One of the pressing problems of recent decades in the field of water treatment is the need to deodorize 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 of low molecular weight alcohols, carboxylic acids, hydroxy acids, ketones, aldehydes, and phenol-containing substances with a strong odor are released into the water.

Organic substances contribute to the development of microorganisms that release hydrogen sulfide, ammonia, organic sulfides, and foul-smelling mercaptans into the external environment. The intensive development and death of algae contributes to the appearance of polysaccharides in the water; oxalic, tartaric and citric acids; substances such as phytoncides. In the decomposition products of algae, the phenol content is 20-30 times higher than the maximum permissible concentration (0.001 mg/l).

Despite the legislative measures taken, industrial wastewater is still discharged into surface water bodies, which leads to their contamination with mineral and organic compounds. Among them are salts of heavy metals, oil and petroleum products, synthetic aliphatic alcohols, polyphenols, acids, pesticides, surfactants, etc.

Pesticides belonging to different classes of organic compounds and found in water in different states are especially dangerous. They have a negative effect on the organoleptic properties of water. The toxicity of pesticides present in water increases when it is treated with chlorine or potassium permanganate.

Oil and petroleum products are poorly soluble in water and very resistant to biochemical oxidation. Large concentrations of oil give water a strong odor, increase its color and oxidability, and reduce the content of dissolved oxygen. With a small oil content in water, its organoleptic characteristics noticeably deteriorate.

When surfactants get into water with household and industrial wastewater, they sharply deteriorate its quality, creating persistent odors (soap, kerosene, rosin) and bitter tastes. As a rule, surfactants enhance the stability of odors of other impurities, catalyze the toxicity of carcinogenic substances, pesticides, aniline, etc. in water.

Humic acids and fulvic acids, lignins and many other organic compounds of natural origin present in the natural waters of the North and central Russia serve as one of the sources of the formation of phenols, which worsen their organoleptic properties. When water containing phenols is chlorinated, dioxins are formed - extremely toxic substances (lethal doses: strychnine 1.5-10-6; botulin - 3.3-10-17, nerve gas - 1.6 10-5 mol/kg). A dose of dioxins - 3.1-10~9 - is lethal, and a dose of 6",5-10~15 mol/kg for people under 70 years of age - the risk of cancer. A hundred times smaller dose affects the immune system (“chemical AIDS") and reproductive functions of the body. The most toxic substance is 2,3,7,8-tetrachlorodibenzodioxin (TCDD). The main toxic substance in emissions from pulp and paper mills are polychlorinated dibenzofurans (PCDF) and the strongest carcinogen - combustion products of fuel oil, gasoline, coal, etc. is benzo(a)pyrene (synergy manifests itself in the dioxin-benzo(a)pyrene pair).

The production of 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 reach people with drinking water, since modern water treatment technologies do not have barrier functions against the latter. It has been established that polychlorinated dibenzo-i-dioxin (PCDD) and polychlorinated dibenzfuran (PCDF) are formed directly during chlorination of water, i.e. the formation of dixins during preliminary chlorination of water is inevitable.

The iron present in water is a catalyst for the additional chlorination of phenols, converting low-toxic dioxins into highly toxic ones during water chlorination. Organic substances present in water pass almost unhindered through the loading of rapid filters, including their toxic dioxin-containing part.

Sometimes the organoleptic properties of water deteriorate due to an overdose of reagents or as a result of improper operation of water treatment facilities. Thus, when water is discolored by coagulation without subsequent stabilization, the corrosive activity of water increases and, as a result, its organoleptic characteristics worsen. When water is chlorinated, a deterioration in its organoleptic characteristics is observed both when the process regime is violated and as a result of the formation of organochlorine compounds that cause unpleasant tastes and odors.

It has been established that traditional methods of water purification have a weak barrier effect, mainly in relation to those chemical contaminants that are found in the water. water in the form of suspensions and colloids or become insoluble form during purification and pre-treatment with chlorine (for example, emulsified petroleum fractions, poorly soluble pesticides, some metals). In relation to such contaminants, the barrier role of treatment facilities can be increased by appropriate selection of reagents for a high degree of water clarification.

Water deodorization in some cases is achieved by coagulating impurities and flocculating them, followed by filtration, but often the use of special technologies is required to eliminate unwanted odors and tastes. Their choice is dictated by the nature of the impurities and the state in which they are located (suspensions, colloids, true solutions, gases).

There are no universal methods of water deodorization today; however, the use of some of them in combination provides the required degree of purification. If substances that cause unpleasant tastes and odors are in a suspended and colloidal state, then their coagulation gives good results. Flavors and odors caused by inorganic substances in a dissolved state are removed by degassing, deferrization, and desalting. etc. Odors and tastes caused by organic substances are very persistent. They are usually removed< путем оксидации и сорбции.

Substances with strong reducing properties (humic acids, iron (II) salts, tannins, hydrogen sulfide, nitrites, poly- and monohydric phenols, etc.) are easily extracted from water by oxidation. More stable compounds (carboxylic acids, aliphatic alcohols, petroleum hydrocarbons and petroleum products, etc.) are poorly oxidized when treated with chlorine and its derivatives, and sometimes even ozone. Sometimes strong oxidizing agents, acting on these substances, significantly enhance the original tastes and odors (for example, organophosphate pesticides). At the same time, the effect of oxidizing agents on easily oxidized compounds leads to their complete destruction or to the formation of substances that do not affect the organoleptic characteristics of water. Thus, the action of oxidizing agents is effective only against a limited number of contaminants.

The disadvantage of the oxidative method is also the need to dose the oxidant 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 use of filters with granular active carbon used as filter media. Filters loaded with granular active carbon, regardless of fluctuations in the level of water pollution, are a permanent barrier to sorbed substances. However, a serious difficulty in using this method of water purification is the relatively low absorption capacity of coal, which necessitates its frequent replacement or regeneration.

In addition, it has been established that hydrophobic substances are well sorbed from water by activated 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 sorbed less effectively by active carbon.

In conditions of increased anthropogenic pollution of water bodies, it is necessary to combine methods of oxidation, sorption and aeration to deodorize water and remove toxic micropollutants.

Water deodorization by aeration

To remove volatile organic compounds of biological origin that cause odors and tastes from natural waters, aeration is widely used.

In practice, aeration is carried out in special installations - bubbler, spray and cascade aerators.

In bubbling-type aerators, the air supplied by blowers is distributed in the water by perforated pipes suspended in the tank (Fig. 15.1) and spray devices located at its bottom. The advantage of the first method is the ease of dismantling the installation.

Air distribution by atomizing devices is often used in spiral water aerators, 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. Research shows that since the equilibrium between the concentrations of odor-bearing substances in the liquid and gaseous phases is achieved instantly, the height of the water layer during bubbling does not play a 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 duct; 2 - water input into the bubbling chamber 5; 3 - perforated plates; 4 - air distributor; 7.1 - drainage of aerated water and supply of source water; 8 - spillway; 9 - stabilized partition; 10 - layer of foam; 11 - fan; 12 - perforated bottom; b - the surface bubbling chamber is chosen arbitrarily. The duration of air blowing, as a rule, does not exceed 15 minutes. Air consumption is 0.37-0.75 m3/min per 1 m3 of water.

Open bubbling units can operate at temperatures below 0°C. The degree of aeration is easily adjusted by changing the amount of air supplied. The cost of installations and their operation is low.

In spray aerators, water is sprayed into small drops by nozzles, thereby 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 speed of the jet and its trajectory, is usually 2 s "(For a vertical jet that is ejected under a pressure of 6 m).

In cascade-type aerators, the treated water falls in jets through several sequentially located weirs. The contact duration 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 aerators, water is simultaneously sprayed and flows in a thin stream from one stage to another. To increase the area of contact between water and air, ceramic balls or coke are used.

A common disadvantage of aerators built on the principle of contact of a film of water with air is their uneconomical nature due to their large area, the impossibility of using them in winter, the need for powerful ventilation when installing them indoors, and, finally, their tendency to fouling.

Aeration of water in the foam layer is carried out in an inca 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 a distribution pipe. A special baffle is used to stabilize the foam layer. The water is aerated with air supplied by a fan. The water, having passed through the ink aerator, is discharged through the spillway.

The formation of a huge boundary surface between the liquid and gaseous phases ensures a high intensity of the deodorization process. The normal ratio of air and water in ink aerators ranges from 30: 1 - 300: 1. Despite the high air consumption, intensive aeration is economically justified (due to the slight loss of pressure, the air is supplied by a fan).

However, aeration cannot eliminate persistent odors and tastes caused by the presence of impurities that have insignificant volatility.

List of used work

Cherkinsky S.N. Sanitary conditions for draining wastewater into reservoirs, M.: Stroyizdat, Abramov N.N. Water treatment, M.: Stroyizdat 1974

Frog B.N. Levchenko A.P. Water treatment, M.: Stroyizdat 1996

To eliminate water odors resulting from the activity of certain algae and microorganisms, water deodorization is used. This includes types of water treatment such as chlorination, ozonation, ammoniation, aeration and treatment with potassium permangamate. Odors and tastes can be eliminated by filtering water through a layer of activated carbon in pressure filters. For this purpose, birch, peat and stone coals are used.

Water often develops an unpleasant odor and taste due to the presence of phenols that enter the source from industrial enterprises. When such water is chlorinated, the slightest content of phenols causes the appearance of chlorophenol odors. Therefore, they try not to chlorinate water containing phenol. An effective way to combat these odors is ammoniation of water, that is, the introduction of a certain dose of ammonia into it.

Ammoniation

Ammoniation is also used in the absence of phenols to eliminate chlorine odors resulting from water chlorination. The bactericidal effect of chlorine decreases, but its duration increases. The contact of water with chlorine during ammoniation must be at least 2 hours. Ammonia is introduced into the water using special devices - ammoniators.

Substances that cause odors and tastes in water are volatile. Therefore, aeration, which is carried out before introducing chlorine or other oxidizing agents into the water, helps reduce odors and tastes. The essence of aeration is that the water being treated is artificially saturated with air in order to oxidize the organic substances it contains. The air released from the water carries with it the smells and tastes there.

A good effect of water deodorization is obtained by using ozone and potassium permanganate. Sometimes potassium permanganate is used with activated carbon.

Water may have a certain, not always pleasant, odor, which is acquired due to the various organic substances it contains, which are products of the vital activity or decay of microorganisms and algae. Water purification from odor (water deodorization) is carried out using various modifications of the method of water chlorination, sorption filtration, carbonization, aeration, ozonation, water treatment with potassium permanganate, hydrogen peroxide and a combination of these methods.

Water treatment with active carbon

If we compare sorption and oxidative deodorization methods, the first is more reliable due to the fact that it is based on the extraction of organic substances from water, and not on their transformation. The most effective sorbents are activated carbons, which absorb phenols well, most petroleum products, polycyclic aromatic hydrocarbons (including carcinogenic ones), chlorine and organophosphorus pesticides, as well as other organic contaminants. But sorption on active carbons is not a universal means of purifying water from organic compounds, since some substances (for example, organic amines) are not retained by them or are retained, but poorly (for example, synthetic surfactants).

Active carbons are used in the form of powder - for carbonizing water and in the form of granules - as loading for filters. It is worth noting a number of disadvantages that limit the implementation of carbonization of water - these are the difficulties of soaking and dosing coal, the need for a container to ensure contact of coal with the treated water, etc. Therefore, this method is used mainly when occasional, short-term deodorization of small volumes of water is required.

The use of granular active carbons as a filter media is a more reliable option. Regardless of fluctuations in the level of water pollution, filters loaded with granular active carbon are an excellent barrier to sorbed substances until the carbon capacity is exhausted.

Carbon filters are located after clarification filters. It is also possible to use combined clarification and sorption filters.

The disadvantage of carbon filters is the need to regenerate active carbon. Restoration of coal loading can be carried out by chemical, thermal and biological methods. When using the chemical regeneration method, coal is first treated with live steam and then with alkali. Despite all the complexity and labor intensity, the method is not effective enough, since the sorption capacity of the material is not completely restored. The thermal method involves burning adsorbed organic compounds at a temperature of 800...900ºC in special ovens. This rather complex regeneration method is accompanied by losses of coal during firing. The biological regeneration method relies on the ability of bacteria to mineralize adsorbed organocarbon compounds, but the rate of this process is very low.

As a rule, in industrial water treatment systems, and even more so in household systems, the use of any of the above types of regeneration is impossible, and if the quality of purification decreases, the filter media is simply replaced.

Oxidation-sorption method of water treatment

Due to the above, the task of increasing the inter-regeneration period of granular activated carbon is urgent, which is successfully solved by treating water with an oxidizing agent before filtering it through the carbon. Such water treatment does not simply result in the summation of two processes, but contributes to the manifestation of the effect of oxidation-sorption interaction. At the same time, coal “works” as an oxidation catalyst, significantly increasing the depth and speed of this process, and, at the same time, many oxidation products are better sorbed on coal. Such simultaneous use of two methods significantly expands the range of organic contaminants removed from water. Practice has also proven the economic advantage of the combined use of oxidizing agents and active carbon.

Initial data, such as the quality of the water being treated, the composition and types of treatment facilities, determine the variety of technical solutions for using the oxidation-sorption method of water purification. For example, filters loaded with granular active carbon, which purify water only from organic contaminants, are located in the technological scheme after. Filters that use granular carbon and, in addition to the specified function, also perform the function of water clarification, are placed after the first stage structures. The loading of such filters has two options: 1) consists entirely of activated carbon; 2) consists of coal and mechanically cleaned material (double-layer loading).

The scheme of contact water clarification also suggests the possibility of placing separate carbon filters after the contact clarifiers or installing contact clarifiers with sand-coal loading. It is worth noting that in the first case, when water filtration occurs sequentially through two separate cascades of filters, there is a significant increase in capital costs for the construction of treatment facilities. However, in this case, the carbon load is used for its intended purpose (to remove chemical contaminants) and is under the most favorable conditions, since clarified water flows to the carbon filter. As a result, the filter requires less frequent washing, which reduces coal loss, grinding and abrasion; Reducing the clogging of coal pores with suspension promotes better sorption of chemical contaminants and increases the service life of coal as a sorbent.

Sanitary-hygienic and technical-economic indicators of water purification and the purpose of the coal loading determine its location in the technological scheme. In all cases, the introduction of an oxidizing agent into the treated water must be carried out before it enters the coal loading.

Options for introducing an oxidizing agent into water:

1) at the beginning of the technological scheme;

3) directly in front of the carbon filter;

4) double introduction of oxidizing agents of different types. Moreover, the place where the oxidizer is introduced is determined by the general tasks assigned to the oxidizer, the rate of its consumption and other factors.

For underground sources, as a rule, the first input option is used, and for surface sources, the second. When using the oxidation-sorption method of water deodorization, it is important to correctly select the type of oxidizing agent used. Currently existing oxidizers, common in the practice of water treatment with reagents, differ in their effectiveness (from technical, economic and sanitary and hygienic points of view) in relation to chemical water contaminants.

It is advisable to use chlorine as an oxidizing agent if there are relatively easily oxidized contaminants in the water (phenols, some substances of natural origin, etc.). Moreover, the conditions for the combined use of chlorine and active carbon require preliminary ammoniation of the water - if necessary, this is carried out during final chlorination.

If water contains mostly difficult-to-oxidize contaminants (soluble fractions of oil and its products, synthetic surfactants, organic pesticides, etc.), it is advisable to use ozone as the most powerful oxidizing agent. In some cases, the use of several oxidizing agents (ozone and chlorine, chlorine and potassium permanganate) is also effective. Through laboratory tests, the oxidant is selected, its dose and place of introduction in the technological scheme of water purification - taking into account maintaining a minimum load on coal as a sorbent. This also takes into account the function of coal as a catalyst for the oxidation process.

A very important issue is the operating time of activated carbon, which is almost impossible to determine by calculation. It depends on the correct selection of the type and dose of oxidizer, as well as a number of other conditions. As practice shows, the combined use of an oxidizer and activated carbon helps maintain the sorption activity of coal for a fairly long period (in practice, it can reach 2 years). In this state of affairs, coal regeneration is not always economically justified, especially considering that in order to compensate for its losses due to grinding, abrasion and entrainment during washing, it is necessary to annually add fresh coal (approximately 10% per year to the volume of coal). At the same time, a sharp decrease in the sorption capacity of coal in relation to organic substances is possible due to its fouling with inorganic contaminants (mainly hydroxides of iron, aluminum, etc.). Therefore, the task is to ensure a high degree of preliminary clarification of water (namely, its deferrization and demanganization) before it enters the coal loading layers. First of all, this relates to filter structures with the combined functions of clarification and purification from chemical contaminants.

U Dear Sirs, if the task of implementing a water deodorization system is urgent for you, please make a request to the company’s specialists Waterman. We will offer you the best technological solution.

Water deodorization

Tastes and odors 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 undesirable tastes and odors from water, aeration, oxidation with chlorine, ozone, potassium permanganate, chlorine and other oxidizing agents are used; sorption by activated carbon.

Odors and tastes caused by the presence of microorganisms in water can also be eliminated by filtering the water through a layer of activated granular carbon in pressure filters or by introducing powdered carbon into the water before filtering on open sand filters. At large doses (more than 5 mg/l), coal should be introduced at the pumping station of the first rise 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 a pulp with a concentration of 5...10%. For coal doses up to 1 mg/l, dry dosing of coal powder is allowed. It is especially advisable to use coal powder when odors and tastes appear periodically. The dose of activated carbon is determined by trial carbonization, the technique of which is similar to trial chlorination. To restore the sorption capacity of granular activated carbon, it is necessary to periodically regenerate it, washing it with a hot solution of alkali and calcium hypochlorite or calcining it in ovens.

To remove odors and tastes, birch BAU, peat TAU, stone stone KAD, and AG-3 coals are most often used. Powdered activated carbon must be stored in a fireproof, dry room in a hermetically sealed container, as it is explosive and capable of spontaneous combustion.

Water acquires an unpleasant odor and taste in the presence of phenols, which enter the source with wastewater from industrial enterprises. When water is chlorinated, the slightest content of phenols causes the appearance of intense chlorophenol odors, an effective means of combating which is ammoniation of water - the introduction of ammonia or a solution of its salts into the water. Ammonia is introduced after chlorination of water: its dose is 10...25% of the dose of chlorine introduced to disinfect water. Ammoniation can also be used in the absence of phenols to eliminate chlorine odors. The bacterial effect of chlorine decreases, but its duration increases. Contact of water with chlorine during ammoniation must be at least 2 hours. Ammonia is introduced into water using ammoniators - 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 introducing chlorine or other oxidizing agents into the water.

A good effect of water deodorization is achieved by using ozone and potassium permanganate, the latter is sometimes used in combination with activated carbon.

Water softening

Softening water is the almost complete elimination or reduction of the amount of hardness salts contained in it. In accordance with current standards and regulations, water intended for household and drinking purposes must be softened if its hardness exceeds 7 mg eq/l, and in special cases - 14.7 mg eq/l. Water softening is required for some industries (for example, textile, paper, etc.), where water hardness is required no more than 0.7...1.07 mg eq/l, laundries, and mainly when treating 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 (cationite way).

Humic acids and fulvic acids, lignins and many other organic compounds of natural origin present in the natural waters of the North and central Russia serve as one of the sources of the formation of phenols, which worsen their organoleptic properties. When water containing phenols is chlorinated, dioxins are formed - extremely toxic substances (lethal doses: strychnine 1.5-10~ 6; botulin - 3.3-10-17, nerve gas - 1.6 10~ 5 mol/kg). A dose of dioxins - 3.1-10~ 9 - is lethal, and a dose of 6",5-10~ 15 mol/kg for people under 70 years of age - the risk of cancer. A hundred times smaller dose affects the immune system (“chemical AIDS") and reproductive functions of the body. The most toxic substance is 2,3,7,8-tetrachlorodibenzodioxin (TCDD). The main toxic substance in emissions from pulp and paper mills are polychlorinated dibenzofurans (PCDF) and the strongest carcinogen - combustion products of fuel oil, gasoline, coal, etc. is benzo(a)pyrene (synergy manifests itself in the dioxin-benzo(a)pyrene pair).

Substances with strong reducing properties (humic acids, iron (II) salts, tannins from solid waste, hydrogen sulfide, nitrites, poly- and monohydric phenols, etc.) are easily extracted from water by oxidation. More stable compounds (carboxylic acids, aliphatic alcohols, petroleum hydrocarbons and petroleum products, etc.) are poorly oxidized when treated with chlorine and its derivatives, and sometimes even ozone. Sometimes strong oxidizing agents, acting on these substances, significantly enhance the original tastes and odors (for example, organophosphate pesticides). At the same time, the effect of oxidizing agents on easily oxidized compounds leads to their complete destruction or to the formation of substances that do not affect the organoleptic characteristics of water. Thus, the action of oxidizing agents is effective only against a limited number of contaminants.