Membrane water filtration. Household membrane filters - pros and cons. Flat Disc Membrane Filters

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 taste in the mouth. In addition, some experts claim 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 retaining harmful impurities. At the end we get tasty water that you can boil or drink right away. The membrane system, operating on the principle of reverse osmosis, does not allow any harmful substances to pass through, does not accumulate them, and, thanks to its design, washes them into the drain. 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 a modern membrane was released only in the 1960s. It is believed that these are the best water purification systems of all existing ones. They retain not only large debris, but also small particles, purifying water at the molecular level.

All major Russian and foreign companies producing water filters have membrane designs in their product range. First of all, they are in demand among apartment residents in big cities.

Externally, the device is a plastic cylindrical box, inside of which there is a membrane and one or more prefilters. It is connected to cold water and discharged to the sink with a separate tap. Each filter has its own service life, since over time it becomes 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 cleaned. The use of such a filter is justified in camping conditions when there is no running water nearby.

In a travel 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 contamination. Acidic ones remove salts well, and alkaline ones remove organic and biological compounds.

Varieties by membrane type

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

Membrane types:

1. Microfiltration. Provides rough water purification and is used at the preparatory stage. Such a filter will cope with cloudy wastewater, but in the future it will require more subtle cleaning.
2. Ultrafiltration. This type of membrane can purify water from high molecular weight compounds and bacteria. It is usually used in industrial enterprises, as it does not remove salts from water.
3. Nanofiltration. Well suited for hard domestic water. In addition to bacteria, it removes chlorine and heavy metals from water.
4. . This system has the smallest holes and traps all substances and contaminants harmful to humans. Salts, bacteria, viruses, and petroleum products are neutralized by 98%. With the help of such filters, sea water can be purified and desalinated; they are used in the production of bottled water, in pharmacology and microbiology.

Types by type of construction

According to the type of design, filters are divided into:

• Tubular. The cleaning element consists of porous tubes. They can be made of metal-ceramic, plastic,... The diameter of the pipe can reach several centimeters. There are symmetrical and asymmetrical membranes. In the former, the pores are evenly distributed, in the latter, one wall has a greater concentration of holes than the other. Water is supplied under pressure into this pipe, and the output is pure liquid, and in a separate container - a concentrate of harmful substances.

• Rolled. 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, simultaneously being purified. Clean water flows through the main pipe, and harmful substances exit from another hole. Such systems are cheap to produce, but quickly become dirty 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 domestic drinking water. The filter element is made in the form of a flat disk. The operating principle 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 consumer's tap, and harmful substances are deposited in a special tank.

Do not worry that all layers of the disk 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:

• Easy to operate and maintain.
• Good degree of cleaning.
• Small sizes.
• Availability of hiking varieties.

Entering Houses And apartments drinking water contains many impurities, dissolved chemicals and bacteria. Most elements have a negative impact on human health, especially young children. Constant consumption of water of inadequate quality leads to the development of dangerous chronic diseases. The optimal solution to the problem is to install a membrane filter that can purify the water as much as possible and improve its drinking quality.

What is a membrane and how does it work

The main element of membrane filters for apartments is suburban at home or industrial The enterprise is a membrane - an ultra-porous thin film that allows oxygen and water to pass through. All organic and inorganic substances whose particle size is larger than the pore diameter remain on the surface of this element. The movement of the liquid is realized according to a tangential scheme - water collects on both sides of the membrane. A larger volume is supplied for cleaning through the filter and enters the storage tank, and the remaining part of the liquid is used for cleansing film from accumulated dirt with a directed flow and its removal into the sewer system.

Membrane filtration systems are designed not only for household needs, but also to obtain ultrapure water for technical and medical purposes, desalination of sea water, and neutralization of wastewater. Track The membrane, in a special configuration, is also used for water purification in emergency situations; its service life allows for its reusable use.

The membrane for water purification is made mainly from lavsan, polysulfone, polypropylene, acetate, ceramics, but other materials with similar properties are also used.

Filtration system installed under the sink

A device with a membrane for water purification household purpose is mounted under the sink and connected to the pipe supplying cold water to the apartment or house. The cleaning process includes several stages:

1. Rough cleaning – retention of solids, partial removal of chlorine used to disinfect tap water;
2. Filtration through a membrane – removal of most microbiological and chemical contaminants;
3. Accumulation of purified water in the tank;
4. Additional mineralization of liquid (when installing a special cartridge);
5. Improving the organoleptic qualities of water - filtering through a so-called post-filter made of pressed activated carbon;
6. Supply of purified water through a separate tap, additionally installed next to the sink.

Membrane filtration devices are also produced, the operation of which is based on a completely different principle. A working element is placed in a container with water, into which the water to be purified flows, while the contaminants remain in the body of the device. The filtered liquid is discharged through a special hose into another container. Such membrane filters are indispensable at the dacha or on a hike when there is no way to connect to a centralized water supply.

The disadvantages of water treatment devices of this type are the need for regular cleaning of membranes using special means, as well as a short service life.

The performance of membrane filters depends on several factors:

• source water quality;
• type of cleaning membrane film;
• the level of pressure under which water flows;
• membrane thickness and area;
• water temperature.

Most water treatment plants, for example, brand " Geyser”, are supplied with all the parts necessary for connection - hoses, fittings, tap. In Tyumen, you can purchase any filters that implement membrane water purification technology from the KVANTA+ company at the best prices in the city.

Types of membrane filters

By membrane type

• "micro"

Pore ​​sizes in membranes of this type vary from 0.1 to 1.0 µm. The film is capable of retaining fine impurities and colloidal particles that impair water transparency.

Microfiltration membranes are used for rough cleaning: preparation for the next stage of filtration or for wastewater treatment.

• "ultra"

Ultrafiltration membranes with pores with a diameter of 0.02-0.1 microns retain high-molecular compounds and colloidal impurities, algae, bacteria, macromolecules, but are powerless against dissolved salts.

Such membranes are installed in household and industrial filters designed to purify water from mechanical impurities while maintaining the salt composition.

• "nano"

In nanofiltration membranes, the pore size is 0.001-0.02 microns. They are used to purify hard water and soften it, removing about 90% of organochlorine substances and heavy metal ions.
When using flow filters with a nanomembrane, the salt composition of water changes slightly less than when using reverse osmosis membranes.

• reverse osmosis membrane filters

Reverse osmosis membranes, characterized by the smallest pores (0.0001-0.001 microns), are capable of filtering:

• all viruses and bacteria;
• organic impurities that affect the color of water;
• a significant portion of dissolved salts;
• heavy metals and iron;
• pesticides, herbicides, insecticides.

Membrane elements of this type retain almost all impurities present in the liquid, allowing only pure water molecules, gases dissolved in it and a small percentage of mineral salts to pass through.

Filters with a reverse osmosis membrane are designed to produce high-quality water not only for domestic purposes, but also for production beverages, pharmaceutical, food, medical and electronics industry.

Due to their extremely small size, the pores of the reverse osmosis membrane are subject to periodic clogging with large particles. For effective and long-term operation of the filter, preliminary preparation of the purified tap water is required, namely:

• coarse filtration;
• fine cleaning;
• softening hard water.

In this case, the supply of pre-prepared liquid to the membrane must be done under a pressure of at least 3 bar, otherwise filtration will be carried out too slowly. If the pressure in the system is too low, special pumps are used to increase it to the required level.

By design type

Filters are equipped with membrane elements having different shapes:

• flat (disc);
• tubular;
• roll;
• hollow fiber.

Different types of membrane filters have different working surface areas.

Flat

Flat membrane elements are manufactured in the form of films of the following types:

• membranes with a substrate, consisting of a working layer and a substrate made of large-porous material;
• membranes without a substrate, made of a homogeneous substance;
• reinforced, in which porous material is applied to a fabric base.

Flat reverse osmosis membranes are most often thin-film composite and consist of three layers

As a base (1st layer), a polymer material (polystyrene) is used, onto which polysulfone with micropores (2) is applied. The second layer allows water to pass through well, but does not compress or deform under pressure. The third layer, which acts as a barrier, is made of aromatic polyamide.

Disc membranes are used for the production of filter-press devices.

The filter consists of membrane elements (1), porous plates (2), two covers (4, 5), pins (6), and a collector (7).

Tubular

A membrane of this type is a tube made of porous material (metal fabric, metal-ceramics, ceramics, plastic).

Membrane tubular filters can be symmetrical, in which the porosity is the same throughout the entire volume, or asymmetrical, in which one of the surfaces is covered with a layer of denser material. It is the dense layer that is working and traps pollutants; the material with larger pores is the substrate and performs drainage functions.

Cleaning the liquid is carried out as follows. Water, passing through a tube (1) with a semi-permeable membrane element, is filtered and collected in a container (2), while the concentrated pollutant comes out of a separate tube. The pump (3) increases the pressure on the incoming solution, after which the throttle (4) releases the contaminant at the outlet.

Rolled

A membrane filter device consists of a drainage tube with three layers of material wound around it: the main membrane, and drainage gaskets in which the membrane material is wrapped on both sides.

Water is supplied from the end of the filter, passes in a spiral through the membrane and gaskets, and then enters the drainage pipe. Pollutants dissolved in water are removed from the roll filter from the other end.

Membrane roll filters have a convenient design. Thin the working layer makes this type of filter one of the most productive, and its pores rarely become clogged.

Hollow fiber

Hollow fiber membranes are tubes with a diameter of about 1 mm with porous walls. The size of the micro-holes through which water is filtered prevents even the smallest contaminants from penetrating through them.

Hollow fiber membrane filters can:

The only brand of water filters in Russia that uses membranes of this type is Aquaphor. The technology is used for final water treatment in “Crystal” series filters, in which a hollow fiber membrane element is combined with a carbon block in one module. You can purchase Aquaphor membrane filters and systems of other popular brands at the best prices in Tyumen from the Kvanta+ company.

Household or ceramic

Ceramic filters are designed for post-purification of water supplied from a centralized water supply system.

The popularity of membrane water treatment devices of this type is due to several reasons:

• performing water purification using ceramic membrane elements without the use of reagents;
• high-quality neutralization of foreign tastes and odors, impurities, bacterial microflora;
• the presence of protection against drying out;
• resistance of the outer surface to abrasive cleaning agents;
• no need to replace membrane elements.

The membrane unit is placed in a housing with a diameter of up to 10 cm and a length of up to 35 cm, made of stainless food steel. The membrane is a bundle of finely porous ceramic tubes through which liquid is supplied under pressure.

The advantages of purification in membrane ceramic filters are considered to be the production of high-quality drinking water without impurities of iron and hardness salts. The systems are not demanding on the quality of the products coming from wells or main water supply systems have a long service life.

Ceramic membranes are made of durable but fragile material, therefore the main conditions for durability and reliability of cleaning are proper transportation of filters, installation and cleaning. To clean the device, rinse it with clean flow-through water using a soft sponge or brush. Cleaning agents should not be used to avoid contamination of drinking water. High-capacity membrane water treatment plants are cleaned by backwashing with demineralized water.

Advantages and disadvantages

Membrane filters differ from other types of water treatment systems in their high efficiency - due to the small pore sizes, the water passing through installation the water becomes absolutely clean and suitable for any needs.

A significant disadvantage of membrane devices is the relatively high cost, which is compensated by a lot of advantages:

• high quality water purified using membrane technology;
• ease of operation and maintenance;
• partial preservation of the salt composition of the liquid after purification;
• removal of the smallest particles suspended in water;
• compact size;

Disadvantages include:

• relatively low water filtration rate; to correct it, the installation of storage tanks is required;
• the need for regular replacement or cleaning of membrane blocks.

Operating conditions of the membrane filter

The service life of any membrane filter, the frequency of cleaning and replacement of working elements are determined by its operating conditions:

• quality of water to be treated;
• volume of fluid passed through;
• pressure in the water supply system.

The exact time frame for cleaning or replacing the membrane element cannot be determined in advance.

If the owner has the financial opportunity, it is recommended to change the membrane unit in filtration devices every year or if the taste of the water deteriorates or its pressure decreases. If annual replacement is burdensome, the membrane should at least be washed. The design of some models provides the possibility of backwashing (by turning on the reverse water supply mode) or cleaning by changing the pressure of the supply flow.

It is almost impossible to wash membrane elements at home, but in the event of a temporary lack of funds, you can try to at least slightly improve the quality of filtered water.

The filter film is thoroughly rinsed under the pressure of warm running water or in a soap solution and put back. In case of heavy contamination, the membrane unit is immersed in warm water with the addition of citric acid, and after being put back into the filter, it is washed for half an hour to completely remove the lemon.

Industrial membranes installed on production lines are washed with a special solution of acid and alkali.

How to choose a membrane filter

In addition to membrane filters, there are many other filters that work on a different principle. The main factor for selecting a membrane filter is what kind of impurities need to be removed from the water, as well as the required filter performance. Before choosing a treatment system, it is necessary to determine which substances are present in the water in the largest quantities and compare the indicator with the maximum permissible value according to SanPin 2.1.4.1074-01. It is also advisable to perform a bacteriological analysis of the water.

For example, if the content of heavy metal salts in water is within the limits established by SanPin, there is no need to install a membrane filter device. In this case, you can get by with a regular carbon sorption filter.

When purchasing a reverse osmosis membrane filter, you should take into account that its operation requires preliminary purification of the incoming water, which leads to the cost of purchasing and installing additional filters. The operation of reverse osmosis technology is impossible at a system pressure below 3 bar, since water will not be able to pass through the pores of the membrane material at the required speed. Low pressure will either stop the water flow completely or slow down the cleaning process.

Filters with a reverse osmosis membrane are sold as a single system consisting of several cleaning units. Each node is located in a separate housing, which has its own marking. The more complex or technologically advanced water purification is meant, the higher the cost of the device and the more difficult the installation.

When selecting a filtration device with a membrane, you must:

• determine its purpose - for wastewater treatment, obtaining water for household needs, drinking and cooking, use in the laboratory, etc.;
• take into account that the price of a filter is directly proportional to its capabilities;
• To reduce water hardness, a nanomembrane is sufficient in the filter;
• For a filter device operating on the principle of reverse osmosis, it is advisable to retrofit it with a mineralizer;
• When purifying heavily contaminated water, it requires additional passage through microfiltration membranes.

Myths about the membrane filter

Membrane filters make water “dead”

A filtration system that performs its functions well allows you to obtain water that can be used for both drinking and technical purposes. To improve the quality of already purified water, systems operating on the principle of reverse osmosis are used. Along with purification from all harmful impurities, complete or partial desalination of water and removal of useful substances occurs. Such water is considered “dead”, but not dangerous.

In fact, the water after purification is not “dead” at all, but desalted and still contains a certain amount of dissolved substances. This water retains all the taste qualities of food and is perfect for gourmets - for preparing the best varieties of tea or coffee, other drinks, and cooking. Since a person receives the main amount of microelements and minerals from food, food and drinks can be prepared using “dead” water, and for drinking it is advisable to pass it through a mineralizer that adds useful substances.

Filtered water somehow affects food

During the filtration process, substances that adversely affect the taste of cooked dishes are removed from the water. The full change in taste is felt in the prepared drink, for example, coffee. Water passed through a membrane filter is considered the optimal basis for making juices and cocktails.

Water purified using reverse osmosis technology does not leave lime deposits inside teapots and other utensils, unlike ordinary tap water.

Tap water contains many harmful impurities and microorganisms. According to experts, ordinary boiling is not able to completely rid water of harmful impurities. And the price of the issue is quite high. The entry of these substances and bacteria into the body can cause irreparable harm to health.

To solve the problem, many resort to installing high-purity filters with membranes. The practice of purchasing bottled water is also widespread. However, in the latter case, there are questions about the quality of water purification. In addition, it is difficult to satisfy all needs with several bottles, and the price for such water is not small. As for membrane filters, they purify water from suspended matter, impurities, bacterial cells and viral particles and preserve the structure and properties of water.

Types of membrane filters

The history of the appearance of membranes dates back to the 19th century. At that time they were made from fiber, but were not widely used. Only in the 60s was a membrane prototype of modern devices made.

The membrane is an ultra-thin synthetic film with pores that is capable of permeating water and oxygen while retaining impurities. The membrane is made from polypropylene, lavsan, cellulose acetate, etc.

The main property of water purification filters is the retention of small colloidal particles and compounds.

Membrane filters for water purification vary in pore size and membrane design. Reducing the size of microholes in the membrane leads to an increase in water pressure in the filter. The number of filter cleaning stages increases the quality of water and the price of equipment.

Membranes are classified according to pore size:

1. Membranes for microfiltration. The size of the membrane microholes is 0.1 – 1.0 µm. Membranes are designed for the primary purification of water from particles and impurities that cause turbidity. In fact, this type of membrane is a preparatory step before subsequent water filtration. The membrane is often used for wastewater treatment.
2. Ultrafiltration membrane filters – 0.02 – 0.1 microns. These membranes allow you to filter out colloidal particles and high-molecular compounds, bacterial cells. Membranes are not able to stop salts dissolved in water. Basically, ultrafiltration membranes are installed in industrial and household filters to purify water from insoluble impurities while maintaining the salt composition.
3. Nanofiltration membrane filters – 0.001 – 0.02 microns. Membranes with such pore sizes are designed to soften water with high hardness levels. Membranes retain organochlorine substances and heavy metal ions. The degree of water purification from the latter reaches 30%. At the same time, the membrane allows 90% of the salts dissolved in water to pass through.
4. Reverse osmosis membrane filters. These membranes have the smallest holes - 0.0001 - 0.001 microns, therefore they are characterized by selective water purification properties. The membranes are designed to remove most impurities and solutes. The membranes in the filter allow water, gases and some salts to pass through. When seawater is filtered in this way, it is desalinated by 97%. Purification on such membranes leads to deep desalting, removal of viral particles, bacterial cells, petroleum products, etc. The filter produces high quality water, which is used for bottling, beverage production, pharmaceutical, food and electronics industries, and for microbiological purposes. The price of such filters with a reverse osmosis membrane is quite high. It is recommended to carry out mineralization after the filter.

The price for any type of filter can be found on the manufacturer’s website and read the detailed description.

Principle of operation

The membrane filter is an ultra-thin membrane with a large number of pores. The membrane in the filter provides the highest degree of water purification. Also, after a filter with a membrane, the composition of salts and microelements is almost completely preserved.

As a result of water filtration through a membrane, it is characterized by a high level of purification, biological value and saturation with minerals.

In membrane filters, there is a “tangential” system of water movement near the membrane and there is one inlet and two outlets. This means that water collects on both sides of the membrane. One part of the water is purified through a membrane and discharged into a container. The other is designed to wash away sediment from the surface of the membrane and discharge it into the drainage zone of the filter.

The performance of a membrane filter depends on:

1. Membrane area.
2. Filter pressure level.
3. Membrane thickness.
4. Water temperatures.
5. Amount of impurities.

Also common in camping conditions are membranes for water purification, for example, Nerox, which work on a completely different principle. A membrane filter is placed in a vessel with dirty water. In this case, clean water is discharged through a special hose into another vessel. The disadvantage of this method is the need to periodically clean the membrane from contamination. This is done manually using special tools. Nerox filter membranes can be washed with plain water.

Inorganic sediment from the membrane in the filter is removed with acidic agents. Organic compounds and biomass from the membrane in the filter are washed out with alkaline compounds.

Advantages and disadvantages

Advantages of membrane filters for water purification:

1. Ease of use and maintenance of membranes.
2. High level of water purification in filters with a membrane.
3. Preservation of the salt composition of water after the filter.
4. Membranes remove even the smallest impurities.
5. Many membrane filters are compact in size (Nerox).
6. Some membrane filters can be used in the field and for wastewater treatment.
7. Some filters, such as Nerox, do not require replacement membranes.

The disadvantages of membrane filters include their high cost. Also, some filters have a low water filtration rate, which requires the installation of storage tanks.

Ultrafiltration membrane filter: video

In the video presented on the website, you can clearly see and study reviews of how an ultrafiltration membrane filter for water purification works. It also talks about the benefits.

Separation by design type

According to the design of the membrane filter, there are:

1. Flat disc membranes are available:

• from one substance (substrate-free membranes),
• on a fabric basis and porous raw materials (reinforced membranes),
• from large-porous raw materials and working layer (substrate membranes).

Disc reverse osmosis membrane filters are most often thin composite membranes, each layer of which is made of different compounds.

1. Tubular membranes are tubes made of porous materials (plastic, ceramic, metal, metal-ceramic, etc.). The diameter of the membrane reaches several centimeters.

There are symmetrical and asymmetrical tubular membranes. In the first case, the density of the membrane pores throughout the entire volume is the same. Asymmetric membranes have a denser material on one surface. It is working and shows the degree of water purification. The role of the large-porous membrane in the filter is reduced to the passage of filtered water.

1. Rolled membrane filters for water purification are a system in which a membrane is screwed onto a drainage hose. When water is supplied, it flows in a spiral. It then collects in the drainage hose and comes out the other end as a concentrate.

The convenient shape and ultra-thin working layer guarantee the membrane filter high performance and low susceptibility to clogging. The membrane can be used for wastewater treatment.

Among the advantages of a membrane filter are an increased packaging frequency and a low degree of metal consumption of the membrane.

1. Hollow fiber membranes, which are made in the form of tubes. A number of membranes are placed in a device to filter water. The result is a filter with increased working surface and increased productivity.

The disadvantage of membranes is the difficulty of controlling the flow of water along the fibers. Therefore, such membrane filters are prone to clogging. Membranes are not recommended for wastewater treatment. Also, judging by the reviews, the membranes are difficult to clean. And the price of filters is high.

In this regard, before supplying water to hollow fiber membrane filters, it must first be treated.

Prices

The cost of a membrane filter depends on the performance of the filter and the degree of water contamination. The table below shows approximate prices for the most popular filters.

More detailed information about each type of filters, membranes and price can be found on the manufacturer’s website.

Modern water supply systems have made significant progress in their development. Now a person can create a completely autonomous water supply complex without special expenses. Water quality, on the other hand, does not improve over time. Which leads to the need to use special filters to purify the liquid.

One of the most popular and effective filters of this type are membrane ones, which are capable of purifying water at the molecular level. We will talk about them now.

1 Features and Operating Principle

Membrane filters for water purification belong to the so-called “deep purification systems” and are used to rid water of harmful components, often as part of water treatment systems (several sequential purification devices for water for various purposes).

The main element of such a filter, as well as a filter using technology, is a membrane, which is made of synthetic materials. The membrane has holes (pores) and when water flows through the membrane, it retains particles that are larger than the diameter of the pores. Thus, water free of impurities comes out.

Purification systems based on filtration membranes with different pore diameters are used for domestic needs, as well as for producing ultrapure water for medical and technical purposes, desalination of sea water,

Also, a track membrane in a special configuration can be used for water purification in emergency situations, while its service life allows reusable use.

1.1 Types of membrane water filters

The membranes with which the filter is equipped may differ in structure and pore diameter. The membrane can be:

• Microfiltration (pores - up to 4 microns);
• Ultrafiltration (from 0.2 to 0.02 microns);
• Nanofiltration (or track) (0.01 – 0.001 microns);
• Reverse osmosis (0.001 – 0.0001 microns).

Depending on the pore size, the purpose of the filter also changes: it can purify water from colloidal contaminants (the largest particles), it can stop heavy metal ions, or it can produce almost complete demineralization of water (reverse osmosis).

Typically, a membrane filter operating using reverse osmosis technology is classified as a separate type, but these units can be part of one purification system. Also, it is worth considering that a membrane with a smaller pore size requires pre-filtration to be carried out before passing through it - so a pre-filtration system will be needed.

Membranes also differ in the shape and structure of the fiber that is used to create them. As a result, each type of membrane has a different working area, which directly affects the performance of the filter (how it works and at what speed).

The following types of membranes for filters are distinguished:

• Hollow fiber membranes;
• Tubular membranes;
• Roll type membranes;
• Flat disc-shaped membranes.

Accordingly, the membrane-type filter can be installed in a replaceable cartridge housing compatible with a sequential filtration system.

1.2 Pros and cons

Filters that use ultrafiltration membrane or filters using reverse osmosis technology are suitable for filtering drinking water. At the same time, the second type also completely removes scale. It should be noted that tap water that has been passed through both varieties is suitable for drinking without boiling.

One of the disadvantages of using membrane water filters is usually that the degree of demineralization of water may be excessive, since the membrane also does not allow substances useful for the human body to pass through.

There is a dependence on the pore size of the membrane, the working area and the pressure in the water supply system - these properties should be taken into account when installing a membrane filter as a component of complex water purification. This type of filter requires access to wastewater drainage, which involves additional work during installation.

Membranes with large pores do not require additional pressure to operate. Typically, the thinner the membrane, the higher its performance, but the smaller its pores, the more additional pressure must be applied when the filter is running to maintain water pressure.

1.3 How to choose and what is better to buy?

In addition to membrane filters, there are others that operate on a different principle. Therefore, the first determining factor will be what impurities or harmful components need to be removed from the water. Depending on where exactly the water differs from sanitary standards, you should select a treatment system.

Cartridge-type filters provide the ability to install several different units (i.e., this is not one housing). It is quite possible that in a particular case, for example, it will be sufficient, but a filter based on an ultrafiltration membrane or a filter operating using reverse osmosis technology is not necessary.

For example, such a situation may arise when the content of heavy metal salts in water is within the sanitary norm.

Installing a filter operating using reverse osmosis technology will necessarily require pre-filtration of the supplied water (that is, installation of additional filters) and creating a pressure not lower than a certain one (usually at least 3 bar).

Without such pressure in the system, the operation of reverse osmosis technology is simply impossible, since water will not be able to pass through small membranes at the proper speed. And this will lead either to a slowdown in the cleaning processes or to their complete stop.

2 How to clean the filtration membrane?

The need to clean or replace the filter membrane and its service life largely depend on the quality of the water supplied to the filter, as well as its quantity. Therefore, determining the universal time when the membrane needs to be replaced or cleaned is quite difficult (on average, from six months to four years).

In the case when the user is not short of money, the membrane in the filter can be simply replaced (in a cartridge-type filter it is enough to simply replace one block with another). One of the options for solving this problem may be not replacing, but washing the filter membrane.

Filters from some manufacturers may also provide for membrane flushing, the mode of which involves supplying water to the membrane from the side opposite to the normal flow or a sharp release of pressure.

Washing the membrane in this way can be organized directly by the user (if the housing and filter design allow this). The membrane is removed and rinsed simply in water, water and soap, or water with citric acid. In addition, the membrane can be washed by directing a stream of water of the same composition onto it.

It is also possible to completely immerse the filter housing in a five percent solution of citric acid and warm water for about five hours, after which it is washed with clean water. After this, the water that comes from the filter cannot be used for the first half hour.

Carrying out such procedures periodically will significantly increase the service life of the membrane. Outside the home, washing (regeneration) of the membrane is done using more complex alkaline or acidic reagents; it is not possible to clean the membrane in this way at home.

The procedure for cleaning industrial membranes that are used for desalination of water or for filtering wastewater is quite complex and is carried out using the operating modes provided by the mechanisms themselves.

2.1 Installation of a membrane filter - stages and features of the process

In the case of household and self-installation of a membrane filter or a filter operating using reverse osmosis technology (usually placed “under the sink”, directly to the faucet that is planned to be used as drinking water, and connected to an elbow for draining wastewater), you need to perform a certain sequence of actions.

It is necessary to clean the space where the filter will be placed and turn off the water. Next, you should unscrew the connection that goes from the line to the mixer.

A threaded tee and a ball valve are installed in the line, which will allow water to be supplied to the filter. Also, a tap for drinking water is installed in the sink and a hole is drilled in the elbow for waste water. If the pressure in the main water supply system is more than 6 bar, you may need to install a pressure reducer (check with a pressure gauge).

Next, the filter operating using reverse osmosis technology is assembled according to the instructions and the filter is connected to the water supply and wastewater drainage system. In this case, you need to ensure that, according to the diagram, the waste water terminals and the supply hose to the drinking water tap are also correctly connected.

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Types of household water filters

Cumulative

• Filter jugs. One of the most popular varieties due to its mobility, accessibility and ease of maintenance. The design consists, in fact, of a jug and an upper funnel with a lid and a cleaning cartridge installed inside. Water flows through several filter layers, is purified and ends up in a storage tank. Cartridges can be of several types - universal or with specific properties (for example, reducing water hardness, removing iron, etc.);
• Dispensers-cleaners. The principle of operation is also simple and unpretentious - water is poured from above and, under its own weight, passes through the filter system into the lower tank. The main difference from jugs is the noticeably larger volume and the presence of a drain tap.

Flow-through

• Faucet attachments. Inexpensive and easy-to-install filters with a one- or two-stage cleaning system, which usually boils down to neutralizing chlorine and rust. Cassettes don't last long, but they are available and inexpensive;
• Tabletop systems “next to the sink”. Representatives of this category have average performance, differ in the method and degree of water filtration, and, accordingly, in price. Disadvantage - they take up a lot of space in the kitchen;
• Under-sink systems. The most effective devices with multi-stage filtration, including disinfection and water softening. The most advanced varieties are models with reverse osmosis, the key component of which is a semi-permeable membrane that allows only water molecules to pass through. But bacteria, viruses, heavy metals and other harmful impurities are not given a chance to “leak through”. The degree of purification is so high that additional mineralization is used to give the water drinking qualities.
• Main or prefilters. They are installed directly into the water supply system and can be used both for individual taps and for the entire apartment or house. The filter element is a special cartridge, and in the simplest examples, a regular metal mesh.