The effects of temperature and viscosity on glucose diffusivity through Saccharomyces cerevisiae biofilms

The present study helps us to understand the effects of temperature and vis cosity on bioprocesses in immobilized cell bioreactors. Glucose diffusiviti es through Saccharomyces cerevisiae biofilms are experimentally investigate d at variable biofilm thickness, temperature, and concentration of carboxym ethylcellulose (CMC) used as viscosity-raising additive. Comparing these ex perimental values with those for free diffusion of glucose in water shows u s that biofilm strongly reduces diffusivity (about 74%), mainly due to a de crease in the effective diffusion area. Only a slight increase in diffusivi ty is observed when biofilm thickness is increased. In addition, the result s obtained in this work demonstrate that the well-known empirical equations of Wilke and Chang, and of Guzman and Andrade can be combined to a relatio nship which takes into account the simultaneous efforts of temperature and viscosity on the effective glucose diffusivity. This equation appears to be valid in glucose aqueous solutions whether or not biofilm is used, whereas it is not applicable when viscosity-raising additives, such as CMC, are us ed.