Massachusetts Wastewater Practice Exam

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Where does the thickened sludge exit from a dissolved air flotation clarifier?

Right side.
Left side.
Bottom.
Top.

The correct answer is: Top.

In a dissolved air flotation (DAF) clarifier, the thickened sludge primarily exits from the top. The mechanism of a DAF system is designed to remove solids and oils from wastewater using a flotation technique. In this system, small air bubbles are generated and introduced into the sludge, causing the solids to rise to the surface. As a result of this flotation process, the thickened sludge accumulates at the top of the clarifier, making it easier to skim off. This method is effective in separating suspended solids from the liquid phase. The clear effluent is typically drawn off from the bottom or side of the clarifier, which allows the heavier solids to float and concentrate near the surface for easy removal. The design of the DAF clarifier inherently promotes the exit of thickened sludge from the top due to the buoyancy of the solids, emphasizing the operational principle of floating rather than settling.