Method for washing a filter having at least two layers of filtering media, in particular for filtering seawater, and equipment for implementing said method

A method for washing a filter having at least two layers of filter media for seawater, a bottom part of the filter being supported by a floor comprising passage orifices and provided with nozzles that allow an injection of washing water and/or air, the seawater flowing from a top part of the filter to the bottom part of the filter through the at least two layers of filter media, and a treated water being collected at the bottom part of the filter, which at the top part comprises at least one weir for collecting the washing water, wherein the following successive steps are carried out:

• (a) a preparation step in which seawater inlet is closed and the filter, where the filter operates under pressure, is depressurized;
• (b) a water level in the filter is lowered;
• (c) air alone is blown under pressure into the bottom part of the filter, this air passing from the bottom part of the filter to the top part of the filter through the at least two layers of the filter and causing the cakes to be reduced to particles;
• (d) rinsing is carried out using water alone as the washing water, the washing water passing from the bottom part of the filter to the top part of the filter, allowing the filter media to separate and causing the particles to rise to a surface, a water-rinsing time being short enough that the water level remains below an upper edge of the at least one weir for collecting the washing water so that the washing water does not enter the at least one weir;
• (e) the washing water is emptied out of the filter by a discharge at the bottom part of the filter;
• (f) steps (c), (d), and (e) are repeated at least once,
• and a final rinsing is performed by passing through a quantity of backwash water which is injected at the bottom part of the filter and discharged from the top part of the filter by a pipe.