To provide a sewage purification plant which has high sludge-decomposing capacity, and can contribute to the reduction of sludge weight and offensive odors.
The sewage purification plant comprises a primary settling basin 2 for precipitating a part of components in influent, an aeration tank 4 for aerating treated water supplied from the primary settling basin, a final settling basin 6 for precipitating treated water supplied from the aeration tank, a path 20 for supplying a part of the sludge precipitated in the final settling basin to the aeration tank as return sludge, and a sludge active tank 13 made by connecting an anaerobic tank 12 and an aerobic tank 11 in series. The treated water of the primary settling basin and a part of the sludge of the final settling basin are supplied to the anaerobic tank, and a part of activated sludge mixture discharged from the anaerobic tank is supplied to the aeration tank. The sludge age of the sludge active tank is higher than that of the aeration tank, and the mean residence time of active microorganisms in the sludge active tank is longer than that of the aeration tank.
HOZUMI SHOGO
MASUDA YOSHISHIGE
TANAKA YOSHITA
