Abstract: Liquid treatment apparatus, principally for effluent purification comprises a liquid basin with a suitable inlet and outlet, and a treatment space in which is disposed a lamellar insert construction forming a plurality of narrow, mutually parallel channels through which liquid flow is laminar and the axes of which are inclined to the vertical. For effluent purification the treatment space is a main sedimentation space downstream of a preliminary sedimentation space. The lamellar insert construction can be suspended from floats connected to a mobile dredger for movement with the latter.