1. The application of ozone improved the water quality of chlorinated swimming pool water.
At present, chlorine or chlorine compounds are widely used as fungicides in water treatment in China, and the sterilization of swimming pool water almost depends on chlorine-containing agents.
As early as 100 years ago, people began to use chlorine agents for disinfection, especially elemental chlorine, which can quickly kill most microorganisms and retain enough residual chlorine in water to maintain inhibition and be popularized. Chlorine gas has the characteristics of low price and convenient source, and is still widely used in the treatment of swimming pool water. The pollutants in swimming pools are mainly urea, that is, bacteria brought in by swimmers. It is said that a swimmer can bring in 3-4 billion bacteria and 0.5 grams of organic matter. Chlorine can kill bacteria, but at the same time it will form amine chloride and trihalomethane (THM) with urea and organic matter. The volatility of amine chloride is the main compound that causes the special smell of indoor swimming pools, which irritates people's eyes, ears, nose and throat mucosa. THM has been proved to be carcinogenic to mice. On July 23rd, 20001year, the Environmental Protection Agency (EPA) of the United States published the argument that THM is harmful to health on the Internet, and claimed that some people drinking water with THM exceeding the standard (EPA standard is 100μg/L) for a long time may cause cancer of the lung, liver and central nervous system, and the existence of THM in swimming pool water may lead to people's breathing and swimming. Environmental protection workers also found that THM, once generated, is not easy to decompose in the natural environment and play into the atmosphere, and the half-life after reaching the troposphere can be as long as 2-3 months, during which it will destroy the atmospheric ozone layer and pose a threat to the sustainable development of mankind.
In view of the above problems, the ozone treatment technology of swimming pool water has been further developed. Ozone has been proved to be the strongest oxidant except fluorine in water treatment. It can decompose organic matter at a reaction speed 100 times higher than that of chlorine, prevent chlorine from synthesizing chloramine from urea, and oxidize the precursor of THM, thus greatly reducing THM. In addition, hydroxyl groups formed in water after ozone decomposition can hydrolyze multivalent metal ions into colloidal compounds, which are filtered out by sand filtration, which not only improves the texture of water, but also oxidizes and decomposes organic substances in water, and then filters them out. Therefore, even in order to prevent cross-infection, the swimming pool needs to keep about 0.5mg/L of residual chlorine, and the dosage of chlorine agent is greatly reduced. Generally, only 15 ~ chlorine agent is needed alone.
Subsequent experience has proved that when the residual ozone in the returned swimming pool water is lower than 0. 15mg/L [10], it will not cause any adverse effects, even if swimming for a long time, it will not cause health hazards. Western industrial countries, especially Europe, not only generally accepted this fact, but also used ozone in about 30,000 swimming pools, and further developed the traditional German standard, realizing the complete elimination of chlorine disinfection. This technology has been widely used in France and some non-German-speaking countries for more than 30 years, and accumulated a lot of useful experience, which provided systematic practical experience for the development of ozone treatment pond water technology. American countries, including the United States, have also noticed this situation in recent years and started to adopt ozone technology in large numbers. The development momentum is very fast, but the application ratio is still lower than that of European countries.
The development of swimming in China is relatively late, the scale of swimming pool construction is small, and ozone technology is not widely used. In recent years, with the opening to the outside world, some swimming pools that hold official competitions or international competitions have been equipped with ozone treatment devices according to national regulations or norms 1. In addition, some public swimming pools, high-end hotels and swimming pools in residential areas have also put forward the requirements of adopting ozone technology. In the harm of SARS, people's awareness of personal hygiene protection has been further strengthened. It can be predicted that the ozone treatment technology of swimming pool water in China will accelerate in the future.
Second, the development of ozone treatment technology for swimming pool water
Ozone, similar to chlorine, has bactericidal effect, killing common Escherichia coli in water with a reaction speed of 100 times faster. Some pathogenic bacteria, such as viruses, amoeba, cysts and so on, have been clarified for many scientists. , can resist chlorine, but they are not spared, killed by ozone. The use of ozone assures swimmers that they can swim safely. Another function of ozone is its oxidizing ability. It can prevent the accumulation of compounds that cause the special smell of swimming pools, including the accumulation of chlorine-containing organic compounds generated by the reaction between swimmer's excrement and chlorine. These compounds include monochloramine, dichloramine, trichloroamine, THM, creatine chloride, chlorourine and so on. Many of them have their own colors or smells and belong to the precursors of THM. In fact, ozone is constantly blocking the production of these precursors, making the swimming pool a fitness place with clear water, fresh air and no irritation to eyelids and nasal membranes. Of course, among them, the significant decline of THM in water is the best state for people who want to keep fit.
The third function of ozone is to assist sand filtration to remove metal salts and organic substances, because organic substances can easily become multipolar compounds in the oxidation process, which can combine with multivalent metal cations, such as calcium, magnesium, iron and aluminum. , forming a complex, micro-flocculating and removing by sand filtration. Ozone can turn green pool water into blue, sparkling and clear water, which is welcome?
Based on how to give full play to the above three functions of ozone, combined with environmental protection, health and economic considerations, the technology of ozone treatment of swimming pool water can be roughly divided into four types, namely:
★ Full flow system
★ Slipstream system
★ Ultraviolet ozone system (ultraviolet ozone)
Third, the whole process system
As the name implies, the full flow system is the method that all swimming pool circulating water contacts with ozone. This method was widely used to treat pool water in the early days, suitable for city publicity, competitions, and some swimming pools with high requirements on pool water quality and air quality. This method was adopted by France and Britain in the mid-1970s. With the improvement of indoor air quality, it can reduce the replacement of fresh air and greatly save power consumption, especially in winter, which can completely offset the increase of energy consumption caused by ozone. Britain, France and other countries put forward the guiding document 3 for the construction and operation of swimming pools, and Germany also revised it in some later specifications. This full-flow ozone system developed very rapidly in the 1980s.
The dosage of ozone is 0.8- 1.0 mg/liter of circulating water. Generally, ozone is generated by the negative pressure generated in the ejector, and the water saturated with ozone in the ejector is combined with the main water flow to react in the contact pool for not less than two minutes, so as to achieve the purpose of sterilization. According to the suggestions of some environmental organizations at that time, the residual ozone returned to the swimming pool should be reduced as much as possible. In early Europe, German experience was cited, and the maximum allowable value of this residual value was 0.05 mg/L 4,5, so that the residual ozone in the water leaving the contact tank would be decomposed in the ozone destruction layer of activated carbon to ensure that the ozone in the water returning to the tank was less than 0.05 mg/L. This technical requirement and design scheme greatly limited the whole system, because in order to make ozone and water have enough reaction time, And the ozone in the residual system should not exceed 0.05 mg/L. The only way is to increase the dosage of ozone or install heavy contact tanks and activated carbon destruction layers, which wastes at least 30~40% of ozone. This method also leads to the consumption of activated carbon. The oxidation of activated carbon makes the particles smaller, even permeates into the water, and the activated carbon layer is easy to accumulate microorganisms, which reduces the turbidity and filtration efficiency of the pool water. In addition, in order to keep some residual fungicides in the pool water, chlorine should be added to ensure the free chlorine content is 0.5-1.0 mg/L. In the late 1980s, the World Health Organization (WHO) announced the allowable ozone water consumption of 5 in Europe and America, and put forward this value as 0. 1mg/L, which was recognized by most countries. Since then, this technical scheme has been further developed. In 1990s, people used WHO to relax the ozone content in water, and after accumulating a lot of experience in the popularization and application of full-flow system, they introduced the second generation ozone treatment method, that is, the generation of sub-flow system technology.
Fourth, the flow distribution system.
British engineers discovered in the early 1980s that:
● When the full-flow system is used in public swimming pools, even if part of the ozone capacity is stopped, it will have little impact on the water quality.
● In 1990s, the United States Environmental Protection Agency (EPA) stipulated that the maximum allowable amount (8h contact) in swimming pool air was 0. 1ppm(v) or 0.2mg/l (wt) 5,6. Even if the ozone content in swimming pool water was 0. 15 mg/L, the air quality still met the requirements. Therefore, the so-called ozone-free removal treatment is proposed for the whole process system.
● Most of the pool water is circulated in countercurrent, and the circulation times are more than 6 times. The time for ozone to reach every point in the pond is less than five minutes, and the half-life of ozone is 20 minutes. Therefore, as long as the residual ozone in the return tank water is between 0.05-0. 1.5 mg/L, the system will ensure the optimal values of all indicators.
● As long as all pool water is exposed to ozone once within 24 hours, the whole system can be sterilized.
Based on the above viewpoint, the British Institute of Electrical Engineering conducted a demonstration device test in the indoor swimming pool of Cirencester Sports Center in 1985- 1986. The test results were put forward by some medical experts of Leisure Swimming Association. The conclusion is that chlorine consumption can be further reduced, indoor chlorine smell can be reduced, and irritation to eyes and nasal mucosa can be avoided, which provides extremely favorable conditions for eliminating asthma.
In the mid-1990s, the traffic distribution system came out. The dosage of ozone is 10 ~ 20% or 0. 1 ~ 0.2 mg/L of the total flow system. In actual operation, 20-25% of the circulating pool water enters the jet pipe, and the ozone dosage is 0.6- 1g/m3. After contact for at least 2 minutes, it is mixed with system water and returned to the swimming pool after chlorination. The activated carbon decomposer is only installed in the ventilation system to ensure that the ozone in the air is below 0. 1ppm. Compared with the whole process, some process systems can save more than 50% ozone consumption.
The flow distribution system is mainly used for the renovation of existing public swimming pools, especially in the case of limited floor space and funds. Some newly-built 50m standard pools are aimed at schools, communities and hotels, that is, they are not as heavy as municipal swimming pools or amusement pools, so they can all adopt the diversion system. It is worth mentioning that in many provinces of Canada, including Ontario, British Columbia and Alberta, almost all public swimming pools have adopted the flow distribution system technology, even large amusement pools and competition pools.
At present, the water distribution system continues to add 0.5- 1.0 mg/L of chlorine after contacting the reaction tank, but there are also many reports that swimming pools without chlorine (bromine) agent at all, that is, chlorine-free swimming pools, have been popularized in Europe.
Verb (abbreviation for verb) ultraviolet ozone system
Adding ultraviolet lamp to ozone generation module is called UV-O3 system. This is the further development of traffic distribution system. It also adopts shunt system technology, which combines the characteristics that ultraviolet rays can stimulate ozone activity and accelerate it to generate hydroxyl radical (OHˉ) with water molecules in one module. OHˉ is an active substance after ozone reacts with water, which is 10- 100 times higher than hypochlorite and its bactericidal performance is 3 125 times higher, which is the theoretical basis of UV-O3 system. On the filter pipe, the bypass part of water is treated by UV-O3 integrated machine and then returned to the system.
In the UV all-in-one machine, the pool water is mixed with ozone through the booster pump and injection pipe in the box, and then reacts in the contact reaction pool and returns to the pool system. Due to ultraviolet radiation, huh? The formation of ozone accelerates oxidation and sterilization, and the ozone in the water leaving the contact pool can be fully decomposed.
The UV-O3 method can not only ensure the same low ozone consumption and the same sterilization and oxidation effect as the split-flow method, but also avoid the high ozone content in swimming pool water (for example, >: 0. 15 mg/L). Because the contact pool is very small under the action of ultraviolet rays, there is no need to use activated carbon to decompose ozone, which ensures the transparency of water quality.
The use of UV-O3 system can reduce the dosage of chlorinating agent. Phil Castle reported that they conducted four-month whole-course, bypass and UV comparison tests on several swimming pools with similar conditions, which proved that the amount of chlorine in the UV system could be further reduced under the condition of meeting the requirements of sterilization and oxidation, and the combined chlorine and free chlorine in the water could be reduced to below 0.2 mg/L and 0.4 mg/L respectively, which made the pool water to a certain extent.
In UV-O3 system, hydroxyl radical (OH-) produced by the synergistic effect of ozone and UV can accelerate the decomposition of organochlorine. The generation of free radicals and their interaction with organic pollutants are almost instantaneous under the action of ultraviolet light, and the time is extremely short, so ozone will not enter the pool water, and the process is safer.
Experiments show that the advantages of high-efficiency process of UV-O3 system can be summarized as follows:
● Effectively control microorganisms.
● Greatly reduce chloramines and trihalomethanes.
● High water transparency and good water quality.
● Indoor air is fresh.
Reduce irritation to skin and eyes.
Do not produce substances harmful to the health of swimmers and staff.
● Avoid the troubles and health problems of using activated carbon tanks.
Reduce the content of free chlorine in water.
● Small workshop area, convenient installation and operation, and simple maintenance.
UV-O3 system has been widely used in some high-end swimming pools. In recent years, it has also been widely promoted in competitive swimming pools.
Safety of ozone water treatment technology.
It has been proved that ozone is harmful to human body, and there are two related factors to prevent its harm to people. First, the ozone content in the air should not be greater than 0. 1ppm, which is not difficult to do, because people can find the existence of ozone with their sense of smell at about 0.0 1ppm, and take corresponding measures to avoid accidents. Suppliers of ozone generators have strict operating instructions for their products, so they only need to follow these instructions. Secondly, chloramine and trihalomethane (THM) in swimming pool water, among which chloramine has a bad smell, but its toxicity is very small, and it is itself a bactericide to remove THM compounds; THM is a problem that many medical experts pay close attention to.
The swimming pool water standards all over the world stipulate that the maximum THM content should be lower than 100μ g/L, which can be fully met by most ozone-based sterilization technologies. Recently, the THM allowed in FINA2002-2005 manual is set at 20μg/L, which can be achieved by strict operation and reduction of chlorine consumption. The integrated machine combining UV and O3 has a higher voice in this respect. At present, China's drinking water implements 100μg/L, and the THM content in swimming pool water is not specified. For example, 100μg/L is still required, which is estimated to be difficult to achieve for some chlorinated swimming pool water. In 1970s and 1980s, the content of THM in foreign countries was around150-450μ g/L. Due to the limitation of THM index, the 2008 Olympic Games will be held in China, and the THM index of swimming pool water will also meet the requirements of FINA. This will greatly promote the development of ozone treatment technology and the application of swimming pool water in China.