GPS-X Technical Reference

COMPOSITE VARIABLES IN CNPIPLIB
GPS-X Composite Variable Calculations 52
The relationships between the state variables and composite variables are similar to the Carbon-
Nitrogen-Phosphorus library (CNPLIB). Table 4-7 through Table 4-15 shows the relationships
between the state and composite variables that are used in the models in CNPIPLIB.
COMPOSITE VARIABLES IN MANTIS2LIB
The composite variable calculation schemes in MANTSI2LIB are shown in Figure 4-7 to Figure
4-11. Figure 4-7 shows the scheme for estimation of soluble BOD 5 (SBOD), particulate BOD 5
(XBOD), BOD 5 (BOD), soluble ultimate BOD (SBOD U), particulate ultimate BOD (SBOD U),
ultimate BOD (BOD U), soluble COD (SCOD), particulate COD (XCOD) and COD (COD). The
list of stoichiometric parameters used in the estimation of composite variables is provided in
Table 4-16.
Table 4-16 - Stoichiometry Parameters used in Estimation of BOD and BOD U
Stoichiometry Default
Parameter Value
Description
yhglobal 0.666 Biomass yield
fuu 0.206 Fraction of unbiodegradable residue in biomass
fssbodtosscod 0.717 BOD 5 to COD ratio of soluble substrate
fpsbodtopscod 0.703 BOD 5 to COD ratio of particulate substrate
fbbodtobcod 0.566 BOD 5 to COD ratio of biomass
The default value of the stoichiometry parameters can be changed in the
System > Input Parameters > Global Fixed stoichiometry menu.
Figure 4-8 shows the scheme for estimation of Volatile Suspended Solid (VSS), Inorganic
Suspended Solid (XISS) and Total Suspended Solid (TSS) concentration. In the estimation of
VSS, each biomass concentration is multiplied by a corresponding VSS to COD factor. For
example, ivsstocodxbh is the VSS to COD ratio for heterotrophic biomass, xbh. The VSS to
COD ratio for each biomass type are calculated based on the biomass composition. The default
composition of biomass can be accessed and changed in the
System > Input Parameters > Global Fixed stoichiometry menu.
As the composition of xs and xi are not well known, the VSS to COD ratios for these states
ivsstocodxs and ivsstocodxi are provided as direct inputs. These ratios can be accessed and
changed in System > Input Parameters > Influent Stoichiometry menu. The state variable of xns
is included in the calculation of VSS for being consistent with the practice of considering the N
fraction in biomass as part of VSS. A stoichiometry factor of 17.0/14.0 is used to convert N to
NH 3.
GPS-X Technical Reference