Hydrodynamic characterization in dissolved air flotation (DAF) contact zone

The mechanism of bubble-flee interaction in a DAF contact zone is poorly un derstood and is usually described by conceptual models. This mechanism is h ighly dependent on the hydrodynamic conditions within the contact zone, i.e . contact time and degree of mixing. A pulse stimulus-response test was use d to characterize the contact zone degree of mixing, in terms of dimensionl ess Peclet Number, and the contact time, in terms of residence time distrib ution. The tracer tests were performed at different hydraulic loading rates and recycle ratios. The experimental results confirmed that the axial disp ersion model can be used to estimate the degree of mixing inside the contac t zone. The results showed that the Peclet Number increased as the hydrauli c loading rate increased, for all experiments performed under the same recy cle ratio. In addition, the degree of mixing slightly increased as the recy cle ratio increased, for all experiments performed under the same hydraulic loading rate. (C) 1998 Published by Elsevier Science Ltd. All rights reser ved.