Filtration device

A filtration system comprising:

• the filtration device;
• and
• a line mixer configured to mix a flocculent with raw water entering a raw water pipe connected to a front end, and connected to the filtration device through a raw water inlet pipe connected to a rear end,
• wherein the filtration device is configured in plural, and connected in parallel to the rear end of the line mixer, and
• wherein the filtration device comprises:
• a filtration tank having the raw water inlet pipe and a backwash water discharge pipe connected to an upper portion thereof, and a treated water discharge pipe, a backwash water inlet pipe, and a backwash air inlet pipe connected to a lower portion thereof;
• a strainer provided in the filtration tank, having a plurality of water passage holes formed on a side surface thereof, and having a lower side in communication with the treated water discharge pipe;
• a filtration unit including a fiber filter medium forming a filtration pore layer on an outer circumferential surface of the strainer, an upper support portion coupled to an upper side of the fiber filter medium, and a lower support portion coupled to a lower side of the fiber filter medium;
• and
• a filtration control unit having a cylinder disposed inside the strainer and a piston elevating or lowering from the cylinder, and configured to control the porosity of the fiber filter medium by compressing or relaxing the fiber filter medium with respect to the strainer while the upper support portion is elevated or lowered according to the elevating or lowering of the piston.