Membrane and Desalination Technologies - TCE Moodle Website

306 J. Paul Chen et al.
l Product conversion rate. It depends on several factors, mainly ionic charge and ionic size. The
higher the ionic charge and the larger the ionic size of the contaminant, the more easily the ion is
removed and the more finished water is recovered relative to the amount of reject water.
6.4. Engineering Design
Membrane module
Feed Permeate Retentate
Fig. 7.19. A batch system.
a b
Feed
Module 1 Module 2
Retentate Feed
Module 1
Retentate
Module 2
Permeate
Permeate
Two-stage stripping cascade Two-stage enriching cascade
Fig. 7.20. Two-stage membrane process: (a) two-stage stripping cascade and (b) two-stage enriching
cascade.
A membrane system can be designed by empirical or semiempirical approaches and
computer-simulation models. The former can be found in the literature such as Geankoplis’
manuscript (27); the later is illustrated by Judd and Jefferson (3). A frequently used design
tool based on a semiempirical approach is given below.
6.4.1. Reverse Osmosis
Mass transfer of substances in a membrane unit can be considered as steady-state diffusion,
which can be described by the following equations (6, 12, 40, 49). A conceptual illustration of
RO is given in Fig. 7.21. Noted that 1 and 2 represent feed and permeate (product) sides,
respectively: