Physical Characteristics of Activated Sludge Flocs

Abstract

In this article, 13 physical characteristics of activated sludge flocs, corresponding measuring techniques, and typical values reported in the literature are reviewed. It appears that floc sizes, filament length and number, floc settling velocity, and floc density have been well defined and can be measured directly by some methods. The determination of floc shape, total surface area, volume, water content, water release, porosity, and floc strength depends more or less on the acceptance of their definitions. Basically, these physical properties cannot be observed directly. The study of floc pore radius and tortuosity, which reveal more detailed floc structure, has just recently begun and its research significance remains to be seen. The physical characteristics reviewed in this study are influenced by or related to many physical, chemical, biological, biochemical, and even methodological factors, which are also discussed.