Page 133 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

CHAPTER 3

SOLID-LIQUID SEPARATION
AND INTERCEPTORS

This chapter will describe the methods used to separate suspended solids (particulates)
and liquids from a feedwater stream. Separation is characterized by the recovery of all
of the processed water and having the flow of the feedwater, in general, pass through
the filter perpendicular to the filter bed or medium. General selection criteria will also be
discussed.

FILTER CLASSIFICATION AND TESTING

There are many ways to classify filters:
1. Filtration types. Depth, surface, skimmers, and screen are general filter types.
2. Driving force. Flow through the filter can be induced by pumps (pressure), centrifugal
force, or gravity.
3. Function. The goal of the filtration process is either retention of the dry solid when
the filter cake is of value or disposal of the filter cake when process liquid is of
value.
4. Operating cycle. The cycle of operation can be batch mode or continuous.
5. Nature of the solid. The accumulation of solids within a filter matrix can be either
deformable (compressible) or rigid (incompressible).
The classification of filters is not exclusive and the distinction between them is arbitrary.
Here the characterization of filters will be based on the type of filtration, the characteristic
generally used in utility and service water filtration systems.
Interceptors, strainers, and filters are all devices used to reduce (or remove) and retain
suspended solids. Other separation processes, such as sedimentation and centrifugation,
that are used to treat large quantities of water or for dewatering, are outside the scope of this
book. Design and selection criteria for specific contaminant removal are provided where
appropriate in various other chapters discussing individual systems.
The distinction between filtration and water purification is arbitrary. Methods such as
membrane and membrane exchange filtration that removes ions, allows preferential pas-
sage of specific substances, and does not conform to the previous definition of filtration are
considered water purification methods and are discussed in Chap. 4.

3.1
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