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, wherein chlorine is also added to the body of water.

Description

Technical Field

[0001] This application claims priority to Australian Provisional Patent Application No. 2020901663 (filed on 22 May 2020), the contents of which are incorporated herein by reference in their entirety.

[0002] This disclosure relates to apparatus and methods for disinfecting water in swimming pools and spas. In particular, the invention relates to the use of chlorine dioxide and chlorine for disinfecting water in swimming pools and spas. However, those skilled in the art will understand that the invention can be used for other water treatment applications. Background Technology

[0003] Chlorine is commonly used for disinfecting swimming pools and spas. Chlorine kills bacteria, algae, and other harmful organisms. However, while chlorine is suitable for disinfection, over-chlorination should be avoided because it has a strong taste and odor that may irritate some swimmers.

[0004] Chlorine exists in two forms in the pool water:

[0005] 1) Free chlorine – This is chlorine that has not yet reacted with any pollutants and can still be used for pool water disinfection and oxidation of organic matter; and

[0006] 2) Combined chlorine (also known as chloramine) - This is "used" chlorine that has reacted with organic matter and can no longer be used for water disinfection. Combined chlorine is the difference between free chlorine and total chlorine.

[0007] Chlorine is typically added to swimming pools and spas in two ways:

[0008] Manually adding chlorine (usually in liquid, granular, or tablet form) is labor-intensive and requires regular pool water testing, typically every two days, to determine the necessary chlorine dosage; or

[0009] A salt chlorinator is used to electrolyze sodium chloride (i.e., salt) into chlorine gas, which is soluble in water. Sodium chloride is typically added to the pool water at a dosage of approximately 4 kg per 1000 liters.

[0010] In addition to achieving the necessary chlorination levels for disinfection, pH balance must also be maintained. For most swimming pool applications, a pH level between 7.2 and 7.6 is required. If the pH level becomes too low, such as below 7, the water becomes acidic. This can cause eye and skin irritation, as well as corrosion of metal pump and impeller components. Conversely, if the pH level becomes too high, such as above 8, chlorine activity will decrease and become ineffective, resulting in inadequate disinfection. This can also cause eye and skin irritation.

[0011] Adding the correct dosage of chlorine to a swimming pool requires consideration of many factors. For example, the volume of water to be treated and the pool's usage (swimming load) are relevant. Furthermore, sunlight and high ambient temperatures increase chlorine dissipation through evaporation, necessitating an increased chlorine dosage. Therefore, simply running a salt chlorinator continuously is insufficient to provide the correct dosage, as various site-specific factors must be taken into account.

[0012] Another factor in adding the correct amount of chlorine to a swimming pool is the formation of chloramines (also known as combined chlorine). Chloramines are formed when free chlorine reacts with ammonia-like compounds called amines.

[0013] Free chlorine + ammonia compound = chloramine

[0014] Amines primarily enter swimming pools through urine and sweat. Chloramine is a substandard disinfectant that significantly reduces the disinfecting power of free chlorine, irritates mucous membranes, causing eye irritation and redness, and irritates the respiratory system. The strong chlorine odor often detected in poorly managed swimming pools is caused by chloramine.

[0015] Australian swimming pool operation guidelines require that chloramine levels in any public swimming pool and spa pool must not exceed 1 mg / L, and pool operators must ensure that the concentration of combined chlorine does not exceed half the concentration of free chlorine.

[0016] Controlling chloramines is both difficult and time-consuming. Current methods include:

[0017] Continuous or daily breakpoint chlorination – a technique that depletes chloramine overnight so that it reaches a breakpoint in the morning.

[0018] Shock superchlorination is a technique used to control severe excesses of chloramine. However, if performed improperly, it can cause further problems for pool operators. Superchlorination must be performed after the pool has been closed to swimmers for the day. Maximum ventilation must be provided to remove all chloramine that has formed and evaporated into the air. Shock superchlorination is implemented by adjusting the pH to 7.5 or lower and by adding enough chlorine to achieve a free chlorine concentration ten times that of the combined chlorine concentration. The pool circulation and filtration systems must run overnight.

[0019] Oxygen shock products – Hydrogen peroxide and potassium persulfate are two common oxygen shock products used to control chloramines in large-scale ponds. These products reduce chlorine demand by oxidizing pond contaminants, thus allowing free chlorine to better perform its disinfection function. Their use may cause a falsely high total chlorine measurement in the pond water for about one to two days after addition.

[0020] Ultraviolet (UV) light systems – Recent evidence suggests that, in addition to providing additional disinfection, UV light systems can also inactivate chlorine-resistant microorganisms such as the parasitic protozoa Cryptosporidium parvum and Giardia lamblia.

[0021] Ozone – Ozone can be used to supplement chlorination, but it cannot replace chlorination. Pools using ozone must have the ozone quenched using a granular activated carbon filter before the water returns to the pool. Once the ozone is thoroughly mixed and dissolved, it reacts rapidly to break down chloramines and disinfection byproducts, thus reducing taste, odor, and eye-irritating compounds.

[0022] Dilution with fresh water – Water can be used to dilute chloramines and reduce total dissolved solids (TDS). However, the introduced tap water may contain monochloramines, and testing should be performed to determine their concentration. High concentrations of monochloramines may not reduce the amount of chloramines in the pool.

[0023] Ventilation – Ventilation is crucial for the effective removal of chloramines and other airborne impurities. When chloramines are released from the pool as a gas, they will redissolve in the pool unless removed by an effective ventilation system. The ventilation system needs to be well-designed to expel stale air and introduce fresh air with lower humidity. Using a pool cover at night prevents chloramines from escaping, and chloramines may reform in the pool.

[0024] Chlorine dioxide is a compound with the chemical formula ClO2. It is one of several oxides of chlorine and is an effective and useful oxidizing agent used in water treatment and bleaching.

[0025] Chlorine dioxide does not form byproducts that cause unpleasant odors (unlike chlorine) and has various applications in the water treatment industry (where chlorine dioxide was previously used to treat wastewater).

[0026] However, several factors limit the commercial viability of chlorine dioxide as a disinfectant for swimming pools and spas. These limitations include (but are not limited to) the following:

[0027] High production costs;

[0028] Chlorine dioxide is inconvenient to mix;

[0029] • Some convenient forms of chlorine dioxide production (such as soluble tablets) are expensive and cannot be fully activated;

[0030] • In-situ systems are expensive to operate and maintain, and they can also be dangerous;

[0031] • In-situ mixing of chlorine dioxide in liquid form can cause occupational health and safety (OH&S) problems. Once mixed on-site, the mixture has a very short shelf life.

[0032] Chlorine dioxide can explode if not mixed properly;

[0033] Chlorine dioxide is highly corrosive, making it difficult to maintain feeding equipment;

[0034] Chlorine dioxide easily vaporizes and escapes from water when stirred; and

[0035] Chlorine dioxide decomposes under ultraviolet light.

[0036] Chlorine dioxide typically forms when sodium chlorite and / or sodium chlorate are activated by secondary chemicals to reduce the chemical reaction. The most common industrial reaction involves activating sodium chlorite / chlorate with hydrochloric acid to form chlorine dioxide. This reaction can be extremely dangerous if not properly controlled. It is precisely the dangers associated with sodium chlorite / chlorate activation that make chlorine dioxide a difficult reagent to use in water treatment.

[0037] There are different types of equipment available for automating the production of chlorine dioxide. Such equipment is typically very expensive and requires regular maintenance. There are several reasons for this high cost, such as:

[0038] High concentrations of chlorine dioxide are highly corrosive – the materials used in the equipment must be able to withstand corrosion, which in turn makes the equipment expensive.

[0039] • If the incorrect concentrations are mixed, the reaction between hydrochloric acid and sodium chlorite / sodium chlorate may result in an explosion - extensive inspections and measures must be taken in equipment that produces high concentrations of chlorine dioxide to prevent the equipment from exploding or releasing high concentrations of chlorine dioxide gas;

[0040] • Due to the highly corrosive environment created by high concentrations of chlorine dioxide, the lifespan of equipment is typically very short; and

[0041] This equipment requires highly skilled technicians to maintain and operate in order to produce high concentrations of chlorine dioxide.

[0042] There are other methods for producing chlorine dioxide for water treatment that do not use automated equipment. One such method involves mixing sodium chlorite / sodium chlorate with a separate powdered activator. The powdered activator can include chemicals such as sodium bisulfite, dichloroisocyanurate, and sodium percarbonate. In use, the mixture of sodium chlorite / sodium chlorate and the activator is prepared in a mixing container. This mixing must use precise chemical concentrations to avoid safety risks such as explosions and excessive gas release. Once prepared, this mixture has a short lifespan because chlorine dioxide deteriorates rapidly upon exposure to air.

[0043] This preparation method is extremely dangerous and can present difficulties due to occupational health and safety requirements (OH & S requirements). Companies have found it difficult to insure locations where this method is used to prepare chlorine dioxide.

[0044] Another method of using chlorine dioxide is in tablet form. A combination of sodium chlorite / sodium chlorate crystals and sodium bisulfate is combined in compressed tablets. When the tablet comes into contact with water, a chemical reaction occurs to form chlorine dioxide. While this is a very convenient method of applying chlorine dioxide to water bodies, the cost of tablets is often prohibitive as a long-term form of water treatment.

[0045] Other challenges in chlorine dioxide formation are closely related to the activation process. Typically, only 60-75% of sodium chlorite / chlorate is activated during the chemical reaction. If used in closed-loop applications, this can lead to the accumulation of unused sodium chlorite / chlorate in the water over time. Furthermore, the waste of unactivated sodium chlorite / chlorate increases the production cost of chlorine dioxide.

[0046] Any discussion of prior art throughout the specification should not be construed as an admission that such prior art is well-known or constitutes part of common general knowledge in the art.

[0047] Purpose of the invention

[0048] The purpose of this invention is to fundamentally overcome or at least improve one or more of the above-mentioned disadvantages, or to provide a useful alternative. Summary of the Invention

[0049] This invention is based on the surprising discovery that chlorine dioxide produced by the electrolysis of sodium chlorite / sodium chlorate is an effective disinfectant and reduces the level of combined chlorine.

[0050] In a first aspect, the present invention provides a method for disinfecting water, comprising the following steps:

[0051] Add sodium chlorite and / or sodium chlorate to the water;

[0052] In an electrolytic cell fluidly connected to a water circulation system, sodium chlorite and / or sodium chlorate are converted into chlorine dioxide; and

[0053] Chlorine is added to the water.

[0054] Chlorine is preferably added to water in the following ways:

[0055] Adding sodium chloride to the water; and

[0056] Sodium chloride is converted into chlorine in an electrolytic cell.

[0057] In another aspect, the present invention provides a method for disinfecting water, comprising the following steps:

[0058] Add sodium chlorite and / or sodium chlorate to the water;

[0059] In an electrolytic cell that is in fluid communication with a water circulation system of a water body, sodium chlorite and / or sodium chlorate are converted into chlorine dioxide;

[0060] Adding sodium chloride to the water; and

[0061] Sodium chloride is converted into chlorine in an electrolytic cell.

[0062] Preferably, sodium chlorite and / or sodium chlorate are added to the water to produce a target chlorine dioxide concentration of 0.1-1.5 ppm.

[0063] Preferably, sodium chlorite and / or sodium chlorate are added to the water to produce a target chlorine dioxide concentration of 0.1-1 ppm.

[0064] Preferably, sodium chlorite and / or sodium chlorate are added to the water to produce a target chlorine dioxide concentration of 0.2-1 ppm.

[0065] Preferably, sodium chlorite and / or sodium chlorate are added to the water to produce a target chlorine dioxide concentration of 0.2-0.5 ppm.

[0066] Preferably, sodium chlorite and / or sodium chlorate are added to the water to produce target chlorine dioxide concentrations 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, about 0.8 ppm, about 0.9 ppm, about 1 ppm, about 1.1 ppm, about 1.2 ppm, about 1.3 ppm, about 1.4 ppm, and about 1.5 ppm.

[0067] Preferably, 1-10 grams of sodium chlorite and / or 0.5-5 grams of sodium chlorate are added per kiloliter of water.

[0068] Preferably, about 3 grams of sodium chlorite and / or about 1.5 grams of sodium chlorate are added per kiloliter of water.

[0069] Preferably, chlorine is added to the water to produce a target free chlorine concentration of 1-10 ppm.

[0070] Preferably, chlorine is added to the water to produce a target free chlorine concentration of 1-6 ppm.

[0071] Preferably, chlorine is added to the water to produce a target free chlorine concentration of 1-3 ppm.

[0072] Preferably, chlorine is added to the water to produce target free chlorine concentrations of about 1 ppm, about 1 ppm, about 2 ppm, about 3 ppm, about 4 ppm, about 5 ppm, about 6 ppm, about 7 ppm, about 8 ppm, about 9 ppm, and about 10 ppm.

[0073] Preferably, sodium chloride is added to the water to produce a target free chlorine concentration of 1-10 ppm.

[0074] Preferably, sodium chloride is added to the water to produce a target free chlorine concentration of 1-6 ppm.

[0075] Preferably, sodium chloride is added to the water to produce a target free chlorine concentration of 1-3 ppm.

[0076] Preferably, sodium chloride is added to the water to produce target free chlorine concentrations of about 1 ppm, about 1 ppm, about 2 ppm, about 3 ppm, about 4 ppm, about 5 ppm, about 6 ppm, about 7 ppm, about 8 ppm, about 9 ppm, and about 10 ppm.

[0077] In a second aspect, the present invention provides a water disinfection system comprising:

[0078] An electrolytic cell, configured to be installed in a water circulation system of a water body, is operable to convert sodium chlorite and / or sodium chlorate into chlorine dioxide and sodium chloride into chlorine;

[0079] The control unit is connected to the electrolytic cell; and

[0080] The sensor is configured to detect the level of chlorine dioxide present in the water.

[0081] The control unit is configured to stop or slow down the electrolysis cell when the sensor determines that the level of chlorine dioxide present in the water exceeds a predetermined threshold.

[0082] Preferably, the water disinfection system further includes a feeding device configured to deliver sodium chlorite and / or sodium chlorate to the water body.

[0083] Preferably, the feeding device delivers sodium chlorite and / or sodium chlorate to the water body at predetermined time intervals.

[0084] Preferably, the feeding device delivers sodium chlorite and / or sodium chlorate to the water body in response to the chlorine dioxide level identified by the sensor.

[0085] Preferably, the control unit is configured to stop or slow down the electrolysis cell when the sensor determines that the chlorine dioxide level is 0.8 ppm or higher.

[0086] Preferably, the electrolytic cell is controlled by a control unit in the following manner:

[0087] If the sensed chlorine dioxide level is less than 1.5 ppm, then increase the production of chlorine dioxide;

[0088] If the sensed chlorine dioxide level is between 0.1 and 1.5 ppm, then reduce chlorine dioxide production; and

[0089] If the sensed chlorine dioxide level is higher than 1.5 ppm, no chlorine dioxide is produced.

[0090] Preferably, the water body is a swimming pool or a hot spring bath.

[0091] Preferably, the water body is a swimming pool.

[0092] Preferably, the water body is a hot spring bath.

[0093] Unless the context explicitly requires otherwise, throughout the specification and claims, the words “comprising” and “including” should be interpreted as inclusive rather than exclusive or exhaustive; that is, “including but not limited to”. Attached Figure Description

[0094] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings and specific examples, wherein:

[0095] Figure 1 This is a schematic diagram of one embodiment of the water disinfection method of the present invention.

[0096] Figure 2 This is a schematic diagram of a further embodiment of the water disinfection method of the present invention. Detailed Implementation

[0097] In some water treatment applications, electrolysis is used to produce chlorine. The most common application is in swimming pools. Often called a brine chlorinator, this equipment requires a TDS (Total Dissolved Solids) level of 4500-6000 ppm to produce enough chlorine to disinfect the pool. Advances in this field have enabled the reduction of TDS levels in water bodies while maintaining sufficient chlorine production to sustain swimming pools. Brine chlorinators operating at TDS levels of 600-1000 ppm are now more commonly found on the market.

[0098] The process of generating chlorine through equipment involves an electrochemical reaction that (partially) produces hypochlorous acid.

[0099] As described in the background section, there are some drawbacks to using chlorine dioxide for water disinfection. To address these issues, the applicant has identified a novel method for forming chlorine dioxide in water. Instead of using the conventional method of mixing sodium chlorite / sodium chlorate with an activator (typically hydrochloric acid) to prepare the substance to be fed into the water, the applicant separates the main components that form chlorine dioxide (sodium chlorite (NaClO2) and / or sodium chlorate (NaClO3)) and adds them directly to the water. The sodium chlorite and / or sodium chlorate are then converted into chlorine dioxide via an electrolytic process as the water flows through an electrochemical cell.

[0100] Some advantages of this process are as follows:

[0101] • All sodium chlorite and / or sodium chlorate added to the main water body will eventually be converted into chlorine dioxide;

[0102] • Because the chemical process occurs in the flow-through tank, the chlorine dioxide produced is highly diluted and will not cause safety issues;

[0103] • Because chlorine dioxide is highly diluted during manufacturing, the possibility of corrosion damage is eliminated or at least significantly reduced;

[0104] • The convenience of adding only sodium chlorite and / or sodium chlorate to water to generate chlorine dioxide reduces the safety risks of needing to premix chemicals to form chlorine dioxide;

[0105] Even if chlorine dioxide is produced simultaneously, the process will continue to produce chlorine normally.

[0106] • Production costs are significantly reduced because the activation of chlorine dioxide can be accomplished using the same equipment as that used for chlorine production.

[0107] Equipment that produces chlorine dioxide in this way is inexpensive and not prone to failure; and

[0108] Sodium chlorite / sodium chlorate has a very long shelf life, so it can be stored on-site without worrying about spoilage.

[0109] The applicant has discovered a water treatment system based on adding sodium chlorite and / or sodium chlorate to a main water body and then passing the water through an electrolysis cell 30 to form chlorine dioxide.

[0110] Water body 50 is in fluid communication with electrolytic cell 30 via pump 40. System 10 operates as a closed loop, so that water pumped from water body 50 returns to water body 50 after passing through electrolytic cell 30.

[0111] The control unit 20 controls the electrolysis rate in the electrolytic cell 30.

[0112] According to the World Health Organization, the recommended concentration of sodium chlorite in drinking water should not exceed 1 ppm. If the water is not intended solely for human consumption, then increasing the sodium chlorite level in major water bodies to above 1 ppm may be feasible, for example, in swimming pools.

[0113] The method for generating chlorine dioxide is mostly applicable to closed-loop scenarios. This will include any form of water storage requiring treatment to remove pathogens and control biofilms. This includes, but is not limited to, swimming pools, spas, aquariums, reservoirs, ponds, aquaculture facilities, and other water storage and retention facilities.

[0114] After circulating this method for 72 hours in a 50,000-liter (indoor) volume of water, the detected chlorine dioxide levels ranged from 0.5 ppm to 1.0 ppm, while the brine chlorinator continued to produce sufficient chlorine to indicate adequate residue in the water. Numerous variations exist in the size of the electrolysis unit, sodium chlorite levels, and TDS, which can increase chlorine dioxide production and make it suitable for a wide range of applications across many different industries that rely on high-quality water free of biofilms and pathogens.

[0115] The advantages of using this method to form chlorine dioxide are significant. These include the following:

[0116] Chlorine dioxide is formed in the recirculation circuit without exposure to outside air. This does not result in the release of gas to dangerous levels, thus posing no potential health risks.

[0117] • The chlorine dioxide formed in the electrolytic cell immediately mixes with the water flowing through the equipment, resulting in immediate dilution of the chlorine dioxide. This prevents equipment degradation because it is not exposed to high concentrations of chlorine dioxide.

[0118] Adding a specific formula of stabilized sodium chlorite to water will not pose any occupational health and safety risks to operators.

[0119] • No specific skills are required to operate the device to produce chlorine dioxide;

[0120] • Because the chlorine dioxide produced is immediately diluted by the water passing through the equipment, there is absolutely no risk of the equipment causing an explosion;

[0121] The equipment is very inexpensive and requires no ongoing maintenance to operate.

[0122] • When there is a certain level of sodium chlorite and a minimum TDS in the water, the equipment will produce a constant amount of chlorine dioxide;

[0123] • Sodium chlorite has a 100% activation rate – other methods can only achieve 75% activation.

[0124] • It simultaneously forms chlorine and chlorine dioxide, thus providing a continuous disinfection system that was previously impossible to obtain from a single device;

[0125] • Stable sodium chlorite can be transported at low cost within existing chemical transport regulations;

[0126] • This method of producing chlorine dioxide is the cheapest possible way; and

[0127] • Its ease of use for operators is unparalleled by any other known method of producing chlorine dioxide.

[0128] Control unit 20 monitors and regulates the production of chlorine dioxide via electrolytic cell 30. Control unit 20 is connected to a 240-volt alternating current (AC) mains power supply.

[0129] The electrolytic cell 30 consists of a series of titanium electrodes with opposite charges. The electrodes are encapsulated in an electrode cage.

[0130] During operation, the control unit 20 supplies power to the electrolytic cell 30 (anode and cathode) and maintains the potential difference between them for a specified period of time. After the period ends, the polarity can be reversed, and the anode becomes the cathode, and the cathode becomes the anode.

[0131] The function of reversing the polarity or potential difference is to remove any calcium deposits that may have accumulated on the cathode. Therefore, this continuous reversal of polarity provides a self-cleaning function, keeping the electrolytic cell 30 clean during operation, free from calcium deposits, providing chemical balance, and ensuring that the flow of water through the electrolytic cell 30 to the pool / thermal bath remains within normal parameters.

[0132] When the target amount of chlorine dioxide and / or chlorine is reached in the water, the control unit 20 can stop or slow down the electrolysis rate.

[0133] The control unit 20 may include a chlorine dioxide sensor 70, or alternatively may be connected to a chlorine dioxide sensor 70 configured to detect the level of chlorine dioxide present in the water body 50 or in the return line extending between the electrolysis cell 30 and the water body 50. Preferably, the chlorine dioxide sensor is located in the line between the pump 40 and the electrolysis cell 30.

[0134] The control unit 20 is configured to stop or slow down the electrolysis cell 30 when the sensor 70 determines that the level of chlorine dioxide and / or chlorine present in the water exceeds a predetermined threshold. The target level for chlorine dioxide is 0.1 ppm to 1.5 ppm, and the target level for free chlorine is 1 ppm to 10 ppm.

[0135] The control unit 20 can also provide early warnings, such as issuing an alarm if the chlorine dioxide level sensed by the sensor 70 is below 0.1 ppm or above 1.5 ppm or some other predetermined threshold. Alternatively, if the chlorine dioxide level sensed by the sensor 70 exceeds 1.5 ppm, the control unit 20 can shut down the electrolytic cell 30.

[0136] For example, electrolytic cell 30 can operate in three settings:

[0137] If the sensed chlorine dioxide level is less than 0.1 ppm, then increase the production of chlorine dioxide;

[0138] If the sensed chlorine dioxide level is between 0.1 and 1.5 ppm, then reduce chlorine dioxide production; and

[0139] If the sensed chlorine dioxide level is higher than 1.5 ppm, no chlorine dioxide is produced.

[0140] System 10 may include an automatic feeding device 60 for feeding and delivering sodium chlorite / sodium chlorate into water body 50. The feeding device 60 may deliver sodium chlorite / sodium chlorate to water body 50 or a return line at a desired rate based on a predetermined schedule, such as daily, every three days, or weekly. Alternatively, the feeding device 60 may deliver sodium chlorite / sodium chlorate to water body 50 based on feedback regarding chlorine dioxide levels detected by sensor 70.

[0141] Although the invention has been described with reference to specific examples, those skilled in the art will understand that the invention can be implemented in many other forms.

[0142] Example

[0143] A field trial was conducted in a 950,000-liter water tank to evaluate... The effect of the electrolysis system (see Table 1) on the combination of chlorine dioxide and chlorine produced from sodium chlorite / sodium chlorite.

[0144] Table 1

[0145]

[0146] 2 kg of sodium chlorite / sodium chlorate was added on February 18, 2021, and 500 g of sodium chlorite / sodium chlorate was added on March 2 and March 8, 2021 (represented by ←).

[0147] On February 22, 2021, due to the presence of chlorine dioxide in the water, the level of free chlorine increased, and the output of the chlorinator decreased by 15%. Tests showed that a constant level of chlorine dioxide was produced during the experiment. The test strip method was used to determine the chlorine dioxide level in the pool.

[0148] The level of combined chlorine in the pool is very high. This concentration can be controlled by adding sodium chlorite / sodium chlorate to the pool and converting it to ClO2 through electrolysis. When free chlorine reacts with amines, it forms combined chlorine (also known as chlorate). Chlorine dioxide is highly reactive to tertiary amines (electron transfer is the main pathway) (Gan et al, Environmental Science: Water Research & Technology, 9:2241-2630, Sep 2020).

[0149] The disinfection efficacy of chlorine and chlorine dioxide can be compared by analyzing the effective contact time (CT) of disinfection in water, determined by multiplying the disinfectant concentration (C, in mg / L) by the contact time (t, in minutes). A low CT value indicates a strong disinfectant. Table 2 shows the CT of free chlorine (1 mg / mL) and ClO2 required to inactivate 99% of bacteria and 99.9% of other pathogens in water.

[0150] Table 2

[0151]

[0152] Table 2 shows that both chlorine dioxide and free chlorine are very effective in inactivating bacteria and viruses, and chlorine dioxide is more effective than free chlorine in inactivating protozoa (such as Giardia and Cryptosporidium).

[0153] The chlorite / chlorite consumption rate was calculated based on field tests. The electrolysis unit (rated to produce 30 g chlorine per hour at optimal TDS and operating for 8 hours per day in a 50,000 liter water tank) consumed 1 ppm chlorite and 0.5 ppm chlorate every 30 days.

[0154] The chlorine dioxide production rate was calculated based on field tests. The electrolysis unit (rated to produce 30 g chlorine per hour at optimal TDS and operating for 8 hours per day in a 50,000 liter water tank) produced a stable level of 0.2–0.4 ppm chlorine dioxide from a solution containing a minimum level of 1 ppm chlorite and 0.5 ppm chlorate.

[0155] It is clear from the above that combining chlorine dioxide with chlorine has several advantages:

[0156] • Adding chlorine dioxide reduces the formation of combined chlorine (i.e., chloramine, which is a poor disinfectant), thus increasing the availability of free chlorine (a good disinfectant);

[0157] Chlorine dioxide is an effective disinfectant against a variety of pathogens and is more effective than chlorine against protozoa; and

[0158] • Adding chlorine dioxide allows for the use of lower doses of chlorine.

Claims

1. A method for disinfecting water in a swimming pool or hot spring bath, wherein the method comprises the following steps: Sodium chlorite and / or sodium chlorate are added to the water body; Add sodium chloride to the water body; In an electrolytic cell in fluid communication with the water circulation system of the water body, the sodium chlorite and / or sodium chlorate are converted into chlorine dioxide; The sodium chloride is converted into chlorine in the electrolytic cell; The level of chlorine dioxide present in the water body was detected using sensors; and When the sensor determines that the level of chlorine dioxide in the water exceeds a predetermined threshold, the control unit stops or slows down the electrolysis cell; and Stopping or slowing down the electrolytic cell includes controlling the electrolytic cell to achieve the following: If the sensed chlorine dioxide level is less than 0.1 ppm, then increase the production of chlorine dioxide; If the sensed chlorine dioxide level is between 0.1 and 1.5 ppm, then reduce the production of chlorine dioxide; and If the sensed chlorine dioxide level is higher than 1.5 ppm, no chlorine dioxide is produced.

2. The method of claim 1, wherein, Sodium chlorite and / or sodium chlorate are added to the water to produce a target chlorine dioxide concentration of 0.1-1.5 ppm.

3. The method of claim 1, wherein, Sodium chlorite and / or sodium chlorate are added to the water to produce a target chlorine dioxide concentration of 0.2-1 ppm.

4. The method of claim 1, wherein, Chlorine is added to the water to produce a target free chlorine concentration of 1-10 ppm.

5. The method of claim 1, wherein, Chlorine is added to the water to produce a target free chlorine concentration of 1-6 ppm.

6. The method of claim 1, wherein, Chlorine is added to the water to produce a target free chlorine concentration of 1-3 ppm.

7. A water disinfection system, comprising: An electrolytic cell, arranged in the water circulation system of a swimming pool or hot spring bath, is operable to convert sodium chlorite and / or sodium chlorate into chlorine dioxide and sodium chloride into chlorine. A control unit, which is connected to the electrolytic cell; and A sensor configured to detect the level of chlorine dioxide present in the water body. The control unit is configured to stop or slow down the electrolysis cell when the sensor determines that the level of chlorine dioxide present in the water exceeds a predetermined threshold; and The electrolytic cell is controlled by the control unit to achieve the following: If the sensed chlorine dioxide level is less than 0.1 ppm, then increase the production of chlorine dioxide; If the sensed chlorine dioxide level is between 0.1 and 1.5 ppm, then reduce chlorine dioxide production; and If the sensed chlorine dioxide level is higher than 1.5 ppm, no chlorine dioxide is produced.

8. The water disinfection system of claim 7, further comprising a feeding device configured to deliver sodium chlorite and / or sodium chlorate to the water body.

9. The water disinfection equipment according to claim 8, wherein, The feeding device delivers sodium chlorite and / or sodium chlorate to the water body at predetermined time intervals.

10. The water disinfection equipment according to claim 8, wherein, The feeding device delivers sodium chlorite and / or sodium chlorate to the water body in response to the level of chlorine dioxide identified by the sensor.

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