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Gas-Sparged Ultrafiltration: Recent Trends, Applications and Future Challenges 689
fouling control, mixing for adsorption and oxygenation for biodegradation. Various strategies
applied to MBRs viz., bubbling, intermittent suction and backwashing can also be used
effectively to optimize the hybrid membrane process performance (1).
6.2. Protein Fractionation and Concentration
Ultrafiltration is widely used for protein desalting and concentration. In recent years,
protein fractionation by UF has generated considerable interest in terms of its applicability
for bioseparation of recombinant protein and plasma products (6). The advantages of UF
compared to other methods like chromatography are: high throughput of products, lower
capital investment and ease of scale-up, while maintaining product purity under ambient
conditions. Efficiency of bioseparation depends on protein–protein and protein-membrane
interactions as well as on operating conditions. Low selectivity and severe decline in permeate
flux have been identified as the major challenges with ultrafiltration. Low selectivity
results from concentration polarization, while decline in permeate flux mainly results from
membrane fouling. Both these problems can be minimized by improving the system hydrodynamics.
Gas sparging has been found to be an attractive way by which system hydrodynamics
could be improved in a cost effective manner.
Ghosh et al. (52) has studied the effect of bubbles on fractionation of BSA (67 kDa) and
lysozyme (14.1 kDa) using a flat-sheet membrane (MWCO 100 kDa). Under the optimal
operating conditions of gas-sparged UF complete separation of these two proteins was
achieved. It can be seen from Table 16.6; about 18-fold increase in selectivity was achieved
simply by sparging a small amount of gas. Further increase in sparging did not have much
effect. Similar effects were observed in hollow fibre modules (47).
Fractionation of HSA (67 kDa) and IgG (167 kDa) by gas-sparged UF using a tubular
PVDF membrane (MWCO 100 kDa) was reported by Li et al. (7). Complete separation of the
Table 16.6
Effect of gas sparging on the fractionation of BSA and lysozyme
Gas flowrate
( 10 6 m 3 /s)
Permeate flux
( 10 2 kg/m 2 s)
Sa for BSA Sa for lysozyme Selectivity (c)
0 0.93 0.078 0.846 10.9
1.67 0.96 0.004 0.776 194.0
3.33 0.97 0.004 0.785 196.3
6.67 1.00 0.004 0.739 184.8
a 0 0.75 0.059 0.780 13.2
a 0.83 0.78 Undetectable 0.724 Nearly complete separation
a 1.67 0.82 Undetectable 0.710 Nearly complete separation
Operating conditions: feed = 2 kg/m 3 BSA þ 2 kg/m 3 lysozyme, buffer = 20 mM phosphate. pH = 7.0, PS
100 kDa membrane, TMP = 0.5 bar, Vl = 8.33 10 6 m 3 /s, ul = 0.074 m/s
a TMP = 0.3 bar, all other operating conditions are same as above