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 fo r the improvement of actual sludge treatment processes. Previous research h as suggested the use of certain sludge rheological parameters for polymer d ose optimization and flee characterization. This research evaluated the use of rheological properties for characterization and control of sludge condi tioning with polyelectrolytes. Rheological characteristics were compared wi th dewaterability in laboratory evaluations, utilizing both synthetic cellu lose suspension and actual sludge. These experiments were designed to ident ify fundamental rheological parameters that may have the potential to be us ed for assessment and control of conditioning and dewatering processes. Thi s paper reports and analyzes results from controlled laboratory experiments ; evaluations of on-line rheology measurements for process control in a nea rby sludge handing facility have been presented elsewhere. Laboratory condi tioning indicators were capillary suction time, liquid stream (centrate) st reaming current and viscosity, and solids measurements. Full-scale dewateri ng indicators were capillary suction time, liquid stream (filtrate) streami ng current, and percent solids recovery. Results indicated lack of correlat ion between the proposed conditioned sludge theology-control parameters and conditioning indices over a wide range of mixing conditions. Mixing parame ters have a substantial effect on the rheological characteristics of the co ncentrated suspensions and shed some light upon flee strength as related to dewaterability.