GPS-X Technical Reference

GPS-X Composite Variable Calculations 60
Displaying Composite Variables
All of the composite variables, including the most common ones such as X (total
suspended solids), TKN (Total Kjeldahl Nitrogen), BOD, COD, etc., can be accessed by
selecting the Display Variables > Composite Variables menu. These variables (and those
found by clicking on the More... button) can be tagged and placed on output graphs.
COMPOSITE VARIABLES CALCULATED FROM NON-MODELLED STATES
Whether stoichiometry has been set globally or locally within each object, the list of composite
variables that are available to be displayed will depend on which library has been used for that
particular GPS-X layout (CNLIB, CNPLIB, etc.).
It is possible to use a model in the layout that does not simulate the fate of all components of a
given library (e.g. mantis in CNPLIB, which does not model phosphorus even though there are
phosphorus state variables in CNPLIB). In these cases, these extra components will be modelled
as if they were inert (i.e. no biological transformation applied, but mixing and settling are
applied).
The composite variable list displayed in the Display Variables > Composite Variables menu is
the list associated with the library used to create the layout (e.g. CNPLIB). All composite
variables are calculated for the given library, even if the component states are not modelled
biologically in the reactor. For the example above (mantis model in CNPLIB), soluble
phosphorus (sp) is not modelled biologically, and therefore behaves the same as si (soluble
inerts); however, because CNPLIB contains the composite variable TP (total phosphorus), it will
be calculated (from sp and other components) even though sp was modelled as an inert.
It is important to take this into consideration when selecting which model and library you will be
using when creating your plant layout.
GPS-X Technical Reference