GPS-X Technical Reference

Suspended Growth Models 132
While this is likely, no change was made to the model in this respect because the amount
of generation in the mixed culture systems is small.
The values of the kinetic parameters, as with the asm1 model, are those for 20 ° C.
The general model is no longer available in GPS-X, in favour of using the newgeneral
model (see below), which corrects deficiencies of the general model.
New General Extension
The newgeneral model is based on the general model with significant changes to
account for so-called 'COD losses' that have been reported in nutrient removal systems.
Some key features of the newgeneral model include:
‘COD’ loss yields
Hydrolysis efficiency factors
Heterotrophic yield coefficients for different electron acceptor conditions.
The modelling of BNR activated sludge systems has identified mass balance problems in
some facilities. That is, several experimental and full-scale evaluations of BNR facilities
have revealed imbalances between what is going into the plant and what is going out (i.e.
less COD is going out than going in, hence the COD 'loss'). Both from a theoretical and
modelling point of view this causes some problems, and there is no world-wide accepted
explanation for these imbalances. Nevertheless, these discrepancies must be modelled. To
account for these mass balance problems (referred to as anaerobic stabilization or COD
losses), four COD loss terms are included in the newgeneral model. These include:
Hydrolysis efficiency factor (anoxic)
Hydrolysis efficiency factor (anaerobic)
Fermentation volatile fatty acid (VFA) yield.
PolyP PHB yield on sequestration of VFAs.
The newgeneral model has proven itself to be a reliable predictive tool for the BNR
process. Nevertheless, users should be aware that the newgeneral model in its default
condition does not result in a COD balance across the system. To eliminate COD losses
(and thus force a COD balance across a newgeneral -based layout) each of these
stoichiometric loss terms should be set to 1.0.
GPS-X Technical Reference