Pelleting flocculation can be viewed as a technique that improves the sludge characteristics, which may be beneficial during the subsequent phase of solid-liquid separation. Generated flocs structures possess an appearance of nearly spherical beads with an enhanced stability. The literature provides two theoretical growth models of such pellet-like flocs: (i) series and (ii) parallel system. The parallel system concerns the formation of aggregates with a high degree of structural order that is called onion-like structure. Consequently, in reported cases of pelleting flocculation this kind of internal buildup of flocs was strongly suggested. Contrary to these statements, the reasoning presented here demonstrates that the predominantly non-uniform interior structure of pellet flocs, here termed raspberry-like structure, is the result of sludge conditioning by pelleting flocculation. The goal of this paper is to present and discuss the structural attributes of pellet floc aggregates in terms of internal buildup and to reorder the available literature on pelleting flocculation according to the proposed reinterpretation of the concepts of this technique. (c) 2006 Elsevier Ltd. All rights reserved.