GPS-X Technical Reference

257 Sedimentation and Flotation Models
The settling function is shown in Figure 8-3. The four regions depicted in this figure are
explained as follows: I) the settling velocity equals zero, as the solids attain the minimum
attainable concentration; II) the settling velocity is dominated by the flocculating nature
of the particles; thus the settling velocity is sensitive to the rfloc parameter; III) settling
velocity has become independent of solids concentration (particles have reached their
maximum size; and IV) settling velocity is affected by hindering and becomes dependent
on the rhin parameter (the model reduces to the Vesilind equation).
Simple Models
Figure 8-3 – Settling Velocity vs. Concentration
In the simple1d sedimentation model, the only numerically integrated variable is the
suspended solids concentration. This model can be used when biological reactions in the
settler can be ignored. The concentrations of particulate state variables in the influent to
the settler (heterotrophic organisms, etc.) are stored as fractions of the total suspended
solids concentration entering the settler. Once the model completes the numerical
integration of the suspended solids in the settler layers (at the end of each numerical
integration time step), the concentrations of particulate state variables in the effluent,
underflow (RAS), and pumped flow (WAS) are restored using those fractions. The
concentrations of soluble state variables are not changed in the simple1d model.
GPS-X Technical Reference