The filtration process allows the removal of solid or colloidal particles escaped of all those in the previous stages of treatment and at the same time ensures an improvement of all other parameters.
SAND FILTRATION
The sand filtration consists in the passage of the water to be treated through a filter bed formed of multiple layers of selected minerals (usually granular low density anthracite and very pure silica sand) having a particle size and specific differentiated weights .
The solids removed from the water are trapped within the pores to the surface of the filter medium, and this involves a progressive clogging of the filter bed, with increase of the load losses that makes it required the periodic removal of deposited solids (“backwash”).
Sand filters are available in different sizes and materials and can be either manual or fully automatic.
ACTIVATED CARBON FILTRATION
The activated carbon filtration, however, is based on the ability of activated carbon to adsorb, due to its porosity, most of the residual organic substances such as hydrocarbons and surfactants contained in the waters to be treated.
The activated carbon can be of vegetable or mineral origin and are subject to availability, therefore, must be replaced periodically.
Also in this case it is necessary to perform against the washes to prevent the formation of deposits that may affect the proper functioning of the filter.
The activated carbon filters are available in different sizes and materials and can be either manual or fully automatic.
It should be noted that the activated carbon filters are also used for treatment of water intended for human consumption to eliminate toxic substances such as chlorine if present in high concentrations, cloroammmine, etc..