GB622474A - Improvements in or relating to method and apparatus for treating liquids containing suspended solids - Google Patents

Abstract

622,474. Gravity-separation apparatus INFILCO, Inc. May 30, 1946, No. 16446. Convention date, Oct. 26, 1942. [Class III] A process of clarifying liquids containing solids, such as sewage, by sedimentation in a tank, includes mixing the liquid to be clarified in a mixing zone with partially thickened sludge drawn from a level substantially spaced above the bottom of the tank whereby the solids suspended in the liquid are conditioned for sedimentation, and discharging the mixture into the tank at a level above the level of withdrawal of thickened sludge and below the liquid level. The mixing zone is preferably arranged within the sedimentation tank. A tank 1 is spanned by beams. 10, from which is suspended a cylinder 11, open at top and bottom, the lower edge being a suitable distance below the water level in the tank so that liquid escaping from under it will be clarified in passing to a launder 7. An inner cylinder 12, also open at top and bottom, is adjustably supported and carries an adjustably-mounted baffle plate 15, of diameter somewhat greater than that of the inner cylinder 12. The bottom of the cylinder 12 is substantially above the bottom ,of the tank 1, and its upper end is substantially below the liquid level but above the lower end of the cylinder 12. In use, the tank is filled with sewage, and a propeller 30 rotated to draw partially-thickened sludge in over the plate 15 into the inner cylinder 12, from which it passes into the cylinder 11 and then downwardly. Raw sewage entering through an inlet pipe 35 will become mixed with the rising column of partially thickened sludge, and its solid matter entrained therein. The mixture passing out from the lower end 21 of the outer cylinder 11, being of a density approaching that of the sludge at the level of the plate 15 tends to level off across the basin, and from this layer a quantity of clarified sewage corresponding to the rate of inflow, will rise to the launder 7. As a result of this levelling across the basin, the circulation effect of the propeller 30 extends to a layer over the whole tank area between the level of the lower edge 21 of the outer cylinder and the baffle plate 15. The space occupied by the mixing zone 11, 12 may thus be made quite small and the effective volume of the tank 1 not materally reduced. Also the circulation causes a substantial quantity of the liquid in the tank to be aerated by exposure to the atmosphere in the cylinder 11.