Fractal dimensions of flocs between clay particles and HAB organisms |
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| Authors: | Hongliang Wang Zhiming Yu Xihua Cao Xiuxian Song |
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| Institution: | (1) Regional Research Center for Coastal Environments of Yellow Sea, Inha University, Incheon, 402-751, Korea;(2) Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China;(3) epartment of Oceanography, Inha University, Incheon, 402-751, Korea |
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| Abstract: | The impact of harmful algal blooms (HABs) on public health and related economics have been increasing in many coastal regions
of the world. Sedimentation of algal cells through flocculation with clay particles is a promising strategy for controlling
HABs. Previous studies found that removal efficiency (RE) was influenced by many factors, including clay type and concentration,
algal growth stage, and physiological aspects of HAB cells. To estimate the effect of morphological characteristics of the
aggregates on HAB cell removal, fractal dimensions were measured and the RE of three species of HAB organism, Heterosigma akashiwo, Alexandrium tamarense, and Skeletonema costatum, by original clay and modified clay, was determined. For all HAB species, the modified clay had a higher RE than original
clay. For the original clay, the two-dimensional fractal dimension (D
2) was 1.92 and three-dimensional fractal dimension (D
3) 2.81, while for the modified clay, D
2 was 1.84 and D
3 was 2.50. The addition of polyaluminum chloride (PACl) lead to a decrease of the repulsive barrier between clay particles,
and resulted in lower D
2 and D
3. Due to the decrease of D
3, and the increase of the effective sticking coefficient, the flocculation rate between modified clay particles and HAB organisms
increased, and thus resulted in a high RE. The fractal dimensions of flocs differed in HAB species with different cell morphologies.
For example, Alexandrium tamarense cells are ellipsoidal, and the D
3 and D
2 of flocs were the highest, while for Skeletonema costatum, which has filamentous cells, the D
3 and D
2 of flocs were the lowest. |
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