Page 45 - Membranes for Industrial Wastewater Recovery and Re-Use

Membrane technology 25

Figure 2.4 Pleated cartridgefilter membrane (by kindpermission ofPall)

Figure2.5 KubotaMFcassette

of the membrane element and radially inwards at the bottom whilst a fraction of
the flow permeates the membrane to form the product water inside the element.
The retentate, i.e. the rejected concentrated water from a single elemental stage, is
then transferred to the next element. There may be hundreds ofelements in a single
stack, producing a very long retentate flow path and allowing commensurately
high conversions, i.e. percentage formation of product water from feed water.
This module can also be configured for each element to be arranged in series
rather than in parallel, giving very short retentate flow paths, which reduce
concentration polarisation-exacerbated fouling (Section 2.2.3) to some extent.
Examples of rectangular pressure-sealed plate-and-frame modules are the
Rhodia-Orelis PLAEIDE UF/MF module (Fig. 2.7) and electrodialysis stacks (Fig.
2.8). The latter are all based on a plate-and-frame design since the process relies