Floc compaction during ballasted aggregation

Ballasted aggregation, a process using the addition of a ballasting agent to improve the settling performance of flocs, appears particularly appropriate for the treatment of humic rich waters that leads to low-density aggregates. In that context, using an aquagenic humic acid coagulated by ferric ch...

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Bibliographic Details
Published in:Water research (Oxford) 2016-11, Vol.105, p.361-369
Main Authors: Sieliechi, J., Lartiges, B., Skali-Lami, S., Kayem, J., Kamga, R.
Format: Article
Language:English
Subjects:
Agglomeration
Aggregates
Ballasted aggregation
Ballasting agent
Chemical engineering
Chemical Sciences
Company structure
Environmental Engineering
Environmental Sciences
Floc compaction
Floc restructuring
Flocculation
Fractal analysis
Fractal dimension
Fractals
Humic acid
Humic Substances
Mathematical models
Models, Theoretical
Reagents
Settling
Turbulent flow
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Summary:Ballasted aggregation, a process using the addition of a ballasting agent to improve the settling performance of flocs, appears particularly appropriate for the treatment of humic rich waters that leads to low-density aggregates. In that context, using an aquagenic humic acid coagulated by ferric chloride in the presence of pozzolana particles as ballasting agent, we show that the origin of improved floc settling in ballasted aggregation is not simply related to an increased specific weight of flocs, but also to a significant restructuring of flocs to a more compact structure induced by the added particles. The floc restructuring is evidenced from the increased lag time before measurable floc growth in the presence of the ballasting agent, the higher fractal dimension of flocs above the micron scale range after incorporation of the particles into the aggregates, and a much smaller sediment volume after settling. A simple model of floc compaction based on the turbulent viscous effects that act on an elastic floc, is described. [Display omitted] •Ballast particles induce a significant floc compaction during ballasted aggregation.•Floc restructuring is revealed by an increased lag time before measurable floc growth.•The fractal dimension of flocs increases above the micron scale range.•Floc compaction is modelled from the turbulent viscous effects on an elastic floc.
ISSN:0043-1354
1879-2448
DOI:10.1016/j.watres.2016.09.015