Abstract: A multi-stage, recycling, centrifugal, flotation separator system, comprising a circular cylindrical vessel with vertical axis, having a horizontal tray positioned inside the vessel near the top, the tray having an axial opening. Means for introducing air under pressure into the vessel at the top thereof, and means for introducing contaminated liquid into the vessel through a tangential pipe, under pressure, at a level below the tray. Means to recycle air from the top of the vessel into the inlet line and to mix the recycled air with the contaminated liquid before entry into the vessel. Means to recycle liquid from the bottom of said vessel, through a tangential pipe into the vessel at a level below that of the contaminated liquid, and means to mix recycled air with the recycled liquid prior to entry into the vessel.

Abstract: A gravity clarifier for separating biological sludge from the water by gravity settling, which comprises a cylindrical tank having a closed bottom with a downwardly depending truncated conical shell attached at its large end to the upper portion of the tank wall, with a peripheral trough near the top end of the tank and a weir for the overflow of effluent liquid into the trough. The influent conduit enters the tank tangentially and flows the raw mixture into the tank in the space between the outside of the inverted conical shell and the tank wall. The sludge is removed from the tank bottom near the center of the tank.