» article Ozone for water treatment. Where will we talk about the use of this gas to create cleaner water.
Ozone for water treatment is a time-tested technology. For more than a century, European countries have used ozonation as the preferred method of water purification. France was the first country to use ozone in water treatment.
The main difference between ozone as a reagent in water treatment compared to other substances is that it is produced from ambient air without the need to purchase replacement elements, reagents, etc.
Ozone is an active chemical compound consisting of three oxygen atoms. This compound is stable, the third extra oxygen atom is easily split off and super-actively interacts with the surrounding compounds. The technology of water ozonation is based on this phenomenon.
Ozone, due to its increased reactivity, oxidizes organic impurities, makes them insoluble, promotes their coarsening and, thus, increases the efficiency of the next stages of water purification, where these compounds are filtered out.
Ozone oxidizes iron, manganese, heavy metals dissolved in water, converts them into an insoluble state and facilitates their further removal.
No unpleasant or harmful odors. If hydrogen sulfide and ammonia are present in water, then ozonation of water completely eliminates these substances.
Ozone has a partial antiscale effect. Water ozonation slows down the formation of calcium salts on the walls of a hot pipeline and partially removes existing chalk deposits.
Modern ozone technologies are becoming less and less expensive due to the use of semiconductors. Since the effect of ozonation is complex, when purifying water for the whole house in many cases, especially with "heavy" water, it is possible to provide for the inclusion of this technology.
An example of the organization of water purification using ozone.
This is not a recipe for all ills, it is an attempt to show by example how ozonation can be used in water treatment.
Assume the situation: source water contains 2.5 mg/l of dissolved iron, oxidizability 12 mgO2/l, turbidity 5 mg/l, color 30 degrees. That is, the water is cloudy, green, a lot of organic matter and iron. Not the worst situation, a simple iron remover can handle this. But let's say we're going to use less expensive ozonation.
There is a rule of thumb that the dose of ozone for water treatment for iron removal is 0.14*, i.e. 0.14 times the iron concentration. Unfortunately I don't remember the source. In our case, the ozone dose will be 0.35 mg/L. Since oxidizability is a complex indicator, and in fact it is not known what is there, it is possible to accurately calculate the dose of ozone only in practice. Approximately ozone in our example needs 2 mg/l. Accordingly, 2000 milligrams of ozone, or 2 grams, is needed per 1000 liters. 1000 liters is the amount of water that a family of 3-4 people needs per day.
Ozonizers are divided by productivity: 1 g/hour, 2 g/hour, 4 g/hour, etc. The more grams per hour, the more expensive. Suppose we have chosen an ozonator for 1 g/hour. So, according to our example, it will take 2 hours to process water. How will we supply ozone? It is very simple - to gurgle with a compressor in a storage tank. Bubbles of air saturated with ozone pass through the water, oxidize everything that can be oxidized, and burst on the surface of the water. Unused ozone must be removed, as ozone is quite toxic. To do this, an activated carbon filter is installed at the outlet of the tank, which decomposes ozone. All this should be in a well-ventilated area.
Water settles, iron and organics are coarsened, and they can already be filtered at the next stage of water purification using conventional cartridge-type mechanical filters. It will not be superfluous to have an activated carbon filter and a mesh backwash filter. But it already needs to be looked at in terms of money.
So, we need: an ozonator with a capacity of 1 g / hour, a storage tank of 1000 liters, a compressor for supplying an ozone-air mixture to the tank, an ozone supply system to the tank, a coarse filter, a pumping station, mechanical water purification filters.
Schematically it will look like this:
So, water comes from a well, is collected in a tank. The water level is controlled by a float from a submersible pump and a solenoid valve. Everything together is connected to a timer, which allows water to be filled only at night. Another timer includes an ozonator and a compressor for supplying an air-ozone mixture to the water. The timer is programmed for 2 hours of operation. After 2 hours, it turns off the ozonizer and compressor.
During these 2 hours, ozone with air enters the tank through a hose with holes for a uniform supply of ozone throughout the entire volume of the tank. Iron is oxidized, organics are oxidized, they become larger and precipitate.
Then the inhabitants of the house get up, open the tap - and the pumping station supplies the already purified water through a series of filters (for example, 100 micron mesh, 30 micron cartridge corrugated, 5 micron cartridge and activated carbon filter) into the house.
As a result, water does not contain iron and has much less organic matter.
In order for the removal of impurities to be more complete, the ozonation time is simply increased. The order of the experiment is simple - they poured water into the tank, passed ozone for 2 hours, an hour, 3 hours, 4 hours and compared the appearance of the water.
It must be remembered that in polluted water, ozone almost completely decomposes and becomes safe for humans in 20, and to be sure, in 30 minutes. That is, you can drink water only after this time.
We count the time: the beginning of filling the tank at one in the morning. Filling the tank 2 hours - 3 am. The time for ozone destruction in water is 30 minutes. 3:30 a.m. Water is ready for use.
The cost of the project is minimal, of the replaceable elements - only cartridges for mechanical cleaning of carbon filtration, which would be present in any water treatment scheme - both with and without ozone. There are no other replaceable elements and consumables - no replacement of the catalytic load, no costs for potassium permanganate or salt.
Where do you get ozone generators? Mostly from those companies that deal with swimming pools. They will prompt and show, and possibly install.
Thus, ozonation, with the right approach, is a complex water treatment.
Based on materials http://voda.blox.ua/2008/10/Kak-vybrat-filtr-dlya-vody-34.html
Unlike chlorination and fluorination of water, ozonation does not introduce anything extraneous into the water (ozone quickly decomposes). At the same time, the mineral composition and pH remain unchanged.
Ozone has the greatest disinfecting property against pathogens.
Organic substances in the water are destroyed, thereby preventing the further development of microorganisms.
Without the formation of harmful compounds, most chemicals are destroyed. These include pesticides, herbicides, petroleum products, detergents, sodium salts, sulfur, nitrogen and chlorine compounds, which are carcinogens. The concentration of asbestos and heavy metals is reduced. Metals are oxidized to inactive compounds, including iron, manganese, aluminum, etc. The oxides precipitate and are easily filtered.
Quickly disintegrating, ozone turns into oxygen, improving the taste and healing properties of water.
Water treated with ozone is bacteriologically and chemically safe.
78. What determines the required time for water treatment?
The ability of ozone to dissolve in water depends on the temperature of the water and the area of contact of gases with water. The colder the water and the smaller the diffuser, the less ozone will be dissolved. The higher the temperature of the water, the faster the ozone breaks down into oxygen and is lost through evaporation.
Larger or smaller concentrations of ozone are needed depending on the degree of water pollution. For example, in Russia, a dose of 2.5 mg of ozone per liter of water is required to purify surface water in the middle and northern regions. For the southern regions, 8 mg per liter is needed.
79. How does ozone affect iron and manganese?
Dissolved iron is often found in natural waters. Its colloidal particles (up to 0.1 - 9.01 microns) cannot be secured by the usual method. They need to be pre-oxidized. Manganese usually accompanies iron. They are easily oxidized by ozone to insoluble compounds, forming large flakes that are easily filtered.
Organic compounds containing iron and manganese are first broken down by ozone and then oxidized. This is the most effective method of purifying water from such compounds.
80. Is additional water filtration necessary after ozonation?
If the water contained a large amount of complex compounds, then as a result of ozone treatment, various precipitations fall out in it. This water needs to be further filtered. For this filtering, you can use the simplest and cheapest filters. At the same time, their service life will be significantly extended.
81. Should I be afraid of a long time of water treatment with ozone?
Treatment of water with an excess amount of ozone does not entail harmful effects. The gas quickly turns into oxygen, which only improves the quality of the water.
82. What is the acidity index of water that has undergone ozonation?
Water has a slightly alkaline reaction PH = 7.5 - 9.0. This water is recommended for drinking.
83. How much does the oxygen content in water increase after ozonation?
The oxygen content in water increases 14-15 times.
84. How quickly does ozone decay in air, in water?
In the air after 10 minutes. the ozone concentration is reduced by half, forming oxygen and water.
In cold water after 15-20 minutes. ozone splits in half, forming a hydroxyl group and water.
85. What determines the concentration of ozone and oxygen in water?
The concentration of ozone and oxygen depends on impurities, temperature, water acidity, material and container geometry.
86. Why is the O 3 molecule used and not O 2 ?
Ozone is about 10 times more soluble in water than oxygen. The lower the water temperature, the longer the storage time.
87. Why is it good to drink oxygenated water?
The consumption of glucose by tissues and organs increases, the oxygen saturation of the blood plasma increases, the degree of oxygen starvation decreases, and blood microcirculation improves. It has a positive effect on the metabolism of the liver and kidneys. The work of the heart muscle is supported. Respiratory rate decreases and tidal volume increases.
88. How long does it take to ozonize water?
The more saturated with impurities the water, the longer the processing time. So, for example, ozonation of 3 liters of tap water takes 10 - 15 minutes. The same volume of water taken from a reservoir, depending on the season of the year and the level of pollution, should be carried out three to four times longer.
89. What is the best way to ozonize water in a bowl or jar?
It is better to choose glassware with a tapering neck (jar) to create a greater concentration of ozone in a limited volume.
90. When is it better to process water for tea, before or after boiling?
91. Is it possible to ozonize mineral water?
All minerals are preserved in such water, it becomes safe and oxygenated.
92. Why ozonize food?
Ozone removes organic and inorganic harmful substances, viruses, mold, and worm eggs from food products.
Chicken, beef, pork, fish, bred under industrial conditions, are fed with antibiotics and anabolics. Plants are fertilized and sprayed with products that accelerate growth and protect them from pests and diseases. These substances, getting into the body with food, are sources of metabolic disorders or, in other words, harm our health.
Ozonation of food products is an environmentally friendly way to cleanse them of various contaminants, which increases their consumer properties.
93. Is it necessary to ozonize cereals?
Yes, you have to.
94. How to process meat?
The meat must not be frozen.
Pre-cut into pieces of about 2 cm and dip in water for 10 minutes. Process 15 to 25 min.
95. Do I need to process products intended for storage?
Preferably. Ozone treatment increases shelf life.
96. Does ozone destroy the nutrients contained in vegetables, meat, fruits?
All nutrients are preserved.
97. Should eggs be processed?
Treating the eggs with ozone extends the shelf life and prevents the possibility of Salmonella contamination.
98. How to handle alcoholic beverages?
Treat vodka and wine in the same way as water, i.e. 10 - 15 min.
99. Can you disinfect dishes with ozone?
Yes! It is good to disinfect children's dishes, canning dishes, etc. To do this, place the dishes in a container with water, lower the air duct with a divider. Process for 10 - 15 minutes.
100. What materials should be utensils for ozonation?
Glass, ceramic, wood, plastic, enamelled (no chips or cracks). Do not use metal, including aluminum and copper utensils. Rubber does not withstand contact with ozone.
101. Shoe processing. Is it possible to get rid of persistent odor?
Yes! Place shoes in a plastic bag. Remove the diffuse stone from the air duct. Direct the jet into the toe of the boot. Tie up the package. Process for 10 - 15 minutes.
102. How to eliminate an unpleasant smell in household appliances?
The outlet air duct of the ozonator without a nozzle is placed in the refrigerator or washing machine and the ozonator is turned on for 10-15 minutes for complete deodorization with the doors of the refrigerator or washing machine closed.
103. How to treat underwear and bed linen with ozone?
Put underwear or bed linen in a plastic bag, where to place the ozonator air duct without a nozzle. Tie the top of the bag without pinching the air duct, and disinfect for 10-15 minutes. This method is very convenient for processing baby clothes and diapers, because. eliminates the need for ironing.
104. Can ozone degrade the color of a material?
The use of ozonated water when washing clothes gives the products brightness, contrast, freshness, and also disinfects them.
105. Is the use of air ozonation effective to eliminate the smells of smoky premises and premises after repair (odors of paint, varnish)?
Yes, it's effective. Processing can be carried out several times.
106. Is it necessary to ozonize the air in air-conditioned rooms?
After the air passes through air conditioners and heating devices, the oxygen content in the air decreases and the level of toxic components of the air does not decrease. In addition, old air conditioners themselves are a source of pollution and infection and lead to the “closed room syndrome”, manifested by headache, fatigue, and frequent respiratory illnesses. Ozonation of such premises is simply necessary.
107. Can an air conditioner be disinfected with ozone?
Yes, you can and should.
108. Can ozonized water be used for plants?
Yes, ozonated water can be used to water indoor plants and treat seeds with it.
109. The principle of operation of the ozonator.
Ozone is obtained from the air entering the device due to the operation of the pump. Under the influence of an electric discharge, oxygen molecules in the air are excited and disintegrate into atoms. The released atoms are attached to oxygen molecules for a while, forming ozone.
110. The term of use of the ozonator.
Warranty period of service - 1 year. The term of use of the ozonizer is from 5 to 10 years, provided that it works no more than 6 hours a day. The time of continuous operation should not exceed 30 minutes. A break between switching on is at least 10 minutes.
111. How to choose the place of work of the ozonizer?
It is best to hang it on the wall. It should be remembered that ozone is heavier than air, so it is advisable to place the device high enough. When treating water, in order to avoid backflow, the ozonizer must be located above the vessel with water.
112. What is the role of diffuse stone? Does it introduce elements of pollution?
A diffuse stone is used in water ozonation and plays the role of an ozone jet divider, creating a large area for the reaction of ozone molecules with water. It does not react with ozone itself. Being constantly in the ozone environment, it is not a source of pollution. The diffuse stone should only be immersed in water. In thick liquids, clogging of the dissecting tubules of the stone occurs. Thick liquids (milk, vegetable fats) should be ozonated using a tube without a diffuser attachment.
If necessary, you can buy similar diffuse stones at a pet supply store.
113. How to check the performance of the ozonator?
Signs of a malfunctioning ozonator:
no ozone smell;
no sound from a running generator or fan;
too noisy operation of the device.
If, with outward signs of normal operation of the ozonizer, you do not smell ozone, drop a few drops of blue ink into a glass of water. Lower the air duct with the diffuse diffuser into the water. A sign of proper operation is the discoloration of the water.
114. Can an ozonator be used continuously?
For rational use, the device must be turned off for 10-15 minutes every 30 minutes of operation.
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Please compare the features of ozone and oxygen according to these criteria! and got the best answer
Answer from Irina Ruderfer[guru]
1. A chemical element that forms a substance - oxygen, chem. symbol O, for both
2. Molecular chemical formula: oxygen O2, ozone O3
3. Aggregate state, color, smell, solubility in water
Oxygen under normal conditions is a colorless, tasteless and odorless gas, slightly soluble in water (4.9 ml/100 g at 0 °C, 2.09 ml/100 g at 50 °C)
Ozone under normal conditions is a blue gas with a specific smell. Solubility in water at 0 ° C - 0.394 kg / cu. m; (0.494 l / kg), it is 10 times higher than oxygen.
4. Reactivity
Both modifications are oxidizers, but ozone is much stronger
As a rule, the oxidation reaction proceeds with the release of heat and accelerates with increasing temperature. Ozone is a powerful oxidizing agent, much more reactive than diatomic oxygen. Oxidizes almost all metals (with the exception of gold, platinum and iridium) to their highest oxidation states. Oxidizes many non-metals.
5. Being in nature
Oxygen is the most common element on Earth, its share (as part of various compounds, mainly silicates), accounts for about 47.4% of the mass of the solid earth's crust. Sea and fresh waters contain a huge amount of bound oxygen - 88.8% (by mass), in the atmosphere, the content of free oxygen is 20.95% by volume and 23.12% by mass. More than 1500 compounds of the earth's crust contain oxygen in their composition.
Ozone is formed in many processes accompanied by the release of atomic oxygen, for example, during the decomposition of peroxides, the oxidation of phosphorus, etc.
When air is irradiated with hard ultraviolet radiation, ozone is formed. The same process takes place in the upper layers of the atmosphere, where the ozone layer is formed and maintained under the influence of solar radiation.
Atmospheric ozone plays an important role for all life on the planet. Forming an ozone layer in the stratosphere, it protects plants and animals from harsh ultraviolet radiation. Therefore, the problem of the formation of ozone holes is of particular importance. However, tropospheric ozone is a pollutant that can threaten human and animal health and damage plants.
6. Meaning
Oxygen - see Wikipedia
The use of ozone is due to its properties:
strong oxidizing agent:
o for sterilization of medical devices
o when receiving many substances in laboratory and industrial practice
o for whitening paper
o for cleaning oils
strong disinfectant:
o for purification of water and air from microorganisms (ozonation)
o for disinfection of rooms and clothes
Answer from 2 answers[guru]
Hello! Here is a selection of topics with answers to your question: Please compare the features of ozone and oxygen according to these criteria!
The interaction of pollutants with ozone occurs due to a direct reaction with ozone molecules or with radicals that appear during its decay. Ozone interacts more actively with anions than with neutral and cationic substances.
Ozone, being an active oxidizing agent, interacts with many organic and inorganic substances. Of the halogens, fluorine does not react with ozone and chlorine practically does not interact. Bromine is oxidized by ozone first to hypobromite and then to bromate compounds. In this case, the resulting bromide can interact in parallel with substances of organic origin and ammonia. Iodine is oxidized by ozone very quickly with the formation of iodates and iodous acid. Salts of halogenated acids are no longer susceptible to ozone oxidation. Almost neutral to ozone are nitrogen and its compounds, including ammonia and ammonium ions, as well as nitrates, with the exception of amines, which interact well with hydroxyl radicals. Toxic cyanides are easily oxidized by ozone to cyanates, further oxidation of which occurs very slowly and accelerates only in the presence of copper ions, slowing down in the presence of iron ions in solution. Sulfur and sulfite, when interacting with ozone, are oxidized to sulfates. As for reactions with metals, ozone rather actively oxidizes iron and manganese, cobalt and nickel, forming oxides and hydroxides that are removed from the solution during flocculation or filtration. Chromium is practically passive with respect to ozone, although under certain conditions it can be oxidized by it to the maximum oxidation state, hexavalent chromium.
1.1 Introduction
Ozone was discovered in 1840 by the Swiss chemist Christian Schombein, after experiments on the electrolysis of acids. Very soon, as a result of a number of studies, it was shown that ozone is triatomic oxygen, a gas under standard conditions, the characteristic properties of which are its ability to oxidize many substances and disinfect microflora. These properties were very soon used in the drinking water treatment industry. At the very end of the 90s of the 19th century, attempts were made in the Netherlands and Germany to disinfect drinking water using ozone. The generally recognized date of birth of ozone water treatment technology is considered to be 1906, when a water treatment plant began operating in the French city of Nice, bearing the symbolic name "Good Way" ("bon voyage") with a water capacity of 22.5 m³ / day. The station operated successfully until 1970, when it was modernized. This practice has since become widespread, as evidenced by the following data: From 30 to 300, and in the USA from 1954 to 1997 from 10 to 5500, respectively.
In Russia, the effectiveness of ozonation for water treatment was evaluated almost at the same time as abroad. In 1901, the 5th water congress heard a report by engineer N.P. Zimin on water ozonation; the latter characterized "ozonation of water as a means of eliminating the shortcomings of its filtration in urban water supply systems."
In 1905, an experimental plant for water ozonation was put into operation at the Peter and Paul Hospital in St. Petersburg. It was found that the number of bacteria was reduced by an average of 98.8%, the taste improved and there was no color in the purified water. In 1911, the largest water ozonation station in the world at that time began to operate in St. Petersburg. When opened, its capacity was 44.5 thousand m³/day of treated water.
An overview of ideas about ozone, its production and application in various fields at the beginning of the 20th century is given in the book of the Russian engineer V.V. Karaff-Korbutt "Ozone and its application in industry and sanitation", published in 1912.
One of the first Soviet monographs on this topic is the book by V.F. Kozhinova and I.V. Kozhinov "Ozonation of water". These works belong to the last century. Significant progress has been made in the production of ozone recently, and very promising new uses for ozone have been opened up.
1.2 Ozone, its properties and basic reactions with various substances.
1.2.1 Physical and chemical properties of ozone.
Under normal conditions, ozone is a gaseous, colorless substance with a pungent odor. It is believed that the smell of ozone is the smell of fresh air after a thunderstorm. This is true, but only if its concentration is very low and is a fraction of the maximum permissible concentrations (MPC). A detailed description of the physicochemical properties of ozone is considered in numerous works, in particular. Some basic physical and chemical properties of ozone are given in the table 1.1 .
Table 1.1.Basic physical and chemical properties of ozone.
Pure ozone is explosive. It is not stable and decomposes quickly. The decomposition of ozone is influenced by many factors: temperature, pH, the presence of substances to be oxidized, etc.
1.2.2 Solubility of ozone in water
When ozone dissolves in water, its concentration gradually increases and reaches the limit values for these conditions.
The solubility of ozone in water can be expressed either in the form of the so-called Bunzea coefficient - β, which shows the ratio of the volume of dissolved ozone reduced to normal conditions to the volume of water (Voz/Vv), or in absolute values of dissolved ozone (g/l). It is assumed that the dissolution process obeys Henry's law, according to which the amount of dissolved ozone is proportional to the pressure of gaseous ozone over the solution. This law can be written as:
C static = β
C stats- ozone solubility, g/l;
β is the Bunsen coefficient;
M– ozone density = 2.14 g/l;
Pγ is the partial pressure of ozone in the considered gaseous medium.
It should be noted that the solubility of ozone is much higher than the main atmospheric gases - nitrogen and oxygen, but weaker than such oxidizing agents as chlorine and chlorine dioxide. The solubility of ozone increases with decreasing water temperature. At the same time, there is a large scatter in the experimental data of various authors, presented in the table 1.2 .
Table 1.2 Solubility of ozone in water.
|
T, °С |
According to |
According to |
According to |
||||
|
Β (l O3/l H2O) |
Solubility, g/l |
Β (l O3/l H2O) |
Solubility, g/l |
Β (l O3/l H2O) |
Solubility, g/l |
||
1.2.3 Decomposition of ozone in water
Simultaneously with the dissolution of ozone in water, its decomposition occurs. At the same time, the rate of its decay, as well as the reciprocal value “lifetime”, depends on the temperature of the water and, mainly, on the composition of the water. First of all, from the presence of various impurities in the water, especially some organic compounds and metal ions.
The lifetime in single-distilled water is 20 minutes, and in ordinary water a few minutes.
1.3 Reactions of ozone with inorganic substances.
Ozone can react with various substances in water by two different mechanisms - directly as ozone (in molecular form) and in the form of the OH* radical, which occurs when ozone decomposes in water. It is believed that in neutral water these 2 reaction channels are distributed equally. In an acidic medium, the molecular mechanism predominates, while in an alkaline medium, a radical one.
Since ozone acts as an oxidizing agent in chemical reactions, its oxidizing ability can be judged by the so-called oxidation potential value. The value of the values of the oxidation potentials of various substances - oxidizing agents are given in the table 1.3 .
Table 1.3. Redox potentials of various substances.
From table 1.3. It follows that ozone is a very strong oxidizing agent. Of the stable substances second only to fluorine And outperforms chlorine by one and a half times.
1.3.1 Reaction of ozone with metals.
Being a strong oxidizing agent, ozone in the gas phase oxidizes most metals with the exception of gold and some metals of the platinum group, oxides of higher oxidation states, but these reactions usually require the presence of traces of moisture. Alkali and alkaline earth metals are oxidized by ozone in the same way as by oxygen, only at a faster rate. Interestingly, plates of gold and platinum (and, to a lesser extent, silver and copper) acquire a negative electrical charge in an atmosphere of dry ozone.
Metallic silver is well oxidized by ozone, both in wet and dry gas in the temperature range from room temperature to 1000C with the formation of brown oxide Ag2O. The latter is a good catalyst for ozone decomposition.
Metallic mercury, like silver, is oxidized by ozone already at room temperature, while the surface loses its inherent mobility, sticks to glass, and the mercury meniscus becomes flatter. Molten tin at 5000C in the presence of 1% ozone is covered with an oxide film. Ozone in the presence of water oxidizes lead to form hydroxide. In the absence of moisture, the main product of this reaction is dark brown lead dioxide. Polishing surfaces of copper, zinc, iron, various steels in an atmosphere of moist ozone are covered with loose oxide films, as in ordinary atmospheric corrosion. In a dry atmosphere, these surfaces are passivated by ozone, forming protective films. A similar picture is observed for copper and zinc.
The interaction of metals with ozone in solutions is more diverse. So, if ozone in the gas phase does not affect gold, then its small additions contribute to the dissolution of gold in solutions of potassium cyanide by 1.5-2 times and silver by 3 times.
The strong oxidizing properties of ozone are proposed to be used for the selective oxidation of minerals in an aqueous medium. This is how barium and strontium sulfates were obtained. Heavy metal sulfides are valuable metallurgical raw materials, so their conversion into water-soluble sulfates (or oxides) has attracted attention for a very long time. At present, a large laboratory or semi-industrial array of experimental data has been accumulated on this issue. We are talking about the creation based on the leaching of metals by ozone from acid slurry sulfides. This hydrometallurgical technology has a number of advantages over currently used pyrometallurgy.
1.3.2 Reactions of ozone with non-metals.
Non-metals react with ozone in different ways. Dry phosphorus, both white and red, is oxidized by ozone to P2O5. Arsenic, like phosphorus, sulfur, selenium, tellurium, in a dry atmosphere is oxidized to oxides, and in the presence of water, the corresponding acids are formed, and in alkaline water, salts.
Nitrogen does not react with ozone, but nitrogen oxides (some of them) react very easily, making it possible to eliminate them from the gas emissions of a number of enterprises. The second nasty ingredient in many gaseous emissions, sulfur dioxide, does not react with ozone in the gas phase, but reacts in solution. Cyanides (cyanide ions) readily react with ozone in aqueous solution, and these processes, as well as the elimination of iron and manganese from water, are discussed in detail below.
Ozone oxidizes all halogens, except for fluorine, and with an increase in the element's atomic number, the ease of oxidation increases. These processes are briefly discussed in the section on water treatment in swimming pools.
1.4. Reactions of ozone with organic compounds.
It is rather difficult to characterize the reactions of all basic organic substances with ozone. It is possible only to note some general points when considering the direct effects of ozone.
Saturated alkyl compounds react very slowly with ozone. Most chlorinated hydrocarbons and even unsaturated hydrocarbons do not react directly with ozone. In this case, indirect interaction with ozone through the OH* radical is necessary. Benzene is oxidized by ozone very slowly, and polycyclic hydrocarbons are faster. The reaction time of ozone with phenolic compounds is a few seconds.
Carboxylic acids, keto acids and a number of similar compounds are the final stable products of the process of oxidation of organic substances with ozone.
Amines at neutral pH values react very slowly with ozone, at pH > 8, oxidation reactions are faster. However, in general, the oxidation reactions of amines proceed through OH radicals. Quaternary amines (aromatic amines) react with ozone faster.
Alcohols can interact with ozone, forming hydroperoxides as intermediates. At the same time, they are oxidized to carboxylic acids, while secondary alcohols are oxidized to ketones. Carboxylic acids with ozone react weakly or do not react at all.
Mercaptans are oxidized with ozone to sulfonic acids. Bisulfites and sulfonic compounds are intermediates. Amino acids containing sulfur (cysteine, cestine and methionine) react quickly.
Amino acids (a component of proteins) react by an electrophilic mechanism.
Among pesticides containing esters of phosphoric acid, parathion is the most well-known. Ozonation of this compound results in paraoxon, which is more toxic than parathion. Further ozonation converts paraoxon into less toxic substances (for example, into nitrophenol, which is then oxidized to end products - nitrates and CO2).
1.5. Ozone as an inactivator of microflora.
As mentioned above, ozone has a powerful bactericidal and virulent (inactivating viruses) effect.
The scientific literature (especially the popular one) often claims that ozone does inactivate bacteria and viruses more than chlorine (and this will be illustrated below), but this benefit must be quantified with certain reservations.
Currently, when evaluating the effectiveness of a disinfectant, the so-called SHT criterion, i.e. the product of the concentration of the reagent and the duration of the action.
It can be said that:
EXPOSURE (INACTIVATION) = Concentration * Exposure time.
Table 2.1. presented for comparison values SHT criteria for various microorganisms - disinfecting agents.
Table 2.1. Meaning SHT criterion for various microorganisms (99% inactivation at 5-25 °C. SHT criterion (Mg/l*min)
Clearly, ozone is superior to disinfectants such as chlorine, chloramine, and chlorine dioxide, but in different ways for different pathogens. For pathogens such as Escherichia coli (E-coli), ozone is more effective than chlorine, but not by much. At the same time, for cryptosporidium, the ratio SHT criteria for these disinfectants approaches 1000. In principle, ozone can compete with disinfectants such as chlorine, bromine, iodine, chlorine dioxide and silver.
Molecular gaseous chlorine, dissolving in water, decomposes, producing hydrochloric acid HOCl, which, in turn, dissociates in water into the anion СlО- and the cation Н+. The degree of this dissociation is determined by the acidity of the medium. It has been established that at pH = 8 the concentration of non-dissociated acid is ≈ 20%, and at pH = 7, the concentration of HClO is ≈80%. Since it is HClO that has a strong bactericidal effect, when using chlorine (even in the form of hypochlorite), it is necessary to maintain the optimal pH value.
Iodine, as a disinfectant, is used to inactivate microflora in small water treatment systems and sometimes in small swimming pools. In terms of its disinfecting properties, iodine is weaker than chlorine, and especially ozone, but it is more convenient to transport.
Bromine, in principle, can be used for disinfection purposes, however, in the presence of other oxidizing agents, it forms bromates, derivatives of the acid HBrO3, which are very harmful and have a low MAC value. This problem - the formation of bromates during the ozonation of bromine-containing waters - is quite serious, and we will dwell on it in the section "Use of ozone for the preparation of drinking water". Silver is an exotic but very weak disinfectant and is rarely used.
In addition, recently, domestic and foreign industry offers a number of organic substances with a strong disinfectant effect. However, they all have certain disadvantages and have not yet been widely used.
Thus, only chlorine can be a real competitor to ozone. Unfortunately, chlorine has significant disadvantages:
For a long time, liquid chlorine from pressurized cylinders was used, which was a big problem in terms of safety. Currently, chlorine is obtained or hypochlorite is used, which, dissolving in water, creates the required concentration of free chlorine. It should be noted that the term "free chlorine" refers to the concentration of hypochlorous acid HClO. The use of hypochlorite necessitates the storage of a supply of reagent, but hypochlorite decomposes during storage, and the free chlorine content drops.
One of the main unpleasant properties of chlorine is that when it reacts with most organic compounds, a whole range of organochlorine derivatives arises, most of which are highly toxic. Chlorophenols and especially polychlorophenols, some of the latter, the so-called dioxins, are among the strongest organic poisons known at present, and the effect of these toxins is to destroy the human immune system, so that when talking about dioxins, the term "chemical AIDS" is sometimes used.
Chlorine reacts very easily with ammonia to form chloramines. These substances have a very weak disinfectant effect, but are extremely irritating to the mucous membranes of the eyes and nasopharynx. Chloramines are often referred to as "combined chlorine". This combined chlorine is 5-10 times more irritant than free chlorine.
Ozone can also form intermediate compounds (by products) during ozonation of gaseous and condensed media. Theoretically, it can be assumed that those formed by products are more toxic than ozone.
This problem has been the subject of research by many scientists around the world. The concentrations and composition of the intermediates that occur during ozonation are highly dependent on whether drinking water or waste water is being ozonated. Of course, in the first case, much less by products are formed and their composition is more obvious. All these issues will be discussed in the relevant sections of the review. The fairly consistent results of years of research can be summarized as follows:
In the vast majority of cases, the intermediate products of ozone oxidation of pollutants are LESS TOXIC than the original ingredients.
A direct comparison of the intermediates formed during comparative experiments on chlorination and ozonation showed that in the first case, much more undesirable by products are formed.
Direct comparison of chlorine and ozone as microflora disinfectants has been made in numerous experimental studies and at operating water treatment plants. Here are just a few of the well-known works:
M. Kane and Gleckner studied the effect of ozone and chlorine on cysts (dense shells that form around single-celled organisms) of Endamoeba hystolica and on the bacteria accompanying these cultures. It has been established that the time required for the destruction of these organisms at a residual ozone concentration of 0.3 mg/l is 2-7.5 minutes, and for chlorine (residual concentration of 0.5-1 mg/l) it is much longer - 15-20 minutes.
In the 1940s and 1960s, virologists in the United States and Germany conducted a series of studies with suspensions of the poliovirus in order to inactivate it with chlorine, ozone, and chlorine dioxide.
The conclusions from these studies can be summarized as follows:
Inactivation of the poliomyelitis virus with chlorine is achieved with a dose of 0.1 mg/l at a water temperature of 18 ºС; at a water temperature of 7 ºС, the dose of chlorine should be at least 0.25 mg/l.
Virus inactivation with ozone is achieved with a dose of 0.1 mg/l at a water temperature of 18 ºС, for cold water 7ºС the dose should be increased to 0.15 mg/l.
When using chlorine dioxide, a dose of 0.6 mg/l (18 ºC) must be used. For water with a temperature of 7 ºС, the dose of chlorine dioxide should be 1 mg/l.
According to Naumann, poliomyelitis pathogens are destroyed by ozone in 2 minutes at a concentration of 0.45 mg/l, while with chlorination at a dose of 1 mg/l, this takes 3 hours.
According to some authors, ozone successfully eliminates microalgae and protozoa more actively than chlorine. So ozone at a concentration of 15 mg/l in 3 minutes destroys the species of protozoa, which retain their activity when water is treated with a dose of chlorine of 250 mg/l for a long time.
Larvae of the mussel zebra mussel died by 90% at an ozone dose of 0.9-1.0 mg/l, 98% at a dose of 2 mg/l, and completely at a dose of 3 mg/l. Adult forms of the mollusk died after a longer treatment with ozonized water (up to 30 min).
True, algae blooms, which usually thrive in open pools in sunlight, are slightly affected by ozone. Here shock doses of chlorine are used. This treatment is usually carried out at night during the preventive cleaning of such pools.
Ridenor and Ingalls from the USA treated suspensions of e-coli in distilled water with chlorine and ozone at Hp = 6.8 and a temperature of 1°C. Under these conditions, the bactericidal doses that caused the death of 99% of e-coli colonies were 0.25–0.3 mg/l for 16 min for chlorine, and 0.5 mg/l for 1 min for ozone.
The long history of the use of these two disinfectants in large wastewater treatment plants contains a wealth of factual material that makes it possible to judge their advantages and disadvantages. In the already mentioned book "Ozonation of Water" a number of interesting examples are given.
Thus, during the long-term operation of the station in Nice, the appearance of bacteria Escherichia coli and Clostridium pertringers has never been detected in ozonated water.
At the Belmont Filtration Station in Philadelphia (USA), ozonation of water has shown results in eliminating e-coli more successfully than results achieved with chlorination.
Studies on water ozonation were carried out at the Eastern Waterworks in Moscow. The effect of water disinfection with ozone when the total number of bacteria in 1 ml is 800-1200 units. is: at an ozone dose of 1 ml/l 60-65%, at a dose of 2 ml/l - 85%, at a dose of 3 ml/l - 90-95%. An acceptable dose of ozone should be considered 3-4 ml/l.
At the Rublevskaya waterworks (Moscow), ozonation of the water of the Moskva River was carried out. The total number of bacteria in 1 ml of water after the introduction of ozone decreased by 92-99% within a time period of 1-25 minutes. The germicidal dose of ozone corresponded to that after treatment, which could not detect e-coli in 500 ml. water. An increase in turbidity from 6.8 to 12 mg/l and color from 3.2 to 18 degrees. required an increase in the bactericidal dose of ozone from 3.2 to 4.1 mg/L.
Thus, comparing the work of the French water treatment station in Saint-Maur and the station in Chicago (USA), V.F. Kozhinov notes that in the first case, diseases of “water origin” were registered only in 1 case per 100 thousand inhabitants, although the concentration of residual ozone in water did not exceed 0.05 mg/l.
At the same time, there were outbreaks of gastrointestinal diseases in Chicago despite the very high chlorine content in tap water.
One of the greatest hygienists of the last century, Watson, expressed the following opinion at the international congress on water supply in Stockholm (July 1964): chlorine. Experiments carried out in Ashton (England) have shown that water decontaminated by ozone, circulating in a serviceable water supply network of pipelines, does not deteriorate in its quality. Control samples of ozonized water taken from the network were completely equivalent to samples containing residual chlorine in water taken from other sources. It has also been established that small amounts of residual chlorine present in pipelines cannot have any disinfecting effect on pollution caused by damage to communications. Those. the presence of residual chlorine in pipelines does not yet mean the indispensable bacterial purity of water, although it is often considered to be just that.
One of the authors of this review discussed this problem with the Zurich plumbing leaders, and they confirmed Watson's opinion that when clean pipes are used in water networks, re-contamination of ozonated water does not occur.
Even from this brief comparison of ozone with other oxidant-disinfectants, the benefits of ozone are undeniable.
Summarizing some results of an extremely brief comparison of ozone, chlorine and chlorine dioxide as an agent for cleaning and disinfecting water, we note that in a certain sense this dispute was resolved by life itself. Indeed, the experience of water treatment plants using ozone and chlorine fully testifies in favor of ozone.
1.6 Other benefits of ozone.
Due to the brevity of the review, we do not dwell here on such positive properties of ozone as the enhancement of coagulation-flocculation processes, effective impact on the microflocculation process, incomparably higher water quality in swimming pools using ozone instead of chlorine, and a number of others.
Finally, there is the issue of cost. There is an opinion that ozonation is much more expensive than chlorination. However, it is not. In the process of chlorination, it becomes necessary to remove excess chlorine from the water, to carry out the so-called dechlorination. This is usually done using special reagents. Taking into account this factor, as well as the trend of continuous price reduction for ozonation equipment and price increase for chlorine and chlorine products, the cost of these processes is currently almost comparable.
However, chlorination, if we talk about our country, is used more often than ozonation. Why? There are several reasons.
Working with chlorine, especially when it comes to bottles of liquid chlorine, is relatively simple. It is enough to unscrew the valve of the cylinder or pour a bucket of hypochlorite into the pool, and, as a first approximation, all problems with disinfection are solved. This is certainly easier than monitoring the concentration of ozone coming out of the ozonizer, given that the ozonizer is a relatively complex machine and you need to be sure that it does not turn off unexpectedly.
This is where the second (and maybe the first) reason for the low prevalence of ozone arises. Until very recently, the reliability of ozonation equipment left much to be desired, and the low level of automation required the use of relatively highly qualified service personnel.
In the section “Production of ozone”, we will dwell on the consideration of this problem in more detail and critically examine existing designs precisely from the angle of reliability and simplicity of equipment. Only the latest generation of Positron ozonizers allows, due to high automation and design reliability, to reduce the maintenance of ozonating equipment to a minimum, more precisely, to pressing one button.
1.7 Ozone toxicology
The toxic properties of ozone have been the subject of numerous studies since the 1940s. At this time, in Los Angeles (USA), and then in many other cities, the appearance of the so-called photochemical smog was observed. Under the influence of solar radiation, automobile emissions (hydrocarbons and nitric oxide) were transformed as a result of a complex chain of photochemical reactions into ozone and organic peroxides, including benzopyrene, a very strong carcinogen. At the same time, in some cases, the ozone concentration reached 10 MPC (≈ 1 mg/m³). Irritation of the eyes and mucous membranes of the respiratory tract has been observed in people exposed to photochemical smoke. After a certain time in the open air, the unpleasant symptoms disappeared.
Technological advances, and especially the use of catalytic converters for automotive emissions, have almost completely eliminated the causes of photochemical smog. Careful experimental studies on humans and animals have clarified quite fully the question of ozone toxicity. It can be said (in our opinion) that in a certain sense the fears about ozone toxicity are a myth. Yes, ozone is classified as a substance with the first class of danger. Its MAC is lower than that of such substances as chlorine and hydrogen cyanide (MAC for chlorine = 1 mg/m³, MAC for hydrogen cyanide = 0.3 mg/m³). The fact is that when establishing the MPC value, not only the lethal dose is taken into account, but also the vapor pressure of a given substance. Since ozone is an extremely volatile gas (Tº bp = -111 ºС), the toxicity value is high. But, it must be emphasized that for a century and a half of mankind's acquaintance with ozone, it is unknown no one case of fatal ozone poisoning. Yes, and it was not observed at all no one a case of severe ozone poisoning that would require a hospital stay. Ozone has the greatest effect on the respiratory system. Changes in respiratory rate, inhaled air volume, vital and residual lung capacity. But in the book of the Hungarian ozone specialist M. Horvath, an experiment is described in which 5 people were placed in a special chamber with a maximum exposure of 6 ppm ozone for 1 hour (6 ppm ≈ 120 MAC) and a minimum of 1.2 ppm (≈ 24 MAC) for 2.5 hours. Sense of taste, blood pressure, pulse rate were not detected. It was found that the sensation of smell was reduced, however it is not clear whether ozone affects the nervous system or "overrides" the smell of the sensor substance. There was also no change in the composition of the blood.
Experiments conducted on small animals have shown that the body becomes addicted to ozone, after which it is able to tolerate lethal doses. However, it is necessary to make an important remark about the lethal doses of ozone.
One of the authors of this review, when working with ozone, due to unforeseen circumstances, inhaled ozone at a concentration of 20-40 g / m³, which corresponds to (10-30) - 10³ ppm, and lies well above the lethal curve 4. The sensation was very unpleasant, but being in the open air completely restored normal breathing. Even if a person has a runny nose and does not smell ozone, there are now simple and reliable “ozone probes” on the market that allow you to quickly find any ozone leak.
1.8 Conclusion
Ozone, as a unique oxidizer-disinfectant, is widely used in the world, primarily in the field of drinking water treatment. In France, for example, there are several thousand water treatment plants that use ozone. Physico-chemical properties of ozone are very peculiar. It dissolves well in water, but decomposes quickly in it, especially if there are impurities of pollutants. Therefore, the lifetime, especially with a neutral pH, can vary from hours (ultrapure water) to seconds (alkaline solutions, organic impurities).
As a strong oxidizing agent (its oxidizing potential is inferior, among stable substances, only to fluorine), ozone oxidizes almost all metals, except for gold. With many substances, ozone reacts explosively. Ozone reacts with chlorine solutions in water, which is essential when these substances are used to treat water in swimming pools. Reactions with organic substances depend primarily on the nature of the organic substances. Compounds with unsaturated bonds oxidize very quickly. Other substances, like organic acids (oxalic, acetic, etc.), as well as alcohols and ketones, react very slowly. The rates of reactions with ozone in solution depend very strongly on the pH of the medium, since in an acidic environment, the molecular mechanism of oxidation is realized, where ozone itself acts, and in an alkaline environment, the OH* radical.
No less, and perhaps more valuable property of ozone is its extremely effective ability to eliminate microflora. Here it surpasses other common disinfectants (primarily chlorine) by 3-1000 times, depending on the type of pathogenic microflora. The effect of ozone on such microorganisms as fungi and algae is also detrimental, although in this case much depends on the processing conditions.
Despite these obvious advantages, in a number of industries (primarily in water treatment), chlorine and its compounds are often used instead of ozone. This is due to a number of prejudices. It is believed that the use of ozone is much more expensive than the use of chlorine. In a number of qualified comparisons of the cost indicators of ozone and chlorine treatment, when the cost of the final dechlorination process was taken into account, it was shown that the total costs are almost the same, and in some cases, when the transportation of chemical reagents is difficult or very expensive, the use of ozone is more profitable than other oxidizers-disinfectants.
True, the production of ozone itself is a technically more complex process than the production of chlorine. Previously, there were often complaints about the complexity of maintenance and reliability of ozonation equipment. Now this situation has changed for the better. The latest developments offered by the VIRIL GROUP are characterized by a high degree of automation. To turn on the ozonizer and its further operation, just press one button.
Finally, there is a preconceived notion about the extremely high toxicity of ozone gas. Indeed, for ozone there is a very low value of the maximum allowable concentration MPC = 0.1 mg/l. BUT this is primarily due to its very high volatility (ozone liquefies at -1110 C) In any case, in the 100 years of the existence of ozone, not a single serious case of ozone poisoning is known, not to mention fatal poisoning
1.9 References
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