Author(s)

N. MARGARIT, C. BAYONA, S. NAVEA, E. FERRERO & J. J. MALFEITO

Abstract

Dissolved air flotation (DAF) technologies are commonly used in water and wastewater treatment. In particular, flotation of suspended solids to pre-treat high salinity water such as seawater is now becoming more widespread, even though conductivity effects on microbubble formation and behaviour are not yet well known. Thus, a series of experiments were conducted with artificial sea water and distilled water to study the effects of conductivity on size and flow patterns of the air bubbles inside a pilot-scale DAF tank. The experimental set-up included a high-speed CCD camera to capture the generated microbubbles. Posterior image processing determined the bubble diameters. Also, fluorescein was used as a fluorescent tracer to follow flow paths. The viability of using fluorescein was first assessed at laboratory scale. The intensity of the dye was determined through molecular fluorescence as a function of the concentration using a high conductivity matrix. Furthermore, a stability study of the intensity along time was performed in order to ensure reliability of the experimental measurements. The results showed that bubble size decreased and dead areas increased when seawater was used instead of distilled water.

Keywords

DAF, desalination, flotation, fluorescein, fluorescence, microbubbles, pre-treatment, seawater