Everything you need to know about membrane filters for water purification. How does a membrane water filter work? What is a membrane filter for?

Purification of water from harmful impurities is relevant not only when it is used as drinking water, but also for technical needs, where high mineralization leads to the appearance of scale, blockages in plumbing equipment and fittings, and incorrect operation of household electrical equipment. One of the effective ways to combat harmful components is a membrane filter for water purification, which is widely used in industrial production and households.

There are a number of membrane devices for water treatment on the market from different manufacturers, when choosing them, one should take into account the nature of the pollution, the intended purpose of the purified water and the volume of its consumption. When installing systems using membrane filters on their own, the degree of contamination plays an important role - with their high intensity, the use of pre-cleaning and softening filtering devices is required. In order to properly assemble a water purification system using any type of filter, it is necessary to conduct a laboratory analysis of its chemical composition, this condition is mandatory for water intake from wells and wells of private houses, country cottages.

The membrane water filter is classified as a deep cleaning device, due to the small pores of the filtration material, it is able to filter out contaminants with a diameter of 0.0001 microns. To understand what such a filter is, consider the phased technology of its production:

A polypropylene mesh is cut into rectangles of the required length and width; it serves as a gasket between the layers of filter material.
They cut off pieces of polyester equal to the size of the mesh, it has the smallest channels through which water passes and harmful impurities are retained, the material is a filter element of the membrane.
Polyester is placed in stacks of 15 sheets and fastened together with high-frequency acoustic waves using ultrasonic welding technology, obtaining one of the assembly elements of the device - a filter.
A roll of special filter paper is unwound and passed through a mixture of liquid plastic with a solvent that covers one of the sides, after the plastic hardens and the solvent evaporates, a unique fine-mesh structure of the membrane is formed on the paper tape.
The membrane is laid out on a table, covered with a mesh 2 times smaller on top, and the second part of the tape is wrapped up - a kind of envelope is obtained from two filtering surfaces, between which there is an insulating mesh.

Glue is applied to the edges of a plastic tube with round holes along the entire length and a stack of a number of polyester filter filters is applied to it, fixing it on the pipe with adhesive tape.
A membrane envelope with a mesh in the middle is laid on the first polyester sheet and glued along the edges, the next filter filter sheet, the membrane are placed on top and glued again.
The operation is repeated several times (the number of filtering membrane layers depends on the quality of the filter), resulting in a kind of membrane sandwich. In inexpensive household appliances, the number of sleeves wound on a drainage tube does not exceed one or two, in high-tech industrial installations where high quality cleaning is required, the number of filter layers reaches 15.
They begin to rotate the tube, winding all the filter elements assembled into a single whole around it, compress and fix the filter layers from above with adhesive tape.
End plastic tips are installed along the edges and fixed with glue.
A glass fiber glued thread is wound on the cylindrical surface of the filter with the necessary tension, excess glue is removed. After the adhesive has dried, a strong fiberglass shell is formed on the filter surface.

Household filter filters during production are assembled from four sheets in the following sequence: a membrane supporting a polyester filter filter, a polyethylene substrate, a mesh. The sheets are folded together in one sleeve and wound on a drainage pipe; there can be several of them in the filter, laid close to each other and twisted into a spiral.

According to the technology discussed above, the most popular rolled membranes are made; membrane softeners in the form of disks or made of other materials (ceramics) are also found on the market.

Principle of operation

Membrane-type roll water filters are most often used in household water treatment systems, their principle of operation is based on passing liquid through a special fine-mesh membrane on an impregnated paper base and removing contaminants with partial capture by a polyester filter. It is necessary for the correct operation of the system - for the filter to work, water is supplied to the membrane under pressure, while the polyester layer creates resistance in the path of the water flow and prevents it from escaping through the purifier. In its absence, water under pressure freely passes through the filter in the longitudinal direction, without being forced into the membrane and then into the drainage pipe.

The operation of the membrane roll filter consists of the following sequence of technological operations:

The purified water enters the end part of the filter and passes along the membrane, from this end the inner plastic tube is sealed and does not have defragmentation.
At the other end, the body is closed by a cover with a small diameter outlet fitting that limits the pressure. As a result, excess pressure appears inside and the purified water is forced through a series of membrane filters to the round holes on the central pipe.
During the punching process, all particles larger than the diameter of the membrane cells are collected in the polyester filter and between the mesh cells, and then washed out by the passing water stream.

Important: If the filter system is not washed with running water, the small cells of the membrane become clogged with harmful impurities in a short time and it ceases to perform its functions.

Thus, the filtered liquid moves simultaneously along the filter and in the radial direction, leaking into the membrane, twisted into a spiral. Purified water (permeate) is discharged to the outside through the central drainage pipe, and contaminated liquid (concentrate) with a high content of harmful impurities is collected at the outlet end of the filter after longitudinal passage through the mesh and polyester substrate.
Salt concentrate is discharged into a storage tank for further use in the household or disposed of by draining into the sewer system.

As can be seen from the principle of operation of this filter, a significant part of the treated liquid (about 3/4) contains a high concentration of harmful impurities and drains, therefore, in the domestic use of such systems, one should consider the rational use of these water volumes for economic purposes.

Tip: A good way out of the situation of high water consumption in apartments with metering devices is to insert a tee with a check valve into the pipeline, through which the contaminated solution is sent back to the water supply system. The filter is turned on during domestic use of water (washing dishes, taking baths) and the concentrate is immediately consumed for household purposes.

Membrane filter system design

There are a large number of membrane-type household filter systems on sale from a domestic manufacturer that have earned positive feedback from consumers, these include well-known brands: Aquaphor, Geyser, Istok, Novaya Voda, Atoll, Rosa. Typical reverse osmosis models consist of the following elements:

Primary filter. It removes large mechanical particles from 5 microns in size, small grains of sand, suspended dirt, and rust from the water stream. The cartridge of this filter is often made of foamed polypropylene; it is used to mechanically purify water from suspended impurities.
adsorption filter. The filter element of the cleaner is activated carbon, the surface layer of which absorbs harmful substances from the water. Coal perfectly purifies water from chlorine compounds, organic impurities.
High quality post-treatment filter. The cartridge filler is briquetted activated carbon, which removes mechanical particles up to 1 micron in diameter from the liquid and performs post-treatment of chlorine compounds and organics.
Reverse osmosis membrane filter. Removes from water all particles ranging in size from 0.001 to 0.0001 microns or 96 - 98% of all contaminants, insoluble divalent metal oxides (manganese, potassium, iron), organic impurities, bacteria and viruses fall into this category.
Mineralizer. Purified sterilized distilled water does not contain minerals and salts useful for human health, which were removed during the purification process along with harmful impurities. When used as a drink, it is passed through a flowing mineralizer with mineral salts, saturating the water, they increase its taste and make it healthy.
storage tank. Drinking water is sent to a metal storage tank for use at any time without waiting for the completion of the purification process.
Electronic control module (optional, needed for low water pressure in the water supply). Starts the pressure pump when the storage tank is empty, cleans the system automatically.

Classification of membranes by pore size

A membrane is a thin elastic film fixed on a bearing surface along the perimeter, this definition is not very suitable for water treatment systems, where the purpose of membrane flexible plates is water filtration.

The pores of the materials used in water treatment are capable of passing impurities of different diameters, taking into account this factor, a system has developed for separating membranes according to the size parameters of the passed particles into the following groups:

Microfiltration (1-0.1 microns). Turbid water and gray sewage have inclusions of this size; similar filters are also used to purify water from large colloidal particles and coarse organic impurities. Filters of such cleaning are classified as mechanical; in domestic pre-treatment systems, similar functions are performed by a polypropylene cartridge.
Ultrafiltration (0.1-0.01 microns). They screen out small colloidal impurities and macromolecular compounds, algae, bacteria, trivalent insoluble metal oxides.
Nanofiltration (0.01-0.001 microns). Used in water softening systems, they are able to purify liquid from soluble divalent oxides of iron, potassium, manganese, chlorine, various types of dyes.
Reverse osmosis (0.001-0.0001 microns). Deep cleaning filters with an efficiency of up to 99% are widely used in industrial seawater desalination. All salts and metal oxides, bacteria, oil products, dyes, pesticides are removed from the liquid. Reverse osmosis systems are widely used in medicine, food and chemical industries to obtain sterilized water.

When choosing a water treatment plant, an important criterion is the pressure in the system, for large pore sizes in membranes, 1–2 atmospheres is sufficient, the highest pressure is required for reverse osmosis filters – at least 3 atmospheres.

Types of membrane filters by design

In addition to dimensional parameters, membrane filters, depending on the design, are divided into the following types:

Disk. This type of filter is rarely used in households, microporous membranes are more often used in the industrial sector for water purification of large volumes of water in large-sized installations. The material of their manufacture is capron, polyamide, polyethersulfone, fluoroplastic, polyethylene terephthalate (lavsan), cellulose acetate. In the production process, cleaning elements with membranes are placed in filters in the following ways:

bezpodozhechny, the filter is made of a homogeneous material;
reinforced with a fabric or polymer mesh base;
substrate - with a base of durable large-pore material.

On the water treatment equipment market, you can purchase disk Geysers made of polymeric materials with built-in grooves that allow particles as small as 100 microns to pass through.

Tubular. They have a simple design in the form of a tube made of porous material, into which the filtered liquid enters through the end cap with holes and then is squeezed out under pressure, passing through the pores of the membrane cleaner. The materials for manufacturing the body of a finely porous membrane can be ceramics, cermets, plastics, and alloys of various metals.

Rolled. The device of such filters was discussed above, they are a sandwich wound on a drainage tube made of a reverse osmosis film, a polyester substrate, a polyethylene film and a mesh. During their operation, water from the end part enters the membrane and flows down in a spiral into the drainage holes, and the concentrate with impurities is disposed of or used for household needs.

Hollow fiber. This type of membrane is designed for industrial use, they are very small filtration tubes folded into a bundle. The purified liquid passes through the capillaries in their walls, the diameter of which prevents the passage of larger impurities. Ultrafiltration membranes have a similar design, screening out particles with a diameter of 0.1 microns.

Track-membrane. This type of membrane is made from thin film polymers 12–23 µm thick by bombarding the surface with krypton ions; as a result, through channels with a fixed diameter of up to 0.05 µm appear (for a polyethylene terephthalate film). One of the simplest devices based on them, used for water purification in the household, is a film membrane with a hole diameter of 0.2-0.4 microns, placed in a closed plastic case.

To operate the device, its body is immersed in a container of water and a drain pipe is connected, lowering it below the liquid level into a reservoir (jar) to collect filtered water. Before filtering, water is sucked in and after the jet mode switches to drip mode (the membrane filterer is put into operation), they begin to collect the filtrate.

Track membrane filters for fine water purification, the average price of which is about 700 rubles, do not require electricity, the device can be taken with you to the country house, on vacation with wild living conditions, or a hiking trip. The advantage of the track system is ease of maintenance - after clogging the pores, the marching membrane filter for water purification is disassembled, the purifier is removed, wiped with a clean sponge from plaque under running water and immersed in a 5% citric acid solution to restore.

A wide range of track filterers is sold on the water treatment equipment market, popular brands are Nerox, Kapel, Snezhinka.

Pros and cons of membrane filters

Among all varieties of membrane filters in households, reverse osmosis plants with an initial cost of about 6,000 rubles, which have the highest water purification efficiency, have been used. Their positive qualities include:

High purity filtered water, which does not contain all types of bacteria, microbes, viruses, metal oxides that cause scale.
The filtration system has a simple design and can be independently maintained by the consumer.
Unlike popular household alternative cleaning methods with aerators and ion exchange resins, a reverse osmosis system takes up little space under the sink.
The service life of the membrane filter, thanks to the technology with constant cleaning of its surface with running water, exceeds the time of using cartridges in jug-type systems and can reach up to 2 years. Systems where automatic cleaning of the membrane is provided operate without changing the filter for 5 years or more.

Despite the highest quality of cleaning, the reverse osmosis membrane filter has a number of disadvantages that limit its widespread use in everyday life:

When operating installations with this filtration method, only 1/4 of the incoming water is effectively purified, the rest will have to be drained into the sewer or sought for use for economic purposes.
High quality cleaning requires strong pressure in the system up to 10 atmospheres to force water through a fine-mesh membrane, such a pressure can only be achieved using an electric pump, which requires electricity to operate - this significantly increases operating costs.
For the correct operation of the reverse osmosis membrane, water must be pre-treated before filtration - as a result, three filters are additionally used (a standard set of Aquaphor trio, Rosa). In two of them, carbon cartridges are subject to mandatory periodic replacement, which leads to additional costs.

Passing through the reverse osmosis system, water loses minerals useful for human health and becomes tasteless, therefore, an additional mineralization unit with consumable components is used to improve the taste.
Compared to other systems, the reverse osmosis filter has a rather low capacity (maximum 0.12 l / min for the popular Geyser Prestige model) and is used only for drinking water.
Many users complain about the noisy operation of the automatic system, which turns on the electric pump forcing water after the storage tank is empty, sometimes the electronics get confused in operation and constantly turn the pump on and off.
The average cost of a reverse osmosis filter is about 7500 rubles. without an injection pump - not everyone can afford such expenses.

How to clean a reverse osmosis filter

The need and frequency of cleaning a reverse osmosis plant depends on the quality of the water, the volume of filtration and the pressure in the system; if there is automation with a built-in water purification function, the cartridge can be used for up to 6 years.

If the installation design does not provide for the possibility of automatic filter maintenance, it can be washed by yourself using one of the following methods:

Take out the cartridge and send a jet of water into it in the opposite direction, due to a small pressure, it will pass through the filter layers through, washing out deposits. After washing, the filter can be put in water with citric acid for several hours.
Modern designs of household filters are notable for the low strength of the casing, which consists of several layers of a polymer film. It is quite simple to unwind it, then straighten out 2 spiral arms, in which it is easy to separate the filter, mesh and substrate from each other. You can lower the entire system into a container of water and thoroughly rinse its components with further settling in a solution of 5% citric acid. After drying, the cartridge is easy to assemble back by fastening the body with tape or tape.

In households, for obtaining high-quality drinking water, a reverse osmosis membrane water purifier has proven itself, producing 95 - 98% filtration of all components harmful and beneficial to the human body. Despite a lot of shortcomings (low performance with utilization of 3/4 of the water volume, high operating costs, lack of useful minerals), the system has no competitors in terms of filtration quality and is the best for obtaining ultra-pure drinking water from communal highways and individual water sources.

Video

How a reverse osmosis system works

How a roll membrane filters water and its device

Track membrane filter - how to use

One of the most popular modern filtering methods. The natural environment is currently in such a state that no one is sure what he actually drinks or uses for food.

Water use around the world has reached a level at which water sources simply do not have time to recover on their own. The level of pollution of natural and waste waters is constantly growing.

Traditional technologies cannot provide the necessary effective water purification. Getting rid of all existing types of pollution requires the use of filter technologies that are themselves environmentally friendly. This makes it necessary to constantly improve new technologies that will allow you to quickly, efficiently and cost-effectively purify natural and waste water.

Membrane water purification system is by far the most advanced technology. Such systems are based on semi-permeable porous membranes through which the water flow passes and purifies it of impurities. Membrane systems trap impurities and act as the finest sieves. Waste retained substances are concentrated in the stream (concentrate), which is not accumulated, but is removed from the system. Purified water passes through the membrane in the form of a filtrate (permeate). The smaller the pores of the membranes, the higher the degree of purification, but also the greater the pressure must be applied for filtration. Membrane water purification systems, depending on the pressure created inside them, are divided into low, medium and high pressure systems. Filters operating with pressure up to 6 atmospheres are most often used to purify fresh water from all kinds of impurities. Medium pressure systems up to 40 atmospheres are used for water demineralization. With high - more than 40 atmospheres - for demineralization of salt solutions or wastewater treatment.

The principle of operation of traditional filters is based on the passage of water through a filter medium, in which pollution eventually accumulates. This leads to the need for regeneration and disinfection of the medium with special solutions or even its replacement. Back in the 18th century, the phenomenon of spontaneous passage of the solvent through the film was discovered. If you take two solutions - less concentrated and more concentrated, and separate them with a film, then the solvent from the less concentrated solution will pass into the more concentrated one.

The phenomenon was called osmosis, and the film was called a membrane. In the sixties, it was discovered that with an increase in pressure in a concentrated solution (above osmotic), the reverse process will occur - solvent molecules begin to move from a concentrated solution to a dilute one. Thus, the phenomenon of reverse osmosis began to be used to purify and desalinate water in submarines. The degree of purification can be adjusted by using membrane filters with pores of different diameters. Ultrafiltration membranes remove microorganisms, organic compounds and colloidal particles, reverse osmosis - up to 97-99% of all impurities, theoretically passing only water molecules.

Membrane purification systems are actively used in the production of food, medicines, electronics, etc. Modern developments can significantly reduce their cost, which made it possible to use them in everyday life for filtering drinking water. He built a mansion with a bathhouse and a swimming pool - do not spare money for water purification for them. Blue water for your own bath will not have a harmful effect on the skin, and a huge pool will look attractive.

Membrane water purification system has a number of advantages: pollution does not accumulate, environmental friendliness, ease of operation and small size and a high degree of automation. This system allows you to get very pure water without impurities. And the service life depends on the composition of the source water. Hardness salts, dissolved iron, and organic compounds have a detrimental effect on them. The filter will last longer if it is made, in the end it will cost less than frequent replacement of cartridges.

We continue the subsection "" with an article. Which, in fact, should have appeared earlier than the article "Ultrafiltration for water disinfection", because ultrafiltration is a subsection of a large group of membrane water purification systems. And, if you notice, we in the "Water" section try to move from the general to the parts. However, ultrafiltration is a special case. And so, in order not to break the sequence, we ran a little ahead. But we are back.

Membrane water purification systems are practically the most advanced water purification technologies (and not only water) that are widely used in industry. Of course, there are more modern technologies that are not related to water - but it will take a lot of time before their mass production.

Why are membrane water purification systems called membrane? Because a membrane is used as a working element. What is a membrane? Membrane- this is a semi-permeable barrier made of a wide variety of materials (metal, plastic, ceramics), which allows something to pass through, but something not. In other words, this barrier allows mixtures to be separated into their constituent components.

A simple example: we have ordinary water. This is nothing but a solution (or mixture) of water and a variety of harmful and unnecessary impurities. And when using membrane water purification systems, impurities are eliminated, and water remains. Clean 🙂

Please note that we didn’t use the word “screened out” for nothing, because the closest household appliance working on a similar technology is flour sieve. So, when we use a sieve, we sift the flour (which passes through a semi-permeable barrier, a sieve), and discard

dirt,
lumps,
cockroaches, etc.

- which, due to their size, do not pass through a semi-permeable barrier.

Precisely because membrane water purification systems use the principle of a sieve, screening out molecules, they are sometimes called " molecular sieve". Of course, strictly speaking, the smallest molecules do not filter out all membrane systems, but only the reverse osmosis system, but these are already nuances. Especially since molecular sieve- it sounds proud 🙂

You can say: "But, excuse me, because water is also, it turns out, a membrane process? After all, there are

on the one hand, dirty water is the same mixture
there is a semi-permeable barrier - a cartridge (on which impurities are retained),
and there is purified water ... "

In fact, in a general theoretical sense, this is exactly what it is. But the membrane and the cartridge are as different as day and night. In particular, by their structure, due to which mechanical filtration cartridges can remove only large impurities (such as sand or rust), and membranes - all much smaller substances.

So, a cartridge is just a bunch of something that prevents dirt from passing through, dirt clogs the cartridge. At their core, early membranes looked and functioned like mechanical cleaning cartridges—and clogged just like conventional cartridges. But gradually the technology for creating membranes improved, and modern membranes do not look like cartridges at all. At a minimum, they are very thin (about the size of a sheet of paper, or a little thicker if you take into account the backing). Well, as a maximum - they separate mixtures much better.

Let's get back to our sieves. Just like a sieve happens

large,
small and
extra small

membranes, in turn, are divided into different categories according to what exactly they let through and what they do not. The ability of a membrane to separate depends on two important things - on the structure of the membrane itself, and on what causes separation.

First, let's figure out what causes separation on the membranes.

Separation on the membranes occurs due to the fact that on the one hand the membrane has more of something, but something is not. And from the side where there is an excess, an effort is made towards the lack. For example, on the one hand there is more alcohol content, and on the other hand there is no alcohol. The membrane passes alcohol, and does not pass everything else. What's happening? Alcohol gradually seeps to the other side in a completely purified form.

What is used to make the membrane have more of something on one side and less on the other? Let's take a look at the sieve as an example. So, Why can a man sift flour?

Well, for starters, he put flour on top of the sieve (that is, excess flour on one side).
Secondly, he left an empty space below so that the flour had a place to pour (that is, where there is no flour).
And finally, the most important thing. A person uses shaking (+ gravity), applies force so that the flour begins to sift.

Thus, the main task of the sieve is performed - to separate flour from cockroaches, flies and pebbles. Which are larger than the cells in the sieve and therefore cannot pass to the other side.

The same is true for membrane technologies. On the one hand, a mixture of substances, among which there are necessary and unnecessary. On the other hand, there is nothing like it. In the best case, there are only necessary (or only unnecessary - depending on what the barrier allows) substances. And, finally, one or another force acts on a mixture of substances. It could be

pressure,
temperature,
concentration,
any other processes.

The result is the same as with a sieve - flies separately, cutlets separately. That is, unnecessary substances in one direction, necessary - in the other.

The most common membranes, the operating force of which is pressure. Simply put, pressure acts on the mixture of substances from one side. These processes have their own scientific name (for those who are interested, baromembrane processes). They also include the already mentioned ultrafiltration. In addition to it, similar membrane water purification systems include:

microfiltration
nanofiltration
hyperfiltration (reverse osmosis).

In general, membrane water purification systems, depending on the diameter of the cells and the size of the removed substances, look like this:

Well, in more detail about the varieties of membrane water purification systems, we will talk in the following articles.

But you can be sure - if you are offered a filter based on membrane systems - this is a deeper cleaning than if it were a mechanical water filter.

Based on materials http://voda.blox.ua/2008/06/Kak-vybrat-filtr-dlya-vody-21.html

Tsugunov Anton Valerievich

Reading time: 5 minutes

Tasteless tap water is the scourge of residents of big cities. Even after boiling, it leaves an unpleasant aftertaste in the mouth. In addition, some experts argue that even boiling cannot cleanse it of harmful impurities and microbes. If you live in an apartment and suffer from bad water, then a membrane filter for water purification will help you.

What is a membrane filter?

All filters perform the function of detaining harmful impurities. As a result, we get delicious water that can be boiled or drunk immediately. The membrane system, operating on the principle of reverse osmosis, does not allow any harmful substances to pass through, does not accumulate them in itself, and, thanks to its design, washes into the drainage. It has pores through which only water and oxygen can pass. There are several types of materials for the production of such a filter: lavsan, polyurethane and others.

The first such systems were invented back in the 19th century, but the prototype of the modern membrane was released only in the 1960s. It is believed that these are the best water purification systems in existence. They trap not only large debris, but also small particles, purifying water at the molecular level.

All major Russian and foreign companies manufacturing water filters have membrane structures in their assortment. First of all, they are in demand among residents of apartments in big cities.

Externally, the device is a plastic cylindrical box, inside which there is a membrane and one or more pre-filters. It is connected to cold water and is displayed on the sink with a separate tap. Each filter has its own service life, as over time it gets dirty and cannot perform its functions.

There are membrane filters that work differently. They are placed in a container with water, it passes through the membrane and, according to the principle of communicating vessels, comes out purified. The use of such a filter is justified in field conditions, when there is no running water nearby.

In the field filter, it is necessary to clean the membrane cartridges from time to time. You can wash them with clean water or use special chemicals. They are selected depending on the type of pollution. Acid removes salts well, and alkaline removes organic and biological compounds.

Varieties by type of membrane

There are several types of membrane filter systems. They differ in structure and pore size. Filters with small holes are considered the best, as they purify water well.

Membrane types:

Microfiltration. Provides rough water purification, used at the preparatory stage. Such a filter will cope with turbid wastewater, but in the future it will require finer purification.
Ultrafiltration. This type of membrane can purify water from macromolecular compounds, bacteria. It is usually used in industrial enterprises, as it does not remove salt from the water.
Nanofiltration. Good for hard domestic water. In addition to bacteria, it removes impurities of chlorine and heavy metals from water.
. Such a system has the smallest openings and retains all substances harmful to humans and contaminants. Salts, bacteria, viruses, oil products are neutralized by 98%. With the help of such filters, it is possible to purify and desalinate sea water; they are used in the production of bottled water, in pharmacology and microbiology.

Types by type of construction

By type of design, filters are divided into:

Tubular. The cleaning element is a porous tube. They can be made of cermet, plastic,. The diameter of the pipe can reach up to several centimeters. There are symmetrical and asymmetric membranes. In the former, the pores are evenly spaced; in the latter, one wall has a greater concentration of holes than the other. Water is supplied under pressure to this pipe, and the output is a pure liquid, and in a separate container - a concentrate of harmful substances.

Roll. This filter is a membrane wound like a roll onto the main pipe. Through a special hole, water enters it and flows in a spiral, being cleansed in parallel. Clean water flows down the main pipe, and harmful substances exit from another hole. Such systems are cheap to manufacture, but quickly become contaminated during operation.
Hollow fiber. They consist of membrane tubes that are placed in a filtration apparatus. This significantly increases the working surface, but such filters quickly become clogged and are difficult to clean.

Disk. They are for laboratory use only and are not used to purify drinking water in the home. The filter element is made in the form of a flat disc. The principle of operation of this design is that water is poured into a reservoir in which a piston with a membrane moves. It can be compared to a household French press. Only the filter has several pistons to increase the amount of filtered water. Clean water goes to the tap to the consumer, and harmful substances settle in a special tank.

Do not worry that all layers of the disc are of chemical origin, the use of such a filter is absolutely safe for health.

Advantages and disadvantages

Compared to other types of filter systems, the membrane design has the following advantages:

Ease of operation and maintenance.
Good degree of cleaning.
Small sizes.
The presence of hiking varieties.

Some industries place higher demands on water quality. For example, for the preparation of medicines, microcircuits, it must be distilled. This quality can be obtained using membrane methods of water purification.

These include: microfiltration, ultrafiltration, reverse osmosis, nanofiltration, electrodialysis. The principle of operation of membrane water purification systems is based on the ability of specially designed membranes to pass water molecules and retain molecules and ions of salts and other substances dissolved in water. The water that has passed through the membrane is called the filtrate, and the remaining water is called the concentrate.

On the picture: Membrane element - Filmtec BW

Theory of semipermeable membranes

There are several theories explaining the principle of operation of semipermeable membranes:

1) Water molecules are smaller in size than the molecules of substances dissolved in it, so they seep through the pores of the membrane, but there are no impurities;

2) Water diffuses through the partition faster due to the higher diffusion coefficient;

3) Water, which is in the thickness of the membrane in a capillary or bound state, constantly forms new hydrogen bonds with water molecules in the concentrate and thus “pulls out” only pure water, because salts cannot form hydrogen bonds.

Material and classification of membranes

Semi-permeable membranes are the main element in the system. The result of softening (removal of salts) directly depends on their quality and type. They must be sufficiently strong, selective (capable of passing some substances and retaining others), chemically resistant to salt solutions, and durable. The main materials for the production of membranes: synthetic and vegetable polymers, resins, silicate glasses, metals, ceramic materials, walls of internal organs, etc. The pore size of the membranes ranges from 0.1 to 10 µm.

It is believed that the separation of membrane purification into separate methods is based on the pore size of the membranes (in ascending order):

1) Reverse osmosis;

2) Nanofiltration;

3) Ultrafiltration;

4) Microfiltration.

Accordingly, the methods give different quality of cleaning and have different applications.

Reverse osmosis and ultrafiltration - in pharmacology, medicine, food industry;

microfiltration and nanofiltration - iron removal of water. In some literature, reverse osmosis and ultrafiltration are taught as synonyms. However, they all have the same scheme: the pumps supply the purified water under the required pressure to the tank, where it passes through the membrane. The difference in electrodialysis is the use of electric current as a driving force instead of pressure. In this case, electrodes (cathode and anode) are lowered into the container, which cause the hydrolysis of salts and the directed movement of ions. Typically, electrodialysis plants have not one, but several semi-permeable membranes.

Membrane technologies differ from simple filtration in that contaminants do not accumulate in the membrane, but remain at its surface in the liquid. They are removed by the following methods: cross flow, backwashing, ultrasonication.