Aerobic granulation in sequential sludge blanket reactor.

Aerobic granulation was studied in a column-type of sequential sludge blanket reactor. Reactor was operated 4 hours per cycle under a chemical oxygen demand (COD) loading rate of 6.0 kg/m3/d by using acetate as substrate. Results showed that aerobic granules with a mean diameter of 0.35 mm were observed at cycle 42. With granulation proceeding, the sludge volume index (SVI) value gradually decreased, and to an average value of 50 mL/g at stable granulation period. Observation of granules' microstructure by scanning electron microscopy (SEM) showed that rod bacteria were dominant in granules with lots of cavities presented. An increase in cell hydrophobicity was observed after the appearance of aerobic granules. The cell hydrophobicity of sludge was found to be about 50% higher after granulation. It appears that high hydrophobicity could induce cell attachment and further strengthen cell-cell interaction; cell hydrophobicity might therefore play a major role in the formation of aerobic granules.