Abstract
In this study, single-phase and gas-sparged hollow fibre ultrafiltration experiments were performed with aqueous 144 kDa dextran solutions with concentrations of 5, 10 and 30 g/l. The purpose-built membrane unit comprised 10 individual polysulphone hollow fibres with a molecular weight cut-off (MWCO) of 50 kDa (dextran marker) and has a total filtration area of 0.033 m 2. The liquid feed crossflow velocities employed were 0.38, 0.72 and 0.99 m s −1, while sparging frequencies employed were: 0, 0.5, 1 and 2 min −1 as well as studies with continuous gas injection. A two-phase flow characterisation system was run simultaneously with the filtration process in order to determine the system hydrodynamics and to quantify the mass and momentum transfer. It was found that flux enhancement was higher under continuous rather than intermittent gas sparging. Enhancements of up to 102% were found with a 10 g/l feed concentration. Results gave good insight into how design and operation parameters affect permeate flux in single phase and gas-sparged hollow fibre ultrafiltration. Flux enhancement was found to rely heavily on thinning of the mass transfer BL as successive gas slugs moved long the membrane. Shorter, more frequently sparged gas slugs provided improved enhancement. The results could assist in optimisation of gas-slug enhanced ultrafiltration in hollow fibre membranes.
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