Breakage, regrowth, and fractal nature of natural organic matter flocs.

The growth, breakage, regrowth, and fractal nature of flocs was investigated by use of a laser diffraction particle sizing device. A range of coagulants were investigated for the coagulation of natural organic matter (NOM) and compared to other coagulated systems. The results showed NOM floc structural characteristics varied in steady-state size depending upon which coagulant was used. When compared to other systems, the order of floc size was Fe precipitate > Fe-NOM > latex (in NaCl solution). Floc regrowth after exposure to high shear was limited for all of the flocs under investigation other than for latex in an inert electrolyte. This highlighted differences in the internal bonding structure of flocs, with the results suggesting that physical bonds have a capacity to re-form after breakage. Fractal dimension analysis by small-angle laser light scattering (SALLS) had limited applicability to large flocs that dominated all of the systems under investigation, but the degree of compaction increased as flocs were broken in high shear. This provided a possible mechanistic reason for the irreversible breakage seen.