Enhancement of membrane permeability by gas-sparging in submerged hollow fibre ultrafiltration of macromolecular solutions: Role of module design

Permeability in membrane filtration processes suffers from two major limiting factors: concentration polarization and membrane fouling. Gas-sparging, which involves bubbling of a gas in close proximity of a membrane, is known to minimise both of these. Gas-sparged membrane filtration is carried out either by pressurising a gas-sparged feed side or by using suction to draw the permeate through a membrane from the un-pressurised, gas-sparged feed side. The first approach is mainly used in ultrafiltration processes. The second approach which is easier to implement and is widely used in microfiltration processes. This paper discusses the enhancement of permeability by gas-sparging in suction-driven, submerged hollow fibre ultrafiltration using two different membrane module types. These modules were prepared using hollow fibre membranes having nominal MWCO of 150 kDa and were used to ultrafilter polysaccharide solutions. Depending on the operating conditions and on the module design, gas-sparging enhanced effective hydraulic permeability by as much as 115%. The extent of membrane fouling was also significantly lower in the gas-sparged mode. The effectiveness of gas-sparging was found to be greater with one membrane module type, clearly highlighting the effect of module design on process efficiency.