Floc Breakup in Turbulent Flocculation Processes

by Denny S. Parker, Proj. Engr.; Brown and Caldwell, Consulting Engrs., San Francisco, CA,
Warren J. Kaufman, Dir., Sanitary Engrg. Research Lab., and Prof. of Sanitary Engrg.; Univ. of California, Berkeley, CA,
David Jenkins, Assoc. Prof. of Sanitary Engrg. and Chf. Chemist, Sanitary Engrg. Research Lab.; Univ. of California, Berkeley, CA,

Serial Information: Journal of the Sanitary Engineering Division, 1972, Vol. 98, Issue 1, Pg. 79-99

Document Type: Journal Paper


Floc breakup theories are developed for the complex activated sludge floc and they are applied as well to inorganic chemical flocs. Rate expressions were developed for two modes of breakup in two hydraulic regimes. In one type of breakup it was assumed that primary particles are eroded from the floc surface when the surface shearing forces exceed the shear strength of the bonds joining the particles to the floc surface. The analysis of this surface shearing force required the description of floc motion in the turbulent environment. Expressions were developed for the peak floc size as a function of shearing conditions. The rate of floc breakup was described as the product of the number of metastable floc, the frequency of metastable floc disruption, and the number of primary particles eroded per disruption. A second form of floc breakup was observed experimentally with activated sludge floc. It appeared that the overall integrity of the floc was controlled by a filament mesh running through the floc allowing the buildup of very large floc prior to breakage. The high strength of these filaments seemed to allow the buildup of flocs to sizes that would not be possible in the absence of filaments.

Subject Headings: Shear strength | Flocculation | Particles | Shear forces | Erosion | Activated sludge | Chemicals | Bonding | Hydraulics

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