The invention concerns a plant comprising, on a vertical axis, a
homogenizing vessel (1) followed by a settling vessel (2) and a
flocculating vat (3). The homogenizing vessel (1) is fed by tangential
intake (92) of the effluent and the input (611) and the output (612) of
the upper tube (61) comprise a helical guide (613, 614) for driving the
effluent in rotation. The lower tube (62) of larger diameter than that of
the upper tube (61) is terminated by an outlet in the form of an
upside-down cone (622) with reduced cross-section (621). The lower
portion (31) of the flocculation vat (3) is truncated, with an apex
angle, smaller than that of the upper portion (32), said lower portion
(31) being parallel to the cone of the outlet of the lower tube (62), and
anti-backflow cones (7, 8) surround the conduit (6) in the settling
vessel (2).