GPS-X Technical Reference

Modelling Fundamentals 22
System Configuration
The General Purpose Simulator can handle practically any flow scheme. Based on our
experience it is very important to identify as closely as possible the hydraulic
characteristics of a plant, including plant by-passes, overflows, flow splits and combiners,
proportional, constant or SRT driven sludge wastage, etc. Parallel trains, multiple units
and plug flow systems are easily simulated, but should be simplified where possible
(unless the required supporting data required for calibration is available).
OPERATIONAL PLANT DATA
Flow Control Variables (Independent Variables)
This is an important data group. For example, if the aeration capacity is not known (or
cannot be estimated from the aerator power or other means), then the correct dissolved
oxygen (DO) level can be set by either changing the K La or some stoichiometric or
kinetic parameters (yield coefficient, growth rate, etc.). This makes the correct estimation
of those parameters difficult. Similarly, model parameters having a strong effect on the
aeration tank Mixed Liquor Suspended Solids (MLSS) are difficult to estimate when the
wastage rate is not known.
Activated Sludge Response Variables
MLSS, Volatile Suspended Solids (VSS), COD of the mixed liquor, DO, and Oxygen
Uptake Rate (OUR) are required to calibrate the activated sludge portion of the model.
Refer to above section (p. 22) for a discussion on the importance of COD for this chapter
(Why COD is Important to Know). In general, the stoichiometry of the mixed liquor
(% VSS and COD/MLSS) is relatively constant over time and can be assessed
occasionally during the course of a calibration/verification study, e.g., on a monthly or biweekly
basis. However, the other parameters are generally dynamic, following the
diurnal patterns of the plant.
It is important to be able to perform a solids mass balance around the system.
Accordingly, the sludge blanket height (and preferably the solids concentration profile)
and underflow solids concentration are required to calibrate the settler portion of the
model.
GPS-X Technical Reference