Abstract: A clarifier for use in treating a liquid containing non-soluble particles in suspension in order to separate these particles from the liquid includes a tank, a liquid supply duct opening into the bottom portion of the tank and an injector for injecting a gas under pressure into at least part of liquid supplied to the supply duct in order to saturate this liquid with the gas and thus to generate gas bubbles as the saturated liquid is subject to depressurization within the tank. The gas bubbles that are so generated adhere to the particles in suspension in the liquid and lift them up to form a floating layer of sludge in the top portion of the tank. A scraper is provided in the top portion of the tank for skimming off the layer of sludge while it is formed. A plurality of plates extend at an angle within the tank above the supply duct. These plates define a set of upwardly inclined channels each having an upper end that is opened and through which the liquid fed into the tank may enter the channel.