In order to produce small enough bubble size to promote good O2 tranfer without creating a rapid rise to the surface and promote mixing of the two layers, you will likely have to create an air saturation tank with several minutes residence time with at least 60-80 psig. This air water mix is then subjected to a quick pressure drop across a mixing valve. This is similar to design for a flotation device used in conventional waste water clarification through flotation ( look for dissolved air flotation design) The effect is tryue dissolved air, unlike diffused air, that looks like milk when 1st allowed through the mixing valve.
