Water disinfection apparatus, system and method

Abstract

A method of disinfecting a body of water comprising the steps of: adding sodium chlorite and / or sodium chlorate to the body of water, and, converting the sodium chlorite and / or sodium chlorate to chlorine dioxide in an electrolytic cell in fluid communication with a water circulation system of the body of water.

Description

TECHNICAL FIELD

[0001] This application claims priority from Australian Provisional Patent Application No. 2020900876 (filed 23 March 2020), the contents of which are incorporated in their entirety.

[0002] The present invention relates to water disinfection apparatus, systems and methods. In particular, the present invention relates to the disinfection of water for swimming pool and spa applications. However, those skilled in the art will appreciate that the present invention can be used for other water treatment applications. BACKGROUND

[0003] To achieve safe swimming pool chemistry, several different aspects need to be addressed. Firstly, it is important to achieve adequate water disinfection and water pH balance.

[0004] With respect to disinfection, chlorine is commonly used to disinfect the water of many pools and spas. Chlorine kills bacteria, algae and other harmful organisms as a disinfectant. However, while chlorine is suitable for disinfection, it is necessary to avoid over-chlorination of the water, as chlorine has a strong taste and odour which can irritate some swimmers.

[0005] In addition to achieving the required disinfection level, it is also necessary to achieve pH balance of the acidity and alkalinity. For most swimming pool applications, it is necessary to achieve a pH level of between 7.2 and 7.6. If the pH level becomes too low, for example below 7, the water becomes acidic. This can cause irritation to the eyes and skin, and corrosion of metal pumps and impeller components. Conversely, if the pH level becomes too high, for example above 8, chlorine activity becomes low and ineffective, resulting in substandard disinfection. This can also cause irritation to the eyes and skin.

[0006] Chlorine exists in two forms in the pool water:

[0007] 1) Free residual chlorine - this is chlorine that has not reacted with any contaminants and is still available for pool water disinfection and oxidation of organic matter; and

[0008] 2) Combined chlorine - this is “used” chlorine that has reacted with organic matter and is no longer available for water disinfection.

[0009] Manual addition of chlorine to a swimming pool is very labour intensive. In practice, this requires regular monitoring of the pool water, typically testing every two days to determine the required dose of chlorine.

[0010] More recently, there has been a trend towards saltwater pools using a salt chlorinator. Saltwater pools use a salt chlorinator to convert ordinary sodium chloride crystals into chlorine gas that is soluble in water. Sodium chloride is typically added to the pool water in a dose of about 4 kg per 1000 litres.

[0011] Salt chlorinators commonly use electrolysis to sanitise swimming pools by passing salt water through an electrolytic cell to convert the salt water into chlorine gas and sodium.

[0012] One problem with existing salt chlorinators is that they can accumulate salt and / or calcium on the cell. This often requires the user to manually clean the cell on a regular basis, for example, every two weeks.

[0013] There are many factors to consider when adding the correct dose of chlorine to a swimming pool. For example, the volume of water to be treated and the usage of the pool (swim load) are both relevant. In addition, sunlight and high ambient temperatures can cause increased dissipation of chlorine through evaporation, requiring increased chlorine dosage. Therefore, simply running a salt chlorinator continuously is not sufficient to provide the correct dose, as various site-specific factors need to be considered.

[0014] Chlorine dioxide is a compound of the chemical formula C102. Chlorine dioxide is one of several oxides of chlorine and is a potent and useful oxidising agent that can be used for the treatment and bleaching of water.

[0015] Chlorine dioxide has several applications in the water treatment industry. It is particularly good at eliminating pathogens that chlorine cannot eliminate (for example, Cryptosporidium can be killed by short contact times and low concentrations of chlorine dioxide, whereas chlorine requires long contact times and extremely high concentrations). Chlorine dioxide does not form by-products that cause unpleasant odours (unlike chlorine). Chlorine dioxide is often used as a secondary sanitiser and still relies on chlorine as the primary sanitiser. There are many potential applications for chlorine dioxide, but there are still factors that limit the commercial viability of mainstream use.

[0016] These limitations include, but are not limited to, the following:

[0017] • high production costs;

[0018] • inconvenient mixing;

[0019] • some convenient forms of chlorine dioxide production (for example, soluble tablets) are expensive and do not fully activate;

[0020] • in situ systems are expensive to operate and maintain. They can also be hazardous.

[0021] • chlorine dioxide in liquid form that is mixed in situ can cause occupational health and safety (OH&S) issues. Once mixed on site, the shelf life of the mixture is short.

[0022] • can explode if mixed incorrectly;

[0023] • chlorine dioxide is highly corrosive, so it is difficult to maintain feed equipment;

[0024] • chlorine dioxide is prone to gasify out of water when agitated; and

[0025] • chlorine dioxide is prone to decompose under UV light.

[0026] Because of the above disadvantages, there are several reasons why chlorine dioxide has not been widely used for water treatment, and certainly not as a primary disinfectant.

[0027] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0028] Invention aims

[0029] It is an object of the present invention to substantially overcome, or at least ameliorate, one or more of the above disadvantages, or to provide a useful alternative. SUMMARY

[0030] In a first aspect, the present invention provides a method of disinfecting a body of water comprising the steps of:

[0031] adding sodium chlorite and / or sodium chlorate to the body of water; and

[0032] converting the sodium chlorite and / or sodium chlorate to chlorine dioxide in an electrolytic cell in fluid communication with a water circulation system of the body of water.

[0033] Preferably, the method further comprises the step of adding hydrogen peroxide to the body of water.

[0034] Preferably, the sodium chlorite and / or sodium chlorate is added to the body of water to produce a target chlorine dioxide concentration of 0.1 - 0.8 ppm.

[0035] Preferably, the sodium chlorite and / or sodium chlorate is added to the body of water to produce a target chlorine dioxide concentration of 0.1 - 0.6 ppm.

[0036] Preferably, the sodium chlorite and / or sodium chlorate is added to the body of water to produce a target chlorine dioxide concentration of 0.1 - 0.5 ppm.

[0037] Preferably, the sodium chlorite and / or sodium chlorate is added to the body of water to produce a target chlorine dioxide concentration of 0.2 - 0.5 ppm.

[0038] Preferably, the sodium chlorite and / or sodium chlorate is added to the body of water to produce a target chlorine dioxide concentration of about 0.1 ppm, about 0.2 ppm, about 0.3 ppm, about 0.4 ppm, about 0.5 ppm, about 0.6 ppm, about 0.7 ppm, or about 0.8 ppm.

[0039] Preferably, sodium chlorite and / or sodium chlorate is added to the water body to produce a target chlorine dioxide concentration of about 0.3 ppm.

[0040] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 10-250 ppm.

[0041] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 30-250 ppm.

[0042] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 30-200 ppm.

[0043] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 30-150 ppm.

[0044] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 30-100 ppm.

[0045] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 30-75 ppm.

[0046] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of about 10 ppm, about 20 ppm, about 30 ppm, about 40 ppm, about 50 ppm, about 60 ppm, about 70 ppm, about 80 ppm, about 90 ppm, about 100 ppm, about 110 ppm, about 120 ppm, about 130 ppm, about 140 ppm, about 150 ppm, about 160 ppm, about 170 ppm, about 180 ppm, about 190 ppm, about 200 ppm, about 210 ppm, about 220 ppm, about 230 ppm, about 240 ppm, or about 250 ppm.

[0047] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of about 10 ppm, about 30 ppm, about 100 ppm, about 150 ppm, or about 200 ppm.

[0048] Preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of about 35 ppm.

[0049] Preferably, sodium chlorite and / or sodium chlorate is added to the water body to produce a target chlorine dioxide concentration of 0.1-0.8 ppm, and, preferably, hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 10-250 ppm.

[0050] Preferably, sodium chlorite and / or sodium chlorate is added to the water body to produce a target chlorine dioxide concentration of 0.2-0.5 ppm, and preferably hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of 30-200 ppm.

[0051] Preferably, sodium chlorite and / or sodium chlorate is added to the water body to produce a target chlorine dioxide concentration of about 0.1 ppm, about 0.2 ppm, about 0.3 ppm, about 0.4 ppm, about 0.5 ppm, about 0.6 ppm, about 0.7 ppm, or about 0.8 ppm, and preferably hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of about 10 ppm, about 20 ppm, about 30 ppm, about 40 ppm, about 50 ppm, about 60 ppm, about 70 ppm, about 80 ppm, about 90 ppm, about 100 ppm, about 110 ppm, about 120 ppm, about 130 ppm, about 140 ppm, about 150 ppm, about 160 ppm, about 170 ppm, about 180 ppm, about 190 ppm, about 200 ppm, about 210 ppm, about 220 ppm, about 230 ppm, about 240 ppm, or about 250 ppm.

[0052] Preferably, sodium chlorite and / or sodium chlorate is added to the water body to produce a target chlorine dioxide concentration of about 0.3 ppm, and preferably hydrogen peroxide is added to the water body to produce a target hydrogen peroxide concentration of about 35 ppm.

[0053] Preferably, 1-10 grams of sodium chlorite and / or 0.5-5 grams of sodium chlorate is added per kilolitre of the water body.

[0054] Preferably, about 3 grams of sodium chlorite and / or about 1.5 grams of sodium chlorate is added per kilolitre of the water body.

[0055] Preferably, 0.05-0.5 grams of hydrogen peroxide is added per kilolitre of the water body.

[0056] In a second aspect, the present invention provides a water disinfection mixture comprising:

[0057] sodium chlorite and hydrogen peroxide;

[0058] sodium chlorate and hydrogen peroxide; or

[0059] sodium chlorite, sodium chlorate, and hydrogen peroxide.

[0060] Preferably, the disinfection mixture is added directly to the water body to be treated.

[0061] In a third aspect, the present invention provides a water disinfection system comprising:

[0062] an electrolytic cell configured to be installed in a water circulation system of a body of water, the electrolytic cell operable to convert sodium chlorite and / or sodium chlorate into chlorine dioxide;

[0063] a control unit in communication with the electrolytic cell; and

[0064] a sensor configured to detect a level of chlorine dioxide present in the body of water,

[0065] wherein the control unit is configured to cause the electrolytic cell to stop or slow down when the sensor determines that the level of chlorine dioxide present in the body of water has exceeded a predetermined threshold.

[0066] Preferably, the control unit is configured to cause the electrolytic cell to stop or slow down when the sensor determines that the level of chlorine dioxide is 0.8 ppm or higher.

[0067] Preferably, the electrolytic cell is controlled by the control unit in the following manner:

[0068] if the sensed level of chlorine dioxide is less than 0.1 ppm, then increasing the production of chlorine dioxide;

[0069] if the sensed level of chlorine dioxide is between 0.1 and 0.8 ppm, then decreasing the production of chlorine dioxide; and

[0070] if the sensed level of chlorine dioxide is higher than 0.8 ppm, then not producing chlorine dioxide.

[0071] Preferably, the water disinfection system further comprises a sensor configured to detect a level of hydrogen peroxide present in the body of water.

[0072] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". BRIEF DESCRIPTION OF DRAWINGS

[0073] Reference will now be made to the drawings, in which the preferred embodiments of the present application will be discussed with specificity, wherein:

[0074] Figure 1 is a schematic representation of a first embodiment of the method of water disinfection of the present application; and

[0075] Figure 2 is a schematic representation of a second embodiment of the method of water disinfection of the present application. DETAILED DESCRIPTION

[0076] Disclosed herein are water treatment apparatus and systems 10, and methods of disinfecting water for swimming pools, hot tubs, and other water treatment applications using water treatment systems 10.

[0077] As mentioned in the background section, there are some drawbacks to using chlorine dioxide for water disinfection. To address these issues, the applicant has identified a new method of forming chlorine dioxide in water. Rather than using the traditional method of mixing sodium chlorite with an activator (usually hydrochloric acid) to make the substance ready for dosing into water, the applicant has isolated the main ingredients that form chlorine dioxide (sodium chlorite (NaClO2) and / or sodium chlorate (NaClO3)) and added it directly into the water. The sodium chlorite and / or sodium chlorate is then converted to chlorine dioxide using an electrolytic process as the water flows through an electrochemical cell.

[0078] Some of the advantages of this process are as follows:

[0079] • All of the sodium chlorite and / or sodium chlorate added to the main water body will eventually be converted to chlorine dioxide;

[0080] • Since the chemical process occurs in a flow-through cell, the production of chlorine dioxide is highly diluted and does not pose a safety issue;

[0081] • Since the chlorine dioxide is highly diluted at the time of manufacture, the potential for corrosion damage is eliminated or at least significantly reduced;

[0082] • The convenience of adding only sodium chlorite and / or sodium chlorate to the water to generate chlorine dioxide reduces the safety risk of needing to premix chemicals to form chlorine dioxide;

[0083] • Chlorine is produced normally even if chlorine dioxide is produced at the same time (only when hydrogen peroxide is not present).

[0084] • Production costs are greatly reduced since the activation of chlorine dioxide can be done by the same equipment used to produce chlorine normally.

[0085] • The equipment to produce chlorine dioxide in this way is inexpensive and not prone to breakdowns; and

[0086] • The shelf life of sodium chlorite is very long so it can be stored on site without worrying about it going bad.

[0087] A further step is added to this process. In particular, in one embodiment, hydrogen peroxide is also added to the main water body when chlorine dioxide is generated by electrolysis in the above-described method. By adding hydrogen peroxide, there can be even better results.

[0088] Hydrogen peroxide is a compound of the chemical formula H2O2. In its pure form, it is a pale blue, transparent liquid that is slightly more viscous than water. Hydrogen peroxide is the simplest peroxide (a compound with an oxygen-oxygen single bond). It is used as an oxidizer, bleaching agent, and antiseptic. Its chemical properties are dominated by the nature of its unstable peroxide bond.

[0089] In the presence of light, hydrogen peroxide is unstable and will slowly decompose. Due to its instability, hydrogen peroxide is usually stored in a slightly acidic solution with a stabilizer. Hydrogen peroxide is present in biological systems including the human body. Enzymes that use or decompose hydrogen peroxide are classified as catalases.

[0090] When used in water treatment applications, hydrogen peroxide presents some limitations. Some of the limitations are as follows:

[0091] • Easy to form biofilm in reticulations lines;

[0092] • Formation of catalase in water that responds to bacteria - catalase destroys hydrogen peroxide; and

[0093] • Slow kill rate - the rate of bacterial inactivation by hydrogen peroxide is much slower than chlorine.

[0094] In view of the above disadvantages, hydrogen peroxide is not suitable as a primary disinfectant for swimming pools or spas if not used with a secondary disinfectant.

[0095] Applicants have found that when chlorine dioxide is used in conjunction with hydrogen peroxide, some of the disadvantages associated with the use of chlorine dioxide as described in the background section can be overcome.

[0096] In particular, applicants have found that when chlorine dioxide is used in conjunction with hydrogen peroxide, chlorine dioxide is more stable in water. For example, field tests have shown that when used in conjunction with hydrogen peroxide, the duration of chlorine dioxide in water is extended by a factor of 5. In addition to this, the chlorine dioxide levels are not affected by agitation. Thus, when used in conjunction with hydrogen peroxide, the need for continuous addition of chlorine dioxide to maintain residual levels is greatly reduced.

[0097] The electrolytic cell produces chlorine dioxide (generated from electrolysis of sodium chlorite and / or sodium chlorate). In the presence of hydrogen peroxide in the water, chlorine is no longer present. Hydrogen peroxide is the primary chemical over chlorine and thus quickly converts to a series of reactive oxygen species including singlet oxygen, hydroxyl radicals, and superoxide. Sodium chlorite / chlorate helps to form these reactive oxygen species (Ali and Mahmood 2017, Environmental Toxicology 32(4): 1343-1353). All of these elements are effective in inactivating pathogens in water in a much more effective manner than the conventional use of chlorine (Jeong et al 2006, Environmental Science and Technology 40(19): 6117-22).

[0098] Additionally, the chlorine dioxide produced from this process also remains more stable in the water body (e.g. swimming pool or spa). The process allows the chlorine dioxide to remain active in the water for 5 days or more. In addition, the chlorine dioxide does not gas off when agitated. Furthermore, the chlorine dioxide does not diminish in the water from UV light.

[0099] The present invention relates to the combination of chlorine dioxide (generated by adding sodium chlorite / sodium chlorate to a water body), hydrogen peroxide (added to the water body) and an electrolysis process (using standard saltwater chlorination hardware to convert sodium chlorite / sodium chlorate to chlorine dioxide). The present invention relates to a revolutionary water treatment platform.

[0100] The electrolysis process can use low levels of TDS (total dissolved solids) as new hardware has been developed to enable electrolysis to occur at very low TDS levels (as low as 600 ppm TDS, which is the maximum allowable level of sodium in drinking water).

[0101] Traditional salt chlorinators for swimming pool applications require 4000-5000 ppm TDS levels to produce chlorine. Currently, the new hardware can also be adapted for swimming pool applications and can use lower TDS levels.

[0102] Based on the above findings, the applicant proposes a new chemical compound or mixture consisting of sodium chlorite and / or sodium chlorate (alone or in combination with hydrogen peroxide) for addition to swimming pools and spas. The chemical can be in powder or liquid form. However, it is also possible to provide hydrogen peroxide and sodium chlorite / sodium chlorate separately and dose independently into the water body.

[0103] Catalase is a common enzyme found in almost all organisms (e.g. bacteria, plants and animals) that are exposed to oxygen. It catalyzes the decomposition of hydrogen peroxide into water and oxygen. It is a very important enzyme that protects cells from oxidative damage by reactive oxygen species (ROS). Also, catalase is one of the fastest enzymes in terms of turnover, with a catalase molecule able to convert millions of hydrogen peroxide molecules into water and oxygen per second.

[0104] Chlorine dioxide controls the presence of catalase and allows hydrogen peroxide to act as a water treatment. Chlorine dioxide and hydrogen peroxide can coexist.

[0105] Hydrogen peroxide is a primary disinfectant, so chlorine and hydrogen peroxide cannot coexist. When hydrogen peroxide and sodium chlorite / sodium chlorate are present in a water body, chlorine dioxide is produced by electrolysis instead of chlorine.

[0106] In chemistry, an oxidizing agent is a substance that is able to oxidize another substance - in other words, to accept its electrons. Common oxidizing agents are oxygen, hydrogen peroxide and halogens.

[0107] In one sense, an oxidizing agent is a chemical substance that undergoes a chemical reaction in which it gains one or more electrons. In this sense, it is a component in an oxidation-reduction (redox) reaction.

[0108] Redox reaction: H202 + C102 + OH - → 02 + C102 + H20

[0109] A redox reaction is a chemical reaction in which the oxidation state of an atom changes. Redox reactions are characterized by the transfer of electrons between chemical species, most commonly between a substance that is oxidized (loses electrons) and a substance that is reduced (gains electrons). The chemical species that loses electrons is said to be oxidized, and the chemical species that gains electrons is said to be reduced.

[0110] The water treatment system 10 includes a control unit 20 that monitors and regulates the production of chlorine dioxide through an electrolytic cell 30. The control unit 20 is connected to a 240-volt alternating current (AC) main power source.

[0111] The water treatment system 10 includes a water circulation system having a pump 40 for circulating water from a pool, spa, or other such body of water to the electrolytic cell 30 and back to the body of water.

[0112] The electrolytic cell 30 is comprised of a series of titanium electrodes 32 with opposite charges. The electrodes 32 are encased in an electrode cage.

[0113] In operation, the control unit 20 supplies power to the electrolytic cell 30 (anode and cathode) and maintains a potential difference between them for a specified period of time. After the period of time ends, the polarity can then be reversed, whereupon the anode becomes the cathode and the cathode becomes the anode.

[0114] The effect of reversing the polarity or potential difference is to remove any buildup of calcium that can have deposited on the cathode. Thus, the continuous reversal of polarity provides a self-cleaning function that keeps the electrolytic cell 30 clean of calcium deposits, provides chemical balance, and keeps the flow of the pool / spa water through the electrolytic cell 30 within normal parameters while in operation.

[0115] When the target amount of chlorine dioxide is reached in the body of water, the control unit 20 can stop or slow the rate of electrolysis.

[0116] The control unit 20 can include, or alternatively be connected to, a chlorine dioxide sensor 50 that is configured to detect the level of chlorine dioxide present in the body of water.

[0117] The control unit 20 is configured to stop or slow down the electrolysis cell 30 when the sensor determines that the level of chlorine dioxide present in the body of water has exceeded a predetermined threshold. The target level of chlorine dioxide is about 0.1 - 0.8 ppm.

[0118] The control unit 20 can also provide a pre-warning, for example, if the sensor 50 senses that the level of chlorine dioxide is below 0.1 ppm or above 0.8 ppm or some other predetermined threshold, an alarm is sounded. Alternatively, if the sensor 50 senses that the level of chlorine dioxide is above 0.8 ppm, the control unit 20 can shut down the electrolysis cell 30.

[0119] For example, the electrolysis cell 30 can operate in three settings:

[0120] If the sensed level of chlorine dioxide is less than 0.1 ppm, then the production of chlorine dioxide is increased;

[0121] If the sensed level of chlorine dioxide is between 0.1 and 0.8 ppm, then the production of chlorine dioxide is decreased; and

[0122] If the sensed level of chlorine dioxide is above 0.8 ppm, then no chlorine dioxide is produced.

[0123] The control unit 20 can also include or alternatively be connected to a hydrogen peroxide sensor 70 configured to detect the level of hydrogen peroxide present in the body of water.

[0124] The control unit 20 can also provide a pre-warning, for example, if the sensor 70 senses that the level of hydrogen peroxide is determined to be too low or too high, an alarm or other such message is sounded. This can be used to prompt the pool owner or technician to add more hydrogen peroxide to the body of water or take other appropriate action.

[0125] Although the present application has been described with reference to specific examples, it will be appreciated by those skilled in the art that the application can be embodied in many other forms.

[0126] Examples

[0127] A piece of equipment was installed to simulate swimming pool conditions according to the guidelines of the Australian Pesticides and Veterinary Medicines Authority (APMV A). A water tank containing 180 litres of water was recirculated by an ECO 100 pump (Waterco) set to low speed. The main unit (Waterco) was connected to a 13 panel low salt pool which was set to run at 100% for the duration of the test. A digital heat unit (Digiheat unit) (Waterco) was set to control the temperature for the duration of the test. A valve (Waterco) was used to estimate the flow rate through the apparatus. The test equipment used was a Pooltest 25 photometer (Palintest) which was used to monitor hydrogen peroxide, alkalinity, calcium hardness, total and free copper and pH. A Kemio TM A test kit (Palintest) was used to monitor chlorine dioxide levels. A WDPH RH PER pool controller was used to monitor pH and oxidation-reduction potential (ORP) during the test.

[0128] The following chemicals were added to a test tank containing 180 litres of drinking water to achieve the target H2O2 and CIO2 concentrations and to simulate pool water (quantities are shown in Table 1):

[0129] • Hydrogen peroxide = Perox 598 (Waterco) - 50% concentration

[0130] • Sodium chlorite = Zydox Sodium Chlorite Solution (Zychem) - 6% concentration

[0131] • Copper = Concide (Water) - 3.2% concentration

[0132] • Benzalkonium chloride = Algatrol Concentrate (Waterco) - 40% concentration

[0133] • Enzyme = Perox Activate (Waterco) - proprietary blend to control biofilm.

[0134] The target H2O2 and CIO2 concentrations were as follows:

[0135] • Solution 1 = 200 ppm H2O2 and 0.6 ppm CIO2

[0136] • Solution 2 = 75 ppm H2O2 and 0.5 ppm CIO2

[0137] • Solution 3 = 35 ppm H2O2 and 0.4 ppm CIO2

[0138] Solution 1 Solution 2 Solution 3 Control H2O2 75ml 25ml 8ml 0ml Sodium chlorite 30ml 30ml 15ml 0ml Copper 4ml 1ml 1ml 0ml Benzalkonium chloride 3ml 1ml 1ml 0ml Enzyme 3ml 1ml 1ml 0ml

[0139] Table 1

[0140] The electrolysis unit was turned on and run at a flow rate of 175 l / min (28°C and pH 7.4). Once the target concentrations of H2O2 and CIO2 were achieved, the pathogen (E. coli or P. aeruginosa) was added to the tank of water.

[0141] E. coli samples were collected every 30 seconds and P. aeruginosa samples were collected every 2 minutes (as per the relevant APVMA guidelines) and viable colony analysis was performed (Tables 2 and 3)

[0142]

[0143] Table 2

[0144]

[0145] Table 3

[0146] The levels of H202, C102, ORP, Total Alkalinity (ALK), Calcium Hardness (CAL), (Total) Copper, Copper (Free) and TDS were also monitored (see Table 4, values in ppm).

[0147]

[0148] Table 4

[0149] The results show that the bacterial reduction of all test solutions was superior to 7 Log (at least 4 Log reduction is required to prove similar bacterial inactivation when using chlorine to inactivate the same pathogens) proving that the combination of hydrogen peroxide and chlorine dioxide is a potent disinfectant even at low concentrations (35 ppm hydrogen peroxide, 0.3 ppm chlorine dioxide).

[0150] Laboratory efficacy trials and water trials completed at field trials show that free chlorine is measurable in the samples but the voltage readings are below 300 mV. Field trials show a correlation between the hydrogen peroxide levels and the free chlorine test results. If the hydrogen peroxide levels are above 200 ppm, the free chlorine test will feedback almost zero results. At hydrogen peroxide levels below 100 ppm, the free chlorine test starts to become measurable in the range of 0.2 - 0.3 ppm. At hydrogen peroxide levels between 15 - 30 ppm, the free chlorine test is in the range of 0.7 - 1.1 ppm. At hydrogen peroxide levels below 10 ppm, a slight chlorine taste can be detected when in contact with water but not in a swimming pool environment. This is important to adhere to the local health department requirements for free chlorine to be measurable in order to adhere to the health department guidelines implemented for commercial swimming pool operators. From the field trials already conducted, the following operating ranges can be achieved:

[0151] • Hydrogen peroxide 20 - 40 ppm

[0152] • Chlorine dioxide 0.2 - 0.4 ppm

[0153] • Free chlorine 0.7 - 1.0 ppm

[0154] The control method of adding hydrogen peroxide in these cases can be accomplished in several ways. An amperometric probe that measures hydrogen peroxide or free chlorine can be used to control the chemical concentration in the pool.

[0155] A hydrogen peroxide probe can be set to dose to control the desired peroxide level. Alternatively, a free chlorine probe can be used to dose hydrogen peroxide when the maximum free chlorine level is reached to prevent free chlorine from dominating in the water.

[0156] The rate of hypochlorite / hypochlorous acid consumption was calculated based on field trials. An electrolytic unit rated to produce 30 grams of chlorine per hour at optimal TDS and operating 8 hours per day in a 50,000 liter pool, consumed 1 ppm of hypochlorite and 0.5 ppm of chlorate every 30 days.

[0157] The rate of hydrogen peroxide consumption was calculated based on field trials. An electrolytic unit rated to produce 30 grams of chlorine per hour at optimal TDS and operating 8 hours per day in a 50,000 liter pool, consumed 750-1000 ml of hydrogen peroxide per day.

[0158] The rate of chlorine dioxide production was calculated based on field trials. An electrolytic unit rated to produce 30 grams of chlorine per hour at optimal TDS and operating 8 hours per day in a 50,000 liter pool, produced a stable level of 0.2-0.4 ppm of chlorine dioxide from a solution containing a minimum level of 1 ppm of hypochlorite and 0.5 ppm of chlorate.

[0159] One chemical reaction noted in efficacy trials was that the rate of chlorine dioxide was significantly affected by pathogen surges. Hydrogen peroxide was not affected as much - the reduction of hydrogen peroxide after a pathogen surge was minimal. Therefore, higher hydrogen peroxide can be beneficial in situations that will experience high bather loads. In situations where the chlorine dioxide level is temporarily reduced due to bather loads, hydrogen peroxide can act as a secondary disinfectant to protect swimmers while the chlorine dioxide level is restored to target levels through electrolysis.

Claims

1. A method for disinfecting a body of water of a swimming pool or spa, comprising the steps of: adding sodium chlorite and / or sodium chlorate to the body of water to produce a target chlorine dioxide concentration of 0.1-0.8 ppm; adding hydrogen peroxide to the body of water to produce a target hydrogen peroxide concentration of 10-250 ppm; converting sodium chlorite and / or sodium chlorate to chlorine dioxide in an electrolytic cell in fluid communication with a water circulation system of the body of water; detecting a level of chlorine dioxide present in the body of water using a sensor; and stopping or slowing the electrolytic cell when the sensor determines that the level of chlorine dioxide present in the body of water has exceeded a predetermined threshold.

2. The method of claim 1, wherein, adding sodium chlorite and / or sodium chlorate to the body of water to produce a target chlorine dioxide concentration of 0.2-0.5 ppm.

3. The method of claim 1, wherein, adding sodium chlorite and / or sodium chlorate to the body of water to produce a target chlorine dioxide concentration of about 0.3 ppm.

4. The method of claim 1, wherein, adding hydrogen peroxide to the body of water to produce a target hydrogen peroxide concentration of 30-200 ppm.

5. The method of claim 1, wherein, adding hydrogen peroxide to the body of water to produce a target hydrogen peroxide concentration of about 35 ppm.

6. The method of claim 1, wherein, adding about 3 grams of sodium chlorite and / or about 1.5 grams of sodium chlorate per kiloliter of the body of water.

7. The method of claim 1, wherein, adding 0.05-0.5 grams of hydrogen peroxide per kiloliter of the body of water.

8. A water disinfection system, comprising: an electrolytic cell disposed in a water circulation system of a body of water of a swimming pool or spa, the body of water comprising a) sodium chlorite and / or sodium chlorate and b) hydrogen peroxide, the electrolytic cell operable to convert sodium chlorite and / or sodium chlorate to chlorine dioxide; a control unit in communication with the electrolytic cell; and a sensor configured to detect a level of chlorine dioxide present in the body of water, wherein the control unit is configured to stop or slow the electrolytic cell when the sensor determines that the level of chlorine dioxide present in the body of water has exceeded a predetermined threshold; the target concentration of chlorine dioxide in the body of water is 0.1-0.8 ppm; the target concentration of hydrogen peroxide in the body of water is 10-250 ppm.

9. The water disinfection system of claim 8, wherein, the control unit is configured to stop or slow the electrolytic cell when the sensor determines that the level of chlorine dioxide is 0.8 ppm or greater.

10. The water disinfection system of claim 8, wherein, the electrolytic cell is controlled by the control unit in the following manner: if the sensed level of chlorine dioxide is less than 0.1 ppm, then increasing the production of chlorine dioxide; if the sensed level of chlorine dioxide is between 0.1 and 0.8 ppm, then decreasing the production of chlorine dioxide; and if the sensed level of chlorine dioxide is greater than 0.8 ppm, then not producing chlorine dioxide.

11. The water disinfection system of claim 8, further comprising a sensor configured to detect a level of hydrogen peroxide present in the body of water. ​

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