Factors affecting the settling of activated sludge flocs: An analysis

This study is aimed at investigating the factors; inherent structural characteristics as well as external and other factors, affecting the settleability of activated sludge flocs. It was found that the longest dimension was the most important factor affecting the settling velocity in comparison with other inherent floc characteristics. The smaller the Sierpinski fractal dimension, the higher the permeability of activated sludge flocs and the higher the settling velocity. The effects of the geometric porosity, the shape factor and the external surface roughness were insignificant. Some conditions, such as high F/M ratio or high DO concentration, and the addition of polymer or salinity, could increase the permeability of activated sludge flocs and thereby result in good settleability of the sludge. The sludge age had, as expected, no obvious effect on the geometric porosity of activated sludge flocs in full-scale systems. SVI proved to be a valid measure of the sludge settleability.