Page 49 - Membranes for Industrial Wastewater Recovery and Re-Use

Membrane technology 29

Figure 2. IO Tubular UF modules: (a) polymeric (PCI Membranes), and (b) ceramic (Kerasep", by Rhodia
Orelis)

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Figure 2.1 1 Hollowfibre module

the internal surface. This allows more control of the hydrodynamics, but the
operational pressure is then limited by the mechanical strength of the fibres,
which relates to the wall thickness. However, both capillary fibres and hollow
fibres can be backflushed (i.e. the flow reversed to wash the foulant from the
membrane surface). This is particularly crucial for hollow fibres, where the lack
of hydrodynamic control is such that fouling is inevitable and a periodic
backflush cycle is essential to maintain a reasonable permeability. Backflushing
can be enhanced by simultaneous air sparging, as is the case with the Memcor
system.

Recent developments: module configurations
There has been very little development in terms of novel membrane geometries
over the last few years: virtually all membrane elements are configured as either
planar or cylindrical. A noteworthy development is the newer 2 7-channel
Kerasep@ ceramic membrane element produced by Rhodia Orelis, which
provides almost 40% more membrane area per unit volume than their
conventional cylindrical 19-channel tubular monolith. Each channel is a 120"
segment, such that the walls dividing a cluster of three channels are planar. This
allows a greater membrane area without compromising mechanical strength.
There has also been a tendency to try and produce less expensive modules either
by using alternative materials or designs that are less complicated in