Abstract: Apparatus for conveying a water-soluble or water swellable particulate material to a make up unit used in the hydration or dissolution of said material comprising: a scroll conveying line (6) comprising a duct (6A) defined by a wall and a scroll conveyor (6B) within said duct, wherein the scroll conveying line has an inlet (6D) through which material enters and an outlet (6C) through which the material leaves the scroll conveying line, and an air conveying line (3) comprising a duct through which an air stream conveys the material to a make up unit (18) in which the material is hydrated or dissolved to form an aqueous dilution or aqueous solution, in which the scroll conveying line (6) is provided with a means for ensuring the material substantially fills the space between the scroll conveyor and the wall of the duct at least at the outlet end of the conveying line, wherein the means is selected from, (a) the scroll conveying line (6) or outlet (6C) is in communication with an element that restricts the flow

Abstract: A process and apparatus therefore in which a sludge treatment stage 24 is controlled in response to the density or solids content of the sludge includes flowing sludge along a flow line 1 towards the treatment stage, taking a sample from the flow line 1, degassing the sample to produce a degassed sample, measuring the density or solids content of the degassed sample, and utilizing the measured degassed density or solids content of the degassed sample for controlling the treatment stage 24.