Effect of air-sparging on the cross-flow microfiltration of microbe/protein bio-suspension

The effect of air-sparging on the performance of cross-flow microfiltration of microbe/protein bio-suspension is studied. A yeast/BSA binary suspension is separated using a two-parallel-plate cross-flow microfilter. The pseudo-steady filtration flux, cake properties and BSA rejection under various operating conditions are measured and discussed. The filtration flux increases with increasing filtration pressure, suspension and air velocities. The cake mass is significantly reduced by sparging air bubbles due to the increase in wall shear stress; however, this impact becomes trivial when air velocity exceeds 0.04 m/s. The average specific cake filtration resistance increases with increasing air velocity in a bubble flow, while suddenly decreases when the flow pattern changes to a slug flow. A drastic increase in BSA rejection is found as air bubbles are sparged into the filter channel. An increase in air flow velocity leads to higher BSA rejection especially in a slug flow regime. Taking filtration flux and BSA rejection into account, the BSA mass flux transported into filtrate decreases with increasing air velocity. Although sparging air bubbles can effectively enhance filtration flux, it is helpless for the separation of BSA from yeast cells. The results also indicate that the fluid flow pattern plays an important role in determining the filtration performance. The cake mass and BSA rejection in different flow regimes can be modeled using a force balance model for particle deposition and the standard capture equation for depth filtration, respectively.