STUDIES OF LIQUID PHASE MIXING AND BED EXPANSION OF GAS PRODUCING ANAEROBIC FLUIDIZED BED BIOREACTOR

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Department of Engineering

ABSTRACT
Liquid phase mixing and holdup are two important parameters required for the modelling and consequent evaluation of the performance of anaerobic fluidized bed bioreactors. Few papers have appeared in recent times, attempting to characterize liquid phase mixing and holdup in simulated biological reactors. But, the peculiar nature of biological systems as regards in situ gas production, which is difficult to simulate, mean that results from simulated studies need to be verified against active biological system. One of the problems hindering this verification is finding suitable tracer for use, in determining the axial liquid dispersion coefficient, with microbial system. In this work, the effects of superficial liquid and gas velocities in the ranges 0.0084 to 0.0351 cm/s and 0.054 to 0.335 cm/s respectively, on axial liquid dispersion coefficient (D2) and liquid holdup (eL), were studied in an anaerobic column bioreactor, of 3.81 cm internal diameter, containing flocculent strains of Saccharomyces cerevisiae. The strains used are Y6 and NCYC 1026. The gas velocities were calculated from the ethanol concentrations and were varied by varying the glucose feed rate. Since D and eL were determined from the liquid residence time distribution, a search for a tracer suitable, for use with the yeast, was conducted. In addition the performance of the bioreactor was studied under the same liquid and gas flow conditions. Five tracers, methyl violet, methyl green, aniline blue, fluorescein and dextran blue, were tested at three stages. In the first stage, shake flask fermentations were performed. Methyl violet was found to affect yeast metabolism by hindering it while methyl green promoted yeast metabolism. These tracers were also partly lost due to adsorption on cells surfaces. Fluorescein, aniline blue