Application of Numerical Simulation to Investigate Fractal Structure of Floc Formed in Flocculation Process of Water Treatment

Efficiency of solid/liquid separation is greatly related to floc structure. In this paper, two-dimensional model of diffusion-limited aggregation (DLA) has been used to simulate the fractal structure of floc. Investigation was carried out to examine how characteristic parameters of floc morphology, such as floc radius of gyration, fractal dimension and void ratio, varied with simulation conditions. The results showed that virtual floc formed by DLA model was an irregular fractal object of randomicity and uncertainty, for which statistic average of simulation results was used to reflect fractal structure of virtual floc under corresponding simulation condition, and the statistic values did not strictly follow some rule changing along with simulation conditions. However, from the whole aspect the statistic characteristics were both floc radius of gyration and void ratio increased and fractal dimension decreased with increasing amount of aggregated particles. The simulation results indicated that increasing escaping radius of moving particle (defined as k value in the paper) and adopting the nearest-neighborhood (NN) manner were beneficial to the formation of compact flocs, and the nearest-neighbor and next-neighbor manner (NNN) benefited the formation of large flocs.