Floculation | EPFL Graph Search

La floculation est le processus physico-chimique au cours duquel des matières en suspension dans un liquide s'agglomèrent pour former des particules plus grosses, généralement très poreuses, nommées flocs. Les flocs sédimentent généralement beaucoup plus rapidement que les particules primaires dont ils sont formés. La floculation peut avoir lieu naturellement ou peut être accélérée par l'ajout d'un floculant comme l'acrylamide par exemple. Mécanisme de la floculation Floculation cationique La plupart des matières en suspension et en particulier les argiles portent des charges négatives : les particules argileuses devraient tomber mais l'effet de gravité reste négligeable par rapport à l'agitation thermique, la poussée d'Archimède et le fait que ces particules négatives se repoussent mutuellement (d'où une vitesse de chute de l'ordre de 0,33 m/h, insuffisante, les particules restant en suspension). Lorsque des cations neutralisent ces particules négatives, ils se

Polymer flocculents and preparation thereof

David Hunkeler

A high molecular weight water soluble graft copolymer having improved flocculating properties is provided. The backbone chain is a heteropolysaccharide comprising amino groups, in particular chitosan, grafted with one or more monoethylenically unsaturated monomers. The polymer is useful in solid/liquid separations such as flocculents and coagulants in processes utilizing water treatment, and as thickening agents.

2002

Suspended sediments in Lake Geneva: Observations, settling behaviour and mechanisms in the Rhône River plume

David Andrew Barry, Valentin Kindschi, Ulrich Lemmin, Violaine Piton, Htet Kyi Wynn

In estuaries and marine environments, primary particles are frequently transported as large flocculated particles. This study provides, for the first time, evidence of in situ flocculation in Lake Geneva, a glacier-fed freshwater lake on the Swiss/French border. Measurements were focused in the nearfield of the Rhône River plume as it flows as an interflow into the stratified lake. Direct observations of flocculated particles in the whole water column with a digital holographic camera (LISST-HOLO 20-2000 μm), permitted estimation of the variability of sediment floc properties (size, nature and shape) with depth. Combined with full depth in situ laser particle sizing (LISST-100X), the measurements revealed that primary particles (< 4 μm) and microflocs (4-100 μm) are dominant in the Rhône River interflow, which exhibited the highest suspended sediment loads in the water column. In the hypolimnion below the interflow, where the sediment loads were the lowest, macroflocs (100-450 μm) were most frequent. The estimated fractal dimension (DF3D) of the flocs in the hypolimnion range between 2.0 and 2.6, highlighting a large variability in the floc shape. Estimates of the settling velocities (Ws) showed an increase from 0.05 to 3 mm s-1 when floc sizes increased from 30 to 500 μm. This emphasizes the important influence of flocculation of fine sediments on the increase of Ws. These estimates are similar to previous estimates of Ws for fluvial flocs (Thonon et al., 2005). However, they are slightly faster (up to 2 times) than Ws estimated for flocs in the vicinity of the Rhône River plume as it flows into the Mediterranean Sea (Many et al., 2019). This difference in Ws between the two Rhône River plume environments is explained by the shapes of the flocs, which overall are less complex and therefore flocs settle faster in Lake Geneva compared to the Mediterranean Sea. Furthermore, the influence of instantaneous turbulent kinetic energy as a factor limiting the maximum floc size within the Rhône River interflow was investigated. The observed turbulence level in the interflow corresponded to an estimated Kolmogorov microscale of less than ~200 μm. This results in the potential breakup of flocs larger than 200 μm into smaller primary particles and microflocs and thus can explain the smaller floc size in the interflow compared to that in the hypolimnion.

2021

An experimental design methodology to evaluate the importance of different parameters on flocculation by polyelectrolytes

Hamideh Ahmadloo, Ineide Cruz Pinheiro, David Hunkeler, Christine Wandrey

Aggregation of particles is fundamental for improving the performance of many solid/liquid processes. Aggregation can be induced by different means, and one of the most common is based on the addition of polymeric additives, namely polyelectrolytes. In this work we have studied the flocculation of precipitated calcium carbonate (PCC), which is used as a filler in papermaking, and is induced by a range of cationic polyacrylamides with different structures, varying in molar mass and degree of branching. The flocculation process was monitored continuously using the LDS technique (laser diffraction scattering), which provides information about the size distribution and structure (fractal dimension) of the aggregates, for each sampling instant and, thus, about the kinetic curve for the flocculation process. This information has then been used to produce a model, based on an experimental design strategy, which allows us to relate flocculation efficiency with the PEL characteristics and concentration. The Partial Least Squares (PLS) regression method was selected to perform the regression, given the significant co linearity among the input variables. The results obtained lead us to conclude that the polymer intrinsic viscosity (related with the PEL molar mass and charge density, and supplying information about the volume of the polymer molecule in the solution) and the degree of branching are the parameters with a stronger influence on flocculation efficiency. The PLS models developed were also successfully validated using an independent data set, which provides confidence on their consistency and prediction accuracy. (C) 2012 Elsevier B.V. All rights reserved.

Elsevier Science Sa2013

Suspended sediments in Lake Geneva: Observations, settling behaviour and mechanisms in the Rhône River plume

David Andrew Barry, Valentin Kindschi, Ulrich Lemmin, Violaine Piton, Htet Kyi Wynn

2021