Abstract: A process for enriching a liquid with oxygen which includes the steps of: introducing a liquid and oxygen into a liquid and oxygen mixer and mixing the liquid with oxygen therein; introducing the liquid into a sealed enriching vessel containing a plurality of plates or trays, and flowing it gradually downwardly; subjecting the interior of the vessel to an oxygen pressure sufficient to enrich the liquid with oxygen; conducting the introduced liquid in a substantially flowing contact with the oxygen, whereby the liquid is enriched with oxygen; and recovering all of the oxygen-enriched liquid.

Abstract: Methods of treating circulating water containing oversprayed waterborne and/or solventborne paint, such as in a paint spray booth operation with copolymer of lignosulfonate and a cationic monomer subunit with Na.sub.2 CO.sub.3 and/or NaOH. The method does not require the use of metal salts or silicates.

Abstract: Waste water containing organic materials is introduced into an aeration tank, and is subjected to aeration treatment in the presence of activated sludge, while supplying oxygen to the aeration tank. The tank provided with an air diffusion pipe at the bottom of the tank, an air dispersion device above the air diffusion pipe and a plurality of inside cylinders above the air dispersion device. An overall circulating stream and partial circulating streams are generated in the aeration tank.