EP2125631A1

EP2125631A1 - Liquid treatment system

Info

Publication number: EP2125631A1
Application number: EP07824637A
Authority: EP
Inventors: Alexander Simpson; Paul Wilkins
Original assignee: Atranova Ltd
Current assignee: Atranova Ltd
Priority date: 2006-11-21
Filing date: 2007-11-20
Publication date: 2009-12-02
Also published as: GB2444056A; GB2444056B; WO2008062170A1; GB0623204D0

Abstract

A liquid treatment system (1) is disclosed. The system comprises a housing (3) having an inlet (7) and an outlet (9). A flow conduit is provided between the inlet (7) and the outlet (9) and an array of electrodes is provided that extends across the flow conduit. The electrodes are connected to power supply terminals so that adjacent electrodes in the array are anodes and cathodes. In one embodiment, the electrodes are mounted in drawers that can be inserted and removed from the housing to facilitate maintenance.

Description

Liquid Treatment System

The present invention relates to an apparatus and method for the treatment of liquid. One embodiment of the invention provides a water treatment system that occupies a small footprint and has low maintenance and running costs.

US 6998031 discloses a water treatment system, comprising two elongate tubular bodied electrodes, made of substoichiometric oxides of titanium

(Ebonex®), and arranged as an inner cathode co-axial with, and surrounded by, an outer anode, with the water to be treated made to pass longitudinally along the annular clearance between the electrodes. Whilst the use of such

Ebonex® electrodes is advantageous due to their stability and long life, the system described in US'031 cannot easily scale to the throughput required for commercial use.

The present invention therefore aims to provide an alternative configuration for treating waste liquid using electrodes made from substoichiometric oxides of titanium that readily scales for commercial use.

According to one aspect, the invention provides a liquid treatment apparatus comprising: a housing having an inlet and an outlet for the liquid; a flow channel extending between the inlet and the outlet and defining a flow path along which liquid can flow; a two dimensional array of non-coaxial electrodes at least some of which are made of substoichiometric oxides of titanium and which extend substantially parallel to each other across said flow channel in a direction transverse to said flow path; and connectors for electrically connecting each of the electrodes to one of the first and second electrical power terminals; wherein the connectors are arranged so that adjacent electrodes in the two dimensional array are connected to different ones of the first and second terminals. All the electrodes in the array are preferably made of substoichiometric oxides of titanium, although one or more of the electrodes may be made of more conventional electrode material, such as graphite, if desired.

In one embodiment the electrodes are arranged in a plurality of rows and connected so that adjacent electrodes in the same row are connected to different ones of said terminals. Adjacent rows of electrodes are preferably staggered from each other in an hexagonal packing arrangement in which the minimum spacing between neighbouring electrodes in the array is about 2mm.

In one embodiment the array of electrodes spans substantially across the whole of the flow conduit, so that the substantial majority of said fluid is constrained to flow through gaps between adjacent electrodes.

In a preferred embodiment a plurality of the electrodes are tubular and the connectors to said tubes each include a sub-connector that extends along and makes contact with the inside surface of the tube at a plurality of spaced apart locations along the length of the tube. This arrangement allows for a more uniform distribution of charge along the length of the electrode.

The array of electrodes is preferably carried by an electrode frame that is detachably mounted within a mounting bay of the housing. This arrangement facilitates maintenance (for example to replace faulty electrodes) as the frame can be removed easily from the housing. The apparatus preferably includes a plurality of electrode arrays (which may or may not be identical) arranged along the flow channel. The elongate electrodes in one or more of the arrays may have a generally circular, square or polygonal cross-section in a direction transverse to its axis. Electrodes in the same array preferably, although not necessarily, have the same cross-section.

In one embodiment the housing is arranged so that, in use, the fluid to be treated is forced along a substantially vertical flow path between the inlet and the outlet. In a preferred embodiment, a switch is provided for switching the electric potential applied to the electrodes, so that electrodes connected to the first terminal become connected to the second terminal and so that electrodes connected to the second terminal become connected to the first terminal. This allows the electrodes to "self clean", without having to disassemble the apparatus and as electrodes of substoichiometric oxides of titanium are being used, such reversal of polarity will not affect the stability and lifetime of the electrodes.

These and other aspects of the present invention will become apparent from the following exemplary embodiments that are described with reference to the accompanying figures in which:

Figure 1 shows a water treatment unit according to one embodiment of the invention;

Figure 2 is a cross-section of the water treatment unit shown in Figure 1 along the xx axis;

Figure 3 is a cross-section of the water treatment unit of Figure 1 , along the yy axis and viewed from the front;

Figure 4 schematically illustrates an electrode drawer that forms part of the water treatment unit shown in Figure 1 ;

Figure 5 is a longitudinal cross-section of one of the elongate rod electrodes that is held in the electrode drawer shown in Figure 4;

Figure 6 illustrates the way in which the rod electrodes in one array are arranged in an hexagonal packing arrangement and connected to positive and negative terminals of a power supply;

Figure 7 illustrates an alternative arrangement of electrodes having a square cross-section; and Figure 8 illustrates an alternative arrangement of electrodes having an hexagonal cross-section.

Housing

Figures 1 to 3 show a water treatment unit 1 , comprising, in this embodiment, an upright elongate housing 3, affixed, in use, to the ground by a base-plate 5, and having three main pipe connectors: an inlet 7, for untreated water, located at the front 8 of the unit, near the base plate 5; an outlet 9, for treated water, at the rear 10 of the unit, near the top 11 of the housing 3; and a drain 13, also at the rear 10 of the unit, near the base plate 5. A gas vent 15 is located at the top 11 of the housing 3, towards the rear 10. In this embodiment, the housing 3 has dimensions of 1900 mm x 150 mm x 400 mm (height x width x depth) and is made from stainless steel. In this embodiment, the flow into the inlet 7 is pumped whereas the flow from the outlet 9 is gravity driven, therefore the diameter of the outlet 9 has been made larger than both that of the inlet 7 and that of the drain 13, in order to prevent the system backing up and overflowing via the gas vent 15. The unit 1 has a shipping (i.e. non-operational or dry) weight of approximately 140 kg.

As illustrated more clearly in Figures 2 and 3, the housing 3 defines an elongate flow channel 17, which is substantially rectangular in cross-section, and which extends between and directs the flow of water from the inlet 7 to the outlet 9, the drain 13 being closed during normal use.

As shown in Figure 3, in this embodiment the housing 3 has six bays 19-1 to 19-6, accessible from the front 8 of the housing 3, and arranged in a linear sequence one after the other along the flow channel 17. Each bay 19 is designed to receive and hold an electrode drawer 21 that is shown in cross- section in Figures 2 and 3 and in perspective in Figure 4.

Electrode drawer

Figure 4 is a perspective view of one of the electrode drawers 21 that forms part of the water treatment unit 1. In this embodiment, all the electrode drawers 21 are the same and each comprises a frame assembly 23, fronted by an inspection window 25 made of glass or Perspex®, that is designed to hold a plurality of rod electrodes 27 orientated substantially parallel to each other and arranged in a two-dimensional array 28. In this embodiment, each electrode drawer 21 is arranged to hold twenty five rod electrodes 27 arranged in successive horizontal rows of 4-3-4-3-4-3-4 rods, with the electrodes in adjacent rows being staggered relative to each other, as shown in Figure 4, so as to form the two-dimensional array 28. As illustrated in Figures 2, 3 and 4, the electrode drawers 21 and the corresponding bays 19 are arranged such that when the electrode drawer 21 is inserted into a bay 19, the longitudinal axis of each rod electrode 27 is transverse to the flow channel 17 (and therefore, during use, will be transverse to the flow of water passing from the inlet 7 to the outlet 9).

Further, when an electrode drawer 21 is inserted into its corresponding bay 19, the rod electrodes 27 extend across the depth of the flow channel 17, between the front 8 of the housing 3 and the rear 10 of the housing 3. Also, the side walls 29 and 31 of the housing 3 in each bay 19 are shaped so that when the electrode drawer 21 is inserted into the bay 19, there is a close fit between the side walls 29 and 31 and the outer rod electrodes 27 in the array 28. These features ensure that the substantial majority of the water to be treated passing along the flow channel 17 is constrained to pass through the electrode array 28 in each bay 19 (and in particular through the gaps between adjacent electrodes 27 in the array 28) as it flows from the inlet 7 to outlet 9.

In this embodiment, with this particular arrangement of rod electrodes 27, the closest separation between immediately adjacent electrode surfaces is 2 mm. This is advantageous because a small separation between adjacent electrodes means that a smaller voltage differential is required to be applied between adjacent electrodes 27 in the array to achieve a given electric field strength in the gap between adjacent electrodes 27. This in turn means that the applied voltage is less likely to damage the rod electrodes 27 whilst also minimising the power consumption of the unit 1. In this embodiment, the water treatment unit 1 has six bays 19 each of which is arranged to receive and hold an electrode drawer 21 containing twenty five rod electrodes 27, for a total of one hundred and fifty electrodes 27 per unit. Watertight blanking plates 32 are provided to seal empty bays 19, such as bays 19-1 and 19-6 in Figures 1 to 3.

Rod Electrode

Figure 5 is a cross-sectional view of one of the rod electrodes 27 showing its construction. In this embodiment, each rod electrode 27 is made from an elongate hollow tube 35 of Ebonex® (the common and commercial name for a conducting ceramic made from substoichiometric oxides of titanium known as Magneli phases). In the preferred embodiment, the Ebonex® tubes 35 are produced according to the method disclosed in the applicant's co-pending British patent application 0618961.7, the contents of which are incorporated herein by reference. The design of the electrodes 27 is in accordance with the electrode design described in US 6998031 , which discloses how an electrical contact is made to the tube by means of a titanium coil 39 that runs along the inside of the tube 35 along its length so that it contacts the inside surface of the tube at a plurality of spaces apart points along its length. This allows a more uniform charge distribution along the length of the electrode.

As mentioned above, the advantages of using Ebonex® material for the electrodes 27 include a high resistance to corrosion and the ability of each rod electrode to function either as an anode or as a cathode.

In this embodiment, the Ebonex® tubes 35 are 316 mm in length, with an external diameter of 18 mm and an internal diameter of 12 mm. At each end of the tube 35 is a plastic cap 41 , 43 and affixed between these end caps is a plastic rod 45 which runs lengthways along the axis of the titanium coil 39. One of the end caps 41 has an electrical contact 47 for making a connection to the titanium coil 39. Electrical Connection

The rod electrodes 27 in each array 28 are held at predetermined potentials by means of an external power supply 49 (shown in Figure 1), which can be regulated by a controller (not shown). In this embodiment, each rod electrode 27 is held at one of two potentials Vi or V₂ , where Vi > V₂ , according to the arrangement as shown in Figure 6, where for clarity Vi has been shown as a positive potential ('+') and V₂ as a negative potential ('-'). In this embodiment, the difference between V₁ and V₂ is 6 volts and as the electrodes all have the same construction, this results in each rod drawing a constant DC current of approximately 0.5 to 1.4 amps. The unit 1 therefore will have a maximum total power consumption of less than 1 kW.

Unit operation

In operation, untreated liquid (in this case water) is pumped into the inlet 7 and flows upwards along the flow channel 17 through the electrode arrays 28. As the water passes through the electrode arrays 28, it passes through electric fields produced between adjacent charged electrodes 27. These electric fields have two main effects on contaminants within the water:

1. small particles combine to form larger particles by a process of electro-coagulation; and

2. microscopic parasites such as Cryptosporidium and bacterium such as legionella pneumophila, the cause of legionnaires' disease, are destroyed by free radicals formed at the electrodes which interfere with and significantly damage the cell walls of the microorganisms. In addition, there may be some precipitation of dissolved solids.

Electro-coagulation is commonly used to separate suspended solids from contaminated water. It works by neutralising electrostatic charges carried on the surfaces of the suspended solids, which prevent them colliding and sticking together to form larger particles which would eventually settle. Common electro-coagulation processes accomplish this using a sacrificial anode that corrodes and dissolves into the solution, thereby releasing charged particles (e.g. iron hydroxide) onto which the smaller suspended solids absorb. In this embodiment, a non-sacrificial electro-coagulation process is carried out using Ebonex anodes, which do not corrode and dissolve into the solution. Instead they achieve electro-coagulation solely by means of the electric field that is formed between the anodes and the cathodes, which causes the larger particles in the solution to become charged and thereby act as coagulants for the smaller particles.

The water then exits as treated water via the outlet 9 at the top of the unit 1. Although not shown, the water output from the outlet 9 is typically filtered to remove the coagulated particles. The increased size of the contaminant particles due to the electro-coagulation process means that effective filtration is more readily accomplished.

During operation, gaseous by-products, for example hydrogen, that are generated are vented via the gas vent 15.

In this embodiment, the unit 1 is designed to run at a substantially constant flow rate of between approximately 5 m³ /hour and 10 m³ /hour, with water taking approximately one minute to pass from the inlet 7 to the outlet 9.

The applicant has found that the present invention is effective at reducing the Chemical Oxygen Demand (COD) of untreated water by over 99% and likewise the Total Suspended Solids (TSS) by over 99%. It has also been shown to significantly reduce other contaminants such as chlorides, ammonia and heavy metals.

Unit Maintenance

With use, the unit 1 will require cleaning of deposited contaminants. This may be achieved by flushing the unit with fresh water and/or by reversing the current polarity applied to each electrode in the arrays 28 every hour. Polarity reversal is done to counteract the adsorption of ions onto the electrode surfaces. These ions, when so adsorbed, form deposits which reduce the effective electrode area and thereby increase the voltage difference and therefore the power required to maintain the working of the unit 1. This ability to self-clean in particular without having to disassemble the unit 1 in particular offers a significant advantage over the co-axial two-component systems of the prior art which must be disassembled to perform routine maintenance tasks.

In the preferred embodiment, an electronic controller is provided for controlling this polarity switching. This allows the polarity switching in one of three ways:

1) a timing circuit configured to switch polarities at frequencies as high as 10Hz, but typically configured to switch polarities once every 2 to 5 minutes.

2) A current threshold switch, which causes the polarity to be switched if the current applied to the electrodes drops below a predefined threshold value.

3) A manual override - to allow polarity switching by a human operator.

Alternatively, instead of applying DC current to the electrodes, AC current may be applied, which will avoid the need for a separate polarity switching module.

Further, the arrangement of the separate arrays 28 of electrodes in the bays 19 also facilitates maintenance as it becomes easy to remove and replace electrodes when they become faulty. In particular, by draining the water from the housing via the drain 13, it becomes possible to remove an electrode drawer (and replace it with another one or seal the opening with a blanking plate) and then carry out maintenance on the removed electrodes. Whilst this maintenance is being carried out, the unit 1 can be operated as normal. Therefore the "down" time for maintenance can be significantly reduced.

Modifications and Alternatives

In the above embodiment, the rod electrodes 27 have a circular cross-section and therefore the electric field they produce is non-uniform. In an alternative embodiment, the rod electrodes 27 can have a rectangular cross-section (as illustrated in Figure 7), resulting in a uniform electric field wherever the faces of adjacent electrodes are parallel. Alternatively still, the electrodes may have a polygonal cross-section, as illustrated in Figure 8. The rods in each array 28 preferably have the same cross-section, although this is not essential. Rods in different arrays or even in the same array may have different cross- sections. The electrodes in the same or different arrays may also have different dimensions. This may allow, for example, more control over the maximum spacing between neighbouring electrodes in each array (which in turn may allow lower voltages to be applied across the electrodes to achieve a desired field strength in the gap between adjacent electrodes).

In the above embodiment, the closest separation between immediately adjacent electrode surfaces is 2 mm. While there is no maximum separation above which the system could not work, the larger the separation between electrodes the larger the voltage required to achieve the desired field strength in the gap between adjacent electrodes. In practice, the maximum separation is therefore preferably less than 75 mm. Conversely, the minimum separation needs to take account of the risk of blockage by contaminant particles, and is therefore preferably no less than 1 mm.

Also in the above embodiment, the water treatment unit 1 was shown with four of the six bays 19 in use. As those skilled in the art will appreciate, any number of the six bays 19 can be used. More or less than six bays may also be provided. The modularity of the unit 1 applies equally to other embodiments, wherein the size of the electrode array 28 can be altered according to the specific requirements of the treatment process.

Furthermore, in the above embodiment, the water treatment unit 1 is arranged so that the flow channel 17 is vertical. In an alternative embodiment, the flow channel may be horizontal (to aid plug flow) or at any other intermediate orientation. In other embodiments, the flow channel 17 need not be linear and may follow a curved path.

In the above embodiment, the electrodes 27 were elongate rods, each of which spanned the width of the flow channel 17, and which were arranged in a two-dimensional array. Alternative embodiments may comprise differently- shaped electrodes arranged in arrays of one, two or three dimensions, for example: • two sets of half-width rod electrodes arranged as two intermeshed two- dimensional arrays;

• a two-dimensional array of small plate electrodes; or

• a three-dimensional array of, for example, spherical or cubic electrodes.

In the above embodiment the electrodes were made of Ebonex. In an alternative embodiment, the electrodes may be made of other materials such as graphite.

In the main embodiment described above, a plurality of arrays of electrodes were arranged parallel to one another along a flow path. In an alternative embodiment, the different arrays may have different orientations relative to the other arrays. For example, some arrays may extend from the front to the back of the housing whilst others may extend from one side to the other.

In the above embodiment the polarity of the electrodes was reversed every hour. Alternative embodiments may involve different polarity reversal schedules, for example a reverse polarity applied for two minutes every four hours.

In the above embodiment, each of the rod electrodes 27 was connected to one of two terminals and was thereby held at one of two potentials \Λ or V₂ , where Vi > V₂ , according to the arrangement as shown in Figure 6, where for clarity Vi was shown as a positive potential ('+') and V₂ as a negative potential ('-'). Specifically, in the above embodiment adjacent electrodes in the same row were connected to the same terminal and were thereby held at the same potential e.g. + + + +. Alternative embodiments may involve different arrangements of connectors. For example, adjacent electrodes in the same row may be connected to different terminals and thereby be held at different potentials such that each row comprises an alternating sequence e.g. + - + -. In the above embodiment, the difference between potentials Vi and V₂ was 6 volts. In other embodiments other potential differences may be used, such as 24 volts. The potential difference used for a given situation will depend on the application to which the treatment system is being used.

In the above embodiment, the water was pumped into the inlet 7 and gravity fed from the outlet 9. In an alternative embodiment, the water to be treated may be pumped into and out of the unit 1. This can allow better control over the flow rate of the water through the unit 1. In particular, the pumps can be controlled by means of three level sensors positioned near the outlet 9 - an upper level sensor positioned above the outlet 9, a middle level sensor positioned at the top of the outlet 9 and a lower level sensor positioned at the bottom of the outlet. In operation, the input pump may be turned on whilst the output pump is switched off. When the water level reaches the level of the middle level sensor, the output pump is switched on. This will result in the level dropping slightly and both pumps will remain on until the water level drops below the lower level sensor or rises above the upper level sensor. If the water level drops below the lower level sensor, then the output pump is switched off until the level rises back above the middle level sensor. If the water level rises above the upper level sensor, then the input pump is switched off until the water level drops below the middle level sensor. In this way, the flow rate of the water to be treated can be controlled by varying the speed of the inlet and outlet pumps. Additionally, by pumping the water from the outlet into a retention tank, a delay can be introduced after the treatment to allow for the effects of the treatment to be completed, before the water is then pumped through a separate filter.

In the above embodiment, the side walls 29 and 31 of the housing 3 in each bay 19 are shaped so that when the electrode drawer 21 is inserted into the bay 19, there is a close fit between the side walls 29 and 31 and the outer rod electrodes 27 in the array 28. In an alternative arrangement, the side walls 29 and 31 may be integrally formed with the electrode drawers 21. This will make the drawer assembly more rigid and will make it easier to install the drawer into the housing 3. In the above embodiment, each electrode drawer 21 carried twenty five electrodes 27. As those skilled in the art will appreciate the drawers may be arranged to carry different numbers of electrodes. For example, one or more of the electrode drawers 21 may be arranged to carry thirty two electrodes 27 - in eight rows of four electrodes 27.

Claims

1. A liquid treatment apparatus comprising: a housing having an inlet for receiving the liquid to be treated and an outlet for outputting the treated liquid; a flow channel extending between the inlet and the outlet and defining a flow path along which liquid received at said inlet can flow to said outlet; a two dimensional array of elongate non-coaxial electrodes at least some of which are made of substoichiometric oxides of titanium and which extend substantially parallel to each other across said flow channel in a direction transverse to said flow path; a power supply having first and second terminals at different electric potentials; and connectors electrically connecting each of said electrodes to one of said first and second terminals; wherein said connectors are arranged so that adjacent electrodes in said two dimensional array are connected to different ones of said first and second terminals.

2. An apparatus according to claim 1 , wherein said electrodes are arranged in a plurality of rows.

3. An apparatus according to claim 2, wherein said connectors are arranged so that adjacent electrodes in the same row are connected to different ones of said first and second terminals.

4. An apparatus according to claim 2, wherein said connectors are arranged so that adjacent electrodes in the same row are connected to the same one of said first and second terminals.

5. An apparatus according to claim 2, 3 or 4, wherein the electrodes in adjacent rows are staggered from each other.

6. An apparatus according to any of claims 2 to 5, wherein the minimum spacing between electrodes in adjacent rows is between 1 mm and 75 mm.

7. An apparatus according to any of claims 1 to 5, wherein the minimum spacing between adjacent electrodes in the array is between 1 mm and 75 mm.

8. An apparatus according to any of claims 1 to 7, wherein a plurality of said electrodes are tubular and wherein the connectors to said tubes each include a sub-connector that extends along and makes contact with the inside surface of the tube at a plurality of spaced apart locations along the length of the tube.

9. An apparatus according to any of claims 1 to 8, wherein said two dimensional array of electrodes is carried by an electrode frame that is detachably mounted within a mounting bay of the housing.

10. An apparatus according to claim 9, wherein the housing comprises a plurality of said mounting bays arranged sequentially along the flow channel.

11. An apparatus according to claim 10, comprising a plurality of said electrode frames, each carrying a respective two dimensional array of electrodes and each being mounted within a respective one of said mounting bays.

12. An apparatus according to claim 11 , comprising more mounting bays than electrode frames.

13. An apparatus according to claim 11 or 12, wherein each electrode frame includes a plate at one end of the electrodes to provide a liquid tight seal with the housing and wherein the connector for each electrode passes through said plate to make contact with the electrode.

14. An apparatus according to claim 12 or 13, wherein a blanking plate is provided for each empty mounting bay.

15. An apparatus according to any of claims 1 to 14, wherein said housing is arranged so that, in use, said fluid to be treated is forced along a substantially vertical flow path between said inlet and said outlet.

16. An apparatus according to any of claims 1 to 15, further comprising a drain outlet for draining fluid from said flow channel.

17. An apparatus according to any of claims 1 to 16, further comprising a gas vent through which gas generated by the treatment of said liquid can escape from said housing.

18. An apparatus according to any of claims 1 to 17, wherein a plurality of said electrodes have a generally circular cross-section.

19. An apparatus according to any of claims 1 to 18, wherein a plurality of said electrodes have a generally square cross-section.

20. An apparatus according to any of claims 1 to 19, wherein a plurality of said electrodes have a polygonal cross-section.

21. An apparatus according to any of claims 1 to 18, wherein the electrodes in the or each array have substantially the same cross-section.

22. An apparatus according to any of claims 1 to 21 , further comprising a switch for switching the electric potential applied to said electrodes, so that electrodes connected to said first terminal become connected to said second terminal and so that electrodes connected to said second terminal become connected to said first terminal.

23. An apparatus according to any of claims 1 to 22, wherein said liquid comprises water.

24. An apparatus according to any of claims 1 to 23, wherein one or more of said connectors comprises a plurality of sub-connectors that are connected in series between the corresponding voltage supply and the corresponding electrode.

25. An apparatus according to any of claims 1 to 6, wherein said array of electrodes spans substantially across the whole of the flow conduit, so that the substantial majority of said fluid is constrained to flow through gaps between adjacent electrodes.

26. A liquid treatment apparatus comprising: a housing having an inlet for receiving the liquid to be treated and an outlet for outputting the treated liquid; a flow channel extending between the inlet and the outlet and defining a flow path along which liquid received at said inlet can flow to said outlet; a two dimensional array of elongate non-coaxial electrodes that extend substantially parallel to each other across said flow channel in a direction transverse to said flow path; a power supply having first and second terminals at different electric potentials; and connectors electrically connecting each of said electrodes to one of said first and second terminals; wherein said connectors are arranged so that adjacent electrodes in said two dimensional array are connected to different ones of said first and second terminals.

27. A liquid treatment apparatus comprising: a housing having an inlet for receiving the liquid to be treated and an outlet for outputting the treated liquid; a flow channel extending between the inlet and the outlet and defining a flow path along which liquid received at said inlet can flow to said outlet; a plurality of mounting bays arranged sequentially along the flow channel; and a plurality of two dimensional arrays of elongate electrodes each array being mounted in a respective one of said mounting bays with the electrodes of each array extending substantially parallel to each other across said flow channel in a direction transverse to said flow path.

28. An apparatus according to claim 27, wherein the arrays of electrodes are mounted in the respective mounting bay so that the electrodes of all the arrays extend substantially parallel to each other.

29. An apparatus according to claim 27, wherein at least one of said arrays of electrodes is detachable from the corresponding mounting bay.

30. An apparatus according to claim 29, wherein said at least one array is slideably detachable from the corresponding mounting bay.

31. An apparatus according to any of claims 27 to 30, comprising the features of any of claims 1 to 26.

32. Use of the apparatus of any of claims 1 to 31 for treating a liquid.