FLUX ENHANCEMENTS WITH GAS SPARGING IN DOWNWARDS CROSS-FLOW ULTRAFILTRATION - PERFORMANCE AND MECHANISM

In this study gas-liquid two-phase crossflow ultrafiltration was studi ed in downwards flow condition. A commercially available tubular membr ane module was installed vertically and the feed solution and the inje cted gas bubbles flow downwards inside the membrane tubes. The permeat e flux achieved in such an operation was compared to conventional sing le phase ultrafiltration and also to gas sparged upwards crossflow ope ration. The effect of operating parameters, including liquid and gas f low rates, transmembrane pressure (TMP) and feed concentrations, was e xamined with dextran solutions. Flux increases of up to 320% were achi eved with gas sparging ill the experimental study compared to single l iquid phase crossflow ultrafiltration. This enhancement is much more p rofound when the liquid phase is in laminar flow, particularly when th e concentration polarisation is more severe, for example, at a high TM P, a higher feed concentration, and a low liquid crossflow velocity. T he enhancing effect is not very significant when liquid flow itself is turbulent. The flow pattern proved to be an important parameter and t he operation could be optimised to achieve maximum enhancement with mi nimum gas injection.