A wastewater treatment plant includes a reaction tank connected to an wastewater supply tube and an aeration apparatus to receive wastewater therein, a sludge separation unit dividing an internal space of the reaction tank into upper and lower sections to increase an amount of dissolved oxygen by increasing an contact area of the wastewater and bubbles and to separate relatively light materials by moving low density matters existed on a surface of each section upward in turn, an air exhaust tube mounted on the reaction tank to exhaust bubbles passing through the sludge separation unit out of the reaction tank, a treated water exhaust tube mounted on the reaction tank to exhaust the wastewater that is treated by passing through the sludge separation unit, and a settling tank provided on a bottom of the reaction tank to concentrate and exhaust the settled sludge.