Wastewater filtering method and apparatus comprising filter media of different sizes

A filtration device for treating wastewater, the device comprising:

• a distribution channel for distributing a wastewater vertically upward or discharging backwash water, received vertically downward, to outside of the filtration device;
• filter media for raising due to a lower specific gravity than water when the wastewater is distributed vertically upward from the distribution channel to filter solids and organics in the wastewater and descending when the backwash water flows in vertically downward to remove the solids and organics that attached on the filter media;
• a treated water storage tank for receiving the treated water from which solids and organics are removed through the filter media and discharging it to the outside or discharging the backwash water flowing in from the outside to the filter media;
• and
• a diffuser configured to supply air to the filter media to create an aerobic environment.