Optimizing Flocculator Power Input

The effect of the intensity and duration of the mixing used during and immediately following coagulant addition (initial mixing), the mixing intensity used for flocculation, the alum coagulant dose, and the length of the flocculation period on residual turbidity after sedimentation were studied using a laboratory jar test-type procedure. For a given flocculation period, T, there is an optimum G value, G*, corresponding to a minimum residual turbidity. The use of G* optimizes the power input to the flocculation basin. The product (G*)².⁸T, in which G is in sec^-¹ and T is in minutes is equal to 4.9 × 10⁵, 1.9 × 10⁵ and 0.7 × 10⁵ for alum doses of 10, 25, and 50 mg/l respectively. The product (G*)².⁸T is not a function of the initial mix conditions. The minimum residual turbidity decreases as the flocculation period, T, increases; however, the rate of decrease diminishes after a flocculation period of approx. 20 min.