GPS-X Technical Reference

Other Models 304
In addition to precipitating the phosphorus, the chemicals flocculate some of the colloidal
organics into particulate matter. In the model this is simulated as a conversion of soluble
inert COD and soluble substrate into particulate inerts and particulate substrate. The
extent of flocculation will depend on the half-saturation constants for each species. These
constants need calibration from plant to plant as the flocculation model is empirical.
Here is a detailed explanation of the constants of the Chemical Dosage menu item:
Number of chemicals: Currently four chemicals (alum, ferrous and ferric, plus a
user defined) are available.
Dosage mode . Mass flow based: in mass/time units.
Flow proportional: in mass/volume units.
The following stoichiometry parameters (for all compounds) are found under the More…
button, and are described in Table 11-1.
Table 11-1 - Chemeq Parameters
Parameter
P precipitation stoichiometry
soluble inert COD flocculation
stoichiometry
soluble substrate flocculation
stoichiometry
metal hydroxide stoichiometry
P precipitation half-saturation coefficient
soluble inert flocculation half-saturation
coefficient
soluble substrate flocculation halfsaturation
coefficient
Description
gP/gMe precipitated stoichiometrically (if
metal is in excess)
gCOD/gMe soluble inert COD converted to
particulate inert COD (si to xi)
gCOD/gMe soluble substrate converted to
particulate substrate (ss to xs)
g of MeOH formed per g of metal added
gP/m 3 concentration at which half the
Metal available for this reaction will be
used to precipitate phosphorus
gCOD/m 3 concentration at which half the
metal available for this reaction will be
used to flocculate soluble inerts
gCOD/m 3 concentration at which half the
metal available for this reaction will be
used to flocculate soluble substrate
The stoichiometry for inorganic inert solids production from P precipitation that was
available as a parameter in previous versions of this model (under the name chemdos) is
now calculated from known stoichiometry.
In addition, the chemeq model is written as an equilibrium model, meaning that all
precipitation and flocculation is assumed to happen instantaneously, and goes to
completion within the flow-through of the In-line Chemical Dosage object.
All nitrogen and phosphorus fractions of COD components are recalculated for mass
balance after the precipitation has taken place.
GPS-X Technical Reference