GPS-X Technical Reference

147 Suspended Growth Models
To model this process, two processes are added in MANTIS2.
44. Growth of anammox microorganism: The stoichiometry factors to express
the yield of biomass, NO2-N consumption and N2 and NO3- are expressed in
terms of per unit NH 4+ -N oxidized. The reaction rate expression uses an
oxygen inhibition function and NO 2-N and NH 3-N saturation functions. Total
(ionized + non-ionized) concentration of both substrates is used in the kinetic
expression.
45. Decay of anammox microorganism: Decay of anammox microorganisms is
modelled using first order reaction rate with respect to the biomass
concentration.
Chemical precipitation processes
The precipitation reactions in MANTSI2 are adapted from Musvoto et al. 2000 with
some modifications. In addition to the processes of precipitation of AlPO 4 and FePO 4
which are included in ASM2d, five commonly observed precipitation processes in
wastewater treatment are included in the model. The key differences from
Musvoto et al. 2000 are: 1) the effect of ion-pair is neglected in the calculations; 2) the
kinetic rate equations use the approach suggested in ASM2d with a few modification and
3) the mole based stoichiometry is replaced with mass based stoichiometry for
maintaining model consistency. The kinetic expression for the precipitation reactions
uses the concentration of participating ions, rate of precipitation and solubility product of
the precipitate. The kinetic rate expression is formulated such that the precipitation and
dissolution reactions can be modeled by a single equation.
46. Precipitation/dissolution of CaCO 3: CaCO 3 is assumed to precipitate as
calcite. The calcite precipitation is assumed to take place in the presence of
Ca 2+ and CO 3
2-
ions in the solution. The concentration of CO 3
2-
is estimated
by using the soluble inorganic carbon and the pH of the system.
47. Precipitation/dissolution of MgNH 4PO 4.6H 2O (struvite): Struvite is the
most commonly observed precipitate in the digester supernatant. The
precipitation of struvite takes place if the Mg 2+ , NH 4
+
and PO 4
3-
species are
present in the solution. The concentrations of NH 4
+
and PO 4
3-
are estimated
based on the solution pH.
48. Precipitation/dissolution of MgHPO 4.3H 2O (newberyite): This is another
precipitate of magnesium with phosphate which is normally observed at
lower pH. For this precipitate, Mg 2+ and HPO 4
2-
ionic species are required.
The concentration of HPO 4
2-
ion is estimated based on pH of the solution.
GPS-X Technical Reference