Patent ID: 8109488

Claim:
A system for aerating a liquid, comprising: a tank having a bottom, wherein the tank holds a volume of the liquid, wherein the tank further comprises a chamber wall spaced from the bottom of the tank that separates the tank into an upper aerated aerobic chamber and a lower anoxic chamber; a rotative shaft having a longitudinal axis; a rotatable surface aerator mounted to the rotative shaft and at least partially immersible into the liquid, wherein the surface aerator is positioned in the upper aerated aerobic chamber and is configured to rotate about the longitudinal axis of the rotative shaft to move the liquid upward and distribute it over the liquid surface; and an elongate draft tube having a longitudinal axis, an exterior surface, a proximal end and a distal end, the draft tube being rotatable about the longitudinal axis of the rotative shaft, wherein the longitudinal axis of the draft tube is substantially co-axial with the longitudinal axis of the rotative shaft; wherein a portion of the draft tube underlies the surface aerator and is positioned within the upper aerated aerobic chamber, wherein the distal end of the draft tube is positioned within the lower anoxic chamber at a predetermined distance from the bottom of the tank, and wherein portions of the exterior surface of the draft tube act on the liquid present in both the upper aerated chamber and the lower anoxic chamber to effect movement of liquid thereabout the tank in the upper aerated chamber and the lower anoxic chamber.