Effect of Calcium Ion Concentration on the Structure of Activated Sludge Flocs

Abstract

The effect of increased calcium ion concentrations up to 10 meq l−1, in the presence of a fixed sodium ion concentration of 4 meq l−1, on the physical structure of activated sludge flocs was studied. Samples of activated sludge were exposed for 15 minutes to solutions with increasing calcium ion concentrations and then the physical structure of the individual flocs was investigated. It was observed that a minimum mean floc size (floc area, equivalent diameter, longest dimension, and perimeter) was achieved at a calcium ion concentration of 4.0 meq l−1 and that the flocs' shape was not correlated with their size. The flocs' porosity decreased with increasing ion concentration until an equilibrium value was achieved. As previously observed, the floc surface profile was found to be more rugged with an increased floc size and smoother with a decreased floc size. Examination of all size distributions revealed that the data were best fitted by a log normal distribution.