GPS-X Technical Reference

223 Attached-Growth Models
The model dimensions are fixed, that is, the number of layers in the biofilm is six (one
liquid layer and five biofilm layers). Also, the number of horizontal and vertical sections
in the model is fixed at six and one respectively.
The next two items in this form, under the heading Speed, concern the integration of the
soluble state variables. Since these variables are diffusing through the biofilm, and
consequently change rapidly when compared to the particulate state variables, which are
changing only due to their growth rates, they tend to dominate the numerical solver. To
increase the speed of simulation, the soluble states can be integrated less frequently
without loss of accuracy. When the variables are scheduled to be integrated their
derivatives are calculated from equations (Equation 7.1) and (Equation 7.2) shown
above. Otherwise, the derivatives are set to zero. There are two variables used to specify
how frequently the soluble states are integrated and the duration for integration or how
long the states are integrated for each period: the soluble integration period and soluble
integration length. These concepts are shown in Figure 7-3 with the results on ammonia
shown in Figure 7-4.
Figure 7-3 - Integration of Soluble Components
Figure 7-4 – Integration
GPS-X Technical Reference