GPS-X Technical Reference

39 GPS-X Composite Variable Libraries
CHAPTER 4
GPS-X Composite Variable Calculations
WHAT IS A COMPOSITE VARIABLE
In GPS-X, a group of state variables (such as oxygen, heterotrophic biomass, nitrate, ammonia,
soluble substrate, particulate substrate, etc.) are calculated for each connection point in the plant
layout. These state variables are the fundamental components that are acted upon by the processes
in the models in each library.
These particular state variable components are not always easily measurable or interpretable in
practical applications. Therefore, a series of composite variables are calculated from the state
variables. The composite variables combine the state variables into forms that are typically
measured, such as total suspended solids (TSS), BOD, COD and Total Kjeldahl Nitrogen (TKN).
STOICHIOMETRY SETTINGS
The way that the composite variables are calculated from state variables changes from library to
library and to a great degree from model to model.
Composite variables are calculated from state variables with the use of stoichiometric constants.
These constants describe the relationships between various states and composites, and depend on
the type of composite calculations used.
STOICHIOMETRY CALCULATIONS
Nomenclature
In this chapter, diagrams and tables are used to depict the relationships between the state
and composite variables included in a library.
GPS-X Technical Reference