Characterization of floc size, strength and structure under various coagulation mechanisms

Abstract

Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. charge neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent γ was of the following hierarchy: charge neutralization (0.6107) N sweep (0.5618) N bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m − 2 . An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated.

Fractal-like structures in colloid science

“…The clusters formed under these conditions are open, with a fractal dimension of about 1.6-1.7, slightly lower than those found in DLCA [60]. However, in practically relevant conditions, this aggregation process is carried out in the presence of shear, which as expected increases the density of clusters, and therefore their fractal dimensions, to values ranging from 2.4 to 2.8, depending on the shear rate used [61]. It is generally observed that clusters obtained from bridging flocculation have lower fractal dimension than the one formed from their counterparts obtained by just addition of high concentration of electrolytes under otherwise identical conditions [62].…”

Effects of Slow-Mixing on the Coagulation Performance of Polyaluminum Chloride (PACI)

“…Many researchers [6][7][8][9][10][11][12] have found that, in addition to slow-mixing conditions, coagulants and coagulation mechanisms have significant effects on the size, strength and structure of flocs. This indicates that the effects of slow-mixing on coagulation are probably influenced by coagulants and coagulation mechanisms.…”

Characterization of kaolin flocs formed by polyacrylamide as flocculation aids

“…The use of polymers in water treatment can achieve rapid flocculation and result in better settling or filtrating behaviors. Several studies have demonstrated that various flocculation mechanisms are responsible for different floc characteristics (Li et al, 2006). It has been established that the polymers can flocculate particles via bridging, charge neutralization, electrostatic patch and depletion flocculation mechanisms.…”