GPS-X Technical Reference

133 Suspended Growth Models
Included in newgeneral are two new heterotrophic yield terms to account for
differences in yield under varying electron acceptor conditions. Where the
general model assumed the same yield irrespective of the electron acceptor,
newgeneral differentiates the yield depending on the presence of oxygen and
nitrate. The added stoichiometric terms include:
Yield (anoxic)
Yield (anaerobic)
In total, two state variables and eight processes have been added to the general model.
State Variables
Non-releasable polyphosphate (XPP)
Soluble inorganic nitrogen (SNI)
Processes
Anoxic hydrolysis of stored/enmeshed COD
Anaerobic hydrolysis of stored/enmeshed COD
XPP lysis on aerobic decay
XPP lysis on anaerobic decay
Anoxic decay of PolyP organisms
XPPR lysis on anoxic decay
XPP lysis on anoxic decay
XBT lysis on anoxic decay
Phosphorus Uptake
As evidence exists that not all polyphosphate is releasable, a new state variable to
represent non-releasable polyphosphate was incorporated. The uptake of phosphorus
(both aerobically and anoxically) in newgeneral results in the storage of both releasable
and non-releasable polyphosphate. The partitioning of the storage is stoichiometrically
determined based on the total phosphorus taken up.
PolyP Decay
In the general model decay of PolyP organisms was modelled as an aerobic or anaerobic
process. The newgeneral model includes anoxic decay of XBP to those processes. This
results in the anoxic lysis of XBT and XPPR modelled in a similar way to the aerobic
lysis of these variables in the general model. To account for the lysis of XPP,
newgeneral includes three new processes: one for aerobic lysis, one for anoxic lysis and
one for anaerobic lysis.
GPS-X Technical Reference