Bubble-free oxygen and carbon dioxide mass transfer in bioreactors using microporous membranes

Increasing gas-liquid mass transfer in bioreactors is a major goal for performance improvement in bioprocesses. The effects of bubble-free oxygen and carbon dioxide mass transfer using microporous membranes were tested in a flat module and a hollow fiber module for applications in a bio-fuel cell and cultivation of microalgae. The volumetric mass transfer coefficient, KLa, was compared to conventional bubbling. Liquid agitation rates influenced the mass transfer, as the limiting factor was the liquid boundary layer thickness. The KLa increased as the membrane hydrophobicity increased. The effect of pore size was found to be negligible for the hydrophobic membranes studied. The KLa for bubble-free aeration was found to be 2-3 times greater than bubbling at reduced power input. The growth rates of Chlorella vulgaris were found to be approximately 1.4 times higher than bubbling when utilizing bubble-free aeration in a hollow fiber module and in a novel flat membrane module