Sorption purification of drinking water. Sorption (wastewater treatment)

Selection of sorbents. The range of sorbents for preliminary water purification produced by industry is very diverse. To purify water from organic substances, activated carbons, gel and macroporous anion exchangers, etc. are used. Activated carbons have slow sorption kinetics from solutions, which requires large filtration areas, poor regenerability using reagents (the residual capacity after the first regeneration is significantly less than half the original), mechanical fragility, high ash content.

Anion exchangers, especially macroporous ones, are free from many of the listed disadvantages. The initial selection of the best of them is carried out under static conditions when the sorbents come into contact with model solutions or with given water for an hour.

After selecting the best samples (in this case they turned out to be domestic sorbents of the polymerization type AB-171 and condensation type IA-1), kinetic studies are carried out. Their goal is to determine the nature of the stage limiting the process, finding diffusion coefficients and the time to establish equilibrium. The stage limiting the process is determined by the following criterion: if stirring the solution accelerates sorption, this indicates the predominant influence of external diffusion; direct evidence of the intradiffusion mechanism is provided by the “interruption” experiment. If after a break the sorption process is resumed and the sorption activity of the solid phase increases, we can confidently speak about the intradiffusion nature of the process.

Sorption of humic substances. Intra-diffusion kinetics, according to data, limits the sorption of humic substances, i.e., sorption preliminary purification of water.

Analysis of this equation shows that the loss of protective effect, expressed in linear or volumetric units of the sorbent, the greater (and the operating period of the column the shorter) the greater the flow rate, the radius of the sorbent grains and the given purification depth.

From kinetic experiments, diffusion coefficients and the time to establish equilibrium in ion exchanger-solution systems are determined and sorption isotherms are constructed. Sorption isotherms of humic and fulvic acids by anion exchangers IA-1 and AB-171 are described by the Langmuir equation.

The works compare the results of the experimental determination of the sorption capacity before the breakthrough of humic substances with the sorption capacity calculated using the equations; discrepancies do not exceed 10-15%. By changing the flow rate, the depth of purification, the radius of the sorbent grain and the sorbent itself, it is possible to determine the loss of time of the protective action of the column for each option. At the same time, it should be remembered that this places a very large responsibility on the accuracy of determining the diffusion and equilibrium coefficients in sorbent-solution systems, which provide the initial data for calculating the dynamics of sorption.

So, the best sorbent for preliminary water purification turned out to be macroporous anion exchanger IA-1, operating in chlorine form, at a pH of the purified solution equal to 3.0-3.5. As for grain size, its choice is limited by the nature of the drainage system and the desired flow rate of water.

Natural waters contain humic and fulvic acids. The former are sorbed worse, and their “breakthrough” practically limits the cleaning process. Therefore, the value should be calculated based on the content of humic acids in the purified water. If they are absent after coagulation purification, the working period of the sorption column is calculated based on the content of fulvic acids in the water.

The fact that the sorption of weakly dissociating humic and fulvic acids is better in an acidic environment and on an anion exchanger in salt form indicates a non-ion exchange mechanism for the absorption of these substances and suggests an economically and technologically advantageous scheme for preliminary water purification. A sorption column with an IA-1 ion exchanger should be installed after the H-form cation exchanger and the following decarbonizer. This eliminates the need to acidify the water, since it acidifies spontaneously during cationization. Thus, the sorption column becomes an integral part of the desalting plant. When combining coagulation purification with sorption, water is 80-85% freed from organic impurities. Further, deeper purification of water from organic impurities is carried out using ion exchangers in the desalting part of the installation.

Extraction of other organic substances. Surface and artesian waters contain organic substances belonging to various classes of compounds. It has been established that substances such as sugars, protein-like substances, amino acids pass through the system of ion exchange columns and enter deeply demineralized water. Moreover, their quantity depends on the composition of the source water and significantly exceeds the content of mineral impurities. Maximum extraction of these substances from water during its preliminary purification by the sorption method is necessary.

The work compares the ability of some activated carbons and macroporous anion exchangers to sorb various analytically determined organic compounds dissolved in natural waters. To do this, 100 volumes of river water were passed through a sorbent layer 60 cm high at a speed of 7 m/h after their H-cationization, which created the most favorable conditions for sorption.

Fulvic acids are extracted better by resins than by coals, and the capacities of ion exchangers for fulvic acids are almost the same. But even in this case, the use of IA-1 ion exchanger is more expedient, since it is regenerated more easily and with less reagent consumption.

The second very significant group of compounds that, when entering deeply demineralized water, can affect its electrical resistivity are carboxylic acids. SKT-VTU-2 coal and AV-171 anion exchanger are most suitable for their sorption. Of these two sorbents, preference should, of course, be given to the ion exchanger, since its capacity can be restored with chemical reagents. To remove simple and complex amino acids, AB-171 anion exchanger should also be used.

Simple and complex sugars that do not affect the electrical resistivity of demineralized water are largely sorbed only by BAU carbon. Therefore, when choosing sorbents for water purification, one should be guided not only by the size of their capacity and the possibility of its recovery, but also by the need to remove a particular compound from the water.

For an approximate assessment of the distribution of organic substances in the layers of these sorbents, the corresponding output curves were recorded. The loading of ion exchangers in chlorine form was 1 liter at a layer height of 60 cm; the solution flow rate is 10 m/h.

The filtrate for analysis was continuously collected in fractions of 10 L each. The duration of the working period of the column is chosen equal to 200 reduced volumes; The pH of the passed water was created by preliminary cationization of the source water. Using various sorbents and their combinations, it is possible to remove a significant portion of organic substances dissolved in water. However, it is hardly possible to obtain water completely freed from organic substances using the listed set of means.

The content and ratio of organic non-electrolytes such as sugars, proteins, esters, etc., vary not only from one geographical zone to another, but also within one region. Therefore, it cannot be expected that with the same technological schemes and demineralization modes, demineralized waters will be the same in terms of the quantitative and qualitative content of organic substances. In this regard, one should be wary of attempts to standardize the dry residue of high-resistivity water without taking into account the composition of the source.

Removal of iron (deferrization). Ferrous waters are waters containing more than 1 mg/l of iron. The cation exchanger sorbs divalent iron ions in approximately the same way as calcium ions, and ferric ions even more effectively. One might expect that during ion-exchange desalting, water would simultaneously be “deironized.” This process is hampered, however, by certain physical and chemical properties of the iron compounds present in natural waters.

In open reservoirs, well aerated, a significant part of the iron is in the form of Fe compounds of varying degrees of hydrolyzation.

During coagulation and subsequent sorption purification, water is freed not only from colored (mainly humus compounds), but also from colloidal and complex forms of iron. Thus, purification from organic substances is at the same time an act of deferrization of water.

Enterprises that consume especially pure demineralized water are recommended to obtain it wherever possible (wherever possible) from groundwater, which is usually free of organic contaminants. It is known that more than 25% of all water supply systems receive underground water with an iron content of 1 to 5 mg/l.

In groundwater deprived of oxygen, iron is mostly found in the form of a partially hydrolyzed bicarbonate solution. If this substance were supplied to the cation exchange resin in an unoxidized and unhydrolyzed form or were not oxidized in the cation exchange resin filter itself, one would expect an almost complete exchange of iron ions for hydrogen ions. However, along with the ion exchange reaction, the rate of which is determined by diffusion processes, there are reactions of hydrolysis of iron salts, oxidation and transition to weakly dissociating and practically insoluble compounds capable of forming colloids. The combination of such processes leads to the fact that water containing, for example, in an equilibrium state 0.16 mg/l of iron in ionic form, can be characterized by a total iron content of 2 mg/l. The cation exchanger will absorb only the ionic form of iron and will dissolve with absorption some of the least persistent hydrolysis products.

The release of hydrogen ions during the operation of the cation exchanger could restrain the reaction and even shift it to the left, especially since the number of hydrogen ions in H-cationized water is determined by the total salt content, which is almost two orders of magnitude greater than the number of iron ions in water.

As the upper layers of the cation exchanger are activated, two circumstances will contribute to a shift of the reaction to the right: the presence of Fe(II) ions in the layer, catalytically accelerating their conversion into Fe(III) ions, and the partial absorption of hydrogen ions by the cation exchanger, exchanging for sodium and calcium ions with which it is filled. spent resin layer. Fe(III) hydroxide and other hydrolysis products formed under these conditions will no longer participate in ion exchange and will transit into H-cationized water, just like that part of such iron compounds that was present in the original water.

A quantitative description of these processes is still difficult. At the same time, the presence of iron in non-ionic form in H-cationized and desalted waters is satisfactorily explained by the proposed concept and indicates the need to remove iron from ferruginous groundwater before feeding it to a desalting ion-exchange installation. The above equation suggests the main ways to remove iron from water. These are aeration (oxygen saturation) and alkalization (binding of hydrogen ions). In bicarbonate waters, the latter occurs spontaneously with the release of a stoichiometric amount of carbon dioxide. Aeration can be accomplished by blowing air, spraying water into the air, or applying ozone; Active chlorine and potassium permanganate can be used as other oxidizing agents. Under the influence of oxidizing agents, ion exchangers “age”, so it is advisable to carry out iron removal using a reagent-free method.

A monograph is devoted to the removal of iron from groundwater, which summarizes both theoretical and technological aspects of the problem. Considering the specifics of obtaining relatively small volumes of highly pure demineralized water for industrial purposes and the specifics of the industries themselves that consume such water, we should focus on the method of simplified aeration followed by filtration.

Above the open filter, water sprays through holes in the supply pipes. The thickness of the sand layer in the filter is usually at least 1.2 m, and the grain size is from 0.8 to 1.6 mm. Filters with a two-layer loading with a total thickness of 1.2-1.5 m and a thickness of the top layer of 0.5 m are distinguished by greater dirt holding capacity. For the bottom layer, quartz sand with a grain size of 0.8-1.2 mm is used, and for the top - anthracite chips of 0.9-2.4 mm. The filtration speed in open filters reaches 10 m/h. As a rule, with a decrease in the speed of water transmission, the dirt holding capacity of filters increases, and therefore open filters should be designed for a speed not exceeding 5-7 m/h.

Depending on the adopted filtration speed, the initial iron content in the water and other factors, the duration of the filters naturally varies. At a filtration speed of 5-7 m/h and an initial iron content in water of 3-4 mg/l, the operating cycle of the installation is 60-100 hours. After this, the filters are washed with a countercurrent intensity of 15-18 l/(s-m2) for 10-15 min.

The volume of wash water for filters in the water deferrization section reaches 4% of the volume of purified water. When the operation of a deferrization installation of this type is well adjusted, the iron content in the filtrate is 0.05-0.1 mg/l.

Unlike distillate, which contains up to 5 µg/l of iron, technical condensate can be enriched with corrosion products. When obtaining especially pure demineralized water from such condensate, preliminary deferrization is necessary. For this purpose, sulfonic carbon filters are used, operating with an efficiency of 25-50%, or more efficient magnetite filters, alluvial cellulose filters, alluvial ionite filters (called powdex abroad). Anion exchanger filters have been proposed, where iron removal is based on the coagulating effect of anion exchanger in the OH form. Alluvial ion exchange filters operate with an efficiency approaching 100% due to the almost instantaneous kinetics of the process. Here, along with the sorption of ions from the liquid phase, mechanical retention of particles of the solid phase, coagulation and formation of complexes with an anion exchanger occur if a mixture of cations and anion exchangers is used for the alluvial layer.

Experiments have shown the suitability of alluvial ion exchange filters for extracting humic substances that complex iron and other metals from water.

The severity of the problem of iron removal as a stage of preliminary water purification was especially revealed in connection with the need to use ultrapure water for microelectronics production. For final purification of water before supplying it for washing instrument parts, a microfilter with pores of 0.2 microns is used, which retains microbial bodies. If iron is not sufficiently removed from demineralized water in the previous stages, then the microfilters quickly become clogged.

Water softening. When partially desalting water using the electrodialysis method or using reverse osmosis, in some cases it is necessary to first soften the water, i.e., free it from calcium and magnesium cations, which, with the appropriate anionic composition of the water, can form sediments on the ion exchange membranes or on the membranes (fibers) used in reverse osmosis units.

It is advisable to carry out softening as a preliminary purification step when desalting relatively small masses of water using the ion exchange method. Regeneration of the cation exchanger, i.e., converting it into sodium form, is carried out by passing a 6-10% sodium chloride solution through the spent sorbent layer and subsequent washing with water.

For reasons that will be discussed below, the consumption of table salt for regeneration exceeds the stoichiometric one by 2.5-5 times. When working with water with a high salt content, it is advisable to use a strong acid cation exchanger of the KU-2 type for softening. At the same time, in comparison with such cation exchangers as sulfonated coal or KU-1, the salt consumption for regeneration is quite significantly reduced.

In general, sorption is understood as the processes of surface (adsorption) and volumetric (absorption) absorption of a substance at the interface between two phases: solid and liquid, solid and gaseous, liquid and gaseous. Sorption processes play an important role in modern technology of semiconductors and dielectrics, since they allow the separation of substances with very similar physicochemical properties (rare earth elements, metals such as zirconium and hafnium, etc.).

The adsorption system consists of adsorbent- the substance on the surface of which absorption occurs, and adsorbate - a substance whose molecules are absorbed. Based on the nature of the processes, physical and chemical adsorption are distinguished. At physical adsorption adsorbate molecules do not enter into chemical interaction with the adsorbent and, thus, retain their individuality on the surface of the absorber; adsorption in this case is due to the action of van der Waals forces. At chemical adsorption, or chemisorption, adsorbed molecules enter into a chemical reaction with the adsorbent to form chemical compounds on the surface. The reverse process - the process of removing molecules from the surface of the adsorbent is called desorption. Physical adsorption, unlike chemisorption, is reversible. The desorption process can also be used as a purification method. Adsorption is a selective process, i.e. On the surface of the adsorbent, only those substances are adsorbed that reduce the free energy of the surface layer, or, in other words, reduce the surface tension relative to the environment. Thus, using the different adsorption abilities of substances found, for example, in solution, it is possible to separate and purify them by absorbing one of them with an adsorbent and leaving the other in solution. A quantitative characteristic of an adsorption system is adsorption isotherm. It expresses the relationship between the concentration of a substance WITH in solution and its amount Cs, adsorbed by a unit of adsorbent surface at a constant temperature under conditions of adsorption equilibrium. 1. The surface of the adsorbent has a limited number of independent adsorption sites, and each site can adsorb only one molecule.

2. . MOS hydride epitaxy of semiconductors.

Most semiconductor compounds A 3 B 5 , A 2 B 6 and A 4 B 6 can be grown using MOC technology. In the case of growth of compounds A 3 B 5, instead of organometallic compounds of elements of the fifth group, hydrides of the corresponding elements can be used. In this case, it is customary to use the term MOC-hydride technology. Some organometallic compounds: Ga(CH 3) 3 - trimethylgallium (TMG), Ga(C 2 H 5) 3 - triethylgallium (TEG), In(CH 3) 3 - trimethylindium (TMI), In(C 2 H 5) 3 – triethylindium (TEI), Al(CH 3) 3 – trimethylaluminum (TMA) (in general – MR3, where M is metal, R 3 – (CH 3) or (C 2 H 5) – alkyl). Hydrides: AsH 3 – arsine, PH 3 – phosphine.

A schematic description of the processes during MOS hydride epitaxy is shown in Fig. 2. The reaction occurs in a gas stream at atmospheric or reduced pressure in a reactor with cold walls. The carrier gas is usually hydrogen. Individual stages of the complete reaction already take place in the gas phase. The final stages and incorporation into the lattice occur on the surface of the semiconductor. Typical reactors allow the connection of multiple organometallic and hydride sources, so alternating layers of different materials can be grown sequentially in a single growth cycle. This makes it possible to obtain multilayer multicomponent epitaxial structures.

The technological process of organometallic epitaxy does not involve etchants, and the growth process is not the result of competition between deposition and etching, as in some other vapor-phase epitaxy methods. As a result, sharp boundaries between layers and uniformity of growing layers in thickness and composition are ensured.

MOS hydride epitaxy is the simplest of all technologies for producing epitaxial layers of A III B V compounds from the gas phase. The overall reaction for the formation of compounds is a reaction of the type

Ga(CH 3) 3 +AsH 3 →GaAs (solid) +3CH 4,

The problem of water purification has long worried humanity. Today there are many ways to cleanse it. One of the most common, without a doubt, is sorption water purification. What is its essence?

From this article you will learn:

What is sorption water purification

How does sorption water purification occur?

What filters are used for sorption water purification

What types of sorbents are used

Sorptive water purification - what is it?

Sorption water purification is a highly effective method of deep purification, in which the effect is achieved by binding particles of chemicals and various impurities at the molecular level. Such water purification allows you to remove even organic compounds that cannot be separated by any other methods.

Modern highly active sorbents work effectively in water with any, even the smallest, concentration of unwanted impurities. As a result of sorption purification, there is practically no residual concentrate in the water.

The term “adsorption” means the absorption of a substance from a gaseous medium or solution by the surface layer of another substance. This process also occurs in the water that we purify when certain substances are added. The adsorbent attracts molecules of unwanted impurities to its surface and never releases them.

Sorption purification is especially effective at the final stage of a high level of purification, when water, having passed through the previous stages of purification, has left almost everything unnecessary on the filters, and now it is necessary to remove the smallest concentrations of unwanted impurities.

How quickly and efficiently this process will take place depends on the following factors:

sorbent structures;

temperature at which the process takes place;

type and concentration of harmful substances in water;

environmental reaction activity.

Why is sorption water purification needed and where is it used?

Sorption water purification has been known to people for quite some time. Both earlier and to this day, for example, they used carbon filtration, which works well in closed systems, deeply cleaning, including from organic matter.

Sorption water purification gives excellent results, removing various organic substances, making it possible to clean wastewater from dyes or other hydrophobic compounds. This method has also gained wide popularity due to the fact that it does not require significant material costs.

Sorption water purification can be used as an independent method, or can be used in combination with biological purification. However, this method cannot be used when contaminated only with inorganic impurities or organic impurities of low molecular weight. It purifies water not only from impurities, which can only be seen in the results of laboratory tests, but also from foreign odors and the taste of chlorine and hydrogen sulfide that are easily detected by humans.

Activated carbon is an effective adsorbent that has micropores in its structure that successfully perform filtration. It is not difficult to obtain: the raw materials for production are wood, peat, nut shells, and animal products. Applying silver ions to the surface of activated carbon particles extends the service life of the adsorbent, preventing it from being damaged by microbes.

Activated carbon is one of the best sorbents used in modern systems today. It comes in different types. The highest quality of sorption water purification will be provided by the one that has the maximum possible number of micropores.

Sorptive water purification with activated carbon is usually used to remove organic matter from water during its preparation before reverse osmosis. At the same time, the liquid is also cleared of chlorine, which makes it more acceptable for hygiene procedures.

Filters filled with activated carbon can become unusable if colloidal particles enter them with water, which prevent micropores from performing their functions. In this case, you have to change the sorbent or restore it.

Sorptive water purification using activated carbon filters significantly improves the quality of the liquid, freeing it not only from chlorine, but also from nitrogenous compounds. With simultaneous sorption and ozonation of water, the capabilities of activated carbon to purify it from impurities are significantly increased. If natural minerals with the addition of Ca, Mg and aluminum oxides are used as a sorbent, the water is purified from phosphorus compounds.

Sorption filters do an excellent job of purifying water from iron when insoluble oxides in the form of solid particles are formed in the liquid after the oxidation process.

What types of sorption water purification are divided into?

The type of sorption purification process is:

periodic;

continuous.

According to the hydrodynamic regime there are:

displacement installations;

mixing installations;

intermediate type installations.

Depending on the state of the layers of the sorbent used, cleaning can be:

moving;

motionless.

According to the direction of filtration, cleaning occurs:

counterflow;

direct flow;

mixed traffic.

Based on the contact of interacting phases, the cleaning process is divided into:

stepped;

continuous.

According to the design of the filter, cleaning can be:

column;

capacitive

Main types of sorbents

We have already said that a very popular type of sorbent for water purification is activated carbon, which perfectly removes organic compounds of natural and artificial origin. But, in addition to activated carbon, other types of sorbent are also used.

Carbon-free sorbents for water purification

The most widely used sorption water purification technology is purification using carbon-free sorbents. They can be of either natural or artificial origin: clay rocks, zeolites, etc.

Non-carbon sorbents have a number of advantages, such as:

increased capacity;

ability to exchange cations;

prevalence and, accordingly, low price.

Clay rocks

Clay rocks often play the role of a water filter in nature. The ability of this material is successfully used for the same purposes by humans. Such rocks have layered rigidity, a well-developed structure with a large number of micropores of various sizes.

Sorptive water purification using filters, where clay rocks act as a sorbent, is a complex process that includes van der Waals reactions. As a result, the water becomes crystal clear in appearance and is freed from toxic organic compounds of chlorine, herbicides, and surfactants.

Clay rocks are also convenient because they are accessible to mining. This increases their consumption.

Zeolites

Zeolites are a group of minerals with a characteristic glassy luster. Today natural and artificial zeolites are used. They have an interesting structure: a three-dimensional aluminosilicate frame with a regular tetrahedral structure and a negative charge. Hydrated ions of alkali and alkaline earth metals are located in the voids of the framework and have a positive charge that compensates for the charge of the framework. Zeolites are called a sieve for molecules, since they trap substances whose molecules are smaller than the voids of the framework.

More than 30 types of zeolites are known. The most used ones, which are easy to mine and process: abasite, mordenite, clinoptilolite.

Before using zeolite as a sorbent, it is calcined with sodium chloride carbonate in an oven at a temperature of +1000 ° C, after which organosilicon compounds are formed on its surface, giving it hydrophobic properties.

Zeolites are used for sorption purification of water in powder form. They purify water from:

organic compounds.

colloidal and bacterial contaminants;

pesticides;

dyes;

Inorganic ion exchangers

Most of them are used in the form of salts, since they cannot exist in the hydrogen form. But this does not allow water to be desalted without the participation of rare anion exchangers of inorganic minerals. Therefore, it is necessary to use organic cation exchangers and anion exchangers based on synthetic organics.

Organic ion exchangers

Many organic ion exchangers have a gel structure. They do not have pores, but in an aqueous solution they swell and can exchange ions.

There are macroporous ion exchangers that work like activated carbon, which are less capacious than gel ones, but have improved exchange and sieve effect, are resistant to mechanical load, and are osmotically stable.

An important achievement of our time has been the possibility of synthesizing organic ion exchangers with specified properties that are not found in nature.

What does a sorption filter for water purification consist of?

Each sorption filter has the following parts:

a body of a certain size in the form of a fiberglass cylinder;

a stationary layer of activated carbon with a gravel backing;

a control valve of a certain type (sometimes a mechanical valve);

pipeline for supplying waste water;

pipeline for removing purified water;

pipeline for supplying loosening water;

drainage and distribution system.

The speed of the filter directly depends on how contaminated the water is to be purified. The grain size of the sorbent also influences (from 1 to 5 mm). The linear rate of water filtration can vary from 1 to 10 m 3 /hour.

The best way to purify water by sorption is to feed it into the filter from the bottom up, when the entire cross-sectional area of ​​the filter is filled with water evenly, and bubbles easily come out of the water.

For regenerative wastewater treatment with subsequent recycling of retained valuable elements in a sorption filter for water purification, filters with a fixed layer of sorbent are used. You can later extract the necessary elements using water vapor or chemical solvents.

You can study in detail the operation of a sorption water purification system using the FSB series filter as an example. This model is designed to work in storm sewer systems. At the entrance to the filter there are pre-filters: a sand catcher and an oil catcher, the task of which is not to miss the first strong contaminants that can quickly damage the filter.

Having passed through the pre-filters, the water enters the sorption block through the pipe, from where the distribution and discharge pipe discharges the water to the lower distribution zone.

When water hits the sorbent located here, it is evenly distributed over it and passes through, being cleaned of impurities. Moreover, the brand and volume of sorbent used is selected depending on the initial and final concentration levels of harmful substances and the required productivity.

Purified water is directed by an ascending flow into a collecting circular tray and discharged through a pipe.

Procedure for installing the system:

Dig a pit of the required size.

Fill its bottom with a 300 mm layer of sand and compact it well.

On a sand bed, pour a reinforced concrete slab with a thickness of at least 300 mm, the dimensions of which are 1000 mm wider than the diameter of the filter housing.

Mount the body of the sorption unit on the stove, carefully maintaining its verticality.

To ensure that the housing is stable, first fill it with water (to the level of the perforated bottom).

Secure the body with anchors so that it does not move when backfilling.

Fill the pit with clean sand to the level of the inlet and outlet pipes. This must be done in stages, in layers of 300 mm, carefully compacting each layer.

Connect the inlet, outlet and overflow pipelines. Next, fill the body with sand to the top, carefully compacting the soil so as not to damage the installed pipes.

Fill the body with filler from bags, constantly carefully distributing it over the entire area of ​​the bottom.

Thoroughly rinse the installed sorbent before putting the system into operation.

Finally, the housing must be filled with clean water.

If your sorption water purification system must purify water from all possible types of pollution, then it is necessary to use a complex of sorbents: activated carbon and various ion exchange substances, which must be selected taking into account the impurities found in the water of your source.

There are many types of sorption water purification systems. To choose the one that’s right for you, study all the factors and conduct laboratory tests of the water. Installing water purification equipment also requires special knowledge. Therefore, it should be performed by professionals.

There are many companies on the Russian market that develop water treatment systems. It is quite difficult to choose one or another type of water filter on your own, without the help of a professional. And even more so, you should not try to install a water treatment system yourself, even if you have read several articles on the Internet and it seems to you that you have figured it out.

It is safer to contact a filter installation company that provides a full range of services - specialist consultation, analysis of water from a well or well, selection of suitable equipment, delivery and connection of the system. In addition, it is important that the company provides filter maintenance.

By collaborating with Biokit, you get the widest selection of reverse osmosis systems, water filters and many other devices designed to purify water and return it to its natural qualities.

We are ready to help you in these areas:

Choose a water filter.

Connect the filtration system.

Select replacement materials.

Troubleshoot equipment problems.

Involve specialist installers.

Provide telephone consultation on questions of interest.

Entrust water purification to Biokit professionals who care about your health.

Sorption methods

Sorption methods are based on the absorption of solid phase radionuclides through the mechanisms of ion exchange, adsorption, crystallization and others.

Sorption is carried out under dynamic and statistical conditions. With dynamic sorption, the initial liquid waste is filtered continuously through the sorbent, and with static sorption, temporary contact of two phases is carried out with stirring with further separation.

Dynamic sorption is carried out in alluvial or bulk filters. The difference is that bulk filters use sorbents in the form of granular durable material; in precoat filters, inorganic and organic materials of artificial and organic origin are used as a sorbent.

To purify liquid radioactive waste from radionuclides, sorbents (ion exchangers) of such types as KB-51-7, KU-2-8 (strong acid cation exchanger), AV-17-8 (strong base anion exchanger), AN-31 and AN-2FN ( weakly basic anion exchangers), vermiculite. Sorbents are produced in the form of granules, which are soaked in a special solution for activation before use. All of the listed sorbents have high purification coefficients and good filtering properties.

Ion-exchange heterogeneous reactions are reversible, which allows for the regeneration of the sorbent, but creates conditions for the leaching of radionuclides during storage of the spent sorbent. Almost all of the exchange capacity of the sorbent is used for the sorption of macrocomponents - salts, due to their similarity with the properties of microcomponents. Then, in order for the sorption of microcomponents (radionuclides) to occur, it is necessary to carry out preliminary desalting. Otherwise, this will lead to frequent regenerations of the sorbent and, consequently, increased cleaning costs.

Liquid radioactive waste with high salinity is unprofitable to purify with organic sorbents due to the fact that when regenerating the sorbent, a 2-2.5-fold excess of alkali and acid is required (the cost of purification increases).

The situation is the opposite for radionuclides, whose properties are different from those of their macrocomponents. Multivalent radionuclides are well sorbed on the cation exchanger in the presence of sodium ions. Therefore, sodium ions found in liquid radioactive waste are not sorbed, which leads to a noticeable reduction in the volume of the regenerator, secondary waste and regeneration frequency.

The use of synthetic organic sorbents makes it possible to remove all radionuclides in ionic form from liquid radioactive waste. But such sorbents have some restrictions on use, which develop into serious disadvantages. When using such sorbents, radionuclides in molecular and colloidal form are not removed from liquid radioactive waste. Also, if liquid radioactive waste contains colloids or organic substances with large molecules, then the sorbent loses its properties and fails due to pore clogging.

In practice, before carrying out ion exchange, filtration on precoat filters is used to remove colloidal particles. The use of the coagulation method instead of filtration leads to the formation of large volumes of waste. Organic compounds from liquid radioactive waste are removed by ultrafiltration. One of the main disadvantages of using ion exchange for the purification of liquid radioactive waste is noticeable - the need for preliminary preparation of such waste.

Synthetic organic sorbents are not used for the purification of highly active liquid waste due to their instability to the effects of highly active radiation. Such exposure leads to the destruction of the sorbent.

To ensure a high degree of purification, the ion exchange purification process is carried out in two stages. At the first stage, salts and small amounts of radionuclides are removed from liquid waste, and at the second stage, nuclides are directly removed from desalted liquid waste. Regeneration of the sorbent is carried out in countercurrent. To increase the performance of the filters, the speed at the beginning of the cycle is set to (90h100) m/h, and at the end of the cycle it is reduced to values ​​of (10h20) m/h.

Purification of desalted waste makes it possible to use effective mixed-action filters (their regeneration is difficult) and precoat filters due to the fact that when cleaning such waste the need for regeneration is minimal. Thanks to the mixed loading of anion exchangers and cation exchangers in the forms H + and OH-, the counterionic effect is eliminated, and this leads to an increase in the degree of purification and the possibility of increasing the filtration speed to 100 m/h.

All liquid radioactive waste contains some amount of suspension, which has a tendency to molecular and ion-exchange sorption. Also, corrosion products with hydrated oxides of iron, manganese, cobalt and nickel can sorb microcomponents. In this regard, it is proposed to separate suspended matter to significantly improve the degree of purification of liquid waste.

To remove components such as 137 Cs, 99 Sr, 60 Co from waste, they use the addition of selective sorbents, in this case nanoclays (montmorillonite), which ensures 98% purification of these components. Sorption on selective components is carried out in combination with coagulation.

Chemical precipitation is one of the effective options for static sorption. The advantages of chemical methods include low cost, availability of reagents, the possibility of removing radioactive microcomponents in ionic and colloidal forms, as well as processing saline liquid waste.

The main feature of chemical deposition is selectivity to various microcomponents, especially to 137 Cs, 106 Ru, 60 Co, 131 I, 90 Sr. Coagulation and softening are chemical precipitation methods; When using these methods, radionuclides are removed from colloidal, ionic and molecular forms.

When using soda-lime softening, CaCO 3 and MgOH 2 precipitate and serve as collectors for 90 Sr, which is removed by crystallization with CaCO 3. Also, the use of this method allows you to remove 95 Zr and 95 Nb.

Cesium (137 Cs) is removed by precipitation of ferrocyanides of iron, nickel (the most effective), copper and zinc, with a purification factor of 100.

Ruthenium (106 Ru) and cobalt (60 Co) are poorly concentrated in sediments due to the large number of their chemical forms. Ruthenium is removed using sorbents such as cadmium sulfide, iron sulfide, and lead sulfide. Cobalt removal is effective on chromium and manganese oxyhydrates. Radioactive iodine 131I is produced by coprecipitation with copper or silver iodide.

Chemical deposition is completed by phase separation procedures. When phases are separated, most of the liquid waste is clarified and the sludge is concentrated. Phase separation is carried out by filtration or by exposing the system to a force field, which can be gravitational (settlers and clarifiers) or inertial (centrifuges). Due to the formation of large volumes of pulps with very high humidity, settling tanks are used extremely rarely, using clarifiers for this purpose. Clarification in such devices occurs at high speeds and provides a high degree of purification.

To further clarify the liquid, filtering is carried out. The use of bulk filters provides finer filtration, such filters have greater productivity, and during their regeneration a small amount of waste is generated. Bulk filters have become more widespread due to their simplicity and reliability, despite the formation of a large amount of secondary waste during regeneration.

1

1. Tarasevich Yu.I. Natural sorbents in water purification processes. – Kyiv: Naukova Dumka, 1989. – 292 p.

2. Rush E.A. Environmental technologies: methods for improving technologies for sorption treatment of industrial wastewater // Engineering ecology. – 2005. – No. 4. – P. 11-28.

The possibility of deep purification of wastewater from railway transport pollutants using the adsorption method with a natural resource - bentonite clay is shown.

Railway transport enterprises are among the main sources that pollute various objects of the natural environment with wastewater discharges. Harmful components contained in wastewater from locomotive and carriage depots, locomotive and car repair plants, washing and steaming stations, galvanic, battery and other workshops include suspended particles of various natures, petroleum products, phenol, salts of heavy metals, surfactants, paints and varnishes, acids , alkalis. Such wastewater cannot be sent directly to biological treatment, since the components it contains are toxic to the “activated sludge” microorganisms of centralized biological treatment plants in cities, and are also resistant to the action of the enzymes of these microorganisms. To remove toxic and biochemically stable substances, it is advisable to subject such wastewater to local treatment. If the physicochemical treatment of such industrial wastewater provides the necessary level of purification for its use as process water, then there is no need to send it for further biological treatment.

In modern wastewater treatment technology, the sorption method is becoming increasingly important. It is known that the effectiveness of this cleaning method depends on the physicochemical nature of both the adsorbent and the sorbed substances.

Limited water resources in Kazakhstan and technical and economic considerations lead to the need to use water circulation in the water use system. The need to use wastewater for economic and technical needs forces us to look for ways and means of more thoroughly purifying it from fine suspended matter and colloidal substances of both inorganic and organic nature. Existing treatment methods make it possible to capture large suspended matter from water in settling tanks and finely dispersed suspended matter in ponds, but however, it is impossible to reduce the level of dangerous pollutants such as heavy metals to the standards required for wastewater when used in the national economy, in particular for irrigating agricultural fields . This requires the use of more advanced methods of cleaning it.

In this regard, based on the results of experimental studies for enterprises of the railway network, we have selected a technological scheme of a local wastewater treatment plant using the adsorption method with a natural resource - alkaline bentonite of local origin (Ibata deposit).

Wastewater treatment includes the following sequence of operations: mechanical treatment; accumulation - averaging; sequential processing with bentonite clay, settling and filtration.

The productivity of treatment facilities, based on the total volume of wastewater, incl. surface, as well as rhythm and flow schedule, is 26-30 m3/h and is designed for an average flow of 27 m3/h. The total operating time of treatment facilities is 24 hours/day, of which 16 hours are for cleaning the main runoff and 8 hours are for cleaning mainly surface runoff.

Below are descriptions and results of wastewater treatment by operation.

Accumulation-averaging. Before entering the accumulator-accumulator, wastewater from various enterprise facilities passes through a metal grid with an area of ​​3.0×2.0 m made of steel strips 40×10 mm with gaps of 16 mm at an angle of inclination to the horizon of 60-70 °C. The flow rate of wastewater does not exceed 1 m3/s. Cleaning the grille can be done manually or mechanically. Then the treated wastewater enters a storage tank - a homogenizer, which ensures a uniform supply of water for further purification. This ensures smoothing of the composition (averaging) across components, which have significant fluctuations in both volumes of receipt and composition.

Simultaneously with averaging in the settling tank-averaging tank, the interaction of the solution components with preliminary purification and partial sedimentation of pollutants occurs, i.e. clarification (Table 1).

Table 1

The degree of purification and composition of water after settling in a settling tank - homogenizer (settling duration 6 hours)

Pollutant	Pollutant concentration, mg/dm3	Amount of pollutant, kg/day	Degree of purification, %
Suspended solids
Ether-soluble substances Petroleum products
Total iron
Paint (suspension)
Sulfate ions
Chloride ions
Carbonate ions
Phosphate ions
Silicate ions
Hydroxide ions

Suspensions accumulating in the settling tank in the form of sediment are mainly represented by components similar to the composition of surface runoff pollutants (sand, loess inclusions, soil components, etc.). The main components are SiO2 up to 70%, calcium compounds - CaO.SiO2 - up to 15%, CaO.Al2O3 up to 10%, Ge2O3. nH2O up to 0.5%, humic substances - up to 4.5%.

In table Table 2 shows the granulometric composition of the suspension before and after settling in the homogenizer - accumulator, and in table. 3 sediment composition.

table 2

Average granulometric composition of suspension before and after settling in the accumulator-averager (%)

Table 3

Qualitative and quantitative composition of the sediment formed in the settling tank-averaging tank

Adsorption-ion exchange wastewater treatment. The water clarified in the settling tank enters an adsorption unit, consisting of two sections, where its main purification occurs. The volume of bentonite used is 12 m3 or 21 tons. The absorption capacity (capacity) ensures the operation of the bentonite adsorbent without replacement for 3-6 months. The absorbing capacity of the adsorbent by elements and compounds of the purified water before its replacement is 1500-1600 kg. The total amount of loading to be replaced and disposed of is about 22 tons, humidity 8-10%.

As can be seen from the data in table. 4, presenting the results of a pilot test of wastewater treatment technology from railway enterprises, bentonite clay particles, which have both positive and negative charges on their surface, are universal precipitators of dispersed impurities from the aquatic environment, and also act as an effective ion exchanger. The intensification of the water clarification process is explained by the good dispersion of bentonite clay in water to elementary particles and their interaction with positive and negative particles of dispersed impurities of water, leading to weighting and sedimentation. At the same time, ions of heavy metals and other organic substances are deposited on the clay particles.

Table 4

Wastewater treatment results

Contaminants and compounds	Concentration in water, mg/dm3			Degree of purification in %
	1st section		after cleaning in the 2nd section
				1st section	2nd section
	before cleaning	after cleaning
Suspended solids
Ether-soluble Petroleum products
Total iron
Paint (suspension)
Sulfate ions
Chloride ions
Carbonate ions
Phosphate ions
Silicate ions

It has been shown that bentonite clays have a high sorption capacity in relation not only to petroleum products, but also to molecules of synthetic surfactants.

Thus, using the adsorption-ion exchange method using bentonite clay, which has the ability to adsorb substances from multicomponent mixtures, it is possible to effectively treat wastewater from railway network enterprises to maximum permissible concentrations with the return of purified water to the technological cycle (washing cars, wheel sets, cooling system) with simultaneous recycling of natural sorbent. This method can be used in complex schemes for deep wastewater treatment, including mechanical, physico-chemical, biological and other treatment methods.

The mechanism of the sorption process on bentonite clay when treating wastewater from substances of various natures is molecular, ion-exchange and chemisorption in nature.

Bibliographic link

Abdimutalip N.A., Sainova G.A., Toychibekova G.B. SORPTION METHOD FOR WASTEWATER PURIFICATION FROM RAILWAY TRANSPORT ENTERPRISES // Modern science-intensive technologies. – 2012. – No. 11. – P. 63-65;
URL: http://top-technologies.ru/ru/article/view?id=31106 (access date: November 26, 2019). We bring to your attention magazines published by the publishing house "Academy of Natural Sciences"