Impacts of structural characteristics on activated sludge floc stability
Journal article, 2003

Activated sludge samples from seven full scale plants were investigated in order to determine the relationship between floc structure and floc stability. Floc stability was determined by shear sensitivity and floc strength. Floc structure was considered in terms of two size scales, the micro and macro-structure. The micro-structure refers to the organisation of the floc components, such as the individual microorganisms. The macro-structure refers to the overall floc. The floc macro-structure was characterized by filament index, sludge volume index (SVI), size, and fractal dimension. It had a significant impact on floc stability. Large and open flocs with low fractal dimensions, containing large numbers of filaments were more shear sensitive and had lower floc strength compared to small and dense flocs. Fluorescent in-situ hybridisation (FISH) analysis indicated that the organization of the bacterial cells might also have an affect on the floc stability.

fractal dimension

floc strength


shear sensitivity


floc size

size distribution


Britt-Marie Wilen

Chalmers, Department of Water Environment Transport, Water Chemistry and Process Technology

B. Jin

University of Queensland

P. Lant

University of Queensland

Water Research

0043-1354 (ISSN)

Vol. 37 15 3632-3645

Subject Categories

Other Environmental Engineering



More information

Latest update