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Gas-Sparged Ultrafiltration: Recent Trends, Applications and Future Challenges 675
Fig. 16.2. Gas–liquid two-phase flow patterns (adapted from Hewitt and Hall-Taylor (32)).
membranes, slug flow is preferred. Figure 16.3 shows various membrane/bubbling arrangements
(1) (Fig. 16.3). A comparison of flux enhancement by using different membrane
modules, operating conditions and test media are summarized in Table 16.1.
4.1. Gas-Sparging in Tubular Membrane Modules
Effect of gas sparging in tubular membrane modules has been extensively studied by many
researchers. Gas sparging has been examined over a wide range of operating conditions (such
as TMP, gas flow rate, and feed concentration) and using different test media such as
dextrans, therapeutic proteins (e.g. IgG, human serum albumin), other proteins (such as
lysozyme, bovine serum albumin) and cells (yeast) (1, 7, 12, 13). The effect of membrane
orientation has also been studied.
The use of gas sparging for permeate flux enhancement was first reported by Cui (12). He
used a vertical tubular membrane module (12.7 mm i.d., PVDF, MWCO: 100 kDa) with
colored dextran solution (MW: 87 kDa) as the test media. Figure 16.4 shows that gas sparging
even at a low gas flow rate (ratio Vg/Vl ¼ 0.07) increased the flux significantly. However,
higher gas flow rates did not seem to increase permeate flux any further. These initial
observations by Cui (12) were later confirmed by many researchers (13, 27, 33–37). The
flux enhancement was found to depend on the type of membrane module and its orientation, and
operating parameters like TMP, feed concentration, gas flow rate, liquid cross-flow velocity.