Let’s try to understand what domestic and foreign filter models are presented in the market today, and how they differ from each other.
Filter. And no bazaar
Whatever they say about the poor quality of our tap water, yet the quality of treatment at urban stations in America is quite high, compared with many countries in the world. But city tap water still needs to be purified before drinking.
First, worn pipes and give impurities: rust, sludge, agricultural waste.
Secondly, the pre-treatment cycle does not guarantee the complete removal of heavy metals, hardness salts, nitrates, pesticides, and organic impurities in interaction with chlorine, they can lead to the formation of substances with carcinogenic and mutagenic action .
Finally, thirdly, in most cases tap water is characterized by high chlorine content, which is added at the stations in order to disinfect water.
In the conditions of a city apartment usually use filters of four basic types.
The principle of filtration in such a device is very simple: the water is filtered through a removable cartridge, the filter does not require a direct connection to the water supply. The capacity of such a jug ranges from 1.8 to 4.8 litres and the filtering rate is a maximum of 0.4 litres per minute.
There is a special sorbent usually an activated granular or fibrous carbon sorbent inside the removable cartridge. One of the important advantages of the models is the possibility of using cartridges for different purposes, i.e.e. It can be used for softening, cleaning from chlorine, etc.d.
The main disadvantage of filters jugs – the need for fairly frequent replacement of cartridges their resource rarely exceeds 350 liters , that is, such filters are not cheap to use. The price range for jug-filters ranges from 400 to 1000 Dollars. Replacement cartridge cartridges for such filters are, depending on the degree of filtration, ranging from 150 to 250 Dollars, and to change them – and, accordingly, buy new ones, it is recommended about every two months.
Special faucet nozzles
The speed of filtration in these models is about the same as in the pitcher-filters, but the resource adsorbing impurities and harmful substances cartridges are two to three times higher. You can buy nozzle filters, depending on the number of degrees of purification, for 200-1200 Dollars. The only serious disadvantage of these models is the need to put a nozzle on the faucet for drinking water.
Desktop flow-through filters
These devices are installed near the water tap and are quickly connected to it with a flexible hose when clean water is needed. Only potable water is purified, and at the expense of technical water – for example, for washing dishes – the cartridge and filter resources are not spent. Filtration rate is 3-4 times faster than in the jug-filters, and the duration of use is almost ten times longer. The cost of such filters is increased, as compared to the pitcher-filters, in proportion to the leading characteristics and ranges from 2700 to 10 000 Dollars.
Stationary flow-through filter
It may consist of one or more housings built into the water system and placed under the sink – side by side or one above the other. In this case, the sink takes out an additional tap for drinking water, and water for non-food purposes, you continue to take from a regular faucet. These filters have a very long filter life from 4,000 to 15,000 liters , they are also characterized by a high filtration rate from 2 l/min . .
How filtration works
In the table we have described the main types of filters for urban apartments. Let’s now look at what technologies are used to purify water in domestic filters, and how they differ from each other.
Sorption filtration is rarely used by itself, more often – in combination with other types of purification. Sorption means “absorption” and activated carbon is usually used as such an “absorbent”. Granular or fibrous activated carbon sorbents absorb chlorinated compounds and pesticides. There are several kinds of sorbents, but the ones most commonly used in industry are coconut made from coconut shells and birch activated carbon.
For the manufacture of sorbent cartridges for water purification prefer to use coconut charcoal. It is mechanically stronger and, therefore, less susceptible to abrasion during transport and subsequent operation.
In addition, it contains fewer impurities, including iron, and has 2-3 times greater sorption capacity compared to activated birch charcoal. Such performance is due to the properties of coconut shells: they have a dense and uniform structure, allowing the “deep” activation of coals without losing the mechanical strength of individual granules.
The action of ion-exchange filtration is aimed at getting rid of heavy metals and salts that make water hard, and also called the process of softening water. Ion exchange resins are involved in the chemical reaction.
In electrochemical filtration, or electrochemical purification, water that passes through several containers of special design that are under a strong electric field, and is subjected to complex redox reactions. This operation completely destroys all harmful impurities, as well as viruses and bacteria. This cleaning method is the most productive and has an almost unlimited filter life. Some inconvenience is that it is not recommended to drink the water which has passed this cleaning system for some hours as its acidity increases.
Membrane filtration or reverse osmosis system. The essence of this extremely popular technology is the same mechanical purification, but already at the molecular level. the filtering thin-film membrane passes only water molecules through the smallest pores about 0,0001 micron , because the diameter of the membrane pores is about 200 times smaller than the size of viruses and 4000 times smaller than the size of bacteria.
The filtration process is provided under the influence of external pressure, exceeding osmotic pressure in which the alignment of concentrations of solutions occurs : the water begins to move from a solution with a higher concentration of salts into the solution with a lower concentration.
Almost all methods of filtration in water purifiers are combined, and recently, filters with multistage purification have been found more and more often in price lists. In such units, the first stage of purification removes undissolved chemical compounds, suspended solids, sand and other similar contaminants down to about 5 microns in size.
In most models of multistage filters, a simple polypropylene filter works at this stage. The next stage is sorption filtration, which absorbs chlorine and other organic compounds if the chlorine-containing compounds are not removed from the water, the subsequent, membrane purification becomes practically impossible, because chlorine acts destructively on the membrane . Finally, the water passes through a membrane, a reverse osmosis system which finally cleanses water from harmful impurities and toxins.
What should drinking water be like??
The problem of water and clean water is a special concern of UNESCO, which encourages initiatives and projects by communities and individuals around the world. In America, for example, schools with UNESCO status do much to implement the Great Volga River Route Project. In many countries of the world, and since 1995 in our country the 22nd of March is marked as “International day of water”.
Chlorine derivatives – chloroform, carbon tetrachloride – accumulate in the body. The World Health Organization estimates that they cause 70% of all cancers. In addition, residual chlorine and aluminum in tap water causes diseases in children malignant tumors, pneumonia, gastritis, eczema and early mortality in adults cancer, Alzheimer’s disease, etc. . According to American researchers, 15 years of daily use of chlorinated tap water increases death rate from colon cancer by 2-3 times compared to those who drank clean ozonized water. Even if you boil chlorinated water, you cannot get rid of all the problems. A number of bacteria remain viable even after boiling, and the chlorine content is reduced by only 30%. There is no reduction in the salt content of heavy metals and organic pollutants in the water. No way to remove toxic organochlorine compounds by boiling, freezing or settling water for a day.
Since 1996 hygienic requirements to drinking water quality in centralized water supply systems are determined by SanPiN 220.127.116.114-01 “Drinking Water”. In this document water quality indicators are divided into epidemic, organoleptic, radiological and chemical. What are these indicators?
Epidemic. Many forms of bacteria, protozoa and higher organisms can live and grow in the water. We don’t analyze every type of water – it’s too expensive and time-consuming. Analysis is performed for the presence of so-called “indicator” microbes, which warn of the possibility of contamination of the source with a particular pathogenic microflora, such as E. coli. Its concentration in 1 liter of water is called the coliform index. The second indicator is the total microbial count. This is the number of colony-forming bacteria in 1 ml of water. According to the requirements of SanPiN, both indicators must be equal to zero. Must be completely absent and protozoa.
Radiological indicators. These values are determined by dosimetric instruments. Total α-radioactivity of water must not exceed 0.1 Bq, and &beta -Radioactivity – 1 Bq per 1 liter of water.
Chemical Indexes. The pH-value is, simply put, the acidity index. According to this principle, water can be neutral pH = 7 , alkaline pH > 7 or acidic pH +10 7 .
Total mineralization is determined by the mass of dry residue obtained by evaporating a set volume of water. It should not exceed 1000 mg/l.
Organic and inorganic substances. The total number of chemicals that may appear in the water as the result of industrial and other human activities exceeds 50,000. Testing water for each of them is simply impossible. Interestingly, as of July 1, 2002. For the first time, not only the upper, maximum permissible element content is mentioned, but also the lower one. Of course, this does not apply to all substances, but only to those minerals, which are habitual and useful for the body. For example, water hardness should be within 1.5-7 mg-eq/l, alkalinity 0.5-6.5 mg/l, calcium 25-80 mg/l, magnesium 5-50 mg/l, potassium 2-20 mg/l, bicarbonates 20-400 mg/l, fluoride ion 0.06-0.2 mg/l and iodide ion 40-60 mkg/l. This approach somewhat limits the use of purification methods that reduce the content of minerals in the water to almost zero.
Organoleptic characteristics. Odor and aftertaste. A five-point scale is used to assess these two indicators: 1 point – very weak 2 – weak 3 – noticeable 4 – distinct 5 – very strong. Drinking water should not have a hardness rating above two points. And not at room temperature, and at 60 ° C, when both smell and taste multiply amplified you, too, can take this method of assessment at armament . However, both are determined, in the language of experts, organoleptically, and simply put, “to taste” and “smell.
The hardness of water is divided into temporary and permanent hardness. Temporal hardness is caused by the content of calcium and magnesium hydrocarbonates in the water, which are deposited in the form of scale during boiling. The hardness of water is determined by calcium and magnesium salts such as nitrates, sulfates etc. d. It is not harmful for humans and is the main source of calcium and magnesium for the body. Water analysis determines total, total hardness in milligram-equivalents per liter mg-eq/L . For drinking water, it should not exceed a value of 7 but not less than 1.5 .
Water acidity. It is caused by the presence of organic substances, as well as a number of easily oxidizable inorganic impurities divalent iron, hydrogen sulfide, etc. . d. . To determine this parameter, the most frequently used method of water oxidation with potassium permanganate manganitsa , according to what the parameter itself is usually called permanganate oxidation. For drinking water, it must not exceed 5 mg/l.