AbstractThe flocculation of polystyrene particles with aluminum sulfate or alum (Al₂ (SO₄)₃) by turbulent shear was studied as a function of the applied shear rates (63–129 s₋₁) and flocculant concentrations (11 and 32 mg/L) in a stirred tank. Increasing the shear rate increased the floc growth rate but decreased the maximum attainable floc size. Increasing the concentration of alum increased the floc growth rate and the maximum floc size. A steady state between floc growth and breakage was attained after which the floc size distribution no longer changed. The normalized steady state size distributions allowed evaluation of the relative contributions of shear rate and flocculant concentration to the performance of the process.