GPS-X Technical Reference

303 Others Models
With a large overdose of metal ion to wastewater, most of the phosphorus would be
removed; however, there would still be trace amounts of phosphorus. To model this
phenomenon, a saturation function was incorporated in the model. The amount of
phosphorus removed (or soluble organic component, si and ss, that would flocculate)
becomes a function of the phosphorus concentration (or soluble organic component
concentration). The stoichiometric amount of removal is only achieved when the
phosphorus concentration is large (with respect to the half-saturation coefficient).
Removal is less than the maximum stoichiometric amount when the phosphorus
concentration is small (with respect to the half-saturation coefficient). This phenomenon
is depicted in Figure 11-3.
Figure 11-3 - Removal as a Function of P Concentration
The mass of chemical precipitant formed is also calculated and added to the particulate
inert inorganic component (xii). The stoichiometric amount of chemical sludge produced
is based on the stoichiometry of the basic reaction. For example, in Equation 11.1, the
mass of chemical precipitant (AlPO 4) is 4.52 g per 1g of aluminum ion reacted.
The model provides the user with two dosage methods: mass flow based and flow
proportional. The former requires the user to specify a continuous flow rate for the
chemical, while the latter allows the user to specify a flow rate of chemical per unit flow
of liquid entering the basin. The dosage rate can be set up as a manipulated variable to
maintain the phosphorus at a specified set point at any location downstream of the
chemical addition.
GPS-X Technical Reference