A settling device (1) for liquid treatment including a plurality of inclined, spaced-apart panels (5) each providing an upper settling surface for receiving settled out solid contents of the liquid to be treated, wherein the panels (5) are supported in a box-like structure (2,3,4) including two side walls, and wherein said device includes an inlet or inlets for liquid to be treated and an outlet or outlets for purified liquid. At least one of the side wall sides of the box-like structure (2,3,4) is provided, at the top, with a top portion to be positioned vertically so as to obtain a purified liquid level inside the device between a low level which is below a upper portion of the inclined panels and a high level which is above said upper portion of the panels.