Method for separating off solid materials

A method for separating solid materials from a suspension comprising the steps of:

• providing a clarification tank having a substantially circular, flat base area and a substantially circular cross-section with a periphery and a center, the tank having an inlet at the periphery and an outlet at the center;
• directing the suspension through a chamber such that he suspension flows through an outlet of the chamber in communication with the tank inlet;
• tangentially introducing the suspension into the inlet of the clarification tank at the periphery of said tank;
• subjecting the suspension to a flotation step wherein bubbles are present to cause the solid materials to float to the surface and form a scum thereon;
• and
• directing the suspension into the outlet at the center of the tank along a substantially spiral path such that the suspension is accelerated along the spiral path;
• transporting, at selected intervals, the scum formed on the surface to a middle portion of the clarification tank and discharging the scum from the tank;
• and
• supplying pressurized air to the suspension and releasing the air into small air bubbles by relaxation before the suspension enters the clarification tank.