ABSTRACT
This chapter presents in-depth insights into the role of settling time in aerobic granulation in sequencing batch reactors (SBR). The fractions of aerobic granules in the reactors seem to be related to the settling times. Research on anaerobic granulation also showed that anaerobic granular sludge in upflow anaerobic sludge blanket reactors was more hydrophobic than the nongranular sludge washed out. It has been reported that high shear force can induce both aerobic biofilms and granules to secrete more extracellular polysaccharides, leading to a balanced structure of biofilm or granules under given hydrodynamic conditions. Aerobic granules can be successfully cultivated and become dominant only in the SBR operated at a short settling time, while a mixture of aerobic granules and suspended sludge is developed at a relatively long settling time. It is most likely that aerobic granulation would be an effective defensive or protective strategy of a microbial community against external selection pressure.
