Journal
JOURNAL OF ENVIRONMENTAL SCIENCES
Volume 101, Issue -, Pages 168-176Publisher
SCIENCE PRESS
DOI: 10.1016/j.jes.2020.08.016
Keywords
Coagulation; Floc size; Additives; Fractal dimension; Zeta potential
Categories
Funding
- National Natural Science Foundation of China [51108444]
- Key Research and Development Plan of the Ministry of Science and Technology [2019YFD1100104, 2019YFC1906501]
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The structure properties of flocs have a significant impact on coagulation efficiency. The addition of ferric salt can facilitate the growth of Al flocs, while phosphate and citric acid have less significant effects. Citric acid has a more striking negative effect on the growth ability of the flocs compared to phosphate.
Structure properties of flocs (size, fractal dimension (D-f), etc.) have a high impact on coagulation efficiency. In this work, the influences of three different additives (ferric salt (Fe), phosphate (P), and citric acid (CA)) on coagulation process/efficiency were investigated. Results showed that a small amount of extra Fe can facilitate the growth of Al flocs by providing more 'active sites'. Although zeta potential and Df showed a limited change, the average floc size increased apparently and the increment was more obvious when Fe was added after the formation of the flocs. In contrast, P addition during the rapid mixing period will decrease the final average floc size, while the influence is less significant when P was added after the growth of the flocs. In terms of CA, a more striking negative effect on the growth ability of the flocs was observed compared to P. The strong complexing/coordination interactions between CA and aluminum hydroxide is the main reason behind the influence. CA also significantly decreased the Df value of the flocs compared to P, and Df showed a comparatively higher decrease when P or CA was added during the rapid mixing stage compared to the addition after the flocs formation. These results indicated that the addition of CA or P during the rapid mixing stage 'inactivated' or occupied more 'active sites' on the preliminarily formed Al NPs during the hydrolysis process, and therefore presented stronger impact on the morphology/size of the formed flocs. (C) 2020 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
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