Polymer dose assessment using the streaming current detector

The streaming current detector (SCD) is an electrokinetic analyzer for characterizing charge properties of particles in aqueous suspension. Irs use in water treatment is well established. This research evaluated its use for automatic monitoring of polymer dosage in three wastewater treatment facilities using centrifuges or belt filter presses for dewatering. Continuous SCD readings from the liquid stream (centrate or filtrate) and other process responses were recorded while imposing stepwise changes in the polymer dose. The polymer caused a transition from negative to positive charge in both the conditioned solids and the liquid stream. Near-zero SCD readings coincided with optimal full-scale dewatering, as indicated by solids measurements and recoveries and by minima in filtrate turbidity, filtrate viscosity, conditioned solids filterability times, and (in some cases) capillary suction times. Thus, charge neutralization is a key mechanism in solids conditioning, and the SCD is suitable for monitoring of polymer dosage. For its use in automatic polymer dose control-evaluated in a subsequent phase of the study-modifications were required to provide more reliable continuous sampling.