1985 Volume 11 Issue 5 Pages 589-595
Flocculation-sedimentation tests by polymeric flocculant addition were carried out in a reactor of large capacity (10 liters) with a gate-type paddle. The effects of solids concentration, flocculant dosage and flocculation mechanism on the optimum mixing conditions were investigated experimentally. Systems of kaolin-cationic polymer and of water works sludge-nonionic polymer were used; flocculation mechanisms were described by the surface charge neutralization and bridge models, respectively. The flocculation effect was assessed in terms of residual turbidity. The following points were determined experimentally. (1) The optimum rapid mixing conditions were given by the root mean square velocity gradient, G=610s-1, and the flocculation period, T= 90 s. (2) The slow mixing conditions could be assessed by the product of G and T. (3) The optimum value of GT was inversely proportional to flocculant dosage per unit mass of solids. This relation was well confirmed for both systems of solids and flocculant in the range of solids concentration from 100 to 500 mg/l.
