The most common water treatment processes are clarification and disinfection.
In addition, there are special ways to improve water quality:
- water softening (removal of water hardness cations);
- desalting of water (reducing the overall mineralization of water);
- deferrization of water (reducing the concentration of iron salts in water);
- degassing of water (removal of gases dissolved in water);
- water neutralization (removal of toxic substances from water);
- decontamination of water (water purification from radioactive contamination).
Disinfection is the final stage of the water purification process. The goal is to suppress the vital activity of pathogenic microbes contained in water.
Based on the method of influencing microorganisms, water disinfection methods are divided into chemical or reagent; physical, or reagent-free, and combined. In the first case, the desired effect is achieved by adding biologically active chemical compounds to the water; Reagent-free disinfection methods involve treating water with physical influences, while combined ones use chemical and physical influences simultaneously.
Chemical methods of disinfecting drinking water include its treatment with oxidizing agents: chlorine, ozone, etc., as well as heavy metal ions. Physical - disinfection with ultraviolet rays, ultrasound, etc.
The most common chemical method of water disinfection is chlorination. This is due to high efficiency, simplicity of the technological equipment used, low cost of the reagent used and relative ease of maintenance.
When chlorinating, bleach, chlorine and its derivatives are used, under the influence of which bacteria and viruses in the water die as a result of oxidation of substances.
In addition to the main function - disinfection, due to its oxidizing properties and preservative aftereffect, chlorine also serves other purposes - controlling taste and odor, preventing algae growth, keeping filters clean, removing iron and manganese, destroying hydrogen sulfide, discoloration, etc.
According to experts, the use of chlorine gas poses a potential risk to human health. This is primarily due to the possibility of the formation of trihalomethanes: chloroform, dichlorobromomethane, dibromochloromethane and bromoform. The formation of trihalomethanes is due to the interaction of active chlorine compounds with organic substances of natural origin. These methane derivatives have a pronounced carcinogenic effect, which contributes to the formation of cancer cells. When chlorinated water is boiled, it produces a powerful poison - dioxin.
Studies confirm the relationship of chlorine and its by-products with the occurrence of diseases such as cancer of the digestive tract, liver, heart disorders, atherosclerosis, hypertension, and various types of allergies. Chlorine affects the skin and hair, and also destroys protein in the body.
One of the most promising methods for disinfecting natural water is the use of sodium hypochlorite (NaClO), obtained at the point of consumption by electrolysis of 2-4% solutions of sodium chloride (table salt) or natural mineralized waters containing at least 50 mg/l chloride ions .
The oxidative and bactericidal effect of sodium hypochlorite is identical to dissolved chlorine, in addition, it has a prolonged bactericidal effect.
The main advantages of water disinfection technology with sodium hypochlorite are the safety of its use and a significant reduction in environmental impact compared to liquid chlorine.
Along with the advantages of water disinfection with sodium hypochlorite produced at the point of consumption, there are also a number of disadvantages, primarily the increased consumption of table salt due to the low degree of its conversion (up to 10-20%). In this case, the remaining 80-90% of the salt in the form of ballast is introduced with a hypochlorite solution into the treated water, increasing its salt content. Reducing the salt concentration in the solution, undertaken for the sake of economy, increases energy costs and consumption of anode materials.
Some experts believe that replacing chlorine gas with sodium or calcium hypochlorite to disinfect water instead of molecular chlorine does not reduce but significantly increases the likelihood of trihalomethanes formation. The deterioration of water quality when using hypochlorite, in their opinion, is due to the fact that the process of formation of trihalomethanes is extended over time up to several hours, and their quantity, other things being equal, the greater the pH (a value characterizing the concentration of hydrogen ions). Therefore, the most rational method of reducing chlorination by-products is to reduce the concentration of organic substances at the stages of water purification before chlorination.
Alternative methods of water disinfection using silver are too expensive. An alternative method to chlorination was proposed for disinfecting water using ozone, but it turned out that ozone also reacts with many substances in water - with phenol, and the resulting products are even more toxic than chlorophenols. In addition, ozone is very unstable and is quickly destroyed, so its bactericidal effect is short-lived.
Of the physical methods of disinfecting drinking water, the most widespread is the disinfection of water with ultraviolet rays, the bactericidal properties of which are due to their effect on cellular metabolism and, especially, on the enzyme systems of the bacterial cell. Ultraviolet rays destroy not only vegetative, but also spore forms of bacteria, and do not change the organoleptic properties of water. The main disadvantage of the method is the complete lack of aftereffect. In addition, this method requires greater capital investment than chlorination.
The material was prepared based on information from open sources
Water is a factor that directly affects the quality of human life. A person’s mood in the morning after washing his face depends on its color and smell, and the well-being and health of the body depends on its composition.
Water, being the basis of life, easily spreads infectious diseases. To prevent the transmission of pathogens through drinking water, disinfection and disinfection of the liquid are used. These processes eliminate fungi, bacteria, bad taste and color, ensuring safe drinking water.
Purification and disinfection of drinking water for supply to residential buildings is carried out at water treatment stations of centralized water supply. There are also methods and installations for local use - in the form of small water purification systems from a well or methods that allow you to purify water collected in a bottle.
Classification of water disinfection methods
To choose the right disinfection method, contaminated water is analyzed. The number and type of microorganisms and the degree of collateral contamination are examined. The volume of water that will be treated and the economic factor are also determined.
Water that has undergone purification is transparent and colorless, odorless and has no taste or aftertaste. To achieve this effect, the following groups of methods are used:
- physical;
- chemical;
- combined.
Each group has its own distinctive characteristics, but all methods, in one way or another, allow the removal of pathogenic microorganisms from water. You can obtain detailed information on equipment for water purification and disinfection from the KVANTA+ company in Tyumen.
The chemical method is working with reagents added to water. Physical disinfection is carried out using temperature or various radiations. Combined methods combine the work of these two groups.
The most effective ways
Infectious safety of water is an important and pressing problem, which is why many methods have been invented to rid water of microorganisms. Disinfection methods continue to improve. They become more effective and accessible. Nowadays, the following methods are considered the best:
- heat treatment using high temperatures;
- ultrasonic treatment;
- reagent methods;
- ultraviolet irradiation of liquid;
- high-power electrical discharges.
Physical methods of water disinfection
Before them, the water must be purified to remove suspended matter and impurities. For this purpose, coagulation, sorption, flotation and filtration are used.
This type of method includes the use of:
- ultrasound;
- ultraviolet;
- high temperatures;
- electricity.
Ultraviolet disinfection
The disinfecting effect of ultraviolet radiation has been known for a very long time. Its work is similar to sunlight, which successfully destroys unadapted microorganisms outside the Earth's ozone layer. Ultraviolet radiation affects cells, creating cross-links in DNA, as a result of which the cell loses the ability to divide and dies (Fig. 2).
The installation consists of lamps placed in quartz cases. The lamps produce research that instantly destroys microorganisms, and the covers do not allow the lamps to cool down. The quality of disinfection when using this method depends on the transparency of the water: the cleaner the incoming liquid, the further the light spreads and the less the lamp becomes dirty. To do this, before disinfection, the water goes through other stages of purification, including mechanical filters. The reservoir through which the water flows is usually equipped with a stirrer. Mixing the layers of liquid allows the disinfection process to proceed more evenly.
Design of a UV disinfection installation It is important to know that lamps and covers require regular maintenance: the structure must be disassembled and cleaned at least once a quarter.
Then the efficiency of the process will not deteriorate due to the appearance of scale and other contaminants. The lamps themselves must be replaced once a year.
Ultrasonic disinfection units
The operation of such installations is based on cavitation. Due to the intense vibrations to which water is subjected due to high-frequency sound, numerous voids are formed in the liquid, as if it “boils”. An instantaneous pressure drop leads to rupture of cell membranes and death of microorganisms.
Equipment for ultrasonic water treatment is effective, but requires high costs and proper operation. It is important that the staff knows how to handle the device - its effectiveness depends on the quality of the equipment settings.
Thermal disinfection
This method is extremely common among the population and is actively used in everyday life. Using high temperature, that is, boiling, water is purified from almost all possible pathogenic organisms. In addition to this, water hardness is reduced and the content of dissolved gases is reduced. The taste of the water remains the same. However, boiling has one drawback: the water is considered safe for about a day, after which bacteria and viruses can again settle in it.
Boiling water is a reliable and simple method of disinfection Electric pulse disinfection
The technique is as follows: electrical discharges entering the water create a shock wave, microorganisms fall under the hydraulic shock and die. This method does not require preliminary purification and is effective even with increased turbidity. Not only vegetative, but also spore-forming bacteria die. The advantage is the long-term preservation of the effect (up to 4 months), but the disadvantage is the considerable cost and high energy consumption.
Chemical methods of water disinfection
They are based on chemical reactions that occur between a contaminant or microorganism and a reagent added to a liquid.
When using chemical disinfection, it is important to control the dose of the reagent.
It must be accurate. A lack of substance will not be able to fulfill its purpose. In addition, a small amount of the reagent will lead to increased activity of viruses and bacteria.
To improve the performance of the chemical, it is added in excess. In this case, harmful microorganisms die, and the effect lasts for a long time. The excess is calculated separately: if you add too much, the reagent will reach the consumer, and he will be poisoned.
Chlorination
Chlorine is widespread and used in water treatment in many countries around the world. It successfully copes with any volume of microbiological contaminants. Chlorination leads to the death of most pathogenic organisms and is cheap and accessible. In addition, the use of chlorine and its compounds makes it possible to extract metals and hydrogen sulfide from water. Chlorination is used in municipal drinking water systems. It is also used in swimming pools where large numbers of people gather.
However, this method has a number of disadvantages. Chlorine is extremely dangerous, causes cancer and cell mutations, and is toxic. If excess chlorine does not disappear in the pipeline but reaches the public, it can lead to serious health problems. The danger is especially strong during transition periods (autumn and spring), when, due to increased pollution of surface waters, the dose of the reagent during water treatment is increased. Boiling such water will not help avoid negative consequences, but on the contrary, chlorine will turn into dioxin, which is a powerful poison. In order to allow excess chlorine to evaporate, tap water is collected in large containers and left for a day in a well-ventilated area.
Ozonation
Ozone has a strong oxidizing effect. It penetrates the cell and destroys its walls, leading to the death of the bacterium. This substance is not only a strong antiseptic, but also discolors and deodorizes water and oxidizes metals. Ozone works quickly and gets rid of almost all microorganisms in water, surpassing chlorine in this characteristic.
Ozonation is considered the safest and most effective method, but it also has several disadvantages. Excess ozone leads to corrosion of metal parts of equipment and pipelines, equipment wears out and breaks down faster than usual. In addition, the latest research notes that ozonation causes the “awakening” of microorganisms that were in conditional hibernation.
Scheme of the ozonation process The method is characterized by high installation costs and high energy consumption. To work with ozonizing equipment, highly qualified personnel are required, because the gas is toxic and explosive. In order to release water to the population, it is necessary to wait out the period of ozone decay, otherwise people may suffer.
Disinfection with polymer compounds
No harm to health, destruction of odors, tastes and colors, long duration of action - the listed advantages relate to disinfection using polymer reagents. This type of substance is also called polymer antiseptics. They do not cause corrosion or damage the fabric, do not cause allergies and are effective.
Oligodynamy
It is based on the ability of noble metals (such as gold, silver and copper) to disinfect water.
The fact that these metals have an antiseptic effect has been known for a long time. Copper and its alloys are often used in field conditions when it is necessary to individually disinfect a small volume of liquid.
For a more extensive effect of metals on microorganisms, ionizers are used. These are flow devices operating on the basis of galvanic couple and electrophoresis.
Disinfection with silver
This metal is considered to be one of the most ancient methods of water disinfection. In ancient times, it was widely believed that silver could cure any disease. It is now known that it has a negative effect on many microorganisms, but it is not known whether silver destroys protozoan bacteria.
This product gives a visible effect in water purification. However, it negatively affects the human body when accumulated in it. It’s not for nothing that silver has a high hazard class. Disinfection of water with silver ions is not considered a safe method, and therefore is practically not used in industry. Silver ionizers are used in isolated cases in everyday life for processing small volumes of water.
Compact household water ionizer (silverizer) Iodination and bromination
Iodine is widely known and used in medicine since ancient times. Scientists have repeatedly tried to use its disinfecting effect in water treatment, but its use leads to an unpleasant odor. Bromine copes well with almost all known pathogenic microorganisms. But it has a significant drawback - high cost. Due to their disadvantages, these two substances are not used for treating wastewater and drinking water.
Combined methods of water disinfection
Integrated methods rely on a combination of physical and chemical methods to improve performance. An example is a combination of ultraviolet radiation and chlorination (sometimes chlorination is replaced by ozonation). UV lamps destroy microorganisms, and chlorine or ozone prevent their re-occurrence. In addition, oxidation and heavy metal treatment work well together. The oxidizing reagent disinfects, and metals prolong the bactericidal effect.
Combination of UV disinfection and ultrasound action How to disinfect water at home
There are five ways to quickly disinfect a small volume of water:
- boiling;
- adding potassium permanganate;
- use of disinfectant tablets;
- use of herbs and flowers;
- infusion with silicon.
Potassium permanganate is added to water in an amount of 1-2 g per bucket of water, after which the contaminants precipitate.
Special tablets for destroying microorganisms are used to neutralize water from a well, well or spring. They are the most modern method, accessible, inexpensive and effective. Many tablets, such as the Aquatabs brand, can be used to purify large volumes of liquid.
If water needs to be disinfected while hiking, you can use special herbs: St. John's wort, lingonberry, chamomile or celandine.
You can also use silicon: it is placed in water and left for a day.
Regulatory documentation in the field of drinking water safety
The state strictly controls water quality through regulations, rules and restrictions. The basis of legislative acts in the field of protection of water resources and control of the quality of water used are two documents: the Federal Law “On the Sanitary and Epidemiological Welfare of the Population” and the Water Code.
The first law contains requirements for the quality of water supply sources from which water is supplied to residential buildings and for agricultural needs. The second document describes the standards for the use of water sources and instructions for ensuring their safety, and also defines penalties.
GOST standards
GOSTs describe the rules by which the quality of waste and drinking water must be monitored. They contain methods for conducting analyzes in the field, and also allow you to divide waters into groups. The most important GOSTs are presented in the table.
SNiPs
Building codes and regulations determine the requirements for the construction of water treatment facilities and for the installation of various types of pipelines and water supply systems. The information is contained in SNiPs under the following numbers: SNiP 2.04.01-85, SNiP 3.05.01-85, SNiP 3.05.04-85.
SanPiNy
Sanitary and epidemiological rules and regulations contain hygienic requirements for the quality of various groups of water, composition, water intake structures and location of water intakes: SanPiN 2.1.4.559-96, SanPiN 4630-88, SanPiN 2.1.4.544-96, SanPiN 2.2.1/2.1 .1.984-00.
Thus, the effectiveness of tap water disinfection is monitored with established regularity and in accordance with many rules and regulations. And a large number of different methods for disinfecting fresh water allow you to choose the best option for any conditions. What makes properly purified and treated water safe for human consumption.
Disinfection of drinking water serves to create a reliable barrier to the transmission of infectious disease pathogens by water. Methods of water disinfection are aimed at destroying pathogenic and opportunistic microorganisms, which ensures the epidemic safety of water.
Water is disinfected at the final stage of purification after clarification and decolorization before entering clean water tanks, which simultaneously serve as contact chambers. To disinfect water, reagent (chemical) and reagent-free (physical) methods are used. Reagent methods are based on the introduction of strong oxidizing agents into water (chlorination, ozonation, manganization, treatment of water with iodine), heavy metal ions and silver ions. Reagent-free treatments include heat treatment, ultraviolet irradiation, ultrasound treatment, y-irradiation, and ultrahigh-frequency current treatment. The method is selected depending on the quantity and quality of the source water, methods of its preliminary purification, requirements for the reliability of disinfection, taking into account technical and economic indicators, conditions of supply of reagents, availability of transport, and the possibility of automating the process.
Disinfection of water with chlorine and its compounds. Today, the most common method of water disinfection at waterworks remains chlorination. Among chlorine-containing compounds, given certain hygienic and technical advantages, liquid chlorine is most often used. It is also possible to use bleach, calcium and sodium hypochlorite, chlorine dioxide, chloramines, etc.
*For use in the practice of domestic and drinking water supply, only fluorine-containing compounds are allowed that have passed hygienic testing and are included in the "List of materials and reagents approved by the Main Sanitary and Epidemiological Directorate of the Ministry of Health of the USSR for use in the practice of domestic and drinking water supply (No. 3235-85)" .*
For the first time in water treatment practice, chlorine was used long before L. Pasteur’s discovery of microbes, R. Koch’s proof of the etiological significance of pathogenic microorganisms in the development of infectious diseases, T. Escherich’s final understanding of the microbiological essence of water epidemics and the bactericidal properties of chlorine. It was used to deodorize water that had an unpleasant “septic” odor. Chlorine turned out to be a very effective deodorant and, in addition, after treating water with chlorine, people were diagnosed with intestinal infections much less often. With the beginning of water chlorination, epidemics of typhoid and cholera stopped in many European countries. It was suggested that the cause of the illnesses was the bad odor and taste of the water, which chlorine effectively eliminated. Only over time did they prove the microbial etiology of water epidemics of intestinal infections and recognize the role of chlorine as a disinfecting agent.
To chlorinate water, liquid chlorine is used, which is stored under pressure in special containers (cylinders), or substances containing active chlorine.
Chlorination of water with liquid chlorine. Chlorine (C12) at normal atmospheric pressure is a greenish-yellow gas, which is 1.5-
2.5 times heavier than air, with a pungent and unpleasant odor, dissolves well in water, and easily liquefies with increased pressure. The atomic weight of chlorine is 35.453, molecular weight is 70.906 g/mol. Chlorine can be in three states of aggregation: solid, liquid and gaseous.
Chlorine is delivered to water supply stations for water disinfection in liquid cylinders under pressure. Chlorination is carried out using chlorinators. A chlorine solution is prepared in them, which is injected directly into the pipeline through which water enters the RHF. L.A. chlorinators are used. Kulsky (Fig. 20), vacuum chlorinators LONII-100, Zh-10, LK-12, KhV-11. The schematic diagram of the LONII-100 chlorinator is shown in Fig. 21.
When the cylinder is connected to a chlorinator, liquid chlorine evaporates. Chlorine gas is purified in a cylinder and on a filter, and after reducing its pressure using a reducer to 0.001-0.02 MPa, it is mixed with water in a mixer. From the mixer, concentrated
Rice. 21. Technological diagram of a typical chlorinator at 3 kg/h: 1 - platform scales; 2 - risers with cylinders; 3 - pollution catcher; 4 - chlorinators LONII-100; 5 - ejectors
The new solution is sucked into the ejector and fed into the pipeline. Chlorinators of the LK type, whose design is simpler and whose accuracy is lower, are used for high-power stations. These chlorinators do not require preliminary purification of chlorine, are not so accurate in dosing, but can supply chlorine water to a height of 20-30 m. After the ejector from LONIA-100, the pressure is only 1-2 m. During the dissolution of chlorine in water, its hydrolysis occurs with the formation of chloride (hydrochloric) and hypochlorite (or hypochlorous) acids:
C12+ H20 ^ HCl + HC10.
Hypochlorous acid HC10 is a weak monobasic unstable acid that easily dissociates to form hypochlorite ion (HC~):
NSYU ^ N+ + SYU".
The degree of dissociation of hypochlorous acid depends on the pH of the water. At pH
In addition, hypochlorous acid decomposes to form atomic oxygen, which is also a strong oxidizing agent:
NSyu It HCl + O".
*Active chlorine is one that is capable of releasing an equivalent amount of iodine from aqueous solutions of potassium iodide at pH 4. There are free (molecular chlorine, hypochlorous acid, hypochlorite ion) and bound (chlorine, which is part of organic and inorganic mono- and dichloramines) active chlorine.*
Previously, it was believed that it was this atomic oxygen that had a bactericidal effect. Today it has been proven that the disinfecting effect of liquid chlorine, as well as bleach, calcium and sodium hypochlorites, two-tertiary calcium salt hypochlorite is due to oxidizing agents that are formed in water when chlorine-containing compounds are dissolved, primarily by the action of hypochlorite acid, and then by the hypochlorite anion and finally atomic oxygen.
Chlorination of water with hypochlorites (salts of hypochlorous acid) is carried out at low-power water supply stations. Hypochlorites are also used for long-term disinfection of water in mine wells using ceramic cartridges, for disinfection of water in the field, including using fabric-carbon filters, etc.
Calcium hypochlorite Ca(OC1)2 is used to disinfect drinking water. During its dissolution in water, hydrolysis occurs with the formation of hypochlorous acid and its further dissociation:
Ca(OC1)2 + 2H20 = Ca(OH)2 + 2HCiu,
Neyu -?. n+ + cicr.
Depending on the method of calcium production, hypochlorite can contain from 57-60% to 75-85% active chlorine. Together with pure hypochlorite, a mixture of calcium hypochlorite and other salts (NaCl, CaCl2) is used to disinfect water. Such mixtures contain up to 60-75% pure hypochlorite.
At stations with active chlorine consumption up to 50 kg/day, sodium hypochlorite (NaCIO 5H20) can be used to disinfect water. This crystalline hydrate is obtained from sodium chloride (NaCl) solution by electrolytic method.
Sodium chloride in water dissociates to form sodium cation and chlorine anion:
NaCl ^ Na+ + SG
During electrolysis, chlorine ions are discharged at the anode and molecular chlorine is formed:
2SG -» C12 + 2e.
The resulting chlorine dissolves in the electrolyte:
С12+Н2О^НС1 + НСУ,
C12+OH-^CI+HCIu.
A discharge of water molecules occurs at the cathode:
H20 + e -> OH- + H+.
Hydrogen atoms, after recombination into molecular hydrogen, are released from solution as a gas. Hydroxyl anions OH" remaining in water react with sodium cations Na+, resulting in the formation of NaOH. Sodium hydroxide reacts with hypochlorous acid to form sodium hypochlorite:
NaOH + HC10 -> NaOCI + H20.
Rice. 22. Technological diagram for the electrolytic production of sodium hypochlorite: 1 - solution tank; 2 - pump; 3 - distribution tee; 4 - working tank; 5 - dispenser; 6 - electrolyzer with graphite electrodes; 7 - sodium hypochlorite storage tank; 8 - exhaust ventilation hood
Sodium hypochlorite dissociates to a large extent with the formation of "sodium hypochlorite", which has high antimicrobial activity:
NaCIO ^ Na+ + CIO",
Xiu- + n+;^nshu.
Electrolysis plants are divided into flow-through and batch. They include electrolyzers and various types of tanks. The schematic diagram of a batch installation is shown in Fig. 22. A sodium chloride solution of 10% concentration is fed into a tank at a constant level, from where it flows out at a constant flow rate. After filling the dosing tank, the siphon is activated and drains a certain volume of solution into the electrolyzer. Under the influence of electric current, sodium hypochlorite is formed in the electrolyzer. New portions of the salt solution push sodium hypochlorite into the supply tank, from which it is dosed by a dosing pump. The storage tank must contain a volume of sodium hypochlorite for at least 12 hours.
The advantage of producing sodium hypochlorite by the electrolytic method at the point of use is that there is no need to transport and store toxic liquefied chlorine. Among the disadvantages are significant energy costs.
Water disinfection by direct electrolysis. The method consists of direct electrolysis of fresh water, in which the natural chloride content is not lower than 20 mg/l, and hardness is not higher than 7 mEq/l. Used at water supply stations with a capacity of up to 5000 m3/day. Due to direct electrolysis at the anode, the chloride ions present in the water are discharged and molecular chlorine is formed, which is hydrolyzed to form hypochlorous acid:
2СГ ^ С12 + 2е, С12 + Н2О^НС1 + НСУ.
During the electrolysis treatment of water with a pH in the range of 6-9, the main disinfection agents are hypochlorous (hypochloritic) acid HSY, hypochlorite anion C10~ and monochloramines NH2C1, which are formed as a result of the reaction between HSY and ammonium salts contained in natural water. At the same time, during the treatment of water by the electrolytic method, microorganisms are exposed to the electric field in which they are located, which enhances the bactericidal effect.
Disinfection of water with bleach is used at small waterworks (with a capacity of up to 3000 m3/day), having previously prepared a solution. Ceramic cartridges are also filled with bleach to disinfect water in mine wells or local water supply systems.
Chlorine is a white powder with a pungent odor of chlorine and strong oxidizing properties. It is a mixture of calcium hypochlorite and calcium chloride. Bleach is obtained from limestone. Calcium carbonate at a temperature of 700 °C decomposes to form quicklime (calcium oxide), which, after interaction with water, turns into slaked lime (calcium hydroxide). When chlorine reacts with slaked lime, bleach is formed:
CaCO3 ^ CaO + CO2,
CaO + H20 = Ca(OH)2,
2Ca(OH)2 + 2C12 = Ca(OC1)2 + CaC12+ 2H20 or
2Ca(OH)2 + 2C12 = 2CaOC12 + 2H20.
The main component of bleach is expressed by the formula:
The technical product contains no more than 35% active chlorine. During storage, bleach is partially decomposed. The same thing happens with calcium hypochlorite. Light, humidity and high temperature accelerate the loss of active chlorine. Bleached lime loses approximately 3-4% of active chlorine per month due to hydrolysis reactions and decomposition in light. In a damp room, bleach decomposes, forming hypochlorous acid:
2CaOC12 + C02 + H20 = CaC03 + CaC12 + 2HCiu.
Therefore, before using bleach and calcium hypochlorite, their activity is checked - the percentage of active chlorine in the chlorine-containing preparation.
The bactericidal effect of bleach, like hypochlorites, is due to the group (OCG), which forms hypochlorous acid in an aquatic environment:
2CaOC12 + 2H20 -> CaC12 + Ca(OH)2 + 2HC10.
Chlorine dioxide (ClOJ is a yellow-green gas, easily dissolves in water (at a temperature of 4 °C, 20 volumes of gaseous ClO2 are dissolved in 1 volume of water). It does not hydrolyze. It is advisable to use it if the characteristics of natural water are unfavorable for effective disinfection chlorine, for example, at high pH values or in the presence of ammonia. However, the production of chlorine dioxide is a complex process that requires special equipment, qualified personnel, additional financial costs. In addition, chlorine dioxide is explosive, which requires strict adherence to safety requirements. The above is limited use of chlorine dioxide for water disinfection in domestic and drinking water supply systems.
Chlorine-containing preparations also include chloramines (inorganic and organic), which are used to a limited extent in water treatment practice, but are used as disinfecting agents during disinfection activities, in particular in medical institutions. Inorganic chloramines (monochloramines NH2C1 and dichloramines NHC12) are formed by the reaction of chlorine with ammonia or ammonium salts:
NH3 + CI2 = NH2CI + HCI,
NH2CI + CI2 = NHCI2 + HCl.
Together with inorganic chlorine compounds, organic chloramines (RNHC1, RNC12) are also used for disinfection. They are obtained by reacting bleach with amines or their salts. In this case, one or two hydrogen atoms of the amine group are replaced by chlorine. Different chloramines contain 25-30% active chlorine.
The process of water disinfection with chlorine-containing preparations occurs in several stages:
1. Hydrolysis of chlorine and chlorine-containing preparations:
C12 + H20 = HCl + HC10;
Ca(OC1)2 + 2H20 = Ca(OH)2+ 2HC10;
2CaOC12 + 2H20 = Ca(OH)2 + CaC12 + 2HC10.
2. Dissociation of hypochlorous acid.
At pH ~ 7.0 HC10 dissociates: HC10
3. Diffusion of the HC10 molecule and the CO ion into the bacterial cell.
4. Interaction of the disinfecting agent with enzymes of microorganisms that are oxidized by hypochlorous acid and hypochlorite ion.
Active chlorine (NCH and CL") first diffuses inside the bacterial cell and then reacts with enzymes. Undissociated hypochlorous acid (NCH) has the greatest bactericidal and virucidal effect. The rate of water disinfection is determined by the kinetics of chlorine diffusion inside the bacterial cell and the kinetics of cell death as a result of metabolic disorders.With an increase in the concentration of chlorine in water, its temperature and with the transition of chlorine into the undissociated form of easily diffusible hypochlorous acid, the overall speed of the disinfection process increases.
The mechanism of the bactericidal action of chlorine consists of the oxidation of organic compounds of the bacterial cell: coagulation and damage to its membrane, inhibition and denaturation of enzymes that provide metabolism and energy. The most damaged are thiol enzymes containing SH groups, which are oxidized by hypochlorous acid and hypochlorite ion. Among thiol enzymes, the most actively inhibited group is dehydrogenases, which ensure respiration and energy metabolism of the bacterial cell1. Under the influence of hypochlorous acid and hypochlorite ion, dehydrogenases of glucose, ethyl alcohol, glycerol, succinic, glutamic, lactic, pyruvic acid, formaldehyde, etc. are inhibited. Inhibition of dehydrogenases leads to inhibition of oxidation processes at the initial stages. The consequence of this is both inhibition of the processes of bacterial reproduction (bacteriostatic effect) and their death (bactericidal effect).
The mechanism of action of active chlorine on viruses consists of two phases. First, hypochlorous acid and hypochlorite ion are adsorbed on the virus shell and penetrate through it, and then they inactivate the RNA or DNA of the virus.
As the pH value increases, the bactericidal activity of chlorine in water decreases. For example, to reduce the number of bacteria in water by 99% at a dose of free chlorine of 0.1 mg/l, the contact duration increases from 6 to 180 minutes when the pH increases from 6 to 11, respectively. Therefore, it is advisable to disinfect water with chlorine at low pH values, that is before introducing alkaline reagents.
The presence in water of organic compounds capable of oxidation, inorganic reducing agents, as well as colloidal and suspended substances that envelop microorganisms, slows down the process of water disinfection.
The interaction of chlorine with water components is a complex and multi-stage process. Small doses of chlorine are completely bound by organic substances, inorganic reducing agents, suspended particles, humic substances and water microorganisms. For a reliable disinfecting effect of water after chlorination, it is necessary to determine the residual concentrations of free or combined active chlorine.
*Energy metabolism in bacteria occurs in mesosomes - analogues of mitochondria.*
Rice. 23. Graph of the dependence of the amount and type of residual chlorine on the administered dose of chlorine
In Fig. Figure 23 shows the relationship between the dose of introduced chlorine and residual chlorine in the presence of ammonia or ammonium salts in the water. When chlorinating water that does not contain ammonia or other nitrogen-containing compounds, with an increase in the amount of chlorine added to the water, the content of residual free chlorine in it increases. But the picture changes if there is ammonia, ammonium salts and other nitrogen-containing compounds in the water, which are an integral part of natural water or artificially introduced into it. In this case, chlorine and chlorine agents interact with ammonia, ammonium and organic salts containing amino groups present in water. This leads to the formation of mono- and dichloramines, as well as extremely unstable trichloramines:
NH3 + H20 = NH4OH;
C12 + H20 = HC10 + HCl;
HCJ + NH4OH = NH2C1 + H20;
NSJ + NH2C1 = NHC12+ H20;
NSJ + NHC12 = NC13 + H20.
Chloramines are combined active chlorine, which has a bactericidal effect that is 25-100 times less than that of free chlorine. In addition, depending on the pH of the water, the ratio between mono- and dichloramines changes (Fig. 24). At low pH values (5-6.5), dichloramines are predominantly formed, and at high pH values (more than 7.5), monochloramines are formed, the bactericidal effect of which is 3-5 times weaker than that of dichloramines. The bactericidal activity of inorganic chloramines is 8-10 times higher than that of chlorinated organic amines and imines. When adding low doses of chlorine to water at a molar ratio of C12: NH*
*There is no ammonia-free water in nature. It can only be prepared in a laboratory from distilled water.*
residual chlorine associated with amines accumulates. As the dose of chlorine increases, more chloramines are formed and the concentration of residual bound chlorine increases to a maximum (point A).
With a further increase in the dose of chlorine, the molar ratio of the introduced chlorine and the NH * ion contained in the water becomes greater than one. In this case, mono-, di- and, especially, trichloramines are oxidized by excess chlorine in accordance with the following reactions:
NHC12 + NH2C1 + NSJ -> N20 + 4HC1;
NHC12 + H20 -> NH(OH)Cl + HCl;
NH(OH)Cl + 2HC10 -> HN03 + ZHC1;
NHC12 + HCIO -> NC13 + H20;
4NH2C1 + 3C12 + H20 = N2 + N20 + 10HC1;
IONCI3 + CI2 + 16H20= N2 + 8N02 + 32HCI.
When the molar ratio Cl2: NH\ is up to 2 (10 mg Cl2 per 1 mg N2 in the form of NH\), due to the oxidation of chloramines with excess chlorine, the amount of residual bound chlorine in water decreases sharply (segment III) to a minimum point (point B), which is called point fracture Graphically, it looks like a deep dip in the residual chlorine curve (see Fig. 23).
With a further increase in the dose of chlorine after the turning point, the concentration of residual chlorine in the water begins to gradually increase again (segment IV on the curve). This chlorine is not associated with chloramines, is called free residual (active) chlorine and has the highest bactericidal activity. It acts on bacteria and viruses like active chlorine in the absence of ammonia and ammonium compounds in the water.
According to research data, water can be disinfected with two doses of chlorine: before and after the turning point. However, when chlorinated with a pre-turnover dose, the water is disinfected due to the action of chloramines, and when chlorinated with a post-turnover dose, it is disinfected by free chlorine.
During water disinfection, the added chlorine is spent both on interaction with microbial cells and viruses, and on the oxidation of organic and mineral compounds (urea, uric acid, creatinine, ammonia, humic substances, ferrous iron salts, ammonium salts, carbamates, etc. ), which are contained in water in a suspended and dissolved state. The amount of chlorine absorbed by water impurities (organic substances, inorganic reducing agents, suspended particles, humic substances and microorganisms) is called the chlorine absorption capacity of water (segment I on the curve). Since natural waters have different compositions, their chlorine absorption is not the same. Thus, chlorine absorption is the amount of active chlorine that is absorbed by suspended particles and spent on the oxidation of bacteria, organic and inorganic compounds contained in 1 liter of water.
You can count on successful water disinfection only if there is a certain excess of chlorine in relation to the amount that is absorbed by bacteria and various compounds contained in the water. An effective dose of active chlorine is equal to the total amount of absorbed and residual chlorine. The presence of residual chlorine in water (or, as it is also called, excess) is associated with the idea of the effectiveness of water disinfection.
When chlorinating water with liquid chlorine, calcium and sodium hypochlorites, and bleach, a 30-minute contact provides a reliable disinfecting effect with a residual chlorine concentration of at least 0.3 mg/l. But when chlorination with preammonization, contact should be for 1-2 hours, and the effectiveness of disinfection will be guaranteed in the presence of residual bound chlorine in a concentration of at least 0.8 mg/l.
Chlorine and chlorine-containing compounds significantly affect the organoleptic properties of drinking water (smell, taste), and in certain concentrations they irritate the mucous membranes of the oral cavity and stomach. The maximum concentration of residual chlorine at which drinking water does not acquire a chlorine smell and taste is set at 0.5 mg/l for free chlorine, and 1.2 mg/l for bound chlorine. According to toxicological characteristics, the maximum concentration of active chlorine in drinking water is 2.5 mg/l."
Therefore, to disinfect water, it is necessary to add such an amount of chlorine-containing preparation that after treatment the water contains 0.3-0.5 mg/l of residual free or 0.8-1.2 mg/l of residual bound chlorine. This excess of active chlorine does not impair the taste of water or harm health, but guarantees its reliable disinfection.
Thus, for effective disinfection, a dose of active chlorine is added to water equal to the sum of chlorine absorption and residual active chlorine. This dose is called the chlorine requirement of water.
Chlorine requirement of water is the amount of active chlorine (in milligrams) required for effective disinfection of 1 liter of water and ensuring the content of residual free chlorine within 0.3-0.5 mg/l after 30 minutes of contact with water, or the amount of residual bound chlorine within 0.8-1.2 mg after 60 minutes of contact. Residual content
*The maximum concentration of chlorine dioxide in drinking water is not higher than 0.5 mg/l, the limiting indicator of water action is organoleptic.*
Active chlorine is controlled after clean water tanks before being supplied to the water supply network. Since the chlorine absorption of water depends on its composition and is not the same for water from different sources, in each case the chlorine requirement is determined experimentally by test chlorination. Approximately, the chlorine requirement of clarified and bleached river water by coagulation, sedimentation and filtration ranges from 2-3 mg/l (sometimes up to 5 mg/l), groundwater interstratal water - within 0.7-1 mg/l.
Factors influencing the process of water chlorination are associated with: 1) biological characteristics of microorganisms; 2) bactericidal properties of chlorine-containing preparations; 3) the state of the aquatic environment; 4) with the conditions in which disinfection is carried out.
It is known that spore cultures are many times more resistant than vegetative forms to the action of disinfectants. Enteroviruses are more persistent than intestinal bacteria. Saprophytic microorganisms are more resistant than pathogenic ones. Moreover, among pathogenic microorganisms, the most sensitive to chlorine are the causative agents of typhoid fever, dysentery, and cholera. The causative agent of paratyphoid B is more resistant to chlorine. In addition, the higher the initial contamination of water by microorganisms, the lower the efficiency of disinfection under the same conditions.
The bactericidal activity of chlorine and its compounds is associated with the magnitude of its redox potential. The redox potential increases at the same concentrations in the series: chloramine -> bleach -> chlorine - chlorine dioxide.
The effectiveness of chlorination depends on the properties and composition of the aquatic environment, namely: the content of suspended solids and colloidal compounds, the concentration of dissolved organic compounds and inorganic reducing agents, the pH of the water, and its temperature.
Suspended substances and colloids prevent the action of the disinfectant on microorganisms located in the thickness of the particle and absorb active chlorine due to adsorption and chemical binding. The effect on the efficiency of chlorination of organic compounds dissolved in water depends both on their composition and on the properties of chlorine-containing preparations. Thus, nitrogen-containing compounds of animal origin (proteins, amino acids, amines, urea) actively bind chlorine. Compounds that do not contain nitrogen (fats, carbohydrates) react less strongly with chlorine. Since the presence of suspended substances, humic and other organic compounds in water reduces the effect of chlorination, for reliable disinfection, cloudy and highly colored waters are first clarified and discolored.
When the water temperature decreases to 0-4 °C, the bactericidal effect of chlorine decreases. This dependence is especially noticeable in experiments with high initial contamination of water and in the case of chlorination with low doses of chlorine. In the practice of water supply stations, if the contamination of the source water meets the requirements of State Standard 2761-84 “Sources of centralized household and drinking water supply. Hygienic, technical requirements and quality control,” a decrease in temperature does not noticeably affect the effectiveness of disinfection.
The mechanism of the influence of water pH on its disinfection with chlorine is associated with the characteristics of the dissociation of hypochlorous acid: in an acidic environment, the equilibrium shifts towards the molecular form, in an alkaline environment - towards the ionic form. Hypochlorous acid in undissociated molecular form penetrates better through the membranes into the middle of the bacterial cell than hydrated hypochlorite ions. Therefore, in an acidic environment, the process of water disinfection is accelerated.
The bactericidal effect of chlorination is significantly affected by the dose of the reagent and the duration of contact: the bactericidal effect increases with increasing dose and increasing the duration of action of active chlorine.
Methods of water chlorination. There are several methods of chlorination. water treatment, taking into account the nature of residual chlorine, the choice of which is determined by the characteristics of the composition of the water being treated. Among them: 1) chlorination with post-turnover doses; 2) conventional chlorination or chlorination according to chlorine demand; 3) superchlorination; 4) chlorination with preammonization. In the first three options, water is disinfected with free active chlorine. During chlorination with preammonization, the bactericidal effect is due to the action of chloramines, i.e., bound active chlorine. In addition, combined chlorination methods are used.
Chlorination with post-breaking doses provides that after 30 minutes of contact, free active chlorine will be present in the water. The dose of chlorine is selected so that it is slightly higher than the dose at which a break in the residual chlorine curve is formed, i.e. in range IV (see Fig. 23). The dose selected in this way causes the least amount of residual free chlorine to appear in the water. This method is characterized by careful dose selection. It provides a stable and reliable bactericidal effect and prevents the appearance of odors in water.
Conventional chlorination (chlorination according to chlorine demand) is the most common method of disinfecting drinking water with centralized domestic drinking water supply. Chlorination according to chlorine demand is carried out with a post-turnover dose that, after 30 minutes of contact, ensures the presence of residual free chlorine in the water within the range of 0.3-0.5 mg/l.
Since natural waters differ significantly in composition and therefore have different chlorine absorption, chlorine demand is determined experimentally by experimental chlorination of water to be disinfected. In addition to the correct choice of the dose of chlorine, a prerequisite for effective water disinfection is thorough mixing and exposure time, i.e., the time of contact of chlorine with water (at least 30 minutes).
As a rule, at waterworks, chlorination according to chlorine demand is carried out after clarification and decolorization of water. The chlorine requirement of such water ranges from 1-5 mg/l. The optimal dose of chlorine is introduced into the water immediately after filtration before RHF.
Based on the chlorine requirement, double chlorination can be carried out, in which chlorine is fed into the mixer for the first time before the reaction chamber, and for the second time after the filters. In this case, the experimentally determined optimal dose of chlorine is not changed. Chlorine, when introduced into the mixer in front of the reaction chamber, improves coagulation and discoloration of water, which makes it possible to reduce the dose of coagulant. In addition, it inhibits the growth of microflora that contaminates the sand in the filters. The total consumption of chlorine with double chlorination practically does not increase and remains almost the same as with single chlorination.
Double chlorination deserves widespread use. It should be used in cases where river water pollution is relatively high or subject to frequent fluctuations. Double chlorination increases the sanitary reliability of water disinfection.
Superchlorination (rechlorination) is a method of water disinfection that uses increased doses of active chlorine (5-20 mg/l). These doses are actually post-fracture doses. In addition, they significantly exceed the chlorine requirement of natural water and cause the presence of high (over 0.5 mg/l) concentrations of residual free chlorine in it. Therefore, the superchlorination method does not require preliminary determination of the chlorine requirement of water and careful selection of the dose of active chlorine, however, after disinfection it is necessary to remove excess free chlorine.
Superchlorination is used in special epidemiological situations, when it is impossible to determine the chlorine requirement of water and to ensure sufficient contact time of chlorine with water, as well as to prevent the appearance of odors in water and combat them. This method is convenient in military field conditions and in emergency situations.
Superchlorination effectively ensures reliable disinfection of even cloudy water. High doses of active chlorine kill pathogens resistant to disinfectants, such as Burnett's rickettsia, dysentery amoeba cysts, mycobacterium tuberculosis and viruses. But even such doses of chlorine cannot reliably disinfect water from anthrax spores and helminth eggs.
With superchlorination, the residual free chlorine in disinfected water significantly exceeds 0.5 mg/l, which makes the water unsuitable for consumption due to the deterioration of its organoleptic properties (the pungent odor of chlorine). Therefore, there is a need to free it from excess chlorine. This process is called dechlorination. If the excess residual chlorine is small, it can be removed by aeration. In other cases, water is purified by filtering through a layer of activated carbon or using chemical methods, such as treating sodium hyposulfite (thiosulfate), sodium bisulfite, sulfur dioxide (sulfur dioxide), iron sulfate. In practice, sodium hyposulfite (thiosulfate) is mainly used - Na2S203 5H20. Its amount is calculated depending on the amount of excess chlorine, based on the following reaction:
Na2S203 + C12+ H20 = Na2S04 + 2HCI + si.
According to the given binding reaction between active chlorine and sodium hyposulfite at a molar ratio of 1:1, 0.0035 g of sodium hyposulfite crystalline hydrate is used per 0.001 g of chlorine, or 3.5MrNa2S203-5H20 per 1 mg of chlorine.
Chlorination with preammonization. The chlorination method in preammonization is used:
1) in order to prevent the appearance of unpleasant specific odors that arise after chlorination of water containing phenol, benzene and ethylbenzene;
2) to prevent the formation of carcinogenic substances (chloroform, etc.) during chlorination of drinking water containing humic acids and methane hydrocarbons;
3) to reduce the intensity of the smell and taste of chlorine, especially noticeable in the summer;
4) to save chlorine with high chlorine absorption of water and the absence of odors, tastes and high bacterial contamination.
If natural water contains phenols (for example, due to pollution of water bodies by wastewater from industrial enterprises) even in small quantities1, then when disinfected with chlorine-containing compounds that hydrolyze to form hypochlorous acid, free active chlorine immediately reacts with phenol, forming chlorophenols, which even in small amounts concentrations give the water a birdlike taste and smell. At the same time, bound active chlorine - chloramine, having a lower redox potential, does not interact with phenol to form chlorophenols, and therefore the organoleptic properties of water do not deteriorate during disinfection. Similarly, free active chlorine is capable of interacting with methane hydrocarbons to form trihalomethanes (chloroform, dibromochloromethane, dichlorobromomethane), which are carcinogens. Their formation can be prevented by disinfecting water with bound active chlorine.
When chlorinating with preammonization, a solution of ammonia2 or its salts is first added to the water that is being disinfected, and after 1-2 minutes chlorine is introduced. As a result, chloramines (monochloramines NH2C1 and dichloramines NHC12) are formed in water, which have a bactericidal effect. Chemical reactions for the formation of chloramines are given on p. 170.
The ratio of substances formed depends on pH, temperature and the amount of reacting compounds. The effectiveness of chlorination with preammonization depends on the ratio of NH3 and C12, and doses of these reagents are used in proportions of 1:2, 1:4, 1:6, 1:8. For each water supply source, it is necessary to select the most effective ratio. The rate of water disinfection with chloramines is lower than the rate of disinfection with free chlorine, therefore the duration of water disinfection in the case of chlorination with preammonization should be at least 2 hours. The features of the bactericidal effect of chloramines, as well as their ability not to form chlorine derivatives that have specific odors, are explained by their significant
*MPC of phenol in water is 0.001 mg/l, the limiting indicator is organoleptic (smell), 4th hazard class.*
*To introduce ammonia into water, it is most convenient to use vacuum chlorinators.*
But less oxidative activity, since the redox potential of chloramines is much lower than that of chlorine.
In addition to pre-ammonization (the introduction of ammonia 1-2 minutes before the introduction of chlorine), post-ammonization is sometimes used, when ammonia is introduced after chlorine directly into tanks with clean water. Due to this, chlorine is fixed longer than the increase in the duration of its action is achieved.
Combined methods of water chlorination. In addition to the considered methods of water chlorination, a number of combined ones have been proposed, when another chemical or physical disinfectant is used together with chlorine-containing compounds, which increases the disinfection effect. Chlorination can be combined with water treatment with silver salts (chlorine-silver method), potassium permanganate (chlorination with manganization), ozone or ultraviolet light, ultrasound, etc.
Chlorination with manganization (with the addition of KMP04 solution) is used when it is necessary to enhance the oxidative and bactericidal effect of chlorine, since potassium permanganate is a stronger oxidizing agent. The method should be used if there are odors and tastes in the water that are caused by organic substances and algae. In this case, potassium permanganate is introduced before chlorination. KMP04 should be added before settling tanks in doses of 1-5 mg/l or before filters in doses of 0.08 mg/l. Reducing itself to water-insoluble Mn02, it is completely retained in settling tanks and filters.
The silver chloride method is used on river fleet vessels (on KVU-2 and UKV-0.5 installations). It provides enhanced disinfection of water and its preservation for a long period (up to 6 months) with the addition of silver ions in an amount of 0.05-0.1 mg/l.
In addition, the silver chloride method is used to disinfect water in swimming pools, where it is necessary to reduce the dose of chlorine as much as possible. This is possible because the bactericidal effect is provided within the total effect of doses of chlorine and silver.
The bactericidal, virucidal and oxidative effects of chlorine can be enhanced by simultaneous exposure to ultrasound, ultraviolet radiation, and direct electric current.
Water samples are taken after clean water reservoirs before being supplied to the water supply network. The effectiveness of chlorination by residual active chlorine is monitored hourly, that is, 24 times a day. Chlorination is considered effective if the residual free chlorine content is in the range of 0.3-0.5 mg/l after 30 minutes of contact, or the residual bound chlorine content is 0.8-1.2 mg/l after 60 minutes of contact.
According to microbiological indicators of epidemic safety, water after RHF is examined twice a day, that is, once every 12 hours. In the water after disinfection, the total microbial number and the coliform index (coli-index) are determined. Water disinfection is considered effective if the coli index does not exceed 3, and the total microbial number does not exceed 100.
Negative consequences of water chlorination for public health. As a result of the reaction of chlorine with humic compounds, waste products of aquatic organisms and some substances of industrial origin, dozens of new extremely dangerous haloform compounds are formed, including carcinogens, mutagens and highly toxic substances with maximum permissible concentrations at the level of hundredths and thousandths of a milligram per 1 liter. In table 3 and 5 (see pp. 66, 67, 101) show some halogen-containing compounds, features of their effect on the human body, and hygienic standards in drinking water. Indicators of this group are trihalomethanes: chloro- and bromoform, dibromochloromethane, bromodichloromethane. In disinfected drinking water and hot water supply, chloroform is detected most often and in higher concentrations - a group 2B carcinogen, according to the IARC classification.
Haloform compounds enter the body with water not only enterally. Some substances penetrate intact skin during contact with water, particularly when swimming in a pool. When you take a bath or shower, haloform compounds are released into the air. A similar process occurs in the process of boiling water, laundry, and cooking.
Taking into account the extreme danger of haloform compounds to human health, a set of measures has been developed to reduce their levels in water. It provides:
Protection of the water supply source from pollution by wastewater that contains precursors of haloform compounds;
Reducing eutrification of surface water bodies;
Refusal of rechlorination (primary chlorination) or its replacement with ultraviolet irradiation or the addition of copper sulfate;
Optimization of coagulation to reduce water color, that is, removal of humic substances (precursors of haloform compounds);
The use of disinfectants that have a lower ability to form haloform compounds, in particular chlorine dioxide, chloramines;
The use of chlorination with preammonization;
Aerating the water or using granular activated carbon is the most effective way to remove haloform compounds from the water.
A radical solution to the problem is to replace chlorination with ozonation and disinfection of water with UV rays.
Ozonation of water and its advantages over chlorination. Ozonation is one of the promising methods of water treatment for the purpose of its disinfection and improvement of organoleptic properties. Today, almost 1000 waterworks in Europe, mainly in France, Germany and Switzerland, use ozonation in their water treatment process. Recently, ozonation has begun to be widely implemented in the USA and Japan. In Ukraine, ozonation is used at the Dnieper water supply
Rice. 25. Technological diagram of the ozonation plant:
1 - air intake; 2 - air filter; 3 - warning valve; 4 - five supply fans; 5 - air plunger; 6 - two refrigerated dryers; 7 - four adsorption dryings; 8 - activated alumina; 9 - cooling of fan heaters; 10 - fifty ozone generators (pictured 2); 11 - dry air; 12 - cooling water inlet; 13 - cooling water outlet; 14 - ozonated air; 15 - three tanks for ozone diffusion; 16 - water level
Stations in Kyiv, in the CIS countries - at water supply stations in Moscow (Russian Federation) and Minsk (Belarus).
Ozone (Os) is a pale violet gas with a specific odor and a strong oxidizing agent. Its molecule is very unstable, easily disintegrates (dissociates) into an atom and an oxygen molecule. Under industrial conditions, an ozone-air mixture is produced in an ozonator using a “slow” electrical discharge at a voltage of 8000-10,000 V.
A schematic diagram of the ozonator installation is shown in Fig. 25. The compressor takes in air, cleans it from dust, cools it, dries it on adsorbers with silica gel or active aluminum oxide (which are regenerated by blowing hot air). Next, the air passes through the ozonizer, where ozone is formed, which is supplied through the distribution system to the water of the contact tank. The dose of ozone required for disinfection for most types of water is 0.5-6.0 mg/l. Most often, for underground water sources, the dose of ozone is taken in the range of 0.75-1.0 mg/l, for surface waters - 1-3 mg/l. Sometimes high doses are needed to discolor and improve the organoleptic properties of water. The duration of contact of ozone with water must be at least 4 minutes1. Indirect indicator
*In accordance with GOST 2874-82, the duration of water disinfection using ozone was at least 12 minutes. The same duration is regulated by SanPiN 2.1.4.559-96 approved by the Ministry of Health of Russia "Drinking water. Hygienic requirements for water quality of centralized drinking water supply systems. Quality control." In accordance with SanPiN "Drinking water. Hygienic requirements for the quality of water from centralized household and drinking water supply", approved by the Ministry of Health of Ukraine, the duration of ozone treatment must be at least 4 minutes.*
The effectiveness of ozonation is the presence of residual amounts of ozone at a level of 0.1-0.3 mg/l after the mixing chamber.
Ozone in water decomposes, forming atomic oxygen: 03 -> 02 + O". It has been proven that the mechanism of ozone decomposition in water is complex. In this case, a number of intermediate reactions occur with the formation of free radicals (for example, HO *), which are also oxidizing agents. More The strong oxidative and bactericidal effect of ozone compared to chlorine is explained by the fact that its oxidation potential is greater than that of chlorine.
From a hygienic point of view, ozonation is one of the best methods of water disinfection. As a result of ozonation, a reliable disinfecting effect is achieved, organic impurities are destroyed, and the organoleptic properties of water not only do not deteriorate, as with chlorination or boiling, but also improve: color decreases, unnecessary taste and smell disappear, water acquires a blue tint. Excess ozone quickly decomposes, producing oxygen.
Ozonation of water has the following specific advantages over chlorination:
1) ozone is one of the most powerful oxidizing agents, its redox potential is higher than that of chlorine and even chlorine dioxide;
2) during ozonation, nothing foreign is introduced into the water and no noticeable changes occur in the mineral composition of the water and pH;
3) excess ozone turns into oxygen after a few minutes, and therefore does not affect the body and does not impair the organoleptic properties of water;
4) ozone, interacting with compounds contained in water, does not cause the appearance of unpleasant tastes and odors;
5) ozone decolorizes and deodorizes water containing organic substances of natural and industrial origin, giving it odor, taste and color;
6) compared to chlorine, ozone more effectively disinfects water from spore forms and viruses;
7) the ozonation process is less susceptible to the influence of variable factors (pH, temperature, etc.), which facilitates the technological operation of water treatment facilities, and monitoring efficiency is no more difficult than with water chlorination;
8) ozonation of water ensures uninterrupted water treatment, eliminating the need to transport and store unsafe chlorine;
9) ozonation produces significantly fewer new toxic substances than chlorination. These are mainly aldehydes (for example, formaldehyde) and ketones, which are formed in relatively small quantities;
10) ozonation of water makes it possible to comprehensively treat water, which can simultaneously achieve disinfection and improve organoleptic properties (color, smell and taste).
Disinfection of water with silver ions. Water treated with silver at a dose of 0.1 mg/l maintains high sanitary and hygienic indicators throughout the year. Silver can be introduced directly by ensuring contact of water with the surface of the metal itself, as well as by dissolving silver salts in water electrolytically. L.A. Kulsky developed ionizers LK-27, LK-28, which provide for the anodic dissolution of silver by electric direct current.
The mechanism of action of chemical disinfectants on microorganisms. The initial stage of the action of any disinfectant on a bacterial cell is its sorption on the cell surface (O.S. Savluk, 1998). After the disinfectants diffuse through the cell wall, the targets of their action are the cytoplasmic membrane, nucleoid, cytoplasm, ribosomes, and mesosomes. The next stage is the degradation of macromolecular, including protein, structures of the bacterial cell as a result of inactivation of highly reactive functional groups (sulfhydryl, amine, phenolic, indole, thioethyl, phosphate, keto groups, endocyclic nitrogen atoms, etc.). The most sensitive are enzymes containing SH groups, i.e. thiol enzymes. Among them, dehydrogenases, which ensure the respiration of bacteria and are localized mainly in mesosomes, are most strongly inhibited.
Among the organelles of the bacterial cell, one of the most damaged by chemical disinfectants is the cytoplasmic membrane. This is due to its easy accessibility to the oxidizing agent (compared to other organelles) and the presence of a large number of active groups (including sulfhydryl groups), which are easily inactivated. Therefore, relatively small amounts of disinfectants are needed to damage the cytoplasmic membrane. Due to the importance of the functions of the cytoplasmic membrane for the life of a bacterial cell, its damage is extremely dangerous.
The nucleoid, the main part of which is the DNA molecule, despite the presence of reactive groups that are potentially capable of interacting with disinfectants, is inaccessible to their molecules and ions. This is caused, firstly, by the difficulties of transporting the disinfectant from an aqueous solution into the nucleoid through the outer and cytoplasmic membranes of the bacterial cell, and hence by the unproductive losses of disinfecting agents. Secondly, the presence of a primary hydration shell on the surface of DNA becomes an obstacle for some disinfectants. In particular, this hydration shell is impermeable to cations.
A significant amount of disinfectant is necessary to inactivate ribosomes and polysomes that contain rRNA, which is due to their high concentration in the bacterial cell (compared to DNA).
Chemical disinfectants must have the widest possible spectrum of bactericidal action and minimal toxicity to the body. Taking into account the mechanism of interaction with bacterial cells, chemical disinfectants are divided into two groups:
1. Substances that affect cellular structures due to chemical and physical effects, i.e. substances with a polar structure that contain lipophilic and hydrophilic groups (alcohols, phenols, cresols, detergents, polypeptide antibiotics). They dissolve fragments of cellular structures - membranes, violating their integrity and, accordingly, their functions. Possessing a wide spectrum of bactericidal action due to the similarity in the structure of cell membranes in various prokaryotes, this class of disinfectants is effective only in high concentrations - from 1 to 10 M.
2. Substances that damage cellular structures due to chemical interaction. They can be divided into 2 subclasses: 1) substances that only inhibit the growth of bacteria; 2) substances that cause their death. The line between them is quite arbitrary and is largely determined by concentration. Disinfectants that cause cell death include almost all heavy metals that form difficult-to-dissociate complexes with sulfhydryl groups, as well as cyan-anions, which form difficult-to-dissociate complexes with iron, thereby blocking the function of the terminal respiratory enzyme cytochrome oxidase. Disinfectants that inhibit the growth of bacteria, when interacting with functional groups of cellular compounds, either lead to their transformation (reversible under certain conditions) into other groups, or inhibit them due to the structural similarity of disinfectants with normal cellular metabolites.
The effectiveness of chemical disinfectants also depends on the possibilities of their transport through cellular structures to the target in the cell. Gracilicute (Gram-negative) and firmicute (Gram-positive) bacteria have different membrane structures, with the main difference being that Gracilicute bacteria have an additional outer layer consisting of phospholipids, lipoproteins and proteins. Both two- and three-layer shell structures provide high selectivity for the penetration of foreign substances from outside into the cell.
In addition to transport restrictions, the effectiveness of chemical disinfectants can be affected by the electrolyte composition of the water being disinfected. For example, when heavy metal cations are used for disinfection, the presence of certain anions (C1~, Br", I", SO^~, POJ", etc.) and an alkaline environment can lead to the formation of highly soluble, poorly dissociated compounds.
The interaction of disinfectants with cell metabolites and chemical compounds contained in it can also lead to a change in the physicochemical properties of the disinfectant. So, according to L.A. Kulsky (1988), the intracellular fluid contains almost 3 mEq/L anions, up to 100 mEq/L HPOj" and almost 20 mEq/L SOj", which is quite sufficient for the conversion of many disinfectants, for example heavy cations metals into slightly dissociated compounds.
The mechanism of bactericidal action makes it possible to explain the synergistic effects that are observed experimentally when water is disinfected with combinations of chemical disinfectants or through physical influence and the action of a chemical disinfectant. From the perspective of the mechanism considered, the action of one of the combination of disinfectants neutralizes the “sacrificial defense” system of the bacterial cell, after which the other disinfectant gains almost unhindered access to the main targets and, interacting with them, inactivates the cell.
Thus, combinations of chemical disinfectants should have optimal bactericidal properties, in which one is capable of irreversibly binding sulfhydryl groups of shell proteins, and the other, having highly selective transport properties, quickly diffuses into the cytoplasm of the cell and, interacting with DNA and RNA, inactivates the bacterial cell. Such highly effective combinations disinfectants are systems C12: H202, C12: 03, C12: Ag+, I2: Ag+, etc. When a combination of physical influence and the action of a chemical disinfectant, as a result of physical impact on the bacterial cell membrane, disorganization or partial destruction of its structure occurs. This facilitates easier transportation of the chemical disinfectant to the cell targets and its further inactivation. The use of combinations of disinfectants is very effective in inactivating mutant bacterial cells, which are found in cell populations in the amount of 10-40%.
The considered mechanism of the bactericidal action of chemical disinfectants makes it possible to explain the patterns of inactivation of viruses and bacteriophages. In particular, the increased resistance of bacteriophages to chemical disinfectants compared to bacterial cells is explained by their presence in the cytoplasm of the bacterium and thus low accessibility to most chemical disinfectants. Inactivation of viruses and bacteriophages outside the bacterial cell by chemical disinfectants is possibly due to denaturation of the protein shells of the virus and interaction with its enzyme systems located under the protein shells.
Disinfection of water by ultraviolet (UV) irradiation. Disinfection of water with UV rays is a physical (reagent-free) method. Reagent-free methods have a number of advantages: when used, the composition and properties of water do not change, unpleasant tastes and odors do not appear, and there is no need for transportation and storage of reagents.
The bactericidal effect is exerted by the UV part of the optical spectrum in the wave range from 200 to 295 nm. The maximum bactericidal effect occurs at 260 nm. Such rays penetrate a 25-centimeter layer of clear and colorless water. Water is disinfected by UV rays quite quickly. After 1-2 minutes of irradiation, vegetative forms of pathogenic microorganisms die. Turbidity and especially color, color and iron salts, reducing the permeability of water to bactericidal UV rays, slow down this process. That is, a prerequisite for reliable disinfection of water with UV rays is its preliminary clarification and bleaching.
Water from underground water sources, the coli index of which is not more than 1000 CFU/l, and the iron content is not more than 0.3 mg/l, are disinfected by UV irradiation using bactericidal lamps. Bactericidal installations are installed on the suction and pressure lines of pumps of the second lift in
Rice. 26. Installation for water disinfection with UV rays (OB AKX-1):
A - section; b - diagram of the movement of water through the chamber; 1 - viewing window; 2 - body; 3 - partitions;
4 - water supply; 5 - mercury-quartz lamp PRK-7; 6 - quartz cover in individual buildings or rooms. If the productivity of a waterworks is up to 30 m3/h, installations with a non-submersible radiation source in the form of low-pressure argon-mercury lamps are used. If the productivity of the station is 30-150 m3/h, then installations with submersible high-pressure mercury-quartz lamps are used (Fig. 26).
When using low-pressure argon-mercury lamps, no toxic by-products are formed in water, whereas under the influence of high-pressure mercury-quartz lamps, the chemical composition of water can change due to photochemical transformations of substances dissolved in water.
The disinfecting effect of bactericidal UV rays is due primarily to photochemical reactions, which results in irreversible damage to the DNA of the bacterial cell. In addition to DNA, UV rays also damage other structural parts of the cell, in particular rRNA and cell membranes. The bactericidal energy yield is 11% at the optimal length of most of the emitted waves.
Thus, bactericidal rays do not denature water and do not change its organoleptic properties, and also have a wider range of abiotic effects - they have a detrimental effect on spores, viruses and helminth eggs that are resistant to chlorine. At the same time, the use of this method of water disinfection complicates the operational control of effectiveness, since the results of determining the microbial number and coli index of water can be obtained only after 24 hours of incubation of crops, and the rapid method, which is similar to the determination of residual free or combined chlorine or residual ozone, does not exist in this case.
Ultrasonic water disinfection. The bactericidal effect of ultrasound is explained mainly by the mechanical destruction of bacteria in the ultrasonic field. Electron microscopy data indicate destruction of the bacterial cell membrane. The bactericidal effect of ultrasound does not depend on turbidity (up to 50 mg/l) and color of water. It applies to both vegetative and spore forms of microorganisms and depends only on the intensity of fluctuations.
Ultrasonic vibrations, which can be used to disinfect water, are produced by piezoelectric or magnetostrictive methods. To obtain water that meets the requirements of GOST 2874-82 "Drinking water. Hygienic requirements and quality control", the ultrasound intensity should be about 2 W/cm2, the oscillation frequency should be 48 kHz per 1 s. Ultrasound with a frequency of 20-30 kHz destroys bacteria in 2-5 s.
Thermal disinfection of water. The method is used to disinfect small amounts of water in sanatoriums, hospitals, on ships, trains, etc. Complete disinfection of water and the death of pathogenic bacteria is achieved after 5-10 minutes of boiling the water. For this type of disinfection, special types of boilers are used.
Disinfection with X-ray radiation. The method involves irradiating water with short-wave X-rays with a wavelength of 60-100 nm. Short-wave radiation penetrates deeply into bacterial cells, causing their significant changes and ionization. The method has not been studied enough.
Disinfection by vacuuming. The method involves the inactivation of bacteria and viruses under reduced pressure. The full bactericidal effect is achieved within 15-20 minutes. The optimal processing mode is at a temperature of 20-60 °C and a pressure of 2.2-13.3 kPa.
Other physical methods of disinfection, such as treatment with y-irradiation, high-voltage discharges, low-power electrical discharges, alternating electric current, are used limitedly due to their high energy intensity, the complexity of the equipment, as well as due to their insufficient knowledge and lack of information about the possibility of formation harmful side compounds. Most of them are currently at the stage of scientific development.
Disinfection of water in the field. The water supply system in the field must guarantee the receipt of high-quality drinking water that does not contain pathogens of infectious diseases. Of the technical means suitable for improving water quality in field conditions, fabric-carbon filters (TCF) deserve special attention: portable, transportable, simple and highly productive.
TUF design by M.N. Klyukanov are intended for temporary use (water supply in field conditions, rural areas,
new buildings, during expeditions). Water is purified and disinfected according to M.N. Klyukanov by simultaneous coagulation and disinfection with increased doses of chlorine (superchlorination) with further filtration through TUV (Fig. 27). Suspended particles are retained on the fabric filter layer, that is, water clarification and discoloration are achieved, and dechlorination is carried out on the carbon filter layer.
For coagulation, aluminum sulfate - A12(S04)3 is used in an amount of 100-200 mg/l. The dose of active chlorine for water disinfection (superchlorination) is at least 50 mg/l. A coagulant and bleach or DTSGK (two-thirds-basic salt of hypo-
Calcium chlorite) in doses of 150 and 50 mg/l, respectively. In this case, coagulation is not affected by the alkalinity of the water:
A) with bleach -
A12(S04)3 + 6CaOC12 + 6H20 -> -> 2A1(OH)3 + 3CaS04 + 3CaC12 + 6HOCI;
B) with DTSGK -
A12(S04)3 + 3Ca(OS1)2 2Ca(OH)2 + 2H20 -> ->2A1(OH)3 + 3CaS04 + 2Ca(OS1)2 + 2HOC1.
Typically, coagulation occurs by the reaction of aluminum sulfate with water bicarbonates, which should be at least 2 mEq/l. In other cases, the water needs to be alkalized.
15 minutes after treatment with the above reagents, the settled water is filtered through TUV. Residual chlorine and organoleptic properties are determined in purified water.
Water supply network and structures on it. The water supply network (water supply distribution system) is an underground system of pipes through which water under pressure (at least 2.5-4 atm for a five-story building) created by a pumping station of the second rise is supplied to a populated area and distributed on its territory. It consists of the main water pipelines through which water from the water supply station enters the populated area, and an extensive network of pipes through which water is supplied to water reservoirs, external water intake structures (street pumps, fire hydrants), residential and public buildings. In this case, the main water pipeline branches into several main lines, which in turn branch into street, courtyard and house lines. The latter are connected to the internal water supply pipe system of residential and public buildings.
Rice. 28. Water supply network diagram: A - dead-end diagram; B - ring circuit; a - pumping station; b - water supply; c - water tower; d - populated areas; d - distribution network
According to the configuration, the water supply network can be: 1) ring; 2) dead end; 3) mixed (Fig. 28). A dead-end network consists of separate blind lines into which water enters from one side. If such a network is damaged in any area, the water supply to all consumers who are connected to the line located behind the point of damage in the direction of water movement is stopped. At the dead-end ends of the distribution network, water can stagnate and sediment may appear, which serves as a favorable environment for the proliferation of microorganisms. As an exception, a dead-end water supply network is installed in small township and rural water supply systems.
The best from a hygienic point of view is a closed water supply network, which consists of a system of adjacent closed circuits, or rings. Damage in any area does not stop the water supply, as it can flow through other lines.
The water supply distribution system must ensure an uninterrupted supply of water to all points of its consumption and prevent water contamination along the entire path of its supply from the main water supply facilities to consumers. To do this, the water supply network must be waterproof. Water pollution in the water supply network during centralized water supply is caused by: leakage of water pipes, a significant decrease in pressure in the water supply network, which leads to the suction of pollution in leaky areas, and the presence of a source of pollution near the site of leakage of water pipes. It is unacceptable to combine household and drinking water supply networks with networks supplying non-potable water (technical water supply).
Water pipes are made of cast iron, steel, reinforced concrete, plastics, etc. Pipes made of polymer materials, as well as internal anti-corrosion coatings, are used only after they have been hygienically assessed and received permission from the Ministry of Health. Steel pipes are used in areas with internal pressure above 1.5 MPa, at intersections with railways, highways, surface reservoirs (rivers), at the intersection of drinking water supply and sewerage. They need to protect the outer and inner surfaces from corrosion. The diameter of drinking water pipes in urban settlements must be at least 100 mm, in rural areas - more than 75 mm. A hermetically sealed connection of individual pipe sections 5-10 m long is achieved using flanges, sockets or couplings (Fig. 29). Flange connections are used only when pipes are laid open (on the surface of the ground), where they are accessible for external inspection and leak testing.
The laying of water supply lines for domestic and drinking water supply must be preceded by a sanitary assessment of the territory by at least 40 m in both directions when the water supply is located in an undeveloped area and by 10-15 m in a built-up area. The soil on which the water supply route will be laid must be uncontaminated. The route should not be laid through swamps, landfills, cemeteries, cattle burial grounds, that is, where the soil is contaminated. It is necessary to organize a sanitary protective strip along the water pipelines (see pp. 129, 130).
Water pipes must be laid 0.5 m below the level of zero temperature in the soil (soil freezing level). Moreover, depending on the climatic region, the depth of laying pipes ranges from 3.5 to 1.5 m. In the southern regions, in order to prevent overheating of water in the summer, the depth of laying water pipes should be such that the soil layer above the pipe is at least 0.0 m thick. 5 m.
Water lines must be laid 0.5 m higher than sewer lines. If water pipes are laid at the same level as parallel sewer lines, the distance between them must be at least 1.5 m for water pipes with a diameter of up to 200 mm and at least 3 m for a diameter over 200 mm. In this case, it is necessary to use metal pipes. Metal water pipes are also used at places where they intersect with sewer lines. In this case, water pipes should be laid 0.5 m higher than sewer pipes. As an exception, at intersections, water pipes can be located below sewer pipes. In this case, it is allowed to use only steel water pipes, additionally protecting them with a special metal casing with a length of at least 5 m on both sides of the intersection in clay soils and at least 10 m in soils with high filtration capacity (for example, sandy). The sewer pipes in the specified area must be cast iron.
The following are installed on water pipelines and water supply lines: butterfly valves (bolts) to isolate repair areas; plungers - to release air during pipeline operation; valves - for the release and admission of air when emptying pipelines of water during repairs and subsequent filling; outlets - for discharging water when emptying pipelines; pressure regulators, valves to protect against water hammer, if you suddenly need to turn off or turn on pumps, etc. The length of repair sections when laying water pipelines in one line should not exceed 3 km, in two lines or more - 5 km.
Shut-off, control and security valves are installed in inspection water supply wells. Inspection wells are also installed at all joints of main, main and street water pipelines. Wells are waterproof reinforced concrete shafts located underground. To descend into the inspection well, there is a hatch with a hermetically sealed lid, which is insulated during the cold season; Cast iron or steel brackets are built into the wall. The danger of water contamination in the water supply network through inspection wells arises when the shaft is filled with water. This can occur as a result of water entering through leaky walls and bottom, storm water through a leaky lid, or water from the water supply network through leaky joints of pipes and fittings. When the pressure in the network decreases, water that has collected in the inspection well can be sucked into the pipes.
Water-pressure (spare) tanks are designed to create a water reserve that compensates for possible discrepancies between water supply and its consumption at certain hours of the day. Reservoirs are filled mainly at night, and during the day, during hours of intensive water use, water from them enters the network, normalizing the pressure.
Water tanks are installed at the highest point of the relief on towers rising above the tallest buildings in the settlement (Fig. 30). The area around the water towers is fenced off. Tanks must be waterproof, made of iron or reinforced concrete. For cleaning, repairing and disinfecting the internal surface of the tank
Rice. 30. Water tower: a - appearance; b - section: I - supply and distribution pipe; 2 - overflow pipe
Hatches with tightly closed and sealed covers are provided. For air exchange, the tanks are equipped with ventilation openings covered with meshes and protected from precipitation. Taps are installed on the pipes supplying and discharging water to take water samples in order to control its quality before and after the tank. Water tanks require periodic (1-2 times a year) disinfection.
On large water pipelines, spare tanks - clean water tanks - are installed underground. From these, water is supplied to the water supply network by pumping stations of the third lift.
Water taps. The population takes water from the water distribution system or through house inlets and taps of the intra-house water supply network, or through external water distribution facilities - standpipes.
Street water taps are the most vulnerable elements of the water supply system. There are many known cases of epidemic outbreaks of infectious diseases, which are called “single column” epidemics.
There are different designs of columns, but the most common are the Cherkunov and Moscow type systems. They are installed in building areas without introducing centralized drinking water supply pipes into the buildings. In this case, the service radius of the column should be no more than 100 m. Recently, in cities with centralized water supply with water intake from surface reservoirs, columns are widely used to organize pump room artesian water supply1.
The water standpipe of the Cherkunov system (Fig. 31) consists of above-ground and underground parts. The underground part (inspection well) looks like a shaft with waterproof reinforced concrete walls and bottom. An ejector is located there (it is installed along the path of water movement from the water main to the internal water tube of the column) and a drain tank with an air tube. A hermetically sealed hatch is located in the reinforced concrete ceiling of the shaft. The ground part of the column has an outlet tube and a handle, which is connected by a rod to a valve located in front of the ejector at the water outlet from the water main. Around the column, within a radius of 1.5-2 m, a blind area is installed with an inclination from the column; under the outlet pipe there is a tray for draining water spilled during use.
When the handle is pressed, the valve opens, and water from the water main rises under pressure through the water pipe and pours out through the outlet pipe of the column. When the handle is released, the valve closes. Since the water remaining in the water pipe freezes and breaks the pipe during the cold season, it is drained into a metal tank at the bottom of the inspection well. In this case, air from the tank enters the shaft through the air tube. When the handle is pressed again and the valve is opened, water, coming out under pressure through a narrowed hole in the water main into the water pipe, activates the ejector. The ejection (suction) effect, which occurs in the first seconds after opening the valve and does not last long, sucks water from the tank into the water tube. The tank is filled with air from the shaft through an air pipe. Thus, the first portions of water coming from the column immediately after pressing the handle are a mixture of water from the water supply network and the drain tank. Due to the suction of water from the tank, the pressure in the ejector is equalized, the ejection effect disappears, after which water is supplied to the consumer exclusively from the water supply network. When the handle is released, the tank is filled again with water from the water tube of the column.
A real threat of water contamination in the dispenser can arise if the dispenser shaft fills with water. The ways in which water enters a mine can be different. Thus, precipitation and surface runoff
*Pump room water supply is provided through local water supply. Its elements are: 1) underground interstratal (preferably artesian) source of class I according to GOST 2761-84; 2) artesian well; 3) underground pumping station with a submersible centrifugal pump; 4) pressure water pipeline; 5) pump room with water dispensers (mainly Moscow type). Pump room artesian water supply is widespread in Kyiv, where centralized water supply is provided through the Dnieper and Desnyansky river and artesian water pipelines.*
Rice. 31. Water dispenser of the Cherkunov system: 1 - part of the ejector and tank; 2 - injector; 3 - coupling; 4 - narrowed end of the water pipe; 5 - counterweight; 6 - tray; 7 - plaster; 8 - flooring made of boards; 9 - air tube; 10 - water pipe; 11 - ejector; 12 - staples; 13 - rod; 14 - sand; 15 - valve (38 mm); 16 - shut-off valve; 17 - tank
They can penetrate into the inspection well through a leaky ceiling or leaking hatch. If the integrity of the reinforced concrete walls and the bottom of the shaft is damaged, water can come from the soil (soil moisture, which is formed during the filtration of atmospheric and melt water), especially when the groundwater level is high. The mine may be flooded with water from the water supply network. This occurs when the pressure in the network drops below 1 atm. Wherein
Transparency and increased color impair the organoleptic properties of well and spring water, limit its use, and sometimes indicate water contamination as a result of errors in the equipment of water intake structures (wells or spring catchments), their improper placement relative to potential sources of pollution, or improper operation. Sometimes the reason for a decrease in transparency and an increase in color of well and spring water can be a high concentration of iron salts (over 1 mg/l).
In well water, which is epidemically safe, the coliform index usually does not exceed 10 (coli-titer is at least 100), the microbial number is no more than 400 per 1 cm3. With such sanitary and microbiological indicators, pathogens of intestinal infections that have a water transmission factor are not detected in water.
The nitrate content in well and spring water should not exceed 45 mg/l, in terms of nitrate nitrogen - 10 mg/l. Exceeding the specified concentration may cause water-nitrate methemoglobinemia (acute toxic cyanosis) in formula-fed infants due to the use of water with a high nitrate content for the preparation of nutritional formulas. A slight increase in the level of methemoglobin in the blood without threatening signs of hypoxia can also be observed in children aged 1 to 6 years, as well as in older people.
An increase in the content of ammonium salts, nitrites and nitrates in well and spring water may indicate contamination of the soil through which the supply water is filtered, as well as the fact that pathogenic microorganisms could have entered along with these substances. With fresh contamination in the water, the content of ammonium salts increases. The presence of nitrates in water in the absence of ammonia and nitrites indicates a relatively ancient intake of nitrogen-containing substances into the water. With systematic pollution in water, both ammonium salts and nitrites and nitrates are detected. Intensive use of nitrogen fertilizers in agriculture also leads to an increase in the content of nitrates in groundwater. An increase in the permanganate oxidation of groundwater above 4 mg/l indicates possible contamination with easily oxidized substances of mineral and organic origin.
One of the indicators of contamination of local water supplies is chlorides. At the same time, high concentrations (over 30-50 mg/l) of chlorides in water can be caused by their leaching from saline soils. Under such conditions, 1 liter of water can contain hundreds and thousands of milligrams of chlorides. Water with a chloride content of more than 350 mg/l has a salty taste and has a negative effect on the body. To correctly assess the origin of chlorides, one should take into account their presence in the water of neighboring water sources of the same type, as well as other indicators of pollution.
In some cases, each of these indicators may have a different nature. For example, organic substances can be of plant origin. Therefore, water from a local source can be considered polluted only under the following conditions: 1) not one, but several sanitary and chemical indicators of pollution are increased; 2) at the same time, sanitary and microbiological indicators of epidemic safety have been increased - microbial number and coli index; 3) the possibility of contamination is confirmed by data from a sanitary inspection of a well or spring capture.
Hygienic requirements for the placement and construction of mine wells. A mine well is a structure with the help of which the population collects groundwater and raises it to the surface. In local water supply conditions, it simultaneously performs the functions of water intake, water lifting and water distribution structures.
When choosing a location for a well, in addition to hydrogeological conditions, it is necessary to take into account the sanitary conditions of the area and the ease of use of the well. The distance from the well to the consumer should not exceed 100 m. Wells are placed along the slope of the area above all sources of pollution located both on the surface and in the thickness of the soil. Subject to these conditions, the distance between the well and the source of pollution (site for underground filtration, cesspool, compost, etc.) must be at least 30-50 m. If the potential source of pollution is located higher in the terrain than the well, then the distance between them is In the case of fine-grained soil, it should be at least 80-100 m, and sometimes even 120-150 m.
The magnitude of the sanitary gap between a well and a potential source of soil pollution can be scientifically substantiated using the Saltykov-Belitsky formula, which takes into account local soil and hydrogeological conditions. The calculation is based on the fact that pollution, moving along with groundwater in the direction of the well, should not reach the point of water intake, that is, there should be enough time to disinfect the pollution. The calculation is made using the formula:
Where L is the permissible distance between the source of pollution and the point of water intake (m), k is the filtration coefficient1 (m/day) determined experimentally or from tables, p, is the groundwater level in the area of contamination of the aquifer, determined experimentally by a level; n2 is the water level of the aquifer at the point of water intake; t is the required time for water to move between the source of pollution and the point of water intake (this time is assumed to be 200 days for bacterial pollution, and 400 days for chemical pollution); ts - active soil porosity2.
*Filtration coefficient is the distance that water travels in the soil, moving vertically downward under the influence of gravity. Depends on the mechanical composition of the soil. For medium-grained sands it is 0.432, for fine-grained sands - 0.043, for loams - 0.0043 m/day.*
*Active porosity is the ratio of the pore volume of a water-bearing rock sample to the total volume of the sample. Depends on the mechanical composition of the soil: for coarse-grained sands - 0.15, for fine-grained sands - 0.35.*
This formula is suitable for calculations only when the water-bearing rock is fine- and medium-grained sand. If the water-bearing layer is represented by coarse-grained sands or even gravelly soils, the safety factor A should be added to the found value:
The coefficient is determined by the formula: A = ai + a2 + a3, where a! - the radius of the depression funnel1 is maximum for coarse sands 300-400 m, for medium gravel - 500-600 m; a2 is the distance over which the pollution plume spreads (depending on the power of the pollution source, it ranges from 10 to 100 m); a3 is the size of the security zone that disrupts the hydraulic connection between the pollution plume and the peripheral end of the radius of the depression funnel (10-15 m).
A well is a vertical shaft of square or round cross-section (with an area of approximately 1 m2), which reaches the aquifer (Fig. 33). The bottom is left open, and the side walls are secured with waterproof material (concrete, reinforced concrete, brick, wood, etc.). A layer of gravel 30 cm thick is poured onto the bottom of the well. The walls of the well must rise above the ground surface by at least 1 m. A clay castle and blind area are installed around the well to prevent the seepage of contaminants along the walls of the well (outside), which are washed out from the surface layers of the soil. To build a clay castle, a hole 2 m deep and 1 m wide is dug around a well and filled with rich clay. For a blind area around the ground part of the well, on top of the clay castle, within a radius of 2 m, a backfill is made with sand and filled with cement or concrete with a slope to divert atmospheric precipitation and water that spills when using the well away from the well. To drain storm water, an intercepting ditch is installed. A fence should be made within a radius of 3-5 m around public wells to restrict vehicle access.
It is advisable to lift water from the well using a pump. If this is not possible, then equip a swing with a public bucket attached to it. It is unacceptable to use your own bucket, as this poses the greatest risk of contaminating the water in the well. The frame of the well is tightly closed with a lid and a canopy is made over the frame and the frame.
Captage is a special structure for collecting spring water (Fig. 34). The water outlet must be fenced with waterproof walls and closed at the top. To prevent surface runoff from entering the spring, diversion ditches are installed. A castle made of greasy clay and a blind area are installed around the walls of the captage. Materials for captage structures can be
*A depression funnel is a zone of low pressure that forms in the water-bearing rock when water is pumped out of a well due to the resistance exerted by the rock. Depends on the mechanical composition of the rock and the speed of pumping out water.*
Rice. 33. General view of a mine well: 1 - bottom three-layer filter; 2 - reinforced concrete rings made of porous concrete; 3 - reinforced concrete rings; 4 - cover; 5 - manhole clamps; 6 - stone blind area; 7 - rotation; 8 - clay castle; 9 - canopy cover
Be concrete, reinforced concrete, brick, stone, wood. To prevent the water in the catchment from rising above a certain level, an overflow pipe is installed at this level.
Sanitation of mine wells. Sanitation of a mine well is a set of measures to repair, clean and disinfect a well in order to prevent contamination of the water in it.
For preventive purposes, the well is sanitized before putting it into operation, and then, if the epidemic situation is favorable, there is no pollution and there are no complaints from the population about the quality of water, periodically once a year after cleaning and routine repairs. It is mandatory to carry out
Rice. 34. Simple capture of a descending spring: 1 - aquifer; 2 - waterproof layer; 3 - gravel filter; 4 - receiving chamber; 5 - inspection well; 6 - inspection well hatch with cover; 7 - ventilation hatch; 8 - partition; 9 - discharge into a sewer or ditch; 10 - pipe supplying water to the consumer
Preventive disinfection after major repairs of a well. Preventive sanitation consists of two stages: 1) cleaning and repair; 2) disinfection.
If there are epidemiological grounds to consider a well a source of spread of acute gastrointestinal infectious diseases, and also if there is a suspicion (especially data) of water contamination with feces, animal corpses, or other foreign objects, sanitation is carried out according to epidemiological indications. Sanitation according to epidemiological indications is carried out in three stages: 1) preliminary disinfection; 2) cleaning and repair; 3) final disinfection.
Methodology for the sanitation of mine wells. Sanitation according to epidemiological indications begins with disinfection of the underwater part of the well using a volumetric method. To do this, determine the volume of water in the well and calculate the required amount of bleach or calcium hypochlorite using the formula:
Where P is the amount of bleach or calcium hypochlorite (g), E is the volume of water in the well (m3); C is the specified concentration of active chlorine in the well water (100-150 g/m3), sufficient to disinfect the walls of the log house and the gravel filter at the bottom, H is the content of active chlorine in bleach or calcium hypochlorite (%); 100 is a constant numerical coefficient. If the water in the well is very cold (+4 °C...+6 °C), the amount of chlorine-containing preparation for disinfecting the well by volumetric method is doubled. The calculated amount of disinfectant is dissolved in a small volume of water in a bucket until a uniform mixture is obtained, clarified by settling and this solution is poured into the well. The water in the well is mixed well for 15-20 minutes with poles or by frequently lowering and raising the bucket on a cable. Then the well is covered with a lid and left for 1.5-2 hours.
After preliminary disinfection, the water is completely pumped out of the well using a pump or buckets. Before a person goes down into the well, they check whether CO2 has accumulated there, for which a lit candle is lowered into a bucket at the bottom of the well. If it goes out, then you can only work in a gas mask.
Then the bottom is cleaned of silt, dirt, debris and random objects. The walls of the log house are mechanically cleaned of dirt and fouling and, if necessary, repaired. Dirt and silt selected from the well are placed in a hole at a distance of at least 20 m from the well to a depth of 0.5 m, filled with a 10% solution of bleach or 5% calcium hypochlorite solution and buried.
For final disinfection, the outer and inner surfaces of the log house are irrigated from a hydraulic console with a 5% solution of bleach or a 3% solution of calcium hypochlorite at the rate of 0.5 dm3 per 1 m2 of area. Then they wait until the well is filled with water to the usual level, after which the underwater part is disinfected using a volumetric method at the rate of 100-150 mg of active chlorine per 1 liter of water in the well for 6-8 hours. After the specified contact time, a water sample is taken from the well and check it for the presence of residual chlorine or do a smell test. If there is no smell of chlorine, add 1/4 or 1/3 of the original amount of the drug and leave for another 3-4 hours. After this, a water sample is taken and sent to the territorial SES laboratory for bacteriological and physicochemical analysis. At least 3 studies must be carried out, each 24 hours later.
Disinfection of a well for preventive purposes begins with determining the volume of water in the well. Then they pump out the water, clean and repair the well, disinfect the outer and inner parts of the log house using the irrigation method, wait until the well is filled with water, and disinfect the underwater part using the volumetric method.
Disinfection of water in a well using dosing cartridges. Among the measures to improve the local water supply, an important place is occupied by the continuous disinfection of water in the well using dosing cartridges. Indications for this are: 1) non-compliance of microbiological indicators of water quality in the well with sanitary requirements; 2) presence of signs of water contamination according to sanitary and chemical indicators (disinfected until the source of contamination is identified and positive results are obtained after sanitation); 3) insufficient improvement in water quality after disinfection (sanitation) of the well (coli titer below 100, coli index above 10); 4) in foci of intestinal infections in a populated area after disinfection of the well until the outbreak is eliminated. Only specialists from the territorial SES disinfect the water in the well using a dosing cartridge, always monitoring the quality of the water according to sanitary-chemical and microbiological indicators.
Dosing cartridges are cylindrical ceramic containers with a capacity of 250, 500 or 1000 cm3. They are made from: fireclay clay, infusor earth (Fig. 35). Bleach or calcium hypochlorite is poured into the cartridges and immersed in the well. Quantity
Rice. 35. Dosing cartridge
The chlorine-containing substances required for water disinfection depend on many factors. These include: the initial quality of groundwater, the nature, degree of contamination and volume of water in the well, the intensity and mode of water withdrawal, the rate of groundwater inflow, and the flow rate of the well. The amount of active chlorine also depends on the sanitary condition of the well: the amount of bottom sludge, the degree of contamination of the log house, etc. It is known that pathogens of intestinal infections in bottom sludge find favorable conditions and maintain vital activity for a long time. This is why long-term disinfection (chlorination) of water using dosing cartridges cannot be effective without first cleaning and disinfecting the well.
The amount of calcium hypochlorite with an activity of at least 52%, required for long-term disinfection of water in a well, is calculated using the formula:
X, = 0.07 X2 + 0.08 X3+ 0.02 X4 + 0.14 X5,
Where X is the amount of drug required to load the cartridge (kg), X2 is the volume of water in the well (m3), calculated as the product of the cross-sectional area of the well and the height of the water column; X3 - well flow rate (m3/h), determined experimentally; X4 - water withdrawal (m3/day), determined by surveying the population; X5 - chlorine absorption of water (mg/l), determined experimentally.
The formula is given to calculate the amount of calcium hypochlorite containing 52% active chlorine. In case of disinfection with bleach (25% active chlorine), the calculated amount of the drug should be doubled. When disinfecting water in a well in winter, the calculated amount of the drug is also doubled. If the content of active chlorine in the disinfectant is lower than calculated, then recalculation is made using the formula:
Where P is the amount of bleach or calcium hypochlorite (kg); X! - the amount of calcium hypochlorite calculated using the previous formula (kg); H, is the content of active chlorine in calcium hypochlorite, taken into account (52%o); H2 is the actual content of active chlorine in the preparation - calcium hypochlorite or bleach (%). In addition, when disinfecting water in a well in winter, the calculated amount of the drug is doubled. To determine the flow rate - the amount of water (in 1 m3) that can be obtained from a well in 1 hour, it is quickly pumped out over a certain period of time.
From it, water is measured, its quantity is measured, and the time of restoration of the initial water level is recorded. Calculate the flow rate of the well using the formula:
Where D is the flow rate of the well (m3/h), V is the volume of pumped water (m3); t is the total time, consisting of the time of pumping and restoration of the water level in the well (min); 60 is a constant coefficient.
Before filling, the cartridge is first kept in water for 3-5 hours, then filled with the calculated amount of a chlorine-containing disinfectant, 100-300 cm3 of water is added and thoroughly mixed (until a uniform mixture is formed). After this, the cartridge is closed with a ceramic or rubber stopper, suspended in the well and immersed in the water column approximately 0.5 m below the upper water level (0.2-0.5 m from the bottom of the well). Due to the porosity of the cartridge walls, active chlorine enters the water.
The concentration of active residual chlorine in the well water is monitored 6 hours after immersion of the dosing cartridge. If the concentration of active residual chlorine in the water is below 0.5 mg/l, it is necessary to immerse an additional cartridge and then carry out appropriate monitoring of the effectiveness of disinfection. If the concentration of active residual chlorine in the water is significantly higher than 0.5 mg/l, remove one of the cartridges and carry out appropriate monitoring of the effectiveness of disinfection. In the future, the concentration of active residual chlorine is monitored at least once a week, also checking microbiological indicators of water quality.
When purifying water, it is necessary to use disinfection methods that eliminate the danger from pathogenic bacteria remaining in it after filtration and coagulation. The main ones are: chlorination, ozonation, the use of heavy metal salts and physical methods of exposure (ultrasound and ultraviolet). Large treatment plants use chlorination and cleaning with chlorine-containing substances. However, is this method so effective and safe?
Use of chlorine and substances containing it
The essence of this method of water disinfection is to create conditions for the occurrence of redox-type chemical reactions. The effect of chlorine on organic compounds disrupts the metabolism of bacterial cells, which leads to their death.
The effectiveness of the reagent depends on the presence of free or combined chlorine in its composition, as well as on its concentration. The optimal option is to match the amount of the reagent with the concentration of bacteria, which will lead to complete oxidation of all impurities of various origins. In case of excessive consumption of chlorine, flakes and lumps appear in the water, formed by the adsorption of suspended substances. As a result, it turns out that bacteria and microbes inside them remain in a protected, untouched state, which is unacceptable.
During the process of water disinfection, destruction, decomposition or mineralization of impurities occurs. If the effluent contains soluble and insoluble elements, the reaction may produce unpleasant odors due to the breakdown of chlorine-containing products, as well as organic substances and organisms. Phenols and aromatic compounds are considered the most unpleasant, since the taste of water changes if they are present in just one ten-millionth part. The situation may worsen even more as the temperature rises in the form of a persistent odor.
Chlorine-containing components also help to filter and clarify wastewater:
- Hypochlorous acid is weak and therefore its action must be ensured by the activity of the environment and the appropriate type of chemical reaction.
- Chlorine dioxide is of greatest interest in disinfection, since after treatment no phenols are formed, and, accordingly, the absence of an unpleasant odor is guaranteed.
To avoid the appearance of odor and taste in water, chlorination and ammoniation are performed. In the process of hydrolysis of chloramines, due to the slow rate of reaction, the antibacterial property is manifested.
However, despite all the advantages of chlorination, this method has a serious drawback, which is the lack of complete sterility of the water. Spore-forming bacteria and some types of dangerous viruses remain in the water in isolated quantities. To destroy them, it is necessary to significantly increase the chlorine concentration and contact time.
Ozonation of water
The ozonation method involves high diffusion of ozone through the shells of microorganisms dissolved in water, followed by their oxidation and death. Possessing a high antibacterial effect, ozone is capable of destroying pathogenic bacteria several times faster than chlorine under other identical conditions. Maximum efficiency is achieved when vegetative bacteria are destroyed. Spore-forming microorganisms are highly resistant and are much less easily destroyed.
An important point in this method is the selection of ozone concentrations in water, since this directly determines which bacteria will be destroyed and which will not. For example, to destroy zebra mussels, a dose of 3 mg/l will be required, which is completely safe for the continued existence of water mites and chiromonids. Therefore, it is necessary to determine the chemical composition of water and determine the types of microorganisms that are found in it, that is, the degree of water contamination. Typically the dose is in the range of 0.5-4.0 mg/l.
The degree of water disinfection and clarification with ozone significantly worsens with increased turbidity. However, the degree of purification is practically independent of water temperature.
Among the advantages of the method are the following:
- Improving the taste of water and the complete absence of additional chemically active substances or their compounds.
- There is no need for additional actions if the ozone concentration is exceeded, as, for example, in the case of chlorination.
- The ability to create ozone through a chemical reaction directly in an aqueous solution or using ozonizers.
Judging from the above, the method is safe and effective, but its widespread use in cleaning has become the need to use a large amount of electricity, as well as the complexity of its technical implementation.
Use of silver ions
Water disinfection using silver ions is based on emerging chemical processes that are not fully understood. However, the following hypotheses have been put forward:
- Ions disrupt the metabolism of bacteria with the external environment, which leads to their death.
- Due to adsorption on the surface of microorganisms, ions perform a catalytic role and oxidize the plasma in the presence of oxygen.
- Ions penetrate inside the harmful cell and reliably connect with the protoplasm, disrupting its functionality and, thus, destroying it.
The rate of a chemical reaction increases with increasing concentration of reactants and increasing temperature of the environment. When heated to 10 0, the reaction rate increases several times after a certain period of time. Therefore, complete disinfection at optimal speed and in the shortest possible time is achieved by heating to a certain temperature level, which depends on the degree of contamination.
Metallic silver is also used for water purification, since it contains silver ions with a low concentration, which act as purifiers. Their accumulation is stimulated by the presence of an increased area of contact with metallic silver. Therefore, when using this method, they achieve an increase in the contact surface due to deposition onto a material with a developed area, through which water is passed.
Technically, this method is implemented by creating electrolytic processes when silver acts as the anode material. By adjusting electrical parameters, it is possible to achieve the desired ion concentration and regulate the water disinfection process with high precision. To accurately dose silver ions, ionizers are used. The concentration is adjusted by assessing the content of salts, which cause changes in the potential between the electrodes. Therefore, “silver water” is prepared separately.
When comparing the silver ionization method with chlorination, scientists highlight the former because it is able to kill bacteria and microorganisms more effectively. However, it is quite difficult for him to cope with certain types of bacteria, for example, coli (Escherichia coli). It is the most stable and therefore, by its presence in the solution, one can qualitatively judge the degree of water purification. Just as with ozonation, the turbidity of the solution and the amount of suspended particles influence the cleaning speed.
Disinfection of water with ultrasonic waves
Ultrasonic disinfection is based on the creation of elastic waves, the frequency of which exceeds 20 kHz and has a certain intensity. They change the properties of the liquid and destroy organic substances by increasing the surrounding pressure by 10 5 atmospheres (cavitation effect). That is, the death of bacteria occurs not due to a chemical reaction occurring, but as a result of mechanical destruction, causing the breakdown of the protein component of the protoplasm. The most vulnerable are single-celled microorganisms, monogenetic flukes, as well as larger organisms that pollute water.
There are several ways to create radiation:
- Piezoelectric effect. When an electric field is created, quartz crystals are capable of deforming and emitting ultrasonic waves. Quartz plates of the same thickness and a certain shape are used, polished and tightly applied on both sides of a thick steel plate. When current is applied to a massive plate in an electric field, it emits ultrasound.
- Magnetostriction effect. It is based on the magnetization of ferromagnetic objects under the influence of a magnetic field, changing their geometric dimensions and volume with a subsequent shift of the axial line. The effect depends on the angle of application of the field relative to the crystal axis, if we are talking about a single crystal. In terms of ultrasound level measurements, this method is more effective than the first.
In laboratory studies, it was found that ultrasound is capable of destroying more than 95% of E. coli in up to two minutes. However, it is worth understanding that at the same time as harmful bacteria, beneficial bacteria are also destroyed. In particular, a violation of the flora and fauna of marine plankton was established. That is, we can conclude that the method is very effective, but when exposed to it, water loses its beneficial properties, which is its main disadvantage.
Heat treatment
The method is based on boiling water by raising the temperature above 100 0 C. A fairly effective method of water disinfection, but slow compared to other methods and requiring significant energy expenditure for heating. Therefore, it is used only in cases where the volume of water is minimal. It is simple and does not require special skills and knowledge, therefore it has become widespread for obtaining small quantities of drinking water in canteens, hospitals, etc. Due to its bulkiness and economic infeasibility, it is not used on an industrial or small scale. 
One of the disadvantages is the fact that heat treatment of water is not able to remove pathogenic spores. Therefore, this method cannot be used when disinfecting aqueous solutions with an unknown chemical composition.
Ultraviolet lamps
Ultraviolet disinfection is achieved through the use of rays with a wavelength in the range of 2000-2950 A, which change the shape of bacteria, completely destroying them. The effect depends on the energy imparted by the radiation, the content of suspended matter in the solution, the number of microorganisms, turbidity and absorption capacity of the aquatic environment. Therefore, it is customary to distinguish between the following degrees of influence of radiation exposure:
- A safe dose of radiation that does not kill bacteria.
- The minimum dose that causes the death of some bacteria of a particular species. However, bacteria that were dormant begin to actively grow and multiply in a specially stimulated environment. With prolonged exposure, they die out.
- Full dose, which leads to water disinfection.
E. coli are the most resistant to UV radiation. Therefore, by their quantity it is possible to qualitatively determine the degree of water disinfection in the absence of spore-forming bacteria. If they are present, the criterion for water purity is the emergence of radiation resistance of bacteria that form spores.
Sources of UV radiation are mercury, argon-mercury or mercury-quartz lamps. The effectiveness and feasibility of their use directly depends on the absorption coefficient. Lamps with low pressure have a maximum bacterial effect, but have a power of up to 30 W, and with a high one - less effect, but increased power.
The advantages of the method are:
- There is no need to use the physical or chemical properties of water or the use of reagents.
- No precipitation or impurities.
- Consistency of color and taste of water, as well as the absence of foreign odors.
- Ease of implementation.
That is, the UV method is the safest and most effective when performing the process of water disinfection and is completely devoid of the disadvantages of all the methods described above. However, before using it, pre-treatment must be performed to reduce the impurity content.
If you need to purify water with disinfection, you should contact professionals who can evaluate the composition and correctly select the most effective methods. The EGA company will be able to complete the assigned tasks in the shortest possible time thanks to the coordinated actions of a team of experienced specialists. As a result, the water will be safe to use as drinking water.
Video
Water is an integral part of our life. We drink a certain amount every day and often don’t even think about the fact that water disinfection and its quality are an important topic. But in vain, heavy metals, chemical compounds and pathogenic bacteria can cause irreversible changes in the human body. Today, serious attention is paid to water hygiene. Modern methods of disinfecting drinking water can clean it of bacteria, fungi, and viruses. They will also come to the rescue if the water smells bad, has foreign tastes, or is colored.
Preferred methods for improving quality are selected depending on the microorganisms contained in the water, the level of contamination, the source of the water supply and other factors. Disinfection is aimed at removing pathogenic bacteria that have a destructive effect on the human body.
Purified water is transparent, has no foreign tastes or odors, and is absolutely safe. In practice, methods of two groups, as well as their combination, are used to combat harmful microorganisms:
- chemical;
- physical;
- combined.
In order to select effective disinfection methods, it is necessary to analyze the liquid. Among the analyzes performed are:
- chemical;
- bacteriological;
The use of chemical analysis makes it possible to determine the content of various chemical elements in water: nitrates, sulfates, chlorides, fluorides, etc. Nevertheless, the indicators analyzed by this method can be divided into 4 groups:
- Organoleptic indicators. Chemical analysis of water allows you to determine its taste, smell and color.
- Integral indicators – density, acidity and water hardness.
- Inorganic – various metals contained in water.
- Organic indicators are the content of substances in water that can change under the influence of oxidizing agents.
Bacteriological analysis is aimed at identifying various microorganisms: bacteria, viruses, fungi. Such an analysis reveals the source of contamination and helps determine disinfection methods.
Chemical methods for disinfecting drinking water
Chemical methods are based on adding various oxidizing reagents to water that kill harmful bacteria. The most popular among such substances are chlorine, ozone, sodium hypochlorite, and chlorine dioxide.
To achieve high quality, it is important to correctly calculate the dose of the reagent. A small amount of a substance may have no effect, and even, on the contrary, contribute to an increase in the number of bacteria. The reagent must be administered in excess, this will destroy both existing microorganisms and bacteria that have entered the water after disinfection.
The excess must be calculated very carefully so that it cannot harm people. The most popular chemical methods:
- chlorination;
- ozonation;
- oligodynamy;
- polymer reagents;
- iodination;
- bromination.
Chlorination
Water purification by chlorination is traditional and one of the most popular methods of water purification. Chlorine-containing substances are actively used to purify drinking water, water in swimming pools, and disinfect premises.
This method has gained popularity due to its ease of use, low cost, and high efficiency. Most pathogenic microorganisms that cause various diseases are not resistant to chlorine, which has a bactericidal effect.
To create unfavorable conditions that prevent the proliferation and development of microorganisms, it is enough to introduce chlorine in a slight excess. Excess chlorine helps prolong the disinfection effect.
During water treatment, the following chlorination methods are possible: preliminary and final. Pre-chlorination is used as close as possible to the point of water intake; at this stage, the use of chlorine not only disinfects the water, but also helps remove a number of chemical elements, including iron and manganese. Final chlorination is the last stage in the treatment process, during which harmful microorganisms are destroyed through chlorine.
There is also a distinction between normal chlorination and overchlorination. Normal chlorination is used to disinfect liquids from sources with good sanitary characteristics. Overchlorination - in case of severe contamination of water, as well as if it is contaminated with phenols, which in the case of normal chlorination only worsen the condition of the water. In this case, the remaining chlorine is removed by dechlorination.
Chlorination, like other methods, along with its advantages, also has its disadvantages. When chlorine enters the human body in excess, it leads to problems with the kidneys, liver, and gastrointestinal tract. The high corrosiveness of chlorine leads to rapid wear of equipment. The chlorination process produces all sorts of byproducts. For example, trihalomethanes (chlorine compounds with substances of organic origin) can cause asthma symptoms.
Due to the widespread use of chlorination, a number of microorganisms have developed resistance to chlorine, so a certain percentage of water contamination is still possible.
The most commonly used water disinfectants are chlorine gas, bleach, chlorine dioxide, and sodium hypochlorite.
Chlorine is the most popular reagent. It is used in liquid and gaseous form. By destroying pathogenic microflora, it eliminates unpleasant taste and smell. Prevents the growth of algae and leads to improved fluid quality.
For purification with chlorine, chlorinators are used, in which chlorine gas is absorbed with water, and then the resulting liquid is delivered to the place of use. Despite the popularity of this method, it is quite dangerous. Transportation and storage of highly toxic chlorine requires compliance with safety precautions.
Chloride of lime is a substance produced by the action of chlorine gas on dry slaked lime. To disinfect liquids, bleach is used, the percentage of chlorine in which is at least 32-35%. This reagent is very dangerous for humans and causes difficulties in production. Due to these and other factors, bleach is losing its popularity.
Chlorine dioxide has a bactericidal effect and practically does not pollute water. Unlike chlorine, it does not form trihalomethanes. The main reason that hinders its use is its high explosion hazard, which complicates production, transportation and storage. Currently, on-site production technology has been mastered. Destroys all types of microorganisms. To the disadvantages This may include the ability to form secondary compounds – chlorates and chlorites.
Sodium hypochlorite is used in liquid form. The percentage of active chlorine in it is twice as high as in bleach. Unlike titanium dioxide, it is relatively safe during storage and use. A number of bacteria are resistant to its effects. In case of long-term storage, it loses its properties. It is available on the market in the form of a liquid solution with varying chlorine content.
It is worth noting that all chlorine-containing reagents are highly corrosive, and therefore they are not recommended for use to purify water entering water through metal pipelines.
Ozonation
Ozone, like chlorine, is a strong oxidizing agent. Penetrating through the membranes of microorganisms, it destroys the cell walls and kills it. both with water disinfection and with its decolorization and deodorization. Capable of oxidizing iron and manganese.
Possessing a high antiseptic effect, ozone destroys harmful microorganisms hundreds of times faster than other reagents. Unlike chlorine, it destroys almost all known types of microorganisms.
When decomposed, the reagent is converted into oxygen, which saturates the human body at the cellular level. The rapid decay of ozone at the same time is also a disadvantage of this method, since after 15-20 minutes. after the procedure, the water may become re-contaminated. There is a theory according to which, when water is exposed to ozone, the phenolic groups of humic substances begin to decompose. They activate organisms that were dormant until the moment of treatment.
When water is saturated with ozone, it becomes corrosive. This leads to damage to water pipes, plumbing fixtures, and household appliances. In the case of an erroneous amount of ozone, the formation of by-products that are highly toxic may occur.
Ozonation has other disadvantages, which include the high cost of purchase and installation, high electrical costs, as well as a high ozone hazard class. When working with the reagent, care and safety precautions must be observed.
Ozonation of water is possible using a system consisting of:
- an ozone generator in which the process of separating ozone from oxygen occurs;
- a system that allows you to introduce ozone into water and mix it with the liquid;
- reactor - a container in which ozone interacts with water;
- destructor - a device that removes residual ozone, as well as devices that control ozone in water and air.
Oligodynamy
Oligodynamy is the disinfection of water through exposure to noble metals. The most studied uses of gold, silver and copper.
The most popular metal for the purpose of destroying harmful microorganisms is silver. Its properties were discovered in ancient times; a spoon or a silver coin was placed in a container of water and the water was allowed to settle. The assertion that this method is effective is quite controversial.
Theories about the influence of silver on microbes have not received final confirmation. There is a hypothesis according to which the cell is destroyed by electrostatic forces arising between silver ions with a positive charge and negatively charged bacterial cells.
Silver is a heavy metal that, if accumulated in the body, can cause a number of diseases. An antiseptic effect can be achieved only with high concentrations of this metal, which is harmful to the body. A smaller amount of silver can only stop the growth of bacteria.
In addition, spore-forming bacteria are practically insensitive to silver; its effect on viruses has not been proven. Therefore, the use of silver is advisable only to extend the shelf life of initially pure water.
Another heavy metal that can have a bactericidal effect is copper. Even in ancient times, it was noticed that water that stood in copper vessels retained its high substances much longer. In practice, this method is used in basic domestic conditions to purify a small volume of water.
Polymer reagents
The use of polymer reagents is a modern method of water disinfection. It significantly outperforms chlorination and ozonation due to its safety. Liquid purified with polymer antiseptics has no taste or foreign odors, does not cause metal corrosion, and does not affect the human body. This method has become widespread in water purification in swimming pools. Water purified with a polymer reagent has no color, foreign taste or smell.
Iodination and bromination
Iodination is a disinfection method that uses iodine-containing compounds. The disinfecting properties of iodine have been known to medicine since ancient times. Despite the fact that this method is widely known and attempts have been made to use it several times, the use of iodine as a water disinfectant has not gained popularity. This method has a significant drawback: dissolving in water, it causes a specific odor.
Bromine is a fairly effective reagent that destroys most known bacteria. However, due to its high cost, it is not popular.
Physical methods of water disinfection
Physical methods of purification and disinfection work on water without the use of reagents or interference with the chemical composition. The most popular physical methods:
- UV irradiation;
- ultrasonic influence;
- heat treatment;
- electric pulse method;
UV radiation
The use of UV radiation is gaining increasing popularity among water disinfection methods. The technique is based on the fact that rays with a wavelength of 200-295 nm can kill pathogenic microorganisms. Penetrating through the cell wall, they affect nucleic acids (RND and DNA), and also cause disturbances in the structure of membranes and cell walls of microorganisms, which leads to the death of bacteria.
To determine the radiation dose, it is necessary to conduct a bacteriological analysis of the water, this will identify the types of pathogenic microorganisms and their susceptibility to rays. Efficiency is also affected by the power of the lamp used and the level of radiation absorption by water.
The dose of UV radiation is equal to the product of the radiation intensity and its duration. The higher the resistance of microorganisms, the longer it is necessary to influence them
UV radiation does not affect the chemical composition of water, does not form side compounds, thus eliminating the possibility of harm to humans.
When using this method, an overdose is impossible; UV irradiation has a high reaction rate; it takes several seconds to disinfect the entire volume of liquid. Without changing the composition of water, radiation can destroy all known microorganisms.
However, this method is not without its drawbacks. Unlike chlorination, which has a prolonged effect, the effectiveness of irradiation remains as long as the rays affect the water.
A good result is achievable only in purified water. The level of ultraviolet absorption is affected by impurities contained in the water. For example, iron can serve as a kind of shield for bacteria and “hide” them from exposure to rays. Therefore, it is advisable to pre-purify the water.
The UV radiation system consists of several elements: a stainless steel chamber in which a lamp is placed, protected by quartz covers. Passing through the mechanism of such an installation, water is constantly exposed to ultraviolet radiation and completely disinfected.
Ultrasonic disinfection
Ultrasonic disinfection is based on the cavitation method. Due to the fact that sharp changes in pressure occur under the influence of ultrasound, microorganisms are destroyed. Ultrasound is also effective in combating algae.
This method has a narrow range of use and is at the development stage. The advantage is insensitivity to high turbidity and color of water, as well as the ability to influence most forms of microorganisms.
Unfortunately, this method is only applicable for small volumes of water. Like UV irradiation, it only has an effect when it interacts with water. Ultrasonic disinfection has not gained popularity due to the need to install complex and expensive equipment.
Thermal treatment of water
At home, the thermal method of purifying water is the well-known boiling. High temperature kills most microorganisms. In industrial conditions, this method is ineffective due to its bulkiness, time-consuming and low intensity. In addition, heat treatment is not able to get rid of foreign tastes and pathogenic spores.
Electropulse method
The electropulse method is based on the use of electrical discharges that form a shock wave. Under the influence of hydraulic shock, microorganisms die. This method is effective for both vegetative and spore-forming bacteria. Able to achieve results even in cloudy water. In addition, the bactericidal properties of treated water last up to four months.
The downside is high energy consumption and high cost.
Combined methods of water disinfection
To achieve the greatest effect, combined methods are used; as a rule, reagent methods are combined with non-reagent ones.
The combination of UV irradiation with chlorination has become very popular. Thus, UV rays kill pathogenic microflora, and chlorine prevents re-infection. This method is used both for drinking water purification and for purifying water in swimming pools.
To disinfect swimming pools, UV radiation is mainly used with sodium hypochlorite.
You can replace chlorination at the first stage with ozonation
Other methods include oxidation in combination with heavy metals. Both chlorine-containing elements and ozone can act as oxidizing agents. The essence of the combination is that oxidizing agents kill harmful microbes, and heavy metals help keep water disinfected. There are other methods of complex water disinfection.
Purification and disinfection of water in domestic conditions
It is often necessary to purify water in small quantities right here and now. For these purposes use:
- soluble disinfectant tablets;
- potassium permanganate;
- silicon;
- improvised flowers, herbs.
Disinfectant tablets can help out when traveling. As a rule, one tablet is used per 1 liter. water. This method can be classified as a chemical group. Most often, these tablets are based on active chlorine. The action time of the tablet is 15-20 minutes. In case of severe contamination, the amount can be doubled.
If suddenly there are no tablets, it is possible to use ordinary potassium permanganate at the rate of 1-2 g per bucket of water. After the water has settled, it is ready for use.
Natural plants also have a bactericidal effect - chamomile, celandine, St. John's wort, lingonberry.
Another reagent is silicon. Place it in water and let it sit for 24 hours.
Sources of water supply and their suitability for disinfection
Sources of water supply can be divided into two types - surface and groundwater. The first group includes water from rivers and lakes, seas and reservoirs.
When analyzing the suitability of drinking water located on the surface, bacteriological and chemical analysis is carried out, the condition of the bottom, temperature, density and salinity of sea water, radioactivity of water, etc. are assessed. An important role when choosing a source is played by the proximity of industrial facilities. Another stage in assessing the source of water intake is calculating the possible risks of water contamination.
The composition of water in open reservoirs depends on the time of year; such water contains various contaminants, including pathogens. The risk of contamination of water bodies near cities, plants, factories and other industrial facilities is highest.
River water is very turbid, characterized by color and hardness, as well as a large number of microorganisms, infection of which most often occurs from waste water. Blooms due to the development of algae are common in water from lakes and reservoirs. Also such waters
The peculiarity of surface sources is the large water surface that comes into contact with the sun's rays. On the one hand, this contributes to the self-purification of water, on the other hand, it serves the development of flora and fauna.
Despite the fact that surface waters can self-purify, this does not save them from mechanical impurities and pathogenic microflora, therefore, when water is collected, they undergo thorough purification with further disinfection.
Another type of water intake source is groundwater. The content of microorganisms in them is minimal. Spring and artesian water are best suited to supply the population. To determine their quality, experts analyze the hydrology of rock layers. Particular attention is paid to the sanitary condition of the territory in the area of water intake, since this affects not only the quality of water here and now, but also the prospect of infection by harmful microorganisms in the future.
Artesian and spring water is superior to water from rivers and lakes; it is protected from bacteria contained in waste water, from exposure to sunlight and other factors that contribute to the development of unfavorable microflora.
Regulatory documents of water and sanitary legislation
Since water is the source of human life, its quality and sanitary condition are given serious attention, including at the legislative level. The main documents in this area are the Water Code and the Federal Law “On the Sanitary and Epidemiological Welfare of the Population.”
The Water Code contains rules for the use and protection of water bodies. Provides a classification of groundwater and surface waters, determines penalties for violation of water legislation, etc.
The Federal Law “On the Sanitary and Epidemiological Welfare of the Population” regulates the requirements for sources from which water can be used for drinking and housekeeping.
There are also state quality standards that determine suitability indicators and put forward requirements for water analysis methods:
GOST water quality standards
- GOST R 51232-98 Drinking water. General requirements for organization and methods of quality control.
- GOST 24902-81 Water for domestic and drinking purposes. General requirements for field methods of analysis.
- GOST 27064-86 Water quality. Terms and Definitions.
- GOST 17.1.1.04-80 Classification of groundwater according to water use purposes.
SNiPs and water requirements
Building codes and regulations (SNiP) contain rules for organizing the internal water supply and sewerage systems of buildings, regulate the installation of water supply, heating systems, etc.
- SNiP 2.04.01-85 Internal water supply and sewerage of buildings.
- SNiP 3.05.01-85 Internal sanitary systems.
- SNiP 3.05.04-85 External networks and structures of water supply and sewerage.
Sanitary standards for water supply
In the sanitary and epidemiological rules and regulations (SanPiN) you can find what requirements exist for the quality of water both from the central water supply and water from wells and boreholes.
- SanPiN 2.1.4.559-96 “Drinking water. Hygienic requirements for water quality of centralized drinking water supply systems. Quality control."
- SanPiN 4630-88 “MPC and TAC of harmful substances in water of water bodies for domestic, drinking and cultural water use”
- SanPiN 2.1.4.544-96 Requirements for water quality of non-centralized water supply. Sanitary protection of sources.
- SanPiN 2.2.1/2.1.1.984-00 Sanitary protection zones and sanitary classification of enterprises, structures and other objects.