To optimize the performance of a DAF unit, which parameters should be controlled?

• A. Dissolved oxygen level
• B. pH
• C. Temperature
• D. Recycled rate, blanket thickness, and air/solids ratio

Answer: (D)

In a dissolved air flotation (DAF) unit, how well solids are removed hinges on controlling the bubble–solid interactions and the stability of the floating layer. The most direct levers are the recycled flow, which sustains the flotation system and keeps the blanket moving without washing out, the thickness of the floating sludge blanket to ensure there is enough surface area for bubbles to lift particles, and the air/solids ratio, which sets how many microbubbles are available to attach to the particles. Together, these three operable parameters govern bubble production, collision and attachment with solids, and the ability of the float to rise to and remain at the surface for removal.

Dissolved oxygen level, pH, and temperature can influence overall wastewater chemistry or bubble behavior in some contexts, but they are not the primary controls used to optimize DAF performance.