Eulerian modelling of the formation and flow of aggregates in dissolved air flotation

Dissolved Air Flotation (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. Particulate matter in the water is flocculated into larger particles (termed flocs). The water, together with flocs, is thereafter mixed with the injected air bubbles. Buoyant aggregates are formed by adhesion of bubbles to the flocs. The aggregates rise to the surface of the unit where they are removed from the water phase. The objective of this paper is to conduct simulations of fluid dynamics of a DAF unit, with a specific aim to capture the formation and flow of aggregates. 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 in the paper that the modelling framework can describe the dynamics of flotation by capturing the formation, change in size and movements of the aggregates through the contact zone of a pilot DAF unit as a function of the properties of the flocs