[Effect of shear stress on morphology, structure and microbial activity of aerobic granules]

The aerobic granules were cultivated in four sequencing batch reactors (SBRs) under the shear stress of 0.189, 0.267, 0.327 and 0.377 N/m2, respectively. The morphology and structure, specific oxygen utilization rate (SOUR) and extracellular polymeric substances of different aerobic granules were studied. Results show that aerobic granules can maintain the stable morphologic characteristics. A close examination of the granule surface revealed the presence of a large diversity of microbial morphotypes, including bacterial rods and cocci, and fungi. These microorganisms are embedded in an extracellular polymeric matrix. The bacterial robs were the dominant microbes in the granules under 0.377 N/m2. In the four reactors, the diameters of the granules are 0.2-0.5, 0.5-1.5, 0.5-1.5 and 0.3-0.5 mm; SOUR are 34.54, 40.08, 46.26 and 46.42 mg/(g x h); the extracellular polysaccharides are 59.71, 66.81, 80.88 and 109.99 mg/g; the extracellular proteins are 9.29, 9.80, 12.35 and 17.02 mg/g; respectively and correspondingly. The positive relationship of the microbial activity of the aerobic granules with the shear stress was introduced depending on the analysis of the variation of SOUR and extracellular polymeric substances.