Laboratory and full-scale studies of liquid stream viscosity and streaming current for characterization and monitoring of dewaterability

Abstract

Many laboratory tests are available to evaluate the dewaterability of a given sludge with a specific type of conditioner. However, most of these are empirical and shed little light on dewaterability mechanisms. The most common laboratory measurements are also not amenable to continuous or flow-through use for actual process application. Viscosity and streaming current are two methods of characterizing the effectiveness of sludge conditioning which may be advantageous in these aspects. Both can be used as measurements characterizing the liquid stream—centrate or filtrate—from the dewatering process. Thus, this study assessed the utility of determining the liquid stream viscosity or streaming current using both lab and full scale experiments. Results were compared to other laboratory measurements of dewaterability, such as the capillary suction time (CST), the conditioned sludge streaming current (SC), and centrate total solids. They were also compared to CST, cake solids content, filtrate turbidity, and percent solids recovery in full-scale dewaterability evaluations. A significant correlation between the centrate viscosity and CST was established, with both related to dewaterability as shown by other parameters. There was also a clear relationship between the CST, the filtrate SC, and these with other dewaterability measures, such as the solids recovery, in the full-scale testing. A minimum CST, SC values near-zero for both centrate and conditioning sludge, and minimum centrate or filtrate viscosity all correlate with maximum solids recovery. These results are of significance both in explaining conditioning and dewatering mechanisms and for possible application in feedback control of polymer dose.