Characterization of alum floc by image analysis

In-situ monitoring of particle characteristics is of general interest for b oth natural and engineered aquatic systems and of particular interest in st udying the fragile flee that typically is formed by the addition of chemica l coagulants. A nonintrusive photographic technique coupled with digital im age processing for in-situ analysis of aggregates formed by the addition of alum [Al-2(SO4)(3). 18H(2)O] to lake water and a montmorillonite clay susp ension is described. The technique is unique in that there is no need for s ample collection and handling. The analysis method is used to test the hypo thesis that charge-neutralization and sweep-flee mechanisms produce fundame ntally different particle characteristics, including differences in fractal dimension. For comparative purposes, particle characteristics prior to coa gulant addition also are reported. It is found that fractal dimension is lo wer for sweep-flee coagulation where larger and more irregular aggregates a re produced. The results presented here provide insight to jar test data an d help explain why better settling often is observed in practice for sweep- flee coagulation as compared to flee produced by a charge-neutralization me chanism.