GPS-X Technical Reference

Suspended Growth Models 148
49. Precipitation/dissolution of Ca 3(PO4) 2 (ACP): As the numbers of water
molecules associated with the precipitate are variable, an anhydrous form is
considered in expressing the mass concentration of the precipitate. It is
indicated that this is probably the least stable precipitate among the possible
precipitates and transforms into more stable forms with time. The Ca 2+ ion
and PO 4
3-
species are required in precipitation process.
50. Precipitation/dissolution of MgCO 3: MgCO 3 (magnesite) is another
precipitate of magnesium that is included in the model. The precipitation
reaction requires Mg 2+ and CO 3
2-
ionic species for its formation.
51. Precipitation/dissolution of AlPO 4: The precipitation of AlPO 4 is required
to model the metal precipitation of phosphorous in the plant. The
stoichiometry of the process is similar to ASM2d; however, the kinetic
expression is modified to include the solubility product of the precipitate.
52. Precipitation/dissolution of FePO 4: The precipitation of FePO 4 is required
to model the metal precipitation of phosphorous in the plant. The
stoichiometry of the process is similar to ASM2d; however, the kinetic
expression is modified to include the solubility product of the precipitate.
Gas liquid transfer processes
Similar to the gas liquid transfer of oxygen, four additional processes as below are added
in the model. The gas-liquid transfer is modeled using a mass transfer constant (K La) and
the gas saturation concentration at the given temperature and pressure. The mass transfer
constant for each gas can be correlated to the oxygen mass transfer using gas
diffusivities. For simplification, fractional factors are applied to the mass transfer
constant of oxygen to obtain respective mass transfer constant.
53. Gas liquid transfer of CO 2: Process describes the stripping/absorption of
CO 2 from/to the liquid. Since the concentration of CO 2 in liquid depends on
the pH, this process is very sensitive to the pH of the solution.
54. Gas-liquid transfer of N 2: Process describes the stripping/absorption of N 2
from/to the liquid.
55. Gas-liquid transfer of CH 4: Process describes the stripping/absorption of
CH 4 from/to the liquid.
56. Gas-liquid transfer of H 2: Process describes the stripping/absorption of H 2
from/to the liquid.
GPS-X Technical Reference