Page 46 - Membranes for Industrial Wastewater Recovery and Re-Use

26 Membranesfor btdustrial Wastewater Recovery and Re-use

Figurc 2.6 Rochem stackeddisc RO module. detailingfluidpath

Figure 2.7 Rhodia Orelis PLABIDB MF membrane module
on transport of ions through the membranes under the action of an electric field
and this configuration presents the simplest means of exposing a large
membrane area to an orthogonal electric field. Electrodialysis is simply a
combination of electrolysis and ion-selective permeation. If a potential difference
(voltage) is applied across a solution of ions they are transported through the
solution by electromigration, giving rise to the flow of a current. If ion-selective
membranes are then placed in the solution then only the counter-ions are
allowed to pass through the membrane via the oppositely charged pores in
membrane material. The placement of alternate cation and anion selective
membranes (Fig. 2.8) produces compartments or cells in which the salts are
alternately concentrated and demineralised by the action of the applied voltage
and the resulting flow of current.
The nature of the ED process makes for a module that is somewhat complex in
design, and is thus comparatively expensive, and which has to be hand