The effect of rapid mixing on the break‐up and re‐formation of flocs

Abstract

Abstract The effect of rapid mixing on floc formation, breakage and re‐formation using aluminium sulfate (‘alum’), polyaluminium chloride and a cationic polyelectrolyte were investigated using a continuous optical monitoring technique. For the aluminium‐based coagulants it was found that, with shorter times of rapid mix, larger flocs were formed, but only limited re‐growth occurred in all cases, indicating a significant irreversibility of the floc break‐up process. For cationic polyelectrolytes, the re‐growth of flocs occurred to a much greater extent and with longer rapid mix times floc breakage was almost fully reversible. Residual turbidity values before floc breakage and after re‐formation were consistent with the dynamic monitoring results. Copyright © 2004 Society of Chemical Industry