Hydrodynamic characterization in dissolved air flotation (DAF) contact zone

The mechanism of bubble-flee interaction in a DAF contact zone is poorly understood and is usually described by conceptual models. This mechanism is highly dependent on the hydrodynamic conditions within the contact zone, i.e. contact time and degree of mixing. A pulse stimulus-response test was used to characterize the contact zone degree of mixing, in terms of dimensionless Peclet Number, and the contact time, in terms of residence time distribution. The tracer tests were performed at different hydraulic loading rates and recycle ratios. The experimental results confirmed that the axial dispersion model can be used to estimate the degree of mixing inside the contact zone. The results showed that the Peclet Number increased as the hydraulic loading rate increased, for all experiments performed under the same recycle ratio. In addition, the degree of mixing slightly increased as the recycle ratio increased, for all experiments performed under the same hydraulic loading rate. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.