ABSTRACT
A higher shear force would result in a stronger and compact biofilm, whereas biofilm tends to become a heterogeneous, porous, and weaker structure when the shear force is weak. Biofilm density correlates very closely with the self-immobilization strength of fixed bacteria, which is determined by the shear force imposed on the biofilms. In anaerobic granulation, it has been observed that granulation proceeded well at relatively high hydrodynamic shear condition in terms of high upflow liquid velocity, whereas anaerobic granulation was absent at a weak hydrodynamic shear force. As shear force has an important role in aerobic granulation and granule stability, a minimum shear force seems necessary for aerobic granulation. The size of aerobic granules is strongly associated with the hydrodynamic shear force where smaller aerobic granules can be developed under higher shear conditions. Hydrodynamic conditions caused by upflow aeration served as the main shear force in the column-type reactor commonly employed for the cultivation of aerobic granules.
