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Assessing Alternative Media for Ballasted Flocculation

Mathieu Lapointe, Catherine Brosseau, Yves Comeau and Benoit Barbeau

Article (2017)

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Most current commercial applications of ballasted flocculation use silica sand to increase floc size and density. Other ballast media with different specific gravity may offer advantages such as increased applicable superficial velocity or increased particulate matter removal. This study assessed the relative effect of five ballast media on ballasted flocculation/settling performance: anthracite, recycled crushed glass, conventional silica sand, garnet sand, and magnetite sand, with a common d50 of 150 μm but variable specific densities of 1.45, 2.58, 2.62, 3.93, and 5.08, respectively. Based on microscopic observations and assuming discrete particle removal in an ideal settler, mean superficial media settling velocities were respectively calculated as 35, 73, 74, 122, and 137  m/h. These values do not account for the effect of lamellae or other specific geometries of different patented clarifiers (e.g., CoMag, Densadeg, Sirofloc, and Actiflo). Although the use of magnetite sand allows the total suspended solids load to increase by more than twofold compared to silica sand, the residual turbidity increased after settling as the mixing intensity needed to maintain denser media in suspension was augmented. Consequently, the lowest residual turbidity (0.78 NTU for surface water and 1.38 NTU for wastewater) was observed when anthracite was used as the ballast medium. The ballast media geometry did not significantly affect turbidity removal and settling velocity. Hence, recycled crushed glass was identified as a potential alternative to conventional silica sand despite its higher angularity.

Uncontrolled Keywords

Flocculation, Density (material), Sandy soils, Sand (material), Turbidity, Silica, Particle velocity, Soil mixing

Subjects: 1000 Civil engineering > 1000 Civil engineering
1000 Civil engineering > 1006 Hydrologic engineering
1000 Civil engineering > 1007 Water resources and supply
Department: Department of Civil, Geological and Mining Engineering
Funders: Industrial-NSERC Chair in Drinking Water (Polytechnique Montréal) research program, Veolia Water Technologies Canada, City of Montréal, City of Laval, City of Repentigny
PolyPublie URL: https://publications.polymtl.ca/9088/
Journal Title: Journal of Environmental Engineering (vol. 143, no. 11)
Publisher: ASCE
DOI: 10.1061/(asce)ee.1943-7870.0001271
Official URL: https://doi.org/10.1061/%28asce%29ee.1943-7870.000...
Date Deposited: 16 Aug 2021 13:10
Last Modified: 09 Apr 2024 01:41
Cite in APA 7: Lapointe, M., Brosseau, C., Comeau, Y., & Barbeau, B. (2017). Assessing Alternative Media for Ballasted Flocculation. Journal of Environmental Engineering, 143(11). https://doi.org/10.1061/%28asce%29ee.1943-7870.0001271


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