UNCOUPLING MASS-TRANSFER LIMITATIONS OF GASEOUS SUBSTRATES IN MICROBIAL SYSTEMS

Hollow fiber membranes were used to enhance gas-liquid transport in a chemo-autotrophic methanogenic completely mixed batch reactor. Studies of the material transfer for gaseous substrates are typically based on the assumption that the primary resistance is transfer through the gas-liquid interface. We uncoupled the gas-liquid and liquid-microbe resistances, and evaluated their relative contributions. A reduction in the velocity gradient under a constant substrate flux into the bulk liquid shifted the observed limiting resistance from the gas-liquid interface to the liquid-microbial interface. This shift was manifested as an increase in the apparent half-saturation value. The result of this work significantly influences biochemical reactor design and/or evaluation. Although a reactor can be categorized as being completely mixed, based on spatial invariability of the biomass concentration, we demonstrated that significant mass transfer resistance may continue to reside in the liquid-microbe boundary layer.