Modelling of formation and flow of aggregates in Dissolved Air Flotation: Comparison between 2D and 3D

Paper i proceeding, 2013

In this paper a framework is proposed for capturing the flow and formation of aggregates in Dissolved Air Flotation (DAF). DAF is a well-established process within the drinking water treatment community. The process is driven by density differences caused by injection of air bubbles into the main water flow. By adhesion of bubbles to solid particles (to be removed from the water) buoyant aggregates are formed. The objective of this paper is to demonstrate a modelling framework, with a specific aim to capture the formation and flow of these aggregates in two- and three-dimensional computational setups. For that purpose, a model has been developed that explains the mechanisms that lead to creation of aggregates and results in estimation of their size. Details on the implementation of the aggregation model into an Eulerian framework are given in the paper. We show here that the modelling framework can describe the dynamics of flotation by capturing the formation, change in size and movements of the aggregates through a pilot DAF unit as a function of the properties of the flocs. The differences between a two- and a three-dimensional setup, in terms of the predicted aggregate sizes, are investigated. The framework is demonstrated to be applicable for both two-dimensional and three-dimensional computational setups.