Heat transfer simulation in solid substrate fermentation.

A mathematical model was developed and tested to simulate the generation and transfer of heat in solid substrate fermentation (SSF). The experimental studies were realized in a 1-L static bioreactor packed with cassava wet meal and inoculated with Aspergillus niger. A simplified pseudohomogeneous monodimensional dynamic model was used for the energy balance. Kinetic equations taking into account biomass formation (logistic), sugar consumption (with maintenance), and carbon dioxide formation were used. Model verification was achieved by comparison of calculated and experimental temperatures. Heat transfer was evaluated by the estimation of Biot and Peclet heat dimensionless numbers 5-10 and 2550-2750, respectively. It was shown that conduction through the fermentation fixed bed was the main heat transfer resistance. This model intends to reach a better understanding of transport phenomena in SSF, a fact which could be used to evaluate various alternatives for temperature control of SSF, i.e., changing air flow rates and increasing water content. Dimensionless numbers could be used as scale-up criteria of large fermentors, since in those ratios are described the operating conditions, geometry, and size of the bioreactor. It could lead to improved solid reactor systems. The model can be used as a basis for automatic control of SSF for the production of valuable metabolites in static fermentors.

[An electron paramagnetic resonance study of 4 salivary calculi treated in an ionized oxygen atmosphere]. / Etude, par résonance paramagnétique électronique, de quatre calculs salivaires traités en atmosphère d'oxygène excité.

Four salivary calculi and synthetically prepared hydroxyapatite, tricalcium phosphate and B-type carbonated fluorapatite or hydroxyapatite were treated under excited oxygen atmosphere. All these samples were studied by Electron Spin Resonance at 100 K. The presence of paramagnetic ozonide ions was observed only in the salivary calculi and in the hydroxyapatite. This indicates that the dominant apatite phase in salivary calculi is weakly carbonated hydroxyapatite.

ESR of CO2- in X-irradiated tooth enamel and A-type carbonated apatite.

Using both low microwave power and weak magnetic field modulation, we have shown that the asymmetric signal arising in X-irradiated tooth enamel as well as in A-type carbonated apatite exposed to X-rays or to excited oxygen has an orthorhombic character and must be attributed to CO2-. Effectively, the mean values found for the three g-tensor components are comparable to those quoted for this defect in single-crystal specimens of calcite and sodium formate.