When the filtering layer begins to clog need cleaning it, which happens every 4 to 6 weeks. The cleaning is manual and involves removing the first layer of sand, sand washing in separate tubs and in reconstruction of filter bed. Quick filters are the most used, particularly in combination with other treatments such as clarification (surface waters) and the removal of iron and manganese (deep waters), and can deal with an input flow rate 40 times higher than that of lens filters (survival water purification systems).
These sources of supply, due to specific characteristics of waters and / or the degree of pollution, must be subjected to cycles of treatments of filtration 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).
We can also make filters consist of two filter layers of materials with different specific weight (dual media). As a rule, in this case the top layer is made from anthracite, lighter, and the lower one is in quartz sand. The layer of asphalt, being formed by the coarser particles of sand, preserves the rapid occlusion of first layers of sand. After a certain time, the retained particles begin to clog the bed draining decreasing the permeability, and determining, at a constant flow rate of inflow, an increase in waters level in tanks filtering. Exceeded the limit level, the layer drained must be subjected to countercurrent washing to restore its efficiency.
Indeed, the presence of substances in suspension, for example, can nullify the effect of final disinfection since such particles may protect microorganisms against the action of disinfectants. In treatment of flocculation will exploit the properties of certain substances, called coagulants, which under certain operating conditions, in form of waters insoluble compounds with electric charge of opposite sign (positive charge) than that of colloids constituents as to eliminate the turbidity (negative charge).
Forms special surface filtration membrane processes are divided according to size of pores in: microfiltration, ultrafiltration, nanofiltration and hyperfiltration or reverse osmosis. Filtration membranes can be used for example as an alternative to or flocculation processes adsorption.
Treatments: also divided into several phases, improve the organoleptic characteristics of waters (adsorption on activated carbon) and lower the content of dissolved solids (demineralization). The interventions of this type are provided, when necessary, upstream of treatment processes of filtration real, and allow the removal of materials and substances which by their nature and size are likely to damage the equipment and compromise the efficiency of subsequent treatment stages.
The 'sodium aluminate is very expensive and is also used in treatment of lime-soda softening species in case of high hardness and magnesium. In some waters, even with a strong dose of coagulant, are unable to develop a staple of suitable density. Inse cases, adjuvants are added to waters coagulation to promote the densification of micro-flakes.
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. Decanters flow or vertical upward flow are generally circular section. Inse tanks the entrance of waters can be centrally from above; in this case waters, to be able to escape from the tank itself is forced along a tortuous path; in fact must first move vertically downwards in order to pass beneath a baffle concentric, said fireplace, subsequently, passed over the obstacle fireplace, must rise and exceed a weir located along the perimeter of tub.
These sources of supply, due to specific characteristics of waters and / or the degree of pollution, must be subjected to cycles of treatments of filtration 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).
We can also make filters consist of two filter layers of materials with different specific weight (dual media). As a rule, in this case the top layer is made from anthracite, lighter, and the lower one is in quartz sand. The layer of asphalt, being formed by the coarser particles of sand, preserves the rapid occlusion of first layers of sand. After a certain time, the retained particles begin to clog the bed draining decreasing the permeability, and determining, at a constant flow rate of inflow, an increase in waters level in tanks filtering. Exceeded the limit level, the layer drained must be subjected to countercurrent washing to restore its efficiency.
Indeed, the presence of substances in suspension, for example, can nullify the effect of final disinfection since such particles may protect microorganisms against the action of disinfectants. In treatment of flocculation will exploit the properties of certain substances, called coagulants, which under certain operating conditions, in form of waters insoluble compounds with electric charge of opposite sign (positive charge) than that of colloids constituents as to eliminate the turbidity (negative charge).
Forms special surface filtration membrane processes are divided according to size of pores in: microfiltration, ultrafiltration, nanofiltration and hyperfiltration or reverse osmosis. Filtration membranes can be used for example as an alternative to or flocculation processes adsorption.
Treatments: also divided into several phases, improve the organoleptic characteristics of waters (adsorption on activated carbon) and lower the content of dissolved solids (demineralization). The interventions of this type are provided, when necessary, upstream of treatment processes of filtration real, and allow the removal of materials and substances which by their nature and size are likely to damage the equipment and compromise the efficiency of subsequent treatment stages.
The 'sodium aluminate is very expensive and is also used in treatment of lime-soda softening species in case of high hardness and magnesium. In some waters, even with a strong dose of coagulant, are unable to develop a staple of suitable density. Inse cases, adjuvants are added to waters coagulation to promote the densification of micro-flakes.
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. Decanters flow or vertical upward flow are generally circular section. Inse tanks the entrance of waters can be centrally from above; in this case waters, to be able to escape from the tank itself is forced along a tortuous path; in fact must first move vertically downwards in order to pass beneath a baffle concentric, said fireplace, subsequently, passed over the obstacle fireplace, must rise and exceed a weir located along the perimeter of tub.