Optimization of a full-scale dewatering operation based on the rheological characteristics of wastewater sludge

Rheology is the science that deals with the flow and deformation of materials, and it has become an important tool in optimizing sludge dewatering. This study presents torque rheology data to illustrate two different methods for polymer optimization. The methods can be used to optimize the polymer dose and mixing intensity, as well as to select the best performing product among a number of candidate polymers. The first method is used for unconditioned sludges, and utilizes the peaks observed after the polymer injection. The second method is used for conditioned sludges and utilizes the entire torque-time rheograms. Both methods were tested at the lab- and full-scale at the Plum Island Water Reclamation Facility (Charleston, SC) using three different polymers. The methods were able to optimize the polymer dose and full-scale mixing, and reduce the polymer consumption by 50% at the treatment plant. This translates into major savings for the utility. Furthermore, the results indicate that the total shear intensity imparted to sludge during full-scale conditioning can be determined using torque rheology, and the jar-tester shear can be matched to the total shear based on the rheological characteristics of sludge. This information is essential to be able to simulate the full-scale mixing using a jar-tester and to precisely determine the optimum polymer dose. The results of this study indicate that well-defined rheological properties of sludge provide a reliable tool for the optimization of conditioning and dewatering operations at wastewater treatment plants.