Quantitative Characterization of Floc Size and Fractal Structure during Dynamic Flocculation Process

Full Title

Quantitative Characterization of Floc Size and Fractal Structure during Dynamic Flocculation Process

Event

IWA World Water Congress 2010

Authors and Affiliations

J. Nan, W. P. He

State Key Laboratory of Urban Water Resource and Environment/School of Municipal and Environmental Engineering, Harbin Institute of Technology,

73 Huanghe Road, Nangang District, Harbin 150090, China

(E-mail: nanjun11@163.com; heweipeng1983@163.com)

Abstract

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Based on the diffusion-limited aggregation (DLA) mechanism, floc aggregation simulation was adopted to investigate how floc characteristic parameters, such as floc size and fractal dimension, would vary during the formation process. Then polyaluminium chloride (PAC) was selected as a coagulant, kaolin and humic acid suspension as testing water samples, and in situ recognition technique for floc configuration of water was employed to extract floc morphological characteristics. The modelling results showed that virtual floc formed by DLA model was an irregular fractal object, and the statistic values did not strictly follow some rule changing along with aggregated particle counts. However, from the whole aspect the statistic characteristics were floc size increased and fractal dimension decreased with aggregated particle amount, which was the same as that in actual flocculation process. Through quantitative description of the evolution on floc characteristics, it was found that hydrodynamic conditions greatly affected the aggregation of suspended particles and flocculation efficiency, and adopting gradually decreased velocity gradient and increased corresponding flocculation time in flocculation reactor design is beneficial to floc formation and flocculation efficiency. The in situ recognition technique provides a useful tool for investigation on how flocs have formed in the flocculation process and how multinomial factors interact to reach a dynamic balance.

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