GAS-LIQUID 2-PHASE CROSS-FLOW ULTRAFILTRATION OF BSA AND DEXTRAN SOLUTIONS

A method is proposed for reducing concentration polarisation and membr ane fouling by injecting air into the feed stream, creating a ps-liqui d two-phase flow across the membrane surface. The injected air promote s turbulence, increasing the superficial cross-flow velocity of the pr ocess fluid, suppressing the polarisation layer and enhancing the ultr afiltration process. Experiments were carried out using a tubular memb rane (PCI, 100 kDa MWCO), mounted vertically and horizontally, with BS A, dextran and dyed dextran solutions. A range of transmembrane pressu res and liquid and gas flow rates were tested, with the liquid in puls atile and steady flow driven by peristaltic and centrifugal pumps. On the addition of air to the liquid stream, permeate flux was observed t o increase by up to 60% for dextran, 113% for dyed dextran and 91% for BSA. The rejection ratios were also improved with an increase of betw een 5 and 10%. Significant enhancements could be achieved at low gas f low rates, with the degree of enhancement increasing further at higher ps flow rates. Vertically mounted membranes showed a 10 to 20% higher permeate flux when compared with horizontally installed membranes und er the same two-phase flow operation.