GPS-X Technical Reference

Suspended Growth Models 96
The correction factors are used to adjust the DO saturation concentration to account for
the temperature of the liquid, the pressure at the submergence level of the diffusers, and
the salts, precipitates, and surface-active substances found in the wastewater.
The temperature correction factor is calculated as follows:
Equation 6.3
where:
C * st
C * s20
= surface DO saturation concentration at temperature of t and 1 atm
(mg/L)
= surface DO saturation concentration at 20°C and 1 atm (mg/L)
The surface DO saturation concentration at liquid temperature t and a pressure of 1 atm is
obtained using a lookup table in GPS-X that is based on temperature. The lookup table
data were taken from Appendix C of the USEPA Design Manual – Fine Pore Aeration
Systems (USEPA, 1989). When the temperature falls between two data points in the
table, GPS-X uses linear interpolation to determine the C * st value. The value of C * s20 is
9.09 mg/L.
The correction factor for salts, particulates, and surface-active substances β, is a
parameter that must be measured or estimated for the wastewater of interest. In
GPS-X, a default value of 0.95 is used.
The pressure correction factor is calculated as shown below:
Equation 6.4
where:
Pb
Ps
pv
pde
= barometric pressure at elevation and air temperature (kPa)
= standard barometric pressure (101.325 kPa)
= vapour pressure of water at liquid temperature (kPa)
= effective pressure at depth of diffuser submergence
GPS-X Technical Reference