Flocculation time is conventionally believed to be proportional to the flocculation efficiency of a cylindrical fluidized bed flocculator.However,in a single-stage velocity gradient situation,the flocculation efficiency decreases when the optimal flocculation time is exceeded.A multi-stage velocity gradient was established in a cylindrical fluidized bed flocculator,based on the hydraulic classification theory.This multi-stage velocity gradient fluidized bed flocculator(MGF) created a more suitable environment for floc growth and protection,which was confirmed by the size distribution of flocs along the bed height.Correspondingly,the abatement efficiencies for Kaolin slurry and dyed wastewater treatment in the MGF were enhanced by5-10%,and by 7-20%,respectively,compared with those in the single-stage velocity gradient fluidized bed flocculators(SGFs).The initial bed height distribution ratio along the velocity gradients was an important factor for MGF optimization.
The efficiency of a fluidized-bed flocculator with 800- m particles of 1360 kg/m3 in density was studied, and the anti-shock capability of the unit was estimated for three kinds of industrial wastewater: heavy turbidity wastewater, dispersed dyeing wastewater and starch wastewater. Steady removal efficiency was contributed by the following characteristics of the flocculator: (1) the dynamic conditions, flocculation time and velocity gradient, which were stabilized at a steady level as the loading rate changed; (2) hydrodynamic characteristics, especially the considerable rise of expanded bed height with increasing superficial velocity when small and light particles were employed as the solid phase; (3) flocs growth characteristics in the fluidized bed, which caused the density and size of the flocs being maintained at a compensational relationship, resulted the stabilized settling velocity of the flocs.
