The sedimented material is conveyed towards a hopper formed on bottom of tank, by means of mechanical pickers that sweep the bottom of same, and from here pumped to sludge treatment line. The size of tanks depends on detention time which is a function of characteristics of solid sediments present in raw waters and the type of decanter chosen.
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.
The filtering layer resting on a draining bottom, which has the function of: surface filters: filtration takes place through filter cloths which prevent the passage from the materials above the size of blind holes (not es.tessuto tissue; in this case the particles are retained on the surface of filter media forming a layer of material that retains the subsequent particles.
Physical and chemical treatments normal and driven: they are divided into several phases and eliminate non-settleable suspended solids (flocculation) and correct the chemical characteristics of waters by eliminating the dissolved substances that are incompatible with the use to which the waters is bound (softening, stabilization, removal of iron, manganese, desilication, fluoridation and defluoration, aeration).
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 filters are formed from cylindrical vessels made of reinforced concrete on the bottom of which special shelves, provided with an adequate number of holes, support the filtering mass. The filter bed consists of fine sand / fine or other material minute. The filter bed is supported by an underlying layer of material, also the filter, formed by a layer of coarse gravel and the overlying layers of gravel gradually finer (mattress draining).
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.
About the Author:
If you like this article please shere it