GPS-X Technical Reference

23 Modelling Fundamentals
Primary and Final Effluent Response Variables
Water quality constituents such as BOD 5 (inhibited), Total Suspended Solids (TSS),
Total Kjeldahl Nitrogen (TKN), ammonia (NH 3) and nitrates (NO 3) are necessary for the
calibration of the various unit processes. For example, BOD (in lack of COD) is used to
calibrate and verify the carbonaceous component of the IAWQ activated sludge model,
while suspended solids measurements can be useful in identifying the settling parameters
of Hydromantis' layered settler model. The nitrogenous compounds are needed to
calibrate the nitrification-denitrification component of the model.
INFLUENT WASTEWATER CHARACTERISTICS
Basic Parameters
Basic influent wastewater characteristics such as BOD 5, BOD u, COD, TSS, VSS, and
TKN are important to know in that they allow us to establish mass balances across the
system. The biochemical oxygen demand (BOD) provides only partial information on the
influent organic load (see Why COD is Important to Know). COD measurements are not
readily available in some wastewater treatment plants. In this case, the BOD 5/BOD u ratio
can better estimate the influent organic load. Suspended solids, influent VSS and BOD
together, can be used to determine the different influent organic fractions, which are
critical for the proper use of the IAWQ activated sludge model, as discussed in GPS-X
Objects. Influent TKN is generally more useful than ammonia concentration alone
BIOLOGICAL REACTOR AND FINAL SETTLER
Organic Compounds
The IAWQ activated sludge model contains a large number of stoichiometric and kinetic
parameters, which describe the degradation of organic matter in the activated sludge
process (Henze et al., 1987a). Some of the analytical tests are laborious and are not
discussed here. Many of the default model parameters can be used with a high degree of
confidence. Site-specific model parameters include the maximum growth rate and the
yield coefficient of the heterotrophs. If the data described in the previous sections are
known (e.g., sludge wastage rate and wastewater influent fractions), it is relatively easy
to optimize the maximum growth rate and yield coefficient of the heterotrophs to match
the measured MLSS, sludge production, and oxygen uptake rate.
GPS-X Technical Reference