A model to estimate the size of aggregates formed in a Dissolved Air Flotation unit

In Dissolved Air Flotation (DAF) a solid phase is separated from a liquid phase with the aid of air bubbles. The solid phase is usually coagulated into larger particles termed flocs. The air bubbles and flocs form aggregates, which rise to the surface of the flotation unit where they are removed. In this paper we propose a model that estimates the size of the formed aggregates. The estimation is based on the local balance of forces describing the approach and attachment of flocs to air bubbles. The interaction of flocs and bubbles is described by surface forces, hydrodynamic forces and the buoyancy force. The model is validated with available experimental results and the obtained aggregate sizes agree reasonable with those obtained by the experiments. The approach proposed here is intended for water treatment applications, but can be modified for other flotation processes. (C) 2012 Elsevier Inc. All rights reserved.