WO2013120147A1

WO2013120147A1 - Improved water sanitisation

Info

Publication number: WO2013120147A1
Application number: PCT/AU2013/000141
Authority: WO
Inventors: Ross Leslie Palmer
Original assignee: Poolrite Research Pty Ltd
Priority date: 2012-02-17
Filing date: 2013-02-18
Publication date: 2013-08-22

Abstract

A method of sanitising swimming pool water including the steps of generating a region of increased water flow velocity at the electrolytic cell and employing a current density of at least 500 amps/m² at said electrolytic cell.

Description

IMPROVED WATER SANITISATION

FIELD OF THE INVENTION

The present invention relates to the field of water treatment. More particularly, this invention relates to electrochemical disinfection of water.

BACKGROUND OF THE INVENTION

Swimming pools (also referred to herein as "pools") are popular for exercising and relaxing in but if they are to be maintained so as to provide a safe and healthy swimming environment then the pool water must undergo regular treatment to remain clear, clean and free from pathogens. Pathogens are of particular concern as their presence can result in bathers being exposed to serious health risks. Pathogens such as Escherichia Coli, Giardia Lamblia and Cryptosporidium are commonly found in pools, particularly commercial pools, and can cause a range of symptoms from fever and diarrhoea to kidney damage and, potentially, even death. The treatment of pool water typically involves maintaining a consistent level of chlorine.

Chlorine is a widely used disinfectant which is generally effective in controlling the levels of harmful organisms such as bacteria, viruses, algae and fungi. Chlorine can be introduced into the pool by regular addition of commercially available chlorine sources such as granular chlorine, chlorine tablets or liquid chlorine. This may involve handling dangerous chemicals and can result in large and undesirable fluctuations in the levels achieved in the pool.

Electrolytic, or saltwater, chlorinators are a preferable solution. This requires the addition of salt (sodium chloride) to the pool and so does not necessitate handling dangerous chemicals. The electrolysis process is achieved by passing the salt water solution through an electrolytic cell which converts sodium chloride in the water into chlorine gas which, when dissolved in water becomes sodium hypochlorite (liquid chlorine). The pool owner must monitor the level of salt within the pool and ensure that it is maintained at an appropriate level to kill pathogens. Although generally effective many users find the chlorine in the pool irritates their eyes or dries out and damages their hair and skin.

More pool owners are now looking to technologies which employ 'electrochemical disinfection' to keep their pool pathogen free. Electrochemical disinfection can be defined as the eradication of microorganisms by means of an electric current passed through the water under treatment by employing suitable electrodes. The main difference between this and the use of electrolytic chlorinators is that no additional chemicals are added to the water being treated during electrochemical disinfection. The electric current used leads to the production of disinfecting active oxygen species from the water itself, such as ozone, hydrogen peroxide and trioxidane which may form from the reaction of ozone and hydrogen peroxide, which may be many times more effective than chlorine in destroying pathogens. This method thus greatly lowers the use of potentially hazardous chemicals.

Ozone has been shown to be a particularly powerful oxidant with an estimated electrochemical oxidation potential (EOP) of about 2.08 V compared with 1.36 V for chlorine and 1.49 V for hypochlorite. It is thus well suited to sanitisation of pool water to remove a wide range of microorganisms of concern. It can be formed by the splitting of the water itself and so does not require the addition of chemicals to the water and does not result in any harmful by products or residues.

Further, ozone has a relatively short half-life of 30 to 60 min at which point it decays to form oxygen and so it does not have to be mopped up or in some way neutralised.

Ozone production has been employed in the disinfection of pool water and is typically generated by either the corona discharge method or by the use of ultra violet (UV) light. The corona discharge method employs an electrical discharge to generate ozone from oxygen in the air. The ozone generated must then be injected into the pool water. This method is greatly affected by ambient conditions and so it is difficult to reliably generate known quantities of ozone. Further, the corona discharge method produces nitrogen oxide as a by-product and this can lead to problematic production of significant quantities of nitric acid in conditions of increasing humidity.

UV production of ozone is less efficient than the corona method and regular maintenance of the equipment involves the replacement of relatively expensive UV bulbs/lights.

Both of these methods suffer from a loss of efficiency in that any quantity of ozone generated must be injected into the pool water. Ozone will be lost in this process and, further, the injection results in relatively poor mixing of the ozone with the body of water meaning that not all areas of the pool water will contact sufficient quantities of ozone prior to its decay.

OBJECT OF THE INVENTION

It is an object of the invention to overcome or alleviate one or more of the above disadvantages or provide the consumer with a useful or commercial choice.

SUMMARY OF THE INVENTION

In one form, which is not necessarily the only or the broadest form, the invention resides in a method of sanitising a body of water including the steps of:

(a) providing an electrolytic cell having a flow path with an inlet and an outlet and at least one anode and at least one cathode located within the flow path;

(b) passing the water through the flow path;

(c) generating a region of increased flow velocity at the at least one anode and at least one cathode; and

(d) applying a current density of at least 500 amps/m² to the at least one anode and/or at least one cathode;

to thereby generate sanitising species from the electrolytic cell to sanitise the body of water.

Suitably, the water being sanitised is swimming pool water.

The region of increased flow velocity around the at least one anode and at least one cathode may be generated by a narrowing of the flow path in the region of the at least one anode and at least one cathode.

In one embodiment, the narrowing of the flow path may be achieved by provision of a wall located in the flow path which is provided with apertures.

Suitably, the velocity of the water flow is increased adjacent the at least one anode and at least one cathode compared to the average flow rate through the flow path.

Preferably, the current density applied to the at least one anode and/or at least one cathode is at least 600 amps/m².

More preferably, the current density applied to the at least one anode and/or at least one cathode is at least 700 amps/m².

Even more preferably, the current density applied to the at least one anode and/or at least one cathode is at least 800 amps/m².

Still more preferably, the current density applied to the at least one anode and/or at least one cathode is about 900 amps/m².

Suitably, the amount of ozone generated after a 60 min period of operation is at least 1.0 ppm, preferably at least 1.5 ppm, more preferably at least 2.0 ppm, still more preferably at least 2.5 ppm, yet still more preferably about 3.0 ppm.

The electrolytic cell may comprise a plurality of anodes and cathodes.

Suitably, the anodes and cathodes may be constructed from nickel and/or molybdenum alloys.

Preferably, the salt concentration of the pool water is less than about

4000 ppm, more preferably less than about 3000 ppm.

In a further form, the invention resides in a method of increasing the amount of ozone generated by an electrolytic cell including the steps of:

(a) locating the electrolytic cell within a flow path having an inlet and an outlet, the electrolytic cell having at least one anode and at least one cathode located within the flow path;

(b) forming a narrowing of the flow path adjacent the at least one anode and at least one cathode;

(c) passing water through the flow path; and (d) applying a current density of at least 500 amps/m² to the at least one anode and/or at least one cathode; to thereby increase the amount of ozone generated by the electrolytic cell.

Throughout this specification, unless the context requires otherwise, the words "comprise", "comprises" and "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

BRIEF DESCRIPTION OF THE FIGURES

In order that the invention may be readily understood and put into practical effect, preferred embodiments will now be described by way of example with reference to the accompanying figures wherein like reference numerals refer to like parts and wherein:

FIG 1 is a front view of one embodiment of an electrolytic cell particularly suitable for use in the method of the present invention;

FIG 2 is a rear view of the electrolytic cell as shown in FIG 1 ;

FIG 3 is a perspective view of an electrolytic cell as shown in FIG 1 ; FIG 4 is an exploded perspective view of the electrolytic cell as shown in FIG 1 ;

FIG 5 is a perspective view of an electrode cartridge in accordance with the first embodiment of the invention;

FIG 6 is a partial perspective view of the cartridge shown in FIG 5; FIG 7 is a perspective view of part of the cartridge as shown in FIG 5;

FIG 8 is an exploded perspective view of part of the cartridge as shown in FIG 5; and

FIG 9 is a graphical representation comparing the ozone output from a standard electrolytic cell and from a cell operating according to the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the expression "swimming poof is also intended to embrace the analogous use of spa baths, hot tubs and the like which are operated in a substantially identical manner to swimming pools.

The terms "sanitise", "sanitised, "sanitising" and "disinfection" as used herein encompass the killing, controlling, reducing of population size or rendering harmless to humans of the population of one or more pathogens. Although the following discussion focuses on the use of the inventive method and system to sanitise pool water it will be understood that it is not so limited. The present invention may be applied mutatis mutandis to any body of water requiring sanitisation such as, but not limited to, water within cooling towers, drinking water supplies and hot water recirculating systems.

The present invention is predicated on the surprising finding that the efficiency of the electrolytic generation of sanitising species including ozone within an electrolytic cell can be greatly improved by optimising a number of factors including the flow velocity within the cell and the related pressure change along with electrode current density and electrolyte concentration. This provides a supply of ozone, and accompanying or subsequent generation of hydrogen peroxide and trioxidane as further sanitising species, which are stronger sanitisers than chlorine. These species can be useful in destroying or rendering harmless to humans any surviving potentially harmful pathogens such as Escherichia Coli, Giardia Lamblia and Cryptosporidium which may not be effectively rendered harmless or prevented from reproducing by the presence of chlorine alone in the pool.

The ozone is produced by the splitting of water resulting in release of high energy free oxygen at the anode and hydrogen at the cathode. The free oxygen can react with molecular oxygen to form ozone while hydrogen peroxide is formed at the cathode. Subsequent reaction of a proportion of the produced ozone and hydrogen peroxide can produce trioxidane which is itself an effective oxidant.

A typical pool electrolytic chlorinator employs an electrolytic cell having anodes and cathodes operating at a current density of about 300 to 400 amps/m². By increasing this current density, according to the present method, surprisingly large gains in ozone production have been observed.

The current density applied to the electrolytic cell should be at least 500 amps/m². At least 500 amps/m² may include from about 500 amps/m² to about 3000 amps/m², preferably from about 700 amps/m² to about 2000 amps/m², more preferably from about 800 amps/m² to about 1200 amps/m².

In one embodiment, the current density applied to the at least one anode and/or at least one cathode is at least 600 amps/m², more preferably at least 700 amps/m², even more preferably at least 800 amps/m² and still more preferably about 900 amps/m².

The configuration of the electrolytic cell and/or flow path and the resulting conditions generated in the region surrounding the at least one anode and/or at least one cathode also have an important influence on the final level of ozone production achieved.

The increased flow velocity and hence reduced internal pressure within the electrolytic cell and particularly in the region surrounding the at least one anode and/or at least one cathode has been found to have a direct effect on the level of ozone which can be produced over a period of time. Specifically, higher flow velocities within the electrolytic cell have been shown to result in a higher ozone output.

An increase in the flow velocity at the electrolytic cell may be achieved in a number of ways which would be understood by a person of skill in the art. Preferably, the region of increased flow velocity around the at least one anode and at least one cathode may be generated by a narrowing of the flow path in the region of the at least one anode and at least one cathode.

This narrowing of the flow path may take the form of a sudden constriction in the flow path, prior to the location of the electrodes, or may present as a tapered narrowing. The narrowing presents a region of the flow path wherein the water flowing through is caused to increase its average flow velocity compared to that experienced, on average, throughout the rest of the flow path. This results in a greater rate of electrolysis induced decay of the water at the electrodes and hence increased production of ozone along with hydrogen peroxide and trioxidane.

Suitably, the velocity of the water flow is increased adjacent the at least one anode and at least one cathode compared to the average flow rate through the flow path. The design of the electrolytic cell should be such that the water is effectively accelerated into the electrolytic cell. This may be achieved by the physical dimensions of the flow path altering or by the introduction of jets or like means which increase the propulsion of water into the cell.

It will be appreciated that the factors of the increased velocity of the water in the region of the cell and the resulting decreased pressure in the same region are generally linked and, indeed, may be achieved by a single design factor such as the aforementioned narrowing of the flow path around the cell.

When the body of water being treated is swimming pool water then the pool will have an amount of salts, such as sodium chloride, dissolved therein. It has been found that reduced salinity can improve the efficiency of ozone production according to the present method and so it is preferred if the water being treated has a salinity generally below that of a typical salt water pool which may contain up to about 6000 ppm sodium chloride.

Preferably, the salt concentration of the pool water is less than about 4000 ppm, more preferably less than about 3000 ppm.

The electrolytic cell will typically comprise a plurality of anodes and cathodes which may be constructed from a range of materials as are well known in the art. The use of metals which are particularly resistant to damage via oxidation is desirable due to the increased production of ozone around the plates. Electrodes constructed from nickel and/or molybdenum alloys may be suitable in this regard.

FIGS 1 to 8 describe one embodiment of an electrolytic cell which is suitable for performing the method of the present invention. It will be appreciated that the desired effects of narrowing of flow path leading to increased flow velocity and pressure surrounding the electrodes may be achieved by a number of different designs and so the invention is not limited to the particular design shown which simply represents one preferred embodiment.

FIGS 1 to 4 show an electrolytic cell 10 used for chlorination of pool water. The electrolytic cell 10 includes a housing 20 and an electrode cartridge 30.

The housing 20 is made up of a base 40, a cap 50 and two side covers 60. The cap 50 is removably attached to the base 40 by a series of cap bolts 51 which extend around a periphery of the cap 50. Bolt holes 41 are located within the base 40 for location of the cap bolts 51 to attach the cap 50 to the base 40. A seal 70 is located between the cap 50 and the base 40 to ensure a join between the cap 50 and the base 40 is water tight. · The side covers 60 fit over the join between the cap 50 and the base

40 to cover the cap bolts 51. The side covers 60 have a series of male members 61 which fit into associated female receivers 42 located on the base 40 to hold the side covers 60 to the base 40. The front side cover 60 also includes a conductor housing cover 62 to cover a conductor box 52 located on the cap 50.

An inlet 80 is located at one end of the base 40 with an outlet 90 located on the other end of the base 40. Both the inlet 80 and the outlet 90 have associated pipe connectors 100 to enable the housing 20 to be connected to associated pipes (not shown). The inlet 80 and outlet 90 are in alignment with each other. However, it should be appreciated that this may not necessarily be the case depending on the design of a pool chlorination system.

The electrode cartridge 30, shown in more detail in FIGS 5 to 8, includes a removable central member 110, inner bracket 120, outer bracket 130 and a series of electrodes 140. The removable central member 110 is made of plastic and is shaped so that it fits into the housing 20, extending both into the base 40 and into the cap 50. The sides 111 of the removable central member 110 are shaped so that the sides 111 abut against the cap 50 and the base 40.

The outer bracket 130 and inner bracket 120 are used to mount the series of electrodes 140. The inner bracket 20 is removably attached to the removable central member 110 using attachment members 121 located on an inner surface 122 of the inner bracket 120. An outer surface 123 of the inner bracket 120 has a series of inner bracket recesses 125 which are used to mount the electrodes 140.

The outer bracket 130 also has a series of outer bracket recesses 131 located on the inner surface 132 of the outer bracket 30. A top 133 and bottom 134 of the outer bracket 130 have a series of apertures 135 located through the top 133 and bottom 134 of the outer bracket 130. This is to allow water to pass through the bracket 130 and over the electrodes 140. The outer bracket 130 is connected to the inner bracket 120 using an interference fit. The top 133 of the outer bracket 130 is shaped so that it fits snugly against an inner surface 132 of the cap 50.

Each electrode 140 in the series is a flat plate and has an arcuate outer edge 141 and inner edge 142. The electrodes 140 are shaped so that they will fit easily within the curved housing 20. It should be appreciated that the electrodes 140 may be sized, shaped and made from a variety of materials which would be evident to a person skilled in the art.

The electrodes 140 are electrically connected using two conductors 150 which passes through the cap 50 via the conductor box 52 and through associated holes in the electrodes 140. The conductors 150 are threaded at each end so that a conductor bolt 141 can be placed on either end of a conductor 150 to hold the series of electrodes 140 tightly against the inner bracket 120 and outer bracket 130. It should be appreciated that the connection of the electrodes 140 to the conductors 150 is well known in the art. It should also be appreciated that the current used may be varied. For example, the mono-polar or bi-polar current may be used.

During operation, the current density applied to the electrodes 140, in the embodiment shown, is about 900 amps/m². This has been found to result in an unexpectedly high level of ozone production compared with that seen in a standard electrolytic cell.

When the removable central member 110 is located within the housing

20, a channel 160 in the shape of a spiral is formed. The spiral shaped channel 160 extends from the inlet 80, through the base 40, through the cap 50, back into the base 40 and out the outlet 90. It should be appreciated that the shape and size of the spiral shaped channel 160 may be varied depending on the particular requirement of the electrolytic cell 10 and associated plumbing of a pool's filtration system.

In use, water flows into the channel 160 through the inlet 80. The water then passes through the base 40 and into the cap 50 passing around an arcuate edge 112 of the removable central member 110. Water does not pass between the housing 20 and the sides 111 of the removable central member 110 due to the shape of the sides 111 of the removable central member 110 matching the housing 20.

Water then passes through the apertures 135 in the top 133 of the outer bracket 130. As the top 133 of the outer bracket 130 abuts against the inner surface of the cap 50, water must pass through the apertures 135 of the top 133 of the outer bracket 130. It will be appreciated that this narrowing effect could be achieved at other positions by the provision of a wall located in the flow path which is provided with apertures, in a similar manner to the top 33 of the outer bracket 30. This reduces the area that the water can flow through. Accordingly, the velocity of the water is increased as it passes through the apertures 135 in the top 133 of the outer bracket 130, passes past the electrodes 140 and out through the apertures 135 in the bottom 134 of the outer bracket 130. As well as causing a velocity increase, this narrowing of the flow path (by narrowing it is intended that any means by which the available area for flow of the water through the flow path is, at least temporarily, reduced) brings about a consequent decrease in pressure in the region of the electrodes 140 which improves the generation of ozone for a given electrode 140 current density and flow rate. The water then passes through the base 40 and out of the outlet 90.

The flow of water from the electrodes 140 will also carry the ozone and other oxidizing species which are generated at the anode or cathode out of the cell and into the pool water. Given the relatively short half-life of ozone it may be that the majority of the oxidizing of microorganisms occurs in the vicinity of the electrodes 140. Since there is a constant level of ozone production this is not a problem as, eventually, all of the pool water will have passed by the electrodes 140 and so will have been sanitized. A significant portion of the ozone will, of course, also have a sanitizing effect in other areas of the flow path including the body of water within the swimming pool itself. The production of ozone and other oxidizing species from the electrode plates provides a number of advantages over the prior art corona discharge and UV methods. Firstly, because the ozone is generated in situ there is no need for apparatus to inject the ozone as is required with the prior art. Since the electrolytic cell produces the ozone there is no need for additional UV or corona discharge lamps and the ozone is made directly from the pool water so no additives are required to be introduced to the pool. Since the ozone is generated into the travelling water flow it is immediately placed into contact with any microorganism populations and so practically all of the ozone generated is being made use of. This is again unlike the prior art approaches discussed where the external generation and then injection of the ozone results in a proportion thereof being lost before it comes into contact with the pool water. ₍

Suitably, the amount of ozone generated after a 60 min period of operation of an electrolytic cell, as described above, with pool water of salinity between about 2500 to 3000 ppm is at least 1.0 ppm, preferably at least 1.5 ppm, more preferably at least 2.0 ppm, still more preferably at least 2.5 ppm, yet still more preferably about 3.0 ppm.

FIG 9 is a graphical representation comparing the ozone output from a standard electrolytic cell ( termed 'standard cell') operating at about 350 amps/m² and from an electrolytic cell as described in FIGs 1 to 8 (termed 'improved cell') operating according to the method of the present invention at a current density of about 900 amps/m².

In the tests the salinity of the pool water was maintained between about 2500 to 2800 ppm. The low salinity improves ozone production, likely by more water molecules being made available for electrolysis induced decay. Preferably, the salt concentration of the pool water is less than about 4000 ppm, more preferably less than about 3000 ppm.

Although the ozone production from both cells rose in the first 30 min it is clear that while the production of the standard cell tapers off during normal operation, the levels of ozone observed in the water for the improved cell continued climbing right up to the measured time limit of 60 min. It is possible that the final level of ozone could have been higher if measured over a longer time period.

As discussed above, these results show that the present method of sanitizing a body of water and/or of increasing the amount of ozone generated by an electrolytic cell is extremely effective in achieving the production of strong oxidizing species, particularly ozone. A combination of steps including the creation of an area of increased flow velocity around the electrodes, the application of a current density of at least 500 amps/m² and a relatively low salinity of the water being treated all combine to produce surprisingly large gains in the amount of ozone made available for the oxidation of microorganisms and organic species in the water.

It will be appreciated by the skilled person that the present invention is not limited to the embodiments described in detail herein, and that a variety of other embodiments may be contemplated which are, nevertheless, consistent with the broad spirit and scope of the invention.

All computer programs, algorithms, patent and scientific literature referred to in this specification are incorporated herein by reference in their entirety.

Claims

1. A method of sanitising a body of water including the steps of:

(b) passing the water through the flow path;

(d) applying a current density of at least 500 amps/m² to the at least one anode and/or at least one cathode to thereby generate sanitising species from the electrolytic cell to sanitise the body of water.

2. The method of claim 1 wherein the region of increased flow velocity at the at least one anode and at least one cathode is generated by a narrowing of the flow path adjacent the at least one anode and at least one cathode.

3. The method of claim 2 wherein the narrowing of the flow path occurs at a point in the flow path immediately prior to the location of the at least one anode and at least one cathode.

4. The method of claim 2 or claim 3 wherein the narrowing of the flow path may be achieved by provision of a wall provided with apertures located within the flow path.

5. The method of claim 2 or claim 3 wherein the narrowing of the flow path may be achieved by a constriction in the walls defining the outer extent of the flow path.

6. The method of any one of the preceding claims wherein the current density applied to the at least one anode and/or at least one cathode is at least 600 amps/m².

7. The method of any one of the preceding claims wherein the current density applied to the at least one anode and/or at least one cathode is at least 700 amps/m².

8. The method of any one of the preceding claims wherein the current density applied to the at least one anode and/or at least one cathode is at least 800 amps/m².

9. The method of any one of the preceding claims wherein the current density applied to the at least one anode and/or at least one cathode is about 900 amps/m².

10. The method of any one of the preceding claims wherein the electrolytic cell comprises a plurality of anodes and cathodes.

11. The method of claim 10 wherein the anodes and cathodes are constructed from nickel and/or molybdenum alloys.

12. The method of any one of the preceding claims wherein the body of water is a swimming pool.

13. The method of claim 12 further including the step of controlling a salt concentration of the pool water to be less than about 4000 ppm.

14. The method of claim 13 wherein the salt concentration is less than about 3000 ppm.

15. The method of any one of the preceding claims wherein the sanitising species are selected from the group consisting of ozone, trioxidane and hydrogen peroxide.

16. The method of claim 15 wherein the.amount of ozone generated after a 60 min period of operation is at least 1.0 ppm, preferably at least 1.5 ppm, more preferably at least 2.0 ppm, still more preferably at least 2.5 ppm, yet still more preferably about 3.0 ppm.

17. A method of increasing the amount of ozone generated by a swimming pool electrolytic cell including the steps of:

(c) passing swimming pool salt water through the flow path; and

(d) applying a current density of at least 500 amps/m² to the at least one anode and/or at least one cathode; to thereby increase the amount of ozone generated by the electrolytic cell.

18. The method of claim 17 according to any one of claims 1 to 16.