Impact of bubble and free surface oxygen transfer on diffused aeration systems.
The primary location of oxygen transfer in a diffused aeration system is examined by separately determining the surface air-water and bubble-water mass transfer coefficients. The mass transfer model developed to determine the mass transfer coefficients advances the McWhirter and Hutter (A.I.Ch.E. J. 35(9) (1989) 1527) model by tracking oxygen and nitrogen transfer into and out of the bubbles as they rise to the water surface. The resulting vertical profiles of the liquid-phase equilibrium concentration inside the bubble and the gas-phase oxygen composition give insight into how the bubble-water concentration gradient changes over depth. The surface mass transfer coefficient, k(Ls)a(s), is 59-85% of the bubble mass transfer coefficient, k(L)a(b), and the driving concentration difference is smaller for surface transfer. Surface transfer and bubble transfer both contribute significantly to oxygen transfer; however, bubble transfer is the primary mode of oxygen transfer for this system at the air flow rates used. Further experiments demonstrate that most of the surface transfer occurs above the bubble plume.
DeMoyer
Connie D
CD
St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, Mississippi River at 3rd Avenue, SE, Minneapolis 55414, USA.
Schierholz
Erica L
EL
Gulliver
John S
JS
Wilhelms
Steven C
SC
D000392:Air Movements; D004058:Diffusion; D007700:Kinetics; D008962:Models, Theoretical; D010100:Oxygen / Q000032:analysis*; D014867:Water / Q000737:chemistry; D014872:Water Movements; D018508:Water Purification / Q000379:methods*; D014881:Water Supply
D014867:Water; D010100:Oxygen