Assessment of the Hydraulic Performance of Flocculation Processes using Computational Fluid Dynamics (CFD)

The mixing energy input required for flocculation process is conventionally measured in terms of the average velocity gradient (G) values. However, it has been recognized that the hydraulic performance of flocculation tank designs in the full- or pilot-scale system cannot be fully quantified using the average parameters alone. Computational fluid dynamics (CFD) was used in this study to investigate the turbulent hydrodynamics characteristics of the full-scale hydraulic flocculator and pilot-scale paddle flocculator hosted at the J.D. Kline Water Supply Plant (JDKWSP) in Halifax, Canada. CFD simulations provided an accurate, economical method for determining the G-values and the local velocity gradient (Glocal) in terms of actual turbulent dissipation rate. One of the significant findings of CFD analysis illustrated the ineffective mixing condition in the hydraulic flocculator designs that might lead to potential negative consequences such as fragile floc (lower floc strength) formation, the reliance of chemical additives to avoid floc break-up.