Effect of Aeration Induced Shear Stress on the Settleability and Activity of Activated Sludge

For the optimization on function of activated sludge system, the effects of aeration induced shear stress on the settleability and activity of activated sludge were studied. Laboratory experiments were carried out using six identical bioreactors. All of the aerated stirred bioreactors, of 2 L each in working volume and seeded with activated sludge, were operated as sequencing batch reactors (SBR) and fed at the same rate with a glucose-based synthetic wastewater. The reactors were supplied with airflow rates of 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 L air/min to induce different shear stresses. The results showed that activated sludge in bioreactors was sensitive to the variation of aeration induced shear stress. As the aeration induced shear stress increased, the settleability of activated sludge improved first and then deteriorated, while the specific oxygen uptake rate and the production of extracellular polymeric substances raised first and then dropped. The shear stress has significant influences on the microorganism ecosystem and structure of activated sludge. The settlement characteristics and activity of activated sludge could be controlled by manipulating the aeration induced shear stress.