The use of various types of filtering devices is the main way to obtain clean drinking water, with carbon containing systems being the most common. It is useful for a consumer who is independently engaged in water purification from a public water main or an individual source of water supply (well, well) to know for effective use what cleans a carbon water filter, its varieties and applications.
The use of charcoal for water purification has been known since ancient times, even now craftsmen, in order to save money, make similar charcoal purification filters on their own. It is also difficult to imagine modern water purification filters without the presence of carbon fillers; they are used both independently and as part of various types of filter systems.
What is a carbon filter
The work of coal as a filter element is based on its sorption qualities – the ability to absorb various components from water due to its porous structure. According to the nature of the binding of substances in the aquatic environment (sorbates), activated carbon refers to adsorbents – substances that concentrate the sorbate on the phase interface (the boundary between the solid surface of coal particles and liquid) or absorb it with their surface layer. That is, coal is different from materials that absorb various substances from the aquatic environment and distribute them throughout the volume (this effect is called absorption).
Due to the adsorption qualities of coal, that is, the concentration of harmful substances on the surface, it becomes clear the principle of operation of many carbon filters, which use the technology of periodic cleaning and restoration of the initial state of the contaminated carbon-containing filler by washing with a strong reverse flow of water.
Unlike the technology of ancient and self-made carbon filters, modern water treatment devices use activated carbon – a porous component obtained by special processing of carbon-containing materials: charcoal, coal, coke from oil refining, coconut shells. After processing, the material receives a huge number of pores, its surface area increases in the same proportion. Depending on the technological process of charcoal activation, 1 gram of the substance has an area of 500 to 2200 square meters – this significantly increases its adsorption qualities compared to conventional untreated charcoal material.
In addition to the adsorption process, due to which coal removes polluting components from water, when it interacts with certain substances, a chemical reaction occurs – catalytic oxidation.
As a result of such an oxidative reaction, free chlorine is converted into hydrochloric acid, which is then neutralized by the bicarbonate alkalinity of the water. The considered process of elimination of chlorine is called dechlorination, while activated carbon does not decompose and is not consumed.
Thus, the strong oxidizing agents chlorine and chloramine contained in water, getting into the activated carbon medium, are removed from it due to catalytic oxidation, and other organic and inorganic components are absorbed when the adsorption mechanism is triggered.
Although tap water in municipal networks meets most of the requirements of state standards (GOST), sanitary norms and rules (SanPiN), higher international standards make it undrinkable for a wide range of parameters. The use of carbon filters can bring health benefits by removing the following negative properties from water or significantly reducing the concentration of the following types of contaminants:
Free chlorine . An unhealthy substance that impairs the smell and taste of water is contained in it as a result of disinfection used to exterminate a large number of different types of pathogens and bacteria. Chlorine-containing components are removed by catalytic oxidation.
Organics . These types of pollution are present in water due to the ingress of organic decay products of living organisms into it, their waste products, and are adsorbed during filtration.
organochlorine compounds . As a result of complex chemical reactions of free chlorine with organic matter present in water (human and animal waste products, decay products of living organisms), organic compounds that are very harmful to human health are formed – trihalomethanes, which include chloroform, bromodichloromethane, dibromochloromethane and tribromomethane. They accumulate in vital organs (liver, kidneys) and can cause cancer due to high carcinogenic properties.
Petroleum products and inorganic compounds . Due to adsorption, carbon filters effectively absorb gasoline, fuel oil, phenols, benzenes, and hydrogen sulfide from water. Purification reduces the levels of oxidizability, the concentration of radionuclides contained in the water, ammonia, nitrates, pesticides, epoxides and their derivatives.
Smells and tastes . Carbon filter for water treatment, along with the elimination of chlorine, adsorption of insoluble salts of iron, lime, bacteria and microorganisms, improves its taste and eliminates the smell of chlorine and mud.
Chromaticity . Coal absorbs organic and clay suspensions, green algae, insoluble ferric iron, which gives the aquatic environment a reddish tint – these factors contribute to a decrease in color and increase the transparency of water.
Types of coal used
The raw materials for the production of activated carbon are natural materials, they are first charred and then subjected to an activation procedure. The essence of the process is to open microscopic pores closed in ordinary coal. Activation is carried out by the thermochemical method, impregnating the coal mass with potassium carbonate, zinc chloride or other solutions, after which it is subjected to heat treatment without the presence of air.
The second method of coal activation is its treatment with superheated steam, carbon dioxide or their mixture at a temperature of 800-850 °C. Since it is difficult to obtain a vaporous medium from water with such temperature parameters, technology is practiced with additional air supply to the working area, while part of the processed coal burns out, which significantly reduces the yield of the activated component.
The technology makes it possible to obtain a specific surface area from 1800 to 2200 square meters per 1 g of the substance from the best brands of activated carbon. The pores themselves are divided into the following categories according to their diameter:
- Macro – have a diameter of more than 50 nanometers (nm), pores of this size are typical for activated carbon fillings based on wood raw materials.
- Meso – pores ranging in size from 2 to 50 nm, are present in overwhelming quantities in the activated composition obtained from coal.
- Micro -pores with a diameter of less than 2 nm are found in activated carbon obtained from coconut shells.
The raw materials for the production of activated carbon are the following materials:
- Wood , it is charred without air access, and then activated. Coal with large pores obtained from it is used for dechlorination of water and its rough cleaning at the preliminary stage at the entrance of the water supply to the house, in home-made treatment devices.
- Stone or bituminous coal , after activation, is able to trap pesticides, phenols, clarify and rid water of chlorine and its smell.
- Coconut shell . Activated carbon obtained from this material is used in most water filter systems. Due to small pores and a correspondingly large working surface, the component activated from charred coconut shell is able to absorb a significant amount and a wide range of elements harmful to human health from the aquatic environment.
Additional components of carbon filters
In addition to activated carbon, the following additional components are often used in filters:
Synthetic fibers . Synthetic materials are used in filter cartridges as elements of mechanical water treatment (discs at the cartridge inlet) from large insoluble impurities, preventing their penetration into the coal mass and clogging its channels. Also, filters made of synthetic porous materials are placed at the outlet of the cartridges for post-treatment, holding the backfill and preventing it from entering the water.
In some filtering systems (Aquaphor), the coal filling is mixed with synthetic fibers that seal its structure and maintain its shape. As a result, a dense mass of activated carbon effectively cleans the water stream from harmful impurities.
Zeolites are natural minerals, hydrated calcium and sodium aluminosilicates, resembling cloudy glass or mother-of-pearl in appearance, are known for their ability to absorb and release water depending on environmental conditions. Another distinguishing feature of zeolites is the ability for cation and ion exchange by absorbing and releasing various substances with their surface structure.
Shungite – (slate stone) rock of the Precambrian period, consisting of 99% carbon, strongly resembles graphite in structure. The mineral has been known since ancient times as an excellent natural water purifier, miraculous healing properties were attributed to shungite water sources during the time of Peter the Great, and soldiers were recommended to carry shungite stone with them on campaigns and purify water with it. At present, shungite is known as a mineral with high absorbent (sorption) and catalytic properties, besides, it is an excellent antioxidant.
Ion-exchange resin is used to soften water, in appearance it resembles small fish caviar with a diameter of not more than 1 mm of brown, yellow, dark colors. The resin exchanges ions with salts of water-soluble metal oxides (calcium, magnesium, iron, manganese), as a result of which they stick to the surface of round granules. When salts of sodium chloride (NaCl) are added to water, a regeneration process takes place, salts of harmful metals are separated from the surface of the ion-exchange resin balls and washed down the drain.
Antibacterial additives. To combat the growth of microbes and bacteria, disinfect water, silver ions are often added to carbon filters in the form of small gray balls.
Quartz fine-grained gravel . It is used as a supporting backfill, which allows the flow to be uniformly passed when the treated water passes through the coal layer, it is used in large-sized coal-containing systems to purify large volumes of water.
High purity zinc and copper . These substances are part of one of the latest patented innovative developments – KDF (Kinetic Degreadation Fluxion) filter media, which has a higher performance and degree of water purification from harmful impurities in comparison with traditional fillers. In addition to metals, KDF contains activated carbon and ion exchange resins.
What filters use charcoal in their composition
When purifying water to the state of drinking, the following factors are taken into account. Typically, chlorinated water is supplied to apartments by public utilities, while the amount of harmful elements contained in it is normalized. To combat chlorine and metal salts, if water is used for drinking purposes, ineffective options for settling or boiling water can be used.
But given that charcoal filters do an excellent job with chlorine, their use in this case will bring a more pronounced effect, save time on dechlorination. Therefore, for drinking-only water treatment from public water mains, most consumers use small-volume carbon filters.
If an autonomous water supply from borehole or well sources is organized on an individual site, other filtration systems will be needed. Often, water enters the house from shallow water layers, which include wells or Abyssinian wells. In this case, there is a high probability that polluted surface waters, various types of microorganisms and microbes, and organic impurities will enter the water basin, while the water itself usually has a small amount of metal salts, which make it hard, worsen its color and taste.
In this case, the use of carbon-containing water purification filters, not only for drinking needs, but also for domestic use, is the best solution, and many users install large-capacity coal containers for cleaning work.
A carbon filter for water purification, if an artesian source with clean water is used on an individual site, usually from harmful elements that has only a high content of metal salts, is not so necessary. In the treatment systems of artesian wells, iron removal installations are mainly used, and coal filtration is used for post-treatment.
The simplest and most popular type of water purification filters for public water supply networks at home is a device in the form of a jug with a replaceable cartridge. According to user reviews, a sorption cartridge in a jug-type filter in urban water supply is usually enough to get drinking water for a family of three within a month.
The filling of cartridges from different manufacturers may differ not only in composition, but also in the quantitative ratio of various components.
Most cartridges from well-known manufacturers (Aquaphor, Brita, Barrier, New Key) are filled with activated carbon obtained from roasted coconut, balls with ionic silver are added to fight microbes, and ion exchange resin is used to soften the water.
Note: Thus, household pitcher filters purify water from chlorine, partially remove metal salts and adsorb insoluble particles of other pollutants.
A flowing carbon filter is installed in the cold water mains in the form of a nozzle on a tap, under the sink in the pipeline, or used in a separate jug with an outlet spout (Spring) connected to the cold water main. The composition of these cartridges is slightly different from pitcher modifications, since water is supplied under pressure, the performance of such systems and the degree of purification are slightly higher than those of gravity-fed devices.
Reusable main-type carbon filters are installed in individual water supply systems of private houses. Structurally, they are made in a glass-shaped body, inside which is placed a tubular cartridge with a filler. The body is hermetically sealed with a threaded lid and a gasket, which has two holes at the top for connection to the water main.
Water enters the filter through the inlet and, after cleaning, is sent to the consumer. At the bottom of the glass there is a tap for backwashing the carbon filler of the cartridge from contamination.
Reverse osmosis plants
The principle of water purification in reverse osmosis systems (popular brands of such installations are Bosfor, Agua, Geyser, Barrier, Atoll) consists in supplying liquid through a thin-walled membrane with ultra-small pores under pressure, resulting in distilled water without metal salts, which cannot be achieved in any one of the considered carbon filters.
For the reverse osmosis unit to work efficiently, the membrane inlet must receive the most purified water, therefore, in a standard system, three flow filters are used to purify it, in two of which activated carbon is the main component.
The following types of carbon filter media are used in reverse osmosis plants:
Granular activated carbon (GAC) . The component, made from burnt coconut shells, effectively purifies water from organics, pesticides, chlorine contaminants, viral and bacterial organisms, and removes extraneous odors. The useful area of 1 g of this substance reaches 1000 square meters.
Granulated carbon with KDF (GAC-KDF) . The additional presence of KDF components in the backfill makes it possible to effectively remove from water, in addition to biological, hydrogen sulfide, pesticide, phenolic, benzene contaminants, also heavy mercury, cadmium, lead, ferrous metal salts.
Pressed activated carbon from CBC coconuts (carbon block) . Compressed high-quality coal is a sorption filter that perfectly removes organic matter, chlorine compounds, oil refinery products, and pesticides from flowing water. After cleaning, the foreign smell is eliminated and the taste of water improves.
Carbon filters of significant volumes are used for water purification on an industrial scale and in public utilities for a large number of consumers. Their main structural element is a container with a lid made of high pressure food polyethylene, fiberglass.
In the lid there are branch pipes for supplying and discharging filtered water, a drainage pipe, as well as a control unit that automatically sets the operating modes for cleaning the system, which allows restoring the initial state of the coal filler. The backfill consists of activated carbon and a gravel substrate of purified and etched quartz with a fraction size of 2–5 mm, the purpose of the gravel is to evenly distribute the water flow.
During the operation of the sorption filter, water enters the tank through the inlet pipe and passes through the activated carbon filler from top to bottom, then it enters the water-lifting pipe with a filter basket at the end, lowered into the gravel backfill, and is sent through it to the consumer through the outlet pipe in the lid.
In the flushing mode, high-pressure water is supplied in the opposite direction: down the water pipe through the filter basket and gravel backfill, stirs up the activated carbon layer and is discharged outside through the drain pipe. At the end of the backwash, the loosened layer of activated carbon is compacted by direct washing, passing water for a short time at high speed from top to bottom and lowering it into the drain. Thanks to the washing procedures, the life of the coal filling in sorption filters reaches one to two years.
Many consumers of water resources, in order to save money, make a simple, efficient do-it-yourself carbon water filter using technology developed many centuries ago on different continents. To do this, a slot is made at the top of the 6-liter bottle for filling the filter components, a series of small holes are drilled in the cork and closed from the inside with cotton pads.
Then crushed activated charcoal is poured inside the bottle (obtained by steaming burned raw materials), its larger fractions, fine and coarse-grained river sand. A charcoal-filtered water bottle can be useful on a long hike if you have to collect polluted, cloudy water from a stream or other source and then filter and boil it.
Pros and cons
The use of carbon filters has the following advantages and disadvantages:
- When coal cleans water from chlorine, a catalytic chemical reaction automatically occurs, while the coal fraction is practically not consumed – this property of coal makes it an indispensable component in water dichlorination.
- Although activated carbon purifies water from a wide range of harmful impurities, it cannot adsorb lead, mercury, cadmium, ferrous salts of heavy metals in traditional filter systems. This drawback has been eliminated in modern KDF fillings with copper and zinc, which have not yet found wide application in cartridges for popular jugs.
- The average life of replaceable jug cartridges is limited to two months, after which the cleaning efficiency is lost and it needs to be replaced. This leads to financial costs, which for some families can be quite significant. In sorption filters, it is also necessary to change the backfill after 1-2 years, because of its large volume, the cost of buying new activated carbon can significantly hit the family budget.
Activated carbon filters are among the effective and cost-effective ways to purify water from a wide range of harmful impurities, especially chlorine. After passing through the carbon-containing backfill, all its organoleptic characteristics are significantly improved. In many purification systems, carbon filtration is an additional unit for preliminary or final water treatment.