INFLUENCE OF TEMPERATURE
AND TURBULENCE ON THE
OXYGEN TRANSFER IN WATER
KLAUS R. IMHOFF and DETLEF ALBRECHT
43 Essen, Kronprinzenstr. 37, Fed. Rep. of Germany
For more than five decades aeration devices of different types and dimensions have
been used in water and wastewater treatment. The choice of a suitable aerator depends on
the oxygen transfer rate, on its circulation rate and efficiency. The oxygenation
efficiency [kg 0 2 /kwh] is the most important factor for an assessment of aeration units.
Since test conditions are nearly always different, it is necessary to convert the measured
oxygen transfer rate to "standard conditions".
The conversion generally implies the directly proportional relationship between
oxygen deficit and oxygen transfer. Strictly speaking only non-flow systems follow this
dependency, which has been demonstrated several times in the technical literature [1],
[2], [3] (p.447). When calculating the oxygen deficit it must also be remembered that
the oxygen saturation value of the water increases with falling temperature and rising
pressure [4]. For wastewater the concentration of surface-active substances [5] is also
often considered.
Nearly all conversions of the oxygen transfer rate, however, neglect the well-known
influence of water turbulence. Water turbulence is important for the movement of
oxygen, because after a very rapid oxygenation of the boundary layer in the absence of
turbulence, a slow diffusion process must take place, which is also dependent on
temperature.
1. INFLUENCE OF TEMPERATURE
Several authors have published differing results on the influence of temperature on
oxygen transfer. These data have been plotted in Fig. 1. For comparison purposes the
relative oxygen transfer was taken to be 1.0 at 10°C. Due to the calculation it applies to
equal oxygen deficit percentages, and the plotted curves thus reveal the temperature
dependency of the different systems.
Adeney and Becker [1] used for their measurements a water-filled glass cylinder, in
which they allowed an air bubble to rise. The results are supposed to describe the natural
reoxygenation rate at the water surface.
In Germany and other West-European countries the correction values of Pasveer [6]
are mostly used. These data are based on the tests of Adeney and Becker and on
supplementary measurements. According to Pasveer nearly constant oxygen transfers are
obtained with temperatures between 5 and 30°C, since with rising temperature the
resulting decreasing oxygen saturation tends to be compensated by an increase of the
oxygen transfer rate. For compressed-air systems this combined effect must be considered
as being correct, after having been confirmed in a recent paper by Bewtra et al. [7].
Downing and Truesdale [8] obtained their values by slow stirring of distilled water.
Churchill et al. [9], [10] in one case employed a small magnetic stirrer (7 X 24 mm),
which transferred only 1 mg 0 2 /1 during a period of several hours (curve A). The values
23
AND TURBULENCE ON THE
OXYGEN TRANSFER IN WATER
KLAUS R. IMHOFF and DETLEF ALBRECHT
43 Essen, Kronprinzenstr. 37, Fed. Rep. of Germany
For more than five decades aeration devices of different types and dimensions have
been used in water and wastewater treatment. The choice of a suitable aerator depends on
the oxygen transfer rate, on its circulation rate and efficiency. The oxygenation
efficiency [kg 0 2 /kwh] is the most important factor for an assessment of aeration units.
Since test conditions are nearly always different, it is necessary to convert the measured
oxygen transfer rate to "standard conditions".
The conversion generally implies the directly proportional relationship between
oxygen deficit and oxygen transfer. Strictly speaking only non-flow systems follow this
dependency, which has been demonstrated several times in the technical literature [1],
[2], [3] (p.447). When calculating the oxygen deficit it must also be remembered that
the oxygen saturation value of the water increases with falling temperature and rising
pressure [4]. For wastewater the concentration of surface-active substances [5] is also
often considered.
Nearly all conversions of the oxygen transfer rate, however, neglect the well-known
influence of water turbulence. Water turbulence is important for the movement of
oxygen, because after a very rapid oxygenation of the boundary layer in the absence of
turbulence, a slow diffusion process must take place, which is also dependent on
temperature.
1. INFLUENCE OF TEMPERATURE
Several authors have published differing results on the influence of temperature on
oxygen transfer. These data have been plotted in Fig. 1. For comparison purposes the
relative oxygen transfer was taken to be 1.0 at 10°C. Due to the calculation it applies to
equal oxygen deficit percentages, and the plotted curves thus reveal the temperature
dependency of the different systems.
Adeney and Becker [1] used for their measurements a water-filled glass cylinder, in
which they allowed an air bubble to rise. The results are supposed to describe the natural
reoxygenation rate at the water surface.
In Germany and other West-European countries the correction values of Pasveer [6]
are mostly used. These data are based on the tests of Adeney and Becker and on
supplementary measurements. According to Pasveer nearly constant oxygen transfers are
obtained with temperatures between 5 and 30°C, since with rising temperature the
resulting decreasing oxygen saturation tends to be compensated by an increase of the
oxygen transfer rate. For compressed-air systems this combined effect must be considered
as being correct, after having been confirmed in a recent paper by Bewtra et al. [7].
Downing and Truesdale [8] obtained their values by slow stirring of distilled water.
Churchill et al. [9], [10] in one case employed a small magnetic stirrer (7 X 24 mm),
which transferred only 1 mg 0 2 /1 during a period of several hours (curve A). The values
23