Abstract: An improvement is provided in the operation of a long vertical shaft bioreactor in the treatment of waste which comprises circulating waste liquor and oxygenating gas through the bioreactor in which the uppermost portion of the shaft (the surface basin) is under supra-atmospheric pressure. The use of a pressurized surface basin subjects the waste to improved oxidizing conditions in a critical zone of the bioreactor and results in more effective biodegradation of the waste. By precise control of surface basin pressure, adequate levels of oxygen in the waste are maintained for biodegradation purposes while unwanted gas, such as carbon dioxide and nitrogen, are disengaged. The pressure on the surface of the waste in the basin is controlled so as to ensure that the concentration of oxygen in the waste is subsaturated and retained while the unwanted gas concentration is super saturated and becomes disengaged.

Abstract: An improved method and apparatus is provided for the treatment of sewage waste in a long vertical shaft bioreactor wherein waste sewage is caused to circulate under air injected oxidizing conditions around a loop comprising adjacent riser and downcomer chambers connected at their upper and lower ends. The improved method comprises the steps of introducing influent waste at depth into the riser chamber at a point higher in the riser than the point of air injection and withdrawing treated effluent from the riser at a point lower in the riser than the point of air injection. A separation chamber may also be operatively connected to the riser chamber to recover sludge for return to the bioreactor. The method provides an improvement in oxygen uptake rate and reduces the anoxic zone in the reactor thus providing additional capacity for BOD.sub.5 removal.

Abstract: In a long vertical shaft bioreactor for the treatment of degradable wastes in a circulating loop, a process is provided for separating and treating the slowly biodegradable components of the waste. The process comprises the steps of aerating and oxidizing the waste liquor in the reactor to produce an effluent and a foam which foam contains the slowly biodegradable components, which have not been degraded in the oxidizing step, separating and collecting the foam, collapsing the foam and subjecting the collapsed foam to further aeration/oxidation treatment to produce a treated effluent. The thus further treated effluent is returned to the bioreactor for reprocessing.

Abstract: An improved method and apparatus is provided for maintaining a constant gas-to-solids ratio in the effluent from a long vertical shaft waste treatment bioreactor. In a vertical bioreactor wherein waste is circulated under air-injected oxidation conditions around a loop comprising adjacent downcomer and riser chambers connected at their terminals and operatively connected to a separation apparatus, the improvement comprises withdrawing treated effluent from the riser chamber into a cylindrical vessel from whence the effluent is directed either to the separation chamber or into the influent stream depending on the total level of fluid in the bioreactor. Removal of large air bubbles from the effluent is also effected in the cylindrical vessel. The method provides improved gas-to-solids ratio in the effluent and improves sludge flotation in the separation apparatus.

Abstract: In a long vertical shaft activated sludge bioreactor for the treatment of waste water and the flotation/separation of solids therefrom, an improvement is provided whereby fluctuations in flow through the bioreactor are maintained level without the use of complex control mechanisms and whereby separation from the effluent of dispersed air bubbles occurs directly in the flotation/separation vessel rather than in the shaft or an auxiliary vessel. The improvement provides for the installation of a holding reservoir between the shaft and the flotation/separation vessel. Influent passes through the reservoir on its way to the bioreactor and some make-up effluent from the flotation/separation vessel is directed into the holding reservoir as the level of liquid in the reservoir falls. In addition, means are provided in the separation/flotation vessel to split off large dispersed gas bubbles which would otherwise disrupt sludge flotation.

Abstract: An improved long vertical shaft bioreactor for the treatment of degradable waste is provided wherein the head tank or basin surmounting the vertical downcomer and riser chambers is surrounded by a foam oxidation vessel. Conduits are provided between the head tank and the foam vessel through which (a) foam accumulated in the head tank is passed to the foam vessel and (b) through which excess fluid in the head tank may be vented.

Abstract: A method and apparatus is provided whereby a pressurized long vertical shaft bioreactor is protected against extreme surges of influent waste liquid. The method provides for the transfer of excess waste from the top of the bioreactor head tank to an adjacent collection vessel where, in response to the pressure created in the bioreactor, the collected waste is caused to overflow and is returned to the influent waste stream. The method permits the return of waste from the reactor to the influent stream while bypassing the normal circulation route through the reactor. Simplification of control is provided and float or level control valves may be eliminated thereby reducing construction, operating and maintenance costs.