Study on the characteristics and mechanism of the flocculation behaviour in a novel fluidized bed flocculator

Fluidized bed flocculator is a novel and efficient flocculation reactor. It has an efficiency that directly affected by flow field parameters. However, the structural characteristics of flocs and their influence on subsequent settling performance in fluidized bed flocculators are not clear. In this study, a multi-stage velocity gradient fluidized bed flocculator (MGF) was constructed for the continuous flocculation-sedimentation of kaolinite to investigate the growth and sedimentation behaviour of flocs. Additionally, MGF was compared with traditional mechanical stirring flocculation (MSF). Results showed that MGF achieved a higher removal efficiency (97.6 +/- 0.7 %) with less coagulant and flocculant than MSF. Moreover, flocs generated in the MGF yielded a faster settling perfor-mance, which can reduce the sedimentation time by 60 times. Comparative analysis of floc structural charac-teristics, as well as their relationship with the settling velocity, demonstrated that flocs in MGF were more compacted than those in MSFs and thus achieved higher settling velocity. The settling velocity was collabora-tively dominated by the size and fractal dimension of flocs. A modified Stokes' settling velocity equation introducing the structural characteristics of flocs was derived, and verified by actual data to accurately and quantitatively describe the settling velocity of irregular flocs. These results indicated that MGFs have a better flocculation and sedimentation performance than MSFs for solid-liquid separation, and may lay a theoretical foundation for the design of efficient fluidized bed flocculators and popularize their application in practical engineering.

Automated summary

This study compared a multi-stage velocity gradient fluidized bed flocculator (MGF) with a traditional mechanical stirring flocculator (MSF). The results showed that MGF achieved higher removal efficiency and faster settling performance, reducing sedimentation time. These findings provide a theoretical foundation for the design and practical application of efficient fluidized bed flocculators.