Strength of ferric hydroxide flocs

Strength and break-up of flocs produced in flocculation of water and effluent with ferric chloride were studied. Floc size was determined by a photographing technique and area and perimeter measurements by a Quantimet apparatus.The experimental results obeyed the expression d_max = GC⁻²γ with γ = 0.3 for effluent and γ = 0.5 for water indicating both viscous and inertial effects in break-up. Floc strength parameter C increased with polymeric coagulant aid addition, higher C values were obtained in water than in effluent.Floc break-up seems to take place by erosion of particles and flocs once disrupted do not grow again.