An apparatus and method for mixing gas and liquid including a dome, lower housing, aerator device and flotation device, wherein intermeshed rotating sets of discs operate on parallel shafts driven by variable speed drives, and strakes are radially mounted on the discs to carry liquid up into a mixing area and to carry air and liquid down into a mixing area resulting in a shear force that drives air into the oxygen depleted liquid. The dome and lower housing create an air tight space, wherein the barometric pressure is raised by a blower, in order to pop foam bubbles and allow for optimum mixing of air into the oxygen depleted liquid, and intake and discharge openings of the lower housing are positioned beneath the liquid line, thereby preventing the escape of foam, noise and odorous gases into the local environment.