Effect of mean velocity gradient and mixing time on particle removal in seawater induced flocculation

Various combinations of mean velocity gradient (G) and mixing time (t d ) in the seawater flocculation of industrial wastewater and oxidation pond effluent were investigated. The optimum product of these parameters (Gt d ) lies within the range of 16,000 to 160,000. Inclusion of a slow mixing phase improved particle removal over that achieved by rapid mixing alone at equal gSGtd. The minimum Gt d at which peak particle removal was achieved decreased as seawater dosage increased. Similar trends were demonstrated with increasing dosages of the flocculant chitosan. An empirical model of flocculation kinetics, having the same form as the partice aggregation-floe breakup model, was found to portray accurately the effects of G and t d .