Process and Apparatus for Production of Ozone

Abstract

The invention relates to an apparatus for generating ozonated water. In particular, the apparatus is able to efficiently produce ozonated fluids in either continuous or batch operation modes, in a fashion that minimises electrolytic cells degradation, and/or that enhances the accuracy of ozone detection.

Claims

1. An apparatus for use in the production of ozone, the apparatus comprising: i) a fluid manifold; and ii) a plurality of electrolytic cells within the fluid manifold; characterised in that each of the electrolytic cells are independently switchable between an on state and an off state.

2. An apparatus according to claim 1, wherein the plurality of electrolytic cells is connected in one of either series or parallel.

3. (canceled)

4. An apparatus according to claim 1, wherein the fluid manifold further comprises one or more conduits and each of the electrolytic cells are contained within one of either a common or a different conduit within the fluid manifold.

5. (canceled)

6. An apparatus according to claim 1, wherein the on state and the off state are one of either an electrically or a mechanically on state and an electrically off state respectively.

7. (canceled)

8. An apparatus according to claim 1, wherein each of the electrolytic cells are substantially the same.

9. An apparatus according to claim 1, further comprising a plurality of power supply units wherein each power supply unit provides power independently to each of the electrolytic cells respectively.

10. An apparatus according to claim 1, further comprising a tank within the fluid manifold.

11. An apparatus according to claim 10, wherein the tank comprises a vent.

12. An apparatus according to claim 1, further comprising a flow cell, said flow cell comprising an ozone sensor.

13. An apparatus for use in the production of ozone, the apparatus comprising: i) a fluid manifold; ii) one or more electrolytic cells within the fluid manifold; and iii) a tank within the fluid manifold; characterised in that the fluid manifold further comprises a flow cell, said flow cell comprising an ozone sensor.

14. An apparatus according to claim 13, wherein the tank comprises at least one of the following: an inlet for an aqueous solution an outlet for an ozonated solution, and a vent.

15. (canceled)

16. An apparatus according to claim 13, wherein the tank is open to the atmosphere.

17. An apparatus according to claim 13, wherein the apparatus comprises a plurality of electrolytic cells within the fluid manifold.

18. An apparatus according to claim 17, wherein each of the electrolytic cells are independently switchable between an on state and an off state.

19. An apparatus according to claim 13, wherein the fluid manifold comprises at least one of the following: a pump adapted to move fluid through the fluid manifold, one or more valves for controlling the passage of fluid through the fluid manifold, and a treatment loop.

20. (canceled)

21. (canceled)

22. An apparatus according to claim 13, wherein the apparatus further comprises a controller in communication with the fluid manifold.

23. An apparatus according to claim 13, wherein the electrolytic cell(s) comprises an anode and a cathode configured such that, in use with an aqueous solution, ozone is produced at the anode and hydrogen is produced at the cathode.

24. An apparatus according to claim 23, wherein the electrolytic cell(s) further comprises an ion exchange membrane between the anode and the cathode.

25. A process for the production of an ozonated solution, the process comprising the step of: i) providing an apparatus according to claim 1; ii) providing an aqueous solution to the apparatus; and iii) electrolysing the aqueous solution using an electrolytic cell to generate ozone.

26. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claim 25.

Description

DESCRIPTION OF FIGURES

[0064] FIG. 1 shows a schematic diagram of the apparatus of the invention.

[0065] FIG. 2 shows the rate of increase in dissolved ozone (mg l.sup.−1) during 3 runs in tap water at slightly increasing temperature.

[0066] FIG. 3 shows the effect of increasing temperature during the day (UK summer) on dissolved ozone (mg L.sup.−1) over an 840 minute period from when the cell was turned on in clean tap water.

[0067] FIG. 4 shows the decline in dissolved ozone concentration over time at 29° C., from the point where the cells were turned off, with water still recirculating through the tank.

[0068] FIG. 5 shows the effect of recycle flow rate (l min.sup.−1) on dissolved ozone (mg L.sup.−1).

[0069] FIG. 6 shows the setpoint for dissolved ozone in an analyser was initially 2.0 mg l.sup.−1.

[0070] FIG. 7 shows dissolved ozone (mg L.sup.−1) produced and maintained at 29° C. over the course of 27 hours where ozonated water was drawn off from time to time, and the tank refilled with fresh tap water.

[0071] FIG. 8 shows the ozonation of 10 litres of tap water from the start (time zero), where 5 litres was withdrawn and the tank refilled to 10 litres on one occasion.

[0072] FIG. 9 shows temperature which is stable over the course of the 32 hour run time, and dissolved ozone.

[0073] FIG. 10 shows the effects of restarting the system after two weeks of downtime. The setpoint for DO3 was 2.0 mg l.sup.−1.

[0074] FIG. 11 shows a general process of the invention.

[0075] FIG. 12 shows three electrolytic cells linked in a parallel in a parallel configuration.

[0076] FIG. 13 shows three electrolytic cells linked in a series in a parallel configuration.

[0077] FIG. 14 shows multiple electrolytic cells used to increase the dissolved ozone concentration in a body of water within a reservoir where water is pumped past the cells within a pipe, and into a water reservoir.

DETAILED DESCRIPTION

[0078] FIG. 1 shows one embodiment of the invention. The apparatus 1 is shown in which a water source 2 (usually mains water) is supplied to tank 3 via inlet 5. The tank is equipped with a vent 6 from which gas is able to escape to the atmosphere. Fluid can be released from the tank via the outlet 7 positioned at the base of the tank. The fluid 4 in the tank 3 is fluidly connected to a first pump 10 via a first valve 9. A second valve 11 is positioned between the first pump 10 and the dry compartment 12. A flow cell 13 is positioned outside the dry compartment 12 comprising a third valve 14 which controls the flow of fluid to an ozone sensor 15. Within the dry compartment 12, a controller is located along with a fourth valve 19 which permits the flow of fluid to electrolytic cells 21, each of which contains an anode, a cathode and a proton exchange membrane (not shown). Only four electrolytic cells 21 are depicted here, however more could be employed. A fifth valve 23 permits the flow of ozonated fluid from the electrolytic cells 21 back into the tank 3.

[0079] Fluid 4 from the tank 3 can be released via the outlet 7 and is actuated by the second pump 28 via valve 27 to provide a stream of ozonated fluid 29 for use in a range of applications, usually sterilisation applications.

Example 1—Experimental

[0080] All batches of ozonated water were generated using 2 cells operating in parallel via a variable speed submersible aquarium pump, feeding a 24 litre water tank. The water used was tap water. Dissolved ozone was measured via a sensor in the tank.

Ozone Generation

[0081] Current is applied to the cell to provide a current density enough to promote the production of ozone from the anode. The applied current density was within the range 50 to 1000 mA cm.sup.−2.

Example 2—Dissolved Ozone Generation

[0082] The following sections describe some of the typical data sets concerning the generation of dissolved ozone in tap water.

Repeatability and the Effect of Water Temperature

[0083] FIG. 2 shows the rate of increase in dissolved ozone (mg l.sup.−1) during 3 runs in tap water at slightly increasing temperature. Specifically, it shows that even where there are slight changes in water temperature, the generation of dissolved ozone from the same cell set-up is repeatable.

Effect of Higher Temperature

[0084] The effect of summer temperatures can be seen in FIG. 3 of dissolved ozone (mg l.sup.−1) over an 840 minute period, where, during the run, temperatures rose from 30° C. to 33° C. This temperature profile is a normal feature of the gradual heating effect of the recirculation pump and the cells in a small batch process.

Effect of Dissolved Ozone Degradation

[0085] FIG. 4 shows the decline in dissolved ozone concentration over time at 29° C., from the point where the cells were turned off, with water still recirculating through the tank. The data show exponential decline in ozone, and indicates an ozone half-life in the range 8 to 12 min at 29° C.

Effect of Changing Recirculation Flow Rate

[0086] The variable speed drive on the pump was altered to increase and decrease the pump rate in the recirculation loop with one cell. This changes the velocity at which the water passes past the cells. At the start of the experiment, the flow rate was 4.6 litres per minute (l min.sup.−1). This was changed to 5 l min.sup.−1 (black line, FIG. 5), and then to 5.5 l min.sup.−1, and finally to 4.3 l min.sup.−1. FIG. 5 shows the effect of recycle flow rate (l min.sup.−1) on dissolved ozone (mg L.sup.−1).

Effect of Changing Setpoint

[0087] FIG. 6 shows the setpoint for dissolved ozone in an analyser was initially 2.0 mg l.sup.−1. Once the setpoint had been reached, the setpoint was reduced to 1.0 mg l.sup.−1 and fresh water added to reduce the dissolved ozone concentration to approximately 1.0 mg l.sup.−1. This concentration was maintained by the controller, and the data indicates that the dissolved ozone can be controlled within quite tight limits using setpoint control and controller tuning.

Effect of Sensor Aberration

[0088] For all these experiments, the dissolved ozone sensor was positioned in the centre of the tank; submerged under the surface. This was done in order to reduce losses of ozone to atmosphere through an open top sensor flow cell. The penalty of this is that, every so often, there are aberrations in the level of dissolved ozone recorded by the sensor, which show as periodic rapid declines and then increases in dissolved ozone. Without being bound by theory, it is believed that this is due to bubble formation and coalescence around the tip of the sensor.

[0089] FIG. 7 shows dissolved ozone (mg l.sup.−1) produced and maintained at 29° C. over the course of 27 hours. The data indicate the frailties of the membrane/electrolyte ozone sensors which we are using.

Effect of Tank Water Top-up

[0090] FIG. 8 shows the ozonation of 10 litres of tap water from the start (time zero). As the dissolved ozone concentration plateaus, and declines slightly (likely due to slight temperature increase), the tank is filled to 20 litres with fresh tap water and, as FIG. 8 shows, a subsequent gradual increase in dissolved ozone level (mg l.sup.−1) in the increased volume.

Effect of Mixed Solutions and Changing Conditions

[0091] FIG. 9 shows temperature (black line) which is stable over the course of the 32 hour run time, and dissolved ozone (grey line). Dissolved ozone setpoint was 2 mg l.sup.−1 but as soon as the concentration reached >1.2 mg l.sup.−1, 10 litres of ozonated water were removed, and the tank then refilled to 24 litres with fresh tap water. This was undertaken 3 times which can be seen by the drop in dissolved ozone concentration, which occurred on those 3 occasions. Dissolved ozone after each refill occasion recovered rapidly. Subsequent to these 3 refills, the cell current was increase twice. These can clearly be seen as two rapid increases in the rate and level of ozone in the tank after approximately 1500 and 1600 minutes respectively.

Effect of Restarting System after 2 Weeks Non-Use (DO3 Probe Effect)

[0092] FIG. 10 shows the effects of restarting the system after two weeks of downtime. The setpoint for DO3 was 2.0 mg l.sup.−1. Restarting the system after it had been shut down for around 2 weeks showed a slow increase in DO3 followed by a plateau over about 7 to 8 hours, after which measured DO3 began to rise (albeit a very saw-tooth pattern of rise and fall) over the next 7 to 8 hours, until the setpoint was reached. This is clearly an artefact of the DO3 probe settling back into true measurement. The reasons may include biofilm growth on the sensor membrane, the membrane/electrolyte re-equilibrating, or biological growth in the water consuming ozone.

[0093] This has ramifications if processes are only using ozone periodically, suggesting that ozone should be run for at least short periods every day to encourage the probe to maintain true DO3 readings.

[0094] The invention also provides a process for producing ozonated water as described below.

[0095] The process is fed with a source of water. This source may be from any source of clean or partially clean water, such that the water preferably contains a low level of suspended solids and gross organic contamination. Such water may be supplied from a variety of sources, including: a mains water network, stored water from rainfall or run-off, natural bodies of water such as lakes, ponds and rivers, water recycled from a downstream process, condensate, or treated waste water.

[0096] The generic process is shown in FIG. 11, where treated water is finally pumped to a downstream process or final point of use via a discharge pump (6). Water enters from the appropriate source and enters the main vessel (9), typically via a control valve (4) which regulates the rate at which water is fed to the process. The vessel acts as both a reaction and mixing vessel for the water and the ozone and other oxidant species generated. The vessel (9) can be open to atmosphere, or closed, but where it is closed, there is provision of a vent line (7) to remove off-gases to an appropriate location away from the main equipment in the process. The process includes a means to provide motive energy to the water in the vessel. Typically, this will be a pump (5) which withdraws water from the vessel and returns it to the vessel, via an electrolytic cell, or manifold of electrolytic cells (1). In some embodiments of the process the pump (5) will be externally mounted (as shown in FIG. 11), and in other embodiments it is a submersible pump situated within the vessel. In either case, the pump feeds water to the electrolytic cells via a recirculation system so that water passing these cells becomes electrolysed and dissolved oxygen based chemical species, particularly ozone, are produced. The electrolytic cell, or cells (1) can be mounted externally or inside the vessel.

[0097] As the process operates from initial start-up, the concentration of dissolved ozone increases in the bulk water within the vessel (9), and this is measured by a submerged ozone sensor somewhere within the process; for example at position (3) or (8), which represent flow-cells from where water from the process can be monitored, or within the main vessel (9). In FIG. 11, one embodiment of the invention shows the sensor within an integrated flow cell (3), taking ozonated water from the side-stream recirculation line, and this small flow of water is discharged to drain after analysis for dissolved ozone and any other parameters which may be measured. The signal from this dissolved ozone sensor can be used to control the activation of the electrolytic cell(s) shown (1), via a central control panel and process control module (2), to provide a means of controlling the dissolved ozone concentration within the water in the vessel (9).

[0098] Similarly, an ozone sensor (or other sensors measuring relevant parameters) can be placed in a flow cell (8) receiving treated water from a downstream process or collection point. This flow cell (8) and the sensors within it can be used to control residual dissolved ozone, or, for example, parameters of critical interest to the application of the process, such as: microbiological activity, colour or turbidity. Water entering and leaving the vessel (9) can be controlled via level switches (12, 13 and 14) sited within the vessel, in order to avoid over-filling or under-filling during process operations. Feed water to the vessel (9) via the control valve (4) can be continuous, when the removal of ozonated water from the vessel (9) via the discharge pump (6) and valves (10) is also continuous. This is the configuration for operation of a continuous process. Equally, the process may operate as a batch process, where valves (10) are closed, and the discharge pump (6) is off during vessel filling via control valve (4). Once filled to the appropriate level, the water in vessel (9) is treated via the electrical activation of the electrolytic cell or cells (1) in the side-stream until the required concentration of dissolved ozone is reached in the water within the vessel (9). At this point, the treated water can be held at the required dissolved ozone concentration, via control achieved by communication between the ozone sensor (3), control panel (2), electrolytic cell or cells (1), and the side-stream recycle pump (5). Once the downstream process requires the ozonated water, the water within the vessel (9) is released via the discharge valves (10) and the discharge pump (6).

[0099] The electrolytic cells (1) used are typically those using boron-doped diamond electrodes separated by a proton exchange membrane. These are operated at current densities conducive to the production of ozone (rather than just oxygen) at the anode. Where multiple cells are used, each cell can be switched on and off independently, either automatically, according to the control parameters within the process and the demand of the process for ozone, or manually.

[0100] Embodiments of the invention are also described in the following items:

[0101] 1a. Dissolved ozone produced in a closed vessel of clean water by a single electrochemical cell or by multiple electrochemical cells, in a pumped side-stream where water is withdrawn from the vessel via a pump or pumps, through pipework in which is inserted an electrochemical cell or cells, and returned to the tank, so that dissolved ozone concentration increases over time, or is held at a stable level within the vessel.

[0102] 2a. A process as described in item 1a where the process operates in batch or continuous mode, whereby the water in the vessel is ozonated to a specified concentration of dissolved ozone, and then used in a process downstream of the vessel.

[0103] 3a. A process as described in item 1a where the process operates in batch or continuous mode, whereby the water in the vessel is ozonated whilst make-up water is added at the same time, on a continuous or semi-continuous basis, whilst ozonated water is similarly released to a downstream process on a continuous or semi-continuous basis.

[0104] 4a. Electrochemical cells mounted externally or inside the vessel in a pipework manifold, where water is recirculated past the cells in equal or similar flow patterns and at equal or similar flow rates, during which they produce ozone (and other by-product gases), which become dissolved in the water.

[0105] 5a. In item 1a, each electrochemical cell in the process is monitored such that each cell will only receive the required electrical current to activate the electrochemical process, and thus generate the ozone (and other gases) when water is flowing, and when the ozone concentration in the water within the vessel has not reached a predetermined required concentration of dissolved ozone.

[0106] 6a. The top of the vessel referred to in items 1a to 5a is closed, but not sealed, such that the gas-filled headspace above the water level contains some of the off-gases from the electrochemical cell, including undissolved ozone.

[0107] 7a. In item 6a, where these headspace gases are held at a pressure equal to or slightly above that of ambient pressure outside the vessel, and are released in a controlled manner via a vent line.

[0108] 8a. Where multiple electrochemical cells are used as described in preceding items, these are switched on and off according to a pattern which ensures that each cell is used for a similar amount of time as the process operates, thereby distributing wear on the cells evenly, even where relatively few cells are required to meet the demand of the process, although many more cells may be on standby at any one time.

[0109] 9a. Water with low suspended solids concentrations supplied to the process in any of the preceding items which may arise from: mains tap water, borehole water, rainwater, river water, water from ponds or lakes, water recycled from another process, or even water generated by the process, then used downstream in another process, and then returned to the process vessel.

[0110] 10a. The process, as defined by the preceding items where the ozonated water is discharged on demand, on a batch or continuous basis, to a ‘Clean In Place’ process for the disinfection and/or cleaning of pipes and equipment.

[0111] 11a. The process, as defined in items 1a to 9a, where the sole aim is to treat the incoming water in order to make it suitable for use elsewhere, whereby the untreated water enters the process, and then contacts water already containing dissolved ozone, and is then discharged, after a suitable contact time, either on a batch or continuous basis, to a final point of use.

[0112] 12a. At all times during operation of the process the electrochemical cells described in preceding items are kept wetted, and receive water above a pre-set minimum flow rate to avoid the possibility of being electrically activated whilst dry.

[0113] 13a. In item 12a where each electrochemical cell is protected from being electrically activated by a flow switch positioned upstream of the cell, so that under conditions of low flow rate this flow switch stops the flow of water and sends an alarm signal to the process control panel.

[0114] 14a. As in preceding items, each electrochemical cell is operated such that the voltage across the cell is measured, and maintained within a pre-set range, despite the application of a constant electrical current to each cell.

[0115] 15a. In item 14a, if the voltage exceeds a high voltage set point, an alarm signal is sent to the process control panel.

[0116] 16a. In item 1a where the inlets and outlets of the pumped side-stream within the vessel are situated in order to produce even liquid-liquid mixing within the water in the vessel in order to improve the homogeneity of the ozonated water within the vessel to obtain an evenly distributed dissolved ozone concentration throughout the bulk liquid, ensuring that the inlet and outlet of the side-stream within the vessel are spatially separated from one another, and that the overall movement of water within the vessel is in a peripheral, circulatory pattern.

[0117] 17a. In all preceding items where the vessel is either open to atmosphere or closed but with a vent line allowing off-gases to be vented from the system to an appropriate location or locations.

[0118] 18a. In all preceding items where the geometry of the vessel is either: cylindrical, spherical, ovoid, cuboid or a shape with multiple vertical sides, such as octagonal in horizontal cross-section, with the height of the vessel being enough to promote adequate mixing and dissolution of the gases formed at the anodes of the electrolytic cells, thus allowing elevated concentrations of dissolved ozone to be achieved.

[0119] 19a. As in preceding items where the vessel, interconnecting pipework, valves and pumps are constructed in materials where the wetted parts are resistant to chemical reaction with or accelerated corrosion in the presence of dissolved ozone in water, where such materials include: plastics such as High Density Polyethylene, vitreous- or enamel-coated steel, stainless steel, and glass, ceramic or glass-lined material.

[0120] 20a. In item 1a and subsequent items where each electrochemical cell comprises two electrodes made from boron-doped diamond, separated by a polymeric proton exchange membrane, and supplied by electrical current applied at an elevated current density suited to the production of ozone at the anode.

[0121] 21a. The process as defined in preceding items, where the concentration of dissolved ozone in the vessel is controlled in order to reach and maintain a predetermined concentration, as measured and controlled by a dissolved ozone sensor or sensors placed within the water in the vessel, where the electrical signal from this sensor(s) is fed to the process control panel, and used as a controlling parameter to turn electrochemical cells on or off according to the dissolved ozone demand of the water in the vessel.

[0122] 22a. In item 21a where the concentration of dissolved ozone in the vessel is controlled in order to reach and maintain a predetermined concentration, as measured and controlled by a dissolved ozone sensor or sensors placed in a flow-cell mounted externally to the main ozonation vessel, where the electrical signal from this sensor(s) is fed to the process control panel, and used as a controlling parameter to turn electrochemical cells on or off according to the dissolved ozone demand of the water in the vessel.

[0123] The invention also provides a use of multiple electrochemical cells to generate dissolved ozone.

[0124] Specifically, using multiple electrolytic cells, each of which produces ozone and other oxidant chemical species at the anode of the cell, in order to treat water flowing past the cells, or to raise the dissolved ozone concentration in a body of water for subsequent use downstream of the process described.

[0125] The electrolytic cells are linked and controlled in an array, in a water pipework manifold. The cells are arranged either in parallel (FIG. 12) or in series (FIG. 13) as water flows past them; either in a pipe, or in an open channel.

[0126] In FIG. 12, three electrolytic cells (3) are shown linked in parallel in a pipe manifold via connectors (4), such that the flow of water indicated by the direction of flow arrows distributes the water across all three cells. Each cell is powered independently by a power supply unit (2), and each power supply unit is linked via a single control panel (1).

[0127] In FIG. 13, three electrolytic cells (3) are shown linked in series in a pipe via connectors (4), such that the flow of water indicated by the direction of flow arrows moves the water across all three cells. Each cell is powered independently by a power supply unit (2), and each power supply unit is linked via a single control panel (1).

[0128] In the case where multiple cells are situated in parallel within a single flow of water (FIG. 12) this can be achieved by either placing individual cells within separate pipes which are linked via a manifold, or by multiple, parallel cells situated within a single larger diameter pipe or body of water.

[0129] Each electrolytic cell is linked electronically though a programmable logic control programme as shown as (1) in FIGS. 12 and 13, so that each electrolytic cell receives a discrete electrical current as well as a similar flow of water, and preferentially produces ozone and oxygen at the anode, and hydrogen at the cathode, as the water flows past.

[0130] Typically, each electrolytic cell comprises an anode and a cathode made from boron-doped diamond, and a proton exchange membrane in between them, allowing the free flow of protons between the two. Each electrolytic cell within the array is operated independently from the other cells, and has a unique electronic signature, in the form of erasable programmable read-only memory, attached to each cell. This read-only memory allows process control software within the control panel, shown as (1) in FIGS. 12 and 13, to identify each cell, monitor its performance as voltage output, and apportion the run time for each cell to maintain a similar run time at any given point for each electrolytic cell in a multiple cell array.

[0131] Electrolytic cells are typically rectangular in shape, and oriented in a vertical or horizontal plane, such that water normally flows along the longitudinal plane of each cell, including its electrodes and membrane, and that, when there is little or no water flow, water drains away from each microcell to reduce the growth of microorganisms on the surfaces of the microcell. Any number of electrolytic cells in an array can be isolated, by means of removing electrical current feed and water flow from the cell, at any time. This may occur, for example, when there is a requirement for maintenance. When such isolation occurs, or when a cell fails to operate for any reason, an equivalent number of off-line cells are automatically brought on-line in order to stabilise the production of anodic ozone across the multiple of cells.

[0132] The multiple electrolytic cells may be used to increase the dissolved ozone concentration in a body of water within a reservoir where water is pumped past the cells within a pipe, and into a water reservoir. This is shown in FIG. 14. Water withdrawn from the reservoir (3) from the same pump (2), or pumps, once passing through the multiple of electrolytic cells (1), is then returned to the reservoir (3) and therefore to the inlet side of the pump(s) so that the water now containing dissolved ozone receives further dissolved ozone from that produced at the anode of each cell. In this embodiment, each cell (1) has its own power supply unit (5), and each power supply unit is connected to a control panel (4) via a data communications cable, wherein programmable control software identifies each unique electrolytic cell (1), and controls the operation of the cells to maintain the required concentration of dissolved ozone in the reservoir (3).

[0133] Whether in a pipeline or an open channel of water, multiple electrolytic cells are spatially separated from each other.

[0134] In a pipe, the cross-section of the pipes is normally circular. In pipes used to house the electrolytic cells, a device to increase flow turbulence, and gas-liquid mixing can be used immediately after the electrolytic cells. This improves dissolution of any gaseous ozone in the gas phase of the pipe. Such devices may include: static mixers, venturis, pipe restrictors and baffles on the inside of the pipe wall.

[0135] Each electrolytic cells can be contained within a separate and distinct section of pipe, and each such section is situated in parallel with a neighbouring section of pipe containing another cell. As water flows past each cell, the individual, parallel flows of water from each cell recombine via a manifold to form either a single flow stream, or a single body of water, or both. Electrolytic cells may be situated in a single water flow pipe, where the cross-section of the pipes is preferentially, but not exclusively circular, and the microcells are spatially separated from one another.

[0136] Embodiments of the invention are also described in the following items:

[0137] 1b. Electrolytic cells linked physically, but not electrically, in an array, in a water pipework manifold, either in parallel or in series, and also linked electronically though a programmable logic controller, whereby each cell receives a similar flow of water and discrete electrical current, and preferentially produces ozone and oxygen at the anode, and hydrogen at the cathode as the water flows past the cells.

[0138] 2b. In item 1b where the electrolytic cells are situated in an open channel of flowing water.

[0139] 3b. Electrolytic cells as in items 1b and 2b, where each cell is switched on and off according to required dissolved ozone concentration downstream of the cells, as measured by a dissolved ozone sensor.

[0140] 4b. In item 3b, where electrolytic cells are turned on and off in a way that ensures an approximately equal use of each cell over time, controlled by a unique electronic signature in the form of erasable programmable read-only memory, attached to each cell, allowing the control software to identify each cell as an individual unit, and control the use of each cell accordingly.

[0141] 5b. Operation of multiple electrolytic cells, where each cell consists of two electrodes either side of a proton exchange membrane with which they are both in direct contact.

[0142] 6b. In item 5b where each electrode has in the range of 0.25 to 2.5 cm.sup.2 surface area in contact with the proton exchange membrane, such that each cell fits within water pipe diameters typical of those encountered in industrial and domestic scenarios.

[0143] 7b. Electrolytic cells as outlined in items 5b and 6b where the proton exchange membrane between the two electrodes extends beyond the edges of the electrodes such that the membrane is larger than the length and width of the electrodes in every direction across the surfaces of the electrodes.

[0144] 8b. Electrodes as outlined in items 5b and 6b where the principal material of construction of the electrodes is boron-doped diamond.

[0145] 9b. Orientation of the multiple electrolytic cells referred to in the preceding items in a vertical or horizontal plane, such that water normally flows along the longitudinal plane of each microcell, including its electrodes and membrane, and that, when there is little or no water flow, water drains away from each microcell to reduce the growth of microorganisms on the surfaces of the cell.

[0146] 10b. Provision of a means of isolating each electrolytic cell in the array so that it receives no water flow, nor applied electrical current, should the need arise.

[0147] 11b. In item 10b where isolation of each electrolytic cell can be achieved either automatically via electronically-activated flow switches, valves and electrical switches, or manually, via actuated or manual valves and electrical switches, when either a cell requires investigation or replacement, or when an individual cell exceeds a maximum, predetermined voltage or temperature.

[0148] 12b. In the event of a situation in items 9b and 10b, where an individual cell or number of electrolytic cells is or are isolated from water flow and electrical feed current, an equivalent number of off-line cells are brought on-line in order to equalise the production of anodic ozone across the multiple of cells.

[0149] 13b. The use of multiple electrolytic cells as outlined in item 1b, where water is pumped, via one or more pumps, past the cells, into a water reservoir, and is then returned to the inlet side(s) of the pump or pumps so that the water now containing dissolved ozone receives further dissolved ozone from that produced at the anode of each cell, so that the concentration of dissolved ozone in the water within the reservoir gradually increases over time.

[0150] 14b. In item 1b, where each electrolytic cell, although receiving separate electrical current from a discrete power source, are situated in water flow pipes, where the cross-section of the pipes is preferentially, but not exclusively circular, and the cells are spatially separated from one another.

[0151] 15b. In preceding items where each electrolytic cell is contained either within a separate and distinct section of pipe, and each such section is situated in parallel with a neighbouring section or sections of pipe containing another or other cells, such that as water flows past each cell, the individual, parallel flows of water from each cell recombine to form either a single flow stream, or a single body of water, or both.

[0152] 16b. In item 1b, where each of the electrolytic cells, although receiving separate electrical current from a discrete power sources, are situated in a single water flow pipe, where the cross-section of the pipes is preferentially, but not exclusively circular, and the cells are spatially separated from one another along its length.

[0153] 17b. In preceding items where the flow of water after each electrolytic cell, or after a number of such cells in series, passes through a device to increase flow turbulence, and therefore gas-liquid contact area between any gas bubbles arising from the anode of the microcells and the bulk water in the pipe, thereby improving the dissolution of any ozone in the gas phase of the pipe.

[0154] 18b. In item 17b where the device preferentially causes little or no drop in water pressure, where the device can include: static mixers, venturis, pipe restrictors and baffles on the inside of the pipe wall.