impervious septum 4 there is provided a circular opening which accommodates a planar separating wall separating disc 7 which is provided with a plurality of holes 7a and which is rotated in the direction of the arrow a by a motor 9 situated in the waste collecting chamber 3b the rotary axis 7b of the separating wall 7 is perpendicular to the surface of the separating wall 7 the shaft 9a of the motor 9 is connected to the center of the circular separating wall 7 it is feasible to arrange the motor 9 externally of the casing 3 as well the openings such as holes 7a may be apertures in sieves wire meshes fabrics perforated panels or may be gaps slots comb like walls or the like it is known that the conventional processing for example ginning of fiber material upstream of the apparatus according to the invention effects the elimination of preponderantly large particles of waste and foreign bodies this processing however is in general not adapted to remove small parts such as dust microdust leaf fragments seed casings and other plant particles gathered from the cotton field or other impurities the perforations of the separating disc 7 have preferably a predetermined size to permit the passage of the above noted small impurities but these openings are sufficiently small to prevent passage of cotton tufts preferably the separating disc 7 is a sieve material whose mesh width may be selected to be coarse or fine according to requirements typically the area of the openings may be 7 mm 2 underneath the separating disc 7 there is provided an arcuate catching element 8 which has an opening 8a within the fiber collecting chamber 3a for collecting fiber tufts dropping from the separating.