Predicting the Floc Characteristics and Settling Velocity of Flocs under Variable Dosage of Polyacrylamide

Abstract

Abstract. In this study, floc characteristics such as fractal dimension and settling velocity were investigated through a flocculantion process with a polyacrylamide (PAM) flocculant over a range of suspended particle concentrations, suspension type and flocculant dosage. The floc's structure and morphology were characterized by optical microscopy and scanning electron microscopy (SEM) methods. Floc settling velocity was measured in a settling column in a laboratory. The results showed that, the surface fractal dimension ranged from 1.044 to 1.415, which quantitatively confirmed the round and layered structure of flocs observed in SEM analyses. The PAM flocculant was proved to be more effective in flocculantion process, increasing the settling velocity. Therefore, an appropriate PAM dosage is an excellent candidate as efficient flocculant. A possible flocculantion mechanism for PAM was further analyzed. For alkaline or neutral environments, adsorption and bridging effects are dominant while charge neutralization is favored in acidic conditions.

Modeling of Flocculation and Sedimentation Using Population Balance Equation

“…Finally, images of the flocs were captured by a microscope imaging system and analyzed by the Image pro Plus 6.0 software; this is how the size of the floc was measured. e detailed results for the flocculation and sedimentation experiments are presented previously [29].…”

“…Considering that the previous experiment of flocculation and sedimentation were carried out in a 1000 ml graduated cylinder, the three-dimensional geometry of this cylinder was built with a 0.068 m diameter and 0.44 m height. e details of the experimental data can be found in the cited references [29]. Meshing was implemented using a structural mesh of 0.04 mm grid sizes.…”

“…It can also be observed from Figure 4 that the settling velocity of u is significantly greater than the settling velocities of either v or w. e effect of the boundary of the settlement area is negligible. Experimental studies were also conducted on the flocculation of cohesive sand suspensions [29]. e settling velocities of the flocs in those experiments were 0.003∼0.011 m•s − 1 for particles whose concentration is 5 g/L and 0.005∼0.015 m•s − 1 for particles whose concentration is 15 g/L, while the calculated settling velocity used in this study is 0.0038∼0.012 m•s − 1 in 15 s∼30 s ( Figure 5).…”