Field

The invention relates to an apparatus for removal of ions comprising multiple stacks, a stack comprising:

a first electrode;

a second electrode; and,

a spacer in between the first and second electrode and allowing water to flow in between the first and second electrode.

Background

In recent years one has become increasingly aware of the impact of human activities on the environment and the negative consequences this may have. Ways to reduce, reuse and recycle resources are becoming more important. In particular, clean water is becoming a scarce commodity. Therefore, various methods and devices for purifying water have been published.

A method for water purification is by capacitive deionisation, using an apparatus provided with a flow through capacitor (FTC) for removal of ions in water. The FTC functions as an electrically regenerable cell for capacitive deionisation. By charging electrodes, ions are removed from an electrolyte and are held in electric double layers at the electrodes. The electrodes can be (partially) electrically regenerated to desorb such previously removed ions without adding chemicals.

The apparatus for removal of ions comprises one or more pairs of spaced apart electrodes (a cathode and an anode) and a spacer, separating the electrodes and allowing water to flow between the electrodes. The electrodes are provided with current collectors or backing layers and a high surface area material, such as e.g. carbon, which may be used to store removed ions. The current collectors may be in direct contact with the high surface area material. Current collectors are electrically conductive and transport charge in and out of the electrodes and into the high surface area material.

A charge barrier may be placed adjacent to an electrode of the flow-through capacitor. The term charge barrier refers to a layer of material which is permeable or semipermeable for ions and is capable of holding an electric charge. Ions with opposite charge as the charge barrier charge can pass the charge barrier material, whereas ions of similar charge as the charge of the charge barrier cannot pass the charge barrier material. Ions of similar charge as the charge barrier material are therefore contained or trapped either in e.g. the electrode compartment and/or in the spacer compartment. The charge barrier is often made from an ion exchange material. A charge barrier may allow an increase in ionic efficiency, which in turn allows energy efficient ion removal.

The apparatus may be provided with a housing comprising a water inlet for letting water into the housing and a water outlet for letting water out of the housing. In the housing of the apparatus for removal of ions electrodes and spacers are stacked in a "sandwich" fashion by compressive force, normally by mechanical fastening. During manufacturing of the stack the electrodes and the spacer may be assembled together in the housing. It may be important that the electrodes and spacers may be precisely held with respect to each other in the housing, making the manufacturing a difficult task.

Summary

It is an object to provide an apparatus for removal of ions with an improved manufacturability.

Accordingly, there is provided an apparatus for removal of ions comprising multiple stacks, each stack comprising:

a first electrode;

a second electrode; and,

a spacer in between the first and second electrode and allowing water to flow in between the first and second electrode;

wherein at least one of the stacks is provided with a tray for holding and positioning the stack within a housing of the apparatus.

By assembling and holding the stack in a tray the apparatus may be manufactured by positioning the trays within the housing. This way the accurate alignment of the electrodes and spacers in the housing may be easier than when the electrodes and spacers are provided separately or individually inside the housing. The tray may comprise several alignment features which may be used to align the first and second electrode and the spacer in the tray and to align multiple trays in the same housing. The alignment is important in order to ensure a good positioning of the electrodes and spacers within the stack and within the housing. As a result the performance of the electrodes and the flow through the spacer may become more equal, independent of the position of the electrodes and spacers in the stack and the position of the stack in the housing. In addition, the trays can slide along at least one central rod during manufacturing of the stacks in the housing, This allows that the compressive force which is applied to the stack during manufacturing may be the same or at least very similar for the individual stacks. This in turn may result in that the desalination performance of the different stacks may be independent of the position of the stack in the housing.

According to a further embodiment there is provided a method of manufacturing an apparatus for removal of ions from water, the method comprises manufacturing a stack by: providing a first electrode in a tray;

providing a spacer against the first electrode in the tray; and

providing a second electrode against the spacer in the tray;

the method further comprises:

positioning the tray within a housing of the apparatus.

By assembling and holding the stack in a tray the apparatus may be manufactured by positioning and aligning the trays within the housing. This way the accurate alignment of the electrodes and spacers in the housing may be easier than when the electrodes and spacers are provided separately or individually in the housing.

The first electrodes may be connected with a first power terminal and the second electrode may be connected to a second power terminal. The stacks may be compressed within the housing. Water may be provided to the stacks within the housing via a water inlet and this water may be allowed to flow through the spacer in between the electrodes to a water outlet while charging the electrodes and removing ions from the water flowing through the spacer.

These and other aspects, features and advantages will become apparent to those of ordinary skill in the art from reading the following detailed description and the appended claims. For the avoidance of doubt, any feature of one aspect of the present invention may be utilised in any other aspect of the invention. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se. Similarly, all percentages are weight/weight percentages unless otherwise indicated. Numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated.

Brief description of the figures

Embodiments of the invention will be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 shows a schematic cross-section of an apparatus for removal of ions produced with a method according to the invention; Figure 2a shows a detail enlargement of the stack 3 of figure 1 ;

Figure 2b shows a detail of figure 1 ;

Figure 3 shows a top view on a tray for use in the method according to the invention; and,

Figure 4 shows a top view on a tray for use in the method according to the invention provided with a stack.

Detailed description of the invention

Figure 1 shows a schematic cross-section of an apparatus for removal of ions 1 produced with a method according to the invention with a part of the housing removed. In the example the apparatus may comprise twelve flow through capacitor stacks 3. The flow through capacitor stack 3 may be provided with repeating units of a first electrode 4 (see figure 2a, which is an enlargement of a stack), a spacer 8, and a second electrode 6. The first electrode 4 may be provided with a first current collectors 5, (see figure 1 ) which may be bundled together with a first connector 1 1. The second electrode 6 may be provided with a second current collectors 9, which may equally be bundled together on the other side of the apparatus with the second connector 10.

The first connector 1 1 (see figure 2b, which is a partial enlargement of figure 1 ) may be used to clamp the first current collectors 5 together. The current collectors 5, 9 and the first connector 1 1 and the second connector 10 may be made of the same material e.g. carbon (e.g. graphite) to lower the electrical resistivity between the current collectors 5, 9 and the connectors 1 1 , 10. The first connector 11 may be provided with inserts 15 e.g. from a metal, such as, for example copper. The inserts 15 may be screwed in the first connector 1 1 so as to assure low electrical resistivity between the insert 15 and the first connector 1 1. The power terminal 27 is a construction that is connected to both the power supply and one or more connectors 10, 1 1. The power terminal 27 may be fixed into the upper and/or bottom part 22, 24 and /or any other part of the housing. The power terminal 27 may be provided with a rail e.g. rod 17 made of, for example, metal e.g. copper to electrically connect all the first connectors 11 via their inserts 15 to a power source (not shown). The first connector 11 and the insert 15 may be provided with an opening for the rod 17. The inserts 15 and the rod 17 may be shielded of from the water inside the apparatus by e.g. resin, glue or a paste which functions as a water barrier. The resin, glue or a paste or any other water shielding material may optionally be applied to the hollow parts 19 of the connector 11 after compression of the stack. To circumvent that the resin may contaminate the stack 3 rubber rings 12 may be provided in the insert 15. A tray 13 may be provided to help manufacturing one stack 3 and assembling the stacks 3 together in a housing 21 of the apparatus. The housing may be watertight. Water may flow around the tray and into the stack. Within the housing the stacks 3 may be compressed between the top and bottom part 22, 24. The top part 23 of the housing 21 is provided with a feed-through allowing the rod 17 to make a connection with a power source. This way electrical charge can enter the first electrode via the first current collector 5 and also leave the electrode again, e.g. during regeneration of the electrodes. Water may be provided to an interior of the apparatus via a water inlet 26 into the housing the water is allowed to flow around the tray and the flow through capacitor stacks 3 and may enter the stacks via the spacers. The flow through capacitor stack 3 may be provided with a hole in the middle of the stack. In the hole a circular tube 29 may be provided and via the space between the hole and the tube the water may flow to an outlet 30. The interior of the tube 29 may be provided with a nut 35 and threaded bar 33 which may help to compress the electrodes in the stacks 3 and for compressing the stacks 3 between the upper and bottom part 22, 24 of the housing 21.

Compressing may occur during production of the apparatus, or optionally during maintenance. By compressing all the stacks at once it may be assured that the compression force is very similar or even equal for each stack and at the same equally or homogeneously distributed over the surface of the electrodes.

During manufacturing of the stack 3 a first electrode comprising a first current collector 5 may be provided in the tray 13. A spacer may be located on top of the first electrode; and a second electrode may be put on top of the spacer. Subsequently a spacer may be put on top of the second electrode followed by another first electrode. This may be repeated until for example 10 first and second electrode units are provided in the stack 3 held by the tray 13 each first electrode separated from a second electrode with a spacer. Subsequently a connector part 11 may be located on top of the current collectors 5 and a metal insert 15 may be screwed from the other side of the stack 3 through the tray 13 and the first current collectors 5 to fix the stack 3 to the tray 13.

The tray 13 and the stack 3 may be connected to the rod 17 of the first power terminal 27 by sliding the insert 15 over the rod 17 to allow a good electrical contact. The hole in the insert 15 may be of such a size that it allows for good electrical contact between the insert 15 and the rod 17 and at the same time allowing the insert 15 to slide over the rod 17. The connector 1 1 may be pressed on the tray 13 with the current collector 5 or multiple current collectors 5 in between the connector 1 1 and the tray 13 by screwing of the insert 15 in the connector part 11 . To assure good electrical conductivity between the connector 11 and the first current collector 5 the pressure on the connector part 15 and the current collector may be less than 100 Bar, preferably less than 50 Bar, more preferably less than 20 Bar and most preferably around 10 Bar. Multiple stacks 3 can be connected to the rod 17 and the stacks 3 may be connected in a similar way to the second connector 10. A force may be exerted on the stacks 3 with the nut 35 and threaded bar 33 via the upper and bottom part 22, 24 so as to compress the first and second electrode in a first direction parallel to the length of the threaded bar 33 which is perpendicular to the main surface of the electrode. The force may exert a pressure on the stack of less than 5 Bar, preferably less than 2 Bar, more preferably less than 1 Bar and most preferably around 0,5 Bar.

The first and second connector 1 1 , 10 allow for movement of the first and second current collector 5, 9 along the rod 17, 18 in the first direction such that the current collectors are not damaged by the compression force on the stack 3. The movements may be in the order of 0,05 to 10% of the height of the multiple stacks 3 in the first direction. After enough pressure is exerted on the stack a resin may be provided along or through the first and /or second connector 11 , 10 in the hollow parts 19 of the connectors 10, 1 1. The resin after hardening fixes the position of the connectors 10, 1 1 and may protect the (metal) inserts 15 and rod 17 from corrosion. The efficiency of the apparatus may be guaranteed for a long period since the water in the interior of the housing may not be in direct contact with the metal insert 15 and rod 17 and therefore corrosion may be prevented and the performance of the apparatus may not deteriorate due to corrosion.

Figure 3 shows a top view of a tray 13 for use in the method according to the invention. The tray 13 may be provided with openings e.g. holes 36a, 36 b, which may be used to slide the tray along the rod 17 (See figure 2) and to position the current collectors in the tray 13. The tray 13 may be provided with pins 37a, 37b for alignment of the electrodes which may positioned within the tray 13. The pins 37a and the hole 36a may be used to align the second current collectors while the pins 37b and the hole 36b may be used to align the first current collectors. The pins may also be used to align different trays with each other. The round openings 39 may function as an inlet for the water and the opening 51 as an outlet for the water. The tray may be produced from polypropylene and may be provided with a reinforcement plate (not shown) e.g. from metal to provide the required stiffness against the pressure of the connector 1 1. The corner 42 may be used to align the spacers. The spacers may be used to electrically insulate the first and the second electrode from each other and to allow for flow in between the first and the second electrode and may be a little larger than the first and second electrodes.

Figure 4 shows a top view of a tray 13 for use in the method according to the invention provided with a stack 3. The stack comprises a first and second electrode provided with current collector 5, 9. A connector part 11 may be provided to clamp the first current collector 5 against the tray 13. The connector part 1 1 may be provided with a screw thread and an insert 15 (see figure 2) may be screwed in the connector part 1 1 while clamping the current collector 5 and the tray 13 together. The height of the stack 3 in the first direction perpendicular to the main surface 41 of the electrode, provided within the tray 13 may be larger than the height of the tray 13. First current collector 5 and first connection part 11 may be provided around the opening 36b so as to allow for movement of the stack 3 along the rod 17. This way it is possible to exert a force on the stack 3 to compress the electrodes together without damaging the current collectors, 5, 9 and or the connectors during compression. The connector 1 1 including the insert 15, and the tray 13 are designed such that they can partly move into each other while being aligned along the rod 17. Please note that the stack 3 and tray 13 constructed in figure 4 may be used upside down in the apparatus according to figure 1. The stack 3 may be provided with charge barrier layers such ion exchange membranes, which can be applied as separate layers on top of the electrodes or integrated with the first and second electrode e.g. as a coating. The tray 13 (see figure 3) may be provided with an alignment feature, for example:

a notch, an edge 38 or a corner 42;

a protrusion or a pin 37; or,

a rod to position the first electrode, the second electrode, and/or the spacer in the tray 13. The first electrode, the second electrode and/or the spacer may be provided with an alignment feature for example an edge 43 to position the first electrode, the second electrode, and/or the spacer in the tray 13. The alignment feature of the tray 13 may be constructed and arranged to match/align the alignment feature of the first electrode, the second electrode and/or the spacer. The tray 13 may be provided with an alignment feature , for example an opening 36a, b to position the tray 13 in the apparatus for removal of ions 1. The apparatus may be provided with an alignment feature, for example the rod 17 to position the tray 13 in the housing 21 of the apparatus 1. The opening 36a, b may be constructed and arranged to cooperate with the rod 17, for example the size of the opening and the rod may be substantially matching.

The alignment feature e.g. rod 17 of the apparatus to position the tray 13 in the apparatus 1 (see figure 1 ) may be part of a connector for electrically connecting the first or second electrode to a power terminal 27. The rod 17 may be made from metal e.g. copper for increasing the electrical conductance of the connector. The alignment feature may have a substantially circular or rectangular shape in one of its cross-sections, such as for example the pin 37a or the opening 36a. The tray 13 may be provided with an opening 39, 40, 51 for water to flow through the tray 13. The opening 36a or 36b in the tray 13 may be constructed and arranged for electrically connecting the first or second electrode to a power terminal 27.

The tray 13 may comprise a main surface 44 facing the main surface 41 of the electrode stack 3 and a rim 45 extending substantially perpendicular to the main surface 44 of the tray 13. Multiple stacks 3 in their respective trays 13 may be stacked within the housing 27 of the apparatus 1. The tray 13 may be provided with a hole 51 for a compressing member e.g. threaded bar 33 compressing the electrodes within the apparatus 1.

The tray 13 may be provided with a pin 37a as an alignment feature to align the tray with other trays. For example the top of the pin 37a which is thinner than the rest of the pin may be received by an opening in another tray, for example on the other side with respect to the main surface 44 of the tray 13. The use of the alignment features is important to assure a good positioning of the electrodes and spacers within the apparatus which is important to assure that all electrodes and stacks equally contribute to the performance of the flow through capacitor.

Electrode

The electrodes (anode and or the cathode) may be made metal free by making them from carbonaceous material, for example activated carbon, which may be bound together in a polytetrafluoroethylene (Teflon™) matrix or carbon aerogels. The electrodes, which may be used in FTC cells may be treated with a concentrated salt solution to promote the ion removal capacity of the electrodes as well as ion conductivity and hence the speed of removal.

The material for storage of the ions may comprise a high surface area layer e.g. a porous carbon layer, which can be a flexible layer, or a non flexible layer.

The carbon used in the electrode layer may comprise activated carbon, and optionally any other carbonaceous material, such as carbon black, carbon aerogels, carbon nanofibres graphene or carbon nanotubes. The carbon may be chemically activated carbon or may be steam activated carbon. The carbon may have a high surface area of at least 500 m2/g, preferably at least 1000 m2/g, and more preferable at least 1500 m2/g. The anode and cathode may even be made out of different carbonaceous materials. Well known non-flexible carbon layers are made from carbon aerogels. These aerogels are often manufactured as composite paper: non-woven paper made of carbon fibers, impregnated with resorcinol- formaldehyde aerogel, and pyrolysis. Depending on the density, carbon aerogels may be electrically conductive, making composite aerogel paper useful as electrodes for deionization in Flow Through Capacitors.

The carbon may be present in the electrode in a concentration of at least 60%, preferably at least 70%, more preferable at least 80%, or even at least 85% by weight of the dry electrode. The use of thermoplastic or viscoelastic material such as latex or curable resins to form monoliths from powdered material is common. Examples of carbon layers that use Poly Fluor Tetra Etheen (PTFE) as binder material are the PACMM™ series (from Material Methods). One embodiment of the invention comprises an active carbon fiber woven layer or carbon cloth, e.g. the Zorflex ® range (from Chemviron Carbon).

One preferred embodiment of the invention comprises a carbon coating comprising: a binder, activated carbon and carbon black, which can be coated directly onto the current collector with a method described in a patent application with application number

PCT/EP2008/064992 incorporated herein by reference to form an electrode.

The electrode may comprise a current collector. The current collector may be made from an electrically conducting material. Suitable metal free materials are e.g. carbon, such as graphite, graphene, graphite sheets or carbon mixtures with high graphite content. It is advantageous to use a metal free electrode and current collector, because metals are expensive and introduce a risk of corrosion. The current collector is generally in the form of a sheet. Such sheet is herein defined to be suitable to transport at least 33 Amps/m ² and up to 2000 Amps/m ² . The thickness of a graphite current collector then typically becomes from 100 to 1000 micrometer, generally 200 to 500 micrometer.

Spacer

The spacer material may comprise an inert type material, such as an open space synthetic material and can be any material made from e.g. a polymer, plastic or fiberglass. The spacer can be a porous or non porous, woven or non woven material . The spacer may be prepared from a material that is electrically insulating, but allows ion conductance.

Suitable spacers are for example the Nitex ® range or Petex ® range (from Sefar), which are open mesh fabrics or filter fabrics, made from polyamide or polyetheentereftalate.

Charge barrier layer

The flow through capacitor may comprise a charge barrier. The charge barrier comprises a membrane, selective for anions or cations, or certain specific anions or cations, which may be placed between the electrode and the spacer. The charge barrier may be applied to the high surface area electrode layer as a coating layer or as a laminate layer.

Suitable membrane materials may be homogeneous or heterogeneous. Suitable membrane materials comprise anion exchange and/or cation exchange membrane materials, preferably ion exchange materials comprising strongly dissociating anionic groups and/or strongly dissociating cationic groups. Examples of such membrane materials are Neosepta ™ range materials (from Tokuyama), the range of PC-SA™ and PC-SK™ (from PCA GmbH), ion exchange membrane materials ex Fumatec, ion exchange membrane materials Ralex™ (from Mega) or the Excellion™range of heterogeneous membrane material (from Snowpure). Stack

A FTC may comprise at least one repeating unit of:

anionic electrode comprising a current collector

optionally an anion exchange membrane as charge barrier

- conventional FTC spacer

optionally a cation exchange membrane as charge barrier

cathode electrode comprising a current collector

multiple repeating units may be used to build up a stack and in the current invention the stacks are provided with a tray for positioning the stack within the apparatus for removal of ions and to obtain equal distribution of pressure and water flow.

Typically the number of repeating units in a FTC stack, as found in practice, is limited by the number of electrode layers than can be practically bundled and connected to the connector. It is preferred that the number of repeating units in a FTC is at least 1 , preferably at least 5, more preferably at least 10, still more preferably at least 20. For practical reasons, the number of repeating units is generally not more than 200, preferably not more than 150, more preferably not more than 100, or even not more than 50.

The stack may be compressed at a pressure of less than 5 Bar, preferably less than 2 Bar, more preferably less than 1 Bar and most preferably around 0,5 Bar.

The stack may be provided with, so called, floating electrodes. Floating electrodes are electrodes not directly being connected to a power source but receiving a polarized charge from other electrodes in the stack which are connected to a power source or from other floating electrodes. Floating electrodes may be positioned parallel and in between master electrodes in the stack. The invention may be used to connect the master electrodes in the stack to the power source. An advantage of using floating electrodes is that the voltages on the connector may be higher while the currents through the connector may be lower.

Electrical loss due to the resistivity in the connector may be lowered significantly by using floating electrodes. Accordingly an embodiment of the invention comprises:

providing a first electrode;

providing a spacer against the first electrode;

providing a second electrode against the spacer, the second electrode being a floating electrode;

providing a spacer against the second electrode:

providing a third electrode against the spacer;

connecting the first electrode with a first connector to a first power terminal;

connecting the third electrode with a second connector to a second power terminal; and exerting a force on the stack so as to compress the first, second and third electrodes to each other the first and/or second connector allowing for movement of the first and/or third electrode with respect to the first and/or second power terminal. A plurality of floating electrodes may be positioned between the first and third electrodes.

While specific embodiments of the invention have been described above, it may be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.

The descriptions above are intended to be illustrative, not limiting. Thus, it may be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the clauses set out below.

Embodiments are also provided in the following numbered clauses:

1. A method of producing an apparatus for removal of ions from water, the method comprises manufacturing a stack by:

providing a first electrode;

providing a spacer against the first electrode; and

providing a second electrode against the spacer;

the method further comprises:

connecting the first electrode with a first connector to a first power terminal;

exerting a force on the stack so as to compress the first and second electrode and the spacer; while,

allowing movement of the first electrode with respect to the first power terminal by the first connector.

2. The method according to clause 1 , wherein during manufacturing of the stack the following steps are repeated multiple times:

providing a first electrode;

providing a spacer against the first electrode;

providing a second electrode against the spacer; and,

providing a spacer against the second electrode.

3. The method according to clause 2, wherein each first electrode is connected with the first connector to the first power terminal; and,

the first connector allowing movement of at least one of the first electrode with respect to the first power terminal.

4. The method according to any of the clauses 1 to 3, wherein the method comprises providing a plurality of stacks each comprising a plurality of first electrodes;

connecting the plurality of first electrodes with a first connectors to the first power terminal; exerting a substantial equal force on the multiple stacks simultaneously; whereby the first connector allows for movement of at least one of the plurality of first electrodes with respect to the first power terminal.

5. The method according to any of the preceding clauses, wherein the method comprises connecting the second electrode to a second power terminal with a second connector and during exerting a force on the stack so as to compress the first and second electrode to each other the second connector allowing for movement of the second electrode with respect to the second power terminal.

6. The method according to any of claims 1 to 4, wherein the second electrode is a floating electrode and the method comprises providing a third electrode against the spacer provided against the second electrode, the method further comprising connecting the third electrode to a second power terminal with a second connector and during exerting a force on the stack so as to compress the first, second and third electrode to each other the second connector allowing for movement of the third electrode with respect to the second power terminal.

7. The method according to any of the preceding clauses, wherein the method further comprises providing a resin, glue, paste or any other water barrier along the first and /or second power terminal and/or through the first and/or second connector.

8. The method according to any of the preceding clauses wherein the method further comprises exerting a force on one or multiple stacks with a resulting pressure between the first and second electrode of less than 5 Bar, preferably less than 2 Bar, more preferably less than 1 Bar and most preferably around 0,5 Bar.

9. The method according to any of the preceding clauses, wherein the method further comprises: connecting the electrode with a first connector while exerting a force between the first electrode and the first connector with a resulting pressure of less than 100 Bar, preferably less than 50 Bar, more preferably less than 20 Bar and most preferably around 10 Bar between the first electrode and the first connector.

10. The method according to any of the preceding clauses, wherein during manufacturing of the stack a tray is provided to hold the stack.

1 1. The method according to clause 10, wherein during manufacturing the first electrode is clamped on the tray using the first connector.

12. The method according to clause 10 or 1 1 , wherein the first electrode is clamped on the tray with a resulting pressure of less than 100 Bar, preferably less than 50 Bar, more preferably less than 20 Bar and most preferably around 10 Bar.

13. The method according to clause 1 1 , wherein the method comprises sliding the first connector over a first rail of the first power terminal. 14. The method according to clause 13, wherein the method comprises aligning the tray with the first rail, with a housing for holding the tray, or with a previous provided tray.

15. An apparatus for removal of ions from water obtainable by a method according to any of the preceding clauses.