An apparatus and method for mixing gas and liquid including a pipe having an enclosure positioned in-line with the pipe, wherein a sealed space is defined, at least one blower, the blower regulates the barometric pressure in the sealed space at or above fluid line pressure in the pipe, 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. Strakes provide leading and trailing rotor wipes to maximize pull of liquid flow from the pipe into the mixing area and back into the pipe and acute angled energy capture strakes for capturing the energy from liquid flow exerted against the back side of strake.