FIGURE 19.1 Relationship between the surface free energy of bioflocculation (AGflocculation(ergs/cm2) and the level of ESS (mg/l).

thermodynamics in explaining sludge floc formation. To date the characterization of the physicochemical properties of microbial floc, particularly hydrophobicity and surface charge, has been an academic activity. Given the relative ease of measuring hydrophobic properties (e.g., microbial adhesion to hydrocarbon and contact angle measurement) and surface charge (e.g., colloidal titration) of flocs, properties that can be correlated to bioflocculation and floc structure,15'16'30 such determinations may be of greater value in assessing sludge separation properties than the emphasis given to the role of filamentous bacteria.31

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