Floc strength evaluation at alternative shearing with presence of natural organic matters

The effects of natural organic matters (NOM) on Al-floc stability were investigated by on-line probing of changes in floc diameters and interior fractal dimensions at alternative shearing using the small angle light-scattering technique. Fine kaolin particles coagulated with polyaluminum chloride (PACl) formed flocs of size adjusted during subsequent alternative shearing. The presence of humic acid or chitosan reduced or boosted floc formation. Floc breakage is completely irreversible at high humic acid concentrations. Certain master curves for floc size versus time curves were assessed, depending on shearing rate and added organic substances but not on the alternative shearing rates. A two-level floc breakage and reformation scheme was proposed in this study to interpret the observation results.