Love-hate relationship with ozone
The protective effect of the ozone layer in the atmosphere on life on Earth is now well known - it absorbs the vast majority of ultraviolet rays emitted by the sun and protects plants and animals from the harmful effects of such rays. In order to compensate for the thinning of the ozone layer and even the hole in the ozone layer, people are trying to do everything possible, such as promoting the use of non-fluorine refrigerants to reduce the destruction of ozone by substances such as Freon. The International Day for the Preservation of the Ozone Layer has been designated for this purpose. The resulting impression seems to be protected by the ozone should be the more the better, in fact, not so, if the ozone in the atmosphere, especially near the ground in the atmosphere of ozone aggregation is too much, for human beings ozone concentration is too high instead of a scourge.
Ozone is a trace gas in the Earth's atmosphere, it is due to the atmospheric oxygen molecules by solar radiation decomposition into oxygen atoms, oxygen atoms and the surrounding oxygen molecules and the combination of the formation of 3 oxygen atoms. More than 90% of the ozone in the atmosphere exists in the upper atmosphere or stratosphere, 10 to 50 kilometers from the ground, which is the atmospheric ozone layer that needs human protection. There are also a small number of ozone molecules hovering near the ground, which can still play a role in blocking ultraviolet light. However, in recent years, it has been found that the ozone concentration in the atmosphere near the ground has been increasing rapidly, which is not good.
Where is all this ozone coming from? Like lead pollution and sulfides, it stems from human activity, with automobiles, fuels, and petrochemicals being important sources of ozone pollution. Walking in the streets of the traffic, often see the air slightly light brown, and a pungent and irritating odor, which is usually called photochemical smog. Ozone is the main component of photochemical smog, which is not directly emitted, but transformed into, for example, nitrogen oxides emitted by automobiles, as long as the sunlight radiation and suitable meteorological conditions can generate ozone. With the increase in automobile and industrial emissions, ground-level ozone pollution has become a common phenomenon in Europe, North America, Japan and many cities in China. According to estimates based on information currently available to experts, by 2005, the near-surface atmospheric ozone layer will become a major pollutant affecting air quality in north China.
Studies have shown that ozone concentration in the air at the level of 0.012 ppm - a level typical of many cities - can cause people's skin to tingle, the eyes, nose and throat, and respiratory tract to become irritated, and lung function to be affected, causing symptoms such as coughing, shortness of breath, and chest pains; and that when the level of ozone in the air is raised to 0.05 ppm in the air, the number of hospital admissions rose by an average of 7% to 10%. The reason for this is that, as a strong oxidizing agent, ozone can react with almost any biological tissue. When ozone is inhaled into the respiratory tract, it reacts quickly with cells, fluids and tissues in the respiratory tract, resulting in reduced lung function and tissue damage. The dangers of ozone are even more pronounced for those who suffer from asthma, emphysema and chronic bronchitis.
By its very nature, ozone can be both helpful and harmful; it is both a God-given umbrella for mankind and, at times, a potent poison. At present, for the positive effects of ozone and human should take what measures to protect the ozone layer, people have reached *** knowledge and do a lot of work. However, for the negative effects of the ozone layer, although people have been recognized, but at present, in addition to atmospheric monitoring and air pollution forecasting, there is no real practical way to solve.
The principle of ozone sterilization can be thought of as an oxidation reaction.
(1) the mechanism of ozone inactivation of bacteria:
Ozone inactivation of bacteria is always carried out very quickly. Unlike other biocides: ozone can react with the bacterial cell wall lipid double bond, penetrate into the bacterial body, the role of proteins and lipopolysaccharides, change the permeability of the cell, thus leading to bacterial death. Ozone also acts on the nuclear material in the cell, such as purines and pyrimidines in nucleic acids to destroy DNA.
(2) The mechanism of ozone inactivation of viruses:
The effect of ozone on viruses is, first of all, the four polypeptide chains of the viral capsid proteins of the viruses, and cause damage to the RNA, in particular, to the proteins that form it. After the phage is oxidized by ozone, electron microscopic observation shows that its epidermis is broken into many fragments, from which a lot of ribonucleic acid is released, interfering with its adsorption to the host body.
The thoroughness of ozone sterilization is not to be doubted.
Destroying the ozone layer, endangering each of us.
Ultraviolet rays affect human health in many ways. The human body will occur such as sun spots, eye diseases, immune system changes, photodamage reactions and skin diseases (including skin cancer). Skin cancer is a persistent disease, and the growth of UV rays increases the risk of developing this disease. UV photons have enough energy to break double bonds. Short- and medium-wave UV rays penetrate deep into the skin, causing inflammation of the skin and damage to the body's genetic material, DNA (deoxyribonucleic acid), which causes normally growing cells to metamorphose into cancerous cells and continue to grow into whole skin cancers. It is also said that the sun's rays penetrate the top layer of the skin. Ultraviolet radiation bombards the basic units of DNA in the nuclei of skin cells, causing many of the units to dissolve into useless fragments. The repair process of these faults may become abnormal, leading to cancer. Epidemiology has confirmed that the incidence of factory non-melanoma skin cancer is strongly correlated with sun exposure. People with all types of skin are at risk of developing non-melanoma skin cancer, but the incidence is higher in light-skinned people. Animal experiments have found that among ultraviolet rays, the ultraviolet B wavelength region is the wavelength region with the strongest carcinogenic effect.
It has been estimated that a 1% reduction in total ozone (i.e., a 2% enhancement of ultraviolet B) will increase the rate of basal cellular carcinogenesis by about 4%. Recent studies have found that UV-B can cause changes in immune system function. Some experimental results suggest that infectious skin diseases may also be associated with UV-B enhancement resulting from ozone reduction. It is estimated that a 1 per cent reduction in total ozone would increase the incidence of skin cancer by 5-7 per cent and cataracts by 0.2-0.6 per cent. Since 1983, the incidence of skin cancer in Canada has increased by 235%, in 1991 the skin disease patients have been up to 4.7 million. The U.S. Environmental Protection Agency, said the United States in the next 50 years died of skin cancer, will be expected to increase 20 million people than in the past. Australians like to sunbathe and get a tan. Despite repeated warnings from scientists that sun exposure can cause skin cancer, they are happy to go dark. As a result, Australians didn't wake up until the incidence of skin cancer was twice as high as anywhere else in the world. Skin cancer now accounts for one-third of all cancers worldwide.
The United Nations Environment Programme has warned that if the Earth's ozone layer continues to deplete and thin at its current rate, the proportion of people with skin cancer worldwide will increase by 26 percent to 300,000 by the year 2000, and if the ozone layer continues to deplete and thin at its current rate at the beginning of the next century, the proportion of people with skin cancer will increase by 26 percent to 300,000, the United Nations Environment Programme said. If the ozone layer decreases by another 10 percent by the beginning of the next century, the number of cataracts worldwide could reach 1.6 million to 1.75 million a year.
Being victimized by ultraviolet light may also induce measles, chicken pox, malaria, scarring, fungal diseases, tuberculosis, leprosy, and lymphoma.
The increase in ultraviolet light can also cause massive deaths of marine plankton and shrimp, crab larvae, and shellfish, resulting in the extinction of certain organisms. UV radiation also causes myopia in rabbits and blindness in thousands of sheep.
Ultraviolet B weakens photosynthesis It has been hypothesized, based on experiments along the African coast, that photosynthesis in plankton is weakened by about 5 percent by enhanced ultraviolet B radiation. Enhanced UV-B can also lead to changes in freshwater ecosystems by destroying microorganisms in the water and thus reducing the self-purification of the water. Enhanced UV-B can also kill young fish, shrimp and crabs. If there is an extreme decline in the original plankton in the Antarctic Ocean, marine life as a whole will change dramatically. However, some plankton are sensitive to UV and some are not. There is a 100-fold difference in how much UV light damages the DNA of different organisms.
Severe hindrance to normal growth of various crops and trees Some plants, such as peanuts and wheat, are better protected against UV-B, while others, such as lettuce, tomatoes, soybeans and cotton, are sensitive. The United States of America University of Maryland Agricultural Biotechnology Center of Trenmola with a sun lamp on six soybean varieties for observation experiments, the results show that three of the soybean varieties are extremely sensitive to ultraviolet radiation. Specific performance, soybean leaf photosynthesis intensity decreased, resulting in yield reduction, but also make soybean seeds in protein and oil content decline. Atmospheric ozone layer loss of 1 percent, soybean production will also be reduced by 1 percent.
Tremora also spent four years observing the effects of high doses of ultraviolet radiation on tree growth. The results showed a significant decrease in wood accumulation, and their root growth was stunted as a result.
Adverse Disruptive Effects on Global Climate The large decrease in upper stratospheric ozone and the associated increase in lower stratospheric and upper tropospheric ozone may act as an adverse disruptive effect on global climate. Vertical redistribution of ozone may warm the lower atmosphere and exacerbate the greenhouse effect caused by increased amounts of carbon dioxide.
Photochemical Air Pollution Excessive ultraviolet light makes polymeric materials such as plastics susceptible to aging and decomposition, resulting in a new type of pollution, photochemical air pollution.
Oxygen
... ...
:O::O:
Ozone
... ...
:O::O::O:
That's it.
The electronic formula for ozone can be obtained by changing it on the electronic formula for carbon dioxide:
... ...
:O::C::O:
But note: ozone and carbon dioxide, while having similar electronic formulas, have different molecular structures. Ozone is folded and carbon dioxide is straight. The explanation for this involves a college knowledge of inorganic chemistry.
Scientists at NASA recently discovered that the giant ozone hole over Earth's Antarctica changed significantly in September from a swirling vortex to an "amoeba" shape with two large ends and a small center.
While the ozone hole appears to have shrunk in size over the past two years, scientists warn that it is too early to say that the ozone layer is "repairing itself". Paul Newman, an ozone expert with the National Aeronautics and Space Administration (NASA), said that rising temperatures in the atmosphere have caused the hole to shrink. In 2000, Antarctica's ozone hole area had once reached 2.8 million square kilometers, equivalent to the area of three continental United States; in early September 2002, Aerospace Agency scientists estimate that the hole shrunk to 1.5 million square kilometers.
An Australian ozone research team has reported good news to the world: because of the effective implementation of environmental protection measures over the years, the ozone hole over Antarctica is shrinking, and it is expected that by 2050, this "infamous" huge hole can be completely "filled".
According to the report, the hole is expected to be completely "filled" by 2050.
The ozone hole over Antarctica has reportedly been one of the problems plaguing environmentalists around the world. At its worst, the ozone hole was once the size of three Australia. Scientists have found that the main culprits of the ozone hole are chlorofluorocarbons (CFCs) in the atmosphere, which are organic compounds containing chlorine, fluorine, and carbon (commonly known as "Freon"). ").
In order to prevent further aggravation of the ozone hole and to protect the ecological environment and human health, countries formulated the Montreal Protocol in 1990, which stipulates strict limits on the emission of chlorofluorocarbons. Now, the tireless efforts of environmental organizations over the years have finally paid off: ozone is back! Paul Fraser, an atmospheric research specialist at Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO), exclaimed, "This is big news. We've been looking forward to this day for a long time!" He said that although there are many other factors affecting the progress of the shrinking ozone hole, such as the greenhouse effect, climate change and so on, "we have come to this conclusion after putting all the factors together: the ozone hole over Antarctica will disappear completely in less than 50 years."
It is reported that from the 1950s onwards, with the massive popularization of refrigerators and air conditioners (the main source of HCFC production), the level of HCFCs in the atmosphere increased year by year, reaching a peak in 2000. It was only later, thanks to new fluorine-free refrigerators, that HCFC levels began to decline significantly.
Scientists find ozone in soil inhibits plant growth
A joint study by European scientists has found that the ozone layer is a natural barrier that protects surface organisms from the harmful effects of the sun's ultraviolet rays, but ozone in the soil is the enemy of plant growth, inhibiting the growth of a wide variety of plants and causing major losses in agricultural production.
Ozone is a naturally occurring atmospheric trace colorless gas with a special odor, the vast majority of ozone exists in the stratosphere about 25 kilometers above the ground, which is often referred to as the ozone layer. The amount of ozone tends to vary with factors such as latitude, season and weather.
French researchers say the ozone layer in the sky absorbs more than 99 percent of the sun's ultraviolet rays, providing a natural protective barrier for life on Earth, while ozone is a serious pollutant when present in the soil. The latest research shows that the more light there is, the more damage ozone causes in the soil, especially to crops.
French researchers believe that the main reason for the increase in ozone levels in the soil is that fossil fuels such as petroleum products produce nitrogen oxides during the combustion process, and these nitrogen oxides float around in the air, where some of the oxygen atoms slowly combine with the oxygen in the air to make up ozone, which is composed of three oxygen atoms. They emphasized that sunlight accelerates this chemical reaction, so that ozone in the soil affects plant growth to different degrees in different climatic regions. In water treatment systems, tanks, exchange columns, and a variety of filters, membranes, and piping are constantly harboring and multiplying bacteria. While all methods of disinfection and sterilization provide the ability to remove bacteria and microorganisms, none of these methods are capable of removing all bacteria and water-soluble organic contamination in a multi-stage water treatment system. The best method currently available for continuous removal of bacteria and viruses in high-purity water systems is with ozone.
Ozone has been used in water treatment since 1905. It is superior to treating water with chlorine and removes halides from the water. The application of this method in domestic water systems is only in its infancy. Overseas, this method of disinfection has become very common, due to the fact that ozone does not produce harmful residues.
The use of ozone disinfection and the installation of ultraviolet lamps in front of the water point to reduce ozone residues is one of the common methods used to disinfect pharmaceutical water systems, especially purified water systems.
(1) Chemical properties and efficacy
Ozone (O3) is an allotropic isomer of oxygen, it is a light blue gas with a special odor. The molecular structure is triangular with a bond angle of 116°. Its density is 1.5 times that of oxygen and its solubility in water is 10 times that of oxygen. Ozone is a strong oxidant, it is in the water redox potential of 2.07V, second only to fluorine (2.5V), its oxidizing ability is higher than chlorine (1.36V) and chlorine dioxide (1.5V), can destroy the decomposition of bacterial cell walls, quickly diffuse into the cell, oxidative decomposition of bacteria inside the oxidation of glucose must be glucose oxidase, etc., but also can be directly with the bacterium, viruses and the role of. Destroy cells, ribonucleic acid (RNA), decomposition of deoxyribonucleic acid (DNA), RNA, proteins, lipids and polysaccharides and other macromolecular polymers, so that the metabolism of bacteria and the reproduction process is destroyed. Bacteria are killed by ozone due to the rupture of cell membranes, a process known as cellular dissipation, caused by the crushing of the cytoplasm in water, and the impossibility of cellular regeneration under the conditions of dissipation. It should be noted that, unlike hypochlorite disinfectants, the bactericidal capacity of ozone is not affected by changes in pH and ammonia, and its bactericidal capacity is 600-3000 times greater than chlorine, and its sterilization and disinfection effect is almost instantaneous, in the water ozone concentration of 0.3-2mg / L, 0.5-1min can be lethal to bacteria. To achieve the same sterilization effect (such as E. coli kill rate of 99%) required ozone water medicine dose is only 0.0048% of chlorine.
Ozone is also active against yeast and parasitic organisms, for example, it can be used to remove the following types of microorganisms and viruses.
①Viruses It has been shown that ozone has a very strong killing effect on viruses, for example, the Poloi virus is inactivated in 2min at ozone concentrations of 0.05-0.45mg/L. The ozone concentration of 0.05-0.45mg/L can be used for the removal of viruses, but it is not possible to remove viruses.
②Sporocysts were completely eliminated in 2.4min at an ozone concentration of 0.3mg/L.
③Spore Due to the protection of spore coat, it is 10-15 times more resistant to ozone than the growth state bacteria.
④Fungi Candida albicans and Penicillium can be killed.
⑤Parasitic organisms Schistosoma mansoni was killed after 3min.
In addition, ozone can oxidize and decompose the pollutants in water, and it has remarkable effect in water treatment for removing odor, decolorization, sterilization, removing phenol, cyanide, iron, manganese and lowering COD, BOD and so on.
It should be noted that although ozone is a strong oxidant, but its oxidizing ability is selective, such as ethanol is easy to be oxidized by the material is not easy and ozone effect.
(2) the generation of ozone and the common concentration
Ozone half-life is only 30-60min. because it is unstable, easy to decompose, can not be stored as a general product, so it needs to be made on site. The concentration of ozone made from air is generally 10-20mg/L, and the concentration of ozone made from oxygen is 20-40mg/L. Air containing 1%-4% (mass ratio) ozone can be used for water disinfection.
The method of producing ozone is to use dry air or dry oxygen as the raw material, through the discharge method. Another method of producing ozone is electrolysis, in which water is electrolyzed to turn it into elemental oxygen, and then the free oxygen in it is turned into ozone.
The main advantages of using an electrolysis system to produce ozone are:
① No ionic contamination;
② The water to be disinfected is the raw material used to produce ozone, so there is no other contamination from outside the system;
③ Ozone is dissolved during the lifetime of the treatment process, i.e., it can be ozonated with less equipment.
If under pressurized conditions, higher concentrations of ozone can be produced.
(3) residual ozone removal method
The ozone disinfection of treated water in the pharmaceutical production before the water should be put into the residual (excess) ozone removal, so as not to affect product quality. The ozone residue should generally be controlled at a level below 0.0005-0.5mg/L. The ozone residue should be removed from the water to avoid affecting the quality of the product. Theoretically, methods to remove or reduce ozone residuals include activated carbon filtration, catalytic conversion, thermal destruction, ultraviolet radiation, and so on. However, the most widely used method in pharmaceutical processes is only the UV method based on catalytic decomposition. Specific practice is to install a UV sterilizer in the pipeline system before the first water point, when the start of water or production before, turn on the UV lamp can be. At night or on weekends when there is no production, the UV lamp can be turned off. General elimination of 1mg / L ozone residue required for the amount of UV irradiation of 90,000?W-s/cm2.
(4) Notes
Ozone is most suitable for water quality and water consumption is relatively stable system, when it changes should be adjusted in a timely manner the amount of ozone. In actual production, timely adjustment is somewhat difficult.
Another issue to be considered is the content of organic matter in the water, when the turbidity of the water is less than 5mg / L, the effect of ozone sterilization effect is minimal, the turbidity increases, affecting the disinfection effect. If the content of organic matter is very high, ozone depletion will rise, its disinfection capacity is reduced, because the ozone will first be consumed in the organic matter, rather than killing bacteria. As a result, the foreign pharmaceutical industry has added a total organic carbon (TOC) monitoring program to pharmaceutical water systems. However, the bad news is that after ozone treatment of heavily organic contaminated influent water, large organic molecules will break down into nutrient sources for microbial metabolism, thus, without maintaining ozone concentration in the network, it will in turn make the sludge increase, which will in turn deteriorate the quality of the water.
In many ways, ozone and chlorine as disinfectants, their advantages are complementary. Ozone has a rapid sterilization and inactivation of viruses, for the removal of smell, taste and color, generally good results. Chlorine, on the other hand, has a long-lasting, flexible and controllable sterilizing effect, and can be used continuously in the pipe network system. So ozone and chlorine used in combination, it seems to be the most ideal way to disinfect the water system.