GPS-X Technical Reference

21 Modelling Fundamentals
Overview of Data Requirements
In general, modelling of large-scale wastewater treatment plants requires that an
extensive number of plant and model parameters be assessed. Many parameters can be
measured directly, while others are based on experimental data taken from the literature.
Those parameters that cannot be measured directly or estimated from the literature are
usually determined using nonlinear dynamic optimization techniques based on actual
plant records and/or experimental data collected at the plant or in the lab. It is recognized
that the reliability of the calibrated model degrades with increasing numbers of
mathematically optimized parameters.
Data requirements fall into one of the following categories:
PHYSICAL PLANT DATA
1. Physical plant data, including: Process flow sheet (flow lines, channels, recycle
lines, by-passes, etc.); Flow pattern (plug flow, Continuously Stirred Tank
Reactor (CSTR), etc.); Sludge collection and withdrawal locations (location,
how when etc.); Dimensions of the various reactors (length, width, depth).
2. Operational plant data, including: Flow, Control variables (independent
variables), and Responsive variables (dependent variables).
3. Influent wastewater characteristics, including: Basic water quality parameters,
influent organic fractions, and influent nitrogen fractions.
4. Kinetic and stoichiometric model parameters for organic, nitrogenous and
phosphoric compounds and settling parameters (primary and secondary).
5. Some of these data and/or parameters vary in the course of a day (i.e. subject to
dry-weather diurnal variations or during a storm even), while others remain
relatively constant.
Elements of this data group are generally easy to obtain from plant blueprints and operation
manuals. It should be remembered that the physical volume of a reactor is only an approximation
of the active or operational volume of the unit. In a well-designed system the effect of dead-space
and hydraulic short-circuiting is normally minimal. In other cases it may be necessary to
determine the true hydraulic characteristics of a particular unit process, as in the case of a quasiplug
flow aeration tank. In this case, a dye-test is normally required, as the number of CSTRs
becomes a model parameter.
GPS-X Technical Reference