Influence of a gas/liquid two-phase flow on the ultrafiltration and microfiltration performances: case of a ceramic flat sheet membrane

Air injection in the feed flow was used to improve filtration performance ( flux, energy consumption) when applied to a ceramic flat sheet membrane dur ing crossflow filtration of a commercially available baker's yeast suspensi on. The effect of different operating parameters (gas flowrate, liquid flow rate, feed concentration) was evaluated with a horizontally and a verticall y installed UF or MF membrane. At low liquid flowrates, the membrane orient ation had a strong influence on the efficiency of the two-phase flow techni que, with a better improvement achieved with horizontally installed membran es. In the presence of a significant cell cake layer on the membrane surfac e, unsteadiness was found to enhance the permeate flux by a factor of nearl y 4 compared with steady microfiltration. It was also shown that the two-ph ase how unsteadiness failed to disrupt completely a previously built-up dep osit, even with increasing proportions of injected gas. Under the overall e xperimental conditions, the consumed energy per unit volume of permeate to achieve the same flux was found to be systematically lower in two-phase how than in single-phase flow. For a given specific energy, the permeate flux could be increased by a factor of 2. (C) 2000 Elsevier Science B.V. All rig hts reserved.