Abstract:

Theoretically, multi-stage velocity gradients contribute to a more suitable environment for flocs growth. However, most studies on the fluidized bed flocculator were based on the single stage velocity gradient by now. Multi-stage velocity gradients were set up with 800 μm and 1 200 μm resin particles as solid phases in this work, and the growth and morphological characteristics of the formed flocs were especially studied. The formed flocs were broken according to size distribution figure in the single-stage velocity gradient fluidized bed with solid phase of 1 200 μm resin particles and a flocculation time of 50.3 s. As a result, the flocculation efficiency decreased 3% as compared with that operated for a flocculation time of 41.8 s. It should be noticed that the size of the flocs increased continuously from 5.7 μm to 70.0-75.0 μm as the flocculation time extended in the multi-stage velocity gradient fluidized bed flocculator. Meanwhile, the flocculation efficiency increased 5%-10% compared with the bed operated under single-stage velocity gradient. The collision among the mini-flocs was the main growth model of the flocs.

Key words: fluidized bed, velocity gradient, flocculation, fractal dimension