Effect of Shear Stress on Properties and Extracellular PolymericSubstances of Aerobic Granules

摘要

Aerobic granules are cultivated successively in four column sequencing batch reactors ( SBRs) with the glucose as carbon source. The shear stress of 0. 189, 0.267 , 0.327 N/m~2 and 0. 377 N/m~2 is carefully and scientifically calculated in four SBRs, respectively. The effect of shear stress on the properties and extracellular polymeric substances ( EPS) production of aerobic granules are studied. With increasing of the shear stress from 0. 189 N/m~2 to 0.327 N/m~2, the granules become more compact, its diameter increases and the water capacity decreases, correspondingly. While shear stress raises to 0. 377 N/m~2, the granules change looser, its diameter decreases, and the water capacity increases, respectively. Aerobic granules appear a cloudy yellow color and elliptic balls with smooth surface. Aerobic granules have various microbial communities with the very clear outline. A plenty of protozoan and metazoan are enmeshed on the surface of sludge, such as epistylises , vorticellas , rotifers, paramecium and other swimming ciliates. Extracellular polymeric substances with good adsorption are the key constituent for the stabilization of aerobic granules. The higher shear stress stimulates more EPS production of the granules. In the four reactors, the extracellular polysaccharide of the granules is 59. 71, 66. 81, 80. 88 mg/g and 109. 99 mg/g respectively; the extracellular protein is 9. 29, 9. 80, 12. 35 mg/g and 17. 02 mg/g respectively and correspondingly.