The effect of disk rotational speed on oxygen transfer in rotating biological contactors.

Lab-scale experiments using a synthetic wastewater were carried out to assess the influence of disk rotational speed on oxygen transfer rate in a RBC unit in the presence of biomass. The overall oxygen transfer coefficient (K(L)a) was computed. Five different disk rotational speeds were tested, in the typical RBC operating range (3-10 RPM). The soluble organic substrate was monitored through TOC analysis. Influent hydraulic organic loadings were in the range of 5.4-35.2 g TOC/m(2)d. The set of kinetic coefficients calculated fitting the experimental data by the selected model resulted in good agreement with the value reported in literature. A correlation for K(L)a as a function of disk rotational speed and disk diameter was obtained. Accordingly, a new expression of the enhancement factor of oxygen transfer was found, and compared to literature data.

EDTA leaching of copper from contaminated soils: experimental study and transport model application for parameters estimation.

EDTA column's extraction were performed on four artificially contaminated soils, followed by the percolation of pure water to ensure the removal of EDTA entrapped in soil. The investigated soils were characterized by a content of organic matter ranging from 1% to 25%. A mathematical model was developed for copper leaching from the soils. The correlation of experimental data shows that while the EDTA transport was not affected by the soil organic fraction, the simulated transport of Cu-EDTA complexes in solution exhibited a delay effect due to the chemical adsorption of such complexes onto the soil organic matter. The distribution coefficient (Kd), between the solid and liquid phases showed a logarithmic increase when the organic content of soil increased. The column's hydrodynamic characteristics (alphaL) and the kinetic coefficients (k) of chelant extraction were estimated independently for each soil. A correlation of kinetic coefficients data versus soil's organic content was also proposed: experimental data showed, in the investigated range, a logarithmic dependence of k on the organic content of soil.

Selectivity in citric acid production by Yarrowia lipolytica.

This experimental study reports about production selectivity in the fermentation of glucose to citric acid by Yarrowia lipolytica as a function of substrate concentration. Batch runs featuring biomass growth and one or two citric acid production phases were carried out in a 15-l stirred tank fermentor. The presented results demonstrate that working at high initial substrate concentration in the production phase is beneficial both in terms of a higher production rate of citric acid, the desired metabolite (reaching 0.077 h(-1)) and of a higher utilization degree of the employed carbon source (yield up to 0.384 g(c.a.)/g(glucose)). The production rate of isocitric acid, the major undesired metabolite, was found to be practically constant over the tested initial substrate concentration range.