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Study on Morphological Evolution of Floc Breakage/Aggregation and Fractal Simulation in Water

Author: LeMingXiang
Tutor: NanJun
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: fractal structure reflocculation diffusion-limited-aggregation (DLA) model simulation
CLC: O661.1
Type: Master's thesis
Year: 2010
Downloads: 119
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Abstract

Flocculation is one of the key units in the process of water treatment, the effect of flocculation has a significant impact on the subsequent operating conditions, the water quality of outflow and the costs of water treatment, so it is always an important field in water treatment engineering. During the process of flocculation, floc structure is closely related to solid-liquid separation section , so it is always the point where people focus on. To form the flocs with large density and excellent sedimentation has become the joint aim of water treatment workers. However, we often encounter the phenomenon of floc breakage in the practical flocculation process. And the structure of flocs would take place great changes after its breakage.In this paper, poly aluminium chloride (PAC) was taken as flocculant and suspended particles of Kaolin and humic acid were regarded as the removal target. By using high definition digital camara to shoot the constant moving floc particles in the reactor, experiments were carried out to study the influence on the floc structure and the transforming procedure of floc fractal structure in the process of flocculation-breakage-reflocculation when hydrodynamic conditions were changed. Results showed that the flocs could recover to a certain extent under given hydraulic stirring after floc breakage. They also indicated that the flocs formed by high dosage of flocculants could have much higher strength through the reflocculation process. And slow flocculation velocity and high reflocculation velocity could both be helpful for forming the compact flocs.Two-dimensional model of diffusion-limited aggregation(DLA) was used to simulate the growing process of the flocs on the platform of Matlab. By changing the population of particles, moving paths and adhering manners, we obtain a series of floc pictures in the process of simulation. After analyzing the virtual flocs formed by different simulation conditions, we could calculate the morphological parameters of floc fractal structure. The results showed that virtual flocs and the real flocs shared the same feature of fractal structure. Both fractal dimension and numerical density decreased with increasing amount of aggregated particles, however, the gyration of floc radius and void ratio increased with increasing amount of aggregated particles. Increasing escaping radius(large k values) or adopting NN adhering manner can both be helpful to form the compact flocs.Method of single-factor and two-factor analysis of variance in statistics were used to analyzing the data obtained from simulation. The results showed that the interaction effect between adhering manners and the amount of aggregated particles had no significant impact on fractal dimension, numerical density and void ratio, however, it had great impact on floc radius of gyration. There was no interaction effect between moving paths and the amount of aggregated particles. Adhering manners had great impact on floc radius of gyration, fractal dimension, numerical density and void ratio. The amount of aggregated particles have great impact on floc radius of gyration, numerical density and void ratio, however, it had no impact on floc fractal dimension. The moving paths of particles had no impact on floc fractal dimension, numerical density and void ratio, however, it had great impact on floc radius of gyration.

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CLC: > Mathematical sciences and chemical > Chemistry > Analytical Chemistry > Fluid analysis, water analysis > Water analysis
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