Search

AbstractThis work aims to evaluate the effect of different velocity gradient and rapid mixing time on floc properties of picophytoplankton, using polyaluminum chloride (PACl) and polysilicato-iron (PSI) as coagulant. The growth, breakage, and re-growth of flocs were followed by a particle size analyzer in order to investigate the underlying mechanisms. Three different zones were found to be depending on Gvalue in coagulation process. At low Gvalue (G < 200 s−1), the aggregation dominated over breakup. At mean Gvalues(G = 250 s−1for Synechococcussp.-PSI flocs and G = 546 s−1for kaolin-PSI flocs; G = 200 s−1for Synechococcussp.-PACl flocs and G = 390 s−1for kaolin-PACl flocs) flocs formation wAS maximized, producing the largest flocs. For large Gvalues (G > 250 s−1for Synechococcussp.-PSI flocs and G > 546 s−1for kaolin-PSI flocs; G > 200 Synechococcussp.-PACl flocs and G > 390 s−1for kaolin-PACl flocs), breakup dominated over floc formation. Broken flocs did not fully re-grow after breakage; however, the re-growth rate of Synechococcussp. flocs was larger than that of kaolin flocs, probably as a result of the surface properties of Synechococcussp. The rapid mixing time of 60 and 90 s led to maximum floc formation Synechococcussp. and kaolin systems, respectively.