What is the mechanism of flotation in wastewater treatment?

In wastewater treatment, flotation is a process that involves the rising of air bubbles that attach to suspended solids, lifting them to the surface. This mechanism is particularly effective in removing light solids and greases that are less dense than water. When air is introduced into the wastewater, tiny air bubbles adhere to these particles, providing the necessary buoyancy to overcome the force of gravity. As the bubbles rise, they carry the attached solids with them, forming a scum or froth at the surface, which can then be easily removed.

This process is distinct from gravity settling, which relies on the weight of solids sinking to the bottom (as mentioned in the first option) and is less effective for separating lighter materials or suspended solids that do not readily settle. Heating water to evaporate contaminants, as stated in another option, is a thermal treatment method rather than a flotation process, and centrifugation involves spinning liquids rapidly to separate based on density, not flotation. Flotation is especially useful for treating oily wastewater or when dealing with fine particulate matter, making it a valuable technique in the overall water treatment process.