 28 and by way of the second manual valve 51 ; the second plumbing circuit drains into the process tank 42 by way of the scrubbing/degassing unit 62.

During such step, the control unit activates and conveniently adjusts the power supply, to which the electrodes 15 and 16 are connected, in order to generate the ion transport process typical of the electrodialysis procedure.

During all of such step of desalination, the solenoid valves 33 and 34 of the first service circuit 28 and the solenoid valve 39 of the second service circuit 37 are adjusted/modulated for the purpose of maintaining the correct pressure levels in the three separate plumbing circuits, the first 21, the second 23, and the circuit of the electrode chambers 26 and 27.

In a fourth step of operation, the control unit 80, after using a salinity sensor arranged in the process tank 12 to read the degree of salinity of the water being desalinated, compares it with a preset reference value and automatically carries out the following operations:

- cut the electric power supply from the electrodes 15 and 16,

- deactivate the first and second pumps 31 and 43,

- completely close the solenoid valves 33, 34 and 39 of the delivery lines to the first and second circuits 21 and 23 and to the electrode chambers 13 and 14. Then, the control unit 80 opens the solenoid valve 40 of the second line 61 of the second service circuit 37, to drain the process tank 42 into an accumulation tank of a user device, and activates the second pump 43.

Proximate to the outlet of the second line 21 there is a filtration assembly for the post-treatment of the desalinated water, which is not shown for the sake of simplicity and which should be understood as being of known type.

The end of the draining of the process tank 21 is reported to the control unit 80 by a depth limiter; as a consequence of such signal the second pump 43 is deactivated and the solenoid valve 40 of the second line 61 of the second service circuit 37 is closed.

The electrodialysis device 10 according to the invention is thus ready for a new desalination cycle.

In a fifth step of operation, the electronic control unit 80 inverts the polarities of the electrodes 15 and 16 and, by suitably driving the solenoid valves of the plumbing means 25, the flows are exchanged between the first and second plumbing circuits 21 and 23, thus giving rise to an "inverse cycle".

Then the control unit repeats the operations to load the fluid to be desalinated, and the entire recirculation operation cycle described previously.

If the electrodialysis device 10 according to the invention should be brought out of service and stored for a period of time that exceeds for example seven days, it is necessary to activate a waiting procedure, i.e. to place it in "standby" mode as described below.

On imparting the "standby" command to the electronic control unit 80, the latter makes the electrodialysis device 10 according to the invention carry out the following operations:

- load the process tank 42 with a quantity of water necessary for it to be held in storage; - on indication of the control unit 80, by way of a display, close the manually actuated valves 50 on the branch for drawing water 29 and the manual valve 51 on the return branch 36, and open the manual valve 52 of the connecting line 54.

Then the process is begun of maintaining the electrodialysis device 10 in standby mode, in which mode it is possible to discontinue supervision of the electrodialysis device 10 for long periods.

The return to service of the electrodialysis device 10 according to the invention occurs by resetting the electrodialysis device and opening the manual valves 50 and 51 and closing the manual valve 52 on the connecting line 54.

The electrodialysis device 10 according to the invention comprises a supporting frame 65, shown for the purposes of example in Figure 2.

The supporting frame 65 is made of stainless steel components, so as to withstand attacks from atmospheric agents, with particular emphasis on the particularly aggressive atmospheric agents that are typical of a marine environment.

The supporting frame 65 comprises at least four angular posts 66, a lower supporting surface 67, an upper supporting surface 68 and intermediate resting elements which define an intermediate resting surface 69.

The supporting frame 65 is designed to be covered with a shell of plastic material, not shown for the sake of simplicity, which is mechanically strong and electrically isolated.

In the present, non-limiting exemplary embodiment, the upper surface

68 supports all the on-board electrical equipment, i.e. the control and electric power components, as shown schematically in Figure 3; on such upper surface the following are arranged:

- the electronic control unit 80,

- an alphanumeric display panel 81, shown as if it were on a side of a schematic box 68, with user-accessible keypad and main switch,

- a telecommunications unit 82, for telemetry and the remote control of the entire system,

- an auxiliary power supply 83 of the control unit 80, and an uninterruptible power supply,

- cable runs 84, for communication with sensors and actuators arranged on the lower surfaces of the supporting frame 65,

- a power supply 85,

- and a unit 86 for inverting the polarities of the electrodes of the desalination assembly 10a.

The intermediate surface 69 accommodates the desalination assembly 10a with the plumbing means 25.

On the intermediate surface 69 there are, therefore:

- the solenoid valves 70 of the plumbing means 25 for the exchange of the water flows from the first plumbing circuit 21 to the second plumbing circuit 23 and vice versa,

- the ends 71, 72, 73 of the ducts inside the desalination assembly 10a, which are connected to the plumbing switching means 25 and to the electrode chambers; of such ends, three lead to the three solenoid valves 33, 34 and 39 of the assembly carried by the lower surface 67 and described below.

The lower surface 67, shown schematically in Figure 5, comprises:

- the two pumps, first and second, 31 and 43,

- the solenoid valves 33, 34 and 35 of the first service circuit 28 and the solenoid valves 39 and 40 of the second service circuit 37,

- the process tank 42,

- as well as a system for filtering and pretreating the supply saline solution, not shown,

- three pipe connectors: a first 75, corresponding to the branch for drawing water 29, a second 76, corresponding to the return branch 36, and a third 77, which corresponds to the line 61 for draining to a desalinated water accumulation tank, for the external plumbing connection of the electrodialysis device 10; such three connectors are arranged at what is established as being the rear of the electrodialysis device 10, similarly to the electrical connecting cable for powering the electrodialysis device 10 according to the invention.

In practice it has been found that the invention fully achieves the intended aim and objects.

In particular, with the invention an electrodialysis device has been devised in which the plumbing service means are simpler and more compact, by virtue of only two pumps, with the first pump adapted to serve both a first plumbing circuit of the desalination assembly and the electrode chambers; in this manner the margin of operating reliability and of continuity of service without requirement for maintenance are increased over the conventional electrodialysis machines.

Furthermore, with the invention an electrodialysis device has been devised that is capable of making desalinated water available more rapidly than the conventional electrodialysis machine.

Furthermore, with the invention an electrodialysis device has been devised that is automated and easily manageable without particular necessities for intervention by an operator.

What is more, with the invention an electrodialysis device has been devised that is compact and in which the components are enclosed and supported in a frame of small dimensions.

Also, with the invention an electrodialysis device has been devised that can be easily transported anywhere required, and which is easy to render operational in a short time.

Furthermore, with the invention an electrodialysis device has been devised that is highly versatile, since the desalinating process can be conducted using a body of water, a well, and/or a storage and settling tank as a source of supply. With regard to the power supply, such electrodialysis device according to the invention can be connected indifferently to a traditional source, such as a single-phase or three-phase electrical grid, or to an electric power generating set, or to a renewable power source, without excessive restrictions on the quality of the waveform of the alternating or pseudo-direct current.

Furthermore, with the invention an electrodialysis device has been devised with which one can carry out a completely automated method for medium- term storage, which is useful in order to prevent hazardous drying- out of the process membranes inside the desalination assembly, thus keeping the plumbing circuits always operational.

What is more, with the invention an electrodialysis device has been devised that is provided with a telecommunications system that offers the possibility, by way of the internet, of tasking a control and assistance center with capabilities for telemetry, remote control and internal/external remote video surveillance, useful when an electrodialysis device according to the invention is not presided over.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

In practice the components and the materials employed, provided they are compatible with the specific use, and the contingent dimensions and shapes, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. 102016000079225 (UA2016A005574) from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. An electrodialysis device (10) for desalinating water with a high concentration of dissolved salts, which comprises, between two heads (11 , 12), two opposite electrode chambers (13, 14) that contain electrodes (15, 16) having opposite polarities, between which a desalination assembly (10a) is arranged which comprises a plurality of reaction chambers of two alternate types, first chambers (17) for ion enrichment, and second chambers (18) for ion depletion, each chamber of a first type being open onto a laterally adjacent chamber of the second type by interposition of an ion- conducting membrane (19, 20), said first chambers (17) being interconnected by plumbing to each other and to said heads so as to define a first plumbing circuit (21) for the transit of a first water flow (22), with ion enrichment, said second chambers (18) being interconnected by plumbing to each other and to said heads so as to define a second plumbing circuit (23) for the transit of a second water flow (24), with ion depletion, there being plumbing means (25) for the exchange of the first and second water flows (22, 24), each electrode chamber (13, 14) being served by a corresponding independent plumbing circuit (26, 27),

said electrodialysis device (10) being characterized in that it comprises:

- a first plumbing service circuit (28) for said first plumbing circuit (21), for ion enrichment, and for said electrode chambers (13, 14), which comprises:

- a branch (29) for drawing water from a source of saline solution (30) for said water flow with ion enrichment (22), provided with a first service pump (31),

- a branch (32) for delivery to said first plumbing circuit (21) and to said electrode chambers (13, 14), with corresponding solenoid valves (33, 34, 35) for sorting and pressure control of the flows,

- a branch (36) for return from said first plumbing circuit (21) and from said electrode chambers (13, 14) to said source (30),

- and a second plumbing service circuit (37) for said second plumbing circuit (23), for ion depletion, which comprises:

- a branch (38) for delivery to said second plumbing circuit (21) with corresponding solenoid valves (39, 40) for sorting and pressure control of the flows,

- a branch (41) for return from said second plumbing circuit (23) to a process tank (42) for containing the water being treated.

2. The electrodialysis device according to claim 1 , characterized in that in the first plumbing service circuit (28), the delivery branch (32) comprises a first line (44), with a first solenoid valve (33), for the first plumbing circuit (21), and a second line (45), with two parallel branches, with a second solenoid valve (34), for the circuits (26, 27) of the two electrode chambers (13, 14), said two first and second lines (44, 45) being in parallel.

3. The electrodialysis device according to one or more of the preceding claims, characterized in that said delivery branch (32) comprises a third line (46), in parallel with the two first and second lines (44, 45), with a corresponding solenoid valve (35) for filling the process tank (42).

4. The electrodialysis device according to one or more of the preceding claims, characterized in that said return branch (36) comprises a first line (47) for return of the first plumbing circuit (21) and a second line (48), which is in parallel with the first line, for return of the circuits (26, 27) of the electrode chambers (13, 14).

5. The electrodialysis device according to one or more of the preceding claims, characterized in that said first plumbing service circuit (28) comprises a first manually actuated valve (50), which is arranged on the branch for drawing water (29), upstream of the first pump (31), a second manually actuated valve (51), which is arranged on the return branch (36) downstream of the two return lines (47, 48), and a third manually actuated valve (52), which is arranged on a connecting line (54) which connects the branch for drawing water (29) to the return branch (36), said first manual valve (50) being arranged downstream of the connection between the branch for drawing water (29) and the connecting line (54).

6. The electrodialysis device according to one or more of the preceding claims, characterized in that in the second plumbing service circuit (37) the delivery branch (38) comprises a first line (60), with a first solenoid valve (39), for the second plumbing circuit (23), and a second line (61), in parallel with the first line (60), with a corresponding second solenoid valve (40), for draining the process tank (42), once the treatment has been completed, into a tank for the accumulation of desalinated water, available to a user device.

7. The electrodialysis device according to one or more of the preceding claims, characterized in that said return branch (41) from said second plumbing circuit (23) to the process tank (42), at the drainage outlet in the process tank (42), has a scrubbing/degassing unit (62), which is adapted to facilitate the separation from the water flow of any gas that has formed inside the desalination assembly (10a).

8. The electrodialysis device according to one or more of the preceding claims, characterized in that it comprises an electronic control unit (80), all the steps of operation being executed and controlled by said central electronic control unit (80).

9. The electrodialysis device according to one or more of the preceding claims, characterized in that it comprises a supporting frame (65), which comprises at least four angular posts (66), a lower supporting surface (67), an upper supporting surface (68) and intermediate resting elements which define an intermediate resting surface (69).

10. The electrodialysis device according to one or more of the preceding claims, characterized in that said supporting frame (65) is made of stainless steel.