Membrane and Desalination Technologies - TCE Moodle Website

274 J. Paul Chen et al.
the rejected material may be either dissolved or suspended depending on its size relative to
that of the pore (3).
Membranes can be organic (polymeric) or inorganic (ceramic or metallic), according to
its composition, and their morphology is dependent on the nature of the material, as shown
in Fig. 7.1.
A membrane separation system separates an influent stream into two effluent streams: the
permeate and the retentate or concentrate, as shown in Fig. 7.2. The permeate is the portion of
the fluid, which has passed through the membrane. The retentate (concentrate) contains the
constituents that have been rejected by the membrane.
2.2. Membrane Separation Processes for Water Treatment
There are various types of membrane separation processes for water treatment, as shown in
Fig. 7.3; the details of the four major processes – MF, NF, UF and RO – are discussed here.
Feed quality and quantity, requirement of products (e.g. permeate or reject), ease in operation
and costs determine selection of process (4–24). The applied pressure for typical membrane
filtration processes is given in Table 7.1.
2.2.1. Microfiltration
Microfiltration is a membrane filtration process that remove micron-sized particles from
fluids. MF membrane has pore sizes ranging from 0.1 to 10.0 mm, through which microorganisms
cannot pass. As a result, microfilters can be used to disinfect water solutions. For
Fig. 7.2. Basic diagram
of a membrane
separation system.
Polymeric membranes
Ceramic membranes
Fig. 7.1. Polymeric and ceramic membranes.
Membrane
Module
Feed
Permeate
Retentate/Concentrate