OPEN ACCESS
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 pilotscale 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.
DAF, desalination, flotation, fluorescein, fluorescence, microbubbles, pre-treatment, seawater
[1] Edzwald, J.K., Dissolved air flotation and me. Water Research, 44(7), pp. 2077–2106, 2010. https://doi.org/10.1016/j.watres.2009.12.040
[2] Kwak, D.H., Jung, H-J., Kwon, S-B., Lee, E-J., Won, C-H., Lee, J-W. & Yoo, S-J., Rise velocity verification of bubble-floc agglomerates using population balance in DAF process. The 5th International Conference on Flotation in Water and Wastewater Systems, Seoul, 2007.
[3] Zimmerman, W.B., Tesar, V., Butler, S. & Bandulasena, H.C., Microbubble generation. Recent Patents on Engineering, 2(1), pp. 1–8, 2008. https://doi.org/10.2174/187221208783478598
[4] Edzwald, J.K. & Haarhoff, J., Adapting dissolved air flotation for the clarification of sea water. Desalination, 311, pp. 90–94, 2013. https://doi.org/10.1016/j.desal.2012.10.035
[5] Vion, P., Pressurised water releasing nozzle for generating microbubbles in a flotation plant. US7651620 Patent, 2003.
[6] Hamme, C. & Emerson, S.R., The solubility of neon, nitrogen and argon in distilled water and seawater. Deep Sea Research, 51(11), pp. 1517–1528, 2004. https://doi.org/10.1016/s0967-0637(04)00119-0