Abstract: A method for aerating waste water, wherein the interface area between air and waste water is enlarged by splashing the water by means of blades and wherein the sludge present in the waste water is kept in suspension by creating flows and/or turbulence in the water. The waste water is set in motion by moving a plurality of blades arranged in a circle through the waste water, in such a manner that the connecting parts interconnecting the blades substantially do not extend into the waste water. The device for aerating waste water is provided with a container for waste water and with a rotor being rotatable about a substantially vertical axis, whose portion pointing downwards may extend into the waste water. The rotor comprises blades having surfaces which are substantially radially and axially oriented, whereby the blade surfaces are at least partially located below the rotor parts interconnecting the blades so that the connecting parts substantially do not extend into the waste water.

Abstract: An apparatus for aerating waste water comprising a surface aerator adapted to rotate about a vertical axis. A cap is disposed over the aerator, said cap being modified in several ways to improve the operation of the apparatus. In one embodiment a gas outlet opening with an exhauster is provided in a wall of the cap. Further circumferential spaced baffles may be disposed inside the cap. The cap may have a side wall with a lower edge extending vertically downwardly or inwardly. Other embodiments of the cap are specifically adapted for use in an installation for treating waste water, in which the apparatus serves also for bringing the liquid into circulation.