The channel in correspondence of grid widens in such a way that the speed of waters downstream of grid, given footprint of bars, is maintained next to one that occurs in upstream portion. The speed of waters passing through the grid must be sufficient to prevent the sedimentation of solids upstream of same but not too high in order not to increase the load losses (portable water purifiers for survival).
In case where it is necessary to perform a removal of coarse solids thrust not settleable and suspended solids do not sediment is expected next to grilling also a sieving (or screening) or a microstacciatura. This type of intervention is normally alternative to primary sedimentation and also is also used for the removal of algae and plankton. The sieve consists of rotating cylinder (drum or noria) stainless steel horizontal axis, closed at its ends and partially immersed in a tank, on which is mounted a metal mesh also made of stainless material.
For a conventional filtration, the most common materials are sand and anthracite. The sand is used alone as a monolayer or associated with the bilayer in anthracite filters. Biological filtration media (iron removal, manganese removal, nitrification, denitrification) are sand and granular activated carbon. Waters purification (or purification) is the removal of contaminants from raw waters to get waters that is fit for normal domestic consumption or for irrigation of fields and also for industrial uses (eg. For use by establishments for food). With the gradual depletion of natural sources of drinking waters (deep waters), is increasingly resorting to surface waters (seas, rivers, lakes and dams).
These sources of supply, due to specific characteristics of waters and / or the degree of pollution, must be subjected to cycles of treatments of purification necessary to modify the characteristics and improve its quality. Often, this happens even for the deep waters with a high content of organic substances and a high microbial contamination, especially if they are present faecal bacteria (eg. Coliforms).
Besides the possibility to retain materials particularly small, as sieving has the advantage, compared to grilling, to retain all the material that has at least one dimension greater than the measurement step of network. The main drawback of sieving however, is the ease with which occur clogging and the need for frequent maintenance and cleaning. The sieving can applied only in case of waters with a low concentration of suspended solids.
It is therefore necessary to use dynamic settling through which one can act on the trajectory for continuously separating particles of different size and density. This type of separator is also called "lamella clarifier". It significantly improves the speed of settling. Decanters are currently used in small installations, horizontal separators; for very large installations, we prefer decanters powered by this principle but with a functioning a little more optimized. After this very important step in settling, it remains to remove even smaller particles by filtration.
The functionality of desanding is linked to ability to allow the sedimentation of inert materials having a diameter exceeding certain values, indicates that the practice in 0.2-0.5 mm. These materials may in fact create problems for subsequent treatments as they can clog pipes and channels, and abrasive electro-mechanical equipment (pumps). With Desanding you reach the goal of eliminating 65-70% of suspended solids and to improve waters quality to be sent to following treatments. In these conditions the speed of sedimentation of particles is adjusted in a first approximation by Stokes law.
This law is valid for strictly spherical particles immersed in a liquid at rest and at constant temperature where the downward motion is not influenced neither by the presence of other particles or from the container walls. The sedimentation is carried out in special tanks, called decanters, within which the waters moves in a laminar flow as possible for a time sufficient to allow the sedimentation of heavier particles.
In case where it is necessary to perform a removal of coarse solids thrust not settleable and suspended solids do not sediment is expected next to grilling also a sieving (or screening) or a microstacciatura. This type of intervention is normally alternative to primary sedimentation and also is also used for the removal of algae and plankton. The sieve consists of rotating cylinder (drum or noria) stainless steel horizontal axis, closed at its ends and partially immersed in a tank, on which is mounted a metal mesh also made of stainless material.
For a conventional filtration, the most common materials are sand and anthracite. The sand is used alone as a monolayer or associated with the bilayer in anthracite filters. Biological filtration media (iron removal, manganese removal, nitrification, denitrification) are sand and granular activated carbon. Waters purification (or purification) is the removal of contaminants from raw waters to get waters that is fit for normal domestic consumption or for irrigation of fields and also for industrial uses (eg. For use by establishments for food). With the gradual depletion of natural sources of drinking waters (deep waters), is increasingly resorting to surface waters (seas, rivers, lakes and dams).
These sources of supply, due to specific characteristics of waters and / or the degree of pollution, must be subjected to cycles of treatments of purification necessary to modify the characteristics and improve its quality. Often, this happens even for the deep waters with a high content of organic substances and a high microbial contamination, especially if they are present faecal bacteria (eg. Coliforms).
Besides the possibility to retain materials particularly small, as sieving has the advantage, compared to grilling, to retain all the material that has at least one dimension greater than the measurement step of network. The main drawback of sieving however, is the ease with which occur clogging and the need for frequent maintenance and cleaning. The sieving can applied only in case of waters with a low concentration of suspended solids.
It is therefore necessary to use dynamic settling through which one can act on the trajectory for continuously separating particles of different size and density. This type of separator is also called "lamella clarifier". It significantly improves the speed of settling. Decanters are currently used in small installations, horizontal separators; for very large installations, we prefer decanters powered by this principle but with a functioning a little more optimized. After this very important step in settling, it remains to remove even smaller particles by filtration.
The functionality of desanding is linked to ability to allow the sedimentation of inert materials having a diameter exceeding certain values, indicates that the practice in 0.2-0.5 mm. These materials may in fact create problems for subsequent treatments as they can clog pipes and channels, and abrasive electro-mechanical equipment (pumps). With Desanding you reach the goal of eliminating 65-70% of suspended solids and to improve waters quality to be sent to following treatments. In these conditions the speed of sedimentation of particles is adjusted in a first approximation by Stokes law.
This law is valid for strictly spherical particles immersed in a liquid at rest and at constant temperature where the downward motion is not influenced neither by the presence of other particles or from the container walls. The sedimentation is carried out in special tanks, called decanters, within which the waters moves in a laminar flow as possible for a time sufficient to allow the sedimentation of heavier particles.
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