17 DEC 2003
GRANULAR MEDIA FILTRATION
Elements of Design and Operating Conditions. Once a granular filter sys-
tem has been selected using the guidance provided in Chapter 4, the following design
features must be established for a given application:
Filter media type, size, and depth.
Terminal head loss.
Method of flow control.
5-1.1.1 For package filtration systems, the manufacturer will have already established
these parameters. The designer should check the design of any proposed system to
ensure that the given parameters fall within expected design ranges.
5-1.1.2 After the waste stream has been characterized, the first step is to establish
the filtration rate and media type, size, and depth. This is normally done based on
regulatory requirements of the governing body having jurisdiction, experience with simi-
lar treatment applications, or pilot testing for a specific application, if necessary and
5-1.1.3 Once the filtration rate for the facility is established, the facility can be sized
on the basis of the required maximum treatment rate. The total filtering area is estab-
lished, and then the number and dimensions for the individual filters are determined. In
determining the numbers of filters required, the designer must evaluate the rate to be
handled by each filter and the corresponding backwash rate that would be necessary for
a certain size of filter. The decision concerning the number and size of the filters affects
the individual filter piping and sizing, flow control requirements, and operational flexibility
of the facility. In addition, the designer must consider the requirement for continuous
flow and redundancy in determining an acceptable number of filters.
5-1.1.4 When not already dictated by the manufacturer, the configuration of the
individual granular media filter may need to be decided. Choices must be made con-
cerning the use of single or dual cell filters and the length and width dimensions of the
filter cell. The length and width of the filter cell is normally established on the basis of
the filter underdrain system and the auxiliary scour system to be used. Manufacturers of
the filter equipment components provide guidelines covering the use of their equipment
and filter bed layout information in their product literature.