Abstract: A rotatable bell is provided having a generally downwardly diverging shape about a central vertical axis, with the outer wall surface of the bell including a circumferentially extending jet flow surface portion with a plurality of gas flow wall openings circumferentially disposed around the base part thereof. Liquid is flowed downwardly over the jet flow surface portion of the wall from the upper part to the base part thereof to provide a high shear jet flow of liquid into which gas is injected for gas-liquid contacting and bulk mixing thereof.

Abstract: The hypolimnion of thermally stratified water bodies is oxygenated by withdrawing water therefrom at rate of 10-200 percent of the hypolimnion volume per month, pressurizing the withdrawn water to superatmospheric pressure below 125 psig, injecting at least 80 percent oxygen gas at rate of 5-300 lbs. O.sub.2 per million pounds withdrawn water but less than a rate to result in O.sub.2 supersaturation at the remixing point, returning the mixture through conduit means and remixing same at rate to produce specified frictional head loss.