Method for anaerobic sludge digestion

Abstract

Method and apparatus for anaerobically digesting sludge by filling an anaerobic sludge digestion vessel having a top and bottom and a substantially vertical draft tube with an upper end spaced downward of the vessel top and a lower end spaced upward of the vessel bottom, with liquid sludge to a level substantially above the draft tube upper end; feeding a pressurized stream of liquid sludge to the inlet side of an upwardly directed jet nozzle operatively positioned and in communication with a substantially vertical venturi tube having a lower inlet and forming part of the draft tube lower end to a lower pressure thereby creating suction at the venturi tube inlet and producing a pumping action which causes a stream of liquid sludge in the vessel bottom space to flow into and upwardly in and out of the draft tube upper end and to thoroughly admix and disperse with the pressurized sludge stream supplied to the jet nozzle and also causing downward circulating flow of liquid sludge in the vessel. Additional sludge mixing can be achieved by placing a similar jet nozzle and venturi tube at the top of the vessel to produce a downward mixing flow of sludge in the draft tube. Also, such a jet pump can be mounted substantially tangentially of the vessel wall to produce helical mixing of the sludge in the vessel. The driving liquid fed to the jet nozzle can be partially digested sludge withdrawn from the vessel, raw sludge or a mixture thereof.