The oil removable is a liquid/solid separation operation. Oils and greases being generally lighter than water and naturally tend to rise to the surface. In order to speed up this process, an aerator placed in the centre of the well, diffuses fine bubbles which bring grease and oil particles to the surface. Before they solidify, they are leaded by a scum deflector which drains the waste out of the tank. The aerated oil separation equipment is used in small and medium-sized facilities and for 2.2 to 7 m diameter tanks.