GPS-X Technical Reference

Sand Filtration Models 272
The filter bed is divided into layers and it is assumed that the specific deposit is uniform across
each layer. During the backwash cycle, the average deposit through all layers of the filter is used.
The average deposit after backwash is used as the initial condition for the subsequent filter run.
Model Parameters
Physical
This section discusses the various model parameters and inputs that the user encounters
when using the simple1d model.
These menu items are found under the Parameters sub-menu item Physical and contain
both real physical dimensions to describe the actual filter modelled, and model
dimensions which allow the user to specify the number of layers and an effective particle
diameter. The real dimensions of the filter are the bed surface area and the bed depth.
Operational
Operational items, found under the Parameters sub-menu, include the basis for the
duration of the filtration run. The duration of the filtration run may be based on a userspecified
time, headloss or effluent suspended solids concentration. The filtration run
may also be set manually. Other operational parameters include the influent flow and
specification of the backwash parameters (duration, rate).
Stoichiometric
Filter
The stoichiometric fractions available for the model are the ratios of particulate COD to
VSS, VSS to TSS and BOD 5 to BOD ultimate.
The filtration constants required for the model are shown in Figure 9-3. The filtration
constants include the clean bed filtration coefficient ( o), the initial porosity of the
filter bed ( o) and the porosity of deposited solids ( d), the ultimate bulk specific
deposit ( u), and the density and dry material content of the solids. The packing factor
is used in the defining equation for the variation of the filtration coefficient with the bulk
specific deposit as given by Ojha and Graham (1992).
GPS-X Technical Reference