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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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Cite this document: Lapointe, M., Brosseau, C., Comeau, Y. & Barbeau, B. (2017). Assessing Alternative Media for Ballasted Flocculation. Journal of Environmental Engineering, 143(11). doi:10.1061/(asce)ee.1943-7870.0001271
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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

Open Access document in PolyPublie
Subjects: 1000 Génie civil > 1000 Génie civil
1000 Génie civil > 1006 Génie hydrologique
1000 Génie civil > 1007 Ressources et approvisionnement en eau
Department: Département des génies civil, géologique et des mines
Research Center: Non applicable
Funders: Industrial-NSERC Chair in Drinking Water (Polytechnique Montréal) research program, Veolia Water Technologies Canada, City of Montréal, City of Laval, City of Repentigny
Date Deposited: 16 Aug 2021 13:10
Last Modified: 22 Oct 2021 16:46
PolyPublie URL: https://publications.polymtl.ca/9088/
Document issued by the official publisher
Journal Title: Journal of Environmental Engineering (vol. 143, no. 11)
Publisher: ASCE
Official URL: https://doi.org/10.1061/(asce)ee.1943-7870.0001271


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