Distribution of Mixing Efficiency in a Split-Cylinder Gas-Lift Bioreactor with ImmobilizedYarrowia LipolyticaCells Used for Olive Oil Mill Wastewater Treatment

Abstract

The distribution of mixing in a split-cylinder gas-lift bioreactor has been investigated for suspensions of immobilized Y. lipolytica cells with particles diameter varying between 3 and 4.2 mm. The results indicated important variation of mixing time on the height of riser or downcomer, as well as different behavior of suspensions flows in these two regions. Therefore, for the riser, the mixing efficiency increases from its bottom to the top, the biocatalyst particles with intermediary size (3.6 mm diameter) allowing reaching the most intense circulation of suspension. The analysis of the suspension flow in the downcomer region revealed that the intermediary positions are associated with the highest mixing mainly for the largest immobilized yeast particles (4.2 mm diameter). In both cases, the influence of aeration on turbulence extent is positive only for air superficial velocity up to 1.05 -1.35x10 -3 m/s, the magnitude of this effect being correlated with the biocatalyst size and position on the riser or downcomer. By means of the experimental data, mathematical correlations for mixing time have been proposed for each circulation region, taking into consideration both the operational parameters and the Downloaded by [University of Otago] at 10:37 05 October 2015 2 distance from the bioreactor bottom. These equations offer a good concordance with the experiment, the average deviation being of 5.82 for the riser and 6.06% for the downcomer zone.

CFD evaluation of hydrophobic feedstock bench‐scale fermenters for efficient high agitation volumetric mass transfer

“…Fermentation mixing efficiency is vital for lipid biodegradation performance. [8] Triple-impeller aerobic fermenters have demonstrated energy-efficient gas-liquid mass transfer but have liquid mixing disadvantages. [9,10] Modeling the oil and air interfacial areas for mass transfer and mixing helps design these processes better.…”