Optimal Design and Operation of Settling Tank in Alternating Activated Sludge Process Based on 3-D Model Simulation

Proper design and operation of settling tank in an alternating activated sludge process is of vital importance for the development of this new technology in China. MIKE 3 HD and MT model is applied to simulate the settling and effluent discharging process of side tank in the alternating activated sludge process. The hydrodynamic modeling indicate that the vertical water flow rate is very low except in the inlet area and outlet weir area, which will provide favorable hydraulic conditions to ensure that the tank possesses long operation time for sludge sedimentation. According to sludge movement modeling, SVI has little impact on the effluent discharging, but the openness of the bottom holes would have a major impact on the tank operation performance. Larger openness of the bottom holes will result in a higher turbulent flow area in the tank, which might cause easier release of SS from the outlet. The tank operation performance would become better with less inflow velocity and smaller openness if the effect of flocculation is considered. It is suggested that design parameters should be carefully selected to balance both inflow velocity and bottom holes openness in these settling tanks.