In this work, the structure of two kaolin sludges and a waste activated sludge are investigated using both light-scattering and free-settling methods. Fractal dimensions estimated by the light-scattering and free-settling techniques (DS and DF respectively) differ significantly and support the hypothesis that naturally occurring aggregates possess a multilevel structure. A two-level floc structural model comprised of (i) a primary floc (of fractal dimension DS) consisting of primary particles and (ii) a secondary floc (of fractal dimension DF) consisting of the microflocs is proposed to interpret the experimental findings. The structural changes of sludge flocs before and after cationic flocculation are interpreted using the proposed two-level model.
Journal of Colloid and Interface Science 252(2), pp.383-392