A combined experimental and numerical approach to the assessment of floc settling velocity using fractal geometry

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dc.contributor.authorMoruzzi, R. B. [UNESP]
dc.contributor.authorBridgeman, J.
dc.contributor.authorSilva, P. A.G. [UNESP]
dc.contributor.institutionUniversidade Estadual Paulista (Unesp)
dc.contributor.institutionUniversity of Bradford
dc.date.accessioned2020-12-12T01:28:10Z
dc.date.available2020-12-12T01:28:10Z
dc.date.issued2020-03-01
dc.description.abstractSedimentation processes are fundamental to solids/liquid separation in water and wastewater treatment, and therefore a robust understanding of the settlement characteristics of mass fractal aggregates (flocs) formed in the flocculation stage is fundamental to optimized settlement tank design and operation. However, the use of settling as a technique to determine aggregates' traits is limited by current understanding of permeability. In this paper, we combine experimental and numerical approaches to assess settling velocities of fractal aggregates. Using a non-intrusive in situ digital image-based method, three- and two-dimensional fractal dimensions were calculated for kaolin-based flocs. By considering shape and fractal dimension, the porosity, density and settling velocities of the flocs were calculated individually, and settling velocities compared with those of spheres of the same density using Stokes' law. Shape analysis shows that the settling velocities for fractal aggregates may be greater or less than those for perfect spheres. For example, fractal aggregates with floc fractal dimension, Df = 2.61, floc size, df > 320 μm and dp = 7.5 μm settle with lower velocities than those predicted by Stokes' law; whilst, for Df = 2.33, all aggregates of df > 70 μm and dp = 7.5 μm settled below the velocity calculated by Stokes' law for spheres. Conversely, fractal settling velocities were higher than spheres for all the range of sizes, when Df of 2.83 was simulated. The ratio of fractal aggregate to sphere settling velocity (the former being obtained from fractal porosity and density considerations), varied from 0.16 to 4.11 for aggregates in the range of 10 and 1,000 μm, primary particle size of 7.5 μm and a three-dimensional fractal dimension between 2.33 and 2.83. However, the ratio decreases to the range of 0.04-2.92 when primary particle size changes to 1.0 μm for the same fractal dimensions. Using the floc analysis technique developed here, the results demonstrate the difference in settlement behaviour between the approach developed here and the traditional Stokes' law approach using solid spheres. The technique and results demonstrate the improvements in understanding, and hence value to be derived, from an analysis based on fractal, rather than Euclidean, geometry when considering flocculation and subsequent clarification performance.en
dc.description.affiliationUNESP Universidade Estadual Paulista Instituto de Geociências e Ciências Exatas
dc.description.affiliationFaculty of Engineering and Informatics University of Bradford
dc.description.affiliationUnespUNESP Universidade Estadual Paulista Instituto de Geociências e Ciências Exatas
dc.format.extent915-924
dc.identifierhttp://dx.doi.org/10.2166/wst.2020.171
dc.identifier.citationWater Science and Technology, v. 81, n. 5, p. 915-924, 2020.
dc.identifier.doi10.2166/wst.2020.171
dc.identifier.issn1996-9732
dc.identifier.issn0273-1223
dc.identifier.scopus2-s2.0-85086681629
dc.identifier.urihttp://hdl.handle.net/11449/199008
dc.language.isoeng
dc.relation.ispartofWater Science and Technology
dc.sourceScopus
dc.subjectDensity
dc.subjectFlocculation
dc.subjectFractal dimension
dc.subjectPorosity
dc.subjectSettling velocity
dc.titleA combined experimental and numerical approach to the assessment of floc settling velocity using fractal geometryen
dc.typeArtigo

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