Gas-liquid two-phase cross-flow ultrafiltration of BSA and dextran solutions

A method is proposed for reducing concentration polarisation and membrane fouling by injection air into the feed stream, creating a gas-liquid two-phase flow across the membrane surface. The injected air promotes turbulence, increasing the superficial cross-flow velocity of the process fluid, suppressing the polarisation layer and enhancing the ultrafiltration process. Experiments were carried out using a tubular membrane (PCI, 100 kDa MWCO), mounted vertically and horizontally, with BSA, dextran and dyed dextran solutions. A range of transmembrane pressures and liquid and gas flow rates were tested, with the liquid in pulsatile and steady flow driven by peristaltic and centrifugal pumps. On the addition of air to the liquid stream, permeate flux was observed to 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 between 5 and 10%. Significant enhancements could be achieved at low gas flow rates, with the degree of enhancement increasing further at higher gas flow rates. Vertically mounted membranes showed a 10 to 20% higher permeate flux when compared with horizontally installed membranes under the same two-phase flow operation. © 1994.