Optimization of slurry flocculation and dewatering based on electrokineticand rheological phenomena

The use of chemical additives known as conditioners or flocculants is cruci al in assuring the proper functioning of many solid-liquid separation proce sses, and dewatering in particular. The additive used is often a water solu ble polymer with high molecular mass, strong adsorptive properties, and oft en a large amount of ionic charge. The type of polymer used, and its exact dose, may change with process or flow conditions, and these changes may lea d to poor operation. However, advances in the understanding of conditioning and flocculation of slurries and sludges now make it possible to develop s cientifically-based strategies for optimizing these processes. These advanc es have utilized new characterization methods that allow insight into funda mental aspects of the process. In several cases the analyses employed are a lso amenable to continuous reading, and therefore to automatic feedback con trol of the process. This paper describes these advances and suggests condi tioning and flocculation control strategies that will allow optimization of subsequent dewatering processes. The research advances described are: (1) use of the streaming current detector for monitoring and controlling dewate rability; (2) evaluation of flee strength by streaming current and rheologi cal and methods; (3) use of rheological characteristics of conditioned resi duals for dose control; (4) application of liquid-stream viscosity for poly mer dose monitoring and control; and (5) quantification and verification of mixing conditions in conditioning processes, and use for mixing similitude . These developments should aid in the proper initial selection of a condit ioner product (flocculant) and its dose, and allow optimization based on co ntinuous monitoring if the sludge conditions vary significantly over time. (C) 2000 Elsevier Science B.V. All rights reserved.