This chapter has defined flocculation, described its environmental importance, and elaborated in detail on the nature of the resultant flocs. Considerable attention has been focused on the structural characteristics of freshwater flocs, from the colloidal components up to gross scale aspects of an entire floc. The composition and interaction of constituent components have been addressed with a conceptual model used to demonstrate how floc architecture influences floc behavior, physically (e.g., transport), chemically (e.g., contaminant uptake and transformation), and biologically (e.g., microbial community structure and biochemical activities). The growth and evolution of flocs and their stability is shown to be a combination of electrochemical and biological influences, with EPS often dominating in this regard. Consideration is given to the roles of suspended nanoscale and colloidal particles in aggregation processes which yield surface active materials for subsequent microbial colonization and floc formation. Flocs are shown to possess many of the same characteristics and functions as biofilms, with relevant biofilm research reported. Finally, the evolution of new technologies applicable to an improved understanding of flocculation processes is described. We anticipate that technology-driven investigations will reveal further relationships between the three-dimensional disposition of individual entities within a floc and specific important activities attributable to specific associations of floc components.

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