GPS-X Technical Reference

231 Attached-Growth Models
The next two items in this form, under the heading Speed, concern the integration of the
soluble components. Since these components are diffusing through the biofilm, and
consequently change rapidly when compared to the particulate components, which are
changing only due to their growth rates, they tend to dominate the numerical solver. To
increase the speed of simulation, it was found that these components can be integrated
less frequently without loss of accuracy. When the soluble variables are scheduled to be
integrated, their derivatives are calculated from equations (Equation 7.1) and (Equation
7.2). Otherwise, the derivatives are set to zero. There are two variables which are used to
specify how frequently the states are integrated: the soluble integration period, and the
duration for integration or how long the states are integrated for each period (soluble
integration length). These concepts are shown in Figure 7-3, with the results for
ammonia shown in Figure 7-4.
Figure 7-11 shows more physical components associated with oxygen solubility. The
oxygen mass transfer coefficient is calculated from the physical conditions within the
filter (thickness of biofilm and diffusion rate of oxygen) and is affected by temperature
and the saturated dissolved oxygen concentration. These values are either input in the
general data entry area or specifically set for each object.
Figure 7-11 – Physical Dimensions of the RBC (More…)
GPS-X Technical Reference