Air sparging in ultrafiltration hollow fibers: relationship between flux enhancement, cake characteristics and hydrodynamic parameters

The gas sparging process consists in injecting a gas with the feed during t he filtration period. Many studies have recently demonstrated the interest of gas sparging for various membrane configurations to enhance the flux or to modify the membrane selectivity. This study focuses on gas sparging in u ltrafiltration hollow fibers to prevent a particulate deposit. New experime ntal results on ultrafiltration of river water are introduced and demonstra te that air sparging is more interesting for waters having a high fouling a bility (low critical flux). On the basis of experimental results for clay s uspensions, an analysis of the influence of the two-phase flow parameters o n the cake characteristics (porosity, thickness and specific resistance) is then introduced and allows to demonstrate that the notion of cake deposit is no more available with a gas/liquid flow. Hydrodynamics of the gas/liqui d two-phase how was characterized, in order to identify the parameters resp onsible for deposit prevention and for flux enhancement. Mixing or turbulen ce near the membrane surface seems to control the flux enhancement whereas the cake structure seems to be linked either to mixing or to the flow inter mittence. To conclude, perspectives of future processes which could involve air sparging are discussed. (C) 2001 Elsevier Science B.V. All rights rese rved.