Rheology as Tool for Polymer Dose Assessment and Control

Rheological characteristics of sludge represent one of the few examples of fundamentally derivable properties that have also been successfully used for the improvement of actual sludge treatment processes. Previous research has suggested the use of certain sludge rheological parameters for polymer dose optimization and floc characterization. This research evaluated the use of rheological properties for characterization and control of sludge conditioning with polyelectrolytes. Rheological characteristics were compared with dewaterability in laboratory evaluations, utilizing both synthetic cellulose suspension and actual sludge. These experiments were designed to identify fundamental rheological parameters that may have the potential to be used for assessment and control of conditioning and dewatering processes. This paper reports and analyzes results from controlled laboratory experiments; evaluations of on-line rheology measurements for process control in a nearby sludge handing facility have been presented elsewhere. Laboratory conditioning indicators were capillary suction time, liquid stream (centrate) streaming current and viscosity, and solids measurements. Full-scale dewatering indicators were capillary suction time, liquid stream (filtrate) streaming current, and percent solids recovery. Results indicated lack of correlation between the proposed conditioned sludge rheology-control parameters and conditioning indices over a wide range of mixing conditions. Mixing parameters have a substantial effect on the rheological characteristics of the concentrated suspensions and shed some light upon floc strength as related to dewaterability.