DIFFUSIONAL CHARACTERISTICS OF A SWELLING GEL AND ITS CONSEQUENCES FOR BIOREACTOR PERFORMANCE

A diaphragm diffusion cell was used to determine the effective diffusi on coefficient Of L-methionine in a modified polyacrylamide gel at dif ferent degrees of swelling. As could be expected from theory, the valu e of the effective diffusion coefficient increased with increasing swe lling. The combined effect of increased radius and increased effective diffusion coefficient is analysed in terms of the Thiele modulus and the effectiveness factor. The results can explain the reduced producti on rate obtained in bioreactors with immobilized enzymes using gel car riers with a shrinking-swelling behaviour during processing.