Evaluating buoyant coarse media flocculation

Abstract

In laboratory and field studies, a two‐stage buoyant coarse media flocculator provided settled water turbidities <2 ntu at loading rates as high as 12 gpm/sq ft. A new type of coarse media flocculator, using buoyant media instead of the heavier gravel in order to facilitate cleaning, was evaluated in laboratory and field studies. The results indicate that a two‐stage buoyant coarse media (BCM) flocculator provided effective treatment at higher loading rates and shorter residence times than are typically employed in designing mechanical flocculators. Source‐water quality and coagulant chemistry directly influenced flocculator performance and dictated the type of flocculator configuration selected. Tapering velocity gradients in the first‐stage flocculator enhanced performance. The authors recommend that additional studies be performed to develop reliable design and operating criteria for full‐scale BCM flocculators.