The influence of starvation phase on the properties and the development of aerobic granules

The current study was to evaluate the influence of starvation phase on surface negative charge, relative hydrophobicity, extra-cellular polymer substances (EPS) and the formation mechanism of aerobic granules. Granules with encouraging settling properties occurred in the reactor about 7 days after the inoculation. The surface negative charge decreased from 0.203 to 0.023 meq g VSS−1 and the relative hydrophobicity increased from 28.8 to 60.3% during the granulation period. Concentrations of protein and carbohydrate decreased from 18.0 to 7.1 and 7.0 to 2.9 mg g VSS−1, respectively in the first period. And from day 13, those values were observed in the range of 5.8–8.6 and 2.9–5.6 mg g VSS−1, respectively. The EPS especially protein concentrations well correlated with surface charge and relatively hydrophobicity. It was concluded that a reasonable amount of EPS should be controlled to form and maintain aerobic granules. It was proposed that aerobic granulation was initiated by starvation phase and then enhanced by anaerobic metabolism.