Oxygen diffusivity in calcium alginate gel beads containing Gluconobacter suboxydans

Gaining insight into the mass transfer characteristics in immobilized enzyme and microorganism systems bears much importance because of their widely increased use in industrial scale production as well as for analysis purposes. In this study, the effective diffusion coefficient of oxygen in calcium alginate gel with and without cells has been determined by the Moment Analysis Method for the first time in literature. When the gel concentration was increased from 1 to 3%, D-e values of oxygen varied between 2.54 x 10(-5) cm(2)/s and 2.58 x 10(-5) cm(2)/s indicating almost no dependency on gel concentration. However, a decrease in effective diffusion coefficient (from 2.55 cm(2)/s to 2.47 cm(2)/s) was observed with increased immobilized Gluconobacter suboxydans concentration in the range of 0 to 6%. Experimental results on liquid-particle mass transfer coefficient revealed a negligible external mass transfer resistance. Effectiveness factor for the bioreactor system was also calculated and found to be 0.39 and 0.21 for gel beads of 0.1 and 0.2 cm radius respectively. It is concluded therefore that the use of smaller gel beads could substantially improve the production efficiency in similar bioreactors.