Abstract: An upflow liquid clarifier for treating a liquid that contains dissolved or suspended solids has a lower chamber with two curved ends connected by a straight section, a centrally-disposed dividing wall extending upwardly from that lower chamber, and an outer wall that extends upwardly and outwardly from the lower chamber. Inlets in communication with the lower chamber provide entry for liquid, which rises in a helical motion through the clarifier. Motion of the water establishes a sludge blanket, through which clarified water rises and can be removed from near the top of the clarifier. A sludge removal structure allows the continuous or periodic removal of sludge.