Development of a System for Evaluating Floc Strength

Abstract

A scheme is described as a basis for estimating floc strength by hydrodynamic shearing in a turbulent flow. Preliminary theory indicates the need to evaluate the floc size, its porosity (linked to its effective density in water) and the rate of energy dissipation in a turbulent flow (ɛ). The design and calibration of a vertical vibrating water column is described. Force transducer measurements gave estimates of (the average over the column) whereas a calorimetric technique and fluid tracer analysis provided additional information about ɛ as a function of vertical position. Flocs sedimenting through the column are subjected to increasing stress until a major rupture occurs. Preliminary experiments with clay-aluminium flocs provided insight into the factors controlling strength (σ) e.g. coagulant dose, size, and the number of primary particles within the floc (i) such that σ/i decreases with increasing floc diameter.