WO2018147723A1

WO2018147723A1 - Device for converting chloride containing water into active chlorine, such as chlorine dioxide, and method for the production of chlorine dioxide

Info

Publication number: WO2018147723A1
Application number: PCT/NL2017/050075
Authority: WO
Inventors: Maurice Paul Tax
Original assignee: Bright Spark B.V.
Priority date: 2017-02-07
Filing date: 2017-02-07
Publication date: 2018-08-16

Abstract

The invention relates to a device for converting chloride containing water into active chlorine, such as chlorine dioxide, which device comprises at least one electrolytic cell, comprising: - a channel, comprising an inlet at a first end of the channel and an outlet at a second end of the channel; - a cathode, arranged in the channel, which cathode comprises a first titanium or stainless steel segment and a second carbon (felt) segment, arranged downstream of the first segment, which first segment and second segment are electrically connected to each other; – a titanium anode, arranged in the channel, provided with a mixed metal oxide coating layer comprising ruthenium oxide and/or iridium oxide, which coating layer faces the cathode; and - a power source, electrically connected to the cathode and the anode which device further comprises a recirculation tube connecting the outlet of the channel with the inlet of the channel for recirculating at least a part of the output of the channel through the inlet of the channel. The invention further relates to a method for the production of chlorine dioxide.

Description

Device for converting chloride containing water into active chlorine, such as chlorine dioxide, and method for the production of chlorine dioxide The invention relates to a device for converting chloride containing water into active chlorine, such as chlorine dioxide.

In order to disinfect water, various techniques may be used. Chlorine dioxide is an example of an oxidising agent which is known for its suitability to disinfect water.

Currently, chlorine dioxide used for treatment of water is typically prepared from sodium chlorite, hydrochloric acid and optionally sodium hypochlorite. The presence of such starting materials is however undesirable in a number of applications, for instance since it presents safety risks, and since it is costly .

It is now an object of the invention to reduce or even obviate the above mentioned drawbacks.

This object is achieved with a device for converting chloride containing water into active chlorine, such as chlorine dioxide, which device comprises at least one

electrolytic cell, comprising:

- a channel, comprising an inlet at a first end of the channel and an outlet at a second end of the channel;

- a cathode, arranged in the channel, which cathode comprises a first titanium or stainless steel segment and a second carbon (felt) segment, arranged downstream of the first segment, which first segment and second segment are

electrically connected to each other;

- a titanium anode, arranged in the channel, provided with a mixed metal oxide coating layer comprising ruthenium oxide and/or iridium oxide, which coating layer faces the cathode; and - a power source, electrically connected to the cathode and the anode

which device further comprises a recirculation tube connecting the outlet of the channel with the inlet of the channel for recirculating at least a part of the output of the channel through the inlet of the channel.

A water stream may be directed through the channel of the device from the first end, then along the anode and the cathode towards the second end. By the application of power through the power source, the concentration of water

disinfecting components, such as chlorine dioxide, will be increased in the water stream.

The application of one anode which faces two cathode segments, defines a first and second zone respectively within the device. It has been found that the creation of the first and the second zone leads to an increase of the content of chlorine oxide (C10₂) . In the first zone, in which the anode faces the mixed metal oxide segment, ionic chloride present in the water is suspected to be converted into (sodium)

hypochlorite, whereas in the second zone, in which the anode faces the carbon based segment, this hypochlorite is suspected to be converted into chlorine dioxide. It is suspected that the formation of chlorine oxide depends on the presence of oxygen (0«) as created in the first zone. It is in this respect in particular found to be important that the second zone is located downstream of the first zone. For the production of chlorine dioxide, it is important that water includes (ionic) chloride, which is normally present in tap water. The use of tap water in conjunction with the device is therefore

preferred.

The carbon based cathode may for instance comprise compressed carbon plates or carbon felt, e.g. made of

graphite. The carbon based segment may optionally be supplied with a conducting grid or layer, preferably made of metal, e.g. a titanium grid or layer, to further assist in

electrically connecting this cathode segment to the circuit.

Since the device will be in contact with water during operation, the metal chosen for the anode and/or cathode preferably comprises and more preferably consists of a metal (or mixed metal oxide) which prevents corrosion, such as titanium. The anode is preferably an acid washed and/or high grade titanium. The ruthenium oxide and/or iridium oxide layer of the anode preferably faces both the first segment and the second segment of the cathode.

At least a part of the output of the electrolytic cell is furthermore recycled by a pump to the input side of the electrolytic cell, in order to further increase the chlorine dioxide yield in each passage over the electrolytic cell. On average, the feed passes the cell at least twice. In this way, the capacity of the electrolytic cell may be kept small, which is for instance advantageous when the amount of space available is limited, e.g. on a floating structure.

The channel is enclosed by one or more channel walls, retaining the water stream within the channel. The channel walls may be connected to each other through

connecting means, in order to increase ease of assembly or disassembly, such as a protrusion and a cooperating cavity.

A filter may be arranged upstream of the

electrolytic cell in order to filter particulate matter out of the water.

Preferably, the inlet and the outlet are arranged in line with each other. By arranging the inlet and the outlet in line with each other, the connection of the device within the range of a straight conduit or to a second device according to the invention will be enhanced. Preferably, the inlet and the outlet also have a matching cross-section in the direction of flow within the inlet and the outlet for this purpose.

More than one of the device according to the

invention may be connected to each other, i.e. with the outlet of a first device to the inlet of the subsequent device, in order to create a chain of devices in order to increase the amount of chlorine dioxide as required.

Preferably, the cathode is at least partially porous, to promote the unwanted process of calcification to occur within the pores of the cathode, thereby reducing the amount of disruptions in the device as a whole as a

consequence of calcification. Preferably, the dimensions of the device and the plates are chosen such that the edges of the plates within the housing are arranged adjacent to at least three walls of the housing to even further increase the effective surface area (based on a housing of the device shaped as a rectangular cuboid) .

Preferably, the ratio of a) the distance from the anode to the cathode perpendicular to the length direction of the anode to b) the length of the anode along the channel is equal or larger than 1 : 5, preferably equal or larger than 1 : 10. While it has been shown that the efficiency of the device is increased with the use of an oblong anode and/or cathode segments, it has in particular been found that

choosing the ratio accordingly, leads to a further increase in the efficiency of the device, in which the further preferred embodiment increases the efficiency even further.

Preferably, the channel wall comprises polypropylene or acrylonitrile butadiene styrene (ABS) . Both materials are found safe for treatment of water and are therefore preferred options as a base material for the fabrication of the housing of the device. Preferably, at least one of the cathode and the anode are arranged in the channel wall. In such a situation, in which at least one of the cathode and the anode functions as a part of the channel wall, retaining the water stream within the channel, it is no longer required to arrange another channel wall along at least a part of the length of the cathode or anode concerned, since the cathode or anode concerned will retain the water within the channel itself. This reduces material costs of the device and prevents a water stream between the tube and the channel wall. An arrangement of the elements concerned along the channel wall may be equated to a situation according to the present embodiment in which the elements are arranged in the channel wall.

This arrangement may in particular be advantageous if the first cathode segment is further arranged along the first leg of a U-shaped channel and the second cathode segment is arranged along the second leg of this U-shaped channel, since the first cathode segment and the second cathode segment may then be electrically connected outside of the channel, without comprising the tightness of the channel and without the necessity of applying adhesives, which may increase the chance of contamination by dissolution in the water stream.

In a first embodiment of the device according to the invention, the device further comprises a tank and a pump and/or a flow switch, arranged between the tank and the at least one electrolytic cell.

By providing, in addition to the cell, a (storage) tank and a pump and/or a flow switch, it is possible to regulate the amount of feed which is fed or recycled from the tank to the electrolytic cell.

In a second embodiment of the device according to the invention, the device comprises a connection to a ballast tank of a floating structure, such as a ship or a boat. In a floating structure such as a boat or a ship, ballast water may be used to balance the structure in the water, dependent on the load of the ship, such as by cargo. In order to purify the ballast water of biological materials, such as plants, animals, viruses and other microorganisms, chlorine dioxide may be used. The device according to the invention may advantageously be installed on such a floating structure, since it is no longer necessary to provide in a stock of chlorine dioxide, since ionic chloride present in the water is converted into chlorine dioxide on the floating structure itself. An output of the ballast tank is preferably connected to the input of the device according to the

invention (before passage of the electrolytic cell), whereas an output of the device (after passage of the electrolytic cell) is connected to the input of the ballast tank. The device may also or alternatively be provided in a harbor for a similar purpose.

In a third embodiment of the device according to the invention, at least one of the cathode and the anode is arranged in the channel substantially parallel to the

direction of flow in the channel, and the anode is arranged at a distance from the cathode in a direction perpendicular to the length of both the cathode and the anode.

In this way, the flow inside the device is along the cathode and anode, which is beneficial for obtaining a good conversion .

The cathode and the anode are preferably oriented with their length direction along the direction of flow within the channel to optimize the contact surface area.

The anode and/or the cathode are preferably oblong, which may mean that the anode and/or the cathode have a length parallel to the direction of flow which is significantly higher than one or both of the main dimensions of the respective cathode or anode.

Preferably, the anode and the cathode (preferably both of the cathode segments) are parallel, i.e. are with their length and depth direction parallel. This increases the efficiency of the device, since the anode and the cathode segments are placed at an equal distance of each other along their length.

In a fourth embodiment of the device according to the invention, one of the cathode and the anode is rod-shaped, and the other of the cathode and the anode is a cylindrical tube, arranged with its height direction parallel to the length direction of the rod-shaped cathode or anode.

The cylindrical tube completely envelopes the solid rod-shaped element and is preferably arranged in or close to the channel wall to minimize a water stream between the tube and the channel wall. The tube and the rod are typically held in a fixed position with respect to the tube by suitable mounting means, preferably to or through the channel wall.

Preferably, the rod is cylindrical. Preferably, the center line of the tube coincides with the length axis of the rod-shaped element, such to arrange the rod in the middle of the tube, in order to equalize the reaction conditions on all sides of the rod.

It is preferred if the rod-shaped element is the anode, since the anode does not comprise two zones and in more cases than the cathode does not have a conducting grid or wire for electrical connection. The tube may be provided more easily with these features than the rod.

In a fifth embodiment of the device according to the invention, the anode and/or at least one and preferably both of the segments of the cathode are plate-shaped, and the surface area of the cathode and the surface area of the anode facing each other are preferably substantially equal.

The use of plate-shaped anodes and/or cathode segments increases the efficiency of the device, since the elements concerned are provided with a large effective surface area .

In particular, the plate-shaped anodes and/or cathode segments may be disc-shaped. If one of the anode and the cathode is disc-shaped, the other of the anode and the cathode is preferably disc-shaped as well in order to optimize exposure of the anode to the cathode and to ease construction of the device.

By furthermore equalizing the surface area of the cathode and the anode which face each order, a balanced execution of the reactions within the device is obtained.

In a sixth embodiment of the device according to the invention, the surface area of the first segment of the cathode facing the channel and the surface area of the second segment of the cathode facing the channel are substantially equal.

By choosing the surface area of the first segment of the cathode and the second segment of the cathode to be substantially equal, a balanced execution of the reactions within the device is obtained.

In a seventh embodiment of the device according to the invention, the channel is substantially U-shaped.

The creation of a device with a U-shaped channel makes the device more compact. Since the inlet is located at the distal end of the first leg of the U-shape (at a distance from the passage opening between the two legs of the U-shape) , and since the outlet is located at the distal end of the second leg of the U-shape, such a U-shape also brings the inlet and the outlet of the channel relatively close to each other, while still obtaining a relatively large area in which the anode and cathode are facing each other. It also assists in the connection of the device to for instance a conduit.

Preferably, the anode extends from the first leg to the second leg of the U-shaped channel. Thereby, it is

possible to actually use one anode which bridges the distance from the first leg to the second leg across the (total) length direction of the anode for both the first leg and the second leg of the U-shaped channel, which functions as the anode in both the first leg and the second leg of the channel. This increases the ease of production of the device, since it is no longer required to arrange two anodes along both of the legs of the U-shaped channel. It also reduces the necessity of placing a channel wall between the first leg and the second leg of the U-shaped channel, since the one anode functions as a channel wall .

More preferably, the first cathode segment is arranged along the first leg of the U-shaped channel and the second cathode segment is arranged along the second leg of the U-shaped channel. By arranging the first cathode segment and the second segment accordingly, a more defined distinction is created in the device between the first zone and the second zone, which may enhance the efficiency or selectivity of reactions in the device.

It may also enhance the easiness of electrically connecting the first cathode segment and the second cathode segment in a reliable way, which may be connected to each other by an AMP connector through a side wall of the device (separate from the anode and the cathode) .

In an eighth embodiment of the device according to the invention, the edge of the second cathode segment overlaps the first cathode segment, wherein the overlapping part of the second cathode segment preferably faces the anode. By creating an overlap between the edge of the first segment of the cathode segment and the second cathode segment, the connection between the segment is further consolidated, reducing the chances of leakage between the segments. A suitable connection, e.g. an adhesive, may be used in the overlapping zone of both segments to further consolidate the connection when required.

The invention further relates to a method for the production of chlorine dioxide, comprising the steps of:

- providing a device according to any of the

preceding claims;

- feeding an aqueous feed with ionic chloride from the inlet towards the outlet of the device with the power source of the device switched on.

In a first embodiment of the method according to the invention, the aqueous feed comprises, at the inlet of the device, a salt selected from wherein R- is selected from

Li, Na, K, Rb, Cs, Fr, and preferably from Na, K, and wherein R₂ is selected from F, CI, Br, I, At, and is preferably CI, most preferably in a concentration of approximately 18 grams per liter or 0.308 moles per liter.

It has been observed that the addition of such salts to the aqueous feed at the inlet side of the device results in an increase of the amount of chlorine dioxide at the outlet side. This effect is especially observed with a concentration of 18 grams per liter NaCl or 0.308 moles per liter. It is thus expected that the same effect is observed for other salts at such a salt molarity.

In a second embodiment of the method according to the invention, the aqueous feed comprises, at the inlet of the device, sodium hydroxide, preferably in a concentration of approximately 100 mL/m³. It has been observed that the addition of sodium hydroxide to the aqueous feed at the inlet side of the device results in a further increase of the amount of chlorine dioxide at the outlet side.

In a third embodiment of the method according to the invention, the method further comprises the step of using the output of the outlet in treatment of ballast water.

In a fourth embodiment of the method according to the invention, the method further comprises the step of using the output of the outlet in treatment in agriculture or horticulture, such as bulb cultivation.

The water obtained with the current device may advantageously be used in applications where large amounts of purified water (free from biological materials) are required. Treatment of ballast water, as well as agriculture or

horticulture are examples of such applications.

These and other features of the invention will be elucidated in conjunction with the accompanying figures.

Figure 1 shows a perspective partly transparent view of a device according to the invention with a U-shaped channel with the legs on top of each other.

Figure 2 shows a cross-section of the device

according to figure 1.

Figure 3 shows a cross-section of a device according to the invention with an elongated channel.

Figure 4 shows a cross-section of another device according to the invention.

Figure 5 shows an exploded view of the device according to figure 4.

Figure 6 shows a cross-section of another device with a U-shaped channel with the legs besides each other according to the invention. Figure 7 shows an exploded view of the device according to figure 6.

Figure 8 shows a diagram of a device according to the invention.

Figure 9 shows the concentration of chlorine dioxide over time in the setup according to figure 8.

Figure 10 shows another embodiment of a device according to the invention.

Figure 1 shows a perspective view of a device 1 according to the invention. The device 1 comprises a housing 2 with an inlet 3 and an outlet 4, and a channel 5 running from the inlet 3 towards the outlet 4 which is U-shaped. The U- shaped channel 5 has a first leg 6 and a second leg 7, connected at a passage opening 8, which is open. First leg 6 and second leg 7 of the U-shaped channel are arranged on top of each other with respect to the path between inlet 3 and outlet 4. An oblong first cathode segment 9 and an oblong second cathode segment 10 are arranged in the channel wall of the housing 2. An oblong anode 11 is located halfway between the first cathode segment 9 and the second cathode segment 10 (i.e. at a distance from both segments 9, 10) in a way that all elements 9, 10, 11 are parallel to each other. The cathode segments 9, 10 run in their length direction from the right side channel wall 12 towards inlet 3 and outlet 4,

respectively and in their depth direction from front channel wall 13 to back channel wall 14. The length and depth of the elements 9, 10 and 11 is equal. The inlet 3 and outlet 4 are arranged in line with each other and their cross-sections are equal. The housing 2 is fully enclosed by walls, either formed by cathode segments 9, 10, channel walls 12, 13, 14, or other walls not further elucidated in figure 1, with the exception of openings for inlet 3 and outlet 4 and for electrically connecting the cathode 9, 10 and anode 11 (not depicted) . As shown in figure 2 in more detail, the anode 11 comprises a titanium base 15 with ruthenium oxide layers 16, 17, each facing one cathode segment 9, 10 in the respective legs 6, 7 of the channel 5. The anode 11 bridges the distance from the first leg 6 of the U-shaped channel 5 to the second leg 7 of the U-shaped channel 5 across the length direction of the anode 11.

An alternative embodiment of a device 21 according to the invention is shown in figure 3. The device 21 comprises a housing 22 with an inlet 23 and an outlet 24, and a channel 25 running from the inlet 23 towards the outlet 24 which is elongated. A first oblong cathode segment 26 and a second oblong cathode segment 27 are arranged in the wall of the channel 25. The second cathode segment 27 forms an overlap 28 with first cathode segment 28, wherein the overlapping part of the second cathode segment 27 faces an oblong anode 29, arranged at a distance from the cathode 26, 27. The anode 29 also is arranged in an opposing wall of the channel 25. The elements 26, 27, 29 are parallel to each other. The length of cathode elements 26 and 27 is equal, and their length in total is equal to the length of anode 29. The housing 22 is fully enclosed by walls with the exception of openings for inlet 23 and outlet 24 and for electrically connecting the cathode 26, 27 and anode 29 (not depicted) . The anode 29 comprises a titanium base 30 with one ruthenium oxide layer 31 facing the cathode segments 26, 27 in the channel 25.

Figure 4 and 5 show another embodiment of a device 30 according to the invention. The device 30 comprises a housing 31 with a first housing part 31a and a second housing part 31b, fixed connectable to each other with connecting flange 32 and a connecting cavity 33, each running around the circumference of the housing parts 31a, b. Inside the housing 31, a solid rod-shaped anode 34 is disposed centrally within the housing 31 connected electrically through an electrical connection 35. The titanium/ruthenium oxide anode 34 is completely enveloped by a cathode 36 in the shape of a

cylindrical tube, connected through an electrical connection 37. The cathode comprises two zones 38, 39, of which the first zone 38 is a titanium based zone, and of which the second zone 39 is a carbon felt zone, facing the anode, and a metal base for electrical connection beneath the carbon layer (not shown) . A water stream is directed from the inlet 40 in direction 41 towards the outlet 42 in direction 43.

Figure 6 and 7 show another embodiment of a device 50 according to the invention. The device 50 comprises a cylindrical housing 51 with a first housing part 51a and a second housing part 51b, fixed connectable to each other with connecting flange 52 and a connecting cavity 53, each running around the circumference of the housing parts 51a, b. Inside the housing 51, a disc-shaped titanium/ruthenium oxide anode 54 is arranged adjacent to the top wall of first housing part 51a, with the ruthenium oxide layer facing the cathode 55, which comprises a first titanium zone 56 and a second pressed carbon plate zone 57, with a titanium base layer 58 attached to the zones 56, 57 for connecting the cathode electrically to connection pin 59. Anode 54 is electrically connected to connection pin 60. Both connection pins 59, 60 extend through the bottom of the housing part 51b through a connection holes 61 to connection box 62. The bottom of the housing part 51b further comprises a wall 63 which makes the zone between anode 54 and cathode 55 U-shaped, with the legs of the U-shape arranged besides each other with respect to the direction from inlet 64 to outlet 65. The flow path within the device 50 is designated in figure 6 with arrows.

In figure 8, a setup 70 with a device 71, such as a device 1 or device 21, is shown, arranged in a cycle. The output 72 of the device 71 is connected to a tank 73, from which at least a part is recycled to the input 74 of the device 71. Circulation through the setup 70 is controlled by a pump 75 provided with a flow switch. The water in the cycle may be exchanged through a connection 76 with a ballast tank of a ship.

Figure 9 is a graph which shows the relation between the concentration of chlorine dioxide over time. As shown, as time passes, the concentration increases to level off to a maximum.

Figure 10 shows another of a device 100 according to the invention, with an inlet 101, an outlet 102, a first zone 103 and a second zone 104. In the first zone 103 and second zone 104, there are a preferably even number (in this case four) of parallel plates 105, which are partly anodes and for the remainder cathodes (preferably in a 1 : 1 ratio) . In first zone 103, the cathodes are titanium or stainless steel, and in the second zone, the cathodes are carbon or carbon felt. In both the first zone 103 and the second zone 104, the anode is a titanium provided with a mixed metal oxide coating layer comprising ruthenium oxide and/or iridium oxide, facing the cathode. In the first zone 103, the flow is allowed both between and around the plates 105, whereas in the second zone 104, the flow is exclusively between the plates 105.

In all of the figures, details are shown not in proportion: some details may be drawn exaggerated compared to other elements for this purpose.

Example

A device with a U-shaped channel according to the invention was created according to figure 1 and 2. The inlet and the outlet are disposed in line with each other and both have an inner radius of 4 mm. The distance between the anode (titanium grade 2 with a Ru0₂-coating facing both legs of the channel) and the cathode perpendicular to the anode in both the first leg (first segment: titanium grade 2) and the second leg (second segment: carbon felt with titanium grid for electrical connection) of the channel is 2 mm. The dimensions of the anode and the first cathode segment are both 40 mm (along the direction of flow in the channel) x 20 mm (the depth of the channel) x 1 mm (the thickness of the anode or first cathode segment, respectively. The dimensions of the second cathode segment is 40 mm x 20 mm x 6 mm in a similar fashion. The passage opening between the first leg and the second leg of the U-shaped channel has a length of 8 mm and a depth of 20 mm. The other walls of the channel were made of polypropylene. The device was arranged in a cycle with a tank and a flow switch.

The cathode and the anode were connected to a 16.22 Volt 130 A power source and a water stream of 7.000 liters per minute with 18 grams per liter of ionic chlorine was directed through the channel. The amount of chlorine dioxide in the tank was 6500 parts per million.

The experiment was repeated with the addition of 100 mL/m³ sodium hydroxide. The amount of chlorine dioxide in the tank was 12000 parts per million.

Claims

1. Device for converting chloride containing water into active chlorine, such as chlorine dioxide, which device comprises at least one electrolytic cell, comprising:

electrically connected to each other;

- a titanium anode, arranged in the channel, provided with a mixed metal oxide coating layer comprising ruthenium oxide and/or iridium oxide, which coating layer faces the cathode; and

- a power source, electrically connected to the cathode and the anode

2. Device according to claim 1, wherein the device further comprises a tank and a pump and/or a flow switch, arranged between the tank and the at least one electrolytic cell .

3. Device according to claim 1 or 2, wherein the device comprises a connection to a ballast tank of a floating structure, such as a ship or a boat.

4. Device according to claim 1, 2 or 3, wherein at least one of the cathode and the anode is arranged in the channel substantially parallel to the direction of flow in the channel, and wherein the anode is arranged at a distance from the cathode in a direction perpendicular to the length of both the cathode and the anode .

5. Device according to any of the preceding claims, wherein one of the cathode and the anode is rod-shaped, and wherein the other of the cathode and the anode is a

cylindrical tube, arranged with its height direction parallel to the length direction of the rod-shaped cathode or anode.

6. Device according to any of the claims 1 to 4, wherein the anode and/or at least one and preferably both of the segments of the cathode are plate-shaped, and wherein the surface area of the cathode and the surface area of the anode facing each other are preferably substantially equal.

7. Device according to any of the preceding claims, wherein the surface area of the first segment of the cathode facing the channel and the surface area of the second segment of the cathode facing the channel are substantially equal.

8. Device according to any of the preceding claims, wherein the channel is substantially U-shaped.

9. Device according to any of the preceding claims, wherein the edge of the second cathode segment overlaps the first cathode segment, wherein the overlapping part of the second cathode segment preferably faces the anode.

10. Method for the production of chlorine dioxide, comprising the steps of:

- providing a device according to any of the

preceding claims;

11. Method according to claim 10, wherein the aqueous feed comprises, at the inlet of the device, a salt selected from Ri¾₂ ^~ , wherein ¾ is selected from Li, Na, K, Rb, Cs, Fr, and preferably from Na, K, and wherein R₂ is selected from F, CI, Br, I, At, and is preferably CI, most preferably in a concentration of approximately 18 grams per liter or 0.308 moles per liter.

12. Method according to claim 11, wherein the aqueous feed comprises, at the inlet of the device, sodium hydroxide, preferably in a concentration of approximately 100 mL/m³.

13. Method according to any of the claims 10, 11 and 12, further comprising the step of using the output of the outlet in treatment of ballast water.

14. Method according to any of the claims 10, 11 and 12, further comprising the step of using the output of the outlet in treatment in agriculture or horticulture, such as bulb cultivation.