Abstract: An apparatus for purifying BOD-containing water by the action of activated sludge, which includes a vessel for containing activated sludge-containing liquid, and an aerator which is installed in the vessel. The aerator has a bubbler which successively takes out the liquid in the vessel for causing the liquid to absorb oxygen, and a settler which calmly returns the oxygen-rich liquid into the vessel.

Abstract: An apparatus for enriching dissolved oxygen in water which comprises a plurality of dissolving devices, each of which comprises: (a) a pair of vertically arranged tubular bodies, the lower end of the first tubular body being provided with an inlet through which raw water is introduced and the lower end of the second tubular body being provided with an outlet for discharging oxygen enriched water; (b) a tube connecting the interior of both tubular bodies at the central portions thereof; (c) a bubbler disposed in the interior of the first tubular body for flowing an oxygen enriched gas into the raw water and for moving the raw water into the second tubular body through the connecting tube; (d) a pipe for connecting the top portions of the tubular bodies which form a chamber for the gas above the liquid level of the raw water in each of the tubular bodies; (e) a means for supplying an oxygen enriched gas into the chamber in the second tubular body; and (f) a means for supplying the gas in the chambers to the bub