GPS-X Technical Reference

GPS-X Composite Variable Calculations 46
The suspended solids composite variable is calculated from the particulate COD (XCOD)
by dividing it by the XCOD:VSS ratio (icv). This changes the units of the XCOD to
gVSS/m 3 , resulting in the composite variable for volatile suspended solids (VSS). To
calculate the suspended solids composite variable (X), VSS is added to the concentration
of inert inorganic particulates (XII), metal hydroxides (xmeoh) and metal phosphates
(xmep), and stored polyphosphate (multiplied by 3 to change from gP/m 3 to g/m 3 ).
The biochemical oxygen demand (BOD) composite variables are calculated from the
state variables. The biodegradable state variables (the state variables that exert BOD,
which are in units of gCOD/m 3 ) are summed to provide a particulate and a soluble
ultimate BOD (XBODU, SBODU). The sum of these components is the total ultimate
BOD measurement (BODU). To determine BOD 5, a stoichiometric fraction, fbod, which
is the ratio of BOD 5:BOD 20, is multiplied by the calculated BODU.
Table 4-6 - CNPLIB BOD, COD, and TSS Composite Variables
SBODU XBODU BODU SBOD XBOD BOD SCOD XCOD COD VSS XISS X
ss 1 1 fbod fbod 1 1
sf 1 1 fbod fbod 1 1
slf 1 1 fbod fbod 1 1
xs 1 1 fbod fbod 1 1 icv -1 icv -1
xbh 1 1 fbod fbod 1 1 icv -1 icv -1
xba 1 1 fbod fbod 1 1 icv -1 icv -1
xpb 1 1 fbod fbod 1 1 icv -1 icv -1
si 1 1
xi 1 1 icv -1 icv -1
xu 1 1 icv -1 icv -1
xgly 1 1 fbod fbod 1 1 icv -1 icv -1
xbt 1 1 fbod fbod 1 1 icv -1 icv -1
xsto 1 1 fbod fbod 1 1 icv -1 icv -1
xii 1 1
xmeoh 1 1
xmep 1 1
xpp 3 3
xppr 3 3
In terms of variables containing nitrogen, the calculation of the composite variables is
similar to the calculations done in the Carbon - Nitrogen library. The differences include
the addition of a new state variable, soluble unbiodegradable organic nitrogen (sni), to the
soluble TKN (STKN), the inclusion of nitrogen components of the new substrate type
(sf), and the inclusion of nitrogen components of poly-phosphate-accumulating organisms
(xbp). See Figure 4-5 for a general diagram of the nitrogen composite variable
calculations.
GPS-X Technical Reference