An apparatus for use in tie treatment of substrates with a solid particulate material, said apparatus comprising a housing having mounted therein a rotatably mounted drum having an inner surface and an end wall, and access means for introducing said substrates into said drum, wherein (a) said drum comprises storage means for storage of said sold particulate material; (b) said drum has at least one elongate protrusion located on said inner surface of said drum wherein the elongate protrusion extends in a direction away from said end wall, wherein said elongate protrusion has an end proximal to the end wall and an end distal to the end wall; (c) the or each elongate protrusion comprises a collecting aperture and a collecting flow path to facilitate flow of said solid particulate material from the interior of said drum to said storage means, wherein said collecting aperture defines the start of a collecting flow path, and wherein the same elongate protrusion further comprises a dispensing aperture and a dispensing flow path to facilitate flow of said solid particulate material from said storage means to the interior of said drum, wherein said dispensing aperture defines the end of a dispensing flow path; (d) wherein said collecting aperture is disposed in a first side of said elongate protrusion, wherein said first side of said elongate protrusion is the leading side of said elongate protrusion during rotation of the drum in a collecting direction; and (e) wherein said flow of said solid particulate material from the storage means towards the interior of the drum is facilitated by the rotation of said drum in a dispensing direction and the flow of said solid particulate material from the interior of tie drum towards the storage means is facilitated by the rotation of said drum in said collecting direction, wherein rotation in said dispensing direction is in the opposite rotational direction to rotation in said collecting direction, characterised in that: (f) said elongate protrusion exhibits one or more harvesting apertures disposed in a second side of said elongate protrusion, wherein the second side is defined as the leading side of said elongate protrusion during rotation of the drum in said dispensing direction, wherein said harvesting aperture(s) are in fluid communication with a harvesting flow path, wherein said harvesting aperture(s) facilitate flow of said solid particulate material from toe interior of said drum via said harvesting flow path to said storage means during rotation of the drum in a dispensing direction.