Oxygen absorption into moving water and tenside solutions

Oxygen absorption into water and waste water is an important process taking place with both natural and technical means, and a tool for a theoretical determination of the oxygen transfer coefficient, KL, is desirable. The objective of this investigation was to study the environment at and near the liquid side of a gas–liquid interface in order to present a model for a theoretical determination of KL. The gas was pure oxygen and the liquids were clean tap water and various concentrations of two types of tenside solutions. Various sized hemispherical oxygen bubbles were impressed by various liquid flow velocities while measuring the liquid flow velocity and the film thickness using a Laser Doppler Anemometer (LDA). The LDA was also used to determine KL. Furthermore, the surface tension and the bulk kinematic viscosity for various liquids were measured. For clean tap water it was found that the Two Film Theory by Lewis and Whitmann [(1924) Industrial and Engineering Chemistry, 16(12), 1215–1220] had to be modified, and that KL can be calculated from a correspondingly modified version of an equation presented by Dobbins [(1956) Biological Treatment of Sewage and Industrial Wastes, Section 2, eds B. J. McCabe and W. W. Eckenfelder Jr, pp. 141–148. Reinhold Publishing Corp., New York]. The calculation is based on a theoretical determination of the liquid film thickness with respect to normal flow which is also presented in this paper. For tenside solutions it was found that KL is a function of the relative flow velocity (vr) (KL increases with increasing vr until a certain limit), the bubble size (KL decreases with increasing bubble size), and the surface tension (KL decreases with decreasing surface tension) but not the kinematic viscosity of the bulk. However, it was not possible to present a thorough calculation model. A more detailed description of the investigation is given in Pedersen [(1998) A study of liquid film, liquid motion, and oxygen absorption from hemispherical air/oxygen bubbles. Ph.D. thesis, Brunel University, London].