Three zone dissolved air flotation clarifier with improved efficiency

Abstract

A compact dissolved-air-flotation (DAF) clarifier and clarification process utilize three zones for clarification which operate in sequence in a single clarifier. Raw water with suspended solids enters a flocculator at the center of an annular tank where microscopic air bubbles introduced to the inflow float flocked contaminants to form a floating sludge layer. A first clarification, calming and degassing occur here. The water then flows radially outwardly into the tank where further quiet clarification occurs. A third level of clarification occurs in a lower portion of the tank, specifically, in a set of plate-like lamellae, radial and conical, which form inclined channels where a final clarification occurs. The bottom wall of the tank has a set of apertures which allow a gravity flow of clarified water through a layer of pressurized gas to an underlying collection compartment. Level sensors control a valve in the clarified outflow line and an air bleed from the pressurized gas layer to regulate liquid levels in the clarifier. A set of rotating paddles push the sludge layer up a ramp to an inclined discharge conduit. Alternatively, a suction head with a mechanical skimmer sweeps around the tank to draw the sludge through a central hollow pipe to a discharge conduit. An offset drive operating through a belt rotates the sludge removal mechanism and the lamellae.