Summary: Deodorization of water. Special water treatment methods Water deodorization
One of the urgent problems of recent decades in the field of water treatment is the needdeodorization of drinking water.The deterioration of the taste qualities of natural waters is due to their mineral and organic composition. Undesirable tastes and odors are caused by inorganic compounds and organic substances of natural and artificial origin.
The presence of dissolved organic substances of biological origin in natural water is the result of the processes of decomposition and subsequent transformation of dead higher aquatic plants, planktonic and benthic organisms, various bacteria and fungi. At the same time, a large amount oflow molecular weight alcohols, carboxylic acids, hydroxy acids, ketones, aldehydes, phenol-containing substanceshaving a strong odor.
Organic substances contribute to the development of microorganisms that secrete into external environment hydrogen sulfide, ammonia, organic sulfides, foul-smelling mercaptans.The intensive development and death of algae contributes to the appearance ofpolysaccharides; oxalic, tartaric and citric acids; substances such as phytoncides.In the decay products of algae, the content of phenol is 20-30 times higher than the MPC (0.001 mg/l).
Despite the legislative measures taken, there is still a discharge of industrial wastewater into surface water bodies, which leads to their contamination with mineral and organic compounds. Among themsalts of heavy metals, oil and oil products, synthetic aliphatic alcohols, polyphenols, acids, pesticides, surfactants and etc.
Of particular danger arepesticides,belonging to different classes organic compounds and in water in different states. They have a negative effectWithyourson the organoleptic properties of water.pest toxicitycides,present in water increases during treatment with chlorine or potassium permanganate.
Oil and oil productspoorly soluble in water and veryresistantto biochemical oxidation. Large concentrations of oil give the water a strong odor, increase its color.nessand oxidizability, reduce the content of dissolved oxygen. With a low content of oil in water, its organoleptic characteristics noticeably deteriorate.
Getting into the water with domestic and industrial wastesurfactantsharply degrade its quality, appearpersistent odors (soapy, kerosene, rosin) and bitter tastes.As a rule, surfactants enhance the stability of odors of other impurities, catalyze the toxicity of carcinogens, pesticides, aniline, etc., found in water.
Present in the natural waters of the North and central Russiahumic acids and fulvic acids, ligninsand many other organic compounds of natural origin are one of the sourcesthe formation of phenols,which impair their organoleptic properties.When chlorinated water containing phenols, dioxins are formed -extremely toxic substances (lethal doses:strychnine 1,5-10~ 6 ; botulinum- 3.3-10 -17, nerve gas - 1,6 10~ 5 mol/kg). Dose of dioxins - 3.1-10~ 9 - lethal, and the dose is 6", 5-10 ~ 15 mol / kg for people under the age of 70 years - the risk of cancer. 100 times less doseaffects the immune system ("chemical AIDS") and reproductive functions of the body.The most toxic substances are2,3,7,8-tetrachlorodibenzodioxin (TCDD).The main toxic substances in the emissions of pulp and paper mills arepolychlorinated dibenzfurans (PCRDs) and the strongest carcinogen - combustion products of fuel oil, gasoline, coal etc. is benzo(a)pyrene(synergism is manifested in a pair of dioxin-benz (a) pyrene).
Obtaining the pesticide 2,4-dichlorophenol by chlorination of phenol is accompanied by the formation of 2,4,6-trichlorophenol, which self-condenses into dioxins that enter from drinking water. waterto people, since modern water treatment technologies do not have barrier functions in relation to the latter. It has been established that polychlorinated dibenzo-n-dioxin (PCDD) and polychlorinated dibenzfuran (PCDF) are formed directly during the chlorination of water, i.e.the formation of dixins during preliminary chlorination of water is inevitable.
present in water iron is a catalyst for the additional chlorination of phenols, converting low-toxic dioxinshighly toxic when chlorinated water. Organic substances present in the water pass through the fast filters almost unhindered, including their toxic dioxin-containing part.
Sometimes organoleptic properties of water deterioratein case of an overdose of reagents or as a result of improper operation of water treatment facilities. Thus, when water is decolorized by coagulation without subsequent stabilization, the corrosive activity of water increases and, as a result, its organoleptic characteristics deteriorate.When water is chlorinated, its organoleptic characteristics deteriorate.both in violation of the process regime, and as a result of the formation of organochlorine compounds that cause unpleasant tastes and odors.
Determined thattraditional methods of water purification have a weakly expressed barrier effectmainly in relation to those chemical contaminants that are in. water in the form of suspensions and colloids or pass into an insoluble form during purification and pre-treatment with chlorine (for example,emulsified oil fractions, poorly soluble pesticides, some metals).In relation to such pollution, the barrier role of treatment facilities can be increased by appropriate selection of reagents at a high degree of water clarification.
Water deodorizationin some cases it is achieved by coagulation of impurities and their flocculation followed by filtration, however, it is often necessary to use special technologies to eliminate unwanted odors and tastes. Their choice is dictated by the nature of impurities and the state in which they are (suspensions, colloids, true solutions, gases).
Today, there are no universal methods for water deodorization, however, the use of some of them in combination provides the required degree of purification. If substances causing unpleasant tastesandodors are in a suspended and colloidal state, then their coagulation gives good results. Tastesandodors due to inorganic substances locatedindissolved state, extracted by degassing, iron removal,desalting. andother Odors and tastes caused by organicsubstanceyou are very durable. Usually theyextract by oxidation and sorption.
Substances with strong reducing properties (humic acids, iron (II) salts, tannins With TVA, hydrogen sulfide, nitrites, poly- and monohydric phenols 0 t.p.) are well extracted from water by oxidation. Moresustainablecompounds (carboxylic acids, aliphaticalcohols,petroleum hydrocarbons and petroleum products, etc.) are poorly oxidized under conditions of treatment with chlorine and its derivatives, and sometimes with ozone. Sometimes strong oxidizing agents, acting on these substances, significantly enhance the initial flavors and odors (for example, organophosphorus pesticides). At the same time, the action of oxidizing agents on easily oxidizable compounds leads to their complete destruction, or to the formationvanitysubstances that do not affect the organoleptic properties of water. Thus, the action of oxidizing agents is effective only in relation to a limited number of contaminants.
The disadvantage of the oxidizing method is also the need to dose the oxidizing agent in extremely precise accordance with the level and type of water pollution, which is extremely difficult, taking into account the complexity and duration of many chemical analyses.
More reliable and economical is the usefilters with granular active carbon,used as a filter media. Filters loaded with granular active carbon, regardless of fluctuations in the level of water pollution, are a permanent barrier in relation to sorbed substances. However, a serious difficulty for the application of this method of water treatment is the relatively low absorption capacity of coal, which necessitates frequent replacement or regeneration.
In addition, it has been established that hydrophobic substances are well sorbed from water by active carbon, i.e., poorly soluble in it and poorly hydrated in solutions (weak organic electrolytes, phenols, etc.). Stronger organic electrolytes and many organic acyclic compounds (carboxylic acids, aldehydes, ketones, alcohols) are less effectively sorbed by active carbon.
Under conditions of increased anthropogenic pollution of water bodies, it is necessary to combine the methods of oxidation, sorption and aeration to deodorize water and remove toxic micro-pollutions.
Water deodorization by aeration
To remove odor-causing volatile organic compounds of biological origin from natural waters and tastes, they are widely usedaeration.
In practice, aeration is carried out in special installations - bubbling, spraying and cascade aerators.
In bubbling type aeratorsair suppliedairwalkers, is distributed in the water by perforated pipes suspended in the tank (Fig. 15.1), spray devices located at its bottom. The advantage of the first method lies in the ease of dismantling the installation.
Air distribution by atomizing devices is often used in aerators with spiral water movement, which are used in large installations.
The depth of the water layer in aerators of this type ranges from 2.7 to 4.5 m. Studies show that since the equilibrium between the concentrations of odorous substances in the liquid and gaseous phases is reached instantly, the height of the water layer during bubbling does not play a role. significant role and can be reduced to 1-1.5 m. The maximum width of the tank is usually twice the depth. Square
Rice. 15.1. Bubble type aerator (a) and inca aerator (b)
6 - main air pipeline; 2 - input of water into the bubbling chamber 5; 3 - perforated plates; 4 - air distributor; 7.1 - removal of aerated and supply of source water; 8 - spillway; 9 - stabilizing partition; 10 - foam layer; 11 - fan; 12 - perforated bottom; b - bubble chamber surfaces are chosen arbitrarily. The duration of air blowing, as a rule, does not exceed 15 minutes. Air flow is 0.37-0.75 m 3 / min per 1 m 3 of water.
Open bubbling units can operate at temperatures below 0°C. The degree of aeration is easily regulated by changing the amount of air supplied. The cost of installations and their operation is low.
In spray aeratorswater is sprayed by nozzles n and small drops, while increasing the surface of its contact with air. The main factor determining the operation of the aerator is the shape of the nozzle and its dimensions. The duration of contact of water with air, determined by the initial velocity of the jet and its trajectory, is usually2 with "(D for vertical jet, which is thrown out under a pressure of 6 m).
In cascade type aeratorstreated water falls in jets through a series of weirs arranged in series. The duration of contact in these aerators can be changed by increasing the number of stages. The pressure loss on cascade-type aerators ranges from 0.9 to 3 m.
In mixed type aeratorswater simultaneously splashes and flows in a thin stream from one stage to another. To increase the area of water contactWithair, ceramic balls or coke are used.
A common disadvantage of aerators built on the principle of contact between a water film and air is their inefficiency due to their large area, the impossibility of using them in winter, the need for powerful ventilation when installed indoors, and, finally, their tendency to fouling.
Aeration of water in the foam layercarried out ininca aerator(Fig. 15.1.6), which is a concrete tank, at the bottom of which there is a perforated stainless steel plate. The water is evenly distributed over the plate by the distribution pipe. A special baffle is used to stabilize the foam layer. Aerate the water with air supplied by a fan. The water, having passed the injector, is discharged through the weir.
The formation of a huge boundary surface between the liquid and gaseous phases provides a high intensity of the deodorization process. The normal ratio of air and water in inkaerators ranges from 30: 1 - 300: 1. Despite the high air consumption, intensive aeration is economically justified (due to a slight loss of pressure, air is supplied by a fan).
However, aeration cannot eliminate persistent odors and tastes due to the presence of impurities with low volatility.
List of used work
Cherkinskiy S.N. Sanitary conditions for the discharge of wastewater into reservoirs, M .: Stroyizdat, Abramov N.N. Water treatment, M.: Stroyizdat 1974
Frog B.N. Levchenko A.P. Water treatment, M.: Stroyizdat 1996
Water deodorization
The tastes and smells of natural waters are of natural and artificial origin, which determines the difference in their chemical composition and the variety of water treatment methods for their localization.
To remove substances that cause unwanted tastes and odors from water, aeration, oxidation with chlorine, ozone, potassium permanganate, chlorine and other oxidizing agents are used; adsorption with activated carbon.
Odors and tastes due to the presence of microorganisms in the water can also be eliminated by filtering the water through a layer of activated granular carbon in pressure filters or introducing powdered carbon into the water before filtering on open sand filters. At high doses (more than 5 mg / l), coal should be introduced at the pumping station of the first lift or simultaneously with the coagulant into the mixer, but not earlier than 10 minutes after the introduction of chlorine. It is recommended to dose activated carbon in the form of pulp with a concentration of 5...10%. At doses of coal up to 1 mg/l, dry dosing of coal powder is allowed. It is especially advisable to use coal powder with the periodic appearance of odors and tastes. The dose of activated charcoal is determined by trial carbonization, the procedure of which is similar to trial chlorination. To restore the sorption capacity of granular activated carbon, it is necessary to periodically regenerate it by washing it with a hot solution of alkali and calcium hypochlorite or by calcining it in furnaces.
To remove odors and tastes, birch BAU, peat TAU, stone fruit CAD, AG-3 coals are most often used. Powdered activated carbon should be stored in a fire-resistant dry room in a hermetically sealed container, as it is explosive and capable of spontaneous combustion.
Unpleasant smell and taste gets water in the presence of phenols, which enter the source of sewage industrial enterprises. When water is chlorinated, the smallest content of phenols causes the appearance of intense chlorophenolic odors, an effective means of combating which is water ammoniation - the introduction of ammonia or a solution of its salts into the water. Ammonia is injected after water chlorination: its dose is 10 ... 25% of the dose of chlorine introduced for water disinfection. Ammonization can also be used in the absence of phenols to eliminate chlorine odors. The bacterial action of chlorine decreases, but its duration increases. The contact of water with chlorine during ammonization should be at least 2 hours. Ammonia is introduced into the water with the help of ammonizers - devices similar in design to chlorine dispensers.
Aeration of water is the simplest and cheapest way to deodorize it, based on the volatility of most substances that cause tastes and odors. Aeration is carried out before the introduction of chlorine or other oxidizing agents into the water.
A good water deodorization effect is achieved using ozone and potassium permanganate, the latter is sometimes used in combination with activated carbon.
Water softening
Water softening is the almost complete elimination or reduction of the amount of hardness salts contained in it. In accordance with the current norms and rules, water intended for household and drinking purposes should be softened if its hardness exceeds 7 mg eq / l, and in special occasions– 14.7 mg eq/l. Water softening is required for some industries (for example, for textile, paper, etc.), where water hardness is required not more than 0.7 ... 1.07 mg eq / l, laundries, and mainly in the treatment of feed water for boiler plants .
Water softening is carried out:
- – precipitation of hardness salts with reagents. Either only lime can be used as reagents (the method is called liming or decarbonization), or together lime and soda ash (the method is called lime-soda),
- - filtering water through a layer of material, the so-called cation exchanger (cationic way).
Water discoloration. Water with increased color and unpleasant odor and taste, which are not completely eliminated during coagulation, is subjected to additional processing.
The color is mainly due to the presence of iron compounds, most often in the form of bicarbonate and iron (II) sulfate. To remove iron bicarbonate, water is aerated in open cooling towers or closed cylindrical tanks, into which compressed air is supplied. In this case, iron is oxidized, forming iron (III) hydroxide, which precipitates, and the released carbon dioxide is carried away with the air.
To remove iron (II) sulfate, water is subjected to lime in special installations.
Deodorization. This is a process during which organic impurities are removed, the presence of which, even in low concentrations, gives the water an unpleasant odor. The removal of these impurities is carried out by oxidation or adsorption.
The most effective oxidizing agent is ozone, however, its use in alcoholic beverage production, where drinking water with a relatively small amount of organic substances is used, is economically unprofitable.
At present, factories mainly use adsorption extraction of organic impurities from water with activated carbon. Coal can be used in powder form (suspension) or in granules (filtered). When choosing a brand of coal, one should proceed from its high adsorption capacity and economic feasibility of use.
A promising method of deodorization is also the treatment of water with potassium permanganate (the method was developed at the Ukrainian Research Institute of the Alcohol Industry and is currently being implemented at some enterprises).
The essence of the method lies in the fact that when introduced into water containing organic matter, oxidizes them, and as a result of the reaction, a finely dispersed flocculent sediment is formed, which has a developed surface and has the ability to absorb organic substances and iron ions that appear in water when it passes through pipelines of city highways.
The dosage depends on the intensity of the foreign odor and is 0.3-0.5 ml / l of a 0.3% solution of KMnO 4 (or 0.13 g of KMnO 4 per 1 m 3 of treated water). The duration of exposure is 15--30 minutes. The optimal environment is slightly alkaline. It is recommended to introduce a KMnO 4 solution into the original tap water before softening. Then softened water should be given for post-treatment with activated carbon.
Cleaning of drains.
Environmental protection is one of the urgent problems of our time. Further development industry is unthinkable without the inclusion in the technological cycle of the processes of neutralization of production waste. A particularly acute question arises in connection with the pollution of natural reservoirs by industrial wastewater. The problem of protecting water bodies is not only in preventing the discharge of pollution, but also in the economical use of fresh water.
The total amount of wastewater from food industry enterprises, and in particular from distilleries and distilleries, is very significant. Therefore, an economically viable measure is the development of schemes for a closed cycle of industrial water supply through the treatment and reuse of wastewater.
The methods used for wastewater treatment can be divided into mechanical, physico-chemical and biological.
Mechanical cleaning methods are used to remove undissolved, coarsely dispersed impurities from wastewater and are carried out by settling followed by filtration. Quartz sand, crushed gravel, charcoal can be used as a filter material. Sieves are used to remove large contaminants. Suspended particles of mineral origin (mainly sand) are retained in the sand traps. A finer suspension is separated by settling, flotation, filtering. From particles of a fine suspension, industrial effluents are released by filtering through a cloth or granular material.
The flotation method has become widespread for the removal of fine particles, in which the resulting complexes of pollutant particles and air bubbles, floating up, form a foam layer, which is then removed.
Mechanical purification as an independent method is used in cases where water after purification is used for industrial needs or is discharged into a reservoir. In all other cases, mechanical cleaning is a preliminary stage before biological cleaning.
The physicochemical method is divided into reagent and reagentless. Reagent processing uses various coagulants and flocculants, as well as oxidizing agents (ozone, chlorine, hydrogen peroxide). Chemical-free cleaning methods include electrochemical, sorption. including the use of ion exchange resins, reverse osmosis, ultrafiltration.
The most widely known physical and chemical methods are clarification using inorganic coagulants or flocculants (active silicic acid, polyacrylamide, starch, sodium polyarylate, etc.), filtration through sand-gravel filters with active carbon and aeration ( stripping of ammonia with air).
During the physical and chemical treatment of wastewater, it is planned to extract from them finely dispersed and dissolved impurities of inorganic substances, as well as organic substances that are difficult to oxidize by the biochemical method, followed by their destruction as a result of physical and chemical effects.
The problem of improving water quality and intensifying the work of treatment facilities is currently being solved by using flocculants. Among the flocculants, the most promising are active silicic acid and polyacrylamide.
The physical and chemical essence of wastewater treatment by aeration is the oxidation of impurities by atmospheric oxygen and the transition of dissolved volatile substances into the gaseous phase. The intensity of the oxidation reaction depends on the concentration of substances, temperature, and pH of the medium.
Aeration of wastewater is carried out primarily in the presence of a large surface of contact between wastewater and air and devices that allow them to be intensively mixed. To do this, partitions are installed on the path of the wastewater flow, cascades, thresholds are arranged, and water is directed into shallow ponds. The intensity of oxidation can be increased by adding nitric acid salts (nitrate).
Among the promising physicochemical methods used in the USSR are ion-exchange methods and hyperfiltration.
The biological cleaning method is the most common, the most mastered and quite economical. It is used to treat wastewater contaminated mainly with organic matter. The method is based on the ability of microorganisms to use many organic and some inorganic compounds contained in wastewater as a nutrient substrate. At the same time, part of the compounds is spent on the biosynthesis of microbial mass, and the other part is converted into harmless oxidation products: water, carbon dioxide, etc. The biological method allows you to remove various organic compounds from wastewater, including toxic ones. Cleaning is carried out under anaerobic and aerobic conditions.
Wastewater treatment by the anaerobic method is carried out in treatment facilities. The process can go at 20--35 and 45--55 °C.
Under anaerobic conditions and at a temperature of 20--35 ° C, organic compounds decompose to methane, carbon dioxide, hydrogen, nitrogen, and hydrogen sulfide. In addition, some amount of fatty acids, sulfides, humic substances and other compounds remain in the liquid. At a temperature of 45--55 ° C, a deeper decay occurs.
Anaerobic biological method used in the treatment of wastewater with a high concentration of organic substances. This method is a preliminary step before aerobic post-treatment.
Aerobic post-treatment is carried out by microorganisms that need an influx of oxygen, and can occur in natural conditions (in reservoirs, ponds, irrigation fields) and in artificial treatment facilities.
The most effective facility for the treatment of industrial wastewater are airtanks using activated sludge (a mass of microorganisms).
Combining different methods in a certain sequence, you can achieve a great effect in wastewater treatment.
One of the most important tasks at present is the creation of a recycling water supply at each enterprise, which will make it possible to minimize the consumption of fresh water from surface and underground sources.
Water is not only the source of life on earth, but also a source of great trouble. Thank God that Russia has enough water. And we can not talk about the deficit, but about the quality indicators of the liquid. To date, 108 million people, or slightly more than 2/3 of the population of the Russian Federation, use centralized water supply. The proportion of cities with water supply is 99%, urban-type settlements - 92%, rural settlements - 31% (that is, 69% of rural settlements do not have centralized water supply). And if the persons carrying it out are responsible for the centralized water supply, then the consumers themselves are responsible for the quality of non-centralized - spring or well - water. Thus, the security of the country's citizens is under threat, since the quality of water largely determines the nature and level of infectious and non-communicable diseases, genetic diseases, and the development of the human body.
Significant, sometimes irreversible, human impact on environment leads to irreparable consequences. Melt waters wash away fertilizers and pesticides from fields, industrial enterprises dump untreated or poorly treated effluents into water bodies, harmful substances that have entered the atmosphere, given the water cycle in nature, eventually end up in a water body. Today we are not talking about total water purification throughout the country, but constant sanitary and epidemiological control is simply necessary.
The safety of drinking water chemical composition determined by compliance with the regulations.
Firstly, according to organoleptic indicators: smell, taste, color, turbidity.
Secondly, according to generalized indicators: the pH value is within 6-9 for drinking water in both water supply systems, hardness, dry residue.
Thirdly, according to the content of harmful chemical substances, most often found in natural waters: nitrates, sulfates, chlorides and other substances.
You can get acquainted with the indicators in table N1, created on the basis of SanPiN 2.1.4.1074-01.
There are a sufficient number of methods and equipment for water purification. The most common among them are the following methods: clarification, deodorization, iron removal, demanganization, softening, disinfection, cleaning with membranes.
Water purification: clarification method
Clarification is designed to combat the turbidity of water, that is, to remove from the liquid: suspended particles of sand, clay, silty organic particles, etc. Industrial clarification counteracts harmful sediment by sedimentation of suspension using gravity, centrifugal forces; a layer of already suspended sediment, filtering through granular materials. At the household level, this happens by the usual passage through a filter (quartz sand, anthracite, aluminosilicate, etc.).
Water purification: deodorization method
Deodorization removes unwanted tastes and odors that arise due to the vital activity of microorganisms, the presence of inorganic and organic compounds in water. Usually, unpleasant phenomena are removed by oxidation (combination with oxygen), sorption (granular activated carbon) and aeration (air saturation).
Water purification: iron removal method
Iron removal removes iron dissolved in water with the help of oxidizing agents (chlorine, sodium hypochlorite, ozone, potassium permanganate and hydrogen peroxide) or without them (reagent-free) using air (showering, that is, a shower or a special water-air injector is used), then water enters into a granular filter.
Water purification: demanganization method
Demanganization purifies water from the manganese ion Mn +2 to Mn +3 and Mn +4 with the formation of sparingly soluble hydroxides. To do this, potassium permanganate, ozone, chlorine and its derivatives, air oxygen are added to the water.
Softening removes hardness cations from water (calcium Ca +2 and magnesium Mg +2). Cations can be harmful, because, having overcome the threshold of 4.5 mg-eq / l, they actively begin to settle on the walls of pipes, dishes in household appliances.
Disinfection is thermal and physical. Physical includes the use of ultrasound, radioactive radiation, ultraviolet rays, oligodynamia (exposure to noble metal ions) and oxidation - the most common and well-known method. It includes the use of oxidants such as chlorine, ozone, sodium hypochlorite. Chlorine is a central remedy against pathogenic bacteria (typhoid, dysentery, tuberculosis, cholera, poliomyelitis, encephalitis), but does not cope with spore-forming bacteria. They are successfully defeated by ozone, which also discolors water and deodorizes.
Recently, UV radiation has become a popular method of combating microbes, especially since it does not change the taste and chemical properties water, faster and more efficiently than chlorine, it deals with all known bacteria, but, unfortunately, does not eliminate water turbidity and does not clean iron. Therefore, it is always recommended for subsequent water treatment.
Water purification with membranes
- one of the most innovative technologies where baromembrane processes are used. It is used both in the food, electronic, pharmaceutical, medical, chemical industries, and in everyday life. The principle of operation is based on the pressure difference on the sides of the membrane. Membranes are classified according to the size of the particles to be separated.Baromembrane processes include: microfiltration, ultrafiltration, nanofiltration and reverse osmosis. Micro work with particles up to 0.1 microns, consisting of mechanical impurities, colloidal particles, bacteria and viruses. Ultra respectively counteract nanoparticles up to 1 nm in size, and these are proteins, peptides, organic compounds, most bacteria and viruses. Reverse osmosis and nanofiltration - also up to 1 nm, but differ from ultra electrostatic interaction of membrane materials with water components. With reverse osmosis and nanofiltration, only water molecules can seep through the membrane.
All these methods are used to some extent today to obtain high-quality water. So what to choose? Experts believe that each specific case should be considered by professionals who are well versed in the water treatment equipment market, since each project requires detailed study. It involves several fundamental steps. The first and, probably, the most important is the receipt, clarification and approval of the terms of reference. The second is the collection of initial data and also the coordination of the information received. The third is the choice of the technological chain, again coordination and, finally, the purchase of equipment and installation of the system.
The main thing at the first stage is to clarify the positions according to the customer's requirements for cyclicity (continuity), supply volumes and water quality indicators.
Since the consequences of such a step can be very problematic and lead to large financial losses. For example, unaccounted for seasonal changes in the chemical composition of water, or incorrect calculation of loads on equipment depending on the time of day, or inaccurate dimensions of water treatment devices during installation that exceeded the size of the working room, etc. - all these errors lead to additional investments in the project .
The collection of initial data is carried out by the contractor and involves technical measurements, calculations and design. You should start with a source, which can be of three types: artesian, surface and centralized water supply. Artesian is characterized as the least troublesome in terms of chemical composition, but the change in water color over time (“iron redness”), turbidity (clay, sand) and an unpleasant aftertaste can cause concern. Surface water has a full range of unpleasant consequences for the consumer's body (mechanical impurities, organic substances, mineral suspensions, microbiological contamination), therefore, it requires maximum purification. Tap water is treated depending on the supplier's capabilities, but on the way to the consumer it is able to purchase additives from a pipe, especially made of ferrous metal. Laboratory analyzes of orphan sources must be carried out regularly, since the chemical and biological properties of water are subject to various changes.
Measurements are carried out according to the principle: measure seven times - cut once, especially with an eye to the equipment. Although there is a simple calculation for kettles of 5 liters of water per day per person, but given the importance of the ratio of consumption volumes to equipment performance, it is better to turn to professionals. Note that these works are regulated by SNiP 2.04.01 - 85 "Internal water supply and sewerage of buildings".
The choice of a purification system and the formation of a set of necessary filters are clearly tied to the technical specifications received from the customer in order to maximize the fulfillment of its water quality requirements. Today, water treatment equipment is a complex technical device. For their successful operation, full compatibility is necessary. The choice of such equipment should be entrusted to a professional. Only a specialist who is well versed in modern trends in water treatment and equipment is able to solve complex problems to obtain the required results.
Moreover, a large number of water treatment equipment is provided on the market. Conventionally, it can be divided according to its purpose into the main, additional and auxiliary. Filters are of the first type. various methods water purification; to the second - ultraviolet sterilizers, flow meters, booster pumps, inlet solenoid valves; to the third - dosing pumps, pumping equipment, compressor equipment. A water treatment plant is usually formed from a whole complex of devices, while one manufacturer should be followed, since it is possible to make a mistake in the calculations and get production and technological incompatibility of devices.
Mechanical filters
Mechanical cleaning filters protect water supply systems, its individual components and equipment from clogging. They are usually located at the inlet and serve for the preliminary removal of mechanical particles, sand, suspensions, rust, etc. There are two types of filters: mesh (ordinary metal mesh) and fine filters with removable cartridges (consist of one or more collapsible housings and filter cartridges).Iron removal filters
Filters for removal of iron - bezreagentny and reagent. Reagent-free remove total iron up to 5 mg / l, manganese - up to 1.5 mg / l. They consist of a pressure tank, a filter medium, an automatic control valve, a drainage distribution system. They operate on the basis of catalytic materials that accelerate oxidation with the help of oxygen. Cleaning is automatic.Reagent filters are able to purify water from total iron up to 15 mg/l, manganese up to 12 mg/l, hydrogen sulfide up to 5 mg/l. They consist of a pressure and reagent tanks, a filter medium, an automatic control valve, a drainage distribution system. The principle of operation is based on the oxidation of metals dissolved in water with reagents and their retention in a layer of granular loading.
Cleaning is done automatically.
Softening filters (softeners) free water from salts and are of periodic and continuous action. Consist of pressure and salt tanks, filter media, automatic control valve, drainage distribution system. Both softeners operate on the basis of the removal of hardness salts by ion exchange using cation exchange resins and differ from each other in the presence of additional reserve tanks. Cleaning is done automatically.
Clarifier filters are able to purify water from mechanical suspensions (20-40 microns): rust, sand, clay, algae, etc. They consist of a pressure tank, a filter medium, an automatic control valve, a drainage distribution system. The principle of operation is based on passing water through a layer of filter material. Cleaning is done automatically.
Adsorbent filters
Adsorbent filters serve to remove organochlorine and organic compounds. They consist of a pressure tank, a filter medium, an automatic control valve, a drainage distribution system. The principle of operation is based on the sorption (extraction) of organic substances from water. A chemical reaction takes place in it, and the surface of the sorbent is oxidized (coal). Flushing required.UV sterilizers destroy microorganisms by damaging their DNA, which leads to the death of animals. The devices use low-pressure gas-discharge mercury-quartz lamps. The principle of operation is based on photochemical reactions.
Membrane filters are the most reliable water purification devices, since they operate on the basis of the passage of water molecules through the thinnest film. The principle of operation is based on the properties of water
- dissolve organic and inorganic compounds. Almost perfect, the filter purifies water by more than 90%. Membrane filters are a roll of a multilayer polymer film and work in real conditions in a technological connection with other water treatment equipment.
And optional and ancillary equipment include: flow meters - installed to monitor water volumes; booster pumps - serve to increase and maintain pressure in the system; inlet solenoid valves - regulate water flows in membrane filters; dosing pumps - measure the required volumes of chemicals and water; tank filling pumps; compressors for supplying oxygen to the system.
In conclusion, it should be noted that modern technologies make it possible to guarantee high quality drinking water. At the same time, it is important to take into account that when choosing quality standards, it is necessary to focus on SanPiN 2.1.4.1074-01, and not on individual consumer tastes. And one more piece of advice, before deciding to purchase or install a filter, you should understand for yourself what harmful organic and inorganic compounds or microorganisms you need to get rid of, that is, conduct a laboratory analysis of tap water.
Special methods for improving the quality of drinking water include conditioning the mineral composition, removing tastes, odors, decontamination, etc. All types of conditioning the mineral composition of water can be divided into 2 groups: 1) removal of excess salts or gases from water (softening, desalination, iron removal, deodorization, decontamination, defluorination, etc.); 2) adding certain salts to water in order to improve its organoleptic properties or increase the content of trace elements that are not enough in water and food products (fluoridation). After special treatment on the water supply, the water is subject to mandatory disinfection.
Deodorization- elimination of smacks and smells of water. It is achieved by water aeration, treatment with oxidizing agents (ozonation, chlorine dioxide, high doses of chlorine, potassium permanganate), filtering through a layer of activated carbon. The choice of deodorization method depends on the origin of tastes and odors.
iron removal produced by spraying water for the purpose of aeration in special devices - cooling towers. In this case, ferrous iron is oxidized to iron (III) hydroxide (see p. 121), which is deposited in the sump or retained on the filter. If the concentration of iron salts exceeds 5 mg/l, preliminary precipitation of its salts is necessary.
Softening- reduction of natural hardness of water. Water softening methods include: 1) reagent; 2) ion exchange; 3) thermal.
Of the reagent methods, the most common soda-lime, with the help of which calcium and magnesium are deposited in the sump in the form of insoluble salts (calcium, magnesium carbonates, etc.). Lime (calcium hydroxide), added to water in a larger amount than necessary to bind carbon dioxide (carbon dioxide), interacts with calcium bicarbonate, forming calcium carbonate, which precipitates: Ca (HC0 3) 2 + Ca (OH) 2 \u003d 2CaC0 3 1 + 2H 2 0, Mg (HC0 3) 2 + Ca (OH) 2 \u003d Mg C0 3\u003e L + CaC0 3\u003e 1 + 2H 2 0.
To remove calcium and magnesium sulfates, a solution of sodium carbonate is added to the water:
CaS0 4 + Na 2 C0 3 = Na 2 S0 4 + CaC0 3 >k
Mg S0 4 + Na 2 C0 3 = Na 2 S0 4 + MgC0 3 i.
More modern method is the filtration of water through filters filled with ion exchangers - cation exchange softening.
Ion exchangers can be of natural or artificial (mineral or organic) origin, practically insoluble in water and organic solvents. They are capable of exchanging their ions for solution ions. Most ion exchangers are high-molecular compounds of a network or simple
early structure. Ion exchangers are divided into cation exchangers (capable of exchanging cations) and anion exchangers (capable of exchanging anions).
In order to soften the water, it is filtered through a layer of natural (glauconite sand) or artificial cation exchangers 2-4 m thick. In this case, calcium and magnesium ions (Ca 2+, Mg 2+) of the water are exchanged for Na + or H + cation exchange resin. In the practice of water treatment, only those cation exchangers that have received a hygienic assessment and are approved for use by the Ministry of Health can be used.
Water softening boiling makes it possible to save water only from removable hardness due to the decomposition of calcium and magnesium bicarbonates to insoluble carbonates, which precipitate (the equations of chemical reactions are given on p. 158).
The choice of one or another method is determined by the required degree of softening (the best result, close to 100%, gives the use of cation exchangers), depends on the amount of water to be treated, technical and economic calculations.
Water desalination- this is the removal of mineral salts dissolved in it to the values recommended by the state standard, at which water becomes suitable for drinking or technical needs. The most common methods of water desalination in water pipes are distillation, chemical (ion exchange, reagent), using selective membranes (electrodialysis, hyperfiltration), etc. Desalinated water is treated, optimizing for drinking: filtered through activated carbon (remove tastes and odors), fluoridated and enriched with mineral salts, passing through filters with marble chips and adding part of undesalinated water.
Desalination of highly mineralized (brackish and saline, including marine and oceanic) waters is a promising way to replenish the shortage of fresh waters in low-water and arid regions. Desalination is achieved either by removing excess salts from water, or by separating H 2 0 molecules. Separation is associated in most cases (except for the extraction method and reverse osmosis) with the transition of water into a vaporous or solid (ice) state, that is, with a change in its state of aggregation.
On an industrial scale, 5 main methods of water desalination are used: distillation, freezing, reverse osmosis, electrodialysis, ion exchange.
distillation the process is one of the cheapest, therefore today, both in terms of the number of desalination plants, and, especially, in terms of their total productivity distillation methods occupy a dominant position.
The performance of evaporative desalination plants significantly depends on the maximum heating temperature of the desalination water and the degree of heat recovery. According to the nature of the use of thermal energy and the degree of its recovery, distillation plants are divided into single-stage, multi-stage and vapor compression.
____ ____
The cost of thermal energy is 30-40% of the cost of water desalination by distillation. In this regard, in areas with a high intensity of solar radiation, greenhouse-type solar desalination plants or mirror reflectors with a concentration of solar heat have found application. Typically, the maximum temperature of water heating in solar installations does not exceed 65-70 °C, and their performance depends on the evaporating surface and ranges up to 4-5 l / m 2 per day. Solar plants are mainly used to obtain a small amount of fresh water.
Water desalination freezing method It is based on the fact that the freezing point of salt water is lower than the freezing point of fresh water. Freezing methods are more economical than distillation. Cooling water at 0 °C is optimal. An important condition is the slow flow of thermodynamic processes. The technology of this group of methods provides for a two-stage process: Stage I - partial desalination of ice during slow freezing of water below 0 ° C (formation of aggregates from crystals fresh ice, between which there are voids filled with frozen brine); Stage II - obtaining fresh water during the slow melting of ice (first the brine melts and drains with the first portions of water, the ice is desalinated and fresh water is formed during further melting).
Membrane methods are the simplest, but they are cost-effective only when treating water with a low salt content.
The electrodialysis method of water desalination is based on the principle of separation of salts in an electric field through selective semi-permeable ion-exchange membranes: salt cations, moving under the influence of electric current to the cathode, freely pass through cation-exchange membranes and are retained by anion exchangers, salt anions - vice versa. The alternating placement of membranes in the electrodialysis apparatus causes the formation of desalinated water chambers alternating with concentrate chambers.
Methodreverse osmosis(hyperfiltration) is based on the desalination of water by filtering it under high pressure(50-100 atm) through semi-permeable membranes that allow water molecules to pass through, but retain larger hydrated ions of salts dissolved in water. Today, membranes made from cellulose acetates, polyamide compounds, polyacrylic acid, and nylon are widely used.
Ion exchange method widely used for desalination of water with a salt content of up to 2-3 g/l, softening and deep desalination of fresh water. It is based on the use of practically water-insoluble ion-exchange granular materials - cation exchangers and anion exchangers.
For water desalination, cation exchangers in hydrogen and anion exchangers in hydroxyl forms are usually used, that is, pre-charged, respectively, with exchangeable hydrogen cations (H-cation exchange resin) or hydroxyl anions (OH-anion exchange resin). Ion exchange reactions obey the law of mass action, therefore, the regeneration of cation exchangers and anion exchangers during their depletion
____
responsibly carried out with sufficiently concentrated solutions of acids and bases.
Desalinated waters are usually not entirely suitable for drinking, which necessitates their appropriate conditioning: improvement of organoleptic properties, post-treatment, correction of macro- and microelement composition, and disinfection. Sanitary and technical requirements for the quality of primary and desalinated waters, as well as for the use of various methods of desalination of highly mineralized waters for drinking purposes, are reflected in the WHO document "Hygienic Aspects of Water Desalination", 1980 ("Guidelines on Health Aspects of Water Desalination", Sidorenko G.I. , Rachmanin Y.A. WHO, Geneva, ETS/80.4 - 60 p.).
Deactivation. Coagulation, sedimentation and filtration of water in water pipes reduces the content radioactive substances in it by 70-80%. For deeper decontamination, water is filtered through cation and anion exchange resins.
Defluorination of water. Indications for the use of this method are an increased (over 1.5 mg/l) fluorine content in water and a large number of patients with dental fluorosis of II and higher degrees among the population. Defluorination of water is indicated only when it is impossible to change the source of water supply or dilute its water with water with a low concentration of fluorine to improve the endemic focus of fluorosis.
During defluorination, the concentration of fluorine in water is adjusted to the optimum for a particular area. To remove excess fluorine from water, many methods have been proposed, which can be divided into reagent (precipitation methods) and filtration methods. Reagent methods are based on the sorption of fluorine by freshly precipitated aluminum or magnesium hydroxides. This method is recommended for the treatment of surface water, since, in addition to fluoridation, clarification and discoloration are also achieved.
Purification of water from excess fluorine can be carried out by filtering it through anion-exchange resins:
Activated and granular aluminum oxide is often used as an ion exchange material. Sometimes it is possible to reduce the fluorine content in water by diluting it with water from a source with a minimum amount of fluorine.
Water fluoridation. The choice of fluoride dose should provide an anti-caries effect. However, if the content of fluorine ion in the water exceeds 1.5-2.0 mg/l, this will lead to the defeat of the population by fluorosis. That is why, during water fluoridation, the content of fluorine ion in it should be within 70-80% of the maximum levels in accordance with different climatic regions - within 0.7-1.5 mg / l.
For fluoridation of drinking water, fluorine-containing compounds can be used, in particular sodium silicon fluoride (Na 2 SiF 6), silicon fluoride
____ ____
hydrochloric acid H 2 SiF 6 , sodium fluoride (NaF), ammonium silicofluoride (NH 4) 2 SiF 6 , calcium fluoride (CaF 2), hydrofluoric acid (HF), etc. 1 There are two ways to fluoridate water: throughout the year single dose and seasonal winter and summer doses. In the first case, the same dose of fluorine is added throughout the year, which corresponds to the climatic conditions of the settlement. If the dose varies depending on the season of the year, then in the cold period, when the average monthly air temperature (at 13.00) does not exceed 17-18 ° C, water can be fluoridated at a level of 1 mg / l, and in the warm period (for example, in June - August) - at a lower level. It depends on the average maximum temperature (at 13.00) during these months. For example, at a temperature of 22-26 ° C, a dose of 0.8 mg / l of fluorine ion is used, at 26-30 ° C and above - 0.7 mg / l.
Drinking water disinfection
Drinking water disinfection serves to create a reliable barrier to transmission by water pathogens of infectious diseases. Methods of water disinfection are aimed at the destruction of pathogenic and opportunistic microorganisms, which ensures the epidemic safety of water.
Water is disinfected at the final stage of purification after clarification and decolorization before entering the tanks pure water, which simultaneously perform the functions of contact chambers. Reagent (chemical) and non-reagent (physical) methods are used for water disinfection. Reagent methods are based on the introduction of strong oxidizing agents into water (chlorination, ozonation, manganation, water treatment with iodine), heavy metal ions and silver ions. Non-reagent ones include heat treatment, ultraviolet irradiation, sonication, y-irradiation, treatment with microwave current. The method is chosen depending on the quantity and quality of the source water, the methods of its preliminary treatment, the requirements for the reliability of disinfection, taking into account technical and economic indicators, the conditions for the supply of reagents, the availability of transport, and the possibility of automating the process.
Disinfection of water with chlorine and its compounds. To date, the most common method of water disinfection at waterworks is chlorination. Among chlorine-containing compounds, given certain hygienic and technical advantages, liquid chlorine is most often used. It is also possible to use bleach, calcium and sodium hypochlorite, chlorine dioxide, chloramines, etc.
For use in the practice of drinking water supply, only fluorine-containing compounds that have passed hygienic testing and are included in the "List of materials and reagents permitted by the Main Sanitary and Epidemiological Directorate of the Ministry of Health of the USSR for use in the practice of drinking water supply (No. 3235-85)" are allowed.
WATER SUPPLY FROM SURFACE WATER SUPPLY
For the first time in the practice of water treatment, chlorine was used long before the discovery of microbes by L. Pasteur, R. Koch's proof of the etiological significance of pathogenic microorganisms in the development of infectious diseases, T. Escherich's final awareness of the microbiological essence of water epidemics and the bactericidal properties of chlorine. It was used to deodorize water, which had an unpleasant "septic" smell. Chlorine proved to be a very effective deodorant and, in addition, after treating water with chlorine, people were much less likely to be diagnosed with intestinal infections. With the beginning of water chlorination, epidemics of typhoid and cholera stopped in many European countries. It has been suggested that the bad smell and taste of the water, which the chlorine effectively eliminated, was the cause of the illnesses. Only with time proved the microbial etiology of water epidemics of intestinal infections and recognized the role of chlorine as a disinfecting agent.
To chlorinate water, liquid chlorine is used, which is stored under pressure in special containers (cylinders), or substances containing active chlorine.
Chlorination of water with liquid chlorine. Chlorine (C1 2) at normal atmospheric pressure is a greenish-yellow gas, which in 1.5-
2.5 times heavier than air, with a sharp and unpleasant odor, dissolves well in water, easily liquefies when pressure increases. The atomic weight of chlorine is 35.453, molecular mass- 70.906 g/mol. Chlorine may be in three aggregate states: solid, liquid and gaseous.
Chlorine is delivered to waterworks for water disinfection in liquid form in pressurized cylinders. Chlorination is carried out using chlorinators. They prepare a solution of chlorine, which is injected directly into the pipeline, through which water enters the RCHV. L.A. chlorinators are used. Kulsky (Fig. 20), vacuum chlorinators LONII-100, Zh-10, LK-12, KhV-11. Schematic diagram of the LONII-100 chlorinator is shown in fig. 21.
When the cylinder is connected to the chlorinator, liquid chlorine evaporates. Gaseous chlorine is cleaned in a cylinder and on a filter, and after reducing its pressure with a reducer to 0.001-0.02 MPa, it is mixed in a mixer with water. From the mixer concentrated
Rice. 21. Technological scheme of a typical chlorination plant for 3 kg/h: 1 - platform scales; 2 - risers with cylinders; 3 - dirt trap; 4 - chlorinators
LONI-100; 5 - ejectors
The solution is sucked in by the ejector and fed into the pipeline. Chlorinators of the LK type, whose design is simpler, and the accuracy is lower, are used for high-capacity stations. These chlorinators do not require preliminary purification of chlorine, they are not so accurate in dosing, but they can supply chlorine water to a height of 20-30 m. After the ejector from LONI-100, the pressure is only 1-2 m. with the formation of chloride (hydrochloric) and hypochlorite (or hypochlorous) acids:
C1 2 + H 2 0 ^ HCl + HC10.
Hypochlorous acid HC10 is a weak, monobasic, unstable acid that readily dissociates to form hypochlorite ion (CH~):
NSU ^ H + + SU".
The degree of dissociation of hypochlorous acid depends on the pH of the water. At pH< 5 (по Л. Кульскому) почти весь свободный хлор остается в виде неиони-зированной хлорноватистой кислоты (НСЮ). При повышении pH возрастает степень диссоциации хлорноватистой кислоты. При pH свыше 9,2 (по Л. Кульскому) почти весь свободный хлор находится в виде иона гипохлорита (СЮ -). Окислительное действие (окислительный потенциал) имеет как гипохлоритная кислота, так и гипохлорит-ион. Именно поэтому обе эти формы способны оказывать бактерицидное влияние. Их называют свободным активным хлором. Окислителем является и молекулярный хлор (С1 2), который также рассматривается как одна из форм свободного активного хлора 1 .
In addition, hypochlorous acid decomposes to form atomic oxygen, which is also a strong oxidizing agent:
NSJ It HCl + O".
Active chlorine is one that is capable of releasing an equivalent amount of iodine from aqueous solutions of potassium iodide at pH 4. There are free (molecular chlorine, hypochlorous acid, hypochlorite ion) and bound (chlorine, which is part of organic and inorganic mono- and dichloramines) active chlorine.
WATER SUPPLY FROM SURFACE WATER SUPPLY
Previously, it was believed that it was this atomic oxygen that had a bactericidal effect. Today it has been proven that the disinfecting effect of liquid chlorine, as well as bleach, calcium and sodium hypochlorites, the two-tertiary salt of calcium hypochlorite, is due to oxidizing agents that are formed in water when chlorine-containing compounds are dissolved, and first of all, by the action of hypochlorite acid, and then by the hypochlorite anion and finally atomic oxygen.
Chlorination of water with hypochlorites(salts of hypochlorous acid) are carried out at waterworks of low power. Hypochlorites are also used for long-term disinfection of water in mine wells using ceramic cartridges, for disinfection of water in the field, including the use of fabric-carbon filters, etc.
Used to disinfect drinking water calcium hypochlorite Ca(OC1) 2 . In the process of its dissolution in water, hydrolysis occurs with the formation of hypochlorous acid and its further dissociation:
Ca (OS1) 2 + 2H 2 0 \u003d Ca (OH) 2 + 2HNS,
her -£. n + + cicr.
Depending on the method of calcium production, hypochlorite can contain from 57-60% to 75-85% active chlorine. Together with pure hypochlorite, a mixture of calcium hypochlorite with other salts (NaCl, CaCl 2) is used to disinfect water. Such mixtures contain up to 60-75% pure hypochlorite.
At stations with an active chlorine consumption of up to 50 kg / day, it can be used for water disinfection sodium hypochlorite(NaCIO 5H 2 0). This crystalline hydrate is obtained from a solution of sodium chloride (NaCl) by an electrolytic method.
Sodium chloride in water dissociates with the formation of sodium cation and chloride anion:
NaCl ^ Na + + SG
During electrolysis at the anode, chlorine ions are discharged and molecular chlorine is formed:
2SG -» C1 2 + 2e.
The resulting chlorine dissolves in the electrolyte:
C1 2 + H 2 O ^ HC1 + NSu,
C1 2 + OH-^CI + NSO.
Discharge of water molecules occurs at the cathode:
H 2 0 + e -> OH- + H +.
Hydrogen atoms after recombination into molecular hydrogen are released from solution in the form of a gas. Hydroxyl anions OH "remaining in water react with sodium cations Na +, resulting in the formation of NaOH. Sodium hydroxide interacts with hypochlorous acid to form sodium hypochlorite:
NaOH + HC10 -> NaOCI + H 2 0.
Rice. 22. Technological scheme of electrolytic production of sodium hypochlorite: 1 - solution tank; 2 - pump; 3 - distribution tee; 4 - working tank; 5 - dispenser; 6 - cell with graphite electrodes; 7 - sodium hypochlorite storage tank; 8 - umbrella
exhaust ventilation
Sodium hypochlorite dissociates to a large extent with the formation of SJ, which has a high antimicrobial activity:
NaCIO ^ Na + + CIO",
syu- + n + ;^nsyu.
Electrolysis plants are divided into flow and batch. They include electrolyzers, various types of tanks. The schematic diagram of the batch plant is shown in fig. 22. A 10% concentration sodium chloride solution is fed into a constant level tank, from where it flows out at a constant rate. After filling the dosing tank, the siphon works and drains a certain volume of solution into the electrolyzer. Under the influence of electric current, sodium hypochlorite is formed in the electrolyzer. New portions of the salt solution push sodium hypochlorite into the supply tank, from which it is dosed by a dosing pump. The storage tank must hold a volume of sodium hypochlorite for at least 12 hours.
The advantage of obtaining sodium hypochlorite by the electrolytic method at the point of use is that there is no need to transport and store toxic liquefied chlorine. Among the disadvantages are significant energy costs.
Disinfection of water by direct electrolysis. The method consists in the direct electrolysis of fresh water, in which the natural content of chlorides is not
WATER SUPPLY FROM SURFACE WATER SUPPLY
the same 20 mg / l, and hardness - not higher than 7 meq / l. Used at waterworks with a capacity of up to 5000 m 3 / day. Due to direct electrolysis at the anode, the chloride ions in the water are discharged and molecular chlorine is formed, which is hydrolyzed to form hypochlorous acid:
2CH ^ C1 2 + 2e, C1 2 + H 2 O^HC1 + HCS.
During electrolysis treatment of water with a pH in the range of 6-9, the main disinfectants are hypochlorous (hypochlorite) acid NSO, hypochlorite anion C10 ~ and monochloramines NH 2 C1, which are formed due to the reaction between NSO and ammonium salts contained in natural water. At the same time, during the treatment of water by the electrolytic method, the microorganisms are affected by the electric field in which they are located, which enhances the bactericidal effect.
Disinfection of water with bleach is used on small waterworks (capacity up to 3000 m 3 / day), after preparing the solution. Chlorine lime is also filled with ceramic cartridges for water disinfection in mine wells or local water supply systems.
Bleach is a white powder with a strong chlorine odor and strong oxidizing properties. It is a mixture of calcium hypochlorite and calcium chloride. Get bleach from limestone. Calcium carbonate at a temperature of 700 ° C decomposes with the formation of quicklime (calcium oxide), which, after interaction with water, turns into slaked lime (calcium hydroxide). When chlorine reacts with slaked lime, bleach is formed:
CaCO3 ^ CaO + CO 2,
CaO + H 2 0 \u003d Ca (OH) 2,
2Ca (OH) 2 + 2C1 2 \u003d Ca (OC1) 2 + CaC1 2 + 2H 2 0 or
2Ca(OH) 2 + 2C1 2 = 2CaOC1 2 + 2H 2 0.
The main component of bleach is expressed by the formula:
The technical product contains no more than 35% active chlorine. During storage, bleach partially decomposes. The same happens with calcium hypochlorite. Light, humidity and high temperature accelerate the loss of active chlorine. Bleach loses approximately 3-4% of available chlorine per month due to hydrolysis reactions and decomposition in the light. In a damp room, bleach decomposes, forming hypochlorous acid:
2CaOC1 2 + C0 2 + H 2 0 \u003d CaC0 3 + CaC1 2 + 2HNS.
____ SECTION I. HYGIENE OF WATER AND WATER SUPPLY OF PUBLIC PLACES ____
Therefore, before using bleach and calcium hypochlorite, their activity is checked - the content of active chlorine expressed as a percentage in a chlorine-containing preparation.
The bactericidal action of bleach, as well as hypochlorites, is due to the group (OSG), which forms hypochlorous acid in the aquatic environment:
2CaOC1 2 + 2H 2 0 -> CaC1 2 + Ca(OH) 2 + 2HC10.
Chlorine dioxide (ClOJ- gas of yellow-green color, easily soluble in water (at a temperature of 4 ° C, 20 volumes of gaseous SYO 2 dissolve in 1 volume of water). Does not hydrolyze. It is advisable to use it if the characteristics of natural water are unfavorable for effective disinfection with chlorine, for example, at high pH values or in the presence of ammonia. However, obtaining chlorine dioxide is a complex process that requires special equipment, qualified personnel, and additional financial costs. In addition, chlorine dioxide is explosive, which requires strict adherence to safety requirements. The above limits the use of chlorine dioxide for water disinfection in drinking water pipelines.
Chlorine-containing preparations include chloramines (inorganic and organic), which are used to a limited extent in the practice of water treatment, but are used as disinfecting agents during disinfection activities, in particular in medical institutions. Inorganic chloramines (monochloramines NH 2 C1 and dichloramines NHC1 2) are formed by the interaction of chlorine with ammonia or ammonium salts:
NH 3 + CI 2 \u003d NH 2 CI + HCI,
NH 2 CI + CI 2 \u003d NHCI 2 + HCl.
Together with inorganic chlorine compounds, organic chloramines (RNHC1, RNC1 2) are also used for disinfection. They are obtained in the process of interaction of bleach with amines or their salts. In this case, one or two hydrogen atoms of the amine group are replaced by chlorine. Different chloramines contain 25-30% active chlorine.
The process of water disinfection with chlorine-containing preparations takes place in several stages:
1. Hydrolysis of chlorine and chlorine-containing preparations:
C1 2 + H 2 0 = HCl + HC10;
Ca (OS1) 2 + 2H 2 0 \u003d Ca (OH) 2 + 2HC10;
2CaOC1 2 + 2H 2 0 \u003d Ca (OH) 2 + CaC1 2 + 2HC10.
2. Dissociation of hypochlorous acid.
At pH ~ 7.0 HC10 dissociates: HC10<± Н + + СЮ".
3. Diffusion of the HC10 molecule and the CO ion into the bacterial cell.
4. Interaction of a disinfecting agent with enzymes of microorganisms, which are oxidized by hypochlorous acid and hypochlorite ion.
WATER SUPPLY FROM SURFACE WATER SUPPLY
Active chlorine (NSO and SU") first diffuses into the bacterial cell, and then reacts with enzymes. The greatest bactericidal and virucidal effect is exerted by undissociated hypochlorous acid (NSO). The rate of the water disinfection process is determined by the kinetics of diffusion of chlorine inside bacterial cell and the kinetics of cell death as a result of metabolic disorders. With an increase in the concentration of chlorine in water, its temperature and with the transition of chlorine to the non-dissociated form of easily diffusible hypochlorous acid, the overall rate of the disinfection process increases.
The mechanism of the bactericidal action of chlorine consists in the oxidation of organic compounds of a bacterial cell: coagulation and damage to its membrane, inhibition and denaturation of enzymes that provide metabolism and energy. The most damaged are thiol enzymes containing SH-groups, which are oxidized by hypochlorous acid and hypochlorite ion. Among the thiol enzymes, the group of dehydrogenases, which provide respiration and energy metabolism of the bacterial cell, is most actively inhibited 1 . Under the influence of hypochlorous acid and hypochlorite ion, dehydrogenases of glucose, ethyl alcohol, glycerol, succinic, glutamic, lactic, pyruvic acids, formaldehyde, etc. are inhibited. Inhibition of dehydrogenases leads to inhibition of oxidation processes at the initial stages. The consequence of this is both the inhibition of the processes of reproduction of bacteria (bacteriostatic action) and their death (bactericidal action).
The mechanism of action of active chlorine on viruses consists of two phases. First, hypochlorous acid and hypochlorite ion are adsorbed on the virus envelope and penetrate through it, and then they inactivate the RNA or DNA of the virus.
As the pH value increases, the bactericidal activity of chlorine in water decreases. For example, to reduce the number of bacteria in water by 99% at a dose of free chlorine of 0.1 mg/l, the contact time increases from 6 to 180 minutes with an increase in pH from 6 to 11, respectively. Therefore, it is advisable to disinfect water with chlorine at low pH values, i.e. before the introduction of alkaline reagents.
The presence in water of organic compounds capable of oxidation, inorganic reducing agents, as well as colloidal and suspended substances enveloping microorganisms, slows down the process of water disinfection.
The interaction of chlorine with water components is a complex and multi-stage process. Small doses of chlorine are completely bound by organic substances, inorganic reducing agents, suspended particles, humic substances and water microorganisms. For a reliable disinfecting effect of water after its chlorination, it is necessary to determine the residual concentrations of free or combined active chlorine.
Energy metabolism in bacteria occurs in mesosomes - analogues of mitochondria.
Rice. 23. Graph of the dependence of the magnitude and type of residual chlorine on the injected dose of chlorine
On fig. 23 shows the relationship between the dose of introduced chlorine and residual chlorine in the presence of ammonia or ammonium salts in the water. When chlorinating water that does not contain ammonia or other nitrogen-containing compounds, "with an increase in the amount of chlorine introduced into the water, the content of residual free chlorine in it increases. But the picture changes if there is ammonia, ammonium salts and other nitrogen-containing compounds in the water, which are an integral part of natural water or artificially introduced into it.At the same time, chlorine and chlorine agents interact with the ammonia present in the water, ammonium and organic salts containing amino groups.This leads to the formation of mono- and dichloramines, as well as extremely unstable trichloramines:
NH 3 + H 2 0 = NH 4 OH;
C1 2 + H 2 0 = HC10 + HCl;
NSYU + NH 4 OH \u003d NH 2 C1 + H 2 0;
NSU + NH 2 C1 = NHC1 2 + H 2 0;
NSY + NHC1 2 = NC1 3 + H 2 0.
Chloramines are bound active chlorine, which has a bactericidal effect, which is 25-100 times less than that of free chlorine. In addition, the ratio between mono- and dichloramines changes depending on the pH of the water (Fig. 24). At low pH values (5-6.5), dichloramines are predominantly formed, and at high pH values (greater than 7.5), monochloramines are formed, the bactericidal effect of which is 3-5 times weaker than that of dichloramines. The bactericidal activity of inorganic chloramines is 8-10 times higher than that of chlorine derivatives of organic amines and imines. When low doses of chlorine are added to water at a molar ratio of C1 2: NH *< 1 образуются моно- и дихлорамины. Поэтому на отрезке II кривой (см. рис. 23) в воде
There is no ammonia-free water in nature. It can only be prepared in the laboratory from distilled water.
residual amine-bound chlorine accumulates. With an increase in the dose of chlorine, more chloramines are formed and the concentration of residual combined chlorine rises to a maximum (point A).
With a further increase in the dose of chlorine, the molar ratio of the introduced chlorine and NH ion * contained in water becomes greater than unity. In this case, mono-, di- and, especially, trichloramines are oxidized by excess chlorine in accordance with the following reactions:
NHC1 2 + NH 2 C1 + NSO -> N 2 0 + 4HC1;
NHC1 2 + H 2 0 -> NH(OH)Cl + HCl;
NH(OH)Cl + 2HC10 -> HN0 3 + ZNS1;
NHC1 2 + HCIO -> NC1 3 + H 2 0;
4NH 2 C1 + 3C1 2 + H 2 0 = N 2 + N 2 0 + 10HC1;
IONCI3 + CI 2 + 16H 2 0 = N 2 + 8N0 2 + 32HCI.
With a molar ratio of Cl 2: NH \ up to 2 (10 mg Cl 2 per 1 mg N 2 as NH \ ) due to the oxidation of chloramines by excess chlorine, the amount of residual combined chlorine in water decreases sharply (section III) to a minimum point (point B), which is called the turning point. Graphically, it looks like a deep dip in the residual chlorine curve (see Fig. 23).
With a further increase in the dose of chlorine after the turning point, the concentration of residual chlorine in the water again begins to gradually increase (segment IV on the curve). This chlorine is not associated with chloramines, is called free residual (active) chlorine and has the highest bactericidal activity. It acts on bacteria and viruses like active chlorine in the absence of ammonia and ammonium compounds in water.
According to research data, water can be disinfected with two doses of chlorine: before and after the fracture. However, when chlorinating with a pre-breaking dose, water is disinfected due to the action of chloramines, and when chlorinating with a post-breaking dose, free chlorine is used.
During water disinfection, the added chlorine is spent both on interaction with microbial cells and viruses, and on the oxidation of organic and mineral compounds (urea, uric acid, creatinine, ammonia, humic substances, ferrous salts, ammonium salts, carbamates, etc.). ), which are contained in water in suspended and soluble
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renny condition. The amount of chlorine absorbed by water impurities (organic substances, inorganic reducing agents, suspended particles, humic substances and microorganisms) is called the chlorine absorption of water (segment I on the curve). Since natural waters have a different composition, the value of chlorine absorption is not the same for them. Thus chlorine absorption- this is the amount of active chlorine that is absorbed by suspended particles and is spent on the oxidation of bacteria, organic and inorganic compounds contained in 1 liter of water.
You can count on successful disinfection of water only if there is a certain excess of chlorine in relation to the amount that is absorbed by bacteria and various compounds contained in the water. An effective dose of active chlorine is equal to the total amount of absorbed and residual chlorine. The presence of residual chlorine (or, as it is also called, excess) in water is associated with the idea of the effectiveness of water disinfection.
When water is chlorinated with liquid chlorine, calcium and sodium hypochlorites, and bleach, a 30-minute contact provides a reliable disinfecting effect at a residual chlorine concentration of at least 0.3 mg/l. But during chlorination with preammonization, the contact should be for 1-2 hours, and the disinfection efficiency will be guaranteed if there is residual combined chlorine at a concentration of at least 0.8 mg/l.
Chlorine and chlorine-containing compounds significantly affect the organoleptic properties of drinking water (smell, taste), and in certain concentrations irritate the mucous membranes of the oral cavity and stomach. The limiting concentration of residual chlorine, at which drinking water does not acquire a chlorine smell and taste, is set for free chlorine at the level of 0.5 mg/l, and for bound chlorine - 1.2 mg/l. According to toxicological signs, the maximum concentration of active chlorine in drinking water is 2.5 mg/l.
Therefore, to disinfect water, it is necessary to add such an amount of a chlorine-containing preparation so that after treatment the water contains 0.3-0.5 mg/l of residual free or 0.8-1.2 mg/l of residual combined chlorine. Such an excess of active chlorine does not impair the taste of water, does not harm health, but guarantees its reliable disinfection.
Thus, for effective disinfection, a dose of active chlorine is added to water, equal to the sum of chlorine absorption and residual active chlorine. This dose is called the chlorine requirement of the water.
Water chloride requirement- this is the amount of active chlorine (in milligrams) necessary for the effective disinfection of 1 liter of water and ensuring the content of residual free chlorine in the range of 0.3-0.5 mg / l after 30 minutes of contact with water, or the amount of residual combined chlorine in the range 0.8-1.2 mg after 60 minutes of contact. Residual content
The maximum concentration of chlorine dioxide in drinking water is not higher than 0.5 mg / l, the limiting indicator of water action is organoleptic.
WATER SUPPLY FROM SURFACE WATER SUPPLY
active chlorine is controlled after clean water tanks before being supplied to the water supply network. Since the chlorine absorption of water depends on its composition and is not the same for water from different sources, in each case the chlorine demand is determined experimentally by test chlorination. Approximately, the chlorine demand for clarified and discolored coagulation, settling and filtration of river water ranges from 2-3 mg / l (sometimes up to 5 mg / l), groundwater interlayer water - within 0.7-1 mg / l.
Factors affecting the process of water chlorination, associated with: 1) biological characteristics of microorganisms; 2) bactericidal properties of chlorine-containing preparations; 3) state aquatic environment; 4) with the conditions under which disinfection is carried out.
It is known that spore cultures are many times more resistant than vegetative forms to the action of disinfectants. Enteroviruses are more resistant than intestinal bacteria. Saprophytic microorganisms are more resistant than pathogenic ones. At the same time, among pathogenic microorganisms, the most sensitive to chlorine are the causative agents of typhoid fever, dysentery, and cholera. The causative agent of paratyphoid B is more resistant to the action of chlorine. In addition, the higher the initial contamination of water with microorganisms, the lower the efficiency of disinfection under the same conditions.
The bactericidal activity of chlorine and its compounds is related to the value of its redox potential. The redox potential increases at the same concentrations in the series: chloramine - > bleach -> chlorine -» chlorine dioxide.
The effectiveness of chlorination depends on the properties and composition of the aquatic environment, namely: on the content of suspended solids and colloidal compounds, the concentration of dissolved organic compounds and inorganic reducing agents, the pH of the water, and its temperature.
Suspended substances and colloids prevent the impact of the disinfecting agent on microorganisms located in the thickness of the particle, absorb active chlorine due to adsorption and chemical binding. The effect on the efficiency of chlorination of organic compounds dissolved in water depends both on their composition and on the properties of chlorine-containing preparations. So, nitrogen-containing compounds of animal origin (proteins, amino acids, amines, urea) actively bind chlorine. Compounds that do not contain nitrogen (fats, carbohydrates) react less strongly with chlorine. Since the presence of suspended solids, humic and other organic compounds in water reduces the effect of chlorination, for reliable disinfection, turbid and high-colored waters are pre-clarified and discolored.
When the water temperature drops to 0-4 °C, the bactericidal effect of chlorine decreases. This dependence is especially noticeable in experiments with high initial contamination of water and in the case of chlorination with low doses of chlorine. In the practice of waterworks, if the pollution of the source water meets the requirements of State Standard 2761-84 "Sources of centralized domestic drinking water supply. Hygienic, technical
SECTION I. HYGIENE OF WATER AND WATER SUPPLY OF PUBLIC PLACES
requirements and quality control", lowering the temperature does not noticeably affect the effectiveness of disinfection.
The mechanism of the influence of the pH of water on its disinfection with chlorine is associated with the features of the dissociation of hypochlorous acid: in an acidic environment, the equilibrium shifts towards the molecular form, in an alkaline environment - ionic. Hypochlorous acid in its undissociated molecular form penetrates better through the membranes into the middle of the bacterial cell than hydrated hypochlorite ions. Therefore, in an acidic environment, the process of water disinfection is accelerated.
The bactericidal effect of chlorination is significantly affected by the dose of the reagent and the duration of contact: the bactericidal effect increases with an increase in the dose and an increase in the duration of action of active chlorine.
Water chlorination methods. There are several methods of chlorination. water treatment, taking into account the nature of residual chlorine, the choice of which is determined by the characteristics of the composition of the treated water. Among them: 1) chlorination with post-fracture doses; 2) conventional chlorination or chlorination according to chlorine demand; 3) superchlorination; 4) chlorination with preammonization. In the first three options, water is disinfected with free active chlorine. During chlorination with preammonization, the bactericidal effect is due to the action of chloramines, i.e., bound active chlorine. In addition, combined methods of chlorination are used.
Chlorination post-fracture doses provides that after 30 minutes of contact, free active chlorine will be present in the water. The dose of chlorine is selected in such a way that it is slightly higher than the dose at which a break is formed on the curve of residual chlorine, i.e., in the range IV (see Fig. 23). The dose selected in this way causes the appearance of residual free chlorine in the water in the smallest amount. This method is characterized by careful dose selection. It gives a stable and reliable bactericidal effect, prevents the appearance of odors in the water.
Conventional chlorination (chlorination according to chlorine demand) is the most common method of disinfecting drinking water in a centralized drinking water supply. Chlorination according to chlorine demand is carried out with such a post-breaking dose, which after 30 minutes of contact ensures the presence of residual free chlorine in the water in the range of 0.3-0.5 mg / l.
Since natural waters differ significantly in composition and therefore have different chlorine absorption, chlorine demand is determined experimentally by experimental chlorination of water to be disinfected. In addition to the correct choice of the dose of chlorine, a prerequisite for effective water disinfection is thorough mixing and exposure time, i.e., the contact time of chlorine with water (at least 30 minutes).
As a rule, at waterworks chlorination according to chlorine demand is carried out after clarification and discoloration of water. The chlorine demand of such water ranges from 1-5 mg/l. The optimal dose of chlorine is introduced into the water immediately after filtration before the RFW.
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Based on chlorine demand, it is possible to carry out double chlorination, in which the first time chlorine is fed into the mixer in front of the reaction chamber, and the second - after the filters. In this case, the experimentally determined optimal dose of chlorine is not changed. Chlorine, when introduced into the mixer in front of the reaction chamber, improves coagulation and water discoloration, which makes it possible to reduce the dose of coagulant. In addition, it inhibits the growth of microflora that contaminates the sand on the filters. The total cost of chlorine with double chlorination practically does not increase and remains almost the same as with single chlorination.
Double chlorination deserves widespread use. It should be consulted in cases where the pollution of river water is relatively high or subject to frequent fluctuations. Double chlorination increases the sanitary reliability of water disinfection.
Superchlorination(rechlorination) is a method of water disinfection, which uses high doses of active chlorine (5-20 mg/l). These doses are actually post-fracture. In addition, they significantly exceed the chlorine demand of natural water and determine the presence in it of high (over 0.5 mg/l) concentrations of residual free chlorine. Therefore, the superchlorination method does not require a preliminary determination of the chlorine demand of water and a careful selection of the dose of active chlorine, however, after disinfection, it is necessary to remove excess free chlorine.
Superchlorination is used in a special epidemiological situation, when it is impossible to determine the chlorine demand of water and ensure sufficient contact time of chlorine with water, as well as to prevent and combat odors in water. This method is convenient in military field conditions, in emergency situations.
Superchlorination effectively provides reliable disinfection even of turbid water. High doses of active chlorine kill pathogens that are resistant to disinfectants, such as Burnett's rickettsiae, amoeba cysts, mycobacterium tuberculosis and viruses. But even such doses of chlorine cannot reliably disinfect water from anthrax spores and helminth eggs.
During superchlorination, residual free chlorine in disinfected water significantly exceeds 0.5 mg / l, which makes the water unsuitable for drinking due to the deterioration of its organoleptic properties (strong smell of chlorine). Therefore, there is a need to free it from excess chlorine. Such a process is called dechlorination. If the excess of residual chlorine is small, it can be removed by aeration. In other cases, water is purified by filtering through a layer activated carbon or by chemical methods such as processing sodium hyposulfite (thiosulfate), sodium bisulfite, sulfur dioxide (sulfur dioxide), iron sulfate. In practice, sodium hyposulfite (thiosulfate) is mainly used - Na 2 S 2 0 3 5H 2 0. Its amount is calculated depending on the amount of excess chlorine, based on the following reaction:
Na 2 S 2 0 3 + C1 2 + H 2 0 = Na 2 S0 4 + 2HCI + si.
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According to the above binding reaction between active chlorine and sodium hyposulfite at a molar ratio of 1: 1, 0.0035 g of sodium hyposulfite crystalline hydrate is used per 0.001 g of chlorine, or 3.5MrNa 2 S 2 0 3 -5H 2 0 per 1 mg of chlorine.
Chlorination with preammonization. The method of chlorination in preammonization is used: 1) in order to prevent the appearance of unpleasant specific odors that occur after chlorination of water containing phenol, benzene and ethylbenzene; 2) to prevent the formation of carcinogenic substances (chloroform, etc.) during chlorination of drinking water containing humic acids, methane hydrocarbons; 3) to reduce the intensity of the smell and taste of chlorine, especially noticeable in the summer; 4) to save chlorine with high chlorine absorption of water and the absence of odors, tastes and high bacterial contamination. If natural water contains phenols (for example, due to contamination of water bodies with wastewater from industrial enterprises) even in small quantities 1 , then when disinfected with chlorine-containing compounds that are hydrolyzed to form hypochlorous acid, free active chlorine immediately interacts with phenol, forming chlorophenols, which even in small concentrations give the water a pharmaceutical flavor and smell. At the same time, the associated active chlorine - chloramine, having a lower redox potential, does not interact with phenol to form chlorophenols, and therefore the organoleptic properties of water do not deteriorate during disinfection. Similarly, free active chlorine is able to interact with hydrocarbons of the methane series with the formation of trihalomethanes (chloroform, dibromochloromethane, dichlorobromomethane), which are carcinogens. Their formation can be prevented by disinfecting water with bound active chlorine.
When chlorinating with preammonization, a solution of ammonia 2 or its salts is first added to the water that is being disinfected, and chlorine is added after 1-2 minutes. As a result, chloramines (monochloramines NH 2 C1 and dichloramines NHC1 2) are formed in the water, which have a bactericidal effect. Chemical reactions for the formation of chloramines are given on p. 170.
The ratio of the resulting substances depends on pH, temperature and the amount of reacting compounds. The efficiency of chlorination with preammonization depends on the ratio of NH 3 and C1 2 , and doses of these reagents are used in proportions of 1:2, 1:4, 1:6, 1:8. For the water of each source of water supply, it is necessary to select the most effective ratio. The rate of disinfection of water with chloramines is lower than the rate of disinfection with free chlorine, therefore, the duration of disinfection of water in the case of chlorination with preammonization should be at least 2 hours.
MPC of phenol in water is 0.001 mg/l, the limiting indicator is organoleptic (smell), hazard class 4.
For the introduction of ammonia into water, it is most convenient to use vacuum chlorinators.
WATER SUPPLY FROM SURFACE WATER SUPPLY
but less oxidative activity, since the redox potential of chloramines is much lower than that of chlorine.
In addition to pre-ammonization (the introduction of ammonia 1-2 minutes before the introduction of chlorine), sometimes post-ammonization is used, when ammonia is injected after chlorine directly into tanks with clean water. Due to this, chlorine is fixed longer than the increase in the duration of its action is achieved.
Combined methods of water chlorination. In addition to the considered methods of water chlorination, a number of combined methods have been proposed, when another chemical or physical disinfectant agent is used together with chlorine-containing compounds, which increases the disinfection effect. Chlorination can be combined with water treatment with silver salts (chlorine-silver method), potassium permanganate (chlorination with manganation), ozone or ultraviolet light, ultrasound, etc.
Chlorination with manganation(with the addition of a KMn0 4 solution) are used, if necessary, to enhance the oxidizing and bactericidal action of chlorine, since potassium permanganate is a stronger oxidizing agent. The method should be used in the presence of odors and flavors in the water, which are caused by organic substances, algae. In this case, potassium permanganate is introduced before chlorination. KMn0 4 should be added before settling tanks at doses of 1-5 mg/l or before filters at a dose of 0.08 mg/l. Recovering to water-insoluble Mn0 2 , it is completely retained in settling tanks and filters.
Silver chloride method used on ships of the river fleet (at KVU-2 and VHF-0.5 units). It provides enhanced disinfection of water and its conservation for a long time (up to 6 months) with the addition of silver ions in the amount of 0.05-0.1 mg/l.
In addition, the silver chloride method is used to disinfect water in swimming pools, where it is necessary to reduce the dose of chlorine as much as possible. This is possible because the bactericidal action is provided within the limits of the total effect of doses of chlorine and silver.
The bactericidal, virucidal and oxidative effects of chlorine can be enhanced by simultaneous exposure to ultrasound, ultraviolet radiation, direct electric current.
Water samples are taken after clean water tanks before being supplied to the water supply network. Monitoring the effectiveness of chlorination by residual active chlorine is carried out hourly, that is, 24 times a day. Chlorination is considered effective if the content of residual free chlorine is in the range of 0.3-0.5 mg/l after 30 minutes of contact, or the content of residual combined chlorine is 0.8-1.2 mg/l after 60 minutes of contact.
According to microbiological indicators of epidemic safety, water after RCV is examined twice a day, that is, once every 12 hours. In water after disinfection,
SECTION I. HYGIENE OF WATER AND WATER SUPPLY OF PUBLIC PLACES
zhivaniya determine the total microbial number and the BGKP index (coli-index). Water disinfection is considered effective if the coli index does not exceed 3, and the total microbial number is not more than 100.
Negative effects of water chlorination on public health. As a result of the reaction of chlorine with humic compounds, waste products of hydrobionts and some substances of industrial origin, dozens of new extremely dangerous haloform compounds are formed, including carcinogens, mutagens and highly toxic substances with MPCs at the level of hundredths and thousandths of a milligram per 1 liter. In table. 3 and 5 (see p. 66, 67, 101) some halogen-containing compounds are given, the features of their effect on the human body, and hygienic standards in drinking water. The indicators of this group are trihalomethanes: chloro- and bromoform, dibromochloromethane, bromodichloromethane. In disinfected drinking water and hot water supply, chloroform is most often detected in higher concentrations - a carcinogen of group 2B, according to the IARC classification.
Haloform compounds enter the body with water not only enterally. Some substances penetrate intact skin during contact with water, in particular when swimming in a pool. While taking a bath or shower, haloform compounds enter the air. A similar process occurs in the process of boiling water, laundry, cooking.
Taking into account the extreme danger to human health of haloform compounds, a set of measures has been developed to reduce their levels in water. It provides:
Protection of the water supply source from pollution by wastewater containing precursors of haloform compounds;
Decreased eutrification of surface water bodies;
Rejection of rechlorination (primary chlorination) or its replacement with ultraviolet irradiation or the addition of copper sulfate;
Optimization of coagulation to reduce the color of water, that is, the removal of humic substances (precursors of haloform compounds);
The use of disinfectants that have a lower ability to form haloform compounds, in particular chlorine dioxide, chloramines;
Use of chlorination with preammonization;
Water aeration or use of granular activated carbon as the most effective way removal of haloform compounds from water.
The cardinal solution of the problem is the replacement of chlorination with ozonation and disinfection of water with UV rays.
Ozonation of water and its advantages over chlorination. Ozonation is one of the promising methods of water treatment for its disinfection and improvement of organoleptic properties. Today, almost 1000 waterworks in Europe, mainly in France, Germany and Switzerland, use ozonation in their water treatment process. AT recent times ozonation began to be widely introduced in the United States and Japan. In Ukraine, ozonation is used at the Dnieper water pipeline
Rice. 25. Technological scheme of the ozonator plant:
1 - air inlet; 2 - air filter; 3 - warning valve; 4 - five supply fans; 5 - air plunger; 6 - two cooled dryers; 7 - four adsorption dryers; 8 - activated alumina; 9 - cooling fan heaters; 10 - fifty ozone generators (shown 2); 11 - dry air; 12 - cooling water inlet; 13 - outlet of cooling water; 14 - ozonated air; 15 - three tanks for ozone diffusion; 16 - water level
stations in Kyiv, in the CIS countries - at waterworks in Moscow (Russian Federation) and Minsk (Belarus).
Ozone(os)- a pale purple gas with a specific odor, a strong oxidizing agent. Its molecule is very unstable, easily decomposes (dissociates) into an atom and an oxygen molecule. Under industrial conditions, the ozone-air mixture is obtained in an ozonizer using a "slow" electric discharge at a voltage of 8000-10,000 V.
The schematic diagram of the ozonator plant is shown in fig. 25. The compressor takes in air, cleans dust, cools, dries on adsorbers with silica gel or active aluminum oxide (which are regenerated by blowing hot air). Then the air passes through the ozonator, where ozone is formed, which is fed through the distribution system into the water of the contact tank. The dose of ozone required for disinfection for most types of water is 0.5-6.0 mg/l. Most often, for underground water sources, the dose of ozone is taken in the range of 0.75-1.0 mg / l, for surface waters - 1-3 mg / l. Sometimes high doses are needed to decolorize and improve the organoleptic properties of water. The duration of contact of ozone with water should be at least 4 min 1 . indirect indicator
In accordance with GOST 2874-82, the duration of water disinfection with ozone was at least 12 minutes. The same duration is regulated by SanPiN 2.1.4.559-96 approved by the Ministry of Health of Russia "Drinking water. Hygienic requirements for water quality in centralized drinking water supply systems. Quality control". In accordance with SanPiN "Drinking water. Hygienic requirements for the quality of water for centralized domestic drinking water supply", approved by the Ministry of Health of Ukraine, the duration of ozone treatment should be at least 4 minutes.
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The effectiveness of ozonation is the presence of residual amounts of ozone at the level of 0.1-0.3 mg/l after the mixing chamber.
Ozone in water decomposes, forming atomic oxygen: 0 3 -> 0 2 + O". It is proved that the mechanism of ozone decomposition in water is complex. In this case, a number of intermediate reactions occur with the formation of free radicals (for example, HO *), which are also oxidizing agents The stronger oxidizing and bactericidal action of ozone compared to chlorine is explained by the fact that its oxidizing potential is greater than that of chlorine.
From a hygienic point of view, ozonation is one of the best methods of water disinfection. As a result of ozonation, a reliable disinfecting effect is achieved, organic impurities are destroyed, and the organoleptic properties of water not only do not deteriorate, as during chlorination or boiling, but also improve: color decreases, excess taste and smell disappear, the water acquires a blue tint. Excess ozone quickly decomposes to form oxygen.
Water ozonation has the following specific advantages over chlorination:
1) ozone is one of the strongest oxidizing agents, its redox potential is higher than that of chlorine and even chlorine dioxide;
2) when ozonizing, nothing extraneous is introduced into the water and there are no noticeable changes in the mineral composition of water and pH;
3) an excess of ozone turns into oxygen after a few minutes, and therefore does not affect the body and does not impair the organoleptic properties of water;
4) ozone, interacting with compounds contained in water, does not cause unpleasant tastes and odors;
5) ozone bleaches and deodorizes water containing organic substances of natural and industrial origin, giving it a smell, taste and color;
6) compared to chlorine, ozone more effectively disinfects water from spore forms and viruses;
7) the ozonation process is less affected by variable factors (pH, temperature, etc.), which facilitates the technological operation of water treatment facilities, and monitoring the efficiency is not more difficult than with water chlorination;
8) water ozonation ensures uninterrupted processing