GPS-X Technical Reference

177 Suspended Growth Models
Equation 6.50
where:
A TSS, A BOD, B TSS, B BOD, K hrt = calibration parameters
n = number of ponds in series
As the empirical equations above only deal with GPS-X composite variables (BOD and
TSS), a methodology is required to transfer this information back to the state variables.
The following list outlines the relationships for the state variables in CNLIB.
A fraction is calculated for each particulate state variable (xbh, xba, xs, xi, xu, xsto for
CNLIB) that is equal to that variable's concentration over incoming xcod.
A new TSS value (x) is calculated from the above empirical REMOVAL equation.
New VSS (vss) and particulate COD (xcod) concentrations are calculated as:
vss = ivt * x
xcod = icv * vss
A new BOD value is calculated from the above empirical REMOVAL equation, and then
compared to the BOD value calculated as the sum of the fractions from step 1 multiplied
by the new xcod multiplied by fbod.
If the BOD calculated from the fractions is less than the BOD calculated from the
empirical equation, excess soluble BOD (the difference between bod and xbod) is
assigned to ss.
If the BOD calculated in step 3 from the fractions is greater than the BOD calculated
from the empirical equation, the excess particulate BOD (xbodu) is assumed to be
converted to xu. Soluble substrate (and soluble BOD) is then assumed to be zero.
Inert and non-reacting variables are mapped through the pond object (si, salk, and snn).
The effluent oxygen concentration (so) and nitrate concentration (sno) are assumed to be
zero in the anaerobic pond environment.
Particulate biodegradable organic nitrogen (xnd) is assumed to be converted to snh as per
the conversion of xs.
Soluble biodegradable organic nitrogen (snd) is assumed to be converted to ammonia
(snh) as per the conversion of ss.
The loss of heterotrophic (xbh) and autotrophic (xba) biomass results in the production
of ammonia (snh).
GPS-X Technical Reference