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Membrane Technologies for Oil–Water Separation 655
hydrophilic microfiltration membrane could effectively separate the diethyl sebacate/water
emulsion. Diethyl sebacate concentrations in the permeate were lowest when the transmembrane
pressure was low and when the membrane was frequently backflushed. Membrane
fouling during oil–water emulsion filtration is mainly due to adsorption of oil on membrane
structure, which causes modification of the critical surface tension. This process exhibits a
good example to apply membrane bioreactor as an effective oil–water separation method (76).
4. ADVANCES IN MEMBRANE TECHNOLOGY
4.1. Modification of Membrane
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Fig. 15.7. Schematic of dual-membrane bioreactor (76).
The most serious limitation of membranes is the continuous decline of flow through the
membrane due to fouling. Permeation rates of macromolecular solutions through membranes
are much smaller than pure water permeation rates and decrease rapidly as the operation
continues. Flux decline has a significant negative impact on the feasibility and economics of
the membrane process. Recently, many works have focused on membrane modification with
a fundamental approach to reduce membrane fouling. Numerous attempts have been undertaken
to modify membrane materials aimed at producing membranes less susceptible to
fouling. One technique widely used for this purpose is blending of the original polymer
with polymers to achieve the required properties (77, 78). For example, to enhance the
membrane hydrophilicity, the polyether sulfonamide) is blended with the original polymer
to obtain a modified poly(etherimide) ultrafiltration membrane (79). To change the adsorption
and permeation properties of the membrane, the addition of polymeric layers on the active
surfaces of membranes is performed (80). Adsorbed hydrophilic polymers were assessed as a
possible means of reducing protein fouling in microfiltration and ultrafiltration membranes
(81–85). Polysulfone ultrafiltration and microfiltration membranes were modified by preadsorption
of water-soluble polymers (85). The preadsorbed polymers cause the narrowing of
pore sizes on the membrane surface. In addition, the desirable anti-fouling effect of the
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