184 Chapter 8
Figure 8.5. Spiral wound UF membrane unit. Reproduced by permission of Fonterra Co - operative Group Ltd.
Figure 8.4. Spiral - wound UF membrane unit. Reproduced by permission of Fonterra Co - operative Ltd.
Permeate Flow rate
(L/h)Feed Flow rate
(L/h)Retentate Flow rate
(L/h)Pi Pois complicated by Donnan exclusion effects.
Therefore, the rejection rate of an ionic spe-
cies depends on not only membrane pore size,
but also retentate concentration and the pres-
ence of various co - ions. The pressures used
in this process vary between 8 and 20 bar.
Microfi ltration ( MF )
Microfi ltration is used to separate large par-
ticles (fat, casein, microorganisms) from
whey or milk. Residual fat must be fully
separated from the protein to produce whey
streams of 90% protein and greater.
In microfi ltration the pore size of the mem-
branes varies between 0.2 and 1.4 μ m. For
the defatting of whey streams, 0.1 to 0.2 μ m
membranes are commonly used (Figure 8.3 ).
The MF process was fi rst introduced with
tubular ceramic membranes, which have
superior pore size uniformity, leading to good
selectivity toward the permeability of whey
proteins and the retention of fat. They also
have a lifetime of more than 10 years.