Abstract Polyaluminum chloride (PACl) is a commonly used coagulant for water treatment. One mode of action of PACl \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$\rm {[ ( AlO_4Al_{12} ( OH ) _{24} ( H_2O ) _{12} ) ^{7 + } ]}$$ \end{document} is reported to be through the formation of polymeric Al-oxyhydroxide precipitate aggregates that bridge between colloids. Although many studies have considered the effectiveness of PACl under a spectrum of conditions for influent suspensions, little is known about the effect of precipitate aggregate size on the subsequent formation of flocs that can be readily removed by sedimentation. Self-aggregation of polymeric Al-oxyhydroxide precipitate and the rate at which this occurs may be used to guide the designs used for...