Multiscale structures of biological flocs

The three-dimensional pore structures in waste activated sludge floe were identified using the fluorescence in situ hybridization and confocal laser scanning microscope images. The interior of sludge floe was confirmed to have a multi scale structure, with pore cross-sectional area of 15-20 mum(2) as the transitional scale. Major advective flow would pass through the large pores, probed as a loosely packed, first level structuration. The chemical flocculation would enlarge the aspect ratio of large pores, while freezing and thawing reduced it. The second level structuration was comprised of fine pores with fractal boundaries, whose detailed structural information was extracted from the constructed floe model. After flocculation, the boundaries of fine pores would become more irregular, and freezing and thawing smoothed it. A sample calculation using the floe model demonstrated the intrafloc transport processes in floes of multiscale structures. (C) 2004 Elsevier Ltd. All rights reserved.