Measurement of the oxygen mass transfer through the air-water interface

• Published in: Environmental science and pollution research international 2005-01, Vol.12 (2), p.66-70
• Main Authors: Mölder, Erik, Mashirin, Alelxei, Tenno, Toomas
• Format: Article
• Language: English
• Subjects: Adsorption; Air; Air-water interface; Cell surface; Conduction; Diffusion; Electrochemistry; Environmental Monitoring - methods; Field study; Fieldwork; Gas exchange; Industrial pollution; Jupiter; Mass transfer; Mathematical models; Models, Theoretical; Oxygen; Oxygen - analysis; Permeability; Pollutants; Surface activity; Surface-Active Agents - chemistry; Surfactants; Volatilization; Waste Disposal, Fluid; Wastewater dilution; Wastewater treatment; Wastewater treatment plants; Water
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1065/espr2004.11.223

Gas mass transfer through the liquid-gas interface has enormous importance in various natural and industrial processes. Surfactants or insoluble compounds adsorbed onto an interface will inhibit the gas mass transfer through the liquid-gas surface. This study presents a technique for measuring the oxygen mass transfer through the air-water interface. Experimental data obtained with the measuring device were incorporated into a novel mathematical model, which allowed one to calculate diffusion conduction of liquid surface layer and oxygen mass transfer coefficient in the liquid surface layer. A special measurement cell was constructed. The most important part of the measurement cell is a chamber containing the electrochemical oxygen sensor inside it. Gas exchange between the volume of the chamber and the external environment takes place only through the investigated surface layer. Investigated liquid was deoxygenated, which triggers the oxygen mass transfer from the chamber through the liquid-air interface into the liquid phase. The decrease of oxygen concentration in the cell during time was measured. By using this data it is possible to calculate diffusional parameters of the water surface layer. Diffusion conduction of oxygen through the air-water surface layer of selected wastewaters was measured. The diffusion conduction of different wastewaters was about 3 to 6 times less than in the unpolluted water surface. It was observed that the dilution of wastewater does not have a significant impact on the oxygen diffusion conduction through the wastewater surface layer. This fact can be explained with the presence of the compounds with high surface activity in the wastewater. Surfactants achieved a maximum adsorption and, accordingly, the maximum decrease of oxygen permeability already at a very low concentration of surfactants in the solution. Oxygen mass transfer coefficient of the surface layer of the water is found to be Ds/ls = 0.13 x 10(-3) x cm/s. A simple technique for measuring oxygen diffusion parameters through the air-water solution surface has been developed. Derived equations enable the calculation of diffusion parameters of the surface layer at current conditions. These values of the parameters permit one to compare the resistances of the gas-liquid interface to oxygen mass transfer in the case of adsorption of different substances on the surface layer. This simple technique may be used for a determination of oxygen permeability of different wa