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 during crossflow filtration of a commercially available baker’s yeast suspension. The effect of different operating parameters (gas flowrate, liquid flowrate, feed concentration) was evaluated with a horizontally and a vertically installed UF or MF membrane. At low liquid flowrates, the membrane orientation had a strong influence on the efficiency of the two-phase flow technique, with a better improvement achieved with horizontally installed membranes. In the presence of a significant cell cake layer on the membrane surface, unsteadiness was found to enhance the permeate flux by a factor of nearly 4 compared with steady microfiltration. It was also shown that the two-phase flow unsteadiness failed to disrupt completely a previously built-up deposit, even with increasing proportions of injected gas. Under the overall experimental conditions, the consumed energy per unit volume of permeate to achieve the same flux was found to be systematically lower in two-phase flow than in single-phase flow. For a given specific energy, the permeate flux could be increased by a factor of 2.