[Influence of hydrodynamic turbulence characteristics on the sedimentation of activated sludge]

For the optimization on design and function of active sludge system, the influences of hydrodynamic turbulence characteristics on the sedimentation of active sludge were studied. Hydrodynamic turbulence conditions were changed by adjustment of stirring paddle in sequencing batch reactor (SBR). With the technology of particle image velocimetry (PIV), the distribution of turbulence intensity under different parts in sequencing batch reactor (SBR) was analyzed. The results show that the turbulence intensity in area within the 15 mm distance around stirring paddle was higher than other areas. The characteristics of turbulence were reflected by the turbulence intensity of string axis in 1-1 section and 2-2 section. With increasing of rotate speed of stirring paddle, the turbulence intensity of different parts in SBR increased gradually, and the sedimentation performances of active sludge improved first and then deteriorated. The best sedimentation performance of active sludge in the experiment, which the smallest sedimentation volume index (SVI) was 67 mL/g, and the largest sedimentation velocity was 0.20 mm/s, occurred when the turbulence intensity of the main part in stirring zone was 1.51% and other part 0.31%. The area of main part in stirring zone was smaller than other parts, and the turbulence intensity of main part in stirring zone was higher than other parts. The hydrodynamic turbulence characteristics of main part had remarkable function on the breaking up of active sludge, while the hydrodynamic turbulence characteristics of other part had higher influence on sedimentation performances of active sludge. Decreasing the hydrodynamic turbulence intensity of main part in stirring zone and increasing the hydrodynamic turbulence intensity of main part in stirring zone can be performed to improve the sedimentation of activated sludge in practice.