Characterization of Polyhydroxybutyrate-rich Aerobic Granules in an SBR under Nitrogen Deficient Conditions

Polyhydroxybutyrate (PHB)-rich aerobic granules were cultivated in a sequencing batch reactor (SBR) under nitrogen deficient conditions through a two-step strategy. In the first step the PHB-storage ability of activated sludge were enhanced by limiting both oxygen and ammonia initially, and PHB content of sludge increased to 43.1 +/- 2.0% at day 70; In the second step granular sludge was cultivated to get a high PHB volumetric productivity. During granulation, the settling ability of the PHB-rich sludge continuously improved. The mature PHB-rich granular sludge, with a PHB content of 40 +/- 4.6%, presented a buff color and regular morphology of elliptical and flat shape regardless of the diameter difference. In addition, the surface properties of activated sludge changed significantly during the cultivation. The surface charge, extracellular polymeric substances (EPS) content and the sludge hydrophobicity all increased during granulation, while the surface energy of sludge decreased to a relatively steady state accompanied with the growth of granular sludge. This study demonstrates that the metabolism of intracellular storages induced microbial to produce EPS, which favored the formation of aerobic granules.