GPS-X Technical Reference

53 GPS-X Composite Variable Calculations
In the calculation of Inorganic Suspended Solid (XISS), each biomass concentration is multiplied
by the inorganic fraction in the biomass. The inorganic fraction for each biomass is estimated by
subtracting the VSS to SS ratio for each individual biomass from one. The VSS to SS ratio for
each individual biomass type is calculated by using the set biomass composition, for example
ivsstossxbh is the VSS to SS ratio calculated for the xbh biomass type.
The composite variable of XISS also includes the contribution from the inorganic states in the
model. The mass contributions from the xpp and xps states are calculated by using a
stoichiometry factor of 95/31. The factor reflects the conversion from molecular weight of P to
molecular weight of PO 4
3-
. For all the other inorganic states a stoichiometry ratio of 1 is used.
The Total Suspended Solid (TSS) concentration is calculated by the sum of estimated VSS and
XISS.
Figure 4-9 shows the scheme for estimation of soluble part of Total Kjeldahl Nitrogen (STKN),
particulate part of Total Kjeldahl Nitrogen (XTKN), Total Kjeldahl Nitrogen (TKN), Total
Nitrogen (TN) and Total Nitrogen including dissolved Nitrogen (TN & dissolved gas). In the
estimation of STKN, the stoichiometry ratio of, insi is used to estimate the organic nitrogen
present in the si state variable. In the estimation of XTKN, each biomass concentration is
multiplied by a corresponding stoichiometry factor representing the N content in the
corresponding biomass. For example, inxbh is the stoichiometry factor representing the N content
in the heterotrophic biomass, xbh. The N fraction for each biomass type is 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. In the calculation of XTKN,
the N contained in the MgNH 4PO 4 is also included. Although, in strict sense this is not a part of
the organic nitrogen, it is assumed that the ammonia contained in the precipitate shall reflect in
the analytical measurement of TKN.
Figure 4-10 shows the scheme for estimation of soluble part of Total Phosphorus (STP),
particulate organic part of Total Phosphorus (XTOP), particulate inorganic part of Total
Phosphorus (XTIP) and Total Phosphorus. In the estimation of STP, the stoichiometry ratio of,
ipnsi is used to estimate the phosphorus present in the si state variable. In the estimation of
XTOP, each biomass concentration is multiplied by a corresponding stoichiometry factor
representing the P content in the corresponding biomass. For example, ipxbh is the stoichiometry
factor representing the P content in the heterotrophic biomass, xbh. The P fraction for each
biomass type is 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. In the calculation of XTIP, the
P contained in various P- precipitates is included. The stoichiometry factor for each precipitate
are estimated based on the composition of the precipitate. These stoichiometry factors are also
available in Global Fixed stoichiometry menu. The composite variable of XTP is estimated by
the sum of XTOP and XTIP. The TP is estimated by the sum of STP and XTP.
GPS-X Technical Reference