In many industries are common processes using physical force to achieve the desired separation of solid and liquid components. These processes are called mechanical separation processes and include sedimentation, centrifugation (mainly hydrocyclone) and filtering. In this book, the interest is focused on environmental applications. Separation processes play an important role in the mechanical cleaning of soil and water. This contribution deals with the modeling of solid-liquid separation processes and the corresponding experiments. The text is divided into two parts: separation by hydrocyclones used for relatively dilute suspensions and separation of sludge by filtration.