Effects of humic acid on recoverability and fractal structure
of alum-kaolin flocs |
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Authors: | Runsheng Zhong Xihui Zhang Feng Xiao and Xiaoyan Li |
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Institution: | 1. Research Center for Environmental Engineering (&) Management, Graduate School at Shenzhen,Tsinghua University, Shenzhen 518055, China 2. Department of Civil Engineering, The University of Hongkong, Hongkong 999077, China |
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Abstract: | Particle surface characteristics, floc recoverability and fractal structure of alum-kaolin flocs were investigated using in situ particle
image velocimetry (PIV) and microbalance with or without humic acid. Experimental results indicated that the zeta potential of
kaolin particle surface after adsorption of humic acid was related with humic acid concentration and its acid-base bu ering capacity.
Adsorption of humic acid resulted in more negative electrophoresis on the particle surface. Coagulant dosages for particles to form
flocs would increase with increasing humic concentration. PIV was used to evaluate floc structural fragmentation, floc surface erosion
as well as recoverability after high shear. It was found that the floc size during the steady phase of growth was small, while the
regrowing capability decreased in the presence of humic acid. The recoverability was closely related with floc breakage modes including
floc structural fragmentation and floc surface erosion. The fractal dimensions of alum-kaolin flocs by mass-size method based on
microbalance would decrease with increasing humic concentration. This study proved that humic acid had adverse influences on the
performance of coagulation process. |
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Keywords: | humic acid particle image velocimetry floc breakage recoverability fractal dimension |
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