Abstract: A waste water treatment system including a vessel having a closed loop flow path, a bottom and a wall. A clarifier is mounted on the vessel wall within the vessel and includes a clarifier wall which is elongated in the direction of the flow path and is relatively narrowly spaced from the vessel wall. A clarifier wall extends from the bottom to a location above the intended level of waste water to define a clarifying chamber that is relatively narrow. Inlets may be located along the length of the clarifier wall and the bottom wall of the clarifying chamber may be provided with sludge outlets.