Electrochemical reactor for wastewater treatment

Abstract

An electrochemical reactor (10) for oxidizing contaminants in water has a cathode (28) having a vertically-oriented rotatable shaft (30) with a plurality of cathode plates (32) affixed to it. The reactor has vertically-stacked oxidation cells (54), each comprising an anode plate (34) and cathode plates (32). The reactor has a modular structure in which the side walls are formed of anode spacer rings (38) and further oxidation cells can be added without increasing the footprint of the reactor. There is a flowpath for water through the reactor from an inlet (24), through each of the oxidation cells in series and to an outlet (26). Reaction zones in the flowpath are in spaces (52A, 52B) between the surfaces of the anode plates and cathode plates for the oxidation of contaminants.

Description

[0001] ELECTROCHEMICAL REACTOR FOR WASTEWATER TREATMENT

[0002] Field of the Invention

[0003] The invention pertains to the treatment of wastewater, and in particular to a reactor for electrochemically oxidizing contaminants in water.

[0004] Background of the Invention

[0005] One method of treating contaminated water is to subject it to electrochemical oxidation that oxidizes the contaminants. Contaminated water may have organic contaminants, inorganic contaminants or both. Contaminated water may include wastewaters such as municipal sewage, storm water, farm leachate, mine leachate, industrial, institutional and commercial wastewater. The contaminated water typically undergoes preliminary processing such as screening to remove large particle contaminants. It may then be subjected to further treatment such as electrocoagulation, as described in WO 2010 / 096891 (Boyle et al), published September 2, 2010. In some water treatment applications, it is advantageous to subject the water to oxidation, following these initial treatments, in order to oxidize any remaining contaminants. In other applications, the contaminated water has little solid contaminants and it can be treated directly by oxidation, without preliminary treatments.

[0006] In some facilities there is limited space to install treatment equipment. It would be desirable to provide an oxidation reactor that has a high ratio of the area of reaction surface to the physical footprint of the reactor. It would be advantageous to allow the addition of more reactive area to the reactor, thereby increasing its capacity, without increasing its footprint. It would also be desirable to be able to generate different oxidation reactions, and combinations of oxidation reactions, as water travels through the reactor, to target specific contaminants in the water. The present invention provides one or more of these advantages over existing oxidation reactors. Summary of the Invention

[0007] One aspect of the invention provides an electrochemical reactor for treating contaminated water. It has a base comprising electrically non-conductive material and having an inlet opening for inflow of water; a top cap comprising electrically non-conductive material and having an outlet opening for the outflow of water; a rotatable cathode having a vertically-oriented cathode shaft and a plurality of cathode plates; and a plurality of vertically-stacked oxidation cells between the base and the top cap, each oxidation cell comprising a non-rotatable anode plate having a cathode plate above it and a cathode plate below it, with spaces between the anode plate and each of the cathode plates. There is a flowpath through the reactor for the flow of water from the inlet, through each of the oxidation cells in series, and to the outlet. The cathode plates and the anode plates are adapted to apply an electric current through water flowing in the spaces between them.

[0008] Further aspects of the invention and features of specific embodiments of the invention are described below.

[0009] Brief Description of the Drawings

[0010] Figure 1 is a vertical cross-sectional view of the electrochemical reactor according to one embodiment of the invention.

[0011] Figure 2A is a close-up view of a part of Figure 1 showing the structure of an individual oxidation cell of the reactor.

[0012] Figure 2B is an enlarged view of part of Figure 2A, showing details of the water flow path.

[0013] Figure 3 is a horizontal cross-sectional view of the electrochemical reactor of Figure 1 looking downward above a cathode plate.

[0014] Figure 4 is a horizontal cross-sectional view of the electrochemical reactor of Figure

[0015] 1 looking downward above an anode plate. Figure 5 is a fragmentary vertical cross-sectional view of a cathode structure for the reactor according to one embodiment.

[0016] Detailed Description

[0017] Referring to Figure 1 , the electrochemical reactor 10 has a top plate assembly 12 and a base assembly 14. The top plate assembly comprises a top cap 16 and a top cover plate 18. The base assembly comprises a base 20 and a base cover plate 22. The base assembly has an inlet opening 24 for the inflow of contaminated water into the reactor 10. The top plate assembly has an outlet opening 26 for the outflow of treated water from the reactor. The top cap 16 and the base 20 are made of electrically non-conductive material, such as fiberglass, PVC, Delrin™ and other structural plastics. The reactor is supported on a stand 21.

[0018] In some embodiments, the reactor does not include top and base cover plates 18, 22, and has just a top cap 16 and a base 20.

[0019] The reactor 10 has a rotatable cathode 28 comprising a vertically-oriented cathode shaft 30 and a plurality of spaced-apart cathode plates 32 affixed to the cathode shaft. The cathode shaft 30 includes cathode spacers 36 positioned between adjacent cathode plates 32 to space them apart a suitable vertical distance.

[0020] The cathode shaft 30 may be a continuous shaft or it may be made in sections. Embodiments in which the cathode shaft 30 is continuous rather than sectional are more suitable where it is intended that the reactor will have a fixed number of oxidation cells and further cells will not be added. Embodiments in which the cathode shaft 30 is in sections are more suitable where it is intended that oxidation cells may be added to the reactor to increase its capacity.

[0021] For simplicity of illustration, Figure 1 depicts the shaft 30 as continuous. In embodiments in which the shaft 30 is sectional, as seen in Figure 5, the cathode 28 comprises a lower shaft section 29, an upper shaft section 33, and cathode plates 32 each separated by cathode spacers 36. To add sections to a sectional cathode 28, the upper shaft section 33 is removed, and additional cathode spacers 36 and cathode plates 32 are added. The upper shaft section 33 is then replaced. The cathode sections, spacers and plates are affixed together, mechanically and electrically. They all rotate together as a unit when the cathode shaft turns.

[0022] The cathode 28 is electrically conductive. In some embodiments, the cathode shaft 30 may be made of stainless steel or titanium. The cathode plates 32 may be made of stainless steel or titanium.

[0023] In the embodiment illustrated in Figure 1 , the reactor has five cathode plates 32A, 32B, 32C, 32D and 32E. In other embodiments, there may be more or fewer cathode plates. The base 20 has a central recess and bearing assembly 42 to receive and rotatably support the lower part 29 of the cathode shaft 30, i.e. , the lower shaft section 29 in the case of a sectional shaft. The reactor includes a bushing and seal assembly 56 surrounding the cathode shaft 30 where the upper part 33 of the shaft passes through the top plate assembly 12, i.e., the upper section 33 in the case of a sectional shaft. Either a bushing or bearing assembly may be used at the lower end of the cathode shaft and where the shaft passes through the top plate assembly.

[0024] The reactor 10 has a plurality of non-rotatable anode plates 34, arranged such that each anode plate is positioned between two cathode plates. The anode plates 34 have a central opening, and the cathode shaft 30 extends vertically through this central opening. The anode plates 34 may be made of titanium with a mixed metal oxide coating applied to generate oxidation reactions. Other reactive materials may be used as coatings on the anode plates. For example, combinations of ruthenium, tantalum and titanium oxides may be used to be oxygen-evolving and target certain organic compounds. Combinations of iridium and ruthenium oxides may be used to be chlorine-evolving for disinfection of the water. Platinum may be used for targeting ammonia. Anode materials such as boron-doped diamond may be used to target specific contaminants, such as perfluorinated compounds. In each of these cases, as in others, increasing the current density used can change the reaction potential and therefore target different contaminants in particular zones of the reactor. Anode spacer rings 38 are arranged to space the anode plates vertically apart. The anode spacer rings 38 are made of electrically non-conductive material, which may be the same material as the top cap and the base. There are four anode spacer rings 38A, 38B, 38C and 38D in the embodiment illustrated in Figure 1. In other embodiments, there may be more or fewer anode spacer rings, depending upon the number of anode plates and cathode plates in the reactor. The anode spacer rings 38 seal against the anode plates 34. The top anode spacer ring 38A seals against the lower surface of the top cap 16. In other embodiments, the top cap 16 may be configured to integrally include the top anode spacer ring. The bottom anode spacer ring 38D seals against the bottom anode plate 34D, and the bottom anode plate 34D seals against the upper surface of the base 20. The anode spacer rings 38 have channels with O-rings 39 therein to seal against the adjacent anode plates.

[0025] The top plate assembly 12, the anode spacer rings 38 and the base assembly 14 are secured together by means of bolts 40, forming a sealed reactor unit. The anode spacer rings effectively form the side walls of the reactor 10.

[0026] In some embodiments, the anode spacer rings 38 also seal against each other at the outer periphery of the side walls of the reactor, and the anode plates 34 are mounted inwardly of that seal.

[0027] In some embodiments, each oxidation cell 54 (as defined below) is attached to the adjacent oxidation cell below, or to the base 20 in the case of the bottom oxidation cell, using screws or bolts, rather than having long bolts 40 that extend through the whole assembly. This facilitates adding or removing oxidation cells.

[0028] In some embodiments, the base 20 may be configured with a spacer ring 38 between it and the bottom anode plate 34D.

[0029] The cathode plates 32 and the anode plates 34 are arranged so as to provide spaces for the flow of water through the reactor from the inlet 24 to the outlet 26. A space 44 is provided between the lower surface of the bottom cathode plate 32E and the upper surface of the base 20. A space 46A is provided between the radially outer edge of the bottom cathode plate 32E and the base 20. Spaces 46B are provided between the radially outer edge of the other cathode plates 32A, 32B, 32C and 32D and the anode spacer rings 38A, 38B, 38C and 38D, respectively. Spaces 48 are provided between the cathode shaft and the radially inner edge of the anode plates 34A, 34B, 34C and 34D. A space 50 is provided between the lower surface of the top cap 16 and the top cathode plate 32A. This space 50 is open to the reactor outlet 26. A space 52A is provided between each anode plate 34 and the upwardly adjacent cathode plate 32, and a space 52B is provided between each anode plate 34 and the downwardly adjacent cathode plate 32. The foregoing spaces 44, 46A, 46B, 48, 50 and 52A and 52B are connected together and thus provide a flow path for water that extends from the inlet 24 to the outlet 26, as shown in Figure 1 and explained below.

[0030] The reactor 10 includes drive means 60 for rotating the cathode shaft, as indicated schematically in Figure 1. The drive means may for example be a motor mounted on the top cover plate 18, with a gearbox that drives the cathode shaft rotation through pulleys.

[0031] The reactor 10 also has suitable means to connect the anode plates 34 and the cathode 28 to a power supply. The cathode shaft may be connected to the power supply by a rotatable slip ring (not shown) above the reactor. The anode plates 34 each have separate connectors 58 to connect them to the power supply. In some embodiments, each anode plate is connected by its connector 58 to a different power supply, or all the anode plates may be connected to the same power supply, or there may be any combinations of connections. This facilitates controlling each reaction zone differently, when desired for particular applications.

[0032] The reactor 10 may include a computerized controller system for control of the cathode rotation, the electrical inputs to the cathode and to the anode plates, and the water flow rate.

[0033] The spaced-apart anode plates 34 and cathode plates 32 comprise a plurality of stacked oxidation cells 54. As best seen in Figure 2, each individual oxidation cell 54 comprises an anode plate 34 connected to the power supply and two adjacent rotating cathode plates 32, which are connected to the cathode assembly and thus to the power supply. As explained above, in some embodiments there may be different power supplies for different anode plates. An anode spacer ring 38 between each anode plate acts as a spacer between adjacent oxidation cells. Each oxidation cell has two reaction zones, namely, an upper reaction zone in the space 52A above the anode plate, and a lower reaction zone in the space 52B below the anode plate. In each oxidation cell 54, the two cathode plates are positioned at a constant gap to the anode plate, with one above and one below the anode plate. Water flowing through the spaces 52A, 52B of these reaction zones completes the electrical circuit for the oxidation reactions in the reactor.

[0034] The embodiment illustrated in Figure 1 has four oxidation cells 54. The top cell comprises anode plate 34A and cathode plates 32A and 32B; the next cell comprises anode plate 34B and cathode plates 32B and 32C; the next cell comprises anode plate 34C and cathode plates 32C and 32D; and the bottom cell comprises anode plate 34D and cathode plates 32D and 32E. Each cathode plate is shared between two oxidation cells 54, except for the top and the bottom cathode plates, 32A and 32E.

[0035] Further oxidation cells 54 can be added vertically to the reactor 10. This increases the water treatment capacity of the reactor without increasing its footprint. For example, by removing the top plate assembly 12, it is possible to add an oxidation cell by installing a cathode spacer ring 36, an anode plate 34, a cathode plate 32 and an anode spacer ring 38 above the top oxidation cell. Once the desired number of cells is added, the top plate assembly is re-installed. As explained above, the cathode shaft 30 may comprise separate pieces, affixed together mechanically and electrically with suitable attachment means, which facilitates the addition of further sections of the cathode when oxidation cells 54 are being added to the reactor. The reactor 10 can have any number of oxidation cells.

[0036] In operation, the rotating cathode plates 32 create relative motion between the anode and cathode surfaces in each oxidation cell 54. This helps to continuously clean the reactive surfaces and provides better mixing of contaminants to make them more likely to be close to one or more reactive surfaces as they flow through the reactor. In some embodiments, the cathode plates 32 have grooves 35 in their surfaces, as shown in Figure 3, configured to generate more turbulence in the water stream, enhancing the cleaning and mixing. Each anode plate 34 has a surface designed to generate oxidation reactions in the water stream when current flows between it and an adjacent cathode plate 32. In one embodiment, the anode plate 34 is a titanium plate with a mixed metal oxide coating on both sides. Each oxidation cell 54 may have a different type of anode plate to facilitate different oxidation reactions in that cell. Anode plates may also have different coatings on each side to generate different reactions in the top and bottom reaction zones of that oxidation cell, i.e. , in the spaces 52A, 52B above and below the anode plate. This provides the ability to tailor the overall treatment process in the reactor by using different anode materials in different oxidation cells to generate different combinations of oxidation reactions as the water travels through the system. Likewise, different treatment zones can be made within the reactor. Each treatment zone can have its own electrical circuit and current application, allowing for different reactive coatings with different potentials to have varying current densities and voltages to target specific contaminants in the water.

[0037] The flow path for water is through each of the oxidation cells 54 in series. In each oxidation cell 54 above the bottom one, water flows into the cell from the cell below. For the bottom cell, water flows in from the inlet 24 and main influent line, through the space 44 and the gap 46A between the outer edge of the lower cathode plate 32E and the base 20. The water then flows towards the center of the reactor through the lower oxidation zone in space 52B between the bottom cathode plate 32E and the bottom surface of the anode plate 34D. The water then flows up through the gap 48 between the inner edge of the anode plate 34D and the cathode shaft 30 and then outwards through the upper oxidation zone in space 52A between the upper surface of the anode plate 34D and the cathode plate 32D. The water then flows out of that oxidation cell through the opening 48B at the outer edge of the cathode plate 32D and into the next upward oxidation cell 54. The flow path continues similarly through the remaining oxidation cells 54 in series. For the top oxidation cell, after flowing through both reaction zones in the cell, the water flows into the space 50 above the top oxidation cell and out of the reactor through the outlet 26. During operation, electric current flows between the anode plates and the cathode plates through the flowing water, and electrochemical reactions occur at both the anode plate and cathode plate surfaces. The electrochemical reactions oxidize contaminants. Examples include organic contaminants, such as polycyclic aromatic hydrocarbons, benzene, toluene, ethylbenzene, xylene and phenol. Ammonia and other inorganic contaminants can likewise be oxidized in the reactor.

[0038] Prior to treatment of the wastewater, an electrolyte, such as sodium chloride, may be added to the influent water to increase conductivity to enhance treatment and / or to reduce power consumption. Also, the pH of the influent water may be adjusted up or down if required to allow desired reactions to occur.

[0039] Figure 5 depicts an embodiment of the cathode shaft 30 that is sealed to keep it from being exposed to the water in the reactor. This may be used in embodiments of the reactor in which the cathode shaft is made of copper or aluminum. The cathode shaft is sectional and comprises cathode spacers 36 made of copper or aluminum that are stacked together. Cathode plates 32 are press fitted into channels 62 in the cathode spacers. Stainless steel rings 64 are affixed around the cathode spacers 36 between adjacent cathode plates 32, with O-rings 66 at the top and bottom of each stainless steel ring 64 for sealing against the cathode plates. The cathode spacers 36 are accordingly not exposed to water.

[0040] Examples

[0041] Tests were conducted using an oxidation reactor according to the embodiment of the invention illustrated in Figure 1. The reactor comprised four identical, 500mm diameter, RuO2 / Ta2Os / TiO2 coated, oxygen-evolving anode plates and five stainless steel cathode plates, all connected to a single power supply. The following results, using various current densities, were obtained.

[0042] Test 1

[0043] Test 2

[0044] In the foregoing table, PAH is polycyclic aromatic hydrocarbons, COD is chemical oxygen demand, and A / in2is the current density in amperes per square inch. The Percent Removed refers to the percentage of the contaminant removed using the highest current density.

[0045] In embodiments of the invention in an industrial scale reactor, the cathode plates may have a diameter of about 2 to 6 feet (0.6 to 1 .8 m) and a thickness of about 3 / 8 to 1 inch (9 to 25 mm). Anode plates may have a diameter of about 2.2 to 6.5 feet (0.7 to 1 .9 m) and a thickness of about 3 / 8 to 1 inch (9 to 25 mm). The distance across the gap between cathode plates and the anode plates may be in the range of 1 / 8 to Vi inch (3.2 to 13 mm). The number of cells in the reactor may be from 2 to 20. Much larger reactors, with larger diameter cathode and anode plates and / or more cells added can also be made in accordance with the invention. The rotation speed of the cathode shaft may be in the range of 15 to 120 rpm. The flow rate through the reactor may be in the range of 5 to 200 imperial gallons (19 to 909 L) per minute.

[0046] The anode plates may all be of a similar material with similar mixed metal oxide coatings, or with one or more of the plates made from a different material and / or with a different mixed metal oxide coating to generate different reactions in the associated cell. For example, a 6-cell reactor may consist of 4 cells using titanium anode plates with a coating consisting of RuC>2, Ta2Os and TiC>2 that may be used to break down some organic compounds, followed by two cells with titanium anode plates with a coating consisting of lrC>2 and RuC>2 used for chlorine generation for disinfection.

[0047] The anode plates may be connected to a single power source, or one or more anode plates may be connected to different power sources to generate different current densities in each cell. For example, using the same configuration described in the paragraph above, the first two cells using anode plates with a RuC>2, Ta2Os and TiC>2 coating may be connected to a power supply set to provide a current density below 2.5 mA per square cm to break down the same organic compounds described above, while the third and fourth cells may use a different power supply set to provide a current density above 3.5 mA per square cm to break down ammonia.

[0048] In the foregoing description, where a component (e.g. an assembly, device, etc.) is referred to, unless otherwise indicated, reference to that component (including reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the same function as the described component, including components which are not structurally equivalent to the disclosed structures which perform the function in the illustrated exemplary embodiments of the invention.

[0049] Throughout the foregoing description and the drawings, in which corresponding and like parts are identified by the same reference characters, specific details have been set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0050] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the following claims.

Claims

Claims1. An electrochemical reactor (10) for treating contaminated water, comprising: a base (20) comprising electrically non-conductive material and having an inlet opening (24) for inflow of water into the reactor; a top cap (16) comprising electrically non-conductive material and having an outlet opening (26) for the outflow of water from the reactor; a rotatable cathode (28) having a vertically-oriented cathode shaft (30) and a plurality of cathode plates (32); a plurality of stacked oxidation cells (54) between the base (20) and the top cap (16), each oxidation cell comprising a non-rotatable anode plate (34) having a cathode plate (32) above it and a cathode plate below it, with spaces (52A, 52B) between the anode plate and each of the cathode plates; a flowpath (44, 46A, 46B, 48, 50, 52A, 52B) through the reactor for the flow of water from the inlet (24), through each of the oxidation cells (54) in series, to the outlet (26); the cathode plates (32) and the anode plates (34) being adapted to apply an electric current through water flowing in the spaces (52A, 52B) between the surfaces of the cathode plates and the anode plates; and means (60) for rotating the cathode shaft.

2. An electrochemical reactor (10) for treating contaminated water, comprising: a base (20) comprising electrically non-conductive material and having an inlet opening (24) for inflow of water into the reactor; a top cap (16) comprising electrically non-conductive material and having an outlet opening (26) for the outflow of water from the reactor; a rotatable cathode (28) having a vertically-oriented cathode shaft (30);a plurality of stacked oxidation cells (54) between the base (20) and the top cap (16), each oxidation cell comprising a non-rotatable anode plate (34) having a cathode plate (32) above it and a cathode plate below it, with spaces (52A, 52B) between the anode plate and each of the cathode plates for the flow of water through the reactor, the anode plates having a central opening therein, the cathode shaft (30) extending through the central opening; a space (46A) at the outer edge of the bottom cathode plate (32E) for the flow of water through the reactor; a space (48) between the cathode shaft (30) and each adjacent anode plate (34) for the flow of water through the reactor; a space (44) between a lower surface of a bottom cathode plate (32E) and the base for the flow of water through the reactor; a space (50) between an upper surface of a top cathode plate (32A) and the top cap (16) for the flow of water through the reactor; the cathode plates (32) being affixed to the cathode shaft (30) for rotation therewith; a plurality of anode spacer rings (38) comprising electrically non-conductive material, arranged to space the anode plates (34) vertically apart from each other; a space (46B) between each anode spacer ring (38) and the radially-outer edge of each adjacent cathode plate (32) for the flow of water through the reactor; the cathode plates (32) and the anode plates (34) being adapted to apply an electric current through water flowing in the spaces (52A, 52B) between the surfaces of the cathode plates and the anode plates; wherein the spaces (44, 46A, 46B, 48, 50, 52A, 52B) comprise a flowpath for water through the reactor; and means (60) for rotating the cathode shaft.

3. An electrochemical reactor (10) for treating contaminated water, comprising:a base (20) comprising electrically non-conductive material and having an inlet opening (24) for inflow of water into the reactor; a top cap (16) comprising electrically non-conductive material and having an outlet opening (24) for the outflow of water from the reactor; a rotatable cathode (28) comprising a vertically-oriented cathode shaft (30) and a plurality of cathode plates (32) affixed to the cathode shaft, the cathode plates comprising:(i) a bottom cathode plate (32E) proximate to the base (20), with a space (44) between the lower surface of the bottom cathode plate and the base for the flow of water through the reactor;(ii) a top cathode plate (32A) proximate to the top cap (16), with a space (50) between the upper surface of the top cathode plate and the top cap for the flow of water through the reactor; and(iii) a plurality of spaced-apart cathode plates (32B, 32C, 32D) between the bottom cathode plate and the top cathode plate; a plurality of non-rotatable anode plates (34) arranged such that each anode plate is between two adjacent cathode plates, with a space (52A, 52B) between each anode plate and the adjacent cathode plates for the flow of water through the reactor, the anode plates having a central opening therein, the cathode shaft (30) extending through the central opening, with a space (48) between the cathode shaft and each adjacent anode plate for the flow of water through the reactor; a plurality of anode spacer rings (38) comprising electrically non-conductive material, arranged to space the anode plates apart from each other; a space (46B) between each anode spacer ring and the radially-outer edge of an adjacent cathode plate for the flow of water through the reactor; a flowpath through the reactor for the flow of water from the inlet (24), through all of the spaces (52A, 52B) between the anode plates and the cathode plates in series, to the outlet (26);the cathode plates (32) and the anode plates (34) being adapted to apply an electric current through water flowing in the spaces (52A, 52B) between the surfaces of the cathode plates and the anode plates; and means (60) for rotating the cathode shaft.

4. An electrochemical reactor (10) according to any one of claims 1 to 3, wherein the cathode shaft (30) comprises cathode shaft sections affixed together such that additional cathode shaft sections can be added to the cathode shaft.

5. An electrochemical reactor (10) according to any one of claims 1 to 3 and 4, wherein the cathode shaft (30) is sectional and comprises a lower shaft section (29), an upper shaft section (33), and cathode spacers (36) arranged between adjacent cathode plates (32).

6. An electrochemical reactor (10) according to any one of claims 1 to 3, wherein the cathode shaft (30) is a continuous shaft.

7. An electrochemical reactor according to claim 1 or 2, wherein the top cap is removable for the installation of additional oxidation cells in the reactor, and is replaceable after said installation.

8. An electrochemical reactor according to claim 3, wherein the top cap is removable for the installation of additional anode plates and cathode plates in the reactor, and is replaceable after said installation.

9. An electrochemical reactor according to any one of the preceding claims, wherein one or more of the anode plates comprises a material different from that of other anode plates.

10. An electrochemical reactor according to any one of the preceding claims, wherein one or more of the anode plates has a different reactive coating on one or both sides thereof from that of other anode plates.

11. An electrochemical reactor according to any one of the preceding claims, wherein the anode plates comprise titanium.

12. An electrochemical reactor according to any one of the preceding claims, wherein the anode plates have a metal oxide coating.

13. An electrochemical reactor according to claim 12, wherein the metal oxide coating comprises one or more of ruthenium oxide, tantalum oxide and titanium oxide.

14. An electrochemical reactor according to claim 12, wherein the metal oxide comprises a combination of iridium oxide and ruthenium oxide.

15. An electrochemical reactor according to any one of claims 1 to 11 , wherein the anode plates have a coating comprising platinum.

16. An electrochemical reactor according to any one of claims 1 to 11 , wherein the anode plates have a coating comprising boron-doped diamond.

17. An electrochemical reactor according to any one of the preceding claims, wherein a current density in one or more oxidation cells is different that a current density in one or more of the other oxidation cells.

18. An electrochemical reactor according to any one of the preceding claims, wherein all of the anode plates are connected to the same power supply.

19. An electrochemical reactor according to any one of claims 1 to 17, wherein one or more of the anode plates is connected to a different power supply from one or more of the other anode plates.

20. An electrochemical reactor according to any one of the preceding claims, wherein the cathode plates comprise stainless steel or titanium.21 . An electrochemical reactor according to any one of the preceding claims, wherein the cathode shaft comprises stainless steel or titanium.

22. An electrochemical reactor according to any one of the preceding claims, wherein one or more of the cathode plates has grooves (35) therein configured to generate turbulence in water flowing through the reactor.

23. An electrochemical reactor according to any one of claims 1 to 3, wherein the cathode shaft (30) comprises a plurality of cathode spacers (36) having channels (62) therein, the cathode plates (32) are fitted into the channels (62), rings (64) are affixed around the cathode spacers between adjacent cathode plates, and are sealed with O-rings (60) against the cathode plates.

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