ABSTRACT
Figure 17.4 shows the effect of rotational speed on the performance of an RDR. As the rotational speed is increased, the percent substrate removal increases up to an upper limit characterized by the other system parameters. Several factors interact to cause this response. First, as shown in Eq. 17.1, the external mass transfer coefficient in the submerged sector increases as the rotational speed of the discs is increased, thereby increasing the overall effectiveness factor. Consequently, substrate is consumed more rapidly by the submerged biofilm as the rotational speed is increased. The events occurring in the aerated sector are more complicated, however. Examination of Eq. 17.3 reveals that an increase in rotational speed will cause the thickness of the liquid film on the aerated sector to increase, which will make the mass transfer coefficient in the liquid film, kLa, decrease (see Eq. 17. 7). The decrease
"' E Cl) (I)
Figure 17.4 Effects of rotational speed on the performance of a single RDR.
