Filtration is one of the most widespread mechanical treatments applied to water: very often, in fact, it is combined with many other chemical-physical or biological treatment processes (such as desalination/demineralization), which act on other water characteristics.

The water to be treated passes through the filter bed in co-current flow (from top to bottom) and as solids and/or pollutants deposit in the free spaces, the resistance to water passage and therefore the pressure drop progressively increases. When the pressure drop (pressure difference between filter inlet and outlet) is around 0.7 bar, it is necessary to perform filter washing to avoid the possibility of pollutant leakage with the consequent decrease in treated water flow rate.

According to a pre-established program, backwashing of the filter media is performed to optimize the process and maintain the efficiency of the filter material over time.

The effectiveness of the filtration and/or absorption process is directly proportional to the speed at which the liquid to be treated passes through the system, and therefore as a function of the contact time with the aforementioned filling materials. Furthermore, such timing is directly dependent on the type of liquid to be treated and must take into account the quantity of substances to be retained/adsorbed and the desired result in terms of efficiency and/or performance of the filtration system itself.