In-situ polyelectrolyte-clay flocculation via radial polymer injection in Taylor-Couette flows

Flocculation of small particulates suspended in solutions is a key process in many industries, including drinking water treatment. The particles are aggregated during mixing to form larger aggregates through use of a flocculant. The flocculation of these particulates in water treatment, however, are subject to a wide spatial variation of hydrodynamic flow states, which has consequences for floc size, growth rate, and microstructure. Floc assembly dynamics are explored here using a commercially available cationic polyacrylamide flocculant and anisotropic Na-bentonite clay under a variety of hydrodynamic mixing conditions. A Taylor-Couette cell with the unique ability to radially inject fluid into the rotating annulus was used to study how specific hydrodynamic flow fields affect floc assembly and structure during the entire flocculation process. Faster floc growth rates and decreased floc fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and shear rounding of the flocs, respectively. This work sheds more light on the complexities of polymer-induced flocculation, towards improving dosing for more efficient large-scale operations.