GPS-X Technical Reference

243 Attached-Growth Models
Filtration Component
The modified Iwasaki equation (Horner et al., 1986) was used to calculate the filtration
rate, while head loss is calculated according to the Kozeny equation. In the filtration
mode, the number of horizontal sections is determined by the plug flow characteristics of
the BAF bed (6 by default). This component of the model is used in predicting solids
capture, effluent suspended solids and other constituents and backwash quality. In
backwash mode, the backwashed fraction of the bed is treated as an ideally mixed tank;
biofilm layers are retained.
The filtration element of the model is available without the biological reactions in the
current sand-filter model in GPS-X described in One-Dimensional Model section of
Chapter 9.
Biological Reactions Component
The BAF models use the same biological reactions found in the suspended-growth
models in the appropriate library. The mantis model has been successfully used in several
biofilm configurations by Hydromantis, and is able to predict ammonia and BOD profiles
in the reactor and in the biofilm. For more specific information on biological models,
please consult Chapter 6 (page 94)
Biofilm Component
The existing biofilm model in GPS-X is based on Spengel and Dzombak (1992). This
model was adapted to the simple and advanced BAF configurations. The model handles
soluble material diffusion, biofilm growth, and particulate attachment and detachment.
Details are described in the Trickling Filter Model section of this chapter.
Mathematical Model
The mathematical equations used within each layer of the biofilm are provided in the
corresponding Model matrix (see Appendix A for the mantis model). The equations used
for the diffusion of the state variables from the bulk liquid into the biofilm are provided
in the Trickling Filter Model section of this chapter. The equations used for the filtration
component are provided in the One-Dimensional Model section of Chapter 9.
Model Parameters
This section discusses the various model parameters and inputs that the user will
encounter when using this model.
GPS-X Technical Reference