THE VELOCITY FIELD AFFECT OF THE DIFFUSIVE OXYGEN TRANSFER THROUGH AN AIR- WATER INTERFACE
Maria Sandberg, Karlstad University, Department of Energy, Environmental & Building Technology
(free)
To find the potential to achieve more efficient, less energy consuming aeration for biological
wastewater treatment plants, laboratory scale trials have been undertaken. During aeration
trials over a flat surface with specific area, clean water has been compared to process effluent
from the pulp and paper industry while the stirring speed has been varied. The stirring speed
affected the surface velocity. The oxygen transfer rate at all tested surface velocities was less
efficient for process effluent. This is due to both lower solubility of oxygen and a thicker
boundary layer closest to the air/liquid interface. Affecting the boundary layer thickness is
probably the most efficient way to increase the oxygen transfer rate. When the oxygen
transfer rate is compared, independent of the influence of solubility, it was shown that the
boundary layer affected the transfer rate at all surface velocities. The effect was comparably
larger at low velocities. Therefore there is a great potential to increase the oxygen transfer
rate at all surface velocities however it is larger for low velocities. If only a part of the potential
is utilised, great values can be saved.
KEY WORDS
Industrial Wastewater, Oxygen transfer rate, Solubility, Boundary layer, surface velocity, diffusive oxygen transfer
