Use of Streaming Current and Other Parameters for Polymer Dose Control in Sludge Conditioning

Abstract

Studies of sludge conditioning were conducted at five different treatment facilities employing both belt presses and centrifuges. Polymer dose was varied while comparing charge measurements to full-scale dewatering efficiency. Near-zero streaming current correlated with optimum or near-optimum dewaterability under a wide range of conditions. Other assessments of sludge conditioning such as cake and liquid-stream solids, capillary suction time, liquid-stream viscosity, and liquid-stream turbidity led to a more comprehensive hypothesis concerning polymer functioning. Charge neutralization appears to be necessary, but not sufficient, for adequate conditioning: shear effects subsequent to polymer addition determine the polymer dose leading to charge neutralization when phase separation is actually effected. Moreover, such shear itself actually determines floc strength, and the polymer must be capable of maintaining floc structure under these conditions. Since mixing conditions are reasonably constant in installed sludge conditioning facilities, use of the SCD for automatic control of polymer dose appears feasible in principle. Some practical aspects of SCD design and use are also presented that enable polymer dose control to be put into practice.