Correlations between floc physical properties and optimum polymer dosage in alum sludge conditioning and dewatering

This paper aims to examine the correlations between floc physical properties, such as size, density, structure (in terms of fractal dimension) and optimum dosage in an alum sludge conditioning with organic polymer and also dewatering using an air pressure plate apparatus. Initially, optimum dosage was evaluated by a modified specific resistance to filtration (SRF). Thereafter, floc size, density and structure were examined in greater detail by means of an image analysis system. The results of this investigation reveal that: (1) polymer conditioning of alum sludge can result in a significant increase of floc size with a plateau to be reached in higher dosages; (2) higher floc effective densities are associated with larger doses; and (3) increased fractal dimensions are associated with increased dose, particularly in small dosages, this reflecting the increased compactness of floc structure. However, no direct correlation was found between floc physical properties and optimum dose both in conditioning and dewatering except for the weak correlation in floc size and optimum dosage.