Filtration apparatus and method for treating granular filtration medium

A method for refreshing a clogged filtering medium maintained in a filtering column which interior is divided by a perforated partition into a filtrate zone and a filtering zone, wherein said filtering zone is adapted to receive a stream of raw-water and a lower portion of its volume is filled with filtering grains, the method comprising:

• providing a Venturi device in fluid communication with said lower portion of said filtering zone and in fluid communication with an upper portion of said filtering zone, said Venturi device is adapted to receive a stream of water and produce a Venturi effect;
• directing a stream of water into said Venturi device thereby removing portion of said filtering grains and separating filtration residues therefrom by means of said Venturi effect;
• directing a stream comprising said stream of water and said separated filtering grains and filtration residues and introducing it into said upper portion of said filtering zone in a direction substantially tangential to the wall said filtering column thereby causing a circular centrally converging flow of said filtration residues inside said column;
• and
• directing a stream comprising filtration residues from said filtering zone to drainage via a drain port centrally located in the upper portion of the filtering zone.

A filtration apparatus comprising:

• a filtration column having a perforated hollow member mounted inside it to define a filtrate zone therein and a filtering zone in the volume of said filtration column external to said hollow perforated member, wherein a portion of said filtering zone is filled with filtering grains up to a level sufficient for entirely covering said hollow perforated member, and wherein said filtrate zone is adapted to receive a filtrate obtained from passage of a stream of raw-water introduced via the upper portion of the filtration column and passed through the filtering grains and the perforations of the hollow perforated member;
• said apparatus further comprising a pressure reducing device in fluid communication with a lower portion of said filtering zone and with an upper portion thereof, wherein said pressure reducing device is adapted to receive a stream of water and responsively to continuously remove filtering grains from said filtering zone and separate filtration residues therefrom by the reduction of pressure conditions thereinside, and direct a stream comprising said stream of water and said separated filtering grains and filtration residues to said upper portion of said filtering zone;
• wherein the pressure reducing device is a Venturi device adapted to receive a stream of water and continuously remove filtering grains from the filtering zone and separate filtration residues therefrom by means of a Venturi effect;
• and
• wherein the Venturi device comprises a pressure chamber having an inlet adapted to receive the stream of water and a tapering outlet adapted to produce the Venturi effect.

A method for refreshing a clogged filtering medium maintained in a filtering column, the interior of which is divided by a hollow perforated member into a filtrate zone and a filtering zone, wherein said filtering zone is adapted to receive a stream of raw-water and a lower portion of its volume is filled with filtering grains;

• the method comprising:
• providing a Venturi device in fluid communication with said lower portion of said filtering zone and in fluid communication with an upper portion of said filtering zone, said Venturi device is adapted to receive a stream of water and produce a Venturi effect;
• directing a stream of water into said Venturi device thereby removing portion of said filtering grains and separating filtration residues therefrom by means of said Venturi effect;
• directing a stream comprising said stream of water and said separated filtering grains and filtration residues and introducing it into said upper portion of said filtering zone in a direction substantially tangential to the wall of said filtering column thereby causing a circular centrally converging flow of said filtration residues inside said column;
• and
• directing a stream comprising filtration residues from said filtering zone to drainage via a drain port centrally located in the upper portion of the filtering zone.