AUGMENTATION OF MASS-TRANSFER THROUGH ELECTRICAL MEANS FOR HYDROGEL-ENTRAPPED ESCHERICHIA-COLI CULTIVATION

Nutrient depletion and in hibitory end-product accumulation are the major problems for hydrogel-entrapment cell cultures. An electrokinetic technique was developed to enhance intrahydrogel mass transfer to overcome these problems. Escherichia coli cells (ATCC 15224) were entrapped in 3.2-mm-thick potassium-K-carrageenan and agarose hydrogel slabs. With a electric current density of 180 A/m(2), the cell densities were increased by 140% (from 3.9 to 9.6 dry cell weight [DCW] g/L) in potassium-kappa-carrageenan and by 80% (from 3.9 to 7.0 DCW g/L) in agarose. A mathematical model taking into account nutrient depletion, inhibitory end-product formation, and cell growth kinetics under facultatively anaerobic conditions was developed to rationalize the overall transport and biological behaviors in the hydrogel. The cell growth in hydrogel was successfully simulated. It is concluded that the augmented transports for glucose and inhibitory end-products accounted for these increases in cell growth. The increase in cell density in potassium-kappa-carrageenan was due to the enhanced removal of inhibitory end-products (through electroosmosis and electrophoresis: 80%) and due to the augmented glucose transport (through electroosmosis: 20%). (C) 1995 John Wiley & Sons, Inc.