Abstract: A rotating gas diffuser for shearing fine gas bubbles from the surface thereof when the diffuser is immersed in a body of liquid and rotated therein. The rotatable shaft of the diffuser may carry a plurality of main rigid structural spokes and an equal number of rigid hollow gas feed conduits positioned alternately around the shaft. A plurality of plates, each in the form of a section of an annulus with its lateral edges radially positioned with respect to the circular rotating gas diffuser, is supported either on the top or the bottom of the diffuser, or on both, near its perimeter. Each porous plate is carried by a plate holder that has a shape similar to its associated porous plates, and with those plates defines a gas plenum having an area substantially equal in extent to, but no greater than, the area of the plates.