Oxygen transfer capacity has greatest influence on activated sludge performance. In
this study, experimental procedure is carried out to determine the effect of airflow rate and the
level of diffusers submergence, on the oxygen transfer rate of diffused air systems. In addition,
a number of readings were also collected from published papers. The data were selected to
cover various scales of plants and operating conditions. After sorting out, all data were treated
and then combined to the experimental readings in order to expand the applicability of the
results. Individual mathematical models to describe the effect of each parameter were also
derived. The results of the study showed that, increasing the airflow rate at fixed water depth
and diffusers submergence enlarge the oxygenation capacity of the system. The equation, which
controls this relationship, is linear. At diffusers submergence of 4.6 m, the slope of the equation
was 11.8. With reduce the depth of diffusers to about 0.4 m; the slope of equation was decrease
to 2.3. At constant airflow rate, the depth of diffusers has a significant effect on both of the
oxygenation capacity and oxygen transfer efficiency of the system. Exponentional form of
equation is shown to be efficient in expressing the relationship between the submergence and
the oxygenation capacity. At 0.4 m, diffusers submergence, the oxygen transfer efficiency was
1.8 whereas; this value is rising to about 11.5 at 4.6m submergence.
Keywords :Oxygen transfer capacity, diffused aeration, airflow rate, diffusers submergence, KLa