In a DAF system, the air present in the pressurized water is best described as which form?

• A. Dissolved and entrained air
• B. Dissolved air
• C. Entrained air
• D. Compressed air bubbles

Answer: (A)

In a DAF system, air is introduced under high pressure so it dissolves in the water. When that pressurized water is released into the flotation chamber, the dissolved air comes out of solution as a large population of tiny bubbles (entrained in the liquid) that attach to suspended particles. So the air present is best described as both dissolved air (in solution under pressure) and the entrained microbubbles that form once the pressure drops. Saying only dissolved air misses the bubble form that actually drives flotation, while calling it just entrained air skips the fact that most of the air is dissolved under pressure before release. It isn’t about large compressed air bubbles, which aren’t the typical form in the flotation process.