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A new technique is proposed for enhancing the crossflow ultrafiltration process by injecting air into the system. The injected air provides a turbulence promoting effect, and can also increase the superficial velocity of the cross-flow, so effectively disturbing and suppressing the concentration polarisation layer, and hence enhancing the ultrafiltration process. Experiments were carried out on the proposed gas-liquid cross-flow ultrafiltration process, with PVDF tubular membranes (PCI, MWCO 100kD) vertically installed and dyed dextran solutions (MW 87kD and 162kD) as the media. It was found that air injection could greatly suppress the effect of concentration polarisation and fouling, while maintaining a high ultrafiltration rate. Compared with the single phase operation, the permeate rate was increased by 70-250% even at a very low gas flowrate. At the same time, the rejection ratio of the membrane is increased considerably. An attempt was made to explain the mechanism for this enhancement. The limitations of the technique were considered and further research on this technique suggested. (Author)


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