title: Oxygen mass transfer and hydrodynamic behaviour in wastewater: determination of local impact of surfactants by visualization techniques.
abstract: Powerful techniques, based on the Planar Laser Induced Fluorescence (PLIF) technique, are deployed to locally visualize and quantify the impact of surfactants in wastewaters on hydrodynamics and oxygen mass transfer. Bubble diameter, aspect ratio, rise velocity, contamination angle, as well as flux, flux density, liquid side mass transfer and diffusion coefficients of transferred oxygen are determined based on these techniques applied in the wake of rising bubbles of diameter 1 mm and through planar gas/liquid interfaces. The initial experiments were performed in demineralized water containing small amounts of surfactant. Different concentrations of surfactant were added to finally reach the Critical Micelle Concentration (CMC). Bubbles have classically been found to be more spherical with a reduced rise velocity in the presence of surfactants up to the CMC. Above the CMC, these hydrodynamic characteristics were found to be almost constant, although the oxygen mass transfer decreased due to the presence of surfactants. Experimental results were markedly lower than predicted by the well-known Frössling equation with rigid surfaces. This is believed to be caused by a barrier of surfactants hindering the oxygen mass transfer at the interface. Similar hindrance of oxygen mass transfer applies to waters from sewage plants (filtered raw water and treated water), making accurate design of aeration tanks difficult.
authors.affiliation: Université de Toulouse, INSA, UPS, INP, LISBP, 135 Av. de Rangueil, F-31077 Toulouse, France; INRA UMR792, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France; CNRS UMR 5504, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France; Fédération de Recherche FERMAT, CNRS, Toulouse, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Jimenez
authors.affiliation: Université de Toulouse, INSA, UPS, INP, LISBP, 135 Av. de Rangueil, F-31077 Toulouse, France; INRA UMR792, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France; CNRS UMR 5504, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France; Fédération de Recherche FERMAT, CNRS, Toulouse, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Dietrich
authors.affiliation: Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, Canada V6T IZ3.
authors.forename: John R
authors.initials: JR
authors.lastname: Grace
authors.affiliation: Université de Toulouse, INSA, UPS, INP, LISBP, 135 Av. de Rangueil, F-31077 Toulouse, France; INRA UMR792, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France; CNRS UMR 5504, Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France; Fédération de Recherche FERMAT, CNRS, Toulouse, France. Electronic address: hebrard@insa-toulouse.fr.
authors.forename: Gilles
authors.initials: G
authors.lastname: Hébrard
mesh_terms: D057446:Hydrodynamics; D008823:Micelles; D010100:Oxygen / Q000032:analysis*; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013501:Surface-Active Agents / Q000737:chemistry*; D062065:Wastewater / Q000032:analysis* / Q000737:chemistry
chemical_list: D008823:Micelles; D010100:Oxygen; D013501:Surface-Active Agents; D062065:Wastewater
keywords: Bubbles; Interface; Mass transfer; PLIF; Surfactants; Wastewater