Optimization of slurry flocculation and dewatering based on electrokinetic and rheological phenomena

Abstract

The use of chemical additives known as conditioners or flocculants is crucial in assuring the proper functioning of many solid-liquid separation processes, and dewatering in particular. The additive used is often a water soluble polymer with high molecular mass, strong adsorptive properties, and often 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 lead to poor operation. However, advances in the understanding of conditioning and flocculation of slurries and sludges now make it possible to develop scientifically-based strategies for optimizing these processes. These advances have utilized new characterization methods that allow insight into fundamental aspects of the process. In several cases the analyses employed are also amenable to continuous reading, and therefore to automatic feedback control of the process. This paper describes these advances and suggests conditioning 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 dewaterability; (2) evaluation of floc strength by streaming current and rheological and methods; (3) use of rheological characteristics of conditioned residuals for dose control; (4) application of liquid-stream viscosity for polymer 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 conditioner product (flocculant) and its dose, and allow optimization based on continuous monitoring if the sludge conditions vary significantly over time.