Filtration is a unitary operation designed to remove solid particles from a liquid. It is particularly useful when solids take a long time to settle or when dealing with high flow rates. The time required for sedimentation depends on the velocity at which the particles settle, which in turn is determined by the difference in density between the sludge and the liquid, following Stoke's law. When flow rates are high or the sludge has a very low density, the sedimentation time can become significantly prolonged, making filtration an essential process for efficient separation.