Temperature effects on oxygen transfer to rotating biological contactors

A laboratory-scale rotating biological contactor (RBC) unit was used to determine the effect of temperature on the oxygen transfer rate. Unsteady-state reaeration tests were performed at 5° to 30°C and in such a manner that direct transfer of oxygen to the liquid in the basin and oxygenation of the thin water film adhering to the disk could be determined. The results demonstrated that the temperature correction factor, θ, varied, but varied as the rate-controlling mechanism changed. At low tip speed (<20 cm/s), the transfer coefficient was dominated by direct transfer to the liquid, and θ was approximately 1.017. When tip speed was higher and film transfer dominated, θ was as high as 1.039. An increase in water temperature caused oxygen transfer to be controlled more by film saturation, which reduced θ. The overall mass transfer rate was generally lower for higher temperatures than for lower temperatures when the liquid oxygen concentration was above 0 mg/l. The results suggest that full-scale units will be more oxygen-transport limited than lab-scale units, especially for higher temperatures.