Comparison of different carriers for adsorption of Saccharomyces cerevisiae and Zymomonas mobilis

Spruce sawdust, activated carbon, crushed brick, crushed firebrick and polystyrene have been tested as carriers for adsorption of Saccharomyces cerevisiae and Zymomonas mobilis cells. The isotope technique was used for the determination of the amount of adsorbed cells. The electrochemical nature of the cell surfaces, as well as zeta potentials, specific surface area and average porosity of the carriers were determined. The adsorption of S. cerevisiae and Z. mobilis on the carriers was quite different. The variance in immobilization capacities of the carriers could not be explained by differences in their internal surface areas and porosities. There was a clear tendency to decreasing capacities, with more negative zeta potentials with Z. mobilis. With S. cerevisiae there was no corresponding correlation between immobilization capacity and the carrier's zeta potential. Ethanol fermentation was used as a model to examine the activity, hydrodynamic behaviour and stability of the cell-carrier systems.