LECTURE No. 3. METHODS OF IMPROVING WATER QUALITY
The use of natural waters from open reservoirs, and sometimes groundwater for domestic and drinking water supply purposes, is practically impossible without first improving the properties of the water and its disinfection. To ensure that the quality of water meets hygienic requirements, pre-treatment is used, as a result of which the water is freed from suspended particles, odor, taste, microorganisms and various impurities.
To improve water quality, the following methods are used: 1) purification - removal of suspended particles; 2) disinfection - destruction of microorganisms; 3) special methods for improving the organoleptic properties of water, softening, removal of certain chemicals, fluoridation, etc.
Water purification. Purification is an important step in the overall set of methods for improving water quality, as it improves its physical and organoleptic properties. At the same time, in the process of removing suspended particles from water, a significant part of microorganisms is also removed, as a result of which complete water purification makes it easier and more economical to carry out disinfection. Cleaning is carried out by mechanical (settling), physical (filtration) and chemical (coagulation) methods.
Settling, during which clarification and partial discoloration of water occurs, is carried out in special structures - settling tanks. Two designs of settling tanks are used: horizontal and vertical. The principle of their operation is that, thanks to the flow of water through a narrow hole and the slow flow of water in the sump, the bulk of suspended particles settles to the bottom. The settling process in settling tanks of various designs continues for 2-8 hours. However, the smallest particles, including a significant part of microorganisms, do not have time to settle. Therefore, sedimentation cannot be considered as the main method of water purification.
Filtration is the process of more completely freeing water from suspended particles, which consists in passing water through a fine-porous filter material, most often through sand with a certain particle size. When filtering, water leaves suspended particles on the surface and in the depths of the filter material. At waterworks, filtration is used after coagulation.
Currently, quartz-anthracite filters have begun to be used, significantly increasing the filtration rate.
To pre-filtrate water, microfilters are used to capture zooplankton - the smallest aquatic animals and phytoplankton - the smallest aquatic plants. These filters are installed in front of the water intake point or in front of the treatment plant.
Coagulation is a chemical method of water purification. The advantage of this method is that it allows you to free water from contaminants that are in the form of suspended particles that cannot be removed by settling and filtration. The essence of coagulation is the addition of a coagulant chemical to water that can react with the bicarbonates in it. As a result of this reaction, large, rather heavy flakes are formed that carry a positive charge. As they settle due to their own gravity, they carry with them negatively charged pollutant particles suspended in the water, and thereby contribute to fairly rapid water purification. Due to this process, the water becomes transparent and the color index improves.
Aluminum sulfate is currently most widely used as a coagulant; it forms large flakes of aluminum oxide hydrate with water bicarbonates. To improve the coagulation process, high-molecular flocculants are used: alkaline starch, ionic flocculants, activated silicic acid and other synthetic preparations derived from acrylic acid, in particular polyacrylamide (PAA).
Disinfection. The destruction of microorganisms is the last final stage of water treatment, ensuring its epidemiological safety. Chemical (reagent) and physical (reagent-free) methods are used to disinfect water. In laboratory conditions, a mechanical method can be used for small volumes of water.
Chemical (reagent) disinfection methods are based on adding various chemicals to water, causing the death of microorganisms in the water. These methods are quite effective. Various strong oxidizing agents can be used as reagents: chlorine and its compounds, ozone, iodine, potassium permanganate, some salts of heavy metals, silver.
In sanitary practice, the most reliable and proven method of water disinfection is chlorination. At waterworks it is produced using chlorine gas and bleach solutions. In addition, chlorine compounds such as sodium hypochlorate, calcium hypochlorite, and chlorine dioxide can be used.
The mechanism of action of chlorine is that when it is added to water, it hydrolyzes, resulting in the formation of hydrochloric and hypochlorous acids:
C1 2 +H 2 O=HC1+HOC1.
Hypochlorous acid in water dissociates into hydrogen ions (H) and hypochlorite ions (OC1), which, along with dissociated hypochlorous acid molecules, have a bactericidal property. The complex (HOC1 + OC1) is called free active chlorine.
The bactericidal effect of chlorine is carried out mainly due to hypochlorous acid, the molecules of which are small, have a neutral charge and therefore easily pass through the bacterial cell membrane. Hypochlorous acid affects cellular enzymes, in particular SH groups, disrupts the metabolism of microbial cells and the ability of microorganisms to reproduce. In recent years, it has been established that the bactericidal effect of chlorine is based on the inhibition of enzyme catalysts and redox processes that ensure the energy metabolism of the bacterial cell.
The disinfecting effect of chlorine depends on many factors, among which the dominant ones are the biological characteristics of microorganisms, the activity of active chlorine preparations, the state of the aquatic environment and the conditions under which chlorination is carried out.
The chlorination process depends on the persistence of microorganisms. The most stable are the spore-forming ones. Among non-spores, the attitude towards chlorine is different, for example, the typhoid bacillus is less stable than the paratyphoid bacillus, etc. The massiveness of microbial contamination is important: the higher it is, the more chlorine is needed to disinfect water. The effectiveness of disinfection depends on the activity of the chlorine-containing preparations used. Thus, chlorine gas is more effective than bleach.
The composition of water has a great influence on the chlorination process; the process slows down in the presence of a large amount of organic substances, since more chlorine is spent on their oxidation, and at low water temperatures. An essential condition for chlorination is the correct choice of dose. The higher the dose of chlorine and the longer its contact with water, the higher the disinfecting effect will be.
Chlorination is carried out after water purification and is the final stage of its processing at a waterworks. Sometimes, to enhance the disinfecting effect and improve coagulation, part of the chlorine is introduced along with the coagulant, and the other part, as usual, after filtration. This method is called double chlorination.
A distinction is made between conventional chlorination, i.e. chlorination with normal doses of chlorine, which are established each time experimentally, and superchlorination, i.e. chlorination with increased doses.
Chlorination in normal doses is used under normal conditions at all waterworks. In this case, the correct choice of the dose of chlorine is of great importance, which determines the degree of chlorine absorption of water in each specific case.
To achieve a complete bactericidal effect, the optimal dose of chlorine is determined, which consists of the amount of active chlorine that is necessary for: a) destruction of microorganisms; b) oxidation of organic substances, as well as the amount of chlorine that must remain in the water after chlorination in order to serve as an indicator of the reliability of chlorination. This amount is called active residual chlorine. Its norm is 0.3-0.5 mg/l, with free chlorine 0.8-1.2 mg/l. The need to standardize these quantities is due to the fact that if the presence of residual chlorine is less than 0.3 mg/l, it may not be enough to disinfect water, and at doses above 0.5 mg/l, the water acquires an unpleasant specific smell of chlorine.
The main conditions for effective chlorination of water are its mixing with chlorine, contact between disinfection water and chlorine for 30 minutes in the warm season and 60 minutes in the cold season.
At large waterworks, chlorine gas is used to disinfect water. To do this, liquid chlorine, delivered to the water supply station in tanks or cylinders, is converted into a gaseous state before use in special chlorinator installations, which provide automatic supply and dosing of chlorine. The most common chlorination of water is a 1% solution of bleach. Bleach is a product of the interaction of chlorine and calcium oxide hydrate as a result of the reaction:
2Ca(OH) 2 + 2C1 2 = Ca(OC1) 2 + CaC1 2 + 2HA
Superchlorination (hyperchlorination) of water is carried out for epidemiological reasons or in conditions where it is impossible to ensure the necessary contact of water with chlorine (within 30 minutes). It is usually used in military field conditions, expeditions and other cases and is produced in doses 5-10 times higher than the chlorine absorption capacity of water, i.e. 10-20 mg/l of active chlorine. The contact time between water and chlorine is reduced to 15-10 minutes. Superchlorination has a number of advantages. The main ones are a significant reduction in the time of chlorination, simplification of its technique, since there is no need to determine the residual chlorine and dose, and the possibility of disinfecting water without first freeing it from turbidity and clarification. The disadvantage of hyperchlorination is the strong smell of chlorine, but this can be eliminated by adding sodium thiosulfate, activated carbon, sulfur dioxide and other substances to the water (dechlorination).
At waterworks, chlorination and preammonization are sometimes carried out. This method is used in cases where the water being disinfected contains phenol or other substances that give it an unpleasant odor. To do this, ammonia or its salts are first introduced into the water to be disinfected, and then chlorine is added after 1-2 minutes. This produces chloramines, which have strong bactericidal properties.
Chemical methods of water disinfection include ozonation. Ozone is an unstable compound. In water, it decomposes to form molecular and atomic oxygen, which is associated with the strong oxidizing ability of ozone. During its decomposition, free radicals OH and HO 2 are formed, which have pronounced oxidizing properties. Ozone has a high redox potential, so its reaction with organic substances in water is more complete than that of chlorine. The mechanism of the disinfecting action of ozone is similar to the action of chlorine: being a strong oxidizing agent, ozone damages the vital enzymes of microorganisms and causes their death. There are suggestions that it acts as a protoplasmic poison.
The advantage of ozonation over chlorination is that this disinfection method improves the taste and color of water, so ozone can be used at the same time to improve its organoleptic properties. Ozonation does not have a negative effect on the mineral composition and pH of water. Excess ozone is converted into oxygen, so residual ozone is not dangerous to the body and does not affect the organoleptic properties of water. Control of ozonation is less complicated than chlorination, since ozonation does not depend on factors such as temperature, water pH, etc. To disinfect water, the required dose of ozone is on average 0.5-6 mg/l with an exposure of 3-5 minutes. Ozonation is carried out using special devices - ozonizers.
Chemical methods of water disinfection also use the oligodynamic effects of heavy metal salts (silver, copper, gold). The oligodynamic effect of heavy metals is their ability to exert a bactericidal effect over a long period of time at extremely low concentrations. The mechanism of action is that positively charged heavy metal ions interact in water with microorganisms that have a negative charge. Electroadsorption occurs, as a result of which they penetrate deep into the microbial cell, forming heavy metal albuminates (compounds with nucleic acids) in it, as a result of which the microbial cell dies. This method is usually used to disinfect small quantities of water.
Hydrogen peroxide has long been known as an oxidizing agent. Its bactericidal effect is associated with the release of oxygen during decomposition. The method of using hydrogen peroxide for water disinfection has not yet been fully developed.
Chemical, or reagent, methods of water disinfection, based on adding one or another chemical substance to it in a certain dose, have a number of disadvantages, which consist mainly in the fact that most of these substances negatively affect the composition and organoleptic properties of water. In addition, the bactericidal effect of these substances appears after a certain period of contact and does not always apply to all forms of microorganisms. All this was the reason for the development of physical methods of water disinfection, which have a number of advantages over chemical ones. Reagent-free methods do not affect the composition and properties of disinfected water and do not impair its organoleptic properties. They act directly on the structure of microorganisms, as a result of which they have a wider range of bactericidal effects. A short period of time is required for disinfection.
The most developed and technically studied method is irradiation of water with bactericidal (ultraviolet) lamps. UV rays with a wavelength of 200-280 nm have the greatest bactericidal properties; the maximum bactericidal effect occurs at a wavelength of 254-260 nm. The radiation source is low-pressure argon-mercury lamps and mercury-quartz lamps. Water disinfection occurs quickly, within 1-2 minutes. When water is disinfected with UV rays, not only vegetative forms of microbes are killed, but also spore forms, as well as viruses, helminth eggs that are resistant to chlorine. The use of bactericidal lamps is not always possible, since the effect of water disinfection with UV rays is affected by the turbidity, color of the water, and the content of iron salts in it. Therefore, before disinfecting water in this way, it must be thoroughly cleaned.
Of all the available physical methods of water disinfection, boiling is the most reliable. As a result of boiling for 3-5 minutes, all microorganisms present in it die, and after 30 minutes the water becomes completely sterile. Despite the high bactericidal effect, this method is not widely used for disinfecting large volumes of water. The disadvantage of boiling is the deterioration of the taste of water, which occurs as a result of volatilization of gases, and the possibility of more rapid development of microorganisms in boiled water.
Physical methods of water disinfection include the use of pulsed electric discharge, ultrasound and ionizing radiation. Currently, these methods are not widely used in practice.
Special ways to improve water quality. In addition to the basic methods of water purification and disinfection, in some cases it becomes necessary to carry out special treatment. This treatment is mainly aimed at improving the mineral composition of water and its organoleptic properties.
Deodorization - removal of foreign odors and tastes. The need for such treatment is determined by the presence in water of odors associated with the vital activity of microorganisms, fungi, algae, decay products and decomposition of organic substances. For this purpose, methods such as ozonation, carbonization, chlorination, water treatment with potassium permanganate, hydrogen peroxide, fluoridation through sorption filters, and aeration are used.
Degassing of water is the removal of dissolved, foul-smelling gases from it. For this purpose, aeration is used, i.e., spraying water into small drops in a well-ventilated room or in the open air, resulting in the release of gases.
Water softening is the complete or partial removal of calcium and magnesium cations from it. Softening is carried out with special reagents or using ion exchange and thermal methods.
Desalination (desalination) of water is often carried out when preparing it for industrial use.
Partial desalination of water is carried out to reduce the salt content in it to the level at which the water can be used for drinking (below 1000 mg/l). Desalination is achieved by distillation of water, which is produced in various desalination plants (vacuum, multi-stage, solar thermal), ion exchange installations, as well as by electrochemical methods and the freezing method.
Deferrization - removal of iron from water is carried out by aeration followed by settling, coagulation, liming, and cationization. Currently, a method has been developed for filtering water through sand filters. In this case, ferrous iron is retained on the surface of sand grains.
Defluoridation is the release of natural waters from excess fluorine. For this purpose, a precipitation method is used, based on the sorption of fluorine by a precipitate of aluminum hydroxide.
If there is a lack of fluoride in water, it is fluoridated. If water is contaminated with radioactive substances, it is subjected to decontamination, i.e., removal of radioactive substances.
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 based on 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 rate 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, various types of wells are used here (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 to lift water is with pumps. In addition to mine wells, various types of tube wells are used to extract groundwater.
: 1 - tube well; 2 - first lift pumping station; 3 - reservoir; 4 - pumping station of the second lift; 5 - water tower; 6 - water supply network
.
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 the correct choice of the dose of chlorine, a necessary condition for effective disinfection is good mixing of the water and sufficient time of contact of water with chlorine: at least 30 minutes in summer, at least 1 hour in winter.
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 treatment facilities, and 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 obviously 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.
In search of reagent-free methods or reagents that do not change the chemical composition of water, we turned our 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 during 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, bacillus 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.
How to improve water quality. How to improve the quality of drinking water at home. List of methods for improving the quality of the aquatic environment. Specific methods. Methods for household use. Advantages and disadvantages of each household method. Features of their use. Ozonation. Boiling. Degassing. Freezing. Improving the quality of water will allow you to protect yourself from many problems caused by drinking low-quality liquid. We will tell you how to improve the quality of drinking water in our article.
Methods for improving water quality
As you yourself understand, the environmental situation and a large number of man-made pollutants lead to a deterioration in the quality of natural waters. But the capabilities of water treatment facilities are not as great as we would like. As a result, we drink almost the same water that is in the rivers and lakes of our region.
In such a situation, improving water quality becomes simply necessary. It is for this purpose that water purification methods have been developed that make it possible to bring the quality of water collected from any source to normal.
The following treatment methods guarantee a significant improvement in water quality:
- settling technique
- clarification of the aquatic environment
- membrane filtration methods
- chemical oxidizing reagents
- adsorption
- removal of dissolved iron
- dechlorination of the aquatic environment
- softening the aquatic environment (reducing salt concentration)
- control of nitrates
- liquid conditioning
- purification from impurities of organic origin
- disinfection of the aquatic environment
There are also specific methods for improving the quality of the aquatic environment:
- water degassing
- liquid deodorization
- ironization of the aquatic environment
- water fluoridation
- desalting of liquid
- water softening
In turn, the method of water disinfection is divided into several methods:
- The chemical method includes the procedures of hydrochlorination, conventional chlorination and purification due to the characteristics of heavy metal salts.
- The physical method involves irradiation with ultraviolet rays.
- Mechanical disinfection uses a special filtration method using special candles.
Methods for improving water quality that you can use yourself:
- Ozonation of the aquatic environment
- Degassing and boiling water
- Freezing liquid
- Using filter devices
What is ozonation?
This method of improving water quality can be used instead of traditional chlorination. Typically, ozone is applied at the last stage of the process. To maximize the effect of the procedure, you need to use an ozone concentration ranging from 0.4 to 1 mg/l. This concentration must be maintained for four minutes.
Also, the ozonation method can be used at the preliminary stage of water treatment. It helps convert dissolved components into colloidal form. As a result, they are easily deposited in filter devices.
Benefits of ozonation:
- Simultaneous decolorization and disinfection of water.
- The organoleptic indicators of taste and smell of the aquatic environment are improved.
- Residual ozone does not change the composition of water, since it quickly turns into oxygen.
- The ozonation method allows you to remove the earthy taste of the aquatic environment.
Disadvantages of ozonation:
- The method is little studied.
- Requires a lot of electricity.
- The use of this method of improving water quality often leads to biomass overgrowing ion-exchange filter devices.
Freezing
Improving the quality of drinking water is more suitable for domestic use, since for production purposes it is necessary to create a too bulky device.
The principle of purification is based on the law of physics, which states that when a liquid freezes, the main component freezes first, and various impurities, sediment and contaminants freeze last. This law is very clearly seen in the example of freezing milk: first, the water at the walls of the package freezes, and only then the fats and other nutrients in its center.
According to this method, water must be frozen at a temperature of -1-6 ° C, the ice must be removed, and the unfrozen residue must be drained. Then this ice can be thawed and eaten. Usually about 1/3 or 1/2 of the water is drained. Remember: the most frequent water is the one that froze first.
If you analyze such a frozen liquid, it will show that only 16 mg/l of calcium remains in the water. Of course, if you heat the water, its structure changes, but the purity and quality remain high, which improves your health and increases longevity.
Degassing and boiling
Improving the quality of water using degassing at home will be difficult, since this requires ridding the liquid of excess gases under vacuum. But the experiments have proven that the degassed liquid is perfectly absorbed by living organisms, increasing their vital activity.
As for boiling water, that is, heating it to a temperature of 100 degrees, this allows you to get rid of almost all harmful microorganisms and bacteria. This process also makes it possible to eliminate a number of toxins and toxic components. And boiling for 10-15 minutes guarantees the death of even heat-resistant viruses. Spores of various fungi will die if water is boiled for two hours. The same effect will occur when heating the aqueous medium in an autoclave.
Advantages of the boiling technique:
- Availability and ease of implementation.
- High efficiency and reliability.
- The effect of boiling does not depend on the composition of the aquatic environment.
- When boiling, neither the organoleptic nor the physicochemical characteristics of the liquid change.
Disadvantages of the method:
- Low profitability.
- It takes a lot of energy to implement it on a global scale.
- The equipment required will be too large.
- Low performance when using available heating elements.
Before choosing a method to improve water quality, you need to analyze the liquid in a laboratory to have an idea of its composition. You can order such an analysis in our laboratory.
General
1. Lightening (removing turbidity)
2. Discoloration
3. Disinfection
Cleaning according to 2 schemes:
1. Settlement, slow filtration
2. Coagulation, sedimentation, rapid filtration
1. Water moves very slowly through horizontal sediments for 4-8 hours, as a result, all large, suspended particles settle to the bottom. Next, the water enters a slow filter - large structures with several layers:
a) underlying.
b) sand. V = 0.1 – 0.3 m/h – filtration.
During the operation of the filter, it “ripens”, a film forms on its surface, efficiency increases, and speed decreases. 99.5% - disinfection efficiency.
2. The water is subjected to coagulation, the flakes formed in the water have a charge, suspended particles are adsorbed on them and, together with the flakes, precipitate. Reagents: Al, Fe sulfate. Al – forms compounds with bicarbonate.
First stage. Determination of bicarbonate hardness (amount of Al). The reaction is sluggish, there are few flakes - having excess aluminum sulfate, it is necessary to introduce alkali to speed up the reaction. When it gets into water, a colloidal solution is formed.
After coagulation, the water is sent to fast filters, the speed is 50-100 times higher than on slow ones.
Disinfection efficiency is 95%.
Disinfection:
Physical, chemical, mechanical methods are used.
a) Chemical methods - chlorination, hydrochlorination, use of heavy metal salts.
b) Mechanical method - filtration through special candles (Chamberlan)
c) Physical method - UV irradiation.
Special methods
Specific methods for disinfection:
1. Deodorization – elimination of unpleasant taste and smell.
2. Degassing
3. Fluoridation
4. Softening
5. Iron plating
6. Desalination
Reagents: Gaseous chlorine, Cl - lime, DTSGC - two-thirds salt of Ca hypochloride.
Chlorination - a normal dose of Cl remains, but after this the water gets rid of excess F.
Cl-requirement is the number of ml of active Cl required for water disinfection standards.
Combined chlorine is used for disinfection, the free chlorine residue is 0.5-0.3 mg/l.
0.3-0.5 – the amount of chlorine does not significantly change the organic properties of water, but indicates the completeness of disinfection.
Connected Cl not more than 0.8 mg/l.
Residual nitrogen 0.3-0.5 mg/l.
Selecting a water supply source
In 1948, GOST “Sources of centralized household water supply 27.84” was adopted
Underground sources are divided into classes, depending on methods for improving water quality
1. Satisfying all SANPIN requirements.
2. There are deviations in some indicators (aeration, filtration, disinfection).
3. They have the same SANPIN requirements as the first, but filtering occurs with preliminary settling.
Surface sources:
Class 1 – disinfection, filtration, coagulation.
Class 2 – coagulation, settling, disinfection.
Class 3 – the same as class 2, only with the use of poly-effector filtering methods.
Places of decentralized water supply:
In rural areas, if there is a source of groundwater. They install either dug or drilled wells.
Dug wells.
The soil is protected from flooding and waterlogging. The walls of the well are more permeable, the elevation above the surface is at least 80 cm. Around the well, soil is removed to a depth of 2 m and a width of 100 by 70 and filled with clay. Water intake must be carried out in such a way that no contamination is carried out.
Bored wells– they drill the ground and install an electric pump at the top.
Advantages: increased depth, walls are not permeable.
Well inspection:
1. Sanitary-epidemiological (detection of water-borne diseases)
2. Sanitary
Treatment of water in a well:
After renovation
In the presence of infectious diseases
Temporary chlorination in case of groundwater contamination 1.5 - 2 l/per 1 m of well.
Continuous - from a volume of 0.25-1 liters, 150-600 grams of lime are added to the supply, the solution diffuses within 30 days.
Raw materials for the production of soft drinks
The wide range of soft drinks is determined by the large number of different types of raw materials that are included in the drink blend.
The raw materials used for the production of BA drinks must meet the requirements of current regulatory and technical documentation.
Water
In brewing production, when preparing non-alcoholic and low-alcohol drinks, water is a technological raw material. Drinks contain 90–95%. The total water consumption per 1 m 3 of the final product is 20 - 25 m 3 in beer production, about 15 m 3 in beverage production. Therefore, increased demands are placed on water quality.
Water – must meet the requirements of SanPiN 2.1.4.559-96 “Drinking water. Hygienic requirements for the quality of centralized drinking water supply systems. Quality control.”
Water must be safe in terms of epidemics and radiation, harmless in chemical composition and have the qualities of drinking water, be transparent, colorless, odorless and tasteless.
Pure natural water always contains soluble salts, which affect the taste of drinks, as well as enzymatic processes. Salt composition is very important for beer production, and the taste of beer largely depends on it. Good water should not contain substances such as NaHCO 3, NH 2, CO 2, HNO 3. For drinking water, there are restrictions on microbiological, toxicological indicators and on components that worsen its organoleptic properties.
Harmful chemicals contained in natural drinking water include (mg/dm 3): aluminum 0.5; barium 0.1; beryllium 0.0002; boron 0.5; cadmium 0.001; arsenic 0.05; copper 1; molybdenum 0.25; nickel 0.1; mercury 0.0005; lead 0.03; selenium 0.01; strontium 7.0; chromium 0.05; cyanides 0.035. Restrictions have been introduced on the content of these substances.
During water treatment, the following harmful substances enter the water supply system (mg/dm3): chloroform (during chlorination) – 0.2; formaldehyde (with ozonation) – 0.05; polyacrylamide – 2; activated silicic acid – 10. The content of these substances in water after treatment is controlled and should not exceed maximum concentrations.
The components that worsen the organoleptic characteristics of water include, mg/dm 3: iron 0.3; manganese 0.1; copper 1; sulfates 500; chlorides 350; zinc 5; nitrates 45; polyphosphates 3.5; ozone 0.3; residual free chlorine 0.3 – 0.5, bound 0.8 – 1.2.
The total microbial number, that is, the number of microorganisms in 1 cm 3, should not exceed 50, bacteria of the E. coli group in 100 cm 3 should be absent.
There are several important indicators of the quality of fresh natural water: acidity pH (or pH), hardness and organoleptic properties.
pH is related to the concentration of hydrogen ions in the environment, is measured using a simple device - a pH meter and gives us the idea of acidic or alkaline properties of the medium (in this case, water): pH< 7 – кислая среда; рН = 7 – нейтральная среда; рН >7 – alkaline environment.
Rigidity is a property of water determined by the content of calcium ions Ca 2+ and magnesium Mg 2+ in it. Hardness is determined using a special method described in GOST standards for drinking water, and its units of measurement are moles per cubic meter (mol/m3) or millimoles per liter (mmol/dm3).
According to hardness (in mmol/dm3), water is classified as follows: up to 0.75 - very soft; 0.75 – 1.5 – soft; 1.5 – 2.25 – medium hardness; 2.25 – 3 – quite hard; 3 – 5 – hard; over 5 – very hard.
There are temporary, permanent and general hardness.
1 Temporary (carbonate, removable) hardness is due to the presence of water-soluble hydrocarbonates [Ca(HCO 3) 2 and Mg(HCO 3) 2], which, when boiled, turn into water-insoluble carbonates CaCO 3 and MgCO 3:
Carbonates precipitate, carbon dioxide evaporates and the water softens.
2 Constant hardness (non-carbonate) is characterized by the content of calcium and magnesium sulfates, chlorides, nitrates and other salts, in addition to bicarbonates. When boiled, these salts remain in solution.
3 The total stiffness consists of temporary and permanent. According to the requirements of sanitary standards, the total hardness of drinking water should be no more than 7 mmol/dm 3. The technology requirements are more stringent: the hardness of water used for preparing beer and soft drinks is not higher than 3 mmol/dm 3 . Water intended for the preparation of non-alcoholic and low-alcohol drinks should be softened to a hardness of 0.35 mmol/dm 3.
The organic compounds contained in water are determined by the amount of oxygen required to oxidize them. This indicator characterizes oxidability permanganate, which should be no more
4 Total mineralization (dry residue) – not higher than 1000 mg/dm3.
Carbonates and especially bicarbonates - Na 2 CO 3, NaHCO 3, CaCO 3, Ca(HCO 3) 2, MgCO 3, Mg(HCO 3) 2, K 2 CO 3, KHCO 3, having alkaline properties, reduce the acidity of the beer mash, which negatively affects subsequent stages of beer preparation. In the production of BA drinks, the increased content of these salts leads to excessive consumption of citric acid and other types of acids added according to the recipe.
Ways to improve water composition
· thermal;
· ion exchange;
· reverse osmosis;
· electrodialysis;
Also, water intended for beer production must be prepared:
· decarbonization with lime;
neutralization of carbonates;
And for the production of BA drinks:
· settling and coagulation;
· filtering;
· lime-soda method.
Related information.
