GPS-X Technical Reference

Tools Object 338
The pH model operation menu item specifies whether the calculation is a standalone pH
estimation using the components under the Wastewater Components (stand-alone model)
header, or uses the components from a specific flow point in the plant layout.
If you select link pH estimation to label, the calculation will use the concentrations of ammonia,
nitrate, etc., from the stream label specified in label of point where pH is to be estimated. If
you would like to estimate the pH at several different points throughout the plant, place one
Toolbox object per pH calculation into the layout, and link each box to a different point in the
layout where pH is to be estimated.
The calculation is based on a model developed by Vavilin et al. (1995). The model is simplified
to include only strong bases, strong acids, total ammonia, total acetate, and total carbon dioxide.
The model uses an iterative process, in combination with the concentration of each component, to
determine the pH value.
The relationship between the concentration of a component and the concentration of its ions is
related through a dissociation constant (K). The concentration of hydrogen ion is used to
determine pH:
Equation 12.1
The initial pH identified on the pH solver set up control form is used to calculate the initial
concentration of hydrogen ion. An example of this control form is shown in Figure 12-1. The
default initial guess for pH is 7.
A second control form, shown in Figure 12-2, is used to input various equilibrium and
temperature constants.
Figure 12-2 – Component Control Form
GPS-X Technical Reference