Effects of salinity on the physical characteristics of activated sludge flocs

grantor: University of TorontoThe effect of increased wastewater salinity on the physical characteristics of activated sludge flocs was studied by exposing samples of activated sludge to increased NaCl concentrations (salinity test), and to varying Ca$\sp{2+}$:Na$\sp+$ ratios (calcium test). The time response of the flocs to the increased NaCl was also measured. Two salinity tests were run and, for both tests, it was determined that as the NaCl concentration was increased, the mean floc size increased, with the flocs also becoming more elongated with decreasing shape factor. The increase in floc size is considered to be due to a combination of electrostatic and hydrophobic interactions. Both the porosity and the boundary fractal dimension were found to provide different values in the two salinity tests. The flocs were found to exhibit two distinct Sierpinski fractal dimensions, thus indicating the presence of two pore size populations. Increased salinity had little effect on the smaller pore size population but a significant effect on the larger pore size population. The time response test indicated that the flocs achieved the new characteristics in about 15 minutes. The calcium test revealed that a minimum mean floc size was achieved at a Ca$\sp{2+}$:Na$\sp+$ ratio of 1.0 and the flocs' shape was not correlated with size. The porosity decreased with increasing ratios until an equilibrium value was achieved. The floc surface profile was found to become more rugged with an increased mean floc size and smoother with a decreased mean floc size. Finally, examination of all size distributions revealed that the data were best fitted by a log normal distribution.M.A.Sc