PURPOSE: To stably, efficiently and uniformly aerate sewage by installing 1 or ≥2 flow regulating plates and/or mixing and stirring bars which change the flow direction of the sewage flowing in the water path in the circulating water path of an aeration tank.
CONSTITUTION: The flow velocity is lower on the inner peripheral side of the water path and is higher on the outer peripheral side and swirling arises in some cases when the flow velocities at the respective points of the aerator are measured by subjecting an aerator 2 to a required operation. The flow regulating plates 3 are installed at one or ≥2 points of the circulating water path so as to uniformize the water flow of the water path over the entire part of the water path in order to prevent the swirling. The flow regulating plates 3 are so installed as to change the water flow in the water path from the outer peripheral side to the inner peripheral side of the water path to increase the flow velocity on the inner peripheral side of the water path. The swirling is prevented in this way and since the sewage is uniformly mixed in the transverse direction of the water path, the sewage is stably, efficiently and uniformly aerated.