Water is the basis of all organic life

Water is the basis of all organic life, without which neither the existence of man, nor the development of mankind as a whole is possible. Water covers more than 70% of the earth’s surface and is about 1/4400 of the total mass of the planet, but the share of fresh water accounts for less than 3% of the total. At the same time about 70% of all fresh water is in the form of glaciers, which makes it difficult to use.
A variety of different pollutants generates no less variety of ways to purify water from them. Nevertheless, they can all be divided into groups according to the principle of action. Thus, the most common classification of cleaning methods is as follows:
Physical;
Chemical;
Biological.

Physical methods
The percolation is the passage of the purified water through various grids and screens, where large pollutants are trapped. Defending consists in separating a part of the mechanical impurities from the water under the influence of gravitational forces, which cause the particles to sink to the bottom, forming a sediment. Defecation can act as both a preliminary stage of purification, on which the largest pollutants are separated, and as intermediate stages. Filtering is based on the passage of the water to be purified through a porous layer of filter material, on which particles of a certain size are detained. By its principle, filtration is similar to filtering, however, it can be used for both coarse and fine cleaning. Ultraviolet disinfection of water, although it does not directly purify itself, but is actively used in the process of water treatment, consists of treating the already purified water with the ultraviolet part of the light spectrum (in particular, a wavelength range of 200-400 nm) invisible to the human eye for the purpose of disinfection water. The death of living organisms under this radiation comes mainly from damage to DNA and RNA molecules, which is caused by photochemical reactions arising in their structure.

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The methods of purification of this group are based on the chemical interaction of certain substances (reagents) with pollutants, as a result of which the latter either decompose into non-hazardous components, or go into a different state (for example, form insoluble compounds falling into the sediment to be separated).
Neutralization is, as the name suggests, the neutralization process, in which the acid-base balance is equalized by the interaction of acids and alkalis, followed by the formation of appropriate salts and water. Neutralization is carried out either by mixing the water to be purified with an acidic and alkaline medium, or by adding reagents that create a reaction medium (acidic or alkaline) in water.
Oxidation and reductionIt is also used to purify water from various pollutants, although in practice the ratio of their use is strongly biased towards oxidants. Chlorination, that is, treatment of water with chlorine-containing compounds, as a process is well developed and widely used in water treatment. Treatment with chlorine also has a prolonged antibacterial action, which is especially important for water supply in worn-out pipelines where secondary water contamination can occur. In addition, the chlorination reagents are relatively cheap and available.
Biological purification can be carried out under the following conditions:
biological ponds;
filtration fields;
biofilters;
aerotanks (oksitenki);
methane tanks.
A biofilter is a structure in which water is purified by filtration through a layer of loading material covered with a layer of aerobic microorganisms, also called biofilm. To ensure the sufficient amount of oxygen necessary for the organism to biodegrade pollutants, an air distribution system is provided. However, aeration can be carried out in a natural way.
Aerotank is a more complex purification plant in which aeration is carried out artificially. As follows from the description, purification by aerobic microorganisms is carried out therein. Before feeding into the aeration tank, water is pre-mixed with the activated sludge

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