The principal advantage of flotation over sedimentation is that very small or light particles that settle slowly may be removed more efficiently and in a much shorter time leading to an increasingly smaller tank volume and footprint.
Sedimentation separates from water, by gravitational settling, suspended particles that have a higher specific weight than water. The terms sedimentation and settling are used interchangeably. Flotation is another operation to separate solids or liquid particles from a liquid phase. Fine gas (usually air) bubbles are introduced into the liquid phase. The bubbles attach to the particulate matter, and the buoyant force of the combined particle and gas bubbles is big enough to cause the particle to rise to the surface. Particles that have a higher density then the liquid can thus be made to rise. The rising of particles with lower density then the liquid can also be facilitated (e.g. oil suspension in water). In wastewater treatment, flotation is used principally to remove suspended matter and to concentrate biological sludges.