Solute diffusion in biocatalyst gel beads containing biocatalysis and other additives

Abstract

Biocatalyst beads can be produced by the entrapment of microorganisms or enzymes into a stabilized hydrocolloidal gel such as alginate or carrageenan. In order to determine and predict the effectiveness of such catalytic material, it will be necessary to know the mass transport properties of substrates and products within the gel beads, especially where there are high concentrations of the biocatalyst or other additives. Diffusion of several solutes within the beads has been studied by measuring the transport of solutes to and from a well-stirred solution of limited volume. Tests have been performed with biocatalyst beads made from alginate and carrageenan covering a range of bead diameter, gel concentration, concentration of biocatalyst and other additives, and solute molecular weight. At low gel concentration with entrapped biocatalyst, a solute of low molecular weight has a diffusion coefficient approaching that measured in water. However, with increased gel concentration, and especially with high loadings of microorganisms and other additives, the diffusion coefficients are significantly decreased. An empirical relationship was developed for the diffusion coefficient as a function of microbial loading.