GPS-X Technical Reference

121 Suspended Growth Models
AERATION OUTPUT VARIABLES
The aeration output variables can be accessed by right-clicking on most biological objects and
selecting Output Variables > Oxygen Transfer. For single tank objects, the same form can be
accessed by right-clicking on the overflow stream. For muli-tank objects such as the plugflow
tank, the total airflow, SOTR, OTR, and mechanical power can be accessed by right-clicking on
the overflow stream and selecting Total Air Flow, Total Oxygen Transfer, or Total
Mechanical Power.
The output variables associated with the blower calculations can be accessed by right-clicking on
the object (single tank objects only) or the overflow stream and selecting
Output Variables > Operating Cost.
MBR Aeration Model
In the Membrane Bioreactor and Completely-Mixed MBR objects the biological air
and cross-flow air in the membrane tanks are tracked separately. The biological air is
handled similarly as in the other objects in GPS-X with the exception that surface
mechanical aeration is not an available option.
The cross-flow air is assumed to be delivered using a coarse bubble aeration system. The
user can enter the following variables for the cross-flow air: air flow, alpha, and SOTE.
The cross-flow air is assumed to be at the conditions specified for the biological air (i.e.
Standard or Field). Unlike other objects in GPS-X, the user can specify whether the air
is at standard or field conditions even if the user is not entering the biological airflow.
GPS-X tracks the biological and cross-flow air separately but also calculates the total air
flow, SOTR, and OTR delivered to the tank.
In the MBR objects, higher default alpha values are used to reflect the high MLSS
concentrations typically found in MBRs.
ACTIVATED SLUDGE BIOLOGICAL MODELS
State Variables
A few comments about the state variables used in each of these models is required. For
all the models, the symbolic name of the state variables is prefixed with either an X for
particulate component, S for soluble component, or in some cases a G for gaseous
component. This designation follows the IWA (Henze et al., 1987a) convention, but is
somewhat arbitrary because some soluble and particulate components are colloidal and
will pass through a 0.45m filter but still be classified as part of a particulate component.
GPS-X Technical Reference