GPS-X Technical Reference

Suspended Growth Models 158
GENERAL MODEL STRUCTURE
The structure of the MBR model combines a conventional activated sludge tank model (plug-flow
or CSTR) with an in-tank solids separation filter, as shown in Figure 6-12. In the case of the
plug-flow MBR, the filter is placed in the final tank (an optional internal recycle is shown for
illustrative purposes). Permeate flow is drawn through the filter at a rate determined by the filter
model.
MBR Model Modes
Figure 6-12 - Membrane Bioreactor Model Structures
Both of the MBR models in GPS-X feature two different modes of operation: Simple
Mode, Intermediate, and Advanced Mode. Simple Mode assumes that the filter is
properly operated to maintain flux, and does not consider the effects of trans-membrane
pressure (TMP), cake formation, fouling, backwashing, and membrane resistance. The
Intermediate model mode calculates the TMP, cake formation, fouling, backwashing,
and membrane resistance based on the specified backwash rate and cleaning frequency,
but the required permeate flux is calculated based on the influent flow and waste flow to
ensure that the liquid volume in the last tank remains constant. The Advanced model
mode is similar to the Intermediate model mode, however the liquid volume in the tank is
variable and can increase or decrease based on the calculated permeate flux. The user
can control the liquid level using a feedback controller that manipulates the transmembrane
pressure. Table 6-3 summarizes the differences between Simple Mode,
Intermediate, and Advanced Mode.
GPS-X Technical Reference