How to improve the quality of drinking water. How to improve the quality of tap water? Water filtration systems
Water is the main component of the liquid medium of the human body. The adult human body is 60% water.
Nowadays tap water contains chemical organic and other compounds and cannot be considered drinking water without preliminary treatment.
To improve the quality of drinking water, the following purification methods can be proposed:
1. Neutralization method. Pour water from the tap into a container (glass or enamel). Leave the container open for 24 hours. During this time, chlorine, ammonia and other gaseous substances will come out of the water. Then boil it for one hour. From the moment of boiling, achieve only a slight bubbling. As a result of heat treatment, a significant part of foreign substances is eliminated. After cooling, the water has not yet been completely freed from chemical and organic substances, but it can already be used for cooking. For drinking purposes, it must be completely neutralized; to do this, add 500 mg of ascorbic acid to 5 liters of boiled water, 300 mg to 3 liters, mix and leave for one hour. Instead of ascorbic acid, you can add fruit juice, colored red, dark red, burgundy to a light pinkish tint, and leave for one hour. To neutralize, you can use drunk tea, which is added to the water until the color changes slightly, and left for one hour.
2. Freezing method. For this, milk and juice bags can be used, into which tap water is poured, adding 1 - 1.5 cm to the edge. The bags filled with water should be placed in the freezer or in the cold for 5 - 8 hours, after which take out the bags, remove the ice crust, pour the water into another bag. Ice crust and ice frozen on the inside of the bag is heavy (harmful) water. Water poured into bags is frozen for 12 to 18 hours. Then the bags are taken out, the outer walls are moistened with warm water, the ice crystals are removed to thaw, and the liquid remaining in the bags is nothing more than a brine consisting of foreign and mineral substances, which must be poured down the drain.
If your bags are frozen and a solid crystal with a middle rod has formed, then, without removing it from the bag, wash the rod with warm water, leaving clear ice, then remove the ice to thaw. To improve the taste, add 1 g of sea salt (purchased at a pharmacy) to a bucket of melt water. If it is absent, add 1/4 - 1/5 cup to 1 liter of melt water mineral water. Freshly melted water obtained from ice, or better yet from snow, has therapeutic and prophylactic properties. When consumed, recovery processes are accelerated. Such water promotes adaptation in extreme conditions (under thermal stress, with reduced oxygen content in the air), it significantly increases muscle performance. Melt water has anti-allergic properties and is used, for example, for bronchial asthma, itchy dermatitis of an allergic nature, and stomatitis. However, this water should be used with caution and should be taken 1/2 glass 3 times a day for an adult. For a child 10 years old - 1/4 cup 3 times a day
Z. I. Khata - M.: FAIR PRESS, 2001
The composition of water can be different. After all, on the way to our home she encounters many obstacles. There are various methods for improving water quality, the general goal of which is to get rid of dangerous bacteria, humic compounds, excess salt, toxic substances, etc.
Water is the main component of the human body. It is one of the most important links in energy information exchange. Scientists have proven that thanks to the special network structure of water, which is created by hydrogen bonds, information is received, accumulated and transmitted.
The aging of the body and the volume of water in it are directly related to each other. Therefore, water should be consumed every day, making sure that it is of high quality.
Water is a powerful natural solvent, therefore, when it encounters different rocks on its way, it quickly becomes enriched with them. However, not all elements found in water are beneficial to humans. Some of them negatively affect the processes occurring in the human body, others can cause various diseases. In order to protect consumers from harmful and dangerous impurities, measures are being taken to improve the quality of drinking water.
Ways to improve
There are basic and special methods for improving the quality of drinking water. The first involves lightening, disinfection and bleaching, the second involves procedures for defluoridation, iron removal and desalting.
Decolorization and clarification remove colored colloids and suspended particles from water. The purpose of the disinfection procedure is to eliminate bacteria, infections and viruses. Special methods - mineralization and fluoridation - involve the introduction of substances necessary for the body into the water.
The nature of the contamination determines the use of the following cleaning methods:
- Mechanical – involves removing impurities using sieves, filters and gratings of coarse impurities.
- Physical – involves boiling, UV and irradiation with γ-rays.
- Chemical, in which reagents are added to wastewater, which provoke the formation of sediments. Today, the main method of disinfecting drinking water is chlorination. Tap water, according to SanPiN, must contain a residual chlorine concentration of 0.3-0.5 mg/l.
- Biological treatment requires special irrigation or filtration fields. A network of channels is formed that are filled wastewater. After purification by air, sunlight and microorganisms, they seep into the soil, forming humus on the surface.
For biological treatment, which can also be carried out in artificial conditions, there are special structures - biofilters and aeration tanks. A biofilter is a brick or concrete structure, inside of which there is a porous material - gravel, slag or crushed stone. They are coated with microorganisms that purify water as a result of their vital activity.
In aeration tanks, with the help of incoming air, activated sludge moves in wastewater. Secondary settling tanks are designed to separate bacterial film from purified water. The destruction of pathogenic microorganisms in domestic waters is carried out using chlorine disinfection.
To assess the quality of water, you need to determine the amount of harmful substances that ended up there after treatment (chlorine, aluminum, polyacrylamide, etc.) and anthropogenic substances (nitrates, copper, petroleum products, manganese, phenols, etc.). Organoleptic and radiation indicators should also be taken into account.
How to improve water quality at home
To improve the quality of tap water at home, additional purification is required, for which household filters are used. Today, manufacturers offer them in huge quantities.
One of the most popular are filters whose operation is based on reverse osmosis.
They are actively used not only at home, but also in enterprises. Catering, in hospitals, sanatoriums, and manufacturing plants.
The filtration system has an auto-flush that must be turned on before filtration begins. Through the polyamide membrane through which water passes, it is freed from contaminants - cleaning is carried out at the molecular level. Such installations are ergonomic and compact, and the quality of filtered water is very high.
Water Purification: Video
There are many methods for improving water quality, and they make it possible to free water from dangerous microorganisms, suspended particles, humic compounds, excess salts, toxic and radioactive substances and foul-smelling gases.
The main purpose of water purification is to protect the consumer from pathogenic organisms and impurities that may be dangerous to human health or have unpleasant properties (color, smell, taste, etc.). Treatment methods should be selected taking into account the quality and nature of the water supply.
The use of underground interstratal water sources for centralized water supply has a number of advantages over the use of surface sources. The most important of them include: protection of water from external pollution, epidemiological safety, consistency of water quality and flow. Flow is the volume of water coming from a source per unit of time (l/hour, m/day, etc.).
Typically, groundwater does not need clarification, bleaching or disinfection. The diagram of the underground water supply system is shown in the figure.
The disadvantages of using underground water sources for centralized water supply include low water flow, which means they can be used in areas with a relatively small population (small and medium-sized cities, urban-type settlements and rural settlements). More than 50 thousand rural settlements have a centralized water supply, but the improvement of villages is difficult due to the dispersed nature of rural settlements and their small number (up to 200 people). Most often used here different kinds wells (shaft, tube).
The location for the wells is chosen on a hill, at least 20-30 m from a possible source of pollution (latrines, cesspools, etc.). When digging a well, it is advisable to reach the second aquifer.
The bottom of the well shaft is left open, and the main walls are reinforced with materials that ensure water resistance, i.e. concrete rings or wooden frame without gaps. The walls of the well must rise above the ground surface by at least 0.8 m. To construct a clay castle that prevents surface water from entering the well, dig a hole 2 m deep and 0.7-1 m wide around the well and fill it with well-compacted fatty clay . On top of the clay castle, they add sand and pave it with brick or concrete with a slope away from the well to drain surface water and spill it during its intake. The well must be equipped with a lid and only a public bucket must be used. The best way lifting water - pumps. In addition to mine wells, various types of tube wells are used to extract groundwater.
: 1 - tube well; 2 - pumping station first rise; 3 - reservoir; 4 - pumping station of the second lift; 5 - water tower; 6 - water supply network
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The advantage of such wells is that they can be of any depth; their walls are made of waterproof metal pipes through which water is raised by a pump. When the formation water is located at a depth of more than 6-8 m, it is extracted by constructing wells equipped with metal pipes and pumps, the productivity of which reaches 100 m3 or more.
: a - pump; b - a layer of gravel at the bottom of the well
The water of open reservoirs is susceptible to pollution, therefore, from an epidemiological point of view, all open water sources are, to a greater or lesser extent, potentially dangerous. In addition, this water often contains humic compounds, suspended substances from various chemical compounds, so it needs more thorough cleaning and disinfection
The water supply diagram for a surface water source is shown in Figure 1.
The main structures of a water pipeline fed by water from an open reservoir are: structures for collecting and improving water quality, a clean water tank, a pumping facility and a water tower. A water conduit and a distribution network of pipelines made of steel or having anti-corrosion coatings depart from it.
So, the first stage of water purification from an open water source is clarification and discoloration. In nature, this is achieved through long-term settling. But natural sedimentation proceeds slowly and the effectiveness of decolorization is low. Therefore, waterworks often use chemical treatment with coagulants, which accelerates the sedimentation of suspended particles. The clarification and bleaching process is typically completed by filtering the water through a layer of granular material (such as sand or crushed anthracite). Two types of filtration are used - slow and fast.
Slow filtration of water is carried out through special filters, which are a brick or concrete tank, at the bottom of which there is drainage made of reinforced concrete tiles or drainage pipes with holes. Through drainage, filtered water is removed from the filter. A supporting layer of crushed stone, pebbles and gravel is loaded on top of the drainage in a size that gradually decreases upward, which prevents small particles from spilling into the drainage holes. The thickness of the supporting layer is 0.7 m. A filter layer (1 m) with a grain diameter of 0.25-0.5 mm is loaded onto the supporting layer. A slow filter purifies water well only after maturation, which consists of the following: biological processes occur in the upper layer of sand - the reproduction of microorganisms, hydrobionts, flagellates, then their death, the mineralization of organic substances and the formation of a biological film with very small pores that can trap even the smallest particles, helminth eggs and up to 99% bacteria. The filtration speed is 0.1-0.3 m/h.
Rice. 1.
: 1 - pond; 2 - intake pipes and coastal well; 3 - first lift pumping station; 4 - treatment facilities; 5 - clean water tanks; 6 - pumping station of the second lift; 7 - pipeline; 8 - water tower; 9 - distribution network; 10 - places of water consumption.
Slow-acting filters are used on small water pipelines to supply water to villages and urban settlements. Once every 30-60 days, the surface layer of contaminated sand is removed along with the biological film.
The desire to accelerate the sedimentation of suspended particles, eliminate the color of water and speed up the filtration process led to preliminary coagulation of water. To do this, coagulants are added to the water, i.e. substances that form hydroxides with rapidly settling flocs. Aluminum sulfate - Al2(SO4)3 - is used as coagulants; ferric chloride - FeSl3, ferric sulfate - FeSO4, etc. Coagulant flakes have a huge active surface and a positive electrical charge, which allows them to adsorb even the smallest negatively charged suspension of microorganisms and colloidal humic substances, which are carried to the bottom of the settling tank by settling flakes. Conditions for the effectiveness of coagulation are the presence of bicarbonates. Add 0.35 g of Ca(OH)2 per 1 g of coagulant. The sizes of settling tanks (horizontal or vertical) are designed for 2-3 hour settling of water.
After coagulation and settling, the water is supplied to rapid filters with a sand filter layer thickness of 0.8 m and a sand grain diameter of 0.5-1 mm. The water filtration speed is 5-12 m/hour. Efficiency of water purification: from microorganisms - by 70-98% and from helminth eggs - by 100%. The water becomes clear and colorless.
The filter is cleaned by supplying water in the opposite direction at a speed 5-6 times higher than the filtration speed for 10-15 minutes.
In order to intensify the operation of the described structures, the coagulation process is used in the granular loading of rapid filters (contact coagulation). Such structures are called contact clarifiers. Their use does not require the construction of flocculation chambers and settling tanks, which makes it possible to reduce the volume of structures by 4-5 times. The contact filter has a three-layer loading. The top layer is expanded clay, polymer chips, etc. (particle size is 2.3-3.3 mm).
The middle layer is anthracite, expanded clay (particle size - 1.25-2.3 mm).
The bottom layer is quartz sand (particle size - 0.8-1.2 mm). A system of perforated pipes is strengthened above the loading surface to introduce the coagulant solution. Filtration speed up to 20 m/hour.
With any scheme, the final stage of water treatment in a water supply system from a surface source should be disinfection.
When organizing a centralized domestic and drinking water supply for small settlements and individual facilities (rest homes, boarding houses, pioneer camps), in the case of using surface reservoirs as a source of water supply, structures of low capacity are required. These requirements are met by compact factory-made Struya installations with a capacity of 25 to 800 m3/day.
The installation uses a tubular sedimentation tank and a filter with granular loading. The pressure design of all elements of the installation ensures the supply of source water by first lift pumps through a sump and filter directly to the water tower and then to the consumer. The main amount of contaminants settles in a tubular settling tank. The sand filter ensures the final removal of suspended and colloidal impurities from water.
Chlorine for disinfection can be introduced either before the settling tank or directly into the filtered water. The installation is washed 1-2 times a day for 5-10 minutes with a reverse flow of water. The duration of water treatment does not exceed 40-60 minutes, whereas at a water station this process lasts from 3 to 6 hours.
The efficiency of water purification and disinfection using the Struya installation reaches 99.9%.
Water disinfection can be carried out by chemical and physical (reagent-free) methods.
Chemical methods of water disinfection include chlorination and ozonation. The task of disinfection is the destruction of pathogenic microorganisms, i.e. ensuring epidemic water safety.
Russia was one of the first countries in which water chlorination began to be used in water supply systems. This happened in 1910. However, at the first stage, water chlorination was carried out only during outbreaks of water epidemics.
Currently, water chlorination is one of the most widespread preventive measures that has played a huge role in preventing water epidemics. This is facilitated by the availability of the method, its low cost and reliability of disinfection, as well as its versatility, i.e. the ability to disinfect water at water supply stations, mobile installations, in a well (if it is contaminated and unreliable), in a field camp, in a barrel, bucket and flask.
The principle of chlorination is based on treating water with chlorine or chemical compounds containing chlorine in an active form, which has an oxidizing and bactericidal effect.
The chemistry of the processes occurring is that when chlorine is added to water, its hydrolysis occurs:
Those. hydrochloric and hypochlorous acid are formed. In all hypotheses explaining the mechanism of the bactericidal action of chlorine, hypochlorous acid is given a central place. The small size of the molecule and electrical neutrality allow hypochlorous acid to quickly pass through the bacterial cell membrane and affect cellular enzymes (BN-groups;), important for metabolism and cell reproduction processes. This was confirmed by electron microscopy: damage to the cell membrane, disruption of its permeability and a decrease in cell volume were revealed.
On large water supply systems, chlorine gas is used for chlorination, supplied in liquefied form in steel cylinders or tanks. As a rule, the normal chlorination method is used, i.e. chlorination method according to chlorine demand.
The choice of dose is important to ensure reliable disinfection. When disinfecting water, chlorine not only contributes to the death of microorganisms, but also interacts with organic substances in water and some salts. All these forms of chlorine binding are combined into the concept of “chlorine absorption of water.”
In accordance with SanPiN 2.1.4.559-96 "Drinking water..." the dose of chlorine should be such that after disinfection the water contains 0.3-0.5 mg/l of free residual chlorine. This method, without impairing the taste of water and not being harmful to health, indicates the reliability of disinfection.
The amount of active chlorine in milligrams required to disinfect 1 liter of water is called chlorine demand.
In addition to choosing the correct dose of chlorine, a necessary condition Effective disinfection is good mixing of water and sufficient time of contact of water with chlorine: in summer at least 30 minutes, in winter at least 1 hour.
Modifications of chlorination: double chlorination, chlorination with ammoniation, rechlorination, etc.
Double chlorination involves supplying chlorine to water supply stations twice: the first time before the settling tanks, and the second time, as usual, after the filters. This improves coagulation and discoloration of water, suppresses the growth of microflora in wastewater treatment plants, increases the reliability of disinfection.
Chlorination with ammoniation involves introducing an ammonia solution into the water to be disinfected, and after 0.5-2 minutes - chlorine. In this case, chloramines are formed in the water - monochloramines (NH2Cl) and dichloramines (NHCl2), which also have a bactericidal effect. This method is used to disinfect water containing phenols to prevent the formation of chlorophenols. Even in minute concentrations, chlorophenols give water a pharmaceutical smell and taste. Chloramines, having a weaker oxidizing potential, do not form chlorophenols with phenols. The rate of water disinfection with chloramines is less than when using chlorine, so the duration of water disinfection should be at least 2 hours, and the residual chlorine should be 0.8-1.2 mg/l.
Rechlorination involves adding deliberately large doses of chlorine to water (10-20 mg/l or more). This allows you to reduce the time of contact of water with chlorine to 15-20 minutes and obtain reliable disinfection from all types of microorganisms: bacteria, viruses, Burnet's rickettsia, cysts, dysenteric amoeba, tuberculosis and even anthrax spores. Upon completion of the disinfection process, a large excess of chlorine remains in the water and the need for dechlorination arises. For this purpose, sodium hyposulfite is added to the water or the water is filtered through a layer of activated carbon.
Rechlorination is used mainly in expeditions and military conditions.
The disadvantages of the chlorination method include:
A) the difficulty of transporting and storing liquid chlorine and its toxicity;
B) long time of contact of water with chlorine and difficulty in selecting the dose when chlorinating with normal doses;
C) the formation in water of organochlorine compounds and dioxins, which are not indifferent to the body;
D) changes in the organoleptic properties of water.
And, nevertheless, high efficiency makes the chlorination method the most common in the practice of water disinfection.
Looking for reagent-free methods or reagents that do not change chemical composition water, paid attention to ozone. The first experiments to determine the bactericidal properties of ozone were carried out in France in 1886. The world's first industrial ozonation plant was built in 1911 in St. Petersburg.
Currently, the method of water ozonation is one of the most promising and is already being used in many countries around the world - France, the USA, etc. We ozonize water in Moscow, Yaroslavl, Chelyabinsk, Ukraine (Kyiv, Dnepropetrovsk, Zaporozhye, etc.).
Ozone (O3) is a pale violet gas with a characteristic odor. The ozone molecule easily splits off an oxygen atom. When ozone decomposes in water, short-lived free radicals HO2 and OH are formed as intermediate products. Atomic oxygen and free radicals, being strong oxidizing agents, determine the bactericidal properties of ozone.
Along with the bactericidal effect of ozone, during water treatment, discoloration and elimination of tastes and odors occur.
Ozone is produced directly at waterworks through a quiet electrical discharge in the air. The installation for water ozonation combines air conditioning units, producing ozone and mixing it with disinfected water. An indirect indicator of the effectiveness of ozonation is the residual ozone at a level of 0.1-0.3 mg/l after the mixing chamber.
The advantages of ozone over chlorine in water disinfection are that ozone does not form toxic compounds in water (organochlorine compounds, dioxins, chlorophenols, etc.), improves the organoleptic properties of water and provides a bactericidal effect with less contact time (up to 10 minutes). It is more effective against pathogenic protozoa - dysenteric amoeba, Giardia, etc.
The widespread introduction of ozonation into the practice of water disinfection is hampered by the high energy intensity of the ozone production process and imperfect equipment.
The oligodynamic action of silver has been considered for a long time as a means of disinfecting primarily individual water supplies. Silver has a pronounced bacteriostatic effect. Even when a small amount of ions is introduced into the water, microorganisms stop reproducing, although they remain alive and can even cause disease. Concentrations of silver that can cause the death of most microorganisms are toxic to humans with prolonged use of water. Therefore, silver is mainly used for preserving water for long-term storage in navigation, astronautics, etc.
To disinfect individual water supplies, tablet forms containing chlorine are used.
Aquasept - tablets containing 4 mg of active chlorine monosodium salt of dichloroisocyanuric acid. Dissolves in water within 2-3 minutes, acidifies the water and thereby improves the disinfection process.
Pantocide is a drug from the group of organic chloramines, solubility is 15-30 minutes, releases 3 mg of active chlorine.
Physical methods include boiling, irradiation with ultraviolet rays, exposure to ultrasonic waves, high-frequency currents, gamma rays, etc.
The advantage of physical disinfection methods over chemical ones is that they do not change the chemical composition of water or impair its organoleptic properties. But due to their high cost and the need for careful preliminary preparation of water, only ultraviolet irradiation is used in water supply systems, and boiling is used in local water supply.
Ultraviolet rays have a bactericidal effect. This was established at the end of the last century by A.N. Maklanov. The most effective section of the UV part of the optical spectrum is in the wave range from 200 to 275 nm. The maximum bactericidal effect occurs on rays with a wavelength of 260 nm. The mechanism of the bactericidal effect of UV irradiation is currently explained by the rupture of bonds in the enzyme systems of the bacterial cell, causing disruption of the microstructure and metabolism of the cell, leading to its death. The dynamics of the death of microflora depends on the dose and initial content of microorganisms. The effectiveness of disinfection is influenced by the degree of turbidity, color of water and its salt composition. A necessary prerequisite for reliable disinfection of water with UV rays is its preliminary clarification and bleaching.
The advantages of ultraviolet irradiation are that UV rays do not change the organoleptic properties of water and have a wider spectrum of antimicrobial action: they destroy viruses, bacilli spores and helminth eggs.
Ultrasound is used to disinfect domestic wastewater, because it is effective against all types of microorganisms, including bacillus spores. Its effectiveness does not depend on turbidity and its use does not lead to foaming, which often occurs when disinfecting domestic wastewater.
Gamma radiation is a very effective method. The effect is instant. The destruction of all types of microorganisms, however, has not yet found application in water supply practice.
Boiling is a simple and reliable method. Vegetative microorganisms die when heated to 80°C within 20-40 s, so at the moment of boiling the water is already virtually disinfected. And with 3-5 minutes of boiling, there is a complete guarantee of safety, even with severe contamination. When boiling, botulinum toxin is destroyed and 30-minute boiling kills bacilli spores.
The container in which boiled water is stored must be washed daily and the water changed daily, since intensive proliferation of microorganisms occurs in boiled water.
Physical and chemical indicators of water quality. When choosing a water supply source, the physical properties of water such as temperature, smell, taste, turbidity and color are taken into account. Moreover, these indicators are determined for all characteristic periods of the year (spring, summer, autumn, winter).
The temperature of natural waters depends on their origin. In underground water sources, the water has a constant temperature regardless of the period of the year. On the contrary, the water temperature of surface water sources varies over periods of the year in a fairly wide range (from 0.1 °C in winter to 24-26 °C in summer).
The turbidity of natural waters depends, first of all, on their origin, as well as on the geographical and climatic conditions in which the water source is located. Groundwater has insignificant turbidity, not exceeding 1.0-1.5 mg/l, but water from surface water sources almost always contains suspended substances in the form of tiny parts of clay, sand, algae, microorganisms and other substances of mineral and organic origin. However, as a rule, the water of surface water sources in the northern regions of the European part of Russia, Siberia and part of the Far East is classified as low-turbidity. On the contrary, water sources in the central and southern regions of the country are characterized by higher water turbidity. Regardless of the geographical, geological and hydrological conditions of the location of the water source, the turbidity of water in rivers is always higher than in lakes and reservoirs. The greatest turbidity of water in water sources is observed during spring floods, during periods of prolonged rain, and the lowest in winter time when water sources are covered with ice. The turbidity of water is measured in mg/dm3.
The color of water from natural water sources is due to the presence in it of colloidal and dissolved organic substances of humic origin, which give the water a yellow or brown tint. The thickness of the shade depends on the concentration of these substances in the water.
Humic substances are formed as a result of the decomposition of organic substances (soil, plant humus) to simpler chemical compounds. In natural waters, humic substances are represented mainly by organic humic and fulvic acids, as well as their salts.
Color is characteristic of water from surface water sources and is practically absent in groundwater. However, sometimes groundwater, most often in swampy low-lying areas with reliable aquifers, becomes enriched with swampy colored waters and acquires a yellowish color.
The color of natural waters is measured in degrees. According to the level of water color, surface water sources can be low color (up to 30-35°), medium color (up to 80°) and high color (over 80°). In water supply practice, water sources are sometimes used whose water color is 150-200°.
Most rivers in the North-West and North of Russia belong to the category of high-color, low-turbidity rivers. The middle part of the country is characterized by water sources of medium color and turbidity. The water of rivers in the southern regions of Russia, on the contrary, has increased turbidity and relatively low color. The color of water in a water source changes both quantitatively and qualitatively over periods of the year. During times of increased runoff from areas adjacent to the water source (melting snow, rain), the color of the water, as a rule, increases, and the ratio of the color components also changes.
Natural waters are characterized by such quality indicators as taste and smell. Most often, natural waters can have a bitter and salty taste and almost never sour or sweet. An excess of magnesium salts gives water a bitter taste, and sodium salts (table salt) give it a salty taste. Salts of other metals, such as iron and manganese, give water a ferrous taste.
Water odors can be of natural or artificial origin. Natural odors are caused by living and dead organisms and plant debris in water. The main odors of natural waters are marshy, earthy, woody, grassy, fishy, hydrogen sulfide, etc. The most intense odors are inherent in the water of reservoirs and lakes. Odors of artificial origin arise due to the release of insufficiently treated wastewater into water sources.
Odors of artificial origin include petroleum, phenolic, chlorophenol, etc. The intensity of tastes and odors is assessed in points.
Chemical analysis of the quality of natural water is of paramount importance when choosing a method for its purification. Chemical indicators of water include: active reaction (hydrogen indicator), oxidability, alkalinity, hardness, concentration of chlorides, sulfates, phosphates, nitrates, nitrites, iron, manganese and other elements. The active reaction of water is determined by the concentration of hydrogen ions. It expresses the degree of acidity or alkalinity of water. Typically, the active reaction of water is expressed by the pH value, which is the negative decimal logarithm of the concentration of hydrogen ions: - pH = - log. For distilled water, pH = 7 (neutral environment). For a slightly acidic pH environment< 7, а для слабощелочной рН >7. Typically, for natural waters (surface and underground), the pH value ranges from 6 to 8.5. Highly colored soft waters have the lowest pH values, while underground waters, especially hard ones, have the highest.
The oxidation of natural waters is caused by the presence of organic substances in them, the oxidation of which consumes oxygen. Therefore, the value of oxidability is numerically equal to the amount of oxygen used to oxidize the pollutants in the water, and is expressed in mg/l. Artesian waters are characterized by the lowest oxidizability (~1.5-2 mg/l, O 2). The water of clean lakes has an oxidability of 6-10 mg/l, O 2; in river water, the oxidability varies widely and can reach 50 mg/l or even more. Highly colored waters are characterized by increased oxidability; in swampy waters, oxidation can reach 200 mg/l O 2 or more.
The alkalinity of water is determined by the presence in it of hydroxides (OH") and carbonic acid anions (HCO - 3, CO 3 2,).
Chlorides and sulfates are found in almost all natural waters. In groundwater, the concentrations of these compounds can be very significant, up to 1000 mg/l or more. In surface water sources, the content of chlorides and sulfates usually ranges from 50-100 mg/l. Sulfates and chlorides at certain concentrations (300 mg/l or more) cause corrosiveness of water and have a destructive effect on concrete structures.
The hardness of natural waters is due to the presence of calcium and magnesium salts in them. Although these salts are not particularly harmful to the human body, their presence in significant quantities is undesirable, because water becomes unsuitable for household needs and industrial water supply. Hard water is not suitable for feeding steam boilers; it cannot be used in many industrial processes.
Iron in natural waters is found in the form of divalent ions, organomineral colloidal complexes and fine suspension of iron hydroxide, as well as in the form of iron sulfide. Manganese, as a rule, is found in water in the form of divalent manganese ions, which can be oxidized in the presence of oxygen, chlorine or ozone to tetravalent, forming manganese hydroxide.
The presence of iron and manganese in water can lead to the development of ferrous and manganese bacteria in pipelines, the waste products of which can accumulate in large quantities and significantly reduce the cross-section of water pipes.
Of the gases dissolved in water, the most important from a water quality point of view are free carbon dioxide, oxygen and hydrogen sulfide. The carbon dioxide content in natural waters ranges from several units to several hundred milligrams per liter. Depending on the pH value of the water, carbon dioxide occurs in it in the form of carbon dioxide or in the form of carbonates and bicarbonates. Excess carbon dioxide is very aggressive towards metal and concrete:
The concentration of oxygen dissolved in water can range from 0 to 14 mg/l and depends on a number of reasons (water temperature, partial pressure, degree of water contamination with organic substances). Oxygen intensifies the corrosion processes of metals. This must be especially taken into account in thermal power systems.
Hydrogen sulfide, as a rule, enters water as a result of its contact with rotting organic residues or with certain minerals (gypsum, sulfur pyrites). The presence of hydrogen sulfide in water is extremely undesirable for both domestic and industrial water supplies.
Toxic substances, in particular heavy metals, enter water sources mainly with industrial wastewater. When there is a possibility of their entry into a water source, determining the concentration of toxic substances in the water is mandatory.
Requirements for water quality for various purposes. The basic requirements for drinking water presuppose that the water is harmless to the human body, has a pleasant taste and appearance, as well as suitability for household needs.
The quality indicators that drinking water must satisfy are standardized by “Sanitary Rules and Norms (SanPiN) 2. 1.4.559-96. Drinking water."
Water for cooling units of many production processes should not form deposits in the pipes and chambers through which it passes, since deposits impede heat transfer and reduce the cross-section of the pipes, reducing the cooling intensity.
There should be no large suspended matter (sand) in the water. There should be no organic substances in the water, as it intensifies the process of biofouling of the walls.
Water for steam power facilities should not contain impurities that can cause scale deposits. Due to scale formation, thermal conductivity decreases, heat transfer deteriorates, and overheating of the walls of steam boilers is possible.
Of the salts that form scale, the most harmful and dangerous are CaSO 4, CaCO 3, CaSiO 3, MgSiO 3. These salts are deposited on the walls of steam boilers, forming boiler stone.
To prevent corrosion of the walls of steam boilers, the water must have a sufficient alkaline reserve. Its concentration in boiler water should be at least 30-50 mg/l.
Particularly undesirable is the presence of silicic acid SiO 2 in the feed water of high-pressure boilers, which can form dense scale with very low thermal conductivity.
Basic technological schemes and structures for improving water quality.
Natural waters are different big variety of contaminants and their combinations. Therefore, to solve the problem effective cleaning water requires different technological schemes and processes, different sets of structures to implement these processes.
Technological schemes used in water treatment practice are usually classified into reagent And reagent-free; pre-treatment And deep cleaning; on single stage And multi-stage; on pressure And free-flow.
The reagent scheme for purifying natural waters is more complex than the non-reagent scheme, but it provides deeper purification. The reagent-free scheme is usually used for pre-treatment of natural waters. Most often it is used in water purification for technical purposes.
Both reagent and non-reagent technological purification schemes can be single-stage or multi-stage, with non-pressure and pressure-type facilities.
The main technological schemes and types of structures most often used in water treatment practice are presented in Figure 22.
Sedimentation tanks are used mainly as structures for preliminary purification of water from suspended particles of mineral and organic origin. Depending on the type of construction and the nature of water movement in the structure, sedimentation tanks can be horizontal, vertical or radial. In recent decades, in the practice of purifying natural waters, special shelf sedimentation tanks with sedimentation of suspended matter in a thin layer have begun to be used.
Rice. 22.
a) two-stage with a horizontal settling tank and filter: 1 - pumping station I lift; 2 - microgrids; 3 - reagent management; 4 - mixer; 5 - flocculation chamber; b - horizontal settling tank; 7 - filter; 8 - chlorination; 9 - clean water tank; 10 - pumps;
b) two-stage with clarifier and filter: 1 - pumping station I lift; 2 - microgrids; 3 - reagent management; 4 - mixer; 5 - suspended sediment clarifier; b - filter; 7 - chlorination; 8 - clean water tank; 9 - II lift pumps;
V) single-stage with contact clarifiers: 1 - pumping station I lift; 2 - drum nets; 3 - reagent management; 4 - restriction device (mixer); 5 - contact clarifier KO-1; 6 - chlorination; 7 - clean water tank; 8 - II lift pumps
Filters included in the general technological scheme water treatment, act as structures for deep purification of water from suspended substances, some of the colloidal and dissolved substances that have not settled in the settling tanks (due to the forces of adsorption and molecular interaction).
