An apparatus for generating and mixing gas bubbles into an aqueous solution includes a structure defining an interior fluid-flow chamber extending along a longitudinal axis between a liquid input end and a liquid output end. The structure is characterized by a gas injection portion and a mixing vane portion. The gas injection portion is located downstream from the liquid input end and upstream from the liquid output end. The gas injection portion defines a first region of the interior fluid-flow chamber and a gas injection lumen that is surrounded by the interior fluid-flow chamber. The gas injection lumen, which extends along a length of the gas injection portion, is configured to inject gas from the interior of the gas injection lumen into the surrounding interior fluid-flow chamber. The mixing vane portion extends in the downstream direction from the gas injection portion and define a second region of the interior fluid-flow chamber.