Apparatus for separation

Apparatus for removal of solid and semi-solid material from a liquid flowing in a channel, said apparatus comprising a conveyor including a conveyor helix rotatable about an axis inclined to the horizontal, and a casing at least partly surrounding the conveyor helix, said conveyor having a lower portion extending into said channel, said casing being perforated in said lower portion to form a screening device to separate solid and semi-solid material from the liquid passing through the screening device so that the solid and semi-solid material can be transported upwardly by the conveyor helix, said conveyor further including an upper portion at which the solid or semi-solid material is discharged, and at least one further screening device extending from said conveyor across said channel, said further screening device comprising a wall having an imperforate wall portion and a perforate wall portion, said imperforate portion being connected to said casing and extending to a bottom of said channel, said perforate portion being confined to an upper portion of said wall in an upper part of said channel.