Assessment of hydraulic flocculation processes using CFD

Abstract

The performance of flocculation tanks either in full‐ or pilot‐scale systems cannot be fully quantified using average velocity gradient values (G values) alone. The computational fluid dynamics (CFD) process was used to investigate the turbulent flow characteristics of a three‐stage hydraulic flocculation facility at the J.D. Kline Water Supply Plant in Halifax, Nova Scotia. Calculations of the local velocity gradient were achieved using predicted energy dissipation rates. CFD analysis showed unbalanced mixing conditions in the hydraulic flocculation tanks resulting from short‐circuiting and from recirculation zones. Inconsistent mixing energy, interrupted with severe spikes in the localized G values at the weir columns, led to little or no mixing energy in most of the regions in the flocculation tanks. Practical outcomes of operating at such varying mixing gradients can be detrimental to the flocculation process and overall organic removal in the treatment plant.