| The theoretical proposition that an optimal loading of biocatalyst to an inert support is offered by the competition between reaction and diffusion has been demonstrated experimentally. An experimental investigation of the effect of cell loading on the productivity of ethanol convertor revealed an extremum at a loading of 45%. The convertor was a fixed bed of Saccharomyces cerevisiae yeast cells entrapped in alginate beads. The feed to the convertors consisted of (per liter acetate buffer solution): 50 g/L glucose, 2.5 g/L Na2HPO4, 0.025 g/L MgCl2.6H20, 1.47 g/L CaCI2.2H20, 0.5g/L KCl and 2.5 g/L yeast extract, at 30°C. The flow rate was 100 ml/hr. Various cell loading (10%, 20%, 35%, 40%, 50% and 65%) were investigated. The reactor reached steady state within 19--24 hours of operation depending on the cell loading. No decline in the steady state was observed up to 3 days of operation. The durability of the steady state was not investigated beyond 3 days. Several batch experiments were conducted that support the finding of an optimal loading. It is argued that the optimal behavior found here is a general characteristic of supported biocatalysts depending on the operating conditions that can result in substantial improvements in reactor productivity.;A mathematical model was developed that includes external mass transfer and reliable diffusion model that is sensitive to cell loading [72]. The bulk phase and the particle phase equations were uncoupled using a relationship between the bulk phase and particle surface concentrations generated a priori. The model was able to match the experimental data. |
