Physical Chemical Waste Water Grade 1 Practice Exam

Dissolved air flotation removes materials that can be buoyed to the surface by tiny air bubbles. Oil and grease fits this well because oils and fats tend to form droplets or emulsions that readily attach to bubbles; when floated, they rise to the surface as a skimmed layer, making them easy to remove. In contrast, nitrates and chlorides are dissolved ions that stay in the water and aren’t removed by flotation, and phosphates are typically removed by chemical precipitation or biological uptake rather than flotation alone. So the substance most effectively removed by DAF is oil and grease.