BACKGROUND: Most studies on the cultivation of aerobic granules to date have been based on the sequencing batch reactor (SBR). A continuous flow airlift fluidized bed reactor (CAFB) was set up, and the operating conditions which promoted granulation in the SBR were not controlled. The distribution characteristics of extracellular polymeric substances (EPS) and cells of the aerobic granules were studied under these operating conditions.
RESULTS: Cells, polysaccharide and protein were all distributed uniformly throughout the granules, confirmed by both confocal laser scanning microscopy and scanning electron microscopy observations. However, for the granules in the SBR, the core of the granules was usually composed of protein and dead cells, and living cells survived only in their outer layers. Such a distribution of granules in the CAFB was confirmed to be related to the advanced oxygen transfer ability and strong shear force in the CAFB. Even microbial cells in the center were supplied with sufficient food to maintain bioactivity. Thus, the CAFB performed COD removal very efficiently.
CONCLUSION: Cells and EPS in the aerobic granules of a CAFB were more uniformly distributed compared with those in granules of the reported SBR reactors, owing to the particular operating conditions of the CAFB. © 2012 Society of Chemical Industry