Filtration is the removal of contaminants from 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) (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.
The flocculation basins have a rectangular shape and can be: Staged: where to achieve greater efficiency, the tank is divided into several zones in series in which the agitation is gradually decreasing. Channels: are horizontal flow, where the pool is subdivided by transverse partitions to form a channel whose width is gradually increased so as to obtain a flow velocity gradually decreasing.
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.
These flocculants, added in small doses, immediately after the coagulant, improve the efficiency of process affecting mainly. The adjuvants used are polyelectrolytes, organic macromolecules obtained through polymerization processes, waters-soluble or dispersible well, characterized by the presence of charged groups or at least polar throughout the chain.
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.
The flocculation basins have a rectangular shape and can be: Staged: where to achieve greater efficiency, the tank is divided into several zones in series in which the agitation is gradually decreasing. Channels: are horizontal flow, where the pool is subdivided by transverse partitions to form a channel whose width is gradually increased so as to obtain a flow velocity gradually decreasing.
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.
These flocculants, added in small doses, immediately after the coagulant, improve the efficiency of process affecting mainly. The adjuvants used are polyelectrolytes, organic macromolecules obtained through polymerization processes, waters-soluble or dispersible well, characterized by the presence of charged groups or at least polar throughout the chain.
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