Membrane and Desalination Technologies - TCE Moodle Website

690 K. Mohanty and R. Ghosh
two proteins was achieved with IgG going thorough the membrane and HSA being rejected.
Figure 16.14 shows that injecting bubble increases permeate flux and reduces protein
transmission. The injection of air reduced HSA transmission to zero resulting in selective
transmission of IgG only. The gas sparging has an on–off effect on increasing permeate flux
and selectivity, i.e. significant enhancement on protein fractionation can be achieved under a
relatively low air flow rate which also reduces the potential damage to proteins due to
foaming.
6.3. Membrane Cleaning
Fig. 16.14. Effect of gas sparging on HSA/IgG fractionation (7).
As mentioned earlier, membrane fouling is the major problem in UF systems. Periodic
cleaning must be incorporated into a membrane operation as a preventive measure against
severe and irreversible fouling. Membranes could be cleaned by various physical, chemical
and physicochemical methods (84–85). Gas sparging has been proved to be an efficient
method for cleaning membranes. The gas is usually sparged on the feed side of the module
sometimes in combination with backwash or reversed permeate flow (86–87). The use of gas
sparging with backwash for cleaning hollow fibre membranes was investigated by Serra et al.
(87). It was found that the cake layer was instantaneously lifted off by the reversed permeate
flux and the injection of air improved material removal and reduced the volume of concentrated
foulant to be flushed. Hence the backwash time was reduced and its efficiency
improved. Verbeck et al. (88) used the airflush technique which involved an intermittent
two-phase flush through the module to dislodge and remove the cake from the membranes.
They found that airflush was a much better cleaning method than single-phase liquid forward
flow at the same velocity.